Single-element Probes Research Articles

Phased array probes for air-coupled ultrasonic testing based on cellular polymer

Air-coupled ultrasonic testing is an established alternative to conventional ultrasonic methods for testing of light-weight components in aerospace and automotive industry. Compared to direct coupled contact technique or immersion technique it is less invasive, so that it offers numerous financial incentives. While phased arrays are already an industrial standard in fluid-coupled mechanized ultrasonic testing, air-coupled testing is usually performed using two single-element probes and a transmission technique. Therefore, advantages of phased arrays such as active focussing and manipulation of the incidence angle are rarely used with air-coupled testing. This paper presents a newly developed air-coupled phased array device with the emphasis on the characterization of the probes. The device consists of a linear array probe, a transmitter unit and a receiver unit. The main novelty is that the array probe is based on high-voltage excitation of charged cellular polypropylene. Charged cellular polymers are referred to as ferroelectrets or as piezoelectrets. They exhibit an extremely low stiffness and acoustic impedance, so that a matching layer is not necessary. Extremely low mechanical cross-coupling enables independent excitation of the elements of the array. The development of the phased array probes is supported by computations of the sound field using point source synthesis. The main intended applications are transmission with focussing, transmission with an electronic sweep and testing with air-coupled guided waves by using beam steering, applied to carbon-fibre-reinforced plates and similar materials. Air-coupled guided waves enable testing of objects with one-sided access. This work was funded from the “Technologietransfer-Programm Leichtbau” by the German Federal Ministry for Economic Affairs and Climate Action, project 03LB1001A.

Optimized integrated design of a high-frequency medical ultrasound transducer with genetic algorithm

Designing efficient acoustic stack and elements for high-frequency (HF) medical ultrasound (US) transducers involves various interrelated parameters. So far, optimizing spatial resolution and acoustic field intensity simultaneously has been a daunting task in the area of HF medical US imaging. Here, we introduce optimized design for a 50-MHz US probe for skin tissue imaging. We have developed an efficient design and simulation approach using Krimholtz, Leedom and Matthaei (KLM) equivalent circuit model and spatial impulse response method by means of Field II software. These KLM model and Field II software are integrated, and a GA algorithm is used to optimize the design of the US transducer to obtain the best imaging performance. As a result, a 50-MHz single element probe is effectively optimized with 5 mm acoustic focal length, 72 upmu {text{m}} lateral, and 42 upmu {text{m}} axial imaging resolution, with an enhancement in imaging resolution over the conventionally designed and simulated probe by 10%. This work has the potential to benefit many applications that require a fast, high-resolution and strong US focus in skin imaging.

Towards an Alternative to Time of Flight Diffraction Using Instantaneous Phase Coherence Imaging for Characterization of Crack-Like Defects.

Time of flight diffraction (TOFD) is considered a reliable non-destructive testing method for the inspection of welds using a pair of single-element probes. On the other hand, ultrasonic phased array imaging has been continuously developed over the last couple of decades, and now features powerful algorithms, such as the total focusing method (TFM) and its multi-view approach to rendering detailed images of inspected parts. This article focuses on a different implementation of the TFM algorithm, relying on the coherent summation of the instantaneous signal phase. This approach presents a wide range of benefits, such as removing the need for calibration, and is highly sensitive to defect tips. This study compares the sizing and localization capabilities of the proposed method with the well-known TOFD. Both instantaneous phase algorithm and TOFD do not take advantage of the signal amplitude. Experimental tests were performed on a ¾″-thick steel sample with crack-like defects at different angles. Phase-based imaging techniques showed similar characterization capabilities as the standard TOFD method. However, the proposed method adds the benefit of generating an easy-to-interpret image that can help in localizing the defect. These results pave the way for a new characterization approach, especially in the field of automated ultrasonic testing (AUT).

Health Monitoring of Single-Element Piezoelectric Transducer Using Its Electromechanical Admittance.

