@article{tang_venkatesh_lin_lu_saeeidi_javanmard_sengupta_2024, title={High Sensitivity and High Throughput Magnetic Flow CMOS Cytometers with 2D Oscillator Array and Inter-Sensor Spectrogram Cross-correlation}, url={http://dx.doi.org/10.1109/tbcas.2024.3367668}, DOI={10.1109/tbcas.2024.3367668}, abstractNote={In the paper, we present an integrated flow cytometer with a 2D array of magnetic sensors based on dual-frequency oscillators in a 65-nm CMOS process, with the chip packaged with microfluidic controls. The sensor architecture and the presented array signal processing allows uninhibited flow of the sample for high throughput without the need for hydrodynamic focusing to a single sensor. To overcome the challenge of sensitivity and specificity that comes as a trade off with high throughout, we perform two levels of signal processing. First, utilizing the fact that a magnetically tagged cell is expected to excite sequentially an array of sensors in a time-delayed fashion, we perform inter-site cross-correlation of the sensor spectrograms that allows us to suppress the probability of false detection drastically, allowing theoretical sensitivity reaching towards sub-ppM levels that is needed for rare cell or circulating tumor cell detection. In addition, we implement two distinct methods to suppress correlated low frequency drifts of singular sensors-one with an on-chip sensor reference and one that utilizes the frequency dependence of the susceptibility of super-paramagnetic magnetic beads that we deploy as tags. We demonstrate these techniques on a 7×7 sensor array in 65 nm CMOS technology packaged with microfluidics with magnetically tagged dielectric particles and cultu lymphoma cancer cells.}, journal={IEEE Transactions on Biomedical Circuits and Systems}, author={Tang, Hao and Venkatesh, Suresh and Lin, Zhongtian and Lu, Xuyang and Saeeidi, Hooman and Javanmard, Mehdi and Sengupta, Kaushik}, year={2024}, month={Feb} }
 @article{lu_venkatesh_tang_sengupta_2024, title={Physical Layer Security Through Directional Modulation With Spatio-Temporal Millimeter-Wave Transmitter Arrays}, volume={5}, ISSN={["1558-173X"]}, url={https://doi.org/10.1109/JSSC.2024.3384373}, DOI={10.1109/JSSC.2024.3384373}, abstractNote={Physical layer security incorporates security features embedded in the communication channels without the need to exchange cryptographic keys. Interest in exploiting such mechanisms has been increasing rapidly for 5G and beyond, due to the low overhead and low-latency properties of such encoding. Although phased arrays, by their nature of the focused beams to users, introduce secrecy, they are still vulnerable to eavesdropping at the sidelobes. In this article, we present a class of spatio-temporal modulated arrays (STMAs) with custom CMOS integrated circuits (ICs) and packaged antennas operating in the 71–76-GHz range that creates secure cones in space by preserving signal fidelity in the intended direction while emulating a time-varying channel outside the secure cone. At unintended directions, the architecture intentionally spectrally aliases signals to create noise-like features and scrambles constellations with a one-to-many mapping (including infinite constellation splitting), making it challenging to invert the mapping by eavesdroppers. Through the architecture, the secure cone can be reconfigured in space on demand and narrowed when we increase the number of elements. We also show how reconfigurable time modulation (such as through frequency chirping) can create a non-repetitive mapping of the constellation to protect against colluding attacks.}, journal={IEEE JOURNAL OF SOLID-STATE CIRCUITS}, author={Lu, Xuyang and Venkatesh, Suresh and Tang, Bingjun and Sengupta, Kaushik}, year={2024}, month={May} }
 @article{wu_ma_venkatesh_mehlman_ozatay_wagner_sturm_verma_2023, title={A Monolithically Integrable Reconfigurable Antenna Based on Large-Area Electronics}, volume={10}, ISSN={["1558-173X"]}, url={https://doi.org/10.1109/JSSC.2023.3322905}, DOI={10.1109/JSSC.2023.3322905}, abstractNote={Reconfigurable antennas introduce unique and dynamic system capabilities for wireless communication and sensing, by enabling controllable radiation pattern, frequency response, and polarization of electromagnetic (EM) waves. The antenna’s physical dimensions are critical to enhancing control of radiative characteristics, making it necessary to distribute RF control devices across a large-area aperture. Previous reconfigurable antennas have been limited in scale and performance by the need to assemble discrete active components. Large-area electronics (LAE) is a technology that can enable monolithic reconfigurable antennas, with flexible and large form factors. However, conventionally the speed of LAE, specifically of thin-film transistors (TFTs), has been restricted to 10–100 MHz. In this work, a reconfigurable antenna based on LAE RF TFTs is achieved through a combination of: 1) materials and device enhancements pushing fundamental TFT performance metrics to the giga-Hertz regime and 2) an architecture that employs the TFTs as passive switches, rather than active amplifiers, to enable aggressive biasing for high-frequency operation, yet within the breakdown limits. A 9 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times$</tex-math> </inline-formula> 9 cm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^2$</tex-math> </inline-formula> reconfigurable antenna consisting of an 11 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times$</tex-math> </inline-formula> 11 array of metal patches as sub-radiators controlled by 208 TFT-based RF switches is demonstrated. Far-field and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$S$</tex-math> </inline-formula> -parameter measurements show reconfigured beam steering by 90 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{\circ}$</tex-math> </inline-formula> and resonant-frequency tuning by 200 MHz.}, journal={IEEE JOURNAL OF SOLID-STATE CIRCUITS}, author={Wu, Can and Ma, Yue and Venkatesh, Suresh and Mehlman, Yoni and Ozatay, Murat and Wagner, Sigurd and Sturm, James C. and Verma, Naveen}, year={2023}, month={Oct} }
 @article{venkatesh_saeidi_sengupta_lu_2023, title={Active and Passive Reconfigurable Intelligent Surfaces at mm-Wave and THz bands enabled by CMOS Integrated Chips}, DOI={10.1109/WAMICON57636.2023.10124895}, abstractNote={Though the initial deployment of 5G millimeter-Wave (mmWave) networks has demonstrated multi-Gb/s wireless links, they are often highly susceptible to blockages, channel disruptions, and fading due to the nature of their directive beams. To overcome this major impediment, the next generation of communication systems will have to be resilient, which encompasses security, adaptability, and autonomy. Reconfigurable Intelligent Surfaces (RISs) have emerged as a potential candidate to address these challenges and have the capability to dynamically reconfigure the radio propagation channels on-the-fly. In this invited article, we present two reconfigurable intelligent electromagnetic surface designs enabled through CMOS ICs namely, a) mm-Wave 57–64 GHz active reconfigurable reflector array b) THz dynamically programmable passive holographic metasurface enabled through CMOS IC tiling approach.}, journal={2023 IEEE WIRELESS AND MICROWAVE TECHNOLOGY CONFERENCE, WAMICON}, author={Venkatesh, Suresh and Saeidi, Hooman and Sengupta, Kaushik and Lu, Xuyang}, year={2023} }
