Hiroshi Kogo

Variable SAW delay line using amorphous TbFe 2 film

This paper describes a large SAW velocity change obtained in a delay line consisting of an amorphous TbFe 2 film on a LiNbO 3 substrate. When an external bias field of about 4 kOe was applied parallel to the direction of SAW propagation, the percentage velocity change attained was -0.27 %. The value of this change is several times as large as that previously reported. The delay line may be used for trimming a small amount of delay time and tuning oscillation frequencies in an SAW oscillator.

Interaction of High-Coupling Leaky SAW with Bulk Waves Under Metallic-Grating Structure on 36° YX-LiTaO 3

The paper deals with leaky SAW (LSAW) propagating under metallic-grating structure on 36OYX-LiTa03, and its interaction with bulk waves. Theoretical analysis has shown that the attenuation of LSAW unusually changes with frequency about the stopband of the grating: the attenuation is negligibly small at frequencies lower than the stopband, whereas it rapidly increases when the frequencies are raised above the stopband, and takes a maximum value of about O.ldB per wavelength. This suggests that the attenuation is mainly attributed to the interaction of LSAW with highly piezoelectric fastshear waves. As to the velocity dispersion, the effect of the metallic-grating upon LSAW is qualitatively similar to that on conventional SAW. Experimental result using an open-circuited metallicgrating was in good agreement with the theoretical prediction. However, the agreement was rather poor for a short-circuited metallic-grating. This may be due to the fact that in the short-circuited grating, the effects of mass loading and electrical perturbation upon LSAW propagation cancel each other.

Frequency Response Measurement for SAW Devices Based on Fourier Analysis of Impulse Response

Methode permettant la separation des differentes reponses et la mesure de la reponse en frequence associee a un mode de propagation specifie. La mesure est faite sans traitement numerique et les resultats sont immediatement affiches sur un analyseur de spectre

A model of the ecosystem with the concentrating processes of a pesticide

Abstract A model of the ecosystem with the concentrating processes of a pesticide, such as DDT, DDD, etc., is proposed from the viewpoint of mass and pesticide flow. This model explains the rule of the concentrating processes and studies the mechanism of the concentration of the pesticide.

Magnetostrictive properties of sputtered Co-Cr film on surface acoustic wave

This paper describes the dependence of SAW velocity change on bias magnetic field in a delay line consisting of a magnetostrictive Co-Cr film and YZ-LiNbO 3 substrate. When the hard direction of magnetization was perpendicular to the film plane, the percent velocity change attained was ∼ 310 ppm. On the other hand, when the easy direction was perpendicular to the plane, it was negligibly small. Since the magnetic anisotropy of the Co-Cr films can be changed by adjusting their composition, they may be useful for the perpendicular recording medium as well as the tunable SAW devices.

Suboptimization of Electrode-Withdrawal Weighted SAW Filters

A method of reducing sidelobes for electrode-withdrawal weighted SAW filters with a relative bandwidth of 24% is proposed. This method is based on searching for some local feasible solutions. I t is shown that some suboptimal solutions, which give a sidelobe level comparable to that given by the optimal solution, are obtained, and that the computational time is considerably reduced by comparison with the optimization method previously reported. Filters designed by the method meet the required bandwidth specification within an error of about 1%. W I . INTRODUCTION ITHDRAWAL OF interdigital electrodes for reducing sidelobes of surface acoustic wave (SAW) filters by using integer optimization has been recently reported [l]. Since the method using integer optimization (hereafter the method will be called the “optimization method”) always gives the optimal solution, which gives the minimum sidelobe level, it has the advantage of conventional statistical and deterministic methods [ 2 ] , which are effective only in narrow bandwidth filters (less than 1%). However, computational time for integer optimization increases very rapidly with an increase in variables and constraints. This may indicate that the optimization method is not suitable for narrow bandwidth filters consisting of many electrodes. In fact, the design becomes impractical for filters with a relative bandwidth of less than about S%, due to an increase in computational time. In addition, the optimization method as well as the statistical and deterministic methods Manuscript received July 19,1978;revised September 12,1978. The authors are with the Faculty of Engineering, Chiba University, Chiba-shi, Japan. cannot exactly satisfy the required bandwidth specification of filters. This paper proposes a suboptimization method of designing electrode-withdrawal weighted SAW filters with a relative bandwidth of 2-5%, for which there have been no useful methods. By the method some suboptimal or optimal solutions can be obtained in less computational time than that required in the optimization method, and the required bandwidth specification can be met almost exactly. local feasible solutions; that is, searching for some feasible solutions in some restricted parts of the domain in which the entire set of feasible solutions exist. Although there is no guarantee that the optimal solution can be obtained in such a restricted domain, some suboptimal solutions may be obtained. This is because [l] has shown that there exist several suboptimal solutions which give a sidelobe level comparable to that given by the optimal solution. Although the computational time is considerably reduced compared with the optimization method, the practical design is limited to filters with a relative bandwidth of more than about 2%. This is because the suboptimization method also uses integer optimization technique in some processes of obtaining the feasible solutions. Successive design was performed for the filters with a relative bandwidth of 2.5-5%. Our results show that the sidelobe level decreases almost monotonically with a decrease in the bandwidth, and that, for example, a sidelobe level of -45.4 dB is obtainable for a filter with a relative bandwidth of 2.68%. By comparison with the results obtained by the opThe suboptimization method is based on searching for some 0018-9537/79/0100-0053

