PVDF Transducer Research Articles

A multi-function integrated PVDF transducer for fault detection and speed measurement of cylindrical roller bearings

Monitoring the condition of bearings in rotating machinery is crucial to ensure reliability, safety, and efficiency. Recently, integrated sensors have become more popular than traditional accelerometers in bearing condition monitoring because of their compact design, cost-effectiveness, and improved efficiency in fault detection through a short transmission path. This study presents a new approach to bearing condition monitoring by developing a bearing with an integrated Polyvinylidene Fluoride transducer. This polymer-based transducer, known as PVDF, has a piezoelectric effect which generates electric charge in response to mechanical excitation. The PVDF transducer was selected for its high sensitivity, flexibility, and thin structure. The developed bearing with the integrated PVDF transducer can detect faults under constant and variable speeds, and the damage size can be estimated with an accuracy of 10%. It outperformed a commercial accelerometer in noisy environments with artificial impacts from an air motor, making it a highly reliable option for bearing condition monitoring in noisy industrial settings. The PVDF transducer can also be used as a low-cost speed sensor with an accuracy of 5.2%, offering a versatile solution for machine monitoring. By simultaneously recording rotational speed and vibration, the developed integrated transducer provides a comprehensive view of machine health and performance as a multi-function transducer, enabling more accurate and efficient maintenance scheduling.

Separate emission/reception transducers for 3D ultrafast ultrasound imaging

Recent advancements in ultrafast 3D ultrasound imaging have revolutionized the field of echography, enabling its extension to novel applications such as cerebral dynamics, cardiac electrophysiology and the quantitative imaging of intrinsic mechanical properties of tumors. To facilitate these advancements, two primary transducer strategies are employed in 3D imaging. The first involves dense 2D probes equipped with a large number of elements, typically exceeding 1024. The second strategy uses row-column addressing, which simplifies the electronic control of the probe elements. Despite their effectiveness, these methods entail complexities in design and fabrication. Addressing these challenges, our study introduces an innovative transducer configuration that distinctly separates emission and reception functionalities. This separation not only simplifies the overall transducer design but also significantly reduces the system's complexity. A sparse array of PVDF transducers, which have been laser micro-machined to ensure acoustic transparency, is used at the reception. For the emission aspect, we employ a specialized acoustic concentrator to emulate point-like emission. The paper presents the detailed design requirements, assembly process, and the operational principles of this novel transducer. Furthermore, an experimental validation is conducted using a CIRS 040GSE phantom model. This validation is crucial to demonstrate the practical applicability and reliability of our transducer in real-world medical imaging scenarios.

The influence of edge waves in local surface skimming longitudinal wave generation using a focused PVDF transducer

Acoustic microscopy is extensively used for high-frequency imaging and material characterization. In a focused ultrasonic transducer, the presence of edge waves from the edge of the transducer is usually considered a disadvantage. For high-frequency imaging applications, the edge waves adversely affect the quality of the image. This paper discusses edge wave's influence on generating a surface wave in bulk metal samples using a limited aperture PVDF transducer. Acoustic microscopy-based defocusing experiments are conducted on aluminum, stainless steel, copper, and brass samples. A detailed wave-path analysis is done to understand the different wave components in a signal as obtained from defocusing experiments. The travel path of each wave component is analytically obtained and compared with the experimental results. The different wave modes observed in the experiments are identified by overlaying the analytical plots on the experimentally obtained B-scans. A good correlation is obtained between the experimental and analytical results. The surface wave velocity of the samples is calculated using the time-resolved method, and the percentage of error in the measurement is estimated. The challenges for using this method in measuring surface wave velocities in samples with bulk longitudinal velocities <5000m/s are also discussed.

