@article{zhong_ricketts_2023, title={14dB Active Gain Magnetic Negative Permeability Metamaterial Cell with Self-coupling Compensation}, DOI={10.23919/EuMC58039.2023.10290148}, abstractNote={Metamaterials are an attractive material to obtain electromagnetic properties that cannot be found in nature. While there have been many successful demonstrations of metamaterials, including those with negative permeability that are able to focus magnetoquasistatic waves, such as in wireless power transfer, they have historically suffered from loss. Overcoming this loss aspect of metamaterials is important for making their impact a reality. In this paper, we introduce an active metamaterial cell that achieves 14 dB of gain and stable amplification for applications in emerging metamaterials.}, journal={2023 53RD EUROPEAN MICROWAVE CONFERENCE, EUMC}, author={Zhong, Hongtao and Ricketts, David S.}, year={2023}, pages={424–427} }
 @article{harris_ricketts_2023, title={Maximum gain enhancement in wireless power transfer using anisotropic metamaterials}, volume={13}, ISSN={["2045-2322"]}, DOI={10.1038/s41598-023-32415-9}, abstractNote={Abstract}, number={1}, journal={SCIENTIFIC REPORTS}, author={Harris, William Carter and Ricketts, David S.}, year={2023}, month={May} }
 @article{ricketts_2020, title={A Modern 16-QAM Digital Radio You Can Design and Build at Home [Application Notes]}, volume={21}, ISSN={["1557-9581"]}, DOI={10.1109/MMM.2020.2985192}, abstractNote={July 2020 In the winter of 1894, Guglielmo Marconi called his mother up to the attic, where he had been tinkering with a new device called a coherer, which could sense electronic signals forming a spark. He showed her how he could ring a bell from a few meters away with an artificial lightning bolt—a spark gap, just like Hertz had made be fore him. The era of wireless communication was born. I m a g i n e t h e l a t e nights of Marconi working in his makeshift laboratory in the attic of his parents’ house, creating his device out of copper wire and ribbon, glass jars, and iron filings using a few rough tools. Marconi had the ability to build something and test it in a few hours—to go from the idea in his head to a prototype in his hands in perhaps only a day. In today’s era of simulation and analysis, microprocessors, digital application-specified integrated circuits, and digital signal processing (DSP), it seems a far-fetched idea that a person could conceive of a modern radio and build it with his or her own hands as Marconi did with his first radio, let alone do it all in one day. However, this article presents a project aimed at doing just that—one that brings the concepts of modern digital communications and radios into a form that you can design, build, and test in as little as a day. Bits2waves [1] is an experiential program that introduces microwave engineers and enthusiasts to a modern quadrature amplitudemodu lated (QA M) radio and takes them step by step through the design, simulation, layout, fabrication, and final testing of the key pieces of today’s radios.}, number={7}, journal={IEEE MICROWAVE MAGAZINE}, author={Ricketts, David S.}, year={2020}, month={Jul}, pages={10–22} }
 @article{shen_ricketts_2020, title={Compact W-Band "Swan Neck" Turnstile Junction Orthomode Transducer Implemented by 3-D Printing}, volume={68}, ISSN={["1557-9670"]}, DOI={10.1109/TMTT.2020.2992065}, abstractNote={A turnstile junction orthomode transducer (OMT) provides polarization separation/combining on a full waveguide bandwidth; however, it bears a complex connecting structure, which accordingly leads to a bulky volume. We present a compact W-band (75–110 GHz) OMT using a “swan neck” twist for the connection between a turnstile junction and an $E$ -plane Y-junction, for minimizing the overall OMT structure. The core volume for the proposed OMT is $9\times $ less than the previously reported stacked-layer OMT. The compact W-band OMT was built by digital light processing (DLP) 3-D printing technology and was postmetallized by silver electroless plating. The return loss of the vertical-polarized port (V-port) and the horizontal-polarized port (H-port) is characterized, as averagely 17 and 15 dB, respectively. The measured average insertion loss from H- and V-ports to the common port is 0.5 and 0.6 dB. The measured isolation between V- and H-ports is averagely 28 dB. Furthermore, the turnstile junction asymmetry along the central axis was revealed in computed tomography (CT) scanned images. The simulation shows a negative effect of the asymmetric structure on the OMT isolation. In addition, the dual-polarized (dual-pol) antenna combining such OMT and a corrugated horn was realized in a compact size. The cross-polarization level of the OMT, characterized in a far-field test of this dual-pol antenna, is averagely −18 dB at the W-band.}, number={8}, journal={IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES}, author={Shen, Junyu and Ricketts, David S.}, year={2020}, month={Aug}, pages={3408–3417} }
 @article{dwye_ricketts_2020, title={The North Carolina State University Rabbit Radar: Build a Frequency-Modulated Continuous-Wave Radar in a Day [Application Notes]}, volume={21}, ISSN={["1557-9581"]}, DOI={10.1109/MMM.2020.2971184}, abstractNote={We present the design and hand fabrication of a frequency-modulated continuous-wave (FMCW) radar that teaches practicing engineers and students the fundamentals of radar theory, microwave systems, and component design. The fabrication can be done by hand-cutting simple shapes of foil with a knife or by cutting more complex shapes of foil with a 2D cutter from a hobby store [1]. We provide a brief overview of the theory of operation for the FMCW system and each component used. We then describe the design procedure for each component along with experimental results from the fabricated components. The frequency of operation was chosen to be 925 MHz, or around 1 GHz. This decision was made for multiple reasons. First, the frequency is within an Industry, Science, and Medicine (ISM) band. Second, this enabled easy fabrication of microwave transmission-line circuits (m/4 is roughly 40 mm) and reasonably easy hand-soldering of discrete components for termination and amplifier biasing. Operation at the 2.4-GHz ISM band for non-North American applications is a simple shift of frequency in the design targets, but the theory remains the same.}, number={5}, journal={IEEE MICROWAVE MAGAZINE}, author={Dwye, Matthew and Ricketts, David S.}, year={2020}, month={May}, pages={136–145} }
 @article{shen_ricketts_2019, title={Additive Manufacturing of Complex Millimeter-Wave Waveguides Structures Using Digital Light Processing}, volume={67}, ISSN={["1557-9670"]}, DOI={10.1109/TMTT.2018.2889452}, abstractNote={Additive manufacturing technology has enabled the manufacturing of complex structures, especially those with intricate internal features. This paper proposes a method for building complex-structured millimeter-wave waveguides using a strategy that combines digital light processing 3-D printing technology, a curved corner design, an off-axis print angle of 45°, and a robust postmetallization process. To demonstrate the capability of this combined-strategy method, a traditional magic tee prototype and an adapted inherently matched magic tee prototype are fabricated for use in the W-band. The measured performance of the fabricated inherently matched magic tee demonstrates return loss better than 13.5 dB, isolation coefficients higher than 15.7 dB, insertion losses smaller than 1.3 dB, and a magnitude imbalance of less than 1.3 dB across 80–105 GHz. The 3-D printed magic tee has a comparable performance to a W-band CNC-machined magic tee but weighs 77.5% less than the metallic one.}, number={3}, journal={IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES}, author={Shen, Junyu and Ricketts, David S.}, year={2019}, month={Mar}, pages={883–895} }
