Semi-anechoic Chamber Research Articles

Simulation Research on Active Noise Control in Turboprop Cabin with Complex Sound Field Environment

This article summarizes the research work on the complex sound field environment in the cabin of a certain turboprop aircraft, the construction of multi-channel noise active control system and the verification of noise reduction effect were carried out. On the basis of spectrum analysis and distribution characteristic analysis of the measured data in the cabin of this turboprop, taking the key peak frequency as the target frequency, a multi-channel noise active control system with 16 inputs and 16 outputs that meets the requirements of noise reduction indicators is built. And a comprehensive verification platform for the noise reduction effect of turboprop aircraft similar to the real environment was built in a semi-anechoic chamber to verify the real environment was built in a semi-anechoic chamber to verify the noise reduction effect of the system. The result show that the system can reduce the sound pressure level at key frequencies by 14.9 dB(A), the system noise reduction effect is significant and effective.

The sound insulation across the plenum window with staggered sound scatter arrays

In this study, experiments and simulations were carried out by a scaled-down model in a semi-anechoic chamber to investigate the acoustic effect of the staggered sound scatter array on the sound insulation of a plenum window. The 1/4 scaled-down plenum window has a gap of 98 mm and the diameter of the sound scatter cylinder is 19 mm. Firstly, the reverberation times of the verified case and reference case were presented to explore the possible effect of the installment of the sound scatter array on the reverberation of the room model. Next, the effect of four sound scatter array arrangements on the sound insulation of the plenum window was analyzed experimentally and numerically. Results show that the installment of the staggered sound scatter array can enhance the sound insulation of the plenum window. Below 600 Hz, enhancement of the staggered sound scatter array on the sound insulation of the plenum window is lower than 2.2 dB. Beyond 600 Hz, the extra transmission loss increases with the frequency and is up to around 6.0 dB. In addition, the trapped mode was observed inside the window cavity and it excited a second higher gap mode which helps improve the sound insulation of the plenum window.

Synthesis of equivalent sources for tyre/road noise simulation and analysis of the vehicle influence on sound propagation

Road traffic noise affects the well-being of people living in urban areas. Amongst the noise sources, tyre/road interaction plays a major role. In this context, predictive acoustic models can be useful for the tyre industry to design quiter tyres. This paper deals with a methodology for simulating tyre/road noise through equivalent monopoles, synthesised using an inverse problem approach, starting from indoor tests performed in a semi-anechoic chamber. A drum with an ISO 10844 road replica is used to obtain realistic tread pattern and road roughness excitations. The experimental setup and a dedicated signal processing technique are described here. To perform the source synthesis, data is combined with acoustic finite element models based on a deformed treaded tyre geometry, in order to take the acoustic resonances at the tyre/road interface into account. The synthesised monopoles are then used to run a numerical simulation including a vehicle in order to consider its influence on sound propagation. The results are then validated by comparing them with indoor measurements.

An Optimization Design of Bi-log Hybrid Antenna with Taguchi’s Method for EMI Measurements

This paper presents a comprehensive design approach for a biconical log-periodic dipole array (Bi-log) hybrid antenna optimized specifically for electromagnetic interference (EMI) measurements. The antenna’s elements, scaling function, feed structure, balanced-to-unbalanced (Balun) geometry, and key parameter selection are carefully considered to achieve enhanced broadband testing capabilities. The proposed compact Bi-log hybrid antenna is optimized using Taguchi’s method within the frequency range of 30 MHz to 6 GHz. The optimization focuses on the discontinuity of the antenna factor (AF), incorporating miniaturized elements. The dimensions of the proposed antenna are minimized, with a length of 95 cm, width of 148.5 cm, height of 60 cm, and weight of 2.5 kg. Simulation results and experimental validations demonstrate its efficacy through comparison. Optimization results indicate that the voltage standing wave ratio VSWR < 2 (with 5 dB attenuator) and symmetry < ±0.5 dB also meet the regulatory standards according to ANSI C 63.4. This makes the proposed antenna suitable for use in various types of semi-anechoic chambers.

