A new design method for a strain sensor using the cross-section modification of a coaxial cable

• A design method for a strain monitoring sensor is proposed by using coaxial cable.
• A dual variable cross section sensor structure is designed and fabricated.
• The characteristic parameters of the sensor are calculated.
• The characteristics of the sensor are validated by simulation and experiment.
• The methods for the improvement of sensitivity and quality factor are discussed.

Strain sensors have been used extensively in structural condition monitoring. In this paper, based upon microwave network theory, a novel design method for a real-time strain monitoring sensor is proposed by using the variable cross section of a coaxial cable to detect the strain-induced frequency shift of the peak frequency at which the S parameter exhibits a peak value. With this method, a dual variable-cross-section sensor is designed and fabricated using coaxial cable as the fabrication element. The S-parameters of the sensor obtained analytically by transmission theory are almost consistent with those obtained by numerical simulation. In experiments, the sensitivity of the sensor achieved 5 MHz/mɛ with the original segment length of 10.345 mm and peak frequency of 5.0 GHz, and the resolution achieved is 140.25 μɛ. The relative small deviation of nearly 3.2% from the theoretical results to the experimental results adequately validated the feasibility of the design method. Adjusting the diameter of the dielectric layer, the length and cascaded periods of the variable cross-section, the quality factor and sensitivity of the sensor can be optimized. Due to the simplicity and ruggedness of the cable based sensor it has great potential application in structural condition monitoring compared to existing sensors.