 @article{ricketts_shi_li_sun_yildirim_ham_2019, title={Electrical Solitons for Microwave Systems}, volume={20}, ISSN={["1557-9581"]}, DOI={10.1109/MMM.2019.2891382}, abstractNote={Nonlinearity and dispersion are often nuisances that microwave engineers seek to curb. However, there is a system that can harmonize these two effects to produce useful-and fascinating-dynamics with unique microwave engineering opportunities: the nonlinear transmission line (NLTL) [1]-[11]. The NLTL is a ladder network of lumped inductors and varactors [Figure 1(a)] that can be alternatively built by periodically loading a smooth transmission line with lumped varactors [Figure 1(b)].}, number={4}, journal={IEEE MICROWAVE MAGAZINE}, author={Ricketts, David S. and Shi, En and Li, Xiaofeng and Sun, Nan and Yildirim, O. Ozgur and Ham, Donhee}, year={2019}, month={Apr}, pages={123–134} }
 @article{harris_stancil_ricketts_2019, title={Improved wireless power transfer efficiency with non-perfect lenses}, volume={114}, ISSN={["1077-3118"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85064392786&partnerID=MN8TOARS}, DOI={10.1063/1.5081629}, abstractNote={Negative refractive index metamaterials (MMs) have found widespread interest in shaping electromagnetic waves. One attractive area is energy transfer using low frequency magnetic waves or wireless power transfer (WPT). Previous reports have presented an isotropic metamaterial with μr = −1 as a “perfect lens” to focus energy and enhance WPT efficiency. In this work, we show that, while the perfect lens condition does enhance efficiency, anisotropic MMs with μr ≠ −1 can provide a larger enhancement in efficiency. These “non-perfect” lenses offer higher efficiency by enhancing the coupled field while incurring lower losses in the magnetostatic waves excited in or on the materials.}, number={14}, journal={APPLIED PHYSICS LETTERS}, author={Harris, William Carter and Stancil, Daniel D. and Ricketts, David S.}, year={2019}, month={Apr} }
 @article{lal_ali_ricketts_2018, title={Analysis and Comparison of High-Resolution GS/s Samplers in Advanced BiCMOS and CMOS}, volume={65}, ISSN={["1558-3791"]}, DOI={10.1109/tcsii.2018.2822785}, abstractNote={High-speed and high-resolution analog to digital converters (ADCs) (10+ bits) are essential components of modern wireless communication systems and mmWave radios. Their performance is often limited by the noise and distortion from the front-end samplers, the design of which can be challenging. Modern ADC design has moved heavily to scaled CMOS technologies due to its attractive digital and integration capabilities, but these processes face challenges of high fabrication costs, and diminishing analog performance that has to be bolstered by extensive digital calibration. On the other hand, BiCMOS processes have advanced and scaled sufficiently that they may be able to offer the best of the mixed signal world. This brief examines, both theoretically and through simulations, the design of samplers for high-speed, low-distortion in CMOS and BiCMOS for GS/s ADCs. Two fully differential samplers, with an equivalent sampling frequency of 5 GS/s and an input frequency range of up to 10 GHz, are designed in a 90-nm BiCMOS and a 28-nm CMOS process, respectively, and their distortion performance is analyzed, simulated, and compared.}, number={5}, journal={IEEE TRANSACTIONS ON CIRCUITS AND SYSTEMS II-EXPRESS BRIEFS}, author={Lal, Deeksha and Ali, Ahmed M. A. and Ricketts, David S.}, year={2018}, month={May}, pages={532–536} }
 @article{tai_abbasi_ricketts_2018, title={Analysis and design of high-power and efficient, millimeter-wave power amplifier systems using zero degree combiners}, volume={105}, ISSN={["1362-3060"]}, DOI={10.1080/00207217.2017.1335798}, abstractNote={ABSTRACT We present the analysis and design of high-power millimetre-wave power amplifier (PA) systems using zero-degree combiners (ZDCs). The methodology presented optimises the PA device sizing and the number of combined unit PAs based on device load pull simulations, driver power consumption analysis and loss analysis of the ZDC. Our analysis shows that an optimal number of N-way combined unit PAs leads to the highest power-added efficiency (PAE) for a given output power. To illustrate our design methodology, we designed a 1-W PA system at 45 GHz using a 45 nm silicon-on-insulator process and showed that an 8-way combined PA has the highest PAE that yields simulated output power of 30.6 dBm and 31% peak PAE.}, number={1}, journal={INTERNATIONAL JOURNAL OF ELECTRONICS}, author={Tai, Wei and Abbasi, Mortez and Ricketts, David S.}, year={2018}, pages={1–11} }
 @inproceedings{ricketts_2017, title={Analog limitations for high-speed digital radios: Where the bits stop working}, DOI={10.1109/mwscas.2017.8052854}, abstractNote={Fundamental physical constraints, such as noise and channel capacity, set an upper bound to theoretical performance of many systems. In this work we examine the limitations of high-speed data in modern digital wireless radio systems. Although physical constraints provide an ultimate limit, we show that signal-to-noise-plus-distortion-ratio (SNDR) and nonlinearity of modern CMOS and Bipolar technologies limit current performance well before physical limitations. By examining several example circuit topologies used in data conversion in digital radios, we show that 3rd order harmonics (HD3) likely set the practical barrier to high data rates at SNDRs above 40 dB and sampling rates above 20 GS/s.}, booktitle={2017 ieee 60th international midwest symposium on circuits and systems (mwscas)}, author={Ricketts, D. S.}, year={2017}, pages={37–40} }
 @inproceedings{shen_aiken_abbasi_parekh_zhao_dickey_ricketts_2017, title={Rapid prototyping of low loss 3D printed waveguides for millimeter-wave applications}, DOI={10.1109/mwsym.2017.8058593}, abstractNote={Traditional hollow metallic waveguide manufacturing techniques are readily capable of producing components with high-precision geometric tolerances, yet generally lack the ability to customize individual parts on demand or to deliver finished components with low lead times. This paper proposes a Rapid-Prototyping (RP) method for relatively low-loss millimeter-wave hollow waveguides produced using consumer-grade stere-olithographic (SLA) Additive Manufacturing (AM) technology, in conjunction with an electroless metallization process optimized for acrylate-based photopolymer substrates. To demonstrate the capabilities of this particular AM process, waveguide prototypes are fabricated for the W- and D-bands. The measured insertion loss at W-band is between 0.12 dB/in to 0.25 dB/in, corresponding to a mean value of 0.16 dB/in. To our knowledge, this is the lowest insertion loss figure presented to date, when compared to other W-Band AM waveguide designs reported in the literature. Printed D-band waveguide prototypes exhibit a transducer loss of 0.26 dB/in to 1.01 dB/in, with a corresponding mean value of 0.65 dB/in, which is similar performance to a commercial metal waveguide.}, booktitle={2017 ieee mtt-s international microwave symposium (ims)}, author={Shen, J. Y. and Aiken, M. W. and Abbasi, M. and Parekh, D. P. and Zhao, X. and Dickey, Michael and Ricketts, D. S.}, year={2017}, pages={41–44} }
