SU1550414A1 - Device for measuring coefficient of reflection of sound from plates - Google Patents

Abstract

This invention relates to technical acoustics and can be used to control the quality of panels and partitions. The aim of the invention is to improve the accuracy of control in the case of oblique incidence of sound on a plate due to the expansion of the region of interference of the incident and reflected waves. The device contains two sound receivers in the form of flat antennas installed in the same plane and rigidly fixed on the axis of the vrash mechanism. In this case, one of the antennas is installed in front of the plate under study, and the second is outside this plate. Electronic components are connected to the antennas, the outputs of which are connected to the inputs of the subtracting unit. A continuous or pulsed electrical signal is supplied to the emitter, which irradiates the plate under study. The acoustic signal is recorded by two antennas. Since the first antenna is placed in front of the plate, the acoustic field at its location is made up of incident and reflected waves. The second antenna is located in a free field and therefore it measures only the incident sound wave. By subtracting the signals from both antennas, the value of the reflected wave is obtained, from which the reflection coefficient is calculated. In the device, the diffraction components of the acoustic interference from the edges of the plate will be significantly reduced due to the spatial selectivity of the two receiving transparent antennas. 4 il.

Description

The invention relates to technical acoustics and can be used to control the quality of panels and partitions.

The purpose of the invention is to improve the accuracy of control in the case of oblique incidence of sound on a plate due to the expansion of the region of interference of the incident and reflected waves.

Fig. 1 shows a device for measuring the reflection coefficient of sound from plates in a medium in the field of a radiator plane wave; Fig. 2 illustrates a particular case of the execution of a device unit in which traveling-wave antennas are used as receiving transparent antennas; in fig. 3 and 4 are cases of the implementation of a unit of the device in which as a receiving transparent antennas are used glossy antenna arrays of electroacoustic transducers.

The device contains an electric generator 1, for example, a generator of sinusoidal oscillations (continuous or pulsed). The output of the electric generator 1 is connected to the radiation 2, which emits an acoustic signal to medium 3 (water). The acoustic signal is recorded by two Receiver identical transparent antennas 4, for example, flat grids from pressure or oscillatory velocity receivers, or traveling wave antennas. The receiving transparent antennas 4 are located at a distance from the radiator 2 equal to

L - 2 5 ± nd,

L TV;

where L is the distance between the radiator

2 and receiving antennas 4; a - distance between receivers

antennas 4;

B is the geometric size of the receiving antenna 4 in the vertical plane;

I is the wavelength in the environment. The outputs of the receiving antennas 4 are connected respectively to the inputs of the blocks 5 forming the characteristics of the antenna. The outputs of the blocks 5 are connected to the inputs of the block 6 subtraction. Subtraction of the signals1 at the output of the adder can be achieved if one of the signals with the sign 6 is connected to the block 9 of registration. Two identical antennas 4 are located in the same plane along one axis of the rotation mechanism 7 at a distance from one another more than half of the largest geometric size of antenna 4 and not less than the wavelength in the medium from the bottom edge of the plate 8 to the top edge of the second receiving antenna 4.

The device works as follows.

A continuous or pulsed electrical signal from the electric generator 1 is fed to the radiator 2, which emits a signal to the medium 3. The acoustic signal is recorded by two receiving transparent antennas. The first receiving antenna 4 is placed in front of the test plate.

fold

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five

0

five

0

five

0

five

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8, and the second - in the free field of the radiator 2 under the first antenna. The acoustic field at the location of the first receiving antenna 4 is folded from the incident plane wave from the radiator 2, the specularly reflected plane wave from the plate 8 and the field scattered by the edges of the test plate 8. The acoustic field at the location of the second receiving antenna 4 is equal only to the incident flat wave from emitter 2. When the plate 8 is rotated through the angle oi, the main lobes of the directivity characteristics of the receiving antennas 4 simultaneously rotate through an angle of 2 °. Synchronous rotation of the main lobes of the directivity characteristics of the antennas 4 can be performed by several designs, which are shown in figure 2-4.

