Acoustic Intensity Measurements Research Articles

Enhanced Underwater Single Vector-Acoustic DOA Estimation via Linear Matched Stochastic Resonance Preprocessing

Underwater acoustic vector sensors (UAVSs) are increasingly utilized for remote passive sonar detection, but the accuracy of direction-of-arrival (DOA) estimation remains a challenging problem, particularly under low signal-to-noise ratio (SNR) conditions and complex background noise. In this paper, a comprehensive theoretical analysis is conducted on UAVS signal preprocessing subjected to gain-phase uncertainties for average acoustic intensity measurement (AAIM) and complex acoustic intensity measurement (CAIM)-based vector DOA estimation, aiming to explain the theoretical restrictions of intensity-based vector acoustic preprocessing approaches. On this basis, a generalized vector acoustic preprocessing optimization model is established in which the principle can be described as “maximizing the denoising performance under the constraints of an equivalent amplitude-gain response and phase-bias response”. A novel vector acoustic preprocessing method named linear matched stochastic resonance (LMSR) is proposed within the framework of matched stochastic resonance theory, which can naturally guarantee the linear gain-phase restrictions, as well achieving effective denoising performance. Numerical analyses demonstrate the superior vector DOA estimation performance of our proposed LMSR-AAIM and LMSR-CAIM methods in comparison to classical intensity-based AAIM and CAIM methods, especially under low-SNR conditions and non-Gaussian impulsive noise circumstances. Experimental verification conducted in the South China Sea further verifies its the effectiveness for practical application. This work can lay a solid foundation to break through the challenges of underwater remote vector acoustic DOA estimation under low-SNR conditions and complex ocean ambient noise and can provide important guidance for future research work.

Optical fiber-based acoustic intensity microphone for high-intensity airborne ultrasound measurement

The increasing use of airborne ultrasonic waves in daily life, driven by advances in parametric and phased arrays, has led to innovative applications like highly directional speakers, non-contact tactile feedback, 3D acoustic levitation, and medical therapies. These advancements necessitate accurate measurement of high-intensity ultrasonic waves, exceeding the capability of traditional microphones limited to around 160 dB, and highlight the growing importance of measuring the sound field not merely as scalar (sound pressure) but as vector (acoustic intensity) to accommodate future technological developments. This paper introduces an acoustic intensity microphone using optical fibers as probes to overcome these limitations. The proposed method replaces the two ordinary microphones used in the traditional acoustic intensity measurement method with thin optical fibers, minimizing sound field disturbance. Experimental validation and the structure of a practical acoustic intensity microphone are discussed, building upon foundational work presented at USE2023 with added verification and insights.

The Design and Process Parameters for the Optimization of an Ultrasonic—Thermal Co-Sterilization System for Liquid Eggs

The sterilization of liquid eggs plays a crucial role in the production of liquid egg products. Traditional pasteurization techniques can easily cause protein denaturation, while non-thermal sterilization techniques are often constrained by processing intensity and time. Improving the effectiveness of liquid egg sterilization while preserving the stability of its functional attributes poses a significant challenge. In response to this issue, a synergistic ultrasonic mild thermal sterilization system for liquid eggs is proposed, accompanied by the optimization of its process parameters. COMSOL is employed to simulate the acoustic field distribution of the ultrasonic–thermal system in the liquid egg medium. Verification is conducted through acoustic intensity measurements, and analysis is performed to obtain the optimal arrangement of ultrasonic transducers. Based on Modbus communication, an ultrasonic–thermal synergistic sterilization system is designed. Sterilization experiments are conducted with both 20 kHz + 28 kHz and 20 kHz + 40 kHz multifrequency ultrasound, compared with traditional 20 kHz single-frequency ultrasound. The results indicate that multifrequency ultrasound improves sterilization efficiency by approximately 15% compared to traditional single-source ultrasound. Utilizing multifrequency ultrasonic–thermal synergistic sterilization experiments, a three-factor, three-level response surface test is conducted with sterilization rate and foaming properties as evaluation criteria. The results indicate a strong correlation between ultrasonic frequency, processing time, heating temperature, and sterilization performance, with the impact magnitude being sterilization temperature > processing time > ultrasound frequency. Parameter optimization analysis is performed using a genetic algorithm, yielding sterilization conditions of 55 °C, 11 min and 30 s processing time, and 20 + 40 kHz ultrasonic frequency. The liquid egg sterilization rate is 99.32%, an average decimal reduction of 3.17 log values, and foaming properties are 42.79%.Through comparative analysis, it is determined that the sterilization rate of the ultrasonic–thermal synergistic sterilization system meets national standards, and functional properties such as foaming are superior to traditional pasteurization. This validates the proposed ultrasonic–thermal synergistic liquid egg sterilization control system as effective and feasible.

