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A variable focus optical lens using a thixotropic gel and ultrasonic vibration is discussed. The surface profile of the gel could be deformed via acoustic radiation force generated by ultrasound. A thixotropic gel in which the viscosity was changed by shear stress was employed as a transparent lens material. The thixotropic gel allowed the lens to maintain shape deformation in the absence of continuous ultrasound excitation. The lens had a simple structure with no mechanical moving parts and included an annular piezoelectric transducer, a glass disk, and the thixotropic gel film. The axisymmetric concentric flexural vibration mode was generated on the lens at 71 kHz, which resulted in static surface deformation of the gel via the acoustic radiation force. The preservation rate was investigated after switching off the ultrasonic excitation. There was a trade-off between the preservation rate of the lens deformation and the response time for focusing. The focal length could be controlled via the input voltage to the lens, and a variable-focus convex lens could be realized; the change in the focal length with 4.0 Vpp was 0.54 mm. The optical transmittance of the lens was measured and the transmittance ranged 70%–80% in the visible spectral region.

In an acoustic standing wave generated in the air between a vibrator and a reflector, a small object is levitated near the nodal positions of the sound pressure where the acoustic radiation force and the gravity are balanced. By controlling the sound field spatially and temporally, the object can be transported without contact. In this report, we experimentally investigated the non-contact high-speed rotation of a small object using ultrasound, which can be applied to measurement techniques of the physical properties of liquids. The experimental system consists of a vibrating disc with four bolt-clamped Langevin-type transducers and a reflector, and an acoustic standing wave is generated between them. The effects of the tilt angle of the reflector with respect to the vibrator on the rotation speed of the object and the acoustic field were investigated. When the tilt angle was around 1.2°, the object was trapped in the air at 31.5 kHz by the standing-wave component in the vertical direction and rotated by the traveling-wave component propagating in the horizontal direction. The maximum sound pressure amplitude and the rotation speed of the object were changed with the tilt angle, and a larger sound pressure amplitude gave a larger rotation speed.

A non-contact acoustic sensing system using changes in the radiation impedance was proposed to detect the position of an object in front of an ultrasonic vibrator. The sensor is composed of a rectangular vibrating plate (20 × 100 × 1 mm3) and a PZT transducer (20 × 20 × 2 mm3). The sensor configuration was determined based on the results of a finite element analysis simulation. The flexural vibration modes were excited on the plate at two resonance frequencies, 29.7 and 46.2 kHz. The radiation angle of ultrasound from the sensor and the acoustic field between the object and the plate were compared at the two frequencies to investigate the detection characteristics. When an acoustic standing-wave field was generated in the air, the electrical impedance of the ultrasound transducers dramatically increased, indicating that the radiation impedance of the sensor was dependent on the object position. By measuring the amplitude of the input current to the transducers and the phase difference between the input current and the voltage applied to the sensor, the object position could be determined uniquely within a two-dimensional area.

Piezoelectric thin film transducers that can receive and transmit high-frequency and high-intensity ultrasound are powerful tools for future medical and industrial applications. Our group has developed acousto-optic devices where the refractive index can be controlled at high speed and high precision using ultrasound, but there are few reports on the interaction between high-frequency (tens to hundreds MHz) and high-intensity (MPa) ultrasound and visible light in liquids. In this study, we evaluated the acousto-optic interaction using polarized CW laser (532 nm) and a piezoelectric KNbO3 thin film transducer formed by hydrothermal method. The transducer was driven continuously at the fundamental or higher resonance frequencies (32, 96, 160, or 210 MHz) in a water cell, and the projection light of a laser beam penetrating perpendicularly to the sound axis was observed. The length of the projection light was elongated in the sound axis on the screen as the driving frequency increased. These results implies that the relationship between the wavelength of ultrasound and the laser beam width is the critical parameter for the acousto-optic phenomenon; the profile of the projection light is dependent on a ratio of the wavelength of ultrasound and the beam width of the laser beam.

Nematic liquid crystal is widely used in optical devices such as liquid crystal displays and controlled by electric fields through the liquid crystal layer. Our group has proposed a control technique of liquid crystal molecular orientation using ultrasound vibration without indium tin oxide electrodes [1]. In this study, using ultrasound and nematic liquid crystal, we realized a variable focus liquid crystal lens. The liquid crystal lens has no transparent electrodes and consists of a simple structure; a nematic liquid crystal layer with a thickness of 50 μm is formed between two circular grass plates. An annular PZT ultrasonic transducer was bonded on the glass plate. By exciting the transducer at the resonance frequencies (28 kHz), the flexural vibration modes were generated. The acoustic radiation force from the vibration changed the molecular orientation of the liquid crystals, which induced the distribution of the execution refractive indices. The liquid crystal layer then worked as a lens. The focal...

