This brief presents an interface design for electromagnetic energy harvesting for wearable applications. A transducer design is proposed. Multiple segments of coils with alternating winding directions improve the induced voltage and power. Due to the source's wideband nature in target applications, we avoid the use of springs common in conventional designs. The corresponding equivalent circuit model is presented. A system-level analysis is then performed that leads to the following power interface circuit design. It includes a differential rectifier and a switched-inductor boost converter. The harvested power is maximized with a constant-resistance load that can be adjusted through a variable-gain amplifier's gain. Implemented in a 0.18-μm CMOS process and tested at 20 Hz, measurement results show 80% impedance matching efficiency with 0.7-V input voltages. The system is able to harvest ~320 μW when shaken by hand at 2.5~3 Hz.
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Wang et al. (2018) studied this question.