Ultrasonic Transducer Elements Research Articles

Research and Development of Digital Assembly Process System for Ultrasonic Transducers

In order to solve the problem of design efficiency of the digital assembly process, the author proposes a research using ultrasonic transducer technology. The main content of this research is to study the ultrasonic transducer elements according to the basic structure of the ultrasonic transducer.Through the study of equivalent circuit of ultrasonic transducer, the model of impedance matching design is constructed. Finally, the feasibility of ultrasonic transducer technology is obtained through experiments. Experimental results show that the transducer multichip structure of the ultrasonic transducer system and the LC matching network circuit can make the AOTF system achieve better results, and the diffraction efficiency is up to more than 70%, which is of great significance to the research and development of the current digital assembly process system. Conclusion. It is proven that the research of ultrasonic transducer technology can meet the needs of digital assembly process design efficiency.

The sparse array elements selection in sparse imaging of circular-array photoacoustic tomography

Photoacoustic imaging (PAI) has been developed, and photoacoustic computed tomography (PACT) is widely used for in vivo tissue and mouse imaging. Simulated annealing (SA) algorithm solves optimization problems, and compressed sensing (CS) recovers sparse signals from undersampled measurements. We aim to develop an advanced sparse imaging framework for PACT, which invloves the use of SA to find an optimal sparse array element distribution and CS to perform sparse imaging. PACT reconstructions were performed using a dummy and porcine liver phantoms. Compared to traditional sparse reconstruction algorithms, the proposed method recovers signals using few ultrasonic transducer elements, enabling high-speed, low-cost PACT for practical application.

Modification of Mechanical and Electromechanical Resonances of Cellular Ferroelectret Films Depending on the External Load.

Ferroelectret films are cellular polymers with electrically charged pores that exhibit piezoelectric response. Among other applications, ferroelectret films have been widely used as active elements in air-coupled ultrasonic transducers. More recently, they have also been tested in water immersion. They show a promising wide frequency band response, but a poor sensitivity produced by the disappearance of the electromechanical resonances. This paper studies in detail the modification of FE films response when put into water immersion, both the mechanical and the electromechanical responses (the latter in transmission and reception modes). The lack of electromechanical thickness resonances when the films are put into water is explained as the result of the different profile of the modification of the polarization vector along the film thickness imposed by the large mechanical load produced by the water. This different electromechanical response can also be the reason for the subtle modification of the mechanical thickness resonances that is also observed and analyzed.

Accurate coupled vibration analysis of a piezoelectric array element by the superposition method

In this paper, the superposition method is extended to obtain analytical solutions for the coupled vibration of a piezoelectric slender bar in a configuration corresponding to a typical ultrasonic linear array transducer element. The problem can be described mathematically by three partial differential equations with electrical and mechanical boundary conditions. To solve this, the vibrations in lateral and thickness directions are referred to as two building blocks. In each building block, the expressions of displacements and electric potential are assumed first based on their symmetry properties and then the induced dynamic responses, such as in-plane stress and electric displacements, are calculated. Finally, the vibration responses of the two building blocks are superimposed to satisfy the boundary conditions using Fourier series expansions. Electrical impedance and mode shapes, represented by the spatial distribution of displacements and electric potential, are calculated analytically and compared with the results of the finite element method. An excellent agreement is observed. The method can be applied to design and optimize piezoelectric array transducers for various applications.

Estimation of speed of sound using coherence factor and signal-to-noise ratio for improvement of performance of ultrasonic beamformer

Ultrasound beamforming is an indispensable process to obtain an ultrasound image. In the conventional ultrasonography, the speed of sound (SoS) in tissue is assumed to be constant to calculate the distance from the scattering point to each ultrasonic transducer element. However, the spatial distribution of the SoS in tissue is inhomogeneous. In this study, we developed a method to estimate the distribution of the SoS. In addition, the accuracy of the proposed method was investigated using a homogeneous phantom with a known SoS distribution. Furthermore, another experiment using a wire phantom was conducted to investigate whether the spatial resolution in a resultant ultrasound image was improved with the SoS distribution estimated by the proposed method. The best spatial resolution was achieved when the size of the transmit aperture was 6.4 mm (32 elements) when both the coherence factor and signal-to-noise ratio factor were evaluated with a 7.5 MHz linear array probe.

