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- since 1996 -
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Technical Discussions
gazi yuksel
gazi yuksel
04:56 May-09-1998
straight beam probe
: Dear sir,

I am a master student in mechanical eng.My thesis subject is to produce
a straight beam UT probe.

I have produce a few prototypes of 1MHz and 2MHz probes.They will be direct contact probes
I have used tungsten-epoxy mixtures( 50% Tungsten-50% Epoxy in volume), plastic for housing.
But I could not decide on the protecting layer.Then I have tried steel and brass plates ( 2 lambda thick)
but I got very high internal noise(Grass)and I could not eliminate it.I am not sure about the
source of these noise. So could you answer the below questions?
1- Are the source of these noises electrical or mechanical(assembly)?
2- What can I do to eliminate these noises?
3- Should I use screening? If so, how?
4- The electrical impedance is: For 1MHz R=6.1 ohm
X=-49 ohm
For 2MHZ R=76 ohm
X=13 ohm
Do I need to impedance matching for above values to 50 ohm generator?



 
 Reply 
 
gazi yuksel
gazi yuksel
05:01 May-09-1998
straight beam probe
: Dear sir,

I am a master student in mechanical eng.My thesis subject is to produce
a straight beam UT probe.

I have produce a few prototypes of 1MHz and 2MHz probes.They will be direct contact probes
I have used tungsten-epoxy mixtures( 50% Tungsten-50% Epoxy in volume), plastic for housing.
But I could not decide on the protecting layer.Then I have tried steel and brass plates ( 2 lambda thick)
but I got very high internal noise(Grass)and I could not eliminate it.I am not sure about the
source of these noise. So could you answer the below questions?
1- Are the source of these noises electrical or mechanical(assembly)?
2- What can I do to eliminate these noises?
3- Should I use screening? If so, how?
4- The electrical impedance is:
For 1MHz R=6.1 ohm X=-49 ohm
For 2MHZ R=76 ohm X=13 ohm
Do I need to impedance matching for above values to 50 ohm generator?

Thanks


 
 Reply 
 
Linas Svilainis
R & D,
Kaunas University of Technology, Lithuania, Joined Nov 1998, 67

Linas Svilainis

R & D,
Kaunas University of Technology,
Lithuania,
Joined Nov 1998
67
01:31 May-11-1998
Re: straight beam probe

: I am a master student in mechanical eng....
Good to hear some news about ultrasonic activities in
Turkey. Are you employed by ASELSAN?

: I have produce a few prototypes of 1MHz and 2MHz probes.They will be direct contact probes
Could you specify more of your design?
It's just a simple piston or something else?
Is it sransmitting or receiving? Both?

: I have used tungsten-epoxy mixtures( 50% Tungsten-50% Epoxy in volume),
But it's very hard to mix at such proportions!

:plastic for housing.
Nevertherless, you should use shielding inside
to protect your active electrode from noise induction

: But I could not decide on the protecting layer.Then I have tried steel and brass plates ( 2 lambda thick)
We think this will cause high resonant response here.
Once heavily backing is applied, by sacrifying the
efficiency of transducer bandwidth will be improved.
So, the 2 lambda is no longer valid and you might have,
say, 10 lambda...So,you have to be aware of resonance
effects...

: but I got very high internal noise(Grass)and I could not eliminate it.I am not sure about the
: source of these noise.
How much of "grass" have you got?

: So could you answer the below questions?
: 1- Are the source of these noises electrical or mechanical(assembly)?
In case the noise is decreasing with distance, then it
is of mechanicall matter. Is this noise present when you excite
the transducer or when it's just receiving?
If it does not depend on distance/excitation
is fluctuating and it's 1MHz transducer, you're
probably picking up SW station signals.

: 2- What can I do to eliminate these noises?
Check our the noise source, whether it's due to
design or electrical. Check out your PRF.
Try shielding.

: 3- Should I use screening? If so, how?
attach additional copper cylinder around the
backing and electrodes (aware of electrical contact!).

: 4- The electrical impedance is:
: For 1MHz R=6.1 ohm X=-49 ohm
: For 2MHZ R=76 ohm X=13 ohm
: Do I need to impedance matching for above values to 50 ohm generator?
Try to change the connecting cable length.
Does anything has changed? If you have sharp
exciting spike, the reflections traveling inside the
cable can produce such effect. But since your generator
is 50ohm, it should not be expressed so much.

Good luck



 
 Reply 
 

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