Hi,

Anyone knows where to get a ultrasonic transmitter with 40kHz center frequency and bandwidth of 20kHz?

 

hi,
The 40KHz is OK, but a 20KHz bandwidth.?? what are you trying to do.

Sounders - Ultra Sonic Trasducers

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For that kind of bandwidth, you are going to need an electrostatic transducer instead of a piezo. Here's a popular one -
SensComp Inst Grade Transducer

 

I am using ultrasonic transmitters for audio transmission in air. I'm aware that PVDF transducers are best but I'm unable to source for one.

 

Hi Duffy, thanks for the recommendation but it's still 10kHz short.

 

Here is the only other electrostatic transducer, other than Senscomp, that I was able to find that was even remotely avallable to regular people like us:

Avisoft-UltraSoundGate CM16/CMPA

If you beg them they will sell you just the transducer...if I remember right the cost was $700 for a single piece.

Well there was one other. GHz bandwidth, bUt $2500 expensive with non-disclosure agreements.

Seems that Senscomp is the only electrostatic transducer for hobbiests

 

Taken from the said link:
"High quality Ultrasonic Receiver (RX). Designed for receiving continuous or modulated waves in the 40kHz region through air. Used in measuring and burglar alarm applications."

why they produce those sensors for modulated waves?
what is the usage?

 

Two reasons -

1. Different materials absorb and reflect different frequencies of ultrasonics. Working with more than one frequency increases your chance of detecting things.

2. Soliton waves (a chirp) are modulated from low to high and back down again. These give you better resolution over a simple pulse train.

 

Thanks for the reply,

They can simply change the freq over the time!? I don't know how does modulating is able to case CHANGEs the output freq? a modulated freq has a carrier plus and minus the sidebands. maybe they intend to use either constant sidebands too?

What kind of modulation they use?

 

There's no "carrier", this isn't RF. You just modulate the frequency you apply to the transducer. Google "ultrasonic chirp".

 

THat IS modulating.

No, you are associating other RF-specific terms with modulatign. Modulate simply means " to change" and does not imply carriers or anything more complex like that. It's just in RF they tend to use modulation along with carriers and sidebands, etc.

See definition:
modulated - definition of modulated by the Free Online Dictionary, Thesaurus and Encyclopedia.

 

What I mean is that the audio signal, being pre-modulated to ultrasound frequency is then transmitted through the ultrasonic transmitter and due to nonlinear air properties, the demodulated audio signal is obtained.

 

You are talking about a system that was developed for muzeums and conference halls where the very high power custom-made ultrasonic transducers blasted a powerful narrow ultrasonic beam that is specially modulated at an object and the interference waves produced demodulated sounds that come "from" the object.
It was also used to beam a foreign language modulated ultrasonic beam at a group of people and different language at the group beside them.

The ultrasonic transducers are very powerful and are made for the company. You can't buy one without buying the entire expensive system.
They spent a fortune developing and marketing the system. I don't know if it is perfected yet.

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Ok.... I guess I will make do with whatever I can find. Thanks audioguru.