Ultrasonic Force Research Articles

Colloidal particle size of fumed silica dispersed in solution and the particle size effect on silica gelation and some electrochemical behaviour in gelled electrolyte

Commercial-grade fumed silica was dispersed by mechanical shearing and/or ultrasonic force to produce dispersed silica particles with different sizes. The light-scattering technique and a diagrammatic method of extrapolation used to eliminate the influence of particle interaction were applied to determine the size of the particles. Then, the effect of particle size on the gelation of fumed silica in sulphuric acid medium, as well as some electrochemical properties, such as ion transfer and redox capacities of lead, in the gelled electrolyte were examined. The results showed that the size of dispersed particles affected the gelation of fumed silica itself: with increasing size, the thixotropy of the system increased and the gelling time decreased, particularly for those particles obtained only by simple stirring. The strength of the gel increased with increasing particle size. At an identical silica content, the increase in particle size led to a decrease in the density of the particles: this weakened the three-dimensional structure of the silica particle network and reduced the efficiency of ion transfer. However, the effect of silica particle size on the redox capacities of lead was negligible.

초음파원자현미경을 이용한 나노스케일 박막 코팅층에 대한 탄성특성 평가

Article history: Ultrasonic atomic force microscopy (Ultrasonic-AFM) has been used to investigate the elastic property of the ultra-thin coating layer in a thin-film system. The modified Hertzian theory was applied to predict the contact resonance frequency through accurate theoretical analysis of the dynamic characteristics of the cantilever. We coat 200 nm thick Aluminum and Titanium thin films on the substrate using the DC Magnetron sputtering method. The amplitude and phase of the contact resonance frequency of a vibrating cantilever varies in response to the local stiffness constant. Ultrasonic-AFM images were obtained using the variations in the elastic property of the materials. The morphology of the surface was clearly observed in the Ultrasonic-AFM images, but was barely visible in the topography. This research demonstrates that Ultrasonic-AFM is a promising technique for visualizing the distribution of local stiffness in the nano-scale thin coatings.

Harmonic motion imaging for abdominal tumor detection and high-intensity focused ultrasound ablation monitoring: an in vivo feasibility study in a transgenic mouse model of pancreatic cancer.

Harmonic motion imaging (HMI) is a radiationforce- based elasticity imaging technique that tracks oscillatory tissue displacements induced by sinusoidal ultrasonic radiation force to assess the resulting oscillatory displacement denoting the underlying tissue stiffness. The objective of this study was to evaluate the feasibility of HMI in pancreatic tumor detection and high-intensity focused ultrasound (HIFU) treatment monitoring. The HMI system consisted of a focused ultrasound transducer, which generated sinusoidal radiation force to induce oscillatory tissue motion at 50 Hz, and a diagnostic ultrasound transducer, which detected the axial tissue displacements based on acquired radio-frequency signals using a 1-D cross-correlation algorithm. For pancreatic tumor detection, HMI images were generated for pancreatic tumors in transgenic mice and normal pancreases in wild-type mice. The obtained HMI images showed a high contrast between normal and malignant pancreases with an average peak-to-peak HMI displacement ratio of 3.2. Histological analysis showed that no tissue damage was associated with HMI when it was used for the sole purpose of elasticity imaging. For pancreatic tumor ablation monitoring, the focused ultrasound transducer was operated at a higher acoustic power and longer pulse length than that used in tumor detection to simultaneously induce HIFU thermal ablation and oscillatory tissue displacements, allowing HMI monitoring without interrupting tumor ablation. HMI monitoring of HIFU ablation found significant decreases in the peak-to-peak HMI displacements before and after HIFU ablation with a reduction rate ranging from 15.8% to 57.0%. The formation of thermal lesions after HIFU exposure was confirmed by histological analysis. This study demonstrated the feasibility of HMI in abdominal tumor detection and HIFU ablation monitoring.

Harmonic motion imaging for pancreatic tumor detection and high-intensity focused ultrasound ablation monitoring

Harmonic motion imaging (HMI) is a radiation force-based elasticity imaging technique that estimates tissue harmonic displacements induced by an oscillatory ultrasonic radiation force to assess tissue stiffness. The objective of this study was to evaluate the feasibility of applying HMI on pancreatic tumor detection and high-intensity focused ultrasound (HIFU) treatment monitoring.

Comparison of Acoustic Radiation Force Impulse Imaging Derived Carotid Plaque Stiffness With Spatially Registered MRI Determined Composition.

