Nonlinear Acoustic Measurements Research Articles

Do the Nonlinear Dynamic Acoustic Measurements, Nonlinear Energy Difference Ratio and Spectrum Convergence Ratio, Correlate with Perceptual Evaluation of Esophageal Voice Speakers?

The acoustic assessment of phonation after total laryngectomy is challenged by signal aperiodicity which makes frequency-based acoustic measures less reliable. This is important for patients who use esophageal voice since voice samples mostly include type III (highly aperiodic) and 4 (chaotic) signals. As such, using non-linear measures, which are better suited for aperiodic phonation, may be useful to investigate the relationship between acoustic signal characteristics and perception of esophageal voice quality. This study aimed to investigate whether nonlinear dynamic acoustic methods, nonlinear energy difference Ratio (NEDR) and spectrum convergence ratio (SCR), were correlated with perceptual measures in subjects who used esophageal phonation. Thirty-one subjects who had undergone total laryngectomy and use esophageal voice as a rehabilitation method were included in this study. Expert and non-expert raters listened to the esophageal voice samples from the subjects and rated vowels and connected speech samples on a scale from 1 to 7 on dysphonia severity and intelligibility. In addition, non-linear acoustic analysis was performed to calculate NEDR and SCR. Analysis from the raters was compared to the non-linear acoustic analysis to find the correlation between the variables. There were no significant correlations between any of the non-linear acoustic measures NEDR and SCR and the perceptual ratings at the significance level of 0.05. Correlations were calculated for each acoustic measure among the expert raters and among the non-expert raters in both connected speech samples and sustained vowel fragments. In conclusion, the nonlinear dynamic acoustic analyses of spectrum convergence ratio and nonlinear energy difference ratio do not have a significant correlation with perceptual measures of esophageal voice.

Application of Fresnel Zone Plate Focused Beam to Optimized Sensor Design for Pulse-Echo Harmonic Generation Measurements.

In nonlinear acoustic measurements involving reflection from the stress-free boundary, the pulse-echo method could not be used because such a boundary is known to destructively change the second harmonic generation (SHG) process. The use of a focusing acoustic beam, however, can improve SHG after reflection from the specimen boundary, and nonlinear pulse-echo methods can be implemented as a practical means of measuring the acoustic nonlinear parameter (β) of solid specimens. This paper investigates the optimal sensor design for pulse-echo SHG and β measurements using Fresnel zone plate (FZP) focused beams. The conceptual design of a sensor configuration uses separate transmission and reception, where a broadband receiver is located at the center and a four-element FZP transmitter is positioned outside the receiver to create a focused beam at the specified position in a solid sample. Comprehensive simulations are performed for focused beam fields analysis and to determine the optimal sensor design using various combinations of focal length, receiver size and frequency. It is shown that the optimally designed sensors for 1 cm thick aluminum can produce the second harmonic amplitude and the uncorrected nonlinear parameter corresponding to the through-transmission method. The sensitivity of the optimal sensors to the changes in the designed sound velocity is analyzed and compared between the odd- and even-type FZPs.

Nonlinear Acoustic Modeling and Measurements during the Fatigue Process in Metals.

The nonlinear spring model combined with dislocation dipole theory was applied to describe the acoustic nonlinearity during the fatigue process in metals. The spring stiffness changes with fatigue degree. For the early stage, spring stiffness approaches infinity, and the heavier nonlinearity mainly results from the increase of dislocation density. Further fatigue leads to the occurrence of micro-cracks, during which spring stiffness begins to decrease. Abundant micro-crack sprouting accelerates the crack’s expansion, and spring stiffness drops quickly, which causes the obvious decline in the transmitted harmonic amplitudes. Solutions obtained from the nonlinear wave equation with dislocation terms were added into the spring model. Varying spring stiffness was chosen for simulating the fatigue process. Then, nonlinear harmonic variation during this process was observed, which was classified into three stages: (I) the early dislocation fatigue stage; (II) the micro-crack sprouting stage; (III) the crack expansion stage. Nonlinear acoustic measurements were carried out on an aluminum alloy specimen during its fatigue process until cracks could be seen clearly. Harmonic variations in experiments can also be classified into the same three stages as the numerical results, which provides a theoretical and experimental reference for fatigue evaluation in metals using the nonlinear acoustic method.

