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Levi P.
R & D,
Dacon Inspection Technologies, Thailand, Joined Jan 2017, 60

Levi P.

R & D,
Dacon Inspection Technologies,
Thailand,
Joined Jan 2017
60
20:35 Feb-11-2018
Ultrasonic phase change

All,
I'm searching for information relating to ultrasonic phase change. Having searched through "Ultrasonic Testing" volume 7 from ASNT & "Ultrasonic Time of Flight Diffraction" 1st Edition from Eclipse Scientific (Ed Ginzel) and searching the web, I have been unable to find the electro or mechanical mechanism that causes phase change, and am having a time trying to relate it to a physical phenomenon. I have read that phase change is related to a reflection from a negative impedance interface but am searching for a concrete answer that I can fully grasp. If anyone has information please share.
-Levi

 
 Reply 
 
Wieslaw Bicz
Engineering,
PBP Optel sp. z o.o., Poland, Joined Feb 2009, 276

Wieslaw Bicz

Engineering,
PBP Optel sp. z o.o.,
Poland,
Joined Feb 2009
276
21:15 Feb-11-2018
Re: Ultrasonic phase change
In Reply to Levi P. at 20:35 Feb-11-2018 (Opening).

The best explanation is to find in school books about elementary physics phenomena. See please for example here: http://www.schoolphysics.co.uk/age16-19/Wave%20properties/Wave%20properties/text/Phase_change/index.html

This is basic knowledge, learned in high school.

 
 Reply 
 
Ed Ginzel
R & D, -
Materials Research Institute, Canada, Joined Nov 1998, 1300

Ed Ginzel

R & D, -
Materials Research Institute,
Canada,
Joined Nov 1998
1300
21:17 Feb-11-2018
Re: Ultrasonic phase change
In Reply to Levi P. at 20:35 Feb-11-2018 (Opening).

Levi, if it is a mathematical explanation you require there is a good source that relates to diffraction in general. I direct you to "Engineering Applications of Ultrasonic Time of Flight Diffraction" Second edition by Charlesworth and Temple, Research Studies Press, 2001. There in Section 2.3.2.7 they indicate how the phase of a signal from the bottom of crack should lag the lateral wave by Pi/4. Technical references to work by authors such as Scruby, Ogilvy & Temple, Coffey & Chapman are provided, but there is also an extensive section in Section A4 of that text wherein the equations are described.

 
 Reply 
 
Levi P
R & D,
Dacon Inspection Technologies, Thailand, Joined Jan 2017, 60

Levi P

R & D,
Dacon Inspection Technologies,
Thailand,
Joined Jan 2017
60
22:48 Feb-11-2018
Re: Ultrasonic phase change
In Reply to Wieslaw Bicz at 21:15 Feb-11-2018 .

All,
Thanks for the information, I'll check out "Engineering Applications of Ultrasonic Time of Flight Diffraction".

As a follow up, what is the mechanical process where by an ultrasonic receiver determines phase?


Wieslaw has provided a simple diagram that describes the physical phenomenon of phase change, (Thanks, as I was unable to attend high school) but the diagram is unable to explain how the same physical flaw can produce two separate waves with opposite phase.

 
 Reply 
 
Anmol Birring
Consultant,
Birring NDE Center, Inc., USA, Joined Aug 2011, 805

Anmol Birring

Consultant,
Birring NDE Center, Inc.,
USA,
Joined Aug 2011
805
01:08 Feb-12-2018
Re: Ultrasonic phase change
In Reply to Levi P. at 20:35 Feb-11-2018 (Opening).

Here is it in simple words
Sound is a pressure wave and at the reflection boundary, the net pressure has to be zero. This is also called the "boundary condition". So in order to balance the the positive pressure component of the incident wave the reflected wave pressure component has to be equal and opposite which means - negative. And vice versa.

