Number 252 (Story #4), December 18, 1995 by Phillip F. Schewe and Ben Stein MICROMACHINED ULTRASONIC TRANSDUCERS have been built which can emit and receive airborne ultrasound at frequencies above 10 MHz, much higher than current ultrasonic transducers which operate at about 50 KHz. Igal Ladabaum of Stanford University (igal@macro.stanford.edu) presented a paper on the new transducers at last month's Acoustical Society of America meeting in St. Louis. Although bats use airborne ultrasound with great success, humans have found it difficult to work with because it attenuates (weakens) rapidly. In order for the new transducers to resonate at high ultrasonic frequencies, they must be much smaller than today's piezo-electric ceramic and electrostatic transducers which operate only at low ultrasonic frequencies. The high-frequency transducers are made up of hundreds of tiny drumheads, each about as wide as a human hair (25 microns) and 100 times thinner than a piece of paper. They vibrate when hit with ultrasound and produce a measurable electrical signal. Conversely, an electrical impulse applied to the drumheads causes them to vibrate, producing ultrasound. Applications for the new transducers include flow sensing, sensitive imaging to evaluate pipelines and structures without destroying them, and more accurate position sensing for robotics. The mass-produced transducers can also be applied to existing fluid ultrasound technologies, such as medical imaging, to provide less expensive equipment.