Ultrasonic Pressure Research Articles

Pulmonary Capillary Hemorrhage Induced by Acoustic Radiation Force Impulse Shear Wave Elastography in Ventilated Rats.

Diagnostic ultrasound (DUS) imaging can induce pulmonary capillary hemorrhage (PCH), possibly related to the ultrasonic radiation surface pressure arising from reflection at the lung blood-air interfaces. Acoustic radiation force impulse (ARFI) elastography is a relatively new DUS mode with high-energy "push pulses" used to move tissue and generate shear waves. The objective of this study was to characterize PCH induced by the ARFI elastographic mode for comparison with other previously tested DUS modes. Pulmonary capillary hemorrhage induction was examined for ARFI elastographic frames with 5.7-MHz push pulses (Acuson S3000; Siemens Medical Solutions, Mountain View, CA), which had a derated PRPA of 2.6 MPa. Groups of rats with tracheal tube placement had no ventilation (spontaneous breathing), intermittent positive pressure ventilation (IPPV), or IPPV plus 8 cm H2 O of positive end-expiratory pressure (PEEP). Exposure was to 1 or 20 manually triggered image frame acquisitions. The PCH area was measured on the lung surface. All 20-frame exposure groups, and even the single-frame group, had significant PCH relative to shams. Single-frame exposures produced significantly less PCH (P = .002) than 20-frame exposures in rats with a tracheal tube only (spontaneous breathing). The PEEP inhibited the PCH and produced about half of the PCH area induced for IPPV without PEEP (P = .014). The PCH results were comparable with those from a previous study using B-mode or color Doppler exposure for 5 minutes; however, these modes delivered many more pulses for continuous imaging frames, suggesting that the ARFI elastographic frames were individually much more effective.

Low-Cost, High-Performance Fiber Optic Fabry⁻Perot Sensor for Ultrasonic Wave Detection.

This study describes a novel fiber optic extrinsic Fabry–Perot interferometric (EFPI) ultrasonic sensor comprising a low-cost and high-performance silicon diaphragm. A vibrating diaphragm, 5 μm thick, was fabricated by using the Microelectromechanical Systems (MEMS) processing technology on a silicon-on-insulator (SOI) wafer. The Fabry–Perot (FP) cavity length was solely determined during the manufacturing process of the diaphragm by defining a specific stepped hole on the handling layer of the SOI wafer, which made the assembly of the sensor easier. In addition, the use of cheap and commercially available components and MEMS processing technology in the development of the sensing system, limited the cost of the sensor. The experimental tests showed that the minimum detectable ultrasonic pressure was 1.5 mPa/sqrt(Hz) −0.625 mPa/sqrt(Hz) between 20 kHz and 40 kHz. As a result, this sensor has the potential to successfully detect weak ultrasonic signals.

The Safety of Diagnostic Ultrasound in Ophthalmology

The literature review presents information about ultrasound use in diagnosis, therapeutic and surgical treatment of eye diseases. Due to experimental studies it was proved that ultrasound of different power, intensity and exposure causes thermal, mechanical and biological effect on the eye tissue. Thermal effect caused by ultrasonic energy absorption by biological tissues, which is converted from acoustic energy into thermal energy. The mechanical effect is determined by the amplitude of ultrasonic pressure acting on the eye structures during the examination. For the safety of ultrasound scanning, such concepts as thermal (TI) and mechanical (MI) indices have been introduced, which allows to control the level of acoustic impact on tissues. Ultrasound diagnosis in ophthalmology went a long way from one-dimensional echography (A-mode) to the complex scanning in real time, which allows to visualize different structural elements of the eye. Ultrasound eye examination is non-invasive and highly informative and thereby one of the main instrumental diagnosis methods in ophthalmology. Combination of images in gray scale, highly sensitive color and energy Doppler, 3D and sonoelastography to date greatly increased the diagnostic capabilities of ultrasound for simultaneous qualitative and quantitative assessment the eye and orbit in normal and pathological conditions. Therefore general ultrasonic diagnostic systems are widely used in clinical practice, with obligatory correction of TI and MI values. Recommendations of the international professional organizations such as Food and Drug Adminisration (FDA) and American Institute of Ultrasound in Medicine (AIUM))are widely used for the ultrasonic examination of eye pathology, according to which the lowest levels of exposure and intensity of the output acoustic signal (TI and MI) should be set to get a high-quality image. There are still a lot of clinical and experimental studies to determine the optimal modes of ultrasound eye and orbit examination. However, the safety of ultrasound and its effect on eye structures are still need to be studied.

