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| (ultra)acoustic in circuit component level crack detector? |
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| coppercone2:
What are the mechanical units for loss from friction and loss from radiation (like ohms and radiation resistance)? |
| rhb:
I was stuck in a waiting room all day and had a long think on the subject. It's highly unlikely that the idea can be made to work. The frequency would have to be so high that I don't think mechanical transducers exist that can do it. The problem is the small size of parts and the size vs wavelength required for resolution. Suppose the compressional velocity is 8333 ft/s (water is 5000 ft/s). That's 100,000 inches per second. So at 1 MHz a wavelength is 0.1" and at 10 MHz it's 0.01". To get 0.01" resolution we'd need a signal at 40 MHz or higher. To make matters worse, even at 13 MHz, the transducer is so small and fragile that putting a strong enough signal into the xtal will probably break it. I'm also very doubtful about attenuation as it would be hard to distinguish poor coupling from a cracked part. I'm going to do some experiments with the xtals I uncanned, but the very narrow response at 13 MHz will make the signal processing very difficult for any type of reflection processing. Experiments to test: Response of the bare xtal to a minimum width impulse from my 33622A Response with a small piece of PCB glued to the xtal Response of a 2nd xtal glued to the PCB as a receiver. It's very likely that the loading by the PCB will either completely kill the impulse response or shift the frequency so low that even the transmission delay time through the PCB will be unresolvable using an 8 bit DSO. |
| coppercone2:
how many bits do you need? is it really that hard so long you don't need microwave level response or complex DSP or all that back end oscilloscope stuff? or do you mean triggering issues with memory storage? Can't you do some kind of predictive sampling triggering based on process time constants? or multiple filtered channels in sync? not sure i am understanding the problem can you make a drawing? What kind of dynamic range and resolution would it need in terms of signal acquisition. It would be actually interesting for me because as of yet any kind of signal sampling higher then something like 500KSPS has been utterly uninteresting for me. I like the slow slower sensors related to thermodynamics and chemistry that don't really need a sample speed higher then like 100KSPS even with the filters and decimation. i am not sure what exactly you are getting at because I am getting shit about lasers on google and its 4am but keep in mind there is literally no real time data accuracy requirement is, you could do various things to the signal and resend impulses with different reciever setups till you got something that looks right if the process is so complicated it requires ridiculous dynamic range or memory, like a SAR DAC or something. |
| DaJMasta:
--- Quote from: coppercone2 on December 21, 2018, 01:34:14 pm ---hmm if i wanted to experiment further, how would i crack ceramics to make test samples? --- End quote --- Actually probably can just mimic a common failure mode - solder a few down and then flex the board a bunch. Could also try thermal shocking by soldering one end and then putting a drop of water on the other or something (though, definitely with eye protection). Don't know enough about the physics to make any accuracy requirement estimate, but you can try enhanced resolution modes on the scope as a baseline, and then trace averaging for a bit more. Even for impulse response, if you measure hundreds impulses or more you should be able to get lower effective noise. Maybe you'll still need some bits to see the information you want beyond that, but once you start seeing an interesting signal you can look into higher resolution converters with that kind of bandwidth (something like the converters in an SA, most modern ones should be able to do realtime/time domain analysis in the 10s of MHz range). |
| coppercone2:
do you think frequency of oscllation would change the crack profile? I thought to make a PCB of particular mechanical lenght with the part in a particular place and use some kind of motor to jiggle the PCB. Like a rotational to linear converter. |
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