 @article{chen_saeidi_venkatesh_sengupta_ghasempour_2023, title={Wavefront Manipulation Attack via Programmable mmWave Metasurfaces: from Theory to Experiments}, url={https://doi.org/10.1145/3558482.3590182}, DOI={10.1145/3558482.3590182}, abstractNote={Reconfigurable surfaces enable on-demand manipulation of electromagnetic wave properties in a controllable manner. These surfaces have been shown to enhance mmWave wireless networks in many ways, including blockage recovery. In this paper, we investigate the security vulnerabilities associated with the deployment of reconfigurable surfaces, i.e., an adversary may deploy new rogue surfaces or tamper with already-deployed surfaces to maliciously engineer the reflection pattern. In particular, we introduceMetasurface-enabled Sideband Steering (MeSS), a new metasurface-in-the-middle attack in which the spectral-spatial properties of the reflected wavefront are manipulated such that a concealed sideband channel is created in the spectral domain and steered toward the eavesdropper location, while maintaining the legitimate link toward the victim intact. We fabricate a custom reconfigurable surface prototype and evaluate MeSS through theoretical analysis as well as over-the-air experiments at the 60 GHz band. Our results indicate that MeSS significantly reduces empirical secrecy capacity (up to 81.7%) while leaving a small power penalty at the victim that can be masked under normal channel fluctuations.}, journal={PROCEEDINGS OF THE 16TH ACM CONFERENCE ON SECURITY AND PRIVACY IN WIRELESS AND MOBILE NETWORKS, WISEC 2023}, author={Chen, Haoze and Saeidi, Hooman and Venkatesh, Suresh and Sengupta, Kaushik and Ghasempour, Yasaman}, year={2023}, pages={317–328} }
 @article{saeidi_venkatesh_chappidi_sharma_zhu_sengupta_2022, title={A $4\times4$ Steerable 14-dBm EIRP Array on CMOS at 0.41 THz With a 2-D Distributed Oscillator Network}, url={http://dx.doi.org/10.1109/jssc.2022.3183163}, DOI={10.1109/jssc.2022.3183163}, abstractNote={Terahertz (THz) beamforming arrays are critical to address emerging applications in wireless communication, sensing, and imaging. Enabling such architectures, particularly with respect to synchronization of distributed radiating THz sources, is very challenging due to the sensitivity of such synchronizations to variations of process, voltage, temperature (PVT), and device mismatches. In this article, we propose and demonstrate a multi-layer THz array architecture to address robust frequency synthesis, optimal harmonic THz power generation, and scalable phase generation for THz beamforming. The bottom-most layer of this multi-layer network consists of a scalable 2-D negative transconductance (−Gm) cells that collectively oscillates at the center frequency of 69.3 GHz, thereby establishing a robust frequency and phase distribution across the entire chip. By eliminating independent oscillation capability of each node and merging resonator and coupling structures into one single network, the 2-D mesh removes the possibility of moving out of synchronization due to PVT variations or device mismatches and forms the underlying frequency synthesis layer. Local frequency multiplication and radiating elements are placed across the 2-D THz array, and beamforming is enabled through varactor control in the <inline-formula> <tex-math notation="LaTeX">$-G_{m}$ </tex-math></inline-formula> cells. We demonstrate the proposed architecture in a <inline-formula> <tex-math notation="LaTeX">$4\,\times \,4$ </tex-math></inline-formula> array with effective isotropic radiation power (EIRP) of +14 dBm at 0.416 THz in a lensless setup using a 65-nm CMOS process with the beamforming capability of ±30° in both <inline-formula> <tex-math notation="LaTeX">${E}$ </tex-math></inline-formula>- and <inline-formula> <tex-math notation="LaTeX">${H}$ </tex-math></inline-formula>-planes.}, journal={IEEE Journal of Solid-State Circuits}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Saeidi, Hooman and Venkatesh, Suresh and Chappidi, Chandrakanth Reddy and Sharma, Tushar and Zhu, Chengjie and Sengupta, Kaushik}, year={2022}, pages={1–14} }
 @article{venkatesh_lu_saeidi_sengupta_2022, title={A Programmable Terahertz Metasurface With Circuit-Coupled Meta-Elements in Silicon Chips: Creating Low-Cost, Large-Scale, Reconfigurable Terahertz Metasurfaces.}, url={http://dx.doi.org/10.1109/map.2022.3176588}, DOI={10.1109/map.2022.3176588}, abstractNote={As we step into a world of ubiquitous connectivity, a spectral regime-spanning, 30−300+-GHz resource is opening up that will serve as the fabric for wireless sensing and communication coexistence, allowing high-resolution sensing (imaging, gesture recognition, and localization) and enabling a network of unmanned and autonomous systems to understand and interact with our environment. This pushes the need for low-profile, low-cost, low-power, high-performance, secure, multifunctional electromagnetic (EM) platforms that can enable such wireless systems. In this article, we present a new circuit-coupled active meta-element design to demonstrate reconfigurable, multifunctional terahertz (THz) holographic metasurfaces with tiled silicon chips. Each such chip consists of a ${12}\,{\times}\,{12}$ array of meta-elements that are individually addressable and reconfigurable at gigahertz (GHz) speed.}, journal={IEEE Antennas and Propagation Magazine}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Venkatesh, Suresh and Lu, Xuyang and Saeidi, Hooman and Sengupta, Kaushik}, year={2022}, pages={2–15} }
 @article{venkatesh_sturm_lu_lang_sengupta_2022, title={Origami Microwave Imaging Array: Metasurface Tiles on a Shape-Morphing Surface for Reconfigurable Computational Imaging}, volume={7}, ISSN={["2198-3844"]}, url={http://dx.doi.org/10.1002/advs.202105016}, DOI={10.1002/advs.202105016}, abstractNote={Abstract}, journal={ADVANCED SCIENCE}, publisher={Wiley}, author={Venkatesh, Suresh and Sturm, Daniel and Lu, Xuyang and Lang, Robert J. and Sengupta, Kaushik}, year={2022}, month={Jul} }
 @article{watson_ford_markvicka_fong_venkatesh_sengupta_majidi_tabor_2022, title={Stretchable Microwave Transmission Lines Using Liquid‐Metal Embedded Elastomers}, volume={5}, url={http://dx.doi.org/10.1002/adem.202200345}, DOI={10.1002/adem.202200345}, abstractNote={The characterization of an RF transmitter composed of insulating and conducting regions of liquid‐metal embedded elastomer (LMEE) is presented along with in situ measurements of LMEE microstrip lines as they are subjected to local material strains up to 40%. The LMEE is comprised of microscale droplets of a gallium–indium alloy that is liquid at room temperature and suspended within a cured elastomer matrix of polydimethylsiloxane (PDMS). The liquid metal microparticles were initially electrically isolated, but applying mechanical loading caused the permanent formation of highly localized conductive traces. Bonding films of LMEE onto a PDMS dielectric layer resulted in a stretchable microstrip structure that is capable of radio frequency (RF) transmission. Scattering parameter (S‐parameter) measurements for reflection and transmission are presented for these microstrip lines as the electrical length increased up to 19%. A customized clamp was utilized to isolate the mechanical strain on the material from the electrical connectors and allow for transmission line characterization under applied strain and dielectric characterization of the LMEE material was performed. The stretchable microstrip lines show remarkable consistency in transmission response at 0.5–5 GHz when mechanically loaded to 40% strain for 1000 loading cycles.}, journal={Advanced Engineering Materials}, publisher={Wiley}, author={Watson, Alexander M. and Ford, Michael J. and Markvicka, Eric J. and Fong, William W. L. and Venkatesh, Suresh and Sengupta, Kaushik and Majidi, Carmel and Tabor, Christopher E.}, year={2022}, month={May}, pages={2200345} }
