High frequency being transformed to a low frequency

[Dimitar63]

Hi Physics,
I have an idea but before i start. I must know am I right. Is it possible?

We have a small room with two objects. The first object is a producer of sound waves out of the human hearing range. This object sends ultra sound waves to the second object. The second object start to resonate and produces a sound that can be heard. This (second object) has an acoustic shape , so small you can hold in your hand. It depends on the material and the shape of the object i know. But is it possible high frequency be transformed to frequency low enough to be heard?

 

[mfb]

It is probably not impossible to make a mechanical device, but a small battery, microphone and speaker would make it much easier. You can skip the battery if you are fine with a low conversion efficiency.

 

[sophiecentaur]

if you are fine with a low conversion efficiency.

Yes. There's the rub. If you are not using dangerous levels of Ultrasound from your 'producer' the losses will be too great. You will need an Active Circuit to achieve what you want, I am sure. If you really need to do without electronics then the alternative would have to be a pretty large (and accurate) device, to catch enough of the reflected ultrasonic energy. Frequency shifting, with a mixer circuit is very easy and there are many circuit designs available. Bat detectors are available at not much cost and they are probably cheaper than you can build yourself unless you already have the basic constructor's kit. These do what you seem to be describing but your need to be a bit fuller in specifying your requirement if you want a practical answer.

 

[NTL2009]

I'm curious about the OP's conditions, not doing it electronically (easy).

I think they are asking - is there some physical means by which a high frequency sound wave can cause another object to produce a much lower frequency wave? Off hand, I don't think there is?

I was thinking of pulsing the ultrasonic wave on/off at the resonant frequency of the lower-tuned object, but I think that would just produce a sound on it's own, which is not what OP is looking for, I think.

What about two ultrasonic waves ~ 1000 Hz apart? Could the resonant device manage to be moved by the difference frequencies in a strictly mechanical means? Would some sort of mechanical non-linearity provide this (as it does in an electrical circuit)?

 

[berkeman]

Would some sort of mechanical non-linearity provide this

I think non-linearity of a material or structure would be needed, but unless the amplitude is very large, it seems difficult to have a mechanical structure exhibit a non-linearity...

 

[mfb]

Contact interactions can be nonlinear. I could imagine a system vibrating at high frequencies mechanically hit another system resonating at lower frequencies. Would give a horrible conversion efficiency, of course.

OP didn't specify the application, unfortunately.

 

[boneh3ad]

Yes it should be possible and yes it would be a nonlinear process. There are ways to generate subharmonics, phase coupled difference interactions, inefficient resonance, and such. It really just depends on the application and specifics of your system.

 

[jerromyjon]

I do wonder though, if the energy of high-frequency ultrasonic waves, converted in somewhat efficient means to low frequency would have enough energy to be clearly audible? I think about the exhibit where you can whisper on one side of a large expanse near a parabolic mirror and it can clearly be heard on the other side of the room. I forget where that is but I've witnessed it...

 

[berkeman]

I forget where that is but I've witnessed it...

The Exploratorium in San Francisco has such an exhibit, or at least they used to. Pretty amazing.

Hey, what about using the Doppler Effect to reduce the frequency of the sound? If you reflected the ultrasound off of a moving membrane, the frequency of the reflected energy would be shifted above and below the original frequency depending on how fast the membrane was oscillating...

EDIT / ADD -- https://www.physicsforums.com/threads/doppler-effect-moving-source-with-reflection.79074/

 

[jerromyjon]

The Exploratorium in San Francisco has such an exhibit, or at least they used to.

I'm east coast, maybe The Smithsonian? It has been so long I forget...

 

[NTL2009]

Contact interactions can be nonlinear. I could imagine a system vibrating at high frequencies mechanically hit another system resonating at lower frequencies. Would give a horrible conversion efficiency, of course.

OP didn't specify the application, unfortunately.

I actually saw this recently, the focus was on our perception and 'filling in' for missing harmonics, but he actually demonstrates a system that provides a 'sub-harmonic'.

Essentially, a resonant chamber making contact with something else, like a piece of foil. But the foil, acting on its own resonance, moves back-forth, making intermittent contact with the source wave. So it vibrates at a lower frequency than the source. This could be tuned and optimized beyond the simple demonstration of principle here, but I suppose the efficiency would be very low - but possible.