Single acoustic vector sensor DOA enhanced by unsaturated bistable stochastic resonance with linear amplitude response constrained

Acoustic vector sensors (AVS) are increasingly utilized for remote target passive perception, but accurate direction-of-arrival (DOA) estimation remains a formidable challenge, particularly in the presence of heavy background noise. In this paper, we propose a novel DOA estimation method that utilizes complex acoustic intensity measurements (CAIM) and unsaturated bistable stochastic resonance with linear amplitude response constrained (LAR-UBSR). The proposed method aims to exploit the excellent denoising performance of stochastic resonance (SR) to enhance the accuracy of DOA estimation. The proposed LAR-UBSR method is based on the theoretical analysis of the signal pre-processing requirements of CAIM, which determines the linear amplitude response and fixed phase shift. LAR-UBSR achieves a stable phase shift and linear amplitude response by utilizing the unsaturated potential well and limited potential parameters adjustment method of SR. We analyze the amplitude response linearity of LAR-UBSR under different signal-to-noise ratios (SNRs) and a wide range of frequencies, demonstrating a larger linear amplitude response interval that meets the signal pre-processing requirements of CAIM. Numerical analysis and application verification show that the proposed DOA method outperforms existing methods, particularly under low SNR conditions. The results suggest the potential for high-accuracy DOA estimation using nonlinear signal processing strategies in the presence of heavy background noise.

Underwater Acoustic Intensity Analysis using Noise Assisted-MEMD with Varying Distances

With current developments, underwater communication using acoustic signals is widely used. Many things need to be prepared to support a reliable underwater communication system, such as taking measurements in a test tank to find out the correct measurement configuration. Underwater acoustic intensity measurements, which are detailed in this paper, are performed in the test tank using distance variation schemes. Measurements were made at various distances of 4, 10, 20, and 50 meters from the signal source. The hydrophone that was used has a sensitivity of -180 dB re 1V/µPa. The hydrophone was placed at a depth of 2 meters below the surface of the water in the test tank, which divided the test tank depth in half to ensure that reflections from the bottom and the surface were kept to a minimum. However, the problem is that there are noisy signals at different frequencies. This paper proposes a method using Noise Assisted - Multivariate Empirical Mode Decomposition (NA-MEMD) to decompose the signal and then calculate the sound intensity. The result shows that an increase in the distance between the transmitter and receiver, also causes a change in the intensity with an average change of 0.467 dB/meter. It is concluded that the NA-MEMD approach was shown to be successful in decomposing the intended signal from the noise to equalize the quality of the signal received at different distances, and the correlation between intensity value and change in distance is resilient, with a correlation value of 0.98, indicating a very strong correlation.

Sound intensity and directivity measurements for a loudspeaker canopy in a restrictive noise environment

It is common to have noise complaints from outdoor event and entertainment venues in urban and non-urban environments due to the loudness of the reinforcement system, rhythmic nature of the music, acoustical spectrum, and the geometric spreading of said system. Complaints about noise from events, bars, and restaurants are on the rise. Increasing traffic, construction, and commercial activities tend to increase the ambient noise level in urban environments, creating noise creep. The pandemic restrictions helped reduce the ambient levels in the urban and non-urban areas. However, after the reopening, more and more noise complaints started to be issued since residents were more sensitive to noise pollution. This paper presents a practical application of the source directivity for a loudspeaker system. The loudspeaker canopy is designed to produce a radiation pattern directing the main beam lobe to the front of the array and reduce the noise propagation to other directions. This device can be implemented in entertainment and outdoor events (such as wedding parties) to reduce the noise impact on sensitive receivers and meet the jurisdictional noise regulations. Real-world acoustic intensity measurements were made to obtain the system's sound power and assess the noise impact at distances up to 35 feet away from the source. The viability of using the system for outdoor activities within locations restricted by the City's ordinances is discussed.

Acoustic Observation, Identification, and Scattering Intensity Measurement of Cold Seep Based on Bubble Resonance

The active “ cold seep “ is indisputable evidence to identify the existence of submarine gas hydrate. Due to the difference in acoustic properties between cold seep bubbles and surrounding seawater, measuring scattering intensity is a new means to detect active cold seep. Cold seep bubbles are the main cause of acoustic scattering, and the scattering ability is closely related to the frequency of the incident sound wave, the radius of the bubble, and the depth of the bubble. The paper introduces a ship-borne cold seep sonar system, which uses the resonance principle of bubbles to measure the scattering intensity at various depths underwater and display it with an intuitive acoustic image. Through the investigation and measurement of the cold seep located in the South China Sea, it is proved that the cold seep sonar system can well identify the submarine cold seep. The measured data are consistent with the theoretical simulation results, confirming that the cold seep bubbles have frequency-selective characteristics for incident sound waves. Compared with other detection methods, it has the characteristics of lossless, fast, and high efficiency.

