A nondestructive ultrasonic imaging system for detection of flawsin metal blocks

An ultrasonic imaging system is presented for the nondestructive evaluation of internal defects in metal blocks. The surfaces of the blocks are coarsely scanned by a single ultrasonic transducer to record multiple A-scans. The recorded A-scans are processed by a synthetic-aperture focusing technique (SAFT) algorithm to search for defects in a metal specimen. The processed information is then sent to a graphics package to be displayed on a CRT screen of a personal computer. The current linear imaging technique is presented and is compared to the SAFT algorithm. The theory and limitations of the SAFT algorithm as well as the hardware implementation are discussed. Images of defects in aluminum blocks are illustrated with varying operating parameters showing the performance of the imaging system     

Dry-contact technique for high-resolution ultrasonic imaging

To accomplish a high-resolution ultrasonic imaging without wetting a sample, the efficiency of the dry-contact ultrasonic transmission is discussed. In this study, a dry-contact interface is formed on a sample by inserting a thin film between water and a sample, and the pressure is working on the interface by evacuating the air between the film and the sample. A model of dry-contact ultrasonic transmission is presented to assess the signal loss accompanied with the transmission. From the determination of the signal loss caused by the transmission using various films, it was found that the higher frequency ultrasound is transmitted effectively into the sample by selecting an optimum film, which can keep the displacement continuity between the film and the sample during ultrasonic transmission. Finally, ultrasonic imaging with the sufficient signal-to-noise ratio (SNR) and high lateral resolution was performed on the delamination in a package and the jointing interface of the ball-grid-array package without wetting the packages.     

Elliptical-Tukey chirp signal for high-resolution, air-coupled ultrasonic imaging

A new signal processing method, which uses a modified chirp signal for air-coupled ultrasonic imaging, is described. A combination of the elliptical and Tukey window functions has been shown to give a better performance than the Hanning windowing used in most pulse-compression algorithms for air-coupled applications. The elliptical-Tukey chirp signal provides an improvement in both the resolution of images and signal-to-noise ratios. In addition, this type of signal also reduces the level of signal voltages required to drive the source transducer while maintaining the performance of the system. This approach, thus, may have wide interest in all forms of wide bandwidth ultrasonic imaging.     

Polyurea thin film ultrasonic transducers for nondestructive testing and medical imaging

Ultrasonic transducers using polyurea piezoelectric thin film are studied in this paper. Aromatic polyurea thin films, prepared by vapor deposition polymerization, have useful characteristics for use as an ultrasonic transducer. This paper presents the fabrication and experimental evaluation of ultrasonic transducers formed using polyurea films. First, the vapor deposition polymerization process using two monomers is briefly reviewed, and the temperature conditions for higher piezoelectric constants are explored. Second, in order to test the fundamental characteristics of this material as a high-frequency, ultrasonic transducer, a polyurea film of 2.5 microm thickness was deposited on a silicon substrate. In the pulse/echo experiment results, a resonant frequency of about 100 MHz was observed. Third, we fabricated a concave point focus transducer and a cylindrical line focus transducer. To examine the performances of the focus transducers, two-dimensional images of a coin and V(z) curve measurements for an aluminum surface were demonstrated.     

Measurement models for ultrasonic nondestructive evaluation

The article reviews ways to use the electromechanical reciprocity relation to construct theoretical models of measurement processes in ultrasonic nondestructive evaluation. This relationship is important because it connects the change in the voltages measured at the electrical terminal of the transducer to the perturbation in the mechanical wavefield caused by the change in the propagation environment. It does so by mixing an unperturbed reference wavefield with one containing the perturbed wavefield. Two problems of progressive difficulty are explored. We begin by investigating the imaging of a one-dimensional sinusoidal fluid-solid interface using a cylindrically focused beam and continue by developing a model of the imaging of the mechanical properties of a two-dimensional, thin solid film using a confocal arrangement of point-focused transducers. This last problem uses an approximation to the thin solid film, which reduces its mechanical response to one similar to that of a membrane. Integral relations are given that can be used to form integral equations or to generate asymptotic approximations to the particle displacements and stresses in the film.     

