KR101432539B1 - Device for filtering acoustic wave - Google Patents

Abstract

The present invention includes a first filtering plate; and a second filtering plate which is separated from the first filtering plate. The resonance range of the first filtering plate and the second filtering plate are determined in the first frequency range of the parametric arrangement of a filtering object which is the rate of the thickness and the width of the first filtering plate and the second filtering plate, respectively. Therefore, the present invention implements a device for filtering an acoustic wave to improve the measurement accuracy of difference frequency.

Description

TECHNICAL FIELD [0001] The present invention relates to an acoustic filtering apparatus,

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an acoustic filtering apparatus, and more particularly, to an acoustic filtering apparatus that improves measurement precision of a difference frequency generated by using a parametric arrangement.

Underwater sonar is commonly used in sound navigation and ranging systems for the purposes of object detection, mapping, submarine ground detection, and underwater communication in undersea environments. These sonar systems detect objects in high resolution, It is preferable to use a high-directivity sound wave in order to minimize the distortion caused by the transmission of the sound wave by the multi-path.

The directivity of the sound wave generally increases as the driving frequency is high or the size of the sound source is large. However, when a high frequency band is used to generate a high directional sound wave, the transmission distance of the sound wave is limited because the high frequency has a high attenuation rate, and the increase in the size of the sound source has physical and cost limitations.

Therefore, a parametric arrangement is used as a method for generating a low-frequency, high-directivity sound wave. The parametric array is a sound source using a nonlinear property of the medium and capable of generating high-directivity sound waves even in a small sound source. The two high-frequency (high-frequency) (fd = f1-f2) is generated as a secondary frequency due to the non-linearity of the medium, and the directivity of the difference frequency fd is very high.

The difference frequency (fd) generated by the parametric arrangement is a high directivity low frequency wave, which can transmit sound waves up to several tens of kilometers. However, in a relatively short distance environment such as a water tank, the high frequencies are not sufficiently attenuated, so that it is difficult to precisely measure the difference frequency.

FIG. 1 is a schematic view showing the use of an acoustic filter used for eliminating high frequencies in an acoustic measurement experiment using a parametric arrangement. The acoustic experiment generally involves transmitting sound waves in the transducer 21 and receiving sound waves in the hydrophone 31. [ At this time, the sound pressure of the primary frequency is 40 ~ 80dB larger than the sound pressure of the difference frequency.

That is, since the sound pressure difference between the primary frequency and the differential frequency is large, it is difficult to precisely measure the difference frequency in the hydrophone 31. [ In addition, there is a problem in that, due to the non-linearity of the hydrophone 31 in addition to the difference frequency generated in the parametric arrangement, a sound wave of a difference frequency is generated and distortion occurs.

Also, in the conventional acoustic filter, the frequency range in which the primary frequency is removed by the damping principle is limited. That is, if only the damping principle is used, the filtering coefficient depending on the frequency is determined according to the material constituting the filter, so that the frequency range in which the filter can be filtered is limited.

V. F. Humphrey, "The Measurement of Acoustic Properties of Limited Size Panels by Use of a Parametric Source ", Journal of sound and vibrarion. 98 (1), 1985. pp. 67-81

An embodiment of the present invention is created to solve the above-described problems. The present invention provides a method of filtering a difference frequency by a parametric arrangement, filtering a sound wave and a primary frequency caused by nonlinearity of a transmission unit, And to provide an improved acoustic filtering apparatus.

In one embodiment of the present invention, a first filtering plate; And a second filtering plate spaced apart from the first filtering plate; Wherein the first filtering plate and the second filtering plate are each determined to have a range in which the first filtering plate and the second filtering plate resonate in a first frequency band of a parametric arrangement in which a ratio of a thickness and a width is to be filtered And an acoustic filtering device.

The ratio of the thickness to the width may be determined in a range where the first filtering plate and the second filtering plate resonate when the first frequency of the parametric arrangement is incident in the thickness direction.

At this time, the ratio of the thickness to the width may be 20 or more.

And as another embodiment of the present invention, a reverberation plate disposed between the first filtering plate and the second filtering plate to reduce reverberation.

At this time, the thickness of the reverberation absorption plate can be determined within a range in which the decay rate determined according to the thickness does not remove the difference frequency generated by the parametric arrangement.

The reverberation absorption plate may be provided in surface contact with the first filtering plate and the second filtering plate, respectively.

According to an embodiment of the present invention, in the first frequency band, the first filtering plate and the second filtering plate are resonated to eliminate the first frequency and pass the difference frequency, thereby improving the measurement accuracy of the difference frequency.

