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This paper presents a concept for a double negative metamaterial (DNM)-based antenna to simultaneously enhance Wireless Power Transfer (WPT) and reduce Specific Absorption Rate (SAR) here for a network of distributed brain microimplants. The DNM copper coils are integrated in a FR-4 substrate, which has a dielectric constant of 4.3 and tangent loss (δ) of 0.025. Occupying a 2 × 2 cm2 area, the DNM structure is introduced into our target wireless brain-machine interface (BMI) system operating at 915 MHz. Preliminary HFSS simulations show it provides 2 dB WPT enhancement and a 20% SAR reduction. We believe the work has the potential to address the WPT/ SAR co-optimization challenges for biomedical implants in general. 

Reverse electrowetting-on-dielectric (REWOD) energy harvesting is an effective energy harvesting method at low frequencies such as the frequencies of human motion. Various REWOD energy harvester designs have been presented in prior works, but these generally use rigid and often expensive substrates and time-consuming and/or costly fabrication methods. To address these challenges, in this work REWOD energy harvesters were fabricated consisting of aluminized polyester sheets as the functional layers and with polycarbonate sheets for added mechanical support. The fabrication of these samples eliminates the need for costly materials, clean room technologies, and high-end equipment. Samples were characterized using a flat arrangement and on a test fixture that simulates the repeated bending that occurs on the back of a bending knee. Without applying any external bias voltage, the maximum voltage and current output for the bending samples were determined to be 25.1 mV and 230 nA, respectively, and the corresponding maximum power is 5.77 nW at a bending frequency of 5 Hz. With an estimated cost of U.S. $ 0.28 for each REWOD harvester (U.S. $ 0.03/cm2), the cost per nanowatt of power is U.S. $ 0.05/nW, which is approximately 380 times lower than the approximately U.S. $ 19/nW of our previous REWOD energy harvesters. Our simple devices provide a low-cost, easily fabricated flexible approach to wearable motion sensing and energy harvesting that can be useful for various healthcare applications. 

A unique method for capturing energy from mechanical electrolyte modulation is known as reverse electrowetting-on-dielectric (REWOD). Prior REWOD studies relied on rigid electrodes which demand a high bias voltage to maximize harvested power, hindering the advancement of self-powered wearable health-monitoring sensors. In addition, the amount of energy harvested via the REWOD technique can be improved to a greater extent with the utilization of a high-dielectric (high-k) metal oxide (HDMO) layer on flexible electrodes. In this study, two distinct sets of electrodes that are flexible are utilized for harvesting energy with the REWOD phenomenon. The samples were coated with HDMO layers, namely, hafnium oxide (HfO2) and manganese dioxide (MnO2), respectively. The material deposition on a polyimide sheet is employed via a sputtering-based physical vapor deposition (PVD). The utilization of MnO2 samples with the proposed flexing REWOD test measurement generated 476.21 μW/cm2 an utmost power density value with an encapsulated electrolyte between electrodes.