Homemade ultrasonic transducer

With the help of this magnetostrictive ultrasonic emitter, you can conduct visual experiments on water spraying, engraving thin metal (aluminum), engraving glass, observe Chladni figures on a plate, etc. On this topic, there is a book that is freely available under the authorship of Mayer "Simple Experiments with Ultrasound", there is also a description of how to make such an emitter and how it works.

The basis of the emitter is a ferrite rod, which can be taken from old radio receivers with LW-MW reception ranges

The length of the ferrite rod is about 8 cm, but you can use another length, for example, 10 cm. The diameter of the ferrite is 8 mm, there are also larger diameters, but I have not tested the work with them. It is the rod that oscillates, compressing and expanding in the coil field, so at the ends of the rod there will be oscillations with a large amplitude at the ultrasound frequency. This is called magnetostriction

For magnetization you will need a magnet from speakers or from a microwave oven magnetron, small neodymium magnets will not work. Without a magnet, the emitter will work poorly. The coil has a frame with a diameter of 17 mm and a length of 6 cm, contains 90 turns of 0.8 mm wire, wound in two layers. The ferrite is inserted into the coil frame in the middle, the gap between the ferrite and the frame is filled with cotton wool on both sides, there is no cotton wool in the middle of the frame. After sealing, the cotton wool must be soaked in glue such. The working part of the rod protrudes from the frame by about 2 cm

In two plastic covers, holes must be made into which the coil frame is inserted and in order to observe the ferrite from below, its installation in the middle

I glued all this stuff and the magnetostrictive emitter is ready

The length of the emitter is 10 cm

A rectangular signal from a frequency-adjustable generator must be fed to the gate of a field-effect transistor, which functions as a key. The amplitude of the generator's oscillations is set at 8 volts (with a swing), although the transistor allows a lower voltage to be fed to the gate. By changing the frequency on the generator, resonance of the ultrasonic emitter is achieved, then the oscillation power of the ferrite will be the greatest. The generator should not be made too powerful, otherwise the ferrite may break from powerful oscillations. The transistor is mounted on a radiator

When the emitter resonates, a drop of water on its end instantly evaporates or splashes, creating a mist of water. You can take a transparent tube and place a metal ball in it, this ball will bounce off the end of the rod