Electricity: magnetically operated switches – magnets – and electr – Magnets and electromagnets – With magneto-mechanical motive device
Reexamination Certificate
2001-06-27
2003-07-29
Donovan, Lincoln (Department: 2832)
Electricity: magnetically operated switches, magnets, and electr
Magnets and electromagnets
With magneto-mechanical motive device
C335S302000
Reexamination Certificate
active
06600400
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to electromagnetic electro-acoustic transducers for generating an incoming indicator tone such as in mobile phones.
BACKGROUND OF THE INVENTION
Referring to
FIG. 5
, a description will be given on a conventional electromagnetic electro-acoustic transducer.
FIG. 5
(
a
) is a top view and
FIG. 5
(
b
) is a cross-sectional view.
The conventional electromagnetic electro-acoustic transducer comprises a first diaphragm
100
, a second diaphragm
101
being a magnetic material attached on the center of the first diaphragm
100
, a center pole
103
disposed opposite the second diaphragm
101
, a coil
104
wound around the center pole
103
, a ring-shaped resin magnet
105
positioned on the outer periphery of the coil
104
, a yoke
106
in contact with or integrated with the center pole
103
, and a cylindrical housing
107
that circumferentially supports the first diaphragm
100
. A description will be given on the operation of an electromagnetic electro-acoustic transducer of the above configuration. In the initial state when no current is flowing in the coil
104
, a magnetic circuit is formed by the resin magnet
105
, second diaphragm
101
, center pole
103
, and yoke
106
, and the second diaphragm
101
is attracted toward the resin magnet
105
and the center pole
103
. Thereby the first diaphragm
100
is displaced to a position that balances with its elastic force.
Next, when an alternating current flows in the coil
104
, an alternating magnetic field is generated by the magnetic circuit where the coil
104
works as a magnetomotive force. The magnetic flux density within the magnetic circuit is determined by the intensity of the alternating magnetic field and the magnetic resistance inside the magnetic circuit. In this case, the magnetic resistance is approximately equal to the combined resistance of the magnetic resistance due to the magnetic gap between the second diaphragm
101
and the center pole
103
, the magnetic resistance due to a magnetic gap between the second diaphragm
101
and the resin magnet
105
, and the magnetic resistance of the resin magnet
105
itself. The specific magnetic permeability of the resin magnet
105
is as low as that of the air and is approximately equal to
1
, so that the magnetic resistance is high.
An alternating driving force is generated on the second diaphragm
101
due to a change in the magnetic flux density. As a result, the second diaphragm
101
moves from the initial position together with the attached first diaphragm
100
due to a static attraction force generated by the resin magnet
105
and a change in the alternating driving force generated by an alternating current. And its vibration radiates a sound.
The above-mentioned resin magnet
105
is a composite material consisting of a hard ferrite magnetic material, a polyamide resin such as nylon
6
, nylon
12
, and low molecular weight rubber. That is, the resin magnet
105
in the conventional transducer uses a composite material of a hard magnetic material and a resin.
By the way, as electromagnetic electro-acoustic transducers are used in mobile phones and the like, their small size and a high sound pressure are required for their alternating driving force. Accordingly, the acuteness of resonance, Q-factor of the mechanical resonant system consisting of the first diaphragm
100
and the second diaphragm
101
is made high, and the lowest resonant frequency of the mechanical resonant system are made close to the regeneration acoustic frequency.
Also, while the lowest resonant frequency of the mechanical resonant system is determined by the effective masses of the first diaphragm
100
and the second diaphragm
101
and the stiffness of the first diaphragm
100
, the stiffness of the first diaphragm
100
is not only affected by the modulus of elasticity and thickness of the material used but also by the configuration of deformation due to the static attraction force by the resin magnet
105
and the center pole
103
.
The conventional electromagnetic electro-acoustic transducer as described above suffered a problem of resolving the complicated situation as described below in order to obtain an electromagnetic electro-acoustic transducer with a desired characteristic.
(1) In order to change the lowest resonant frequency of the mechanical system depending on the regenerated acoustic frequency, it is necessary to change the effective mass and stiffness of the mechanical resonant system. In doing this, it is necessary to change the thickness of the first diaphragm
100
and the thickness and diameter of the second diaphragm
101
, or to change the magnetic gap between the second diaphragm
101
and the center pole
103
in order to change the static attraction force. Such changes in the thickness and diameter of the second diaphragm
101
will result in changes in the magnetic resistance and in various interacting mechanical parameters including effective mass and vibration mode the regeneration acoustic frequency. Consequently such a design change to get a desired characteristic become complicated.
(2) As the acuteness of resonance, Q-factor of the mechanical resonant system is high, the ratio of contribution of the lowest resonant frequency to sound pressure is extremely high, making sound pressure variation due to a slight change in a magnetic gap or in the thickness of the diaphragm large.
However, in order to make the acuteness of resonance, Q-factor low, although lightening of the mass of the vibratory system or an increase in the driving force (force coefficient) is necessary, lightening of the mass of the vibratory system makes the volume of the second diaphragm
101
, being a magnetic material, small and will result in an increase in the magnetic saturation and magnetic resistance thus resulting in a decrease in the force coefficient.
Also, in order to increase the force coefficient, it is necessary to increase either direct current magnetic flux density or alternating current magnetic flux density; and in order to increase the direct current magnetic flux, it is necessary to increase energy of the magnet or upsize the diaphragms thus leading to upsizing of the total size or an increase in the mass of the vibratory system.
Although it is necessary to decrease the magnetic resistance in order to increase the alternating current magnetic flux, it is difficult as the magnetic permeability of conventional resin magnet
105
is low. There is other approach such as making the magnetic gaps small but it makes vibration amplitude of the diaphragms small.
DISCLOSURE OF THE INVENTION
The present invention resolves the above-described problems and provides an electromagnetic electro-acoustic transducer in which the cost is low, the lowest resonant frequency of the mechanical system is variable, and variation of sound pressure at high sound pressures is narrow.
A first embodiment of the present invention comprises a first diaphragm, a second diaphragm attached at the center of the first diaphragm and consisting of a magnetic material smaller than the first diaphragm, a center pole provided underneath the center
6
f the second diaphragm with a magnetic gap in between, a coil wound around the outer periphery of the center pole, a ring-shaped resin magnet, and a yoke disposed in a manner such that it comes in contact with the lower parts of the center pole. Here, the magnetic powder of said resin magnet consists of powders of a hard magnetic material and a soft magnetic material, the magnetic flux density and the magnetic permeability can be controlled by changing their compounding ratio, so that lowest resonant frequency and the high sound pressure can be set very easily.
A second embodiment of the present invention is one in which the magnetic powder orientation of the resin magnet of the first embodiment is aligned by injection molding in magnetic field. Magnetic energy is enhanced when magnetizing the hard magnetic material in the resin magnet, -thereby obtaining a resin magnet with a high magnetic flux densi
Andou Kimihiro
Enomoto Mitsutaka
Minaga Katsuhiko
Saiki Shuji
Suzumura Masaki
Donovan Lincoln
Matsushita Electric - Industrial Co., Ltd.
McDermott & Will & Emery
Rojas Bernard
LandOfFree
Electromagnetic electro-acoustic transducer does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Electromagnetic electro-acoustic transducer, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Electromagnetic electro-acoustic transducer will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3008695