Transducer Side Research Articles

Numerical simulations of partial elements excitation for hemispherical high-intensity focused ultrasound phased transducer* *Project supported by the National Natural Science Foundation of China (Grant No. 81272495) and the Natural Science Foundation of Tianjin (Grant No. 16JC2DJC32200).

The hemispherical phased transducer maximizes the coverage of the skull and the ultrasonic energy per unit area of the skull is minimized, thereby reducing the risk of skull burns, but the transducer has a small focal area adjustment range, increasing the focal length of treatment is an urgent question for this type of transducer. In this paper, a three-dimensional high-intensity focused ultrasound (HIFU) transcranial propagation model is established based on the human head structure. The finite difference time domain (FDTD) is combined with the Westervelt acoustic wave nonlinear propagation equation and Penne's biological heat conduction equation for numerical simulation of the sound pressure field and temperature field. Forming a treatable focal area in a small-opening hemispherical transducer with a small amount of numerical simulation calculation focusing at a set position to determine the minimum partial excitation area ratio of focusing. And then, applying these preliminary results to a large-opening diameter hemispherical transducer and the temperature field formed by it or full excitation is studied. The results show that the focus area with the excitation area ratio of less than 22% moves forward to the transducer side when the excitation sound is formed. When the excitation area ratio is greater than or equal to 23%, it focuses at the set position. In the case of partial incentives, using 23% of the partial array, the adjustable range of the treatable focal area formed in the three-dimensional space is larger than that of the full excitation.

Forming and loading giant unilamellar vesicles with acoustic jetting.

Giant unilamellar vesicles (GUVs) are a useful platform for reconstituting and studying membrane-bound biological systems, offering reduced complexity compared to living cells. Several techniques exist to form GUVs and populate them with biomolecules of interest. However, a persistent challenge is the ability to efficiently and reliably load solutions of biological macromolecules, organelle-like membranes, and/or micrometer-scale particles with controlled stoichiometry in the encapsulated volume of GUVs. Here, we demonstrate the use of acoustic streaming from high-intensity focused ultrasound to make and load GUVs from bulk solutions, without the need for nozzles that can become clogged or otherwise alter the solution composition. In this method, a compact acoustic lens is focused on a planar lipid bilayer formed between two aqueous solutions. The actuation of a planar piezoelectric material coupled to the lens accelerates a small volume of liquid, deforming the bilayer and forming a GUV containing the solution on the transducer side of the bilayer. As demonstrated here, acoustic jetting offers an alternative method for the generation of GUVs for biological and biophysical studies.

Applications of airborne ultrasound in human–computer interaction

Airborne ultrasound is a rapidly developing subfield within human–computer interaction (HCI). Touchless ultrasonic interfaces and pen tracking systems are part of recent trends in HCI and are gaining industry momentum. This paper aims to provide the background and overview necessary to understand the capabilities of ultrasound and its potential future in human–computer interaction. The latest developments on the ultrasound transducer side are presented, focusing on capacitive micro-machined ultrasonic transducers, or CMUTs. Their introduction is an important step toward providing real, low-cost multi-sensor array and beam-forming options. We also provide a unified mathematical framework for understanding and analyzing algorithms used for ultrasound detection and tracking for some of the most relevant applications.

Microbubble behavior in an ultrasound field for high intensity focused ultrasound therapy enhancement

The enhancement of heating due to inertial cavitation has been focused to reduce the long treatment time of conventional high-intensity focused ultrasound (HIFU) therapy. The influences of the physical properties of surrounding tissues, initial void fraction, and spatial distribution of bubbles on microbubble-enhanced HIFU are examined. A bubble dynamics equation based on the Keller-Miksis equation is employed in consideration of the elasticity of surrounding tissue. The mixture phase and bubbles are coupled by the Euler-Lagrange method to take into account the interaction between ultrasound and bubbles. As a result, the temperature around the target increases with the initial void fraction. But at the high void fraction of 10(-5), ultrasound is too attenuated to heat the target, and the heating region moves to the transducer side. On the other hand, both the viscosity and shear elasticity of the surrounding media reduce the attenuation of ultrasound propagation through the bubbly mixture. Numerical results show that localized heating is induced with increasing viscosity or shear elasticity, though it depends on the pressure amplitudes. In addition, it was numerically confirmed that the localization of the microbubble distribution is important to obtain efficient localized heating.

An investigation on the corrosion of flue gas sensor in boiler stack

A commercial gas velocity sensor used for flue gases monitoring was subject to severe corrosion failure. An investigation was conducted based on visual inspection, microstructural study and SEM observation coupled to EDX analysis. A combination of mechanisms was proposed including a dominating severe dew point corrosion for both transducer and its covering, galvanic attack and an eventual hydrogen attack for the transducer side part. Recommendations were proposed to avoid a future severe damage to such type of sensor including an insulation between transducer and covering metals and an up-grade of the titanium alloy used.

