Tricking Mother Nature with Matching Layers

Acoustic energy behaves like waves crashing against a sea wall.  Vic Chattigny CEO of Taskill; a 30 year veteran of sensor design used this analogy when explaining matching layer technology in a presentation last year. 

In the mix of interesting and sometimes strange inquiries we get surrounding our piezoelectric film there’s usually a pattern. Design and capability questions that are either identical or overlap in some way from application to application. Impedance matching and frequency range for instance. Piezoelectric film transforms electrical energy into mechanical energy via the inverse piezoelectric effect. Here is one example of how that mechanical energy is managed to match impedance.

PVDF Matching Layer Technology

For this explanation, we’ll focus on the transmit function of the transducer with the goal of transferring energy. If you blindly launch a wave (acoustic energy) at a wall (metal)  90% (or more) of that wave is going to bounce back off that wall. Not an ideal situation if your transmitting acoustic energy at ultra sound frequencies. The goal is to transfer energy. Further, your goal is to be as efficient as possible in that energy transfer.

There’s an Art to Tricking or Matching Mother Nature

The key is to match the impedance of the object is by engineering a series of layers that mimic your target objects impedance. This is the art of the design. Selecting materials that are both complementary and readily available that can be adhered to the PVDF reliably. Kureha is one of the largest producers of PVDF in the world, I can tell you the latter is no gimme. Neither is the arrangement or order of those layers.

Stop Wasting Energy

Piezo Films - The Power of Flexibility
Piezo Films – The Power of Flexibility

What if you transmit sound without these considerations? You might get 10% energy transfer, or less. However, if you properly implement these considerations you can boost that that transfer from 10% up to 60%-70%. But, that requires selecting the right substrates, materials and the arrangement of those materials to maximize transfer.

Piezoelectric PVDF Transducers

As for underwater transducers, how does PVDF perform? Piezoelectric PVDF has always excelled in this application. There’s no lead (RoHS), it’s light weight, non-toxic and its low acoustic impedance very close to water (and tissue). Not to mention, Piezo PVDF can withstand tremendous hydrostatic pressure.

Whether a material like Piezo is successful usually starts with the context of the application. But, how you use it plays an equally important role in whether it’s successful for you.


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