The secondary Bjerknes force between two oscillating bubbles in Kelvin-Voigt-type viscoelastic fluids driven by harmonic ultrasonic pressure

The interaction between two small bubbles experiencing transient cavitation in a nonlinear Kelvin-Voigt fluid is investigated. The time-delay effect in the interaction is incorporated in the coupled Keller-Miksis model. The refined model predicts that bubbles with radii smaller than 2μm will be repelled by large bubbles, in contrast to predictions from previous models. The matching pressure needed to obtain same level of transient cavitation in different Kelvin-Voigt fluids is shown to depend mainly on the shear modulus and is insensitive to other parameters, which makes it a useful parameter to correlate the results. When the radii of the bubbles fall between 4μm and 6μm, the secondary Bjerknes force obtained with matching pressures shows only weak dependence on the shear modulus. For the pressure amplitudes investigated, equilibrium distances can be found between two bubbles when the equilibrium radius of one of the bubbles is in a narrow range around 2 μm. The equilibrium distance decreases when the shear modulus is increased. A simple relation between the two quantities is established.

Macrophage response and surface analysis of dental cementum after treatment with high intensity focused ultrasound

ObjectiveTo investigate effects of HIFU on macrophage phenotype, surface micro-topography and nano-scale surface mechanical properties of dental cementum. Materials and methodsRoot discs (2 mm thickness) were cut apical to CEJ and sectioned into quadrants. HIFU setup with bowl-shaped piezo ceramic transducer submerged in a water tank was used for exposure on each specimen for 15 s, 30 s or 60 s. The specimens of the control group were left without any HIFU exposure. HIFU was generated with a continuous sinusoidal wave of 120Vpp amplitude, 250 KHZ resonance-frequency and highest ultrasonic pressure of ∼10 bar at the focus. Specimens for SEM were viewed, and micro-topography characterization performed, using AFM and Ra parameter and surface area (SA) calculated by specialized SPM surface analysis software. For nano-indentation testing, experiments were carried out using AFM. Macrophage cell isolation and culturing was performed on cementum to receive the HIFU treatment at different time periods. Raman spectroscopy were scanned to create spectra perpendicular to the cementum substrate to analyze generation of standard spectra for Raman intensity ratio of hydroxyapatite normalized to the peaks ν1 960 cm−1. Data was expressed as means ± standard deviations and analyzed by one-way ANOVA in term of Ra, SA, H and Er. Different points for fluorescence intensity ratio were analyzed by Raman using Wilcoxon rank sum test. ResultsHIFU exposure at 60 s removed the smear layer and most of cementum appeared smoothened. AFM characterisation, showed a slight decrease in the irregularity of the surface as exposure time increased. Intact macrophages can be identified in control and all experimental HIFU groups. The level of fluorescence for the control and HIFU 15 and 30 s were low as compared to HIFU 60 s. ConclusionIf HIFU can be successfully implemented, it may be a possible alternative to current methods used in periodontal therapy to achieve smooth root surfaces.