According to an embodiment of the present invention, the ratio of the thicknesses and the widths of the first filtering plate and the second filtering plate is determined in a range where the first filtering plate and the second filtering plate resonate in the first frequency band, Can be filtered.

According to an embodiment of the present invention, the reverberation absorbing plate is provided between the first filtering plate and the second filtering plate to eliminate the reverberation generated by the two plates, thereby preventing the difference frequency from being distorted.

1 is a schematic view of an acoustic measurement experiment by a parametric arrangement using a conventional acoustic filter,
FIG. 2 is a schematic view showing transmission waves and reflected waves of a sound wave incident on an acoustic filtering apparatus according to an embodiment of the present invention,
3 is a perspective view of an acoustic filtering apparatus according to an embodiment of the present invention,
Figure 4 is a side view of the embodiment shown in Figure 3,
FIG. 5 is a schematic diagram of an acoustic measurement experiment by a parametric arrangement using one embodiment of FIG. 3;
FIG. 6 is a graph showing acoustic test results measured in the experimental environment of FIG. 5 and simulation results using MATLAB.

3 is a perspective view of an acoustic filtering apparatus according to an embodiment of the present invention. FIG. 4 is a cross-sectional view of an acoustic filtering apparatus according to an embodiment of the present invention. 3 is a side view of the embodiment shown in Fig. 2 to 4, an acoustic filtering apparatus according to an embodiment of the present invention will be described in detail.

When the acoustic filtering apparatus 100 according to the embodiment of the present invention is installed between the first medium 50 as shown in FIG. 2, the incident wave is reflected by the reflected wave by the embodiment of the present invention, It is divided into waves. At this time, the thickness L of the acoustic filtering device 100 can be determined so that the primary frequency of the parametric arrangement is reflected and the difference frequency generated by the parametric arrangement is transmitted.

As shown in FIG. 2, if there is an acoustic filtering apparatus 100, which is another medium, between the same first medium 50, the transmission coefficient T of the sound wave passing through the medium can be expressed by Equation (1) . Where ρ is the density, c is the sonic velocity, and k is the wave number.

[Equation 1]

When the ratio of the thickness L to the length of the acoustic filtering device 100 is 20 or more and the sound wave is incident in the thickness direction of the acoustic filtering device 100, the sound velocity C of the sound wave is expressed by Equation (2) . Where E is the Young's modulus, σ is the poisson's ratio, and ρ is the density of the material.

&Quot; (2) "

In order to reduce the distortion due to the primary frequency in the measurement of the difference frequency by the parametric arrangement, the transmission coefficient T must be low in the first frequency band, so that the minimum value of the transmission coefficient is included in the first frequency band. The thickness (L) of the substrate can be calculated and designed. A value satisfying these conditions can be expressed by the following equation (3).

&Quot; (3) "

One embodiment of the present invention, which may be designed in the manner described above, specifically includes a first filtering plate 111, a second filtering plate 112, a reverberation plate 121, and a fastening bolt 130.

The first filtering plate 111 and the second filtering plate 112 filter the sound waves generated due to the primary frequency and the non-linearity of the transmitting unit. Specifically, the first filtering plate 111 and the second filtering plate 112 are formed in the same shape and are formed in a square shape. However, the shapes of the first and second filtering plates 111 and 112 do not have to be the same and may be any shape symmetrical with respect to the center of the sound source in the axial direction. For example, the first and second filtering plates 111 and 112 may be circular or regular polygonal.

의 값을 25로 결정하여 해당 1차주파수에서 공진하도록 설계할 수 있다. The first filtering plate 111 is determined as a value resonating within a frequency band where the ratio of the thickness l1 and the width x1 is used as the primary frequency of the parametric arrangement. For example, when the primary frequency to be removed by the first filtering plate 111 is 100 kHz to 110 kHz

Is set to 25 so that it can be designed to resonate at the corresponding primary frequency.

Similarly to the first filtering plate 111, the second filtering plate 112 is also determined to have a resonance value in a frequency band where the ratio of the thickness and the width is used as the primary frequency of the parametric arrangement.

The first filtering plate 111 and the second filtering plate 112 may be formed of a metal material. For example, the first and second filtering plates 111 and 112 are made of aluminum. Each of the first filtering plate 111 and the second filtering plate 112 is formed with one through hole at each corner thereof so that the fastening bolt 130 is inserted. However, the materials of the first and second filtering plates 111 and 112 are not limited thereto. Also, the first filtering plate 111 and the second filtering plate 112 may be formed of different materials as long as the above-described equations (1) to (3) are satisfied.