Numerical Study of Square Border Ultrasonic Transducer Element Arrays for Breast Imaging in Ultrasound Computed Tomography with Waveform Inversion Method

Ultrasound computed tomography (USCT) is a promising approach for early breast cancer screening. Existing studies that estimate breast images using Waveform inversion (WI) methods utilize a Circular ultrasonic transducer element array (CUTA) to collect the measurement data. However, very accurate transducer element positioning and directivity are required for signal calibration in the hardware system of these studies, thereby causing difficulties in hardware manufacturing. The purpose of this study is to estimate high-resolution USCT images using a WI method with a Square border ultrasonic transducer element array (SUTA), which reduces the difficulty of hardware manufacturing and creates accurate correspondence between the continuous and discrete forms of the transducer element positions. Therefore, in this study, an SUTA is adopted to collect the measurement data of breast imaging using the WI method. A penalized least-squares optimization problem is constructed to obtain the numerical solution of a sound speed distribution. Computer simulations are conducted to compare images reconstructed from the measurement data that are collected using an SUTA and a CUTA. The performance is evaluated using a numerical breast phantom. Results suggest that the biases of the images reconstructed are less than 1% with the evenly distributed SUTA and 1% with the CUTA, under a noise condition.

A Reconfigurable Ultrasound Transceiver ASIC With <inline-formula> <tex-math notation="LaTeX">$24\times40$ </tex-math> </inline-formula> Elements for 3-D Carotid Artery Imaging

This paper presents an ultrasound transceiver application-specific integrated circuit (ASIC) designed for 3-D ultrasonic imaging of the carotid artery. This application calls for an array of thousands of ultrasonic transducer elements, far exceeding the number of channels of conventional imaging systems. The $3.6 \times 6.8$ mm2 ASIC interfaces a piezo-electric transducer (PZT) array of $24 \times 40$ elements, directly integrated on top of the ASIC, to an imaging system using only 24 transmit and receive channels. Multiple ASICs can be tiled together to form an even bigger array. The ASIC, implemented in a 0.18 $\mu \text{m}$ high-voltage (HV) BCD process, consists of a reconfigurable switch matrix and row-level receive circuits. Each element is associated with a compact bootstrapped HV transmit switch, an isolation switch for the receive circuits and programmable logic that enables a variety of imaging modes. Electrical and acoustic experiments successfully demonstrate the functionality of the ASIC. In addition, the ASIC has been successfully used in a 3-D imaging experiment.

Investigation of Silicon Nitride as an Excellent Membrane Material for MEMS Ultrasonic Transducers

Silicon micromachining techniques developed over the last few decades’ aid in precise control over nanometer scale structures. Using these techniques to fabricate transducer elements with small electrode spacing efficient and broadband ultrasonic air transducers can be made. In this paper frequency response profile of a circular capacitive micromachined ultrasonic transducer (CMUT) element with silicon nitride as the membrane material is analytically modelled and compared with FEM simulation results. It is observed that the resonance frequency is highly dependent on the membrane material and structural properties. Silicon nitride serves as an excellent material for generation and detection of ultrasonic waves in air. The results are compared with published experimental values and appreciable agreement is obtained.

Characterization of Nanoscale Ultrasonic Transducer Elements as Effective Acoustical Devices

The generation and detection of ultrasound in air has many applications in the field of ranging, non-destructive evaluation, microscopy and the most impactful in medical imaging. Conventional designs of electrostatic transducers have large electrode spacing of 50-100 μm which reduces the sensitivity of these capacitors. In the last one and a half decade silicon micromachining is used to define capacitors with gap spacing as small as 500Å, making it possible highly efficient capacitive micromachined ultrasonic transducers (CMUTs). In this paper a CMUT element is analytically characterized and FEM simulated. The observations are compared with published experimental results and excellent agreement is found between them.

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.

A novel dual-frequency imaging method for intravascular ultrasound applications

Intravascular ultrasound (IVUS), which is able to delineate internal structures of vessel wall with fine spatial resolution, has greatly enriched the knowledge of coronary atherosclerosis. A novel dual-frequency imaging method is proposed in this paper for intravascular imaging applications. A probe combined two ultrasonic transducer elements with different center frequencies (36MHz and 78MHz) is designed and fabricated with PMN–PT single crystal material. It has the ability to balance both imaging depth and resolution, which are important imaging parameters for clinical test. A dual-channel imaging platform is also proposed for real-time imaging, and this platform has been proven to support programmable processing algorithms, flexible imaging control, and raw RF data acquisition for IVUS applications. Testing results show that the −6dB axial and lateral imaging resolutions of low-frequency ultrasound are 78 and 132μm, respectively. In terms of high-frequency ultrasound, axial and lateral resolutions are determined to be as high as 34 and 106μm. In vitro intravascular imaging on healthy swine aorta is conducted to demonstrate the performance of the dual-frequency imaging method for IVUS applications.

