How to construct something with a specific resonant frequency?

[green_archer]

I just want to ask how can i construct a material of  a specific resonant frequency? What are the parameters and concepts that I need to consider? I'm currently working on a thesis and I need to construct a landmine enclosure with a 1000Hz resonant frequency. Any kind of help is very much appreciated. Thanks!

[zer0w1ng]

What is a landmine enclosure? An enclosed bomb?
What is its purpose?

Resonance is done by setting the capacitive reactance equal to the inductive reactance.

[Shey]

kindly give us more details.. medyo interesting kasi ang project mo 

[green_archer]

yep, its just the casing of the landmine. I know the relationship but I'm more inclined on the physical explanation. Based from what I've read, the object's dimension and type of material that it is made of greatly affects the resonant freq of an object. I just dunno how construct with an exact resonant freq that I want.

Well the basic idea of our study is to detect AP mines using ultrasonic via the vibrations that the mines will emit when we trigger it to its resonance state..

[zer0w1ng]

You mean acoustic resonance? 
Trigger and blow the mine using sound? 

It maybe possible. You could do a slow acoustic sweep with a HI-FI baffle and a high-power audio amplifier.

[rdpzycho]

medyo mahirap yan. maraming trial and error at kailangan marami kang alam about materials. you may also try to study mechanical audio filters (like mufflers) as they also try to study resonance of a given material in a given volume and dimension. makikita 'to sa Mechanical Engineer's Handbook pero marami rin siguro sa Web.

[green_archer]

Actually its really possible but we're not suppose to blast it. Where supposed to just detect the vibration emitted by the landmine. Well theoretically the landmine's not suppose to go 'BANG' when they vibrate because the vibration's weak enough to trigger it.

And what do you mean by trial and error? Isn't there a direct or even just a relationship between the material's dimension to its resonant frequency. I mean when it small its supposed to have smaller resonant freq value something like that?

[rdpzycho]

dependent pa rin sa material (actually, construction) pero malaki effect ng size and shape. IIRC, sa Mechanical Engineer's Handbook makikita 'to on chapter regarding mufflers. sa Electronics Engineer's Handbook meron din ata on chapter regarding Baffles.

kaya kailangan ng trial and error kasi hindi ka pa rin sure kung tama yung parameters ng unang test "landmine". you're circuit maybe working right but the "landmine" may not resonate at that frequency.

I think the best person to consult with this would be a physicist, or a mechanical engineer.

[Shey]

ang resonant freqeuncy ng isang bagay ay dependent sa dalawang bagay.. Mass and Elasticity.. same din dun sa computation sa resonant frequency ng speakers at baffles.. ang simpleng paraan para makuha mo ang resonant frequency ng isang bagay ay pokpokin mo lang siya ng hammer tapos i-record mo yung sound na na-generate niya then use a spectrum analyzer para makita mo yung characteristic frequency niya..

Take note: yung resonant frequency ng landmine would also be affected by the type of soil kung saan siya nakabaon.. kung nakabaon siya sa sand expect a much higher resonant frequency compared kung nakabaon siya sa clay..

[green_archer]

thanks electron! thats a start.

[rdpzycho]

the process is called "pinging" IIRC. it is the inverse of designing (i.e. measuring) the object with a specific resonant frequency. this is as what sir zerowing said, a slow sweep of the frequency.

dropping a ball bearing to the metal package may be more appropriate than the hammer as the results of the hammer would be dependent on your stroke. you can use a microphone or any transducer and connect it to your PC MIC input to see the characteristics.

the method is that you play specific frequencies (or sweep it) and look at the ringing. the slower the ringing decays the closer you are to the object's resonance. this is also used in glass goblets to determine what frequency a certain goblet will break, and play music.

[rdpzycho]

nakalimutan ko yung ball bearing method.

dun sa ball bearing method magkakabit ka rin ng mic or any suitable transducer na nakakabit sa PC MIC (kung may Spectrum Analyzer mas maganda). ibabagsak yung ball bearing at titignan yung results sa Spectrum Analyzer. the highest response would be the resonant frequency. commercial meters use this method but with the ball attached to a chain and the transducer is an accelerometer.

sa method above, time domain titignan mo (unless gagawa ng circuit na magcompare ng output ng loudspeaker at output ng transducer).

sa method na 'to frequency domain titignan mo.

[Shey]

this is a nice thread  hehehe.. the next problem would be compensating for the characteristics of the soil.. like I said in my previous post mag-iiba yung resonant frequency nung landmine once binaon na natin siya sa lupa.. to make the matters worst, kapag iba ang klase ng lupa, iba din ang tunog nung landmine..

[green_archer]

wait guys, i dont need to know how to get the resonant freq, I need to construct with a specific resonant freq. Or is there no DIRECT way of doing that without doin the above mention methods?

[green_archer]

Thanks for the heads up electron and for the comment too. Aprreciate it man.

[Shey]

alam ko lang ay trial and error method eh.. bang the material tapos use the spectrum analyzer.. change the thickness or weight of the material until you get your required resonant frequency.. ganun lang..

[green_archer]

Good day guys!

I am an undergraduate BS-ECE student and me and my group are currently having a little problem with our thesis entitled "PC-based Ultrasonic Landmine Detector". We are trying to find the resonant frequency of our dummy landmine enclosure that we made.What we did was to excite the landmine with our signal generator. We try to vary the signal's frequency at a constant volume. We then used a microphone to receive the signal being emitted by the landmine and then connect it to an oscilloscope (in FFT mode). According to one of the physics experts in another site, the resonant frequency will be the frequency with the highest magnitude. But the microphone seems to be receiving only the sound coming from the signal generator so the freq with highest magnitude will be the freq of the signal generated.

Is this the correct way to get the resonant frequency of an object?  I really hope hope you can help us with this. thanks!

[glutnix_neo]

pwede rin madamped or magibaresonant frequency when the object is in contact with other materials diba?like kung soil or sand ang pinaglubugan nya.

 

[Ganda692002]

maybe try constructing 2 very rigid body inside your landmine enclosure(make sure pressure and temperature will be constant inside).. then strap and stretch a guitar string between it.. then you detect the resonant frequency of the string not the enclosure.. this way even if you put it underground the resonant frequency of the string is unaffected by the soil or whatever is holding the enclosure.....

[rdpzycho]

hmmmm. you should sweep the audio generation. kung saan yung point na yung output/input ratio is greatest, yun yung resonance.