 @article{chabalko_besnoff_laifenfeld_ricketts_2017, title={Resonantly Coupled Wireless Power Transfer for Non-Stationary Loads With Application in Automotive Environments}, volume={64}, ISSN={["1557-9948"]}, DOI={10.1109/tie.2016.2609379}, abstractNote={Resonantly coupled wireless power transfer (RWPT) has become a popular means to deliver energy without direct contact between the source and load. One challenging application is nonstationary loads; those that move spatially in time. Such loads change the coupling between the source and load and with it the efficiency and maximum power transfer possible. One emerging application is in the automotive environment, where nonstationary loads such as powered seats and doors exist. Moreover, the automotive environment is particularly challenging due to the presence of metallic objects and the safety requirements of the passengers. In this work, we examine RWPT for nonstationary loads and present a design methodology for optimal efficiency and power transfer and show an RWPT of 70 W across a 24 cm distance in an automotive environment. We also examine the impact of the metallic environment and show how its effects can be mitigated. Finally, we examine the field intensity during RWPT and examine the safety of the passengers. We show that 70 W can be transmitted within 10 cm of a passenger while operating below safety limits.}, number={1}, journal={IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Chabalko, Matthew and Besnoff, Jordan and Laifenfeld, Moshe and Ricketts, David S.}, year={2017}, month={Jan}, pages={91–103} }
 @article{besnoff_chabalko_ricketts_2016, title={A Frequency-Selective Zero-Permeability Metamaterial Shield for Reduction of Near-Field Electromagnetic Energy}, volume={15}, ISSN={["1548-5757"]}, DOI={10.1109/lawp.2015.2466172}, abstractNote={Wireless power transfer and other near-field applications can generate large magnetoquasistatic fields that can potentially be harmful to humans or interact negatively with the environment. Several shields have been proposed for the magnetic near field, such as ferrite sheets or metallic shields. While each can be effective, there are tradeoffs to each, namely loss, weight, and cost. In addition, metallic and ferrite shields are broadband and block large portions of the electromagnetic spectrum. In this letter, we introduce a new type of magnetic near-field shield, a zero-permeability near-field metamaterial (NF-MM) shield. This shield operates by canceling the incident magnetic flux without significant additional loss to the system. Moreover, the zero-permeability shield is frequency-selective, blocking only a single or small bandwidth of frequencies, enabling shielding only at the desired frequency while allowing the remainder of the electromagnetic spectrum through. We show that a zero-permeability NF-MM shield can reduce magnetic field strength by 22.84 dB in simulation and demonstrate 77% reduction in an experimental prototype.}, journal={IEEE ANTENNAS AND WIRELESS PROPAGATION LETTERS}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Besnoff, Jordan and Chabalko, Matthew and Ricketts, David S.}, year={2016}, pages={654–657} }
 @inproceedings{harris_nicholst_abbasi_ricketts_2016, title={A Versatile mm-wave micromachined anti-reflective layer}, DOI={10.1109/apmc.2016.7931298}, abstractNote={Micromachined millimeter-wave anti-reflective layers (mm-AR) offer a highly customizable and effective method to maximize power transmission through dielectric media. The power transmitted through an air-dielectric interface is maximized by adding an anti-reflective layer whose thickness is a quarter-wavelength and whose dielectric constant is the geometric mean of air and the dielectric, in analogous fashion to a quarter-wave transformer in transmission line theory. The mm-AR is an artificial dielectric material with controlled thickness and dielectric constant. A DRIE process forms a sub-wavelength lattice in a substrate that controls the material's effective dielectric response. The resulting anti-reflective layers were used to improve transmission through a silicon-air interface from an average of 40% across the W-band to 95%. While silicon was used in this work, the demonstrated impedance matching technique can be used for a wide variety of dielectric materials.}, booktitle={2016 asia-pacific microwave conference (apmc2016)}, author={Harris, W. and Nicholst, T. and Abbasi, M. and Ricketts, D.}, year={2016} }
 @article{abbasi_ricketts_2016, title={A high-power, broadband 245-285 GHz balanced frequency doubler in 45 nm SOI CMOS}, volume={58}, ISSN={["1098-2760"]}, DOI={10.1002/mop.29586}, abstractNote={ABSTRACT}, number={2}, journal={MICROWAVE AND OPTICAL TECHNOLOGY LETTERS}, author={Abbasi, Morteza and Ricketts, David S.}, year={2016}, month={Feb}, pages={423–426} }
 @inproceedings{shen_aiken_ladd_dickey_ricketts_2016, title={A simple electroless plating solution for 3D printed microwave components}, DOI={10.1109/apmc.2016.7931434}, abstractNote={Using a modified version of the Tollens' Test, acrylate-based polymer prints made using a consumer-grade Digital Light Projection Stereolithographic (DLP-SLA) 3D printer are successfully silver plated, without the need for complex surface preparation techniques. A single-piece prototype waveguide design is used for testing the plating process, and a discussion is provided on minimizing printing process variables such as polymerization shrinkage and undesirable geometric tolerance variance. Measurement results of plated WR-10 1-inch waveguide sections show reflection coefficients of less than −21dB and an insertion loss of less than 0.53dB, which are comparable to similar studies using specialized plating and split-block designs. Furthermore, this approach shows great potential in providing an affordable passive microwave component rapid prototyping solution for research environments.}, booktitle={2016 asia-pacific microwave conference (apmc2016)}, author={Shen, J. Y. and Aiken, M. and Ladd, C. and Dickey, Michael and Ricketts, D. S.}, year={2016} }
 @article{besnoff_abbasi_ricketts_2016, title={High data-rate communication in near-field RFID and wireless power using higher order modulation}, volume={64}, number={2}, journal={IEEE Transactions on Microwave Theory and Techniques}, author={Besnoff, J. and Abbasi, M. and Ricketts, D. S.}, year={2016}, pages={401–413} }
