Two-dimensional Transducer Array Research Articles

Gigahertz Optomechanical Photon-Phonon Transduction between Nanostructure Lines.

High-frequency surface phonons have a myriad of applications in telecommunications and sensing, but their generation and detection have often been limited to transducers occupying micron-scale regions because of the use of two-dimensional transducer arrays. Here, by means of transient reflection spectroscopy we experimentally demonstrate optically coupled nanolocalized gigahertz surface phonon transduction based on a gold nanowire emitter arranged parallel to linear gold nanorod receiver arrays, that is, quasi-one-dimensional emitter-receivers. We investigate the response up to 10 GHz of these individual optoacoustic and acousto-optic transducers, respectively, by exploiting plasmon-polariton longitudinal resonances of the nanorods. We also demonstrate how the surface phonon detection efficiency is highly dependent on the nanorod orientation with respect to the phonon wave vector, which constrains the symmetry of the detectable modes, and on the nanorod acoustic resonance spectrum. Applications include nanosensing.

Fabrication of 2D Capacitive Micromachined Ultrasonic Transducer (CMUT) Arrays on Insulating Substrates With Through-Wafer Interconnects Using Sacrificial Release Process

A critical component in a three-dimensional (3D) ultrasound imaging system is a two-dimensional (2D) transducer array. A 2D transducer array is also essential for the implementation of a compact form factor focused ultrasound system for therapeutic applications. Considering the difficulty associated with developing 2D transducer arrays using piezoelectric technology, capacitive micromachined ultrasonic transducer (CMUT) technology with the inherent advantages has emerged as a candidate to develop these devices. Previously, we demonstrated that 2D CMUT arrays can be fabricated with through-glass-via interconnects on borosilicate substrates using anodic bonding. In this paper, we present a fabrication process for implementing $16\times 16$ -element 2D CMUT arrays on an alkali-free glass substrate using the sacrificial release method. The vacuum-sealed $16\times 16$ -element 2D CMUT array is built on an SGW3 glass substrate with copper through-glass interconnects. The fabrication process developed for the 2D CMUT array is described in detail. Across the 256 elements of the 2D CMUT array, the mean resonant frequency is measured as 4.76 MHz with a standard deviation of 46.6 kHz. Also, the mean device capacitance across the array is measured as 1.17 pF with a standard deviation of 0.12 pF, and these results agree with the finite-element analysis. This study shows an alternative method to fabricate 2D CMUT arrays on glass substrates with metal interconnects, especially when the substrate is not suitable for anodic bonding. In addition to improved reliability and reduction in parasitic interconnect capacitance and resistance, this fabrication method benefits from the flexibility of developing 2D CMUT arrays on any type of insulating substrate, and still attain optimum uniformity in both yield and functionality of the fabricated devices. [2019-0246]

Two-dimensional ultrasonic transducer array for shear wave elastography in deep tissues: a preliminary study

This paper investigates the use of shear wave elastography (SWE) in deep tissues with a two-dimensional (2D) transducer array. A 130-element 800-kHz 2D array for SWE in regions deeper than 100 mm is designed, fabricated, and characterized. SWE simulations are performed with the proposed 2D array in a tissue-like medium. The pressure field of the proposed transducer was recorded and utilized to simulate the generation of acoustic radiation force in deep tissues. The elasticity map of the tissue was successfully reconstructed by tracking the speed of shear wave propagation at 120 mm depth. This study suggests that a 2D transducer with proper parameters may provide a means for extending the depth range of SWE.

Calculation and optimization of acoustic radiation force produced by a two-dimensional transducer array

The beam-shape coefficients of a focused sound field from a two-dimensional transducer array are obtained by using the translational addition theorem for spherical functions, and the acoustic radiation force function of a sphere is given in terms of the beam-shape coefficients and the scattering coefficients. The numerical results of acoustic radiation force function show that when the radius of the sphere is much smaller than the acoustic wavelength, the acoustic radiation force function increases sharply with the increase in the radius, while it begins to decrease as the radius continues to increase. Increasing the vibration frequency of the transducer, the array element spacing and the number of elements will enhance the directivity of the acoustic beam and make the acoustic radiation force distribution much more concentrated at the bottom of the sphere. Through optimization of acoustic radiation force distribution by adjusting the phase distribution of the transducer array, the acoustic radiation force distribution range at the bottom of the sphere becomes wider.

