Secondary Sound Sources Research Articles

The rebar corrosion length evaluation technique based on nonlinear ultrasonic guided wave energy flow

In offshore reinforced concrete (RC) structures, phenomena of rebar corrosion are widespread, seriously threatening the durability of the structures. However, the issue of entire rebar corrosion process detection, especially for the evaluation of local corrosion states and the scope, is also challengeable. The paper aims at utilizing the nonlinear ultrasonic guided wave (UGW) energy flow to identify reinforcement corrosion level and length during the entire corrosion process in RC structures and establishing a corresponding corrosion evaluation algorithm. Therefore, a corroded rebar with the surrounding concrete cover is simplified into a cylindrical layered structural model. Meanwhile, piezoelectric transducers are used for the actuation and reception of UGWs, and a granular material contact (GMC) model is applied to illustrate the mechanism for generating surface-contact-induced nonlinear components in scattering waves. Then, the propagation behavior of the nonlinear UGWs is analyzed by regarding the corrosion layer as a secondary sound source changing the wave energy flow. A corrosion evaluation algorithm based on the GMC model is established and validated by both experiment and finite element (FE) analysis. The results show that for a harmonic UGW excitation signal, the periodic relationship between the second-order nonlinear coefficient of received signal and the corrosion length is found in which the period is associated with the difference (kd) of 2 times of fundamental frequency wave number (2 kω) and double frequency wave number (k2ω). Particularly, as kd trends to zero, a degraded linear relationship is found for establishing the corrosion length evaluation algorithm with the relatively high evaluation precision and convenient evaluation technique.

Selective noise control by adaptive bandpass filter and secondary aural cartilage source

When a transducer is put on an aural cartilage, the transmitted vibration generates sound in the external auditory canal (i.e., cartilage conduction). Different from conventional earphones, the cartilage conduction technology enables the use of earphones without occluding the canal. However, the opening ears allow both desired sounds (e.g., speech) and unwanted noises to reach the eardrums. To minimize only the noise selectively, our study introduced filtered-x least means square algorithm combined with adaptive bandpass filter (ABF-FxLMS). The ABF-FxLMS stored the narrowband noise separating from a speech and transferred it to the FxLMX as a secondary sound source produced via the cartilage conduction. The adaptive bandpass filter actively adjusted to changes in the center frequency of noise, and the ABF-FxLMS ensured effective noise reduction permitting the passing of speech. Our simulations demonstrated achieving approximately 19 dB reduction in the noise while keeping the speech quality. A coming cartilage conduction device will enable conversations in noisy environments.

Sound reduction of side-branch resonators: An energy-based theoretical perspective

For over a century, side-branch resonators have served as effective acoustic filters, yet the explanation for their sound reduction capability has varied. This paper introduces a novel theory applicable to all types of side-branch resonators from an energy perspective and explains sound reduction as a consequence of acoustic energy redistribution. Our theory posits that a standing wave inside the resonator induces air vibration at the opening, which then acts as a secondary sound source, emitting acoustic energy predominantly in the form of kinetic energy. Due to the formation process of the standing wave, the sound wave generated by the resonator undergoes a phase shift relative to the original sound wave in the main pipe. Consequently, this generated sound wave, while matching the amplitude, possesses an opposite phase compared to the original noise wave within the main pipe. This antiphase relationship results in the cancellation of sound waves when they interact post-resonator in the main pipe. Our theory, grounded in an energy perspective, is derived from the principles of standing wave vibration and energy conservation.

Research progress of piezoelectric polymer PVDF in sound absorption technology

Owing to its impedance properties and piezoelectric effect, the piezoelectric polymer polyvinylidene fluoride (PVDF) finds application in the field of noise control. Traditional sound-absorbing materials have gradually fallen short of the demands of sound-absorbing functionality and environmental adaptability in today’s increasingly acute noise pollution environment. When PVDF is added to sound absorption, materials or structures have an additional loss path for the conversion of sound energy to electric energy. This helps to increase the low-frequency sound absorption band and improve low-frequency sound absorption performance. Through the action of viscosity, friction, relaxation, piezoelectric effect, and dielectric loss, the sound energy in the passive sound-absorbing material containing PVDF is transformed into energy dissipation in the form of heat energy, electric energy, and so on under the matching of PVDF low impedance. In active control, secondary sound and force sources can be supplied by PVDF-based transducers and actuators to reduce noise. This paper first provides an overview of the piezoelectric characteristics of β-phase PVDF and its optimization techniques. It then goes on to discuss the use of PVDF in passive sound-absorbing materials, active controls, and hybrid sound absorption systems. Finally, it summarizes the benefits, issues that still need to be resolved, and future directions for these three noise reduction techniques.

