Acoustic Response Signals Research Articles

Explaining the correlation between subharmonic amplitude and ambient pressure for subharmonic-aided pressure estimation (SHAPE)

BackgroundSubharmonic aided pressure estimation (SHAPE) is an innovative non-invasive technique that leverages ultrasound subharmonic imaging to estimate pressure. This method exploits the “negative correlation between subharmonic amplitude and ambient pressure” observed in experimental settings. Despite extensive experimental validation and some promising results in clinical studies, the underlying mechanism of SHAPE remains incompletely understood. Although some studies have attempted to provide theoretical explanations, definitive conclusions have yet to be reached. In addition, theoretical investigations have mainly focused on the steady oscillation of bubbles under long pulse excitation, which contrasts with the short pulse excitation required for clinical SHAPE applications. An understanding of the SHAPE principle under short pulse excitation is needed. MethodsThe exponential elasticity model (EEM) was used to simulate Sonazoid bubbles, and a probe-to-probe acoustic propagation model was introduced to mimic a practical SHAPE scenario. The simulated acoustic signals in response to three-cycle sinusoidal pulse excitations were analyzed for spectral composition. The relationship between microbubble oscillation patterns and subharmonic characteristics was identified through detailed investigation. ResultsFor the excitation pulse of 2.5 MHz frequency and 350 kPa magnitude, bubbles larger than the resonance radius (2.29 μm) exhibited significant subharmonics in the magnitude spectrum, while bubbles smaller than the subharmonic resonance radius (3.85 μm) showed the activity of scattering subharmonic energy and the sensitivity to ambient pressure. The emergence of subharmonics when increasing excitation power was related to the increasing amplification of the bubble self-oscillation and the period-doubling features in the acoustically forced oscillation. The negative correlation between subharmonic amplitude and ambient pressure was attributed to the reduced self-oscillation caused by increasing ambient pressure and hence bubble size reduction. Microbubbles falling between 2 and 3 μm showed the desired subharmonic sensitivity to ambient pressure under the specified excitation conditions. ConclusionThe transient oscillatory behavior of microbubbles in response to short pulse excitation, characterized by a ringing down self-oscillation after the acoustic forcing effect has ceased, is crucial for understanding the subharmonic emergence and the observed negative correlation between subharmonic amplitude and ambient pressure. The proposed concepts of subharmonic resonance radius, subharmonic-significant bubbles, and subharmonic-active bubbles provide valuable insights into the diverse subharmonic behavior of microbubbles. The theoretical explanation of this negative correlation highlights the importance of using subharmonic-significant-and-active bubbles for SHAPE applications.

Detection and Analysis of Abnormal High-Current Discharge of Cylindrical Lithium-Ion Battery Based on Acoustic Characteristics Research

The improvement of battery management systems (BMSs) requires the incorporation of advanced battery status detection technologies to facilitate early warnings of abnormal conditions. In this study, acoustic data from batteries under two discharge rates, 0.5 C and 3 C, were collected using a specially designed battery acoustic test system. By analyzing selected acoustic parameters in the time domain, the acoustic signals exhibited noticeable differences with the change in discharge current, highlighting the potential of acoustic signals for current anomaly detection. In the frequency domain analysis, distinct variations in the frequency domain parameters of the acoustic response signal were observed at different discharge currents. The identification of acoustic characteristic parameters demonstrates a robust capability to detect short-term high-current discharges, which reflects the sensitivity of the battery’s internal structure to varying operational stresses. Acoustic emission (AE) technology, coupled with electrode measurements, effectively tracks unusually high discharge currents. The acoustic signals show a clear correlation with discharge currents, indicating that selecting key acoustic parameters can reveal the battery structure’s response to high currents. This approach could serve as a crucial diagnostic tool for identifying battery abnormalities.