Nematic liquid crystals are widely used in optical devices such as liquid crystal displays and controlled by electric fields through the liquid crystal layer. The authors have proposed a technique to control the orientation of liquid crystal molecules using ultrasound vibration without indium tin oxide electrodes. An ultrasound liquid crystal cell was fabricated; it consists of a liquid crystal layer sandwiched by two glass plates having two ultrasound PZT transducers. When exciting the transducers at the resonance frequencies, the flexural vibration modes were generated on the cell and the acoustic radiation force acted to the liquid crystal molecules so that the orientation direction can be changed. The relationship between the molecular orientation and the vibration distribution of the cell was investigated from the transmitted light distribution of the liquid crystal cell under the crossed Nicol condition. In addition, the orientation of liquid crystal molecules was evaluated as ultrasonic wave velocity in the GHz range by the Brillouin scattering method. The ultrasonic wave velocity in the long axis direction of the liquid crystal molecules was higher than that in the short axis direction, which indicates the uniaxial anisotropy of the liquid crystal molecules.

A movable optical lens array that utilizes acoustic radiation force was investigated. The lens array consists of a rectangular glass plate, two piezoelectric bimorph transducers, and a transparent viscoelastic gel film. By electrically exciting the transducers, the flexural vibration mode was generated along the glass plate. The acoustic radiation force acts to the surface of the gel so that the surface profile can be deformed and the lens array can be fabricated. A cylindrical lens array with the lens pitch of 4.6 mm was fabricated at 113 kHz. The lens positions correspond with the loop positions of the flexural standing wave, and the lens pitch corresponds with half the wavelength of the flexural vibration of the glass plate. The focal points of the lens could be changed by the input voltage, and the lens can act as a variable-focus lens. The lens positions could be moved in the length direction by two-phase drive. The moving distance of the lens was 4.6 mm when the driving phase difference between the two transducers changed from 0 to 360°. The translation of the lens array was applied as an optical scanner.

In the field of environmental measurements, robust and simple sensors with no electric power supply are required. In the river, the size distributions of sand and small stones in river-bed are important factor for river disaster prevention. In this report, a passive piezoelectric sensor for measurement of the particle distribution in flow was investigated. The sensor consists of an aluminum circular plate (diameter: 50 mm; thickness: 2 mm) and an annular piezoelectric transducer (inner radius: 5 mm; outer radius: 10 mm). Alumina spheres with several diameters (φ = 3, 5, and 8 mm) were employed as small particles. When the particles hit the surface of the sensor, the flexural vibration is excited on the circular plate and the electric power is generated through the piezoelectric effect. Two main peaks at 16.3 and 66.7 kHz appeared in the output signal, and the ratio of these peaks depended on the particle size. From the finite element analysis, it was found that these frequencies of 16.3 and 66.7 kHz corre...

To establish safety criteria of ultrasound for blood, we examined hemolysis induced by low-intensity pulsed ultrasound and performed in vitro experiments using bovine blood. Quantitative evaluation by microscopic observations and the relationship between the hemolysis and cavitation microbubbles were discussed. Hemolysis was evaluated by red blood ghost cell. The presence of red blood ghost cells in the plasma component implies that the cell membrane was broken and the internal hemoglobin flowed out to surrounding blood plasma. Pulsed ultrasound at 1 MHz with the maximum sound pressure amplitude of 200 kPa was irradiated for one minute, and the ratio of non-exposure time (0—80%) was changed. After ultrasound exposure, the blood samples were centrifuged and divided into two layers: blood cells and plasma components. 10 μL of the plasma components was sampled and the number of the red blood ghost cells was counted. The number of red blood ghost cells increased gradually with the decrease in the ratio of non...

Nematic liquid crystals used in optical devices such as liquid crystal displays are controlled by the electric fields. Although indium tin oxide (ITO) is generally employed as the transparent electrode material to apply the electric field, it includes the rare metal indium and needs complicated processes such as sputtering deposition method. Our group has been investigating control techniques of molecular orientation of liquid crystals using ultrasound. In this study, we have applied these techniques to optical variable-focus lenses and the optical characteristics were examined. The ultrasonic liquid crystal cell has a simple structure with no transparent electrodes; it consists of has an annular ultrasound PZT transducer (inner diameter: 30 mm; thickness: 2 mm) and a liquid crystal cell in which a nematic liquid crystal layer (thickness: 25 μm) was formed between two glass substrates (thickness: 0.7 mm) and orientational films. The concentric flexural vibration modes could be generated on the cell at the...

