T. Yasuda

SAW humidity sensor using dielectric hygroscopic polymer film

A surface acoustic wave (SAW) sensor for measurement of humidity is described. SAW devices have the ability to directly respond to the inertial mass and elastic mechanical properties of materials in contact with the device surface. Feature enables them to directly sense mass and mechanical properties of their environment. In this paper, we show a new SAW humidity sensor that uses the changes in the film permittivity rather than the mass. A dual SAW delay line fabricated on a piezoelectric substrate was coated with cellulose acetate. For a 128° YX LiNbO3 substrate, the hygroscopic polymer-coating caused a SAW velocity change of 0.33 m/s per 10% relative humidity. The response was linear in the range from 10% to 70% in relative humidity. The results suggest that the SAW humidity sensor using the dielectric interaction with the SAW electric field is quite promising

Measurement of acoustic properties of liquids using SH-type surface acoustic waves

A surface acoustic wave (SAW) viscosity sensor for liquid phase sensing utilizing a shear horizontal displacement of a leaky SAW is presented. The sensor is based on a dual SAW delay line oscillator. Leaky SAWs with shear horizontal displacement were excited on a 41 degrees -rotated Y-cut X-propagation LiNbO/sub 3/ substrate by using interdigital transducers (IDTs). It is shown that the viscosity sensor has a sensitivity of about 80 Hz/cP at an operating frequency of 30 MHz, with a threshold sensitivity of about 1 cP.<<ETX>>

Humidity sensor using surface acoustic waves propagating along polymer/LiNbO/sub 3/ structures

A surface acoustic wave (SAW) sensor for measurement of humidity in ambient atmosphere is presented. The majority of SAW sensors utilize the effect of mass loading. In this paper, we propose a new SAW humidity sensor that is based on the changes in the film conductivity rather than the mass. The phase velocity and propagation loss were computed for the SAW propagating on a piezoelectric (128d YX LiNbO3) substrate, which is coated with a hygroscopic conductive polymer. In experiments, a 30 MHz dual SAW delay line fabricated on 128d YX LiNbO3 was coated with the sodium salt of polystyrene sulfonate. This hygroscopic polymer coating caused a SAW velocity change of 20 m/s per 10% relative humidity. The response was quite linear in the range from 40 to 80% RH

Two Dimensional Mapping of SAW Propagation Constants by Using Fresnel-Phase-Plate Interdigital Transducer

The methods of measuring the acoustic properties of solids by using the acoustic beams from interdigital transducers (IDT) is described. An IDT can radiate acoustic waves into liquid in oblique directions with respect to the substrate surface, and the wave fronts can be arbitrarly controlled by designing the IDT shape. One IDT couple is used to measure the acoustic properties of a solid sample. In the present study, we show a new method for focusing the beam from an IDT and measuring the acoustic properties of solids. An interdigital electrode is divided into several sections, each of which is placed to form a one dimensional Fresnel phase plate (FPP) on a piezoelectric substrate. It has been found that the FPP IDT generates a converging beam onto a focal plane, and the present system is suitable for measuring the two dimensional variation of leaky SAW phase velocity on a sample surface.

Precise estimation of viscosity of liquid using leaky surface acoustic waves propagating along liquid/polymer/LiNbO/sub 3/ structures

A surface acoustic wave (SAW) propagating on a LiNbO/sub 3/ substrate has a large shear horizontal (SH) displacement. However, it is not possible to make a good estimate of the viscosity using the substrate for the case of the small viscosity liquids, such as water, because the propagation loss is relatively large. The polymer film/LiNbO/sub 3/ structure is proposed for the leaky SAW substrate. By using this substrate, an almost perfect SH mode can be attained. The loss is caused principally by the viscous coupling. Consequently, the viscosity coefficient can be well estimated even in the case of water.<<ETX>>

Precise measurement of SAW velocity using SAW delay line

A method of nondestructive evaluation (NDE) by measuring the acoustic properties of materials using a surface-acoustic-wave (SAW) delay line is presented. A SAW delay line with three interdigital transducers (IDTs) deposited on a piezoelectric substrate is used to measure the SAW velocity of the sample material, using a fluid couplant. The SAW velocity is obtained from the frequency dependence of the delay line, and movement in the z-direction is not required. Measurements have been made for an anisotropic material at frequencies from 35 to 55 MHz. The experimental results agree well with the theoretical results. Moreover, it has been found that the focused SAW excited from a Fresnel-phase-plate IDT is suitable for mapping the two-dimensional variation of SAW velocity on an anisotropic sample surface.<<ETX>>

One-port surface acoustic wave resonator for sensing in liquids

A one-port resonator utilizing shear horizontal surface acoustic waves (SH-SAWs) has been designed for a sensing element of a liquid phase sensor. SH-SAWs are excited on a 36 degrees rotated Y cut, X propagating LiTaO/sub 3/ substrate by using interdigital transducers (IDTs). The sensitivity of the resonance frequency and the Q value for the viscosity of liquids are measured. Experimental results show that the Q value and resonance frequency of the SH-SAW resonator vary with the viscosity of the loaded sample liquid.<<ETX>>

Analyses of layered SAW substrates by time dependent particle displacement

It is known that the particle displacement relevant to surface acoustic wave (SAW) propagation becomes ellipsoidal. The time-dependent particle displacement is calculated for layered substrates. It is found that there exists a correlation between the particle displacement distribution and the SAW velocity dispersion. The origin of the appearance of the maximum and minimum points in the dispersion curve is discussed on the basis of mechanical impedance matching.<<ETX>>

Study of ZnO/Quartz for SAW Device Materials

zno/sappnire (Ist Ilodc, 5800-6800 A ZnO/Z-cut quartz and a Si02/ZnO/Zcut quartz structure have been proposed for surface acoustic wave (SAW) device materials. The dispersion of the SAW phase velocity, the coupling coefficient and the temperature coefficient of delay have been theoretically calculated, and the optimum structural parameters have been determined. Experimentally, ZnO was deposited on Z-cut quartz by a DC sputtering method, and the SAW delay lines were fabricated. It was found from the various measurements that high quality ZnO films grew on quartz substrates and SAW devices with a good temperature stability would be realized by using those layered structures. 31 Slngle-crystal 1.0

Humidity sensor using surface acoustic waves propagating along layered structures

A surface acoustic wave (SAW) sensor for measurement of humidity in ambient atmosphere is presented. The majority of the SAW sensors have utilized the effect of mass loading. In this paper, we propose a new SAW humidity sensor based on the changes in the film conductivity rather than the mass. The phase velocity and propagation loss were computed for the SAW propagating on a piezoelectric substrate which is coated with a hygroscopic conductive polymer. In experiments, a 30 MHz dual SAW delay line fabricated on 128/spl deg/ YX LiNbO/sub 3/ was coated with the sodium salt of polystyrene sulfonate. This hygroscopic polymer coating caused the SAW velocity change of 20 m/s per 10% in the relative humidity. The response was quite linear in the range from 40 to 80%RH.<<ETX>>