Novel Near-Wellbore Fracture Diagnosis for Unconventional Wells Using High-Resolution Distributed Strain Sensing during Production

SummaryThe characteristics of hydraulic fractures in the near-wellbore region contain critical information related to the production performance of unconventional wells. We demonstrate a novel application of a fiber-optic-based distributed strain sensing (DSS) technology to measure and characterize near-wellbore fractures and perforation cluster efficiency during production. Distributed fiber-optic-based strain measurements are made based on the frequency shift of the Rayleigh scatter spectrum, which is linearly dependent on strain and temperature changes of the sensing fiber. Strain changes along the wellbore are continuously measured during the shut-in and reopening operations of a well. After removing temperature effects, extensional strain changes can be observed at locations around the perforation cluster during a shut-in period. We interpret that the observed strain changes are caused by near-wellbore fracture aperture changes caused by pressure increases within the near-wellbore fracture network. The depth locations of the measured strain changes correlate well with distributed acoustic sensing (DAS) acoustic intensity measurements that were measured during the stimulation of the well. The shape and magnitude of the strain changes differ significantly between two completion designs in the same well. Different dependencies between strain and borehole pressure can be observed at most of the perforation clusters between the shut-in and reopening periods. We assess that this new type of distributed fiber-optic measurement method can significantly improve understanding of near-wellbore hydraulic fracture characteristics and the relationships between stimulation and production from unconventional oil and gas wells.

Acoustic Measurement of Ship Wave–Induced Sediment Resuspension in a Large River

This paper presents a proof of concept that acoustic velocity and backscatter intensity measurements can provide essential information on ship wave–induced sediment transport processes in the littoral zone of a large river. Through a case study in the Hungarian section of Danube River, a combined application of an acoustic Doppler velocimeter (ADV) and a formerly calibrated acoustic backscatter sensor (ABS) is introduced for parallel measurements of 3D flow velocities and suspended sediment concentration (SSC) in a characteristic point of the near-bank zone. SSC times series detected by the ABS supported the calibration of the ADV backscatter, which eventually enabled the analysis of the temporal behavior of flow velocity and SSC conditions altered by ship waves. A suitable method for the separation of primary and secondary waves provided essential information on the turbulence intensities and sediment fluxes, and was found that the low-frequency primary waves are rather responsible for the lateral sediment transport instead of the dynamic secondary waves. The introduced data processing techniques and the main findings of the paper mean an important step toward the better understanding of the impacts of ship waves on the riverbanks, inherently playing a crucial role in the hydro-morphological and habitat conditions of river systems.

Acoustic intensity technique applied to monitor planetary gears

Condition monitoring of gear trains by classic techniques based on vibrations and/or extensometry measurements requires the preparation of the sensor contact surfaces and the cables installation. In the case of planetary gear trains, this task is more difficult due to their compactness and the complexity of the relative movements among their different elements. As an alternative, the authors studied the possibility of using acoustic measurements for the planetary gear-set characterisation, as well as for predictive maintenance of this mechanical system. In order to perform this study, a suitable measurement equipment was selected and a bespoke software was developed to control it, to process the data, as well as to represent the results. This informatic tool was used to perform the acoustic characterisation, in which acoustic pressure and intensity measurements were combined with advanced algorithms, such as sincronous-average technique. In this study, two different failures were experimentally recreated in a commercial gearbox, representing the results by frequency and order spectra and intensity maps. The obtained results were compared with those obtained in the box without defect.

Objective measurement of acoustic intensity of coughing for clearance of penetration and aspiration on video-fluoroscopy

Purpose This preliminary, exploratory study evaluated the acoustic intensity of effective and ineffective clearance of penetrated and aspirated material from the laryngeal vestibule in patients with dysphagia. Method A lapel microphone was attached anterior to participants’ tragus and recorded coughing in decibels during their videofluoroscopic swallowing studies (VFSS). Result Eighty-eight patients were recruited. Thirteen patients, with visible airway invasion and coughing were included in the final analysis. No coughs were effective at expelling aspirated material from the airway (n = 10). Both effective (4/7) and ineffective (3/7) coughing to penetration were recorded. The mean acoustic intensity of effective coughing to penetration was –44.0 dBFS (decibel level relative to full scale) [SD = 7.3, 95% CI = −51.14, −36.86], and ineffective coughing to penetration was only marginally lower at –42.9 dBFS [SD = 2.0, 95% CI = −45.21, −40.59]. Conclusion No coughs were effective at expelling aspirated material from the airway. Some coughs effectively expelled penetrated material from the airway. However, the relationship between acoustic intensity and cough effectiveness is unclear due to the limited number of observations. Given that perceptual evaluation of coughing is widely used in dysphagia clinical practice to determine cough effectiveness, this is an important area for future research.

