Piezocomposite Transducer Research Articles

A Composite Fuselage under Mechanical Load: a case study for Guided Wave-based SHM

The introduction of composite materials in aeronautics has brought numerous advantages, along with unique damage and failure modes. The structure health is currently ensured by a damage-tolerant design and non-destructive inspections. Among other techniques, Guided Wave-based Structural Health Monitoring (GW-SHM) has gained interest as a cost and time effective alternative to traditional non-destructive techniques. One of the main challenges for GW-SHM is the influence of environmental and operational conditions on the damage identification capability. Aircraft structures undergo a broad range of mechanical load conditions, affecting the GW-SHM system. The study of load influence is meaningful in view of applications where the SHM system is expected to work under varying load conditions. Such applications may be in-flight monitoring, but also on-ground only usage and structural test monitoring. A full-scale CFRP door surrounding structure was instrumented with a GW-SHM system and tested under mechanical load. A hydraulic test rig was used to apply three representative load cases in quasi-static conditions on the structure. A network of robust piezocomposite transducers to monitor the structure has been designed and manufactured. The network is organized in arrays, which include the transducers, cabling and a connecting base plate for optimized sensor installation. A multiplexing module is directly connected to the base plate enabling a fast and reliable sensor connection, a drastic cable weight reduction, and a modular design. The combined influence of load and temperature on the propagation of Guided Waves has been assessed. Finally, a data-driven approach to damage identification has allowed the detection and localization of barely visible impact damage introduced during the test campaign.

Neuro-Evolutionary Framework for Design Optimization of Two-Phase Transducer with Genetic Algorithms.

Multilayer piezocomposite transducers are widely used in many applications where broad bandwidth is required for tracking and detection purposes. However, it is difficult to operate these multilayer transducers efficiently under frequencies of 100 kHz. Therefore, this work presents the modeling and optimization of a five-layer piezocomposite transducer with ten variables of nonuniform layer thicknesses and different volume fractions by exploiting the strength of the genetic algorithm (GA) with a one-dimensional model (ODM). The ODM executes matrix manipulation by resolving wave equations and produces mechanical output in the form of pressure and electrical impedance. The product of gain and bandwidth is the required function to be maximized in this multi-objective and multivariate optimization problem, which is a challenging task having ten variables. Converting it into the minimization problem, the reciprocal of the gain-bandwidth product is considered. The total thickness is adjusted to keep the central frequency at approximately 50-60 kHz. Piezocomposite transducers with three active materials, PZT5h, PZT4d, PMN-PT, and CY1301 polymer, as passive materials were designed, simulated, and statistically evaluated. The results show significant improvement in gain bandwidth compared to previous existing techniques.

Design of sonar receivers for shallow water buried object imaging

Downward looking synthetic aperture sonar can detect and localize proud and buried objects, such as unexploded ordinance (UXO), in very shallow water environments. These sensors generate three-dimensional imagery from a two dimensional array that is a hybrid of a synthetic and real aperture sonar. Achieving high-resolution imaging with these sensors places stringent requirements on the sonar hardware. The acoustic signals generated by the sensor are wide bandwidth, low frequency, and high dynamic range. Receiver spacing and directivity also play an important role in image quality but create competing design constraints at low frequency. This work will present the results of a recent design study to develop receivers for a buried UXO imaging system. Achieving the stringent hardware requirements necessitated that the transducers, baffle, housing, and electronics were designed in concert. Finite element and one-dimensional models were used to evaluate several candidate designs based upon piezocomposite, spherical, and hemispherical transducers and identify tradeoffs with each. The analysis will focus on both simulated and experimental results of the receiver components. Results from the component level also informed system level models to quantify the point spread function and resolution improvement of the sensor.

