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1. When in-memory computing meets spiking neural networks—A perspective on device-circuit-system-and-algorithm co-design

   https://doi.org/10.1063/5.0211040  

   Moitra, Abhishek; Bhattacharjee, Abhiroop; Li, Yuhang; Kim, Youngeun; Panda, Priyadarshini (September 2024, Applied Physics Reviews)

   This review explores the intersection of bio-plausible artificial intelligence in the form of spiking neural networks (SNNs) with the analog in-memory computing (IMC) domain, highlighting their collective potential for low-power edge computing environments. Through detailed investigation at the device, circuit, and system levels, we highlight the pivotal synergies between SNNs and IMC architectures. Additionally, we emphasize the critical need for comprehensive system-level analyses, considering the inter-dependencies among algorithms, devices, circuit, and system parameters, crucial for optimal performance. An in-depth analysis leads to the identification of key system-level bottlenecks arising from device limitations, which can be addressed using SNN-specific algorithm–hardware co-design techniques. This review underscores the imperative for holistic device to system design-space co-exploration, highlighting the critical aspects of hardware and algorithm research endeavors for low-power neuromorphic solutions. 

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2. A Wirelessly Rechargeable AA Battery Using Electrodynamic Wireless Power Transmission

   https://doi.org/10.3390/en14092368  

   Smith, Spencer E.; Halim, Miah A.; Chyczewski, Stasiu T.; Rendon-Hernandez, Adrian A.; Arnold, David P. (May 2021, Energies)

   null (Ed.)

   We report the design, fabrication, and characterization of a prototype that meets the form, fit, and function of a household 1.5 V AA battery, but which can be wirelessly recharged without removal from the host device. The prototype system comprises a low-frequency electrodynamic wireless power transmission (EWPT) receiver, a lithium polymer energy storage cell, and a power management circuit (PMC), all contained within a 3D-printed package. The EWPT receiver and overall system are experimentally characterized using a 238 Hz sinusoidal magnetic charging field and either a 1000 µF electrolytic capacitor or a lithium polymer (LiPo) cell as the storage cell. The system demonstrates a minimal operating field as low as 50 µTrms (similar in magnitude to Earth’s magnetic field). At this minimum charging field, the prototype transfers a maximum dc current of 50 µA to the capacitor, corresponding to a power delivery of 118 µW. The power effectiveness of the power management system is approximately 49%; with power effectiveness defined as the ratio between actual output power and the maximum possible power the EWPT receiver can transfer to a pure resistive load at a given field strength. 

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3. Auger effect limited performance in tunnel field effect transistors

   https://doi.org/10.1109/E3S.2017.8246156  

   Ahmed, Sheikh; Tan, Yaohua; Truesdell, Daniel; Ghosh, Avik (October 2017, 2017 Fifth Berkeley Symposium on Energy Efficient Electronic Systems & Steep Transistors Workshop (E3S))

   null (Ed.)

   Tunnel field-effect-transistors (TFETs) are promising candidates for next generation transistors for low power applications, as the TFETs promise low subthreshold swing (SS). Different from traditional MOSFET, the TFETs rely on energy-efficient switching of band-to-band tunneling (BTBT), therefore the SS in TFETs is not limited by the 60 mV/decade Boltzmann limit. This reduction in energy consumption makes TFETs suitable candidates to replace standard MOSFETs in low power applications. However, most experimentally demonstrated TFETs suffer from low on current[1], and the theoretical low SS is compromised by impurities and Auger generation. To understand the underlying physics and predict the device characteristics of TFETs, sophisticated numerical simulations can be used. On the other hand, physics based compact models are also required to provide fast predictions for existing and new device concepts. Furthermore, a physics based compact model is more efficient to model the effects like Auger generation which could be time-consuming for numerical calculations. In this work, we introduce a physics based compact model for homojunction TFETs with Auger generation effect considered. This compact model is based on the modified Simmons' equation at finite temperature[2]. With our compact model, the possible impact of Auger generation effect to off-current and SS is explored. 

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4. Energy scavenging from ultra-low temperature gradients

   https://doi.org/10.1039/c8ee03084g  

   Kishore, Ravi Anant; Davis, Brenton; Greathouse, Jake; Hannon, Austin; Emery Kennedy, David; Millar, Alec; Mittel, Daniel; Nozariasbmarz, Amin; Kang, Min Gyu; Kang, Han Byul; et al (March 2019, Energy & Environmental Science)

   Thermal energy harvesting from natural resources and waste heat is becoming critical due to ever-increasing environmental concerns. However, so far, available thermal energy harvesting technologies have only been able to generate electricity from large temperature gradients. Here, we report a fundamental breakthrough in low-grade thermal energy harvesting and demonstrate a device based on the thermomagnetic effect that uses ambient conditions as the heat sink and operates from a heat source at temperatures as low as 24 °C. This concept can convert temperature gradients as low as 2 °C into electricity while operating near room temperature. The device is found to exhibit a power density (power per unit volume of active material) of 105 μW cm −3 at a temperature difference of 2 °C, which increases to 465 μW cm −3 at a temperature difference of 10 °C. The power density increases by 2.5 times in the presence of wind with a speed of 2.0 m s −1 . This advancement in thermal energy harvesting technology will have a transformative effect on renewable energy generation and in reducing global warming. 

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5. Magnetoelectric backscatter communication for millimeter-sized wireless biomedical implants

   https://doi.org/10.1145/3495243.3560541  

   Yu, Zhanghao; Alrashdan, Fatima T.; Wang, Wei; Parker, Matthew; Chen, Xinyu; Chen, Frank Y.; Woods, Joshua; Chen, Zhiyu; Robinson, Jacob T.; Yang, Kaiyuan (October 2022, MobiCom '22: Proceedings of the 28th Annual International Conference on Mobile Computing and Networking)

   This paper presents the design, implementation, and experimental evaluation of a wireless biomedical implant platform exploiting the magnetoelectric effect for wireless power and bi-directional communication. As an emerging wireless power transfer method, magnetoelectric is promising for mm-scaled bio-implants because of its superior misalignment sensitivity, high efficiency, and low tissue absorption compared to other modalities [46, 59, 60]. Utilizing the same physical mechanism for power and communication is critical for implant miniaturization, but low-power magnetoelectric uplink communication has not been achieved yet. For the first time, we design and demonstrate near-zero power magnetoelectric backscatter from the mm-sized implants by exploiting the converse magnetostriction effects. The system for demonstration consists of an 8.2-mm3 wireless implantable device and a custom portable transceiver. The implant's ASIC interfacing with the magnetoelectric transducer encodes uplink data by changing the transducer's load, resulting in resonance frequency changes for frequency-shift-keying modulation. The magnetoelectrically backscattered signal is sensed and demodulated through frequency-to-digital conversion by the external transceiver. With design optimizations in data modulation and recovery, the proposed system archives > 1-kbps data rate at the 335-kHz carrier frequency, with a communication distance greater than 2 cm and a bit error rate less than 1E-3. Further, we validate the proposed system for wireless stimulation and sensing, and conducted ex-vivo tests through a 1.5-cm porcine tissue. The proposed magnetoelectric backscatter approach provides a path towards miniaturized wireless bio-implants for advanced biomedical applications like closed-loop neuromodulation. 

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