Numerical analysis of the ultrasound induced arc pressure increment in plasma arc welding

A mathematical model is developed to investigate numerically the interaction mechanism between the ultrasonic vibration and the plasma arc in a plasma arc welding (PAW) process variant, i.e. ultrasonic assisted keyholing PAW (U-PAW). It is found that when ultrasound is exerted into the plasma arc from the tungsten electrode, the arc pressure is greatly increased, but the increment at different regions in arc space is varied. Near the anode surface, the difference between the peak value of the plasma arc pressure in U-PAW and the arc pressure in PAW is much larger than the additional acoustic pressure, indicating that the plasma arc pressure in U-PAW is not simply a superposition of plasma arc pressure and ultrasonic pressure. Experimental measurements of plasma arc pressure at anode are conducted in both PAW and U-PAW, and the numerical simulation results are in good agreement with the measured ones. This work lays foundation for understanding the underlying phenomena in U-PAW.

Enhanced microbubble contrast agent oscillation following 250\u2009kHz insonation

Microbubble contrast agents are widely used in ultrasound imaging and therapy, typically with transmission center frequencies in the MHz range. Currently, an ultrasound center frequency near 250 kHz is proposed for clinical trials in which ultrasound combined with microbubble contrast agents is applied to open the blood brain barrier, since at this low frequency focusing through the human skull to a predetermined location can be performed with reduced distortion and attenuation compared to higher frequencies. However, the microbubble vibrational response has not yet been carefully evaluated at this low frequency (an order of magnitude below the resonance frequency of these contrast agents). In the past, it was assumed that encapsulated microbubble expansion is maximized near the resonance frequency and monotonically decreases with decreasing frequency. Our results indicated that microbubble expansion was enhanced for 250 kHz transmission as compared with the 1 MHz center frequency. Following 250 kHz insonation, microbubble expansion increased nonlinearly with increasing ultrasonic pressure, and was accurately predicted by either the modified Rayleigh–Plesset equation for a clean bubble or the Marmottant model of a lipid-shelled microbubble. The expansion ratio reached 30-fold with 250 kHz at a peak negative pressure of 400 kPa, as compared to a measured expansion ratio of 1.6 fold for 1 MHz transmission at a similar peak negative pressure. Further, the range of peak negative pressure yielding stable cavitation in vitro was narrow (~100 kPa) for the 250 kHz transmission frequency. Blood brain barrier opening using in vivo transcranial ultrasound in mice followed the same trend as the in vitro experiments, and the pressure range for safe and effective treatment was 75–150 kPa. For pressures above 150 kPa, inertial cavitation and hemorrhage occurred. Therefore, we conclude that (1) at this low frequency, and for the large oscillations, lipid-shelled microbubbles can be approximately modeled as clean gas microbubbles and (2) the development of safe and successful protocols for therapeutic delivery to the brain utilizing 250 kHz or a similar center frequency requires consideration of the narrow pressure window between stable and inertial cavitation.

Forming of silver nano-ribbons with utrasonic pressure process

Silver nano-ribbons were obtained with plastically deforming of silver nanowires by ultrasonic pressure process with different flattening degrees on polyethylene terephthalate. The degree of flatting was decided on the value of input energy which is the product of the press value and press time. Atomic force microscope was used to investigate the hardness of silver nano-ribbons. It was verified that Ag nano-ribbons exhibited the same work-hardening phenomenon of macroscopically silver material during the process of flatting.

Effect of ultrasound on dissolution of Al in Sn

This study investigated the dissolution behavior of the aluminum substrate in molten tin at 523 K, 573 K, and 623 K with and without applied ultrasonic vibration (USV) respectively. In order to reveal the mechanism of accelerated dissolution by USV, the ultrasonic pressure distribution in the molten pool and the cavitation thermal effect were simulated by finite element analysis. Furthermore, the microstructures after the dissolution were observed. The results showed USV greatly accelerated the dissolution rate (by 21–27 times) at the interface, where an uneven ultrasonic pressure distribution in the molten pool caused inhomogeneous dissolution. The amount of Al dissolved in Sn at a particular temperature after 5 s of USV was equivalent to a holding time of 30 min without USV. The simulation results showed that the cavitation-thermal effect caused by USV increased the temperature (up to the melting point of Al) at the interfacial micro-region. It is evident that the combined effect of cavitation-thermal and ultrasonic streaming caused by USV increase the dissolution rate.