Experimental measurement of thermal shock wave in C/Ph induced by electron beam radiation

The attenuation characteristic of thermal shock wave in a new type of carbon phenolic (C/Ph) radiated by pulsed electron beam were studied experimentally on “FLASH II” accelerator with PVDF transducer. The attenuation trend of thermal shock wave produced by electron beam radiation in the material is calculated by means of numerical simulation. Experimental results show that: when electron beam energy fluxes are in the range of 169-531 J·cm-2 and the electron’s mean energy is about 0.6 MeV, stress at 4 mm from the irradiation surface of C/PH are in the range of 0.12-2.22GPa. The experimental results of the attenuation trend of thermal shock waves are in good agreement with the simulation results.

High-Frequency Acoustic Imaging Using Adhesive-Free Polymer Transducer.

The piezoelectric polymer PVDF and its copolymers have a long history as transducer materials for medical and biological applications. An efficient use of these polymers can potentially both lower the production cost and offer an environment-friendly alternative for medical transducers which today is dominated by piezoelectric ceramics containing lead. The main goal of the current work has been to compare the image quality of a low-cost in-house transducers made from the copolymer P(VDF-TrFE) to a commercial PVDF transducer. Several test objects were explored with the transducers used in a scanning acoustic microscope, including a human articular cartilage sample, a coin surface, and an etched metal film with fine line structures. To evaluate the image quality, C- and B-scan images were obtained from the recorded time series, and compared in terms of resolution, SNR, point-spread function, and depth imaging capability. The investigation is believed to provide useful information about both the strengths and limitations of low-cost polymer transducers.

Evaluation of adhesive-free focused high-frequency PVDF copolymer transducers fabricated on spherical cavities

A layer-by-layer deposition method for fabricating a focused ultrasonic transducer from piezoelectric copolymers has been developed. The fabrication process involves engraving a spherical cavity of 2 mm diameter on polyethyleneimines (PEI) polymer substrate. Surface roughness of the engraved spherical cavity is measured and compared with simulated line scan. Then, the transducer response was investigated by observing the acoustic pulse reflection from the glass plate used as reflector in a focal point. The average central frequency responses were measured to be 48.5 MHz, with a lower and upper −6 dB frequencies of approximately 25 and 76.5 MHz, yielding a bandwidth of 94.2%. A scanning hydrophone system has been employed to determine the focal zone of the transducer and compared with simulation using COMSOL Multiphysics. Two-dimensional surface scanning was performed on the test sample to provide the ultrasonic imaging of the transducer prototype and compare the image with commercial PVDF transducer with a center frequency of (48.5 ± 1) MHz.

Quasi-Spherical PVDF Ultrasonic Transducer With Double-Cylindrical PVDF Structure

In this paper, a quasi-spherical PVDF airborne ultrasonic transducer for three-dimensional (3D) ultrasonic location systems is designed and fabricated using two strips of cylindrical PVDF film. The 3D solid model of the transducer was created and the acoustic directivity pattern of the transducer was simulated using the finite-element method and the COMSOL Multiphysics™ software. Measurements of the frequency response, pulse response and beam directivity performance are presented. The measurement and simulation results show that the proposed transducer has a spherical beam pattern, and its resonant frequency is consistent with that of the cylindrical PVDF transducers. Because of its spherical beam pattern, it is very suitable for 3D ultrasonic location systems as a transducer to achieve wide coverage.

Research and validation of design principles for PVDF wideband ultrasonic transducers based on an equivalent circuit model

With the increasing use of ultrasonic measurement technology in many fields, the demand for the wideband ultrasonic transducers is also growing. In order to design a wideband piezoelectric ultrasonic transducer, the design principles of wideband PVDF piezoelectric ultrasonic transducers are studied in this paper. A new equivalent circuit model of piezoelectric ultrasonic transducer is used here to simulate the piezoelectric ultrasonic transducer, which combines with the controlled source model and the lossy transmission line model. Based on this model, the relationships between physical structures and properties of PVDF transducers are studied both in simulation and experiment. It shows that the center frequency and many other property parameters of PVDF ultrasonic transducers are strongly related to the physical structures of it. Finally, a wideband PVDF piezoelectric ultrasonic transducer is produced with the center frequency of about 5.3 MHz ± 0.1 MHz and the bandwidth of more than 90%.

