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Technical Discussions
kostas papas
kostas papas
03:43 Dec-17-2004
alternative generation of ultrasound waves

The use of piezoelectric transducers is well spread for the generation and receive of ultrasound waves. The use of microphones is also an existing technique for receiving acoustic and ultrasonic waves.
However what about microphone-speaker technology to generate and transmit ultrasound waves through solid material?
Is mechanical coupling (efficiency coef) a problem when generating waves by means of speakers?
This is an academic question that was brought about after using piezoelectric transducers.



    
 
 Reply 
 
Godfrey Hands
Consultant,
PRI Nadcap, United Kingdom, Joined Nov 1998, 298

Godfrey Hands

Consultant,
PRI Nadcap,
United Kingdom,
Joined Nov 1998
298
09:42 Dec-20-2004
Re: alternative generation of ultrasound waves
----------- Start Original Message -----------
: The use of piezoelectric transducers is well spread for the generation and receive of ultrasound waves. The use of microphones is also an existing technique for receiving acoustic and ultrasonic waves.
: However what about microphone-speaker technology to generate and transmit ultrasound waves through solid material?
: Is mechanical coupling (efficiency coef) a problem when generating waves by means of speakers?
: This is an academic question that was brought about after using piezoelectric transducers.
------------ End Original Message ------------

Microphones tend to be limited in frequency to tens of KHz (up to about 40). This will efectively limit the frequency of ultrasound that you can generate and receive, which in turn will limit the detectability of smaller defects (conventionally it is accepted that 0.25 wavelength down to 0.1 wavelength is the detection limit).
There is an "Air Scan" system that operates with lower frequency ultrasound. This (I believe) has piezo transducers, but operates at a significantly reduced frequency (in the KHz region). There is also the acoustic mis-matching problem to overcome between Air and most solids that are being interrogated.

Other alternative generation methods for ultrasound (at "Normal" or elevated frequencies, i.e. 1 MHz to 20 MHz) are EMAT or Laser Generation.

Hope this helps your studies.

Godfrey Hands


    
 
 Reply 
 
Wolfgang Bisle
Wolfgang Bisle
04:12 Dec-20-2004
Re: alternative generation of ultrasound waves
Some remarks:
Airscan (is a trademark not a method) you mean airborne UT or NCU (nonContactUT) or aircoupled UT:
It is not limited to frquencies in the KHz range. recent systems can go up to 10MHz (Ultran) but realistic around 2..5MHz.
Usually they are Piezo.based with special matching layers, but electrostatic devices are also known, which sometimes work more broadband but they lack a mechanical sturdiness...

Besides the EMAT's which are good for metallics, also Magnetostrictive Probes are used in case of ferrous metalls. (another method)

Finally sparc sound guns are used as a sound transmitter in systems, which operate noncantact using vibrometers for detection (Honeywell, SAM/RAID system)...

so looking a little around one finds a lot more ways to introduce and receive sound then just Piezos


    
 
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kostas papas
kostas papas
06:33 Dec-21-2004
Re: alternative generation of ultrasound waves
Thank you very much for the usefull information you provided.

I was wondering whether the standard technology used for speakers (where a magnet is vibrated by means of a magnetic field generated by a coil) can be used for the generation of ultrasound waves.

I am mostly interested in contact applications (where the sourse is in contact with the solid under interrogation) and not for airborne applications. Such an apllication would be challenging since there would be no need for a wired stimulation of the wave source, since one has only to drive the coil and not the magnet. Can such a speaker work for high frequencies?

Again, thank you very much for your feedback.


    
 
 Reply 
 
Joel Vargas
Joel Vargas
02:38 Aug-18-2005
Re: alternative generation of ultrasound waves
Dear Srs.
Let me first introduce. I am Joel Vargas and I am working with LRUT for pipelines inspection and as you know it works with piezoelectric efect. So the point is if some body knows the diference betwen LRUT and Magnetostrictive wave generations methods..

the second is that in LRUT I can use torsional mode and longitudinal mode. It is possible with Magnetostrictive method?

By other hand EMAT transducer are the same of Magnetostrictive transducers or it is a diferent method of wave Generation?

I hope some one of you can help me.

PS:Sorry for my enghish.

--- Start Original Message -----------
: The use of piezoelectric transducers is well spread for the generation and receive of ultrasound waves. The use of microphones is also an existing technique for receiving acoustic and ultrasonic waves.
: However what about microphone-speaker technology to generate and transmit ultrasound waves through solid material?
: Is mechanical coupling (efficiency coef) a problem when generating waves by means of speakers?
: This is an academic question that was brought about after using piezoelectric transducers.
------------ End Original Message ------------




    
 
 Reply 
 
Godfrey Hands
Consultant,
PRI Nadcap, United Kingdom, Joined Nov 1998, 298

Godfrey Hands

Consultant,
PRI Nadcap,
United Kingdom,
Joined Nov 1998
298
00:26 Aug-20-2005
Re: alternative generation of ultrasound waves
Dear Joel,
It is possible to produce and detect LRUT with magnetostrictive methods. The normal wave produced with the SwRI Guided Wave Ultrasonic system (from San Antonio, Texas) produces Torsional mode in Pipe and SH0 (Shear Horizontal) in plate.
Both of these waves are similar in propagation, and the velocities are constant for all frequencies unlike most of the other modes at lower frequencies. Also it will be almost entirely this mode of wave which is produced, so very little interference from other modes.

EMAT is somewhat different in mode of generation. With magnetostricive, you generate the particle movement on a strip of magnetostrictive material bonded to the metal, and with EMAT, you generate the wave on the surface of the material. This means you can generate EMAT under a thick coating, but not Magnetostrictive, unless you affix the magnetostrictive material under the coating (or rely on the natural magnetostrictive effect of the pipe).

Hope this helps.

Godfrey Hands
----------- Start Original Message -----------
: Dear Srs.
: Let me first introduce. I am Joel Vargas and I am working with LRUT for pipelines inspection and as you know it works with piezoelectric efect. So the point is if some body knows the diference betwen LRUT and Magnetostrictive wave generations methods..
: the second is that in LRUT I can use torsional mode and longitudinal mode. It is possible with Magnetostrictive method?
: By other hand EMAT transducer are the same of Magnetostrictive transducers or it is a diferent method of wave Generation?
: I hope some one of you can help me.
: PS:Sorry for my enghish.
: --- Start Original Message -----------
: : The use of piezoelectric transducers is well spread for the generation and receive of ultrasound waves. The use of microphones is also an existing technique for receiving acoustic and ultrasonic waves.
: : However what about microphone-speaker technology to generate and transmit ultrasound waves through solid material?
: : Is mechanical coupling (efficiency coef) a problem when generating waves by means of speakers?
: : This is an academic question that was brought about after using piezoelectric transducers.
------------ End Original Message ------------




    
 
 Reply 
 

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