Stretchable Multi-Band Radio Frequency Sensor for Strain Measurement

A stretchable Radio Frequency (RF) tension sensor is presented in this paper. The sensor is based on a filter that, in the absence of strain, operates as a dual band-pass filter at 1.2 GHz and 1.95 GHz and a dual band-stop filter at 1.67 GHz and 2.27 GHz. Two logarithmically scaled spiral-shaped Defected Ground Structures (DGS) are etched from the ground planes of a Coplanar Waveguide Transmission Line (CPW) to produce the dual band-stop operation. In addition, two U-shaped slot capacitors are etched from the feeding line of the CPW to ensure the appropriate operation of the filter when stretched. The magnitudes of the reflection and transmission coefficients undergo a gradual shift in their operational frequencies, which corresponds to the degree of stretching. The filter is fabricated and tested in different stretching states where its ability to accurately sense the applied strain level is validated.