High Temperature Ultrasonic Transducers Research Articles

Porous Metal Backing for High-Temperature Ultrasonic Transducers

Improving the performance of high-temperature ultrasonic transducers is a goal of major importance in many industrial applications. To this aim, we propose to use porous metals that support high temperatures as backings. Thus, the acoustic properties of stainless steel and porous stainless steel with porosity of 25% and 35% are determined at ambient temperature and up to 400 °C. Over the temperature range, the longitudinal wave velocity variation is comprised between 5% and 6% in the porous metals. We find that temperature does not significantly affect the attenuation in the material. The pulse-echo response and frequency response of a LiNbO3-based transducer with a porous backing are simulated using a one dimensional electroacoustic model. These simulations, compared to those of a reference transducer, show that the axial resolution with such a design allows these transducers to be used for imaging and/or Non-Destructive Testing and evaluation at high temperature.

Broad bandwidth and excellent thermal stability in BiScO3-PbTiO3 high-temperature ultrasonic transducer for non-destructive testing

High-temperature ultrasonic transducer (HTUT) is essential for non-destructive testing (NDT) in harsh environments. In this paper, a HTUT based on BiScO3-PbTiO3 (BS-PT) piezoelectric ceramics was developed, and the effect of different backing layers on its bandwidth were analyzed. The HTUT demonstrates a broad bandwidth and excellent thermal stability with operation temperature up to 400°C. By using a 10mm thick porous alumina backing layer, the HTUT achieves a broad -6dB bandwidth of 100%, which is about 4 times superior to the transducer with an air backing layer. The center frequency (fc) of the HTUT remains stable with fluctuations of less than 10% across the temperature range from room temperature to 400°C. The HTUT successfully detected simulated defects in pulse-echo mode for NDT over 200°C. This research not only advances high-temperature ultrasonic transducer technology but also expands the NDT applications in harsh environmental conditions.

0.36BiScO3-0.64PbTiO3/Epoxy 1-3-2 High-Temperature Composite Ultrasonic Transducer for Non-destructive Testing Applications.

The development of high-temperature nondestructive testing (NDT) requires ultrasonic transducers with good temperature resistance and high sensitivity for improved detection efficiency. Piezoelectric composite can improve the performance of transducers because of its high electromechanical coupling coefficient and adjustable acoustic impedance. In this study, 1-3-2 composites and 1-3-2 high-temperature composite ultrasonic transducers (HTCUTs) based on 0.36BiScO3-0.64PbTiO3 (BSPT), which are preferred piezoelectric materials at 200°C-300°C, and high-temperature epoxy with a center frequency of 6 MHz were designed and fabricated. From 25°C to 250°C, 1-3-2 composites show a higher electromechanical coupling coefficient kt especially at high temperatures (~0.53 at 25°C, and ~0.64 at 250°C) than monolithic BSPT (~0.5). The signal of the pulse-echo response of 1-3-2 HTCUTs is distinguishable up to 250 °C and remains stable (Vpp~500 mV) below 150°C, exhibiting higher sensitivity (improved by 7 dB) than that of monolithic BSPT high-temperature ultrasonic transducers (HTUTs). Bandwidth has been greatly enhanced especially at high temperatures (~103250°C) compared with that of monolithic BSPT HTUTs(~30250°C). To verify the excellent performance, B-mode scanning imaging measurement of a stepped steel block and defect location detection of a steel block were performed, showing the potential for high-temperature NDT applications.

High-temperature piezoelectric ultrasonic transducer based on BiScO3-PbTiO3 ceramics

High-temperature piezoelectric ultrasonic transducer based on BiScO3-PbTiO3 ceramics

Design of an Ultrasonic Transducer Encapsulation for High-Temperature Applications

A novel approach to designing the encapsulation for a high-temperature ultrasonic transducer to be capable of continuous operation over a temperature range of 25 to 650 °C is proposed. The transducer’s active element is a heavily damped lithium niobate disc of 3 MHz resonance frequency, operating in pulse-echo mode. The initial encapsulation design is developed based on the geometrical, thermal, mechanical, electrical, and ultrasonic requirements. Two finite element modeling systems are developed to analyze the thermal-induced stresses in the transducer at low and high temperatures as well as its ultrasonic performance. The simulation results are used to optimize the design before manufacturing a transducer prototype. The prototype is tested at room and elevated temperatures to verify performance.

Development and Investigation of High-Temperature Ultrasonic Measurement Transducers Resistant to Multiple Heating-Cooling Cycles.

