PVDF is one of the best piezoelectric polymers, and has a good acoustic impedance match with water. It is often used in ultrasonic receivers, but it seems like people don't use it for transmitters. Why not?
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Going by this datasheet, I'd say that they don't transmit as well as the other transducer types.
From the datasheet:
Transducers made from it [PVDF] tend to be very wide bandwidth devices, but typically have a lower transmit response than conventional bulk piezoceramic devices.
That said, I saw several research papers about using PVDF transducers (transmit and receive) for medical devices. PVDF transducers are so much cheaper than piezoceramics that there's research into using it in disposable ultrasound heads - toss the plastic in the recycling bin instead of sterlizing it like you'd have to do the more expensive piezoceramic heads.
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\$\begingroup\$ I guess the part that confuses me, is why people seem to treat transmit and receive differently. They should be reciprocal operations, right? \$\endgroup\$ Commented Aug 19, 2022 at 19:28
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\$\begingroup\$ Reciprocal, yes. If they were ideal transducers then it wouldn't matter. You could use the same transducer for both directions. That is often done with typical piezo ceramic transducers. The PVDF transducers seem to be so "not quite ideal" that it often makes more sense to not use them as transmitters. Kind of like LEDs. An LED can also be used to generate current. Theoretically, an LED should be as good a light receiver as it is a light emitter. In reality, an LED makes a poor light receiver. \$\endgroup\$– JRECommented Aug 19, 2022 at 19:34