Ultrasound Transceiver Beamformer and Delay-control Scheme for a Finger Vein-pattern Sensor based on a 2D Transducer Array

This paper proposes an ultrasound transceiver beamformer (BF) and a delay-control scheme for a finger vein-pattern sensor based on a two-dimensional (2D) transducer array. To facilitate sequential volume scanning without intermittent acquisition of delay information through external interface, delay encoding schemes for each transmitter (TX) and receiver (RX) BF are proposed. Both delay encoding schemes are based on an initialization of on-chip memory. With this delay-encoding scheme and its controller, both TX beamforming and dynamic RX beamforming can be performed sequentially for a 20 x 20 2D array. A TX BF and a RX-BF controller using onchip memory are implemented using register transfer level Verilog. Also, a delay-decoding circuit, which is based on a shift register, is implemented at the transistor level. Through RTL simulation, a sequential focusing operation of TX BF and a delay-encoding result of RX BF are illustrated. Also, a mixed-signal simulation for the BF controller along with the RX BF is performed to show a dynamic RX beamforming operation. A chip incorporating proposed TX BF and BF controller is implemented using a 180-nm (bipolar-CMOS-DMOS) BCD process. In simulation results, achieved power and active area per channel are 0.24 mW and 0.22㎟, respectively.

Two-sided residual refocusing for an acoustic lens-based photoacoustic imaging system

In photoacoustic (PA) cameras, an acoustic lens-based system can form a focused image of an object plane. A real-time C-scan PA image can be formed by simply time gating the transducer response. While most of the focusing action is performed by the lens, residual refocusing is needed to image multiple depths with high resolution simultaneously. However, a refocusing algorithm for a PA camera has not been studied so far in the literature. In this work, we reformulate this residual refocusing problem for a PA camera into a two-sided wave propagation from a planar sensor array. One part of the problem deals with forward wave propagation while the other deals with time reversal. We have chosen a fast Fourier transform (FFT) based wave propagation model for the refocusing to maintain the real-time nature of the system. We have conducted point spread function (PSF) measurement experiments at multiple depths and refocused the signal using the proposed method. The full width at half maximum (FWHM), peak value and signal to noise ratio (SNR) of the refocused PSF is analyzed to quantify the effect of refocusing. We believe that using a two-dimensional transducer array combined with the proposed refocusing can lead to real-time volumetric imaging using a PA camera.

A Wearable Transcranial Doppler Ultrasound Phased Array System.

Practical deficiencies related to conventional transcranial Doppler (TCD) sonography have restricted its use and applicability. This work seeks to mitigate several such constraints through the development of a wearable, electronically steered TCD velocimetry system, which enables noninvasive measurement of cerebral blood flow velocity (CBFV) for monitoring applications with limited operator interaction. A highly-compact, discrete prototype system was designed and experimentally validated through flow phantom and preliminary human subject testing. The prototype system incorporates a custom two-dimensional transducer array and multi-channel transceiver electronics, thereby facilitating acoustic beamformation via phased array operation. Electronic steering of acoustic energy enables algorithmic system controls to map Doppler power throughout the tissue volume of interest and localize regions of maximal flow. Multi-focal reception permits dynamic vessel position tracking and simultaneous flow velocimetry over the time-course of monitoring. Experimental flow phantom testing yielded high correlation with concurrent flowmeter recordings across the expected range of physiological flow velocities. Doppler power mapping has been validated in both flow phantom and preliminary human subject testing, resulting in average vessel location mapping times <14 s. Dynamic vessel tracking has been realized in both flow phantom and preliminary human subject testing. A wearable prototype CBFV measurement system capable of autonomous vessel search and tracking has been presented. Although flow phantom and preliminary human validation show promise, further human subject testing is necessary to compare velocimetry data against existing commercial TCD systems. Additional human subject testing must also verify acceptable vessel search and tracking performance under a variety of subject populations and motion dynamics-such as head movement and ambulation.