Loudspeaker Abnormal Sound Classification Using Auditory Perception Weighted by Energy Entropy

In order to improve the classification accuracy of loudspeaker abnormal sounds, this paper proposes a method based on time-varying specific loudness weighted by energy entropy and principal component analysis. This method simulates human auditory perception mechanism to process loudspeaker sound response signal to obtain more effective features. The human hearing system can be divided into many parallel and functionally independent conduction pathways according to frequency. The energy of the acoustic signal in each pathway can be discerned. Therefore, the time-varying specific loudness is calculated firstly to build the quantitative correlation of loudspeaker’s acoustic response signals and human hearing sensations. Each sub band loudness is weighted by energy entropy to highlight the acoustic strength variation with time and frequency. Then, important features are extracted by two dimensional-principal component analysis (2D-PCA). Finally, the whale optimization algorithm-least squares support vector machine (WOA-LSSVM) is adopted for classification. Visual analysis of the extracted features shows that this method can extract loudspeaker response signal features with better discriminability. Classification experimental results show that the average accuracy of this method reached 98.4%, which is higher than the classification method based on traditional time-frequency domain statistical features. The loudspeaker abnormal sound classification method in this paper simulates human auditory perception to extract features and is able to improve classification accuracy and automation effectively.

Evaluation of the influence of preliminary low-velocity impacts on the residual fatigue life of CFRP composites

PurposeThe main purpose of this study was to evaluate the mechanical behaviour of layered fibrous carbon-fibre reinforced plastic (CFRP) under complex low-speed bending and impact loads and subsequent cyclic tensile loads.Design/methodology/approachA comprehensive approach was adopted to study the damage accumulation processes using state-of-the-art testing and diagnostic equipment. In the course of the study, a microstructure analysis of damages caused by a transverse impact and cyclic tension was performed.FindingsA dependence of residual fatigue life of the studied composite material on the intensity of the preliminary impact bending was established. Temperature field distribution fields on the surface of the sample during tests were shown. Data on damage accumulation processes were presented, which were obtained during the registration of acoustic emission signals.Originality/valueA connection was established between changes of registered acoustic response signals and thermal imaging camera data, which was supported by the results of an experimental study. The results of the comprehensive approach showed a qualitative correlation.

Comprehensive evaluation of fatigue damage accumulation and failure of specimens with operational stress concentrators

The paper presents the results of studying the mechanical behavior of laminated carbon-fiber-reinforced plastic under complex low-velocity impact three-point bending followed by cyclic tension. An integrated approach to studying damage accumulation patterns is implemented with the use of state-of-the-art testing and diagnostic equipment. The residual fatigue life of the composite is related to the intensity of preliminary impact bending. The fields of temperature distribution in the active zone of the samples during the tests are shown. Data on damage accumulation obtained by recording acoustic emission signals are presented. Relation of the change in the recorded acoustic response signals to infrared thermal scanning data has been detected, which is supported by the results of an experimental study. The use of additional equipment for infrared thermal scanning and recording of acoustic emission signals gives a complete picture of damage accumulation and failure in composite materials, with a good agreement with experimental data.

A mathematical model for the impact of noise on population dynamics of a single species experiencing Lombard effect

Noise is a form of pollution resulting from the undeniable increase in industrialization worldwide. Consequently, it is becoming increasingly important to understand the underlying mechanisms and potential effects of noise on ecosystems. In this study, we propose a deterministic mathematical model that uses a system of nonlinear, non-autonomous differential equations to describe the population dynamics of a single species exposed to noise. The Lombard effect is a phenomenon that involves increasing the intensity of acoustic signals in response to noise, which can mask and degrade acoustic signals and prevent them from being recognized or discriminated by their target receivers. However, when the anthropogenic noise is chronic and critical (i.e., that by its long duration and high intensity positively affects the mortality rate), the increase in the intensity of acoustic signals (due to the Lombard effect) only increases the chronic critical anthropogenic noise and also increase energetic, behavioral and predation costs. Therefore, the critical noise generated by the use of higher intensity acoustic signals (due to the Lombard effect) together with the chronic critical anthropogenic noise, negatively affect population survival. We analyzed the persistence of the population and found that our results are consistent with the observed ecological data as they suggest that, the maximum intensity level of critical chronic anthropogenic noise, consequently, by the Lombard effect, the maximum intensity of self generated acoustic signals, must decrease to ensure population persistence. However, when the maximum intensity level of critical chronic anthropogenic noise is uncontrollable, it is sufficient to reduce its mean intensity level to ensure persistence in the population mean. Furthermore, decreasing the degree to which noise affects the population favors the survival of the species. Finally, to validate our results, we performed numerical simulations.

