Tsutomu Yasuda

Metalorganic vapor phase epitaxy of low‐resistivity p‐type ZnSe

Low‐resistivity p‐type ZnSe layers have been successfully grown on GaAs substrates by metalorganic vapor phase epitaxy with the use of dimethylzinc and diethylselenide as source materials and lithium nitride as the dopant. The lowest resistivity achieved is 0.2 Ω cm, and the highest carrier concentration is 9×1017 cm−3. ZnSe p‐n diodes fabricated by this technique have shown blue emission; the spectral peak is located at 467 nm.

Photoelectric Effects in Organic Diodes

Photovoltaic behavior of the merocyanine dye family with a rhodanine ring has been systematically studied by employing eight different derivatives in the diode structure Al/evaporated dye/Ag. Each dye film behaves like a p-type semiconductor with a rectifying barrier at Al interface and an Ohmic contact at Ag electrode. The open circuit photovoltage as high as Voc1.5 V was observed for one of the derivatives, while the fill factor remained f.f.0.25 in all cases. The chemical stability of the dye molecules during and after evaporation is also discussed on the basis of the results obtained by the thin-layer chromatography.

Study of SAW propagation characteristics by frequency‐translated holography

Under the condition of continuous acoustic generation the patterns of forward, backward, and standing SAW’s propagating on a y‐cut z‐propagating LiNbO3 crystal were observed clearly by the frequency‐translated holographic technique. The parameters of surface‐wave propagation velocity, reflectivity, and transmissivity for an interdigital transducer could be obtained by this technique.

Surface acoustic wave liquid sensors based on one-port resonator

A one-port resonator utilizing shear horizontal surface acoustic waves (SH-SAWs) has been used for sensing applications in liquids. SH-SAWs have been excited on a 36°-rotated Y-cut X-propagating LiTaO3 substrate using interdigital transducers and the one-port resonator configuration has been used as a sensing element in liquids. The sensitivity of the resonance frequency and the Q value for the viscosity of liquids have been measured. Experimental results showed that the resonance frequency and the Q value of the SH-SAW resonator varied with the viscosity of the loaded sample liquid.

Humidity Sensor Using Surface Acoustic Wave Delay Line with Hygroscopic Dielectric Film

A surface acoustic wave (SAW) sensor for measurement of humidity in ambient atmosphere is presented. SAW technology is increasingly being used in sensors. The majority of the work reported on SAW sensors to date has studied the effect of mass loading. In this paper, we propose a new SAW humidity sensor that uses the changes in the film permittivity rather than the mass. A 30 MHz dual SAW delay line fabricated on 128° YX LiNbO3 was coated with cellulose acetate. This hygroscopic polymer coating caused a SAW velocity change of 0.36 m/s per 10% relative humidity. The response was linear in the range from 10% to 80% in relative humidity.

An application of pvdf-film to medical transducers

Abstract A fetal heart sound transducer and an uterine contraction monitor transducer are designed utilizing an extended PVDF-film with the transverse effect due to d 31 constant and silicone rubber. A receiving and a transmitting part of array are fabricated on the film constructing the transducer so that the frequency response of the transducer on abdominal wall can be detected for each patient. The useful clinical data on fetal heart sound and the frequency spectrum have been obtained and uterine contraction monitoring is performed.

Measurement of Velocity and Viscosity of Liquid Using Surface Acoustic Wave Delay Line

There is increasing use of surface acoustic wave (SAW) in sensors, and the majority of the work reported on sensors to date has used Rayleigh waves on piezoelectric materials. In this paper, a leaky SAW delay line was used for measuring the acoustic properties of liquids. The leaky SAW with the shear horizontal displacement is excited on a piezoelectric substrate using interdigital transducers. The velocity and viscosity of liquids are measured using the leaky SAW delay line. Experiments are made with a rotated Y cut LiNbO3 substrate. Results shown that the method is very suitable for sensing liquid.

Precise Measurement of Surface Acoustic Wave Velocity Using a Swept Frequency IDT-NDE System

A method of measuring the surface acoustic wave (SAW) velocity is presented. Three interdigital transducers (IDTs) deposited on a piezoelectric substrate are used to measure SAW velocity of sample materials using a fluid couplant. The output voltage of the IDT is measured as a function of the acoustic wave frequency. A unique curve is obtained by the interference between the two outputs of the close IDTs. The SAW velocity is obtained from the frequency dependence of the curve. Measurements are made for anisotropic materials at frequencies from 20 to 30 MHz. The experimental results obtained in this manner agreed with the theoretical ones.

Measurement of Humidity Using Surface Acoustic Wave Device

A surface acoustic wave (SAW) sensor utilizing the acoustoelectric effect has been designed for measurement of humidity in sensing ambient atmosphere. Most of the studies reported on sensors utilize the effect of mass loading. In this paper, we propose a somewhat different SAW humidity sensor that uses the changes in the film conductivity rather than the mass. A 30 MHz dual SAW delay line fabricated on 128° YX LiNbO3 was coated with the sodium salt of poly(styrene) sulfonate. This hygroscopic polymer coating caused the SAW velocity change of 10 m/s per 10% relative humidity. The response was quite linear in the range from 20 to 70%RH.

Liquid Sensor Using Two-Port Surface Acoustic Wave Resonator

A two-port SAW resonator has been designed for a stabilizing element of an SAW liquid sensor. There is increasing use of SAWs for sensors, and most of the works reported on sensors to date are concerning delay lines. In this paper, SAW resonators have been studied in order to reduce an acoustic loss and a distortion of the delay lines. SH type SAWs are excited on a 36° YX LiTaO3 substrate by using IDTs. The two port SH-SAW resonators have been used for sensing the liquid. The sensitivity of the SAW resonance frequency and Q value for the viscosity of liquids have been measured.