Incident Angle Identification Based on First-Echo Energy Attenuation in Ultrasonic Thickness Measurement.

Ultrasonic pulse technology has been widely employed for thickness measurement in the industrial field. Generally, the ultrasonic transducer is required to be perpendicular to the test sample surface when using the longitudinal wave. However, the transducer posture deviation (i.e., incident angle) of ultrasonic beam relative to the local surface normal is always inevitable. In addition, the received ultrasonic pressure will be weakened significantly because of the variation of echo propagation path and the attenuation of echo amplitude. As a result, the incident angle induced thickness error is generated. Therefore, it is necessary to investigate and quantify the negative effect of incident angle on ultrasonic thickness measurement. This paper focuses on the incident angle identification based on the first-echo energy attenuation. First, the influence mechanism of incident angle on pulse-echo pressure is analyzed theoretically by adopting an equivalent transducer model. Furthermore, a novel approach for the incident identification based on the first-echo energy attenuation is developed. A compensation model is established to correct the incident angle induced thickness error. To verify the feasibility of the proposed method, a series of incident angle calibrations and experiments were designed using the developed ultrasonic pulse measurement system. It was indicated that the proposed angle identification and error compensation approach had the capacity to improve the measurement accuracy of ultrasonic thickness.

초음파 센서의 진동분포에 따른 음향 특성

This paper deals with acoustic directivity according to vibration displacement distribution of ultrasonic sensors for distance measurement. It is necessary to determine the vibration displacement distribution improving the directivity because the measurable distance is longer with better directivity, which depends on the vibration of the ultrasonic sensor's housing plate. Directivity for circular housing plate with uniform vibration displacement distribution was theoretically expressed. Vibration displacement distribution and acoustic characteristics of real ultrasonic sensors were obtained by finite element analysis. Functional distribution of vibration displacement and sensor symmetry were considered in the analysis. As the vibration displacement distribution is gentle and approaches the uniform one, the ultrasonic sound pressure level in the direction of central axis is large and acoustic directivity is good. We have achieved the basis of improving the acoustic directivity for design of long-distance ultrasonic sensors.

Real-time Optical Imaging of Microbubble Destruction with an Acoustic Lens Attached Ultrasonic Diagnostic Probe in Microfluidic Capillary Models.

In this work, an ultrasonic diagnostic system with an attachable acoustic lens was demonstrated for real-time optical imaging of ultrasound-mediated microbubble destruction in a microfluidic capillary model using an inverted microscope. Microbubble destruction under ultrasonic pressure was monitored via an EM-CCD camera with the frame rate of 70 fps. The acoustic field distribution of the transducer with the attachable acoustic lens was simulated via a finite element method (FEM) and measured by a hydrophone. The result of acoustic field distribution shows unfocused beam profiles with 50% decreased pressure of original focal area. With the unfocused beam, inertial cavitation of the microbubbles as a function of transducer input voltages of 30-60 Vpp was studied. In addition, the acoustic cavitation parameters such as frequency of 2 MHz, pulse length of 16 μs, and pulse repetition frequency (PRF) of 1 kHz were investigated under static and dynamic flow conditions in the microfluidic model. In our system, above 45 Vpp, the microbubbles were destroyed more than 50% within 20 seconds so that the threshold for the inertial cavitation was determined to be 45 Vpp in the channel without flow. In the microfluidic capillary model with fluidic flow, it is investigated that shape of microbubble mass continuously changed with acoustic pressure with 60 Vpp.

