Echo Amplitude Research Articles

Significance of terminal frequency in FM sweeps for bat echolocation

For echolocation of CF-FM bats, the CF component is expected to detect wing-beat of flying insects. However, it also plays an important role to serve as a stable signal carrier from a distant target. Then, once the carrier frequency is removed, echo signal can be easily detected. For this purpose, Doppler-shift compensation and echo amplitude compensation must be conducted to stabilize the signal carrier. What about the FM bats? FM bats also appear to utilize a relatively long pseudo-CF component to detect wing-beats of flying insects. They might also utilize pseudo-CF component for an echo signal carrier. However, Doppler-shift compensation in FM bats has not been reported. In the inferior colliculus, majority of neurons are tuned to the pseudo-CF frequency, 20 kHz for Eptesicus fuscus while 40 kHz for Pipistrellus abramus, which are corresponding to the terminal frequencies of downward FM sweep. Overrepresentation of a particular frequency may enhance frequency discrimination, detection of insect wing-beat. Therefore, we may expect majority of cochlear nerve fibers are also tuned to the pseudo-CF frequency. However, overrepresentation of hair cells for a particular frequency does not appear to be shown. [Research supported by MEXT, Japan and Shandong University, China.]

Автоматическая регулировка чувствительности каналов дефектоскопа с использованием адаптивного порога

Introduction. With high-speed total ultrasonic testing (UT) of the rails, the urgent task is to provide the required testing sensitivity under the impact of a significant number of adverse factors caused by the following reasons:
  unstable acoustic contact;
  incorrect flaw detector channel settings due to underskilled staff;
  a misalignment, for example when passing a small radius curve or when rails have significant lateral wear.
 The listed factors lead to level changing of echo signals within a wide dynamic range as well as to echo amplitudes ratio changing of useful and noise signals. In contrast to manual testing when an operator has the possibility of multiple scanning, total rails testing by a mobile diagnostic system is fulfilled by only a single scan.
 The objective of the work was to develop an optimal algorithm of flaw detector channels sensitivity adjustment and formulate the reasonable requirements for a mathematical model and hardware.
 Method. Theoretical researches and experimental work were conducted and resulted in the development of a multichannel flaw detector for inspection of rails by mobile means. The analysis of different mathematical models has enabled the optimal algorithm for automatic channels sensitivity adjustment to be developed.
 Results. The developed algorithm has allowed minimizing the impact of the negative factors and compensating the sensitivity to the level that enables high-speed single-scan rails testing to be fulfilled and maximum information at a high level of reliability to be recorded. Implementation of the adaptive threshold principle has made it possible to develop and offer the technique and technology for automatic flaw detector channels sensitivity adjustment.
 Conclusion. The offered technique and technology can be fully put into practice with the developed flaw detector and its control software.

Эталонирование чувствительности и обеспечение её равномерности в прозвучиваемом сечении при ультразвуковом контроле сварных соединений с применением ФР-преобразователей

Introduction. The approach and practical implementation for the sensitivity calibration and its equalizing within entire insonified cross-section of the material have been presented in the article for 3 most common reference artificial reflectors, namely the flat bottom hole (FBH) situated at parallel to the weld bevel plane, the EDM notch (N), and the side drilled hole (SDH).
 The method. The issue of inhomogeneous sensitivity over cross-section covered through phased array (PA) sectorial scan plan is due to several factors, which are highlighted and explained. 5 of them are independent on the reference reflector’s shape. In addition the FBH and N reference reflectors are characterized by the strong dependency of the echo amplitude on the angle, under which the ultrasonic wave hits their surface (factor 6, which differs the FBH and N from the omnidirectional SDH). The approach for equalizing the sensitivity over sectorial-scan-insonified cross-section of the material for all types of reference reflectors has been proposed and explained. It is based on the ability of ultrasonic PA flaw detector to implement each pulsing-receiving cycle among the plurality of the scan-plan-forming set of focal laws with individually and independently settled gain and other key settings including Distance Amplitude Correction / Time Corrected Gain (DAC / TCG). The Sonotron NDT’s ISONIC Series PA instruments (ISONIC 3510, ISONIC 2010, and ISONIC 2009 UPA Scope) are featured with the said ability uniquely: in the said units the DAC / TCG mechanism is used purely for compensating the dependency of echo amplitude on the material travel distance while the feature of varying Gain per Focal Law is utilized just for the forming of easy-reproducible Angle Gain Compensation (AGC) plan. Both the DAC / TCG and AGC plans are created independently on each other with use of the same reference reflectors.
 The results. Combining of the independent DAC / TCG and AGC mechanisms for the first time ever provides the equalizing of the sensitivity for all types of reference reflectors independently on their X, Y position over the entire cross-section of the material — this is confirmed by a number of experimental results presented.
 Conclusion. At last the single group sectorial scan only becomes sufficient for the complete coverage of the whole cross-section of the weld. This allows reducing the dimensions of required PA probes and wedges in use and the width of the area for the scanning along the fusion line. And finally this increases the maximal possible speed of scanning along with reducing of the inspection cost.

