@article{oh_kordsmeier_askari_adams_2023, title={Low Profile GRIN Lenses With Integrated Matching Using 3-D Printed Ceramic}, volume={4}, ISSN={["2637-6431"]}, DOI={10.1109/OJAP.2022.3227747}, abstractNote={In this paper, we investigate a shortened horn antenna with high gain that is enabled by a 3D-printed gradient index (GRIN) lens composed of high permittivity zirconia <inline-formula> <tex-math notation="LaTeX">$(ZrO_{2})$ </tex-math></inline-formula>. The baseline H-plane sectoral horn antenna is designed with length that is 1/3 of the optimal horn antenna and exhibits a low gain due to the high flaring rate of the horn. Increased gain is achieved by adding a flat GRIN lens at the horn aperture. High permittivity <inline-formula> <tex-math notation="LaTeX">$ZrO_{2}\,\,(\varepsilon _{r} = 23)$ </tex-math></inline-formula> enables lens miniaturization; however, when interfaced with air, reflections at the air interface increase the impedance mismatch. Two different methods for mitigating the reflections are studied. One is a simple <inline-formula> <tex-math notation="LaTeX">$\lambda /4$ </tex-math></inline-formula> matching layer that matches the bulk permittivity of <inline-formula> <tex-math notation="LaTeX">$ZrO_{2}$ </tex-math></inline-formula> to air. As expected, the <inline-formula> <tex-math notation="LaTeX">$\lambda /4$ </tex-math></inline-formula> layers reduce the reflections in part of the 13–18 GHz band but produce high reflection in other parts. The second approach is a GRIN lens with integrated tapered matching layer to match phase and impedance simultaneously. Three tapering methods are studied (exponential, Klopfenstein, linear) for impedance matching. Analytical expressions of the minimum thickness and permittivity distribution are derived. The lens is discretized for print and three types of unit cells are proposed to create a wide range of permittivities ranging from bulk ceramic to air. A <inline-formula> <tex-math notation="LaTeX">$ZrO_{2}$ </tex-math></inline-formula> lens prototype printed with an XJet Carmel 1400 is measured and results show good agreement with simulations, including gain performance equivalent to a horn of 2.4x longer length. The measured gain and beamwidth of the lens are 5.4dB higher and 52° narrower than those of the shortened horn alone at 15 GHz, respectively.}, journal={IEEE OPEN JOURNAL OF ANTENNAS AND PROPAGATION}, author={Oh, Yongduk and Kordsmeier, Neal and Askari, Hussain and Adams, Jacob J.}, year={2023}, pages={12–22} }
 @article{adams_genovesi_yang_antonino-daviu_2022, title={Antenna Element Design Using Characteristic Mode Analysis: Insights and Research Directions.}, volume={2}, ISSN={["1558-4143"]}, DOI={10.1109/MAP.2022.3145718}, abstractNote={This article provides a comprehensive review of recent applications of characteristic mode analysis (CMA) to innovative antenna element designs, including multiport, circularly polarized, wideband, reconfigurable, and dielectric resonator antennas (DRAs). Emphasis is placed on the interpretation of the characteristic modes (CMs) for those unfamiliar with the method and physical insights gained from the characteristic eigenvalues and eigenvectors of an antenna. In addition, we review CMA-based design strategies and specific design examples that highlight the application of CMA to various types of antennas. Ultimately, this article seeks to demonstrate the value of CMA-based design insights for antenna engineering and look toward promising new research directions for CMA and antenna research.}, journal={IEEE ANTENNAS AND PROPAGATION MAGAZINE}, author={Adams, Jacob J. and Genovesi, Simone and Yang, Binbin and Antonino-Daviu, Eva}, year={2022}, month={Feb} }
 @article{yang_kim_adams_2022, title={Fundamental Limits on Substructure Dielectric Resonator Antennas}, volume={3}, ISSN={["2637-6431"]}, DOI={10.1109/OJAP.2021.3133725}, abstractNote={We show theoretically that the characteristic modes of dielectric resonator antennas (DRAs) must be capacitive in the low frequency limit and that as a consequence of this constraint and the Poincaré Separation Theorem, the modes of any DRA consisting of partial elements of an encompassing super-structure with the same spatial material properties cannot resonate at a lower frequency than the encompassing structure. Thus, design techniques relying on complex sub-structures to miniaturize the antenna, including topology optimization and meandered windings, cannot apply to DRAs. Due to the capacitive nature of the DRA modes, it is also shown that the Q factor of any DRA sub-structure will be bounded from below by that of the super-structure at frequencies below the first self-resonance of the super-structure. We demonstrate these bounding relations with numerical examples.}, journal={IEEE OPEN JOURNAL OF ANTENNAS AND PROPAGATION}, author={Yang, Binbin and Kim, Jaewoo and Adams, Jacob J.}, year={2022}, pages={59–68} }
 @article{srivastava_adams_2022, title={Transient analysis of dynamically switched frequency shift keyed transmitters}, volume={4}, ISSN={["1751-8733"]}, DOI={10.1049/mia2.12237}, abstractNote={A dynamically switched matching network for transmitting a wideband frequency shift keyed (FSK) signal from an electrically small monopole antenna is studied. The effects of switch synchronization, frequency deviation, the antenna's impedance, and Q-factor at the two carrier frequencies are studied. It is found that the average energy per bit of the transmitted FSK waveform is maximum when the loss of reactive energy between states transition is minimised by switching it at the instant of peak voltage across the antenna's terminals. However, a switching network topology that stores more energy is shown to be less sensitive to the synchronization condition. In addition, we show that this dynamically switched system transmits more bit energy when the carriers are closely spaced due to a smaller change in stored energy levels between states. Results are presented using a detailed analytical study and full wave simulation. Near field measurements from a monopole antenna circuit model show that under proper conditions, an FSK signal can be transmitted at a rate 7 times greater than the bandwidth of the transmit antenna with minimal signal quality degradation.}, journal={IET MICROWAVES ANTENNAS & PROPAGATION}, author={Srivastava, Shruti and Adams, Jacob J.}, year={2022}, month={Apr} }
 @article{xie_adams_tong_2021, title={An UHF Reconfigurable Liquid-Metal Monopole Antenna Based on a 2-D Surface}, volume={11}, ISSN={["2156-3985"]}, DOI={10.1109/TCPMT.2021.3116056}, abstractNote={This article demonstrates an ultrahigh frequency (UHF) liquid-metal monopole antenna qualified for reconfiguring its resonant frequency by stretching or shortening its length on a 2-D surface. The proposed antenna consists of liquid eutectic gallium and indium (EGaIn) and NaOH solution. A power supply generates a direct current (DC) potential between the EGaIn and NaOH solution. Depending on the electrically-driven method to push or withdraw the EGaIn, the antenna is capable of forming different lengths to redistribute the current of the radiating element. Compared with the microchannel liquid-metal antenna, the proposed antenna can be tuned on a 2-D surface, rather than relying on the microchannel for shaping. By varying the length of EGaIn on a 2-D surface, the proposed antenna can provide continuously tunable frequency range and repeatability. For EGaIn monopole antenna with lengths from 50 to 10 mm, the measured resonant frequency operates from 0.78 to 2.42 GHz for a tuning ratio 3.1:1. The application of the design, operation of tuning liquid-metal antenna at several frequencies, and measurement process are explained in this article.}, number={11}, journal={IEEE TRANSACTIONS ON COMPONENTS PACKAGING AND MANUFACTURING TECHNOLOGY}, author={Xie, Feng and Adams, Jacob J. and Tong, Mei Song}, year={2021}, month={Nov}, pages={1980–1987} }
 @article{huang_schab_dusenbury_sluss_adams_2021, title={DC-Assisted Stabilization of Internal Oscillations for Improved Symbol Transitions in a Direct Antenna Modulation Transmitter}, volume={8}, ISSN={["1557-9670"]}, DOI={10.1109/TMTT.2021.3103209}, abstractNote={Internal oscillations in switched antenna transmitters cause undesirable fluctuations of the stored energy in the system, reducing the effectiveness of time-varying broadbanding methods, such as energy-synchronous direct antenna modulation. To mitigate these parasitic oscillations, a modified direct antenna modulation system with an auxiliary DC source is introduced to stabilize energy storage on the antenna. A detailed circuit model for a direct antenna modulation system is used to identify the origin of the oscillations and to justify the selection of the DC source. Measured phase shift keyed waveforms transmitted using the modified system show significant increases in signal fidelity, including a 10–20-dB reduction in error vector magnitude compared to a time-invariant system. Comparison to an equivalent, scalable time-invariant antenna suggests that the switched transmitter behaves as though it has 2–3 times lower radiation Q-factor and 20% higher radiation efficiency.}, journal={IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES}, author={Huang, Danyang and Schab, Kurt and Dusenbury, Joseph K. and Sluss, Brandon and Adams, Jacob J.}, year={2021}, month={Aug} }
 @article{yang_oh_hu_adams_2021, title={Implementation of A Flat-Bottom Luneburg Lens Based on Conformal Transformation Optics}, ISSN={["2576-7216"]}, DOI={10.1109/IMS19712.2021.9574844}, abstractNote={Using transformation optics based on numerical conformal mapping, a 2D flat-bottom Luneburg lens is designed and realized using isotropic materials. The gradient-index material profile is discretized and realized through unit cells. Full wave simulation is conducted to verify the performance. Maximum 2D directivity of 14.9 dBi is achieved for a line source when the 2D lens has a free-space electrical size of 10λ. A wide field of view (~ 120 degree) is obtained for a set of planar offset feed points spanning 3.3λ.}, journal={2021 IEEE MTT-S INTERNATIONAL MICROWAVE SYMPOSIUM (IMS)}, author={Yang, Binbin and Oh, Yongduk and Hu, Xinchen and Adams, Jacob J.}, year={2021}, pages={556–558} }
