Patent ID: 7602672

Claim:
A quasi-self focusing ultrasonic transducer including a backing; and a plurality of piezo-electric crystal sheets, wherein: the backing has a double layer structure and there is an air cavity between the layers, at least four piezo-electric crystal sheets of the plurality of piezo-electric crystal sheets are adhered on an inside focusing face of the backing, a protective layer covers a surface of the sheets; said backing is made of a material with low loss and high acoustic resistance; the inside focusing face of the backing is a concave spherical zone surface; a thickness of an inner layer of the backing is an integral multiple ±35% of ½ of a wavelength of a sound wave in the backing material under a working frequency emitted by the piezo-electric crystal sheets; and the plurality of piezo-electric crystal sheets comprise between 4 and 24 piezo-electric crystal sheets of similar electroacoustical characteristics, with a radius of curvature at all points substantially identical to that of corresponding points of the inside focusing face of the backing, the between 4 and 24 piezo-electric crystal sheets being adhered on the inside focusing face of the backing.