Broadband transmission of ultrasound in water using capacitive, micromachined transducers is reported. Transmission experiments using the same pair of devices at 4, 6, and 8 MHz with a signalhyphen;tohyphen;noise ratio greater than 48 dB are presented. Transmission is observed from 1 to 20 MHz. Better receiving electronics are necessary to demonstrate operation beyond this range. Furthermore, the same pair of transducers is operated at resonance to demonstrate ultrasound transmission in air at 6 MHz. The versatile transducers are made using silicon surface micromachining techniques. Computer simulations confirm the experimental results and are used to show that this technology promises to yield immersion transducers that are competitive with piezoelectric devices in terms of performance, enabling systems with 130 dB dynamic range. The advantage of the micromachined transducers is that they can be operated in highhyphen;temperature environments and that arrays can be fabricated at lower cost. copy;1996 American Institute of Physics.
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