Simulation and Optimization of Ultrasonic Transducer

The ultrasonic transducers have numerous applications in industries, including medical probes for performing ultrasound scans. One of the significant drawbacks of the ultrasonic transducer is the wastage of a large portion of energy, due to high acoustic impedance, while transmitting ultrasonic waves to the target object. The present study is aimed to investigate the material design of the piezo-composite transducer and improve its performance. Different piezo-composite transducers were simulated in the COMSOL environment by varying input parameters, and three key performance indicators (KPI) were calculated. Many constraint-based multivariable optimization algorithms have been used to maximize the KPIs. A set of parameters, such as Sensitivity and Fractional Bandwidth, have been found to increase the performance of piezo-composite transducer model and its overall efficiency. This study is intended to impinge unidirectional property to the transducer which is found to be beneficial in more accurate medical as well as structural reports and cost savings.

Design and Development of a Solar Electric Delivery Pod

The ultrasonic transducers have numerous applications in industries, including medical probes for performing ultrasound scans. One of the significant drawbacks of the ultrasonic transducer is the wastage of a large portion of energy, due to high acoustic impedance, while transmitting ultrasonic waves to the target object. The present study is aimed to investigate the material design of the piezo-composite transducer and improve its performance. Different piezo-composite transducers were simulated in the COMSOL environment by varying input parameters, and three key performance indicators (KPI) were calculated. Many constraint-based multivariable optimization algorithms have been used to maximize the KPIs. A set of parameters, such as Sensitivity and Fractional Bandwidth, have been found to increase the performance of piezo-composite transducer model and its overall efficiency. This study is intended to impinge unidirectional property to the transducer which is found to be beneficial in more accurate medical as well as structural reports and cost savings.

Underwater single crystal piezocomposite transducer with extended usable frequency band

A single crystal/epoxy 1–3 composite plate transducer with air backing and two acoustic matching layers was modelled, fabricated and compared to a similar PZT transducer. For the relevant underwater applications, the usable frequency band is restricted by reactive electrical power. The design goal was to provide an underwater transmitter that could be operated over a wide range of frequencies, but not necessarily create a single pulse spanning the entire frequency band. The thicknesses and the characteristic acoustic impedances of the matching layers were therefore optimized for a wide passband rather than a maximally flat passband. The resulting single crystal transducer had reactive power below 50 % in a frequency band 132 % wide relative to the center frequency.

Determination of homogenized material constants of the 2–2 mode piezocomposite

2–2 mode piezocomposites are widely used for the drive section of acoustic transducers. Typically, piezocomposites have been developed using theoretical or numerical methods such as the finite element method. However, rigorous analysis of piezocomposites has always been difficult due to their complicated two-phase structure, which necessitates homogenization of the structure with a single-phase material with properties identical to those of the original two-phase piezocomposite. In this study, we determined the material properties of the equivalent single-phase material using the resonator method. The asymptotic averaging method was used to obtain the initial properties of the homogenized material, which had some accuracy limitations. We improved the accuracy by using multiple resonators, each of which reflected the effect of different material constants. We adjusted the material constants that influence each resonator to minimize the difference between the original piezocomposite’s resonant and antiresonant frequencies and those of the equivalent single-phase material. The optimization technique was used to facilitate this adjustment. The homogenized material with the optimized material constants represented the original two-phase piezocomposite very well. The new method proposed in this study to homogenize the 2–2 mode piezocomposites can be applied to the accurate design of various piezocomposite transducers.

Matching layer design of a 2–2 piezo-composite ultrasonic transducer for biomedical imaging

Matching layer design of a 2–2 piezo-composite ultrasonic transducer for biomedical imaging

Optimization of Matching Layers to Extend the Usable Frequency Band for Underwater Single-Crystal Piezocomposite Transducers.

