JPH06165283A - Acoustic transducer - Google Patents

Abstract

PURPOSE:To provide the low frequency acoustic transducer able to be used at a deep depth by making the size of the transducer small and the weight light and adopting an inner and outer pressure balance structure for a drive section of a magnetic fluid. CONSTITUTION:The transducer is provided with an outer shell 1 of a rigid body of a cylinder whose both ends are open, a bag 2 having water-tightness and air-tightness and accommodated in the outer shell 1, two sets of support metallic fixtures 6 stretching the inside of the bag 2 to form an air-tight chamber between the outer shell 1 and the bag 2, a drive electromagnet comprising a core 4 and a coil 5 fixed in the inside of the bag 2 and a magnetic fluid 3 packed in the inside of the bag 2.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION This invention relates to low frequency acoustic transducers for use in deep water.

[0002]

2. Description of the Related Art A typical example of a conventional underwater acoustic transducer is a Langevin type transducer,
Alternatively, there are known bending shell type transducers such as a flextensional type and a ring shell type devised in order to solve the problems of the Langevin type transducer.

[0003]

However, the conventional Langevin type transducer has a problem that the size and weight increase with respect to low frequencies.

Further, the bending shell type transducer devised to solve the problems of the Langevin type transducer can be reduced in size and weight as compared with the Langevin type transducer, but due to its structure, it has a hydrostatic pressure. Weak and problematic in deep use.

An object of the present invention is to provide a low frequency acoustic transducer which can be used even at a deep depth by reducing the size and weight of the transducer and using a magnetic fluid drive unit as an internal / external pressure balance structure.

[0006]

According to the present invention, a cylindrical rigid outer shell whose both ends are open, a watertight and airtight bag which is housed inside the outer shell, and From two sets of support fittings that expand from the inside of the bag to form an airtight chamber between the outer shell and the bag, a driving electromagnet fixed inside the bag, and a magnetic fluid filled inside the bag. An acoustic transducer characterized by the following is obtained.

[0007]

Embodiments of the present invention will be described in detail below with reference to the drawings.

As shown in FIGS. 1 and 2, an acoustic transducer as an embodiment of the present invention includes an outer shell 1, a bag 2, a magnetic fluid 3, a core 4, a coil 5, a support metal 6, a compressed gas 7, It is composed of an airtight stopper 8 and a pair of terminals 9.

Here, the outer shell 1 is formed of a cylindrical rigid body made of a non-magnetic material with both ends open. Bag 2
Has watertightness and airtightness, and is fixed to both inner ends of the outer shell 1. Further, both end surfaces of the bag 2 form acoustic emission surfaces 10. The magnetic fluid 3 is filled inside the bag 2.

The electromagnet composed of the core 4 and the coil 5 is fixed inside the bag 2 by two sets of support fittings 6 made of a non-magnetic material. These two sets of support fittings 6
Also has a role of fixing the bag 2 to both inner ends of the outer shell 1 by sandwiching it.

A compressed gas 7 such as air or helium is enclosed between the outer shell 1 and the bag 2. The airtight stopper 8 has a role of closing the opening of the outer shell 1 provided for enclosing the compressed gas 7. A pair of terminals 9
Are pierced through the outer shell 1 and the bag 2 and connected to both ends of the coil 5, respectively.

By the way, a hydrostatic pressure Fw as shown in FIG. 3 acts on the acoustic radiation surface 10 of the bag 2 of the acoustic transducer in water.

Therefore, in order to balance the hydrostatic pressure Fw and the internal pressure of the acoustic transducer, the pressure FG1 of the compressed gas 7 enclosed between the outer shell 1 and the bag 2 is changed to the hydraulic pressure at the working depth of the acoustic transducer. Adjust the pressure to match.

The acoustic transducer of the present embodiment constructed as described above operates as follows. In FIG. 4, a changeover switch S for changing the type of power supply used
When W is connected to the switching terminal A side, the core 4
A constant voltage (DC signal) is applied to the electromagnet including the coil 5 and a predetermined magnetic force is generated in the electromagnet.
As a result, the magnetic fluid 3 filled in the bag 2 is
A predetermined force FM is drawn to both ends of the electromagnet. As a result, the acoustic radiation surface 10 of the bag 2 is + in FIG.
Displace to the side to obtain the bias displacement.

The pressure FG2 in FIG. 4 is the pressure of the compressed gas 7 when this bias displacement is obtained. Next, FIG.
In, when the changeover switch SW is changed over to the changeover terminal B side, an AC signal is superimposed on the DC signal, and the acoustic radiation surface 10 of the bag 2 vibrates in accordance with this AC signal.

The displacement of the acoustic radiation surface 10 described above is shown in the form of a graph in FIG.

At point a in FIG. 3, when an AC signal is applied to the electromagnet without bias displacement, even if the polarity of this electromagnet is reversed, the generated driving force will have a magnitude of the magnetic force regardless of the polarity. Therefore, the displacement of the sound emitting surface 10 is
Only in the + direction.

Therefore, by giving a bias displacement amount x at point b in FIG. 5 and superimposing an AC signal on it at point c, this AC signal also has only a strong and weak magnetic force.
It can be converted as a displacement of the acoustic radiation surface 10.

In the above embodiment, the compressed gas 7 has a constant pressure according to the depth of use. However, the pressure of the compressed gas 7 is not constant, for example, the airtight plug 8 is
A pressure correction device capable of adjusting the atmospheric pressure according to the depth of use may be attached so that the pressure can be freely changed from shallow depth to deep depth.

[0020]

According to the present invention, since magnetic fluid having a lower acoustic velocity than conventional materials such as metal and ceramics is used, the transducer can be made smaller and lighter, and its driving portion can be formed inside and outside. Since it has a pressure balance structure, it is possible to provide a low-frequency acoustic transducer that can be used even in deep depth.

[Brief description of drawings]

FIG. 1 is a longitudinal cross-sectional view of an acoustic transducer according to an embodiment of the present invention.

FIG. 2 is a radial cross-sectional view of the acoustic transducer of the embodiment of the present invention.

FIG. 3 is an operation principle diagram showing a force relationship when there is no driving force in water of the acoustic transducer of the embodiment of the present invention.

FIG. 4 is a schematic diagram showing the operating principle of the acoustic transducer of the embodiment of the present invention in a state where a bias displacement is applied in water.

FIG. 5 is a diagram showing the relationship between the displacement amount of the acoustic radiation surface and the bias displacement in the acoustic transducer of the embodiment of the present invention.

[Explanation of symbols]

 1 Outer shell 2 Bag 3 Magnetic fluid 4 Core 5 Coil 6 Supporting metal 7 Compressed gas 8 Airtight plug 9 Terminal 10 Acoustic emission surface

Claims (2)

[Claims] 1. An outer shell body of a cylindrical rigid body whose both ends are open,
A watertight and airtight bag that is housed inside the outer shell, two sets of support fittings that are expanded from the inside of the bag to form an airtight chamber between the outer shell and the bag, and the bag An acoustic transducer comprising a driving electromagnet fixed inside and a magnetic fluid filled inside the bag. 2. The acoustic transducer according to claim 1, further comprising a pressure compensator capable of automatically adjusting the pressure of the air chamber formed between the outer shell and the bag according to the depth of use.