 @article{ma_bharambe_persson_bachmann_joshipura_kim_oh_patrick_adams_dickey_2021, title={Metallophobic Coatings to Enable Shape Reconfigurable Liquid Metal Inside 3D Printed Plastics}, volume={13}, ISSN={["1944-8252"]}, url={https://doi.org/10.1021/acsami.0c17283}, DOI={10.1021/acsami.0c17283}, abstractNote={Liquid metals adhere to most surfaces despite their high surface tension due to the presence of a native gallium oxide layer. The ability to change the shape of functional fluids within a three-dimensional (3D) printed part with respect to time is a type of four-dimensional printing, yet surface adhesion limits the ability to pump liquid metals in and out of cavities and channels without leaving residue. Rough surfaces prevent adhesion, but most methods to roughen surfaces are difficult or impossible to apply on the interior of parts. Here, we show that silica particles suspended in an appropriate solvent can be injected inside cavities to coat the walls. This technique creates a transparent, nanoscopically rough (10-100 nm scale) coating that prevents adhesion of liquid metals on various 3D printed plastics and commercial polymers. Liquid metals roll and even bounce off treated surfaces (the latter occurs even when dropped from heights as high as 70 cm). Moreover, the coating can be removed locally by laser ablation to create selective wetting regions for metal patterning on the exterior of plastics. To demonstrate the utility of the coating, liquid metals were dynamically actuated inside a 3D printed channel or chamber without pinning the oxide, thereby demonstrating electrical circuits that can be reconfigured repeatably.}, number={11}, journal={ACS APPLIED MATERIALS & INTERFACES}, publisher={American Chemical Society (ACS)}, author={Ma, Jinwoo and Bharambe, Vivek T. and Persson, Karl A. and Bachmann, Adam L. and Joshipura, Ishan D. and Kim, Jongbeom and Oh, Kyu Hwan and Patrick, Jason F. and Adams, Jacob J. and Dickey, Michael D.}, year={2021}, month={Mar}, pages={12709–12718} }
 @article{bharambe_ma_dickey_adams_2021, title={RESHAPE: A Liquid Metal-Based Reshapable Aperture for Compound Frequency, Pattern, and Polarization Reconfiguration}, volume={69}, ISSN={["1558-2221"]}, url={https://doi.org/10.1109/TAP.2020.3037803}, DOI={10.1109/TAP.2020.3037803}, abstractNote={We demonstrate a single-feed planar antenna capable of independently reconfiguring its operating frequency, radiation pattern, and polarization using stretchable, encapsulated liquid-metal (LM) parasitic elements. The LM is contained within elastomeric fibers that can be mechanically translated, stretched, or relaxed to alter the position or length of each conducting element on a 2-D surface, physically reshaping the metal on the antenna aperture. This eliminates several practical challenges associated with fluidic actuation of LM and makes the actuation scheme much faster and more reliable than other recent approaches. Using this scheme, the reshapable aperture (RESHAPE) design supports continuously reconfigurable operating frequencies from 2.45 to 6.5 GHz while supporting either linear $\hat {y}$ - or $\hat {\textrm {z}}$ -polarizations. At the same time, the radiation pattern can also be reconfigured in all planes, over a continuous range, to a maximum of ±45° away from the broadside direction for most frequencies. For all these possible states, the antenna maintains a 2:1 VSWR and a total efficiency of >60%. We explain the operation of the design at several frequencies, analyze the coverage area, and present measurements of a fabricated prototype.}, number={5}, journal={IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Bharambe, Vivek T. and Ma, Jinwoo and Dickey, Michael D. and Adams, Jacob J.}, year={2021}, month={May}, pages={2581–2594} }
 @article{burden_oh_mummareddy_negro_cortes_du plessis_macdonald_adams_li_rojas_2021, title={Unit cell estimation of volumetrically-varying permittivity in additively-manufactured ceramic lattices with X-ray computed tomography}, volume={210}, ISSN={["1873-4197"]}, DOI={10.1016/j.matdes.2021.110032}, abstractNote={Additive manufacturing of ceramics is transforming electromagnetics by providing density-varying lattices and stochastic foams within arbitrary envelopes. Periodic structures can now be fabricated with zirconia which offers the highest permittivity of any 3D printable material possible to be printed with nearly-full-density. By arranging a lattice with variation in the strut and node sizings as well as unit cell dimensions, the effective density of a structure can be spatially-modulated gracefully and with unprecedented freedom. These variations in density directly translate into variations in the effective permittivity of the bulk lattice (estimated locally and globally with a combination of mixing formulas, curve fits, and capacitance models). A lattice had previously been fabricated with a rectangular envelope for evaluation of effective global permittivity of the overall structure using a network analyzer. For this work, the structure was scanned with X-ray computed tomography (CT) to capture the three dimensional density of the structure including both the solid ceramic elements as well as the interstitial space. Software was developed that reads CT scan data and provides a 3D data structure with a pointwise unit cell estimation of the effective permittivity throughout the volume - a model well suited for electromagnetic simulations to optimize advanced microwave devices. The proposed technique serves as a foundation for the non-destructive estimation of space-varying permittivity within 3D printed lattices and foams.}, journal={MATERIALS & DESIGN}, author={Burden, Edward and Oh, Yongduk and Mummareddy, Bhargavi and Negro, Dylan and Cortes, Pedro and Du Plessis, Anton and MacDonald, Eric and Adams, Jacob and Li, Frank and Rojas, Roberto}, year={2021}, month={Nov} }
 @article{bharambe_oh_adams_negro_macdonald_2020, title={3D Printed Zirconia for UWB Stacked Conical Ring DRA}, ISSN={["1522-3965"]}, DOI={10.1109/IEEECONF35879.2020.9330248}, abstractNote={In this paper, we present a 3D printed ultrawideband (2.95 GHz-20 GHz) dielectric resonator antenna (DRA) fabricated using Nano-Particle Jetting (NPJ) of high permittivity, low loss, mechanically tough ceramic, zirconia. 3D printing enables fabrication of geometrically complex DRA design without machining or high pressure shaping. The wideband impedance response was achieved with a hybrid monopole/DRA design that uses the fundamental and higher order modes of the monopole and the parasitic DRA rings for a wide impedance bandwidth (VSWR lt; \mathbf{3}$). In the future, the 3D printing technique can enable building DRAs with more complex shapes or ceramic lattices to build graded index lenses.}, journal={2020 IEEE INTERNATIONAL SYMPOSIUM ON ANTENNAS AND PROPAGATION AND NORTH AMERICAN RADIO SCIENCE MEETING}, author={Bharambe, Vivek T. and Oh, Yongduk and Adams, Jacob J. and Negro, Dylan and MacDonald, Eric}, year={2020}, pages={41–42} }
 @article{dusenbury_huang_adams_2020, title={A Circuit Model for Energy Synchronous Direct Antenna Modulation Using an Electrically Small Loop}, ISSN={["1522-3965"]}, DOI={10.1109/IEEECONF35879.2020.9329560}, abstractNote={A simple circuit model for a broadband electrically small loop transmitter using energy synchronous direct antenna modulation (DAM) is presented. The concept of energy-synchronous DAM using a loop antenna is briefly described and compared to a conventional narrowband transmitter, via time domain simulations of the current on the loop. A brief analysis of the affect of ohmic loss on the stored current is presented. Initial results suggest that the dissipation in the loop is negligible over short symbol durations, but motivates a discussion about the need for a more comprehensive parametric study for this class of DAM transmitters.}, journal={2020 IEEE INTERNATIONAL SYMPOSIUM ON ANTENNAS AND PROPAGATION AND NORTH AMERICAN RADIO SCIENCE MEETING}, author={Dusenbury, Joseph and Huang, Danyang and Adams, Jacob J.}, year={2020}, pages={459–460} }
 @article{yang_adams_2020, title={A Decoupling Network Based on Characteristic Port Modes}, ISSN={["1522-3965"]}, DOI={10.1109/IEEECONF35879.2020.9329790}, abstractNote={In this paper, we present a novel decoupling network for coupled antenna systems using characteristic port modes. Specifically, we observe that the the port response of a multiport antenna is the superposition of the characteristic modal responses, while the superposition relation for multi-port antennas can be represented as a transformer bank. By developing a transformer network that inverts the superposition relation, we realize a decoupling network for the coupled multi-port antennas. Depending on the antenna's property, this decoupling network could be a broadband, e.g. for symmetric networks, or a narrowband realization.}, journal={2020 IEEE INTERNATIONAL SYMPOSIUM ON ANTENNAS AND PROPAGATION AND NORTH AMERICAN RADIO SCIENCE MEETING}, author={Yang, Binbin and Adams, Jacob J.}, year={2020}, pages={1667–1668} }
