Optimization Design of Ultrasonic Transducer With Multimatching Layer.

Due to the low efficiency of traditional design method, an efficient optimization design method is developed to design and fabricate high-performance ultrasonic transmitting transducer (UTT) based on PiezoCAD software and particle swarm optimization (PSO) algorithm. Based on the data of design and performance parameters of UTT obtained by PiezoCAD software, the genetic algorithm-based back-propagation neural networks (GA-BPNNs) are established to describe their mapping relationship. The optimality criterions are established based on the performance parameters including center frequency (CF) and maximum echo amplitude (MEA). Then, based on the established GA-BPNNs and optimality criterions, the optimization design method of UTT is developed under the framework of PSO algorithm. According to the desired performance, the design parameters of UTT, including the thickness and diameter of PZT-4 (Pb(Zr x Ti1-x)O3), the acoustic impedance of backing, are optimized by the developed method, and they are 2 mm, 30 mm and 3 MRayl, respectively. Based on the optimized design parameters, the CF and MEA simulated by PiezoCAD are 1.05 MHz and -45.1 dB, which are in good agreement with the designed ones (1 MHz and -45 dB). In addition, the CF of the fabricated UTT is 1.07 MHz, and its insertion loss is -7.2 dB at 1.075MHz, which implies that the fabricated UTT has excellent performance. Therefore, the developed optimization design method is effective to fabricate high-performance UTT.

Inversion layer technique can increase the centre frequency ( f 0 ) and the −6 dB bandwidth of the ultrasound transducer without reducing thickness of active material. However, it suffers from the reduced −6 dB bandwidth when the centre frequency is increased more than 1.5 f 0 . A modified inversion technique is proposed and applied it to high‐frequency intravascular ultrasound (IVUS) transducer. The performance was computationally verified by using finite element method (FEM) simulation. The proposed IVUS transducer consists of two sub‐elements with each aperture size of 0.6 × 0.6 mm, and each sub‐element has different types of inversion layer using PMN‐PT and PZT‐5H. The initial thickness of overall active material was designed for 40 MHz centre frequency and the FEM simulation showed that the centre frequency was increased by about 1.8 f 0 maintaining the −6 dB fractional bandwidth compared with the conventional transducer.

We have calculated the parameters for an optimal matching layer between a waveguide and a laterally coupled photodetector for TE and TM modes. We find a difference on the order of a few percent between the classical and exact calculations based on optical modes concerning the optimal matching layer thickness. Also, the thickness of the matching layer depends critically on the thickness of the absorbing layer. Comparing TE and TM modes, the absorption maxima for TE(TM) and the minima for TM(TE) coincide approximately, and the maxima and minima depend on the matching layer thickness.

An acoustic matching layer is an essential component of an ultrasound transducer to achieve maximum ultrasound transmission efficiency. Here, we develop a flexible printed circuit board (FPCB) with a composite structure consisting of multiple polyimide and copper layers and demonstrate it as a novel acoustic matching layer. With a flexible substrate and robust ACF bonding, the FPCB not only serves as an acoustic matching layer between piezoelectric elements and the surrounding medium but also as a ground for the electrical connection between the transducer array elements and the folded substrate. A 1D linear ultrasound transducer array with the FPCB matching layer exhibits larger output pressure, wider -3dB bandwidth, and higher ultrasound beam intensity compared to that of an ultrasound transducer array with the alumina/epoxy matching layer, which is one of the most commonly applied composite matching layers. The enhanced transmission performance verifies that the proposed FPCB is an excellent matching layer for 1D linear ultrasound transducer arrays.

In order to solve the problem that it is difficult to detect the local ice layer debonding when the thermal protection system is working, an on-line ultrasonic detection method for the melting degree of interface between skin and ice layer based on the theory of ultrasonic transmission in multi-layer media was studied. A multi-layer medium acoustic model including skin, water film, ice water transition layer, ice layer and air layer is constructed. Ultrasonic pulse waves with different center frequencies are used as excitation sources, and the echo signals of multi-layer medium interface are obtained by using the numerical calculation. The ultrasonic signal processing algorithm for ice melting and debonding measurement is developed. The original echo signal is processed and the characteristic parameters of the echo signal of interface between skin and ice layer are extracted. The ultrasonic reflection coefficient of interface between skin and ice layer is proposed to evaluate the degree of ice melting. The ultrasonic ice detection system was built, and the low-temperature ultrasonic sensor was designed and fabricated. The ability of the system to measure the degree of ice melting under the action of electric heating was verified in the low-temperature environment. The ultrasonic ice detection system was built, and the low-temperature ultrasonic sensor was designed and fabricated. The ability of the system to measure the degree of ice melting under the action of electric heating was verified in the low-temperature environment. The theoretical results show that when the ice on the skin melts and produces a thin water film, the degree of ice melting can be reflected by the change of ultrasonic reflection coefficient at the skin-attachment interface. In this paper, the ultrasonic reflection coefficient more than 0.8 is used as the criterion of ice melting. With the increasing of center frequency of the ultrasonic signal, the thinner water film can be identified. The identification thickness of the water film corresponding to 7.5 MHz center frequency signal is 10 μm. The experimental results show that under the conditions of clear ice, mixed ice and frost ice, the ultrasonic detection system can out-put the ice layer debonding signal at the initial stage of electric heating. The propagation characteristics of ultrasonic pulse wave of interface between skin and ice layer in the thermal protection are preliminarily explored. The present method for detecting the degree of ice melting is expected to further reduce the energy consumption of thermal protection.

