Measurement Of Acoustic Signals Research Articles

Acoustic emission monitoring of composite marine propellers in submerged conditions using embedded piezoelectric sensors

Flexible composite marine propellers can aid the marine industry in reducing carbon emissions and underwater radiated noise pollution. The structural integrity of the blades can be assessed using structural health monitoring. One of these methods is the measurement and analysis of damage-induced acoustic emission signals. This paper experimentally investigates the feasibility of using embedded piezoelectric sensors for the measurement of acoustic emissions throughout a submerged flexible composite marine propeller blade. A full-scale glass-fibre reinforced polymer blade has been manufactured with 24 embedded sensors. While suspended in artificial seawater, acoustic emissions were simulated on the blade. The measurements show that the embedded piezoelectric sensors can measure acoustic emissions while the blade is submerged. Further, the distance from source to sensor over which the acoustic emission is measurable was investigated. For a noise level of 40 dB and a source amplitude of 70 dB between 100 and 250 kHz, an average maximum measurable distance of 124 mm was obtained. For higher frequencies, the distance drops and for lower noise levels the distance increases.

Measurement of Acoustic Signals to Characterize Household Appliance Based on Sound Power and Directivity Analysis

Measurement of acoustic signals to characterize the household appliance is very important for developing appropriate measures to avoid health hazards of in-house personnels. Acquisition and characterization of loud noise generated from a vacuum cleaner as a household machine is presented in the present paper. The common assumption regarding the community noise level is that the directivity of the sound radiation from a machine or any acoustic source is axisymmetric. However, it is true that this assumption does not valid when the condition of flow does not hold on. Particularly, if the characteristics of the sound source changes regarding to the signal features like frequency, intensity the directivity pattern of the sound radiation also changes. This characteristic has great influence to the noise reduction process as well. In the present paper the directivity of sound signal has been analyzed in anechoic chamber. Remarkable variations in acoustic signal propagation from the vacuum cleaner are recorded in the case of varying signal frequency with significant acoustic features. Furthermore, signal power from the tested devise is also clarified accordingly. Keywords: Acoustic Measurement, Sound Pressure Level, Directivity Analysis, Signal frequency, Household Appliance

Partial Discharge Localization in Power Transformers Using Invariant Extended Kalman Filter

This paper proposes a novel invariant extended Kalman filter (IEKF), a recently modified version of the extended Kalman filter (EKF), to estimate partial discharge (PD) location in a transformer insulation system model. An acoustic signal measurement is utilized to localize the PD location. Unlike conventional EKF methods, where the correction term used to update the state is linearly proportional to the output error, the correction term of the proposed algorithm is independent of the output error, resulting in a fast response with a significant reduction in the estimation error. In contrast to the EKF, the proposed method can successfully mimic the nonlinear dynamics and mitigate measurement noise stochasticity. Moreover, even if the measurement model fails to fully capture the PD’s dynamics, the IEKF will still sustain a reasonable performance. In contrast, conventional EKFs can easily diverge if a mismatch between the measurement model and the true measurement occurs. Experimental results are shown to verify the proposed method’s performance compared to a recently published variant of the EKF.

PHYSICOCHEMICAL ASPECTS OF THE WORK OF PASSENGER CAR BRAKE LININGS. PART II THE EFFECT OF LUBRICATING ADDITIVES

The paper presents the influence of various systems of lubricating additives which determine the performance of the friction materials of brake linings. The base hybrid friction material formulation was modified with various types of lubricating additives. These additives are divided into groups containing commonly used lubricating materials: carbons and sulphides, compounded in various proportions, influencing the formation and structure of the so-called third body layer (TBL) on the surface of the brake disc because of braking. Raman Spectroscopy (RS), time of flight Secondary Ion Mass Spectroscopy (ToF-SIMS) and high-resolution scanning electron microscopy with an X-ray analyser (SEM-EDS) equipped with a focus ion beam (FIB) were used for chemical and morphological analysis of the surface layer of brake disc after breaking tests. The results of the physicochemical analysis of TBL were correlated with the results of tribological tests (according to the SAE-J2522 procedure, commonly known as AK-Master) on a brake dynamometer adapted to the measurements of acoustic signals (NVH – noise, vibration, and harshness). The obtained results confirm the important role played by the so-called third body layer, formed on the surface of the brake disc for safety (COF), durability (wear of friction elements) and the acoustic spectrum accompanying braking.

