Ultrasonic Transducer Array Research Articles

A Prototype System With Custom-Designed RX ICs for Contrast-Enhanced Ultrasound Imaging

This work presents a prototype system based on a multichannel receiving (RX) integrated circuit (IC) for contrast-enhanced ultrasound (CEUS) imaging. The RX IC is implemented in a 40-nm low-voltage CMOS technology and is designed to interface to a capacitive micromachined ultrasonic transducer array. To enable a direct connection of the RX electronics to the transducer, an analog multiplexer with on-chip protection circuitry is developed. Stress tests confirm the reliability of this arrangement when combined with a high-voltage pulser. The RX IC is equipped with a highly programmable bandpass filter to capture harmonic signals from ultrasound contrast agents (UCAs) while suppressing fundamental components. In order to examine the impact of analog front-end (AFE) bandpass filtering, in vitro acoustic experiments are performed with UCAs. A spatial resolution analysis suggests that the AFE bandpass filtering combined with a pulse inversion (PI) technique can improve the lateral resolution by 38% or 9% compared to the original full-bandwidth approach or a stand-alone PI approach, respectively, while the impact on axial resolution is negligible. A phantom study shows that compared to digital bandpass filtering, the AFE bandpass filtering enables better use of the dynamic range of the RX electronics, resulting in better generalized contrast-to-noise ratio from 0.44/0.53 to 0.57/0.68 without or with PI.

Application of Phased Array Ultrasonic Transducers for Guided Wave Scanning of Plates Using Multi-point Focusing Technique

Application of Phased Array Ultrasonic Transducers for Guided Wave Scanning of Plates Using Multi-point Focusing Technique

Arrangement design for horizontally omnidirectional audible sound source using facing ultrasonic transducer arrays

We developed an audible sound source with horizontal omnidirectional patterns using facing ultrasonic transducer arrays. The arrays emitted sound with different ultrasonic frequencies from each side, and an audible sound with a differential frequency is generated between input ultrasonic signals. In particular, we designed and created a new array that can control the number of transducers driven in the array. We evaluated the frequency–amplitude characteristics and directivity when the transducers in the array were driven in an annular shape. There is an optimum array shape and number of transducers that can be driven for a specific distance between arrays.

Crosstalk optimization of 5 MHz linear array transducer based on PZT/epoxy piezoelectric composite

Array ultrasonic transducers using electronic scanning method can obtain high frame rate and high-accuracy images compared with single-element transducers. However, for array transducers, crosstalk is a common problem and has bad influence on imaging quality. In this work, a 5 MHz linear array transducer with low crosstalk level is developed using PZT/epoxy piezoelectric composite. This PZT/epoxy composite has higher thickness electromechanical coupling coefficient (65.1%) and lower acoustic impedance (19.4 MRayls) compared with PZT ceramics. The influence of the width and depth of kerf on crosstalk is simulated by PZFlex software and the optimized kerf sizes are width 0.3 mm and depth 0.1 mm. The linear array transducer is fabricated according to the simulation results and the crosstalk level is measured. The experimental results are consistent with simulation and the transducer with this optimized kerf size has smaller crosstalk level (−24.1 dB). The central frequency and − 6 dB bandwidth of fabricated linear array transducer measured by impulse-echo response method are 4.82 MHz and 60.2% respectively. Compared with transducers made of PZT ceramic, this linear array transducer made of PZT/epoxy composite has wider bandwidth. The 5 MHz linear array transducer fabricated in this work has good acoustic performance and low crosstalk level and it is expected to obtain high-quality images in medical ultrasound imaging.

Development of an Integrated Haptic Sensor System for Multimodal Human–Computer Interaction Using Ultrasonic Array and Cable Robot

This paper presents the design and development of a novel haptic sensor system. It integrates cable-driven force and ultrasonic tactile feedback, which can produce multimodal haptic stimuli. The sensing element includes a Leapmotion, an ultrasonic transducer array, tension sensors, and rotary encoders, which are used to capture hand posture, project tactile points, measure cable force and length, respectively. Firstly, a 6-DOF cable-driven force feedback apparatus based on parallel mechanism is designed and ultrasonic phased array is combined to form a multimodal haptic feedback system. Secondly, a multimodal haptic fusion method for cable-driven force and ultrasonic tactile is firstly proposed to invoke realistic compound haptic sensations. To enhance the rendering effects of each subsystem, admittance control is developed for a cable robot, and a new perceived magnitude model is established for ultrasound tactile rendering. A psychophysical experiment is conducted to study the perceived characteristics of multimodal haptic stimuli. To verify the proposed system, a series of experiments were carried out, whose results indicated that the system performs well at multi-property haptic rendering and confirm the accuracy and sensitive advantage of our system in virtual reality applications. The results of our study indicate that this device has great application potential in human-computer interaction.