MEDICAL IMAGING APPARATUS

The time for obtaining ultrasonic images can be reduced by using a two-dimensional transducer array and good radiation images can be obtained even when radiation imaging is performed with the fixed array. The medical imaging apparatus includes a radiation generating unit for generation radiation, a radiation detecting unit for detecting radiation, an ultrasonic transducer array provided between the radiation generating unit and the radiation detecting unit and including two-dimensionally arranged ultrasonic transducers, a radiation image data generating unit for generating radiation image data based on a detection result of the radiation detecting unit, and an image processing unit for performing image processing on the radiation image data generated based on a detection result of radiation transmitted through an object to be inspected and the ultrasonic transducer array, thereby removing an image of the ultrasonic transducer array from a radiation image represented by the radiation image data.

SYSTEM AND METHOD FOR ULTRASOUND IMAGING WITH A CONFIGURABLE RECEIVE APERTURE

A system and method of ultrasound imaging includes a beamformer including a plurality of channels, a two-dimensional transducer array including a plurality of elements, and a plurality of signal pathways linking the plurality of elements to the plurality of channels. The system and method also include a plurality of switches positioned along the plurality of signal pathways. The plurality of switches being configured to actively connect a subset of the plurality of elements to the plurality of channels in order to form a receive aperture. The plurality of switches are further configured to control an aspect ratio of the receive aperture by changing which of the plurality of elements are actively connected to the plurality of channels.

Steered Continuous Wave Doppler Methods and Systems for Two-Dimensional Ultrasound Transducer Arrays

Steered Continuous Wave Doppler Methods and Systems for Two-Dimensional Ultrasound Transducer Arrays

Steered continuous wave Doppler methods and systems for two-dimensional ultrasound transducer arrays

Methods and systems for acquiring spectral and velocity information with a multi-dimensional array are provided. For example, a dedicated receive aperture is formed at a multi-dimensional array for steered continuous wave imaging. Other elements not within the dedicated receive aperture are used for transmitting continuous waves or transmitting and receiving pulsed waveforms in other modes of imaging. As another example, switches or other structures are provided for selecting between a plurality of possible apertures for a steered continuous wave aperture. The selection is performed in response to a configuration of an ultrasound system, such as selection of a focal location or steer direction. The aperture is then used for either transmit or receive operations of steered continuous wave imaging. As yet another example, at least part of the steered continuous wave beamformer is provided within a transducer assembly. The transducer assembly includes a probe housing and a connector housing electrically connected by a cable. In yet another example, at least one angle of a three-dimensional indication of flow direction is input from a user. Velocity values in either steered continuous wave imaging or pulsed wave imaging are corrected as a function of a three-dimensional indication of flow direction.

Steered continuous wave Doppler methods and systems for two-dimensional ultrasound transducer arrays

Steered continuous wave Doppler methods and systems for two-dimensional ultrasound transducer arrays

