Reply by jim April 15, 20102010-04-15

CCoder wrote:

> I am trying to measure coating thickness (100µ to 500µ) on a metal object > (.5-20mm thick).
Is the idea to develop a non-destructive quality control test for paint (or whatever the coating material is)? Have you looked at signals from different samples with known coating thickness? -jim
> > >For identifying the presence and location > >of discontinuities, a matched filter is probably a better choice. > > Which one? Amplitude level doesn't seem to give me any indication, maybe > the frequency does, but I still have to check that part. > > >Either one will have to take the presence of noise into account; correct > >deconvolution in a no-noise environment would be a horrible noise > >enhancer, in the matched filter case the filter itself wouldn't change > >much, but setting the threshold properly would get more and more dicey > >as the noise went up. > > As far as I understand it now, noise is the factor which makes it difficult > to find the correct thickness. In other words, the problem is to find the > *correct* peak.
Reply by Rune Allnor April 15, 20102010-04-15
On 15 apr, 12:22, "CCoder" <michel.timos@n_o_s_p_a_m.gmail.com> wrote:

> >Are you trying to get a detailed picture, ala the prenatal baby pictures > >that expecting parents get from the nice technician during prenatal > >exams? &#2013266080;Or are you sliding in a material with a known construction and > >looking for the exact positioning of known discontinuities? &#2013266080;Or are you > >doing something else yet again? > > I am trying to measure coating thickness (100&#2013266101; to 500&#2013266101;) on a metal object > (.5-20mm thick).
Let's assume 100e-6m thickness and c = 2500 m/s (which might be low, depending on what kind of material we are talking about). That should give a 2-way time-of-flight through the coating on the order of 80 ns. That number will be significantly smaller if we are talking about metals. You are certainly pushing the envelope if you try and measure that sort of delay by means of a pulsed ultrasonic set-up. Don't know how to measure that coating, but naive pulsed ultrasound is *not* the way to go.
> As far as I understand it now, noise is the factor which makes it difficult > to find the correct thickness. In other words, the problem is to find the > *correct* peak.
No, it isn't. You are pushing way beyond the limits of what a pulsed ultrasound measurement can do. There might be ways of measuring what you want by means of ultrasound (although I doubdt it), but if so, they will be at the level where you need a 3-year MSc degree and an additional 5-year PhD degree in specialized studies to come up with a working system. In short: Pay somebody to do the measurement for you. Rune
Reply by CCoder April 15, 20102010-04-15
>Rune Allnor wrote: >> On 14 apr, 18:37, "CCoder" <michel.timos@n_o_s_p_a_m.gmail.com> wrote: >> >> When I say 'exactly' I actually mean 'exactly'. >> >> For starters, what are >> >> 1) The dimensions of the object? >> 2) The number of materials involved? >> 3) The expected impedances of the matreials involved? >> 4) The expected relative sizes of the materials? >> 5) The carrier frequency for the pulse? >> 6) The bandwidth of the pulse? >> 7) The type of pulse? (Frequency sweep? Monochromatic?) >> 8) The duration of the pulse? >> 9) The geometric configuration of the sensor? >> (Mono/bistatic? Dimensions?) >> 10) The physical dimensions of the sensor(s)? >> >3a -- are the materials isotropic, or are they at least only weakly >anisotropic? Nothing too exotic? I'll bet that sound propagates really >oddly in oriented-strand carbon-fiber epoxy. > >8a -- what's the _real_ duration of the pulse _out of the generator_, >not just the excitation to it? > >11 (or 8b) -- does the receiver overload when the generator is active, >and how long does it take to recover with respect to the first >"interesting" event that you're looking for? >