Measurements of plaque stiffness may provide important prognostic and diagnostic information to help clinicians distinguish vulnerable plaques containing soft lipid pools from more stable, stiffer plaques. In this preliminary study, we compare in vivo ultrasonic Acoustic Radiation Force Impulse (ARFI) imaging derived measures of carotid plaque stiffness with composition determined by spatially registered Magnetic Resonance Imaging (MRI) in five human subjects with stenosis > 50%. Ultrasound imaging was implemented on a commercial diagnostic scanner with custom pulse sequences to collect spatially registered 2D longitudinal B-mode and ARFI images. A standardized, multi-contrast weighted MRI sequence was used to obtain 3D Time of Flight (TOF), T1 weighted (T1W), T2 weighted (T2W), and Proton Density Weighted (PDW) transverse image stacks of volumetric data. The MRI data was segmented to identify lipid, calcium, and normal loose matrix components using commercially available software. 3D MRI segmented plaque models were rendered and spatially registered with 2D B-mode images to create fused ultrasound and MRI volumetric images for each subject. ARFI imaging displacements in regions of interest (ROIs) derived from MRI segmented contours of varying composition were compared. Regions of calcium and normal loose matrix components identified by MRI presented as homogeneously stiff regions of similarly low (typically ≈ 1 μm) displacement in ARFI imaging. MRI identified lipid pools > 2 mm(2), found in three out of five subjects, presented as softer regions of increased displacement that were on average 1.8 times greater than the displacements in adjacent regions of loose matrix components in spatially registered ARFI images. This work provides early evidence supporting the use of ARFI imaging to noninvasively identify lipid regions in carotid artery plaques in vivo that are believed to increase the propensity of a plaque to rupture. Additionally, the results provide early training data for future studies and aid in the interpretation and possible clinical utility of ARFI imaging for identifying the elusive vulnerable plaque.

Utilizing NeuroTouch, a virtual reality simulator, to assess and monitor bimanual performance during brain tumor resection

Background: NeuroTouch simulator provides the potential to determine performance metrics, but validation and easily utilized software are essential before implementation of this platform into neurosurgical training. Objectives: Evaluate and validate neurosurgical performance metrics for simulated brain tumors resection. Develop software and a global web based system to allow utilization of these metrics. Methods: The bimanual resection of 8 simulated brain tumors with differing complexity was evaluated. Software was developed to automatically generate all the metrics from NeuroTouch data output including: blood loss, tumor percentage resected, total brain volume removed, maximum and sum of forces utilized, efficiency index, ultrasonic aspirator path length index (UAPLI), coordination index and ultrasonic aspirator bimanual forces ratio (UABFR). Six neurosurgeons and 12 residents were evaluated. Results: Resident performance was significantly more impaired than neurosurgeon by increasing tumor complexity. Significant differences were found between neurosurgeons, senior, and junior residents on efficiency index and UAPLI. UABFR outlined significant differences between senior and junior residents. Coordination index demonstrated significant differences between junior residents and neurosurgeons. Conclusions: Utilizing metrics employed the NeuroTouch platform differentiated novice from expert performance. Software was developed for metrics and will be made available online for all NeuroTouch users allowing global comparison of neurosurgical performance.

Acute stress decreases bimanual psychomotor performance during resection of simulated brain tumors

Background: Objective methods to assess the influence of significant stress on neurosurgical bimanual psychomotor performance have not been developed. We utilized NeuroTouch, a virtual reality simulator, to answer two questions: 1) What is the impact of significant stress on bimanual psychomotor performance during the resection of a simulated tumor? 2) Does stress influence performance immediately following the stressful episode? Methods: Uncontrollable ‘intraoperative’ bleeding during one of the tumor resections resulting in simulated patient cardiac arrest served as the acute stressor. Six neurosurgeons, 6 senior and 6 junior neurosurgical residents and 6 senior medical students were studied. The evaluated advanced tier 2 metrics were efficiency index, ultrasonic aspirator path length index, suction coordination index and ultrasonic aspirator bimanual forces ratio. Results: The stress scenario significantly decreased the efficiency index of all groups and significantly decreased performance for many groups for suction coordination index and ultrasonic aspirator path length index. Performance in all advanced tier 2 metrics returned to pre-stress levels in post stress resection scenarios. Conclusions: Our results are consistent with the concept that acute stress initiated by severe intraoperative bleeding significantly decreases bimanual psychomotor performance during the acute episode but had no significant influence on immediate post stress operative performance.

