Wireless sensing of pressure from extracted capacitances using shielded external coils

Abstract

This paper presents a method to extract capacitances for pressure-related applications. The external coils and internal circuit are inductively coupled to transmit power and to extract the capacitances in terms of the reflected impedance. The extracted frequency is 13.56 MHz, which is both the working frequency of the Near Field Communication (NFC) standards and the industrial, scientific and medical (ISM) band. The internal inductor with the shape of shorter helical coils is fabricated. The shielded external coils are designed using Ansys HFSS, and the shielded external coils make it more robust than unshielded external coils when the distance is increased. The measurement results show that the proposed method to extract the capacitances is realized under applied pressure from 1.02 to 1.32 bar. Based on the results, the pressure is wirelessly inferred from the extracted capacitances.