Anthropogenic noise, song, and territorial aggression in southern house wrens

Anthropogenic noise constrains the transmission of birdsong and alters the behavior of receivers. Many birds adjust their acoustic signals to minimize the interference of anthropogenic noise on signal transmission. Birds may also change their acoustic signals to exchange information during aggressive interactions. However, it is unclear how birds deal with a potential trade‐off between adjusting their acoustic signals to better transmit in noisy environments versus mediating aggressive interactions. Additionally, we do not know how urbanization and anthropogenic noise alters the territorial behavior of receivers. We investigated the interplay among song, territorial aggression, urbanization, and anthropogenic noise, in males of the southern house wren Troglodytes aedon musculus, using recordings of spontaneous songs (non‐aggressive context) and a playback experiment simulating a male territorial intrusion (aggressive context). We found that urban wrens behaved more aggressively in response to the intruder by singing more and spent more time closer to the intruder than rural wrens regardless of noise. Males produced songs with lower minimum frequency and trills with wider frequency bandwidth and higher vocal performance under acute (playback) than relaxed (post‐playback) aggressive encounters. These results suggest that males use songs to communicate aggressive intent or fighting ability. Urban wrens produced higher‐pitched songs and trills than rural wrens irrespective of aggressive context. Urban wrens in the noisiest territories also produced the highest‐pitched trills but only in the non‐aggressive context. Rural wrens in the noisiest territories tended to produce the longest songs (non‐aggressive context) or produced the shortest songs (aggressive context). Results suggest that urbanization affects territorial and vocal behaviors in southern house wrens. Males in this species seem to primarily adjust acoustic signals in response to the territorial intruder rather than noise.

Urban cycles of human activity do not significantly alter the behaviour of a duetting bird

The weekend effect hypothesis predicts that weekly cycles of human activity impact animal behaviour and physiology. This hypothesis has been supported in the context of recreational activity in natural environments but it is unknown whether it also applies to urban animals. We tested this hypothesis by comparing the sentinel (territorial vigilance), foraging and vocal behaviours of an urban‐dwelling bird, the Rufous Hornero Furnarius rufus, between weekdays and weekends (and holidays) within a university campus in central Brazil. The level of human activity (noise, traffic and pedestrian flow) increases greatly on weekdays on this campus. We predicted that the birds would perceive a greater predation risk and would need to adjust their acoustic signals in response to anthropogenic noise on weekdays. Thus, we expected that the birds would spend more time as sentinels and less time foraging, and would sing for longer periods and at a higher pitch on weekdays than on weekends. We also expected weaker duet responsiveness (answering partner‐initiated song) on noisier weekdays than on weekends, assuming that noise would disrupt signal transmission between partners. We found that birds spent slightly more time (˜ 4%) in sentinel behaviour and less time (˜ 2–5%) foraging on weekdays than on weekends, but these effects were small and not statistically significant. Birds were equally likely to sing solos, start duets and answer partner‐initiated duets on weekends and weekdays. Finally, phrase duration and acoustic parameters of duets were similar on weekends and weekdays. Our results provide little support for the weekend effect hypothesis, suggesting that these urban‐dwelling birds may be habituated or indifferent to periodic variation in human activity levels.

