Anyu Sun

A new method for evaluating the degeneration of articular cartilage using pulse-echo ultrasound

This paper presents a novel nondestructive ultrasonic technique for measuring the sound speed and acoustic impedance of articular cartilage using the pulsed Vz,t technique. Vz,t data include a series of pulsed ultrasonic echoes collected using different distances between the ultrasonic transducer and the specimen. The 2D Fourier transform is applied to the Vz,t data to reconstruct the 2D reflection spectrum Rθ,ω. To obtain the reflection coefficient of articular cartilage, the Vz,t data from a reference specimen with a well-known reflection coefficient are obtained to eliminate the dependence on the general system transfer function. The ultrasound-derived aggregate modulus (Ha) is computed based on the measured reflection coefficient and the sound speed. In the experiment, 32 cartilage-bone samples were prepared from bovine articular cartilage, and 16 samples were digested using 0.25% trypsin solution. The sound speed and Ha of these cartilage samples were evaluated before and after degeneration. The magnitude of the sound speed decreased with trypsin digestion (from 1663 ± 5.6 m/s to 1613 ± 5.3 m/s). Moreover, the Youngs modulus in the corresponding degenerative state was measured and was correlated with the ultrasound-derived aggregate modulus. The ultrasound-derived aggregate modulus was determined to be highly correlated with the Youngs modulus (n = 16, r>0.895, p<0.003, Pearson correlation test for each measurement). The results demonstrate the effectiveness of using the proposed method to assess the changes in sound speed and the ultrasound-derived aggregate modulus of cartilage after degeneration.

Determination of the multiple local properties of thin layer with high lateral resolution by scanning acoustic microscopy.

Simultaneous determination of the multiple local acoustic and geometrical properties of the thin layer with a high lateral resolution is of great interest in ultrasonic non-destructive evaluation. In this paper, we propose a technique based on the V(z, t) data to simultaneously determine the four local properties of the thin layer, namely, the thickness, the sound velocity, the acoustic impedance, and the density. First, the V(z, t) data are collected from both the thin layer and the reference material. Then the sound velocity and the thickness are calculated by focusing the point-focusing transducer on the front and back surfaces of the thin layer, with the confocal positions determined by averaging the peak positions in the V(z) curves at different frequencies. Second, the acoustic impedance of the thin layer is obtained based on the experimental and theoretical two-dimensional reflection spectrum using the echo from the front surface of the layer. Finally, the density can be obtained by dividing the acoustic impedance by the sound velocity. The four local properties of an aluminum layer are accurately obtained using our method. The largest relative error of determining the four properties is around 1%. This technique opens a new way of simultaneously measuring the multiple local acoustic and geometrical properties of thin layers.

Deconvolution imaging of weak reflective pipe defects using guided-wave signals captured by a scanning receiver

Guided-wave echoes from weak reflective pipe defects are usually interfered by coherent noise and difficult to interpret. In this paper, a deconvolution imaging method is proposed to reconstruct defect images from synthetically focused guided-wave signals, with enhanced axial resolution. A compact transducer, circumferentially scanning around the pipe, is used to receive guided-wave echoes from discontinuities at a distance. This method achieves a higher circumferential sampling density than arrayed transducers-up to 72 sampling spots per lap for a pipe with a diameter of 180 mm. A noise suppression technique is used to enhance the signal-to-noise ratio. The enhancement in both signal-to-noise ratio and axial resolution of the method is experimentally validated by the detection of two kinds of artificial defects: a pitting defect of 5 mm in diameter and 0.9 mm in maximum depth, and iron pieces attached to the pipe surface. A reconstructed image of the pitting defect is obtained with a 5.87 dB signal-to-noise ratio. It is revealed that a high circumferential sampling density is important for the enhancement of the inspection sensitivity, by comparing the images reconstructed with different down-sampling ratios. A modified full width at half maximum is used as the criterion to evaluate the circumferential extent of the region where iron pieces are attached, which is applicable for defects with inhomogeneous reflection intensity.

Simultaneous ultrasonic parameter estimation of a multi-layered material by the PSO-based least squares algorithm using the reflection spectrum.

HighlightsProposing the PSO‐based least squares algorithm for parameters estimation.Simultaneous properties measurement of multi‐layered material.Analyzing the unpredictable effect from properties of multi‐layered structure on the reflection spectrum.Improving the widely‐used least squares inversion method by particle swarm optimization. ABSTRACT Advanced multi‐layered materials with superior performance are required for many applications. The non‐destructive characterization of multi‐layer properties is a hot spot of current research. The least squares inversion method using the reflection spectrum has been developed and widely used to estimate the properties of thin single layers simultaneously. However this method has the problems of a loss in speed and simplicity, and a local optimal solution, especially in the cases of a multi‐layered structure because of the increasing estimated parameters and the uncertainty influence from the parameters. Particle swarm optimization (PSO) is a robust global search algorithm similar to ‘bird’ foraging, which can be used to improve the performance of the least squares inversion algorithm. This paper has proposed a PSO‐based least squares estimation using the ultrasonic reflection spectrum to make simultaneous measurement. The simulation and experiment, carried out on the aluminum‐TC4 bi‐layered material, tested and proved the capability of the new algorithm. The real measured parameters and the estimated parameters were obtained. The results have been compared to analyze the errors of the estimated parameters.