A Kriged Compressive Sensing Approach to Reconstruct Acoustic Fields From Measurements Collected by Underwater Vehicles

This article presents a kriged compressive sensing (KCS) approach to reconstruct acoustic fields using measurements collected by underwater mobile sensing platforms. The KCS approach has two steps. First, initial estimates are obtained from a kriging method by leveraging spatial statistical correlation properties of the acoustic fields. Second, selected initial estimates, treated as virtual samples, are combined with the measurements to perform field reconstruction through compressive sensing. To differentiate the fidelity between real measurements and virtual samples, we use the kriging variance to determine weight coefficients for the virtual samples estimated from kriging. Simulation results show that the proposed KCS approach can improve the reconstruction performance, in terms of the peak signal-to-noise ratio and structural similarity metrics. The KCS performance has been validated based on the acoustic intensity measurements collected by an autonomous underwater vehicle in a lake. The KCS methods have also been applied to process the ambient sound level measurements collected by an underwater glider in the South China Sea. The proposed KCS method leads to better performance than either the compressive sensing or the kriging method alone.

On the viability of the complex-intensity-based near-field acoustical holography method

Because of the instrumentation difficulties of Fourier acoustical holography, it is desirable to find a holography method that does not require reference signals during array scanning. Among the methods that have been investigated to remove the need for references are those based on acoustic intensity measurements, including the complex-intensity-based near-field acoustical holography (CIBNAH) method [A. Nejade, J. Sound Vib. 333(16), 3598–3608 (2014); Appl. Acoust. 116, 348–356 (2017)]. The CIBNAH method has previously been applied to simple contrived sources and real-world machinery but has not been verified using analytical source models. This work shows the application of CIBNAH to an analytical model of a simply-supported plate, revealing key shortcomings of the method. The theory behind CIBNAH is discussed in light of these shortcomings. It is shown that while CIBNAH may be useful for finding radiation hot spots, it is not an adequate method to overcome the need for references in scan-based acoustical holography. [Work supported by NSF.]

Realization of an ultrathin acoustic lens for subwavelength focusing in the megasonic range

In this study, we report the first experimental realization of an ultrathin (0.14λ, λ = 1.482 mm means wavelength at 1 MHz in the water medium) subwavelength focusing acoustic lens that can surpass the Rayleigh diffraction limit (0.61λ/NA, NA means numerical aperture). It is termed a Super-Oscillatory Acoustic Lens (SOAL), and it operates in the megasonic range. The SOAL represents an interesting feature allowing the achievement of subwavelength focusing without the need to operate in close proximity to the object to be imaged. The optimal layout of the SOAL is obtained by utilizing a systematic design approach, referred to here as topology optimization. To this end, the optimization formulation is newly defined. The optimized SOAL is fabricated using a photo-etching process and its subwavelength focusing performance is verified experimentally via an acoustic intensity measurement system. From these measurements, we found that the proposed optimized SOAL can achieve superior focusing features with a Full Width at Half Maximum (FWHM) of ~0.40λ/NA ≃ 0.84 mm (for our SOAL, NA = 0.707) with the transmission efficiency of 26.5%.

An improved target detection and azimuth angle estimation method using a single acoustic vector sensor

In this paper, an improved underwater acoustic target detection and azimuth angle estimation method using a single acoustic vector sensor (AVS) is proposed based on time-reversal and convolution theory. The proposed method can be applied in the active and the passive sonar detection system. According to the conventional detection and estimation method based on complex acoustic intensity measurement, the mathematical and physical model of this proposed method is described in detail. Computer modelling and simulation is applied to demonstrate the proposed method’s effectiveness. In order to further verify the practical application performance of the proposed method, the research group carried out the open lake experiments. The computer simulation and open lake experiments results indicate that this method can realize the azimuth angle estimation with high precision by using only a single AVS. Compared with these conventional methods, the proposed method achieves better detection and estimation performance.

Morphometric analysis of high-intensity focused ultrasound-induced lipolysis on cadaveric abdominal and thigh skin.