 @article{yu_lu_gu_venkatesh_mao_2022, title={mmWave Spatial-Temporal Single Harmonic Switching Transmitter Arrays for High back-off Beamforming Efficiency}, url={http://dx.doi.org/10.1109/tap.2022.3177551}, DOI={10.1109/tap.2022.3177551}, abstractNote={This paper presents a spatial-temporal single harmonic switching (STHS) transmitter array architecture with enhanced efficiency in the power back-off (PBO) region. STHS is an electromagnetic and circuit co-designed and jointly optimized transmitter array that realizes beamforming and back-off power generation at the same time. The temporal dimension is originally added in STHS to achieve back-off efficiency enhancement, which can be combined with conventional PBO enhancement methods such as Doherty amplifiers and envelope tracking. The design is validated through a simulation of a two-stage power amplifier in 65-nm CMOS at 77 GHz, which achieves a peak drain efficiency (DE) of 24.2%, a 22% DE at 3-dB PBO, 16% DE at 6-dB PBO, and 10.2% at 9-dB PBO. The efficiency exhibits a 57% improvement at 3-dB PBO, 100% improvement at 6-dB PBO, and 190% improvement at 9-dB PBO compared with class A/B amplifiers.}, journal={IEEE Transactions on Antennas and Propagation}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Yu, Zhehao and Lu, Xuyang and Gu, Changzhan and Venkatesh, Suresh and Mao, Junfa}, year={2022}, pages={1–1} }
 @inproceedings{zhu_maldonado_tang_venkatesh_sengupta_2021, title={18.2 CMOS-Driven Pneumatic-Free Scalable Microfluidics and Fluid Processing with Label-Free Cellular and Bio-Molecular Sensing Capability for an End-to-End Point-of-Care System}, url={http://dx.doi.org/10.1109/isscc42613.2021.9365843}, DOI={10.1109/isscc42613.2021.9365843}, abstractNote={The emergence of the pandemic has demonstrated the necessity of point-of-care (POC) molecular diagnostic platforms that encompass an end-to-end system (from sample fluid to diagnostic information) with the ability to allow rapid analysis on the spot. While POC sensing technologies have been demonstrated in miniaturize chip-scale platforms [1–5], the bottlenecks in enabling end-to-end low-cost handheld platforms have often been bio-sample handling, filtering, mixing with re-agents that are critical to the robustness of the assay chemistry and sensing sensitivity/specificity. These processes are typically carried out either manually or by employing complex pneumatic flow control with multiple bulky syringe pumps, which have been a severe limitation to enable end-to-end biosensing systems (Fig. 18.2.1). While electrically driven droplets, molecular and cell manipulation techniques, such as electro-wetting, electrophoresis and dielectrophoresis, have been demonstrated in singular systems before [1], they do not have the ability to process bulk bio-sample fluids that is required for POC devices. In this paper, we present a scalable approach that merges the functionalities of sample processing and cellular/bio-molecular sensing in a single system and eliminates any pneumatic pumping mechanisms by exploiting CMOS-based electrically driven electro-kinetic flow of bulk fluids. We demonstrate, for the first time, a CMOS-microfluidic system that is capable of 1) pumping bulk electrolyte fluid with AC electro-osmosis, 2) cell manipulation and separation with dielectrophoresis (DEP), 3) label-free biomolecular and cell sensing, classification with dedicated 16-element impedance spectroscopy receivers. While we demonstrate these kernel functionalities in a multichip module/microfluidic interface (Fig. 18.2.1), the overall architecture, fluidics and sensing components can be massively scaled up for various POC applications due to elimination of pressure-driven flows (Fig. 18.2.1).}, booktitle={2021 IEEE International Solid- State Circuits Conference (ISSCC)}, publisher={IEEE}, author={Zhu, Chengjie and Maldonado, Jesus and Tang, Hao and Venkatesh, Suresh and Sengupta, Kaushik}, year={2021}, month={Feb} }
 @inproceedings{saeidi_venkatesh_lu_sengupta_2021, title={22.1 THz Prism: One-Shot Simultaneous Multi-Node Angular Localization Using Spectrum-to-Space Mapping with 360-to-400GHz Broadband Transceiver and Dual-Port Integrated Leaky-Wave Antennas}, volume={64}, url={http://dx.doi.org/10.1109/isscc42613.2021.9366041}, DOI={10.1109/isscc42613.2021.9366041}, abstractNote={The spectrum above 100GHz is expected to spawn a generation of ultra-high-speed wireless links and intelligent sensing and imaging applications. They are meant to be supported through a heterogeneous and dynamically reconfigurable wireless network fabric in 5G and beyond. Such wireless communication and sensing applications require rapid localization and direction finding of mobile nodes [1]. This functionality is paramount for communications-on-the-move applications, wireless link discovery, and rapid beam alignment/tracking at mm-wave and THz frequencies [2]–[9]. The current protocols for direction finding and beam alignment in 5G mm-wave systems are based on iterative algorithms that are often non-scalable, time-consuming, and computationally expensive, posing serious challenges for low-latency applications. Thus there is a need to process such direction-finding methods at the ‘edge nodes’, to enable secure scalable networks with very low latencies [10]. In this article, we present a spectrum-to-space mapping principle, where localization information can be processed at the edge ‘sensor node’ through the spectrum sensing. The conceptual idea is presented in Fig. 22.1.1, which shows an access point (transmitter/receiver) that acts as a THz prism casting different spectral portions of a broadband THz signal across space. If the mapping is unique, multiple edge nodes can simultaneously localize themselves in a single-shot fashion through localized spectrum sensing, avoiding the use of the slow iterative process and bi-directional communication. In this paper, we present a scalable 360-to-400GHz transceiver architecture in 65nm CMOS with frequency-dependent beam synthesis using two dual-port integrated frequency-dispersive leaky-wave antennas. The two antennas when excited/sensed across the two opposite end-ports, cover a 1D spatial angle $across \pm 40^{\circ}$, and enable 2D localization with two such ICs covering both orthogonal basis vectors with a frequency-offset radiation (Fig. 22.1.1). Exploiting the cross-correlation of the spectrum-to-space mapping (Fig. 22.1.1), the system achieves 2D localization accuracy of $\sigma_{\varphi},= 1.9$ ° and $\sigma_{theta}= 1.95^{\circ}$ for a measurement resolution bandwidth (RBW) of 20Hz.}, booktitle={2021 IEEE International Solid- State Circuits Conference (ISSCC)}, publisher={IEEE}, author={Saeidi, Hooman and Venkatesh, Suresh and Lu, Xuyang and Sengupta, Kaushik}, year={2021}, month={Feb}, pages={314–316} }
 @article{liu_sharma_chappidi_venkatesh_yu_sengupta_2021, title={A 42–62 GHz Transformer-Based Broadband mm-Wave InP PA With Second-Harmonic Waveform Engineering and Enhanced Linearity}, volume={69}, url={http://dx.doi.org/10.1109/tmtt.2020.3037092}, DOI={10.1109/tmtt.2020.3037092}, abstractNote={Indium phosphide (InP) heterojunction bipolar transistors (HBTs) with <inline-formula> <tex-math notation="LaTeX">$f_{t}/f_{\max}$ </tex-math></inline-formula> of 350/675 GHz are studied and explored for a linear, high efficiency and broadband power amplifiers (PAs) at mm-wave frequencies. Unlike the conventional transmission-like-based design, this article presents a compact, broadband transformer-based power combining and impedance matching using the waveform engineering approach. We present, for the first time, mm-wave (40–60 GHz) InP topologies incorporating the following: 1) on-chip transformer for broadband, efficient and compact impedance matching and power combining; 2) synthesis of optimal second-harmonic impedance through transformer center tap to achieve high-efficiency differential PA operation; and 3) biasing techniques to reduce AM–PM distortion for linearity enhancement. This work reports a transformer-based push–pull InP PA in <inline-formula> <tex-math notation="LaTeX">$0.25~\mu \text{m}$ </tex-math></inline-formula> technology across 42–62 GHz demonstrating a peak power added efficiency (PAE) of 39.5% and peak <inline-formula> <tex-math notation="LaTeX">$P_{\text{sat}}$ </tex-math></inline-formula> of 20.6 dBm. The PA supports 4 GHz bandwidth at 52 GHz with an EVM of −22.9 dB and an adjacent channel leakage ratio (ACLR) of −32 dBc for an 8 Gb/s QPSK signal at 13.3 dBm average output power. This work presents one of the highest efficiency with wide bandwidth and highest linearity mm-wave PAs in integrated technology.}, number={1}, journal={IEEE Transactions on Microwave Theory and Techniques}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Liu, Zheng and Sharma, Tushar and Chappidi, Chandrakanth Reddy and Venkatesh, Suresh and Yu, Yiming and Sengupta, Kaushik}, year={2021}, month={Jan}, pages={756–773} }