Round-robin tests of the different types of sensors for floor impact sounds and vibrations

Recently, floor impact noise monitoring system was introduced for residents to control making noises spontaneously using sound and vibration sensors. The present study aims to investigate the performance and characteristics of various current using sound and vibration sensors which can be eventually compatible with the floor impact noise monitoring system. For measurements of sound sensors, 7 sound microphones were used including 2 condenser types, 4 dynamic types, and 1 electro condenser type. Also, 6 vibration meters were used including 2 MEMS types, 2 Piezo types, and 2 spring types. Sound levels were measured in a semi-anechoic chamber using white noise in the frequency range from 63 Hz to 12.5 kHz. Vibrations were measured using high density wooden panel with an impact ball in the frequency range from 16 Hz to 4 KHz. Round-robin tests were done to confirm the exact performances of all the sensors under same condition. As a result, it was found that dynamic type microphones show the most similar response characterization in comparison with the reference condenser microphone especially in the air-borne sound frequency range from 250 Hz to 2 KHz. Also, it was found that spring type vibration meters show the most appropriate characterization at 63 Hz, most critical structure-borne sound frequency. Thus, the results drawn from the round-robin tests could be used for floor impact noise monitoring systems with the benefit of both economy and performance.

A Fast Approach to Optimize Tread Pattern Shape for Tire Noise Reduction

Impact force induced by tread pattern is one of the major mechanisms of tire noise; thus, how to reduce tire impact noise has been an important issue in regard to tire technology. In this paper, the mechanism of tire–pavement interaction noise is briefly described, and a prediction model for pattern noise is proposed. The prediction model was validated with indoor semi-anechoic chamber and pass-by noise experiments. Then, an optimization method for the tread pattern was proposed by using the basis vector method, and the synthetic pattern shape was generated through a linear combination of basis shape vectors. Finally, a novel multi-objective function was proposed, aimed at minimizing the impact noise generated by the tire pattern, and the weight factors of the basis vectors were optimized with a genetic algorithm. The method proposed in this paper can be used to evaluate or improve pattern performance and reduce trial and error in the pattern design stage.

Simulation and experimental study of active noise barrier based on multiple-channel and decentralized system design

Active noise barrier (ANB) was helpful to enhance the noise reduction performance of noise barrier especially in low-frequency range. But it was quite difficult to realize an ideal effect in the far-field as most of the exiting work of ANB took the realization of soft boundary at the edge of noise barriers as the target. An active control strategy based on the decentralized system design was proposed in this paper. The virtual sensor technology was used in order to obtain the far-field noise signal with the help of near-field sensor, while multiple-channel design of both centralized system and decentralized system was studied. An experimental ANB system was then built in semi-anechoic chamber. The performance of the above control strategies was calculated with the actual measured parameters, and the advantages and disadvantages of different systems were compared and studied. The effectiveness of the new strategy was verified through the noise reduction tests of active noise control. The ANB established in this paper which was based on decentralized system design, could be extended to large scale usage directly in the future.

A CSI Dataset for Wireless Human Sensing on 80 MHz Wi-Fi Channels

In the last years, several machine learning-based techniques have been proposed to monitor human movements from Wi-Fi channel readings. However, the development of domain-adaptive algorithms that robustly work across different environments is still an open problem, whose solution requires large datasets characterized by strong domain diversity, in terms of environments, persons andWi-Fi hardware. To date, the few public datasets available are mostly obsolete - as obtained via Wi-Fi devices operating on 20 or 40 MHz bands - and contain little or no domain diversity, thus dramatically limiting the advancements in the design of sensing algorithms. The present contribution aims to fill this gap by providing a dataset of IEEE 802.11ac channel measurements over an 80 MHz bandwidth channel featuring notable domain diversity, through measurement campaigns that involved thirteen subjects across different environments, days, and with different hardware. Novel experimental data is provided by blocking the direct path between the transmitter and the monitor, and collecting measurements in a semi-anechoic chamber (no multi-path fading). Overall, the dataset - available on IEEE DataPort [1] - contains more than thirteen hours of channel state information readings (23.6 GB), allowing researchers to test activity/identity recognition and people counting algorithms.

