High-performance Ultrasonic Transducers Research Articles

Investigations of high-Performance Ultrasonic Transducers based on PMN-PT Single Crystals

Ultrasonic transducers for NDE applications are commonly based on Lead Zirconate Titanate or PZT, an inorganic compound and ceramic perovskite material. Until now the advantages of PMN-PT are used in medical applications, but are not implemented in NDE. Lead Magnesium Niobate-Lead Titanate (PMN-PT) is well known for its high sensitivity and broad frequency spectrum. While conventional PZT materials have an electromechanical coupling factor K33 (a measure of the conversion between electrical and acoustic energy) of about 0.72, PMN-PT materials reach peak values of more than 0.93. For applications with low signal amplitudes, high electronic noise and small transducer elements, the performance of ultrasonic probes can be significantly enhanced by using Lead Magnesium Niobate-Lead Titanate (PMN-PT) instead of PZT. This single-crystal material offers significantly better piezo parameters and leads to a higher sensitivity and larger bandwidth. There is a better depth resolution possible with this transducers as practical tests have shown. Similar to PZT it can also be fabricated in 1-3 piezo- composite technology. In a cooperation between Fraunhofer IKTS, iBULe Photonics, and IFU Diagnostic Systems, PMN-PT ultrasonic transducers are developed and optimized. The performance of phased array probes and single element transducers was measured by a so called PCUS® pro electronic front end from Fraunhofer and compared with equivalent PZT-based probes. As a result various single element and phased array transducers with im-proved performances are available for NDT of typical aerospace materials and applications. These test setups were used to weigh up the advantages and disadvantages, such as achievable precision or costs, for the implementation of a PMN-PT-based UT matrix probe. Based on this, a wiring variant adapted to the PMN-PT was developed and optimised for the matrix setups by pre- assembling the matching layers. The most favourable setup turned out to be bonding the PMN- PT composites to the prefabricated matching layers together with a rigid-flexible PCB frame. This enabled direct wire bonding of 64 matrix elements to the matching PCB pads on the rigid frame.

Broadband ultrasonic transducer based on nested composite structure with gradient acoustic impedance

This study introduces an innovative Broadband Ultrasonic Transducer employing a Nested Composite Structure with Gradient Acoustic Impedance, significantly enhancing the performance in medical diagnostics and non-destructive testing. The developed transducer, based on a unique nested PZT/epoxy composite design, achieves an optimized acoustic impedance gradient from 36.56 MRayls to 4.53 MRayls. This strategic design effectively addresses the impedance mismatch, a long-standing challenge in ultrasonic imaging. Rigorous Finite Element Analysis (FEA) using PZFlex software indicates that the transducer offers a −6 dB bandwidth of 69.31%, a substantial improvement over the existing models. Experimental results corroborate with theoretical predictions, demonstrating enhanced bandwidth (∼71.24%) and transmission efficiency. This advancement highlights the potential of gradient impedance in fabricating high-performance ultrasonic transducers, setting a new benchmark for ultrasonic imaging applications.

Simulation and structural design of 2–2 PIMNT/epoxy piezoelectric composites

Piezoelectric materials are commonly used in transducers to convert electromechanical signals due to their energy conversion characteristics. We designed a PIMNT/epoxy 2–2 composite to take full advantage of the excellent beam-mode piezoelectric and acoustic features of PIMNT single crystals. Following the approach used for piezoelectric ceramic composites, we selected PIMNT piezoelectric single crystal and EPO-TEK301-2 epoxy resin for the composite, and combined finite element analysis with experimental preparation. We prepared, tested and analyzed 2–2 piezoelectric single crystal composites with varying volume fractions, which showed high electromechanical coupling properties ([Formula: see text]%) and low acoustic impedance ([Formula: see text][Formula: see text]MRayl). These encouraging findings suggest the possibility of devising high-performance ultrasonic transducers utilizing the PIMNT/epoxy 2–2 composite.