On the Use of Oblique Acoustic Leakage to Measure the Wavenumber Spectrum of Propagating Lamb Waves.

Lamb waves propagating within a waveguide often have similar frequency content. If there are multiple Lamb wave modes with the same frequency content, the wavenumber spectrum can be used to distinguish between them. As a result, the wavenumber spectrum is an important tool for determining the modal content of signals. In this paper, we propose a new method for measuring wavenumber spectra that uses an air-coupled transducer for reception and Snell’s law instead of a fast-Fourier transform. The method employs an angular scan rather than a translational scan. The advantages and disadvantages of the method are discussed along with some suggestions for potential improvements. Finally, experimental results comparing the proposed method to a more conventional method, which used a PVDF transducer, demonstrate the feasibility of the proposed method.

Velocity measurements of cylindrical surface waves with a large aperture line-focus acoustic transducer

Acoustic microscopy has been widely applied in the measurements of the mechanical properties. However, the measurement of wave velocity on a curved cylindrical surface by acoustic microscopy was seldom reported. In this paper, we adopted a large aperture line-focus PVDF transducer and a defocusing measurement system to measure the velocity of a cylindrical surface waves. The theoretical model was established to study the relationship among the propagation path of surface waves, the geometric parameters of a transducer, and the diameter of a shaft specimen. Based on theoretical deduction and mathematical modeling, theoretical oscillation curves of phase difference were obtained. According to the improved V(f,z) analysis method, the V(f,z) curves were obtained through analyzing experimental data at different frequencies by Fourier transform. Then the surface wave velocity of the cylindrical tungsten steel specimen (Ø 20mm) could be determined by fitting the V(f,z) curves with the theoretical curves. The measurement results were consistent with the theoretical values, indicating that the measurement method was feasible. This study laid the basis for the ultrasonic measurement of the mechanical properties on the layer-coated cylinders.

Cylindrical Rayleigh surface waves on a layer-coated cylinder measured by PVDF transducer and defocusing measurement method

This paper develops a measurement method for accurately determining dispersion curves of Rayleigh-type surface waves propagating on layer-coated elastic cylinders. It utilizes PVDF acoustic transducers and a defocusing measurement system. To deal with the cylindrically curved surface, a new cross-correlation waveform processing approach is proposed and verified. Cylindrical Rayleigh wave velocities of layered cylindrical solid samples have been successfully measured over a frequency range from 3 to 20MHz. The measured dispersion curves are in good agreement with their theoretical counterparts. It demonstrates the potential application for non-destructive evaluation of coating layers deposited on cylindrical solids.

Ultrasonic wave velocities in radial direction of bovine cortical bone

The ultrasonic axial transmission (AT) techniques have been proposed to evaluate the cortical bone of arms and legs. For the mode analysis of propagating waves, the information of anisotropy and heterogeneity of the cortical bone is important. Yamato has pointed that longitudinal wave velocity in the axial direction of bovine cortical bone changes due to the measurement positions and microstructures. In this study, we have investigated longitudinal wave velocities in radial direction of cortical bone. The cuboid samples were obtained from the cortical bone of bovine femur. During ultrasonic pulse immersion experiments, a sinusoidal ultrasonic wave in the range from 3 to 10 MHz was transmitted from a PVDF transducer, which passed through the sample in the radial direction. By reducing the sample thickness gradually, wave velocities were measured. The average velocities in radial direction of samples were around 3450 m/s and depended on the positions of the samples in the femur. They variation of the velocities due to the thickness was about 7 %. These data give us the information of heterogeneity of cortical bone in radial direction which should be considered in the AT techniques. [1] Y. Yamato, et al., Jpn. J. Appl. Phys., 47, 4096–4100 (2008).

