Mass sensor and mass sensing method

• US 20050016277A1
• Filed: 08/25/2004
• Published: 01/27/2005
• Est. Priority Date: 09/08/1997
• Status: Active Grant

• Current Assignee: NGK Insulators Limited
• Original Assignee: NGK Insulators Limited
• Inventors: Kimura, Koji, Takeuchi, Yukihisa, Ohnishi, Takao
• Granted Patent: US 6,895,829 B2
• Time in Patent Office: Days
• US Class Current: 73/580
• CPC Class Codes: B06B 1/06 operating with piezoelectric effect or with electrostriction piezoelectric or electrostrictive devices per se H10N30/00
• CPC Class Codes: B06B 1/0648 of rectangular shape
• CPC Class Codes: B06B 1/0692 with a continuous electrode on one side and a plurality of electrodes on the other side
• CPC Class Codes: G01G 3/16 measuring variations of frequency of oscillations of the body
• CPC Class Codes: G01H 11/08 using piezoelectric devices
• CPC Class Codes: G01N 2035/00217 involving measurement of weight
• CPC Class Codes: G01N 2035/00237 Handling microquantities of analyte, e.g. microvalves, capillary networks
• CPC Class Codes: G01N 2291/02827 Elastic parameters, strength or force
• CPC Class Codes: G01P 15/09 by piezoelectric pick-up
• CPC Class Codes: G01P 15/0922 of the bending or flexing mode type
• CPC Class Codes: G01P 2015/0814 for translational movement of the mass, e.g. shuttle type
• CPC Class Codes: H10N 30/20 with electrical input and mechanical output, e.g. functioning as actuators or vibrators
• CPC Class Codes: H10N 30/2041 Beam type
• CPC Class Codes: H10N 30/2047 Membrane type
• CPC Class Codes: H10N 30/302 Sensors

Abstract

A mass sensor in which a connection plate and a diaphragm are joined together at their respective sides; a sensing plate is joined to the connection plate at their respective sides in the direction perpendicular to the direction where the diaphragm is joined to the connection plate; a piezoelectric element consisting of a piezoelectric film and an electrode is installed on at least either one of plate surfaces of the sensing plate; and a resonating portion consisting of the diaphragm, the sensing plate, the connection plate, and the piezoelectric element is joined to a sensor substrate. Change in the mass of the diaphragm is measured by measuring change in the resonant frequency of the resonating portion accompanying the change in the mass of the diaphragm.

Claims

1. A method for sensing a mass with a mass sensor in which a side of at least one diaphragm is joined to a side of a sensing plate so that a surface of said diaphragm is perpendicular to a surface of said sensing plate on which a piezoelectric element is installed, and the other side of said sensing plate is joined to a sensor substrate, wherein said piezoelectric element measures a resonant frequency based on at least one of:

(a) a θ

-mode swing oscillation of said diaphragm, wherein said diaphragm performs a pendular oscillation centered on an axis perpendicularly passing through a center of a fixed plane defined by the joining surface of said diaphragm and said sensing plate in a direction perpendicular to a side of said diaphragm and also perpendicular to said perpendicular axis;

(b) a φ

-mode swing oscillation of said diaphragm, wherein said diaphragm performs a pendular oscillation centered on said perpendicular axis, swinging in a direction perpendicular to a side of said diaphragm and also perpendicular to said perpendicular axis and in a direction parallel to the side of said diaphragm;

or

(c) an oscillation of said diaphragm in the direction of said perpendicular axis.

2. A method for sensing a mass with a mass sensor having at least one piezoelectric element, in which a connection plate is joined to a diaphragm at respective sides thereof, at least one sensing plate is joined to said connection plate at respective sides thereof in a direction perpendicular to the joining direction of said diaphragm and said connection plate, and wherein at least a portion of at least one side of said connection plate and said sensing plate are joined to a side of a sensor substrate;

wherein said piezoelectric element measures a resonant frequency based on at least one of;

(a) a θ

-mode swing oscillation of said diaphragm, wherein said diaphragm performs a pendular oscillation centered on an axis perpendicularly passing through a center of a fixed plane defined by the joining surface of said connection plate and said sensor substrate in a direction perpendicular to a side of said diaphragm and also perpendicular to said perpendicular axis;

or

(b) a φ

-mode swing oscillation of said diaphragm, wherein said diaphragm performs a pendular oscillation centered on said perpendicular axis, swinging in a direction perpendicular to said side of said diaphragm and also perpendicular to said perpendicular axis accompanied by a swing in a direction parallel to said side of said diaphragm.

3. A method for sensing a mass with a mass sensor having at least one piezoelectric element, in which an assembly of a diaphragm being sandwiched between two connection plates by joining at respective sides thereof is placed across respective side surfaces of a depression or across a through-hole formed in a sensor substrate, a plurality of sensing plates are interposed between said respective connection plates and a bottom side of said depression or a side of said through-hole, or between said diaphragm and said bottom side of said depression or said side of said through-hole, in a direction perpendicular to the direction of said respective connection plates sandwiching said diaphragm, wherein said piezoelectric element measures a resonant frequency based on at least one of:

(a) a θ

-mode swing oscillation of said diaphragm, wherein said diaphragm performs a pendular oscillation centered on a perpendicular axis perpendicularly passing through the center of a fixed plane defined by the joining surface of said connection plate and said sensor substrate in a direction perpendicular to a side of said diaphragm and also perpendicular to said perpendicular axis;

(b) a φ

-mode swing oscillation of said diaphragm, wherein said diaphragm performs a pendular oscillation centered on said perpendicular axis, swinging in a direction perpendicular to said side of said diaphragm and also perpendicular to said perpendicular axis accompanied by a swing in a direction parallel to said side of said diaphragm;

(c) a swing oscillation of said diaphragm centered on said perpendicular axis, oscillating parallel to a direction perpendicular to said side of said diaphragm and also perpendicular to said perpendicular axis;

or

(d) a rotating oscillation of said diaphragm with respect to said surface of said diaphragm.

4. A mass sensor comprising:

a sensor substrate;

at least one connection plate extending along a first direction and having a first end attached to a first portion of said sensor substrate and an opposed second end;

at least one diaphragm attached to said second end of said connection plate;

at least one sensing plate arranged in a substantially parallel planar relationship with respect to said sensor substrate, said sensing plate having a first end attached to a second portion of said sensor substrate and an opposed second end attached to one of said diaphragm and said connection plate;

at least one piezoelectric element arranged on at least a portion of a surface of said sensing plate;

wherein said at least one connection plate, said at least one diaphragm, said at least one sensing plate and said at least one piezoelectric element define a resonance portion; and

means for measuring a change in the resonant frequency of said resonance portion.