Study of GSO-GL based secondary source configuration optimization method for broadband sound field reproduction

Sound field reproduction is a method that uses multiple secondary sound sources to reproduce a predefined desired sound field in a listening area. The configuration of the secondary sound sources is a key factor affecting the reproduction performances. To optimize the secondary source configuration, this study proposes a new method that combines the Gram-Schmidt orthogonalization method with the group Lasso method, which is called GSO-GL method. Firstly, it selects a certain number of the secondary sources from all the alternative secondary sources using the Gram-Schmidt orthogonalization method. The excitation sources are then further selected from the secondary sources selected in the previous step using the group Lasso method. The sound field simulation from the 2D room model show that the GSO-GL method outperforms the Gram-Schmidt orthogonalization method or the group Lasso method alone, combining the high system stability of the Gram-Schmidt orthogonalization method with the high reproduction accuracy of the group Lasso method.

A unidirectional secondary sound source for local active noise control in enclosures

Directional secondary sources are beneficial for local active noise control in cabins with multiple seats. In this paper, a method of designing a unidirectional compound sound source composed of two units is introduced. A prototype was implemented using two closed-box speakers and an analog circuit, and the directivity of the compound source was measured in the anechoic chamber to verify the effectiveness of the proposed design method. Furthermore, the sound radiation characteristics of the compound sound source in a car cabin are reported and analyzed. The average sound pressure level at the driver's seat and rear seats is reduced by over 3.5 dB and 8.3 dB respectively in the frequency range from 125 Hz and 500 Hz when a single loudspeaker box located at the front passenger's seat is replaced by the compound sound source.

Research on seat active noise control of driver's cab ground platform based on far-point secondary sound sources

Driver's cab noise has an impact on the long-term driving environment and physical health of drivers. The locomotive driver's cab has significant low-frequency noise due to structure-borne sound, which is suitable for effective suppression by the active noise control system. However, on the one hand, the seat headrest system hinders the driver's movement space, on the one hand, the active noise control for space zones in the driver's cab has limited noise reduction effect due to the large control area. Therefore, a ground research test platform of driver's cab for active noise control was designed, and its structure and control method were introduced in this study. Based on the near-point seat active noise reduction control system, the coherence of the reference acoustic signal of the chair to the acoustic signal at the driver's left ear is very close with the one on the floor, and both of their active noise reduction in the full frequency band from 50 Hz to 5000 Hz are very close (about 4.5 dB (A)). In order to alleviate the interference of the headrest system installed with secondary sound sources on the driver's operating space, a far-point active noise reduction control system was proposed. The results showed that when two reference microphone signals from the seat back and floor position are used at the same time, the active noise reduction next to the driver's left ear in the full frequency band of 50 Hz to 5000 Hz is 4.0 dB(A), which is still significant. This provides a useful reference for the engineering application of active noise control systems in rail driver's cabs.

Active Low-Frequency Noise Control Implementing Genetic Algorithm on Mode Coupling of a Compound Source

A system for low-frequency noise control in small, enclosed sound fields is proposed, using compound sound sources optimized by a genetic algorithm (GA). It is the integration of the developed low-Bl driver compound sources with a GA computer program in the Python language, aiming to control the modal field. The lack of appropriate free space in small rooms is critical for positioning the secondary sound sources; therefore, the proposed system has been designed to adapt to any available position. Two quadrupole topologies of the secondary compound source are applied and examined in a room. The convergence of the algorithm to the optimal solutions is attained through parametric configuration. The spatial radiation of the compound source at a single fixed position is adapted to couple with the modal noise field and attenuate it. The experimental results indicate that the proposed system can successfully control resonances of different low frequencies down to 50 Hz at multiple positions. The tonal noise attenuation reaches up to 32 dB at 100 Hz, confirming the applicability of the small subwoofer loudspeaker configurations for low-frequency control. This new method offers a practical and effective alternative to the typical abatement techniques that use distributed monopole sources in limited spaces.