Noncontact, high-resolution ultrasonic imaging of wood samples using coded chirp waveforms

A noncontact ultrasonic inspection technique has been developed to study the properties of wood samples in air. The system makes use of two broad bandwidth capacitive transducers, combined with signal processing techniques. A coded chirp signal was used in the current application to provide a waveform that could be postprocessed to provide sufficient sensitivity for transmission across samples of wood. It will be shown in this paper that the signal-to-noise ratio (SNR) can be greatly improved using two signal recovery techniques, namely pulse compression and swept frequency multiplication (SFM). A simulation of both techniques is presented and compared to experimental data. As will be seen from the experimental results, it is possible to perform noncontact ultrasonic experiments to extract a range of useful information such as ring density and the presence of microcracks.     

A new system for real-time synthetic aperture ultrasonic imaging

The authors devised a way to generate in real time a cross-sectional image of an object with uniformly high resolution based on the synthetic aperture focusing technique (SAFT). A computer simulation was conducted to study the effects of essential parameters on the resulting images. An imaging system was built that produces a cross-sectional image composed of an assembly of line images of depth direction, i.e. processed A-scan images, and displays a scroll picture on a CRT (cathode ray tube) with no interruption regardless of the object size. It takes only 3 ms from the start of transmission of the ultrasonic wave to the completion of a line image reconstruction, and the framed image on a CRT is updated at the TV rate of 1/30 s. Imaging experiments were conducted using the system, and its expected performance was demonstrated.     

Guided wave nuances for ultrasonic nondestructive evaluation

Recent developments in guided wave generation, reception, and mode control show that increased penetration power and sensitivity are possible. A tone burst function generator and appropriate signal processing are generally used. Variable angle beam and comb-type transducers are the key to this effort. Problems in tubing, piping, hidden corrosion detection in aging aircraft, adhesive and diffusion bonding, and ice detection are discussed. Additionally, sample configurations, inspection objectives, and logic are being developed for such sample problems as defect detection and analysis in lap splice joints, tear straps, cracks in a second layer, hidden corrosion in multiple layers, cracks from rivet holes, transverse cracking in a beam, and cracks in landing gear assembly. Theoretical and experimental aspects of guided wave analysis include phase velocity, group velocity, and attenuation dispersion curves; boundary element model analysis for reflection and transmission factor analysis; use of wave structure for defect detection sensitivity; source influence on the phase velocity spectrum, and the use of angle beam and comb transducer technology. Probe design and modeling considerations are being explored. Utilization of in-plane and out-of-plane displacement patterns on the surface and longitudinal power distribution across the structural cross-section are considered for improved sensitivity, penetration power, and resolution in nondestructive evaluation. Methods of controlling the phase velocity spectrum for mode and frequency selection are available. Such features as group velocity change, mode cut-off measurements, mode conversion, amplitude ratios of transmission, and reflection factors of specific mode and frequency as input will be introduced for their ability to be used in flaw and material characterization analysis.     

Disposable PVDF ultrasonic transducers for nondestructive testingapplications

Disposable ultrasonic contact transducers have been constructed with inexpensive PVDF films for nondestructive testing (NDT) applications. This paper reports the temperature-dependent ultrasonic performance of commercial polyvinylidene fluoride (PVDF) films and PVDF sensors. PVDF film was evaluated for its material properties of interest for ultrasonic transducer performance including the relative dielectric constant ε_r, dielectric loss tangent tan δ_e , electromechanical coupling constant k_t, mechanical quality factor Q_m, and acoustic impedance Z. Disposable PVDF transducers were then coupled to both low and high acoustic impedance test panels and their ultrasonic insertion loss/sensitivity and frequency bandwidth measured as a function of temperature in both the pulse-echo and pitch-catch modes. The results yielded center frequencies in the 3.5-16 MHz range, with -6-dB fractional bandwidths for some of the transducers exceeding 100%. The temperature dependence of the transducers' performance is reported for the -40 to 80°C range and shows an approximate linear decrease in center frequency and increase in fractional bandwidth with increasing temperature. These measured results are compared with predictions from computer simulations based on Mason's model. These tests showed that the same disposable transducers can be used for both ultrasonic and acoustic emission sensing NDT applications. This paper summarizes the quantitative ultrasonic and vibration sensing performance for all of the disposable PVDF film transducers which were tested     

