A Stretchable, Conductive Thread-Based Sensor Towards Wearable Monitoring of Muscle Atrophy.

OBJECTIVE: We present the first wearable sensor designed for frequent monitoring of muscle atrophy and validate performance upon canonical phantoms. METHODS: Our approach relies on Faraday's law of induction and exploits the dependence of magnetic flux density on cross-sectional area. We employ wrap-around transmit and receive coils that stretch to fit changing limb sizes using conductive threads (e-threads) in a novel zig zag pattern. Changes in the loop size result in changes in the magnitude and phase of the transmission coefficient between loops. RESULTS: Simulation and in vitro measurement results are in excellent agreement. As a proof-of-concept, a cylindrical calf model for an average-sized subject is considered. The frequency of 60 MHz is selected via simulation for optimal limb size resolution in magnitude and phase while remaining in the inductive mode of operation. We can monitor muscle volume loss of up to 51%, with an approximate resolution of 0.17 dB and 1.58° per 1% volume loss. In terms of muscle circumference, we achieve resolution of 0.75 dB and 6.7° per centimeter. Thus, we can monitor small-scale changes in overall limb size. CONCLUSION: This is the first known approach for monitoring muscle atrophy with a sensor designed to be worn. Additionally, this work brings forward innovations in creating stretchable electronics from e-threads (as opposed to inks, liquid metal, or polymer). SIGNIFICANCE: The proposed sensor will provide improved monitoring for patients suffering from muscle atrophy. The stretching mechanism can be seamlessly integrated into garments which creates unprecedented opportunities for future wearable devices.

High-Contrast Low-Loss Antenna: A Novel Antenna for Efficient Into-Body Radiation.

We present a biocompatible high-contrast low-loss antenna (HCLA) designed for efficient into-body radiation for applications as diverse as medical telemetry, sensing, and imaging. The HCLA is wearable with a compact size of 2.62 cm3 and operates across the 1 to 5 GHz bandwidth. The quasi-bowtie antenna is loaded with a high-contrast (i.e., alternating layers of high and low permittivity materials) and low-loss dielectric to improve directivity and gain into the biological tissues. Measurement results at 2.4 GHz are in good agreement with simulations and show 5.72 dB improvement in transmission loss over the most efficient into-body radiator reported in the past. At the high end of the frequency bandwidth, simulation results for two antennas placed across each other with tissue in between show ~12.5 dB improvement in transmission loss. The HCLA is fabricated with stable, low-loss materials that allow for repeatability and consistency in the fabrication process, thus, addressing limitations of the current state-of-the-art. It is also made from biocompatible materials that enable it to be placed directly on the skin for real-world implementation. In this paper, we discuss the operation principle and design of the HCLA, its transmission performance, radiation patterns, and specific absorption rate.