Acoustic structure quantification by using ultrasound Nakagami imaging for assessing liver fibrosis.

Acoustic structure quantification (ASQ) is a recently developed technique widely used for detecting liver fibrosis. Ultrasound Nakagami parametric imaging based on the Nakagami distribution has been widely used to model echo amplitude distribution for tissue characterization. We explored the feasibility of using ultrasound Nakagami imaging as a model-based ASQ technique for assessing liver fibrosis. Standard ultrasound examinations were performed on 19 healthy volunteers and 91 patients with chronic hepatitis B and C (n = 110). Liver biopsy and ultrasound Nakagami imaging analysis were conducted to compare the METAVIR score and Nakagami parameter. The diagnostic value of ultrasound Nakagami imaging was evaluated using receiver operating characteristic (ROC) curves. The Nakagami parameter obtained through ultrasound Nakagami imaging decreased with an increase in the METAVIR score (p < 0.0001), representing an increase in the extent of pre-Rayleigh statistics for echo amplitude distribution. The area under the ROC curve (AUROC) was 0.88 for the diagnosis of any degree of fibrosis (≥F1), whereas it was 0.84, 0.69, and 0.67 for ≥F2, ≥F3, and ≥F4, respectively. Ultrasound Nakagami imaging is a model-based ASQ technique that can be beneficial for the clinical diagnosis of early liver fibrosis.

Monitoring Radiofrequency Ablation Using Ultrasound Envelope Statistics and Shear Wave Elastography in the Periablation Period: An In Vitro Feasibility Study.

Radiofrequency ablation (RFA) is a minimally invasive method for treating tumors. Shear wave elastography (SWE) has been widely applied in evaluating tissue stiffness and final ablation size after RFA. However, the usefulness of periablation SWE imaging in assessing RFA remains unclear. Therefore, this study investigated the correlation between periablation SWE imaging and final ablation size. An in vitro porcine liver model was used for experimental validation (n = 36). During RFA with a power of 50 W, SWE images were collected using a clinical ultrasound system. To evaluate the effects of tissue temperature and gas bubbles during RFA, changes in the ablation temperature were recorded, and image echo patterns were measured using B-mode and ultrasound statistical parametric images. After RFA, the gross pathology of each tissue sample was compared with the region of change in the corresponding periablation SWE image. The experimental results showed that the tissue temperature at the ablation site varied between 70°C and 100°C. Hyperechoic regions and changes were observed in the echo amplitude distribution induced by gas bubbles. Under this condition, the confounding effects (including the temperature increase, tissue stiffness increase, and presence of gas bubbles) resulted in artifacts in the periablation SWE images, and the corresponding region correlated with the estimated final ablation size obtained from the gross pathology (r = 0.8). The findings confirm the feasibility of using periablation SWE imaging in assessing RFA.

