High Frequency Ultrasonic Transducers Research Articles

Micromachining of High-Quality PMN-PT/Epoxy 1-3 Composite for High-Frequency (>30 MHz) Ultrasonic Transducer Applications.

Fabricating PMN-PT composites, the core component of high-frequency (>30 MHz) transducers, remains challenging due to their poor machinability and ultra-small kerfs. This urgent problem is significantly impeding the development of PMN-PT ultrasonic transducers for use in clinical research, biomedical sciences, and nondestructive testing. In this study, high-quality PMN-0.3PT/epoxy 1-3 composites at 30 MHz and 50 MHz were manufactured using a modified picosecond (1.5 ps) laser technique. Their performance was thoroughly analyzed, which was comparable to that with low-stress dry plasma etching. There were fewer microcracks around PMN-PT pillars. The minimum kerf was less than 4.5 μm and the highest aspect ratio was larger than 7.5. The micro domain morphology and hysteresis loops of PMN-PT pillars further confirmed that composites still maintained excellent piezoelectric performance and suffered fewer damages during laser cutting. The characterization results exhibited a large electromechanical coupling (>0.77), a high dielectric constant (>1600), and a relatively low acoustic impedance (<17 Mrayls). The ultrasonic transducers with centre frequencies of 30 MHz and 50 MHz were designed and prototyped to validate the performance of composites. The transducers showed broad bandwidth (>80%), high two-way insertion loss (>-23 dB), and imaging resolution superior to 40 μm. Finally, the C-scan experiments of IC chips were also used to further illustrate the applicability of transducers. These encouraging results further demonstrated that ultrafast laser technology will bring more accessible and affordable methods for fabricating high-frequency PMN-PT composite transducers with excellent performance.

Feasible Optimization and Fabrication of Multidimension Composites for High-Frequency Ultrasonic Transducer

Feasible Optimization and Fabrication of Multidimension Composites for High-Frequency Ultrasonic Transducer

Design and test of a small high frequency ultrasonic cleaning transducer

In order to solve the problem of cleaning of complex surfaces and micro blind holes in industrial products, a small high frequency ultrasonic cleaning transducer was designed and tested. Firstly, the finite element model of the transducer was established, and the influence of structural parameters on the first order longitudinal vibration frequency was analyzed. By adjusting the structural parameters of the transducer, the first order longitudinal vibration frequency of the transducer was determined to be 58716hz.The harmonic response of the transducer was analyzed. The results showed that when the voltage amplitude applied on the piezoelectric ceramic sheet was 80V, the transducer produced resonance at 58716 Hz, and the end face of the front cover of the transducer produced an axial displacement of about 3.34 µm . The transducer was made according to the theoretical analysis results, and the frequency sweep test was carried out on the transducer. The theoretical analysis results were consistent with the test results, which showed that the designed small high frequency ultrasonic cleaning transducer could meet the requirements of high frequency cleaning.

Preparation and simulation of lead free NBBT/epoxy 1–3 piezoelectric composites for high frequency medical ultrasound

This paper presents the modeling and fabrication of the (1-x)Na0.5Bi0.5TiO3-xBaTiO3 single crystal/epoxy 1–3 piezoelectric composite (NBBT 1–3 composite) with large electromechanical coupling factor (kt) for high frequency ultrasonic transducers. The NBBT 1–3 composite has been modeled by performing the finite element method using the COMSOL Multiphysics software. The parameters related to NBBT crystal are refined in the modeling process and the simulation results agree well with that of the experiment. The composite has been fabricated by the dice-and-fill method with a pitch of 12 μm. The measured resonance frequency, antiresonance frequency and electromechanical coupling factor (kt) with the values of 31.88 MHz, 43.16 MHz and 71.06% are obtained, respectively. The excellent performance of NBBT/epoxy 1–3 piezoelectric composite is comparable to that of lead-based Pb(Mg1/3Nb2/3)O3–PbTiO3/epoxy 1–3 piezoelectric composites. The excellent performance and the lead-free advantages make the NBBT/epoxy 1–3 piezoelectric composites quite attractive in high frequency medical ultrasound applications especially within the human body like intravascular ultrasound imaging (IVUS).