High-performance ultrasonic transducer based on PZT piezoelectric ceramic for high-temperature NDE

Piezoelectric ultrasonic transducers (PUT) are applied in a wide range of fields such as non-destructive evaluation (NDE), medical imaging and petroleum exploration, etc. Nevertheless, most PUTs cannot achieve high performance and high operating temperatures simultaneously because of the inverse correlation between piezoelectric property and operating temperature. In this paper, a high-performance ultrasonic transducer based on PZT-5A type piezoelectric ceramic (S35) for high-temperature NDE over 300 °C was proposed. Firstly, it is found that the d33, kp, and kt of the S35 ceramic plate show great temperature stability from 50 °C to 300 °C, which is attributed to the stabilisation of the phase structure and no occurrence of obvious depolarization behavior before the Curie temperature. And then, a single-element PUT based on S35 was fabricated, and pulse-echo tests from 50 °C to 300 °C in confined heating environments were executed. The peak-to-peak value (Vpp) varies from 2.58 V to 0.753 V, which results from the increase of the permittivity of the piezoelectric element and the degradation of the acoustic contact, and the −6dB BW demonstrates excellent temperature stability with a variation less than 10%. These results indicate the great potential of this high-performance ultrasonic transducer for high-temperature NDE.

Electrical Characteristics of High-Performance Ultrasonic Transducer for Non-Destructive Testing

Electrical Characteristics of High-Performance Ultrasonic Transducer for Non-Destructive Testing

(Invited) Adding a New Sensing Dimension to Soft Electronics: From the Skin to below the Skin

Soft electronic devices that can noninvasively and continuously acquire vital signs from the human body represent an important trend for healthcare. Combined strategies of materials design and advanced microfabrication allow the integration of a variety of components and devices on a soft platform, resulting in functional systems with minimal constraints on the human body. In this presentation, I will demonstrate a wearable multichannel patch that can sense a collection of signals from the human skin in a wireless mode. Additionally, integrating high-performance ultrasonic transducers on the stretchable substrate adds a new third dimension to the detection range of conventional soft electronics. Ultrasound waves can penetrate the skin and noninvasively capture dynamic events in deep tissues, such as blood pressure and blood flow waveforms in central arteries and veins. This soft platform holds profound implications for a wide range of applications in consumer electronics, sports medicine, defense, and clinical practices. Figure 1

An optimization design strategy of 1–3 piezocomposite ultrasonic transducer for imaging applications

An optimization design strategy based on finite element method (FEM) and particle swarm optimization (PSO) algorithm is developed to fabricate high-performance 1–3 piezocomposite ultrasonic transducer. In this strategy, the structure and performance of ultrasonic transducer are simulated by FEM based PZFlex software to analyze the effect of design parameters (ceramic volume fraction and kerf width) on its performance. Due to the time-consuming of FEM simulation, based on the data obtained by simulations, artificial neural network models are established to describe the mapping relation of the design parameters and performance parameters (center frequency and high electromechanical coupling coefficient). The multi-objective optimization criterion is constructed for ultrasonic transducer, and then the modified PSO algorithm are adopted to optimize design parameters. According to the optimized design parameters, the FEM simulation and experiment are conducted to validate the effectiveness of the developed strategy. The simulation and experiment results are in agreement with the designed performance, which indicates that the developed strategy can be used to optimize design parameters for fabricating high-performance ultrasonic transducer. In addition, the imaging experiments of tungsten wires and RMB coin prove the high imaging performance of the ultrasonic transducer fabricated by the developed strategy.

Magnesium Alloy Matching Layer for PMN-PT Single Crystal Transducer Applications.