Dissipative solitons in optical microresonators

<p indent="0mm">A soliton is a stationary local structure that keeps its waveform and spreading speed during propagation. Recent research shows that chip-scale optical microresonators can support dissipative solitons with surprisingly high energy efficiency and stability. The formation of optical microresonator dissipative solitons requires two balances, gain-loss balance and dispersion-nonlinearity balance. The gain-loss balance maintains the soliton’s amplitude while the dispersion-nonlinearity balance keeps its width. In this paper, we review the formation, development, and applications of dissipative optical solitons, as well as dissipative mechanical solitons in optical microresonators, and analyze the balances in different solitons. This review mainly consists of two parts: Optical microresonator dissipative solitons and opto-mechanical microresonator dissipative solitons. The first part discusses a typical kind of solitons named dissipative Kerr solitons. Dissipative Kerr solitons balance the propagation dispersion through Kerr nonlinearity in optical microresonators and are widely studied due to their easy implementation in silicon-based microcavities. In order to improve the practical performance of dissipative Kerr solitons, researchers have proposed many schemes to improve their stability and efficiency. Meanwhile, various high-precision sensing applications based on dissipative Kerr solitons, such as photonic radar, range measurement, and absorption spectrum detection, have drawn extensive attention. The second part introduces the dissipative solitons in optomechanical microresonators. A recently-discovered type of solitons, optomechanical dissipative solitons, is introduced. Unlike the dissipative Kerr solitons, the optomechanical dissipative solitons gain their power from phonon lasing, and compensate the propagation dispersion by optomechanical nonlinearity. The dynamics of the optomechanical dissipative solitons are described by the modified Korteweg-de Vries equation. Low-frequency optomechanical dissipative solitons can achieve kHz-accuracy acoustic signal measurement, which can be used in acoustic detection and communication. Finally, we summarize the formation, development, and applications of dissipative solitons in optomechanical microresonators. We also provide an outlook for future applications like radio-frequency calibration, radio-frequency communications, and underwater tomography.

PHYSICOCHEMICAL ASPECTS OF THE WORK OF PASSENGER CAR BRAKE LININGS. Part I: THE EFFECT OF FRICTIONAL ADDITIVES

The paper presents the influence of various systems of abrasive additives which determine the performance of the friction materials of brake pads. A friction material was used for the tests, in which the base recipe was modified with various types of abrasive additives: 1. “low steel” – of low steel content, containing aluminium and chromium oxides; 2. “hybrid” – containing in addition to abrasive components from the low steel family, abrasive components such as zirconium silicate, magnesium oxide or iron oxides, which are characteristic of the family of asbestos-free organic materials (NAO); and 3. “mild hybrid” – containing abrasive components found in the friction materials of the NAO family, on the formation and structure of the so-called third body on the surface of the brake disc as a result of braking. High-resolution scanning electron microscopy with an X-ray analyser (SEM-EDS) equipped with a focus ion beam (FIB) was used to study film thickness, morphology, and chemical composition. The results of the physicochemical analysis of the third body were correlated with the results of tribological tests on a brake dynamometer adapted to the measurements of acoustic signals (NVH – noise, vibration and harshness). The tests were carried out in accordance with the SAE-J2522 procedure, commonly known as AK-Master. The obtained results confirm the important role played by the so-called third body, formed on the surface of the brake disc for safety (COF), durability (wear of friction elements) and the acoustic spectrum accompanying braking.

