Acoustic Transducer Dimension of the in-plane poled piezoelectric diaphragm: electrode width=60 μ m; electrode spacing=250 μ m; radius=3.5 mm. The effective coupling coefficient is 3.08 %. The quality factor Q value is 39.96. Schematic diagram of the test setup for evaluating the acoustic transmission performance of the devices. The setup was in an anechoic chamber. A BK 4196 microphone with known sensitivity as reference. Both the sensitivity and the sound pressure level (SPL= 20log(sound pressure /20 μ Pa)), peaks appear at the resonance of 13.71 kHz. The 1 kHz sensitivity of the d 33 mode diaphragm (126.21 μ V/Pa), is nearly 20 times of the sensitivity (6.5 μ V/Pa) of a d 31 mode thick film diaphragm with the same material and similar dimensions. A 3 × 3 array was fabricated. Each element can be controlled independently. Directivity pattern of the array was tested. The array has the potential to be used as a phase array. For more information, please refer to: Zhiyuan Shen , Jingyu Lu, Chee Wee Tan, Jianmin Miao, Zhihong Wang, “ d 33 mode piezoelectric diaphragm based acoustic transducer with high sensitivity” , Sensor and Actuator A: Physical , 189, (2013), pp. 93-99.