 @article{lu_venkatesh_saeidi_2021, title={A review on applications of integrated terahertz systems}, volume={18}, url={http://dx.doi.org/10.23919/jcc.2021.05.011}, DOI={10.23919/jcc.2021.05.011}, abstractNote={A review on Terahertz end-to-end systems with an emphasis on integrated approaches is presented. Four major catalogs of THz integrated systems, including THz communication systems, THz imaging systems, THz radars, and THz spectroscopy systems, are reviewed in this article. The performance of integrated systems is compared with non-integrated solutions, followed by a discussion on the trend in future research avenues and applications.}, number={5}, journal={China Communications}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Lu, Xuyang and Venkatesh, Suresh and Saeidi, Hooman}, year={2021}, month={May}, pages={175–201} }
 @article{viswanathan_venkatesh_schurig_2021, title={Optimization of a Sparse Aperture Configuration for Millimeter-Wave Computational Imaging}, url={https://doi.org/10.1109/TAP.2020.3030946}, DOI={10.1109/TAP.2020.3030946}, abstractNote={We present two techniques for optimizing the position of transmitter and receiver modules on a sparse aperture for a millimeter-wave computational imaging system. The first technique uses an easily computable spatial representation of the transmitter and receiver array, called the coarray, to ideally distribute the spatial frequency components probed by the imaging setup. The second approach involves maximizing the information added by a complete measurement of the scene by the system. This approach is analogous to the system capacity maximization frequently employed in wireless communication. We show that employing aperture configurations optimized using these two techniques over commonly used standard aperture configurations results in 30% less mean-squared error when used to reconstruct a particular ensemble of 400 arbitrary 2-D objects. Finally, we discuss the similarities and differences between the two optimization strategies in terms of imaging performance and computational speed, including a case when one strategy performs better than the other.}, journal={IEEE Transactions on Antennas and Propagation}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Viswanathan, Naren and Venkatesh, Suresh and Schurig, David}, year={2021}, month={Feb}, pages={1–1} }
 @article{venkatesh_lu_tang_sengupta_2021, title={Secure space–time-modulated millimetre-wave wireless links that are resilient to distributed eavesdropper attacks}, volume={4}, url={http://dx.doi.org/10.1038/s41928-021-00664-z}, DOI={10.1038/s41928-021-00664-z}, number={11}, journal={Nature Electronics}, publisher={Springer Science and Business Media LLC}, author={Venkatesh, Suresh and Lu, Xuyang and Tang, Bingjun and Sengupta, Kaushik}, year={2021}, month={Nov}, pages={827–836} }
 @inproceedings{venkatesh_lu_sengupta_2021, title={Spatio-temporal modulated mm-Wave arrays for physical layer security and resiliency against distributed eavesdropper attacks}, url={http://dx.doi.org/10.1145/3477081.3481673}, DOI={10.1145/3477081.3481673}, abstractNote={Ensuring security for the next-generation of millimeter-Wave and Terahertz networks, while simultaneously ensuring multi-Gbps data rates and ultra-low latency (sub-millisecond) is becoming increasingly challenging. Physical layer security that exploits the physics of wireless propagation to incorporate security features into the signal is becoming increasingly popular as a component for a holistic approach towards ensuring security. In this regard, there are prior works that have exposed severe vulnerabilities in the well-established principle of security that involve directional narrow beams. In this article we highlight security features using mm-Wave interface design, and present a generalized approach towards physical-layer security. Security in our approach is ensured by enforcing fundamental loss of information by selective spectral aliasing towards the direction of eavesdroppers while maintaining robust, high fidelity wireless link towards the intended receiver. In a custom-designed integrated transmitter array, spectral aliasing is achieved by dynamically reconfigurable symbol-to-antenna mapping principle that can synthesize a fast time-varying channel towards the direction of the eavesdroppers. We demonstrate this principle experimentally for the first time with mm-Wave directional links (71-76 GHz unlicensed spectrum). We also experimentally show the resilience of such links against distributed and synchronized eavesdropper attacks for the first time in the mm-Wave bands.}, booktitle={Proceedings of the 5th ACM Workshop on Millimeter-Wave and Terahertz Networks and Sensing Systems}, publisher={ACM}, author={Venkatesh, Suresh and Lu, Xuyang and Sengupta, Kaushik}, year={2021}, month={Oct} }
 @article{saeidi_venkatesh_lu_sengupta_2021, title={THz Prism: One-Shot Simultaneous Localization of Multiple Wireless Nodes With Leaky-Wave THz Antennas and Transceivers in CMOS}, volume={56}, url={http://dx.doi.org/10.1109/jssc.2021.3115407}, DOI={10.1109/jssc.2021.3115407}, abstractNote={In this article, we propose and demonstrate a spectrum-to-space mapping principle for localizing multiple wireless nodes in a simultaneous and single-shot fashion at terahertz (THz) frequencies. Spectrum-to-space mapping is achieved through two dual-port chip integrated waveguide (CIW)-based leaky-wave antennas (LWAs). Interfacing with the two LWAs, we integrate two transmitting and receiving chains operating between 360- and 400-GHz range in a single chip realized in a 65-nm bulk CMOS process. Utilizing the carefully engineered dispersive nature of the LWA and its frequency-dependent radiation patterns, we create unique spectrum-to-space calibration maps for both 1-D and 2-D angular localizations. The measured one-shot localization error variance is less than 1° in 1-D space with 200-Hz-resolution bandwidth (BW) and less than 2° in 2-D space for a 20-Hz-resolution BW. The high-resolution nature of the localization principle in a single-shot fashion makes this approach attractive for multi-wireless node localization, link discovery, beam-forming, beam-management, and beam-optimization methods.}, number={12}, journal={IEEE Journal of Solid-State Circuits}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Saeidi, Hooman and Venkatesh, Suresh and Lu, Xuyang and Sengupta, Kaushik}, year={2021}, month={Dec}, pages={3840–3854} }
 @article{mmwave spatial-temporal single harmonic switching transmitter arrays for high back-off beamforming efficiency_2021, year={2021}, month={Jun} }