Silicon-photonics acoustic detector for optoacoustic micro-tomography

Medical ultrasound and optoacoustic (photoacoustic) imaging commonly rely on the concepts of beam-forming and tomography for image formation, enabled by piezoelectric array transducers whose element size is comparable to the desired resolution. However, the tomographic measurement of acoustic signals becomes increasingly impractical for resolutions beyond 100 µm due to the reduced efficiency of piezoelectric elements upon miniaturization. For higher resolutions, a microscopy approach is preferred, in which a single focused ultrasound transducer images the object point-by-point, but the bulky apparatus and long acquisition time of this approach limit clinical applications. In this work, we demonstrate a miniaturized acoustic detector capable of tomographic imaging with spread functions whose width is below 20 µm. The detector is based on an optical resonator fabricated in a silicon-photonics platform coated by a sensitivity-enhancing elastomer, which also effectively eliminates the parasitic effect of surface acoustic waves. The detector is demonstrated in vivo in high-resolution optoacoustic tomography.

Time-Frequency analysis of acoustic signals from tyre-pavement interaction.

The acoustic responses of a dynamical system reflect the characteristics of the external excitation and vibrating system. The objective in an identification problem is to characterise the system and excitation from the measured responses. This becomes challenging if the characteristics of the dynamical system are time-varying. The analysis of the acoustic signal generated as a result of the tyre-pavement interaction (TPI) is one such situation, where in order to study the time-varying nature there is a need to obtain the characteristics of the instantaneous response. This study explores the single frequency filtering analysis of signals to examine the time-varying characteristics of tyre-pavement interaction noise (TPIN). Field measurements of TPI acoustic signals were obtained for a two-wheeler driven at different speeds on asphalt and cement concrete pavements. The time-frequency characteristics of the tyre tread impact and of the air cavity resonances are analysed by investigating the effect of vehicular speed and pavement type on TPIN. The specific features of TPIN such as the harmonics due to periodic tread impact and the frequency response due to resonances of the air cavities are examined in detail. The analysis presented in this paper will be useful in developing methods for health monitoring of tyre and pavement systems.

Research on Characteristics of Broadband Acoustic Sensor Based on Silicon-Based Grooved Microring Resonator

In order to meet the requirements of having a small structure, a wide frequency band, and high sensitivity for acoustic signal measurement, an acoustic sensor based on a silicon-based grooved microring resonator is proposed. In this paper, the effective refractive index method and the finite element method are used to analyze the optical characteristics of a grooved microring resonator, and the size of the sensor is optimized. The theoretical analysis results show that, when the bending radius reaches 10 μm, the theoretical quality factor is about 106, the sensitivity is 3.14 mV/Pa, and the 3 dB bandwidth is 430 MHz, which is three orders of magnitude larger based on the sensitivity of the silicon-based cascaded resonator acoustic sensor. The sensor exhibits high sensitivity and can be used in hydrophones. The small size of the sensor also shows its potential application in the field of array integration.

KM3NeT underwater autonomous power supply system

The KM3NeT Collaboration aims to build in the depths of the Mediterranean Sea a neutrino telescope that consists of a kilometer-cube grid of photosensors encapsulated into transparent pressure resistant glass spheres. A crucial component of the detector is the acoustic positioning system, which provides the position of photodetectors and structures in the deep sea with an accuracy of about 10 cm. The system is based on measurements of acoustic signals between fixed seabed emitters and receiving hydrophones. A subset of the required acoustic beacons is powered by an autonomous power supply system based on a high-charge battery pack. This paper describes the innovative design used to build the battery packs, derived from the expertise in the construction of underwater detectors encapsulated in glass vessels. The battery pack uses a pressure resistant 17-inch glass sphere as housing, which contains a cluster of 96 batteries properly connected to supply an output DC voltage of 12 V with a total capacity of 410 Ah. The cluster of batteries is surrounded by silicone glue, that stacks all the part together, ensuring mechanical connection with the housing and protecting the batteries against humidity. In order to increase the operating time of the beacon, a custom designed wake-up board is added to implement a duty cycle operating mode. An electronic switch controlled by an ARDUINO microprocessor connects the battery pack to the beacon only for a defined time. So far, 8 supply systems have been deployed at the KM3NeT sites. The beacon battery pack could be easily modified for multipurpose deep-sea applications.

