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To maximize the piezoelectric transducer reception/transmission power we must choose the correct backing/matching layer materials, I'm working on a project to measure a steel tank liquid level (non invasive from the bottom, sensor must be glued) and we have the electronic board finished and the ceramic piezoelectric disk, but we are lacking of knowledge of choosing this material that I mentioned.

The tank that we'll measure is a 3 meters tall, 8mm steel bottom wall.

As far as I read the material selection must take in consideration the acoustic impedance, am I right? Also someone recommend using closed cell foam as backing material and stainless steel as matching layer, but we're not sure about the thickness.

Do anyone have recommendations regarding the correct materials/layer thickness for this application?

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I am assuming that you are using the TDC1000 Analog Front End (AFE). This is because you are using an image snippet from the the image below.

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If so I suggest that you use cyanoacrylate (CYA) glue also known as crazy glue. It is important that the transducer has good mechanical coupling to the stainless steel material. I have tried a material similar to closed cell foam and did not have much success. I believe this is because the foam material attenuates the acoustic signal. You also might want to consider roughen the attachment area with a sandpaper. Below are some images to help you.

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Also consider adding some hot glue around the transducer.

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Completed assembly

Also you might need a High Voltage boost circuit to measure 3 meters of liquid level. Note density might also be a factor.

One other factor to consider in improving piezoelectric transducer reception/transmission power is to create a cavity as shown in the below images

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References

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