 @inproceedings{29.9 a 4×4 distributed multi-layer oscillator network for harmonic injection and thz beamforming with 14dbm eirp at 416ghz in a lensless 65nm cmos ic_2020, url={http://dx.doi.org/10.1109/isscc19947.2020.9063076}, DOI={10.1109/isscc19947.2020.9063076}, abstractNote={Integrated high-power THz arrays with beamforming ability can enable new applications in communication, sensing, imaging, and spectroscopy [1]. However, due to the limited power-generation capability of a single source above the device fmax [2], efficient spatial power combining from multiple coherent sources becomes necessary to generate mW level of power. To create this 2D array of distributed frequency and phase-locked sources, prior works have shown central LO-signal distribution with local harmonic upconversion [3]. However, this requires high power consumption in the LO distribution. In addition, phase-matching with PVT variations across the sources at the harmonic-radiating THz frequency can be quite challenging. A small ∆θ perturbation at the fundamental frequency translates to N∆θ at the radiated Nth harmonic, thus corrupting the array beam pattern. Another method to synchronize multiple distributed radiating sources (ƛ/2 spaced at Nfo) is through a mutual coupling network with active/passive elements in a coupled oscillator array [4], [5]. However, the locking range in these methods is typically narrow (∆flocking~ f0/20 to f0/10) and PVT variations can easily cause desynchronization. In such a network, each cell is a self-sustaining oscillator, and the coupling network tries to establish injection signals to force synchronization between these individual free-running oscillators. In this paper, we used a 2D oscillating network with negative Gm(–Gm) cells at each node that do not oscillate individually but only collectively, establishing a robust frequency and phase distribution network across the chip for high THz-power generation. By making this network as the lowest layer, we can now separate the locking mechanism and the power-generation sources. This avoids loading and sub-optimal operation of the power sources. The distributed oscillating network at the lowest layer operates at 69.3GHz, and multi-layer local harmonic generation produces a radiated power of −3dBm and +14dBm EIRP at 416GHz in a 4×4 array.}, booktitle={2020 IEEE International Solid- State Circuits Conference - (ISSCC)}, year={2020}, month={Feb} }
 @inproceedings{lu_venkatesh_tang_sengupta_2020, title={4.6 Space-Time Modulated 71-to-76GHz mm-Wave Transmitter Array for Physically Secure Directional Wireless Links}, url={http://dx.doi.org/10.1109/isscc19947.2020.9062929}, DOI={10.1109/ISSCC19947.2020.9062929}, abstractNote={Security in wireless networks has traditionally been addressed above the physical layer. With the expected proliferation of applications in 5G, the mm-wave spectrum and new network architectures, traditional methods of data encryption may not be scalable for energy-constrained applications. Thus, there has been a surge of interest in physical layer security that aims to impart confidentiality by exploiting the physics of the wireless communication channel without the need for exchanging secret cryptographic keys [1], [2]. The idea of a secure directional wireless link between a TX/RX pair is to preserve the signal information within a secure cone where the intended receiver is located while scrambling signals everywhere else to prevent eavesdropping. In a phased array, the same temporal digital information is fed to all the TX elements, transmitting the same information to all directions albeit at different power levels. This information can be recovered (especially at the side lobes) with a sensitive enough receiver. Spatial modulation with I, Q radiated out through separate antennas, and modulation of parasitic elements can distort the constellation in other directions [3], [4]. However, this one-to-one (bijective) mapping allows potential decoding by the eavesdropper, particularly using various signal processing and machine-learning-based classification techniques. Time modulation in an antenna array can incorporate such physical layer security through careful mapping of symbols to antennas in a time-modulated fashion.}, booktitle={2020 IEEE International Solid- State Circuits Conference - (ISSCC)}, publisher={IEEE}, author={Lu, X. and Venkatesh, S. and Tang, B. and Sengupta, K.}, year={2020}, pages={86–88} }
 @article{venkatesh_lu_saeidi_sengupta_2020, title={A high-speed programmable and scalable terahertz holographic metasurface based on tiled CMOS chips}, volume={3}, url={http://dx.doi.org/10.1038/s41928-020-00497-2}, DOI={10.1038/s41928-020-00497-2}, number={12}, journal={Nature Electronics}, publisher={Springer Science and Business Media LLC}, author={Venkatesh, Suresh and Lu, Xuyang and Saeidi, Hooman and Sengupta, Kaushik}, year={2020}, month={Dec}, pages={785–793} }
 @inproceedings{sharma_liu_chappidi_saeidi_venkatesh_sengupta_2020, title={Broadband PA architectures with asymmetrical combining and stacked PA cells across 50--70 GHz and 64--110 GHz in 250 nm InP}, booktitle={IEEE MTT-S Int. Microw. Symp. Dig.}, author={Sharma, T and Liu, Z and Chappidi, CR and Saeidi, H and Venkatesh, S and Sengupta, K}, year={2020} }
 @inproceedings{wu_ma_venkatesh_mehlman_wagner_sturm_verma_2020, title={Gigahertz Large-Area-Electronics RF Switch and its Application to Reconfigurable Antennas}, url={http://dx.doi.org/10.1109/iedm13553.2020.9372057}, DOI={10.1109/iedm13553.2020.9372057}, abstractNote={Future IoT and 5G networks place significant new demands on antennas, where unguided EM waves are generated to access densely distributed sensor nodes. Reconfigurable antennas, capable of changing key parameters (directionality, frequency response, polarization), are starting to play a critical role, but are limited by the assembly of discrete RF components across the large antenna apertures typically desired. This work presents the design, and use in a reconfigurable antenna, of RF switches for 2.4 GHz-band wireless applications, based on large-area-electronics (LAE) zinc-oxide (ZnO) thin-film transistors (TFTs). ZnO TFTs can be fabricated monolithically on meter-scale and flexible substrates, as done in flat panel displays, but where their frequencies have been limited to 10’s of MHz. RF switch performance is enabled for ZnO TFTs (fabricated at flex-compatible temp. <200°C) via self-aligned processing, thick-composite gate electrodes, breakdown-safe biasing, and resonant operation, leveraging high-Q LAE inductors. Reconfigurable antenna radiation patterns are demonstrated.}, booktitle={2020 IEEE International Electron Devices Meeting (IEDM)}, publisher={IEEE}, author={Wu, Can and Ma, Yue and Venkatesh, Suresh and Mehlman, Yoni and Wagner, Sigurd and Sturm, James C. and Verma, Naveen}, year={2020}, month={Dec} }
 @inproceedings{sengupta_lu_venkatesh_tang_2020, title={Physically Secure Sub-THz Wireless Links}, booktitle={2020 IEEE International Conference on Communications Workshops (ICC Workshops)}, author={Sengupta, Kaushik and Lu, Xuyang and Venkatesh, Suresh and Tang, Bingjun}, year={2020}, pages={1–7} }
 @inproceedings{sengupta_lu_venkatesh_tang_2020, title={Physically Secure mm-Wave Wireless Links with Spatio-temporal Modulated Arrays}, booktitle={2020 Third International Workshop on Mobile Terahertz Systems (IWMTS)}, author={Sengupta, Kaushik and Lu, Xuyang and Venkatesh, Suresh and Tang, Bingjun}, year={2020}, pages={1–4} }
 @inproceedings{sengupta_saeidi_lu_venkatesh_wu_2020, title={Terahertz Chip-scale Systems}, url={http://dx.doi.org/10.1109/ecoc48923.2020.9333156}, DOI={10.1109/ecoc48923.2020.9333156}, abstractNote={In this paper, we highlight the advances in chip-scale technologies in the terahertz spectrum between 100 GHz and 10 THz, particularly focusing on silicon-based integrated chip technology that can have a transformative impact in wireless communication, sensing and imaging.}, booktitle={2020 European Conference on Optical Communications (ECOC)}, publisher={IEEE}, author={Sengupta, Kaushik and Saeidi, Hooman and Lu, Xuyang and Venkatesh, Suresh and Wu, Xue}, year={2020}, month={Dec} }
