MA40S4R is an ultrasonic receiver sensor. MA40S4R consists of piezoelectric ceramics, metal plates, resonators, and resin cases. The resonator has a funnel shape to transmit ultrasonic waves which are generated by the vibration of the resonator to the air efficiently(or to concentrate ultrasonic waves from the air on the center of resonance). Sound pressure level(S.P.L.) is the most important characteristic of ultrasonic transducers. For example, in measuring distance application, a high S.P.L. transducer enables to detect the further distance. High S.P.L. and high sensitivity Compact size (10.0mm dia.) Open type structure (used for indoor applications)