Youichi Ito

Study of Atomization of a Water Jet by High-Intensity Aerial Ultrasonic Waves

An experimental study has been carried out on the atomization of a water jet by aerially radiating it with high-intensity ultrasonic waves. A sound source that enables the linear generation of high-intensity aerial ultrasonic waves (frequency: approximately 20 kHz) is combined with a cylindrical reflection plate in order to create a standing-wave sound field. An attempt has been made to atomize a water jet of 1 mm diameter by passing it through the above sound field at a velocity of approximately 30 m/s. It has been clarified that nodes of sound pressure in the standing-wave sound field are effective for the atomization of a water jet. In addition, the atomizing phenomenon of a water jet has been observed precisely. The relation between the intensity of sound waves required for atomization and the radiation duration has also been clarified. Even the radiation of sound waves for only 2 ms atomizes water. This suggests that a very fast water jet at 300–500 m/s might be atomized.

Fundamental Study of Detecting Internal Defect in Building Materials Using High-Intensity Aerial Ultrasonic Waves with Finite Amplitude

An impact acoustic method and an infrared method are often used to detect peeling in building materials such as concrete and tile. However, both of these methods are susceptible to human error and require long measurement times. In this study, we examine a new method that uses high-intensity aerial ultrasonic waves to detect peeling in building materials. Specifically, we have developed a noncontact method of detecting defects in building materials by analyzing the vibration of an object excited with high-intensity aerial ultrasonic waves of finite amplitude at a frequency of 26.8 kHz. We prepared artificial peeling samples consisting of tile and concrete plates. The results indicated that there is clearly a large difference in vibration velocity and distortion rate between the area with artificial peeling and the area without peeling. Therefore, it is possible to detect peeling of building materials by this method.

The Motion of High-Intensity Aerial Ultrasonic Waves (20 kHz) Entering a Perforation

The motion of high-intensity aerial converged ultrasonic waves (frequency: 20 kHz) as studied as they entered a perforation which had a smaller diameter than the wavelength of the radiated acoustic waves (approx. 17.4 mm). In addition, the characteristics of the sound field created in the perforation were studied experimentally. The acoustic waves incident upon the perforation were convergent, having a spreading angle of approx. 90°. As a result, it was elucidated that the acoustic waves favorably entered the perforation with a sufficiently smaller diameter (5 mm max) than the wavelength of the acoustic waves. A sound field of standing waves was created with the sound pressure being the maximum at the bottom of the perforation. The sound pressure increased in the ratio of the 0.5th power of the electric power supplied to the sound source. When the electric power supplied to the sound source was 50 W, a very powerful ultrasonic field of approx. 170 dB was created at the bottom of the perforation.

Examination of Noncontact Excitation of Acrylic Board Using High-Intensity Aerial Ultrasonic Waves Having Finite Amplitudes

We examined the possibility of exciting an object in a noncontact manner using high-intensity aerial ultrasonic waves. We performed experiments using various acrylic samples having different thicknesses and high-intensity aerial ultrasonic waves (at the frequency of 20 kHz) which were converged into a circular area of about 1 cm in diameter. The results indicated that the vibration displacements occurring in the samples were proportional to the sound pressure of the ultrasonic waves radiated onto the samples. In addition, the distribution of vibration displacements corresponded to the distribution of sound pressures formed by the ultrasonic waves radiated on the surfaces of the samples. The radiated ultrasonic waves used for these experiments had finite amplitudes so that they contained harmonic components at frequencies that were integral multiples higher than the fundamental frequency. Therefore, it was concluded that the samples irradiated with the ultrasonic waves vibrated not only at the fundamental frequency (20 kHz), but also at the frequencies of 40, 60, 80, and 100 kHz at the same time.

Removal of Liquid Leaked into Narrow Channel Using High-Intensity Aerial Ultrasonic Waves

We tried to remove a liquid leaked into a narrow channel immediately by radiating high-intensity aerial ultrasonic waves (at a frequency of 20 kHz) onto the liquid to atomize and disperse it into the atmosphere. Channels of 0.3 to 2 mm width and 1 to 10 mm depth with and without a bottom were used. The results of experiments showed that an ultrasonic radiation of 170 dB or more could remove a liquid in each of the channels immediately, by atomizing and dispersing it. The processes of atomization and dispersion of the liquid in each channel without a bottom largely varied, depending on the channel width and depth as well as the ultrasonic radiation intensity.

