Piezoelectric sensor and acceleration sensor

• US 6,043,588 A
• Filed: 07/18/1996
• Issued: 03/28/2000
• Est. Priority Date: 07/18/1995
• Status: Expired due to Term

• Current Assignee: Murata Manufacturing Co Limited
• Original Assignee: Murata Manufacturing Co Limited
• Inventors: Unami, Toshihiko, Tabota, Jun, Ogiura, Mitsugu
• Primary Examiner(s): BUDD, MARK OSBORNE
• Application Number:
  US08/683,231
• Time in Patent Office: 1,349 Days
• Field of Search: 310/354, 310/328, 310/333, 310/344, 310/329, 310/332, 310/348, 310/366, 310/367, 310/368
• US Class Current: 310/329
• CPC Class Codes: G01N 2291/02827 Elastic parameters, strength or force
• CPC Class Codes: G01P 15/0922 of the bending or flexing mode type
• CPC Class Codes: H10N 30/302 Sensors

Abstract

A piezoelectric sensor has a piezoelectric element having a specific axis of sensitivity and a package for the piezoelectric element. The package has a rectangular parrallelopiped configuration with opposite longitudinal end surfaces having a height-to-width ratio of about 1:1. External lead electrodes are formed to cover at least the longitudinal end surfaces. A method and apparatus for detecting if the sensor is disposed in the proper posture is also disclosed.

Claims

1. An acceleration sensor comprising:

a bimorph element having an axis of highest sensitivity extending in a direction which substantially coincides with a line normal to the plane of a circuit board; and

a case assembly for fixing and supporting both longitudinal ends of said bimorph element, said case assembly being adapted to be mounted on said circuit board at both its longitudinal ends which are in support of both said longitudinal ends of said bimorph element;

wherein said bimorph element comprises a pair of piezoelectric ceramic plates each having a signal electrode and an intermediate electrode formed on opposite major surfaces thereof, said piezoelectric ceramic plates being joined to each other face to face at the surfaces having said intermediate electrodes such that said intermediate electrodes are coupled to each other;

each said piezoelectric ceramic plate having sections in the longitudinal direction of said bimorph element, there being three sections including a central section and an end section at each end of the central section, the sections being positioned such that, when said bimorph element is deformed in response to deflection of said circuit board, a quantity of charges is generated in said central section equal to a sum of the quantities of charges generated in both said end sections, said central section and both said end sections of each said piezoelectric ceramic plate being polarized thicknesswise of said piezoelectric ceramic plate in opposite directions of polarization, the directions of polarization of said central section and both said end sections of one of said piezoelectric ceramic plates being opposite to those of the other of said piezoelectric ceramic plates.

2. A piezoelectric sensor, comprising:

a piezoelectric element having a specific axis of sensitivity and detecting an acceleration along said specific axis; and

a package in which said piezoelectric element is provided;

wherein said package has a rectangular parallelopiped configuration comprising four major surfaces with end surfaces having a height-to-width ratio approximating 1;

1, wherein external lead electrodes are formed on at least said end surfaces, and wherein said package is mountable on a surface of a circuit board such that any one of said four major surfaces may be mounted on the circuit board;

wherein said piezoelectric element comprises a pair of strip-shaped piezoelectric ceramic plates each having on its major surfaces a signal pickup electrode and an intermediate electrode, and said pair of strip-shaped piezoelectric ceramic plates is joined face to face at the intermediate electrodes thereof;

and further wherein each of the strip-shaped piezoelectric ceramic plates is divided into a center section and two end sections interposing said center section, and said center section is polarized in a direction opposite to that of said end sections.

3. A piezoelectric sensor, comprising:

a piezoelectric element having a specific axis of sensitivity and detecting an acceleration along said specific axis; and

a package in which said piezoelectric element is provided;

wherein said piezoelectric element has a pair of strip-shaped piezoelectric ceramic plates joined to each other, and said package includes a pair of clamping members for clamping at least one longitudinal end of said piezoelectric element from the upper and lower sides thereof so as to support said piezoelectric element, and a pair of side cover members secured to both sides of said clamping members so as to cover left and right side surfaces of said piezoelectric element; and

wherein said package has a substantially rectangular parallelopiped configuration comprising four major surfaces with end surfaces having a height-to-width ratio approximating 1;

1, and external lead electrodes are formed on at least said end surfaces, and wherein said package is mountable on a surface of a circuit board such that any one of said four major surfaces may be mounted on the circuit board;

wherein said piezoelectric element comprises a pair of strip-shaped piezoelectric ceramic plates each having on its major surfaces a signal pickup electrode and an intermediate electrode, and said pair of strip-shaped piezoelectric ceramic plates is joined face to face at the intermediate electrodes thereof;

and further wherein each of the strip-shaped piezoelectric ceramic plates is divided into a center section and two end sections interposing said center section, and said center section is polarized in a direction opposite to that of said end sections.