Optimization of Element Parameters for a New OPFC Ultrasonic Phased Array Transducer

An orthotropic piezoelectric fiber composite (OPFC) element and related OPFC ultrasonic phased array transducer which applied in damage detection of metal structures are investigated by theoretical analysis, numerical simulation and experimental verification methods. Based on electromechanical coupling, the influence of the material characteristics and geometry parameters on actuation performance is studied for the thickness expansion type OPFC elements. In view of lack in the mechanic-electronic parameter design of the existing single PZT element for modern ultrasonic phased array transducer, the related OPFC ultrasonic phased array transducer which used in metal structural damage detection is designed, which have the merits such as low voltage and limit the effects on grating lobe. The focusing acoustic field distribution is analyzed by finite element method together with directivity analysis in metals. The optimal array parameters such as phased array element interval, array element width and number of element are obtained by studying the total displacement changes as various parameters changes at focus point. The preparation of OPFC actuator used in metal structural damage detection is studied. The performance of interdigital OPFC element is also obtained by testing and comparing with the traditional PZT element. The experimental results displayed good agreement with the theoretical predictions.

Compressed-sensing photoacoustic computed tomography in vivo with partially known support

Compressed sensing (CS) can recover sparse signals from under-sampled measurements. In this work, we have developed an advanced CS framework for photoacoustic computed tomography (PACT). During the reconstruction, a small part of the nonzero signals’ locations in the transformed sparse domain is used as partially known support (PKS). PACT reconstructions have been performed with under-sampled in vivo image data of human hands and a rat. Compared to PACT with basic CS, PACT with CS-PKS can recover signals using fewer ultrasonic transducer elements and can improve convergence speed, which may ultimately enable high-speed, low-cost PACT for various biomedical applications.

A 32 x 32 capacitive micromachined ultrasonic transducer array manufactured in standard CMOS

As ultrasound imagers become increasingly portable and lower cost, breakthroughs in transducer technology will be needed to provide high-resolution, real-time 3-D imaging while maintaining the affordability needed for portable systems. This paper presents a 32 x 32 ultrasound array prototype, manufactured using a CMUT-in-CMOS approach whereby ultrasonic transducer elements and readout circuits are integrated on a single chip using a standard integrated circuit manufacturing process in a commercial CMOS foundry. Only blanket wet-etch and sealing steps are added to complete the MEMS devices after the CMOS process. This process typically yields better than 99% working elements per array, with less than ±1.5 dB variation in receive sensitivity among the 1024 individually addressable elements. The CMUT pulseecho frequency response is typically centered at 2.1 MHz with a -6 dB fractional bandwidth of 60%, and elements are arranged on a 250 μm hexagonal grid (less than half-wavelength pitch). Multiplexers and CMOS buffers within the array are used to make on-chip routing manageable, reduce the number of physical output leads, and drive the transducer cable. The array has been interfaced to a commercial imager as well as a set of custom transmit and receive electronics, and volumetric images of nylon fishing line targets have been produced.

パラレル受波ニードルビーム探傷技術

A new ultrasonic testing technique and a new test system using a transducer array have been developed. The test system works as follows: (1) Ultrasonic waves are transmitted from all the ultrasonic transducer elements in the array at the same time; and (2) By additively synthesizing time-converted ultrasound signals transformed from echo signals received by all the ultrasonic transducer elements in the array at the same time, lines of continuously focused receiving beam (receiving needle beam) are closely formed under the transducer array (parallel receiving needle beam). Also, internal flaws in a cross-section are detected at once using the parallel receiving needle beam. The results of experiments using a 50-MHz transducer array and the developed system have proven that ultra-minute internal flaws 20 µm in diameter can be detected at a scan speed of 1000 mm/s. In addition, the focal zone formed is very long as compared with conventional point-focused beam forming. It is concluded that the system is suitable for simultaneous testing of a cross-section of a test object at high scanning speed.

