What you "meant" bears no relation to the question being asked. We do appear to have a communication problem.
What is required is an experimental method to measure the concentration of energy in the ultrasound beam after being transmitted across the air-soil interface and travelling to a depth of 3 cm in the soil. Do you have the physics background to devise one?
I presume you must have a target (at the plant roots) intensity figure (in watts per square centimetre) in mind, if so what is it?
That sounds like a very schoolboyish question to me. That would be for you to find out.
One more question from me. Do you currenlty have an ultrasound transducer with which to help conduct an experiment like the one I suggested above?
If so, please supply its make, model and full technical specifications.
@Galu so yes I have the transducers (they are not mine) but they are the small ones with a few watts used as sensors. as regards the power limit of the roots it is around less than 1 watt/cm2 therefore very low. but as always the problem remains overcoming the acoustic impedance, however now that I think about it the wavelength of 20 khz is 1.7 cm so I can decrease the frequency and thus increase the wavelength and increase the penetration what do you say ?
We would need the make, model and technical specifications of these transducers that are designed for use as sensors.
Without accurate knowledge of beam pattern and initial intensity I don't see how we could even start devising an experiment such as I suggested.
High frequency is attenuated by a smaller depth of material. However, if you decrease the frequency from 20 kHz it will no longer be ultrasound.
You could use a super tweeter!
P.S. May I ask how you determined the target figure of 1 watt/cm^2?
Without accurate knowledge of beam pattern and initial intensity I don't see how we could even start devising an experiment such as I suggested.
High frequency is attenuated by a smaller depth of material. However, if you decrease the frequency from 20 kHz it will no longer be ultrasound.
You could use a super tweeter!
P.S. May I ask how you determined the target figure of 1 watt/cm^2?
@Galu the transducers they have in the laboratory are the classic ones used for proximity sensors, they do not have a legible brand, they cost a few euro cents and in any case they are not effective because they have very little power. but this information is useless because it is known that such small transducers do not penetrate. but what if more powerful 20 khz transducers are used instead? you still aren't answering my question and that is, how can I overcome the acoustic impedance and make the ultrasound penetrate into the ground?
That's the crux of the problem - too many what ifs!
I made an attempt at answering that question back in post #29.
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This is not a door that opens and closes. You seem to be trying to fix something that you haven't yet confirmed is a problem.
@AllenB @Galu Anyway I'll tell you about my idea, I've studied this case a lot, and I believe that impedance is a big problem. but I thought that I can use two beams, one of 15000 khz and the other of 15100 khz. The values are random, but if they meet, they interfere and produce an addition wave of 30100 khz, therefore ultrasound. I use frequencies of 15000 khz because they penetrate more easily, what do you think? Obviously not necessarily 15000 but also other values
When two waves of slightly different frequencies interfere with each other, the result is a wave of a frequency that is the average of the two. This wave fluctuates in amplitude, or 'beats', with a difference frequency called the beat frequency.
If they were audible sound waves then we would hear an average frequency that gets louder and softer (warbles) at the beat frequency.
The beat frequency onstructed is also lower in frequency than the "carriers", which seems opposite to the hoped effect. You could create a phased array of drivers but then you're probably entertaining fundamental drive frequencies lower in the audible band at annoyingly high and potentially dangerous levels. We still haven't talked about how long this thing needs to be on and in one spot. ?
Of course, we do. And abstract is missing since then ...
Yes, and with enough SPL, humans (and other creatures) may also be able to hear the 'carrier' itself, at 15kHz.
It is quite possible that they might intermodulate due to the non-linear properties of the medium (soil).
https://en.wikipedia.org/wiki/Nonlinear_acoustics
https://en.wikipedia.org/wiki/Nonlinear_acoustics
Yes, it is.. but at what modulation index? Besides, what would it take to make it happen precisely at the needed depth and not before?
I don't believe OP should be pursuing such a complicated plan. I suspect it would be much better to approach it simply. Perhaps beam as much as necessary at the problem and identify issues with measurement.. then correct.
I don't believe OP should be pursuing such a complicated plan. I suspect it would be much better to approach it simply. Perhaps beam as much as necessary at the problem and identify issues with measurement.. then correct.
Since the two given ultrasounds would first distort on their own and then make beat frequencies of all the distortion components, the total energy would be shared amongst the very many sum and difference frequencies, making it difficult to predict exactly how much of the total energy would fall at the desired fundamental difference beat. Besides, the soil properties could also change after some time, due to the churning / compacting effect of the incident beam(s).
EDIT: And this is the energy that reaches the plant, after all the losses and attenuation take place,
Agreed, and it maybe easier to bury the transducer in the soil, as mentioned by Galu, N Brock etc. or alternatively beam a strong ultrasound at the required location, in good faith.
I don't know what it means, I was talking about that if 2 waves of slightly different frequencies interfere, two more waves with addition and subtraction frequencies are created