Transducers Characteristics Explained

Elcometer NDT offer a state-of-the-art range of Ultrasonic Gauge transducers.

When selecting a transducer it is important to choose one which will meet the specific application's needs. The type of material to be tested, the measurement range, the shape of the substrate (curved or flat) and the size of the material should be considered when selecting the appropriate transducer.

Selecting the right ultrasonic transducer

Selecting the right ultrasonic transducer for your application is essential to maximise performance.

Choosing the right frequency/diameter combination for the measurement application

Different materials have different acoustic properties. In some a sound wave can travel easily, in others it's absorbed which can make achieving an accurate measurement difficult.

Different frequencies of sound allow measurement of different materials, so when selecting a transducer the material type and therefore the frequency are the first consideration.

Low frequency ultrasonic transducers have the highest power and can penetrate deeply into a material in the same way that the bass notes of music from a car stereo can penetrate the body of a car and be heard outside. Low frequency ultrasonic transducers are best materials that absorb sound like plastics or composites. A low frequency transducer increases the chance of getting a strong return echo and a good quality measurement on these materials.

High frequency ultrasonic transducers are ideal for precision measurement because the pulse they emit is highly focused, reducing the risk of return echos outside of the measurement area. The high frequency and shorter wavelength also lends itself well to measuring thin materials. A third advantage is that high frequency ultrasonic transducers reduce troublesome “surface noise” that can be present on some metals such as aluminium or titanium and can cause measurement error.

Larger diameter probes feature larger crystals which transmit and receive the sound wave. A large crystal transmitter will produce a more powerful sound wave and a larger receiving crystal will be more sensitive. As a result, larger ultrasonic transducers tend to have better penetration characteristics than the smaller types. If this extended range is not required, the smaller ultrasonic transducers can be placed more precisely and in hard to reach areas such as narrow grooves in a material. Smaller diameter transducers also couple more easily to curved surfaces so have applications in corrosion testing pipes and cylinders.