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Sonotron NDT
Original developer and manufacturer of advanced ultrasonic instruments

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Technical Discussions
Wieslaw Bicz
Wieslaw Bicz
00:18 May-04-1999
Pulser for EMAT´s

We have developer a quite simple (not very expensive) pulser that can drive an EMAT transducer with 2 micro Henry inductance
and produces a short pulse (about 50 ns - see the attached picture)) with a peak current of about 26 Ampere.
It seems to be possible, to make a pulser with similiar technology, that can produce a pulse
with about 60 Amperes.

Does somebody know, if it is possible to make a shorter pulse with larger peak current?
Maybe there is allready somebody, who produces such device?
We are not interested in very large and expesive devices.

Wieslaw Bicz
http://www.optel.com.pl



    
 
 
Dipl.-Ing. Martin Heinz
Dipl.-Ing. Martin Heinz
09:01 May-04-1999
Re: Pulser for EMAT´s
For knowing if it is possible to receive shorter pulses with higher peek current using
this technology, it is necessary to know more about the circuit concept of your pulser.
Principly it is possible to optimize any circuit, especially if the complex impedance of the
transducer is used exactly for setting up the circuit design. Using methods of the system
theory nearly any transducer can be made possible to produce ideal output signals.




    
 
 
Wieslaw Bicz
Wieslaw Bicz
01:45 May-04-1999
Re: Pulser for EMAT´s
: For knowing if it is possible to receive shorter pulses with higher peek current using
: this technology, it is necessary to know more about the circuit concept of your pulser.
: Principly it is possible to optimize any circuit, especially if the complex impedance of the
: transducer is used exactly for setting up the circuit design. Using methods of the system
: theory nearly any transducer can be made possible to produce ideal output signals.

The problem is: if you want to make a very short pulse, you need something (transistor or something else) that can switch you current
quickly enough. It is not important, how you have designed your circuit. If you need very short pulses it is also not possible to use parallel
switched elements.

My problem is: We have not find an element, that can switch larger currents in such short time, but may be somebody has an idea, how to overcome
this problem.

Wieslaw Bicz

http://www.optel.com.pl


    
 
 
William Friedman
R & D,
Lockheed Martin, USA, Joined Nov 1998, 6

William Friedman

R & D,
Lockheed Martin,
USA,
Joined Nov 1998
6
09:57 May-05-1999
Re: Pulser for EMAT´s
: We have developer a quite simple (not very expensive) pulser that can drive an EMAT transducer with 2 micro Henry inductance
: and produces a short pulse (about 50 ns - see the attached picture)) with a peak current of about 26 Ampere.
: It seems to be possible, to make a pulser with similiar technology, that can produce a pulse
: with about 60 Amperes.

: Does somebody know, if it is possible to make a shorter pulse with larger peak current?
: Maybe there is allready somebody, who produces such device?
: We are not interested in very large and expesive devices.

: Wieslaw Bicz
: http://www.optel.com.pl

It looks like you are switching at least 2000 volts to be able to drive 25 amps into such
an inductance. We used to use a stack of avalanche transistors to switch in nanosecond
time scales to drive the deflection plates in optical streak cameras.
The trick was to find transistors that could stand off several 100 volts
and then use them in series. The problem is that the avalanche characteristic is not
controlled in manufacturing and you have to find what is the current transistor
type that meets this need. Often it is an inexpensive transistor, not one sold for
this purpose and you will have to find what is available.

William Friedman




    
 
 
Wieslaw Bicz
Wieslaw Bicz
05:08 May-05-1999
Re: Pulser for EMAT´s
: : We have developer a quite simple (not very expensive) pulser that can drive an EMAT transducer with 2 micro Henry inductance
: : and produces a short pulse (about 50 ns - see the attached picture)) with a peak current of about 26 Ampere.
: : It seems to be possible, to make a pulser with similiar technology, that can produce a pulse
: : with about 60 Amperes.

: : Does somebody know, if it is possible to make a shorter pulse with larger peak current?
: : Maybe there is allready somebody, who produces such device?
: : We are not interested in very large and expesive devices.

: : Wieslaw Bicz
: : http://www.optel.com.pl

: It looks like you are switching at least 2000 volts to be able to drive 25 amps into such
: an inductance. We used to use a stack of avalanche transistors to switch in nanosecond
: time scales to drive the deflection plates in optical streak cameras.
: The trick was to find transistors that could stand off several 100 volts
: and then use them in series. The problem is that the avalanche characteristic is not
: controlled in manufacturing and you have to find what is the current transistor
: type that meets this need. Often it is an inexpensive transistor, not one sold for
: this purpose and you will have to find what is available.

: William Friedman
:

It seems, that we have find a better solution - we are using a very simple circuit with only one
transistor and abot 500V voltage.

But may be, there is even better solution.

Wieslaw Bicz


    
 
 

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