Surface Wave Losses Research Articles

DIPOLE-EXCHANGE SURFACE WAVE DISPERSION AND LOSS FOR A METALLIZED FERRITE FILM

The frequency versus wavenumber dispersion for a conductor on an insulating ferromagnetic film is calculated including dipolar, exchange and conductivity effects. Conductivity losses dominate for fδ ~ 1 while propagation losses are largest for αf2 ≥ where f is the surface wave propagation constant, δ the skin depth and α is the exchange constant. The surface wave dispersion curve exhibits a variety of shapes depending upon the values of δ and α and ratio δ2/α. The general features of magnetic surface wave dispersion and loss are summarized.

Microwave Frequency Acoustic Surface-Wave Loss Mechanisms on LiNbO3

The temperature and frequency dependence of the attenuation of 0.5–5-GHz acoustic surface waves on LiNbO3 has been measured. For propagation in vacuum a frequency-squared dependence of the total attenuation is obtained with a value at 1 GHz of 0.9 dB/μsec. Temperature-dependence measurements using a novel three-transducer technique show the dominant loss (0.7 dB/μsec at 1 GHz) mechanism to be the interaction with thermally excited elastic waves. Propagation in air results in an additional loss linearly proportional to frequency with a value of 0.2 dB/μsec at 1 GHz. The effects of beam steering and diffraction losses are also investigated both theoretically and experimentally. Both misalignment of transducers with respect to pure mode propagation axes and misalignment of the propagation-plane perpendicular can add significantly to delay line insertion loss. This beam steering loss on Y-cut Z-propagating LiNbO3 is considerably higher than on the 41.5° rotated-cut X-propagating orientation. The loss mechanisms measured in this paper are sufficient to completely account for the insertion loss of surface-wave delay lines.

The Generation and Propagation of Acoustic Surface Waves at Microwave Frequencies

The generation and propagation of acoustic surface waves is reviewed with particular emphasis on the microwave-frequency range. Theoretical work on optimizing the generation efficiency and the bandwidth of interdigital transducers is compared with recent experimental results. The minimum Iinewidth of 0.9 /spl mu/m which can be produced by optical photolithographic techniques places an upper limit of about 1 GHz on the maximum frequency that can be generated at the fundamental mode. Overtone operation has been used to generate 3 GHz surface waves on LiNbO/sub 3/ but this method has the disadvantage of reduced efficiency plus the complication of volume-wave generation. A better solution for generation above 1 GHz is the fabrication of interdigital transducers by means of electron beam exposure of the photoresist. The surface-wave propagation loss gives a significant contribution to the total insertion loss of delay lines operating at microwave frequencies. Losses of 1.1 dB//spl mu/s and 3.8 dB//spl mu/s at 0.9 GHz and 2 GHz, respectively, have been measured for propagation along the Z-direction of Y-cut LiNbO/sub 3/ by means of a laser deflection method. Larger losses have been observed for quartz. The additional complexities for surface-wave propagation due to the anisotropic single-crystal substrates which are necessary at microwave frequencies are also described.