A METHOD OF RECONSTRUCTING HORIZONTALLY‐INHOMOGENEOUS IONOSPHERIC STRUCTURE USING HF SKY‐WAVE BACKSCATTER IONOGRAMS

AbstractHigh‐frequency (HF) sky‐wave backscatter sounding, as a powerful tool for detecting the ionosphere and studying the characteristics of radio channels, can be used to monitor the ionosphere continuously at a remote distance and to acquire the ionospheric parameters in a large area. Backscatter ionograms show the relationship between operating frequency, group path, and echo amplitude. Since an ionogram carries the information of the ionospheric profile along the detection path, the ionospheric parameters can be evaluated through the inversion technique. An algorithm for backscatter sounding ionogram inversion is developed based on the restriction of solution space to reconstruct the horizontally inhomogeneous structures of the ionosphere. Furthermore, the Newton‐Kontorovich method that generally treats nonlinear operator equations and the Tikhonov regularization method that generally deals with ill‐posed problems are effectively combined to resolve the equations. The algorithm can get a stable and unique solution under the solution space limitation. The algorithm we have developed was tested against both model data and observation data, and compared with the method of Fridman and Fridman (1994). Test results prove that the method in this paper has reliable convergence, is insensitive to measurement errors, and has higher accuracy for the inversion of ionospheric structures than the method of Fridman and Fridman (1994). Our algorithm not only can inverse horizontal changes in electron density under quiet conditions (at night or during the daytime at mid‐latitudes), but also can diagnose the horizontally inhomogeneous structures of the ionosphere during sunrise or sunset periods with high accuracy. This consequently demonstrates the application value of the proposed algorithm in the treatment of the complex and volatile measured backscatter ionograms.

Study on the scale distribution of the field-aligned irregularities in E-region

The field-aligned backscattering region in the ionospheric E-region is considered to contain many small irregularities, which are arrayed along the magnetic lines. The scale and number of these irregularities in the backscattering region are different. The irregularities of a certain scale can reflect the radio wave of the corresponding wavelength on the basis of the Bragg scattering theory. The more the irregularities of a scale, the stronger is the backscattered power. Thus, the scale distribution can be estimated by the function relationship between the scale and the echo amplitude, while the incidence direction of the wave path is perpendicular to the geomagnetic field. Moreover, the echoes with oblique incidence direction can also be used to estimate the scale distribution, considering the factor of the angle between the wave path and the perpendicular field direction.

Mathematical Modeling of Ultrasonic Gas Flow Meter Based on Experimental Data in Three Steps

According to experimental data, the features of ultrasonic echo are studied, and a new mathematical model of ultrasonic gas flow meter is built so as to reflect the effects of the excitation signal and gas flow rate on ultrasonic echo. This mathematical model consists of three parts, and is established in three steps. An amplitude sub-model expressed as a polynomial is set up with the curve fitting method to express the non-linear relationship between the echo amplitude and the gas flow rate. A process sub-model described as an output-error model is established by the system identification method to reveal the influence of excitation on the echo shape. A delay time sub-model is built with piecewise fitting to obtain a relationship between the propagation time and the gas flow rate. These sub-models can quantitatively analyze the relationship between the excitation signals, gas flow rates, ultrasonic echo amplitudes, shapes, and propagation time.

ОСОБЕННОСТИ САМОДИФФУЗИИ В НЕФТИ ТУЛЬСКОГО ГОРИЗОНТА ЯМАШИНСКОГО МЕСТОРОЖДЕНИЯ

Using the NMR method with a pulsed magnetic field gradient the features of crude oil self-diffusion were investigated on samples of oil from the Tula horizon, the oil field Yamashinskoye. It was found that the samples were characterized by a complicated (non-exponential) form of diffusion attenuation of the NMR spin echo amplitude which required the introduction of the concept of effective (average over the entire sample volume) coefficient of selfdiffusion Deff. The temperature dependences of Deff within the temperature range 303-363 K are satisfactorily described by the equation of Arrhenius type equation which enabled to determine the values of self-diffusion activation energy ED in the studied systems. The correlation between the parameters of the studied systems self-diffusion, Deff, ED and their dynamic viscosity was found.