Multidimensional synergy-induced high piezoelectricity and reliability KNN piezoceramics for high-frequency ultrasonic transducers

High-frequency ultrasonic transducers have been implemented as a powerful tool for modern medical diagnosis and therapy. Most current transducers use piezoelectric ceramics for electromechanical couplings, which will undergo periodic electro-acoustic transitions at high frequencies (≥20 MHz), thereby requiring high reliability. This work presents a structural engineering strategy to improve the piezoelectricity and reliability of potassium sodium niobate (KNN)-based ceramics with potential high-frequency ultrasonic imaging transducers. The KNN-based ceramics exhibit fatigue-free behavior with enhanced piezoelectricity (d33 ∼550 ± 20 pC N−1), and the mechanisms are discussed in view of multi-dimensions from macroscopy to microscopy. Considering the synergistic effect of multi-phase coexistence, well-kept microstructure, and flexible domain rotation, property-worsening cracks during fatigue are restrained; furthermore, the aggregation of space charges is hindered, thereby reducing the pinned domain and improving the fatigue resistance. Based on the high-performance piezoceramics, the fabricated ultrasonic transducer has high reliability with a steady sensitivity and an unchanged broad bandwidth (∼76%) from room temperature to 80°C. In addition, images of a tilapia eyeball are scanned to confirm the imaging capability of transducers. We expect that the novel approach to achieving high performance through the structural strategy promotes KNN-based ultrasonic devices for biomedical imaging.

Potassium Sodium Niobate-Based Lead-Free High-Frequency Ultrasonic Transducers for Multifunctional Acoustic Tweezers

Ultrasonic transducers may need to operate in direct contact with the human body, especially with the skin or closer to blood vessels. Eco-friendly lead-free materials and devices are therefore being vigorously developed for biosafety considerations. This work presents high-performance potassium sodium niobate [(K,Na)NbO3, KNN]-based lead-free ceramics with composition-driven multiphase coexistence and their application on high-frequency ultrasonic transducers for multifunctional acoustic tweezers. A high piezoelectric constant d33 value of 332 pC/N, a good Curie temperature TC value of 348 °C, and improved in situ temperature stability were obtained in the piezoceramics via the construction multiple phases near room temperature and domain engineering. One to three piezocomposites were further fabricated based on the synthesized ceramics for higher electromechanical coupling properties. Lead-free high-frequency transducers as multifunctional acoustic tweezers for precise and selective manipulation of microparticles were designed and manufactured with a high center frequency of 23.4 MHz and a broad -6 dB bandwidth of 75.4%. Additionally, a stable transducer performance was obtained over a test temperature range of 23-60 °C, indicating good thermal stability in environments with fluctuating temperatures. Research on lead-free high-frequency transducers for ultrasound imaging and precise and selective manipulation of microparticles demonstrates their broad potential in fields such as medical therapy and diagnosis.

A Review of High-Frequency Ultrasonic Transducers for Photoacoustic Imaging Applications.

Photoacoustic imaging (PAI) is a new and rapidly growing hybrid biomedical imaging modality that combines the virtues of both optical and ultrasonic (US) imaging. The nature of the interaction between light and ultrasound waves allows PAI to make good use of the rich contrast produced by optics while retaining the imaging depths in US imaging. High-frequency US transducers are an important part of the PAI systems, used to detect the high-frequency and broad-bandwidth photoacoustic signals excited by the target tissues irradiated by short laser pulses. Advancement in high-frequency US transducer technology has influenced the boost of PAI to broad applications. Here, we present a review on high-frequency US transducer technologies for PAI applications, including advanced piezoelectric materials and representative transducers. In addition, we discuss the new challenges and directions facing the development of high-frequency US transducers for PAI applications.

Ultrawide Bandwidth High-Frequency Ultrasonic Transducers With Gradient Acoustic Impedance Matching Layer for Biomedical Imaging.

