Telemetric Technique for Wireless Strain Measurement From an Inkjet-Printed Resistive Sensor

Strain monitoring allows obtaining critical information regarding the conditions of several systems. It would help, for example, to avoid possible structural damages. However, not all the existing devices are suitable to accomplish this task for a great number of applications, because of the characteristics of measurement environment, which prevent the use of batteries or wired connections. The use of telemetric devices may overcome these limitations, since they rely on the magnetic coupling between two inductors for wireless sensor supply and data transmission. The work treated in this paper presents a technique that permits us to calculate the output of a resistive strain gauge from a measurement of system impedance phase performed at a specific frequency, when distance between the inductors is fixed. We validated the method using a real device working with a low-cost sensor fabricated through inkjet-printing technology on a flexible substrate. We applied successive deformations, until 1% of sensor length at rest position. Calculated strain presents a percentage deviation from measured values going from 0.7% to 7%, whereas the highest uncertainty is 0.02% of sensor length at rest. Experimental results put in evidence, on one hand, the potential of inkjet printing to fabricate valid sensing elements and, on the other hand, that the proposed approach is successful in strain estimation.