NASA Langley Research Center researchers have developed a wireless, low-profile sensor that uses a magnetic field response measurement acquisition system to provide power to the sensor and to acquire physical property measurements from it. Unique to this sensor is the shape of the electrical trace that eliminates the need for separate inductance, capacitance, and connection circuitry. This feature gives the sensor a smaller circuit footprint to enable a smaller, flexible, and easy-to-fabricate sensor package. The shape of the electrical trace can be readily modified to sense different physical properties. Also, arranging multiple low-profile sensors together can permit the wireless data acquisition system to read the responses from all the sensors by powering just one of them.
The low-profile sensor is configured with a spiral electrical trace on flexible substrate. In typical inductor designs, the space between traces is designed to minimize parasitic conductance to reduce the impact of the capacitance to neighboring electronics. In this low-profile sensor, however, greater capacitance is desired to allow the operation of an inductor-capacitor circuit. This allows the traces to be closer together, decreasing the overall size of the spiral trace.
The sensor receives a signal from the accompanying magnetic field data acquisition system. Once electrically active, the sensor produces its own harmonic magnetic field as the inductor stores and releases magnetic energy. The antenna of the measurement acquisition system is switched from a transmitting to a receiving mode to acquire the magnetic-field response of the sensor. The magnetic-field response attributes of frequency, amplitude, and bandwidth of the inductor correspond to the physical property states measured by the sensor. The received response is correlated to calibration data to determine the physical property measurement. When multiple sensors are inductively coupled, the data acquisition system needs to activate and read only one sensor to obtain measurement data from all of them.
The wireless sensor enables measurements in areas previously impractical to reach due to wiring constraints, and enables use under corrosive, radioactive, extreme temperature, and other hazardous conditions. It also eliminates the risk of electrical arcing in explosive conditions.
This technology can be used in automotive, motor sports, and trucking applications to measure tire pressure, tread wear, wheel speed, fuel level, and engine temperature. It can also be used in aerospace applications for landing gear health and fuselage integrity, and in industrial systems to measure foundry kiln temperature and cryogenic liquid level.