Haruhiko Nakajima

Shear Horizontal Acoustic Plate Mode Viscosity Sensor

Mode analysis of a LiTaO3 (LTO) plate has been carried out numerically, and an interference-free shear horizontal acoustic plate mode (SH-APM) suitable for measuring the liquid viscosity was found. A viscosity sensor having a liquid container on the side opposite to interdigital transducers (IDTs) was fabricated on X-cut 148° Y-prop LTO. Satisfactory agreement was obtained between the calculated frequency spectrum and the experimental one. A loading test was carried out for a series of Newtonian liquids, which showed good agreement with the perturbation theory.

Acoustic study of a critical binary mixture of nitrobenzene and n-hexane at low and ultrasonic frequencies

Abstract As a continuation of a previous paper on aniline/cyclohexane, the acoustic anomaly of a critical mixture of nitrobenzene/ n -hexane ( T c = 19.89°C) was studied. The dispersion of the low-frequency adiabatic compressibility (18-900 Hz) near T c is discussed and the zero-frequency velocity u 0 is extrapolated. Ultrasonic velocity and absorption at 2.56 and 8.93 MHz above T c along with u 0 are analysed after the mode coupling theory by Shiwa and Kawasaki and the renormalization group theory by Kroll and Ruhland. The dependence of the ratio of dispersion to absorption on the reduced frequency was found to agree with that of aniline/cyclohexane in the previous paper. Both dispersion and absorption normalized by the critical amplitude agree also respectively with those of aniline/cyclohexane on the assumption that the critical amplitude is proportional to ϵ −0.11 where ϵ is the reduced temperature.

Acoustic anomaly in a critical binary mixture of aniline and cyclohexane at low and ultrasonic frequencies

Low frequency adiabatic compressibility at 18–900 Hz is measured for a critical mixture of aniline/cyclohexane and the zero frequency sound velocity uo is determined. Ultrasonic velocity u and absorption α at 2.56 and 8.93 MHz along with uo are analyzed by Kawasaki, Shiwa-Kawasaki (SK), Kroll-Ruhland (KR) and Bhattacharjee-Ferrell (BF) theories. The dependences of dispersion and critical absorption on the reduced frequency ω* are satisfactorily reproduced by SK, KR and BF theories in the whole range of ω*. The critical amplitude is discussed from thermodynamic standpoints and the agreement in order of magnitude is obtained between theory and experiment for various critical mixtures. Frequency dependences of velocity and critical absorption at the critical point and the temperature dependence of the critical part of zero frequency adiabatic compressibility are discussed by the theory of Ferrell and Bhattacharjee.

New Instrument for Rapid and Accurate Measurement of Ultrasonic Velocity and Attenuation Using a Minicomputer System

A new instrument has been developed for rapid continuous recording of temporal changes in ultrasonic velocity and attenuation constant in a material. A set of data of changes in velocity and attenuation is obtained within the interval of one echo train, usually 0.1 msec or longer. A high-speed minicomputer is used for controlling the whole electronic system and data processing. The accuracy is 10-5 to 10-6 for the velocity change and 10-3 for the attenuation change in a sample length of 3 cm. Data showing the speed and accuracy of the instrument are given.

Sound Velocity in Critical Binary Mixtures

This paper describes the significance of sound velocity measurement in exploring the acoustic anomaly of critical binary mixture and the methods for measuring ultrasonic and low frequency sound velocities in such a mixture.

Analysis of VHF Ultrasonic Resonator

The behavior of a VHF ultrasonic resonator is analyzed with a one-dimensional three layer (solid-liquid-solid) model, and resonant frequencies and the half-value width (HVW) are calculated. In contrast to an ideal liquid resonator, HVW periodically depends on the thickness of the liquid layer, which can reproduce the scattered HVW data of our previous experiment. The reason why the VHF resonator has sharper resonant peaks than the ideal liquid resonator is also explained.

A new apparatus for measurement of capacitance change in soft materials.

We have developed an apparatus with LC resonance circuit to measure a fast capacitance change accompanied by freezing of a supercooled water droplet that was placed in a capacitor space formed by a set of a needle and a copper plate. A trace of the capacitance change obtained exhibits a first rapid increase, a gradual growth, and a final steady state. The experimental capacitance change is in good agreement with that of the capacitance calculated with the finite element method.

A Supplemental Method for Evaluating Quartz Transducers

A supplemental method, called double balanced bridge (DBB), is proposed to measure the quality of piezoelectric transducers. The DBB consists of a power divider, two RF bridges with device under test (DUT) terminals and a combiner, which form a doubly balanced bridge with upper and lower arms. In the DBB, the effect of parallel capacitance C0 is directly canceled by a hardware, whereas the phase information is collected with a network analyzer employed in the standard method. The DBB seems to be useful because it gives a symmetrical admittance curve which is proportional to the amplitude of the particle velocity of the transducer. Reproducibility is found to be better than that obtained using the Japanese Industrial Standard method even for the transducers with spurious modes. It can be concluded that the DBB method provides a compatible testing tool for the piezoelectric transducers.

VHF Ultrasonic Resonator for Soft Materials

An ultrasonic resonator for measuring sound velocity in soft materials over a wide frequency range is designed and constructed, with special attention paid to the thickness matching and parallelism between transmitting and receiving transducers. The resonator is composed of x-cut quartz disks and has shown a very sharp spectrum in the frequency range of 3 to 200 MHz with practical signal strength. As an exemplifying data, the sound velocity change in the process of gelation of a chemical gel is presented. The possibility of a composite cavity which is operational over three decades of the MHz range is discussed.

Transducer Matching in Ultrasonic Traveling Wave Interferometric Network Method

In the ultrasonic TWIN method thickness controlled silver layers were deposited on the surfaces of a sapphire disk pair making the resonant frequencies exactly coincide up to higher overtones. The optimum thickness for the respective disks was found to be 1 ?m and 5 ?m. An improved transducer system was successfully implemented at frequencies from 30 MHz to 350 MHz.