Ibraheem,

Well, the free-running frequency of a 555 is determined by two resistors and a capacitor.

f = 1.44 / ((R2+2R).C1)

And the mark-space ratio is set by R and C1.

So you can either tweak R2 or C1.

Mind, if you're looking for any kind of stability, the 555 isn't a great choice. The tolerance on C1 will be your limiting factor: hope that you're using a polystyrene or some other tight tolerance capacitor.

:/

I'm not sure you actually mean 'standing waves'. A standing wave needs a medium through which to propagate, and is characterised by having all its peaks and troughs at measurably identical intervals - a bit like the 'coherence' criterion for a laser wave.

The nearest thing to a 'medium' available in SPICE is a tapped delay line. You might try that.

The waveform you obtained is double side band suppressed carriers which is a multiplication of two sine waves one has much higher frequency than the other.

Adding to James as you want to get sine wave and the three fives gives square wave you have to change the output filter to resonate at the required frequency of 40KHz. Then you gave to scale down both L and C by the frequency ratio.

It is not clear how do you coupled the audio signal to the 555 oscillator.

Best wishes

As Mark and Abdelhalim pointed out, it is not clear you want "standing wave" or Amplitude modulation (AM) with suppressed carrier.

If you want AM wave, 555 timer is not suitable, you may try another IC MC9416.

https://www.onsemi.com/pub/Collateral/MC1496-D.PDF

Sorry, correct AM IC name is MC1496, not MC9416.

Just so we're clear. This is suppressed carrier, and its spectrum, followed by amplitude-modulation, and its spectrum. (Wish I'd chosen a higher carrier frequency...)

Thanks a lot for your answers, I appreciate a lot.

actually i'm new in this field, but i have red an article since 2 month about standing wave usage.

the researchers used an AM wave(characterized by nodes and anti_nodes) to feed piezoelectric Ultra sound to generate standing wave.!

i know that AM is used to carry informations ,so i am looking for a signal has a similar characteristics to it (nodes and anti_nodes)..

now i got confused, what is the differences between AM and suppressed carrier (both combined of two sine wave and one of them with high frequency)??

MR. Mark Sitkowski thanks for your answers.

why we cannot consider the air as a medium for the standing wave??

Actually, I had a feeling this was for an ultrasonic application, as I have worked on a 'loudspeakerless loudspeaker' using these techniques. The trick was to run two transducers in opposition and antiphase, so that the nodes and antinodes of the two standing waves cancel. If you then frequency-modulate one of the transducers, you generate a beat note (wave interference) which can be audio, or any other information. Your idea with the AM will probably be difficult to demodulate, but try FM - that just needs a bandpass filter.

Sorry, Ibraheem, forgot to answer your earlier question.

Suppressed carrier is (sinA*(sinB) which produces an upper and lower sideband at (f1+f2) and (f1-f2), while AM is (sinA*sinB)+sinA and produces a carrier at f1, plus the two sidebands.

I think he means that he wants to transmit an ultrasonic wave, such that it produces regions of compression and rarefaction of the air which occur at intervals of the period of the sound, like:

ccccccccrrrrrrrrccccccccrrrrrrrrccccccccrrrrrrrr

< t >< t >< t > t >< t > t >

where 2t is the period of the wave. It's a standing wave because the air itself doesn't travel - like a wave in the sea.