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1. Modeling and Characterization of Scaling Factor of Flexible Spiral Coils for Wirelessly Powered Wearable Sensors

   https://doi.org/10.3390/s20082282  

   Biswas, Dipon K. ; Sinclair, Melissa ; Le, Tien ; Pullano, Salvatore Andrea ; Fiorillo, Antonino S. ; Mahbub, Ifana ( April 2020 , Sensors)

   null (Ed.)

   Wearable sensors are a topic of interest in medical healthcare monitoring due to their compact size and portability. However, providing power to the wearable sensors for continuous health monitoring applications is a great challenge. As the batteries are bulky and require frequent charging, the integration of the wireless power transfer (WPT) module into wearable and implantable sensors is a popular alternative. The flexible sensors benefit by being wirelessly powered, as it not only expands an individual’s range of motion, but also reduces the overall size and the energy needs. This paper presents the design, modeling, and experimental characterization of flexible square-shaped spiral coils with different scaling factors for WPT systems. The effects of coil scaling factor on inductance, capacitance, resistance, and the quality factor (Q-factor) are modeled, simulated, and experimentally validated for the case of flexible planar coils. The proposed analytical modeling is helpful to estimate the coil parameters without using the time-consuming Finite Element Method (FEM) simulation. The analytical modeling is presented in terms of the scaling factor to find the best-optimized coil dimensions with the maximum Q-factor. This paper also presents the effect of skin contact with the flexible coil in terms of the power transfer efficiency (PTE) to validate the suitability as a wearable sensor. The measurement results at 405 MHz show that when in contact with the skin, the 20 mm× 20 mm receiver (RX) coil achieves a 42% efficiency through the air media for a 10 mm distance between the transmitter (TX) and RX coils. 

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2. Position-Insensitive Wireless Power Transfer Based on Nonlinear Resonant Circuits

   O. B. Abdelatty, X. Wang ( March 2019 , IEEE transactions on microwave theory and techniques)

   Near-field resonant-based wireless power transfer (WPT) technology has a significant impact in many applications ranging from charging of biomedical implants to electric vehicles (EVs). The design of robust WPT systems is challenging due to its position-dependent power transfer efficiency (PTE). In this paper, a new approach is presented to address WPT's strong sensitivity to the coupling factor variation between the transmit and receive coils. The introduced technique relies on harnessing the unique properties of a specific class of nonlinear resonant circuits to design position-insensitive WPT systems that maintain a high PTE over large transmission distances and misalignments without tuning the source's operating frequency or employing tunable matching networks, as well as any active feedback/control circuitry. A nonlinear-resonant-based WPT circuit capable of transmitting 60 W at 2.25 MHz is designed and fabricated. The circuit maintains a high PTE of 86% over a transmission distance variation of 20 cm. Furthermore, transmit power and PTE are maintained over a large lateral misalignment up to ±50% of the coil diameter and angular misalignment up to ±75°. The new design approach enhances the performance of WPT systems by significantly extending the range of coupling factors over which both load power and high PTE are maintained. 

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3. Design of a Multi-layered On-chip Wireless Power Transfer (WPT) System Design for Brain Neuromodulation Applications

   https://doi.org/10.1109/WMCS49442.2020.9172383  

   Biswas, Dipon K. ; Rangel, Bernabe ; Mahbub, Ifana ( May 2020 , 2020 IEEE Texas Symposium on Wireless and Microwave Circuits and Systems (WMCS))

   null (Ed.)

