DE2030952C - Ultrasound examination unit - Google Patents

Description

The invention relates to an ultrasonic examination unit in which an electroacoustic unit is in a housing Converter and one on the side of the converter facing away from the object of investigation located reflective surface are arranged. Such an examination unit can be used non-destructively Examination of a workpiece for cracks, defects or other discontinuities as well as for measurement the thickness of a workpiece can be used.

A commonly used method for non-destructive material testing is at Krautkrätner, J. H .: "Material testing with ultrasound", second edition, Berlin-Heidelberg-New York 1966, described. Then ultrasonic pulses are sent into the workpiece to be examined, and that The signal reflected or received on the other side of the workpiece is amplified and displayed on an oscilloscope made visible as a train of impulses. The distribution of the pulse needles on the oscilloscope is proportional to the path that the acoustic signal travels in the workpiece, the location of a crack or any other discontinuity caused by needles occurring at irregular intervals will.

In order to achieve sufficiently large useful signals, the question of coupling the examination unit to the workpiece to be tested is of great importance. The one described in the above cited reference The process works with the so-called immersion technique, in which the coupling is via an intermediate Liquid route takes place. In other processes, a continuous flow of water is used Coupling of the sound waves into the workpiece. Still other systems work with glycerine or the like Coupling agents that are applied to the workpiece surface before the examination. the Has the use of additional coupling agents

ίο always disadvantages. The one after the diving technique or devices operating with a waterway are difficult and inconvenient to use while the Glycerine paste technique requires thorough cleaning after the exam.

5 An ultrasonic microphone is known from US Pat. No. 3,109,111, in which one or two electroacoustic transducers and a reflective surface located on the side of the transducer or transducers facing away from the object to be examined are arranged in a housing. Such a microphone is also suitable for non-destructive testing of materials, for example in accordance with the method known from German patent 746 405. However, if the well-known microphone is used without additional coupling

»5 lungs medium used, d. i.e., located between the microphone and the workpiece to be examined only air, so the signals in particular when working with high-frequency energy, attenuated so that the resolution and evaluation

processing of the received signals becomes difficult.

The invention is based on the object of an air-coupled ultrasonic examination unit the intensity of the ultrasonic vibrations to be transmitted or received

to increase the known devices in the effective area of the ultrasonic transducer and disruptive to weaken reflected ultrasonic vibrations on the surface of the workpiece to be examined or turn it off.

According to the invention, this object is achieved in an examination unit of the type indicated at the beginning Kind in that the reflective surface aufweirt a projecting part of the opposite the electroacoustic transducer is arranged, and that in the housing at a certain distance from the A further reflector is arranged on the side of the transducer facing the object of investigation. In the restricted area 2: wipe the transducer and the protruding surface area is formed

a pressure concentration of the ultrasonic vibrations, whereby the sensitivity of the examination unit is increased; said further reflector serves to weaken unwanted vibrations reflected on the workpiece surface.

If this further reflector is preferably i * i a distance corresponding to a quarter of the wavelength of the ultrasonic vibrations from the former arranged reflective surface of the examination unit, so any stubborn Standing waves between the examination unit and the workpiece surface are suppressed.

The invention thus creates a better separation of the useful signals from interfering signals and a stronger response of the examination unit to the useful signals. This makes the examination unit according to the invention particularly suitable for air coupling.
The invention is characterized by the following detailed

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resonance frequency at 25 kHz. In this embodiment, the reflector 62 is a quarter wavelength λ / 4 from the reflective surface 80. In operation, it is desirable to keep standing waves reflected from the surface of the workpiece 17 as small as possible. Since the signals reflected by the reflector 62 all re-

delete flexions from surface 80 because they are phase shifted by 180 ° due to the Λ / 4 distance, the standing waves are switched off. These canceled signals therefore do not hit the crystal 49, and only those signals are received by this that come directly from the transmitter converter come.

1 sheet of drawings

Claims (5)

Patent claims: 1. Ultrasonic examination unit, in which an electroacoustic one in a housing Converter and one on the side of the converter facing away from the object of investigation located reflective surface are arranged, characterized in that the reflective surface (80) has a protruding partial surface (44) opposite the electroacoustic Converter (49) is arranged, and that in the housing (40) at a certain distance from the side of the transducer facing the object of investigation, another reflector (62) is arranged. 2. Examination unit according to claim 1, characterized in that the protruding Partial area (44) lies between the vibration nodes (76, 78) of the transducer (49). 3. Examination unit according to claim 1 or 2, characterized in that the further Reflector (62) at a distance of a quarter wavelength from one reflective surface (80) is arranged. 4. Examination unit according to one of claims 1 to 3, characterized in that on the reflective surface (80) symmetrically to its center, fastening pins (46, 48, 50, 52) are arranged, on which elastic elements (56) for mounting the transducer (49) are attached are. 5. Examination unit according to claim 4, characterized in that the further reflector (62) is attached to the mounting pins (46, 48j.