Pulse-echo Mode Research Articles

Ultrasonic Analysis for Monitoring Li-Ion Batteries

To seek for increasing accuracy in LIBs monitoring a new trend is to rely on data indicative of material properties whose variations are induced by Li ions intercalation and deintercalation. A wider variety of information can be achieved if data are referred to a specific layer of the battery. Since ultrasounds propagate at different speed according to materials properties and are reflected every time they hit an interface, ultrasonic analysis (UA) has the potential to improve the quality of LIB monitoring providing in operando and through thickness information.In this work NMC-graphite LIBs are cycled and monitored in operando via UA in pulse-echo and through-thickness modes with a temporal resolution of 7 ns (which to the best of our knowledge is the highest ever tested) and a 5 MHz frequency. First, the effect of (i) temperature and (ii) C-rate on the waveform evolution was investigated: (i) a 100% charged battery was kept at rest in a thermal chamber at fixed temperatures varying between 10 and 50°C, the ultrasonic signal was acquired after 30 min at rest; (ii) an initially 100% charged battery underwent two subsequent discharge-charge cycles at constant current with fixed C-rates varying between 0.2 and 2C. Then a series of cycles at 50°C aimed at causing battery degradation was performed while acquiring the ultrasonic signal every 2 min. The efficacy of the degradation protocol was assessed through EIS prior and post cycling the battery. Surprisingly, results show an opposite (but systemic) trend with respect to what is reported in literature, with an increasing time of flight (ToF) for increasing state of charge (SoC). Additionally, it is observed that most of the peaks increase their ToF with the number of cycles. Signal amplitude shows a periodical behavior as well but values vary as degradation has gone on. It is also observed that within a cycle some peaks increase their intensity during charge while others decrease, suggesting that they belong to opposite electrodes.

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 10 mm thick porous alumina backing layer, the HTUT achieves a broad −6 dB 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.

Use of Non-Destructive Ultrasonic Techniques as Characterization Tools for Different Varieties of Wine.

In this work, we have verified how non-destructive ultrasonic evaluation allows for acoustically characterizing different varieties of wine. For this, a 3.5 MHz transducer has been used by means of an immersion technique in pulse-echo mode. The tests were performed at various temperatures in the range 14-18 °C. The evaluation has been carried out studying, on the one hand, conventional analysis parameters (velocity and attenuation) and, on the other, less conventional parameters (frequency components). The experimental study comprised two stages. In the first, the feasibility of the study was checked by inspecting twelve samples belonging to six varieties of red and white wine. The results showed clearly higher ultrasonic propagation velocity values in the red wine samples. In the second, nine samples of different monovarietal wine varieties (Grenache, Tempranillo and Cabernet Sauvignon) were analyzed. The results show how ultrasonic velocity makes it possible to unequivocally classify the grape variety used in winemaking with the Cabernet Sauvignon variety having the highest values and the Grenache the lowest. In addition, the wines of the Tempranillo variety are those that present higher values of the attenuation coefficient, and those from the Grenache variety transmit higher frequency waves.

PMUT-Based System for Continuous Monitoring of Bolted Joints Preload.

In this paper, we present a bolt preload monitoring system, including the system architecture and algorithms. We show how Finite Element Method (FEM) simulations aided the design and how we processed signals to achieve experimental validation. The preload is measured using a Piezoelectric Micromachined Ultrasonic Transducer (PMUT) in pulse-echo mode, by detecting the Change in Time-of-Flight (CTOF) of the acoustic wave generated by the PMUT, between no-load and load conditions. We performed FEM simulations to analyze the wave propagation inside the bolt and understand the effect of different configurations and parameters, such as transducer bandwidth, transducer position (head/tip), presence or absence of threads, as well as the frequency of the acoustic waves. In order to couple the PMUT to the bolt, a novel assembly process involving the deposition of an elastomeric acoustic impedance matching layer was developed. We achieved, for the first time with PMUTs, an experimental measure of bolt preload from the CTOF, with a good signal-to-noise ratio. Due to its low cost and small size, this system has great potential for use in the field for continuous monitoring throughout the operative life of the bolt.