   Chronic pain is a common disease and as a negative consequence can cause paralysis to an individual in the long run. Noninvasive brain stimulation is an effective method to reduce pain in the short term. However, for long-term treatment, neural data analysis along with the stimulation is highly desirable. In this work, a unique multilayer spiral coil with a total dimension of 500 μm×500 μm is designed in a 0.5 μm CMOS process to make it suitable for a fully implantable system. The electrical modeling of the coil is also analyzed and simulated using Keysight's Advanced Design System (ADS) software to compare the theoretical modeling results with the simulation results. The electromagnetic (EM) simulation to characterize the on-chip coil in-terms of scattering parameters (S-parameters), Q -factor, power transfer efficiency (PTE) is performed using the Ansys High-Frequency Structure Simulator (HFSS) software. The operating frequency of the WPT system is chosen to be within 402-405 MHz which is the Medical Implant Communication System (MICS) band. The simulated Q -factor of the proposed on-chip coil is approximately 15 at 402 MHz. The on-chip coil is integrated with an on-chip seven-stage rectifier and some commercial off-the-shelf (COTS) components such as a DC-DC converter and a μ LED to design the complete optogenetic neuro-stimulation system. A minimum power transfer efficiency (PTE) of 0.4% is achieved through a 16 mm thick tissue media using the proposed WPT system. With that efficiency, the proposed system is able to provide constant power to light up a μ LED and proves to be a good candidate for neuromodulation applications. 

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4. A Wireless Power Transfer based Gate Driver Design for Medium Voltage SiC MOSFETs

   https://doi.org/10.1109/IFEEC53238.2021.9661739  

   Wei, Yuqi ; Du, Liyang ; Du, Xia ; Machireddy, Venkata Samhitha ; Mantooth, Alan ( November 2021 , IEEE International Future Energy Electronics Conference (IFEEC))

   Wide band gap (WBG) devices have been widely adopted in numerous industrial applications. In medium voltage applications, multi-level converters are necessary to reduce the voltage stress on power devices, which increases the system control complexity and reduces power density and reliability. High voltage silicon carbide (SiC) MOSFET enables the medium voltage applications with less voltage level, simple control strategy and high power density. Nevertheless, great challenges have been posed on the gate driver design for high voltage SiC MOSFET. Wireless power transfer (WPT) can achieve power conversion with large airgap, which can satisfy the system isolation requirement. Thus, in this article, a WPT based gate driver is designed for the medium voltage SiC MOSFET. The coil is optimized by considering voltage isolation, coupling capacitance, size, and efficiency. Experimental prototype was built and tested to validate the effectiveness of the proposed WPT based gate driver. 

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5. Wirelessly Powered 3-D Printed Headstage Based Neural Stimulation System for Optogenetic Neuromodulation Application

   https://doi.org/10.1109/JERM.2022.3225972  

   Biswas, Dipon K. ; Saha, Nabanita ; Mahbub, Ifana ( January 2023 , IEEE Journal of Electromagnetics, RF and Microwaves in Medicine and Biology)

   This work presents a miniaturized wireless power transfer (WPT) system integrated with a neuromodulation headstage for duty-cycled optical stimulation of freely moving rodents. The proposed WPT system is built using the commercially available off-the-shelf components (COTS) for the optogenetic neuromodulation system consisting of a bridge rectifier, a DC-DC converter, an oscillator circuit, an LED driver, and a μLED. The total power consumption of the stimulation system is 14 mW which is provided using the WPT method. The WPT system includes a novel transmitter (TX) coil implemented on a printed circuit board (PCB), and a solenoid receiver (RX) coil wrapped around a customized 3-D printed headstage. The proposed TX coil is designed in such a way that the magnetic field all across the TX coil is sufficient to provide the required power to the optical stimulation system that is worn as a headstage by the freely moving rat. The headstage device's dimension is 18.75 mm × 21.95 mm, weighing 4.75 g. The ratio of the weight of the headstage and rat is 4.75:300. The proposed system is able to achieve a maximum overall efficiency of ∼63% at 5 cm separation between the TX and RX coils, where the maximum power transfer efficiency (PTE) of the WPT system is ∼88% and the power conversion efficiency (PCE) of the rectifier is 71.6%. The proposed system with reconfigurable stimulation frequency is suitable for exciting different brain areas for long-term health monitoring. 

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