Quartz crystal resonator with supplemental electrodes for controlling the Q factor

Claim 1

In a quartz crystal resonator of the type comprising an AT type cut quartz plate substantially defined by a pair of opposed surfaces spaced apart by a predetermined quartz thickness, each of said opposed surfaces having at least a main electrode applied thereon, each of said main electrodes at least having a respective active electric field generating portion which is superimposed with respect to the opposed surface main electrode, said active electric field generating portions each having an associated perimetral surface, said main electrodes being connectable to a first electric potential for generating a main electric field in said resonator, said resonator having an associated resonance frequency and Q-factor and associated spurious resonance frequencies; the improvement comprising at least one metallized supplementary control electrode respectively applied to each of said opposed faces and being disposed thereon in surrounding relationship to the perimetral surface of the main electrode active electric field generating portion on said respective opposed face substantially in the form of an aureole, said main electrode being metallized and said opposed surfaces being non-metallized and providing a non-metallized unused portion for said plate over a substantial portion of said opposed surfaces, said supplementary control electrodes each having at least a respective active field generating portion which is superimposed with respect to the opposed surface supplementary control electrode, said suplementary control electrodes being connectable to a second electric potential for generating a supplementary electric field in said resonator, each of said supplementary control electrodes having at least an associated parameter of width, thickness, density, air gap distance from said respective main electrode, and applied second electric potential, each of said main electrodes having at least an associated corresponding parameter of width, thickness, density and applied first electric potential, at least one of said associated parameters of said supplementary electrodes being different from said corresponding associated parameter for said respective main electrodes for controlling said associated Q-factor and frequency of said spurious resonance frequencies, said generated supplementary electric field cooperating with said generated main electric field for controlling the associated Q-factor and frequency of at least the spurious resonance frequencies of said resonator.