A combined iterative complex eigenvalue method and finite element-boundary element method for acoustic analysis of the railway steel bridge deck damped with constrained layer damping

This paper presents a combined method to predict structure-borne noise from the railway steel bridge deck damped with constrained layer damping (CLD), in which the frequency-dependent properties of the viscoelastic material are accurately considered through the iterative complex eigenvalue method (ICEM). Then, a 1:4 steel bridge deck model is designed and manufactured, and a series of hammer tests of the CLD-damped steel bridge deck are carried out in a semi-anechoic chamber to verify the proposed method. Then, the noise reduction effect of CLD is discussed in detail. It shows that the overall SPLs at the near field point S-3 and the far field point S-8 are reduced by 7.5 dB and 11.1 dB, respectively, and the noise attenuation rate along with distance is also improved significantly after damped with CLD. Finally, the influences of the key design parameters of CLD on noise reduction are quantitatively analyzed, so as to provide reference for the research and application of CLD in railway bridge engineering.

Experimental Study on Wind Turbine Airfoil Trailing Edge Noise Reduction Using Wavy Leading Edges

Aerodynamic noise produced by the rotating blade is an important hindrance for the rapid development of modern wind turbines. Among the various noise sources, the airfoil trailing edge noise contributes a lot to the wind turbine noise. The control of wind turbine airfoil trailing edge self-noise by bio-inspired sinusoidal wavy leading edges is experimentally studied in a semi-anechoic chamber. The noise radiated by the baseline NACA 0012 airfoil and various wavy airfoils is measured using a planar microphone array consisting of fifty-two microphones. The noise source identifications are achieved by using the CLEAN-SC method. The effects of velocity and angle of attack on noise radiation of the baseline airfoil are analyzed in detail. The noise control law of the wavy amplitude and wavelength on airfoil trailing edge noise is explored. Based on the acoustic beamforming results, the noise control effects of the wavy leading edges are intuitively demonstrated. In general, the wavy leading edge with a larger amplitude and smaller wavelength has a better effect on the airfoil trailing edge noise reduction. The maximum sound pressure level reduction can be up to 33.9 dB. The results of this study are expected to provide important information for wind turbine aerodynamic noise control.

A Compact Broadband Monopole Tapered Slot Antenna With High Field Uniformity for Vehicle EMC Test From 20 to 220 MHz

A compact broadband monopole tapered slot antenna (MTSA) for vehicle electromagnetic compatibility (EMC) tests in the semi-anechoic chambers (SAC) is proposed and investigated. The proposed MTSA takes the metal ground of the SAC as part of an antenna. With the mirroring effect of the ground plate in the SAC, the proposed MTSA acts as a conventional tapered slot antenna (TSA) but with only a half size of the conventional TSA, and also avoids the adverse effect of the ground reflections on the field uniformity effectively. Moreover, the MTSA has a slot on its flaring plate that reduces its weight by 30%. Both the simulated and the measured results show that the proposed MTSA achieves a standing wave ratio (VSWR) below 2:1 from 20 MHz to 220 MHz, and a good uniformity, with radial uniformity better than 3 dB, transverse uniformity better than 4 dB. The simulated gains are from 6 dBi to 13.5 dBi with radiation efficiencies over 90% across almost the entire bandwidth.

The Radiation Efficiency Measurements of Real System of a Thin Circular Plate Embedded Into a Thick Square Baffle

Most of sound sources are complex vibroacoustic objects consist of numerous elements. Some coupled vibrating plates of different shapes and sizes can be easily found in urban environments. The main aim of this study is to determine the sound radiation of coupled plates system of practical importance. The investigated vibroacoustic system consist of a thin circular plate coupled with a thick flat baffle with a circular hole. The circular plate has been mounted to the baffle’s hole using screws and two steel rings. The measurement setup was located inside a semi-anechoic chamber to assure the free field conditions. It was necessary to take into account the whole system surface to obtain the radiation efficiency based on the Hashimoto’s method. Such an approach can be troublesome and time-consuming. Therefore, the criterion has been proposed which allows the vibration velocity measurements and calculations to be performed only for the thin plate’s area. An alternative approach has been proposed based on the classical Rayleigh integral formula. Its advantage is a simpler implementation in a computer code. The obtained results have been compared with the theoretical results obtained for the elastically supported circular plate. A good agreement has been obtained at low frequencies.

