Volume 128, Issue 3, September 2010
Index of content:
- TRANSDUCTION 
A micro-machined piezoelectric flexural-mode hydrophone with air backing: A hydrostatic pressure-balancing mechanism for integrity preservation128(2010); http://dx.doi.org/10.1121/1.3458837View Description Hide Description
Although an air-backed thin plate is an effective sound receiver structure, it is easily damaged via pressure unbalance caused by external hydrostaticpressure. To overcome this difficulty, a simple pressure-balancing module is proposed. Despite its small size and relative simplicity, with proper design and operation, micro-channel structure provides a solution to the pressure-balancing problem. If the channel size is sufficiently small, the gas-liquid interface may move back and forth without breach by the hydrostaticpressure since the surface tension can retain the interfacesurface continuously. One input port of the device is opened to an intermediate liquid, while the other port is connected to the air-backing chamber. As the hydrostaticpressure increases, the liquid in the micro-channel compresses the air, and the pressure in the backing chamber is then equalized to match the external hydrostaticpressure. To validate the performance of the proposed mechanism, a micro-channel prototype is designed and integrated with the piezoelectric micro-machined flexural sensor developed in our previous work. The working principle of the mechanism is experimentally verified. In addition, the effect of hydrostaticpressure on receiving sensitivity is evaluated and compared with predicted behavior.
A micro-machined piezoelectric flexural-mode hydrophone with air backing: Benefit of air backing for enhancing sensitivitya)128(2010); http://dx.doi.org/10.1121/1.3467757View Description Hide Description
A micro-machined underwater acoustic receiver that utilizes the flexural vibration mode of a silicon thin plate and piezoelectric transduction material was investigated. In particular, air was used as the backing material for the hydrophone in order to improve sensitivity in the audible frequency range. To evaluate the effects of air backing on receiving sensitivity, a transduction model incorporating mechanical/electrical/acoustical design parameters was used in designing a piezoelectric micro-machined hydrophone. The sensitivity and displacement responses of the sensor were simulated using the model for air backing and water backing cases, and the benefit of using air backing to enhance sensitivity was confirmed. The micro-machined piezoelectric transducer was fabricated, assembled in the shape of a hydrophone, and tested to ascertain its characteristics as an underwater sensor. These characteristics, such as frequency response and sensitivity, were measured and compared with the simulated results.
Objective evaluation of the sweet spot size in spatial sound reproduction using elevated loudspeakersa)128(2010); http://dx.doi.org/10.1121/1.3467763View Description Hide Description
In a previous study, three crosstalk cancellation techniques were evaluated and compared under different conditions. Least-squares approximations in the frequency and time domain were evaluated along with a method based on minimum-phase decomposition and a frequency independent delay. In general, the least-squares methods outperformed the method based on the minimum-phase decomposition. However, the evaluation was only done for the best-case scenario, where the transfer functions used to design the filters correspond to the listener’s transfer functions and his/her location and orientation relative to the loudspeakers. This paper presents a follow-up evaluation of the performance of the three inversion techniques when the above mentioned conditions are relaxed. A setup to measure the sweet spot of different loudspeaker arrangements is described. The sweet spot was measured for 21 different loudspeaker configurations, including two- and four-channel setups. Lateral and frontal displacement were measured along with head rotations. The setups were evaluated at different elevation angles. The results suggest that when the loudspeakers are placed at elevated positions, a wider effective area is obtained. Additionally, the two-channel configurations showed to be more robust to head misalignments than the four-channel configurations.