In this paper, we propose using magnesium alloy as the matching layer for the ultrasonic transducer made of 0.68 Pb(Mg1/3Nb2/3)O3-0.32PbTiO3 (PMN-0.32PT) single crystal. The complete sets of elastic constants of AZ31B, GW83, and ZK60 magnesium alloys have been measured, which is practically a homogeneous material. The AZ31B magnesium alloy has an acoustic impedance of 10.36 MRayl, which is suitable for the development of high-performance ultrasonic transducers. A 3.5-MHz PMN-PT single crystal transducer has been designed and fabricated successfully using AZ31B magnesium alloy as the first quarter-wavelength matching layer. The -6-dB bandwidth and two-way insertion loss at the center frequency of the transducer are about 67% and 11.4 dB, respectively, much superior to the transducer fabricated using 0-3 composite matching layer. The high performance of this transducer indicates that the magnesium alloy is indeed an excellent matching layer material for ultrasonic transducer applications.

Dice-and-fill processing and characterization of microscale and high-aspect-ratio (K, Na)NbO3-based 1–3 lead-free piezoelectric composites

Piezoelectric composites with high-aspect-ratio lead-free piezoelectric microrods embedded in a polymer matrix were fabricated by applying the modified dice-and-fill method to a (K,Na)NbO3-based piezoelectric ceramic, 0.9475[Li0.02(K0.48Na0.53)0.98](Nb0.80Ta0.20)O3–0.0525AgSbO3–0.5wt% MnO2 (abbreviated as LKNNT–AS–M) with enhanced piezoelectricity but low mechanical strength. The Pb-free LKNNT–AS–M/polymer composite specimens containing ∼10–23vol% ceramic pillars with sectional width ∼50μm, separation ∼55–110μm and high aspect ratio ∼11, were prepared and investigated with an emphasis on their electrical properties. The developed composites possess a higher thickness factor kt ∼63–67%, lower planar factor kp ∼27–34% and enhanced kt/kp ratio ∼2.3. The composites also possess favorable properties which includes low electrical (tanδ ∼0.029) and mechanical (Qm ∼6) losses, low acoustic impedance Z ∼4.2–7.8Mrayl and ∼5 times higher voltage coefficient g33 compared to LKNNT–AS–M piezoceramic. The promising results indicate that the LKNNT–AS–M/polymer composites have the potential to be used as active elements in high performance ultrasonic transducers.

Ternary piezoelectric single-crystal PIMNT based 2-2 composite for ultrasonic transducer applications

In order to take the full advantage of excellent beam-mode piezoelectric and acoustic properties of Pb(In1/2Nb1/2)O3–Pb(Mg1/3Nb2/3)O3–PbTiO3 (PIMNT) single crystal, PIMNT/epoxy 2-2 composite was designed and prepared with PIMNT volume percent of 69. Excellent properties for ultrasonic transducer applications were achieved, including ultrahigh thickness electromechanical coupling coefficient (kt=86%), large piezoelectric coefficient (d33=1200pC/N), and low acoustic impedance (Z~20MRayls). Based on the improved properties, a 2MHz PIMNT/epoxy 2-2 composite ultrasonic transducer was designed, fabricated, and its performance was compared with a PIMNT/epoxy 1-3 composite ultrasonic transducer and a PIMNT single-crystal ultrasonic transducer, respectively. The PIMNT/epoxy 2-2 composite ultrasonic transducer showed a significant enhancement in both relative pulse-echo sensitivity and −6dB bandwidth, which were 4dB higher and 20% broader than those of the PIMNT single-crystal ultrasonic transducer and as excellent as the PIMNT/epoxy 1-3 composite ultrasonic transducer. These promising results suggested the great potential for developing high-performance ultrasonic transducers using the PIMNT/epoxy 2-2 composite.

35 MHz PMN-PT Single Crystal Annular Array Ultrasonic Transducer

Lead magnesium niobate–lead titanate (PMN–PT) single crystal has ultra-high piezoelectric properties compared with conventional piezoelectric materials and is suitable for high-performance ultrasonic transducer application. In this paper, an improved process has been used for fabricating an annular array ultrasonic transducer using PMN-PT single crystal. A 35 MHz annular array with 8 elements has been built. The bandwidth of the array elements were around 45%. At the center frequency, the insertion loss ranged from −21dB to −28dB. The electrical cross-talk between the adjacent elements was in a range of −24dB to −31dB.

