CN2662214Y - Wideband acoustic impedance measuring device - Google Patents

Abstract

The utility model discloses a measuring device for measuring the broad band acoustic impedance of the silencer, the flexible take over and the sound insulating material. The utility model comprises a fore and a back measuring housing, wherein, the back housing is a cross-section variable housing. The tested piece is arranged between the fore and the back housing. An exciting board is arranged on the top of the fore measuring housing, a measuring accelerometer is arranged on the exciting board. A vibration excitor is arranged on the top of the exciting board; a vibration exciting rod is connected between the exciting board and the vibration excitor; a hydrophone housing is arranged on the wall of each of the fore and back measuring housing, and the two hydrophone housing are communicated with the relative measuring housing separately, and each hydrophone housing is provided with a hydrophone inside. The broad band acoustic impedance measuring device has a long back measuring housing where the hydrophone is arranged, and also can enable the measurement under the high frequency.

Description

Broadband acoustic impedance measurement device

(1) technical field

The utility model relates to a kind of acoustic impedance measurement device.Specifically, be the broadband acoustic impedance measurement device that is used to measure sound suppressor, flexibility connection pipe and sound insulating material acoustic impedance.

(2) background technology

The acoustic impedance of sound suppressor, flexibility connection pipe and sound insulating material is a basic parameter in the ship acoustics design, and it can reflect acoustics components and parts and properties of materials objectively.According to acoustic impedance, can carry out quantitative forecast and design to the pipe system of boats and ships and the acoustical behavior of sound insulating material.

Acoustic impedance is divided into the input acoustic impedance and transmits acoustic impedance, and they are defined as respectively:

$Z_{11}=\frac{p_1}{V_1}{|}_{{\mathrm{<figure-callout\; id="2"\; label="V"\; filenames="Y20032012038300072.png"\; state="\{\{state\}\}">V</figure-callout>}}_2=0},Z_{12}=\frac{p_2}{V_1}{|}_{{\mathrm{<figure-callout\; id="2"\; label="V"\; filenames="Y20032012038300072.png"\; state="\{\{state\}\}">V</figure-callout>}}_2=0}$

In the formula, p ₁, p ₂Be respectively the input and output acoustic pressure, V ₁, V ₂Be respectively the input and output side volumetric velocity.

Traditional acoustic impedance measurement device as shown in Figure 1, it contains forward and backward measurement chamber, the bore in this forward and backward measurement chamber equates and is straight barrel shape that promptly the cross section of its each point is identical.Inserted between the forward and backward measurement chamber with bore by side components and parts or sound insulating material.Upper end, preceding measurement chamber is the sealing shape and is fixed with excitation plate, and the thickness of this excitation plate and material design according to survey frequency decides.The vibration survey accelerometer is installed above the excitation plate, and disposes vibrator, be connected to exciting rod between excitation plate and vibrator; On the chamber wall in forward and backward measurement chamber the nautical receiving set chamber is arranged all, this two nautical receiving sets chamber is communicated with corresponding measurement chamber respectively, in each nautical receiving set chamber nautical receiving set is arranged all.During measurement, produce plane sound wave by vibrator after by exciting rod effect excitation plate in preceding measurement chamber, the part of this plane sound wave is measured the chamber by being imported into the back by side components and parts or sound insulating material.According to the propagation principle of sound wave in the pipe, can derive following acoustic impedance expression formula:

$Z_{11}=\frac{{\tilde{H}}_1\cos {\mathrm{kL}}_1-\frac{i{\mathrm{\&rho;}}_0{c}_0}{s_1}\sin k(L_1-x_1)}{\cos k(L_1-x_1)-i{\tilde{H}}_1\frac{s_1}{{\mathrm{\&rho;}}_0{\mathrm{<figure-callout\; id="0"\; label="c"\; filenames="Y20032012038300072.png"\; state="\{\{state\}\}">c</figure-callout>}}_0}\sin {\mathrm{kL}}_1}$

$Z_{12}=\frac{{\tilde{H}}_2\cos {\mathrm{kx}}_1\cos {\mathrm{kL}}_2}{[\cos k(L_1-x_1)-i{\tilde{H}}_1\frac{s_1}{{\mathrm{\&rho;}}_0{\mathrm{<figure-callout\; id="0"\; label="c"\; filenames="Y20032012038300072.png"\; state="\{\{state\}\}">c</figure-callout>}}_0}\sin {\mathrm{kL}}_1]\cos k(L_2-x_3)}$

In the formula:

Be transport function; L ₁, L ₂Be respectively the length in forward and backward measurement chamber; x ₁, x ₃It is respectively the installation site of nautical receiving set; ρ ₀, c ₀Be respectively the water-mass density and the velocity of sound.By measuring the transport function of excitation plate acceleration and forward and backward measurement chamber nautical receiving set signal

With Can calculate by the input acoustic impedance of side components and parts or sound insulating material and output acoustic impedance.

