Remote Monitoring of Skin Temperature Through a Wristband Employing a Printed VO Sensor

Abstract

The need for highly sensitive, environmentally stable, mechanically flexible, and low-cost temperature sensors for on-body measurements has been increasing with the wide adoption of personal Healthcare-Internet-of-Things (H-IoT) devices. Printed electronics (PE) is a good platform for such sensors because it enables the realization of flexible devices through simple and rapid methods at a relatively low cost. However, previously reported printed temperature sensors suffer from poor sensitivity and/or environmental instability. In this paper, we report a custom Tungsten (W)-doped Vanadium Dioxide (VO2) ink-based screen-printed temperature sensor having the highest Temperature-Coefficient-of-Resistance (TCR) of 2.78%•°C -1 with a resolution of 0.1°C between 30°C and 40°C. To protect it from environmental effects, a fluoropolymer-based passivation layer is added for accurate temperature readings even in 90% relative humidity. The sensor is printed on a flexible substrate and shows minimal deterioration in performance over 1000 bending cycles. For wearability and remote monitoring, the sensor is integrated with a custom Bluetooth Low Energy (BLE) wireless readout in the form of a wristband. The BLE readout comprises an ultrathin and flexible patch antenna optimized for both BLE bandwidth and human wearability. It demonstrates a minimal SAR value of only 0.068W/kg, making it safe to wear. Despite the antenna's thin structure (0.004λ), it has a gain of 1.65dBi, enabling an excellent communication range. The proposed wristband is tested on ten volunteers and under daily activities, which shows promising results with a maximum error of 0.16°C with reference to those of a commercial thermometer.

Wireless Antenna Sensors for Biosimilar Monitoring Toward Cyber-Physical Systems: A Review of Current Trends and Future Prospects

“…For instance, a wireless sensor system for monitoring microbial fuel cells that provides real-time data on the voltage output and substrate concentration has been developed [87]. In a variety of biosimilar monitoring applications, including biosensing and diagnostics [88], medication delivery systems [89], quality control [90], environmental monitoring [91], and bioprocessing, wireless antenna sensors have demonstrated significant promise. Due to their ability to provide non-invasive [92], real-time monitoring and their compatibility with flexible materials [93], they are ideal for incorporation into peripheral and implantable devices.…”

Improving Definition of Screen-Printed Functional Materials for Sensing Application

“…Integrated smart systems have been key in the development of printed electronics. This field is widely explored for fabricating antennas and smart tags , that can be used in food industry and medication control, among others. In other fields such as sport fitness or healthcare monitoring, where wearable devices are required for detecting variations in blood pressure, temperature, or specific biomolecules, printing technologies have been also used because they allow the fabrication of lightweight, thin, and conformable electronics …”

Temperature-Switching Flexible Strain Sensors Based on Vanadium Dioxide for Intelligent Packaging Applications

“…This sensor provides stable monitoring throughout the day and is well suited for real-time skin temperature monitoring in Healthcare-Internet of Things (H-IoT) applications. 40 Liao and co-workers reported a flexible respiratory sensor by transfer-printing VO 2 films on PDMS substrates, which exhibited high feasibility for respiratory detection in various environments and provided real-time, high-quality clinical data. Therefore, VO 2 (M) materials have demonstrated potential in intelligent sensing and control systems.…”

“…Fatani and co-workers reported a customized W-doped VO 2 ink-based temperature sensor with a resolution of 0.1 °C between 30 and 40 °C and a maximum error of only ±0.16 °C. This sensor provides stable monitoring throughout the day and is well suited for real-time skin temperature monitoring in Healthcare-Internet of Things (H-IoT) applications . Liao and co-workers reported a flexible respiratory sensor by transfer-printing VO 2 films on PDMS substrates, which exhibited high feasibility for respiratory detection in various environments and provided real-time, high-quality clinical data.…”