An electric ultrasonic transducer is developed by using a silicon IC process. Design considerations are first presented to obtain high sensitivity and the desired frequency responses in air. The measured transmitter sensitivity is 19.1 dB (0 dB=1 mubar/V) at a point 50 cm away from the devices, when the devices are operated at 150 kHz. The receiving sensitivity is 0.47 mV/Pa in the 10-130-kHz range, with bias voltages as low as 30 V. An electronic sector scanning operation is also achieved by time-sequentially driving seven elements arranged in a linear array on the same chip. The results should be helpful in the design of phased-array transducers integrated with electronic scanning circuits.

We have developed a new MEMS (microelectromechanical system) resonator with a digitally tunable resonant-frequency function. A 20-µm-thick silicon main beam, 10 × 760 µm, has multiple sets of 20-µm-thick short beams, 10 × 100 µm, along the longitudinal direction. The bending of the short beams exerts a moment on the main beam. The frequency of the maximum amplitude in the main beam has been measured to vary at 85.5, 223, and 400 kHz by selecting three sets of exciting electrodes. The resonator has been measured to have Q-factor of higher than 10 000 under vacuum. The frequency can be easily increased up to several tens of megahertz by reducing the device size. Therefore, this new resonator should be useful for wide multiband frequency applications. 

Resonators based on microelectromechanical systems (MEMS) have received considerable attention for their applications for wireless equipment. The requirements for this application include small size, high frequency, wide bandwidth and high portability. However, few MEMS resonators with wide-frequency tuning have been reported. A fishbone-shaped resonator has a resonant frequency with a maximum response that can be changed according to the location and number of several exciting electrodes. Therefore, it can be expected to provide wide-frequency tuning. The resonator has three types of electrostatic forces that can be generated to deform a main beam. We evaluate the vibrational modes caused by each exciting electrodes by comparing simulated results with measured ones. We then successfully demonstrate the frequency tuning of the first to fifth resonant modes by using the algorithm we propose here. The resulting frequency tuning covers 178 to 1746 kHz. In addition, we investigate the suppression of the anchor loss to enhance the Q-factor. An experiment shows that tapered-shaped anchors provide a higher Q-factor than rectangular-shaped anchors. The Q-factor of the resonators supported by suspension beams is also discussed. Because the suspension beams cause complicated vibrational modes for higher frequencies, the enhancement of the Q-factor for high vibrational modes cannot be obtained here. At present, the tapered-anchor resonators are thought to be most suitable for frequency tuning applications.

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