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1. Intelligent Remote Powering System With PTE Auto-Balancing For a Wireless and Batteryless EEG Cap

   https://doi.org/10.1109/AP-S/USNC-URSI47032.2022.9886950  

   SharafiMasouleh, M.; Sajedi, M.; Adjouadi, M. (July 2022, 2022 IEEE International Symposium on Antennas and Propagation and USNC-URSI Radio Science Meeting)

   This work presents a fully battery-less and wireless (untethered) EEG readout cap. The powering system is equipped with a highly efficient and compact power transmitter mosaicked by an array of 8×11 Tx resonators in a certain pattern operating at the lowest ISM band of 6.78 MHz. The front-end’s power receiver block Rx includes multi-resonators mounted all-around an EEG cap that can be worn by a subject. Furthermore, considering the subject's head which could assume different positions, a well-designed positioning system and an intelligent feeding setup are developed to balance the efficiency drop due to misalignment and to involve the most associated resonators with the powering scenario with the potential of switching off the extraneous resonators that are not engaged with Transmit and Receive (Tx-Rx) power. 

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2. Efficient on-chip terahertz generation and detection with GaN photoconductive emitters

   https://doi.org/10.1038/s41377-025-01870-6  

   Uzundal, Can_B; Feng, Qixin; Tang, Weichen; Hu, Chen; Sanborn, Collin; Yoon, Yoseob; Chen, Sudi; Ruan, Jiawei; Louie, Steven_G; Wang, Feng (June 2025, Light: Science & Applications)

   Abstract Photoconductive emitters for terahertz generation hold promise for highly efficient down-conversion of optical photons because it is not constrained by the Manley-Rowe relation. Existing terahertz photoconductive devices, however, faces limits in efficiency due to the semiconductor properties of commonly used GaAs materials. Here, we demonstrate that large bandgap semiconductor GaN, characterized by its high breakdown electric field, facilitates the highly efficient generation of terahertz waves in a coplanar stripline waveguide. Towards this goal, we investigated the excitonic contribution to the electro-optic response of GaN under static electric field both through experiments and first-principles calculations, revealing a robust excitonic Stark shift. Using this electro-optic effect, we developed a novel ultraviolet pump-probe spectroscopy for in-situ characterization of the terahertz electric field strength generated by the GaN photoconductive emitter. Our findings show that terahertz power scales quadratically with optical excitation power and applied electric field over a broad parameter range. We achieved an optical-to-terahertz conversion efficiency approaching 100% within the 0.03–1 THz bandwidth at the highest bias field (116 kV/cm) in our experiment. Further optimization of GaN-based terahertz generation devices could achieve even greater optical-to-terahertz conversion efficiencies. 

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3. Energy efficient downlink massive MIMO: Is 1-bit quantization a solution ?

   https://doi.org/10.1109/ISWCS.2019.8877256  

   Marcastel, Alexandre; Fijalkow, Inbar; Swindlehurst, Lee (August 2019, Proc. 16th International Symposium on Wireless Communication Systems (ISWCS))

   Massive MIMO aims to build wireless base stations with hundreds of coherently operating antennas serving tens of single antenna users in order to improve both the transmission capacity by a factor 10-50 and the energy-efficiency trade-off by up to a thousand times. Pre-coding at the base station has been proposed to efficiently implement digital beamforming. It implies a high signal dynamic range and therefore a power backoff resulting in less energy-efficiency. One-bit quantized Zero-Forcing precoding has been proposed to efficiently handle the RF front-end when the array is implemented with so many antennas. In this paper, we analyze the energy-efficiency of the quantized Zero-Forcing precoded systems for a large number of users and a massive MIMO base station. 

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4. Simultaneous Improvement of the Power Conversion Efficiency and Stability of Perovskite Solar Cells by Doping PMMA Polymer in Spiro‐OMeTAD‐Based Hole‐Transporting Layer

   https://doi.org/10.1002/solr.202100408  

   Xia, Pufeihong; Guo, De'en; Lin, Siyuan; Liu, Shan; Huang, Han; Kong, Deming; Gao, Yongli; Zhang, Wenhao; Hu, Yue; Zhou, Conghua (September 2021, Solar RRL)

   Improving efficiency and stability has become an urgent issue in the application of perovskite solar cells (PSCs). Herein, a kind of long‐chain polymer or polymethylmethacrylate (PMMA) is added into the spiro‐OMeTAD matrix to improve the film formation process and hence the device performance. It is observed that, after modification, the spiro‐OMeTAD‐based hole‐transporting layer becomes uniform, continuous, and condensed. Meanwhile, the power conversion efficiency of the devices is upgraded. Compared with the control device, open‐circuit voltage of the modified one (with moderate doping) increases from 1.06 (±0.03) to 1.10 (±0.02) V, fill factor increases from 72.20 (±3.44)% to 75.59 (±3.35)%, and the power conversion efficiency increases from 18.82 (±1.06)% to 20.51 (±0.82)% (highest at 21.78%) under standard test condition (AM 1.5G, 100 mW cm⁻²). Transient photocurrent/photovoltage decay curves, time‐resolved photoluminance, and impedance spectroscopy studies show that the modification could accelerate charge transfer and retard interfacial recombination. In addition, the modification improves device stability. Due to the strengthened barrier against penetration of “H₂O/O₂/Ag,” the efficiency of the unsealed device could retain 91.49% (by average) of the initial one after 100 days storage in the dark [relative humidity = 30(±5)%]. This work shows that long‐chain polymer doping could simultaneously improve efficiency and stability of spiro‐OMeTAD‐based PSCs. 

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5. Batteryless, Wireless, and Secure SoC for Implantable Strain Sensing

   https://doi.org/10.1109/OJSSCS.2022.3230000  

   Abdelhamid, Mohamed R.; Ha, Unsoo; Banerjee, Utsav; Adib, Fadel; Chandrakasan, Anantha P. (December 2022, IEEE Open Journal of the Solid-State Circuits Society)

   The past few years have witnessed a growing interest in wireless and batteryless implants, due to their potential in long-term biomedical monitoring of in-body conditions such as internal organ movements, bladder pressure, and gastrointestinal health. Early proposals for batteryless implants relied on inductive near-field coupling and ultrasound harvesting, which require direct contact between the external power source and the human body. To overcome this near-field challenge, recent research has investigated the use of RF backscatter in wireless micro-implants because of its ability to communicate with wireless receivers that are placed at a distance outside the body (∼0.5 m), allowing a more seamless user experience. Unfortunately, existing far-field backscatter designs remain limited in their functionality: they cannot perform biometric sensing or secure data transmission; they also suffer from degraded harvesting efficiency and backscatter range due to the impact of variations in the surrounding tissues. In this paper, we present the design of a batteryless, wireless and secure system-on-chip (SoC) implant for in-body strain sensing. The SoC relies on four features: 1) employing a reconfigurable in-body rectenna which can operate across tissues adapting its backscatter bandwidth and center frequency; 2) designing an energy efficient 1.37 mmHg strain sensing front-end with an efficiency of 5.9 mmHg·nJ/conversion; 3) incorporating an AES-GCM security engine to ensure the authenticity and confidentiality of sensed data while sharing the ADC with the sensor interface for an area efficient random number generation; 4) implementing an over-the-air closed-loop wireless programming scheme to reprogram the RF front-end to adapt for surrounding tissues and the sensor front-end to achieve faster settling times below 2 s. 

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