| A low cost, non-intrusive interdigitated comb capacitive strain sensor for wireless monitoring of CNC tool cutting forces was designed. Wireless resonant strain sensors were fabricated using the capacitive strain sensor and an inductive trace printed on a flexible film. A parallel-plate capacitance model matched experimental results of capacitive sensors tested in bending and torsion. An optimal sensor design of 12 fingers and a 2.54 mm grid length resulted in an average sensor gauge factor of 0.6910 +/- 0.0646 in bending and 0.9091 +/- 0.1406 in torsion. The wirelessly measured resonant strain sensor was measured to have an average gauge factor of 0.6418 +/- 0.0467 in uniaxial compression. A low cost simplified network analyzer was designed, fabricated, and evaluated. While it was able to identify resonant peaks, it was determined that additional port correction and calibration were necessary to closely match commercial analyzer accuracy. |