Surface and interfacial interactions of multilayer graphitic structures with local environment

In order to exploit the potential of graphene in next-generation devices, such as supercapacitors, rechargeable batteries, displays and ultrathin sensors, it is crucial to understand the solvent interactions with the graphene surface and interlayers, especially where the latter may be in competition with the former, in the medium of application deployment. In this report, we combine quartz crystal microbalance (QCM) and ultrasonic force microscopy methods to investigate the changes in the film–substrate and film–environment interfaces of graphene and graphene oxide films, produced by diverse scalable routes, in both polar (deionised water) and non-polar (dodecane) liquid and vapour environments. In polar liquid environments, we observe nanobubble adsorption/desorption on the graphene film corresponding to a surface coverage of up to 20%. As no comparable behaviour is observed for non-polar environment, we conclude that nanobubble formation is directly due to the hydrophobic nature of graphene with direct consequences for electrode structures immersed in electrolyte solutions. The amount of water adsorbed by the graphene films was found to vary considerably from 0.012 monolayers of water per monolayer of reduced graphene oxide to 0.231 monolayers of water per monolayer of carbon diffusion growth graphene. This is supported by direct nanomechanical mapping of the films immersed in water where an increased variation of local stiffness suggests water propagation within the film and/or between the film and substrate. Transferred film thickness calculations performed for QCM, atomic force microscopy topography and optical transmission measurements, returns results an order of magnitude larger (46±1 layers) than Raman spectroscopy (1 - 2 graphene layers) on pristine pre-transferred films due to contamination during transfer and possible turbostratic structures of large areas.

Neurosurgical Assessment of Metrics Including Judgment and Dexterity Using the Virtual Reality Simulator NeuroTouch (NAJD Metrics).

Advances in computer-based technology has created a significant opportunity for implementing new training paradigms in neurosurgery focused on improving skill acquisition, enhancing procedural outcome, and surgical skills assessment. NeuroTouch is a computer-based virtual reality system that can generate output data known as metrics from operator performance during simulated brain tumor resection. These measures of quantitative assessment are used to track and compare psychomotor performance during simulated operative procedures. Data output from the NeuroTouch system is recorded in a comma-separated values file. Data mining from this file and subsequent metrics development requires the use of sophisticated software and engineering expertise. In this article, we introduce a system to extract a series of new metrics using the same data file using Excel software. Based on the data contained in the NeuroTouch comma-separated values file, 13 novel NeuroTouch metrics were developed and classified. Tier 1 metrics include blood loss, tumor percentage resected, and total simulated normal brain volume removed. Tier 2 metrics include total instrument tip path length, maximum force applied, sum of forces utilized, and average forces utilized by the simulated ultrasonic aspirator and suction instrument along with pedal activation frequency of the ultrasonic aspirator. Advanced tier 2 metrics include instrument tips average separation distance, efficiency index, ultrasonic aspirator path length index, coordination index, and ultrasonic aspirator bimanual forces ratio. This system of data extraction provides researchers expedited access for analyzing the data files available for NeuroTouch platform to assess the multiple psychomotor and cognitive neurosurgical skills involved in complex surgical procedures.

Structural, optical and electrostatic properties of single and few-layers MoS2: effect of substrate

We have decoupled the intrinsic electrostatic effects arising in monolayer and few-layer MoS2 from those influenced by the flake-substrate interaction. Using ultrasonic force microscopy nanomechanical mapping, we identify the change from supported to suspended flake regions on a trenched substrate. These regions are correlated with the surface potential as measured by scanning Kelvin probe microscopy. Relative to the supported region, we observe an increase in surface potential contrast due to suppressed charge transfer for the suspended monolayer. Using Raman spectroscopy we observe a red shift of the E12g mode for monolayer MoS2 deposited on Si, consistent with a more strained MoS2 on the Si substrate compared to the Au substrate.

Ultrasonic assisted cross-flow ultrafiltration of starch and cellulose nanocrystals suspensions: Characterization at multi-scales

This study investigates for the first time the behaviors of starch and cellulose nanocrystals (SNC and CNC) suspensions which are simultaneously subjected to pressure, shear flow and ultrasound (US) during cross-flow ultrafiltration. This multi-forces process was characterized from macro-scales to nano-scales, with a custom designed “SAXS Cross-Flow US-coupled Filtration Cell”. In addition, rheological behaviors of SNC samples at different concentrations/temperatures have been investigated. In both cases (ultrafiltration of SNC and CNC suspensions), better performances were observed with US. The in-situ SAXS measurements revealed that for SNC suspensions, no structure change occurred at the length scales range from 10 to 60nm in this multi-forces process, while CNC particles exhibited an ordered arrangement within the concentrated layer during the same process. SNC particles accumulated on the membrane surface forming a “fragile” concentrated layer which was removed very quickly by subsequent applied US. In contrary, the CNC particles accumulation was very severe, the additional ultrasonic force led to a disruption but not a totally removal of the CNC concentrated layer.

