Power Efficiency and Power Delivery Measurement in Inductive Links with Arbitrary Source and Load Impedance Values

Abstract

Paper describes a method for measuring power transfer efficiency (PTE) and power delivered to the load (PDL) in inductive links with desired source and load impedances using Network Analyzer (NA) and Spectrum Analyzer (SA). Characteristics of an inductive link vary by the source (input) and load (output) resistors. Although measuring the PTE and PDL using NA and SA is simple, straightforward, and accurate, the measured results are valid only for the ports' impedances at $\mathbf{50}\ \Omega$. We present a method that allows using NA and SA for measurement with any desired source and load resistances that match the actual operating conditions. For this purpose, we 1) add resistors in series or in parallel with the NA ports, 2) measure PTE by NA and PDL by SA (over $\mathbf{50}\ \Omega$), and 3) calculate the actual PTE and PDL. This method provides more flexibility in design and optimization of inductive links by finding the optimal load resistor and model from measurement of the link. We have verified the functionality of the proposed method by simulating, implementing, and measuring the performance of a prototype inductive link for energizing small implants.