A Simple Method of Reducing Sidelobes for Electrode-Withdrawal Weighted SAW Filters

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Propagation Characteristics of SAW on a ZnO/SiO2/high-velocity-substrate Structure

A simple method of reducing sidelobes for electrode withdrawal weighted SAW filters with a relative bandwidth o f 0.5 to 5 percent is proposed. In the method, some electrodes are withdrawn from, and are added to, a given original transducer successively. By comparison with other methods previously reported, sidelobe levels obtained by the method are comparable to those given by the optimal and suboptimal solutions. An approximate estimation of computational time shows that the present method is of practical use for filters not only with broad bandwidth but also with narrow bandwidth up to about 0.5 percent. The method can take account of SAW coupling strength of the electrode o f interest, which varies depending upon adjacent electrode configurations. 0 I . INTRODUCTION PTIMIZATION and suboptimization methods of reducing sidelobes for electrode-withdrawal weighted surface acoustic wave (SAW) filters have been recently reported [ l ] , [2]. Although these methods can always find optimal or suboptimal solutions which give good results in sidelobe reduction, they are limited to rather broad bandwidth filters. This is because they employ integer optimization technique which usually requires much computational time. In fact design becomes impractical for filters with a relative bandwidth of less than 2 t o 3 percent. On the other hand, deterministic and statistical methods are well-known for unequally spaced phased array antenna synthesis [ 3 ] . The former, however, may not be directly applicable to SAW filter design, since the closest spacing between adjacent electrode pairs is limited to about one wavelength in SAW filters. This may result in far-off large sidelobes. The latter is probably effective only in very narrow bandwidth filters with a relative bandwidth of far less than 1 percent, although it is relatively simple and can be readily implemented. Of course, it should be noted that there is no guarantee that the statistical method always finds practically useful results. From these points of view, a simple method of reducing sidelobes for the electrode-withdrawal weighted SAW filters with a relative bandwidth of 0.5 t o 5 percent is developed in the present paper. In the method, electrodes of the same number are withdrawn from, and are added to, a given original transducer successively so that sidelobes are effectively reduced. That is, sidelobes are lumped together into a single merit function, of which value is minimized by withdrawing and adding electrodes. Since the method does not employ integer optimization technique, computational time required for design can be Manuscript received December 19, 1978; revised April 23 , 1979. The authors are with Department of Electrical Engineering, Faculty of Engineering, Chiba University, Chiba-shi, Japan 260. considerably reduced, compared with the optimization and the suboptimization methods. This makes design of filters with a relative bandwidth u p to about 0.5 percent possible. empirical, it is effective in obtaining good results in sidelobe reduction. Hereafter, the method will be called the simple method. Some filters were practically designed and were compared with those designed by the optimization, the suboptimization and the statistical methods. Results obtained show that, for broad bandwidth filters, sidelobe levels obtained by the simple method are comparable to those obtained by the optimization and the suboptimization methods. For rather narrow bandwidth filters, sidelobe levels are more than 2 dB less than those obtained by the statistical method. The simple method is successfully applied to the filters of which input and output transducers are not identical. The use of different electrodes for the input and output transducers results in effective sidelobe reduction. An approximate estimation for the computational time required was made, and it shows that the simple method is useful for filters with a relative bandwidth of 0.5 to 5 percent. SAW coupling strength of the electrode of interest which varies depending upon adjacent electrode configurations. effective in the practical design of the electrode-withdrawal weighted SAW filters. Although algorithm for the method is very simple and rather It is also shown that the simple method can take account of Consequently, the simple method proposed in this paper is 11. SIMPLE METHOD Let us suppose that electrodes of the same number are withdrawn from, and are added to, a given original transducer consisting of 2K + 1 equally spaced electrode pairs, as was assumed in the suboptimization method. Fig. 1 shows the basic electrode arrangement for the transducer employed, in which 0, 1, . . . , N represent the electrode positions. By assuming that the central electrode of the original transducer is always retained and that the electrodes are symmetrical about the center of the transducer, the transducer transfer function HtO) is expressed by 0018-9537/79/0900-0334S00.75

Effect of Surface Electrical Boundary Condition on Temperature Stability of SAW Devices

The paper describes surface acoustic wave (SAW) propagation on a ZnO/SiO2/high-velocity-alumina-substrate multi-layered structure. It was shown that, quite independent of the elastic properties of the alumina substrate, the electromechanical coupling factor k2 and temperature coefficient of frequency (TCF) reflect those for Lamb waves in a ZnO/SiO2 composite membrane. This suggests a simple guiding principle to find multi-layered structures with moderate temperature stability and k2 for SAW, that is, TCF could be compensated without greatly reducing k2 by the proper choice of substrate materials.

Automated Acousto-Optic Measurement System of Bulk Acoustic Waves Launched from an IDT

The paper deals with the effect,of the surface electrical boundary condition on the temperature stability of an SAW device. The temperature coefficient of delay (TCD) was characterised, both theoretically and experimentally, for SAW and LSAW propagating under electrically open and shorted periodic metal strips, and for those propagating on free and metallised surfaces. The result showed that for some crystals and/or cuts, this sort of surface electrical boundary condition markedly affects the temperature stability of a device. It was also shown that the temperature stability can be controlled by using electrically loaded IDT-type grating strips.