Comparisons of Temporal Characteristics of Respiration and Swallowing Coordination between Young and Elderly

Objectives: The relationship between breathing and swallowing is very dynamic during swallowing and these are highly temporally coordinated to protect the airway. The ability to protect airways during swallowing deteriorates with aging. In this study, we attempted to compare the breathing-swallowing pattern and temporal change in the respiration and swallowing coordination between young and elderly adults in Korea.Methods: A total of 80 normal people, including 40 young and 40 elderly people participated in this study. For measurement of breathing and swallowing coordination, Digital Swallowing Workstation&lt;sup&gt;TM&lt;/sup&gt; was used during a 5 mL water swallowing task. Temporal parameters related to breathing-swallowing including AS (acoustic start), AP (acoustic peak), AD (acoustic duration), SAS (swallowing apnea or respiration pause start), SAD (swallowing apena duration), sES (submental sEMG start), sEP (submental sEMG peak), sED (submental sEMG duration). Additionally, DHI (Dysphagia Handicap Index) was evaluated for self-assessment of the degree of difficulty swallowing.Results: Older adults displayed delayed swallowing-related acoustic signal measurements, swallowing apnea measurements, surface EMG measurements, and delayed sequential coordination time of swallowing-related structures during swallowing. There were no significant differences according to gender. Furthermore, a significant positive correlation was observed between the total K-DHI scores and as well as swallowing apnea duration in the elderly.Conclusion: In the older population, the different breathing-swallowing pattern from that of young adults may increase the risk of dysphagia. In addition, swallowing delays due to aging can be an indicator of elderly swallowing disorders. Moreover, an increase in apnea time during swallowing may be a phenomenon that appears as a mechanism for airway protection in the elderly. However, the high correlation between apnea time and K-DHI score in the elderly may make it difficult to maintain respiration for a long time during swallowing as the respiratory function decreases due to aging, which may increase the risk of experiencing symptoms such as choking and affect the degree of subjective swallowing disorder. This suggests that even if classified as a normal elderly person without a pathological swallowing disorder, swallowing training is needed to prevent swallowing disorders and to enhance swallowing ability for older people with degraded swallowing-related abilities.

A Non-Contact Fault Diagnosis Method for Bearings and Gears Based on Generalized Matrix Norm Sparse Filtering.

Fault diagnosis of mechanical equipment is mainly based on the contact measurement and analysis of vibration signals. In some special working conditions, the non-contact fault diagnosis method represented by the measurement of acoustic signals can make up for the lack of contact testing. However, its engineering application value is greatly restricted due to the low signal-to-noise ratio (SNR) of the acoustic signal. To solve this deficiency, a novel fault diagnosis method based on the generalized matrix norm sparse filtering (GMNSF) is proposed in this paper. Specially, the generalized matrix norm is introduced into the sparse filtering to seek the optimal sparse feature distribution to overcome the defect of low SNR of acoustic signals. Firstly, the collected acoustic signals are randomly overlapped to form the sample fragment data set. Then, three constraints are imposed on the multi-period data set by the GMNSF model to extract the sparse features in the sample. Finally, softmax is used to as a classifier to categorize different fault types. The diagnostic performance of the proposed method is verified by the bearing and planetary gear datasets. Results show that the GMNSF model has good feature extraction ability performance and anti-noise ability than other traditional methods.

Research of eddy current sensors applied to displacement-based vector hydrophones

This paper provides insights into the principle of eddy current sensors applied to displacement-based vector hydrophones by both theoretical and experimental analyses. These displacement-based vector hydrophones provide excellent performances at the Ultra-Low Frequency. First, theoretical calculations are presented to demonstrate the feasibility of the eddy current sensors for measurements of underwater acoustic signals. Theoretical models are then established to calculate the transduction constants of eddy current sensors with the flat, spherical, and cylindrical conductive materials, respectively. The influence of the axial offset of eddy current sensors on the transduction constant is analyzed by finite element models lastly. The theoretical models are further validated by comparison with experimental results. The experiment results show that, when the radii of the spherical and cylindrical conductive materials are greater than eight times the coil radius, the spherical and cylindrical conductive materials are equivalent to the flat conductive material. Moreover, the axial tolerable offset between the conductive material and the coil is proportional to the radius of the spherical or cylindrical conductive material.

