Magnetostrictive Speakers

In simple terms, magnetostrictive speakers derive from a magetostrictive property. This is a general property of ferromagnetic materials that causes them to change their shape or dimensions during the process of magnetization. The variation of the materials’s magnetization is due to the applied magnetic field changes of the magnetostrictive strain.

Eventually, it reaches its saturation value, which is λ. The magnetostrictive effect is responsible for the low-pitched humming sound perceived by the human ear. Transformers typically generate this sound with their noises. As a result, this effect causes energy loss due to frictional heating in susceptible ferromagnetic cores. It was first discovered by observing a sample of iron.

The Physics Behind Magnetostrictive Speakers

Magnetostrictive transducers are based on the principle that iron-rich materials can contract and expand within a magnetic field. The thin metal plates pile up, creating a ferromagnetic core. The ferromagnetic core is wrapped around with copper wire and placed inside a canister. When electrical current runs through the copper coil, it creates a magnetic field. In turn, this generates a complete change of the core’s shape. When you turn off the electrical current, the coil returns immediately to its original shape. In sum, the contraction and expansion of the magnetic field help generate ultrasonic waves.

Outstanding Characteristics of Magnetostrictive Speakers

Magnetostrictive speakers are quite resistant. In addition, because they use iron-based metals within their construction, there tends to be no degradation over the course of time. Nickel is a common metal in these types of transducers. The diaphragms used with magnetostrictive transducers are usually very thick, which eliminates the risk of cavitation erosion wear-through. Although magnetostrictive speakers have a high mass, they tend to have limited use, since they can only create frequencies that range between 22Hz and 30kHz. Their energy generation process is quite efficient because it involves three main steps of energy conversion: electric energy to magnetic energy to mechanical energy.

If you’re interested…

A good exercise would be for you to compare this type of speakers to the magnetostatic ones. They are both based on magnets, but each of their results is different.