2D Transducer Research Articles

High Frequency MoS2 Nanomechanical Resonators

Molybdenum disulfide (MoS2), a layered semiconducting material in transition metal dichalcogenides (TMDCs), as thin as a monolayer (consisting of a hexagonal plane of Mo atoms covalently bonded and sandwiched between two planes of S atoms, in a trigonal prismatic structure), has demonstrated unique properties and strong promises for emerging two-dimensional (2D) nanodevices. Here we report on the demonstration of movable and vibrating MoS2 nanodevices, where MoS2 diaphragms as thin as 6 nm (a stack of 9 monolayers) exhibit fundamental-mode nanomechanical resonances up to f0 ~ 60 MHz in the very high frequency (VHF) band, and frequency-quality (Q) factor products up to f0 × Q ~ 2 × 10(10)Hz, all at room temperature. The experimental results from many devices with a wide range of thicknesses and lateral sizes, in combination with theoretical analysis, quantitatively elucidate the elastic transition regimes in these ultrathin MoS2 nanomechanical resonators. We further delineate a roadmap for scaling MoS2 2D resonators and transducers toward microwave frequencies. This study also opens up possibilities for new classes of vibratory devices to exploit strain- and dynamics-engineered ultrathin semiconducting 2D crystals.

OP02.08: Safe/Speedy CVS using needle‐guide and pre‐procedural color/power Doppler

The risk of CVS has still been controversial. CVS has been mostly performed as free-hand method and fetal loss/abortion rate is about 1%. Free-hand method needs expertise and sometimes uterine contraction during tap procedure leads to insufficient sample or the second tap. Between 2009 April and 2012 January, we performed 2,360 CVSs with needle-guided method. The equipment used are Voluson E8 Expert (GE healthcare), transabdominal 2D transducer (4C) with needle-guide, combination of 18G PTC needle (15 cm)/20G PTC needle (20 cm). Just before CVS procedure, CRP is examined and CRP + tive patients postponed the procedure. Pre-procedural color/power Doppler for every CVS was introduced from 2011 April. The risk of this method was calculated and compared to published data. In 2,360 CVS, no case (0%) required multiple tapping excluding 46 DCDA/TCTA. 15 cases (0.64%) had bleeding after procedure. One case (0.04%) had progressive abortion after 4 weeks. Maternal contamination, culture failure were 1/358, 1/358 respectively between April 2009 and January 2010 because of insufficient sample and 0/2002 cases thereafter. There were 4 IUFD cases/1458 (0.27%) with non-hydrops/normal karyotype between 2009 April and 2011 March and after introduction of pre-procedural color/power Doppler for every CVS, 1/902 (0.11%). Needle-guided CVS has advantages of safe and precise tap with no hesitation because of swift tap, steady sheath during procedure therefore no need of assistant. As for 4 cases of IUFD in the first year of our series, the cause was still unknown but our trial to use color/power Doppler for avoiding tap around cord insertion seems to be helpful for lessening CVS risk. The overall risk was less than 0.5%. Disadvantage of needle guide is only the cost.

Recent Results in Nonlinear Strain and Modulus Imaging

We report a summary of recent developments and current status of our team's efforts to image and quantify in vivo nonlinear strain and tissue mechanical properties. Our work is guided by a focus on applications to cancer diagnosis and treatment using clinical ultrasound imaging and quasi-static tissue deformations. We review our recent developments in displacement estimation from ultrasound image sequences. We discuss cross correlation approaches, regularized optimization approaches, guided search methods, multiscale methods, and hybrid methods. Current implementations can return results of high accuracy in both axial and lateral directions at several frames per second.We compare several strain estimators. Again we see a benefit from a regularized optimization approach. We then discuss both direct and iterative methods to reconstruct tissue mechanical property distributions from measured strain and displacement fields. We review the formulation, discretization, and algorithmic considerations that come into play when attempting to infer linear and nonlinear elastic properties from strain and displacement measurements. Finally we illustrate our progress with example applications in breast disease diagnosis and tumor ablation monitoring. Our current status shows that we have demonstrated quantitative determination of nonlinear parameters in phantoms and in vivo, in the context of 2D models and data. We look forward to incorporating 3D data from 2D transducer arrays to noninvasively create calibrated 3D quantitative maps of nonlinear elastic properties of breast tissues in vivo.

On the use of Gegenbauer reconstructions for shock wave propagation modeling

In therapeutic ultrasound, the presence of shock waves can be significant due to the use of high intensity beams, as well as due to shock formation during inertial cavitation. Although modeling of such strongly nonlinear waves can be carried out using spectral methods, such calculations are typically considered impractical, since accurate calculations often require hundreds or even thousands of harmonics to be considered, leading to prohibitive computational times. Instead, time-domain algorithms which generally utilize Godunov-type finite-difference schemes are commonly used. Although these time domain methods can accurately model steep shock wave fronts, unlike spectral methods they are inherently unsuitable for modeling realistic tissue dispersion relations. Motivated by the need for a more general model, the use of Gegenbauer reconstructions as a postprocess tool to resolve the band-limitations of the spectral methods are investigated. The present work focuses on eliminating the Gibbs phenomenon when representing a steep wave front using a limited number of harmonics. Both plane wave and axisymmetric 2D transducer problems will be presented to characterize the proposed method.

Three-dimensional ultrasound imaging

This review is about the development of three-dimensional (3D) ultrasonic medical imaging, how it works, and where its future lies. It assumes knowledge of two-dimensional (2D) ultrasound, which is covered elsewhere in this issue. The three main ways in which 3D ultrasound may be acquired are described: the mechanically swept 3D probe, the 2D transducer array that can acquire intrinsically 3D data, and the freehand 3D ultrasound. This provides an appreciation of the constraints implicit in each of these approaches together with their strengths and weaknesses. Then some of the techniques that are used for processing the 3D data and the way this can lead to information of clinical value are discussed. A table is provided to show the range of clinical applications reported in the literature. Finally, the discussion relating to the technology and its clinical applications to explain why 3D ultrasound has been relatively slow to be adopted in routine clinics is drawn together and the issues that will govern its development in the future explored.