Coherent Brillouin spectroscopy in a strongly scattering liquid by picosecond ultrasonics

In a modification of a picosecond ultrasonic technique, a short acoustic pulse is launched into a liquid sample by a laser pulse absorbed in a semitransparent transducer film and is detected via coherent Brillouin scattering of a time-delayed probe pulse. With both excitation and probing performed from the transducer side, the arrangement is suitable for in vivo study of biological tissues. The signal is collected from a micrometer-thick layer next to the transducer and is not affected by the diffuse scattering of probe light deeper in the sample. The setup, utilizing a 33 nm thick single crystal SrRuO(3) transducer film, is tested on a full fat milk sample, with 11 GHz acoustic frequency recorded.

Micro-bubble enhanced HIFU

High intensity focused ultrasound (HIFU) treatment that employs microbubbles to provide enhanced heating has been investigated in order to develop a less invasive and more rapid tumor ablation therapy. It has been demonstrated that microbubbles have significant effects on heating enhancement in vitro and in vivo experiments, however ultrasound propagation could be disturbed when there are too many microbubbles between the transducer and the focus. In this study, we develop a method to make a clear pass way for obtaining enhanced heating by using microbubbles just at the focus, thus avoiding heating on the pass way from the transducer to the target region. In this method, microbubbles are destroyed in front of the HIFU focus (on the transducer side) by irradiating a intense burst wave of microsecond order, before irradiating the ultrasound waves for heating the target region. The experiment is conducted in a medium of a polyacrylamide gel containing microbubbles, and a temperature-sensing liquid crystal sheet is set in the focus to observe the temperature distribution. The ultrasound frequency was 2.2 MHz and the intensity was 5000 W/cm2, and 20 burst waves were irradiated at pulse repetition frequency of 1 kHz. The number of wave pulses was varied. The continuous-wave frequency, intensity and irradiation time are 2.2 MHz, 1000 W/cm2 and 60 sec, respectively. As the number of pulses increased, the heating region moves from the transducer side to the focus. This is because microbubbles in front of the focus are destroyed and the ultrasound propagates around the target position effectively. These results suggest that the microbubble distribution and the heating position in the developed HIFU system can be controlled.

Quantitative monitoring of bone healing process using ultrasound

In this paper, results of the simulated interaction of ultrasound waves with a fractured Tibia are presented. The Tibia bone fracture is one of the most difficult fractures to treat because of the slow healing process which may take up to 5 months. The human body is modeled as a four layer medium: skin, fasciae with fat, muscle and bone. Each of these layers is characterized by its acoustic impedance. These impedances influence the incident, transmitted and reflected ultrasound pressure waves. A mathematical model which describes these interactions was developed and used to compute the reflection coefficient at the transducer side. This coefficient will then be used to quantify the bone healing process.

Internal ported band pass enclosure for sound cancellation

A transducer arrangement for active noise cancellation in conduits, for example, in motor vehicles where an electronic control produces a drive signal for a transducer that emits cancellation pulses phased 180° from the sound pressure pulses passing through an exhaust conduit, where both front and rear sides of the transducer are acoustically coupled to improve the efficiency of the transducer operation. Preferably, the acoustic coupling comprises an enclosed chamber partitioned to expose a first transducer side to a chamber portion and a second transducer side to a second chamber portion. A first port couples one of the chambers to the other and a second port couples one of the chambers to the conduit. Each port for communicating with the conduit can be tuned to resonate at predetermined frequencies. When both sides of the transducer are so coupled to the conduit, the transducer has increased efficiency over a band of frequencies, to accommodate the frequencies generated by a source of noise while limiting access of fluid or heat in the conduit to the transducer. A tandem transducer mounting arrangement according to the present invention reduces vibration of the housing. The system is particularly suitable for use in adapting noise cancellation techniques to replace or combine with passive mufflers on motor vehicles.

Calibration of instrumentation for “acoustic intensity measurements.”

The increasing application of acoustic intensity measuring instrumentation has also increased the demand for practical calibration methods. The most general used intensity probe utilizes the two-microphone method. The accuracy probe utilizes the two-microphone method. The accuracy of the intensity measured in W/m2, and the capability to measure the intensity vector in a very reactive field depend on the equal performance of the two microphones, on the absolute pressure sensitivity and the relative phase between them. The calibration accuracy at low frequency depends mainly on the air equalization, and the high-frequency accuracy mainly on geometry. The absolute calibration of pressure sensitivity can be referred to a standardized reciprocity calibration. The long term stability is determined by rather few possible variables on the transducer side, and a test method is proposed for the electronic instrumentation. The capability to measure intensity within a reactive field of a certain strength is determined by the phase relationship between the two microphones, by their spacing Δr and by the frequency. The capability to calibrate and measure these parameters will discussed.

The importance of ultrasonic side-lobe artifacts.

Transducer side lobes consist of multiple low-intensity sound beams located outside of the main ultrasound beam. Although the echoes generated by side lobes originate outside of the main beam, they appear as specular or diffuse artifactual echoes within the beam. They are visible with both static and real-time equipment. Specular side-lobe artifacts occur near strong, curved, highly reflecting surfaces such as the diaphragm, or near large cystic masses such as the urinary bladder or gallbladder. Diffuse artifacts originate from bowel gas adjacent to cystic structures. These echoes can be confused with particulate material or sludge in organs such as the urinary bladder and gallbladder, or in abnormal cystic masses. We illustrate the genesis of these artifactual echoes and provide clinical examples of commonly visualized side-lobe artifacts.