Comparison of two state-of-the-art rotating dipole sound source imaging technologies: Models, algorithms and applications

The acoustic imaging technology for rotating dipole sources has been one of the topics concerned. In recent years, two state-of-the-art imaging technologies for rotating dipole sources were proposed, including beamforming technologies based on the predefined axis direction (PAD-DBF) and frequency-domain deconvolution (FDD-DBF). However, a systematic comparison of these two imaging technologies does not currently exist. In this paper, the models and imaging algorithms are firstly systematically compared and analyzed to explore the differences between the two technologies and provide guidance on the application of the technology. Secondly, extensive simulations are investigated to analyze the performance of the two imaging technologies under different working conditions. Finally, the two imaging technologies are applied to the semi-anechoic chamber test for rotating dipole sources and the actual BO105 rotor wind tunnel test, respectively, which is further used to compare and validate the imaging effectiveness and applicability of the two technologies. The analysis shows that both technologies can effectively achieve rotating dipole source localization. The PAD-DBF technology can achieve a more accurate rotating dipole source location, higher imaging resolution at a lower time cost, and it can get more robust imaging results in the low signal-to-noise ratio (SNR) of the wind tunnel environment. In contrast, the FDD-DBF technology can get a more accurate sound source magnitude while effectively imaging the rotating dipole source.

Experimental and numerical study on a new noise reduction design for a small axial fan

The broadband noise of an axial fan is highly related to the vortex shedding at the blade trailing edge and the secondary flow at the blade tip. Herein, a circular arc design is proposed to modify the shape of blade tip and trailing edge together with the features of simple structure and easy manufacture. The experimental and numerical studies were conducted to investigate the effect of circular arc design on the aerodynamic and acoustic characteristics of a small cooling axial fan through the experimental method of the semi-anechoic chamber and LES simulation combined with FW-H. The tested and calculated results show that the SPE of the fan with R7 circular trailing edge can be improved for the entire flow rate range. And the SPC is decreaed as the increasing of arc radius. For the fan with R7, the SPE can be increased by 2.1% and the SPC is decreased by 4.8% at the designed flow rate. In terms of acoustic characteristics, the modified impeller can suppress the broadband noise in the range of 1000 ∼ 3000 Hz, and this suppression can be improved with the growth of flow rate. The R7 design shows the best noise reduction performance, with 2.4 dB reduction over the prototype.

Impact of Antenna Tilt on Measurements Below 1 GHz in Semi-Anechoic Chamber

The conditions of measurement of radio disturbance emission are defined in EN 55016-2-3 standard. It defines the detailed requirements of the measuring system and the methodology of the test. In case of the measurement up to 1 GHz the antenna height scan is required but there is no regulation regarding the antenna tilt in current edition of standard. As a result most laboratories perform measurements of radiated emission with a fixed antenna angle of 0∘ -the antenna is located in parallel with the ground plane despite the actual height. Knowing that the antenna inclination angle in relation to the emission source affects its characteristics, it can lead to omit the measurement configuration at which the measured field strength is the highest. The article investigates the influence of receiving antenna inclination angle on measurements of radiated disturbances from a reference emission source and real TV-set.

An Estimation Method for EMI Radiated Emissions Using Measured Source Voltages

A method applicable for estimating radiated emissions from printed circuit board traces and connecting cables is proposed. Empirical formulae are derived to predict emission levels in a conventional 10 m semianechoic chamber in the 30–1000 MHz range, which is required for electromagnetic compatibility/electromagnetic interference (EMI) tests in CISPR 32 and EN 55032. The objective of the proposed technique is to facilitate product and component EMI compliance evaluations in the early design stage. Instead of time-consuming measurement processes within the range, estimations can be made in terms of near-field probing results and transformation formulae. According to trace and cable lengths, either long- or short-length mode equations can be employed. Estimations of mock-up and actual circuit boards made with the proposed method were compared with 10 m measurement range results to validate the effectiveness of this approach. Good agreements are observed. This method can be a time-efficient and cost-effective diagnosis tool for products required to pass the EMI compliance test.