Although I do not have all the answer that you request I will certainly try to answer them as best I know how. ad 1) steel/metal 0.5 mm to 20mm. ad 2) 2, being the object itself and the coating . ad 3) You mean the acoustic impedance right? I only know the difference will be small. How small? I don't know either. ad 3a) Yes, they are uniform in any direction. ad 4) Coating is somewhere between 100&micro;m and 400 &micro;m on a 0.5-20mm object ad 5) 250kHz ad 6) I'm not sure what you mean by bandwidth. Its a blockwave with rise times <1&micro;s ad 7) Blockwave ad 8) approx. 28&micro;s ad 8a) Im not a native english speaker (gee :-)) so i am a little unsure what you mean by excitation. Do you expect it to be longer due to lag of reflections? Distortions? ad 9) We could use these: http://www.prowave.com.tw/english/products/ut/ep/480ep900.htm ad 10) see 9 ad 11) The receiver is active when we generate the signal. The time it takes for the signal to travel from transmitter to receiver is short, as in <1sec. Hopefully this give you enough info. Thanks
Reply by CCoder April 15, 20102010-04-15
>CCoder wrote: >>> On 14 apr, 17:33, "CCoder" <michel.timos@n_o_s_p_a_m.gmail.com> wrote:
But according to research papers I've read
>> I am quite sure I need deconvolution. As far as I know 'Blind >> deconvolution' is used to deconvolve something (i.e. an image) that you >> don't know the source shape of. In my case I know the shape since I >> generate it. >> Problem is, there are quite a few variations on deconvolution, I don't
know
>> which one to start looking at. > >How old are the research papers? How much did the researchers actually >use the results? How well respected were these researchers in industry? > How many ultrasonic imaging companies actually used the results?
Well, this one is from 2007: http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=APCPCS000894000001000563000001&idtype=cvips&gifs=yes&ref=no Others are older: http://www.ndt.net/article/wcndt00/papers/idn158/idn158.htm Or really old :-) : http://www.ndt.net/article/wt1097/panam/panam.htm
>Many academic fields have drifted away from >actual useful results, and are investigating various ramifications that >are either unreasonably computationally intensive, put unreasonable >demands on the input data, solve hardware problems that have already >been fixed, or offer improvements that are only trivial. > >OTOH, there's still a lot of good stuff out there -- so you have to do >some sorting.
That is exactly my intention and the reason I wound up on this list :-) I am trying to figure out what are dead ends, which ones are promising and so on. And off course, in the shortest amount of time possible since i need to code a gazillion other things as well :-)
>Do you know the phase of the pulse picked up, or do you just get a >magnitude back? How does the damping/blanking time of the generator and >pickup compare with the travel time in your 'few millimeter' sample? >I'll wager that knowing the phase would make a huge difference to what >you can do, and having to deal with residue of the pulse when your first >reflection is coming back complicates things in itself.
I do not know the phase, just the amplitude. I have measurement results that give me amplitude at a fixed 10 megasamples/sec. Unfortunatly I do not know how to post attachments here, I do have nice looking PDF's.
>Are you trying to get a detailed picture, ala the prenatal baby pictures >that expecting parents get from the nice technician during prenatal >exams? Or are you sliding in a material with a known construction and >looking for the exact positioning of known discontinuities? Or are you >doing something else yet again?
I am trying to measure coating thickness (100&micro; to 500&micro;) on a metal object (.5-20mm thick).
>For identifying the presence and location >of discontinuities, a matched filter is probably a better choice.
Which one? Amplitude level doesn't seem to give me any indication, maybe the frequency does, but I still have to check that part.
>Either one will have to take the presence of noise into account; correct >deconvolution in a no-noise environment would be a horrible noise >enhancer, in the matched filter case the filter itself wouldn't change >much, but setting the threshold properly would get more and more dicey >as the noise went up.
As far as I understand it now, noise is the factor which makes it difficult to find the correct thickness. In other words, the problem is to find the *correct* peak.