Usually for non-destructive testing at high temperatures, ultrasonic transducers made of PZT and silver electrodes are used, but this could lead to damage to or malfunction of the ultrasonic transducer due to poor adhesion between PZT and silver. Soldering is one of the most common types of bonding used for individual parts of ultrasonic transducers (protector, backing, matching layer, etc.), but silver should be protected using additional metal layers (copper) due to its solubility in solder. A mathematical modelling could help to predict if an ultrasonic transducer was manufactured well and if it could operate up to 225 °C. The observed von Mises stresses were very high and concentrated in metal layers (silver and copper), which could lead to disbonding under long-term cyclic temperature loads. This paper presents a multilayer ultrasonic transducer (PZT, silver electrodes, copper layers, backing), which was heated evenly from room temperature to 225 °C and then cooled down. In the B-scan, it was observed that the amplitude of the reflected signal from the bottom of the sample decreased with an increase in temperature. However, after six heating-cooling cycles, the results repeated themselves and no signs of fatigue were noticed. This ultrasonic transducer was well manufactured and could be used for non-destructive testing when the environment temperature changes in cycles up to 225 °C.

Morphology of lithium niobium oxide thin film ultrasonic transducers deposited by RF magnetron sputtering

Morphology of lithium niobium oxide thin film ultrasonic transducers deposited by RF magnetron sputtering

PZT-based high-temperature ultrasonic dual mode transducer applicable to cubic-anvil apparatus for sound velocity measurement

The ultrasonic transducer is an indispensably critical component for sound velocity measurement. With the increasing demand of high-temperature ultrasonic dual mode transducer applicable to cubic-anvil apparatus, where experiments of high-pressure and high-temperature sound velocity are routinely conducted, a PZT-based ultrasonic dual mode transducer was presented in this study. It was made of a sandwich of two PZT piezoceramic wafers, the upper one generating P-waves and the lower one generating S-waves. The transducer was directly bonded onto a WC anvil of cubic-anvil apparatus using high-temperature adhesive, and then heated in an oven while measuring the bottom echoes from the WC anvil. The results showed that the high-temperature transducer could work up to 140 °C. The transducer features low cost, easy fabricating, and highquality signals, and so we believe it is useful for sound velocity measurement at high temperatures in cubic-anvil apparatus.

Directly mounted sol-gel composite piezoelectric devices by spray coating technique for high temperature ultrasonic transducers

Directly mounted sol-gel composite piezoelectric devices by spray coating technique for high temperature ultrasonic transducers

LiNbO3-based sol-gel composite ultrasonic transducer poled at low temperatures

A LiNbO3 (LN) based sol-gel composite could be suitable for high temperature ultrasonic transducer application at 700 °C, however, poling requires high temperature above 550 °C and it shows relatively low signal strength. In order to realize the polarization temperature reduction of an LN-based sol-gel composite ultrasonic transducer, alumina (AO) and strontium doped titanium oxide (TO) were chosen as sol-gel phase material, and LN/AO and LN/TO films were fabricated onto Inconel substrates. In each polling process, corona discharge after heat treatment in the furnace at 400 °C and at 200 °C was executed for LN/AO and LN/TO, respectively. Ultrasonic measurements up to 700 °C were performed and both transducers were able to confirm the reflected echoes and ultrasonic performance stability at 700 °C. Especially LN/TO showed the highest signal strength compared to previously developed high temperature lead-free sol-gel composite materials, Bi4Ti3O12 (BiT)/BiT and CaBi2Ta2O9 (CBTa)/BiT.

Ultrasonic transducer with BiScO3-PbTiO3-based ceramics of operating temperature over 400°C

Ultrasonic transducers are widely employed in many fields such as non-destructive testing (NDT), petrochemical refineries, aerospace field, etc., in which high temperature ultrasonic transducers are necessary because many measurements must be done at elevated temperature. In this work, 4.5 MHz high temperature ultrasonic transducers with delay line were designed and fabricated based on BiScO3-Pb(Ti0.99Zn0.01)O3 (BS-0.01PZnT) piezoelectric ceramics possessing excellent temperature stability and high Curie temperature. The experimental results revealed that −6 dB bandwidth and the center frequency of high temperature ultrasonic transducers are around 129% and 4.5 MHz, respectively, which are almost stable from room temperature to 400 °C. The peak-to-peak values (Vpp) is as large as 1.5 V at RT, indicating very high sensitivity. More importantly, the ultrasonic transducers with customized BS-0.01PZnT ceramics can work reliably at high temperature of 380 °C and 450 °C by in-situ measurement at elevated temperatures. This work verifies the great potential application values of ultrasonic transducers with BS-0.01PZnT ceramics in high temperature applications.

