Hybrid Coils-Based Wireless Power Transfer for Intelligent Sensors

Abstract

Most wearable intelligent biomedical sensors are battery-powered. The batteries are large and relatively heavy, adding to the volume of wearable sensors, especially when implanted. In addition, the batteries have limited capacity, requiring periodic charging, as well as a limited life, requiring potentially invasive replacement. This paper aims to design and implement a prototype energy harvesting technique based on wireless power transfer/magnetic resonator coupling (WPT/MRC) to overcome the battery power problem by supplying adequate power for a heart rate sensor. We optimized transfer power and efficiency at different distances between transmitter and receiver coils. The proposed MRC consists of three units: power, measurement, and monitoring. The power unit included transmitter and receiver coils. The measurement unit consisted of an Arduino Nano microcontroller, a heart rate sensor, and used the nRF24L01 wireless protocol. The experimental monitoring unit was supported by a laptop to monitor the heart rate measurement in real-time. Three coil topologies: spiral-spiral, spider-spider, and spiral-spider were implemented for testing. These topologies were examined to explore which would be the best for the application by providing the highest transfer power and efficiency. The spiral-spider topology achieved the highest transfer power and efficiency with 10 W at 87%, respectively over a 5 cm air gap between transmitter and receiver coils when a 200 Ω resistive load was considered. Whereas, the spider-spider topology accomplished 7 W and 93% transfer power and efficiency at the same airgap and resistive load. The proposed topologies were superior to previous studies in terms of transfer power, efficiency and distance.

Keywords: arduino; heart rate sensor; nRF24L01; transfer efficiency; transfer power.

Figure 1

Block diagram of the use of a magnetic resonator coupling (MRC) for a heart rate sensor.

Figure 2

A method of wrapping (a) spiral coil and (b) spider coil.

Figure 3

Types of coils (a) spiral coil and (b) spider coils.

Figure 4

A snapshot of the MRC system at 7 cm for first topology at load.

Figure 5

A snapshot of the MRC system at 9 cm for first topology for real time.

Figure 6

A snapshot of the MRC system at 7 cm for the second topology under load.

Figure 7

A snapshot of the MRC system at 20 cm for the second topology for real time.

Figure 8

A snapshot of the MRC system at 20 cm for the third topology.

Figure 9

The voltage waveforms using the spiral–spiral topology at 7 cm for 50 Ω load: (a) transmitter coil, (b) receiver coil, and (c) voltage load.

Figure 10

The voltage waveforms using the first topology at 9 cm for the measurement unit: (a) transmitter coil, (b) receiver coil, and (c) voltage load.

Figure 11

Performance at different loads for first topology: (a) transfer efficiency at different loads (RL), (b) transfer power at RL, and (c) transfer power on Rx_C at RL.

Figure 11

Performance at different loads for first topology: (a) transfer efficiency at different loads (RL), (b) transfer power at RL, and (c) transfer power on Rx_C at RL.

Figure 12

The voltage waveforms using second topology at 7 cm for: (a) transmitter coil and (b) receiver coil.

Figure 13

The voltage waveforms using second topology at 20 cm for measurement unit: (a) transmitter coil, (b) receiver coil, and (c) voltage load.

Figure 14

Performance at different loads for second topology: (a) transfer efficiency at RL, (b) transfer power at RL, and (c) transfer power on Rx_C at RL.

Figure 14

Performance at different loads for second topology: (a) transfer efficiency at RL, (b) transfer power at RL, and (c) transfer power on Rx_C at RL.

Figure 15

The voltage waveforms using third topology at 7 cm for: (a) transmitter coil and (b) receiver coil.

Figure 16

The voltage waveforms using the third topology at 20 cm for measurement unit: (a) transmitter coil, (b) receiver coil, and (c) voltage load.

Figure 17

Performance at different loads for third topology: (a) transfer efficiency at RL, (b) transfer power at RL, and (c) transfer efficiency on Rx_C at RL.

Figure 17

Performance at different loads for third topology: (a) transfer efficiency at RL, (b) transfer power at RL, and (c) transfer efficiency on Rx_C at RL.

Figure 18

Transfer power at RL based-topologies at: (a) 40 Ω and (b) 200 Ω.

Figure 19

Transfer efficiency of RL based topologies into: (a) 40 Ω and (b) 200 Ω.

Figure 20

Transfer power on Rx_C at RL based on topologies at (a) 40 Ω and (b) 200 Ω.