Abstract A surface-wave filter has a wave-propagating medium of ferroelectric material that exhibits a rate of change of surfacewave velocity which increases with increasing degree of poling more rapidly than its surface-wave coupling factor increases as the poling level is raised. The ultimate transducer interaction efficiency is a function of the coupling factor. Moreover, the material is poled in an amount that effects a desired surfacewave velocity while, at the same time, producing a surface-wave coupling factor that is significantly less than that corresponding to an optimum value with respect to transducer interaction efficiency. Completing the structure, an input transducer serves to launch acoustic surface waves and an output transducer responds to those waves by developing an output signal.
A method as defined in claim 1 in which said controlled degree of temperature is higher than any temperature to which said material subsequently is subjected during completion of said filter.
Claim 2
Dependent Claim
155 words
A surface wave filter comprising: a wave-propagating medium of ferroelectric material exhibiting a rate of change of surface-wave velocity that increases with increasing degree of poling more rapidly than its surface-wave coupling factor increases with said increasing degree of poling, the transducer interaction efficiency of said material being proportional to said surface-wave coupling factor, the degree of poling of said material being represented by its invariant coupling factor, said material being poled in an amount effecting a desired surface-wave coupling factor significantly less than that corresponding to the maximum value of said transducer interaction efficiency and at an invariant coupling factor of less than 0.5; an input transducer disposed on a surface of said medium near one end thereof and responsive to input signals for launching acoustic surface-waves along said surface; and an output transducer disposed on said surface near the other end thereof and responsive to said acoustic waves for developing an output signal.