Resonance/frequency and sounds 1

[jimmylovesni]

I am hitting glass plate with high power ultrasound. The ultrasound pulses are 1MHtz pulsed at 1KHz.

As a by product, we are getting an audible component, a high pitched ringing. As we change the pulsing rate, say over the range of 0.5KHz to 2KHz, the pitch that we hear changes.

Why is this? I was thinking it was the natural frequency at first, but since its changing with frequency of the pulsing, it cant be.

thanks

 

[Twoballcane]

"sounds" like harmonics...LOL get it sound...harmonics

Tobalcane
"If you avoid failure, you also avoid success."
“Luck is where preparation meets opportunity”

 

[electricpete]

I assume that the frequencies that you hear are not simply varying in direct proportion to your fundamental pulse frequency.

Based on that assumption, I suspect at the high frequencies of your excitation, the modal density is large (lots of different modes closely spaced). The presence of an excitation rich in harmonics (periodic pulses) compounds the situation because you have many exciting frerquencies at one time -> more chance of hitting a resonance. Bottom line, you have lots of excitation frequencies, lots of resonant frequencies, and you are hitting (amplifying) different resonant frequencies (and mode shapes) as you vary frequency.


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(2B)+(2B)' ?

 

[drawoh]

jimmylovesni,

Is your 1MHz pulsed on and off at 0.5kHz to 2kHz?

Audible frequencies are between 30Hz and 20kHz. You cannot hear ultrasound, which is why it is called ultrasound. Even us middle aged rock and roll fans can hear stuff at 0.5kHz to 2kHz. When you change from 0.5 to 2kHz, you should hear a change of pitch. There may or may not be resonance happening. Definitely, there is a forcing function.

What you hear is your pulsing.

JHG

 

[electricpete]

That's a better answer than mine.

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(2B)+(2B)' ?

 

[GregLocock]

Get a microphone and post some screen dumps (or wavs) of the noise.



Cheers

Greg Locock


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[jimmylovesni]

ok, I uploaded some figures of it at various frequencies. I didnt have a microphone handy so used a hydrophone. Ill try the microphone later.

It seems like there is a resonance that is building up and going to a higher pulsing frequency cuts off this build up.. but this doesn't explain the change in pitch.

this is a very high pitch noise, id guess over 10kthz, its high enough that the older people like me cant hear it so its on the upper end of the audible range..

http://files.engineering.com/getfil...9823-4ae6-b9fc-4a9ecebcafb0&file=Untitled.bmp

 

[jimmylovesni]

and btw.. the very first part of the signal, right where the pulse is turned on is a flextural wave, a lamb wave, its probably different from this resonance signal although Im wonder if it is helping building it up higher than normal?

Is the resonance related to the piezoelectric transducer or the lamb wave.. something for me to think about for tonight while im in bed.

 

[GregLocock]

I'd start by figuring out the frequency, unfortunately not possible from your screenshots. BTW my subjective estimates of the frequency of high frequencies are usually far too high, unless I have a tone to compare them with.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

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[drawoh]

jimmylovesni,

Does the pitch vary with your pulsing frequency, or does it vary some other way?

JHG

 

[jimmylovesni]

im still not sure what it is at this point.

there are some increases in the harmonics (overtones) that i can see via FFT in matlab..

the hydrophone through air is recording the 1MHz pulsing at 1KHz.

its probably just a combination of both. thanks everyone