Here you go - he demonstrates it in the first 10 seconds!



The entire video, and his others in the series are pretty amazing. I subscribed.

 

[boneh3ad]

I do wonder though, if the energy of high-frequency ultrasonic waves, converted in somewhat efficient means to low frequency would have enough energy to be clearly audible? I think about the exhibit where you can whisper on one side of a large expanse near a parabolic mirror and it can clearly be heard on the other side of the room. I forget where that is but I've witnessed it...

https://en.wikipedia.org/wiki/Acoustic_mirror

 

[Dimitar63]

Okay boys, first I want to thank you for your replies.
And.. I start thinking, what if I use a quartz crystal as a resonator? Is it possible quartz to produce a voltage and power small buzzer?
ultrasound waves --> quartz crystal --> small buzzer

 

[mfb]

What is the application you have in mind?
Where does the ultrasound come from?

 

[sophiecentaur]

Okay boys, first I want to thank you for your replies.
And.. I start thinking, what if I use a quartz crystal as a resonator? Is it possible quartz to produce a voltage and power small buzzer?
ultrasound waves --> quartz crystal --> small buzzer

No way, without a battery / power source. Quartz crystals are not good for passive operation. In any case, you are wanting frequency conversion (twice?) which means loss loss loss which has to be made up with amplification.

 

[ahiddenvariable]

There are some ways. Electronically, it's easy, and there are such devices, called leak detectors. You point them in the direction you think there might be a leak in a pressurized system and it will detect ultrasound leaks, translating them to a hiss at a frequency within ear range.

If your source of the sound could transmit two ultrasound signals at slightly different frequencies, a resonant receiver can interact and produce heterodyne frequencies, which are a series of frequencies that are additions, subtractions, and their multiples of the original frequencies. One of these lower frequencies can then be within hearing range. Heterodyne frequencies are used in FM radio transmission and in other devices such as micro wave ovens.

 

[rude man]

Hey, what about using the Doppler Effect to reduce the frequency of the sound? If you reflected the ultrasound off of a moving membrane, the frequency of the reflected energy would be shifted above and below the original frequency depending on how fast the membrane was oscillating...

Nifty idea b. , might work if the ultrasound frequency isn't too far above the limits of audibility. The Doppler formula ( f' = fv/[v+v_s] ) is valid only if the moving source speed is << speed of the incident sound. I'm no expert here for sure but I read that linearity between air molecular displacement and restoring force is lost & you get weird things like sonic booms etc. At what point the breakdown v_s/v starts to occur I don't know. My Resnick & Halliday just says "when v_s becomes appreciable in magnitude with v".

)

 

[Mark Harder]

Hi Physics,
I have an idea but before i start. I must know am I right. Is it possible?

We have a small room with two objects. The first object is a producer of sound waves out of the human hearing range. This object sends ultra sound waves to the second object. The second object start to resonate and produces a sound that can be heard. This (second object) has an acoustic shape , so small you can hold in your hand. It depends on the material and the shape of the object i know. But is it possible high frequency be transformed to frequency low enough to be heard?

If the second object resonates it will resonate with the frequency of the broadcasted sound and higher harmonics. If the radiated frequency is higher than hearing range, the higher harmonics will also be ultrasonic. Or am I missing what you are asking?

 

[sophiecentaur]

It's a shame that the information we have been fed is so sparse. Without some idea about the power levels involved and the nature of the 'Objects', there is very little to be said. I wish people would be more forthcoming with their initial questions. It would save a lot of time and avoid misunderstandings. This is an Engineering project and the numbers really count!

 

[.Scott]

My first thought would be for the transmitter to send two ultrasound signals. One designed to be converted to electric power, the other to be received as the signal. This would allow you to place the piezo-electric crystal in a resonant environment with the hope of capturing some significant portion of the audio power collected through the aperture. It also allows the power converter to be optimized for that one frequency.

I would say it could certainly be done. All the OP has requested is that it be heard - not that it be especially loud.

 

[sophiecentaur]

All the numbers are important here. What is the output power? What is the efficiency of both transducers and mixer? What power output of the system is required?
This won't work just because it sounds like a nice idea.
It strikes me that if such a system were workable it would already be for sale as a novelty, if nothing else.