Reply by Tim Wescott April 14, 20102010-04-14
Rune Allnor wrote:
> On 14 apr, 18:37, "CCoder" <michel.timos@n_o_s_p_a_m.gmail.com> wrote: > >>> Now, explain *exactly* the set-up you use. >>> Rune >> An ultrasonic generator, an object a few milimeters in size with different >> materials in it and a pickup sensor. > > When I say 'exactly' I actually mean 'exactly'. > > For starters, what are > > 1) The dimensions of the object? > 2) The number of materials involved? > 3) The expected impedances of the matreials involved? > 4) The expected relative sizes of the materials? > 5) The carrier frequency for the pulse? > 6) The bandwidth of the pulse? > 7) The type of pulse? (Frequency sweep? Monochromatic?) > 8) The duration of the pulse? > 9) The geometric configuration of the sensor? > (Mono/bistatic? Dimensions?) > 10) The physical dimensions of the sensor(s)? > > And again: When I say 'exactly' I *mean* 'exactly'.
3a -- are the materials isotropic, or are they at least only weakly anisotropic? Nothing too exotic? I'll bet that sound propagates really oddly in oriented-strand carbon-fiber epoxy. 8a -- what's the _real_ duration of the pulse _out of the generator_, not just the excitation to it? 11 (or 8b) -- does the receiver overload when the generator is active, and how long does it take to recover with respect to the first "interesting" event that you're looking for? -- Tim Wescott Control system and signal processing consulting www.wescottdesign.com
Reply by Tim Wescott April 14, 20102010-04-14
Rune Allnor wrote:
> On 14 apr, 17:33, "CCoder" <michel.timos@n_o_s_p_a_m.gmail.com> wrote: >>> The book I previously mentioned, "Deconvolution of Images and Spectra" >>> There is also an older book: "Deconvolution with applications >>> in spectroscopy." >> Okay, here is my setup: I generate an ultrasonic pulse which travels >> throught the object I want to measure. The resulting reflections are read >> back into the system. > > How do you get reflections if the pulse travels *through* the > object?
Goodness you're cranky today, Rune. Of course he means "through with reflections".
>> What comes back will have little peaks in it which indicate a change in >> material. > > No, it doesn't. Any reflections indicate abrupt changes in acoustic > impedance. If the materials have the same impedance or the change > between materials is not abrupt, you will not see any reflections.
Clearly in the material he's dealing with it does, and he's either neglecting to mention, or neglecting to think about, those cases where the transition is smoother. It sounds like he's inspecting metal parts or some such; I would imagine that even two otherwise homogeneous samples that are glued together would have a discontinuity at the interface. If they really are different metals as he says, then there will almost certainly be a discernible difference.
>> Suppose I have a block that has 2 layers of (different) metals. >> One peak will indicate where the wave entered the object, a second one >> where the second layer starts. And a third where the wave exited the >> object. >> >> I want to measure the distances (thickness if you like) between the peaks. > > No, you don't. You want to measure the time delay between > reflections.
I don't know why _I'm_ being cranky today, but he really does want to measure the distances between the metals, he's just stated it poorly. I went out for a drive today, and I looked at the speedometer. I wasn't interested in estimating the angle of the little orange needle with respect to the little white numbers, but that's what I did, unconsciously, and just as unconsciously converted that reading into a speed "measurement". If I told you I needed an angle sensor to use with a speedometer to measure my speed, I'd argue with you if you tried to tell me that I really wanted to know the angle if the little needle! That's a necessary issue, but it's still a side issue.
>> I know I do not need 'blind' deconvolution since I know the input pulse. > > No, you don't. If you know the pulse shape emitted - and you use > a 'simple' geometry (i.e. monostatic source-recever set-up) - you > might get away with an ordinary matched filter.