An optical fiber Bragg grating (FBG) sensor is capable of simultaneous measurement of sound pressure and temperature. The FBG is a type of refractive index grating constructed in a short segment of optical single mode fiber that reflects particular wavelengths of light. This Bragg wavelength depends on both of the sound pressure and the temperature. We reported the simultaneous measurement of sound pressure and temperature in water under the conditions of medical application. In this study, temperature rise of a tissue mimicking material (TMM) caused by exposure to ultrasound in the range of 0.3 to 5 MPa were measured. The TMM is made of agar-gel with Glycerin solution of 11.21%. The FBG of 1 mm in length constructed in the optical fiber of 0.25 mm in diameter was used in the experiments. As a result, as the measured sound pressure was 5 MPa, the measured temperature rise was 6.0 degree. Thus this sensor is capable of simultaneous measurement of sound pressure and temperature rise of biological tissues exposed to the ultrasound. [This study was supported by MEXT-Supported Program for the Strategic Research Foundation at Private Universities, 2013–2017.]

A technique to form an optical micro-lens array using surface acoustic wave (SAW) was investigated. The lens has no mechanical moving parts, such as gearing systems, and is composed of a simple structure. A viscoelastic transparent silicone gel film with the thickness of 20 μm was formed on a 128°-rotated Y-cut X-propagation LiNbO3 (LN) substrate between two interdigitated transducers (IDTs). The IDT electrodes consisted of 30 finger pairs with the aperture length of 9.1 mm and the periodic pitch of 200 μm were fabricated on the LN substrate. The IDTs was excited with a continuous sine wave with the amplitude of 0 to 15 Vpp at the resonance frequency (20 MHz) to generate the SAW. The leaky SAW propagated into the gel, and the acoustic radiation force acted to the surface of the gel film so that the surface profile of the gel could change and a micro-lens array could be fabricated on the gel. The lens height could be controlled by varying the voltage applied to the IDTs.

Arterial filters are employed in extracorporeal circulations to remove microbubbles and thrombus from the blood flow and prevent the emboli. Filters with mesh structure have a risk to generate the thrombi when the blood flows through it. In this report, a meshless filter using ultrasound is discussed. The filter consists of an aluminum cylinder (length: 130 mm; inner diameter: 30 mm) and two annular ultrasound PZT transducers. The filter has one inlet at the center of the side and two outlets at both ends. By exciting the transducer, the acoustic traveling wave can be generated in the liquid inside the filter. Air bubbles flowing from the inlet can be led toward the outlet by acoustic radiation force. The characteristics of the filter were investigated through a circulation system using distilled water at the driving frequencies of 200 kHz and 1 MHz. Flow and injected air were set as 5.0 l/min and 10 ml/min, respectively. The microbubbles were filtered by using ultrasound and the amount of filtered bubbles was increased with theinput voltage to the transducer: 50.6 and 53.7% of microbubbles were filtered at 200 kHz and 1 MHz, respectively, when the input voltage was 100 Vpp.

Acoustic radiation force impulse (ARFI) has been actively studied in the field of medical ultrasonics. ARFI generates shear wave in the tissue to evaluate the tissue hardness using that velocity, and this method is applied to the diagnosis of liver tumor. Generally, long pulses are used for ARFI; therefore, we need to take account of thermal and physical effects on biological body. According to the regulation of Food and Drug Administration (FDA), the acoustic output of diagnostic ultrasound is approved as follows: Ispta.3

A new technique to destroy the gas‐filled capsule is proposed, making use of the collapsing bubble near the capsule in the ultrasound field. At the moment of collapses under the ultrasound irradiation, the bubble causes flow and acoustic wave radiation. These phenomena are expected to assist the destruction of the capsule. We observed the effect of the bubble on this destruction, using a high‐speed video camera which enables the real‐time imaging. In this experiment, we use gas‐filled capsule made of polyvinyl chloride. When no bubble was near the capsule at sound pressure of 60kPa, the capsule showed no vibration. However, in the presence of neighboring bubble, the capsule showed the destruction behavior of the deformation and the emission of internal gas. At higher sound pressure such as over 100kPa, the capsule showed above destruction behavior even if the bubble was not located near the capsule. In the presence of the bubble, however, the capsule was destructed in a shorter time. These experimental results give significant knowledge to a technique manipulating the gas‐filled capsule destruction in the drug delivery system.