 @article{chabalko_besnoff_ricketts_2016, title={Magnetic Field Enhancement in Wireless Power With Metamaterials and Magnetic Resonant Couplers}, volume={15}, ISSN={["1548-5757"]}, DOI={10.1109/lawp.2015.2452216}, abstractNote={We report on the magnetic field and coupling enhancement for increased wireless power transfer (WPT) efficiency using intermediate materials. We examine the physical mechanisms for enhancement using a metamaterial (MM) and magnetic resonant field enhancement (MR-FE) and present an analytical and simulation analysis as well as an experimental study of these enhancement mechanisms. While both increase the mutual coupling, the loss of the contrasting enhancement mechanisms significantly impacts WPT efficiency enhancement. Our analysis shows that the MR-FE approach can have up to a 4-times-higher efficiency over the MM approach due to the lower loss of its field enhancement mechanism.}, journal={IEEE ANTENNAS AND WIRELESS PROPAGATION LETTERS}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Chabalko, Matthew J. and Besnoff, Jordan and Ricketts, David S.}, year={2016}, pages={452–455} }
 @article{karagozler_goldstein_ricketts_2016, title={Scalable self-assembly process for the fabrication of sub-millimetre three-dimensional cylindrical tubes}, volume={11}, ISSN={["1750-0443"]}, DOI={10.1049/mnl.2015.0107}, abstractNote={The analysis, simulation and experimental fabrication of three-dimensional (3D) cylindrical tubes formed from 2D aluminium/silicon dioxide (Al/SiO2) substrates are presented. The photolithographically fabricated planar Al/SiO2 substrates bend under residual mechanical stress after release, self-assembling into 3D cylindrical tubes. They present an analytical model that allows them to reliably predict the resulting radius of curvature of bi-layer Al/SiO2 tubes with uniform cross-sections, and provides an approximate solution for SiO2 substrates with patterned Al cross-sections. Finite element analysis simulations and measurements of fabricated tubes show agreement with the model. In addition, they show through a series of batch experiments that the self-assembly process is repeatable with proper design of the substrates.}, number={1}, journal={MICRO & NANO LETTERS}, author={Karagozler, Mustafa Emre and Goldstein, Seth Copen and Ricketts, David S.}, year={2016}, month={Jan}, pages={4–8} }
 @inproceedings{abbasi_ricketts_2016, title={W-band corrugated and non-corrugated conical horn antennas using stereolithography 3D-printing technology}, DOI={10.1109/apmc.2016.7931300}, abstractNote={we are ideally looking for a cost-effective fabrication technique for any form structure light-weigh repeatable}, booktitle={2016 asia-pacific microwave conference (apmc2016)}, author={Abbasi, M. and Ricketts, D. S.}, year={2016} }
 @inproceedings{abbasi_ricketts_2016, title={mm-wave and THz multipliers: Advances and opportunities}, DOI={10.1109/apmc.2016.7931425}, abstractNote={This paper introduces a new way of evaluating performance of mm-wave integrated multiplier chains based on the power efficiency. Although superior performance of III–V technologies are acknowledged, focus of the paper will be on Silicon circuits which are more suited for large-scale multi-element integrated arrays. It will be discussed that power efficiency of the multiplier chain including the dc power required for generating the input RF signal is a very important metric for selecting the topology and configuration of the system. We will demonstrate that proper choice of topology as well as optimized circuit design yield state-of-the art output power at 260GHz–280GHz in SiGe and CMOS circuits.}, booktitle={2016 asia-pacific microwave conference (apmc2016)}, author={Abbasi, M. and Ricketts, D. S.}, year={2016} }
 @article{abbasi_ricketts_2015, title={275-285 GHz balanced frequency quadrupler chain in 45 nm SOI CMOS}, volume={51}, ISSN={["1350-911X"]}, DOI={10.1049/el.2015.2100}, abstractNote={A 280 GHz broadband balanced frequency quadrupler chain is presented. The quadrupler can be used to generate as high as 200 μW over a −3 dB bandwidth of 275–285 GHz, which enables emerging applications in sub-millimetre-wave communications and remote sensing. The circuit is designed and fabricated in a 45 nm silicon on insulator (SOI) CMOS technology and occupies an area of 0.21 mm2 including the pads. The chip consumes 85 mA dc current from a 1.1 V supply.}, number={18}, journal={ELECTRONICS LETTERS}, author={Abbasi, M. and Ricketts, D. S.}, year={2015}, month={Sep} }
 @inproceedings{tai_ricketts_2015, title={A compact, high-gain Q-band stacked power amplifier in 45nm SOI CMOS with 19.2dBm P-sat and 19% PAE}, booktitle={Ieee topical conference on power amplifiers for wireless and radio}, author={Tai, W. and Ricketts, D. S.}, year={2015}, pages={34–36} }
 @article{ricketts_chabalko_hillenius_2015, title={Erratum: “Experimental demonstration of the equivalence of inductive and strongly coupled magnetic resonance wireless power transfer” [Appl. Phys. Lett. 102, 053904 (2013)]}, volume={107}, ISSN={0003-6951 1077-3118}, url={http://dx.doi.org/10.1063/1.4926660}, DOI={10.1063/1.4926660}, abstractNote={First Page}, number={4}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={Ricketts, David S. and Chabalko, Matthew J. and Hillenius, Andrew}, year={2015}, month={Jul}, pages={049901} }
 @article{chabalko_ricketts_2015, title={Experimental characterization of Fabry-Perot resonances of magnetostatic volume waves in near-field metamaterials}, volume={106}, ISSN={["1077-3118"]}, DOI={10.1063/1.4907046}, abstractNote={In this work, we report on the experimental demonstration of magnetoquasistatic volume wave resonances in a 2-dimensional near field metamaterial (MM). Previous works have described only theoretically the magnetostatic waves in near field MMs and have reported peaks and valleys in the mutual coupling of MM enhanced wireless power transfer that they have attributed to Fabry-Perot resonances, however, neither has been experimentally measured nor characterized. We report on the direct magnetic field measurement of magnetostatic volume waves in a 2D near-field MM and show that the periodic peaks and valleys in mutual coupling observed previously are indeed due to a Fabry-Perot oscillation. In addition, we show that these resonances can be predicted from experimentally extracted permeability and the dimensions of the system.}, number={6}, journal={APPLIED PHYSICS LETTERS}, author={Chabalko, Matthew J. and Ricketts, David S.}, year={2015}, month={Feb} }
 @article{ricketts_chabalko_hillenius_2015, title={Experimental demonstration of the equivalence of inductive and strongly coupled magnetic resonance wireless power transfer (vol 102, 053904, 2013)}, volume={107}, number={4}, journal={Applied Physics Letters}, author={Ricketts, D. S. and Chabalko, M. J. and Hillenius, A.}, year={2015} }
 @inproceedings{besnoff_ricketts_2015, title={Near field wireless power transfer and quadrature amplitude modulated (QAM) communication link}, DOI={10.1109/wpt.2015.7139131}, abstractNote={We present a near field wireless power transfer (NF-WPT) link which is also capable of data communication through complex, quadrature amplitude (QAM) load modulation. We present a method for designing a 4QAM constellation that allows for minimal degradation of the NF-WPT link efficiency by minimizing the complex reflection coefficient. Using a modulation board and a resonant 4-coil NF-WPT system we demonstrate 307.2kbps data transmission, representing a 12.7% fractional bandwidth, over a distance of 1-coil diameter (29cm) at a carrier frequency of 2.428MHz. Efficiency of the NF-WPT is only reduced from 68% to approximately 63.1% when used for data communication as well as power transfer.}, booktitle={2015 IEEE Wireless Power Transfer Conference (WPTC)}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Besnoff, Jordan and Ricketts, David S.}, year={2015}, month={May} }
