Novel Impedance Sensing via Semiconductor Strain Gauge and Magnetic Resonant Coupling for Wireless Force Measurement

Wireless force measurement (WFM) can be used for those scenarios where cable connection and power supply are not available, such as wheel rail force measurement. To enhance the sensitivity and extend the lift-off [the distance between the transmitter (Tx) and receiver (Rx)] for WFM, this article introduces a novel approach based on impedance sensing through magnetic resonant coupling (MRC), coupled with a semiconductor strain gauge (SSG), and measured by a developed inductance to digital converter (LDC)-based system. Initially, a simulation was performed to investigate the influence of SSG at various coupling coefficients using parallel-parallel (PP) and series-parallel (SP) MRC topologies. Subsequently, the experiment conducted loading tests on a carbon steel specimen. A traditional strain gauge (SG) was also compared with the SSG in the same experimental set-up. Additionally, the response and sensitivity of the two topologies were analyzed at various lift-offs and SSGs. The results demonstrate that the approach based on impedance sensing, MRC, and a miniaturized LDC-based system achieved WFM with high sensitivity and high lift-offs. Both equivalent parallel resistance ( $R_{\mathrm { Peq}}$ ) and resonant frequency ( $f_{\mathrm { res}}$ ) exhibited an excellent linear relationship with the force. The sensitivity in $R_{\mathrm { Peq}}$ was found to be relatively stable near the critical coupling region, while $f_{\mathrm { res}}$ exhibited only an exponential curve. SSGs affected the optimal lift-off for both PP and SP topologies. The proposed approach is highly suitable for WFM, offering low cost, portability, and fast response advantages.