EXPERIMENTAL INVESTIGATIONS OF THE INFLUENCE OF SCREENS AND PROTECTIVE EQUIPMENT ON THE LEVEL OF ACOUSTIC SIGNAL IN A ROOM WITH GLASS AND METAL PLASTIC

In the digital stage of world development, information is constantly expanding its facets. That is why the exchange of information is a leading component of constant change in life. Although humanity is gradually moving to the use of electronic technology, acoustic information still plays a key role in information circulation. This applies to official communication in public institutions up to the highest level, business contacts in commercial structures and private communication between people. The process of transmitting information in acoustic form has dangerous consequences. The use of appropriate devices, such as directional acoustic microphones or technical intelligence acoustic antennas, which may be outside the scope of the information activity, makes it possible to obtain unauthorized information that should not reach third parties. Therefore, the task of detecting and protecting information leakage channels, including acoustic ones, is gaining a new degree of importance every day. The protection of the premises or building, where acoustic information regularly circulates, provides a set of organizational and technical measures and means of protection of information circulation, taking into account the peculiarities of the location and arrangement of the object. This study involves the study of the dependence of the level of the acoustic signal on ways to prevent leakage of information through the acoustic channel, which includes vibration noise by means of technical protection and coverage of improvised materials (shielding) of enclosing structures of information activities (OID). The experiment determines the degree of influence of density, sound-absorbing properties of materials and their combinations on acoustic oscillations, the source of which is in the OID. The object of the study was a basic room, where the enclosing structures are walls with windows and doors, ceiling and floor. It is also worth noting that the acoustic signal measurements were not performed in complete silence, which directly affected the accuracy of the results. This step was taken in order to best reproduce the conditions in which criminals often work.

Identification of Gate Turn-off Thyristor Switching Patterns Using Acoustic Emission Sensors.

Modern seagoing ships are often equipped with converters which utilize semiconductor power electronics devices like thyristors or power transistors. Most of them are used in driving applications such as powerful main propulsion plants, auxiliary podded drives and thrusters. When it comes to main propulsion drives the power gets seriously high, thus the need for use of medium voltage power electronics devices arises. As it turns out, power electronic parts are the most susceptible to faults or failures in the whole electric drive system. These devices require efficient cooling, so manufacturers design housings in a way that best dissipates heat from the inside of the chips to the metal housing. This results in susceptibility to damage due to the heterogeneity of combined materials and the difference in temperature expansion of elements inside the power device. Currently used methods of prediction of damage and wear of semiconductor elements are limited to measurements of electrical quantities generated by devices during operation and not quite effective in case of early-stage damage to semiconductor layers. The article presents an introduction and preliminary tests of a method utilizing an acoustic emission sensor which can be used in detecting early stage damages of the gate turn-off thyristor. Theoretical considerations and chosen experimental results of initial measurements of acoustic emission signals of the medium voltage gate turn-off thyristor are presented.

Process Monitoring in Heavy Duty Drilling Rigs—Data Acquisition System and Cycle Identification Algorithms

The monitoring of drilling processes is a well-known topic in the mining industry. It is widely used for rock mass characterization, bit wear monitoring and drilling process assessment. However on-board monitoring systems used for this purpose are installed only on a limited number of machines, and breakdowns are possible. There is a need for a data acquisition system that can be used on different drilling rigs and for an automatic data analysis procedure. In this paper, we focused on the automatic detection of drilling cycles, presenting a simple yet reliable system to be universally installed on drilling rigs. The proposed solution covers hardware and software. It is based on the measurement of electric current and acoustic signals. The signal processing methods include threshold-based segmentation, a short-time envelope spectrum and a spectrum for the representation of results. The results of the research have been verified on a real drilling rig within the testing site of its manufacturer by comparing the results with the data of the on-board monitoring system installed on the machine. Novel aspects of our approach include the detection of the pre-boring stage, which has an intermediate amplitude that masks the real drilling cycles, and the use of the percussion instantaneous frequency, which is estimated by acoustic recordings.

