ULTRASONIC PROBE CONSTRUCTION: Compression Probes, Single crystal, Twin crystal, Cross-talk, Ultrasonic thickness measurement

ULTRASONIC PROBE CONSTRUCTION

 Compression Probes

The simplest form of compression wave probe is the single crystal probe; this can act as the transmitter of ultrasonic waves and also as the receiver.

 

When using a single crystal probe and the pulse echo system, the probe acts as both the transmitter and receiver by ‘listening’ for the echo during the non-productive delay between emitting each pulse.

 

The twin crystal probe is basically the same as the single crystal probe but uses one as transducer for continually transmitting ultrasonic waves and one receiving.


To prevent ‘cross-talk’ between the two crystals a cork insulator is used to separate the probe into two, and the
thickness of the perspex shoe is increased- This has important side effects, which will be discussed
later.

In ultrasonic thickness measurement compression probes are generally used. These will introduce ultrasound into the material at right angles to the surface of the material. No refraction takes place at the first surface and only compression waves enter
the material. Thus longitudinal or compression waves
are used when normal (C) compression probes are used for ultrasonic thickness measurement.

All crystals in probes emit compression waves. However, a probe can be designed to operate in the sheer mode by having a wedged
shaped frontal member so that the probe directs compression waves at an angle to the surface of the test part. The angle of incidence is such that only shear waves enter the material. In general, the angle indicated on the probe refers to the angle from the vertical (normal) in steel.

 

 

 

ULTRASONIC PROBE CONSTRUCTION  Compression Probes The simplest form of compression wave probe is the single crystal probe; this can act as the transmitter of ultrasonic waves and also as the receiver, (Figure 10). When using a single crystal probe and the pulse echo system, the probe acts as both the transmitter and receiver by 'listening' for the echo during the non-productive delay between emitting each pulse. The twin crystal probe is basically the same as the single crystal probe but uses one as transducer for continually transmitting ultrasonic waves and one receiving (Figure 11). To prevent 'cross-talk' between the two crystals a cork insulator is used to separate the probe into two, and the thickness of the perspex shoe is increased- This has important side effects, which will be discussed later. In ultrasonic thickness measurement compression probes are generally used. These will introduce ultrasound into the material at right angles to the surface of the material. No refraction takes place at the first surface and only compression waves enter the material. Thus longitudinal or compression waves are used when normal (C) compression probes are used for ultrasonic thickness measurement.      All crystals in probes emit compression waves. However, a probe can be designed to operate in the sheer mode by having a wedged shaped frontal member so that the probe directs compression waves at an angle to the surface of the test part. The angle of incidence is such that only shear waves enter the material. In general, the angle indicated on the probe refers to the angle from the vertical (normal) in steel.
 ULTRASONIC PROBE CONSTRUCTION

Leave a Comment