 @inproceedings{sengupta_lu_venkatesh_wu_2020, title={Terahertz to bits and bits to terahertz}, url={http://dx.doi.org/10.1145/3411295.3411319}, DOI={10.1145/3411295.3411319}, abstractNote={The high millimeter-Wave and Terahertz spectrum above 100 GHz will form the underpinning of a broad set of game-changing future technology including high resolution sensing, imaging, robotics, autonomous systems, and wireless communication. In the last decade, we have seen a tremendous surge in efforts towards enabling chip-scale technology to address signal generation and detection in the THz spectrum. However, there lie several fundamental challenges to translate these efforts into versatile technology that can operate in complex environments that requires properties such as dynamic reconfigurability and rapid adaptability. In this paper, we highlight a new design space that emerges by eliminating the classical block-by-bock design approach. The fundamental principle behind this approach is that the unique wavelength scale at THz (of the order of millimeter/sub-millimeter) is comparable to a typical chip dimension. This wavelength/chip dimension equivalence allows the chip to operate in a new electromagnetic (EM) regime with novel scattering and radiating properties, while the integrated active devices have the ability to actively synthesize, manipulate and sense THz EM fields at sub-wavelength scales. This approach opens up the a new design space that can break many of the trade-offs in the classical design regime. In this paper, we provide design examples that aims towards the ultimate programmable THz sensor/source in silicon-based chips that range from fully integrated chip-scale THz spectroscopes to programmable THz sensors, sources and spatio-temporal modulated arrays for physical layer security. These design examples serve to illustrate the unique opportunities enabled through such a holistic design approach.}, booktitle={Proceedings of the 7th ACM International Conference on Nanoscale Computing and Communication}, publisher={ACM}, author={Sengupta, Kaushik and Lu, Xuyang and Venkatesh, Suresh and Wu, Xue}, year={2020}, month={Sep} }
 @inproceedings{liu_sharma_chappidi_venkatesh_sengupta_2020, title={Transformer-based broadband mm-wave InP PA across 42--62 GHz with enhanced linearity and second harmonic engineering}, booktitle={IEEE MTT-S Int. Microw. Symp. Dig.}, author={Liu, Z and Sharma, T and Chappidi, CR and Venkatesh, S and Sengupta, K}, year={2020} }
 @article{young professionals in space: transformation through democratization [around the globe]_2020, url={http://dx.doi.org/10.1109/mmm.2019.2963757}, DOI={10.1109/mmm.2019.2963757}, abstractNote={April 2020 Traditionally, satellites and related space technologies mainly found their application in remote sensing, security, and direct-to-home broadcast services. With the burgeoning quest for high-speed data access, high-tech conglomerates have started to look to the skies. The main players in space technology—SpaceX, Amazon, and OneWeb— are investing heavily in space Internet infrastructure and megaconstellations consisting of both lowand mediumEarth orbit satellites [1]. This potential trillion dollar market [1] requires innovations from wide-ranging aspects of science and engineering fields (chemical sciences for efficient rocket fuels, electrical engineering for modern communication systems, and mechanical/ aerospace engineering for novel propulsion systems). Rapid innovations in space technology require smart and immediate adaptation. This can be achieved by training and grooming the young talents of today who will be the stakeholders of tomorrow. Young Professionals in Space (YPinSpace) is a technical program conceived by Dr. Tushar Sharma (Figure 1) in 2016 with the dream of achieving this goal [2]. The program’s main objective is to bring world-renowned experts from different fields of space technology to share their experiences with YPs from all over the world under one umbrella [2]. Since its inception, YPinSpace has completed three successful events in Bangalore, India, in 2017, Barcelona, Spain, in 2018, and Dubai, United Arab Emirates, in 2019 (Figure 2). This article highlights and recaps some of the success stories of the YPinSpace program, including the recently held YPinSpace event in Dubai this past November. The space sector has been perceived to be an extremely close-knit community dominated by a few countries. However, some innovations and breakthroughs are currently being led by YPs of different nationalities, including from developing countries. This positive change is evident in the kinds of startups in this area, leading to the Young Professionals in Space: Transformation Through Democratization}, journal={IEEE Microwave Magazine}, year={2020}, month={Apr} }
 @inproceedings{tang_venkatesh_lin_lu_saeidi_rather_bertino_lin_javanmard_sengupta_2019, title={2D Magnetic Sensor Array for Real-time Cell Tracking and Multi-site Detection with Increased Robustness and Flow-rate}, DOI={10.1109/CICC.2019.8780363}, abstractNote={In this article, we present a 2D oscillator array-based magnetic sensor CMOS IC for flow cytometry. The CMOS IC packaged with a microfluidic channel eliminates the need for hydro-focusing by allowing uninhibited flow over the 2D chip surface. The chip exploits multi-site detection capability allowing simultaneously high flow rate for trace cell detection, reduced false positives, and real-time cell tracking. We demonstrate these functionalities with a $7 \times 7$ array in 65-nm CMOS with lymphoma cancer cells.}, booktitle={2019 IEEE Custom Integrated Circuits Conference (CICC)}, author={Tang, H. and Venkatesh, S. and Lin, Z. and Lu, X. and Saeidi, H. and Rather, G. M. and Bertino, J. R. and Lin, C. and Javanmard, M. and Sengupta, K.}, year={2019}, pages={1–4} }
 @article{venkatesh_schurig_2019, title={Transformation optics design of a planar near field magnifier for sub-diffraction imaging}, volume={27}, url={http://www.opticsexpress.org/abstract.cfm?URI=oe-27-4-4694}, DOI={10.1364/OE.27.004694}, abstractNote={It is well established that, under certain conditions, imaging systems with either isotropic negative index, or hyperbolic (indefinite) media can achieve super-resolution. However, achieving sub-diffraction limited imaging along with uniform aberration-free magnification can be challenging. In this article, we design, simulate, and evaluate the performance of planar 2D near-field magnifying lenses, based on the transformation-optic design principle. Specifically, we investigate a grid-relaxed transformation, that results in material properties that are more amenable to implementation. We discuss possible design choices in terms of: material properties, achievable resolution enhancement, adverse effect of loss tangent, magnification factor, and other design constraints affecting the imaging performance. We also present imaging performance results for a planar, near-field, 3× magnifier operating on a standard resolution target, based on a rigorous, 3D, electromagnetic simulation. This computational intensive result was achieved using cylindrical harmonic decomposition and the 2.5D electromagnetic simulation technique. Further, we investigate and propose a path to achieve higher magnification factors using cascaded elements.}, number={4}, journal={Opt. Express}, publisher={OSA}, author={Venkatesh, Suresh and Schurig, David}, year={2019}, pages={4694–4713} }
