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■ Directive air acoustic transformer for ultrasonic waves ◎ Japanese Patent Application No. 453881 [Phase] Application No. 45 (1970) January 16 @ inventor Fukuda Naomi Machida
Shigefahara-cho 100 Applicants International Electric Co., Ltd. Tokyo Minato-ku Shibishi Kubo
Sakuragawacho 9 ■ 代理人 Attorney Attorney Toshio Shiramizu 1 outside
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of an embodiment of an
ultrasonic directed air acoustic transformer according to the present invention, and FIGS. 2 and 3
are side views of another embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION The present invention is directed to an air
microphone or speaker with high efficiency or high sensitivity and excellent directivity for
ultrasound. In the conventional ultrasonic airborne microphones (one used in air for an
underwater microphone is referred to as an airborne microphone), the alignment is generally a
diaphragm to improve the acoustic transmission efficiency between the diaphragm and air. The
characteristic impedance ρC (ρ is the density of the diaphragm material and C is the speed of
sound propagation in it) due to the material of the material is extremely low and transmission
efficiency is extremely low. For this reason, it is common to use an acoustic transformer such as a
wrapper attached to a diaphragm as a countermeasure for improvement. In order to reduce the
directivity angle in order to improve the directivity of the microphone, it is effective to increase
the thickness of the diaphragm vibrating in the same phase or to use a wrapper, but as ultrasonic
waves, When using several tens of KHz, the dimensions of the diaphragm become too large
compared to the wavelength, making it difficult to perform the same phase oscillation, and there
are various limitations such as the dimensions of the wrapper can not be made too large. It is
also practical to use a reflector, but it is a drawback that it is troublesome in production
[111111]. Next, when the ultrasonic aerial microphone is used for distance measurement etc.,
excellent distance resolution can be obtained unless the duration of the pulse wave of the emitted
ultrasonic wave and the received pulse wave, ie, the pulse width is not shortened as much as
possible. The measurement can not be made accurately. This is related to the damping
characteristics of the speaker and microphone. If these damping characteristics are not
improved, the rise of the pulse wave is bad and it takes time to reach steady vibration. It will be
too much. For this reason, in general, the Q of the speaker or the microphone is lowered (for
example, several tens or less), while lowering the Q brings with it the disadvantage that the
sensitivity is degraded. The present invention overcomes these drawbacks and realizes a
microphone and a speaker with good directivity, high efficiency and high sensitivity, which will
be described in detail with reference to the drawings. FIG. 1 is a block diagram of one
embodiment of the ultrasonic air acoustic transformer according to the present invention, where
a is a cross sectional view and b is a front view. In the figure, A is a disk-type electrostrictive
vibrator using a thin electrostrictive material for causing vibration in a radial mode (radial
direction), and its characteristic characteristic impedance is ocooco. Such a disk vibrator vibrates
at any of thickness vibration (high frequency, a few hundred KHz) and radial mode vibration (low
frequency, for example 10, TG (z), among which radials resonating at low frequencies. Use mode
B and C are also disks, but B has a smaller ρC than the electrostrictive vibrator (hereinafter
referred to as a transducer) A (ρC of the B disk is ρ, cl). And a disk made of a material that
lowers the Q of the ABC composite, for example, a plastic with a small value of ρC, a light weight
and a large loss, ie, nylon, whose thickness tB is that of the oscillator A to cause thickness
vibration. With respect to the resonance frequency fA, the speed of sound in B is set to a value
close to 1/4 wavelength. Also, the diameter DB is made equal to or larger than the diameter DA
of the transducer A. In the latter case, there is a limit to performing [111111] EndPage: 1 with
the same phase oscillation in the radiation plane 1. Next, for the C disk, ρC is thicker than the
oscillator A (ρC of the C disk is ρ2C2), and a material with a high Q, for example, a mild steel
disk, is used. And the diameter Dc is made equal to DA to facilitate processing. Thus, the vibration
as a whole of the combined vibrator consisting of A, B and C, that is, the acoustic transformer
becomes an axial thickness vibration regulated by the radial vibration of the vibrator disc A. As
an actual structure of the acoustic transformer according to the present invention, both surfaces
2 and 3 of the vibrator A are formed by electrode plating or the like, and the lead wires 4 and 5
are drawn from the both electrodes to vibrate the disks B and C. It is bonded to the child A to
form a composite resonator. If a voltage of synthetic resonance frequency is applied from the
lead wires 4 and 5, a speaker having 1 as a radiation surface becomes a speaker, and conversely,
a high performance microphone as an ultrasonic detection microphone of a resonance frequency
received from the surface 1 can get. The thickness of the B and C disks is adjusted so that the
resonance frequency of this composite resonator is a frequency close to the resonance frequency
fh of the radial mode of only the vibrator A. For example, fA = 42 KHz In the case, the combined
resonant frequency was about 50 KHz. In addition, the surface of the ultrasonic wave is only the
surface 1 of the eight disks, and in order to prevent the radiation from the surface 6 of the C disk
from interfering with the radiation from the surface 1, Although a sound absorber is arranged, it
is omitted in the drawing. Here, the characteristics of the acoustic transformer of the present
invention will be described. First, since the resonance frequencies of the three vibrators of A, B
and C are similar, the composite resonator is easily vibrated and the amplitude becomes large.
The sensitivity is good for both transmission and reception. The radiation efficiency at the
radiation surface (or received wave) 1 of B is 関係 □ C, where the characteristic characteristic
impedance relationship is ρ. C。 Therefore, the radiation efficiency is significantly better than
when using the electrostrictive oscillator A as a single unit (this is easily confirmed by
experiments, but has a low impedance, so the matching with the air as the radiation medium is
improved. It is the biggest advantage that is).
Since the Q of the disk B is low, even if the Q of the disk C is high, the Q of the ABC composite
vibrator is low, the damping is completed, the rise of the vibration is fast, and the disappearance
of the vibration is also fast. Since the disk C has a high Q, the internal loss is small [111111] and
its ρ 2 G 2 is ρ of the oscillator A. Since the value is larger than co, the amount of radiation of
reactive acoustic energy in the direction of C is smaller than in the case of the transducer A
alone. As for the diameter of the radiation surface 1 of the disc B, the resonant frequency of the
disc resonator is inversely proportional to rV / に 対 し て with respect to its radius r1 density ρ.
Therefore, the diameter of the eight disks can be increased to such an extent that the equal phase
vibration condition of the radiation surface is not lost, so that the directivity is improved. In
addition, since a large combined transducer can be used at such a ratio of frequencies and
transmission efficiency is good, power larger than that of the conventional one can be sent in,
and a good S wave can be obtained as an ultrasonic wave transmission / reception system. There
are many outstanding advantages such as practical use. FIG. 2 is a side view of another
embodiment of the present invention, A. FIG. B and C are the same as those in FIG. 1, but the
radiation angle is made narrower than that in FIG. FIG. 3 is a side view of still another
embodiment of the present invention, in which A, B and C are the same as FIG. On the contrary,
as a countermeasure for the case where the directivity shown in FIG. 1 is too good, it is used to
widen only the directivity without losing its advantage. In the above, the case where the 8-disc is
a synthetic resin and the C-disc is a metal has been described, but it is also used when both the B
and C discs are synthetic resins, in which case the conversion efficiency is somewhat reduced.
The synthetic Q is further lowered to provide a feature that transient damping is improved.
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