Unidirectional SAW Transducers Research Articles

Extraction of all coefficients of coupled-mode equations for natural, single-phase, unidirectional SAW transducers from dispersion characteristics computed by hybrid finite element method.

A numerical method is presented for determining all of the coefficients of coupled-mode equations for natural, single-phase, unidirectional SAW transducers (NSP-UDTs). Substituting numerical results computed by the hybrid finite element method for infinite NSPUDTs with shorted and open electric ports into several relations derived from the coupled-mode theory, we can determine all of the coefficients. Specifically, the edge frequencies of a stop-band and the static capacitances yield the self-coupling coefficients and the amplitudes of mutual-coupling and transduction coefficients, and the electric potential standing wave on the substrate surface, which can be derived from the projection of the standing wave distributions of particle displacements and electric potential in the whole substrate onto the set of those predicted by the coupled-mode theory, yields the phases of mutual-coupling and transduction coefficients. NSPUDTs on ST-25 degrees X quartz, Y-51.25 degrees Z LiTaO3, and 50 degrees Y-25 degrees X La3Ga5SiO14 substrates are investigated. Our results agree well with the earlier experimental ones.

Quasi-static analysis of floating-electrode unidirectional SAW transducers.

The quasi-static theory of SAW transducers is a simplified Green's function analysis that has previously been shown to be effective for transducers in which short-circuit reflections are negligible. Here, the theory is extended to allow for floating electrodes, which occur in floating-electrode unidirectional transducers (FEUDTs). An analysis for the coupled-mode (COM) parameters of FEUDTs is developed, giving the capacitance, transduction, and reflection parameters and the locations of the transduction and reflection centers. For a FEUDT with six electrodes per period, algebraic results are obtained in terms of Legendre function expressions, giving the COM parameters as functions of metalization ratio. These results agree with earlier derivations by other authors, but they are obtained much more simply. Numerical results are straightforward to obtain. A FEUDT with five electrodes per period is also analyzed, showing that it performs similarly to the six-electrode type.

Directivity of group-type single phase unidirectional SAW transducers

It is shown that the centre-frequency directivity for a SPUDT comprising conventional transducers alternating with reflecting gratings is determined simply by the grating reflection coefficient. This applies if the transducers and gratings are varied to weight the device. If the grating strips are all identical the directivity is proportional to the total number of grating strips. >

A New Unidirectional SAW Transducer with a Simplified External Network

A group-type unidirectional SAW transducer with new electrode constitution and new phase shifter has been developed. It is designed to have non-quadratic geometrical phase difference between sending and reflecting electrodes and the electrodes have different finger pairs. In addition, the phase shifter is constituted by only one capacitor and is fabricated on the same piezoelectric substrate. Consequently, inductors of the external network can be reduced. Furthermore, as suppression of backward response is more optimal, the transducer eliminates any adjustment with low loss and low ripple.

A Unidirectional SAW Transducer with Different Finger Pairs between Sending and Reflecting Electrodes

An intentionally imperfect unidirectional transducer has been studied for SAW TV IF filter. It is constituted of different finger pairs between sending and reflecting electrodes to extend impedance matching range. And a thin film phase shifter is monolithically fabricated on a substrate. As the result low insertion loss and no matching adjustment can be achieved at the same time, and that without any increase of chip size and electrical parts.

Wide-Band and Low-Loss Unidirectional SAW Filter

An improved group-type unidirectional SAW transducer has been proposed which reduces the geometrical phase difference between sending and reflecting electrodes. A 90° phase shifter delays the phase of the reflection side electrodes. In consequence, both the wider frequency band width for triple transit suppression and low insertion loss can be achieved.

Piezoelectric thin film unidirectional SAW transducer and filter

Small passband ripple piezoelectric thin film unidirectional transducers and filters are presented. ZnO thin film deposited on a fused silica was used in the experiment. As the result, the characteristics of no pass-band ripple and minimum insertion loss of 5.2 dB, and also the directionality of 22 to 29 dB per one transducer are obtained.