@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{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{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{bharambe_adams_2020, title={Planar 2-D Beam Steering Antenna Using Liquid Metal Parasitics}, volume={68}, url={https://doi.org/10.1109/TAP.2020.2998219}, DOI={10.1109/TAP.2020.2998219}, abstractNote={We demonstrate a single-feed planar antenna capable of 2-D beam-steering using pumped liquid metal (LM) parasitics. Instead of relying on phase shifters for beam-steering, the proposed antenna employs LM plugs acting as parasitic elements to achieve up to ±48° steering in the H-plane and ±54° steering in the E-plane. The antenna can also steer in diagonal and OFF-diagonal planes using a combination of the E and H plane steering techniques. Simultaneously, the antenna maintains a 2:1 VSWR for all the states. By creating a composite realized gain plot for all these states, it is seen that the antenna can cover as much as 23% of the spherical area with at least 5 dBi of realized gain, compared to 4.5% in the absence of LM parasitic elements for beam-steering. We also quantify the pattern diversity (PD) and illustrate that the antenna achieves a greater PD than an electrically scanned <inline-formula> <tex-math notation="LaTeX">$2 \times 2$ </tex-math></inline-formula> phased array occupying an equivalent aperture (<inline-formula> <tex-math notation="LaTeX">$0.55\lambda _{0} \times 0.66\lambda _{0}$ </tex-math></inline-formula>).}, number={11}, journal={IEEE Transactions on Antennas and Propagation}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Bharambe, Vivek T. and Adams, Jacob J.}, year={2020}, month={Nov}, pages={7320–7327} }
 @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{bharambe_ma_dickey_adams_2019, title={Planar, Multifunctional 3D Printed Antennas Using Liquid Metal Parasitics}, volume={7}, url={https://doi.org/10.1109/ACCESS.2019.2942058}, DOI={10.1109/ACCESS.2019.2942058}, abstractNote={This paper describes a liquid metal-based multifunctional antenna capable of wideband frequency tuning, dual band operation, and polarization reconfiguration. The radiating elements consist of parasitically-excited plugs of room-temperature liquid metal in 3D printed channels. Syringe pumps flow the gallium-alloy plugs in proximity to a capacitive feeding structure. This non-contact feeding scheme separates the metal flow path from the SMA connector and lends mechanical robustness at the feed while allowing impedance matching over a wide range of frequencies. Sliding the plug along a right-angle bend enables linear polarization reconfiguration, while simultaneously placing plugs in both orthogonal channels can generate circular or 45° linear polarization. Dual band operation is also supported by infusing plugs of two dissimilar lengths into the two channels. Simulation and measurement results demonstrate that this antenna can tune its impedance over a decade (10:1 frequency range) maintaining a 2:1 VSWR and achieve a polarization diversity >12 dB. The pumped plugs can circulate at a peak velocity of 50 mm/s, currently limited only by our pumping equipment. Repeatability analysis is also performed by cycling the plug actuation more than 1100 times. More complex designs can exploit this design concept to develop new types of highly versatile, multi-functional antennas.}, journal={IEEE Access}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Bharambe, Vivek T. and Ma, Jinwoo and Dickey, Michael D. and Adams, Jacob J.}, year={2019}, pages={134245–134255} }
 @article{mukai_bharambe_adams_suh_2018, title={Effect of bending and padding on the electromagnetic performance of a laser-cut fabric patch antenna}, volume={89}, 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 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{barbee_mondal_deng_bharambe_neumann_adams_boechler_dickey_craig_2018, title={Mechanochromic Stretchable Electronics}, volume={10}, ISSN={["1944-8252"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85052280661&partnerID=MN8TOARS}, 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{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{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} }