title: Comparison between ST-cut quartz 25 degrees and -60 degrees NSPUDT propagation directions.
abstract: This paper discusses directivity and other propagation properties of natural single phase unidirectional transducer (NSPUDT) propagation directions on ST-cut quartz. The work focuses on the comparison of surface acoustic wave (SAW) directivity and propagation properties between the ST-cut quartz -60 degrees, Euler angles: (0 degrees, 132.75 degrees, -60 degrees), and the ST-cut quartz 25 degrees, Euler angles: (0 degrees, 132.75 degrees, 25 degrees), NSPUDT propagation directions, including predicted and measured directivity responses for both propagation directions. The well-known SAW 25 degrees propagation direction is used for low loss, high performance SAW filter designs for consumer products and communications applications. The ST-cut quartz -60 degrees propagation direction has been predicted to have a reflection coefficient 2.5 times larger than ST-cut quartz 25 degrees. In addition the ST-cut quartz -60 degrees satisfied the NSPUDT 90 degrees reflection coefficient phase condition much more closely, resulting in an improved directivity response. For the delay line structures used in the experiments, the measured directivity is 10.1 dB for the -60 degrees propagation direction. For the same structures, the measured directivity along the 25 degrees propagation direction is about 5.0 dB. The experimental results given in this paper verify that indeed ST-cut quartz -60 degrees has a higher directivity than ST-cut quartz 25 degrees, confirming the theoretical predictions. In addition, this work compares other propagation properties for both directions, namely, phase velocities, electromechanical couplings, temperature coefficients of delay, power flow angles, and metallic strip reflection coefficient amplitudes and phases.
authors.affiliation: Department of Electrical and Computer Engineering, University of Maine, Orono 04469, USA. mdacunha@eece.maine.edu
authors.forename: Maurício Pereira
authors.initials: MP
authors.lastname: da Cunha
authors.forename: Alberto Yoshihiro
authors.initials: AY
authors.lastname: Nakano