Air-coupled ultrasonic inspection of resin materials using single-probe vertical reflection method

Air-coupled ultrasonic inspection is a noncontact and convenient nondestructive testing method. However, its vertical reflection method using a single probe (i.e., pulse-echo mode) is known to be difficult to achieve, even though it is frequently used inspection mode in conventional contact or water immersion ultrasonic testing. This is because the reflectivity of ultrasonic waves at the boundary between air and the surface of inspection object is enormous, and faint signals received after transmitting into the object are difficult to detect. In this study, in order to achieve the air-coupled ultrasonic single-probe reflection method, transmitting chirp signals (waves with a linearly frequency modulation) with an appropriate window function and applying a pulse compression technique (a cross-correlation process between the received signal and a reference chirp signal) was examined, and its effectiveness was investigated through experiments for polystyrene specimens. Experimental results showed that the proposed method was effective in detecting faint reflection signals after propagating through the specimens, and that the difference in plate thickness could be detected by observing the change of the signal-receiving period of multiple reflection signals between the top and bottom surfaces of the specimens. These results demonstrate the feasibility of nondestructive testing using the air-coupled ultrasonic vertical reflection method and could show an important step toward its future practical applications.

A technique for medium-range through-thickness focusing using Lamb waves

Medium-range guided wave testing is commonly employed for inspection of areas with restricted access. The technique usually works in pulse echo mode and at high frequency-thickness products, around 20 MHz ⋅ mm, offering good sensitivity and resolution. Defect sizing is based on the reflection amplitude of the received mode(s). However, the scattering of guided waves is complex, and the amplitude of the reflected modes does not provide sufficient information for defect sizing. This work aims to overcome this limitation using a focusing technique based on Lamb waves. Specifically, multiple Lamb wave modes are excited individually and superimposed to form a new mode with a desired through-thickness energy distribution. This way, energy is focused on a single point in the structure. Using weighting functions, the location of the focal point is swept across the thickness of the sample. The technique allows for accurate sizing of flaws, such as cracks and wall loss.

Advancement in understanding ultrasonic wave propagation in metallic pipes by simulation and experimental validation

ABSTRACT Ultrasonic gauging and defect detection of metallic pipes is a multi-disciplinary task, as it has to be performed in situ and involves several difficulties due to their curvature, limited access and corroded/eroded surface roughness due to harsh operating conditions. This research paper focuses on the investigation of employing a focused piezoelectric transducer in an immersion pulse-echo (PE) mode to measure the wall thickness (WT) from the inner side of the metallic pipes and to detect defects in the pipes. This paper also provides advances for understanding ultrasonic wave propagation in metallic pipes by simulation study using modern finite element technology and validating the results experimentally using battery-operated, water-immersible, IP67-grade stand-alone two-channel ultrasonic instrumentation that can move inside the pipe under test in flowing liquids such as water or oil. A simulation model has been established for time-of-flight (TOF) measurements for metallic pipes with various wall thicknesses, detection of standard defects and wall-thinning by inspecting the inner diameter (ID) surface of pipes and the pipe filled with water. The simulated results for the metallic pipes are in good agreement with the experimental data, providing an accurate and quantitative assessment of WT in the presence or absence of defects.

Birefringence Technique for Evaluating Thermal Stresses in Railroad Rails

This paper discusses the development of an in situ noncontact electromagnetic acoustic transducer (EMAT) nondestructive evaluation technology to determine rail neutral temperature and estimate rail stress in continuous welded rail (CWR). Stresses develop in CWR due to a lack of expansion joints to accommodate thermal expansion and contraction of the rail when ambient temperatures vary over time. The novelty of the work presented is the usage of ultrasonic birefringence properties using EMATs to estimate thermally induced stresses in rails. EMATs produce polarized shear waves propagating through the rail web in the pulse-echo mode. Experimental tests were performed on machined 136RE and 141RE rail material with applied compressive and tensile stresses to explore the stress-birefringence behavior. Two additional sets of experimental tests were conducted on full-size rail sections with in situ surface conditions to study variations in the in situ birefringence and the acoustic stress constant in different rail materials including 115RE rail, 119RE rail, two different 136RE rails, and 141RE rail. The results show a highly linear relationship between the stresses applied and the measured acoustic birefringence.