 @article{schab_huang_adams_2020, title={An Energy-Synchronous Direct Antenna Modulation Method for Phase Shift Keying}, volume={1}, ISSN={["2637-6431"]}, DOI={10.1109/OJAP.2020.2972842}, abstractNote={A novel scheme for transmitting broadband phase shift keyed signals from electrically small antennas using energy-synchronous direct antenna modulation is described. We outline fundamental operating principles of the method and experimentally compare its performance to that of a conventional band-limited transmit antenna with the same electrical size and radiation efficiency. Transmitted waveforms are analyzed in the time domain both at RF and baseband. Results show significant increases in signal quality, suggesting a larger effective transmit bandwidth and greater potential throughput when the proposed direct antenna modulation scheme is used.}, journal={IEEE OPEN JOURNAL OF ANTENNAS AND PROPAGATION}, author={Schab, Kurt and Huang, Danyang and Adams, Jacob J.}, year={2020}, pages={41–46} }
 @article{oh_bharambe_adams_negro_macdonald_2020, title={Design of a 3D Printed Gradient Index Lens Using High Permittivity Ceramic}, ISSN={["1522-3965"]}, DOI={10.1109/IEEECONF35879.2020.9330193}, abstractNote={In this paper, we investigate the design of a gradient index (GRIN) horn-integrated lens using a zircona lattice printed using a Nanoparticle Jetting process. The electrical properties of the ZrO2 lattice for a range of geometric parameters are simulated to realize a range of effective dielectric constants from 3 - 23. The properties of a 3D printed lattice are found to be consistent with the simulations. A shortened horn antenna combined with a flat GRIN lens is designed to collimate the beam and enhance directivity. The simulated directivity is 14.6 dBi at 15 GHz, which is 6.2 dB higher than the same horn without the lens.}, journal={2020 IEEE INTERNATIONAL SYMPOSIUM ON ANTENNAS AND PROPAGATION AND NORTH AMERICAN RADIO SCIENCE MEETING}, author={Oh, Yongduk and Bharambe, Vivek T. and Adams, Jacob J. and Negro, Dylan and MacDonald, Eric}, year={2020}, pages={1431–1432} }
 @article{huang_adams_schab_2020, title={Investigation of Ringing Effects on Phase Shift Keyed Direct Antenna Modulation Transmitters}, ISSN={["1522-3965"]}, DOI={10.1109/IEEECONF35879.2020.9330246}, abstractNote={In this paper, a method of direct antenna modulation (DAM) transmitting phase shift keyed (PSK) high data rate signals using a narrowband antenna is described. We analyze the result of an over the air DAM PSK measurement and degradation are observed in QPSK DAM compared to the ideal case. We demonstrate that it is the parasitics of the circuit that reduce the ability of the system to store voltage and achieve fast transitions, particularly between certain combinations of symbols. This degradation is studied and it can be predicted by circuit model simulation.}, journal={2020 IEEE INTERNATIONAL SYMPOSIUM ON ANTENNAS AND PROPAGATION AND NORTH AMERICAN RADIO SCIENCE MEETING}, author={Huang, Danyang and Adams, Jacob J. and Schab, Kurt}, year={2020}, pages={1817–1818} }
 @article{wang_lei_dong_dickey_adams_2020, title={Investigation of biasing conditions and energy dissipation in electrochemically controlled capillarity liquid metal electronics}, volume={56}, ISSN={["1350-911X"]}, DOI={10.1049/el.2019.3925}, abstractNote={This Letter investigates the trade-off between the biasing conditions (biasing current and electrolyte concentration) and energy dissipation in high-frequency liquid metal electronics using electrochemically controlled capillarity (ECC). ECC can control the interfacial tension of liquid metal via DC current as a method to move the metal in capillaries. It requires a conductive electrolyte to facilitate the electrochemical reactions. Here, the authors measure the withdrawal rate of liquid metal under different biasing currents and electrolyte concentrations. The results indicate that a larger biasing current and a more concentrated electrolyte induce a faster withdrawal motion of liquid metal. This Letter also explores the change of antenna efficiency when different electrolyte concentrations are chosen. The selection of electrolyte concentration for high-antenna efficiency conflicts with the need for fast withdrawal speed and low-DC power consumption of the liquid metal system, therefore requiring a balance among the various parameters when ECC is applied in practical liquid metal electronics.}, number={7}, journal={ELECTRONICS LETTERS}, author={Wang, Meng and Lei, Wen Tai and Dong, Jian and Dickey, Michael D. and Adams, Jacob J.}, year={2020}, month={Mar}, pages={323–324} }
 @article{srivastava_adams_2020, title={Transmission of a broadband FSK signal from a dynamically tuned narrowband antenna}, volume={14}, ISSN={["1751-8733"]}, DOI={10.1049/iet-map.2020.0387}, abstractNote={: A frequency reconfigurable patch antenna is dynamically tuned to transmit frequency-shift keying (FSK) signals over a range of frequencies much broader than the static impedance bandwidth of the antenna. Experiments are conducted for two binary FSK schemes having different carrier spacing. In both cases, dynamic tuning of the antenna is shown to increase the amplitude of the radiated signal by providing a better match than the static antenna. However, the average energy of the radiated bit at each carrier frequency decreases as the symbol rate increases beyond the 3 dB bandwidth of the antenna. Therefore, the bandwidth of the antenna is found to be a limiting factor for the maximum achievable data rate in this scheme. As an alternative to shorter bit durations, the authors show that a higher level FSK scheme using dynamic tuning is able to increase throughput beyond what is possible with a static antenna.}, number={13}, journal={IET MICROWAVES ANTENNAS & PROPAGATION}, author={Srivastava, Shruti and Adams, Jacob J.}, year={2020}, month={Oct}, pages={1651–1654} }
 @article{yang_zhou_adams_2019, title={A Shape-First, Feed-Next Design Approach for Compact Planar MIMO Antennas}, volume={77}, ISSN={["1098-8963"]}, DOI={10.2528/PIERM18100903}, abstractNote={Employing characteristic mode theory (CMT), a shape-first feed-next design methodology for compact planar antennas is proposed, which facilitates rapid and systematic design of self-matched, multi-port antennas with optimal bandwidth and high isolation. First, the optimal antenna shape with multiple self-resonant modes is synthesized using a binary genetic algorithm. Then, the optimal feed positions that provide good input matching and high isolation between the excitation ports are specified using a virtual probe modeling technique. A two-port microstrip antenna with an electrical size of 0.45λd × 0.297λd is designed, fabricated and measured. The measured operating frequency is within 1% of the full wave simulation, and the overall S parameter characteristics and far field patterns agree well with the simulation result, validating our design methodology. Mutual coupling S21 < −35 dB at the center frequency is achieved in this design.}, journal={PROGRESS IN ELECTROMAGNETICS RESEARCH M}, author={Yang, Binbin and Zhou, Juncheng and Adams, Jacob J.}, year={2019}, pages={157–165} }
 @article{oh_bharambe_mummareddy_martin_mcknight_abraham_walker_rogers_conner_cortes_et al._2019, title={Microwave dielectric properties of zirconia fabricated using NanoParticle Jetting (TM)}, volume={27}, ISSN={["2214-7810"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85064914088&partnerID=MN8TOARS}, DOI={10.1016/j.addma.2019.04.005}, abstractNote={Additive manufacturing of ceramics has been actively investigated with the objective of fabricating complex structures that compete in terms of material performance with traditionally manufactured ceramics but with the benefit of increased geometric freedom. More specifically, zirconia provides high fracture toughness and thermal stability. In addition, its dielectric permittivity may be the highest among materials available for 3D printing, and may enable the next generation of complex electromagnetic structures. NanoParticle Jetting™ is a new material jetting process for selectively depositing nanoparticles and is capable of printing zirconia. Dense, fine-featured parts can be manufactured with layer thicknesses as small as 10 μm and jetting resolution of 20 μm after a final sintering step. For this study, 3D printed zirconia using NanoParticle Jetting™ was characterized in terms of chemistry, density, crystallography, sintering shrinkage and dielectric properties as a foundation for developing high performance radio frequency (RF) components. The experimental results indicate a yttria-stabilized ZrO2 structure exhibiting a bulk relative permittivity of 23 and a loss tangent of 0.0013 at microwave frequencies. A simple zirconia dielectric resonator antenna is measured, confirming the measured dielectric properties and illustrating a practical application of this material.}, journal={ADDITIVE MANUFACTURING}, author={Oh, Yongduk and Bharambe, Vivek and Mummareddy, Bhargavi and Martin, John and McKnight, Jeremy and Abraham, Martin A. and Walker, Jason M. and Rogers, Kirk and Conner, Brett and Cortes, Pedro and et al.}, year={2019}, month={May}, pages={586–594} }
 @article{schab_huang_adams_2019, title={Pulse Characteristics of a Direct Antenna Modulation Transmitter}, volume={7}, ISSN={2169-3536}, DOI={10.1109/ACCESS.2019.2902365}, abstractNote={Direct antenna modulation (DAM) methods using time-varying matching networks offer the possibility to reduce the detrimental effects on broadband signal transmission from a narrowband antenna. We propose time- and frequency-domain models for the effects of a DAM scheme for the transmission of ON–OFF-keyed RF signals and test the validity of the proposed models through over-the-air measurements at 27.12 MHz. Random bit sequences are transmitted separately using both a switched-mode DAM transmitter and a conventional transmitter and received in the far field. Comparison of measured data with our frequency-domain models shows that the DAM transmission method partially removes the effects of narrowband filtering due to the transmit antenna. Models and measurements also demonstrate that the removal of this filter improves the signal quality as observed in eye diagrams of the demodulated received signals. Finally, a simple time-domain model of the DAM transmitter is shown to predict the radiated transient signal under varying synchronization conditions.}, journal={IEEE Access}, author={Schab, K. and Huang, D. and Adams, J. J.}, year={2019}, pages={1–1} }