The ongoing robotic revolution in oceanic science puts new requirements on sonar technology. Small platforms require compact multi-purpose transducers, with strict requirements on power consumption and heat dissipation. Introducing single-crystal ferroelectrics as the active material of the transmitter can be one way of meeting the new requirements. The large electromechanical coupling coefficient of single crystals can enable an extension of the usable frequency band compared to conventional PZT. For the applications considered in this work, the usable frequency band is restricted by both the transmitted acoustic power and the reactive electrical power. Single crystals as the active materials can double the usable band, but the acoustic matching required for this can be difficult to obtain in practice. We investigated an air-backed, plane 1-3 composite transducer, matched to water by acoustic matching layers. For many applications, the diversity provided by a large usable frequency range is more important than a flat acoustic power response, and the transducer can be used far beyond the -3-dB limit. We defined the usable band by requiring maximum -12-dB ripple in transmitted acoustic power and maximum 50% reactive power. The matching layers were optimized to maximize the usable band according to this definition, in contrast to the conventional approach where matching layers are optimized for maximally flat response. Under the chosen definitions, our modeling showed that with a single crystal as the active material we could achieve 188% usable frequency band relative to the resonance frequency, compared to 121% for a PZT.

Wave attenuation in 1-3 phononic structures with lead-free piezoelectric ceramic inclusions

The unit cell wave attenuation of elastic Bloch waves in 1-3 piezoelectric phononic structures with BaTiO3 inclusions in a polymeric matrix is reported. This attenuation can be observed by the evanescent Bloch waves in the complex dispersion diagram of the periodic piezoelectric ceramic structure. Full and complete Bragg-type band gaps are observed. The piezoelectricity of the periodic lead-free ceramic inclusions improves the band gap width and wave attenuation in a specific frequency spectrum. These characteristics can be used for the wave attenuation design using smart periodic structures, for surface acoustic wave (SAW) filter and 1-3 piezocomposite transducer design using piezoelectric phononic structures with BaTiO3 inclusions.

Cold ablated high frequency PMN-PT/Epoxy 1-3 composite transducer

PMN-PT has excellent piezoelectric properties, but its fragileness limits its application in high-frequency transducers. 1-3 composite materials based on PMN-PT and Epoxy can maintain excellent piezoelectric properties as well as machining capacity. However, the current process such as dicing and backfilling, tape casting, etc. has its shortcomings, such as time-consuming, insufficient precision, complex process, and so on. Therefore, in this work, a cold ablation process method is investigated to prepare the PMN-PT/Epoxy 1-3 composite, and a high frequency piezocomposite transducer is developed. The finite element method (FEM) is built to optimize the technical parameters. The 1-3 composite material is prepared using the cold laser ablation technique with ultraviolet picosecond pulse, and the corresponding transducer is fabricated. Experimental results show that the transducer has a center frequency of 52.1 MHz and a bandwidth of 73.3%. Its imaging resolution is superior to 25 μm. The results verify the feasibility of the cold ablation method in fabricating PMN-PT/Epoxy 1-3 composite, which is very suitable for high-frequency ultrasound imaging.

Intelligent optimization design of 2–2 piezo-composites for ultrasonic transducer

2–2 piezo-composite material (PCM) with high electromechanical coupling coefficient and low acoustic impedance is a kind of common PCMs for fabricating piezo-composite ultrasonic transducer (PCUT). The performance of PCUT is obviously influenced by the design parameters (DPs) of 2–2 PCM, such as its thickness, kerf, and slice width. Combining the finite element analysis simulation and artificial intelligence methods, an intelligent optimization design method is proposed to optimize the DPs of 2–2 PCM to fabricate high-performance 2–2 PCUT. In the proposed method, the neural network models are trained by the simulation data to build up the relationship between the DPs and the performance of PCUT. Using the optimization criteria established based on the center frequency (CF), bandwidth (BW), and peak-to-peak voltage (PV), the modified particle swarm optimization algorithm is employed to determine the DPs of 2–2 PCM. The desired CF, BW, and PV are 4 MHz, 40% and 3.2 V, and the optimized thickness, kerf and slice width of 2–2 PCM are 376 µm, 69.6 µm, and 34.4 µm, respectively. Finally, the optimized 2–2 PCUT is fabricated based on the optimized DPs, and then characterized systematically. The optimized 2–2 PCUT exhibits a CF of 4.57 MHz, a BW of 41.6%, a PV of 2.89 V, and an electromechanical coupling coefficient of 0.71. The simulation and experiment results are consistent with the designed targets, which verifies the availability of the proposed method.