Treefrogs adjust their acoustic signals in response to harmonics structure of intruder calls

AbstractSpectral properties of animal acoustic signals may help individuals to assess the characteristics of rivals and to adjust their competitive strategies in territorial disputes. Thus, we hypothesized that the distribution of energy across frequency bands in anuran calls determines behavioral responses in male–male competition. Using playback experiments, we investigated the relevance of the harmonic calls in the acoustic communication of the treefrog Dendropsophus minutus. We exposed territorial males to three synthetic acoustic stimuli composed of aggressive notes: 1) standard call (all harmonics and peak frequency corresponding to the second band); 2) inverted-energy call (all harmonics and peak frequency corresponding to the first band); and 3) concentrated-energy call (all energy contained in the second harmonic). Males responded aggressively to all stimuli, mainly by increasing the rate and duration of their aggressive notes. However, when exposed to stimuli with different harmonic configurations, males changed the harmonic structure of their own calls, emitting more A- and B-notes with peak power in the fundamental frequency, particularly when exposed to the concentrated-energy call. Our results suggest that male frogs may use the harmonic structure of calls to assess opponents and modulate territorial and aggressive behavior, triggering complex acoustic adjustments. This study contributes to our knowledge about the functions of acoustic traits in amphibian social interactions, and particularly of the presence of harmonics that has received less attention compared to other acoustic properties in the study of animal acoustic communication.

Study on Mechanical Properties of Basalt Fiber‐Reinforced Concrete with High Content of Stone Powder at High Temperatures

Concrete materials are an important part of global structure, and their fire resistance directly affects the safety of buildings and tunnels. In this study, basalt fiber was used to reinforce concrete with high content of stone powder in order to enhance its high‐temperature performance. The mechanical properties and ultrasonic characteristics at different temperatures were studied using the cube compressive strength test and nonlinear ultrasonic test. The results indicated that the addition of basalt fiber in specimens improved their compressive strength; however, this strength did not continuously increase with increases in the fiber length and fiber content, and the optimal values for fiber length and fiber content were determined to be 12 mm and 1 kg/m3 at 600°C, respectively. With increases in temperature, the unconfined compressive strength increased first and then decreased. When the temperature was 400°C, the unconfined compressive strength of the specimens reached their highest values and then decreased. When the temperature was 400°C and 600°C, the strength of the stone powder concrete with fiber was higher than that without fiber, which shows that fiber can improve the mechanical properties of concrete at high temperatures. Based on the Box‐Behnken design (BBD) method, the unconfined compressive strength response regression model of basalt fiber‐reinforced concrete with high content of stone powder, which follows parameters including fiber content, fiber length, and temperature at high‐temperature environments, was established, and it was found that the interaction of fiber content, fiber length, and the temperature was significant based on multifactor interaction analysis. The analysis of ultrasonic signals based on the S transform showed that, with increases in temperature, the amplitudes of the acoustic response signals, the corresponding frequency spectrum, and the time‐frequency spectrum were clearly reduced. At the same temperature, the amplitudes of the acoustic response signals of different concrete testing blocks did not change much and remained at the same level.

Species sensitivities to a global pollutant: A meta-analysis on acoustic signals in response to anthropogenic noise.

Anthropogenically driven environmental changes affect our planet at an unprecedented rate. Among these changes are those in the acoustic environment caused by anthropogenic noise, which can affect both animals and humans. In many species, acoustic communication plays a crucial role to maintain social relationships by exchanging information via acoustic signals. However, how species relying on acoustic communication differ in their adjustments to anthropogenic noise is little understood. Yet, this is crucial because protecting species effectively depends on our capability to predict how species differ in their response to human‐induced environmental changes. Using a phylogenetically controlled meta‐analysis, we quantified differences in adjustments of acoustic signals to anthropogenic noise among species. The effect sizes included in the analysis were obtained from noise exposure experiments, as only carefully controlled experiments allow to establish cause‐and‐effect relationships. We found that animals changed acoustic signals when exposed to noise, but the magnitude and the direction of adjustments differed among species. Given the importance of communication in the animal kingdom, these adjustments can affect social relationships in many species. The diversity of responses among species highlights the necessity to assess the effect of environmental stressors not only for a few species, because an effect may be positive in one species but negative in another depending on the species’ biology. Thus, an effective conservation approach to protect different species is to preserve natural soundscapes of ecosystems to which species have adapted to by reducing or mitigating the emission of anthropogenic noise into the environment.