Ultrasonic Features for Evaluation of Adhesive Joints: A Comparative Study of Interface Defects.

Ultrasonic non-destructive evaluation in pulse-echo mode is used for the inspection of single-lap aluminum adhesive joints, which contain interface defects in bonding area. The aim of the research is to increase the probability of defect detection in addition to ensuring that the defect sizes are accurately estimated. To achieve this, this study explores additional ultrasonic features (not only amplitude) that could provide more accurate information about the quality of the structure and the presence of interface defects. In this work, two types of interface defects, namely inclusions and delaminations, were studied based on the extracted ultrasonic features in order to evaluate the expected feasibility of defect detection and the evaluation of its performance. In addition, an analysis of multiple interface reflections, which have been proved to improve detection in our previous works, was applied along with the extraction of various ultrasonic features, since it can increase the probability of defect detection. The ultrasonic features with the best performance for each defect type were identified and a comparative analysis was carried out, showing that it is more challenging to size inclusion-type defects compared to delaminations. The best performance is observed for the features such as peak-to-peak amplitude, ratio coefficients, absolute energy, absolute time of flight, mean value of the amplitude, standard deviation value, and variation coefficient for both types of defects. The maximum relative error of the defect size compared to the real one for these features is 16.9% for inclusions and 3.6% for delaminations, with minimum errors of 11.4% and 2.2%, respectively. In addition, it was determined that analysis of the data from repetitive reflections from the sample interface, namely, the aluminum-adhesive second and third reflections, that these contribute to an increase in the probability of defect detection.

Li-Ion Cell in Operando Monitoring and Prognostication Using CMUT Devices

Capacitive micromachined ultrasonic transducer (CMUT) devices are ideal solutions for in operando battery monitoring applications especially for consumer electronics. Their minute size (2mm x 1mm x 0.5mm) allows direct placement on the battery without affecting the form factor of the device, the volume production techniques used for their manufacture allow for a very low-cost device, and they can be easily integrated with front-end integrated circuits either in a single device or in a discrete multichip form. Together with industry partners we have developed CMUT devices that we use to continuously monitor the behavior of a battery while it is cycling.For this work we used CMUTs (close-up shown in Fig. 1(a)) developed to operate with a low bias voltage (less than 30 V) which reduces the complexity of the driving hardware. The impulse response and its frequency content are shown in Fig. 1(b). In collapse mode, the peak frequency is 4.0 MHz and the one-way –3 dB BW is 76%, which allows flexibility in setting the drive conditions to interrogate the battery. Our testing also shows that the CMUTs show good device-to-device uniformity and they have a very stable performance in variable temperature environments (e.g. 0℃ - 60℃ ).The cell is interrogated in pulse-echo mode. The CMUT is excited by a wide-band unipolar pulse and the returned analog signal is filtered and amplified. The signal is then digitized and processed to extract features that allow us to quantify the state of the battery. Figure 1(c) depicts such signal features change under baseline cell cycling conditions (three cycles at a charge rate of C/4). These changes are the result of mechanical material property changes in the cell e.g., electrode stiffness and density [1] which directly affect the acoustic wave propagation inside the cell. Figure 1(d) depicts signal feature change due cell overcharge (red line). Ultrasound is especially sensitive to gas generation which occurs as the cell voltage extends beyond normal operating range [2]. Signal features provide early warning notice that cell is outside of normal operating conditions.Figure 1. a) Close-up image of CMUT device. b) CMUT impulse response and corresponding frequency content. c) Signal features (RMS and Time of Flight (ToF)) and thickness change during C/4 charge and discharge. d) Signal features during cell constant current overcharge. Cell overcharged after 4.4V (red line). Chang, W. et al. Measuring effective stiffness of Li-ion batteries via acoustic signal processing. Mater. Chem. A 8, 16624–16635 (2020).Appleberry, M. C. et al. Avoiding thermal runaway in lithium-ion batteries using ultrasound detection of early failure mechanisms. Journal of Power Sources 535, 231423 (2022). Figure 1

