Research on the Measuring System of Polymer-based Capacitive Micromachined Ultrasonic Transducer Array for Circular Planar Target

The purpose of this research is using a polymer-based capacitive micro-machined ultrasonic transducer (CMUT) array to determine the position and dimension of circular planar target. The polymer-based CMUT is consist of an indium tin oxide-polyethylene terephthalate (ITO-PET) substrate and SU-8 sidewall and vibrating membranes. The CMUT has advantages of flexibility, low cost and large sensing area application comparing with silicon-based sensor. A four-quadrant (4Q) array is used to determine the position of the circular target based on the time of flight (TOF) and magnitude of the acoustic echo signals reflected from the target. The measuring system is designed to determine diameter and position of the transparent objects for pick and place on a conveyor. The four quadrant array has an overall dimension of 6 mm x 6 mm and can detect target diameter up to 3.6 mm with a maximum eccentricity of 1.2 mm. An algorithm is proposed to correct nonlinearity error when the target is away from the center of the four-quadrant array. The ultrasonic measuring system is constructed and tested to demonstrate its feasibility. The experimental results show the position error of 0.052 mm and dimension error of 0.42% in area at the worst scenario.