Flaw detection of wellbore systems by combining time reversal methods and nonlinear acoustic measurements

A wellbore system consisting of a steel pipe cased in cement is susceptible to cracking and delamination. Such flaws greatly reduce the integrity of the wellbore and can lead to significant leakage. To resolve the location and extent of the defects, we have combined a unique time reversal method with nonlinear acoustic evaluation. The time reversal method generates a compact high-amplitude wave only in a localized area that can be used to probe the acoustic properties spot by spot of a three dimensional region. Additionally, the nonlinear acoustic signal an object exhibits is far more sensitive to damage and defects than conventional linear analysis. The nonlinear behavior can be locally determined by observing the changes in elastic properties as the amplitude of the time-reversed focus wave is increased. The experimental setup consist of an array of piezoelectric transducers for generating the focused energy and a laser vibrometer mounted on a scanning frame for focusing and measuring nonlinearity on th...

Detecting alkali-silica reaction: A multi-physics approach

A multi-physics approach for the assessment of alkali silica reaction (ASR) generates new foundational understanding of the nature of the reaction, which ultimately can be used for the development of techniques and tools for the assessment and monitoring of existing concrete structures. The approach combines two nondestructive evaluation techniques: (1) nonlinear acoustic measurements, which are sensitive to microcracking; and (2) microwave materials characterization measurements, which are sensitive to moisture including the transition of water from its free state in the pore solution to a bound state within accumulating ASR gel. Comparison with assessment of expansion and damage rating index obtained from petrographic analysis on standard mortar bars shows a correlation between all of the measures. Specifically, a strong correlation is found between the cumulative average nonlinearity parameter and expansion, and there is also agreement of the microwave measurements with the damage rating index.

Correction for frequency-dependent hydrophone response to nonlinear pressure waves using complex deconvolution and rarefactional filtering: application with fiber optic hydrophones.

Nonlinear acoustic signals contain significant energy at many harmonic frequencies. For many applications, the sensitivity (frequency response) of a hydrophone will not be uniform over such a broad spectrum. In a continuation of a previous investigation involving deconvolution methodology, deconvolution (implemented in the frequency domain as an inverse filter computed from frequency-dependent hydrophone sensitivity) was investigated for improvement of accuracy and precision of nonlinear acoustic output measurements. Timedelay spectrometry was used to measure complex sensitivities for 6 fiber-optic hydrophones. The hydrophones were then used to measure a pressure wave with rich harmonic content. Spectral asymmetry between compressional and rarefactional segments was exploited to design filters used in conjunction with deconvolution. Complex deconvolution reduced mean bias (for 6 fiber-optic hydrophones) from 163% to 24% for peak compressional pressure (p+), from 113% to 15% for peak rarefactional pressure (p-), and from 126% to 29% for pulse intensity integral (PII). Complex deconvolution reduced mean coefficient of variation (COV) (for 6 fiber optic hydrophones) from 18% to 11% (p+), 53% to 11% (p-), and 20% to 16% (PII). Deconvolution based on sensitivity magnitude or the minimum phase model also resulted in significant reductions in mean bias and COV of acoustic output parameters but was less effective than direct complex deconvolution for p+ and p-. Therefore, deconvolution with appropriate filtering facilitates reliable nonlinear acoustic output measurements using hydrophones with frequency-dependent sensitivity.