Monitoring Viscosity and Total Solids Content of Milk Protein Concentrate Using an Inline Acoustic Flowmeter at Laboratory Scale.

Control of milk concentrate viscosity and total solids (TS) content prior to spray drying can improve dairy ingredient manufacture. However, the availability of hygienic and appropriately pressure rated process viscometers for inline monitoring of viscosity is limited. An acoustic flowmeter (FLOWave) is an inline process analytical technology (PAT) tool that measures changes in acoustic signals in response to changes in liquid properties (i.e., acoustic transmission (AT), acoustic impedance (AI), temperature and volume flowrate). In this study, an acoustic flowmeter is evaluated as an inline PAT tool for monitoring viscosity of milk protein concentrate (MPC85), protein and TS content of (MPC85), and standardised MPC (sMPC). Laboratory scale experiments were carried out at 45 °C for five different concentrations (4–21%) of MPC85 and sMPC. Results showed that AT decreased with an increase in MPC85 viscosity (e.g., AT was 98.79 ± 0.04% and 86.65 ± 0.17% for 4% and 21% TS content, respectively). Non-linear regression was carried out to develop a relationship between AT and offline viscosity (R2 (coefficient of determination) value = 0.97 and standard error of prediction = 1.86 mPa·s). AI was observed to increase at higher protein and TS content which was dependent on protein to total solid ratio (P_TSR). Multiple linear regression was carried out to develop the relationship between AI, protein content, TS content and P_TSR. Results demonstrated that AI could be used to monitor the protein and TS content of milk protein concentrate (R2 > 0.96). Overall this study demonstrated the potential of an inline acoustic flowmeter for monitoring process viscosity, protein and TS during dairy concentrate processing.

Evaluating internal condition of hardwood logs based on AR-minimum entropy deconvolution combined with wavelet based spectral kurtosis approach

Abstract The aim of this research was to explore the potential of acoustic impact test to evaluate the condition of hardwood logs in regard to internal decay, void, crack and defect ratio using an acoustic signal separation and enhancement algorithm. Longitudinal acoustic signals were obtained from 15 logs of four hardwood species through acoustic impact testing. The defect components were separated from the acoustic response signals and enhanced based on the autoregressive minimum entropy deconvolution (AR-MED) method, and from which the kurtosis was derived and used as the global feature parameter for evaluating the internal condition of logs. Compared with the acoustic velocity obtained directly from the original signal, the kurtosis was deemed to be a more powerful predictor of log defect ratio with higher coefficient of determination (R 2 = 0.89) and was not affected by log species. To identify the type of defects, a complex Morlet wavelet-based spectral kurtosis (SK) method was proposed. The research results indicated that the SK can not only determine the type and primary and secondary major defects, but also be able to identify those that were not detectable by global acoustic parameters.

Assessing internal soundness of hardwood logs through acoustic impact test and waveform analysis