Broadband attenuation measurements of tissue-mimicking phantoms employed for histotripsy

Tissue-mimicking phantoms have previously been developed for assessing the efficacy of therapeutic ultrasound. A new modality of focused ultrasound, histotripsy, relies on the formation of shockwave-induced cavitation to ablate tissue mechanically. The objective of this study was to use a broadband ultrasound method to determine the frequency-dependent attenuation for histotripsy tissue phantoms. An agar tissue phantom was developed with evaporated milk to mimic the acoustomechanical properties of prostate tissue, a key target for histotripsy. The attenuation of this tissue phantom was measured between 2 and 20 MHz using a through-transmission technique with a single pair of PVDF transducers. The power law dependence of the acoustic attenuation spectra was linear with frequency (R 2 = 0.98). The attenuation coefficient of the tissue phantom was 0.62 ± 0.02 dB/cm/MHz, which is lower than that reported for ex vivo human prostate at 5 MHz. The broadband measurements techniques utilized provide a straightforward metric for the attenuation spectrum of tissue phantoms developed for shocked insonation regimes.

Measurement of cylindrical Rayleigh surface waves using line-focused PVDF transducers and defocusing measurement method

Line-focused PVDF transducers and defocusing measurement method are applied in this work to determine the dispersion curve of the Rayleigh-like surface waves propagating along the circumferential direction of a solid cylinder. Conventional waveform processing method has been modified to cope with the non-linear relationship between phase angle of wave interference and defocusing distance induced by a cylindrically curved surface. A cross correlation method is proposed to accurately extract the cylindrical Rayleigh wave velocity from measured data. Experiments have been carried out on one stainless steel and one glass cylinders. The experimentally obtained dispersion curves are in very good agreement with their theoretical counterparts. Variation of cylindrical Rayleigh wave velocity due to the cylindrical curvature is quantitatively verified using this new method. Other potential applications of this measurement method for cylindrical samples will be addressed.

Effect of a Bonding Layer between Electrodes on the Performance of a -Mode PVDF Ultrasound Transducer

양 전극 사이에 압전층 외에 비압전성의 접합층이 존재하는 <TEX>${\lambda}/4$</TEX> 모드 PVDF 초음파 트랜스듀서에 있어서 그 접합층이 트랜스듀서의 성능에 미치는 영향을 등가회로에 의해 해석하였다. 등가회로로서는 Kikuchi 등이 제안한 전송선로 모델[Sound of IEICE, 55-A, 331-338 (1981)]을 도입하였는데, 먼저 그 모델에 의한 해석의 타당성을 <TEX>$80{\mu}m$</TEX> 두께의 PVDF 압전막이 동(Cu) 후면체에 부착되는 세 가지 경우를 가정한 KLM 모델과의 비교를 통해 검증하였다. 다음으로, 그 압전막과 더불어 <TEX>$5{\mu}m{\sim}20{\mu}m$</TEX> 두께의 에폭시 접합층을 갖는 다섯 개의 트랜스듀서를 제작하여 펄스 에코 응답을 측정한 후 시뮬레이션 결과와 비교하였다. 두 결과는 서로 잘 일치하였는바, 도입한 Kikuchi 모델에 의해 접합층이 트랜스듀서의 성능에 미치는 영향을 파악할 수 있음을 알았는데, 접합층이 <TEX>$20{\mu}m$</TEX>일 때는 그 접합층이 없을 때에 비해 중심주파수와 대역폭은 각각 약 19.7 %, 25.0 % 감소하고, 삽입손실은 57.2 % 증가하는 것으로 나타났다. The effect of a bonding layer on the performance of a quarter-wave (<TEX>${\lambda}/4$</TEX>) mode PVDF ultrasound transducer having not only a piezoelectric layer but also a non-piezoelectric layer between two electrodes was analyzed. The equivalent circuit of a transmission line model by Kikuchi et al.[Sound of IEICE, 55-A, 331-338 (1981)] was introduced for the analysis. The validity of the model was confirmed by comparison with a KLM model for three postulated adhesion cases of a <TEX>$80{\mu}m$</TEX> thick piezoelectric PVDF film to a copper (Cu) backer. The pulse-echo responses of five PVDF transducers, each fabricated with a different thickness (<TEX>$5{\mu}m{\sim}20{\mu}m$</TEX>) of the bonding layer, were measured and the results were compared with those by simulation. The two results were in good agreement with each other and it was noted that the effect of the bonding layer on the performance of the transducer could be analyzed by the Kikuchi model. In detail, the <TEX>$20{\mu}m$</TEX> bonding layer decreased the center frequency and the bandwidth by about 19.7 % and 25.0 %, respectively, and increased the insertion loss by 57.2 %.