Sound Insertion Loss Performance of Baffles with Devulcanized Waste Rubber

In this study, the insertion loss of devulcanized waste rubber baffles was evaluated. Acoustic baffles are suitable for reducing noise from the devices or machines by interfering with their emitting sound waves. Knowledge of the acoustic properties of the material used is of significant importance in ensuring the effectiveness of the acoustic properties of the baffle. Basic properties include airborne sound insulation, which is usually determined during laboratory testing. Baffle consists of sound absorbing and sound insulating materials. In this study, plasterboards were used as sound insulating material and devulcanized waste rubber as sound absorbing material. Devulcanization targets mostly the scission of sulphur crosslinks. Devulcanization techniques that have been explored in rubber recycling include thermos-chemical, microbiological, ultrasonic microwave thermos-chemical devulcanization in a supercritical carbon dioxide medium (scCO2). In this study, two types of rubber granules were devulcanized by grinding method and one other type was chemically devulcanized. Three types of rubber granules were mixed together in increasing 25 % proportion steps and glued with patented polyurethane glue. Total of 15 different composition devulcanized waste rubber granule boards were made. Rubber boards were attached together with the plasterboards. Insertion loss of the different composite baffles was measured in semi-anechoic chamber in a purposefully designed stand in 1/3rd-octave bands. The results showed that the insertion loss of the baffles depends mostly on the rubber granule board density. Increasing the density of the rubber board, insertion loss also increased. 5–6 dB insertion loss difference was measured between the most and the least dense rubber granule board baffles.

Convolutional neural network with data augmentation for object classification in automotive ultrasonic sensing

Today's low-cost automotive ultrasonic sensors perform distance measurements of obstacles within the close range of vehicles. For future parking assist systems and autonomous driving applications, the performance of the sensors should be further increased. This paper examines the processing of sensor data for the classification of different object classes and traversability of obstacles using a single ultrasonic sensor. The acquisition of raw time signals, transformation into time-frequency images, and classification using machine learning methods are described. Stationary and dynamic measurements at a velocity of 0.5 m/s of various objects have been carried out in a semi-anechoic chamber and on an asphalt parking space. We propose a scalogram-based signal processing chain and a convolutional neural network, which outperforms a LeNet-5-like baseline. Additionally, several methods for offline and online data augmentation are presented and evaluated. It is shown that carefully selected augmentation methods are useful to train more robust models. Accuracies of 90.1% are achieved for the classification of seven object classes in the laboratory and 66.4% in the outdoor environment. Traversability is correctly classified at an accuracy of 96.4% and 91.5%, respectively.

Study on the scattered sound modulation with a programmable chessboard device

Metasurfaces open up unprecedented potential for applications in acoustic deflection. Achieving adaptive control of a scattered sound field (SSF) using a flexible metasurface structure is of great scientific interest. However, as the conventional finite element method (FEM) is limited by computational efficiency, it is necessary to develop a fast and accurate method to predict the SSF. In this work, we design a chessboard device with an array of square grooves for the modulation of SSF and develop a fast calculation method for 3D SSF using a Kirchhoff approximation phase correction. Several SSF spatial modulations obtained using the chessboard model are computed with a fast algorithm. In addition, an experimental test-case in a semi-anechoic chamber, contrasted and analyzed scattered acoustic pressure using FEM, is designed to regulate the SSF performance of the chessboard device. Field measurements obtained show that the spatial directivity of chessboard device can be modified by artificially programming the phase or depth distribution of the groove array. The chessboard device and associated fast calculation method lend themselves to applications in the acoustic stealth of targets in air or water.

Biocompatible Piezoelectric Polymer Poly(Lactic Acid)-Based Stethoscope for Wearable Health Monitoring Devices

With the development of wearable devices and the Internet of Things (IoT), there is a growing demand for portable and comfortable human health monitoring devices. Because of the advantages of biocompatibility, relatively large piezoelectric coefficients, and nonpyroelectricity, poly(L-lactic acid) (PLLA) polymers have been greatly utilized in the applications of tissue engineering, sensors, and energy harvesting devices. In this investigation, the PLLA film was fabricated for the first time for real-time wearable stethoscope and pulse wave sensor applications. First, the stretched PLLA film was glued onto a Mylar film as the active layer of the PLLA film-based stethoscope (PFS) and pulse sensor device. After the PFS device was measured in a semianechoic chamber, the device showed a sensitivity of –53.4 dB at 1 kHz and it also exhibited a stable frequency response in the range of 100 Hz–4 kHz. In addition, the PFS device showed an output voltage of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sim $ </tex-math></inline-formula> 90 mV when measuring the heart rate and pulse signal of an adult volunteer. Furthermore, the PFS device was integrated a portable stethoscope system, which can detect a clear pulse signal and send it to a data collection application designed in a cellphone. The biodegradability, stable frequency response, and temperature stability indicate the great potential of PFS device for wearable human health monitoring devices.