The transducer is an essential part of all ultrasonic systems used for applications such as medical diagnostics, therapy, nondestructive evaluation, and cleaning because its health condition is vital to their proper operation. Defects within the active element, backing or other constitutive elements, and loss of adhesion between layers can significantly weaken the performance of a transducer. The objective of this work is to determine procedures to monitor the behavior of a single-element probe during its lifetime and detect degradations before they significantly affect the performance of the system. To achieve this, electromechanical admittance (EMA)-based method is envisaged numerically and experimentally. A simplified single-element transducer consisting of a piezoceramic disk, a bonding layer, and a backing is studied and the influence of bonding delamination on EMA is investigated. This study considers three different types of delaminations, which are named, respectively, "center" (circular delamination from the center of the disk toward the peripheric zone), "peripheric" (annular delamination from the peripheric zone toward the center), and "wedge" (wedge-shaped delamination with a given angle). For each case, a numerical model based on the finite-element (FE) method is developed: a 2-D FE analysis is implemented for the first two types of delaminations, taking advantage of their axisymmetric structure, and "wedge" delamination is modeled in 3-D. Then, transducers with different shapes of 3-D printed backings are mounted and experiments are conducted using an impedance analyzer. Finally, experimental results are found to be in good agreement with numerical solutions and it shows that changes in EMA can particularly reveal the occurrence and extent of delamination in an ultrasound probe.

Generalised bisection method for optimum ultrasonic ray tracing and focusing in multi-layered structures

Ultrasonic testing has been used for many decades, proving itself very efficient for detecting defects in many industrial sectors. The desire to apply ultrasonic testing to geometrically complex structures, and to anisotropic, inhomogeneous materials, together with the advent of more powerful electronics and software, is constantly pushing the applicability of ultrasonic waves to their limits. General ray tracing models, suitable for calculating the proper incident angle of single element probes and the proper time delay of phased array, are currently required. They can support the development of new imaging techniques, as Full Matrix Capture and Total Focusing Method, and the execution of very challenging ultrasonic inspections. This paper introduces a generalized iterative method for the computation of ultrasonic ray paths, when ultrasonic source and target are separated by multiple complex material interfaces in the two dimensional and three dimensional domains. The manuscript starts with a review of the well-known bisection method, and extends the applicability of the method to cases with increasing complexity. An application example, in the field of in-process weld inspection, shows that the introduced generalised bisection method can enable the computation of optimum incidence angles and focal delays for accurate ultrasonic focusing. There is no restriction on the analytical interfaces to be surjective. Interface folding is permitted. It is not necessary to know, a priori, with what sequence the interfaces are crossed by the rays. The presented implementation of the method completes each iteration of the bisection method in 4 ms, for a case with a single interface, and in 960 ms for the case with 52 interfaces.

Numerical analysis of piezoelectric probe for beam forming of longitudinal and shear waves

In this study, we propose and evaluate an ultrasonic probe for the beam forming of longitudinal and shear waves by the two-dimensional finite element method. Ultrasonic probes for longitudinal and shear waves are used in industrial fields for nondestructive testing. Among the ultrasonic probes, array probes can undertake a range of inspections from a single location, and so are more flexible than single-element probes. Most types of array can be used to produce images at each test location. This allows rapid visualization of the internal structure of a component. In order to restrain artifacts for an ultrasonic array flaw-detecting method, we propose an array probe with three degrees of freedom. Operations of the probe were verified using the two-dimensional finite element method. In the case of transmission, we found that secondarily generated beams that might be artifacts were restrained by controlling the vibration direction of the proposed probes; for reception, an array of proposed probes could obtain the direction of particle displacement. Thus, the results suggest that an array of the proposed probes can distinguish longitudinal from shear waves.

Ultrasonic Phased Array Design Study for High Speed Axle Inspection using an Electronically Rotating Beam

For in-service inspections on wheelset axles with a hollow drilling, mechanized ultrasound inspection systems with single element probes are typically used. The ultrasonic testing in the zones close to the external surface of the railway axles can be realized from the inside of the bore hole, without demounting the wheelset and without dismantling the wheels and the brake discs. The testing system must be able to find flaws in the external surface of the hollow shafts, whose surface lies in the radial-radial plane, these are called transversal flaw. Presently testing systems are used, where scanning is realized in the circumferential direction by mechanical rotation of the probe system in the actual drilling. The phased array probe system, which is presented here, can carry out the rotation scan electronically. The scan can be carried out by simply moving the system forward and backwards through the drilling without mechanical rotation. Manipulation becomes simpler and the inspection time can be shortened considerably. The ultrasonic beam can be inclined exactly and be focused in the plane vertical to the specimen axis.The probe is designed with help of indispensable simulations using especially designed software developed by BAM. The feasibility and the alignment between the simulated and experimental results were shown in earlier projects reported by Boehm et al. (2006) and Völz et al. (2012). The main task here is to optimize a probe for bore holes with a diameter of 65 mm with an increase in sensitivity and a high spatial resolution. This development will be carried out by use of extensive simulations and result in certain changes of the relevant probe parameters.