Three-dimensional photoacoustic imaging using a two-dimensional CMUT array

In this paper, we describe using a 2-D array of capacitive micromachined ultrasonic transducers (CMUTs) to perform 3-D photoacoustic and acoustic imaging. A tunable optical parametric oscillator laser system that generates nanosecond laser pulses was used to induce the photoacoustic signals. To demonstrate the feasibility of the system, 2 different phantoms were imaged. The first phantom consisted of alternating black and transparent fishing lines of 180 mum and 150 mum diameter, respectively. The second phantom comprised polyethylene tubes, embedded in chicken breast tissue, filled with liquids such as the dye indocyanine green, pig blood, and a mixture of the 2. The tubes were embedded at a depth of 0.8 cm inside the tissue and were at an overall distance of 1.8 cm from the CMUT array. Two-dimensional cross-sectional slices and 3-D volume rendered images of pulse-echo data as well as photoacoustic data are presented. The profile and beamwidths of the fishing line are analyzed and compared with a numerical simulation carried out using the Field II ultrasound simulation software. We investigated using a large aperture (64 x 64 element array) to perform photoacoustic and acoustic imaging by mechanically scanning a smaller CMUT array (16 x 16 elements). Two-dimensional transducer arrays overcome many of the limitations of a mechanically scanned system and enable volumetric imaging. Advantages of CMUT technology for photoacoustic imaging include the ease of integration with electronics, ability to fabricate large, fully populated 2-D arrays with arbitrary geometries, wide-bandwidth arrays and high-frequency arrays. A CMUT based photoacoustic system is proposed as a viable alternative to a piezoelectric transducer based photoacoustic systems.

Correlation analysis of three-dimensional strain imaging using ultrasound two-dimensional array transducers

Two-dimensional (2D) transducer arrays represent a promising solution for implementing real time three-dimensional (3D) ultrasound elastography. 2D arrays enable electronic steering and focusing of ultrasound beams throughout a 3D volume along with improved slice thickness performance when compared to one-dimensional (1D) transducer arrays. Therefore, signal decorrelation caused by tissue motion in the elevational (out-of-plane) direction needs to be considered. In this paper, a closed form expression is derived for the correlation coefficient between pre- and postdeformation ultrasonic radio frequency signals. Signal decorrelation due to 3D motion of scatterers within the ultrasonic beam has been considered. Computer simulations are performed to corroborate the theoretical results. Strain images of a spherical inclusion phantom generated using 1D and 2D array transducers are obtained using a frequency domain simulation model. Quantitative image quality parameters, such as the signal-to-noise and contrast-to-noise ratios obtained using 1D, 2D, and 3D motion tracking algorithms, are compared to evaluate the performance with the 3D strain imaging system. The effect of the aperture size for 2D arrays and other factors that affect signal decorrelation are also discussed.

Fabrication and evaluation of fully-sampled, two-dimensional transducer array for “Sonic Window” imaging system

A low-cost, fully-sampled, 3600 element 2D transducer array operating at 5 MHz and designed for use in a hand-held ultrasound system is described here. Four array configurations are presented – (1) array with both matching and pedestal backing layers, (2) array with a matching layer but no backing pedestal, (3) array with a backing pedestal but no matching layer, and (4) array with neither matching layer nor backing pedestal. Each array was characterized in terms of impedance measurements, pulse-echo response, and experimental beamprofile. Comparative finite element analysis simulations are also presented. Average estimated active element yield for the four arrays was 94%. The array with pedestal layer proved the most promising, providing a 26% bandwidth and a 1.7 dB improvement in sensitivity with respect to the array with neither pedestal nor matching layer. Although this bandwidth is acceptable for our specific application (C-scan imaging), reverberations within the substrate material remain a potential challenge. We are currently working to fabricate a custom PCB material to address this concern, and may also consider using a pre-compensated transmit waveform or matched digital filter approach to further reduce the effects of such reverberations.

Integration of 2D CMUT arrays with front-end electronics for volumetric ultrasound imaging

For three-dimensional (3D) ultrasound imaging, connecting elements of a two-dimensional (2D) transducer array to the imaging system's front-end electronics is a challenge because of the large number of array elements and the small element size. To compactly connect the transducer array with electronics, we flip-chip bond a 2D 16 x 16-element capacitive micromachined ultrasonic transducer (CMUT) array to a custom-designed integrated circuit (IC). Through-wafer interconnects are used to connect the CMUT elements on the top side of the array with flip-chip bond pads on the back side. The IC provides a 25-V pulser and a transimpedance preamplifier to each element of the array. For each of three characterized devices, the element yield is excellent (99 to 100% of the elements are functional). Center frequencies range from 2.6 MHz to 5.1 MHz. For pulse echo operation, the average - 6-dB fractional bandwidth is as high as 125%. Transmit pressures normalized to the face of the transducer are as high as 339 kPa and input-referred receiver noise is typically 1.2 to 2.1 mPa/pHz. The flip-chip bonded devices were used to acquire 3D synthetic aperture images of a wire-target phantom. Combining the transducer array and IC, as shown in this paper, allows for better utilization of large arrays, improves receive sensitivity, and may lead to new imaging techniques that depend on transducer arrays that are closely coupled to IC electronics.