Tissue characterization of skin ulcer for bacterial infection by multiple statistical analysis of echo amplitude envelope

To characterize skin ulcers for bacterial infection, quantitative ultrasound (QUS) parameters were estimated by the multiple statistical analysis of the echo amplitude envelope based on both Weibull and generalized gamma distributions and the ratio of mean to standard deviation of the echo amplitude envelope. Measurement objects were three rat models (noninfection, critical colonization, and infection models). Ultrasound data were acquired using a modified ultrasonic diagnosis system with a center frequency of 11 MHz. In parallel, histopathological images and two-dimensional map of speed of sound (SoS) were observed. It was possible to detect typical tissue characteristics such as infection by focusing on the relationship of QUS parameters and to indicate the characteristic differences that were consistent with the scatterer structure. Additionally, the histopathological characteristics and SoS of noninfected and infected tissues were matched to the characteristics of QUS parameters in each rat model.

Stability evaluation of parameter estimation of multi-Rayleigh model for ultrasound B-mode image of liver fibrosis

A diagnosis of liver fibrosis using an ultrasound B-mode image has the advantages of real-time observation and noninvasive properties. In our previous study, a multi-Rayleigh model was proposed to express a probability density function (PDF) of echo amplitudes from a fibrotic liver. From the multi-Rayleigh model, fibrosis parameters, such as the amount of fibrotic tissue and its progressive ratio, can be extracted. To quantitatively evaluate liver fibrosis using the multi-Rayleigh model, it is important to evaluate the stability of the estimation method of multi-Rayleigh model parameters. In this study, a numerical simulation using random variables following the multi-Rayleigh model was performed and the estimation stability of the parameters of the multi-Rayleigh model with two components was examined. From the simulation results, it was found that estimation becomes unstable under a certain condition owing to statistical variations of moments, which are inputs in the estimation algorithm. The instability of estimated parameters could be evaluated by focusing on changes in moments upon changes in multi-Rayleigh model parameters. It was indicated that we can evaluate the reliability of the estimated parameters of the multi-Rayleigh model only from the estimated values.

Measurement of cantilever vibration using impedance-loaded surface acoustic wave sensor

In this study, an impedance-loaded surface acoustic wave (SAW) sensor was demonstrated to monitor the vibration frequency. Commercialized pressure sensors and a variable capacitor were chosen as external sensors, which were connected to a reflector on a SAW device. As the reflection coefficient of the reflector depended on the impedance, the echo amplitude was influenced by changes in the impedance of the external sensor. The vibration frequency of the cantilever was determined by monitoring the echo amplitude of the SAW device. Moreover, the attenuation constant of an envelope was estimated. The results of our feasibility study indicate that the impedance-loaded SAW sensor can be applied as a detector for structural health monitoring.

Ultrasound characterization of the mastoid for detecting middle ear effusion: A preliminary clinical validation.

Ultrasound detection of middle ear effusion (MEE) is an emerging technique in otolaryngology. This study proposed using ultrasound characterization of the mastoid to noninvasively measure MEE-induced mastoid effusion (ME) as a new strategy for determining the presence of MEE. In total, 53 patients were enrolled (Group I: normal, n = 20; Group II: proven MEE through both otoscopy and tympanometry, n = 15; Group III: patients with MEE having effusions observed during grommet surgery, n = 18). A 2.25-MHz delay-line transducer was used to measure backscattered signals from the mastoid. The Nakagami parameter was estimated using the acquired signals to model the echo amplitude distribution for quantifying changes in the acoustic structures of mastoid air cells. The median Nakagami parameter and interquartile range were 0.35 (0.34–0.37) for Group I, 0.39 (0.37–0.41) for Group II, and 0.43 (0.39–0.51) for Group III. The echo amplitude distribution observed for patients with MEE was closer to Rayleigh distribution than that without MEE. Receiver operating characteristic (ROC) curve analysis further revealed that the area under the ROC was 0.88, sensitivity was 72.73%, specificity was 95%, and accuracy was 81.13%. The proposed method has considerable potential for noninvasive and comfortable evaluation of MEE.

