How to make a magnetostrictive emitter and conduct experiments with ultrasound

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magnetostrictive emitter

Using this simple and simple device called a magnetostrictive emitter, you can conduct various experiments with ultrasound: make a low-power ultrasonic engraver, spray water, etc. You can learn these experiments from Mayer’s book “Simple Experiments with Ultrasound”. The essence is simple: a ferrite core of the emitter at frequencies of tens of kHz, it begins to oscillate with these frequencies. We do not see or hear these oscillations, but they exist. If you drop water on the end of the ferrite, the water will instantly turn into fog. Glue a sharp nail to the end of the ferrite and get a low-power ultrasonic engraver. They can make inscriptions on a thin sheet of aluminum.

What we need. We need a round magnet that can be obtained from a speaker or a faulty magnetron from a microwave oven. We also need a ferrite rod from a radio magnetic antenna for the emitter. These can be found in old radios such as Vega 141 and others. I used a rod with a diameter of 8 mm and 8 cm long. In fact, the length and diameter of the rod are not particularly critical (8-12 cm or slightly different sizes), only the resonant frequency of the emitter will change.

On a thick paper frame with an inner diameter of approximately 17 mm, it is necessary to wind 90 turns of wire with a diameter of 0.6 mm, in several layers. The length of the frame is 5 cm.

Then we fix the ferrite rod in the frame as shown in the photo. The ferrite is installed exactly in the middle of the frame and is held with cotton wool, which is impregnated with glue to stiffen it.

The ferrite coil must be installed in the middle of the round magnet at a small distance from it. I set this distance using two plastic caps.

The emitter itself will still have to be tuned to the best performance together with the generator, so all that has been said is just the basis. The adjustment consists in setting such a distance between the magnet and the ferrite, at which there will be the most powerful vibrations of the ferrite.

The key is assembled on an IRL3103 field-effect transistor mounted on a radiator. Other suitable field-effect transistors can also be used.

So, when everything is assembled, it’s time to set up the whole thing and check it in operation. We apply a rectangular signal to the key gate through a resistor with a frequency of about 35 kHz (this is with my ferrite dimensions) and an amplitude of 10.5 Volts. Set the voltage to 14 Volts on the power source. We install a blade on the end of the ferrite and begin to change the frequency of the signal on the generator. When there are the most powerful vibrations of the blade, then there will be a resonance of the emitter

Now we drop a drop of water on the end of the ferrite and again slightly adjust the frequency and at resonance a drop of water is sprayed. For more powerful oscillations, increase the voltage of the power source to 16 Volts. this must be remembered.

Install a metal ball with a tube on the end of the ferrite. During the oscillation of the rod, the ball in the tube will jump.