A generic hybrid model for bulk elastodynamics, with application to ultrasonic nondestructive evaluation

Practical ultrasonic inspection requires modeling tools that enable rapid and accurate visualization; because of the increasing sophistication of practical inspection, it is becoming increasingly difficult to use a single modeling method to represent an entire inspection process. Hybrid models that utilize different or interacting numerical schemes in different regions, to use their relative advantages to maximal effect, are attractive in this context, but are usually custom-made for specific applications or sets of modeling methods. The limitation of hybrid schemes to particular modeling techniques is shown here to be related to their fundamental formulation. As a result, it becomes clear that a formalism to generalize hybrid schemes can be developed: an example of the construction of a generic hybrid modeling interface is given for the abstraction of bulk ultrasonic wave phenomena, common in practical inspection problems. This interface is then adapted to work within a prototype hybrid model consisting of two smaller finite element model-domains, and explicitly demonstrated for bulk ultrasonic wave propagation and scattering examples. Sources of error and ways to improve the accuracy of the interface are also discussed.     

Airborne ultrasonic imaging system for parallelepipedic objectlocalization

An ultrasonic image device was designed for use in robotic applications where parallelepipedic objects need to be manipulated. It is based on ranging measurement by an array of ten identical airborne ultrasonic transducers with an operating frequency of 200 kHz and a detection cone angle of approximately 7 degrees. An electronic scanning associated with a mechanical displacement of the array covers an area of 0.4×0.4 m in less than 0.5 seconds (100 measurement points). The system was tested in an automatic packaging line. It allowed a real-time localization of cubic objects as small as 2 cm and the determination of an emplacement in which a new object can be put by a robot arm     

A high-frame rate high-frequency ultrasonic system for cardiac imaging in mice

We report the development of a high-frequency (30-50 MHz), real-time ultrasonic imaging system for cardiac imaging in mice. This system is capable of producing images at 130 frames per second (fps) with a spatial resolution of less than 50 microm. A novel mechanical sector probe was developed that utilizes a magnetic drive mechanism and custom-built servo controller for high speed and accuracy. Additionally, a very light-weight (< 0.28 g), single-element transducer was constructed and used to reduce the mass load on the motor. The imaging electronics were triggered according to the angular position of the transducer in order to compensate for the varying speed of the sector motor. This strategy ensured the production of equally spaced scan lines with minimal jitter. Wire phantom testing showed that the system axial and lateral resolutions were 48 microm and 72 microm, respectively. In vivo experiments showed that high-frequency ultrasonic imaging at 130 fps is capable of showing a detailed depiction of a beating mouse heart.     

A nondestructive integrity test for membrane filters based on air-coupled ultrasonic spectroscopy

This work describes the application of an ultrasonic air-coupled characterization technique to membrane filters. Coefficient of transmission of sound at normal incidence through each membrane in the frequency range 0.55 MHz-2.4 MHz was measured. For all cases, at least one thickness resonance was observed. From these measurements density, velocity, and attenuation of ultrasonic longitudinal waves are calculated and compared to available filtration data such as water flux measurements and bubble point data, both provided by manufacturers. Results show that velocity of ultrasonic waves in membrane filters depends on the membrane grade and can be correlated to filtration properties; attenuation per wavelength is independent of membrane grade but sensitive to moisture content. Advantages of this technique over other conventional membrane tests are pointed out.     

New transducers for high-resolution ultrasonic testing

High resolution NDT requires ultrasonic transducers which can produce very short pulses with well-defined constant shape throughout the field. The theory, construction and applications of such transducers are discussed.     