Dynamics of 4-oxo-TEMPO-d16-15N nitroxide–propylene glycol system studied by ESR and ESE in liquid and glassy state in temperature range 10–295 K

ESR spectra and electron spin relaxation of nitroxide radical in 4-oxo-TEMPO-d16-15N in propylene glycol were studied at X-band in the temperature range 10–295K. The spin–lattice relaxation in the liquid viscous state determined from the resonance line shape is governed by three mechanisms occurring during isotropic molecular reorientations. In the glassy state below 200K the spin–lattice relaxation, phase relaxation and electron spin echo envelope modulations (ESEEM) were studied by pulse spin echo technique using 2-pulse and 3-pulse induced signals. Electron spin–lattice relaxation is governed by a single non-phonon relaxation process produced by localized oscillators of energy 76cm−1. Electron spin dephasing is dominated by a molecular motion producing a resonance-type peak in the temperature dependence of the dephasing rate around 120K. The origin of the peak is discussed and a simple method for the peak shape analysis is proposed, which gives the activation energy of a thermally activated motion Ea=7.8kJ/mol and correlation time τ0=10−8s. The spin echo amplitude is strongly modulated and FT spectrum contains a doublet of lines centered around the 2D nuclei Zeeman frequency. The splitting into the doublet is discussed as due to a weak hyperfine coupling of nitroxide unpaired electron with deuterium of reorienting CD3 groups.

Echo-level compensation and delay tuning in the auditory cortex of the mustached bat.

During echolocation, bats continuously perform audio-motor adjustments to optimize detection efficiency. It has been demonstrated that bats adjust the amplitude of their biosonar vocalizations (known as 'pulses') to stabilize the amplitude of the returning echo. Here, we investigated this echo-level compensation behaviour by swinging mustached bats on a pendulum towards a reflective surface. In such a situation, the bats lower the amplitude of their emitted pulses to maintain the amplitude of incoming echoes at a constant level as they approach a target. We report that cortical auditory neurons that encode target distance have receptive fields that are optimized for dealing with echo-level compensation. In most cortical delay-tuned neurons, the echo amplitude eliciting the maximum response matches the echo amplitudes measured from the bats' biosonar vocalizations while they are swung in a pendulum. In addition, neurons tuned to short target distances are maximally responsive to low pulse amplitudes while neurons tuned to long target distances respond maximally to high pulse amplitudes. Our results suggest that bats dynamically adjust biosonar pulse amplitude to match the encoding of target range and to keep the amplitude of the returning echo within the bounds of the cortical map of echo delays.

Ultrasonic Defect Characterization in Heavy Rotor Forgings by Means of the Synthetic Aperture Focusing Technique and Optimization Methods.

Ultrasonic nondestructive testing of steel forgings aims at the detection and classification of material inhomogeneities to ensure the components fitness for use. Due to the high price and safety critical nature of large forgings for turbomachinery, there is great interest in the application of imaging algorithms to inspection data. However, small flaw indications that cannot be sufficiently resolved have to be characterized using amplitude-based quantification. One such method is the distance gain size method, which converts the maximum echo amplitudes into the diameters of penny-shaped equivalent size reflectors. The approach presented in this contribution combines the synthetic aperture focusing technique (SAFT) with an iterative inversion scheme to locate and quantify small flaws in a more reliable way. Ultrasonic inspection data obtained in a pulse-echo configuration are reconstructed by means of an Synthetic Focusing Technique (SAFT). From the reconstructed data, the amount and approximate location of small flaws are extracted. These predetermined positions, along with the constrained defect model of a penny-shaped crack, provide the initial parametrization for an elastodynamic simulation based on the Kirchhoff approximation. The identification of the optimal parameter set is achieved through an iteratively regularized Gauss-Newton method. By testing the characterization method on a series of flat-bottom holes under laboratory conditions, we demonstrate that the procedure is applicable over a wide range of defect sizes. To show suitability for large forging inspection, we additionally evaluate the inspection data of a large generator shaft forging of 0.6-m diameter.

Analysis of Coherent and Diffuse Scattering Using a Reference Phantom.