The objective of this study was to explore the potential of an acoustic impact test as a nondestructive evaluation procedure to assess the soundness of hardwood logs in terms of internal decay, void, and defect ratio. Fifteen logs of four hardwood species (black cherry, white oak, red oak, and cottonwood) were obtained and subjected to acoustic impact testing. The logs were subsequently dissected for visual examination and physical mapping of the internal defects. The acoustic response signals were analyzed to derive acoustic velocity (through FFT), time centroid (through moment analysis), and the first- and second-order damping ratio (through continuous wavelet transform). The longitudinal acoustic velocity was found to have a negative, nonlinear relationship with defect ratio (R2 = 0.72), but it lacked sensitivity to small defects and was affected by species. Time centroid proved to be a better predictor than acoustic velocity with an improved correlation with log defect ratio (R2 = 0.87). Wavelet-based damping ratio was found to have a close linear relationship with log defect ratio. Comparing with the first-order damping ratio, the second-order damping ratio had a better predicting power (R2 = 0.92) and was not affected by type and location of defects. The results further indicated that a combination of acoustic velocity, time centroid, and the first- and second-order damping ratios could yield the optimal prediction of log defect ratio. However, considering the sensitivity and simplicity of the waveform analysis, the second-order damping ratio of the response signals could be the best single predicting parameter for assessing the internal soundness of hardwood logs.

Anti-predator responses in the Chilean Swallow Tachycineta leucopyga breeding in northwest Patagonia

ABSTRACTCapsuleBreeding Chilean Swallows Tachycineta leucopyga in Argentina use visual and acoustic signals in response to potential threats from a predator, but these did not vary with brood age.AimsTo study anti-predator behavioural responses in breeding Chilean Swallows from North Patagonia, Argentina, by using a nest-box experiment.MethodsAt days eight and 14 after the first nestlings hatched, Chilean Swallow breeding adults were exposed to a stuffed decoys of either a natural local predator, the Austral Pygmy-Owl Glaucidium nana, or a neutral decoy, a stuffed Rufous-Collared Sparrow Zonotrichia capensis.ResultsAnti-predator behavioural responses consisted of displaying dives, circling flights and group mobbing around the predator decoy, together with the emission of several vocalizations, among which a mobbing alarm call was the most frequent. We did not find significant differences in the intensity of parental nest defence behaviours at different nestling ages (8 and 14 days old).ConclusionAnti-predator behaviour of breeding Chilean Swallows consists of visual and acoustic signals, involving swallows other than the nest owners, and without variation during the nestling period. Our exploratory assessment on the anti-predator behaviour of Chilean Swallows is the first description of the southernmost Neotropical swallow defence behaviour and will therefore help delineate future research.

Do singing humpback whales (Megaptera novaengliae) favor specific frequency bands?

Many species alter their acoustic signals in response to environmental or anthropogenic factors. Differential use of frequency bands may occur as a result of overlapping biotic and abiotic sounds that interfere with communication signals between conspecifics. Singing humpback whales produce units with frequencies ranging from 30 Hz to over 10,000 Hz, but may favor specific frequency bands during song production. We tested the prediction that singing humpback whales consistently produce units with energy focused in specific spectral bands by measuring the consistency of peak frequency bands in the southeastern Pacific stock G population of humpback whales in the Gulf of Tribugá, Colombian Pacific. Preliminary results document extensive use of units with peak frequencies clustered in two different bands between 300 Hz and 1000 Hz for the dominant theme, and additional peak frequency bands between 300 Hz and 3000 Hz for other song themes. These analyses will allow for further spatial and temporal comparisons across distinct population segments, and can be used in future studies to assess whether singers change their use of frequency bands in response to increased anthropogenic noise or as themes evolve over time.

ИССЛЕДОВАНИЕ ВОЗМОЖНОСТИ ОЦЕНКИ СОСТОЯНИЯ СТАЛЬНЫХ ОБРАЗЦОВ С ПРИМЕНЕНИЕМ ДИНАМИЧЕСКИХ СПЕКТРОГРАММ АКУСТИЧЕСКИХ СИГНАЛОВ

