Drive control method of electrostatic-type ultrasonic transducer, electrostatic-type ultrasonic transducer, ultrasonic speaker using electrostatic-type ultrasonic transducer, audio signal reproducing method, superdirectional acoustic system, and display

Abstract

A push-pull-type electrostatic-type ultrasonic transducer includes a first electrode having through holes, a second electrode having through holes each of which is paired with the corresponding through hole of the first electrode, and an oscillation film sandwiched between a pair of the first and second electrodes and having a conductive layer to which direct current bias voltage is applied. When a wavelength obtained from a resonance frequency at a mechanical oscillation resonance point of the oscillation film is λ, a thickness t of the respective fixed electrodes is (λ/4)·n or substantially (λ/4)·n (where λ: wavelength of ultrasonic wave, n: positive odd number). AC signals as modulation waves produced by modulating carrier waves in an ultrasonic frequency band by signal waves in an audio frequency band are applied between a pair of the electrodes.