I do question the need for deconvolution at all, if he's just interested in measuring thicknesses of different materials. If he's trying to image first, and measure second, then he'll need deconvolution to sharpen up the image -- but that may not be the best way for a machine to get a reading. -- Tim Wescott Control system and signal processing consulting www.wescottdesign.com
Reply by Tim Wescott April 14, 20102010-04-14
CCoder wrote:
>> On 14 apr, 17:33, "CCoder" <michel.timos@n_o_s_p_a_m.gmail.com> wrote: > >>> Okay, here is my setup: I generate an ultrasonic pulse which travels >>> throught the object I want to measure. The resulting reflections are > read >>> back into the system. >> How do you get reflections if the pulse travels *through* the >> object? > > An ultrasound wave is sent at the object and it gives me reflections. You > known, like a sonar. > >>> What comes back will have little peaks in it which indicate a change in >>> material. >> No, it doesn't. Any reflections indicate abrupt changes in acoustic >> impedance. If the materials have the same impedance or the change >> between materials is not abrupt, you will not see any reflections. > > I have data from the ultrasonic transducer that shows me (little) peaks on > entering, exiting and when the material changes. That is sufficient. > >>> Suppose I have a block that has 2 layers of (different) metals. >>> One peak will indicate where the wave entered the object, a second one >>> where the second layer starts. And a third where the wave exited the >>> object. >>> >>> I want to measure the distances (thickness if you like) between the > peaks= >> . >> >> No, you don't. You want to measure the time delay between >> reflections. > > I need to convert the time delay to distance, yes. > >>> I know I do not need 'blind' deconvolution since I know the input > pulse. >> No, you don't. > > Well okay I don't know for sure. But according to research papers I've read > I am quite sure I need deconvolution. As far as I know 'Blind > deconvolution' is used to deconvolve something (i.e. an image) that you > don't know the source shape of. In my case I know the shape since I > generate it. > Problem is, there are quite a few variations on deconvolution, I don't know > which one to start looking at.
How old are the research papers? How much did the researchers actually use the results? How well respected were these researchers in industry? How many ultrasonic imaging companies actually used the results? And in case you're wondering -- yes, I'm doing my part for the Diogenes Appreciation Society today. Many academic fields have drifted away from actual useful results, and are investigating various ramifications that are either unreasonably computationally intensive, put unreasonable demands on the input data, solve hardware problems that have already been fixed, or offer improvements that are only trivial. OTOH, there's still a lot of good stuff out there -- so you have to do some sorting.
> If you know the pulse shape emitted - and you use >> a 'simple' geometry (i.e. monostatic source-recever set-up) - you >> might get away with an ordinary matched filter. >> >> Now, explain *exactly* the set-up you use. >> >> Rune > > An ultrasonic generator, an object a few millimeters in size with different > materials in it and a pickup sensor.
Do you know the phase of the pulse picked up, or do you just get a magnitude back? How does the damping/blanking time of the generator and pickup compare with the travel time in your 'few millimeter' sample? I'll wager that knowing the phase would make a huge difference to what you can do, and having to deal with residue of the pulse when your first reflection is coming back complicates things in itself. Are you trying to get a detailed picture, ala the prenatal baby pictures that expecting parents get from the nice technician during prenatal exams? Or are you sliding in a material with a known construction and looking for the exact positioning of known discontinuities? Or are you doing something else yet again? Which question you're trying to answer makes a big difference -- for imaging you probably want some form of deconvolution, and the closer you can get to something that has already been done with your materials the better your starting point. For identifying the presence and location of discontinuities, a matched filter is probably a better choice. Either one will have to take the presence of noise into account; correct deconvolution in a no-noise environment would be a horrible noise enhancer, in the matched filter case the filter itself wouldn't change much, but setting the threshold properly would get more and more dicey as the noise went up. -- Tim Wescott Control system and signal processing consulting www.wescottdesign.com
Reply by Rune Allnor April 14, 20102010-04-14
On 14 apr, 18:37, "CCoder" <michel.timos@n_o_s_p_a_m.gmail.com> wrote:

> >Now, explain *exactly* the set-up you use. > > >Rune > > An ultrasonic generator, an object a few milimeters in size with different > materials in it and a pickup sensor.