High-Frequency 0.36BiScO3-0.64PbTiO3 Ultrasonic Transducer for High-Temperature Imaging Application.

( 1- x )BiScO3- x PbTiO3 (BS-PT) ceramics have excellent piezoelectricity and high Curie temperature at its morphotropic phase boundary (MPB) ( x = 0.64 ), so it is a promising piezoelectric material for fabricating high-temperature ultrasonic transducer (HTUT). Electric properties of 0.36BS-0.64PT ceramics were characterized at different temperatures, and an HTUT with the center frequency of about 15 MHz was designed by PiezoCAD based on the measuring results. The prepared HTUT was tested in a silicone oil bath at different temperatures systematically. The test results show that the HTUT can maintain a stable electrical resonance until 290 °C and get a clear echo response until 250 °C with slight changes of the center frequency. Then, a stepped metal block submerged in silicone oil was imaged by the HTUT until 250 °C. Velocity of silicone oil and axial resolution of the HTUT at different temperatures was calculated. The results verify the capability of 0.36BS-0.64PT-based HTUT for high-temperature ultrasonic imaging applications.

A Method of Electrodeless Contacting of a Piezo Material in a High-Temperature Resistant Ultrasonic Transducer for Use in the Immersion Technique in Electrically Conductive Liquids

A Method of Electrodeless Contacting of a Piezo Material in a High-Temperature Resistant Ultrasonic Transducer for Use in the Immersion Technique in Electrically Conductive Liquids

Partial discharges location in power transformers using piezoceramic sensors

The detection and the spatial localization of partial discharges in high-voltage electrical machines are considered as an effective method in predictive maintenance that can provide valuable information on the health of the insulation system and allow to determine accurately the location of the risky insulation elements, which in turn will avoid any premature equipment’s deterioration by scheduling preventive maintenance action. After confirming in a previous published paper the efficiency of a new generation of piezoceramics sensors (high temperature ultrasonic transducers) to detect and characterize partial discharges, we are going to investigate, in this work, a second potential of this technology to locate the partial discharge sources by relying on its ability to detect acoustic signals emitted by partial discharge sources. We will present experimental results, demonstrating the effectiveness of these sensors to locate partial discharges sources and, we will also present an algorithm for calculating the partial discharge foci, based on the acoustic wave flight time.

High Temperature Ultrasonic Transducers: A Review.

There are many fields such as online monitoring of manufacturing processes, non-destructive testing in nuclear plants, or corrosion rate monitoring techniques of steel pipes in which measurements must be performed at elevated temperatures. For that high temperature ultrasonic transducers are necessary. In the presented paper, a literature review on the main types of such transducers, piezoelectric materials, backings, and the bonding techniques of transducers elements suitable for high temperatures, is presented. In this review, the main focus is on ultrasonic transducers with piezoelectric elements suitable for operation at temperatures higher than of the most commercially available transducers, i.e., 150 °C. The main types of the ultrasonic transducers that are discussed are the transducers with thin protectors, which may serve as matching layers, transducers with high temperature delay lines, wedges, and waveguide type transducers. The piezoelectric materials suitable for high temperature applications such as aluminum nitride, lithium niobate, gallium orthophosphate, bismuth titanate, oxyborate crystals, lead metaniobate, and other piezoceramics are analyzed. Bonding techniques used for joining of the transducer elements such as joining with glue, soldering, brazing, dry contact, and diffusion bonding are discussed. Special attention is paid to efficient diffusion and thermo-sonic diffusion bonding techniques. Various types of backings necessary for improving a bandwidth and to obtain a short pulse response are described.