 @article{bernety_venkatesh_schurig_2018, title={Analytical Phasing of Arbitrarily Oriented Arrays Using a Fast, Analytical Far-Field Calculation Method}, url={https://doi.org/10.1109/TAP.2018.2823731}, DOI={10.1109/TAP.2018.2823731}, abstractNote={We propose an analytical approach for far-field calculation of antenna arrays comprised of arbitrarily oriented, identical elements using a straightforward rotation matrix calculation method. In addition, here we present a Constructive Analytical Phasing (CAP) method for arbitrary configurations of linearly polarized array elements. Conformal spherical and randomly oriented planar arrays of microstrip patch antennas are given as examples, wherein analytical results are verified by full-wave simulations. This approach provides substantial speed up compared to full-wave simulations, facilitating significantly broader tradeoff studies and optimizations, for a variety of antenna performance parameters.}, journal={IEEE Transactions on Antennas and Propagation}, author={Bernety, Hossein Mehrpour and Venkatesh, Suresh and Schurig, David}, year={2018}, month={Apr}, pages={1–1} }
 @inproceedings{bernety_venkatesh_schurig_2018, title={Constructive Analytical Phasing (CAP) for Arbitrarily Oriented Arrays of Linearly Polarized Elements}, DOI={10.1109/APUSNCURSINRSM.2018.8608344}, abstractNote={In this paper, we present a near-optimal phasing method, referred to as Constructive Analytical Phasing (CAP) to perform beamforming for arbitrary oriented antenna arrays of linearly polarized elements. Also, we investigate the resulting electric far-field polarization using Monte Carlo simulations. This simple but efficient method enables us to direct the beam to any desired point in space. In addition, it can be utilized to speed up any further optimization goals for a variety of antenna performance parameters such as pattern synthesis and side lobe level (SLL) reduction.}, booktitle={2018 IEEE International Symposium on Antennas and Propagation USNC/URSI National Radio Science Meeting}, author={Bernety, H. M. and Venkatesh, S. and Schurig, D.}, year={2018}, pages={105–106} }
 @inproceedings{viswanathan_venkatesh_schurig_2018, title={Exploiting Inter Voxel Correlation in Compressed Computational Imaging}, url={http://www.osapublishing.org/abstract.cfm?URI=COSI-2018-CTu2E.5}, DOI={10.1364/COSI.2018.CTu2E.5}, abstractNote={An ensemble of representative targets contains apriori correlation information, quantified by the intervoxel covariance matrix. Thresholding according to the eigenvalues of his matrix and reconstructing only those eigenmodes, a faster, more accurate reconstruction is obtained.}, booktitle={Imaging and Applied Optics 2018 (3D, AO, AIO, COSI, DH, IS, LACSEA, LS&C, MATH, pcAOP)}, publisher={Optical Society of America}, author={Viswanathan, Naren and Venkatesh, Suresh and Schurig, David}, year={2018}, pages={CTu2E.5} }
 @article{bernety_venkatesh_schurig_2018, title={Performance Analysis of a Helmet-Based Radar System for Impact Prediction}, volume={6}, url={https://doi.org/10.1109/ACCESS.2018.2882768}, DOI={10.1109/ACCESS.2018.2882768}, abstractNote={We analyze the performance of a helmet-based frequency modulated continuous wave (FMCW) radar system for use in impact prediction in contact sports, or other risky environments. It has been shown that the head trauma and concussions can have significant detrimental effects on the health and quality life of contact sport athletes, from the high school to professional level. Impact prediction capability could be an important part of a comprehensive, helmet-based system for mitigating the neurological damage caused by impacts. Mitigation strategies include using imminent impact information in an audible warning system, or dynamic preloading and control of an active helmet suspension. Our analysis centers on the prediction of an impact offset parameter (and its uncertainty) in a representative player interaction scenario. We consider realistic radar measurement specifications consistent with our player interaction scenario, and COTS radar hardware, including oscillator phase noise, operation frequency, sweep frequency, bandwidth, range, target scattering cross-section, and antenna gain.}, journal={IEEE Access}, publisher={IEEE}, author={Bernety, Hossein Mehrpour and Venkatesh, Suresh and Schurig, David}, year={2018}, pages={75124–75131} }
 @inproceedings{bernety_venkatesh_schurig_2017, title={Analytical far-field calculation of arbitrarily oriented antenna arrays}, DOI={10.1109/APUSNCURSINRSM.2017.8072285}, abstractNote={In this paper, we present an analytical approach to calculate the far-field radiation pattern of conformal arrays, consisting of arbitrarily oriented antennas. In particular, we focus on spherical arrays of microstrip patch antennas. This approach reduces the computational time and resource requirements as compared to a full-wave conventional EM solver. It should be mentioned that this method is not limited to spherical arrays only and can be applied to any other configurations as well. Also, this analytical approach makes it possible to run optimization processes faster, and to meet various design objectives.}, booktitle={2017 IEEE International Symposium on Antennas and Propagation USNC/URSI National Radio Science Meeting}, author={Bernety, H. M. and Venkatesh, S. and Schurig, D.}, year={2017}, pages={485–486} }
 @article{abbasi_abe_othman_abu-zayyad_allen_anderson_azuma_barcikowski_belz_bergman_et al._2017, title={First upper limits on the radar cross section of cosmic-ray induced extensive air showers }, volume={87}, url={http://www.sciencedirect.com/science/article/pii/S0927650516301682}, DOI={http://dx.doi.org/10.1016/j.astropartphys.2016.11.006}, abstractNote={TARA (Telescope Array Radar) is a cosmic ray radar detection experiment colocated with Telescope Array, the conventional surface scintillation detector (SD) and fluorescence telescope detector (FD) near Delta, Utah, U.S.A. The TARA detector combines a 40 kW, 54.1 MHz VHF transmitter and high-gain transmitting antenna which broadcasts the radar carrier over the SD array and within the FD field of view, towards a 250 MS/s DAQ receiver. TARA has been collecting data since 2013 with the primary goal of observing the radar signatures of extensive air showers (EAS). Simulations indicate that echoes are expected to be short in duration (∼ 10 µs) and exhibit rapidly changing frequency, with rates on the order 1 MHz/µs. The EAS radar cross-section (RCS) is currently unknown although it is the subject of over 70 years of speculation. A novel signal search technique is described in which the expected radar echo of a particular air shower is used as a matched filter template and compared to waveforms obtained by triggering the radar DAQ using the Telescope Array fluorescence detector. No evidence for the scattering of radio frequency radiation by EAS is obtained to date. We report the first quantitative RCS upper limits using EAS that triggered the Telescope Array Fluorescence Detector.}, journal={Astroparticle Physics}, author={Abbasi, R.U. and Abe, M. and Othman, M. Abou Bakr and Abu-Zayyad, T. and Allen, M. and Anderson, R. and Azuma, R. and Barcikowski, E. and Belz, J.W. and Bergman, D.R. and et al.}, year={2017}, pages={1–17} }
 @article{venkatesh_schurig_2016, title={Computationally fast EM field propagation through axi-symmetric media using cylindrical harmonic decomposition}, volume={24}, url={http://www.opticsexpress.org/abstract.cfm?URI=oe-24-25-29246}, DOI={10.1364/OE.24.029246}, abstractNote={We describe and provide a systematic procedure for computationally fast propagation of arbitrary vector electromagnetic (EM) fields through an axially symmetric medium. A cylindrical harmonic field propagator is chosen for this purpose and in most cases, this is the best and the obvious choice. Firstly, we describe the cylindrical harmonic decomposition technique in terms of both scalar and vector basis for a given input excitation field. Then we formulate a generalized discrete Fourier-Hankel transform to achieve efficient vector basis decomposition. We allow a slower, pre-computation step, that finds a representation of the axi-symmetric medium as a transfer matrix in a discrete, cylindrical-harmonic basis. We find this matrix from a series of axi-symmetric (2D) finite element simulations (also known as the 2.5D technique). This transfer matrix approach significantly reduces the computational load when the transverse size or range exceeds about 30 wavelengths. This matrix is independent of the input excitation field for a given space-bandwidth product and hence makes it reusable for different excitation fields. We numerically validate the above approaches for different axi-symmetric EM scattering media which include a hemispherical gradient-index Maxwell's fish-eye lens, a transformation optics designed spherical invisibility cloak, a thin aspheric lens, and a cylindrical perfect lens.}, number={25}, journal={Opt. Express}, publisher={OSA}, author={Venkatesh, Suresh and Schurig, David}, year={2016}, pages={29246–29268} }