Evaluation of the intergranular corrosion in austenitic stainless steel using collinear wave mixing method

Failures due to intergranular corrosion in components of austenitic stainless steel have always been a tough problem in engineering practice. In this paper, the collinear wave mixing was investigated to evaluate the intergranular corrosion in austenitic stainless steel. An acoustic nonlinearity parameter related to the bispectrum, the propagation distance and the amplitudes of fundamental waves in measured signal is proposed. Nonlinear acoustic measurements were conducted on four tubes with different degree of intergranular corrosion. The experimental results demonstrated that the proposed acoustic nonlinearity parameter is sensitive to intergranular corrosion in samples, and is well correlated with the degree of damage.

Membrane hydrophone phase characteristics through nonlinear acoustics measurements

This work considers the need for both the amplitude and phase to fully characterize polyvinylidene fluoride (PVDF) membrane hydrophones and presents a comprehensive discussion of the nonlinear acoustic measurements utilized to extract the phase information and the experimental results taken with two widely used PVDF membrane hydrophones up to 100 MHz. A semi-empirical computer model utilized the hyperbolic propagation operator to predict the nonlinear pressure field and provide the complex frequency response of the corresponding source transducer. The PVDF hydrophone phase characteristics, which were obtained directly from the difference between the computer-modeled nonlinear field simulation and the corresponding measured harmonic frequency phase values, agree to within 10% with the phase predictions obtained from receive-transfer-function simulations based on software modeling of the membrane's physical properties. Cable loading effects and membrane hydrophone resonances were distinguished and identified through a series of impedance measurements and receive transfer function simulations on the hydrophones including their hard-wired coaxial cables. The results obtained indicate that the PVDF membrane hydrophone's phase versus frequency plot exhibits oscillations about a monotonically decreasing line. The maxima and minima inflection point slopes occur at the membrane thickness resonances and antiresonances, respectively. A cable resonance was seen at 100 MHz for the hydrophone with a 1-m cable attached, but not seen for the hydrophone with a shorter 0.65-m cable.

Non-linear acoustic measurements to assess crack density in trabecular bone

Three methods to measure qualitative and quantitative aspects of bone non-linearity were investigated in the context of diagnosis of bone “biomechanical health”: i.e. harmonic generation, parametric emission and parametric reception using phase modulation. Trabecular bone exhibited hysteretic non-linear behavior due to microcracks in bone tissue, and parametric reception using phase modulation seemed to be the best configuration for in vivo application. However, the relationship between level of non-linearity and crack density needs to be validated by histological analysis.

Modelling localized nonlinear damage and analysis of its influence on resonance frequencies

Nonlinear acoustic techniques have proven to be extremely sensitive for damage detection in structural materials or composites. Damage characterization, however, also involves localization and quantification, as well as detection. For this purpose, models developed to describe the response of localized damage (due to micro-features) to acoustic excitation may help to study the influence on the specimen resonance frequency of the position, length and damage level of the defective region. We present here some numerical results to show how nonlinear acoustic measurements of the resonance frequencies of higher modes may be used for damage localization, with possible applications in non-destructive testing of materials.

Nonlinear acoustic detection of weathered, low compliance landmines

Two potential impediments to acoustic landmine detection are soil weathering processes and low compliance landmines. To bury landmines, the soil within a mine diameter is removed and replaced such that bulk density, compression, and shear strength all decrease, leaving an acoustic scar detectable with the linear acoustic measurement technique. After a few soil wetting and drying cycles, this contrast is reduced. Linear acoustic mine detection measurements were made on a low impedance contrast landmine before the first rainfall on several occasions over the subsequent 5 years. During this period of time, both the spatial and frequency resolution had to be increased to maintain an on/off target velocity ratio that allowed detection. In some cases, the landmine remains undetectable. To address this, two-tone nonlinear acoustic measurements have been made on these landmines. When the landmine is detectable with linear acoustics, two tones are broadcast at the frequency where the on/off target velocity ratio is the largest. For the cases when the landmine is undetectable, a two-tone sweep is performed and the operator observes the real-time velocity FFT, noting nonlinear sidebands. Next, two-tone tests are conducted at these sidebands to determine nonlinear velocity profiles. [Work supported by U.S. Army RDECOM, NVESD.]