The width x2 of the reverberation absorption plate 121 is smaller than that of the first and second filtering plates 111 and 112 and the thickness of the reverberation absorption plate 121 is larger than that of the first and second filtering plates 111 and 112 do. The reverberation absorption plate 121 absorbs reverberations that may occur when the first filtering plate 111 and the second filtering plate 112 are separated from each other and stacked. In addition, the reverberation absorption plate 121 is laminated so as to be concentric with the first filtering plate 111 and the second filtering plate 112, so that the reverberation can be uniformly absorbed. The reverberation absorption plate 121 may be made of an elastic material, for example, a rubber material. However, the material of the reverberation absorbing plate 121 is not limited thereto, and unlike the present embodiment, the reverberation absorbing plate 121 may not be provided if the reverberation of the transmission coefficient is small.

The fastening bolts 130 are inserted into the through holes formed in the first filtering plate 111 and the second filtering plate 112 and fastened to the nuts (not shown) to form the first filtering plate 111 and the second filtering plate 112 are fixed to each other and the reverberation absorption plate 121 provided therebetween is also fixed. The reverberation absorbing plate 121 is in contact with the first filtering plate 111 in close contact with the second filtering plate 112 and is fixed to the other surface of the reverberation absorbing plate 121 in tight contact with the fastening bolt 130. The fastening bolt 130 may be fixed by a nut (not shown), or any well-known fastening bolt may be used.

FIG. 5 is a schematic view of an acoustic measurement experiment using a parametric arrangement according to an embodiment of FIG. 3, and FIG. 6 is a graph showing acoustic measurement results measured in the experimental environment of FIG. 5 and simulation results using a MATLAB.

First, water is contained in the semi-anisotropic water tank 400 and a tone burst signal is generated using the signal generator 210. The generated signal is amplified using a power amplifier, and the amplified signal is input to a sound source 220 and sent to the hydrophone 320. The sound waves generated in the sound source 220 are propagated by the medium, water, and input to the hydrophone 320 through the embodiment 100 of the present invention. The input signal can be observed with the oscilloscope 310. The transmission coefficient of the embodiment 100 of the present invention is shown in FIG. 6 by a solid line graph 510 and the transmission coefficient simulated by using Equations 1 and 2 is represented by a one-dot chain line graph 520 ).

Referring to FIG. 6, it can be confirmed that the result of the experiment of the embodiment 100 of the present invention is similar to the simulation result.

As described above, those skilled in the art will understand that the present invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. Therefore, it should be understood that the above-described embodiments are to be considered in all respects as illustrative and not restrictive. The scope of the present invention is defined by the appended claims, rather than the detailed description, and all changes or modifications derived from the meaning and scope of the claims and equivalents of the claims are to be construed as being included within the scope of the present invention do.

1: Test plate 10: Conventional acoustic filter
20: Sound Transmitter 21: Transducer
30: Acoustic receiving device 31: Hydrophone
50: First medium 100: Acoustic filtering device
111, 112: first and second filtering plates 121: reverberation absorption plate
130: fastening bolt L: thickness of acoustic filtering device
l1: thickness of first and second filtering plates l2: thickness of reverberation absorption plate
x1: width of first and second filtering plates x2: width of reverberation plate
200: sound transmitting device 210: signal generator
220: sound source 300: sound transmitting device
310: Oscilloscope 320: Hydrophone
400: Deodorant tank
510: Graph measured using one embodiment of the present invention
520: Graph simulated with MATLAB

Claims (6)

A first filtering plate; And
And a second filtering plate spaced apart from the first filtering plate,
Wherein the first filtering plate and the second filtering plate are determined in a range in which the first filtering plate and the second filtering plate resonate in a first frequency band of a parametric arrangement in which a ratio of a thickness and a width is a filtering object, Acoustic filtering device. The method according to claim 1,
Wherein the ratio of the thickness to the width is determined in a range where the first filtering plate and the second filtering plate resonate when the first frequency of the parametric arrangement is incident in the thickness direction. The method according to claim 1,
Wherein the ratio of the thickness to the width is 20 or more. The method according to claim 1,
And a reverberation plate disposed between the first filtering plate and the second filtering plate to reduce reverberation. 5. The method of claim 4,
Wherein the thickness of the reverberation absorption plate is determined within a range in which the attenuation factor determined according to the thickness does not remove the difference frequency generated by the parametric arrangement. 5. The method of claim 4,
And the reverberation absorption plate is in surface contact with the first filtering plate and the second filtering plate, respectively.

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