Increasing the transmission efficiency of transcranial ultrasound using a dual-mode conversion technique based on Lamb waves.

Transcranial focused ultrasound (FUS) is a noninvasive treatment for brain tumors and neuromodulation. Based on normal incidence, conventional FUS techniques use a focused or an array of ultrasonic transducers to overcome the attenuation and absorption of ultrasound in the skull; however, this remains the main limitation of using FUS. A dual-mode conversion technique based on Lamb waves is proposed to achieve high transmission efficiency. This concept was validated using the finite element analysis (FEA) and experiments based on changes in the incident angle. Aluminum, plexiglass, and a human skull were used as materials with different attenuations. The transmission loss was calculated for each material, and the results were compared with the reflectance function of the Lamb waves. Oblique incidence based on dual-mode conversion exhibited a better transmission efficiency than that of a normal incidence for all of the specimens. The total transmission losses for the materials were 13.7, 15.46, and 3.91 dB less than those associated with the normal incidence. A wedge transducer was designed and fabricated to implement the proposed method. The results demonstrated the potential applicability of the dual-mode conversion technique for the human skull.

Lead-Free Ultrasonic Phased Array Transducer for Human Heart Imaging.

Substantial advancement has been made in recent years on lead-free piezoelectric materials, but up to date, it is still a challenge to make a true medical imaging ultrasonic array transducer with center frequency <3 MHz. There are two major obstacles: the difficulty of fabricating large enough uniform lead-free piezoelectric materials with high piezoelectric coefficient, and the severe electrical impedance mismatch of an array element to the imaging system due to the relatively low dielectric constant of lead-free materials compared to lead-based piezoelectric materials. We resolved these two issues by employing texture engineering and stacking piezoelectric-layer design, which allowed us to fabricate an 80 element phased array transducer with the center frequency of 2.9 MHz and a bandwidth >80% for human heart imaging. The high-quality lead-free (Ba0.95Ca0.05)(Ti0.94Zr0.06)O3 textured ceramic plate has the size of 23×22×0.8 mm3 with the piezoelectric constant d33 = 570 pC/N. Phantom imaging and internal clinical human heart imaging demonstrated that this lead-free phased array can produce comparable imaging quality to that of a commercial PZT-5H ceramic-based phased array transducer, which demonstrated the practicality of using lead-free materials to replace PZT ceramics in phased array transducers for medical imaging applications.

Eye-Tracking Monitoring Based on PMUT Arrays

As <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$a$ </tex-math></inline-formula> common and natural activity of human beings, eye movement has been regarded as an indicator of human physiological and psychological health; eye movement tracking has been applied to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$a$ </tex-math></inline-formula> wide range of domains, such as disease diagnostics, drug therapy testing and human-computer interaction. Conventionally, eye movement is captured by three approaches, i.e., recording video using <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$a$ </tex-math></inline-formula> camera, measuring time-varying Electrooculography (EOG) signals using electrodes, and detecting reflected infrared light using infrared sensor. However, all these techniques incur certain limitations that impede their adoption for practical eye tracking, such as privacy violation, high computation resources, discomfort and strong light reliability. This paper presents <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$a$ </tex-math></inline-formula> portable and robust eye tracking technique based on ultrasound. Specifically, piezoelectric MEMS ultrasonic transducer arrays integrated on glasses are used to transmit and receive bio-safe pulse echo ultrasound individually. With experiment on volunteers, the developed devices can accurately track the rotation and direction of eyeball movement in real-time, based on the time of flight (TOF) principle. The tracking device is lightweight (< 25 mg) and compact (millimeters in size), showing <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$a$ </tex-math></inline-formula> great potential for wearable eye tracking application like virtual reality. [2021-0193]

Development of Cardiac Phased Array With Large-Size PZN-5.5 %PT Single Crystals.