Revealing the flexoelectricity in the mixed-phase regions of epitaxial BiFeO3 thin films.

Understanding the elastic response on the nanoscale phase boundaries of multiferroics is an essential issue in order to explain their exotic behaviour. Mixed-phase BiFeO3 films, epitaxially grown on LaAlO3 (001) substrates, have been investigated by means of scanning probe microscopy to characterize the elastic and piezoelectric responses in the mixed-phase region of rhombohedral-like monoclinic (MI) and tilted tetragonal-like monoclinic (MII,tilt) phases. Ultrasonic force microscopy reveal that the regions with low/high stiffness values topologically coincide with the MI/MII,tilt phases. X-ray diffraction strain analysis confirms that the MI phase is more compliant than the MII,tilt one. Significantly, the correlation between elastic modulation and piezoresponse across the mixed-phase regions manifests that the flexoelectric effect results in the enhancement of the piezoresponse at the phase boundaries and in the MI regions. This accounts for the giant electromechanical effect in strained mixed-phase BiFeO3 films.

Nonlinear Effects in Ultrasound Fields of Diagnostic-type Transducers Used for Kidney Stone Propulsion: Characterization in Water.

Newer imaging and therapeutic ultrasound technologies require higher in situ pressure levels compared to conventional diagnostic values. One example is the recently developed use of focused ultrasonic radiation force to move kidney stones and residual fragments out of the urinary collecting system. A commercial diagnostic 2.3 MHz C5-2 array probe is used to deliver the acoustic pushing pulses. The probe comprises 128 elements equally spaced at the 55 mm long convex cylindrical surface with 38 mm radius of curvature. The efficacy of the treatment can be increased by using higher transducer output to provide stronger pushing force; however, nonlinear acoustic saturation effect can be a limiting factor. In this work nonlinear propagation effects were analyzed for the C5-2 transducer using a combined measurement and modeling approach. Simulations were based on the 3D Westervelt equation; the boundary condition was set to match low power pressure beam scans. Focal waveforms simulated for increased output power levels were compared with the fiber-optic hydrophone measurements and were found in good agreement. It was shown that saturation effects do limit the acoustic pressure in the focal region of the transducer. This work has application to standard diagnostic probes and imaging.

OS6-16 A Study of Relation between Scattering Parameter for Ultrasonic Waves and Axial Force in Bolt Conclusions(Measurement Techniques using Ultrasonics (1),OS6 Ultrasonic non-destructive testing and evaluation,MEASUREMENT METHODS)

OS6-16 A Study of Relation between Scattering Parameter for Ultrasonic Waves and Axial Force in Bolt Conclusions(Measurement Techniques using Ultrasonics (1),OS6 Ultrasonic non-destructive testing and evaluation,MEASUREMENT METHODS)

A Numerical Analysis of Phononic-Assisted Control of Ultrasound Waves in Acoustofluidic Device

The ability to precisely sort individual microparticles/cells/droplets in suspension is important for various chemical and biological applications such as cancer cell detection, drug screening etc. The past decade, label- free particle handling of particle suspensions by ultrasonic radiation forces and streaming has received much attention, since it relies solely on mechanical properties such as particle size and contrast in density and compressibility. We present a theoretical study of phononic-assisted control of ultrasound waves in acoustofluidic devices. We propose the use of phononic crystal diffractors, which can be introduced in acoustofluidic structures. These diffractors can be applied in the design of efficient resonant cavities, directional sound waves for new types of particle sorting methods, or acoustically controlled deterministic lateral displacement. The PnC-diffractor-based devices can be made configurable, by embedding the diffractors, all working at the same excitation frequency but with different resulting diffraction patterns, in exchangeable membranes on top of the device.