Parallel Receiving Needle Beam Ultrasonic Testing Technique

A new ultrasonic testing technique and a new test system using a transducer array have been developed. The test system works as follows: (1) Ultrasonic waves are transmitted from all the ultrasonic transducer elements in the array at the same time; and (2) By additively synthesizing time-converted ultrasound signals transformed from echo signals received by all the ultrasonic transducer elements in the array at the same time, lines of continuously focused receiving beam (receiving needle beam) are closely formed under the transducer array (parallel receiving needle beam). Also, internal flaws in a cross-section are detected at once using the parallel receiving needle beam. The results of experiments using a 50-MHz transducer array and the developed system have proven that ultra-minute internal flaws 20 μm in diameter can be detected at a scan speed of 1000 mm/s. In addition, the focal zone formed is very long as compared with conventional point-focused beam forming. It is concluded that the system is suitable for simultaneous testing of a cross-section of a test object at high scanning speed.

Crosstalk effects caused by the geometry of piezoelectric elements in matrix ultrasonic transducers

Crosstalk is a result of the deficiency in the electrical or mechanical isolation between elements. It is a function of the proximity between piezoelectric elements of the transducer or between connections. It can be caused by a series of factors, such as: the deficiency in the electromagnetic shield, the capacitive effect between the elements or the electrical connections, or by the transmission of vibration modes to adjacent elements due to insufficient mechanical isolation. It also depends on the geometry of the elements and the connecting material between elements. The evaluation of the crosstalk effects caused by the geometry of the piezoelectric elements in matrix ultrasonic transducers is presented. Measurement methods of the radiation patterns and vectorial impedance for the identification of crosstalk are described. The procedure of the measurement of crosstalk, done by Sanchez Dominguez and von Kruger (2002), was applied to an eight elements phase onedimension matrix transducer for Doppler ultrasound application. In fact, two cases are presented, in one of them a piezoelectric element of the matrix with initial dimensions of 10.0 × 4.4 × 0.66 mm was used, and in the other case a piezoelectric element with initial dimensions of 10.0 × 0.7 × 0.66 mm was used (element are made of Lead Zirconate Titanate, also called PZT). From the results we deduce that it is possible to reduce the crosstalk effect using insulating material with low electromechanical coupling coefficient between the ceramics of the array or using materials that promote good mechanical insulation between the ceramics.

Capacitive Ultrasonic Probe Device

Within the tip portion of a cylindrical shaped sheath a capacitive ultrasonic transducer which is an array type two-dimensionally arrayed on the outer surface of the cylindrical face is disposed. Capacitive ultrasonic transducer units employ m capacitive ultrasonic transducer elements arrayed in the longitudinal direction of the cylindrical face as a division unit, thereby providing an arrangement wherein the respective capacitive ultrasonic transducer units are readily disposed in the circumferential direction, whereby radial scanning or the like can be performed within a body cavity.

Apparatus For Two-Dimensional Transducers Used In Three-Dimensional Ultrasonic Imaging

A single chip transducer apparatus that includes on-chip electronic circuitry which, when connected properly to a two-dimensional matrix of ultrasonic transducer elements, provides enough information to an external imaging system to form three-dimensional images of the subject of interest. In a preferred embodiment, the circuitry provides an amplifier for each transducer element, and then conditions the output of the amplifier in several ways. In one embodiment of the invention, the elements' analog voltages are stored in a sample and hold circuit, and time multiplexed into a high speed line driver that sends many elements data down the interconnect to the system's high speed Analog to Digital converters. In another embodiment, the gain of the amplifiers can be controlled in time to provide aperture translation and time based expansion for translating and focusing image slices in the elevation direction.

Ultrasonic transducer structures

The present invention provides an ultrasonic transducer structure, comprising a first ultrasonic transducer element ( 1 ), arranged and operable for transmitting an ultrasonic signal from a front face of the structure, damping material ( 2 ) at the back of the first ultrasonic transducer element ( 1 ), and a second ultrasonic transducer element ( 3 ) in or on the damping material behind the first ultrasonic transducer element ( 1 ), arranged and operable to receive sound energy propagated through the damping material ( 2 ) when the first ultrasonic transducer element ( 1 ) is operated to transmit an ultrasonic signal from the front face. Although sound energy propagating through the damping material ( 2 ) is rapidly attenuated, sound energy of a sound pulse travelling to the second ultrasonic transducer ( 3 ) from the back face of the first transducer element 1 can be received and the size or amplitude and time delay (arrival time) of this pulse can be monitored and from this information the performance of the first transducer element ( 1 ) concerned can be monitored.