the position of the ultrasonic emitter 5 can be adjusted with respect to the receiving transducers 7 and 9 and a spring 4 thus the overall arrangement is somewhat similar to that of a c clamp it will be noted that the mode of contact between the ultrasonic emitter 5 and the receiving transducers 7 and 9 and the object to be tested is not limited to direct contact with the embodiments disclosed the same effect can be achieved as the prior art arrangements wherein oil or water have been used and or the arrangements wherein rubber tires have been utilized fig8 shows a sensor assembly 105 according to a fifth embodiment of the present invention this embodiment is essentially identical to the first and third ones with the major exception that the display 17 is mounted directly on the housing unit 203 this arrangement has the advantage that the operator of the sensing device can see the display 17 indicating the internal condition of the object to be tested in real time without having to take his or her eyes from the object under test thus it is easy to visually pinpoint the spot on the surface the object to be tested beneath which a defect is present a further advantage of this arrangement is that the display can indicate to the user exactly when and where on the object the proper contact between the sensor assembly and object to be tested becomes inadequate to provide an accurate indication of the internal state of the object to be tested in other words when the output of the receiving transducers 7 and 9 fall beneath a predetermined value in.