Papers by Keyword: Anechoic Chamber

Abstract: Anechoic chambers are widely used in performing EMC measurements according to the established EMC standards. In space area, the elements of EMC measurements such as emission, immunity and susceptibility are critically important to ascertain that all of electrical and electronic components in the satellite body will function correctly without fail, thus ensures the smoothness of satellite operation upon launching into space. Realising this, level of anechoic chamber performance should always be in the optimum state as possible. This paper presents the specific tests that were carried out in the anechoic chamber as to determine the accuracy of its performance. All four types of tests were run in main chamber, control and amplifier room within frequencies range of 10 kHz to 20GHz. The tests will characterize the shielding effectiveness of RF shielded enclosure, the Field Uniformity Area (FUA), Site VSWR and Normalised Site Attenuation (NSA) of anechoic chamber. The basis of the measurement techniques is described and typical test results are discussed. Based on the results, it is concluded that the anechoic chamber is in good condition, ready for testing and capable to produce reliable output.

Abstract: The design, manufacture and installation of a practical and cost-effective anechoic chamber for aero-acoustic measurements are presented in this paper. The work was undertaken with a view to measure the aerodynamically generated noise of wind turbines under laboratory conditions. The chamber was designed to be used in conjunction with a wind tunnel. Tests were carried out to compare the reduction of noise levels from external sources with and without the chamber. The results obtained suggest a clear reduction of noise levels with different wind speeds, and as expected, resulted with higher reductions at higher wind tunnel speeds.

Abstract: Abstract. This paper presents the results of experimental studies of the noise of marine application pump axial flow fan. Axial flow fan is verified by both geometrical and experimental approaches. This section includes grid system used in geometric simulation, and boundary conditions. In order to know the complicate and complex physical features of an axial flow fan, a commercial computational fluid dynamics code, FLUENT, is utilized to perform the flow field analysis, which solves the Navier–Stokes equation using an amorphous finite volume-method. As a commercial computational fluid dynamics code, FLUENT has been extensively used in many turbo machinery applications. In this paper the noise predicted according to geometrical results will be compare with investigational results.

Abstract: The article considers the previously presented manipulating mechanism for positioning of a microphone during acoustical measurements in anechoic chamber. Usually the aims of acoustical measurements in anechoic chamber are: estimation of Sound Power Level of the noise source, measurement of directional characteristics of an electroacoustical transducer, measurement of the sound diffusion characteristic of a given structure and a measurement of Sound Pressure Level on a given measurement grid. The specific of that kind of measurements brings up the need of measurement microphone positioning in many points of the measurement space accordingly to relevant standards. In most cases during the tests it is necessary to position the microphone in certain points on the hemisphere. In such cases utilizing of typical microphone stands impedes the measurement and extends the time needed for the tests. The presented manipulation system for a measurement microphone allows positioning the microphone on the hemisphere around the tested object as required by the standards on the Sound Power Level measurement. Its construction is a simple, rigid form aiming at little effect on the acoustic field inside the chamber whereas the control system and the software are targeted at the maximal flexibility that allows not only standard testing but also scientific research in freely selected scenarios. Since its initial introduction the system has been extended by an additional axis that is used for rotating the microphone, which allows its positioning on the line that is coincident with the centre of rotation of the turntable. Such an extension eliminates the problem of use of the corrections of the directional characteristics of the microphone when measuring the sound signal. The microphone can be positioned directly towards the source of the sound. The article briefly reviews the mechanical construction of the positioning mechanism and focuses on the structure of the control section of the drive system constructed in the manipulator. The method for cooperation of actuators and the control system is presented. Also the description is given for the internal structure of the multi-level control circuits built in the applied drives. Finally the structure of the control application is presented.

Abstract: The article presents the structural and geometric synthesis and mechanical parameter choice for a manipulation mechanism for measurement microphone positioning during acoustical tests in anechoic chamber. Usually the aims of acoustical measurements in anechoic chamber are: noise source Sound Power Level estimation, electroacoustical transducer directional characteristics measurement, sound diffusing characteristic of a structure measurement, measurement of Sound Pressure Level on a given measurement grid The specific of that kind of measurements brings up the need of measurement microphone positioning in many points of the measurement space accordingly to relevant standards. In most cases during the tests it is necessary to position the microphone in certain points on the hemisphere. In such cases utilizing of typical microphone stands impedes the measurement and extends the time needed for the tests. Those circumstances led to idea of measurement manipulator construction that would allow changing the microphone position during the measurement accordingly to a specified algorithm. The following assumptions for construction were taken: measurement microphone moves on the hemisphere with a maximal radius of 2 m, the weight of transported object (microphone or other) does not exceed 1 kg, positioning accuracy is 1 mm. Structural and geometric synthesis was made taking into account mounting conditions in anechoic chamber in Department of Mechanics and Vibroacoustics AGH-UST. There were several variants labored that fulfilled the assumptions. The choice of particular solution was made based on: • manipulator drives possible installation analysis with regard to their acoustical noise emission • structure stiffness analysis with regard to assumed positioning accuracy of the microphone Finally a modular construction of manipulator was chosen, which is composed of industrial turntable (built in the level of the wire netting) and two linear motion modules (long axis, short axis). That solution means that the device under test fixed on the turntable rotates in the range of 2π, and the measurement microphone moves on the track of one quarter of a circle. Specific angular position of the linear modules was chosen which allows minimal dimensions of linear modules. Simultaneously the control structure and the software part are developed. The usefulness of the manipulator will be definitely confirmed by a research that should evaluate the influence of the construction elements on the acoustical free field in an anechoic chamber.

Abstract: The paper presents the structure of control section of measurement manipulator for acoustical tests in anechoic chamber. The specific of that kind of measurements brings up the need of measurement microphone positioning in many points of the measurement space accordingly to relevant standards. In most cases during the tests it is necessary to position the microphone in certain points on the hemisphere. The paper presents hardware structure and software to control the measurement manipulator accordingly to a specified algorithm. A modular construction of manipulator was chosen, which is composed of industrial turntable and two linear motion modules. That solution means that the device under test fixed on the turntable rotates in the range of 2π, and the measurement microphone moves on the track of one quarter of a circle.