Numerical analysis of surface and leaky surface acoustic waves in new piezoelectric KNBO3, PKN, and LGN crystals

We perform a numerical analysis of the properties of surface acoustic waves (SAW) as well as leaky surface acoustic waves (LSAW) in piezoelectric KNbO₃, Pb₂KNb₅O₁₅ (PKN) and La₃Ga_5.5Nb_0.5O₁₄ (LGN) crystals. We determine optimal thermostable cuts and directions in which the SAWs have high phase velocity, a very high coefficient of electromechanical coupling. and a small angle between the phase and group velocities. We also found the cuts and directions in which the LSAWs can exist. The characteristics of the LSAWs (velocity, the coefficient of electromechanical coupling, angle between the phase and group velocities, temperature coefficient of velocity, and coefficient of surface absorption along the LSAW propagation direction) are calculated. N. I. Lobachevsky State University, Nizhny Novgorod, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 42, No. 5, pp. 485–493, May 1999.     

Temperature-stable orientations in LGS and LGN piezoelectric crystals for surface acoustic waves

The temperature characteristics of surface acoustic waves (SAW) propagating in LGS and LGN crystals are numerically analyzed. The optimal orientations that correspond to the zero value of the first-order temperature coefficient of delay (TCD) for SAW propagating in these crystals are considered. The second-order TCD for SAW is calculated for a wide range of operating temperatures. It is shown that the temperature dependences of the material constants of LGS and LGN crystals are strongly nonlinear. The characteristics of SAW propagating in a structure that consists of an isotropic layer overlying an LGS or LGN piezoelectric crystal are numerically calculated. It is shown that, in the presence of a thin aluminum layer of a certain thickness on the crystal surface, in some cases it is possible to extend the operating temperature range within which the TCD for SAW is equal to zero.     

The temperature coefficients of delay of surface acoustic waves in LGS and LGN crystals in a wide temperature range

Numerical analysis of the first-and second-order temperature coefficients of the delay of surface acoustic waves (SAWs) in LGS and LGN crystals was carried out. The calculations were performed along thermostable directions in a wide temperature range. The effect of an aluminium layer having a finite thickness on the SAW temperature characteristics is shown.     

Numerical analysis of the properties of slit electroacoustic waves

The properties of slit electroacoustic waves that propagate in a system of two semi-infinite piezoelectric media separated by a vacuum gap, in a system consisting of a thin piezoelectric plate and a semi-infinite piezoelectric medium separated by a gap, and in a system consisting of two thin piezoelectric plates separated by a vacuum gap are studied. The process of transformation of slit electroacoustic waves to generalized surface acoustic waves or to Lamb waves is considered.     

Thermal stabilization of SAW devices by metal films

The characteristics of surface acoustic waves (SAW) propagating in a structure that consists of a metal layer overlying an YX-cut quartz crystal are numerically analyzed for a wide range of operating temperatures. It is shown that the presence of a metal film of a certain thickness on the surface of an YX-cut quartz crystal considerably improves the thermal stability of the characteristics of SAW propagating in such a structure.     

New optimal orientations for surface acoustic waves in langasite, langanite, and langatate piezoelectric crystals

Spatial regions and optimal orientations for surface acoustic waves in langasite, langanite, and langatate piezoelectric crystals are analyzed. An objective function for the search for optimal orientations in the piezocrystals is suggested. New optimal spatial regions and orientations that are promising for SAW-based devices are found.     

Calculation of Surface Acoustic Waves in Crystals Using the Global Optimization Procedure

The characteristics of surface acoustic waves are calculated using the procedure of searching for the global extremum of a multivariable function. This procedure is used to minimize the determinant of the boundary conditions to seek orientations in piezocrystals that are optimal from the viewpoint of acoustic-wave characteristics and to find pseudosurface (leaky) acoustic waves existing only in the vicinity of specific orientations.     

Parameter optimization of surface acoustic waves via multilayer structures

A method and algorithm for numerical analysis and optimization of the basic parameters of electroacoustic surface waves propagating in multilayer piezoelectric structures are described. Combinations of layer materials and piezoelectric substrates for which an electroacoustic surface wave has optimal parameters of propagation (low dispersion, high electromechanical coupling coefficient, high thermal stability, low diffraction losses, etc.) are found.     

Electroacoustic lamb waves in piezoelectric crystal plates

The main characteristics of various types of plate electroacoustic waves propagating in piezoelectric single-crystal plates of various thickness are numerically studied. A number of piezoelectric plates and orientations in them with record high values of the electromechanical coupling coefficient for transverse plate waves are proposed.