A feedforward and feedback composite active noise reduction headset based on inverse filter frequency equalization and its DSP system implementation

The principle of active noise reduction headset is to reduce the original noise by generating inverted noise through the loudspeaker. The loudspeaker system will introduce spectrum distortion inevitably. This distortion will increase the complexity of the secondary channel model, which adversely affect identification of the primary channel in the real-time active noise reduction system. To improve the inherent frequency spectrum distortion of the speaker system, this paper proposes a new frequency equalization method based on inverse filtering. This method is applied to a feedforward and feedback compound active noise reduction earphone system, and a new active noise reduction headphone system is obtained. In order to improve the noise reduction effect, the pollution caused by the secondary sound source to the reference signal is compensated in the active noise reduction control scheme of this paper. Simulation and real-time noise reduction experiments based on DSP solution show that this new active noise reduction control system can achieve better noise reduction effects.

Research on follow-up active noise control with phased-array secondary sound source

Based on the traditional active noise control method, a phased-array secondary sound source was designed to replace the traditional sound source. Adopting a 4 × 4 array distributed design, we still maintain a single-in single-out system. Simulations show that the phased-array secondary sound source better controls noise reduction in a certain area of space, with better noise reduction effect, larger static area, and less impact on other non-control areas. A verification experiment was performed in a semi-anechoic chamber, with noise reduction conducted in different directions. The noise reduction effect of the phased-array secondary sound source was >10 dB higher than that of the traditional secondary sound source, with less influence on other points. The phased-array secondary sound source can be combined with tracking equipment to achieve a better follow-up noise reduction effect in space.

Fault detection method of secondary sound source in ANC system based on impedance characteristics

As an indispensable component in an active noise control system, the working states of the secondary sound sources affect directly noise reduction and the robustness of the system. Therefore, it is very crucial to detect the working states of the secondary sound sources in the process of active control in real time. In this study, a real-time fault detection method for secondary sound sources during the process of active control is presented, and the corresponding detection algorithm is numerically given and experimentally verified. By collecting the input voltage and output current of the speaker unit, the sound quality factor is calculated to comprehensively judge the working state of the secondary sound sources. The simulation and experimental results show that the present method is simple and has low computational cost, can accurately reflect accurately the working states of the secondary sound sources in real time, and provides a basis for judging the operation of the active noise control system.

Engine noise cancellation with optimum array of speakers inside vehicle enclosures

In this study, a computational optimization framework is presented to identify active noise control systems for vehicle enclosures. The adopted optimization approach determines optimum configuration of an array of secondary sound sources to suppress noises with low frequency (under 500 Hz) due to engine performance. The overall framework is conducted via a particle swarm optimization algorithm coupled with a modified modal interaction method developed to estimate sound field inside enclosures. The applicability of the proposed optimization approach has been examined with two enclosures of different size by considering 1-speaker and 2-speaker array options as a secondary sound source. The numerical investigation shows that, with the determined optimum configurations, a significant noise reduction may be obtained in vehicle enclosures.

A Study of Engine Intake Noise Control Based on the Improved Filtered-x Least Mean Square Algorithm

To reduce the intake noise of automobile engines, an active control system model of engine intake noise is established with the Filtered-x least mean square (FxLMS) algorithm. The offline identification method is adopted to identify the secondary path. The engine speed signal is used to construct the reference signal of a sound source to avoid interference of a secondary sound source to the reference signal. A variable-step algorithm is proposed, in which parameters are added to the normalized algorithm instead of the sinusoidal variable-step algorithm to adjust the amplitude range. This algorithm not only has the advantages of fast convergence speed and small steady-state error but also adapts to the characteristics of a time-varying reference signal and easy selection of parameters. In this paper, the noise of automobile engines under the New European Driving Cycle (NEDC) is studied and the proposed algorithm has faster convergence speed compared with the normalization algorithm, better adaptability to the change of the reference signal, and better stability compared with the sinusoidal variable step-size algorithm. The results show that the algorithm proposed can effectively reduce the intake noise of the engine at each speed and the noise reduction effect can reach 23.11 dB at a certain frequency. Meanwhile, the stability of the system is improved.