Lead-free piezoelectric single crystal based 1–3 composites for ultrasonic transducer applications

In this work, lead-free 1–3 composites based on piezoelectric 0.947Na0.5Bi0.5TiO3–0.053BaTiO3 (NBT–0.053BT) single crystal and epoxy are fabricated for ultrasonic transducer applications by a modified dice-and-fill method. Excellent properties for ultrasonic transducer applications have been achieved, such as high electromechanical coupling coefficient (kt=73%), lower acoustic impedance (Z=16MRayl) and moderate dielectric constant. Based on this lead-free piezoelectric single crystal composite, single-element ultrasonic transducer and linear array have been fabricated and characterized. Both types of transducers exhibit similar performance with broad bandwidth of exceeding 100%. The promising results show that these lead-free composites have the potential to be used for high-performance ultrasonic transducers.

Nonlinear piezoelectricity in PZT ceramics for generating ultrasonic phase conjugate waves

We have succeeded in the generation of acoustic phase conjugate waves with nonlinear PZT piezoelectric ceramics and applied them to ultrasonic imaging systems. Our aim is to make a phase conjugator with 100% efficiency. For this purpose, it is important to clarify the mechanism of acoustic phase conjugation through nonlinear piezoelectricity. The process is explained by the parametric interaction via the third-order nonlinear piezoelectricity between the incident acoustic wave at angular frequency ω and the pump electric field at 2 ω. We solved the coupling equations including the third-ordered nonlinear piezoelectricity and theoretically derived the amplitude efficiency of the acoustic phase conjugation. We compared the efficiencies between the theoretical and experimental values for PZT ceramics with eight different compositions. Pb[(Zn 1/3Nb 2/3) 1− X Ti X ]O 3 ( X=0.09, PZNT91/9) piezoelectric single crystals have been investigated for high-performance ultrasonic transducer application, because these have large piezoelectric constants, high electrical–mechanical coupling factors and high dielectric constants. We found that they have third-order nonlinear piezoelectric constants much larger than PZT and are hopeful that the material as a phase conjugator has over 100% efficiency.

The performance of a 1–3 mode piezocomposite ultrasonic transducer in relation to the properties of its polymer matrix

For the further development of a 1–3 mode piezocomposite ultrasonic transducer, this paper investigates both experimentally and theoretically the effects of a polymer matrix on the performance of a transducer and identifies the direct relationship. It is important for a polymer matrix to have a low density and low acoustic impedance in order to facilitate a high sensitivity, large bandwidth and small ringdown time in the transducer. In addition, a polymer should comply with the structural requirement of good adhesion to the piezoceramic pillars, with no inclusion of pores. However, adhesion strength does not play a vital role once it exceeds a certain level. Thus, when selecting a matrix polymer a higher priority should be placed on the exclusion of pores after curing. The importance of these requirements was verified through experimentation. After testing many types of commercially available polymers, UPR (Unsaturated Polyester Resin) matched all the requirements and gave the best performance in line with the theoretical simulation results. The results in this paper can be directly utilized in the selection of appropriate polymers for matrices for 1–3 mode piezocomposite materials and in the further development of high performance ultrasonic transducers.

High Performance Ultrasonic Transducers Employing ZnO/Pyrex-glass Diaphragm Structure on a Si Substrate

The paper describes the development of high performance underwater ultrasonic transducers employing ZnO/Pyrex-glass composite diaphragm structure on a Si substrate. It is shown that the transducer successfully radiates and detects ultrasonics at the fundamental frequency of 155 MHz with a relative -3 dB band width of 11.1% and a minimum transduction loss of 4.3 dB, both of which are in good agreement with theoretical prediction. The possibility of the application of the transducer to sensor devices is described for the measurement of ultrasonic wave velocity in liquid.