 @article{wang_kilgore_steer_adams_2018, title={Characterization of Intermodulation Distortion in Reconfigurable Liquid Metal Antennas}, volume={17}, ISSN={["1548-5757"]}, DOI={10.1109/lawp.2017.2786078}, abstractNote={The intermodulation distortion produced by passive and tunable liquid metal (LM) antennas is investigated. Four kinds of monopoles, including a passive copper monopole, a varactor-tuned copper monopole, a passive LM monopole, and a tunable LM monopole using electrochemically controlled capillarity (ECC), are compared for their linearity and power-handling capabilities. Linearity is assessed using a two-tone distortion test, in which two fundamental tones close in frequency result in third-order intermodulation tones at frequencies above and below the original tones separated by the frequency difference. The passive LM monopole has comparable linearity to the passive copper monopole, while the linearity of the ECC-tuned LM monopole is at least 40 dB better than that of the active varactor monopole. The reconfigurable LM antenna also handles higher power (31 dBm) before failure than does the active varactor-tuned antenna (24 dBm).}, number={2}, journal={IEEE ANTENNAS AND WIRELESS PROPAGATION LETTERS}, author={Wang, Meng and Kilgore, Ian M. and Steer, Michael B. and Adams, Jacob J.}, year={2018}, month={Feb}, pages={279–282} }
 @article{mukai_bharambe_adams_suh_2018, title={Effect of bending and padding on the electromagnetic performance of a laser-cut fabric patch antenna}, volume={9}, ISSN={0040-5175 1746-7748}, url={http://dx.doi.org/10.1177/0040517518801202}, DOI={10.1177/0040517518801202}, abstractNote={A fabrication and characterization procedure is detailed for a flexible planar antenna integrated into textiles by interfacing thin metal-coated fabric sheets on a polyester fabric substrate. From the full-wave electromagnetic simulations and measurements, it is observed that the low dielectric dissipation in the porous woven polyester enables the fabric antenna to achieve a high gain of 8.4 dBi. It is comparable to other antennas fabricated with engineered substrates of low-loss polymer composites. Using this antenna, the impact of cylindrical concave bending deformation is observed in terms of the impedance matching and radiation performance. The simulated and measured results agree reasonably well. A 1.2% frequency shift is observed when the antenna is bent concavely along its length, while bending along its width showed only a marginal impact. On the other hand, the gain is reduced by as much as 1.0 and 0.5 dB when the antenna is bent along its length and width, respectively. The impact of padding layers was also investigated when placed above the radiating patch and below the ground plane. Because the textile padding layers have complex permittivity closer to air due to their highly porous structure, it is expected to observe only small influence on the radiation performance. However, the simulations and measurements show that padding the radiating patch lowers both the operating frequency and the realized gain by up to 1.6% and by up to 0.9 dB, respectively, due to dielectric loading and dissipation.}, number={14}, journal={Textile Research Journal}, publisher={SAGE Publications}, author={Mukai, Yusuke and Bharambe, Vivek T and Adams, Jacob J and Suh, Minyoung}, year={2018}, month={Sep}, pages={004051751880120} }
 @article{bharambe_parekh_ladd_moussa_dickey_adams_2018, title={Liquid metal-filled 3D antenna array structure with an integrated feeding net-work}, volume={17}, number={5}, journal={IEEE Antennas and Wireless Propagation Letters}, author={Bharambe, V. and Parekh, D.P. and Ladd, C. and Moussa, K. and Dickey, M.D. and Adams, J.J.}, year={2018}, month={May}, pages={739–742} }
 @article{bharambe_parekh_ladd_moussa_dickey_adams_2018, title={Liquid-Metal-Filled 3-D Antenna Array Structure With an Integrated Feeding Network}, volume={17}, ISSN={["1548-5757"]}, url={https://doi.org/10.1109/LAWP.2018.2813309}, DOI={10.1109/lawp.2018.2813309}, abstractNote={This letter describes the fabrication and characterization of a microstrip patch array and a three-dimensional (3-D) coaxial feed network embedded within a 3-D printed part. Internal cavities within the acrylic structure are filled with a gallium-based liquid metal alloy using a vacuum-driven process to form conducting elements. In this way, four rectangular patch elements and a feeding network, including power dividers and vertical transitions, are embedded within a single 3-D printed acrylic geometry. Simulations and measurements of a 6 GHz array show that the array produces a matched response and moderate gain at the design frequency. This procedure can be employed to integrate numerous radiating elements and their corresponding feeding networks into a single monolithic acrylic structure, eliminating the need for separate fabrication of printed-circuit-board-based antennas and feeds. The procedure can serve as a convenient approach for rapid prototyping of complex array designs that exploit the additional spatial degrees of freedom to enhance their electromagnetic performance. Furthermore, manipulating the liquid-phase metallization inside these acrylic cavities can potentially be used to produce frequency- or pattern-reconfigurable arrays in the future.}, number={5}, journal={IEEE ANTENNAS AND WIRELESS PROPAGATION LETTERS}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Bharambe, Vivek and Parekh, Dishit P. and Ladd, Collin and Moussa, Khalil and Dickey, Michael D. and Adams, Jacob J.}, year={2018}, month={May}, pages={739–742} }
 @article{schab_yang_hughes_adams_2018, title={Lower bounds on sub-structure antenna Q-factor}, volume={66}, number={7}, journal={IEEE Transactions on Antennas and Propagation}, author={Schab, K.R. and Yang, B. and Hughes, B.L. and Adams, J.J.}, year={2018}, month={Apr} }
 @inproceedings{adams_huang_schab_2018, place={Monticello, IL}, title={Measuring direct antenna modulation transmitters}, booktitle={Proceedings of the 2018 Allerton Antenna Applications Symposium}, author={Adams, J.J. and Huang, D. and Schab, K.}, year={2018}, month={Sep}, pages={236–247} }
 @article{barbee_mondal_deng_bharambe_neumann_adams_boechler_dickey_craig_2018, title={Mechanochromic Stretchable Electronics}, volume={10}, ISSN={["1944-8252"]}, url={https://doi.org/10.1021/acsami.8b09130}, DOI={10.1021/acsami.8b09130}, abstractNote={Soft and stretchable electronics are promising for a variety of applications such as wearable electronics, human-machine interfaces, and soft robotics. These devices, which are often encased in elastomeric materials, maintain or adjust their functionality during deformation, but can fail catastrophically if extended too far. Here, we report new functional composites in which stretchable electronic properties are coupled to molecular mechanochromic function, enabling at-a-glance visual cues that inform user control. These properties are realized by covalently incorporating a spiropyran mechanophore within poly(dimethylsiloxane) to indicate with a visible color change that a strain threshold has been reached. The resulting colorimetric elastomers can be molded and patterned so that, for example, the word "STOP" appears when a critical strain is reached, indicating to the user that further strain risks device failure. We also show that the strain at color onset can be controlled by layering silicones with different moduli into a composite. As a demonstration, we show how color onset can be tailored to indicate a when a specified frequency of a stretchable liquid metal antenna has been reached. The multiscale combination of mechanochromism and soft electronics offers a new avenue to empower user control of strain-dependent properties for future stretchable devices.}, number={35}, journal={ACS APPLIED MATERIALS & INTERFACES}, publisher={American Chemical Society (ACS)}, author={Barbee, Meredith H. and Mondal, Kunal and Deng, John Z. and Bharambe, Vivek and Neumann, Taylor V. and Adams, Jacob J. and Boechler, Nicholas and Dickey, Michael D. and Craig, Stephen L.}, year={2018}, month={Sep}, pages={29918–29924} }
 @inproceedings{schab_adams_2018, place={London, UK}, title={Modal decomposition of transients in direct antenna modulation systems}, booktitle={Proceedings of the 2018 European Conference on Antennas and Propagation (EuCAP)}, author={Schab, K. and Adams, J.J.}, year={2018}, month={Apr} }
 @article{joshipura_ayers_castillo_ladd_tabor_adams_dickey_2018, title={Patterning and Reversible Actuation of Liquid Gallium Alloys by Preventing Adhesion on Rough Surfaces}, volume={10}, ISSN={1944-8244 1944-8252}, url={http://dx.doi.org/10.1021/acsami.8b13099}, DOI={10.1021/acsami.8b13099}, abstractNote={This work reports a simple approach to form, study, and utilize rough coatings that prevent the adhesion of gallium-based liquid metal alloys. Typically, liquids with large interfacial tension do not wet nonreactive surfaces, regardless of surface topography. However, these alloys form a surface oxide "skin" that adheres to many substrates, even those with low surface energy. This work reports a simple approach to render closed channels and surfaces, including soft materials, to be "oxide-phobic" via spray-coating (NeverWet, which is commercially available and inexpensive). Surface spectroscopic techniques and metrology tools elucidate the coatings to comprise silica nanoparticles grafted with silicones that exhibit dual length scales of roughness. Although prior work shows the importance of surface roughness in preventing adhesion, the present work confirms that both hydrophobic and hydrophilic rough surfaces prevent oxide adhesion. Furthermore, the coating enables reversible actuation through submillimeter closed channels to form a reconfigurable antenna in the gigahertz range without the need for corrosive acids or bases that remove the oxide. In addition, the coating enables open surface patterning of conductive traces of liquid metal. This shows it is possible to actuate liquid metals in air without leaving neither metal nor oxide residue on surfaces to enable reconfigurable electronics, microfluidics, and soft electrodes.}, number={51}, journal={ACS Applied Materials & Interfaces}, publisher={American Chemical Society (ACS)}, author={Joshipura, Ishan D. and Ayers, Hudson R. and Castillo, Gilbert A. and Ladd, Collin and Tabor, Christopher E. and Adams, Jacob J. and Dickey, Michael D.}, year={2018}, month={Dec}, pages={44686–44695} }