Rotation of the main lobes of the directivity characteristics of antennas 4 at an angle of 2 оЈ can be performed by the rotation mechanism 7 of uncompensated antennas 4 at an angle of 2 revolutions, which is designed as a gearbox rotating the plate at an angle ot, and antenna 4 at an angle of 2oi; units 5, which, when the plate is rotated by an angle oi by the rotation mechanism 7, rotate the main lobes of the directivity characteristics of the antennas 4 by an angle of 2 °; mechanism 7 of rotation, turning the plate 8 and the antenna 4 on the corner; units 5, which additionally turn the main lobes of the directivity characteristics of the antenna 4 by an angle of. .

When the plate 8 is mechanically rotated by the angle ОЈ and the antennas 4 are at an angle of 2oi, the plate 8 and the antennas 4 are synchronously rotated through a mechanical gearbox. During the electron-mechanical rotation of the main lobes of the antenna 4 and the plate 8 can be rotated by a single rotation mechanism 7. With the electronic rotation of the main lobes of the antennas 4, the latter are rigidly fixed along the axis of the rotation mechanism 7 and do not rotate in space. The mechanical rotation of the main lobes of the directivity characteristics of antennas 4, for example, traveling wave antennas, the axis of rotation of the receiving antennas 4 can be as close as possible to the plate under study 8. With the mechanical rotation of the main lobes of the receiving antennas 4, the distance between the axis of the mechanism 7 is vertical

The arms, receiving antennas 4 and plate 8 are selected so that the receiving antenna 4 can rotate without hitting the plate 8.

When electronically scanning the main lobes of the directivity characteristics of the antennas 4, the plate 8 is placed from the receiving antennas 4 at a distance that provides no contact with the antenna 4. With the electro-mechanical rotation of the main lobes of the directivity characteristics of the antennas 4, the plane of placement of the antennas 4 can be combined with the surface of the test plate 8, which allows the use of a large part of the reflecting surface to determine the reflection coefficient of sound from the plate 8 (Fig. 3).

The outputs of the receiving antennas 4 are connected respectively in parallel to the inputs of the receiving units 5, at the output of which the directivity characteristics of the antennas 4 in a given direction are formed. The electronic units 5 are adjusted so that the signals at their outputs are equal in amplitude and phase in the absence of a reflecting plate 8. In this case, the alignment of the phases and amplitudes is performed by the tuning elements included in the blocks 5. Subtraction of the signals at the output of the subtractor 6 can be performed if the signals at the output of the blocks 5 are shifted each relative to the circle using the tuning elements by 180 and summed at the adder.

If the recorder at the output of the subtraction circuit is calibrated so that, in the absence of the plate 8, its indication when only one is connected

146

receive antenna 4, the maximum of the characteristics of which is directed to emitter 2, to be taken as a unit, then its indications when inserting plate 8 and turning on both antennas 4 will give, in units of this received unit, the value of the modulus of the reflection coefficient of sound from the plate multiplied by some phase factor. In this case, the diffraction components of the acoustic interference from the edges of the plate 8 will be significantly reduced due to the spatial selectivity of the antennas 4.

Claims (1)

Invention Formula A device for measuring the reflection coefficient of sound from the plates, containing a sound emitter, an electrical signal generator connected to the sound emitter, a sound receiver in the form of a sound transparent antenna, an antenna characteristic shaping unit connected to the antenna output, and a rotation mechanism with an antenna attached to its axis , characterized in that, in order to increase the control accuracy in case of oblique sound falling on the plate of the incident and reflected waves, it is equipped with a second sound receiver in the form of a sound an antenna antenna identical to the first one and fixed on the axis of the rotation mechanism, and installed in the plane of the first receiver, a second antenna characteristic shaping unit connected to the second antenna, a subtractive unit whose inputs are connected to the outputs of the antenna characteristic shaping units, and a recording unit.  -fefl FIG. 2 fig.Z FIG 4