How does this piezo transducer couple?

I would think the bolt is to mount it and the energy coupled by inertia. There are some more from which I make the assumption.

I agree with your assumption. But if the bolt goes completely through the transducer, it cannot allow piezo (mechanical) movement in the axial direction.

Note:

1. The non-business end is very heavy, steel or such
2. What you see protruding from the cone end (the "business end") is just a short stud. This can be welded or otherwise adhered to whatever you want to drive with this transducer and the transducer screwed onto the stud. I think this stud is not the other end of the bolt head you see at the heavy end.
3. The bolt begins at the back (steel end) and goes... where? This is the conundrum. It can't go all the way through.
4. The heavy end acts as the large mass (I think of it like an anchor) against which the piezo works the other end (the "business end") of the transducer.

But the question remains: where does the allen bolt thread into? ::

The bolt goes all the way through - think of it as a spring - its stiffness compared with that of the piezo disks is quite low - it's much longer than the disk stack and has a much smaller area. Scaling by eye from the photo the bolt cross sectional area is about 25 times less than that of the piezo discs and it's at least 5 x longer. The elastic modulus of stainless 316 is about 190 Gpa and that for PXE5 piezo material about 125, so at a rough guess the bolt is 125 * 125/190 = 82x less stiff in the axial direction than the piezo discs.

So in simple terms the bolt might as well not be there as far as affecting the axial stiffness of the structure.

Michael Kellett

The bolt applies compression force to the piezo elements so that the entire structure will resonate:

(Notice that the mass that bonds to the tank may be cylindrical or conical, depending on the application.)

Mark L. Fergerson

You don't need pre-load (which the bolt supplies) to make the stack resonate. It would resonate at much the same frequency if it was just glued together. If you want to drive the piezo material to get the maximum mechanical output you do need preload because the ceramic material is weak in tension so if you just used glue you wouldn't be able to drive the transducer very hard before the ceramic broke. (and the conducting electrode is also very weak in tension).

Michael Kellett

Think ultrasonic. the vibrational amplitude is so tiny that it traverses through the medium and the surface becomes the emitter.

Those frequencies move through solid mediums pretty well.

Were it in our range, it would need to move air to "be heard". At this frequency, the local medium is what is moving, not air.

One guess is that the bolt might be supposed to go through the surface you want to insonicate and continues into some sort of support post or structure. It's probably not to be torqued down with gusto, only meant to hold the transducer in place.

Alternatively, the device may be mountable using a large soft washer and insonication occurs by using its large mass, as Rheilly wrote. That washer would have to be able to tolerate a lot of stress.

The red stuff around the bolt could be some sort of spacer material that makes sure the bolt won't touch the PZT.

Why not ask the seller about the manufacturer's name?

Various poorly translated web pages say that the bolt is a spring and the metal cone is for impedance matching. It sounds like you shouldn't mess with the bolt.

It looks like you need some high grade epoxy adhesive:

The bolt running through the center appears (repeat: appears) to bolt the ends of this transducer together. Which defeats the goal of a transducer of this type (to vibrate in the axial direction).

How does this transducer couple the brown ceramic disc piezos to the "business end" (upper, in the main photo)?

Someone suggested that the bolt is actually a threaded tube with some kind of driver stud in the center (if you look closely there does appear to be 2 separate pieces that make up what looks like the "bolt").

??

Stick it up your ass, I'm sure it will couple to the inside of you colon!!