Transducer Power Levels

[demedeirosa]

I am new to the acoustics area, and I am trying to determine what I am missing as far as transducer power levels are concerned. I am currently in the process of characterizing how ultrasonic energy propagates through a building. To do so, I wish to develop a high power ultrasonic transmitter which can be variably attenuated.

Manufactures list an SPL rating for their transducers in the spec sheets given at a known distance, usually 30cm. How can a small low power transducer, (Prowave 250ST180) have more SPL output than a 400W tweeter at 25kHz? Is there some parameter that I am not taking into consideration here? I would assume that SPL is directly related to the amplitude of the moving air particles, if a larger tweeter moves more air, isnt there more SPL?

Clearly this EE knows nothing about acoustics!


Prowave 250ST180 Link
Motorola KSN-1142 Link

 

[LiteYear]

Just a WAG: focus? A tweeter is designed to spread sound out so you can hear it equally everywhere. A ultrasonic transducer usually focuses the sound in a narrow beam so it can be directed. SPL will drop significantly if the source energy is spread over a large cone by the time it reaches the measuring distance.

 

[demedeirosa]

That makes sense, therefore there is no missing parameter... Phew

Given that fact, what would be the most reasonable approach to selecting a transducer for use in the application? Again, we want to measure ultrasound inside of a building with the source being outside. We're looking for the minimum power required to get us through X walls of a building. Our current approach is to attenuate the source until we can no longer detect it inside.

 

[IRstuff]

One caveat is whether the 400W is specified at the frequency of interest, or is it the maximum output possible

TTFN
faq731-376

 

[Strong]

I have used airborne ultrasound to detect air leaks in building walls. The sound power was not sufficient to pass through the wall structure, but it could transmit through air leaks and glazing/glass materials. It depends on what is the purpose of your measurements and the type of wall contruction to determine the transmitter sound power and the receiver sensitivity. I use SDT products, but UE Systems is also prominant for leak/integrity testing, if that's your interest. Here is a link for general sensor knowledge:

http://www.massa.com/fundamentals.htm

Walt

 

[demedeirosa]

Thanks for the link, MASSA seems to have a wide variety of ultrasonic products.

Its difficult for me to get into detail about my application,I need to evaluate how much power I will need to allow for detection of ultrasound inside of a building. The building construction will be of various types. Wood, brick, and other materials.

My goal now is to build a very high power, 100+W, transmitter. My assumption is that I can then determine the attenuation of the building as well as a minimum transmitter power required to penetrate the building.

I apologize for the vagueness, unfortunately I cannot divulge much information!

Thanks!

 

[Strong]

You can choose the highest powered transmitter, but that may not be the issue. The ultrasound frequency and the building acoustics will determine what sound gets into building. The sound will enter the path of lowest Transmission Loss. An ultrasound transmitter being very directional can be located close to a building wall and away from air leaks and glazing, if the purpose is to transmit through substantial materials like wood, metal, concrete, brick, and wallboard. I suspect that a lot of test and evaluation will be needed for your project.

Walt

 

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Thanks.