The high-frequency ultrasonic transducers with larger bandwidths yield excellent imaging performance in the biomedical field. However, achieving perfect acoustic impedance matching from the piezo-element to the target medium in the operating frequency spectrum is still a challenge. Conventional matching layers are mostly fabricated by only one or two uniform materials which are limited by their acoustic property. We propose a novel composite matching layer with gradient acoustic impedance based on a 1-3 gradient composite structure and multilevel matching theory. The proposed gradient-composite matching layer applied for ultrasonic transducer provides efficient impedance matching and ultrawide bandwidth which can significantly improve the quality of biomedical imaging. The active aperture size of the matching layer is 5× 5 mm2, and the overall thickness for five equivalent layers is 115 [Formula: see text]. The -6-dB bandwidth and the center frequency obtained by the ultrasonic transducer equipped with the 1-3 gradient composite matching layer are 141.7% and 22.3 MHz, respectively. The exceedingly good imaging performance of the fabricated ultrasonic transducer was demonstrated by the tungsten wire phantom and study on the biological tissues of a zebrafish and porcine eyeball. The theoretical and experimental results provide a novel train of thought for improving the quality of biomedical ultrasonic imaging.

Enhancement of the Transmission Performance of Piezoelectric Micromachined Ultrasound Transducers by Vibration Mode Optimization.

Ultrasound is widely used in industry and the agricultural, biomedical, military, and other fields. As key components in ultrasonic applications, the characteristic parameters of ultrasonic transducers fundamentally determine the performance of ultrasonic systems. High-frequency ultrasonic transducers are small in size and require high precision, which puts forward higher requirements for sensor design, material selection, and processing methods. In this paper, a three-dimensional model of a high-frequency piezoelectric micromachined ultrasonic transducer (PMUT) is established based on the finite element method (FEM). This 3D model consists of a substrate, a silicon device layer, and a molybdenum-aluminum nitride-molybdenum (Mo-AlN-Mo) sandwich piezoelectric layer. The effect of the shape of the transducer’s vibrating membrane on the transmission performance was studied. Through a discussion of the parametric scanning of the key dimensions of the diaphragms of the three structures, it was concluded that the fundamental resonance frequency of the hexagonal diaphragm was higher than that of the circle and the square under the same size. Compared with the circular diaphragm, the sensitivity of the square diaphragm increased by 8.5%, and the sensitivity of the hexagonal diaphragm increased by 10.7%. The maximum emission sound-pressure level of the hexagonal diaphragm was 6.6 times higher than that of the circular diaphragm. The finite element results show that the hexagonal diaphragm design has great advantages for improving the transmission performance of the high-frequency PMUT.

Development of high frequency piezocomposite with hexagonal pillars via cold ablation process

This paper reports on the fabrication of 1–3 piezocomposite with hexagonal pillars for high frequency ultrasonic transducer based on the cold ablation technique. The piezocomposite with hexagonal pillars was designed, simulated, and fabricated using an ultraviolet picosecond laser. It performs better than the piezocomposite with other pillar shapes like square. The edge length and height of the hexagonal PZT pillar were 10 μm and 36 μm, the width of the kerf was about 5 μm. The 1–3 piezocomposite with a resonance frequency of 51.2 MHz and a coupling coefficient of 0.69 was fabricated. The transducer with fabricated 1–3 piezocomposite was prototyped and characterized. Compared to the conventional dice-and-fill technique, the cola ablation process allows for the manufacturing of 1–3 piezocomposites with higher variability of pillar design and distribution as well as smaller structural size. It suggests that the cold ablation process proves to be suitable for the fabrication of high frequency composite and transducers.

Lead-Free KNN-Based Textured Ceramics for High-Frequency Ultrasonic Transducer Application.

