Development of a Printed Coil for Wirelessly Charging a Tracking Elderly Patch

Monitoring systems for elderly require a compromise between reduced size and operational autonomy. The latter to get a system as independent as possible and to fit with our application needs for daily use. Our patch is developed as a surveillance system for old people; we chose to equip it with a wireless charging system for greater ease of use, imperceptible in the everyday life and waterproofing. This paper presents the development of a printed receiver coil to be integrated in a wireless charger to be used in an elderly tracking patch. The proposed design is validated using simulation that presents a good agreement with measurement results: Simulation (@150 KHz: L = 10.74 µH; R = 3 Ω) and Measurement (@150 KHz: L = 10.8 µH; R = 3.16 Ω). The receiver coil is elaborated on a polyimide substrate in the cleanroom of our laboratory LAAS-CNRS (Laboratory for Analysis and Architecture of Systems-National Center for Scientific Research) and a PCB (Printed Circuit Board) charger prototype is fabricated to test its performances before the integration of the wireless charging property in the tracking patch. The proposed coil presents a good compromise between small size and efficiency. For a charging current of 7.5 mA, this coil can ensure the recharging of the patch up to a distance of 4.8 mm between the Qi transmitter and receiver which is more than enough for our application.