A High Gauge Factor Capacitive Strain Sensor and its Telemetry Application in Biomechanics

A highly sensitive strain sensing system has been developed using a capacitive MEMS bending strain sensor for telemetry application in biomechanics such as spinal fusion monitoring. This telemetry sensor system is capable of detection with a linear gauge factor as high as 249 in frequency domain. The task is accomplished by converting the capacitive strain to frequency using a low power capacitance-frequency converter circuit that modulates the 125 kHz magnetic carrier source from the interrogating reader. The reader demodulates the 125 kHz signal and recovers the strain information from the sensor. Experimentally, various situation tests were performed with loads on a material test system (MTS) machine up to 1000 micro- strains to simulate corpectomy model on a stainless rod. Strain measurements were proved reliable within 10 cm range.