Wireless Power Transfer based on Spiral–Spider Coils for a Wireless Heart Rate Sensor

Abstract

Wireless power transfer (WPT)–based magnetic resonance coupling (WPT-MRC) is an encouraging technique for medium-power medical devices and other similar applications. Most wearable medical devices are operated based on several batteries. Generally, the batteries of such devices cannot be used for an extended time and typically involve a replacing or recharging process. WPT-MRC is a candidate technology that can resolve the charging of such batteries or it can directly supply power to the medical device. This paper aims to design and implement WPT based on the spiral–spider coils (WPT-S/S) for transferring high power over different air gaps to address the power problem. A heart rate measurement unit (HRMU) was implemented practically to confirm the functionality of the presented WPT-S/S. The proposed system comprises three main parts: monitoring, measurement, and power. The power unit contains receiver/transmitter coils, a capacitor resonator, and a rectifier. The measurement part contains an Arduino Nano platform (microcontroller), an nRF24L01 wireless technology for transmitting the HR measurement to the monitoring unit, and the biomedical sensor (HR sensor). The WPT-S/S system achieved 87% transfer power efficiency and 10 W DC output power over a 5-cm distance between the source coil (transmitter) and destination coil (receiver) when a resistance load of 200 Ω was employed. Also, the spiral–spider configuration succeeded in achieving adequate DC output voltage (i.e., 5 V) for supplying the HRMU at a distance of 20 cm between the coils.