A Wireless Strain Sensor Using Frequency Modulation Technique

A compact wireless strain sensor using a Frequency Modulation (FM) technique is proposed. The sensor employs a conventional resistive strain gauge such that the resistance changes as the measured structure is mechanically strained. When the strain gauge is connected to a frequency modulation circuit, the change in the resistance appears as a frequency shift in the output signal that is transmitted wirelessly to a remote station. The received signal is then demodulated and the buried strain measurement data can be retrieved. Using this technique, a dynamic strain measurement is possible without any wire connection between the sensing point and the measurement equipment. This type of sensors have numerous applications in the strain or vibration measurement of moving or rotating structures such as fans on a turbine engine. The proposed concept of the wireless strain sensor is experimentally demonstrated by measuring vibration of a cantilevered beam with a wired transmission of the measurement data from the transmitter to the receiver.