Homogenized electromechanical coefficients and effective parameters of 1–3 piezocomposites for ultrasound imaging transducers

Analytical models can be useful tools to develop efficient transducers dedicated to a specific application field. This work proposes a homogenization technique for establishing the effective coefficients and parameters of 1-3 piezocomposite whose both phases are piezoelectrically active. Such piezocomposite materials may have homogenized electromechanical properties resulting from positive hybrid effect. A numerical simulation of the effective parameters resulting from a PZT-5A / PVDF-TrFE composition shows that, volume fraction influences significantly on the properties of the piezocomposite and consequently on its behaviour in service. As an end-user application for ultrasound imaging, those piezocomposite materials are effectively integrated in a piezocomposite transducer, coupled with a dedicated backing. The resulting characteristics in terms of impulse response and associated electroacoustic echo are compared and discussed for typical configurations. A method for the optimization of the design of such piezocomposite transducer is presented. Specific estimators based on the bandwidth flatness BWF and bandwidth amplitude product BWA are proposed as stable and smooth criteria for an optimization procedure.

Dispersion Diagram of Trigonal Piezoelectric Phononic Structures with Langasite Inclusions

The dispersion relation of elastic Bloch waves in 1-3 piezoelectric phononic structures (PPnSs) with Langasite (La3Ga5SiO14) inclusions in a polymeric matrix is reported. Langasite presents promising material properties, for instance good temperature behaviour, high piezoelectric coupling, low acoustic loss and high quality factor. Furthermore, Langasite belongs to the point group 32 and has a trigonal structure. Thus, the 2-D bulk wave propagation in periodic systems with Langasite inclusions cannot be decoupled into XY and Z modes. The improved plane wave expansion (IPWE) is used to obtain the dispersion diagram of the bulk Bloch waves in 1-3 PPnSs considering the classical elasticity theory and D3 symmetry. Full band gaps are obtained for a broad range of frequency. The piezoelectricity enhances significantly the band gap widths and opens up a narrow band gap in lower frequencies for a filling fraction of 0.5. This study should be useful for surface acoustic wave (SAW) filter and 1-3 piezocomposite transducer design using PPnSs with Langasite.

Ceramic additive manufacturing for enhanced piezocomposite transducers

Ceramic additive manufacturing for enhanced piezocomposite transducers

Micromachined High Frequency 1-3 Piezocomposite Transducer Using Picosecond Laser.

In this article, a PZT/Epoxy 1-3 piezoelectric composite based on picosecond laser etching technology is developed for the fabrication of high-frequency ultrasonic transducer. The design, fabrication, theoretical analysis, and performance of the piezocomposite and transducer are presented and discussed. According to the test results, the area of the PZT pillar is [Formula: see text], the average width of the kerf is [Formula: see text], and the thickness of the piezocomposite is [Formula: see text]. The fabricated 1-3 piezocomposite has a resonant frequency of 46.5 MHz, a parallel resonant frequency of 65 MHz, and an electromechanical coupling coefficient of 0.73. According to the wires phantom imaging, its imaging resolution can reach [Formula: see text]. This study shows that the proposed picosecond laser micromachining technique can be applied in the fabrication of high frequency 1-3 piezocomposite and transducer.