In vivo imaging of ocular blood flow using high-speed ultrasound.

Clinical ophthalmic ultrasound is currently performed with mechanically scanned, single-element probes, but these are unable to provide useful information about blood flow with Doppler techniques. Linear arrays are well-suited for the detection of blood flow, but commercial systems generally exceed FDA ophthalmic safety limits. A high-speed plane-wave ultrasound approach with an 18-MHz linear array was utilized to characterize blood flow in the orbit and choroid. Acoustic intensity was measured and the plane-wave mode was within FDA limits. Data were acquired for up to 2 sec and up to 20,000 frames/s with sets of steered plane-wave transmissions that spanned 2*θ degrees where 0 degrees was normal to the array. Lateral resolution was characterized using compounding from 1 to 50 transmissions and -6-dB lateral beamwidths ranged from 320 to 180 μm, respectively. Compounded high-frame-rate data were post-processed using a singular value decomposition spatiotemporal filter and then flow was estimated at each pixel using standard Doppler processing methods. A 1-cm diameter rotating scattering phantom and a 2-mm diameter tube with a flow of blood-mimicking fluid were utilized to validate the flow-estimation algorithms. In vivo data were obtained from the posterior pole of the human eye which revealed regions of flow in the choroid and major orbital vessels supplying the eye.

Reconstructing the Deflector Images From the Ultrasonic Echo Signals by the Maximum Entropy Method

This article proposes using the maximum entropy method (MEM) for processing the ultrasonic echo signals in order to restore the deflectors images with high signal/noise ratio and small lateral petals of the point scattering function. When processing the ultrasonic echo signals, it is possible to take into consideration the pulses propagation paths, together with both their deflections from uneven boundary of inspected object and the respective wave type transformation. In model experiments the images of deflectors were received in two registering modes: in the combined mode - by using the conventional single element probe; in double and triple scan mode - by using the antenna array. The deflection from uneven surface during the echo signals acquisition had been taken into account in both modes. The restored images had a resolution exceeding the one required by Rayleigh criterion. MEM allows obtaining the defect images of low-level lateral petals by processing less than 10 % of echo signals full set.

Assemblable Hand for Laparoscopic Surgery with Phased Array and Single-Element Ultrasound Probes

During laparoscopic surgery, large internal organs should often be manipulated while being internally visualized. For this purpose, we study an assemblable two-fingered hand implemented with an ultrasound probe. The fingers are separately introduced into the abdominal cavity through small incisions and are assembled into a hand sufficiently large to grasp or manipulate the large organ. Two types of ultrasound probes are employed; a phased array probe of a commercially available ultrasound diagnosis system, and a single-element probe. Using the latter probe, the hand is assembled through 12 mm trocars and is assessed in an in vivo experiment. Ultrasound echo sensing is found to retrieve diagnostic information regarding specific internal organs. It also visualizes the finger and its back during grasping, which can improve the safety of hand grasping and manipulation. Furthermore, ultrasound echo sensing can assist the measurement of the relative position and orientation of the two grasping fingers.

Excitation and Receiving Circuit Design for the Multi-Element Medical Ultrasonic Endoscope Probe

Multi-element ultrasonic probe applied in vivo, compared with the traditional probe applied in vitro or single-element probe, has its own specialty in working environment and structure. This paper designed an analog circuit applied in vivo including excitation and reception amplification for multi-element ultrasonic probe. The circuit provides an excitation and receiving front-end for the self-developed multi-element ultrasound endoscope imaging system. This ultrasound analog circuit can be used for d / 2 ultrasonic scanning along with the 16 element ultrasound transducer.

