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1. Dual-Transduction Electromechanical Receiver for Near-Field Wireless Power Transmission

   https://doi.org/10.1109/MEMS51782.2021.9375416  

   Smith, Spencer E.; Halim, Miah A.; Rendon-Hernandez, Adrian A.; Arnold, David P. (January 2021, 2021 IEEE 34th International Conference on Micro Electro Michancial Systems (MEMS))

   null (Ed.)

   We report the design, fabrication, and experimental characterization of a chip-sized electromechanical micro-receiver for low-frequency, near-field wireless power transmission that employs both electrodynamic and piezoelectric transductions to achieve a high power density and high output voltage while maintaining a low profile. The 0.09 cm 3 device comprises a laser-micro-machined titanium suspension, one NdFeB magnet, two PZT-5A piezo-ceramic patches, and a precision-manufactured micro-coil with a thickness of only 1.65 mm. The device generates 520 μW average power (5.5 mW•cm -3 ) at 4 cm distance from a transmitter coil operating at 734.6 Hz and within safe human exposure limits. Compared to a previously reported piezoelectric-only prototype, this device generates ~2.5x higher power and offers 18% increased normalized power density (6.5 mW•cm -3 •mT -2 ) for potential improvement in wirelessly charging wearables and bio-implants. 

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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. Design, Modeling, and Simulation of a 2.4 GHz Near-field Phased-Array based Wireless Power Transfer System for Brain Neuromodulation Applications

   https://doi.org/10.1109/WMCS55582.2022.9866412  

   Saha, Nabanita; Mahbub, Ifana (April 2022, 2022 IEEE Texas Symposium on Wireless and Microwave Circuits and Systems (WMCS))

   To avoid interruption of experiment and risk of infection, wireless power transfer (WPT) techniques have been used to eliminate the bulky wires and batteries attached to the animals in rodent electrophysiological applications for long-term in-vivo electrophysiological recordings. Headstage-based neuromodulation device has become one of the most popular methods for neural stimulation in recent times. In this work, a wireless power transfer system is designed which provides a constant power to a headstage based optogenetic stimulator. The proposed research is composed of two parts: i) a unidirectional 28 cm × 21 cm phased array transmitter antenna, and ii) an electrically small bi-directional 2.4 cm × 2.4 cm receiver antenna. A phased array transmitter antenna is designed to provide a uniform power transmission over the 27 cm × 23 cm × 16 cm rat behavioral cage area. The proposed WPT scheme utilizes a near-field power transmission scheme at 2.4 GHz frequency. Simulation results show that the transmitter antenna achieves a -24 dB and receiver antenna achieves a −27 dB return loss (S 11 ) at the resonating frequency. The proposed WPT system shows a maximum of 24.5% power transfer efficiency (PTE) when the receiver is in the center position and is 10 cm distance apart from the transmitter, which is much higher compared to the other state-of-the-art works. The transmitter antenna steers beam from −21° to 27° in ϕ axis and −108° to 74° in θ axis which covers the maximum 6.27 cm 2 area of the cage. The preliminary simulation results of the proposed WPT module show a better prospect for future optogenetics based applications. 

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4. A Novel 3-D Printed Headstage and Homecage based WPT System for Long-term Behavior Study of Freely Moving Animals

   https://doi.org/10.1109/RWS45077.2020.9050034  

   Biswas, Dipon K.; Martinez, Jose H.; Daniels, Jacob; Bendapudi, Abhijeet; Mahbub, Ifana (March 2020, 2020 IEEE Radio and Wireless Symposium (RWS))

   null (Ed.)

   Wirelessly powered neural stimulation and recording system is crucially important for the long-term study of the animal behaviors for the treatment of chronic neuropathic diseases. Headstage based neural implant is one of the popular methods to stimulate the neurons. In this work, a homecage based wireless power transfer (WPT) system is developed to supply power to a 3-D printed headstage which consists of a receiver (RX) coil, a rectifier and a light-emitting diode (LED) for optogenetic stimulation. A multilayer transmitter (TX) coil is designed to provide power over the 28.5 cm × 18 cm homecage area. The proposed system is able to achieve a maximum of 41.7% efficiency at 5 cm distance through air media using less number of headstage resonators compared to the other state-of-the art works. 

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5. Magnetoelectrics enables large power delivery to mm-sized wireless bioelectronics

   https://doi.org/10.1063/5.0156015  

   Kim, Wonjune; Tuppen, C Anne; Alrashdan, Fatima; Singer, Amanda; Weirnick, Rachel; Robinson, Jacob T (September 2023, Journal of Applied Physics)

   To maximize the capabilities of minimally invasive implantable bioelectronic devices, we must deliver large amounts of power to small implants; however, as devices are made smaller, it becomes more difficult to transfer large amounts of power without a wired connection. Indeed, recent work has explored creative wireless power transfer (WPT) approaches to maximize power density [the amount of power transferred divided by receiver footprint area (length × width)]. Here, we analyzed a model for WPT using magnetoelectric (ME) materials that convert an alternating magnetic field into an alternating voltage. With this model, we identify the parameters that impact WPT efficiency and optimize the power density. We find that improvements in adhesion between the laminated ME layers, clamping, and selection of material thicknesses lead to a power density of 3.1 mW/mm2, which is over four times larger than previously reported for mm-sized wireless bioelectronic implants at a depth of 1 cm or more in tissue. This improved power density allows us to deliver 31 and 56 mW to 10 and 27-mm2 ME receivers, respectively. This total power delivery is over five times larger than similarly sized bioelectronic devices powered by radiofrequency electromagnetic waves, inductive coupling, ultrasound, light, capacitive coupling, or previously reported magnetoelectrics. This increased power density opens the door to more power-intensive bioelectronic applications that have previously been inaccessible using mm-sized battery-free devices. 

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