Electrical audio signal processing systems and devices – Electro-acoustic audio transducer – Electromagnetic
Reexamination Certificate
2001-11-07
2003-12-02
Nguyen, Lee (Department: 2682)
Electrical audio signal processing systems and devices
Electro-acoustic audio transducer
Electromagnetic
C381S396000, C340S388100
Reexamination Certificate
active
06658133
ABSTRACT:
This Application is a U.S. National Phase Application of PCT International Application PCT/JP00/03083.
1. Technical Field
The present invention relates to an electroacoustic transducer for use in a portable communication device, e.g., a cellular phone or a pager, for reproducing an alarm sound, a melody, or an audio sound voice, responsive to an incoming call.
2. Background Art
FIGS. 18A and 18B
show a plan view and a cross-sectional view, respectively, of a conventional electroacoustic transducer
200
of an electromagnetic type (hereinafter referred to as an “electromagnetic transducer”). The conventional electromagnetic transducer
200
includes a cylindrical housing
107
and a disk-shaped yoke
106
disposed so as to cover the bottom face of the housing
107
. A center pole
103
, which may form an integral part of the yoke
106
, is provided in a central portion of the yoke
106
. A coil
104
is wound around the center pole
103
. Spaced from the outer periphery of the coil
104
is provided an annular magnet
105
, with an appropriate interspace maintained between the coil
104
and the inner periphery of the annular magnet
105
around the entire circumference thereof. The outer peripheral surface of the magnet
105
is abutted to the inner peripheral surface of the housing
107
. An upper end of the housing
107
supports a first diaphragm
100
which is made of a non-magnetic disk so that an appropriate interspace exists between the first diaphragm
100
and the magnet
105
, the coil
104
, and the center pole
103
. In a central portion of the first diaphragm
100
, a second diaphragm
101
which is made of a magnetic disk is provided so as to be concentric with the first diaphragm
100
.
Now, the operation and effects of the above-described conventional electromagnetic transducer
200
will be described. In an initial state where no current flows through the coil
104
, a magnetic path is formed by the magnet
105
, the second diaphragm
101
, the center pole
103
, and the yoke
106
. As a result, the second diaphragm
101
is attracted toward the magnet
105
and the center pole
103
, up to a point of equilibrium with the elastic force of the first diaphragm
100
. If an alternating current flows through the coil
104
in this state, an alternating magnetic field is generated in the aforementioned magnetic path, so that a driving force is generated on the second diaphragm
101
. Such driving force generated on the second diaphragm
101
causes the second diaphragm
101
to vibrate from its initial state, along with the fixed first diaphragm
100
, due to an interaction with a attraction force which is generated by the magnet
105
. This vibration transmits a sound.
A resonance frequency of the electromagnetic transducer
200
having the above-described structure depends on the deformation of the first diaphragm
100
in a state where the elastic force of the first diaphragm
100
and the attraction force which is generated on the second diaphragm
101
by the magnet
105
are at equilibrium.
FIG. 19
illustrates the relationship between a force-displacement curve of the first diaphragm
100
and the attraction force generated on the second diaphragm
101
by the magnet
105
. The vertical axis of the graph represents the force, whereas the horizontal axis of the graph represents the displacement of the first diaphragm
100
. As shown in
FIG. 19
, the force-displacement curve of the first diaphragm
100
and the attraction force curve (generated by the magnet
105
on the second diaphragm
101
) intersect each other at an intersection A. In other words, the intersection A shows a point at which the elastic force and the static attraction are at equilibrium. The resonance frequency is determined by the elastic constant of the first diaphragm
100
at the intersection A.
In order to decrease the resonance frequency, it is necessary to increase the mass of the vibrating system (i.e., the first diaphragm
100
and the second diaphragm
101
) or decrease the elastic constant of the vibrating system. However, it is undesirable to increase the mass of the vibrating system because it results in a decrease in the efficiency of the electromagnetic transducer
200
. On the other hand, decreasing the elastic constant of the vibrating system too far would produce a force-displacement characteristic curve shown by the broken line in
FIG. 19
, which does not intersect the attraction force curve (generated on the second diaphragm
101
by the magnet
105
). As a result, the second diaphragm
101
will be attracted, along with the first diaphragm
100
, onto a magnetic circuit without establishing equilibrium at any position.
In other words, since the elastic constant must be kept within a range such that the elastic constant curve intersects the attraction force curve, there is a lower design limit to the resonance frequency. Although it becomes possible to decrease the elastic constant by decreasing the attraction force as well, this results in a decrease in the generated driving force, so that a sufficient reproduced sound pressure level cannot be obtained.
DISCLOSURE OF THE INVENTION
An electromagnetic transducer according to the present invention includes: a first diaphragm disposed so as to be capable of vibration; a second diaphragm disposed in a central portion of the first diaphragm, the second diaphragm being made of a magnetic material; a yoke disposed so as to oppose the first diaphragm; a center pole disposed between the yoke and the first diaphragm; a coil disposed so as to surround the center pole; a first magnet disposed so as to surround the coil; and a second magnet disposed on an opposite side of the first diaphragm from the center pole.
In one embodiment of the invention, the electromagnetic transducer further includes: a first housing for supporting the first diaphragm; and a second housing in which the second magnet is disposed.
In another embodiment of the invention, the second magnet has a disk shape.
In still another embodiment of the invention, the second magnet has an annular shape.
In still another embodiment of the invention, an outer diameter of the second magnet is equal to or smaller than an outer diameter of the second diaphragm in the case of the second magnet having a disk shape.
In still another embodiment of the invention, an outer diameter of the second magnet is equal to or greater than an outer diameter of the second diaphragm in the case of the second magnet having an annular shape.
In still another embodiment of the invention, the electromagnetic transducer further includes a third magnet in a central portion of at least one face of the first diaphragm or the second diaphragm.
In still another embodiment of the invention, the second magnet is magnetized in the same direction as the first magnet.
In still another embodiment of the invention, the second magnet is magnetized along a radial direction with respect to an axis through a center of the center pole.
In still another embodiment of the invention, the second diaphragm has a thickness which allows a magnetic saturation to occur when the second diaphragm is deflected toward the center pole by a predetermined distance.
In still another embodiment of the invention, the first diaphragm is made of a magnetic material.
In still another embodiment of the invention, the first diaphragm is made of a non-magnetic material.
In still another embodiment of the invention, the electromagnetic transducer further includes a first magnetic plate provided between the first magnet and the first diaphragm.
In still another embodiment of the invention, the first magnetic plate has an annular shape.
In still another embodiment of the invention, the electromagnetic transducer further includes a second magnetic plate disposed on the second magnet.
In still another embodiment of the invention, the second magnetic plate has a disk shape.
In still another embodiment of the invention, the second magnetic plate has an annular shape.
In still another embodiment of the invention, the first diaphragm is shaped s
Saiki Shuji
Usuki Sawako
Nguyen Lee
RatnerPrestia
LandOfFree
Electromagnetic transducer and portable communicating device 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 transducer and portable communicating device, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Electromagnetic transducer and portable communicating device will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3097093