 
 Reply 
 
Levi P
R & D,
Dacon Inspection Technologies, Thailand, Joined Jan 2017, 60

Levi P

R & D,
Dacon Inspection Technologies,
Thailand,
Joined Jan 2017
60
01:38 Feb-12-2018
Re: Ultrasonic phase change
In Reply to Anmol Birring at 01:08 Feb-12-2018 .

Thanks Anmol!

All,
I don't think I'm doing a good job of asking questions that are taking me down the right path. Please allow me to start again.

When an X cut piezoelectric element is excited by a pressure wave:

The element distorts in direction "positive Y" lets say, while returning to its natural resting position, it crosses zero and enters into a "negative Y" position and so forth until all energy has been exhausted.

Question:

1) Do both positive and negative distortions of the element create voltage spikes sent to the receiver?

2) If they do, can these be differentiated in a meaningful way?

3) If they are differentiated, what is the means used to accomplish this?

4) Is there any physical difference in the upper and lower diffracted pressure waves from a volumetric flaw (assuming same wave type)

Thank you for any help
-Levi

 
 Reply 
 
John Norman
Consultant, owner of business
NTS Ultrasonics Pty Ltd, Australia, Joined Oct 2012, 117

John Norman

Consultant, owner of business
NTS Ultrasonics Pty Ltd,
Australia,
Joined Oct 2012
117
02:12 Feb-12-2018
Re: Ultrasonic phase change
In Reply to Levi P at 22:48 Feb-11-2018 .

Hi Levi.
My main goto book for questions on ultrasonics is "Ultrasonic Testing of Materials" by Krautkramer. I have the second edition, but there are several newer editions available. In my edition there is a good explanation of the derivation of the reflection coefficient, and its dependence on impedance. There is also a good explanation of the working of piezoelectric transducers and how they can detect phase.

For detection of phase, a piezoelectric transducer responds to changes in thickness of the piezoelectric plate. The thickness changes in response to changes in pressure of the ultrasonic pulse or wave. This is the mechanical process.

Pressure can be positive or negative, so the output of the transducer can be positive or negative. If negative follows positive the phase might be 0 degrees, but if positive follows negative, the phase might be 180 degrees.
John N

 
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Levi P.
R & D,
Dacon Inspection Technologies, Thailand, Joined Jan 2017, 60

Levi P.

R & D,
Dacon Inspection Technologies,
Thailand,
Joined Jan 2017
60
04:49 Feb-12-2018
Re: Ultrasonic phase change
In Reply to John Norman at 02:12 Feb-12-2018 .

All,
Thank you for the information, I now have two promising avenues to research the subject, "Engineering Applications of Ultrasonic Time of Flight Diffraction" & "Ultrasonic Testing of Materials".
-Levi

 
 Reply 
 
John Norman
Consultant, owner of business
NTS Ultrasonics Pty Ltd, Australia, Joined Oct 2012, 117

John Norman

Consultant, owner of business
NTS Ultrasonics Pty Ltd,
Australia,
Joined Oct 2012
117
08:36 Feb-12-2018
Re: Ultrasonic phase change
In Reply to Levi P at 01:38 Feb-12-2018 .

Hi again Levi.
Things suddenly got more complicated. The following answers are my understanding, but I may be wrong, so don't rely too much on my answers.

1. Both positive and negative pressures (or excursions) create an output from the piezoelectric element of the transducer. With NDT type ultrasonic pulses, the positive and negative responses should be more or less equal, i.e. linear. In some materials, particularly when stresses are applied, and when ultrasonic pulse amplitudes are very high, the positive and negative responses may not be equal, and the situation is "non-linear".

2. The positive and negative voltage outputs from the transducer are part of a continuous signal. Electronics can be used to capture just the positive half-cycles or the negative half-cycles. There are probably some fancy signal processing methods that can do the same. This is called half-wave rectification.