According to the definition of acoustic impedance, the particle vibration velocity that requires the measured piece rear end is zero, and perhaps acoustic impedance is tending towards infinitely great.But actual acoustic impedance measurement device can not satisfy this ideal conditions.During actual measurement, the acoustic impedance that requires the measured piece rear end than the big 20dB of characteristic impedance of acoustic medium promptly approximate think satisfy measuring condition.Measuring the chamber end in the back is under the situation of desirable rigid boundary, and the acoustic impedance of measured piece rear end is:

$Z_b=-i\frac{{\mathrm{\&rho;}}_0{\mathrm{<figure-callout\; id="0"\; label="c"\; filenames="Y20032012038300072.png"\; state="\{\{state\}\}">c</figure-callout>}}_0\mathrm{ctg}{\mathrm{kL}}_2}{s_1}$

By following formula as seen, cavity length is measured in the back increases (or survey frequency increase), and then measured piece rear end acoustic impedance reduces.For satisfying above-mentioned measurement requirement, kL ₂Should be less than or equal to 0.1, corresponding measurement lower limit frequency is determined by following formula:

$f<\frac{{0.1\mathrm{<figure-callout\; id="0"\; label="c"\; filenames="Y20032012038300072.png"\; state="\{\{state\}\}">c</figure-callout>}}_0}{2\mathrm{\&pi;}{\mathrm{<figure-callout\; id="2"\; label="L"\; filenames="Y20032012038300072.png"\; state="\{\{state\}\}">L</figure-callout>}}_2}$

In the formula, measure cavity length L if get the back ₂Be 0.05m, then measure upper limiting frequency and be approximately 500Hz.If require survey frequency to bring up to 1000Hz, then the length in back measurement chamber can only be got 0.025m, and nautical receiving set can't be installed in Duan back measurement chamber like this, and acoustic impedance measurement is difficult to realize.

(3) summary of the invention

The purpose of this utility model is to provide a kind of broadband acoustic impedance measurement device.This broadband acoustic impedance measurement device, it is longer to measure cavity length thereafter, and nautical receiving set can be installed, or can realize acoustic impedance measurement under upper frequency.

Above-mentioned purpose of the present utility model is realized by following technical solution:

Broadband acoustic impedance measurement device of the present utility model comprises forward and backward measurement chamber, and forward and backward measurement is connected to by the side part between the chamber.There is excitation plate the preceding upper end, chamber of measuring, and the measurement accelerometer is installed on the excitation plate.Vibrator is arranged at excitation plate top, is connected to exciting rod between excitation plate and vibrator.On the chamber wall in forward and backward measurement chamber the nautical receiving set chamber is arranged all, this two nautical receiving sets chamber is communicated with corresponding measurement chamber respectively, in each nautical receiving set chamber nautical receiving set is arranged all.Its design feature is that measurement chamber, said back is that the variable cross section formula is measured the chamber.The epimere diameter in chamber is measured greater than hypomere in the back.The nautical receiving set chamber that the back is measured on the wall of chamber, chamber is on the chamber wall of measurement chamber, back hypomere.

Adopt such scheme, have the following advantages:

Because broadband acoustic impedance measurement device of the present utility model, measuring the chamber thereafter is that the variable cross section formula is measured the chamber, and its epimere is greater than hypomere.Utilize the acoustic impedance enlarge-effect of varying cross-section duct to improve the acoustic impedance of measured piece rear end, thereby enlarged the survey frequency scope, improved measuring accuracy.

Again because the chamber is measured in the back is that the variable cross section formula is measured the chamber, and the diameter of its epimere makes its total length increase greater than hypomere.So, under the requirement of same frequency range and measuring accuracy, solved the problem that nautical receiving set can't be installed because measurement cavity length in back is too short.

(4) description of drawings

Fig. 1 is traditional acoustic impedance measurement apparatus structure synoptic diagram;

Fig. 2 is a broadband acoustic impedance measurement apparatus structure synoptic diagram of the present utility model;

Fig. 3 is that variable cross section compares s ₂/ s ₁Get 2 and different kl ₁, kl ₂Z ' during value _bWith Z _bThe ratio change curve;

Fig. 4 is that variable cross section compares s ₂/ s ₁Get 3 and different kl ₁, kl ₂Z ' during value _bWith Z _bThe ratio change curve.

