A multi-cycle Q-modulation for dynamic optimization of inductive links

Abstract

This paper presents a new method, called multicycle Q-modulation,to modulate the quality factor (Q) of the receiver (Rx) coil and dynamically optimize the load impedance to maximize the power transfer efficiency (PTE) in two-coil links. A key advantage of the proposed method is that it can be easily implemented using off-the-shelf components without requiring fast switching at or above the carrier frequency, which is more suitable for integrated circuit design. Moreover, the proposed technique does not need any sophisticated synchronization between the power carrier and Q-modulation switching pulses. The multicycle Q-modulation is analyzed theoretically by a lumped circuit model, and verified in simulation and measurement using an off-the-shelf prototype. Automatic resonance tuning in the Rx, combined with multicycle Q-modulation helped maximizing PTE of the inductive link dynamically in the presence of environmental and loading variations, which can otherwise significantly degrade the PTE in multicoil settings. In the prototype conventional two-coil link, the proposed method increased the power amplifier plus inductive-link efficiency from 4.8% to 16.5% at (R L = 1 kW, d 23 = 3 cm), and from 23% to 28.2% at (R L = 100 Ω, d 23 = 3 cm) after 11% change in the resonance capacitance, while delivering 168.1 mW to the load (PDL).