Ultrasonic measurement of temperature distributions in extreme environments: Electrical power plants testing in utility-scale steam generators

Thermal heterogeneities within energy conversion and storage, material processing, nuclear processes, aerospace, and military applications are often inaccessible to characterization by insertion sensors. When sensor deployment is possible, conventional pointwise temperature probes quickly degrade when inserted into harsh environments typical of such processes. We developed spatially-resolved ultrasonic thermometry to noninvasively measure the spatial distributions of thermal properties in such applications, even when sizable thermal gradients are present. Our method divides the path of ultrasonic propagation into segments bound by echogenic features, which create echoes in pulse-echo mode, encoding the information about interior temperature distributions. We use the acquired ultrasonic responses to estimate the internal temperature distributions by solving an inverse problem or concatenating segmental estimates. This work describes the implementation and industrial testing of the developed method at a coal-fired electrical power generation plant. We inserted an echogenically segmented Inconel 625 waveguide into the combustion zone of the utility-scale boiler and continuously acquired ultrasonic data while keeping sensitive components away from the damaging combustion environment. The accuracy of the time-dependent temperature distributions reconstructed from the ultrasonic measurements was comparable to that of thermocouples. The resiliency of ultrasonic thermometry to harsh combustion conditions was far superior to conventional insertion sensors. The measurements obtained during plant operation captured daily steam generation cycles in response to changing customer demand and intermittent contributions of renewable power sources to the power grid. These measurements have revealed new insights into the relationship between the dynamic power generation load and the conditions inside the steam generator. The successful industrial testing of spatially-resolved ultrasonic thermometry in solids indicates that the developed technology has matured to become an attractive alternative to conventional sensing in solving challenging problems of long-term thermal characterizations in extreme environments.

Robust Imaging of Speed of Sound Using Virtual Source Transmission.

Speed of sound (SoS) is a novel imaging biomarker for assessing the biomechanical characteristics of soft tissues. SoS imaging in the pulse-echo mode using conventional ultrasound (US) systems with hand-held transducers has the potential to enable new clinical uses. Recent work demonstrated that diverging waves (DWs) from a single element (SE) transmit to outperform plane-wave sequences. However, SE transmits have severely limited power and hence produce a low signal-to-noise ratio (SNR) in echo data. We herein propose Walsh-Hadamard (WH) coded and virtual-source (VS) transmit sequences for the improved SNR in SoS imaging. We additionally present an iterative method of estimating beamforming (BF) SoS in the medium, which otherwise confounds SoS reconstructions due to beamforming inaccuracies in the images used for reconstruction. Through numerical simulations, phantom experiments, and in vivo imaging data, we show that WH is not robust against motion, which is often unavoidable in clinical imaging scenarios. Our proposed VS sequence is shown to provide the highest SoS reconstruction performance, especially robust to motion artifacts. In phantom experiments, despite having a comparable SoS root-mean-square error (RMSE) of 17.5-18.0 m/s at rest, with a minor axial probe motion of ≈ 0.67 mm/s the RMSE for SE, WH, and VS already deteriorate to 20.2, 105.4, and 19.0 m/s, respectively, showing that WH produces unacceptable results, not robust to motion. In the clinical data, the high SNR and motion resilience of VS sequences are seen to yield superior contrast compared to SE and WH sequences.

Application of Odd Harmonic Resonances of a Single Crystal to Generation and Reception of Superharmonic Waves for Sensitive Monitoring of Heat-Treated Materials.

