Background

The most common type of ultrasonic or acoustic transducer is a pressure wave or longitudinal wave transducer. Pressure or longitudinal waves cause a particle displacement in the same direction as the direction of propagation. A common illustration is the way a compression wave travels through a slinky. A good animation of pressure waves can be seen at the link in this sentence.

Shear waves cause a particle displacement normal to the direction of propagation. A common illustration of a shear wave is the motion in a rope when one end is pinned in place and person whips the other end. Shear waves cause a particle displacement normal to the direction of propagation. A common illustration of a shear wave is the motion in a rope when one end is pinned in place and person whips the other end. Shear waves only exist in media that have significant shear moduli, or friction between neighboring planes of particles. In theory these are solid materials, although shear waves are present in fluids at a much smaller ratio compare to a pressure wave. A good animation of shear waves can be seen at this link.

Measuring and comparing shear and pressure wave signals can give information about a medium i.e. composition, frailties, and inconsistencies. Such methods are used from geological surveys to non-destructive testing.

Capabilities and Contributions

Constantine Technologies has the experience necessary to tackle piezo design for shear and pressure wave transducers in solid media. CTL has developed some clever novel shear wave generating techniques to acoustically separate the persistent pressure wave presence in shear wave transducers (see model below). Additionally, when working with a solid transmission medium, it is important to have a strong foundation in signal processing to distinguish the various acoustic features when both shear and pressure waves are present.
Pressure wave presence in shear wave signal without CTL technology.

Figure 1: Pressure wave presence in shear wave signal without CTL technology.

Pressure wave reduction in shear wave signal with CTL technology.

Figure 2: Pressure wave reduction in shear wave signal with CTL technology.

The above figures show a comparison of the signals received, as recorded and displayed by an oscilloscope, from a transducer without CTL technology and a transducer with CTL technology. When using CTL’s transducer designs it is not uncommon to see a 35dB difference in the targeted shear wave component compared to transient pressure wave component of the acoustic signal.