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     

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.     

Piezo-polymer transducers for ultrasonic imaging in air

Airborne polyvinylidenefluoride transducers have been designed for robotic applications in air. Characteristics of transducer prototypes are: working frequencies from 61 kHz to 86 kHz, quality factor Q from 4 to 6, and two-way insertion loss of about 90 dB. The small dimension, the lightness, and the low-cost fabrication technology allow the development of arrays or matrices for ultrasonic imaging systems in air. In this work two different image reconstruction algorithms are proposed: the first carries out a combined spectral and aperture synthesis for detecting isolated scatterers with a spatial resolution of about 2 mm; the second is based on an accurate ranging algorithm with sub-millimeter resolution at distances up to 50 cm. Finally, this work's application to the reconstruction of three-dimensional object profiles is discussed.     

MEMS ultrasonic transducers for the testing of solids

Arrays of capacitive diaphragm ultrasonic transducers could potentially be used for non-destructive ultrasonic testing and structural monitoring. In this paper, we consider the efficiency of coupling of these transducers to solid media. We show that efficient coupling can be realized by using a silicone coating as a coupling medium. We present the results of experimental characterization of ultrasonic transducers coupled to solids in this way. We show that these transducers can be used with piezoelectric emitting transducers within the range from 1 to 5 MHz, and we demonstrate the use of several transducers as a phased array to determine the direction and distance of an ultrasonic source.     

Time reversal processing in ultrasonic nondestructive testing

In this paper, we present a novel and completely different approach to focusing on defects beneath plane or curved surfaces: the time reversal mirror method. The time reversal technique is based on the concept of time reversal of ultrasonic fields and takes into account both the phase and modulus information coming from the defect. This technique is self-adaptative and requires only the presence of a target in the solid sample. In highly scattering media, it is shown that the time reversal process allows a new approach to speckle noise reduction. Experimental results obtained with a 121-channel time reversal mirror on titanium and duralumin samples are presented. They demonstrate the ability of time reversal to compensate for the distortions induced by liquid-solid interfaces of different geometries and to detect small defects in a noisy background     

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.     

Piezoelectric ceramics with high dielectric constants for ultrasonic medical transducers

Complex system ceramics Pb(Sc(1/2)Nb(1/2))O3-Pb(Mg(1/3)Nb(2/3))O3-Pb(Ni(1/2)Nb(1/2))O3-(Pb0.965,Sr0.035) (Zr,Ti)O3 (PSN-PMN-PNN-PSZT abbreviated PSMNZT) have been synthesized by the conventional technique, and dielectric and piezoelectric properties of the ceramics have been investigated for ultrasonic medical transducers. High capacitances of the transducers are desired in order to match the electrical impedance between the transducers and the coaxial cable in array probes. Although piezoelectric ceramics that have high dielectric constants (epsilon33t/epsilon0 > 5000, k'33 < 70%) are produced in many foundries, the dielectric constants are insufficient. However, we have reported that low molecular mass B-site ions in the lead-perovskite structures are important in realizing better dielectric and piezoelectric properties. We focused on the complex system ceramics PSMNZT that consists of light B-site elements. The maximum dielectric constant, epsilon33T/epsilon0 = 7, 200, was confirmed in the ceramics, where k'33 = 69%, d33 = 940 pC/N, and T(c) = 135 degrees C were obtained. Moreover, pulse-echo characteristics were simulated using the Mason model. The PSMNZT ceramic probe showed echo amplitude about 5.5 dB higher than that of the conventional PZT ceramic probe (PZT-5H type). In this paper, the electrical properties of the PSMNZT ceramics and the simulation results for pulse-echo characteristics of the phased-array probes are introduced.     

Air-coupled piezoelectric micromachined ultrasonic transducers for surface stain detection and imaging

This paper proposes an air-coupled piezoelectric micromachined ultrasonic transducer(PMUT)for detection and imaging of surface stains.A 508 kHz PMUT array is de...     

管道超声导波无损检测技术应用研究

利用研制的磁致伸缩超声导波无损检测装置对长直无缝钢管、舰用锅炉U型管和弯管进行了大量试验研究．研究发现，通过对该装置中磁致伸缩传感器的放置位置及方向进行适当调整，此装置即可在管道中激发纵向导波；该技术对管道壁厚减薄、磨损或腐蚀、裂纹、焊缝等缺陷同样具有检测能力；选择低频（20～40kHz）激励脉冲信号有利于减少波的发散特性和提高缺陷的检测能力；导波在管道中传播衰减缓慢，适用于长距离、大范围、快速、非接触管道检测．     