Optical ultrasound (OpUS): a novel concept for intravascular imaging

Abstract Aims To evaluate whether Optical Ultrasound (OpUS), a novel method for performing ultrasound imaging, could provide compelling, real-time visualizations of coronary vasculature. Methods and results With current commercial intravascular ultrasound (IVUS) devices, piezoelectric transducers are used to electrically generate and receive Ultrasound (US). With this paradigm, there are several challenges that limit further improvement in image resolution. Firstly, with increasing miniaturization of these piezoelectric transducers it can be difficult to achieve adequate sensitivity and bandwidth for high resolution imaging. Secondly, the complexities associated with fabricating and electrically connectorising broadband piezocomposite transducers can result in high manufacturing costs. Lastly, with increasing interest in identifying the molecular composition of atherosclerotic plaque, it has been challenging to achieve high resolution and high imaging depths, whilst also allowing for hybrid imaging with photoacoustics (PA) or near-infrared spectroscopy (NIRS). With OpUS, US is generated at the surface of a fibre optic transducer via the photoacoustic effect. Here, pulsed or modulated light from a laser source is transmitted along the fibre, absorbed in a coating on the fibre surface and converted to thermal energy. The subsequent heat rise leads to a corresponding pressure rise within the coating which propagates as ultrasound. This process is facilitated through the use of custom, engineered nanocomposite materials comprising an optical absorber with an elastomeric host. US reflections from tissue are received with optical interferometry in a method similar to optical coherence tomography (OCT) signal interrogation. For this study we included these elements into a probe and imaged ex-vivo coronary artery tissue. A novel, optically-selective nanocomposite coating enabled concurrent OpUS and PA imaging for molecular contrast using the same imaging probe. Using OpUS we demonstrated high resolution imaging (<40 microns axial), large imaging depths (>2 cm) of coronary tissue and performed a comparison with histology. Numerous features of atherosclerotic plaque were identifiable, including a lipid pool, a calcified nodule, and the different layers comprising the vessel wall. The fiber-optic transducer generated ultra-high pressures and bandwidths: 21.5 MPa and 39.8 MHz respectively. Hybrid imaging using OpUS and PA was also demonstrated, highlighting regions with high lipid content. Conclusion This new platform for intravascular imaging offers high resolution equivalent to 60 Mhz high-definition IVUS whilst maintaining deep tissue penetration. Hybrid imaging with PA can be used for directly visualizing lipid plaque. OpUS transducers are highly flexible, with small diameters (<400 microns) and have low fabrication costs, making them well suited for incorporation into interventional devices. Funding Acknowledgement Type of funding source: Private grant(s) and/or Sponsorship. Main funding source(s): Wellcome Trust/EPSRC, National Institute for Health Research Biomedical Research Centre - University College London

The electro-acoustic output behavior and thermal stability of 1–3 piezoelectric composite transducers applied to FUS surgery

For 1–3 piezoelectric composite high-power transducers applied to FUS surgery, avoiding the electro-acoustic output performance fluctuating with the temperature is an important task. In this work, 1–3 type piezocomposites were fabricated with dice and fill method. The PZT4 piezoceramic was used as active phase, and mica powder modified epoxy resin E51 was used as passive phase: the mass ratio of the epoxy and mica powder was 10:x. Those composites were evaluated for power transducer applications with air backing and without front layer. The effect of mica powder modified polymer filler on the electro-acoustic output behavior and thermal stability of the transducer were detailed investigated. The results show that mica power could increase the storage modulus and the toughness of the polymer. As a result, an elevated kt of 0.7 was observed when the adding amount was 50 wt%. The electro-acoustic conversion efficiency (ηea) of the transducer substantial increased to 81–83% and with good thermal stability when x = 1–5. The research results show that adding mica powder in the filler materials was one of the potential methods to prepare high-power piezocomposite transducer.

Ultrasonic Propagation in Highly Attenuating Insulation Materials.

Experiments have been performed to demonstrate that ultrasound in the 100–400 kHz frequency range can be used to propagate signals through various types of industrial insulation. This is despite the fact that they are highly attenuating to ultrasonic signals due to scattering and viscoelastic effects. The experiments used a combination of piezocomposite transducers and pulse compression processing. This combination allowed signal-to-noise levels to be enhanced so that signals reflected from the surface of an insulated and cladded steel pipe could be obtained.

The theoretical model of 1–3 piezocomposite transducer with matching layer

To guide the design of 1–3 piezocomposite transducer with matching layer, a theoretical model was established using electromechanical equivalence principle and acoustics theory. The transmitting voltage response equation of the transducer was obtained. Then, the dependences of the transmitting voltage response and bandwidth on matching layer parameters were analyzed. The transducer samples were prepared and tested. Test result reveals that the experiment result is consistent with the theoretical model, and it is indicated that the theoretical model can effectively predict transducer performance.