In recent years, the manufacturing process of lead zinc niobate-lead titanate [Pb(Zn1/3Nb2/3)O3-PbTiO3, also called PZN-PT], has been enhanced with improvements in size, consistency, and a suitable compromise between piezoelectric properties and phase transition temperature, which means that it is possible to obtain PZN-PT single crystals in sufficient size for performance characterization studies and batch manufacturing to produce high-performance medical ultrasonic transducers. This article mainly focuses on the development of the 64-element phased array ultrasonic transducer based on novel large-size PZN-PT piezoelectric single crystals. The composition of the single crystal was chosen as PZN-5.5 %PT. The designed center frequency of the phased array is 3.0 MHz, which is suitable for cardiac ultrasound imaging. The array elements were spaced at a 0.254-mm pitch, and interconnected through a custom-designed flexible circuit. Double matching layers with a light backing structure were applied in the transducer fabrication process to improve the performance of the array. The test results of the developed phased array showed a center frequency of 3.0 MHz, and an average -6 dB fractional bandwidth of 72%. In the vicinity of the center frequency, the two-way insertion loss (IL) was about -46 dB, while a crosstalk between the adjacent elements was less than -31 dB. The wire phantom can be distinctly imaged with the phased array, and the axial and lateral resolutions were measured to be 660 and [Formula: see text], respectively. The image of a standard phantom was acquired to present the imaging performance of the transducer. The final results indicate that the transducer arrays based on novel large-size PZN-PT single crystals are quite promising for use in medical ultrasound imaging applications.

Fabrication of 2-D Capacitive Micromachined Ultrasonic Transducer (CMUT) Array through Silicon Wafer Bonding.

Capacitive micromachined ultrasound transducers (CMUTs) have broad application prospects in medical imaging, flow monitoring, and nondestructive testing. CMUT arrays are limited by their fabrication process, which seriously restricts their further development and application. In this paper, a vacuum-sealed device for medical applications is introduced, which has the advantages of simple manufacturing process, no static friction, repeatability, and high reliability. The CMUT array suitable for medical imaging frequency band was fabricated by a silicon wafer bonding technology, and the adjacent array devices were isolated by an isolation slot, which was cut through the silicon film. The CMUT device fabricated following this process is a 4 × 16 array with a single element size of 1 mm × 1 mm. Device performance tests were conducted, where the center frequency of the transducer was 3.8 MHz, and the 6 dB fractional bandwidth was 110%. The static capacitance (29.4 pF) and center frequency (3.78 MHz) of each element of the array were tested, and the results revealed that the array has good consistency. Moreover, the transmitting and receiving performance of the transducer was evaluated by acoustic tests, and the receiving sensitivity was −211 dB @ 3 MHz, −213 dB @ 4 MHz. Finally, reflection imaging was performed using the array, which provides certain technical support for the research of two-dimensional CMUT arrays in the field of 3D ultrasound imaging.

Ultrasonic Imaging in Liquid by Migration of Receiving Array Transducer

A non-destructive imaging technique of sediments in a turbid liquid was developed using an ultrasonic array transducer. In this study, the full-waves sampling and processing (FSAP) technique was modified to reconstruct the sediment image using scattered signals measured at multisite by the migration of the array transducer. The imaging performance using the FSAP was checked with simulated signals by the finite integration technique.

Three-Dimensional Velocity Distribution Measurement Using Ultrasonic Velocity Profiler with Developed Transducer

This study describes an ultrasonic velocity profiler that uses a new ultrasonic array transducer with unique 5-element configuration, with all five elements acting as transmitters and four elements as receivers. The receivers are designed to reduce the amount of uncertainty. As the fluid moves through this setup, four Doppler frequencies are obtained. The multi-dimensional velocity information along the measurement line can be reconstructed. The transducer has a compact geometry suitable for a wide range of applications, including narrow flow areas. The transducer’s basic frequency and sound pressure are selected and evaluated to be compatible with the application. First, to confirm the measurement ability, the measurement of the developed system in two-dimensional flow is validated by comparing it to the theoretical data. The uncertainty of measurement was within 15%. Second, the three-dimensional measurement in turbulent and swirling flow is proved experimentally to check the applicability of the proposed technique.

