The development of an innovative wireless strain sensing technology has a great potential to extend its applications in manufacturing, civil engineering and aerospace industry. This paper presents a novel wireless and powerless strain sensor with a multi-layer thick film structure. The sensor employs a planar inductor (L) and capacitive transducer (C) resonant tank sensing circuit, and a strain sensitive material of a polarized polyvinylidene fluoride (PVDF) piezoelectric thick film to realize the wireless strain sensing by strain to frequency conversion and to receive radio frequency electromagnetic energy for powering the sensor. The prototype sensor was designed and fabricated. The results of calibration on a strain constant cantilever beam show a great linearity and sensitivity about 0.0013 in a strain range of 0-0.018.
A remotely-powered wireless temperature sensor to monitor a bearing health has been developed. The device employs a pair of miniaturized temperature sensitive capacitors in a simple inductor-capacitor (L-C) oscillator configuration. The bearing temperature is encoded in the frequency of the oscillator’s signal. The signal is wirelessly monitored by a receiver, which is connected to a PC for further analysis. Energy for the sensor circuit’s operation is supplied by a second electromagnetic radio signal, produced by an exciter coil. Thus, no wires or batteries are attached to the sensor circuit. The devices are fabricated on Dupont Kapton thick film substrates using surface mount components, and can be integrated onto bearing cages during fabrication. The circuits are designed to have small size, low power consumption, wide dynamic range and very low cost. After a brief introduction, this article describes the circuits employed. Calibration results are then presented.