 @inproceedings{besnoff_ricketts_2015, title={Quadrature amplitude modulated (QAM) communication link for near and mid-range RFID systems}, DOI={10.1109/rfid.2015.7113086}, abstractNote={We present the theory and design equations for leveraging vector modulation in the form of M-ary quadrature amplitude modulation (QAM) for LF near and mid-range RFID systems, which can allow for the design of high bandwidth passive near and mid-range devices. The theory is developed through the impedance transformations that occur in coupled coil antennas. Using the developed theory along with system simulations, we determine the necessary load impedances for 4-QAM constellations at various distances for a carrier frequency of approximately 2.4 MHz and present 3 prototype boards that yield the desired reflections. The achievable data rates are investigated through a custom IQ demodulator, and we show that for communication distances of 17 cm, 29 cm, and 45 cm, which represent scaled coil diameter distances, data rates of 409.6 kbps, 307.2 kbps, and 153.6 kbps can be achieved. This corresponds to bandwidth percentages of 17%, 12%, and 6.5%, which surpasses the bandwidth percentage of typical NFC communication systems of about 3% for a carrier of 13.56 MHz (424 kbps).}, booktitle={2015 IEEE International Conference on RFID (RFID)}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Besnoff, Jordan and Ricketts, David}, year={2015}, month={Apr}, pages={151–157} }
 @inproceedings{besnoff_ricketts_2015, title={Wide bandwidth for high-speed communication in mid-range, resonant WPT and RFID systems}, DOI={10.1109/eumc.2015.7345721}, abstractNote={In this paper we present an experimental wireless power transfer (WPT) prototype that has achieved a 118 kHz power transfer bandwidth operating at the maximum achievable efficiency. Using a simulation and analytical model we show that the power transfer bandwidth of an optimally tuned WPT system is determined by the loaded Q of the system and not by the Q of the resonant tanks. This observation lead to the realization of a WPT communication system that can transmit data at high data rates greater than 8% of the carrier frequency, a data rate significantly greater than has previously been proposed for resonant WPT and RFID systems.}, booktitle={2015 European Microwave Conference (EuMC)}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Besnoff, Jordan and Ricketts, David S.}, year={2015}, month={Sep}, pages={147–150} }
 @article{tai_ricketts_2014, title={A COMPACT, 36 TO 72 GHz 15.8 dBm POWER AMPLIFIER WITH 66.7% FRACTIONAL BANDWIDTH IN 45 nm SOI CMOS}, volume={56}, ISSN={["1098-2760"]}, DOI={10.1002/mop.28062}, abstractNote={ABSTRACT}, number={1}, journal={MICROWAVE AND OPTICAL TECHNOLOGY LETTERS}, author={Tai, Wei and Ricketts, David S.}, year={2014}, month={Jan}, pages={166–169} }
 @inproceedings{tai_ricketts_2014, title={A W-band 21.1 dBm power amplifier with an 8-way zero-degree combiner in 45 nm SOI CMOS}, DOI={10.1109/mwsym.2014.6848585}, abstractNote={This paper presents a W-band power amplifier (PA) in 45 nm SOI CMOS. The PA incorporates an 8-way zero-degree combiner to efficiently combine 8 parallel PA units, each of which is a 2-stage cascode PA. At 80 GHz, the PA achieves a saturated output power (Psat) of 21.1 dBm, 10.1 dB peak gain, 5.2% peak PAE, and 12 GHz 3-dB bandwidth, and it consumes 1 mm2 of die area. The Psat of 21.1 dBm is the highest among reported W-band PAs in CMOS technology.}, booktitle={2014 ieee mtt-s international microwave symposium (ims)}, author={Tai, W. and Ricketts, D. S.}, year={2014} }
 @inproceedings{chen_carley_ricketts_2014, title={A process-technology-scaling-tolerant pipelined ADC architecture achieving 6-bit and 4 GS/s ADC in 45nm CMOS}, DOI={10.1109/sirf.2014.6828533}, abstractNote={A process-technology-scaling-tolerant pipelined ADC architecture has been demonstrated achieving 4 GS/s and 6-bit resolution in 45nm SOI CMOS. It utilizes open-loop, op-amp-less residue amplifier stages employing background master-slave gain calibration in order to achieve 4 GS/s clock rates while maintaining compatibility with deeply scaled CMOS processes. The pipelined ADC consumes 38 mW of power from a 1.4 V supply while operating at 4 GS/s and occupies a core area of only 0.04 mm2 due to its use of compact open-loop residue amplifiers. The measured DNL and INL are -0.8/1.0 LSB and -1.0/0.9 LSB, respectively. The ADC SNDR at 4 GS/s is 31.6 dB with a 250 MHz input and 27.3 dB with a 1.8 GHz input.}, booktitle={2014 IEEE 14th Topical Meeting on Silicon Monolithic Integrated Circuits in RF Systems (SIRF)}, author={Chen, M. W. and Carley, L. R. and Ricketts, D. S.}, year={2014}, pages={16–18} }
 @article{williams_corson_sharma_krishnaswamy_tai_george_ricketts_watson_dacquay_voinigescu_2014, title={Calibrations for Millimeter-Wave Silicon Transistor Characterization}, volume={62}, ISSN={["1557-9670"]}, DOI={10.1109/tmtt.2014.2300839}, abstractNote={This paper compares on-wafer thru-reflect-line (TRL) and off-wafer short-open-load-thru (SOLT) and line-reflect-reflect-match (LRRM) vector-network-analyzer probe-tip calibrations for amplifier characterization and parasitic-extraction calibrations for transistor characterization on silicon integrated circuits at millimeter-wave frequencies. We show that on-wafer calibrations generally outperform off-wafer and LRRM probe-tip calibrations at millimeter-wave frequencies. However, certain parasitic-extraction algorithms designed specifically to remove contact pads, transmission-lines, and access vias correct for much of the error in off-wafer calibrations.}, number={3}, journal={IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES}, author={Williams, Dylan F. and Corson, Phillip and Sharma, Jahnavi and Krishnaswamy, Harish and Tai, Wei and George, Zacharias and Ricketts, David S. and Watson, Paul M. and Dacquay, Eric and Voinigescu, Sorin P.}, year={2014}, month={Mar}, pages={658–668} }
 @inproceedings{trotter_griffin_ricketts_2014, title={Enhanced accuracy for a complex image theory position estimator using frequency diversity}, DOI={10.1109/wisnet.2014.6825505}, abstractNote={Complex image theory has been proposed as a means to efficiently calculate the fields induced by a magnetoquasistatic source above the earth. In position location applications, this has enabled an accurate determination of position from measured field strengths. While promising, complex image theory is only an approximation of the true field; inherent errors in position estimation occur due to the limitations of this approximation. In this work we show that the estimation errors are frequency dependent and that by combining multiple frequency signals, the overall RMS estimation error can be significantly reduced. We demonstrate this by finding the estimation error over an xy plane of 20 m for two frequencies individually and then combined. Our results show a 12.9 % and 45.2 % reduction in position error over the respective individual frequencies.}, booktitle={2014 ieee topical conference on wireless sensors and sensor networks (wisnet)}, author={Trotter, M. S. and Griffin, J. D. and Ricketts, D. S.}, year={2014}, pages={52–54} }