Measurement of Residual Particles by High-Intensity Aerial Ultrasonic Waves

When high-intensity aerial ultrasonic waves (with a frequency of approximately 20–50 kHz) are applied to drops of liquid adhering to the surface of an object, the drops instantaneously atomize and peel off from the object and scatter in the air. If extremely strong sound waves (approximately 170 dB(sound pressure level; SPL)) are applied, it is also possible to cause the solid particles remaining on the surface of an object to peel off and scatter in the air. In this report, we describe a study in which we investigated a new method that uses the above-mentioned effects produced by aerial ultrasonic waves to quantitatively evaluate the cleanness, with regard to the particles remaining on their surface, of semiconductor manufacturing jigs that have been precision-cleaned. This method has various features, including (1) it can be conducted without touching the target object, (2) it can be used on a specific area of the object, (3) it does not depend on the shape of the object, and (4) its measurements can be easily carried out.

Basic study of an estimation method for fire damage within concrete sample using high-intensity ultrasonic waves and optical equipment

After a fire in a concrete building, concrete walls may need to be entirely or partially repaired depending on the size of the fire. If the building is to be repaired, it is necessary to determine the extent and cost of the work. To do so, a method is needed for determining the level of fire damage within concrete walls, particularly along the depth direction. In a previous work, we have investigated a noncontact, nondestructive method using high-intensity aerial ultrasonic waves and optical equipment to detect the level of fire damage on the concrete surface, and we have demonstrated the feasibility of obtaining such information. Yet it is also important to determine the level of fire damage within concrete sample, particularly along the depth direction, in order to determine the extent of necessary repairs. In this study, we examined a new noncontact, minimally destructive method for estimating the level of fire damage within concrete sample. The results show that the level of fire damage could be determined along the depth direction.

Creation of Acoustic Field in Linear or Partially Bent Holes by High-Intensity Aerial Convergent Ultrasonic Waves

Using high-intensity convergent ultrasonic waves (frequency: 19.65 kHz; wavelength: 17.6 mm), a study was conducted on basic properties resulting from these acoustic waves entering linear holes with cross-sectional dimensions being less than 1/4 of the wavelength of the acoustic waves. The sound field formed inside the holes, whose length ranged from 2 to 60 mm, had the same characteristics as that formed when plane waves entered an acoustic tube with a closed end. In addition, even when the hole had a bent part of up to 90°, it was possible for the convergent acoustic waves to enter the hole. In this case, extremely high-intensity ultrasonic waves of approximately 174 dB were created at the bottom of the hole.

Erratum: “Basic Study of Detecting Defects in Solid Materials Using High-Intensity Aerial Ultrasonic Waves”

Recently, developments have improved methods employing aerial ultrasonic waves for detecting defects in solid materials such as metals, pipe walls, and fiber-reinforced plastics. These methods can be performed using a noncontacting aerial ultrasonic probe. In a previous study, we developed a new method using high-intensity aerial ultrasonic waves to successfully detect peeling, artificially created by inserting an air gap between tiles and concrete plates. In the present study, we use the same method to detect the depth and size of defects in a homogeneous medium.

Experimental Investigation of Deflection of High-Speed Water Current with Aerial Ultrasonic Waves

Inside a simulated standing wave sound field that was formed with high intensity aerial ultrasonic waves with a frequency of 20 kHz and a rigid plate, we passed a high-speed current of water with a diameter of approximately 0.6 mm and a speed of 5–30 m/s and deflected the current using primarily the force of the fields sound radiation pressure. Together with the acoustic radiation force, acoustic streaming, produced from convergent ultrasonic waves and moving in a direction away from the rigid plate, generated a force that acted on a small object placed inside the standing wave sound field. The water current was deflected almost proportionally to the magnitude of this compound force. The currents angle of deflection depended on the electric power supplied to the sound source that produced the convergent ultrasonic waves and on the speed of the current.