When I say 'exactly' I actually mean 'exactly'. For starters, what are 1) The dimensions of the object? 2) The number of materials involved? 3) The expected impedances of the matreials involved? 4) The expected relative sizes of the materials? 5) The carrier frequency for the pulse? 6) The bandwidth of the pulse? 7) The type of pulse? (Frequency sweep? Monochromatic?) 8) The duration of the pulse? 9) The geometric configuration of the sensor? (Mono/bistatic? Dimensions?) 10) The physical dimensions of the sensor(s)? And again: When I say 'exactly' I *mean* 'exactly'. Rune
Reply by CCoder April 14, 20102010-04-14
>On 14 apr, 17:33, "CCoder" <michel.timos@n_o_s_p_a_m.gmail.com> wrote:
>> Okay, here is my setup: I generate an ultrasonic pulse which travels >> throught the object I want to measure. The resulting reflections are
read
>> back into the system. > >How do you get reflections if the pulse travels *through* the >object?
An ultrasound wave is sent at the object and it gives me reflections. You known, like a sonar.
>> What comes back will have little peaks in it which indicate a change in >> material. > >No, it doesn't. Any reflections indicate abrupt changes in acoustic >impedance. If the materials have the same impedance or the change >between materials is not abrupt, you will not see any reflections.
I have data from the ultrasonic transducer that shows me (little) peaks on entering, exiting and when the material changes. That is sufficient.
>> Suppose I have a block that has 2 layers of (different) metals. >> One peak will indicate where the wave entered the object, a second one >> where the second layer starts. And a third where the wave exited the >> object. >> >> I want to measure the distances (thickness if you like) between the
peaks=
>. > >No, you don't. You want to measure the time delay between >reflections.
I need to convert the time delay to distance, yes.
>> I know I do not need 'blind' deconvolution since I know the input
pulse.
>No, you don't.
Well okay I don't know for sure. But according to research papers I've read I am quite sure I need deconvolution. As far as I know 'Blind deconvolution' is used to deconvolve something (i.e. an image) that you don't know the source shape of. In my case I know the shape since I generate it. Problem is, there are quite a few variations on deconvolution, I don't know which one to start looking at. If you know the pulse shape emitted - and you use
>a 'simple' geometry (i.e. monostatic source-recever set-up) - you >might get away with an ordinary matched filter. > >Now, explain *exactly* the set-up you use. > >Rune
An ultrasonic generator, an object a few milimeters in size with different materials in it and a pickup sensor.
Reply by Rune Allnor April 14, 20102010-04-14
On 14 apr, 17:33, "CCoder" <michel.timos@n_o_s_p_a_m.gmail.com> wrote:
> >The book I previously mentioned, "Deconvolution of Images and Spectra" > >There is also an older book: "Deconvolution with applications > >in spectroscopy." &#2013266080; > > Okay, here is my setup: I generate an ultrasonic pulse which travels > throught the object I want to measure. The resulting reflections are read > back into the system.
How do you get reflections if the pulse travels *through* the object?
> What comes back will have little peaks in it which indicate a change in > material.
No, it doesn't. Any reflections indicate abrupt changes in acoustic impedance. If the materials have the same impedance or the change between materials is not abrupt, you will not see any reflections.
> Suppose I have a block that has 2 layers of (different) metals. > One peak will indicate where the wave entered the object, a second one > where the second layer starts. And a third where the wave exited the > object. > > I want to measure the distances (thickness if you like) between the peaks.
No, you don't. You want to measure the time delay between reflections.
> I know I do not need 'blind' deconvolution since I know the input pulse.
No, you don't. If you know the pulse shape emitted - and you use a 'simple' geometry (i.e. monostatic source-recever set-up) - you might get away with an ordinary matched filter. Now, explain *exactly* the set-up you use. Rune