Period doubling bifurcation and chaos in oscillations of two interacting cavitation bubbles under ultrasonic

Two interacting bubbles oscillator under ultrasonic is a highly nonlinear system. The nature of the cavitation will be understood more deeply in the study of two interacting bubbles’ internal mechanism. In this paper, the model to describe the oscillation motion of the two interacting bubbles in the sound field is the Keller-Miksis equation. The dynamics of two interacting bubbles has been studied by adopting the methods of time domain wave, phase trajectory, Poincaré section, power spectrum and bifurcation diagram. We also studied the nonlinear oscillations of bubbles with different initial radii and characteristics of bifurcation structure of normalized radius as ultrasonic pressure amplitude changed. Results show that two bubbles oscillation traverses the similar mode of period doubling bifurcation to cascade chaos. Furthermore, the motion of two interacting bubbles shows discrepant oscillation characteristics under the action of same sound field. In addition, the periodic window and chaotic region of bubble’s oscillation occur alternately with the increase of pressure amplitude.

Numerical and Experimental Evaluation of High-Frequency Unfocused Polymer Transducer Arrays.

High-frequency unfocused polymer array transducers are developed using an adhesive-free layer-by-layer assembly method. The current paper focuses on experimental and numerical methods for measuring the acoustic performance of these types of array transducers. Two different types of numerical approaches were used to simulate the transducer performance, including a finite element method (FEM) study of the transducer response done in COMSOL 5.2a Multiphysics, and modeling of the excited ultrasonic pressure fields using the open source software k-Wave 1.2.1. The experimental characterization also involves two methods (narrow and broadband pulses), which are measurements of the acoustic reflections picked up by the transducer elements. Later on, measurements were undertaken of the ultrasonic pressure fields in a water-scanning tank using a hydrophone system. Ultrasonic pressure field measurements were visualized at various distances from the transducer surface and compared with the numerical findings.

Quantitative measurement of ultrasonic pressure field using combination of optical phase contrast and nonlinear acoustic holography methods

Ultrasound has been widely used in medicine for both diagnosis and therapeutics. To assure its safety and efficacy, it is necessary to establish a fast and accurate method of measuring an ultrasonic field. Hydrophone scanning, which is a standard method for pressure measurement, requires a long measurement time and may disturb the field. In this study, an optical phase contrast method is combined with an acoustic holography method with nonlinear propagation simulation. The nonaxisymmetric pressure field of pulse ultrasound upstream of the focus was measured by the optical phase contrast method combined with a computed tomography (CT) algorithm, and the entire three-dimensional pressure field was reconstructed by acoustic holography. The result obtained by the proposed method agreed well with that by the hydrophone measurement without absolute pressure calibration and confirmed the markedly reduced required measurement time.

Rapid Ultrasonic-Assisted Soldering of AZ31B Mg Alloy/6061 Al Alloy with Low-Melting-Point Sn–xZn Solders Without Flux in Air

A novel ultrasonic-assisted low-temperature soldering was developed to join AZ31B Mg alloy and 6061 Al alloy with a series of Sn–xZn solders. The average maximum shear strength of the joints reaches up to 87.5 MPa at soldering temperature of 300 °C under ultrasonic assistance for only 5 s using Sn–20Zn solder. The fracture path propagates completely in the soldering seam. The results indicate that the microjet generated by ultrasonic pressure in liquid solder could strike and splinter the Mg2Sn intermetallic compounds into small pieces, which contributes to the enhancement of the joint strength. In addition, the primary Al(Zn) solid solution phase formed during cooling stage could also strengthen the joint due to the prevention of microcracks propagation.