 @article{shahariar_soewardiman_muchler_adams_jur_2018, title={Porous textile antenna designs for improved wearability}, volume={27}, ISSN={0964-1726 1361-665X}, url={http://dx.doi.org/10.1088/1361-665x/aaaf91}, DOI={10.1088/1361-665x/aaaf91}, abstractNote={Textile antennas are an integral part of the next generation personalized wearable electronics system. However, the durability of textile antennas are rarely discussed in the literature. Typical textile antennas are prone to damage during normal wearable user scenarios, washing, and heat cycling over time. Fabricating a durable, washable, flexible, and breathable (like textile materials) antenna is challenging due to the incompatibility of the mechanical properties of conductive materials and soft textile materials. This paper describes a scalable screen printing process on an engineered nonwoven substrate to fabricate microstrip patch antennas with enhanced durability. This work used an Evolon® nonwoven substrate with low surface roughness (∼Ra = 18 μm) and high surface area (∼2.05 mm2 mm−2 of fabric area) compared to traditional textile materials, which allows the ink to penetrate evenly in the fiber bulk with its strong capillary wicking force and enhances print resolution. The composite layer of ink and fiber is conductive and enables the antennas to maintain high mechanical flexibility without varying its RF (Radio Frequency) properties. Additionally, the antennas are packaged by laminating porous polyurethane web to make the device durable and washable. The fully packaged antennas maintain the structural flexibility and RF functionality after 15 cycles of washing and drying. To improve the air permeability and enhance flexibility the antenna is also modified by incorporating holes in the both patch and ground layer of the antenna. The antennas were analyzed before and after submerging in water to observe the effect of wetting and drying with respect to frequency response. The porous antenna with holes recovered 3x times faster than the one without holes (solid) from fully wet state (saturated with water) to the dry state, demonstrating its potential use as a moisture sensor system.}, number={4}, journal={Smart Materials and Structures}, publisher={IOP Publishing}, author={Shahariar, Hasan and Soewardiman, Henry and Muchler, Clifford A and Adams, Jacob J and Jur, Jesse S}, year={2018}, month={Mar}, pages={045008} }
 @inproceedings{bharambe_adams_joshipura_ayers_dickey_2018, title={Reversibly Reconfigurable Liquid Metal Patch Antenna Using A Superhydrophobic Spray-Coating}, ISBN={9781538671023}, url={http://dx.doi.org/10.1109/apusncursinrsm.2018.8608814}, DOI={10.1109/apusncursinrsm.2018.8608814}, abstractNote={Liquid metal-based reconfigurable antennas typically must be flushed with an electrolyte to remove the nanometer-thick oxide skin of EGaln that adheres the walls of the microchannels. The EGaln residue prevents repeatable actuation, but the presence of electrolyte introduces other challenges owing to its often corrosive and electrically conductive nature. To overcome this issue, we present a technique for enabling reversible infusion and withdrawal of EGaln into acrylic micro-channels and wide planar cavities by coating the surfaces with a silica-particle based superhydrophobic coating. The coating prevents adhesion of the liquid metal to the acrylic media and allows it to be reconfigured multiple times without the typical flushing process.}, booktitle={2018 IEEE International Symposium on Antennas and Propagation & USNC/URSI National Radio Science Meeting}, publisher={IEEE}, author={Bharambe, Vivek and Adams, Jacob J. and Joshipura, Ishan D. and Ayers, Hudson R. and Dickey, Michael D.}, year={2018}, month={Jul}, pages={287–288} }
 @article{wang_khan_dickey_adams_2017, title={A Compound Frequency- and Polarization-Reconfigurable Crossed Dipole Using Multidirectional Spreading of Liquid Metal}, volume={16}, ISSN={["1548-5757"]}, DOI={10.1109/lawp.2016.2556983}, abstractNote={We present a crossed dipole with frequency and polarization agility using electrochemically actuated liquid metal. For the first time, this antenna uses multidirectional displacement of liquid metal to enable frequency and polarization reconfiguration without the need for mechanical pumps or semiconductor devices. The dipole arms are composed of liquid metal that can be shortened and lengthened within the capillaries by applying DC voltages to each arm. Varying the lengths of the dipole arms generates two independently tuned, linearly polarized resonances from 0.8 to 3 GHz and polarization that can be switched from linear to circular over a portion of this band (0.89–1.63 GHz). Moreover, a circuit model predicts the circular polarization frequency from the input impedance. Simulation and experimental results validate the antenna concept and analysis techniques.}, journal={IEEE ANTENNAS AND WIRELESS PROPAGATION LETTERS}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Wang, Meng and Khan, Mohammad Rashed and Dickey, Michael D. and Adams, Jacob J.}, year={2017}, pages={79–82} }
 @article{srivastava_adams_2017, title={Analysis of a Direct Antenna Modulation Transmitter for Wideband OOK With a Narrowband Antenna}, volume={65}, ISSN={["1558-2221"]}, DOI={10.1109/tap.2017.2734063}, abstractNote={The characteristics of a narrowband antenna transmitting a broadband on–off-keyed signal using direct antenna modulation (DAM) are studied. The DAM technique has previously been proposed to generate a broadband signal using a rapidly time-varying antenna, but the signals produced using this technique and its limitations are not well understood. In this paper, we quantitatively compare the performance of a DAM transmitter to a conventional time-invariant transmit antenna. We show that the fall time of an RF pulse produced with the DAM configuration is measurably shorter than with the conventional system; however, the pulse rise time using both systems is identical. The performance of each system is then analyzed in terms of the bit error rate over a simple point-to-point link using analytical models, numerical simulation, and measurement. DAM reduces the intersymbol interference (ISI) by reducing the discharging time; however, the overall performance remains similar to the conventional system because of their similar charging times. While the DAM configuration does radiate a qualitatively broader spectrum as observed in previous studies, this does not translate into quantitative improvement in the characteristics of a transmitted data signal.}, number={10}, journal={IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION}, author={Srivastava, Shruti and Adams, Jacob J.}, year={2017}, month={Oct}, pages={4971–4979} }
 @inproceedings{schab_yang_adams_2017, place={Verona, Italy}, title={Antenna bounds for reduced basis problems}, booktitle={Proceedings of the 2017 International Conference on Electromagnetics in Advanced Applications (ICEAA)}, author={Schab, K.R. and Yang, B. and Adams, J.J.}, year={2017}, month={Sep}, pages={855–857} }
 @inproceedings{schab_adams_2017, title={Calculation of radiation transients in direct antenna modulation systems}, booktitle={2017 ieee international symposium on antennas and propagation & usnc/ursi national radio science meeting}, author={Schab, K. and Adams, J.}, year={2017}, pages={521–522} }
 @inproceedings{schab_yang_adams_2017, place={Paris, France}, title={EFIE singularity treatments and their effects on characteristic mode dynamic range}, booktitle={Proceedings of the 2017 European Conference on Antennas and Propagation (EuCAP)}, author={Schab, K. and Yang, B. and Adams, J.J.}, year={2017}, month={Mar}, pages={2673–2675} }
 @inproceedings{yang_adams_2017, title={Quality factor calculations for the characteristic modes of dielectric resonator antennas}, ISBN={9781946815002}, url={http://dx.doi.org/10.1109/usnc-ursi-nrsm.2017.7878293}, DOI={10.1109/usnc-ursi-nrsm.2017.7878293}, abstractNote={Characteristic mode theory (CMT) is employed to calculate the eigenmodes of dielectric objects based on the volume integral equation. With the knowledge of modal current, the quality factor (Q) of the characteristic modes are then calculated. In contrast to most conventional analysis techniques, the modal Qs are now available at any frequency, rather than only their resonant frequencies. This method offers additional information that can be used for single and multi-port dielectric resonator antenna (DRA) design and shape optimization. To verify our method, a cylindrical dielectric resonator is studied, and the Q factors at its natural resonance frequencies are compared with results from previous literature. This approach can be readily applied to geometries of arbitrary shape.}, booktitle={2017 United States National Committee of URSI National Radio Science Meeting (USNC-URSI NRSM)}, publisher={IEEE}, author={Yang, Binbin and Adams, Jacob J.}, year={2017}, month={Jan} }