유한요소 해석을 이용한 초음파원자현미경 캔틸레버의 접촉 공진주파수 특성 분석

Ultrasonic atomic force microscopy(Ultrasonic-AFM) can be used to obtain images of the elastic properties of a subsurface and to evaluate the elastic properties by measuring the contact resonance frequency. When a tip is in contact with the sample, it is necessary to understand the cantilever behavior and the tip-sample interaction for the quantitative and reliable analysis. Therefore, precise analysis models that can accurately simulate the tip-sample contact arerequired; these can serve as good references for predicting the contact resonance frequency. In this study, modal analyses of the first four modes were performed to calculate the contact resonance frequency by using a spring model, and the deformed shapes of the cantilever were visualized at each mode. We presented the contact characteristics of the cantilever with a variety of contact conditions by applying the contact area, contact material thickness, and material properties as the parameters for the FEM analysis.Received 5 August 2014Revised 15 September 2014Accepted 7 October 2014

Processing and structural properties of random oriented lead lanthanum zirconate titanate thin films

Polycrystalline lead lanthanum zirconate titanate (PLZT) thin films have been prepared by a polymeric chemical route to understand the mechanisms of phase transformations and map the microstructure and elastic properties at the nanoscale in these films. X-ray diffraction, atomic force microscopy (AFM) and ultrasonic force microscopy (UFM) have been used as investigative tools. On one side, PLZT films with mixed-phase show that the pyrochlore phase crystallizes predominantly in the bottom film-electrode interface while a pure perovskite phase crystallizes in top film surface. On the contrary, pyrochlore-free PLZT films show a non-uniform microstrain and crystallite size along the film thickness with a heterogeneous complex grainy structure leading to different elastic properties at nanoscale.

Local thermal-assisted ultrasonic embossing for the fabrication of polymer microstructures

A new technique was developed for embossing microstructures on thermoplastic substrates, which can achieve high accuracy replication with little loss of the production efficiency. The technique is no need of the preheating process and cooling device. In the new technique, just the surface layer of the polymer substrate was heated through heat transmission and ultrasonic viscoelastic heating was the major heat source. For our new technology, the temperature of the mould just provided the initial temperature of the mould-substrate interface and a higher boundary temperature for embossing. The replication accuracies of three embossing technologies were contrasted, including ultrasonic embossing at room temperature (HER), thermal assisted ultrasonic embossing (TUE) and local thermal assisted ultrasonic embossing (L-TUE). The results indicated that, the replication accuracy of L-TUE was approximate with TUE. Moreover, the effects of the processing parameters on the replication quality, including average replication depth and uniformity over the entire chip, were investigated. Different with our prediction, the replication accuracy did not monotonously improved with the ultrasonic force and the temperature of the mold. Finally, the temperature test was carried out to study the temperature characteristic of our new technology.

Multimodal microscopy using ‘half and half’ contact mode and ultrasonic force microscopy

Advances in the design and fabrication of multifunctional nanostructured materials require characterization techniques capable of simultaneously mapping multiple material properties with nanoscale resolution. We show that this can be achieved by combining nanomechanical information from ultrasonic force microscopy (UFM) with simultaneously acquired friction force and conductivity measurements from contact mode scanning. This utilizes a ‘half and half’ approach, where the AFM is operated alternatively in UFM and contact mode, with the switching rate sufficiently fast that simultaneous contact mode and UFM information is acquired at each pixel of an image. We demonstrate the potential of such a multimodal approach through its application to composite systems consisting of graphene islands on a copper surface, single-walled carbon nanotubes (SWNTs) on a silicon oxide substrate, and a graphene epoxy composite. The half and half approach enables the friction force to be measured without topographical cross-talk. Application to the SWNT sample reveals a further advantage; due to the superlubricity of UFM it enables standard contact mode imaging techniques to be applied to delicate samples.

Interface Functionalities in Multilayer Stack Organic Light Emitting Transistors (OLETs)

Herein is described a multidisciplinary approach to understand the performance limitations of small molecule organic light emitting transistors (OLETs) based on a layered architecture, an innovative architecture potentially competitive with the state of the art and more flexible for spectral emission control. The processes of charge injection and field‐effect transport at metal/organic and organic/organic interfaces are analysed using microscopic and spectroscopic techniques in coordination. Atomic force microscopy and ultrasonic force microscopy are employed to characterize the interface morphology and the initial growth stages of organic films where charge transport actually occurs. X‐ray diffraction and near edge X‐ray dichroic absorption with linearly polarised light allow to determine the unit cell packing and the molecular orientation at the active organic interfaces, as well as the amount of non‐ordered domains. Moreover, chemical reactivity at the interfaces is measured by X‐ray photoelectron spectroscopy. It is found that a strong reaction occurs at the metal‐organic interfaces, with molecular fragmentation. Additionally, the transport properties strongly depend on the nature of the materials forming the organic stack. Specifically, amorphous conjugated films as bottom layers can promote an increased molecular disorder in the upper active layer, with a concomitant deterioration of the conduction properties.