5. What is Ultrasound? Ultrasound is a mechanical, longitudinal wave with a frequency exceeding the upper limit of human hearing, which is 20,000 Hz or 20 kHz.
6. ULTRASOUND – How is it produced? Produced by passing an electrical current through a piezoelectrical crystal
23. Operating Principles of CMUTs When a DC voltage is applied between the metallized membrane and the substrate of a CMUT, the membrane is attracted toward the bulk by the electrostatic force, and induced stress within the membrane balances the attraction. Driving the membrane with an AC voltage superposed on the bias generates ultrasound. If the biased membrane is subjected to ultrasound, a current is produced due to the capacitance change under constant bias voltage. The amplitude of the current is a function of frequency, bias voltage, and device capacitance. The efficiency of CMUTs is determined by the electromechanical transformer ratio, which can be expressed as the product of the device capacitance and the electric field strength across the gap. Planar fabrication enables building a thin membrane above a sub-micron sealed cavity, which is crucial to obtain high electric fields for improved transducer performance. Operating Principles of CMUTs
24. When a DC voltage is applied between the metallized membrane and the substrate of a CMUT, the membrane is attracted toward the bulk by the electrostatic force, and induced stress within the membrane balances the attraction. Driving the membrane with an AC voltage superposed on the bias generates ultrasound. If the biased membrane is subjected to ultrasound, a current is produced due to the capacitance change under constant bias voltage.
