We investigated the effects of a 1,2-dimyristoyl-sn-glycerol-3-phosphocholine (DMPC) molecular film surrounding microbubbles on their collapse under ultrasound irradiation. We defined the ejection of the internal gas from the microbubble (i.e. “daughter” bubbles) as bubble collapse. In particular, we measured the sound-pressure thresholds for microbubble collapse in water and a DMPC solution. Bubbles with the DMPC film had a smaller resonance size than naked bubbles. The measured contact angles of the bubbles were lower after collapse, implying that DMPC molecules on the bubble surface partially desorbed between the processes of vibration and collapse.

We have previously developed a compact circular vibrating plate aerial ultrasonic source with a grooved uniform rod that can produce a large vibration displacement by using piston vibration and emit intense sound waves perpendicular to the vibration surface. In this paper, to create a compact ultrasonic source that can radiate intense aerial ultrasonic waves, we produced a compact aerial ultrasonic source integrating the transverse vibration part with a bolt-clamped Langevin transducer and we investigated the sound source characteristics. These results demonstrated that compared with a conventional source, the length of our source was shorter, the sound pressure was higher, and its structure was simpler.

Our previous study has revealed that acoustic resonances have non-negligible effects on photoacoustic signals for a liquid sample confined in a thin tube. In this paper, we present numerical and experimental studies on the effects of tube hardness on the directivity of the generated photoacoustic signal. A thin glass capillary and silicone tube of 1 mm in diameter were tested using a pulsed light of 637 nm wavelength. Black ink was confined in the glass capillary and silicone tube as a photoacoustic sample material. In the glass capillary, acoustic resonance modes in the glass capillary were efficiently excited, and clear directivity was observed in the generated photoacoustic signals. On the other hand, little resonance was stimulated in the silicon tube because of the acoustic impedance matching between the sample and surrounding media, which resulted in the weak confinement of acoustic waves. The results suggest a possibility of characterization of the physical properties of thin tubes.

In an RF ablation procedure for treating hepatocellular carcinoma and metastatic liver cancer, plucking out an ablation antenna from incompletely cauterized tumor tissues can cause neoplastic seeding; hence, it is demanded to properly evaluate the thermal denaturation of tumor tissue before plucking out the antenna. In the present ex vivo study, we show that the degree of thermal denaturation inside porcine liver tissue induced with RF current heating can be evaluated by binarized two-dimensional Nakagami parametric image indicating the weighted average of the Nakagami shape parameter m. Moreover, we present that the pre-Rayleigh distribution is dominant in ultrasonic backscattered envelopes obtained from incompletely cauterized liver tissue, whereas the Rayleigh distribution is dominant in those obtained from completely cauterized liver tissue which has coagulative necrosis region. The result indicates that the change in scatterer distribution would be occurred inside liver tissue by coagulative necrosis caused by RF current heating in this study.

In conventional bone conduction (BC) devices, a vibrator is typically applied to the mastoid or condyle processes. Recently, however, BC-sound presentations to facial parts such as the nose have also been investigated. As the face is among the most complex structures in the human body, BC sounds presented to facial parts are likely to show different perception and propagation characteristics from those presented to conventional parts. We measured hearing thresholds, ear canal sound pressures in both ears, and head vibrations at both mastoid processes when BC sounds were presented to the facial (nasal, infraorbital region, zygomatic, jaw angle, and chin) and conventional (mastoid and condyle processes and forehead) parts of normal-hearing subjects. The results indicated that the facial parts and mastoid process had similar threshold characteristics. By changing the stimulus parts on the face, the hearing thresholds did not change, whereas the amplitudes of each propagation component changed significantly.

This paper proposed a board-mounted ultrasonic variable-focus liquid crystal (LC) lens. The lens controls the focus using the acoustic radiation force generated by the resonant flexural vibration mode. The LC lens was fixed to an aluminum substrate with a hole whose aperture corresponded to the inner diameter of the transducer. The part of the LC lens attached to the substrates functioned as a fixed condition, and the flexural vibration mode was successfully generated. The fixed lens exhibited a gradual focal change with current, confirming that fixing the condition affected the rate of focal change.

This paper investigates a thin sensor used to detect the position of an object in front of an ultrasonic transducer using changes in the radiation impedance. The sensor consists of a rectangular plate and a piezoelectric transducer, and the configuration is determined based on the results of a finite element analysis simulation. Stripe flexural vibration modes are generated on the plate, radiating sound waves into the air between the plate and the object. The radiation angle of these sound waves is dependent on the driving frequency, resulting in a change in the sound field and the electrical admittance characteristics. The sensing performance is examined using two resonant vibration modes. The sensor can determine the position of an object uniquely within a two-dimensional area, and the lower resonant mode gave a wider measurable range. The sensitivity is improved six-fold over that of our conventional sensor using the same sensing mechanism.

As a high-resolution 3D phased-array imaging method, a piezoelectric and laser ultrasonic system (PLUS) was proposed, which is a combination of a piezoelectric transmitter and an ultra-multiple scan of a laser Doppler vibrometer. Thus far, PLUS has used an identical mode for incident and scattered waves. On the other hand, the ultrasonic scattering phenomena can accompany the mode conversion, which may provide further information on defects. In this paper, we propose multi-mode PLUS to enhance its imaging capability and attain more robustness. After describing the principle of multi-mode PLUS, we validated the imaging algorithm and demonstrated the improvement in the image resolution using a dataset of simulated received waves for the longitudinal-wave incidence to scatterers. Furthermore, we experimentally demonstrated the efficacy of multi-mode PLUS in a specimen with branched stress corrosion cracking.

The electromagnetically spinning method for viscosity measurement was enhanced for applications in a confined reaction chamber. In the reaction chamber, the immersion of the rotor into the sample might trigger the precipitation and aggregation of ingredients to the pivot of the probe rotor, which leads to harmful frictional torque of the rotation. To address this problem, an upper-point-type auto-standing probe rotor was developed and applied for the long-term measurement of the solution process of rock sugar in water. In addition, we propose the adoption of a punched board, instead of a solid board, as the lower substrate of the plate-plate-type rotational viscometer, which allows rapid exchange of the sample fluid between the interior and exterior of the narrow measurement area through molecular diffusion. We investigated the effect of punches from the perspective of the diffusion process of momentum and determined the geometrical conditions.