3. Most ultrasonic flaw detectors allow the user to select positive or negative half wave rectification. The signals are usually a bit different. Looking at it a different way, a positive half-cycle might represent energy flowing into the transducer and a negative half-cycle energy flowing back out. Some software techniques can analyze the flow of energy in a signal, and it is worth reading up on the Hilbert Transform, if this interests you.

4. The differences in positive and negative half-cycles probably have more to do with the properties of the material than the nature of a volumetric flaw. However, a tightly closed crack may have a non-linear response to an ultrasonic pulse, and techniques such as harmonic analysis take advantage of this. If the positive and negative half-cycle are different, this represents a type of distortion (i.e. a departure from a pure sine wave), which alters the frequency content of the signal.

Like I wrote above, this is how I think about things, but I may be wrong.

John N

 
 Reply 
 
Wieslaw Bicz
Engineering,
PBP Optel sp. z o.o., Poland, Joined Feb 2009, 276

Wieslaw Bicz

Engineering,
PBP Optel sp. z o.o.,
Poland,
Joined Feb 2009
276
11:48 Feb-12-2018
Re: Ultrasonic phase change
In Reply to Levi P at 22:48 Feb-11-2018 .

Levi,

it seems for me, that you want to understand, how the ultrasonic transducer is generating and receiving sound waves. And may be also to understand, how the flaw is transforming the wave that is hitting it.

The second effect can be described with diffraction theory, but this could be complicated and requires the knowledge about the parameters of the shape of the wave front.

If you want to understand, how the ultrasonic transducer is generating and receiving sound waves it would be better to read such books as for example: Ultrasonic Transducers for Nondestructive Testing, by M. G. Silk .

You must be always aware, that transducer is not a single membrane, but typically has two walls and the signal is generated on each wall only, causing, that the form of signal leaving the transducer is composed from many oscillations and is sometimes quite complicated. Its function depends naturally on many factors, such as type of piezomaterial, its thickness, backing, matching layers, but also electric matching, cable and naturally by the electronics used. All this together is quite complicated.

Simple speaking: It is difficult to generate a pulse, that is short and has only positive or negative amplitude and it is difficult to create a piezoelectric receiver, that would be able to receive such pulse in a pure form.

 
 Reply 
 
Randy Fong
USA, Joined Aug 2012, 6

Randy Fong

USA,
Joined Aug 2012
6
21:16 Feb-12-2018
Re: Ultrasonic phase change
In Reply to Levi P. at 20:35 Feb-11-2018 (Opening).

Levi,

The piezo is pulsed electrically with a + and a - (ground). Let's say your looking at an RF return signal from a side drilled hole. Say the return signal goes down up down. If you then reverse the polarity of the pulse (i.e. the + and -) on the crystal, the same return signal now be up down up (i.e. reversed). This is called a "Phase Change". In Tofd one characterizes defects by looking at this phase change. Typically the top tip of a diffraction signal will be 180 out of phase form the bottom tip. The same happens when the sound reflects off the back surface, its phase will change by 180. Without going into detail, when using TOFD, one needs to understand (know what it looks like) the phase differences between the Front Surface Wave, a Top Tip, a Bottom Tip, and the L wave back wall reflection. If you can recognize these changes, then one will know what is what.

Randy

 
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Vadim Kniazev
R & D, Director
Wave Process Simulation System Laboratory, Russia, Joined Jun 2010, 4

Vadim Kniazev

R & D, Director
Wave Process Simulation System Laboratory,
Russia,
Joined Jun 2010
4
17:55 Feb-19-2018
Re: Ultrasonic phase change
In Reply to Levi P. at 20:35 Feb-11-2018 (Opening).

zoom image



zoom image



Dear Levi,

I think you will be interested in ultrasonic wave phase changing while nonlinear defect passing (microcracks, debondings, delaminations and microstructural material damages):
www.researchgate.net/publication/232708284 ........

It is presented by figures 6 and 7 in the article.