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.

3D estimation of soft biological tissue deformation from radio-frequency ultrasound volume acquisitions

The current research and development of 2D (matrix-shaped) transducer arrays to acquire 3D ultrasound data sets provides new insights into medical ultrasound applications and in particular into elastography. Until very recently, tissue strain estimation techniques commonly used in elastography were mainly 1D or 2D methods. In this paper, a 3D technique estimating biological soft tissue deformation under load from ultrasound radiofrequency volume acquisitions is introduced. This method locally computes axial strains, while considering lateral and elevational motions. Optimal deformation parameters are estimated as those maximizing a similarity criterion, defined as the normalized correlation coefficient, between an initial region and its deformed version, when the latter is compensated for according to these parameters. The performance of our algorithm was assessed with numerical data reproducing the configuration of breast cancer, as well as a physical phantom mimicking a pressure ulcer. Simulation results show that the estimated strain fields are very close to the theoretical values, perfectly discriminating between the harder lesion and the surrounding medium. Experimental strain images of the physical phantom demonstrated the different structures of the medium, even though they are not all detectable on the ultrasound scans. Finally, both simulated and experimental results demonstrate the ability of our algorithm to provide good-quality elastograms, even in the conditions of significant out-of-plane motion.

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.

Stack based multidimensional ultrasonic transducer array

Multilayer piezoelectric fabrication methods are used to produce nD (e.g., 1.5D and 2D) ultrasonic transducer arrays. One embodiment concerns a 1.5 linear transducer in which impedance compensation is provided between the elemental transducers forming the array by varying the number of layers in each row of transducers. In another embodiment, a 2D transducer array is provided wherein elemental transducers are produced by dicing a conventional multilayer actuator to form equal sized elements which are embedded in a polymer matrix.

Terminology of three-dimensional and four-dimensional ultrasound imaging of the fetal heart and other moving body parts.

Terminology of three-dimensional and four-dimensional ultrasound imaging of the fetal heart and other moving body parts.

Two-dimensional (2D) transducer arrays for medical ultrasonic imaging

L'echographie du debut des annees 70 fut marquee par l'avenement du temps reel, evoluant rapidement au cours de la decennie suivante avec la technologie du balayage electronique. L'agilite du balayage electronique autorisera en parallele le perfectionnement de l'imagerie Doppler (CFM) et le niveau de qualite d'image actuel an mode B, comme en CFM, est remarquable. Il est vite devenu evident que la qualite de ces images etait la base limitee par la densite des capteurs du reseau et le nombre de canaux elecfroniques de l'imageur. En revanche, et malgre une activite d'etude considerable, les systemes commercialement viables capables de gerer au moins en partie la deuxieme dimension du reseau 2D commencent juste a apparaitre. Les perspectives de progres ouvertes par cette technique sont extremement attractives: d'une part elle leve deux limitations fondamentales a la qualite image qui sont l'absence de focalisation transverse dynamique et l'impossibilite de correction d'aberration, et d'autre part elle rend possible un veritable mode d'imagerie 3D temps reel. Nous presentons ici l'etat de l'art des technologies des sondes bidimensionnelles. L'expose comporte en outre une breve introduction expliquant les principes physiques justifiant l'avantage de ces nouvelles techniques d'imagerie ainsi que les raisons d'ordre technologique qui les rendent maintenant accessibles et laissent prevoir une rapide generalisation dans les 5 prochaines annees.

Broad-bandwidth radiation patterns of sparse two-dimensional vernier arrays

The fabrication of a dense (one-half wavelength element spacing) two-dimensional (2D) transducer array suitable for medical ultrasound imaging is unrealistic using existing technology. Consequently, there is interest in developing sparse 2D transducer arrays. In this paper, we present the results of a study looking at the broad-bandwidth radiation patterns of 72 different sparse 2D vernier arrays. Suppression of grating lobes is achieved by choosing a different arrangement of transmit and receive elements using an analogy with a vernier scale. The broad-bandwidth radiation patterns were investigated by simulating volumetric sector scan of a point target. We summarize these results by deriving a set of design curves that predicts the minimum number of elements, element spacing, and apodization required for a desired beam width and maximum secondary lobe. The results show that a sparse vernier array can be designed with significantly lower average and peak secondary lobes compared with a sparse random array with the same number of elements and aperture size.

Management of dental trauma: development of a 2D data acquisition system to evaluate passivity of dental splints.

Management of dental trauma in children sometimes requires the use of dental splints, which can be constructed from orthodontic materials. Past studies of the mechanical properties of dental splints have only been interested in their flexibility and not passivity. The purpose of this study is to determine the passivity of splints constructed from orthodontic materials. A specific data acquisition system, with a 2D transducer, is developed for evaluation of its neutrality. The transducer detects the displacements of the splinted tooth generated by the splint. The splints are constructed with 0.406 mm round, straight or Arch Blank preformed stainless-steel wires, with 0.559 mm standard edgewise brackets and with 0.254 mm stainless-steel or 3.05 mm elastomeric ligatures. Results show that mean output voltages generated by the splints range from 1.13 V to 2.48 V. The best control of passivity is obtained with the splints constructed with a preformed archwire and with elastomeric ligatures (p < 0.05), and the worst control is obtained with those constructed with a straight wire and with stainless-steel ligatures (p < 0.05).

Ultrasonic cleaning today

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.