 @article{ozcan_hu_sitti_bain_ricketts_2014, title={Investigation of tip current and normal force measured simultaneously during local oxidation of titanium using dual-mode scanning probe microscopy}, volume={9}, ISSN={["1750-0443"]}, DOI={10.1049/mnl.2014.0089}, abstractNote={In this reported work, scanning probe microscopy is used to perform localised oxidation of Ti as a bottom-up nanofabrication method. The effects of normal force setpoint and oxidation voltage on oxide nanofeatures during atomic force microscopy (AFM) mode and scanning tunnelling microscopy (STM) mode oxidation are investigated. The normal force between the probe and sample and electrochemical current in the anodic oxidation process are measured using a custom control system, and the effects of these variables on the size and resistivity of oxidised nanopatterns are investigated. It is shown that a direct relation exists between oxidation voltage and written oxide resistivity as well as written feature width in the STM mode oxidation. In AFM mode oxidation, the normal force setpoint is shown to have a positive correlation with feature size, but an inverse relation with oxide resistivity. By leveraging the presented system's ability to operate in both AFM and STM mode, the dynamics and feature fabrication dependencies are shown to be a continuum of writing voltage and normal force. This reported work suggests that STM and AFM mode oxidation can be thought of as similar processes but working at different operating points in terms of normal force and tip-surface spacing.}, number={5}, journal={MICRO & NANO LETTERS}, author={Ozcan, Onur and Hu, Weihua and Sitti, Metin and Bain, James and Ricketts, David S.}, year={2014}, month={May}, pages={332–336} }
 @inproceedings{chabalko_ricketts_2014, title={Low-frequency metamaterial permeability retrieval for near-field applications}, DOI={10.1109/aps.2014.6904448}, abstractNote={Existing methods for permeability measurement of metamaterials have been limited to far-field applications, where the fields interacting with the metamaterial are plane waves. In near-field applications, such as wireless power transfer, the previous plane-wave approach is not viable. In this work, we present a simple and accurate method for extracting the complex permeability of a near-field metamaterial.}, booktitle={2014 ieee antennas and propagation society international symposium (apsursi)}, author={Chabalko, M. J. and Ricketts, D. S.}, year={2014}, pages={233–234} }
 @inproceedings{chabalko_alarcon_bou_ricketts_2014, title={Optimization of WPT efficiency using a conjugate load in non-impedance matched systems}, DOI={10.1109/aps.2014.6904653}, abstractNote={Maximum power transfer and maximum efficiency are two important design constraints in wireless power transfer applications. Several works have investigated the proper load and impedance match conditions to optimize either efficiency or power transfer. In this paper we show that the optimal load for maximum power transfer and maximum efficiency is the same (a conjugate matched load) when the source resistance is zero. This is important, as many WPT systems have a relatively low, unknown source impedance. Since the optimal load for both efficiency and power is the same as the source impedance approaches zero, the designer can use a bi-conjugate load for a near optimal design for both maximum power and efficiency. As the source impedance becomes significant, the bi-conjugate matched system provides higher power, but at the expense of lower efficiency. Maximum efficiency is achieved with a non-bi-conjugate load, when the source impedance is non-negligible.}, booktitle={2014 ieee antennas and propagation society international symposium (apsursi)}, author={Chabalko, M. and Alarcon, E. and Bou, E. and Ricketts, D. S.}, year={2014}, pages={645–646} }
 @inproceedings{chabalko_ricketts_2014, title={The effects of magneto-static resonances in metamaterials on the quality factor of coils in near field applications}, DOI={10.1109/aps.2014.6904545}, abstractNote={In this work we examine the effects of near field metamaterials (NF-MM) on the quality factor (Q) of an excitation (i.e. source) coil. We show that when the permeability becomes negative, magneto-static resonances (MR) occur that are coupled strongly to the excitation coil and increase the loss in the coil. Our simulation and experimental results show that Q can be degraded by a factor of 4 or more due to the MR induced loss in an excitation coil.}, booktitle={2014 ieee antennas and propagation society international symposium (apsursi)}, author={Chabalko, M. J. and Ricketts, D. S.}, year={2014}, pages={426–427} }
 @article{arumugam_griffin_stancil_ricketts_2014, title={Three-Dimensional Position and Orientation Measurements Using Magneto-Quasistatic Fields and Complex Image Theory}, volume={56}, ISSN={["1558-4143"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84901979580&partnerID=MN8TOARS}, DOI={10.1109/map.2014.6821771}, abstractNote={Traditional wireless position-location systems, operating using propagating waves, suffer reduced performance in non-line-of-sight (NLoS) applications. Traditional systems that use quasistatic fields have instead been limited to short ranges, progressive direction-finding applications, require RF fingerprinting, or do not provide complete immunity to dielectric obstacles (use of electric fields). These limitations impose severe restrictions in applications such as tracking an American football during game play, where position and orientation tracking may be required over long ranges, and when the line-of-sight (LoS) is blocked by groups of people. A technique using magneto-quasistatic fields and complex image theory was recently shown to circumvent these problems, and to enable accurate long-range one-dimensional and two-dimensional measurements. In this work, we present three-dimensional position and orientation measurements using the magneto-quasistatic system and complex image theory over an area of 27.43 m × 27.43 m. Inverting the theoretical expression for the voltage measured at the terminals of the receiving loops to determine three-dimensional position and orientation resulted in mean and median geometric position errors of 0.77 m and 0.71 m, respectively; inclination orientation mean and median errors of 9.67° and 8.24°, respectively; and azimuthal orientation mean and median errors of 2.84° and 2.25°, respectively.}, number={1}, journal={IEEE ANTENNAS AND PROPAGATION MAGAZINE}, author={Arumugam, Darmindra D. and Griffin, Joshua D. and Stancil, Daniel D. and Ricketts, David S.}, year={2014}, month={Feb}, pages={160–173} }