A new type of radial ultrasonic transducer was fabricated in this study. The performances of five radial ultrasonic transducers of different thickness were investigated in this paper. It was found that the radial ultrasonic transducers possess the greatest sensitivity when the matching layer thickness is 2.5 mm. The addition of tungsten powder in the backing layer could effectively absorb noise, which improved the acoustic attenuation performance of the backing layer and their sensitivity. To study the directivity, the ultrasonic transducer was put into water. It was found that the transducer could achieve transmitting ultrasound in all radial directions and the ultrasonic signal is similar along all radial directions, i.e., the transducer exhibits isotropic properties, which makes it a good candidate for nondestructive testing of concrete when embedded in concrete elements and structures.

PSPICE approach for designing the ultrasonic piezoelectric transducer for medical diagnostic applications

During the manufacture and the installation process, defects are easy to introduce in prefabricated cable accessories. The existing standards of cable accessories product require that there should be no defects such as bubbles and metal impurities in insulation, but no corresponding detection means are put forward. At present, the main defect detection methods are high voltage test and partial discharge test after installation. It is easy to misjudge because of the installation process, environmental noise and other reasons, and cannot locate the specific location of the defect. It is useful to find these defects through ultrasonic detection and ensure the safety of the cable accessories. In this paper, a set of ultrasonic automatic defect detection system for SR (silicone rubber) was developed. The relationships between the detection ability and the system parameters were investigated. The axial resolution and sensitivity of the ultrasonic wave in the SR Cable joint sample were measured using excitation signal with different pulse width. The relationships between the resolution (or the sensitivity) and pulse width were investigated. The attenuation coefficient and axial resolution were measured by ultrasonic probes with different central frequencies. The relationships between the attenuation coefficient (or the axial resolution) and the central frequency were also investigated. Finally, the negative pulse with pulse width of 200ns was selected as the excitation signal and 2.5MHz was selected as the central frequency of the probe. With the proper system parameters, the attenuation coefficient was 0.059dB/mm and the axial resolution was about 3mm in SR. Two different defect imaging methods were developed by analyzing the amplitude, phase and frequency spectrum of the ultrasonic echoes. The first imaging method, which applied to defects such as air gaps and impurities, constructed images using the amplitude of the flaw echo. The second imaging method, which applied to defects such as uneven distribution of material, constructed images using the average sound velocity. SR samples with different thicknesses and types of defect (air gaps, and metal impurities) were scanned by the system. The results showed that the detection system could accurately identify defects larger than 1 mm. The depth of defects could reach 50mm. The ultrasonic detection method could be applied to instruct the insulation diagnosis for SR Cable accessories.

This paper investigates the impact of different matching layers on the ultrasonic transducers’ performance. Matching layers are mostly used to solve the acoustic impedance matching problem between the piezoelectric element and the test specimen. To design good matching layers, we merged the metal–polymer and mass–spring systems. Their thickness was also optimized using the quarter-wavelength approach. Silver, alumina, and copper served as mass components, while parylene served as the polymer spring component. This was the first time to use such matching materials with lead zirconate titanate (PZT) transducers. The transducers’ sensitivity increased, the beam diameter broadened, the signal-to-noise ratio reduced, and the echo-height increased. According to the findings, the developed matching layers were extremely efficient in upgrading PZT transducers, making them ideal for a variety of non-destructive ultrasonic applications such as identifying defects in various materials. In addition, the new developed transducers may be useful in calibration.

Fine scale 1 - 3 fiber composites and PbTiO3 are promising materials for high frequency (greater than 30 MHz) ultrasonic transducers because of their high thickness coupling coefficients and good mechanical flexibility. This work focus on improvements in the fiber composite and PbTiO<SUB>3</SUB> ceramic transducer performance through innovative tuning techniques and optimized materials selection. For the fiber composite transducers, a 45% volume fraction of PZT fibers with 17 micrometer fiber diameter was selected to obtain high coupling (approximately 0.60) and ensure pure thickness vibration mode at high frequency. Microballoons mixed with epoxy formed a low acoustic impedance backing material and parylene was deposited as a front matching layer. The PbTiO<SUB>3</SUB> ceramic was first processed to provide high density and then polished to the required thickness. Conductive epoxy was then chosen as backing and parylene was deposited as a front matching layer. The focus for both transducers was achieved by spherical shaping. The fiber composite transducers with center frequency around 40 MHz showed 6 dB bandwidth as high as 100%, and round-trip insertion losses near -36 dB. Compared to fiber composite transducers, the PbTiO<SUB>3</SUB> ceramic transducers can work at much higher frequencies (near 90 MHz). In a similar frequency range as fiber composite transducers, they showed improvement sensitivity as marked by an insertion loss around -24 dB. In addition, they still displayed good bandwidth as a result of electrical tuning.