Environment-friendly lead-free piezoelectric materials with excellent piezoelectric properties are needed for high-frequency ultrasonic transducer applications. Recently, lead-free 0.915(K0.45Na0.5Li0.05)NbO3-0.075BaZrO 3-0.01(Bi0.5Na0.5)TiO3 (KNLN-BZ-BNT) textured piezo- electric ceramics have high piezoelectric response, superior thermal stability, and excellent fatigue resistance, which are promising for devices applications. In this work, the KNLN-BZ-BNT textured ceramics were prepared by the tape-casting method. Microstructural morphology, phase transition, and electrical properties of KNLN-BZ-BNT textured ceramics were investigated. High-frequency needle-type ultrasonic transducers were designed and fabricated with these textured ceramics. The tightly focused transducers have a center frequency higher than 80 MHz and a -6-dB fractional bandwidth of 52%. Such transducers were built for an f -number close to 1, and the desired focal depth was achieved by press-focusing technology associated with a set of customer design fixture. Its lateral resolution was better than [Formula: see text] by scanning a 15- [Formula: see text] tungsten wire target. These promising results demonstrate that the lead-free KNLN-BZ-BNT textured ceramic is a good candidate for high-frequency ultrasonic transducer applications.

비파괴 검사용 고주파 초음파 트랜스듀서 제작

The development of high frequency ultrasonic transducer is crucial for detecting cracks or internal defects of some materials such as semiconductors, PCBs, and display panels with a size of few microns for the scanning acoustic microscopy (SAM) system. In this study, high frequency ultrasonic transducer was fabricated with a 13 μm thick ZnO film deposited on a sapphire substrate by DC sputtering machine. Ultrasonic transducer with 100 MHz center frequency, -6 dB bandwidth of 21% and the insertion loss of -68 dB was designed for the SAM system. Experimental results show that high frequency ultrasonic transducer device may have potential for high resolution application of nondestructive test and can be applied for various acoustic imaging system such as photoacoustic imaging in the future.

2Pb4-4 Evaluation of ultrasonic spray coating using high intensity and high frequency ultrasonic transducer with hydrothermal piezoelectric films

2Pb4-4 Evaluation of ultrasonic spray coating using high intensity and high frequency ultrasonic transducer with hydrothermal piezoelectric films

Applying a network of high frequency ultrasonic transducers for removal of Reactive Red 120 dye from aqueous solution: experimental design and statistical analysis

In this study a network of high frequency ultrasonic’s transducers without additives was introduced for removing the Reactive Red 120 dye from aqueous solution. pH, irradiation time, initial concentration and number of piezoelectric were input variables at constant temperature of 25 °C. The results revealed that the ultrasonic waves played an important role in cracking the hydrocarbon bonds due to the cavitation phenomenon and OH° attacks. The effects of the variables and their interactions were investigated by the central composite design (CCD) method as one of the response surface methodologies (RSM). Maximum dye removal’s efficiency (76.05%) was attained at initial concentration of 5 mg/l, irradiation time of 50 min; pH 10 and 5 ultrasonic’s transducers. It was in a good agreement with the experimental, 78%. Finally, to more evaluates, the RSM model was compared to the artificial neural network (ANN) model. Performance’s functions reported that the RSM was better than the ANN in predicting the dye removal’s efficiency (R%).

Multi-layer polymer-metal structures for acoustic impedance matching in high-frequency broadband ultrasonic transducers design

Although high-frequency (≥100 MHz) ultrasound has demonstrated its capability in a variety of applications, the fabrication of high frequency ultrasonic transducers with both high sensitivity and broad bandwidth remains challenging. One main reason is the mismatch of acoustic impedance between piezoelectric materials and the loading medium. Due to reliance on both specific acoustic impedance of matching materials and precise thickness control, the conventional quarter wavelength (1/4 λ) matching layer design is impractical for high-frequency transducers. Based on the transmission line theory and Mason model, our work interfaced polymer-metal-polymer matching layers for transducers over 100 MHz. The modeling result comparison between transducers without matching layer and those with two conventional matching layers demonstrated that the matching performance of polymer-metal-polymer matching layers could be as good as the one of conventional matching layers. Meanwhile, unlike conventional 1/4 λ matching layer design, our design is independent on materials with specific acoustic impedance, while precise thickness control of polymer and metal can be achieved by deposition. The polymer-metal-polymer matching layers scheme paves the way to high frequency ultrasonic transducers.