We propose a novel ultrasonic imaging technique by transmitting ultrasonic pulse of dual‐frequency and receiving multifrequency echoes from the biological tissues. When the ultrasonic pulse of two frequencies is transmitted from a transducer, the secondary waves are generated during the nonlinear propagation through the biological media. A choice of f0 and 4f0 as the dual‐frequency results in the generation of 2f0, 3f0, and 5f0 components as the secondary waves. Multifrequency echoes are capable of improving the image quality by reducing the speckle noise. We have developed the following annular type transducer. The PZT disk of 7 mm in diameter is coaxially arranged in the PZT ring of 9 mm in inner diameter and 17 mm in outer diameter. The ring and circular transducers transmit the pulses of 2 and 8 MHz, respectively. It was confirmed that this transducer formed the ultrasonic beams of 4, 6, and 10 MHz as well as the beams of 2 and 8 MHz in degassed water. Then the experiments of imaging the agar‐gel phan...

This paper describes a low‐profile miniature ultrasonic pump consisting of a disk‐bending vibrator and a pipe‐end located vertically to the disk center via a small gap. First, we explored the relationships between the pump performance and the geometrical conditions of the pump experimentally: the pipe diameter, the gap, and vibration distributions. Based on those results, the thickness distribution of the bending disk was designed using finite‐element simulations so that the vibration distribution near the pipe might become uniform. Maximum pump pressure of 20.6 kPa was obtained with a 30‐mm‐diam bending disk and electrical power consumption of 3.8 W. For optimization, we constructed a model of the pump operation in this study. Nonlinearity in the elastic constant of the working fluid was introduced into the model because the temporal change rate of the gap caused by the ultrasonic vibration of the disk vibrator considerably affects the pump’s pressure generation. Results show that the calculated pump pressure well simulates the measured dependence of the gap on the pressure. The acoustic pressure was measured using a fiber optic pressure probe and was compared to the calculated pressure value.

An ultrasonic linear motor using ridge‐mode traveling waves on a substrate is proposed for precision positioning. In our experiments, two parallel ridges are machined on an alumina ceramic substrate with the spacing of 19 mm. The width, height, and length of the ridge are 3 mm, 9 mm, and 186 mm, respectively. Two piezoelectric elements, 19 mm in length and 5×5 mm2 in cross section, were installed at the position of 15 mm from each end of the ridge, and excited at 87.136 kHz in their fundamental longitudinal mode to stimulate the fundamental ridge mode. Elliptical particle motions are formed, due to traveling waves along the ridge waveguides by the phased drive of the two transducers. An alumina ceramic slider pressed to the two waveguides is moved at 13 mm/s in the opposite direction to the traveling wave through the friction forces. The moving direction can be switched by changing the propagation direction of the traveling wave. The detailed characteristics are experimentally studied.

Polyurea thin film exhibits useful characteristics as a high‐frequency ultrasonic transducer such as a low acoustic impedance of 70% of that of PVDF, considerably high piezoelectric constants compatible with conventional piezoelectric polymers, and a higher Curie temperature. A polyurea thin film transducer working at over 100 MHz can be made on any surfaces through vapor deposition polymerization with a high controllability of thickness. To enhance the transducer performance, a multilayered configuration is studied in this study. A special twin‐vacuum‐chamber is used for laminating the polyurea layers and the aluminum electrodes alternately. We fabricate two‐ and three‐layered transducers with 1.5‐μm polyurea thin films as well as single‐layer transducers. To evaluate the transducer performances, we measure the capacitances, the electrical admittances, the coupling factors, and the Q values. The pulse/echo measurements are also conducted to determine the transmission and receiving characteristics of the ...

A method to measure micro liquid volume less than 300 ln with the accuracy of 0.1% is highly needed in biogenetic and biochemical industries. The authors propose a novel method to estimate micro liquid volume in a small well using acoustic resonance. In our experiments, liquid is in a container 6.5 mm in inner diameter and 9 mm in height, and the sound pressure near the well is measured by sweeping the illuminating sound field from 6 to 11 kHz. According to the relationship between the resonance frequency and the volume, we can successfully estimate the small volume with the accuracy of 0.1% and an excellent repeatability. For simultaneous multipoint measurements, we experimentally investigate the effect of adjacent wells on resonant frequency of the target well. It is revealed that the resonance frequency shift due to the mutual coupling between the adjacent wells is negligible if the well interval is less than 5 mm.