The invention relates to an air-coupled capacitive micromachining ultrasonic
transducer, a preparation method and application. A
transducer array comprises 16 array elements; each
array element is formed by multiple sensing units; each sensing unit is structurally formed by an upper
electrode 1, a vibrating diaphragm 2, a cavity 3 and a base 5 sequentially from top to bottom; and each base is usedas a lower
electrode. The working frequency of the designed
transducer is 100kHz to 2MHz. The transducer array is manufactured based on an SOI
bonding process; each vibrating diaphragm is made of
monocrystalline silicon; each upper
electrode is gold or aluminum; an insulating layer 4 is
silicon dioxide or
silicon nitride; and the array elements of the transducer are divided through
etching the low-resistance-
silicon bases to form grooves, so that the array with the multiple array elements is formed. According to the air-coupled ultrasonic transducer, an ultrasonic wave in a
metal plate or a
composite plate is excited through an air
coupling manner and is used for nondestructively detecting internal defects of the plate. The transducer is matched with a
phased array system, and pulse drivesignals of the array elements are
delay-controlled, so that the phase-controlled deflection and the focusing of an acoustic beam are adjusted, and the freedom degree of detecting is increased.