In nonlinear ultrasonic testing, the quadratic and more recently cubic nonlinearity parameters are frequently measured as a quantitative indicator of damaged material state. Application of higher-order harmonics can improve the sensitivity of detection and monitoring for damages and microstructures due to their higher values of nonlinearity parameters. The excitation and reception of higher-order harmonics, so-called superharmonics, which use the third to fifth harmonics arising from nonlinear wave propagation, is not sufficiently investigated and applied. The purpose of this communication is to develop a highly sensitive superharmonic nondestructive technique that efficiently generates and receives third- and fifth-order harmonics using the odd harmonic resonances of a single piezoelectric crystal. The method focuses on the measurement of fifth harmonic generation and reception, and the calculation of the relative quintic nonlinearity parameter (δ'). The method also addresses the issue of source nonlinearity that may be contained in the measured fifth harmonic amplitude. The measurement results of δ' for a series of precipitation heat-treated samples clearly show a much better sensitivity than the results of the cubic nonlinearity parameter (γ'). The proposed method enables a highly sensitive and true pulse-echo mode nonlinear ultrasound testing.

Quadratic versus linear models to estimate the mean scattering spacing as a function of temperature in ex-vivo tissue

Previous works have shown the feasibility of temperature estimation during ultrasonic therapy using pulse-echo diagnostic ultrasound. These methods are based on the measurement of thermally induced changes in backscattered RF echoes due to thermal expansion and changes in ultrasonic velocity. They assume a joint contribution of these two parameters and a linear dependence with temperature. In this work, the contributions of velocity changes and thermal expansion to the evolution of the mean scatterer spacing of ex vivo bovine skeletal muscle tissue samples were decoupled. This was achieved by employing an experimental setup which allows measuring the absolute velocity value, using the through-transmission technique in a direct transmission configuration. The mean-scatterer spacing was estimated from spectral analysis of the backscattered signals obtained in pulse-echo mode. We propose a quadratic model of the thermal expansion coefficient to fit the evolution of the mean-scatterer spacing with temperature. The temperature increase estimated by the linear model, in the range of 29.5–47 °C, presents a percentage error (mean square error) of 11 %, while for the quadratic model the error is 4.8 %.

On the ultrasonic characterization of the stacking sequence of CFRP laminates

Ultrasound in pulse-echo scan mode has already been demonstrated for the extraction of local fiber angle distribution in composite laminates. Depending on the ultrasonic (scan) parameters employed, different sensitivity, spatial resolution, and dynamic depth range can be reached.This study investigates the use of pulse-echo ultrasound testing in different frequency ranges to characterize the in-plane fiber angle distribution and ply stacking sequence in a multi-layer composite laminate. Minimization of the Mumford-Shah functional is performed as an edge-preserving smoothing procedure for the recorded ultrasonic dataset, followed by the application of a Gabor Filter-based Information Diagram approach to extract a 3D tomographic image of the fiber angles. The performance of the method is experimentally studied on ultrasonic datasets, recorded at various center frequencies, of a 5.5 mm thick 24-layer quasi-isotropic carbon fiber reinforced polymer laminate with stacking sequence [+45/0/−45/90]3s. For quantitative analysis, statistical metrics are employed to evaluate the accuracy and precision of the extracted angles over depth, and to better understand the interfering influence of adjacent plies. For the given case study, a 15 MHz ultrasound frequency is recommended as it provides a good balance between precision, accuracy, and depth range. To understand the influence of scan parameters on the fiber angle characterization, the 15 MHz ultrasonic dataset is analyzed for various noise conditions as well as different spatial step size of the scan.

Non-contact Ultrasonic Sonar-based Ranging Technique for In-motion 3D Railroad Tie Deflection Measurements

This paper presents an ultrasonic technique for non-contact surface deflection mapping of railroad ties using concepts of sonar-based ranging. The technique utilizes an array of capacitive ultrasonic transducers arranged along the length of the railroad tie at a lift-off distance of 3 in. from the rail surface to ensure contactless measurements. The transducer array is used in pulse-echo mode and distances from the transducers to the tie surface are measured by tracking the time-of-flight of the waves reflected from the tie surface. A reference-based cross-correlation operation is introduced to compute the time-of-flight, wherein one of the transducers is used as a reference for the distance measurements. The reference-based cross-correlation ensures accurate peak-detection for time-of-flight based differential distance measurements. An acoustic signal strength-based technique is utilized to differentiate between signals reflected from ties and those reflected from ballast. Laboratory scale tests were first performed as a proof-of-concept on a slender wooden beam to measure deflections in loaded and unloaded conditions. Dynamic tests were also performed on this beam to determine the ability to track time-varying positions. Field tests on a replica test track with wood ties were performed at the Rail Defect Testing Facility at University of California San Diego by mounting the prototype on a test-cart moved at walking speed. A dynamic assessment of the prototype was also performed to determine natural frequencies of the mounting beam that may be relevant for future uses at higher speeds. The results indicate the potential of this non-contact system to measure full-field tie deflections in 3D in-motion. This ability may potentially be used to detect conditions of poor tie support that may cause derailments.