 @article{ricketts_chabalko_hillenius_2014, title={Tri-Loop Impedance and Frequency Matching With High-Q Resonators in Wireless Power Transfer}, volume={13}, ISSN={["1548-5757"]}, DOI={10.1109/lawp.2014.2299896}, abstractNote={Resonant wireless power transfer (WPT) using magneto quasi-static fields is an attractive means for delivering power in many applications. Central to the efficient delivery of power in these systems is the use of high-ratio impedance transformers to impedance-match the load to the source via the WPT network. Mini-loop transformers, which use a resonant tank for impedance matching, have become popular as they provide high-ratio impedance matching and low loss. Key to the low loss is the use of high- Q resonators. There are two challenges with this approach. The first is impedance matching the resonators to source/load impedances, and the second is adjusting the center frequency of resonance to exactly match the operating frequency, which can be very difficult with helical coils that use their parasitic capacitance for resonance. In this letter, we introduce a tri-coil impedance-matching network for WPT that provides accurate impedance matching and precise frequency tuning for high- Q coils to overcome these limitations.}, journal={IEEE ANTENNAS AND WIRELESS PROPAGATION LETTERS}, author={Ricketts, David S. and Chabalko, Matthew and Hillenius, Andrew}, year={2014}, pages={341–344} }
 @article{tai_ricketts_2013, title={74 GHz, 17.2 dBm power amplifier in 45 nm SOI CMOS}, volume={49}, ISSN={["0013-5194"]}, DOI={10.1049/el.2013.1052}, abstractNote={A millimetre-wave power amplifier (PA) fabricated in 45 nm SOI CMOS is reported that achieves 17.2 dBm saturated output power at 74 GHz without power combining using a 2.2 V supply, over twice the output power of previously reported single CMOS PAs. The peak gain and PAE are 14.3 dB and 11.1%, respectively. The PA also achieves a 3 dB bandwidth of 31 GHz while occupying a small die area of 0.23 mm2.}, number={12}, journal={ELECTRONICS LETTERS}, author={Tai, W. and Ricketts, D. S.}, year={2013}, month={Jun}, pages={758-+} }
 @article{hu_bain_ricketts_2013, title={An AFM/STM multi-mode nanofabrication approach allowing in situ surface modification and characterisation}, volume={8}, ISSN={["1750-0443"]}, DOI={10.1049/mnl.2012.0859}, abstractNote={A report is presented on a new multi-mode nanofabrication method that uses a compliant conductive atomic force microscope (AFM) probe for both AFM and scanning tunnelling microscope (STM) operation and it is demonstrated that these modes can be switched ‘on-the-fly’ during the measurement or fabrication of nanostructures. The authors oxidised Ti with the same conductive AFM probe in AFM and STM modes, alternately in a continuous writing step. An in-plane Ti–TiOx–Ti junction was fabricated by combining AFM and STM modes and electrically characterised by taking current images in conductive AFM mode. After measurement, additional features were written to increase the electrical isolation, thus realising in situ nanoscale modification.}, number={1}, journal={MICRO & NANO LETTERS}, author={Hu, Weihua and Bain, J. and Ricketts, D.}, year={2013}, month={Jan}, pages={43–46} }
 @article{xu_ricketts_2013, title={An Efficient, Watt-Level Microwave Rectifier Using an Impedance Compression Network (ICN) With Applications in Outphasing Energy Recovery Systems}, volume={23}, ISSN={["1558-1764"]}, DOI={10.1109/lmwc.2013.2278276}, abstractNote={We present a transmission line based impedance compression network (ICN) for application in RF-to-dc conversion. We show that the ICN is able to significantly compress the undesired input impedance variation that occurs when there is a large variation of input power. We designed and measured an ICN for a 4 W, 4.6 GHz rectifier and show that the impedance is significantly compressed with the ICN. We then demonstrate the ICN in an outphasing system where we achieve up to a 37% improvement in efficiency at back-off power and an overall more efficient design over large input power variation.}, number={10}, journal={IEEE MICROWAVE AND WIRELESS COMPONENTS LETTERS}, author={Xu, Junfeng and Ricketts, David S.}, year={2013}, month={Oct}, pages={542–544} }
 @article{ricketts_chabalko_hillenius_2013, title={Erratum: “Experimental demonstration of the equivalence of inductive and strongly coupled magnetic resonance wireless power transfer” [Appl. Phys. Lett. 102, 053904 (2013)]}, volume={102}, ISSN={0003-6951 1077-3118}, url={http://dx.doi.org/10.1063/1.4796125}, DOI={10.1063/1.4796125}, abstractNote={First Page}, number={14}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={Ricketts, David S. and Chabalko, Matthew J. and Hillenius, Andrew}, year={2013}, month={Apr}, pages={149902} }
 @article{ricketts_chabalko_hillenius_2013, title={Experimental demonstration of the equivalence of inductive and strongly coupled magnetic resonance wireless power transfer}, volume={102}, ISSN={["0003-6951"]}, DOI={10.1063/1.4788748}, abstractNote={In this work, we show experimentally that wireless power transfer (WPT) using strongly coupled magnetic resonance (SCMR) and traditional induction are equivalent. We demonstrate that for a given coil separation, and to within 4%, strongly coupled magnetic resonance and traditional induction produce the same theoretical efficiency of wireless power transfer versus distance. Moreover, we show that the difference between traditional induction and strongly coupled magnetic resonance is in the implementation of the impedance matching network where strongly coupled magnetic resonance uses the mini-loop impedance match. The mini-loop impedance mach provides a low-loss, high-ratio impedance transformation that makes it desirable for longer distance wireless power transfer, where large impedance transformations are needed to maximize power transfer.}, number={5}, journal={APPLIED PHYSICS LETTERS}, author={Ricketts, David S. and Chabalko, Matthew J. and Hillenius, Andrew}, year={2013}, month={Feb} }
 @article{li_ricketts_2013, title={Loss minimisation in lambda/4 impedance transformers using multiple lambda/4 segments}, volume={49}, ISSN={["0013-5194"]}, DOI={10.1049/el.2012.3382}, abstractNote={Presented is an analysis of loss in quarter-wavelength impedance transformers. It is shown that the loss of an impedance transformer, S 21, is a function not only of the dielectric and conductor loss, but also the transformation ratio. S 21 is derived as a function of both loss and transformation ratio and it is shown that for high transformation ratios, using two or even three quarter-wavelength impedance transformers results in an overall lower loss.}, number={4}, journal={ELECTRONICS LETTERS}, author={Li, C. and Ricketts, D. S.}, year={2013}, month={Feb}, pages={274–276} }
 @article{arumugam_griffin_stancil_ricketts_2013, title={Magneto-quasistatic tracking of an American football: A goal-line measurement}, volume={55}, number={1}, journal={IEEE Antennas and Propagation Magazine}, author={Arumugam, D. D. and Griffin, J. D. and Stancil, D. D. and Ricketts, D. S.}, year={2013}, pages={137–146} }