Good luck,
Vadim
 
 Reply 
 
Levi P.
R & D,
Dacon Inspection Technologies, Thailand, Joined Jan 2017, 60

Levi P.

R & D,
Dacon Inspection Technologies,
Thailand,
Joined Jan 2017
60
01:37 Feb-20-2018
Re: Ultrasonic phase change
In Reply to Vadim Kniazev at 17:55 Feb-19-2018 .

Thanks for the info, the link to the Theory of Numerical Methods for Computer Simulation of Ultrasonic Waves Passing through the Nonlinear Flaws is quiet interesting and will be a weekend read for me. Thanks.
-Levi

 
 Reply 
 
Henry Herrera
R & D,
UT Quality, Canada, Joined Jun 2000, 19

Henry Herrera

R & D,
UT Quality,
Canada,
Joined Jun 2000
19
23:13 Feb-22-2018
Re: Ultrasonic phase change
In Reply to Levi P. at 01:37 Feb-20-2018 .

Hi Levi,
John Norman gave some good answers to your 4 questions. Ed Ginzel is also sending you to the text with the answer to question 4. I'll just comment on the phase rotation of tip diffracted signals on your question 4.

The original description comes from "Diffraction of elastic waves by cracks: application to time-of-flight inspection" by J.A.OgilvyJ.A.G.Temple. Ultrasonics Volume 21, Issue 6, November 1983, Pages 259-269.

This text is from the paper:
"When a sound wave is incident on a crack tip it may undergo a phase change on diffraction. The value of this phase change may be obtained from the expressions for Fp(theta,beta) and Gp(theta,beta) given earlier since these are always complex. Knowledge of the relative phase difference between the signals diffracted from the top and bottom of the crack may be useful in determining the points of origin of diffracted signals from a complex defect or set of defects.
Calculations show that for incident and diffracted compression waves there is always a phase difference of PI between the signals from the top and bottom of a crack."

I have seen the long equations on the paper to describe the amplitudes and the answer is in there. The maximum amplitude of the diffracted signal for the top of the crack is for the diffracted angle theta > 90 degrees. when this happen sin(theta) is positive and cos(theta) is negative. This should invert the sign of Gp(theta, beta).

On the other hand, for the bottom of the crack, the maximum happens when the diffraction angle theta is between (0 - 90) degrees. In this case, sin(theta) and cos(theta) are both positive, the sign of Gp(theta, beta) should be positive.

You can not see the phase change in diffraction in the same way of the phase change during reflection which is basically a phase inversion due to impedance change. For diffraction just imagine two new point sources. When the ultrasound pulse hits the defect both tips are new point sources vibrating at 90-degree phase shift.

Regards,
Henry




 
 Reply 
 
Henry Herrera
R & D,
UT Quality, Canada, Joined Jun 2000, 19

Henry Herrera

R & D,
UT Quality,
Canada,
Joined Jun 2000
19
19:27 Feb-23-2018
Re: Ultrasonic phase change
In Reply to Henry Herrera at 23:13 Feb-22-2018 .

Hi Levi,

In my previous comment, the last sentence should read 180-degree phase shift.

"When the ultrasound pulse hits the defect both tips are new point sources vibrating at 180-degree phase shift."

There is an earlier thread of this forum on a similar question - TOFD phase inversion. See this link:

http://www.ndt.net/forum/thread.php?admin=&forenID=0&msgID=67812&rootID=51453#67812

Regards,

 
 Reply 
 
Levi P.
R & D,
Dacon Inspection Technologies, Thailand, Joined Jan 2017, 60

Levi P.

R & D,
Dacon Inspection Technologies,
Thailand,
Joined Jan 2017
60
03:59 Feb-27-2018
Re: Ultrasonic phase change
In Reply to Henry Herrera at 19:27 Feb-23-2018 .

Henry,
Thank you for this information. I have been reading, learning, and reading more! The people who posted here have been genuinely helpful and I appreciate it.

-Levi

1
 
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