A PSO-based computational framework to design active noise cancelation systems for smart vehicle enclosures

In this study, active noise cancelation (ANC) systems are developed by a computational optimization framework based on particle swarm optimization (PSO), aiming to attenuate engine noise inside smart cubic vehicle enclosures. To have rapid estimation of acoustic properties, the main PSO algorithm is coupled with an analytical solution based on modified modal interaction method to evaluate the cost function. The optimum configurations, i.e., best positions and volume velocities of secondary sound sources, are defined for each resonant frequency. For numerical simulations, two vehicle enclosures of different size are considered to assess the applicability of the optimization algorithm. The overall performance of determined ANC systems is investigated, and it is shown that substantial noise reduction is achieved.

Optimized nonlocal active sound control in frequency domain

In the active sound control problem considered in the paper, a quite arbitrary closed region is acoustically shielded from ambient noise generated outside via implementation of secondary sound sources which are situated at the perimeter of the domain to be protected. It is presumed that the information available for the operation of control is only limited by the acoustic field that can be measured on a closed surface around the shielded region. The problem becomes much more complicated if there are desired sound sources situated inside the shielded region. In this case the input field is determined by contributions from noise, desired sound and controls. It is supposed that only the total acoustic field is available that makes the statement of the problem quite general and realistic. As the output, it is required to attenuate noise while preserving the desired field unaffected. To tackle the problem, a recently developed algorithm based on the nonlocal control is applied. From the point of view of a practical realization, the number of microphones and loudspeakers should be minimized. We propose for the first time some ways to essentially optimize distribution patterns of controls and sensors for the nonlocal control with preservation of desired sound. Numerical experiments are carried out for noise attenuation in a cube to study the trade-off between the level of noise reduction and number of sensors and controls. It is demonstrated that the nonlocal control can be efficiently realized with a reasonable number of sensors and controls. As shown, with only two controls per wavelength the achieved level of noise attenuation exceeds 10 dB. This result matches the optimal local control when any desired sound is absent.

Microcrack localization using a collinear Lamb wave frequency-mixing technique in a thin plate

A novel Lamb wave frequency-mixing technique is proposed for locating microcracks in a thin plate, which does not require the resonance condition of Lamb wave mixing and can accurately locate the microcracks through only one-time sensing. Based on the bilinear stress-strain constitutive model, a two-dimensional finite element (FE) model is built to investigate the frequency-mixing response induced by the interaction between two primary Lamb waves and a microcrack. When twoprimary Lamb waves of A0 and S0 modes with different frequencies excited on the same side of the plate simultaneously impinge on the examined microcrack, under the modulation of the contact acoustic nonlinearity, the microcrack itself can be deemed as the secondary sound source and it will radiate the Lamb waves of new combined frequencies. Based on the timeof flight of the generated A0 mode at difference frequency, an indicator named normalized amplitude index (NAI) is defined to directly locate the multi-microcracks in the given plate. It is found that the number and location of the microcracks can be intuitively visualized by using the NAI based frequency-mixing technique. It is also demonstrated that the proposed frequency mixing technique is a promising approach for the microcrack localization.

Method for Establishing a Traveling Wave Sound Field with Adaptive Control in a Water-Filled Sound Tube

The transfer function method is a common method for establishing a traveling wave field in a sound tube to measure the reflection and transmission coefficient of underwater material. The voltage applied to the secondary sound source can be calculated in accordance with the transfer matrix between the sound sources and hydrophones, then a traveling wave field can be established in the sound tube. However, the transfer function must be remeasured when the measurement frequency needs to be changed. A checking procedure of the traveling wave field in the sound tube is essential before measuring underwater acoustic material. If it is not an accurate traveling wave field, the secondary sound source signal should be corrected until the traveling wave field meets the requirements. To address these problems, an adaptive control method for generating plane traveling waves is proposed. The phase difference of sound pressures measured using the two hydrophones between the secondary sound source and the sample is used as the objective function in the adaptive algorithm, and the amplitude and phase of the secondary sound source can be obtained using the adaptive control system in the frequency domain. When a traveling wave field is formed, the reflection and transmission coefficient of the sample can be measured at the same time. With this method, the procedure of testing the traveling wave field is omitted. If the state of the primary sound source changes, the signal form of the secondary sound source can be changed immediately. Therefore, the efficiency of material measurement is improved. Theoretically, this method can obtain the most matching signal form of the secondary sound source, such that the accuracy of this method is remarkably high. Simulation and experimental results in this paper show that the measurement accuracy is reliable within the frequency range of 100–2500 Hz.