 @article{tamaru_ricketts_2013, title={Measurement of ultra-low power oscillators using adaptive drift cancellation with applications to nano-magnetic spin torque oscillators}, volume={84}, ISSN={["0034-6748"]}, DOI={10.1063/1.4804650}, abstractNote={This work presents a technique for measuring ultra-low power oscillator signals using an adaptive drift cancellation method. We demonstrate this technique through spectrum measurements of a sub-pW nano-magnet spin torque oscillator (STO). We first present a detailed noise analysis of the standard STO characterization apparatus to estimate the background noise level, then compare these results to the noise level of three measurement configurations. The first and second share the standard configuration but use different spectrum analyzers (SA), an older model and a state-of-the-art model, respectively. The third is the technique proposed in this work using the same old SA as for the first. Our results show that the first and second configurations suffer from a large drift that requires ∼30 min to stabilize each time the SA changes the frequency band, even though the SA has been powered on for longer than 24 h. The third configuration introduced in this work, however, shows absolutely no drift as the SA changes frequency band, and nearly the same noise performance as with a state-of-the-art SA, thus providing a reliable method for measuring very low power signals for a wide variety of applications.}, number={5}, journal={REVIEW OF SCIENTIFIC INSTRUMENTS}, author={Tamaru, S. and Ricketts, D. S.}, year={2013}, month={May} }
 @inproceedings{ricketts_chabalko_2013, title={On the efficient wireless power transfer in resonant multi-receiver systems}, DOI={10.1109/iscas.2013.6572455}, abstractNote={In this paper we present an analysis of resonant wireless power transfer in systems with multiple receivers. We show that maximum power transfer can be achieved when the source is impedance matched to the set of receivers, i.e. matched to their equivalent impedance as seen by the source. The interaction of the receivers, or coupled modes, simply represent an interdependence of impedances that can be modeled and impedance matched. We explore three methods to achieve impedance matching: frequency tuning, impedance transformation and resonant tuning and show that the later two can achieve the maximum theoretical power transfer for a wide range of coupling between receivers.}, booktitle={2013 ieee international symposium on circuits and systems (iscas)}, author={Ricketts, D. S. and Chabalko, M. J.}, year={2013}, pages={2779–2782} }
 @inproceedings{ricketts_chabalko_hillenius_2013, title={Optimization of wireless power transfer for mobile receivers using automatic digital capacitance tuning}, booktitle={2013 european microwave conference (eumc)}, author={Ricketts, D. S. and Chabalko, M. J. and Hillenius, A.}, year={2013}, pages={515–518} }
 @article{arumugam_ricketts_2013, title={Passive orientation measurement using magnetoquasistatic fields and coupled magnetic resonances}, volume={49}, ISSN={0013-5194 1350-911X}, url={http://dx.doi.org/10.1049/EL.2013.0766}, DOI={10.1049/EL.2013.0766}, abstractNote={A passive position orientation measurement method is presented which leverages the spatial variation of the reflected magnetoquasistatic field from a mobile loop to determine the loop's spatial orientation. The azimuthal orientation was measured from 0° to 360° at a distance of 1 m from the fixed measurement loop. Inverting the theoretical expressions to estimate orientation from measured field values resulted in an average and RMS error of 3.15° and 4.55°, respectively. This technique offers a means to accurately determine the orientation of the mobile loop through purely passive methods.}, number={16}, journal={Electronics Letters}, publisher={Institution of Engineering and Technology (IET)}, author={Arumugam, D.D. and Ricketts, D.S.}, year={2013}, month={Aug}, pages={999–1001} }
 @article{birt_an_tsoi_tamaru_ricketts_wong_khalili amiri_wang_li_2012, title={Deviation from exponential decay for spin waves excited with a coplanar waveguide antenna}, volume={101}, ISSN={0003-6951 1077-3118}, url={http://dx.doi.org/10.1063/1.4772798}, DOI={10.1063/1.4772798}, abstractNote={We have investigated the propagation of surface spin waves in a Permalloy thin film excited by an asymmetric coplanar antenna. A surprising oscillatory behavior superimposed on the exponential decay is observed in the spin wave intensity mapped with the micro-Brillouin light scattering technique. The oscillations can be modeled as the interference between a propagating spin wave and a background magnetization with spatially uniform phase. We use a simple closed-form equation that includes both contributions to fit our experimental results. From the fit results, we extract the spin wave propagation length and the spin wave vector in a frequency range limited by the antenna bandwidth.}, number={25}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={Birt, Daniel R. and An, Kyongmo and Tsoi, Maxim and Tamaru, Shingo and Ricketts, David and Wong, Kin L. and Khalili Amiri, Pedram and Wang, Kang L. and Li, Xiaoqin}, year={2012}, month={Dec}, pages={252409} }
 @article{hu_bain_ricketts_2012, title={In situ quantification of electrical isolation in STM-fabricated TiOx nanostructures}, volume={7}, ISSN={1750-0443}, url={http://dx.doi.org/10.1049/mnl.2011.0678}, DOI={10.1049/mnl.2011.0678}, abstractNote={In this Letter, a combination of conductive atomic force microscopy (AFM) and scanning tunnelling microscopy (STM) with a compliant cantilever is used to electrically probe oxidised TiO 2-x nanostructures in situ. In STM mode, both the written width and the effective resistivity of material in the written line increase with write bias. At low writing voltages (~3.5 V), the STM written lines are narrow (30 nm), but they are not resistive enough to allow patterns with a 1-2 μm perimeter to provide electrical isolation above 10 MΩ. Raising the bias to 8.5 V during writing allows similar structures to provide isolation of better than 250 MΩ. The resistivity in the lines written at the latter with high bias is 28 Ω m. From electrical estimates, the oxidation appears to go through the thickness at all voltages, but is more chemically incomplete (larger value of x) at low voltage. The data are not consistent, with a small amount of metallic Ti remaining under the written mark, that is, partial penetration of the oxidation. The thickness of this Ti layer would have to be unphysically small (1 million times smaller than an atomic layer thickness) to allow this interpretation.}, number={4}, journal={Micro & Nano Letters}, publisher={Institution of Engineering and Technology (IET)}, author={Hu, W. and Bain, J.A. and Ricketts, D.S.}, year={2012}, pages={334} }
 @article{evarts_cao_ricketts_rizzo_bain_majetich_2009, title={Spin transfer torque switching of magnetic tunnel junctions using a conductive atomic force microscope}, volume={95}, ISSN={0003-6951 1077-3118}, url={http://dx.doi.org/10.1063/1.3240884}, DOI={10.1063/1.3240884}, abstractNote={We show that a nonmagnetic conductive atomic force microscopy probe can be used to read and write magnetic bits using current passed between the tip and bit. The bits were patterned using electron beam lithography from a magnetic tunnel junction (MTJ) film with in-plane shape anisotropy using an MgO tunnel barrier. Probes were made having a thick Pt coating and could deliver up to several milliamps, so that MTJ structures were easily switched repeatedly using the spin transfer torque effect.}, number={13}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={Evarts, Eric R. and Cao, Limin and Ricketts, David S. and Rizzo, Nicholas D. and Bain, James A. and Majetich, Sara A.}, year={2009}, month={Sep}, pages={132510} }