Novel transmit protection scheme for ultrasound systems

The problem of protecting or isolating extremely sensitive receive circuitry from high-voltage transmit circuitry is commonly addressed through the use of diode bridges, transformers, or high-voltage switches, which prove to be prohibitively expensive, bulky, and power consuming for use in portable, low-cost, battery-powered systems. These approaches also compound the interconnect difficulties associated with two-dimensional (2-D) transducer arrays. In this paper we present a novel transmit protection scheme that allows compact MOSFET shunting devices to be brought on-chip within each receive channel implemented in a standard CMOS integrated circuit process. During transmit, the high voltage transmit pulse is driven onto the common connection of the transducer array and the on-chip MOSFET devices shunt the current to ground. During receive, these devices are turned off, the common connection of the transducer array is shunted to ground, and the received echo can be detected as usual. The transmit protection scheme was experimentally shown to shunt a 16 mA peak current resulting from the equivalent of a 100-V, 25-ns-risetime transmit pulse through a 4 pF transducer element. The scheme was also incorporated into a prototype 1024-channel, low-cost, ultrasound system successfully used to form pulse echo images.

Transesophageal and transnasal, transesophageal ultrasound imaging system

A semi-invasive ultrasound imaging system for imaging biological tissue includes a transesophageal probe or a transnasal, transesophageal probe connected to a two-dimensional ultrasound transducer array, a transmit beamformer, a receive beamformer, and an image generator. The two-dimensional transducer array is disposed on a distal portion of the probe's elongated body. The transmit beamformer is connected to the transducer array and is constructed to transmit several ultrasound beams over a selected pattern defined by azimuthal and elevation orientations. The receive beamformer is connected to the transducer array and is constructed to acquire ultrasound data from the echoes reflected over a selected tissue volume. The tissue volume is defined by the azimuthal and elevation orientations and a selected scan range. The receive beamformer is constructed to synthesize image data from the acquired ultrasound data. The image generator is constructed to receive the image data and generate images that are displayed on an image display. Preferably, the image generator is constructed to generate, from the image data, several orthographic projection views over the selected tissue volume.

Two-dimensional ultrasonic transducer array having transducer elements in a non-rectangular or hexagonal grid for medical diagnostic ultrasonic imaging and ultrasound imaging system using same

Two-dimensional transducer arrays used for one-, two- and three-dimensional medical diagnostic ultrasonic imaging. The transducer arrays have transducer elements that are arranged in a non-rectangular, and preferably hexagonal grid. In a preferred embodiment, the transducer array has hexagonally shaped transducer elements. The transducer arrays may be fabricated as single or multiple layer structures. Sparse transducer arrays may be fabricated in a hexagonal grid by connecting selected transducer elements to the imaging system. Also, the transducer array may comprise random, vernier and spiral arrays fabricated in a hexagonal grid.

A small 2D ultrasonic array for NDT applications

A prototype of two-dimensional transducer array with reduced number of elements, based on segmented annular distribution is presented. The capability of this array to produce volumetric imaging is compared to the equivalent conventional 2D squared matrix array. The comparison between both apertures is made for the cases of the full-array emission/reception mode and SAFT mode. From the analysis it is deduced that the segmented annular arrays produce lower grating lobes than squared arrays, improving the image contrast. The fabrication process of a segmented annular array of 64 elements and the experimental work made with this array transducer is also presented in this paper.