Piezoelectric Micromachined Ultrasonic Transducer for Arterial Wall Dynamics Monitoring.

In this article, a [Formula: see text] piezoelectric micromachined ultrasonic transducer (PMUT) array is designed and driven with one cycle of a 5-MHz sinusoid at 10 [Formula: see text] for radial artery motion tracking. The transmit and receive performance figure of merit (FOM) of an individual PMUT over operating frequency is modeled and validated using laser Doppler vibrometer (LDV) measurements. Given a fixed cross section, the FOM inversely scales with frequency. The array aperture size is selected to obtain enough pressure and received signal to measure the radial artery wall reflection at a 5-mm depth in tissue. The 2-mm acoustic beamwidth provides enough lateral resolution for radial artery wall motion tracking. Single-line ultrasonic pulse-echo measurements with high time resolution, also called M-mode ultrasound imaging, are demonstrated to reproduce a known target motion profile with a precision of around 0.5 [Formula: see text]. In vivo radial artery dynamics are measured by placing the sensor on the wrist of a volunteer. The measured diameter change waveform of the radial artery is consistent with reports in the literature and captures key arterial pulse waveform features, including systolic upstroke, systolic decline, dicrotic notch, and diastolic runoff. The system has sufficient accuracy and precision to measure both the 50 [Formula: see text] overall diameter change and the 5- [Formula: see text] diameter change due to the dicrotic notch. A heart rate of 70 beats/min is also derived. This demonstrates the great potential of custom PMUT arrays for continuous cardiovascular system monitoring.

A Hand-Held 190+190 Row–Column Addressed CMUT Probe for Volumetric Imaging

This paper presents the design, fabrication, and characterization of a 190+190 row-column addressed (RCA) capacitive micromachined ultrasonic transducer (CMUT) array integrated in a custom hand-held probe handle. The array has a designed 4.5 MHz center frequency in immersion and a pitch of 95 μm which corresponds to ≈ λ/4. The array has a 2.14 × 2.14 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> footprint including an integrated apodization scheme to reduce ghost echoes when performing ultrasound imaging. The array was fabricated using a combination of fusion and anodic bonding, and a deposit, remove, etch, multistep (DREM) etch to reduce substrate coupling and improve electrode conductivity. The transducer array was wire-bonded to a rigid-flex printed circuit board (PCB), encapsulated in room temperature vulcanizing (RTV) silicone polymer, electromagnetic interference (EMI) shielded, and mounted in a 3D-milled PPSU probe handle. The probe was characterized using the SARUS experimental scanner and 3D volumetric imaging was demonstrated on scatter and wire phantoms. The imaging depth was derived from tissue mimicking phantom measurements (0.5 dB MHz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> attenuation) by estimating the SNR at varying depths. For a synthetic aperture imaging sequence with 96+96 emissions the imaging depth was 3.6 cm. The center frequency measured from the impulse response spectra in transmit and pulse-echo was 6.0 ± 0.9 MHz and 5.3 ± 0.4 MHz, and the corresponding relative bandwidths were 62.8 ± 4.5 % and 86.2 ± 10.4 %. The fabrication process showed clear improvement in relative receive sensitivity and transmit pressure uniformity compared to earlier silicon-on-insulator (SOI) based designs. However, at the same time it presented yield problems resulting in only around 55 % elements with a good response.

Lumped-Parameter Equivalent Circuit Modeling of CMUT Array Elements

Design and modeling are key steps in the value chain of Capacitive Micromachined Ultrasonic Transducer (CMUT) arrays. Although CMUT array element models are very powerful, most of them are still limited in their use as tools for electronic design assistance. The electroacoustic equivalent circuits developed are mainly based on a distributed-element approach while lumped-parameter electrical circuits are better suited for electronic software design tools interoperations. To meet this need, the present study aims to implement an electroacoustic equivalent scheme of a full array element, based on a two-port network representation made of lumped-parameters. After an extensive bibliographical review of CMUT models, the new model is set-up from a fully distributed approach using Foldy’s electroacoustic definitions at the element level. Transmit and receive modes are implemented using scalar equations given by the lumped parameters. Moreover, based on a reciprocity analysis, the performance of the complete measurement chain in emission and reception will be defined using the relevant transfer functions. Finally, to help one design CMUT array elements for a given application, a method based on the computation of membranes thickness-size master curves is proposed. The two-port network representation of a full CMUT-based array element allowed by the new lumped-parameter modeling opens a wide range of possibilities regarding array design, electronic integration, operations with acoustic propagation simulation tools and more.