Transmission of Images on High-Temperature Nuclear-Grade Metallic Pipe with Ultrasonic Elastic Waves

Transmission of information using elastic ultrasonic waves on existing metallic pipes provides an alternative communication option for a nuclear facility. The advantages of this approach consist of transmitting information through barriers, such as the containment building wall, with minimal modification of the existing hardware. Because bit rates on the order of kilobits per second are achievable, relatively large volumes of data, such as images, can be transmitted. A viable candidate for an ultrasonic communication channel is a stainless steel pipe of the chemical volume control system (CVCS) that penetrates through the reactor containment building wall through a sealed tunnel. To study ultrasonic communication under simulated nuclear facility conditions of high temperature, a test article was developed by installing heating tapes, temperature controllers, and thermal insulation on a laboratory CVCS-like stainless steel pipe. High temperature and radiation-resilient lithium niobate ultrasonic transducers were utilized for information transmission on the heated pipe. The amplitude shift keying (ASK) digital communication protocol was developed and implemented in a GNU Radio software–defined radio environment. A root-raised-cosine filter was introduced to suppress ultrasonic transducer ringing and thus reduce inter-symbol interference. This resulted in the enhancement of the data transmission bit rate compared to information encoding with square pulses. Demonstrations of communication at high temperature included transmission of a 90-KB image at the bit rate of 10 Kbps with a bit error rate of 10−3 across a 6-ft-long straight pipe heated up to 230°C. Additional preliminary studies were conducted to evaluate ultrasonic communication system resilience to environmental degradation and damage.

Diagnosis of multi-stage injection molding process by ultrasonic technology at a T-shape extension nozzle

Abstract In this study, a modified T-shape extension nozzle (TsEN) with a high temperature (HT) ultrasonic transducer (UT) rod connected to its barrel and mold to carry out the injection molding (IM) process diagnosis is used. Two integrated HTUTs were fabricated on both sides of a rod for monitoring IM process at elevated temperatures real-time, non-intrusively as well as non-destructively. Two plastics, polypropylene (PP) and acrylonitrile–butadiene–styrene (ABS), were employed to demonstrate the effects of various operation settings and materials on the molded sample quality. Based on the provided information, an innovative way of controlling the supply to structure process in regards to the plastic from the barrel into the nozzle, mold and the final product during the IM process is presented. Each phase of the process, including closing mold, injecting material, packing, and feeding material can be analyzed by an ultrasonic waveform during the various settings of the IM process of PP and ABS plastics. The various injection speeds of the PP and ABS plastics cause different deflection performance of the molded samples. This phenomenon can be observed by measuring the ultrasonic velocity at the beginning stage of molding. Therefore, a modified TsEN with an HTUT rod could provide a rigid structure and an innovative solution for how to run continual diagnosis during the IM process to verify the dynamics of process and analyze the flow rate and the state of the molten plastic to ensure better product quality.

2Pa1-4 Study of High Temperature Ultrasonic Transducer in LiNbO3 Based Sol-gel Composite

2Pa1-4 Study of High Temperature Ultrasonic Transducer in LiNbO₃ Based Sol-gel Composite

Development of Ultrasonic Guided Wave Transducer for Monitoring of High Temperature Pipelines.

High-temperature (HT) ultrasonic transducers are of increasing interest for structural health monitoring (SHM) of structures operating in harsh environments. This article focuses on the development of an HT piezoelectric wafer active sensor (HT-PWAS) for SHM of HT pipelines using ultrasonic guided waves. The PWAS was fabricated using Y-cut gallium phosphate (GaPO4) to produce a torsional guided wave mode on pipes operating at temperatures up to 600 °C. A number of confidence-building tests on the PWAS were carried out. HT electromechanical impedance (EMI) spectroscopy was performed to characterise piezoelectric properties at elevated temperatures and over long periods of time (>1000 h). Laser Doppler vibrometry (LDV) was used to verify the modes of vibration. A finite element model of GaPO4 PWAS was developed to model the electromechanical behaviour of the PWAS and the effect of increasing temperatures, and it was validated using EMI and LDV experimental data. This study demonstrates the application of GaPO4 for guided-wave SHM of pipelines and presents a model that can be used to evaluate different transducer designs for HT applications.

Brazing Strategies for High Temperature Ultrasonic Transducers Based on LiNbO3 Piezoelectric Elements

Long-term installation of ultrasonic transducers in high temperature environments allows for continuous monitoring of critical components and processes without the need to halt industrial operations. Transducer designs based on the high-Curie-point piezoelectric material lithium niobate have been shown to both be effective and stable at extreme temperatures for long-term installation. In this study, several brazing techniques are evaluated, all of which aim to provide both mechanical bonding and acoustic coupling directly to a bare lithium niobate piezoelectric element. Two brazing materials—a novel silver-copper braze applied in a reactive air environment and an aluminum-based braze applied in a vacuum environment—are found to be suitable for ultrasound transmission at elevated temperatures. Reliable wide-bandwidth and low-noise ultrasound transmission is achieved between room temperature and 800 °C.