President’s Honour Lecture: The flexural ultrasonic transducer – what it is, how it works and where we might use it
Professor S Dixon
Department of Physics and School of Engineering, University of Warwick, UK
The most prolific type of ultrasonic transducer in the world is the flexural ultrasonic transducer – the same type of transducer that is used in ultrasonic parking sensors. These transducers are related to unimorph, flextensional and cymbal type transducers, but have some distinct differences and properties when compared to these other transducers. This talk will describe their basic operation principle and look at how and why they work. They are an interesting transducer, as they are extremely efficient at generating and detecting ultrasound in fluids, and can be completely hermetically sealed and encased in a metal housing such as titanium and can withstand pressures of 300 bar with suitable adaptions. Most common sensors operate at 40 kHz, and leading manufacturers will often claim that these types of transducers are more limited in their range of operation than they actually are with statements such as, “At frequencies above 70 kHz, conventional bending oscillators cannot deliver practical characteristics.” In fact, once one understands how they operate it is straightforward to use them at hundreds of kHz, but for many applications lower frequencies are actually perfectly adequate. These transducers have found applications in air or gas flow measurement and anemometry, in addition to the more standard proximity sensing, but there are also potential applications in NDT for air-coupled and immersion testing. When we first started looking at the world’s most common type of ultrasonic transducer, we were amazed at how little information there was in the scientific literature to explain their operation – for some suitable NDT applications they may be worth serious consideration.
