すだれ電極を分割直列接続した弾性表面波トランスジューサ

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In this paper, the results of experiments on two novel interdigital surface wave transducers with divided electrodes are presented and their properties are discussed. These divided electrode transducers are composed of minor transducers whose electrodes are connected in series. These electrodes are formed by dividing either the finger-length or finger-number of a conventional interdigital transducer(IDT) into m segments. The electrode patterns for the two types of transducers are shown in Figs. 1(divided finger-length type) and 2 (divided finger-number type). The equivalent circuit for an IDT composed of n spaces of finger electrodes can be represented by a cascade connection of alternately polarized equivalent circuits for the longitudinal vibrator as shown in Fig. 3. The fundamental equation of electroacoustic transformation for the acoustic terminal 1-1' in Fig. 3 is given by Eq. 1. Each coefficient is derived according to transmission-line theory. The force factor, A_n, and the damped admittance, Y_<dn>, are difined Eqs. 3 and 4, respectively. A characteristic of the divided-electrode transducers is that the free impedance for the divided finger-length type increases by m^2 compared to that for the undivided type, where m is the number of divided segments. For use in tuning, the condition for minimizing the effective attenuation is given by Eq. 12. A design formula in the form of Eq. 15 can be derived by substituting Eq. 14 fodr a coplanar electrode capacitance into Eq. 12. The transducer of the divided finger-number type consists of an array of several small transducers which are separated by suitable distances so that the generated waves are in phase with each other at each of the small transducers. When a transducer of the conventional type having a number n of intervals for finger electrodes is divided into m small transducers, the free impedance Z_<nm> is given by Eq. 18. Therefore, the Z_<nm> is increased m^2 times that of the conventional type. Experimental first, the divided finger-length electrode pair (m=3, n=11) and the undivided finger-length electrode pair (m=1, n=11) were made by photo-etching on a PZT ceramic substrate in order to compare their characteristics(Fig. 6). The characteristics obtaind for these transducers (center frequency:5. 3MHz)are shown in Figs. 7 and 8. Next, the divided finger-number electrode(m=2, n=15) and the undivided finger-number electrode (m=1, n=15) were made on each side of the undivided finger-number electrode for sending transducer on a PZT ceramic substrate (Fig. 10). The characteristics obtained for these transducers (center frequency:14. 5MHz) are shown in Figs. 11 and 12. In conclusion, from a theoretical analysis and experiments, it is clear that the real part of the free impedance increaces and input-output voltage ratio is improved with little sacrifice in the frequency bandwidth by dividing the interdigital electrodes and connecting them in series.
社団法人日本音響学会の論文
1974-10-01

すだれ電極を分割直列接続した弾性表面波トランスジューサ

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