Quartz piezo-electric element vibrating in a coupled mode
AssigneeSociete Suisse pour l'Industrie Horlogere Management Services S.A.
InventorsAlphonse Ernst Zumsteg, Jean Engdahl, Raymond Huguenin
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Abstract
This specification describes a rectangular quartz crystal which has been igned with specific length-width-thickness ratios whereby vibration takes place in the thickness shear mode strongly coupled with flexural vibrations. The choice of the specific ratios permits an improved performance insofar as dynamic capacitance range, temperature dependent variations of frequency and finally quality factor are concerned. The dimensions and proportions make the crystal suitable for use as a high frequency time piece resonator.
Claims9
A piezo-electric resonator in rectangular bar form cut from a quartz crystal in a rotated Y orientation of 34.degree. 48' .+-. 20' and having its greatest dimension along Z' (YZW 34.degree. 48' .+-. 20' arranged to vibrate in a mode which is the resultant of coupling of a thickness shear (XY') mode and a flexural (XY') mode, the width (X)-thickness(Y') ratio of the resonator being selected from the following ranges:
- between 1.1 and 1.9 for the second flexure harmonic
- between 2.2 and 3.6 for the fourth flexure harmonic
- between 3.6 and 5.3 for the sixth flexure harmonic
- between 5.1 and 6.8 for the eighth flexure harmonic said quartz crystal being provided with electrodes on its opposed XZ' surfaces, such electrodes extending over the entire width X of the resonator but having a length in the Z' direction less than the length of the resonator thereby to establish an energy trapping zone within the portion of the resonator between the electrodes.
A piezo-electric resonator in rectangular bar form cut from a quartz crystal in a rotated Y orientation of approximately 34.degree.48', .+-. 20' and having its greatest dimension along Z' (YZW 34.degree.48' .+-. 20' said resonator having a width(X)-thickness(Y') ratio approximately equal to one of the values 1.35, 2.8, 3.125, 4.4, 5.9, said ratio being such that said resonator vibrates in a mode which is the resultant of coupling of a thickness shear (XY') mode and a flexural (XY') mode.
Method of making a rectangular quartz crystal resonator capable of vibrating in a mode which is the resultant of coupling of a thickness shear mode and a flexural mode and which exhibits a temperature dependent frequency behavior which in a temperature range of 20.degree. C to 30.degree. C and a tolerance of .+-. 2' for a given angle of cut provides a maximum frequency deviation of less than 1PPM comprising:
- cutting a crystal into a rectangular bar having its greatest dimension along Z', and in a rotated Y orientation of an angle falling within the zone of 34.degree.48' .+-.20' (YZW 34.degree.48' .+-. 20' and having a width(X)-thickness(Y') ratio of a value which is less than 6.8.
Dependencies are inferred from the claim text.