 @inproceedings{huang_schab_srivastava_adams_2017, place={Monticello, IL}, title={Transmission of broadband signals using narrowband antennas: theory, measurement and limitations}, booktitle={Proceedings of the 2017 Antenna Applications Symposium}, author={Huang, D. and Schab, K. and Srivastava, S. and Adams, J.J.}, year={2017}, month={Sep}, pages={212–225} }
 @article{bharambe_parekh_ladd_moussa_dickey_adams_2017, title={Vacuum-filling of liquid metals for 3D printed RF antennas}, volume={18}, ISSN={["2214-7810"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85031777244&partnerID=MN8TOARS}, DOI={10.1016/j.addma.2017.10.012}, abstractNote={This paper describes a facile method to fabricate complex three-dimensional (3D) antennas by vacuum filling gallium-based liquid metals into 3D printed cavities at room temperature. To create the cavities, a commercial printer co-prints a sacrificial wax-like material with an acrylic resin. Dissolving the printed wax in oil creates cavities as small as 500 μm within the acrylic monolith. Placing the entire structure under vacuum evacuates most of the air from these cavities through a reservoir of liquid metal that covers a single inlet. Returning the assembly to atmospheric pressure pushes the metal from the reservoir into the cavities due to the pressure differential. This method enables filling of the closed internal cavities to create planar and curved conductive 3D geometries without leaving pockets of trapped air that lead to defects. An advantage of this technique is the ability to rapidly prototype 3D embedded antennas and other microwave components with metallic conductivity at room temperature using a simple process. Because the conductors are liquid, they also enable the possibility of manipulating the properties of such devices by flowing metal in or out of selected cavities. The measured electrical properties of fabricated devices match well to electromagnetic simulations, indicating that the approach described here forms antenna geometries with high fidelity. Finally, the capabilities and limitations of this process are discussed along with possible improvements for future work.}, journal={ADDITIVE MANUFACTURING}, publisher={Elsevier BV}, author={Bharambe, Vivek and Parekh, Dishit P. and Ladd, Collin and Moussa, Khalil and Dickey, Michael D. and Adams, Jacob J.}, year={2017}, month={Dec}, pages={221–227} }
 @inproceedings{yang_adams_2016, title={A modal approach to shape synthesis and feed placement for planar MIMO Antennas}, booktitle={2016 ieee antennas and propagation society international symposium}, author={Yang, B. B. and Adams, J. J.}, year={2016}, pages={15–16} }
 @article{yang_adams_2016, title={Computing and Visualizing the Input Parameters of Arbitrary Planar Antennas via Eigenfunctions}, volume={64}, ISSN={["1558-2221"]}, DOI={10.1109/tap.2016.2554604}, abstractNote={We propose a method for modeling planar multiport antennas of arbitrary shape using characteristic mode theory (CMT) without physically including the feeds. The characteristic modes of the feed-free structure are expanded to form a basis for the eigenfields, and a virtual probe is introduced to excite the antenna. We develop a broadband multiport circuit model for the antenna impedance based on the excitation of each mode, where the feed locations only affect transformer ratios in the model, enabling design and analysis of arbitrary feed combinations over a wide frequency range. Because a CMT expansion can be computed for any planar geometry, the shape of the radiating element can also be arbitrary. While this approach is approximate, several examples are presented to demonstrate that its accuracy and flexibility make it suitable for various planar antenna design applications. With the rapid evaluation of input impedance at multiple excitation points, input parameters, such as the multiport S, Y, or Z parameters, can be plotted as a heat map on the antenna structure, facilitating planar multiport antenna optimization and feed selection.}, number={7}, journal={IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION}, author={Yang, Binbin and Adams, Jacob J.}, year={2016}, month={Jul}, pages={2707–2718} }
 @inproceedings{yang_adams_2016, title={Mode-based analytical models for arbitrary wire and planar antennas}, DOI={10.1109/eucap.2016.7481186}, abstractNote={We describe new methods to generate circuit models for arbitrary wire and planar antennas. We first use the characteristic modes of the structure to develop a set of eigenimpedances that are independent of feed position. Once the antenna's eigenimpedances are known, the input impedance can be computed for a feed placed anywhere on the structure through simple calculations (products and sums). Therefore, the input impedance at all points on the structure can be determined very quickly relative to conventional simulation methods. While this approach is inherently approximate, it provides accurate results for many topologies while requiring far fewer calculations than port simulation. Furthermore, the approach applies to multi-port antennas where the complexity of evaluating many possible port combinations greatly increases the cost of conventional port simulation.}, booktitle={2016 10th european conference on antennas and propagation (eucap)}, author={Yang, B. B. and Adams, Jacob}, year={2016} }
 @article{yang_adams_2016, title={Systematic Shape Optimization of Symmetric MIMO Antennas Using Characteristic Modes}, volume={64}, ISSN={["1558-2221"]}, DOI={10.1109/tap.2015.2473703}, abstractNote={We introduce a systematic approach to the shape optimization of compact, single-aperture MIMO antennas. Because the characteristic modes of a radiator represent its complete set of possible responses to an excitation, any port on the antenna must display the properties of a combination of one or more of these characteristic modes. By restricting our consideration to a class of symmetric antennas, the lowest order characteristic modes of a structure can be separated with practical decoupling networks, studied, and excited independently. We show that the quality factor of each characteristic mode effectively bounds the performance of any individual port excitation, and can be used to evaluate the fitness of the antenna for multiport excitation. Under this framework, we apply a genetic algorithm (GA) to synthesize low Q MIMO antennas while minimizing conductor area. Feed locations are specified on the optimized shape based on the weighted excitation strength of the desired modes, and a two-port MIMO antenna is implemented and measured, verifying the proposed theory.}, number={7}, journal={IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION}, author={Yang, Binbin and Adams, Jacob J.}, year={2016}, month={Jul}, pages={2668–2678} }
 @article{adams_slimmer_bernhard_lewis_2015, title={3D-printed spherical dipole antenna integrated on small RF node}, volume={51}, ISSN={0013-5194 1350-911X}, url={http://dx.doi.org/10.1049/el.2015.0256}, DOI={10.1049/el.2015.0256}, abstractNote={New three-dimensional (3D) printing techniques enable the integration of an antenna directly onto the package of a small wireless sensor node. This volume-filling approach ensures near-optimal bandwidth performance of the small antenna, increasing a system's battery life, data rate or range. Simulated results show that the fabricated spherical antenna's bandwidth-efficiency product is more than half of the fundamental limit and radiation pattern measurements exhibit a dipole pattern with −0.7 dBi gain.}, number={9}, journal={Electronics Letters}, publisher={Institution of Engineering and Technology (IET)}, author={Adams, J.J. and Slimmer, S.C. and Bernhard, J.T. and Lewis, J.A.}, year={2015}, month={Apr}, pages={661–662} }
 @article{wang_trlica_khan_dickey_adams_2015, title={A reconfigurable liquid metal antenna driven by electrochemically controlled capillarity}, volume={117}, ISSN={["1089-7550"]}, DOI={10.1063/1.4919605}, abstractNote={We describe a new electrochemical method for reversible, pump-free control of liquid eutectic gallium and indium (EGaIn) in a capillary. Electrochemical deposition (or removal) of a surface oxide on the EGaIn significantly lowers (or increases) its interfacial tension as a means to induce the liquid metal in (or out) of the capillary. A fabricated prototype demonstrates this method in a reconfigurable antenna application in which EGaIn forms the radiating element. By inducing a change in the physical length of the EGaIn, the operating frequency of the antenna tunes over a large bandwidth. This purely electrochemical mechanism uses low, DC voltages to tune the antenna continuously and reversibly between 0.66 GHz and 3.4 GHz resulting in a 5:1 tuning range. Gain and radiation pattern measurements agree with electromagnetic simulations of the device, and its measured radiation efficiency varies from 41% to 70% over its tuning range.}, number={19}, journal={JOURNAL OF APPLIED PHYSICS}, publisher={AIP Publishing}, author={Wang, M. and Trlica, C. and Khan, M. R. and Dickey, M. D. and Adams, J. J.}, year={2015}, month={May} }
 @article{lin_cooper_wang_adams_genzer_dickey_2015, title={Handwritten, Soft Circuit Boards and Antennas Using Liquid Metal Nanoparticles}, volume={11}, ISSN={["1613-6829"]}, DOI={10.1002/smll.201502692}, abstractNote={Soft conductors are created by embedding liquid metal nanoparticles between two elastomeric sheets. Initially, the particles form an electrically insulating composite. Soft circuit boards can be handwritten by a stylus, which sinters the particles into conductive traces by applying localized mechanical pressure to the elastomeric sheets. Antennas with tunable frequencies are formed by sintering nanoparticles in microchannels.}, number={48}, journal={SMALL}, publisher={Wiley}, author={Lin, Yiliang and Cooper, Christopher and Wang, Meng and Adams, Jacob J. and Genzer, Jan and Dickey, Michael D.}, year={2015}, month={Dec}, pages={6397–6403} }