Improved TOA Estimation Method for Acoustic Ranging in a Reverberant Environment

Indoor localization based on the time-of-arrival (TOA) measurements of acoustic signals has advantages of low cost, high accuracy and no electromagnetic interference compared with other location technologies such as Bluetooth and Wi-Fi. However, conventional TOA estimation approaches based on peak extraction or fixed thresholds have difficultly maintaining high ranging accuracy and robustness in reverberant indoor enclosed environments. To address this situation, this paper presents an improved TOA estimation method for acoustic ranging in a reverberant environment that is composed of two processes. One is an acoustic reverberant cancellation technique based on the signal power spectra, and the other is a first-extremum-based match filter. To verify the performance of the improved TOA estimation method, indoor experiments were conducted in an enclosed noisy and reverberant underground parking garage. The experimental results demonstrate that the proposed algorithm is superior to a traditional quadratic cross-correlation and match filter in terms of estimation accuracy and robustness.

Shock Acoustic Emission upon Collision of a Droplet of Variable Shape with the Water Surface

Sound emission at the stage of supersonic expansion of a contact spot upon collision of a droplet with the water surface is discussed in theoretical and experimental setting. Measurements of acoustic signals were carried out with simultaneous video recording of the falling drop. The shock pulse amplitude does not depend on the shape of the underwater drop segment; it is determined only by the impact velocity and current geometric parameters of the surface segment, of which the shape is fixed in the video frame that is last one before impact. The shape envelope is approximated by continuous function that is used to simulate the supersonic expansion of the contact spot and calculate the shock pulse amplitude. Closeness of the calculated and experimental data confirms the stability of the shape of the surface drop segment during the shock pulse emission.

Nonlinear characteristics analyses of particle motion for predicting flow regimes

Gas–solid flow regimes have a significant impact on particle transport and separation in a fluidized bed reactor. In this study, to determine flow regime transitions in gas–solid fluidized beds, an acoustic technique was used to detect and analyze the behavior of gas and solids. Algorithm complexity, fluctuation complexity, and Shannon entropy analyses of acoustic emission signals were performed to examine nonlinear system characteristics, and to determine the flow regime transition velocities uc, uk, and uFD. Moreover, using the standard deviation of pressure signals, pressure measurements and acoustic measurements were compared. The relative deviations (RDs) between the experimental and empirical values of uk were 8.8%, 13.7%, 8.8%, and 30.4% for the algorithm complexity, fluctuation complexity, Shannon entropy, and pressure signal standard deviation, respectively, while the respective RDs for uFD were 15.7%, 23.9%, 15.7%, and 97.8%. The RDs between the experimental and empirical values of uc were all 6.4%. The experimental values obtained from acoustic signal measurements were therefore closer to the empirical values. In summary, the integration of non-intrusive acoustic measurements, complexity analysis, and Shannon entropy analysis is suitable for identifying flow regime transitions.

T* of Relaxor Ferroelectric (1 − x) Pb(Zn1/3Nb2/3)O3‐xPbTiO3 Single Crystals Revisited Using Brillouin Spectroscopy

The relaxor characteristics of Pb[(Zn1/3Nb2/3)1–xTix]O3 (PZN‐xPT) single crystals (with x = 0 and x = 0.08) are investigated using temperature‐dependent Brillouin scattering spectroscopy. The longitudinal acoustic (LA) mode shows typical relaxor behaviors for PZN, whereas its mode frequency exhibits a discontinuous change at the phase transition temperature (TC) for PZN‐8%PT. The transverse acoustic (TA) mode, which is forbidden in an ideal cubic phase at the backscattering geometry, appears in both samples at a certain temperature above either the dielectric maximum temperature (Tm) or TC. This breakdown of the Brillouin selection rule in the cubic phase indicates that the noncubic polar regions become appreciable at this temperature where the interaction between the acoustic waves and the polar nanoregions (PNRs) is strong enough to enable the appearance of the TA mode. The intermediate characteristic temperature T* is determined in terms of the minimum of the temperature derivative of the half width of the LA mode, and the values are nearly the same as those determined via the acoustic emission signal measurements. These comparisons reveal the universal feature of the local phase transformation from dynamic to quasistatic PNRs at T*, giving rise to the appearance of the TA mode.