Paul T. Williams

Transducers for transmitting and/or receiving ultrasonic energy

Improved ultrasonic energy transducers each include a material contacting member secured to a piezoelectric element at an interface region between oppositely operated first and second regions of the piezoelectric element. The material contacting member intensifies and amplifies movement of the interface region as the first and second regions of the piezoelectric element operate in a push-pull mode relative to the interface region. The first and second regions of the piezoelectric element can be electrically driven to move the material contacting member for transmission of ultrasonic energy or mechanically driven by the material contacting member for receipt of ultrasonic energy. A variety of piezoelectric elements can be used in the improved transducers including, for example, generally rectangular bars and discs segmented into two or more portions. A variety of material contacting members can also be used including, for example, a cylindrical stud and a more narrow dowel.

Hybrid silencer transmission loss above a duct’s plane wave region

For large ducts, the removal of low frequency and tonal noise is normally achieved through the use of inefficient dissipative silencers; however, a combination of dissipative and reactive solutions could be more effective. But reactive noise control solutions are rarely applied to large diameter duct systems since it is commonly assumed that the low cut-on frequency of higher order modes severely restricts their efficiency. However, it is possible for a reactive silencer to remain operational outside of the plane wave region, provided the reactive elements are distributed across the cross-section of the duct. Of course, at higher frequencies, the sound field within a duct will have nonplane wave modal content, and the transmission loss is expected to differ compared to the plane wave condition. This effect is investigated here using numerical (FEM) predictions for hybrid dissipative-reactive parallel baffle silencers and the performance of the reactive elements is explored under different excitations. The...

The influence of higher order incident modes on the performance of a hybrid reactive-dissipative splitter silencer

A hybrid reactive-dissipative splitter silencer offers the potential to attenuate turbomachinery noise over a wide frequency range, including the problematic low to medium frequencies. This article uses a theoretical model to investigate the performance of a hybrid parallel baffle silencer for different complex incident sound fields. This includes an incident sound field with equal modal energy density, as well as the excitation of individual higher order modes. It is shown that provided horizontal and vertical partitions are used in the reactive element, the sound attenuation performance of the reactive chamber under complex incident sound fields is equivalent to that obtained using plane wave excitation over the frequency range of interest. Furthermore, it is demonstrated that the reactive elements work at frequencies above the first cut-on mode in the inlet duct, and so they are capable of extending sound attenuation into the low to medium frequency range. This delivers an efficient hybrid silencer des...