 @article{joshi_miller_ogden_kavand_jamali_ambal_venkatesh_schurig_malissa_lupton_et al._2016, title={Separating hyperfine from spin-orbit interactions in organic semiconductors by multi-octave magnetic resonance using coplanar waveguide microresonators}, volume={109}, url={https://doi.org/10.1063/1.4960158}, DOI={10.1063/1.4960158}, abstractNote={Separating the influence of hyperfine from spin-orbit interactions in spin-dependent carrier recombination and dissociation processes necessitates magnetic resonance spectroscopy over a wide range of frequencies. We have designed compact and versatile coplanar waveguide resonators for continuous-wave electrically detected magnetic resonance and tested these on organic light-emitting diodes. By exploiting both the fundamental and higher-harmonic modes of the resonators, we cover almost five octaves in resonance frequency within a single setup. The measurements with a common π-conjugated polymer as the active material reveal small but non-negligible effects of spin-orbit interactions, which give rise to a broadening of the magnetic resonance spectrum with increasing frequency.}, number={10}, journal={Applied Physics Letters}, author={Joshi, G. and Miller, R. and Ogden, L. and Kavand, M. and Jamali, S. and Ambal, K. and Venkatesh, S. and Schurig, D. and Malissa, H. and Lupton, J. M. and et al.}, year={2016}, pages={103303} }
 @article{venkatesh_viswanathan_schurig_2016, title={W-band sparse synthetic aperture for computational imaging}, volume={24}, DOI={10.1364/oe.24.008317}, abstractNote={We present a sparse synthetic-aperture, active imaging system at W-band (75 - 110 GHz), which uses sub-harmonic mixer modules. The system employs mechanical scanning of the receiver module position, and a fixed transmitter module. A vector network analyzer provides the back end detection. A full-wave forward model allows accurate construction of the image transfer matrix. We solve the inverse problem to reconstruct scenes using the least squares technique. We demonstrate far-field, diffraction limited imaging of 2D and 3D objects and achieve a cross-range resolution of 3 mm and a depth-range resolution of 4 mm, respectively. Furthermore, we develop an information-based metric to evaluate the performance of a given image transfer matrix for noise-limited, computational imaging systems. We use this metric to find the optimal gain of the radiating element for a given range, both theoretically and experimentally in our system.}, number={8}, journal={Opt. Express}, publisher={The Optical Society}, author={Venkatesh, S. and Viswanathan, N. and Schurig, D.}, year={2016}, month={Apr}, pages={8317} }
 @inproceedings{venkatesh_viswanathan_schurig_2015, title={Receiver/transmitter configuration optimization for compressed computational millimeter-wave imaging}, DOI={10.1109/usnc-ursi.2015.7303304}, abstractNote={Millimeter wave (mmw) imaging is gaining popularity in surveillance systems as it provides good tradeoff between high resolution (optical/IR imaging) and high penetration depth (microwave). Conventional mmw Fourier transform based holographic imaging systems (D.M. Sheen et. al., MTT, IEEE Transactions on, vol.49, no.9, Sep 2001) require as many measurements as the required space-bandwidth product (M) of the target image. However, in compressed imaging systems (Guy Lipworth et. al., JOSA A, Vol. 30, Issue 8, 2013), apriori knowledge of the target object to be imaged can considerably reduce the number of measurements required. General priors such as sparsity can almost always be used, but more target specific priors can be used for further reducing the number of measurements needed.}, booktitle={2015 USNC-URSI Radio Science Meeting (Joint with AP-S Symposium)}, publisher={Institute of Electrical & Electronics Engineers (IEEE)}, author={Venkatesh, Suresh and Viswanathan, Naren and Schurig, David}, year={2015}, month={Jul} }
 @inproceedings{venkatesh_viswanathan_schurig_2015, title={W-Band Sparse Synthetic Aperture for Computational Imaging}, DOI={10.1364/aoms.2015.jt5a.17}, abstractNote={We present a sparse synthetic aperture system at W-Band (75 - 110 GHz) using sub-harmonic mixer modules. The active computational imaging system consists of a scanned transmitter module, a fixed receiver module and a vector network analyzer as the backend. We demonstrate standoff diffraction limited imaging of 2D and 3D targets.}, booktitle={Imaging and Applied Optics 2015}, publisher={The Optical Society}, author={Venkatesh, Suresh and Viswanathan, Naren and Schurig, David}, year={2015} }
 @article{venkatesh_shrekenhamer_xu_sonkusale_padilla_schurig_2013, title={Interferometric direction finding with a metamaterial detector}, volume={103}, DOI={10.1063/1.4851936}, abstractNote={We present measurements and analysis demonstrating useful direction finding of sources in the S band (2–4 GHz) using a metamaterial detector. An augmented metamaterial absorber that supports magnitude and phase measurement of the incident electric field, within each unit cell, is described. The metamaterial is implemented in a commercial printed circuit board process with off-board back-end electronics. We also discuss on-board back-end implementation strategies. Direction finding performance is analyzed for the fabricated metamaterial detector using simulated data and the standard algorithm, MUtiple SIgnal Classification. The performance of this complete system is characterized by its angular resolution as a function of radiation density at the detector. Sources with power outputs typical of mobile communication devices can be resolved at kilometer distances with sub-degree resolution and high frame rates.}, number={25}, journal={Appl. Phys. Lett.}, publisher={AIP Publishing}, author={Venkatesh, Suresh and Shrekenhamer, David and Xu, Wangren and Sonkusale, Sameer and Padilla, Willie and Schurig, David}, year={2013}, pages={254103} }
 @article{shrekenhamer_xu_venkatesh_schurig_sonkusale_padilla_2012, title={Experimental Realization of a Metamaterial Detector Focal Plane Array}, volume={109}, DOI={10.1103/physrevlett.109.177401}, abstractNote={We present a metamaterial absorber detector array that enables room-temperature, narrow-band detection of gigahertz (GHz) radiation in the S band (2-4 GHz). The system is implemented in a commercial printed circuit board process and we characterize the detector sensitivity and angular dependence. A modified metamaterial absorber geometry allows for each unit cell to act as an isolated detector pixel and to collectively form a focal plane array . Each pixel can have a dedicated microwave receiver chain and functions together as a hybrid device tuned to maximize the efficiency of detected power. The demonstrated subwavelength pixel shows detected sensitivity of -77 dBm, corresponding to a radiation power density of 27 nW/m(2), with pixel to pixel coupling interference below -14 dB at 2.5 GHz.}, number={17}, journal={Phys. Rev. Lett.}, publisher={American Physical Society (APS)}, author={Shrekenhamer, David and Xu, Wangren and Venkatesh, Suresh and Schurig, David and Sonkusale, Sameer and Padilla, Willie J.}, year={2012}, month={Oct} }