The main purpose of this work was to study the possibility of estimating the changes in properties of bearing steel during heat treatment by visualization using dynamic spectrograms (sonograms) that display changes in the spectral characteristics of acoustic signals within time. The changes of spectral characteristics of the point impact acoustic response in the steel specimens were studied depending on the microstructure changes generated in the specimens using heat treatment with various parameters. The analysis and comparison of acoustic response signals were performed using software spectrum analyzer. The informativeness of the applied technique aimed at estimating changes in the microstructure of steel as a result of heat treatment is shown. The analysis of dynamic spectrograms allowed revealing indicative spectral features, such as shifting in the resonant frequencies and change in the damping decrement. A clear dependence of the shift of the resonant frequencies and the damping decrement of the signal on the tempering temperature of the quenched ball-bearing steel specimens was found. After the tempered specimens were re-quenched, reverse changes in the resonant harmonics frequencies and the damping decrement were observed. Changes in the observed indicative spectral characteristics correspond to changes in hardness and microstructure of the steel. This technique can be used for development of nondestructive testing express methods to evaluate changes in the state of steel structural elements and perform quality control during heat treatment.

Nondestructive firmness measurement of differently shaped pears with a dual-frequency index based on acoustic vibration

An acoustic setup was developed to simultaneously detect the resonant frequencies f1 from equator and f2 from calyx shoulder of pear (Pyrus bretschneideri Rehd.). A proposed index based on these two frequencies was used for firmness evaluation of non-spherical pear. We confirmed the stability of this setup by repeatability analysis of acoustic response signal. When predicting the firmness of pears with large difference in fruit shape, the dual-frequency index was highly correlated with Magness-Taylor (MT) penetration firmness (r = 0.951). Compared with two types of single frequency-based indices, the firmness sensitivity of the dual-frequency index is mostly close to that of MT penetration test. The firmness index can classify pears with a high total accuracy (93.4%), making it suitable for nondestructive detection of firmness of differently shaped pears.

Characterization of the vibration response of miniature microphones by subtraction

Presented is a test methodology for characterizing the vibration sensitivity of miniature microphones for hearing aids. A common method for obtaining the vibration sensitivity of a system is to use an electrodynamic shaker to deliver a calibrated vibration input and measure the corresponding output. When the system under test is a microphone, it is difficult to obtain the vibration response since the measured output will also be due to coherent sound created by the vibration delivery system. The method models the microphone as a system with two inputs, vibration and sound, with one electronic output. Using frequency-domain signal processing, this method extracts the vibration response from a shaker-driven signal by subtracting a synthesized acoustic response signal. When compared to vibration measurements under vacuum, the vibration responses from the two methods generally agree. The vibration response estimates produced using this algorithm are more accurate than vacuum chamber data due to the loading and stiffening effects caused by the presence of air, as would occur under standard operating conditions. This test method allows the rapid acquisition of microphone vibration responses by eliminating the need for a vacuum chamber, or carefully designed acoustic baffling.

Process control of particle deposition systems using acoustic and electrical response signals

The implementation of statistical quality control methods for monitoring and control of powder abrasion/deposition is of increasing importance in a manufacturing environment. For the wider adoption of both current and new powder coating technologies, quality control systems need to be developed, which are easily installed, non-invasive and work in real time. This study evaluates the use of a dual electro-acoustic and electrostatic surface-charge measurement technique as means of realising real-time process control. Simultaneous changes in the signals were obtained under both powder flow-on and -off conditions and also for edge detection of the substrate. It was discovered that the most important variables which governed changes in the acoustic response signal were due to variations in the deposition pressure and stand-off distance, whilst those for the electrostatic response signal came from changes in particle size and deposition stand-off distance. A phenomenological predictive equation was developed based on a two-level full factorial design with five variables for both response factors. The coefficients of determination, r2, for the models were 93% and 98%, respectively, with respective χ2 probability values of 99% and 99.5%. This enabled the use of specific limits for any variation of variables amongst those tested to be set up, resulting in the apparatus necessary for the development of a sensitive continuous control system. Examining variations in surface roughness with electrostatic signal was observed to show a linear relationship, decreasing at a rate of 0.19μm per 0.01eV, as the effective particle size of Al2O3 was increased.