(5) embodiment

As shown in Figure 2, broadband acoustic impedance measurement device of the present utility model is measured chamber 6 before containing and chamber 10 is measured in the back, and this forward and backward measurement chamber is cylindric.Wherein, the two ends in preceding measurement chamber 6 are uncovered, and the upper end in measurement chamber 10, back is uncovered, the lower end is closed and promptly is desirable rigid boundary.Before measure 6 upper ends, chamber and be fixed with excitation plate 4, be connected mutually by O-ring seal 5 and securing member 13 between this excitation plate and 6 upper ends, preceding measurement chamber, measurement accelerometer 3 is installed above it.Vibrator 1 is arranged on the excitation plate 4, and this vibrator is implemented excitation by 2 pairs of excitation plate of exciting rod 4.Be arranged between forward and backward measurement chamber 6 and 10 by side part 9, the upper end Joint in chamber 10 is measured at its two ends respectively with the lower end in preceding measurement chamber 6 and back.On forward and backward measurement chamber 6 and 10 the chamber wall respectively design nautical receiving set chamber 8 and 11 are arranged, this two nautical receiving sets chamber is communicated with upper and lower measurement chamber 6 and 10 respectively, is separately installed with nautical receiving set 7 and 12 in it.Chamber 10 epimeres are measured greater than hypomere in said back, measure the chamber thereby make it form the variable cross section formula.Wherein, the nautical receiving set chamber 11 on the 10 chamber walls of back measurement chamber is arranged on the chamber wall of measurement chamber, back 10 hypomeres.

Suppose that it is desirable rigid boundary that 10 lower ends, chamber are measured in the back, then behind the amplification of variable cross section to acoustic impedance, the acoustic impedance of measured piece 9 rear ends is provided by following formula:

$Z_b^{\&prime;}=-\frac{{\mathrm{i\&rho;}}_0{c}_0}{s_1}\mathrm{ctgk}{l}_1\frac{\frac{s_2}{s_1}-\mathrm{tgk}{l}_1\mathrm{<figure-callout\; id="2"\; label="tgk\; l"\; filenames="Y20032012038300072.png"\; state="\{\{state\}\}">tgk</figure-callout>}{l}_{}{}_2}{1+\frac{s_2}{s_1\mathrm{ctg}{\mathrm{kl}}_1\mathrm{<figure-callout\; id="2"\; label="tgk\; l"\; filenames="Y20032012038300072.png"\; state="\{\{state\}\}">tgk</figure-callout>}{l}_{}{}_2}}$

In the formula: s ₁, s ₂, l ₁, l ₂Be respectively the back and measure chamber 10 upper and lower two sections sectional area and length.Fig. 3 and Fig. 4 have shown that variable cross section compares s ₂/ s ₁Get 2 and 3 and different kl ₁, kl ₂The acoustic impedance Z ' of measured piece 9 rear ends during value _bWith Z _bRatio calculation result.By Fig. 3 and Fig. 4 as seen, measure under the certain situation of chamber 10 length in the back, the variation in cross section can make Z ' _bCompare Z _bIncrease by 1.5～3 times.So, under same measuring accuracy required, survey frequency just can improve 1.5～3 times.In other words, in same survey frequency scope, can improve measuring accuracy, also can make originally to be achieved because of the too short problem that nautical receiving set 12 can't be installed in measurement chamber 10, back.

Wherein, the back is measured the length and the actual of section ratio in 10 upper and lower sections in chamber and is chosen, and determines according to concrete measurement requirement.When chamber 10 variable cross sections were measured in the back, the computing formula of its input acoustic impedance was constant, and the computing formula of transmitting acoustic impedance is:

$Z_{12}=\frac{\cos {\mathrm{kx}}_1[\cos {\mathrm{kl}}_1{\cos \mathrm{kl}}_2-\frac{s_2}{s_1}\sin {\mathrm{kl}}_1{\sin \mathrm{kl}}_2]{\tilde{H}}_2}{\cos k(l_2-x_3)[\cos k(L_1-x_1)-i{\tilde{H}}_1\frac{s_1}{{\mathrm{\&rho;}}_0{\mathrm{<figure-callout\; id="0"\; label="c"\; filenames="Y20032012038300072.png"\; state="\{\{state\}\}">c</figure-callout>}}_0}\sin {\mathrm{kL}}_1]}$

Claims (3)

1. broadband acoustic impedance measurement device comprises forward and backward measurement chamber (6 and 10), is connected to by side part (9) between forward and backward measurement chamber (6 and 10); There is excitation plate (4) the preceding upper end, chamber (6) of measuring, is equipped with on the excitation plate (4) and measures accelerometer (3); Vibrator (1) is arranged at excitation plate (4) top, is connected to exciting rod (2) between excitation plate (4) and vibrator (1); Nautical receiving set chamber (8 or 11) is all arranged on the chamber wall in forward and backward measurement chamber (6 and 10), and this two nautical receiving sets chamber is communicated with corresponding measurement chamber respectively, and nautical receiving set (7 or 12) is all arranged in each nautical receiving set chamber; It is characterized in that it is that the variable cross section formula is measured the chamber that chamber (10) is measured in said back.

2. broadband acoustic impedance measurement device according to claim 1, the epimere diameter that it is characterized in that measurement chamber, back (10) is greater than hypomere.

3. broadband acoustic impedance measurement device according to claim 2 is characterized in that the nautical receiving set chamber (11) that the back is measured on the wall of chamber, chamber (10) is on the chamber wall of measurement chamber (10), back hypomere.

Images