すだれ電極表面波トランスジューサの分割電極構成による特性の改善
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概要
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This paper describes an improvement in frequency characteristics of interdigital surface wave transducers (ISWTs) effected by modifying the electrode structure of the ordinary ISWT. These modified transducers (Divided electrode-pairs ISWT) are composed of several minor ISWTs connected electrically in series and acoustically in tandem as shown in Fig. 1. These minor ISWTs are formed by dividing the electrode-pairs of the ordinary ISWT into several segments. The improvement of frequency characteristics by modifying the electrode structure are effected by changing the number of electrode-pairs of minor ISWT or by changing the length of coupling lines between the individual minor ISWTs. The equivalent circuit of the divided electrode-pairs ISWT composed of 3-minor ISWTs can be expressed as a tandem connection of equivalent circuit for the ordinary ISWTs and coupling lines as shown in Fig. 2. Therefore, characteristics of these ISWTs may be obtained by calculating the tandem connection of Y-matrices. Fig. 3 indicates the insertion loss of the delay lines which are composed of two indentical divided electrode-pairs ISWTs having the coupling line of one wave length. If the number of electrode-pairs of the middle minor ISWT is less than that of those at both ends, side lobes of frequency characteristics can be suppressed. Moreover since the motional impedance of this transducer becomes greater than that of the ordinary ISWT, the insertion loss is diminished at high frequencies where the motional impedance decreases. Fig. 4 shows an applicable range of the divided electrode structure to diminish the insertion loss. Fig. 5 shows the effect of variation in the coupling line-lengths upon the frequency characteristics of output open circuit voltage. It is shown that the narrow bandwidth can be obtained by using the coupling line-length of an integer multiple of the wave length. In experiments, these ISWTs are fabricated on the piezoelectric ceramics plates by photo-etching, the electrode dimensions being shown in the respective figures. Fig. 7 and 8 show the insertion loss of delay lines using 3-divided electrode ISWT as the transmitting ISWT. The side lobes of divided ISWT was suppressed more noticeably than that of the frequency characteristics of the undivided ISWT. The divided electrode structure becomes useless to diminish the insertion loss at low frequencies, but the output open circuit voltage increases regardless frequency range (Fig. 9). Fig. 10 shows the characteristics of narrow bandwidth obtained by variation of coupling line-lengths between the individual minor transducers without increasing the number of the electrode-pairs.
- 社団法人日本音響学会の論文
- 1978-09-01
著者
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