三维超声地震模型实时成像系统

室内水槽实验是研究地质沉积过程及其演化规律的重要手段,高精度获取沉积过程中的地质体的变化是这类模拟实验非常关键的环节。文章介绍了新研制的三维超声地震模型实时成像系统的主要组成及关键技术。该系统用于模拟海上地震,可以在沉积实验后通过快速测量及对数据的实时偏移处理与成像可以获取变化的多层复杂地质模型动态图像,极大地提高了实验效率和成像精度。该系统具有良好的实时性、成像质量以及探测范围,在对研究地质沉积、海洋地质以及三维地震模型研究等方面有着广泛应用前景。     

Two-photon interferometry for high-resolution imaging

This paper discusses the advantages of using non-classical states of light for two aspects of optical imaging: the creation of microscopic images on photosensitive substrates, which constitutes the foundation for optical lithography, and the imaging of microscopic objects. In both cases, the classical resolution limit given by the Rayleigh criterion is approximately half of the optical wavelength. It has been shown, however, that by using multi-photon quantum states of the light field, and a multi-photon sensitive material or detector, this limit can be surpassed. A rigorous quantum mechanical treatment of this problem is given, some particularly widespread misconceptions are addressed, and turning quantum imaging into a practical technology is discussed.     

Blind multiridge detection for automatic nondestructive testing using ultrasonic signals

Ultrasonic imaging has been a significant means for nondestructive testing (NDT). Recently the NDT techniques via the ultrasonic instrumentation have shown the striking capability of the quality control for the material fabrication industry. To the best of our knowledge, all existing signal processing methods require either the a priori information of the ultrasonic signature signals or the manual segmentation operation to achieve the reliable parameters that characterize the corresponding mechanical properties. In this paper, we first provide a general mathematical model for the ultrasonic signals collected by the pulse-echo sensors, then design a totally blind novel signal processing NDT technique relying on neither a priori signal information nor any manual effort. Based on the automatic selection of optimal frame sizes using a proposed new criterion in our scheme, the signature signal can be blindly extracted for further robust multiridge detection. The detected ridge information can be used to estimate the transmission and attenuation coefficients associated with any arbitrary material sample for the fabrication quality control.     

A knowledge-based system for nondestructive testing of polymeric composite components

This paper presents a formalization of the knowledge domain of nondestructive quality control of polymeric composite components. The formalization scheme presented in this paper has been implemented in a prototype knowledge-based expert system (KBES), called NICC for nondestructive inspection of composite components, to help in the quality assurance of these parts. Geometric and bonding characteristics of individual and assembled components are taken into account, as opposed to the better understood evaluation of well-behaved test specimens. The use of nondestructive techniques in the inspection of plastic and polymeric composites is fairly recent and hence, the knowledge required to develop a KBES is still very scattered and not yet fully covered in the literature. This study demonstrates both the feasibility of compiling and representing this knowledge domain and the possibility of translating it into an efficient automated tool capable of giving reliable expert-like advice at low cost. The reasoning process is divided into three stages. In the first stage, a polymetric composite component is completely defined according to features that are relevant for nondestructive inspection. In the second stage, all the discontinuities that may be present in the component are determined. Finally, in the third stage, appropriate nondestructive testing procedures are identified to detect each of the possible discontinuities.     

High-power high-resolution pulser for air-coupled ultrasonic NDE applications

This paper describes the design and development of a high-power high-resolution pulser designed especially for air-coupled ultrasonic nondestructive evaluation applications requiring high material penetration capability. The pulser can deliver up to 800 V in a spike excitation type pulse to appropriate low/medium frequency transducers. Moreover, the pulser operates in three different modes: single pulse, double pulse (pulse cancellation technique), and external reference signal, where the last two operating modes are intended to enhance the axial resolution of ultrasonic inspections. Experimental results show that the received pulse duration can be significantly reduced, and reduction factors of 2 or 3 in the pulse duration can be easily achieved.     

一种用于相控阵B超成像的数字波束合成器的设计

本文介绍了一种能沿任意波束指向全程动态聚焦的数字波束合成器的设计，此合成器用于相控阵Ｂ超成像系统。回声信号的延时量分解为“指向延时”和“聚焦延时”两部分，分别用产生相控发射激励的时序逻辑电路和一个“动态聚焦延时量表”实现。通过对Ａ／Ｄ采样时钟的控制及对Ａ／Ｄ采样时钟、地址计数时钟和存储器写时钟的时序配合，实现了同相位数据点采样及无冗余数据的缓冲存储器。所设计的数字相控波束合成器只用廉价的高速数字电路即可实现，成本极低。实验结果验证了该方案的可行性。