 @inproceedings{yang_adams_2015, place={Monticello, IL}, title={Modal Q and efficiency limits on the characteristic modes of multiport apertures}, booktitle={Proceedings of the 2015 Antenna Applications Symposium}, author={Yang, B. and Adams, J.J.}, year={2015}, month={Sep}, pages={131–141} }
 @inproceedings{yang_adams_2015, title={Modal Q as a bounding metric for MIMO antenna optimization}, booktitle={2015 31st International Review of Progress in Applied Computational Electromagnetics (ACES) vol 31}, author={Yang, B. B. and Adams, J. J.}, year={2015} }
 @inproceedings{muchler_cui_zhu_adams_2015, title={Multi-resonant AgNW/PDMS patch antenna for biaxial strain sensing}, booktitle={2015 ieee international symposium on antennas and propagation & usnc/ursi national radio science meeting}, author={Muchler, C. and Cui, Z. and Zhu, Y. and Adams, J. J.}, year={2015}, pages={1878–1879} }
 @inproceedings{adams_yang_2015, title={Physics-based circuit models for MIMO antennas using characteristic modes}, booktitle={2015 ieee international symposium on antennas and propagation & usnc/ursi national radio science meeting}, author={Adams, J. J. and Yang, B. B.}, year={2015}, pages={852–853} }
 @inproceedings{wang_khan_trlica_dickey_adams_2015, title={Pump-free feedback control of a frequency reconfigurable liquid metal monopole}, DOI={10.1109/aps.2015.7305500}, abstractNote={We demonstrate a pump-free method to control the length of liquid metal in a capillary as a means to change the operating frequency of a monopole antenna. An applied DC voltage controls the surface tension of the liquid metal filament, causing it to lengthen or contract, varying the antenna's resonant length. A closed-loop feedback system tracks the antenna's operating frequency and adjusts the applied voltage to shape the liquid metal towards the desired response. Measurements show that the process is controlled and fully reversible, dynamically adjusting to a programmed frequency.}, booktitle={2015 ieee international symposium on antennas and propagation & usnc/ursi national radio science meeting}, author={Wang, M. and Khan, M. R. and Trlica, C. and Dickey, Michael and Adams, Jacob}, year={2015}, pages={2223–2224} }
 @inproceedings{adams_2014, title={Accelerated frequency interpolation of antenna impedances using characteristic modes}, booktitle={2014 ieee antennas and propagation society international symposium (apsursi)}, author={Adams, J. J.}, year={2014}, pages={1413–1414} }
 @article{song_myers_adams_zhu_2014, title={Stretchable and Reversibly Deformable Radio Frequency Antennas Based on Silver Nanowires}, volume={6}, ISSN={["1944-8252"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84896995952&partnerID=MN8TOARS}, DOI={10.1021/am405972e}, abstractNote={We demonstrate a class of microstrip patch antennas that are stretchable, mechanically tunable, and reversibly deformable. The radiating element of the antenna consists of highly conductive and stretchable material with screen-printed silver nanowires embedded in the surface layer of an elastomeric substrate. A 3-GHz microstrip patch antenna and a 6-GHz 2-element patch array are fabricated. Radiating properties of the antennas are characterized under tensile strain and agree well with the simulation results. The antenna is reconfigurable because the resonant frequency is a function of the applied tensile strain. The antenna is thus well suited for applications like wireless strain sensing. The material and fabrication technique reported here could be extended to achieve other types of stretchable antennas with more complex patterns and multilayer structures.}, number={6}, journal={ACS APPLIED MATERIALS & INTERFACES}, author={Song, Lingnan and Myers, Amanda C. and Adams, Jacob J. and Zhu, Yong}, year={2014}, month={Mar}, pages={4248–4253} }
 @article{adams_bernhard_2013, title={Broadband Equivalent Circuit Models for Antenna Impedances and Fields Using Characteristic Modes}, volume={61}, ISSN={["1558-2221"]}, DOI={10.1109/tap.2013.2261852}, abstractNote={An approach for modeling antenna impedances and radiation fields in terms of fundamental eigenmodes is presented. Our method utilizes the simple frequency behavior of the characteristic modes to develop fundamental building blocks that superimpose to create the total response. In this paper, we study the modes of a dipole, but the method may be applied to more complicated structures as the modes retain many of their characteristics. We show that the eigenmode-based approach results in a more accurate model for the same complexity compared to a typical series RLC resonator model. Higher order modes can be more accurately modeled with added circuit complexity, but we show that this may not always be necessary. Because this method is based on the physical behavior of the fundamental modes, it also accurately connects circuit models to radiation patterns and other field behavior. To demonstrate this, we show that far field patterns, gain, and beam width of a dipole can be accurately extrapolated over a decade of bandwidth using data at two frequency points.}, number={8}, journal={IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION}, author={Adams, Jacob J. and Bernhard, Jennifer T.}, year={2013}, month={Aug}, pages={3985–3994} }
 @inproceedings{adams_2013, place={Monticello, IL}, title={Exploiting patterns in characteristic modes for efficient analytical and numerical modeling}, booktitle={Proceedings of the 2013 Antenna Applications Symposium}, author={Adams, J.J.}, year={2013}, month={Sep}, pages={145–157} }
 @inproceedings{adams_bernhard_2013, title={Modeling of dense metallic grids for transparent transmission lines and antennas}, booktitle={2013 ieee antennas and propagation society international symposium (apsursi)}, author={Adams, J. J. and Bernhard, J. T.}, year={2013}, pages={700–701} }
 @inproceedings{adams_bernhard_2012, place={Monticello, IL}, title={Eigenmode-based circuit models for antennas}, booktitle={Proceedings of the 2012 Antenna Applications Symposium}, author={Adams, J.J. and Bernhard, J.T.}, year={2012}, month={Sep}, pages={25–37} }
 @inproceedings{adams_slimmer_lewis_bernhard_2012, place={Las Vegas, NV}, title={Three-dimensional package-integrated antennas for electrically small sensor nodes}, booktitle={Proceedings of the Government Microwave Applications and Critical Technology Conference (GOMAC)}, author={Adams, J.J. and Slimmer, S.C. and Lewis, J.A. and Bernhard, J.T.}, year={2012}, month={Mar} }
 @article{adams_bernhard_2011, title={A Modal Approach to Tuning and Bandwidth Enhancement of an Electrically Small Antenna}, volume={59}, ISSN={0018-926X 1558-2221}, url={http://dx.doi.org/10.1109/tap.2011.2109683}, DOI={10.1109/tap.2011.2109683}, abstractNote={We describe the physical phenomena that contribute to the behavior of an electrically small TM10 antenna using characteristic mode theory. The application of characteristic modes to antenna tuning and bandwidth enhancement serves as demonstration of the broad utility of the modal technique. A modal analysis of the TM10 antenna's impedance match yields several interesting observations as to the nature of resonances and antiresonances, which has implications for the impedance matching of small antennas in general. Furthermore, to overcome the bandwidth limitations inherent in small antennas, we determine that multiple resonances must be combined and use a conductance ratio as a figure of merit for design. We then investigate the TM10 antenna's potential for multiresonant operation by examining different candidate modes. Using the appropriate characteristic modes to form multiple resonances, we show how the bandwidth of the TM10 antenna can be designed to be nearly double that expected from the physical limit for a single resonance.}, number={4}, journal={IEEE Transactions on Antennas and Propagation}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Adams, Jacob J. and Bernhard, Jennifer T.}, year={2011}, month={Apr}, pages={1085–1092} }
 @inproceedings{adams_slimmer_lewis_bernhard_2011, place={Monticello, IL}, title={Bandwidth limitations, matching, and fabrication of multimode electrically small antennas}, booktitle={Proceedings of the 2011 Antenna Applications Symposium}, author={Adams, J.J. and Slimmer, S.C. and Lewis, J.A. and Bernhard, J.T.}, year={2011}, month={Sep}, pages={162–179} }
 @article{adams_slimmer_malkowski_duoss_lewis_bernhard_2011, title={Comparison of Spherical Antennas Fabricated via Conformal Printing: Helix, Meanderline, and Hybrid Designs}, volume={10}, ISSN={1536-1225 1548-5757}, url={http://dx.doi.org/10.1109/lawp.2011.2178999}, DOI={10.1109/lawp.2011.2178999}, abstractNote={The design tradeoffs between three spherically conformal electric monopoles-the spherical helix (SH), spherical meanderline (SM), and a hybrid design-are explored through both simulation and measurement. We show that the SH is efficient, but can be difficult to impedance match without external components. On the other hand, the SM antenna has a widely controllable impedance with slightly increased loss. Thus, a hybrid design is proposed that retains the desirable qualities of both the SH and SM. All three designs are fabricated using a conformal printing technique for comparison. We describe the design tradeoffs and physical insights gained through evaluating the efficiency, Q, and matching behavior of these antennas.}, journal={IEEE Antennas and Wireless Propagation Letters}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Adams, Jacob J. and Slimmer, Scott C. and Malkowski, Thomas F. and Duoss, Eric B. and Lewis, Jennifer A. and Bernhard, Jennifer T.}, year={2011}, pages={1425–1428} }