Study of the nonlocal active sound control with preservation of desired field in time domain.

In the active sound control, a domain is protected from externally generated noise via constructing secondary sound sources, which are called controls. These controls are applied on the boundary of the shielded domain. Apart from the external noise, a desired sound generated by interior sources should also be retained inside the shielded domain. However, it turns out it is a challenge to preserve the internally generated sound unaffected due to both the reverse effect of the controls on the input data and sparse distribution on the boundary. To take into account the reverse effect, an innovative algorithm based on nonlocal control is implemented in the time domain for the first time. Its real-time practical implementation may include preliminary tuning to the real surrounding conditions. A number of test cases are considered including external broadband noise and internal monochromatic desired sound. A sensitivity analysis is carried out with respect to some key design parameters such as density of sensors and controls as well as respective geometrical displacement from one another determined by the Hausdorff distance. It is demonstrated that the nonlocal control provides the noise attenuation level, which is not very sensitive to the presence of the desired sound.

Characterization of Microcrack Orientation Using the Directivity of Secondary Sound Source Induced by an Incident Ultrasonic Transverse Wave

In this paper, characterization of the orientation of a microcrack is quantitatively investigated using the directivity of second harmonic radiated by the secondary sound source (SSS) induced by the nonlinear interaction between an incident ultrasonic transverse wave (UTW) and a microcrack. To this end, a two-dimensional finite element (FE) model is established based on the bilinear stress–strain constitutive relation. Under the modulation of contact acoustic nonlinearity (CAN) to the incident UTW impinging on the microcrack examined, the microcrack itself is treated as a SSS radiating the second harmonic. Thus, the directivity of the second harmonic radiated by the SSS is inherently related to the microcrack itself, including its orientation. Furthermore, the effects of the stiffness difference between the compressive and tensile phases in the bilinear stress–strain model, and the UTW driving frequency, as well as the radius of the sensing circle on the SSS directivity are discussed. The FE results show that the directivity pattern of the second harmonic radiated by the SSS is closely associated with the microcrack orientation, through which the microcrack orientation can be characterized without requiring a baseline signal. It is also found that the SSS directivity varies sensitively with the driving frequency of the incident UTW, while it is insensitive to the stiffness difference between the compressive and tensile phases in the bilinear stress–strain model and the radius of the sensing circle. The results obtained here demonstrate that the orientation of a microcrack can be characterized using the directivity of the SSS induced by the interaction between the incident UTW and the microcrack.

Adaptive Active Vehicle Interior Noise Control Algorithm Based on Nonlinear Signal Reconstruction

In this study, to reduce secondary sound source pollution in the reference signal of active noise control (ANC), a novel ANC algorithm, based on signal reconstruction, is proposed for vehicle interior noise. This algorithm combines the processes of ear-sides noise reconstruction and ANC. First, to reduce non-stationarity and nonlinearity, multi-source noise signals outside the vehicle are decomposed into a finite number of intrinsic mode function (IMF) components by empirical mode decomposition (EMD). Second, the IMFs are reconstructed by the energy-extreme division method into three components: high-frequency, intermediate-frequency and low-frequency. The radial basis function neural network (RBFNN) parameters are adjusted by the proportions of the components. Model training is performed to obtain the high-precision EMD–RBFNN reconstruction model (EMD–NNRM). The reconstructed noise signal is used as the reference signal of the variable step-size least mean square (VSS-LMS) algorithm, to control the passenger ear-sides noise. The effectiveness of the EMD–NNRM is validated using four noise signals from the outside of a vehicle. The interior noise of a high-speed vehicle is processed by the proposed algorithm and the traditional VSS-LMS algorithm for comparison. The reconstruction results show that the mean absolute error is improved by 77.64% compared with the back propagation neural network reconstruction model. Reconstructed passenger ear-sides noise can be utilized for ANC. The active control results suggest that the proposed algorithm can not only effectively suppress the interior noise but can also avoid pollution from secondary sound sources.