Measurement of temperature and pressure distribution during ultrasonic processes by sensor foils from polyvinylidene fluoride

Micro and nano structures and systems are generated in polymer surfaces with cycle times of a few seconds by ultrasonic processes such as ultrasonic hot embossing, welding and thermoforming paving the way for a variety of new products. However, measuring temperature and pressure during these processes is very difficult because the polymer is enclosed between an anvil and a sonotrode. Temperature and pressure distribution during ultrasonic processing now have been measured inside of a stack of thermoplastic polymer layers by sensor foils from polyvinylidene fluoride, 55 µm in thickness. The measurements are based on the piezoelectric and pyroelectric effect of polyvinylidene fluoride allowing to achieve resolutions in temperature and pressure of up to ± 1 °C and ± 0.5 kPa, respectively. The achieved resolutions in time and in normal and lateral direction are approximately 1 µs, 60 µm and 1 cm, respectively. The maximum temperature inside a foils stack that could be measured was 73 °C because the sensor foils lost sensitivity when heated up more. Every single oscillation of the polymer was measured as a pressure change. The difference in temperature change and ultrasonic pressure amplitude measured in lateral direction below a sonotrode with outer dimensions of 8 × 12 cm are approximately 12 °C and 4 kPa, 25 and 60%, respectively, indicating the width required for process windows of ultrasonic processing. Moreover, phase shifts are measurable and thus analysis of oscillation characteristics of sonotrodes were investigated.

Geometric approximation of radiation stress projections for canonical objects

Modulated ultrasonic radiation pressure facilitates the selective excitation of modes of objects through modulation of appropriate surface stress projections [P. L. Marston and R. E. Apfel, J. Acoust. Soc. Am. 67, 27–37 (1980)]. For some large objects, it can be impractical to evaluate the needed stress projections using standard analytical or computational methods. For highly reflecting objects geometric approximations may provide useful insight into the relevant stress projections. The simplest projection gives the translational radiation force on the object. In that case, ray analysis of the far-field scattering was shown to recover the radiation force on large perfectly reflecting spheres in plane waves [P. L. Marston, J. Acoust. Soc. Am. 120, 3518–3524 (2006)]. In the present research, the appropriate force limit is also recovered through integrating a geometrically approximated local stress projection on the object’s surface. Appropriate limiting forces for other canonical objects or situations invo...

Enhanced intracellular delivery via coordinated acoustically driven shear mechanoporation and electrophoretic insertion

Delivery of large and structurally complex target molecules into cells is vital to the emerging areas of cellular modification and molecular therapy. Inadequacy of prevailing in vivo (viral) and in vitro (liposomal) gene transfer methods for delivery of proteins and a growing diversity of synthetic nanomaterials has encouraged development of alternative physical approaches. Efficacy of injury/diffusion-based delivery via shear mechanoporation is largely insensitive to cell type and target molecule; however, enhanced flexibility is typically accompanied by reduced gene transfer effectiveness. We detail a method to improve transfection efficiency through coordinated mechanical disruption of the cell membrane and electrophoretic insertion of DNA to the cell interior. An array of micromachined nozzles focuses ultrasonic pressure waves, creating a high-shear environment that promotes transient pore formation in membranes of transmitted cells. Acoustic Shear Poration (ASP) allows passive cytoplasmic delivery of small to large nongene macromolecules into established and primary cells at greater than 75% efficiency. Addition of an electrophoretic action enables active transport of target DNA molecules to substantially augment transfection efficiency of passive mechanoporation/diffusive delivery without affecting viability. This two-stage poration/insertion method preserves the compelling flexibility of shear-based delivery, yet substantially enhances capabilities for active transport and transfection of plasmid DNA.

Ultrasonic strengthening improves tensile mechanical performance of fused deposition modeling 3D printing

Wire-by-wire and layer-by-layer printing processes used in fused deposition modeling (FDM) three-dimensional (3D) printed parts result in poor mechanical properties. In this study, 3D printed acrylonitrile butadiene styrene (ABS) samples strengthened by ultrasonic vibrations are studied by a controlled variate method. The effects of ultrasonic strengthening pressure and ultrasonic strengthening time on the tensile mechanical properties of samples are studied. The tensile strength of the samples increases by 11.3%, the Young’s modulus increases by 16.7%, and the surface roughness decreases after ultrasonic strengthening. Ultrasonic strengthening after FDM 3D printing significantly improves the tensile mechanical properties of the sample and broadens the potential applications for FDM 3D printing technology.