Abstract: An ultrasonic imaging apparatus includes an ultrasonic transducer for outputting an ultrasonic beam and converting the echo of the ultrasonic beam into an echo signal, a transmitter section for supplying a drive signal to the ultrasonic transducer, a receiver section for receiving the echo signal output from the ultrasonic transducer and converting the echo signal into an image signal, and a coaxial cable for coupling the ultrasonic transducer to the transmitter and receiver sections. The ultrasonic transducer is constituted by a two-layer ultrasonic transducer having an impedance smaller than an impedance of the coaxial cable.

Abstract: Disclosed is an ultrasonic probe comprising a piezoelectric element in which a first and second electrodes provided respectively on both surfaces of a piezoelectric material are arranged in such a way that said electrodes have end portions facing each other near the center of, and with the interposition of, the piezoelectric material.

Abstract: A ceramic product is exposed to a light from a tungsten lamp, so that a specified region of the product is heated. In this heating process, acoustic emissions from the ceramic product are detected by an AE sensor which is acoustically coupled to the ceramic product by means of a waveguide passage. A temperature gradient directed from the surface toward the inner part of the ceramic product is formed by heating, and thermal stress is applied to the product so that tensile stress is produced in the inner part of the product. In practical use, a crack constituting the core of fracture is caused to grow by the thermal stress, and an acoustic emission is released. The existence of a defect can be evaluated by detecting the acoustic emission. Also, the location of the defect in the product can be detected by heating part of the product. The equivalent crack dimension a.sub.