A Novel Ultrasound Imaging System Based on Endoscopic Array Probe

A novel ultrasound imaging system based on endoscopic array probe is presented in this paper. The system utilizes an endoscopic linear-array probe instead of the conventional single-element probe to implement ultrasound scanning in vivo. For the system, a micro linear-array ultrasound probe sized Φ10mm×20mm is firstly designed. And then the excitation circuit, gating circuit and echo receiving and processing circuit are all designed cored by a center control unit FPGA. Finally the research of d/2 focusing algorithm is implemented on the basis of the system. After processed, the gray image of echoes reflected by a glass jar’s wall is obtained and shown on a computer.

Rectangular Microstrip Antenna on Ridge Ground Plane to Control the Resonant Modes for Improved Bandwidth using Transverse Resonance Method

A single layer single element rectangular microstrip antenna on ridge ground plane for improved bandwidth is theoretically investigated with a view to develop a concrete physical insight in to the phenomenon. The simple single element probe fed rectangular microstrip antenna fabricated on conventional PTFE (Poly Tetra Fluride Ethelene) substrate have many advantages except its narrow bandwidth. The present study proposes the technique to control the resonant modes of a microstrip antenna for yielding better bandwidth using transverse resonance method. The present antenna is designed to fabricate on ridge ground plane which has been compared with conventional structure and around 6% - 7% improvement in bandwidth is revealed. The detailed variation of radiation pattern across its frequency band has been studied and presented in this paper. The proposed idea has been verified through a commercial software package (High Frequency Structure Simulator) for a patch operating in X band and explained quantitatively. The electric surface current distribution over the patch surface for both the conventional and proposed antenna is presented to explain the broad banding effect physically.

Two-dimensional subwavelength-focused imaging using a near-field probe at a λ/4 working distance

Two-dimensional (2D) subwavelength imaging using a near-field antenna array probe is demonstrated experimentally at a probe-to-object separation distance of λ/4. Field perturbations caused by the presence of small objects are detected by monitoring the input reflection coefficient as the probe is scanned. The probe is designed to produce a subwavelength focal spot with a 0.217λ full-width half-maximum beam width. Propagating components are suppressed through destructive interference, enhancing the evanescent field enough to resolve objects spaced by 0.259λ. The poor resolving capability of a conventional single-element probe at this working distance is also addressed; it is shown that even objects spaced over a wavelength apart are inaccurately detected. A full 2D imaging experiment is carried out using eight scattered objects. The single element probe is unable to resolve any of the objects, while all but the two most closely spaced pairs are resolved by the array probe.

Ultrasonic backscatter sizing using phased array – developments in tip diffraction flaw sizing

This paper presents a study of a new backscatter sizing technique that permits assessment of both flaw vertical height and orientation of planar flaws that are not necessarily surface connected. Although the system works best using the features of phased array raster scanning, the principles can be applied to waveform analysis of single-element probe B-scans. Examples of the verification of the technique are provided using machined notches and actual flaw samples. Advantages of the backscatter sizing technique over conventional time-of-flight diffraction (forward scattering) are given.

In Vivo Results with a New Device for Ultrasonic Monitoring of Pig Skin Cryosurgery: The Echographic Cryoprobe

One of the main difficulties encountered in cryosurgery is the uncertainty in the extent and depth of the tissue effectively treated during the freezing process. The objective of this study was to evaluate in vivo ultrasonic control of skin cryosurgery using a new echographic cryoprobe. An echographic cryoprobe, developed specifically for dermatology applications, combines a high-frequency (20 MHz) miniature ultrasonic transducer and a N2O-driven closed cryoprobe. Knowledge of the ultrasound velocity of frozen skin is a prerequisite for monitoring the iceball formation kinetics. Therefore, in a first study, we estimated the ultrasound velocity of frozen skin specimens. In a second step, the operation of the echographic cryoprobe was assessed, under in vivo conditions similar to those used in human therapeutics, on normal skin of three female "Large-White" pigs under anesthesia. The mean value of ultrasound velocity of frozen skin obtained by pooling the data from all the skin specimens included in this study was 2865 +/- 170 m per s. The average rates of growth (10(-2) mm per s) of the iceballs were found to be 12.2 +/- 1.0 (pig 1), 9.0 +/- 1.0 (pig 2), and 8.4 +/- 0.9 (pig 3). The echographic cryoprobe had a built-in high-frequency ultrasonic transducer that served two functions. It enabled in vivo real-time monitoring of depth penetration of the iceball and it gave important feedback to the operator or to the console relating to the rate of growth of the iceball. Automatic (i.e., operator-independent) detection of the echo signal from the freezing front and calculation of the depth penetration of the iceball was possible.