A new method to enhance the tip vibration amplitude output of the high frequency piezoelectric ultrasonic transducer used in the thermosonic bonding

The vibration amplitude output of the high frequency piezoelectric ultrasonic transducer used in the thermosonic bonding system can be reduced owing to many factors, among which the mounting clamp, taking charge of installing the whole transducer on the mounting bracket in bonding machine, is one such factor. To minimize the negative effect of the coupling between the transducer and the mounting bracket through the mounting clamp, and enhance the vibration amplitude output of the transducer, a new kind of flexible mounting clamp is proposed, which combines the traditional mounting clamp and the flexure hinge. Several high frequency ultrasonic transducers with different flexible clamps were designed and fabricated. A measurement system was specially set up to investigate the vibration characteristics of the transducers. Results show that the proposed flexible mounting clamps are able to increase the tip vibration amplitude output of the transducer significantly, whether the transducer vibrates at resonance or not. The promotion effect is closely related to the compliance and the decoupling potential of the clamp. The method newly proposed is a meaningful and useful attempt, and it also can be used for the ultrasonic transducers in other applications.

3J1-1 Development of high intensity and high frequency ultrasonic transducers using piezoelectric films

3J1-1 Development of high intensity and high frequency ultrasonic transducers using piezoelectric films

Design and fabrication of high frequency ultrasonic transducer based on lead-free Mn-doped (K0.44Na0.56)NbO3 single crystal

In this work, a high-frequency lead-free ultrasonic transducer was designed and fabricated based on high-performance (K0.44Na0.56)NbO3-0.5mol%Mn (Mn-KNN) piezoelectric single crystal. The Krimholtz, Leedom, and Mattaei (KLM) equivalent circuit model was utilized to simulate and optimize the pulse-echo response combined with PiezoCAD software. Theoretically a ∼20MHz medical ultrasonic transducer with an optimized bandwidth up to 85.1% was obtained. The experimental results exhibited a center frequency of 20.9MHz with −6dB bandwidth of 65.3%. The excellent acoustic performance makes this lead-free single-crystal transducer potential for practical applications.

High frequency transducer for vessel imaging based on lead-free Mn-doped (K0.44Na0.56)NbO3 single crystal

We report a high frequency ultrasonic transducer up to 50 MHz for vessel imaging based on a lead-free (K0.44Na0.56)NbO3–0.5 mol. % Mn (Mn-KNN) single crystal, which has a high electromechanical coupling coefficient kt of 0.64 and a large thickness frequency constant Nt of 3210 kHz · mm. The Krimholtz, Leedom, and Mattaei (KLM) equivalent circuit model was utilized to simulate and optimize the pulse-echo response combined with PiezoCAD software. Theoretically, a high -6 dB bandwidth of 74.94% was obtained at a center frequency of 50.47 MHz and optimized matching conditions. The experimental results showed a center frequency of 51.8 MHz with a −6 dB bandwidth of 70.2%. The excellent global performance makes this lead-free single-crystal transducer quite potential in an environmentally friendly vessel imaging transducer.

High frequency and high intensity ultrasonic transducers for medical applications using oriented piezoelectric thick films by hydrothermal method

Recently, high-frequency ultrasonic transducers are proposed for medical applications using piezoelectric crystal. In this case, it is known that the high piezoelectric constant and the higher limitation of vibration velocity are important for high power application. Normally, the piezoelectric ceramics has limitation due to maximum vibration velocity. Thus it is very difficult to radiate for high intensity ultrasound with nonlinear acoustics due to the limitation of maximum vibration velocity. Therefore, we tried to develop a very high intensity and high frequency ultrasonic transducer using hydrothermal KNbO3 thick film. The piezoelectric constant was over 80 pm/V and the vibration velocity of thickness mode of KNbO3 thick film was 2.5 m/s or over at 20 MHz. This maximum vibration velocity is twice of reported piezoelectric materials. Then, a radiation sound-pressure from the prototype ultrasonic transducer with KNbO3 thick film was measured. The result of radiation ultrasound was 4 MPa or over in a wat...