According to the technical difficulties of the air-coupled piezoelectric ultrasonic transducer, 1-3 type piezoelectric composites and double matching layers structure are adopted in order to solve the acoustic impedance mismatch at the interface between the piezoelectric materials and air. The optimal design of the matching layer thickness for double matching layers structure air-coupled ultrasonic transducer is also completed through experiments. Based on this, 440 kHz flat-plate and focused air-coupled piezoelectric ultrasonic transducer are designed, fabricated and characterized. Finally, surface cracks are detected using the focused air-coupled piezoelectric ultrasonic transducer.

Piezoelectric micromachined ultrasonic transducers (PMUTs) play a crucial role in the advancement of portable and wearable ultrasound imaging devices. Matching strategy of conventional thickness mode transducer for acoustic propagation is quite well developed yet. However, PMUTs which employ thin film’s flexural mode vibration lack systematic acoustic matching guidelines critical for optimizing performance. This study introduces the first comprehensive design framework for PMUT matching layers, integrating theoretical modeling, finite element method analysis and ultrasound characterization as well as phased-array ultrasound imaging validation. Being different from conventional thickness mode devices, the results indicate that a matching layer cannot simultaneously improve PMUT’s sensitivity and bandwidth (BW). Employing the matching layer thickness to be a quarter ultrasound wavelength, materials having an acoustic impedance above 1.5 MRayl enhance sensitivity, whereas those with an impedance below 1.5 MRayl improve BW. For our developed PMUT having center frequency of 6.3 MHz, a PDMS with an acoustic impedance of 1 MRayl was selected as matching layer, and it increases the PMUT’s BW from 20% to 39% while resulting in a 41% reduction in sensitivity. The results align closely with the theoretical predictions. To enhance PMUT’s sensitivity, matching materials like polybutadiene and thermoplastic polyurethane are more effective. These guidelines provide a foundation for rapid material selection and dimensional optimization, facilitating the broader application of miniaturized PMUTs in medical imaging and industrial sensing.

The transparent ultrasound transducer (TUT) has recently emerged as an attractive platform for development of multiscale photoacoustic imaging (PAI) systems. TUT allows an easy co-alignment of optical illumination and acoustic detection paths on the tissue surface, averting the complex beam arrangements employed by the current PAI systems that use opaque conventional ultrasound transducers. However, TUTs suffer from narrow bandwidth and low sensitivity due to the lack of suitable transparent acoustic matching and backing layers. To address the above challenges, in this study we explored a novel optically translucent acoustic matching layer made out of glass beads suspended in transparent epoxy to improve both the transducer bandwidth/sensitivity and light fluence on the tissue surface. Our experiments with 13 MHz center frequency TUTs coated with varying glass bead concentration demonstrated that both pulse-echo bandwidth and sensitivity increases with glass bead concentration. Approximately 3.3 fold improvement in bandwidth and a 2.5 times higher pulse-echo sensitivity was measured with TUT fabricated with an acoustic matching layer of 40%GB. Optical measurements were conducted to confirm that the translucent glass bead layer can act as a light diffuser to help achieve uniform light distribution on the tissue surface.

Disposable ultrasonic contact transducers have been constructed with inexpensive PVDF films for nondestructive testing (NDT) applications. This paper reports the temperature-dependent ultrasonic performance of commercial polyvinylidene fluoride (PVDF) films and PVDF sensors. PVDF film was evaluated for its material properties of interest for ultrasonic transducer performance including the relative dielectric constant /spl epsi//sub r/, dielectric loss tangent tan /spl delta//sub e/, electromechanical coupling constant k/sub t/, mechanical quality factor Q/sub m/, and acoustic impedance Z. Disposable PVDF transducers were then coupled to both low and high acoustic impedance test panels and their ultrasonic insertion loss/sensitivity and frequency bandwidth measured as a function of temperature in both the pulse-echo and pitch-catch modes. The results yielded center frequencies in the 3.5-16 MHz range, with -6-dB fractional bandwidths for some of the transducers exceeding 100%. The temperature dependence of the transducers' performance is reported for the -40 to 80/spl deg/C range and shows an approximate linear decrease in center frequency and increase in fractional bandwidth with increasing temperature. These measured results are compared with predictions from computer simulations based on Mason's model. These tests showed that the same disposable transducers can be used for both ultrasonic and acoustic emission sensing NDT applications. This paper summarizes the quantitative ultrasonic and vibration sensing performance for all of the disposable PVDF film transducers which were tested.

Evaluation of ultrasonic transducer response and structural integrity using coded photoacoustic imaging.