A 20 MHz single-element ultrasonic probe using 0.91Pb(Zn/sub 1/3/Nb/sub 2/3/)O/sub 3/-0.09PbTiO/sub 3/ single crystal

A 20 MHz single-element ultrasonic probe using 0.91Pb(Zn(1/3 )Nb(2/3))O(3)-0.09PbTiO(3) (PZN-PT 91/9) single crystal has been fabricated. The single crystal of PZN-PT 91/9 orientated to the (001) plane has longitudinal coupling factor of k(33)>90%, which is much larger than the k(33)=70 to 80% of conventional Pb(Zr(1-x),Ti(x))O(3) (PZT) based ceramics. A single crystal of PZN-PT 91/9 without inclusion or crack has been grown with dimensions of about 25x15x5 mm by the self-flux method. Because mechanical strength in the fabrication of disk transducers orientated to the (001) plane was sufficiently strong, under the same conditions as are applied to conventional PZT ceramics, a piston single-element probe with a diameter of 2.0 mm and a frequency of 20 MHz was successfully fabricated. The bandwidth of the PZN-PT 91/9 probe was 13-26 MHz, which was 4 MHz broader than that of the conventional PZT probe.

Intraoperative tumor detection: relative performance of single-element, dual-element, and imaging probes with various collimators

Accurate tumor staging depends on finding all tumor sites, and curative surgery requires the removal of ail cancerous tissue from those sites. One technique for locating tumors is to inject patients before surgery with a radiotracer that is preferentially taken up by cancerous tissue. Then, an intraoperative gamma-sensitive probe is used to locate the tumors. Small (<1-cm diameter) tumors, often undetectable by external imaging and by the standard surgical inspection with sight and touch, can be found with probes, Simple calculations and measurements with radioactive tumor models show that small tumors should be detected by single-element probes, but often such probes fail to detect these small tumors in practice. This discrepancy is often caused by the use of a uniform background to predict probe performance, Real backgrounds are nonuniform and can decrease probe performance dramatically. Dual-element, coincidence, or imaging probes may solve the background problem. The authors devised a method to predict probe performance in a realistic background which includes variations in normal organ uptakes. They predict the relative performance of both existing probes and those in the design stage so that optimal detector and collimator configurations can be determined. The procedure includes a Monte-Carlo-calculated point-response function, a numerical torso phantom, and measured biodistributions of a monoclonal antibody. The Hotelling Trace Value, a measure of tumor-detection performance, is computed from the probe responses in simulated studies.

Multiscan echofetography: application to the study of fetal breathing movements

The recording and interpretation of fetal breathing movements is an area of human perinatology which is currently receiving much attention. A multi-element echographic instrument, originally developed for the real-time cross-sectional visualization of moving cardiac structures in the human body (Bom, Lancee, Van Zwieten, Kloster and Roelandt, 1973), was applied to the visualization of fetal breathing movements, and the technique called multiscan echofetography. By utilizing one of the 20 elements of the transducer as a single-element probe, fetal breathing movements, visualized in real-time, were recorded by the conventional M-mode display on a hardcopy recorder. From 17 patients, with 19 fetuses, 27 separate recordings have been obtained. In 22 of these recordings fetal breathing movements were present; in 5, such movements were observed not to occur during the 30-minute monitoring period.

A Practical Field Plotter Using a Hybrid Analog Computer

An automatic device for plotting the equipotential contours of two-dimensional fields, that utilizes an analog hybrid computer in conjunction with two x-y recorders has been developed. It eliminates the need for multielement probes which were used by earlier workers in this field including P. E. Green, J. K. Mickelsen, and D. H. Andrews. The main advantage of the new method is that multivalued fields in both x and y directions can be plotted using only a single element probe.