Mass sensor and mass sensing method

A mass sensor, comprising:

• a sensor substrate;
• at least one diaphragm;
• at least one connection plate joined at one end thereof to said sensor substrate and at another end thereof to said diaphragm;
• at least one sensing plate arranged in parallel with said connection plate, and being joined at one end thereof to said sensor substrate and at another end thereof to said diaphragm;
• and
• 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.

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.

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.

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.

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.