Volume 120, Issue 2, August 2006
Index of content:
- TRANSDUCTION 
120(2006); http://dx.doi.org/10.1121/1.2214149View Description Hide Description
Broadband array transducers are widely used in medical imaging systems, and their beam patterns determine the imaging quality. The characteristics of the beam patterns such as mainlobe beamwidth and sidelobe levels are the major criteria for designing and optimizing sparse array systems. The spatial impulse response approach can be used to calculate the beam patterns rigorously in both near field and far field. However, it is time consuming due to the high sampling frequency required, and thus not suitable for array optimization. On the other hand, assuming the array elements to be omnidirectional point sources the field calculation can be much simplified and fast but at the expense of poor accuracy. This paper presents a modified model that has the accuracy comparable to that from the impulse response model while keeping the efficiency close to that of the simple point source model. The developed algorithm is particularly suitable for stochastic methods for two-dimensional (2D) sparse arrays design and optimization such as genetic algorithms (GA), in which the iterative beam pattern calculation dominates the optimization program running time.
120(2006); http://dx.doi.org/10.1121/1.2216561View Description Hide Description
The advent of siliconmicromachiningtechnology has opened up numerous opportunities for the commercialization of many miniaturized sensors and one of the beneficiaries is the siliconcondensermicrophone. Simple analytical expressions, such as those formulated by Škvor/Starr for mechanical-thermal noise calculation, are used to describe the mechanical performance of a microelectromechanical system(MEMS)microphone. However, the location effect of acoustic holes is usually not considered on both frequency response and mechanical-thermal noise. In this paper, the theory of a condensermicrophone is reviewed and a new analytical modeling method for the MEMScondensermicrophones is proposed based on Zuckerwar’s model. With reference to a B&K MEMSmicrophone, the theoretical results obtained by the modeling method are in very good agreements with those experimental ones reported. It is also concluded that there is an optimum location for acoustic holes in the backplate. Finally, a new design for MEMSmicrophone with a polarization voltage of is proposed, which has an open-circuit sensitivity of (or ref. ), a bandwidth of , an -weighted mechanical-thermal noise of , and a signal-to-noise ratio of . This proposed microphone can be easily micromachined by using MEMStechnology such as the deep reactive ion etching and wafer bonding technology.