5/7/2023 0 Comments Simple math acoustic![]() However, It turns out that this is not the case. Initially I thought that the transducers would have to be a set distance apart so that they would constructively interfere to double the output power. You can see that on my setup, the screw has a pitch of 1 mm so roughly 4 turns causes 180 degree phase shift between the transmitted signal and the received signal. This means that the levitation zones are spaced out by roughly 5 mm. The wavelength of the sound can be calculated by λ = c / ν, which is ~0.9 cm for a 40 kHz wave travelling at 340 m/s. ![]() To test the setup you can connect one of the transducers to act as a speaker, and the other to act as a microphone which can viewed on the oscilloscope. The jig can be 3D printed and transducers glued on with hot glue.Īs you can see the wiring it pretty simple and there is no need to worry about the polarity of the transducers here as I will explain in the next section. It turns out that this has very little effect but it did make for some nice results. I designed a 3-piece jig to hold the speakers and change their separation by turning the center screw. To double the power you can use two speakers facing each other. ![]() This will turn the 40KHz 5V signal into a 40kHz 18V signal which can then power the transducers. It is possible to power the speakers straight from a digital IO pin however the 5V amplitude does not generate much power, so I would recommend using a step up converter module to generate 18V and power a mosfet driver IC such as the TC4427. If not then you can simply use an arduino. If you have a signal generator then set it to the resonance frequency and crank up the amplitude as high as it goes. Next we need a way to generate the 40kHz signal to power the speakers. If you want more power then you can buy higher quality transducers from farnell, I measured them to have twice the acoustic power. These speakers are quartz crystals which usually resonates at 40 kHz, and the cheapest place I found to get them is to desolder them from cheap HC-SR04 range finder modules, but you can also buy them directly. Luckily these can be found pretty cheap as they are used for range finder applications. Therefore these frequencies are typically in the ultrasound region(< 20 kHz), so we need a special speaker to generate the sound. The frequency of sound used to levitate objects must be high enough so that the object doesn't fall out of the levitation zone (also called pressure node) during a single cycle of the wave.
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