Thickness-extensional mode piezoelectric resonator with poisson{3 s ratio less than one-third

Claim 2

A piezoelectric resonator comprising a thin plate of piezoelectric material having a Poisson''s ratio less than onethird, said plate having two flat spaced major surfaces on opposite sides thereof and a flat bottomed recess in at least one of said two major surfaces, and a pair of electrodes, one on the bottom of said recess and the other on the major surface at least in the area opposite the position of said recess, said recessed part of said plate vibrating in the fundamental thicknessextensional mode at a pre-selected frequency when an electrical signal is applied thereto, the thickness t of said plate at said recess and the thickness t'' of said plate at said flat part being in the relationship (NTA/2NS) < (t/t'') < (NTS/NTA) where NS, NTS and NTA are frequency constants for the thickness-shear vibration, the thickness-extensional vibration and the antiresonant thickness-extensional vibration, respectively, whereby the resonant frequency of said fundamental thickness-extension vibration of said plate at said recessed part is higher than the resonant frequency of said plate at said flat part.

Claim 3

A piezoelectric resonator as claimed in claim 1, further comprising a pair of electrical terminals on said two major surfaces respectively, said electrical terminals being connected to said electrodes respectively and with the area of one major surface on the opposite side of the plate from one of said electrical terminals being different from the area on said one major surface, covered by the other electrical terminal provided on said one major surface.

Claim 4

A piezoelectic resonator as claimed in claim 1, wherein said piezoelectric plate has one recess provided in one of said two major surfaces, one of said electrodes being in said recess and the other electrode being on the other major surface at a portion which includes at least the area opposite said recess.

Claim 5

A piezoelectric resonator as claimed in claim 3, wherein said other electrode is on the whole area of said other major surface and said other major surface has no recess therein.

Claim 6

A piezoelectric resonator as claimed in claim 1, wherein said piezoelectric plate has a recess in each of said two major surfaces, respectively, said two recesses being opposite each other and said electrodes being in said recesses, respectively.

Claim 7

A piezoelectric resonator as claimed in claim 1, wherein said piezoelectric plate is of a lead titanate piezoelectric ceramic and the ratio of the thickness of said plate between said recess and the thickness of said plate at said flat part being from 0.859 to 0.908.

Claim 8

A piezoelectric resonator as claimed in claim 1, wherein said lead titanate ceramic has as its main component a solid solution of PbTiO3.

Claim 9

A piezoelectric resonator vibrating in the thickness-extensional vibration mode comprising a thin plate of a lead titanate piezoelectric ceramic having a Poisson''s ratio of less than one third and which plate vibrates in the thickness-extensional mode at a preselected frequency when an electrical signal is applied thereto, said piezoelectric plate having a flat part defined by two spaced flat major surfaces on opposite sides thereof and an elastic wafer having a hole therein on each major surface, said holes defining a pair of recesses, one on each of said two major surfaces respectively, said recesses being opposite each other through said plate, a pair of electrodes with one electrode in each of said recesses, and a pair of electrical terminals, one on each of said two major surfaces respectively, said electrical terminals being connected to the respective electrodes with the area of one major surface on the opposite side of the plAte from one of said electrical terminals being different from the area on said one major surface, covered by the other electrical terminal provided on said one major surface, and the ratio of the thickness of said plate between said recesses and the thickness of said plate at said flat part being ranged from 0.859 to 0.908.

Claim 10

A piezoelectric resonator vibrating in the thickness-extensional vibration mode comprising a thin plate of a lead titanate piezoelectric ceramic having a Poisson''s ratio of less than one third and which plate vibrates in the thickness-extensional mode at a preselected frequency when an electrical signal is applied thereto, said piezoelectric plate having a flat part defined by two spaced flat major surfaces on opposite sides thereof and an elastic wafer having a hole therein on each major surface, said holes defining a pair of recesses, one on each of said two major surfaces respectively, said recesses being opposite each other through said plate, a pair of electrodes with one electrode in each of said recesses, and a pair of electrical terminals, one on each of said two major surfaces respectively, said electrical terminals being connected to the respective electrodes with the area of one major surface on the opposite side of the plAte from one of said electrical terminals being different from the area on said one major surface, covered by the other electrical terminal provided on said one major surface, and the ratio of the thickness of said plate between said recesses and the thickness of said plate at said flat part being ranged from 0.859 to 0.908.

Claim 11

A piezoelectric resonator vibrating in the thickness-extensional vibration mode comprising a thin plate of a piezoelectric ceramic material having a Poisson''s ratio of less than one-third and which plate vibrates in the thickness-extensional mode at a preselected frequency when an electrical signal is applied thereto, said piezoelectic plate having two spaced flat major surfaces on opposite sides thereof, an elastic wafer having a hole therein on at least one major surface, said hole defining a recess, a pair of electrodes with one electrode in said recess and the other being on the opposite surface of said plate in at least the area corresponding to said one electrode, said part of said plate in said recess vibrating in the fundamental thickness-extensional mode at said pre-selected frequency when an electrical signal is applied thereto, the thickness t of said plate at said recess and the thickness t'' of said plate plus said wafer being in the relationship (NTA/2NS) < (t/t'') < (NTS/NTA) where NS, NTS and NTA are frequency constants for the thickness-sheer vibration, the thickness-extensional vibration, and the anti-resonant thickness-extensional vibration, respectively, whereby the resonant frequency of said fundamental thickness-extension vibration of said plate at the part corresponding to said recess is higher than the resonant frequency of the remainder of said plate.

Claim 12

A piezoelectric resonator vibrating in the thickness-extensional vibration mode comprising a thin plate of a piezoelectric ceramic material having a Poisson''s ratio of less than one-third and which plate vibrates in the thickness-extensional mode at a preselected frequency when an electrical signal is applied thereto, said piezoelectic plate having two spaced flat major surfaces on opposite sides thereof, an elastic wafer having a hole therein on at least one major surface, said hole defining a recess, a pair of electrodes with one electrode in said recess and the other being on the opposite surface of said plate in at least the area corresponding to said one electrode, said part of said plate in said recess vibrating in the fundamental thickness-extensional mode at said pre-selected frequency when an electrical signal is applied thereto, the thickness t of said plate at said recess and the thickness t'' of said plate plus said wafer being in the relationship (NTA/2NS) < (t/t'') < (NTS/NTA) where NS, NTS and NTA are frequency constants for the thickness-sheer vibration, the thickness-extensional vibration, and the anti-resonant thickness-extensional vibration, respectively, whereby the resonant frequency of said fundamental thickness-extension vibration of said plate at the part corresponding to said recess is higher than the resonant frequency of the remainder of said plate.