Flexible acoustic emission sensor array with thermoresponsive actuator enhancing sensitivity for monitoring osteoarthritis

This paper presents a novel flexible piezoelectric lead zirconium titanate (PZT) thin film acoustic emission (AE) sensor array with thermoresponsive polymer actuators enhancing its sensitivity (Fig. 1). A hydrothermal PZT film is grown on a micromachined titanium-film four beam array as an acoustic sensing material. Thermoresponsive polymer Poly(N-isopropylacrylamide) (PNIPA), is structured on the beam array to electrically control the sensing beam array along with beneath micro-pins to achieve excellent couple to the detecting target so as to increase the sensitivity. Also, the array configuration makes AE source detection more accurate than regular single detection-head sensor. The flexible metal sheet based AE sensor can be easily fitted curved surfaces for detection, which is difficult for the conventional AE sensor anchored by screws. The characteristic frequencies shift of the sensed signal is monitored when overusing the cartilage of knee joint.