Electrodynamic head with nanodispersed magnetic fluid

The proposed invention relates to sound reproducing equipment and can be used in the manufacture of electrodynamic loudspeakers.

Electrodynamic heads are widely known (Ephrussi M.M. Loudspeakers and their use. M .: Energiya, 1971, p. 11), containing the core forms a working gap with one of the flanges.

Electrodynamic head with nanodispersed magnetic fluid consists of three main parts (Fig. 1.): magnetic system 1, movable system 2 and diffuser holder 3. The movable system of the electrodynamic head includes a diffuser 4, a voice coil 5, a centering washer 6, a dust cap 7 …

The magnetic system consists (Fig.2) of a permanent magnet 8, an upper flange 9, a lower flange 10, a core 11.

The upper flange 9 and the core 11 form a working gap 12 filled with nanodispersed magnetic fluid 13. A voice coil 5 is placed in the working gap 12. An annular groove 14 is made on the surface of the core 11, spaced from the end of the core at a distance equal to the width of the upper flange 9, in the groove a short-circuited ring 15 is placed, made of a material with high electrical conductivity, for example copper, while the cross-sectional shape of the ring 15 coincides with the cross-sectional shape of the annular groove 14 of the core 11.

The edges of the core 11 and the upper flange 9, located in the area of ​​the working gap 12, are rounded. The surfaces of the core 11 and the upper flange 9, in contact with the nanodispersed magnetic fluid 13, have a nonmagnetic electrically conductive coating 16. The outer surface of the electrically conductive ring 15 is located on the same level with the surface of the nonmagnetic electrically conductive coating 16 of the core 11. The surfaces of the parts forming the inner cavity of the magnetic system 17 of the core 11, the lower flange 10, the permanent magnet 8, the upper flange 9, have an electrically conductive coating 18.

The study of the magnetic field in the gap of the magnetic system of the dynamic head showed that near the surface of the core 11 and the upper flange 9 there are zones of increased magnetic field strength (figure 3), located in the region of the edges of the parts. In these zones, the magnetic field strength can significantly exceed the field strength in the gap 12 of the magnetic system.

These zones are the places where the nanodispersed magnetic fluid 13 does not withstand internal overvoltages and collapses over time. The disadvantages of this dynamic head are low sound quality, reliability and resource. So in the work (stereo.ru Dynamic heads) it is noted that the use of colloidal solutions or suspensions of ferromagnetic particles limits the service life of the head due to a significant increase in their viscosity over time. Filling the gap of the magnetic system of the dynamic head with suspension does not provide stable time characteristics of the dynamic head.

Suspension is a coarsely dispersed system with a solid dispersed phase and a liquid dispersion medium.

Particles of the dispersed phase are large (more than 10 microns) and settle over time under the action of gravity (sediment). In magnetic suspensions, solid particles are made of magnetic materials. The density of magnetic materials is several times higher than the density of the used dispersion media; therefore, even during storage under normal conditions, such suspensions are unstable and quickly stratify.

Placing magnetic suspensions in a magnetic field only intensifies this process, and there is no need to talk about the stability of the characteristics of technical devices with magnetic suspensions, including dynamic heads.

Source: patent RU 2 399 165 C1