Sound Wave Energy loss question

[nst.john]

Hello everyone!

I am currently working on a project where I have a piezoelectric sound transducer connected to a glass tube via an aluminum disc. I got two aluminum discs with one twice the thickness as the other. I wanted to know which aluminum disc would work best, the thin one or the thick one, to transfer sound from the transducer to the tube. The tube will be filled with water as well if that makes any difference. Thank you for your help and hope to hear from somebody soon!

 

[Paul Colby]

It would help to know more about the geometry and desired frequency. Which medium the sound waves are to propagate in the glass or the water? In general the coupling between materials will depend on the change in wavelength between the two materials. If the wavelength in a material is long compared to the dimensions or small? Even with all this I would still have to lookup the reflection coefficient as a function frequency and so forth.

 

[nst.john]

The geometry of the glass is an outside diameter of 100mm, wall thickness of 5mm and a length of 415mm. The desired frequency is 40kHz approximately but we will be working in a range between 20-60kHz. The sound waves are to propagate in the water.

 

[Paul Colby]

Great, a quick Google gives the range of sound speed in aluminum as 3100 to 6400 m/s. I assume that this is dependent on the alloy selected. The sound speed in water is 1484 m/s. As a general rule of thumb is to match as closely as possible the speed of sound in the two medium. I would select an aluminum closer to 3100 m/s. I would also neglect the tube for now. At 40kH the wavelength is 8ish cm. This is much larger than the aluminum thickness. So I would go with the thinner of the two to minimize losses which I'm guessing are small in aluminum.

 

[nst.john]

Thank you very much for all of your help. That answer helps with everything!

 

[nasu]

The 3100 m/s is probably the speed of the transverse waves in aluminum.