Development of Flexible Wireless Wall Temperature Sensor for Combustion Studies

A polyimide-based flexible wireless wall temperature sensor has been proposed for unsteady wall temperature measurements of internal combustion (IC) engines. The sensor is equivalent to an LCR resonant circuit including a sensing capacitor and a planar coil, which is coupled with an external read-out coil. The temperature changes lead to shifts of the resonant frequency, which is determined with the dip in the phase angle of complex impedance. The 1 mm-square sensing capacitor consists of suspended interdigitated electrodes sandwiched by two Al
₂
O
₃
layers, which is fabricated using the microelectromechanical systems processes on a polyimide substrate. The cylinder wall temperature in an IC engine is measured with a 1.2 ms time interval. Due to the high sensitivity and quality factor of –15.1 kHz/°C and 120, accuracy of the unsteady temperature measurement up to 0.2 °C has been achieved. It is demonstrated that 137 temperature data are obtained in a single engine cycle at a rotational frequency of 730 r/min.