Piezoelectric micromachined ultrasonic transducers based on PZT thin films

This paper describes fabrication and characterization results of piezoelectric micromachined ultrasonic transducers (pMUTs) based on 2-microm-thick Pb(Zr0.53Ti0.47O3) (PZT) thin films. The applied structures are circular plates held at four bridges, thus partially unclamped. A simple analytical model for the fully clamped structure is used as a reference to optimize design parameters such as thickness relations and electrodes, and to provide approximate predictions for coupling coefficients related to previously determined thin film properties. The best coupling coefficient was achieved with a 270-microm plate and amounted to kappa2 = 5.3%. This value compares well with the calculated value based on measured small signal dielectric (epsilon = 1050) and piezoelectric (e3l,f = 15 Cm(-2)) properties of the PZT thin film at 100 kV/cm dc bias. The resonances show relatively large Q-factors, which can be partially explained by the small diameters as compared to the sound wavelength in air and in the test liquid (Fluorinert 77). A transmit-receive experiment with two quasi-identical pMUTs was performed showing significant signal transmission up to a distance of 20 cm in air and 2 cm in the test liquid.     

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     

Design of efficient, broadband single-element (20-80 MHz) ultrasonic transducers for medical imaging applications

This paper discusses the design, fabrication, and testing of sensitive broadband lithium niobate (LiNbO/sub 3/) single-element ultrasonic transducers in the 20-80 MHz frequency range. Transducers of varying dimensions were built for an f# range of 2.0-3.1. The desired focal depths were achieved by either casting an acoustic lens on the transducer face or press-focusing the piezoelectric into a spherical curvature. For designs that required electrical impedance matching, a low impedance transmission line coaxial cable was used. All transducers were tested in a pulse-echo arrangement, whereby the center frequency, bandwidth, insertion loss, and focal depth were measured. Several transducers were fabricated with center frequencies in the 20-80 MHz range with the measured -6 dB bandwidths and two-way insertion loss values ranging from 57 to 74% and 9.6 to 21.3 dB, respectively. Both transducer focusing techniques proved successful in producing highly sensitive, high-frequency, single-element, ultrasonic-imaging transducers. In vivo and in vitro ultrasonic backscatter microscope (UBM) images of human eyes were obtained with the 50 MHz transducers. The high sensitivity of these devices could possibly allow for an increase in depth of penetration, higher image signal-to-noise ratio (SNR), and improved image contrast at high frequencies when compared to previously reported results.     

Materials and transducers for ultrasonic flowmeters

The construction and operation of a lead zirconate-titanate (TsTS-19) piezoelectric transducer as a component of the model UZR-V ultrasonic flowmeter with an Akustron counter is analyzed. Techniques are proposed for enhancing the operating efficiency of ultrasonic flowmeters. The study has resulted in the development of the UZD-1 and UZD-3 transducers, which utilize the new materials and have parameters superior to those of a standard transducer using TsTS-19 ceramic. The new transducers are recommended for systems designed to monitor cold and hot water flow in conduits from 30 mm to 1000 mm in diameter.Translated from Izmeritel'naya Tekhnika, No. 7, pp. 57–58, July, 1993.     

Beam transformation techinques for ultrasonic medical imaging

Data acquisition rates in pulsed ultrasound scanners are limited by the speed of sound in the human body. This poses severe limitations to the design of future ultrasound equipment, such as 3-D imaging scanners. The authors describe a technique for higher data acquisition rates based on the simultaneous transmission of multiple beams. By using a linear combination of the received beams, interbeam interference due to the sidelobe energy of the transmitting beams can be significantly reduced. The transformation coefficients are found by using a least squares minimization criterion. A simulation environment used for the evaluation of the authors' methodologies and various simulation results are presented.     

Chirp signal matching and signal power optimization in pulse-echomode ultrasonic nondestructive testing

Chirp pulse compression is a signal correlation technique that uses frequency modulated pulses as transmitted signals. Usually, signals with linear frequency modulation are applied. They can be generated rather easily, but their spectra are not totally matched to the transfer function of ultrasonic systems. In pulse-echo mode operation, with signal duration and consequently the time-bandwidth product being critical parameters, waveforms should be applied which make full use of the available power and bandwidth resources. We report here two methods to improve the overall efficiency of an ultrasonic pulse-echo system. Transmitter signals with constant amplitude level and nonlinear frequency modulation can be generated in such a way that they are spectrally matched to the system. A formula for the calculation of such a matched nonlinear chirp signal is presented. This modulation scheme also leads to a side-lobe level reduction of the compressed pulses. The application of square wave chirps derived from sine type chirps yields an additional gain of echo signal amplitude. Moreover, the complexity of the signal generation hardware is reduced. The methods are illustrated by an example