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[Industrial field of application] In the present invention, a coil is inserted in the magnetic gap of a
magnetic circuit, such as an electrodynamic speaker, an electrodynamic microphone, etc., and an
oscillating current is flowed through the coil to make the coil or the magnetic circuit. The present
invention relates to an improvement of a magnetic circuit used for an electro-mechanical
vibration converter which induces an oscillating current in a coil by mechanically vibrating or
mechanically vibrating a coil or a magnetic circuit. [Prior Art] An example of an electrodynamic
speaker, which is an example of a conventional electro-mechanical vibration converter, is shown
in FIGS. In FIG. 6, 1 is a top plate, 2 is a magnet, 3 is a pole piece, 4 is a back plate, and a ringshaped gap is formed between the pole piece 3 and the top plate 1. The magnetic flux from the
magnet 2 forms a magnetic circuit that flows with the back plate 4, the pole piece 3, the ringshaped gap, and the top plate 1, and the ring-shaped gap is a magnetic gap. When a coil is
inserted into this magnetic gap and an alternating current flows through it, a driving force is
generated between the coil and the magnetic flux of the magnetic gap, the coil vibrates according
to the waveform of the alternating current, and this vibration is transmitted to the diaphragm
And propagate in the air as sound waves. In this magnetic circuit, Pg in FIG. 6 is the permeance
of the magnetic gap, Pf, Pf2. Pf、。 Pfol、Pfo2. Pf4. P R indicates the
permeance of the leakage flux generated outside the magnetic gear / b. Therefore, the total
permeance PT is Pi = Pg + 2Pf ++ pf2 + pf3 + pfo ++ Pfoz + Pf4 + PR, and the leakage coefficient
.sigma. Of this magnetic circuit is represented by .sigma. = Pt / Pg. Leakage magnetic flux Pf1-P1
can be said to be a magnetic circuit with high efficiency, so that the smaller the leakage magnetic
flux Pf1-P1, the leakage coefficient .sigma. In order to reduce the leakage coefficient σ, the
magnetic circuit of FIGS. 7 and 8 is proposed. The magnetic circuit of FIG. 7 has a magnet 6
magnetized in the direction opposite to the magnet 2 attached to the back of the back plate 4.
This magnetic circuit pushes back the leakage flux Pf of FIG. 6 coming out of the back plate 4 to
the back plate 4 by the repulsion by the magnetic flux of the reverse polarity of the magnet 2,
thereby reducing the leakage flux Pft. The magnetic circuit of FIG. 8 further comprises a
magnetic shield cap 7 fitted to the magnetic circuit of FIG. This magnetic shielding cap 7 has a
leakage flux Pf shown in FIG.
1. The PF 02 is short-circuited between the back plate 4 and the top plate 1 to lead it into the
magnetic circuit to contain the leakage flux. [Problems to be Solved by the Invention] Although
the magnetic circuit shown in FIGS. 7 and 8 can reduce the leakage flux to reduce the leakage
coefficient, it is necessary to assemble the magnet 6 of the opposite polarity. Therefore, there is a
disadvantage that the repulsion makes the work remarkably difficult and remagnetization in case
of failure can not be made. Furthermore, in addition to the expensive parts such as the magnet 6
and the magnetic cap 7, the cost of the operation is increased due to the difficulty of the
operation. SUMMARY OF THE INVENTION The present invention is intended to solve the abovementioned problems in a conventional magnetic circuit for an electro-mechanical vibration
converter, focusing on the fact that the superconducting material has a diamagnetic effect, and a
room-temperature superconducting material has recently been used. In view of the tendency to
be developed, it is an object of the present invention to prevent leakage flux from a magnetic
circuit by its diamagnetic property, to efficiently converge the magnetic flux to a magnetic gap,
and to provide a high efficiency, low leakage magnetic circuit. [Summary of the Invention] In
order to achieve the above object, the present invention covers at least a portion of a dynamic
magnetic circuit having a magnetic gap in which a coil is inserted, at least a portion where
leakage flux is generated, with a room temperature superconducting material. As the abstract.
magnetic circuit for a speaker according to the present invention will be described below with
reference to FIG. In the figure, 1 is a top plate, 2 is a magnet, 3 is a pole piece, 4 is a back plate,
and a magnetic gap for inserting a voice coil is formed between the pole piece 3 and the top plate
1 Is the same as the external magnet type magnetic circuit of the conventional electrodynamic
speaker. And, the leakage fluxes Pf, Pf2. Pf3. Pfo +, Pfoz, PF3. The portion where the pH is
generated is coated with a substance 5 exhibiting a superconducting phenomenon at normal
temperature. As a substance exhibiting a superconductivity phenomenon at this normal
temperature, a substance having an oxygen deficient probsquite structure is promising as an
oxide ceramic mainly composed of barium, strontium, yttrium and copper. This material is a form
of oxide ceramics in which the proportion of barium is replaced by strontium in an oxide ceramic
having a ratio of 2 barium, 1 yttrium, and 3 copper which exhibits a stable superconductivity
phenomenon at around -180 ° C. The electrical resistance became almost zero at ° C. A
superconducting substance exhibits perfect diamagnetism (Meissner effect) when placed in a
magnetic field below its critical magnetic field, and is not permeable to magnetic flux, but at the
same time tries to push back the magnetic flux from the magnetic circuit in the opposite
direction. .
That is, in the present embodiment, the magnetic flux to be leaked acts to flow forcibly through
the yoke below the saturation magnetic flux density of the yokes of the top plate 1, the back
plate 4 and the like. Therefore, no leakage flux is generated from the portion covered with the
room temperature superconducting material 5, and the leakage flux is converged to the magnetic
gap, and a magnetic gap of high magnetic flux density can be obtained. This indicates that it is
possible to miniaturize the magnetic circuit when it is not necessary to increase the magnetic flux
density of the magnetic gap. FIGS. 2 to 5 show the respective embodiments of the present
invention when the configuration of the magnetic circuit is changed, and in any of them, the
portion where the leakage flux is generated is covered with the room temperature
superconducting material 5 The effect is the same as in the previous embodiment. In the figure,
reference numeral 8 denotes a yoke. In each of the above embodiments, only the portion where
the leakage magnetic flux is generated is covered with the room temperature superconducting
material 5, but the entire magnetic circuit other than the magnetic gap may be covered.
Furthermore, the present invention can also be used for the magnetic circuit of an
electrodynamic vibration transducer such as a microphone other than a speaker and a pickup.
[Effects of the Invention] As described above, the present invention can prevent leakage flux from
coming out of the magnetic circuit of the electric-mechanical vibration converter, so when used
in an appliance using a Braun tube such as a television, color shift, Polarization, distortion of the
image, etc. can be prevented, and a correct image can be secured. In addition, since the leakage
coefficient can be lowered and the magnetic flux density of the magnetic gap is increased, the
driving force of the coil or the electromotive force by the coil vibration can be increased, and the
electromechanical vibration converter such as a speaker or a microphone It is possible to
increase the efficiency. Furthermore, when it is not necessary to increase the magnetic flux
density of the magnetic gap, it is effective to obtain a small and inexpensive magnetic circuit.
Brief description of the drawings
FIG. 1 is a cross-sectional view of one embodiment of the present invention, FIGS. 2 to 5 are
cross-sectional views of other embodiments, and FIGS. 6 to 8 are cross-sectional views of a
conventional magnetic circuit.
1 top plate 2 magnet 3 pole piece 4 back plate 5 room temperature superconducting substance
Patent applicant Pioneer Corporation 60th 80th
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