 @article{adams_duoss_malkowski_motala_ahn_nuzzo_bernhard_lewis_2011, title={Conformal Printing of Electrically Small Antennas on Three-Dimensional Surfaces}, volume={23}, ISSN={0935-9648}, url={http://dx.doi.org/10.1002/adma.201003734}, DOI={10.1002/adma.201003734}, abstractNote={J. J. Adams ,[+] Prof. J. T. Bernhard Department of Electrical and Computer Engineering University of Illinois at Urbana-Champaign Urbana, IL 61801, USA E-mail: jbernhar@illinois.edu Dr. E. B. Duoss ,[+,++] T. F. Malkowski ,[+] Dr. B. Y. Ahn , Prof. J. A. Lewis Department of Materials Science and Engineering University of Illinois at Urbana-Champaign Urbana, IL 61801 USA E-mail: jalewis@illinois.edu Dr. M. J. Motala , Prof. R. G. Nuzzo Department of Chemistry University of Illinois at Urbana-Champaign Urbana, Illinois 61801, USA [+] These authors contributed equally to this work. [++] Presently at Lawrence Livermore National Laboratory, Center for Microand NanoTechnology, Livermore, CA 94550 USA}, number={11}, journal={Advanced Materials}, publisher={Wiley}, author={Adams, Jacob J. and Duoss, Eric B. and Malkowski, Thomas F. and Motala, Michael J. and Ahn, Bok Yeop and Nuzzo, Ralph G. and Bernhard, Jennifer T. and Lewis, Jennifer A.}, year={2011}, month={Jan}, pages={1335–1340} }
 @inproceedings{adams_duoss_malkowski_lewis_bernhard_2011, place={Spokane, WA}, title={Design of spherical meanderline antennas}, booktitle={Proceedings of the 2011 IEEE International Symposium on Antennas and Propagation}, author={Adams, J.J. and Duoss, E.B. and Malkowski, T.F. and Lewis, J.A. and Bernhard, J.T.}, year={2011}, month={Jul}, pages={765–768} }
 @article{adams_duoss_malkowski_motala_ahn_nuzzo_bernhard_lewis_2011, title={Microfabrication: Conformal Printing of Electrically Small Antennas on Three-Dimensional Surfaces (Adv. Mater. 11/2011)}, volume={23}, ISSN={0935-9648}, url={http://dx.doi.org/10.1002/adma.201190032}, DOI={10.1002/adma.201190032}, abstractNote={Jennifer A. Lewis, Jennifer T. Bernhard, and co-workers demonstrate on p. 1335 the conformal printing of electrically conductive meander lines onto hemispherical glass substrates. The bandwidth of these electrically small antennas approaches the fundamental limit for their size. This space-filling design offers nearly an order of magnitude improvement over rudimentary monopole antennas. Cover design by T. Malkowski and R. Durdle (Beckman Institute ITG), University of Illinois.}, number={11}, journal={Advanced Materials}, publisher={Wiley}, author={Adams, Jacob J. and Duoss, Eric B. and Malkowski, Thomas F. and Motala, Michael J. and Ahn, Bok Yeop and Nuzzo, Ralph G. and Bernhard, Jennifer T. and Lewis, Jennifer A.}, year={2011}, month={Mar}, pages={1304–1304} }
 @article{russo_ahn_adams_duoss_bernhard_lewis_2011, title={Pen-on-Paper Flexible Electronics}, volume={23}, ISSN={0935-9648}, url={http://dx.doi.org/10.1002/adma.201101328}, DOI={10.1002/adma.201101328}, abstractNote={Figure 1 . a) Optical image of a rollerball pen loaded with a conductive silver ink. The background shows conductive text written on Xerox paper. b and c) SEM images of the side and top views of the rollerball pen. d) Optical image of the rollerball pen tip, captured during writing a conductive silver track on a Xerox paper. Printed electronics constitute an emerging class of materials with potential application in photovoltaics, [ 1 ] transistors, [ 2 , 3 ] displays, [ 4–6 ] batteries, [ 7 ] antennas, [ 8 ] and sensors. [ 9 , 10 ] Recent attention has focused on paper substrates as a low-cost, enabling platform for fl exible, lightweight, and disposable devices. [ 11–13 ]}, number={30}, journal={Advanced Materials}, publisher={Wiley}, author={Russo, Analisa and Ahn, Bok Yeop and Adams, Jacob J. and Duoss, Eric B. and Bernhard, Jennifer T. and Lewis, Jennifer A.}, year={2011}, month={Jun}, pages={3426–3430} }
 @inproceedings{adams_bernhard_2010, place={Monticello, IL}, title={Tuning small monopole antennas: modes, stubs, and Q}, booktitle={Proceedings of the 2010 Antenna Applications Symposium}, author={Adams, J.J. and Bernhard, J.T.}, year={2010}, month={Sep}, pages={256–269} }
 @inproceedings{adams_bernhard_2009, place={Monticello, IL}, title={Bandwidth enhancement of a small antenna by modal superposition}, booktitle={Proceedings of the 2009 Antenna Applications Symposium}, author={Adams, J.J. and Bernhard, J.T.}, year={2009}, month={Sep}, pages={1–15} }
 @inproceedings{bernhard_adams_anderson_martin_2009, title={Measuring electrically small antennas: Details and implications}, ISBN={9781424443956}, url={http://dx.doi.org/10.1109/iwat.2009.4906959}, DOI={10.1109/iwat.2009.4906959}, abstractNote={This paper discusses the details surrounding the measurement of electrically small antennas, common errors in measurements, and the implications of these errors on system performance. Issues of small ground planes, cable effects, and efficiency measurements are examined for their apparent and interrelated effects on input impedance, radiation patterns, and system performance.}, booktitle={2009 IEEE International Workshop on Antenna Technology}, publisher={IEEE}, author={Bernhard, J. T. and Adams, J. J. and Anderson, M. D. and Martin, J. M.}, year={2009}, month={Mar} }
 @article{adams_bernhard_2009, title={Tuning Method for a New Electrically Small Antenna With Low $Q$}, volume={8}, ISSN={1536-1225 1548-5757}, url={http://dx.doi.org/10.1109/lawp.2009.2015437}, DOI={10.1109/lawp.2009.2015437}, abstractNote={We theoretically describe and experimentally demonstrate a new class of electrically small spherical antennas with near-minimum radiation Q. The antenna operates by supporting the TM10 spherical mode and minimizing excitation of higher order modes. The antenna compares favorably to existing electrically small antennas and can be easily designed for any frequency or with any electrical size. The antenna can be matched without an external network using methods described in this work. Measurements of two antennas of different electrical sizes are presented to demonstrate the tunability of the structure.}, journal={IEEE Antennas and Wireless Propagation Letters}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Adams, J.J. and Bernhard, J.T.}, year={2009}, pages={303–306} }
 @inproceedings{adams_bernhard_2008, place={Monticello, IL}, title={A class of electrically small spherical antennas with near-minimum Q}, booktitle={Proceedings of the 2008 Antenna Applications Symposium}, author={Adams, J.J. and Bernhard, J.T.}, year={2008}, month={Sep}, pages={165–175} }
 @inproceedings{adams_bernhard_2008, title={A low Q electrically small spherical antenna}, ISBN={9781424420414}, url={http://dx.doi.org/10.1109/aps.2008.4619194}, DOI={10.1109/aps.2008.4619194}, abstractNote={This paper proposes an electrically small antenna with minimum Q, the TM10 mode must be excited while minimizing excitation of other modes. The TM10 antenna is expected to exhibit an omnidirectional pattern. Indeed, the pattern is found to be that of a monopole with the null directed normal to the ground plane. Cross-polarization is extremely small, suggesting that other modes are not significantly excited.}, booktitle={2008 IEEE Antennas and Propagation Society International Symposium}, publisher={IEEE}, author={Adams, J.J. and Bernhard, J.T.}, year={2008}, month={Jul} }
 @article{sharp_adams_machiraju_lee_crane_2007, title={Physics-Based Subsurface Visualization of Human Tissue}, volume={13}, ISSN={1077-2626}, url={http://dx.doi.org/10.1109/tvcg.2007.1003}, DOI={10.1109/tvcg.2007.1003}, abstractNote={In this paper, we present a framework for simulating light transport in three-dimensional tissue with inhomogeneous scattering properties. Our approach employs a computational model to simulate light scattering in tissue through the finite element solution of the diffusion equation. Although our model handles both visible and nonvisible wavelengths, we especially focus on the interaction of near infrared (NIR) light with tissue. Since most human tissue is permeable to NIR light, tools to noninvasively image tumors, blood vasculature, and monitor blood oxygenation levels are being constructed. We apply this model to a numerical phantom to visually reproduce the images generated by these real-world tools. Therefore, in addition to enabling inverse design of detector instruments, our computational tools produce physically-accurate visualizations of subsurface structures}, number={3}, journal={IEEE Transactions on Visualization and Computer Graphics}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Sharp, Richard and Adams, Jacob and Machiraju, Raghu and Lee, Robert and Crane, Robert}, year={2007}, month={May}, pages={620–629} }
 @inproceedings{sharp_adams_machiraju_lee_crane_2006, title={Simulating Transillumination in Organic Material with Near Infrared Light}, ISBN={1424402778 1424402786}, url={http://dx.doi.org/10.1109/lssa.2006.250415}, DOI={10.1109/lssa.2006.250415}, abstractNote={We investigate problems involving light diffusion through arbitrary meshes with inhomogeneous scattering properties. We focus on three main areas: rapid source calculation, efficient solution and solution updates and robust quality adaptive meshing. Preliminary results show that we have a speedup of an order of magnitude compared to naive implementations with similar error rates. We expect this work to be valuable to researchers who are interested in efficient accurate solutions when simulating near infrared subsurface scattering in tissue to validate or understand the physics behind their experiments}, booktitle={2006 IEEE/NLM Life Science Systems and Applications Workshop}, publisher={IEEE}, author={Sharp, Richard and Adams, Jacob and Machiraju, Raghu and Lee, Robert and Crane, Robert}, year={2006}, month={Jul} }