A Piezoelectric Energy Harvester for Rotary Motion Applications: Design and Experiments

This paper investigates the analysis and design of a vibration-based energy harvester for rotary motion applications. The energy harvester consists of a cantilever beam with a tip mass and a piezoelectric ceramic attached along the beam that is mounted on a rotating shaft. Using this system, mechanical vibration energy is induced in the flexible beam due to the gravitational force applied to the tip mass while the hub is rotating. The piezoelectric transducer is used to convert the induced mechanical vibration energy into electricity. The equations of motion of the flexible structure are utilized along with the physical characteristics of the piezoelectric transducer to derive expressions for the electrical power. Furthermore, expressions for the optimum load resistance and maximum output power are obtained and validated experimentally using PVDF and PZT transducers. The results indicate that a maximum power of 6.4 mW at a shaft speed of 138 rad/s can be extracted by using a PZT transducer with dimensions 50.8 mm × 38.1 mm × 0.13 mm. This amount of power is sufficient to provide power for typical wireless sensors such as accelerometers and strain gauges.

1P3-4 Analysis of the Effect of Non-piezoelectric Bonding Layer between Electrodes on PVDF Transducer Performance(Poster Session)

1P3-4 Analysis of the Effect of Non-piezoelectric Bonding Layer between Electrodes on PVDF Transducer Performance(Poster Session)

1P2-30 Detection of cracks using laser scanning PVDF transducer(Poster Session)

1P2-30 Detection of cracks using laser scanning PVDF transducer(Poster Session)

Effects of boundary conditions on the two wave phenomenon in cancellous bone

After the successful observation of two wave phenomenon in cancellous bone, wave characteristics have been investigated by in vitro studies. However, there still exists strong necessity to understand the effects of bone boundary conditions on the phenomenon, because the cancellous bone is always covered by a cortical layer in vivo. This paper is dedicated to the experimental and simulation studies of the effects on the two wave phenomenon. A sample of cancellous bone (76.1x45.2x12.9 mm3) and two cortical plates (thickness: 1.2 and 1.9mm) were obtained from the left radius of a racehorse. Longitudinal pulse waves around 1MHz were measured by a conventional ultrasonic pulse technique using PVDF transducers. With 3-D CT image of the sample, wave propagation was also investigated by a 3-D elastic FDTD method. We then compared wave propagation in the sample covered with cortical layers or not. In both experimental and simulation approaches, two wave phenomenon was observed in the covered sample. However, the slow wave amplitude was very sensitive to the interface conditions between the cancellous bone and cortical layers. In addition, the waves often became small due to the conditions, telling the importance of sensitive wave observation in some cases.

Ultrasonic properties of fast and slow longitudinal waves propagating in the cancellous bone

Longitudinal wave in cancellous bone separates into fast and slow waves depending on the alignment of trabeculae. Here, the fast wave mainly propagates in trabeculae, whereas slow wave propagates in the soft tissue (bone marrow). Because these two waves usually overlap, the evaluation of each wave has still remained difficult. In this study, then, we have tried to evaluate the wave properties (attenuation and velocity), making use of the plane wave in an acoustic tube. 3-D image of the bone specimen was obtained by X-ray micro CT. In an acoustic tube, a cancellous bone specimen was set between home-made PVDF transducers. A function generator delivered a single sinusoidal signal in the range of 0.5 to 1.5 MHz to the transmitter. By filing a part of bone specimen away, we have tried to obtain the attenuation and velocity of the specimen. The two wave phenomenon clearly occurred in our specimen. In some trabecular bones of big animals, the wave separated perfectly. We have then tried to obtain ultrasonic properties of both waves and investigated the reflection and transmission at the interfaces.