Non-focused ultrasound and high-intensity focused ultrasound (HIFU) devices induce lipolysis by generating acoustic cavitation and coagulation necrosis in targeted tissues. We aimed to investigate the morphometric characteristics of immediate tissue reactions induced by 2MHz, 13-mm focused HIFU via two-dimensional ultrasound images and histologic evaluation of cadaveric skin from the abdomen and thigh. Acoustic fields of a 2MHz, 38-mm HIFU transducer were characterized by reconstruction of the fields using acoustic intensity measurement. Additionally, abdominal and thigh tissues from a fresh cadaver were treated with a HIFU device for a single, two, and three pulses at the pulse energy of 130J/cm2 and a penetration depth of 13mm. Acoustic intensity measurement revealed characteristic focal zones of significant thermal injury at the depth of 38mm. In both the abdomen and thigh tissue, round to oval ablative thermal injury zones (TIZs) were visualized in subcutaneous fat layers upon treatment with a single pulse of HIFU treatment. Two to three HIFU pulses generated larger and more remarkable ablative zones throughout subcutaneous fat layers. Finally, experimental treatment in a tumescent infiltration-like setting induced larger HIFU-induced TIZs of an oval or columnar shape, compared to non-tumescent settings. Although neither acoustic intensity measurement nor cadaveric tissue exactly reflects in vivo HIFU-induced reactions in human tissue, we believe that our data will help guide further in vivo studies in investigating the therapeutic efficacy and safety of HIFU-induced lipolysis.

An Improved Azimuth Angle Estimation Method with a Single Acoustic Vector Sensor Based on an Active Sonar Detection System.

In this paper, an improved azimuth angle estimation method with a single acoustic vector sensor (AVS) is proposed based on matched filtering theory. The proposed method is mainly applied in an active sonar detection system. According to the conventional passive method based on complex acoustic intensity measurement, the mathematical and physical model of this proposed method is described in detail. The computer simulation and lake experiments results indicate that this method can realize the azimuth angle estimation with high precision by using only a single AVS. Compared with the conventional method, the proposed method achieves better estimation performance. Moreover, the proposed method does not require complex operations in frequency-domain and achieves computational complexity reduction.

3D Acoustic Field Intensity Probe Design and Measurements

Abstract The aim of this paper is two-fold. First, some basic notions on acoustic field intensity and its measurement are shortly recalled. Then, the equipment and the measurement procedure used in the sound intensity in the performed research study are described. The second goal is to present details of the design of the engineered 3D intensity probe, as well as the algorithms developed and applied for that purpose. Results of the intensity probe measurements along with the calibration procedure are then contained and discussed. Comparison between the engineered and the reference commercial probe confirms that the designed construction is applicable to the sound field intensity measurements with a sufficient effectiveness.

Comparison of pressure-based intensity measurements for different probe designs and estimation methods

Acoustic intensity measurements have traditionally used cross spectral methods with multimicrophone probes to estimate the required pressure and particle velocity. The phase and gradient estimator (PAGE) method increases probe bandwidth without modifying microphone spacing as compared to the traditional cross spectral method [D. C. Thomas et al., J. Acoust. Soc. Am. 137, 3366–3376 (2015)]. In this study, high-frequency probe bandwidth obtained using both the PAGE method and the traditional method is compared across three different multimicrophone probe designs: a three-axis, six-microphone probe with variable solid spacer, a three-axis, four-microphone spherical probe, and a two-axis, four-microphone probe developed in-house for rocket measurements. Broadband, anechoic loudspeakermeasurements are used to examine the performance of each probe and estimation method. These include a single 7.6 cm diameter, enclosed loudspeaker driver, and two drivers of equal strength but opposite phase. Intensity measurements in a grid of 41 × 41 points inside a one square meter area are presented. Probe design robustness is determined by considering bias errors in calculation methods and probe scattering. [Work supported by NSF.]

Active control of noise radiated from an x-ray tube

The application of implementing an active noise control system to globally attenuate noise radiated from a medical x-ray tube has been investigated. The noise radiated from the x-ray tube is characterized by the presence of numerous tonal peaks distributed over a broad frequency bandwidth. Furthermore, there is sufficient variability in the radiated field that coherence in the acoustic field was also found to be a challenge. It was determined that a properly placed structural sensor could be used as a reference signal to achieve good coherence between the reference signal and error microphone. In order to achieve global control, speakers were placed in close proximity to areas that had been identified as source regions through the use of SLDV and acoustic intensity measurements. The frequency band below 1500 Hz was targeted, and it was found that effective attenuation could be achieved at over ten of the most prominent frequencies, resulting in attenuations in that bandwidth on the order of 7 dB. Some of ...