The estimation of many spectral-based quantitative ultrasound parameters assumes that backscattered echo signals are from a stationary, incoherent scattering process. The accuracy of these assumptions in real tissue can limit the diagnostic value of these parameters and the physical insight about tissue microstructure they can convey. This work presents an empirical decision test to determine the presence of significant coherent contributions to echo signals and whether they are caused by low scatterer number densities or the presence of specular reflectors or scatterers with periodic spacing. This is achieved by computing parameters from echo signals that quantify stationary or nonstationary features related to coherent scattering, and then comparing their values to thresholds determined from a reference material providing diffuse scattering. The paper first presents a number of parameters with demonstrated sensitivity to coherent scattering and describes criteria to select those with the highest sensitivity using simulated and phantom-based echo data. Results showed that the echo amplitude signal-to-noise ratio and the multitaper-generalized spectrum were the parameters with the highest sensitivity to coherent scattering with stationary and nonstationary features, respectively. These parameters were incorporated into the reference-based decision test, which successfully identified regions in simulated and tissue-mimicking phantoms with different incoherent and coherent scattering conditions. When scatterers with periodic organization were detected, the combination of stationary and nonstationary analysis permitted the estimation of the mean spacing below and above the resolution limit imposed by the pulse size. Preliminary applications of this algorithm to human cervical tissue ex vivo showed correspondence between regions of B-mode images showing bright reflectors, tissue interfaces, and hypoechoic regions with regions classified as specular reflectors and low scatterer number density. These results encourage further application of the algorithm to more structurally complex phantoms and tissue.

Photon echo transients from an inhomogeneous ensemble of semiconductor quantum dots

An ensemble of quantum dot excitons may be used for coherent information manipulation. Due to the ensemble inhomogeneity any optical information retrieval occurs in form of a photon echo. We show that the inhomogeneity can lead to a significant deviation from the conventional echo timing sequence. Variation of the area of the initial rotation pulse, which generates excitons in a dot sub-ensemble only, reveals this complex picture of photon echo formation. We observe a retarded echo for {\pi}/2 pulses, while for 3{\pi}/2 the echo is advanced in time as evidenced through monitoring the Rabi oscillations in the time-resolved photon echo amplitude from (In,Ga)As/GaAs self-assembled quantum dot structures and confirmed by detailed calculations.

Evidence for variable grounding-zone and shear-margin basal conditions across Thwaites Glacier, West Antarctica

Definitive interpretation of ice-sheet basal conditions from radar-sounding data beneath outlet-glacier grounding zones and shear margins can be problematic due to poorly constrained and spatially variable englacial attenuation rates and losses from propagation through a rough ice surface. To correct for spatially variable attenuation rates, we developed a novel radar analysis approach that provided improved empirical attenuation correction by fitting linearly variable attenuation rates along radar-sounding profiles from the ice-sheet interior to the grounding zone. We also corrected for ice-surface propagation losses by using surface echo amplitude distributions to constrain the loss of coherent power for surface reflections and two-way propagation through a rough ice surface. By applying this approach to airborne radar-sounding observations of the Thwaites Glacier catchment in West Antarctica, we produced relative reflectivity profiles, which show grounding-zone basal conditions varying across the Amundsen Sea Embayment. Additionally, these techniques provided improved characterization of basal conditions across shear margins, showing that — contrary to previous interpretations — the eastern shear margin of Thwaites Glacier corresponded to a change in basal conditions consistent with a transition from frozen to thawed bed.

Research on evaluating laser welding quality based on two-dimensional array ultrasonic probe

In this paper, an evaluating method of laser welding quality for stainless steel lap joint has been studied based on the ultrasonic nondestructive testing technology. The two-dimensional array ultrasonic probe is used to inspect the weld joint, analyzing the effect of fusion state on A-scan echo amplitude, and C-scan image of internal contact surface is established. A concept of equivalent weld width as the quantitative characterization of fusion state is defined, and a computational model of equivalent weld width is discussed based on statistical method. Testing results show that this method is simple and feasible, and its accuracy could completely meet the requirements of engineering application.