Numerical and experimental analysis of a focused reflected wave in a multi-layered material based on a ray model

HighlightsUsing a reflective focal probe for simultaneous sound‐velocity and thickness measurements of a multi‐layered material.We study the multi‐mode wave focus to identify the focused longitudinal waves.Proposing the ‘bottom left’ principle to identify longitudinal‐wave focus.A phase differentiation theory is proposed to find the incident angle for the focus of the tilted rays. ABSTRACT A focal probe is used for the acoustic measurement of a thin layer of a material with unknown sound velocity. This is now possible, because an algorithm, based on the focused ray model, has been found. However, there are still several problems such as the assumption that the half‐aperture angle equals the incident angle, the identification of the longitudinal‐wave focus, and the composition of the signal. In this work, we study the multi‐mode wave focus numerically and experimentally to identify the focused longitudinal waves. A theoretical multilayered focusing model has been introduced based on geometrical acoustics. In addition, a phase differentiation theory is proposed to find the incident angle for the focus of the tilted rays, which is referred to as maximum half‐aperture angle in other studies. The Symbol curve of a single layer, with a thickness of 1.5 mm and 2.0 mm, and a multi‐layer are obtained using vertical translational movement. Both thickness and sound velocity are derived from the curve simultaneously. Our single layer experiments show that it is possible to focus multimode waves. The single and multi‐layer experiments confirm the multi‐layered focused ray model and phase differentiation theory. Furthermore, experiments are conducted to analyze the measured results. Symbol. No caption available.

A rotary scanning method to evaluate grooves and porosity for nerve guide conduits based on ultrasound microscopy

Grooved nerve guide conduits (NGCs) have been effective in the clinical treatment of peripheral nerve injury. They are generally fabricated from a micro-structured spinneret using a spinning process, which easily can cause a variety of pores and morphological deviation. The topography of internal grooves as well as the porosity can greatly influence the therapeutic effect. Traditional optical or scanning electron microscopy (SEM) methods can be used to image the grooves; however, these methods are destructive and require slicing NGCs to prepare specimens suitable for imaging. Moreover, lengthy experiments and large batches of NGCs are required to ensure reliable results from both in vitro experiments and clinical studies. In this paper, a non-destructive method for evaluating the grooves and porosity of NGCs is proposed using ultrasonic imaging combined with rotary scanning and an image analysis algorithm. Two ultrasonic methods were used: a 25-MHz point-focus ultrasonic transducer applied to observe axial cross sections of the conduits and a 100-MHz point-focus ultrasonic transducer to detect large pores caused by defects. Furthermore, a theoretical algorithm for detecting the local porosity of a conduit based on density is proposed. Herein, the proposed acoustic method and traditional optical methods are evaluated and compared. A parameter representing the specific surface area of the internal grooves is introduced and computed for both the optical and acoustic methods, and the relative errors of the computed parameter values for three different NGCs were 7.0%, 7.9%, and 15.3%. The detected location and shape of pores were consistent between the acoustic and optical methods, and greater porosity was observed in the middle of the conduit wall. In this paper, the results of the acoustic and optical methods are presented and the errors relating to the acoustic factors, device characteristics, and image processing method are further analyzed.

Full area covered 3D profile measurement of special-shaped optics based on a new prototype non-contact profiler

A new prototype non-contact profiler based on surface tracking has been specially developed. Surface tracking is carried out by a specially designed dual stage probe system with the aid of a four-Degree Of Freedom high-precision motion platform. The dual stage probe system keeps a short-range optical probe constantly tracking the surface by a self-developed voice coil motor servo, by which a wide measuring range of up to 10 mm is realized. The system performance evaluation including resolution, repeatability, and scanning speed proved the good capability of the new prototype non-contact profiler. To realize a full area covered 3D profile measurement of special-shaped optics within one scanning procedure, a signal intensity monitor integrated in the surface tracking controller is specially developed. In the experiment, a snip-single-corner-rectangular-shaped freeform surface was successfully measured over full area by the new non-contact profiler. This work provides an effective solution for 3D profile measurement of special-shaped optical surfaces over full reflecting area. Experimental results demonstrate that the proposed measuring system is of great significance in quality evaluation of optical surfaces.