Study of the sound speed of components in a medical ultrasonic one-dimensional array transducer

In this work the sound speed of components in a one-dimensional array transducer used to acquire ultrasonic cross-sectional images for medical diagnosis was studied. The transducer is composed of several channels having a similar width and thickness, so the sound speed of these components depends on their dimensions. First, the components of the transducer were divided into active and passive components, and then the sound speed according to dimensions was derived using coupled-mode theory and the Rayleigh–Lamb frequency equation. After classifying the aspect ratios of the components according to the range of change, different wave velocities were proposed according to this range. For transducers made of different materials with various frequencies, the sound speed of the components was derived by applying the devised method. After making a prototype of each transducer, its performance was measured and the feasibility of the devised method presented.

Design, simulate and performance an embedded fan-out package for 2-D ultrasonic transducer arrays

Design, simulate and performance an embedded fan-out package for 2-D ultrasonic transducer arrays

Development of Dual-Frequency PMUT Arrays Based on Thin Ceramic PZT for Endoscopic Photoacoustic Imaging.

This paper presents a dual-frequency piezoelectric micromachined ultrasonic transducer (pMUT) array based on thin ceramic PZT for endoscopic photoacoustic imaging (PAI) applications. With a chip size of 7 × 7 mm2, the pMUT array consists of 256 elements, half of which have a lower resonant frequency of 1.2 MHz and the other half have a higher resonant frequency of 3.4 MHz. Ceramic PZT, with outstanding piezoelectric coefficients, has been successfully thinned down to a thickness of only 4 μ by using wafer bonding and chemical mechanical polishing (CMP) techniques and employed as the piezoelectric layer of the pMUT elements. The diaphragm diameters of the lower-frequency and higher-frequency elements are 220 μm and 120 μm, respectively. The design methodology, multiphysics modeling, fabrication process, and characterization of the pMUTs are presented in detail. The fabricated pMUT array has been fully characterized via electrical, mechanical, and acoustic measurements. The measured maximum responsivities of the lower- and higher- frequency elements reach 110 nm/V and 30 nm/V at their respective resonances. The measured cross-couplings of the lower-frequency elements and higher-frequency elements are about 9% and 5%, respectively. Furthermore, PAI experiments with pencil leads embedded into an agar phantom have been conducted, which clearly shows the advantages of using dual-frequency pMUT arrays to provide comprehensive photoacoustic images with high spatial resolution and large signal-to-noise ratio simultaneously.

A Low-Power Wearable E-Nose System Based on a Capacitive Micromachined Ultrasonic Transducer (CMUT) Array for Indoor VOC Monitoring

Volatile organic compounds (VOCs) are pervasive in the environment and their real-time continuous monitoring can facilitate better understanding of their effects on human health by combining environmental factors with physiological conditions. The scope of wearable sensors for detection of VOCs is evident as the accuracy of the sensor prediction depends on its proximity to the VOC source along with the sensitivity and selectivity of the sensor itself. In this paper, we present a low-power wearable e-nose system based on a capacitive micromachined ultrasonic transducer (CMUT) array. CMUTs offer inherent benefits of excellent mass resolution, easy array fabrication, and integration with electronics, which make them an appropriate choice as a transducer element for gravimetric e-nose systems. A 5-channel CMUT sensor array was chemically functionalized and used for the detection of four volatiles, ethanol, toluene, p-xylene, and styrene. All the channels of the sensor array achieved a resolution below 10 ppm within 0.2–3% of OSHA-PEL time-weighted average (TWA) for each volatile. For each test cycle, the maximum frequency shift, the rate of adsorption, and the rate of desorption were extracted as features. Linear discriminant analysis (LDA) was applied to visualize the discrimination performance of the sensor array. The system performance was characterized using an automated testing system. The presented sensor system can be used for identification of volatiles with suitable pattern-recognition techniques.

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.