Ultrasonic Wave Mode-Based Application for Contactless Density Measurement of Highly Aerated Batters.

An ultrasonic wave mode-based method for density measurement in highly foamed batters was developed. Therefore, a non-contact ultrasonic sensor system was designed to generate signals for batch-wise processes. An ultrasonic sensor, containing a piezoelectric ceramic at the fundamental longitudinal frequency of 2 MHz, was used to take impedance measurements in pulse-echo mode. The ultrasonic signals were processed and analysed wave-mode wise, using a feature-driven approach. The measurements were carried out for different mixing times within a container, with the attached ultrasonic sensor. Within the biscuit batter, the change to the ultrasonic signals caused by density changes during the batter-mixing process was monitored (R2 = 0.96). The density range detected by the sensor ranges between 500 g/L and 1000 g/L. The ultrasonic sensor system developed also shows a reasonable level of accuracy for the measurements of biscuit batter variations (R2 > 0.94). The main benefit of this novel technique, which comprises multiple wave modes for signal features and combines these features with the relevant process parameters, leads to a more robust system as regards to multiple interference factors.

Aerosol jet printing of piezoelectric surface acoustic wave thermometer

Surface acoustic wave (SAW) devices are a subclass of micro-electromechanical systems (MEMS) that generate an acoustic emission when electrically stimulated. These transducers also work as detectors, converting surface strain into readable electrical signals. Physical properties of the generated SAW are material dependent and influenced by external factors like temperature. By monitoring temperature-dependent scattering parameters a SAW device can function as a thermometer to elucidate substrate temperature. Traditional fabrication of SAW sensors requires labor- and cost- intensive subtractive processes that produce large volumes of hazardous waste. This study utilizes an innovative aerosol jet printer to directly write consistent, high-resolution, silver comb electrodes onto a Y-cut LiNbO3 substrate. The printed, two-port, 20 MHz SAW sensor exhibited excellent linearity and repeatability while being verified as a thermometer from 25 to 200 ∘C. Sensitivities of the printed SAW thermometer are -96.9times 1{0{}^{-6}}^{circ }C−1 and -92.0times 1{0{}^{-6}}^{circ }C−1 when operating in pulse-echo mode and pulse-receiver mode, respectively. These results highlight a repeatable path to the additive fabrication of compact high-frequency SAW thermometers.

Railroad Sleeper Condition Monitoring Using Non-Contact in Motion Ultrasonic Ranging and Machine Learning-Based Image Processing.

An ultrasonic sonar-based ranging technique is introduced for measuring full-field railroad crosstie (sleeper) deflections. Tie deflection measurements have numerous applications, such as detecting degrading ballast support conditions and evaluating sleeper or track stiffness. The proposed technique utilizes an array of air-coupled ultrasonic transducers oriented parallel to the tie, capable of "in-motion" contactless inspections. The transducers are used in pulse-echo mode, and the distance between the transducer and the tie surface is computed by tracking the time-of-flight of the reflected waveforms from the tie surface. An adaptive, reference-based cross-correlation operation is used to compute the relative tie deflections. Multiple measurements along the width of the tie allow the measurement of twisting deformations and longitudinal deflections (3D deflections). Computer vision-based image classification techniques are also utilized for demarcating tie boundaries and tracking the spatial location of measurements along the direction of train movement. Results from field tests, conducted at walking speed at a BNSF train yard in San Diego, CA, with a loaded train car are presented. The tie deflection accuracy and repeatability analyses indicate the potential of the technique to extract full-field tie deflections in a non-contact manner. Further developments are needed to enable measurements at higher speeds.

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.