fadY

Quite clever :idea: 8)

Actually you're right. They're nothing more than a piece of aluminium...

bogdanfirst

thats correct Mosfet....
they are no more then a piece of a aluminium...i hot a sheet of Al about 30x40cm wich i cut from and make my heatsinks...but there is a bit of a problem....it is durealuinium, and its damn hard to cut it........

kinjalgp

Well, heatsinks are pieces of aluminium but specially deisgned so that maximum surface area comes in contact with air and thus heat transfer takes rapidly as compared to plain aluminium plate.

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bogdanfirst

yep, they come in differend shapes and sizes....
some have copper too...i dont know why they dont use copper that much from what i know its therma conductance is as good as Al....

kinjalgp

Thats because copper corrodes very fast when comes in contact with air. If you use any protective coating on copper then its thermal conductivity will reduce.

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Sebi

And copper is very expensive...

bogdanfirst

yes, i think that this is why copper is not so used, but in extreme cases you can use the copper from a PCB as a heatsink...well not so extreme

Ricky

May I add that when using a heatsink it may be wise to use silicone grease for a more efficient heat transfer from the device to the heatsink material .

mechie

Bogdanfirst
Take a look at ...
http://www.electro-tech-online.com/v...ght=ultrasonic

This explains the soundbeam theory.

Heatsinks -- I have used copper (bits of old hot wter cylinder) - perfectly OK, steel works (not as good but still fine).

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fadY

here is the modulator circuit:

C1=100n
C2=100n
C3=100n
R1=56R
R2=1K
R3=1K
R4=6.8K
R5=470R
R6=470R
R7=470R
R8=680R
R9=potentiometer 50K
R10=56R
R11=680R
R12=56R
R13=3K
R14=3.9K
R15=3.9K
ic1, ic2=CA3046

I send a 34kHz sine wave as a carrier and the audio signal I want to hear as signal. I, then, send the output to the amp.

Then the output of the amp is connected in series with a 150µH inductor, a 4.7R power resistance and the ultrasonic (25µ PVDF film) speaker which has a resistance of 2Ohm and a capacity of 160nF.

The most wide the speaker the most directional sound you have because you have less diffraction. The speaker is hard to find; my school had it given by ATC which has developed this application ( http://www.atcsd.com/pdf/01-WPHSS-0001-RevC.pdf ).

Concerning the narrowness of the beam, I haven't measured it yet but the effect is quite amazing!

Attached Images

modulateur.gif (11.2 KB, 439 views)

fadY

I tried my circuit on a class T amp and I have problems with the output filter. Actually class T amps modulate the analogic signal before amplifying it. After JFET transistors amplification, one have to demodulate by low pass filtering.

The filter I use is a second order LC low pass circuit which resonantes at 80kHz. But the filter has to be damped by an RC filter to prevent resonant curents so the RC filter in parallel with the capacity of the LC previous filter has to decrease the quality factor Q of the LC filter.


My problem is that, at ultrasonic frequencies, a lot of current go through this filter which make it heat (I put a high power resistor) a lot and make me loose a lot of the power given by the amp.
Do you know how I could to improve that?

Attached Images

filtre.gif (7.5 KB, 427 views)