Double-headed mass sensor and mass sensing method

Abstract

There is provided a double-headed mass sensor ( 25 ) in which between a first connecting plate ( 22 A) joined to a first diaphragm ( 21 A) at respective sides and a second connecting plate ( 22 B) joined to a second diaphragm ( 21 B) at respective sides, a first sensing plate ( 41 A), on which a main element ( 44 ) is provided on at least one plane surface, is bridged, and a resonating portion comprising the diaphragms ( 21 A), ( 21 B), the connecting plates ( 22 A), ( 22 B), the first sensing plate ( 41 A) and the main element ( 44 ) is joined to a sensor substrate ( 27 ). Change in the mass of each of the diaphragms ( 21 A), ( 21 B) is measured by measuring change in the resonant frequency of the resonating portion accompanying the change in the mass of the diaphragms ( 21 A), ( 21 B). The mass sensor of the present invention enables the easy and highly accurate measurement of a minute mass of a nanogram order including microorganisms such as bacteria and viruses, chemical substances, and the thickness of vapor-deposited films.

1 . A double-headed mass sensor characterized in that between a first connecting plate joined to a first diaphragm at respective sides and a second connecting plate joined to a second diaphragm at respective sides, a resonating portion comprising the first connecting plate, the second connecting plate, the first diaphragm, the second diaphragm, and a first sensing plate, and a main element being provided on at least one plane surface of the first sensing plate, bridged in the direction perpendicular to the joining direction of each of said connecting plates and each of said diaphragms, is joined to a sensor substrate at at least a part of sides of said first connecting plate and said second connecting plate.  
     
     
         2 . The double-headed mass sensor according to  claim 1  characterized in that said main element is split in the direction perpendicular to the joining direction of said first sensing plates and each of said connecting plates.  
     
     
         3 . A double-headed mass sensor characterized in that, 
 a first connecting plate is joined to a first diaphragm and a second connecting plate is joined to a second diaphragm at respective sides,    said first connecting plate is positioned between a first sensing plate and a second sensing plate, said second connecting plate is positioned between said first sensing plate and a third sensing plate, so that the respective sides are joined to each other, and    a resonating portion comprising the first connecting plate, the first diaphragm, the second connecting plate, the second diaphragm, the first sensing plate, the second sensing plate, the third sensing plate, a main element provided on a part of at least one plane surface of said first sensing plate and/or a subsidiary element provided on at least a part of at least one of the plane surface of said second sensing plate and said third sensing plate, is joined to a sensor substrate at at least a part of sides of said respective connecting plates.    
     
     
         4 . The double-headed mass sensor according to  claim 3  characterized in that said main element and/or subsidiary element is split in the direction perpendicular to the joining direction of each of said sensing plates and each of said connecting plates.  
     
     
         5 . The double-headed mass sensor according to any one of claims  1  through  4  characterized in that the direction of the extension of the center line equally dividing the plane surface of said first sensing plate and perpendicular to the joining direction of said first sensing plate and each of said connecting plates is parallel to the joining direction of said first connecting plate and said first diaphragm, and the joining direction of said second connecting plate and said second diaphragm, and 
 said resonating portion has a shape symmetrical about said center line.  
 
     
     
         6 . The double-headed mass sensor according to any one of claims  1  through  5  characterized in that a position sensor consisting of a pair of electrodes on said sensor substrate is provided at the central position between each of said diaphragms and said main element.  
     
     
         7 . A double-headed mass sensor characterized in that a side of each diaphragm is joined to a side of each connecting plate so that a first diaphragm is sandwiched between a first connecting plate and a second connecting plate, and a second diaphragm is sandwiched between a third connecting plate and a fourth connecting plate; 
 a first sensing plate is bridged across said first connecting plate and said third connecting plate, and a second sensing plate is bridged across said second connecting plate and said fourth connecting plate; and    a resonating portion comprising the first connecting plate, the first diaphragm, the second connecting plate, the second diaphragm, the third connecting plate, the fourth connecting plate, the first sensing plate, the second sensing plate, and a main element provided on at least one plane surface of each of said sensing plates, is bridged across the gap or space between the sides of a sensor substrate facing to each other, so that at least a part of the side of each of said connecting plates is joined to the sides of the sensor substrate.    
     
     
         8 . The double-headed mass sensor according to  claim 7  characterized in that said main element is split in the direction perpendicular to the joining direction of each of said sensing plates and each of said connecting plates.  
     
     
         9 . A double-headed mass sensor characterized in that a side of each diaphragm is joined to a side of each connecting plate so that a first diaphragm is sandwiched between a first connecting plate and a second connecting plate, and a second diaphragm is sandwiched between a third connecting plate and a fourth connecting plate; 
 each of said connecting plates is joined at the respective sides so that said first connecting plate is positioned between a first sensing plate and a third sensing plate, said third connecting plate is positioned between said first sensing plate and a fourth sensing plate, said second connecting plate is positioned between a second sensing plate and a fifth sensing plate, and said fourth connecting plate is positioned between said second sensing plate and a sixth sensing plate;    a resonating portion comprising the first connecting plate, the first diaphragm, the second connecting plate, the second diaphragm, the third connecting plate, the fourth connecting plate, the first sensing plate, the second sensing plate, the third sensing plate, the fourth sensing plate, the fifth sensing plate, the sixth sensing plate, main elements provided on at least a part of at least one of the plane surface of said first sensing plate and said second sensing plate, and/or subsidiary elements provided on at least a part of at least one plane surface of one or more of said third sensing plate, said fourth sensing plate, said fifth sensing plate, and said sixth sensing plate, is bridged across the gap or space between the sides of a sensor substrate facing to each other, so that at least a part of the side of each of said connecting plates is joined to the sides of the sensor substrate.    
     
     
         10 . The double-headed mass sensor according to  claim 9  characterized in that each of said main elements and/or each of said subsidiary elements is split in the direction perpendicular to the joining direction of each of said sensing plates and each of said connecting plates.  
     
     
         11 . The double-headed mass sensor according to any one of claims  7  through  10  characterized in that the center line equally dividing the plane surface of said first sensing plate and perpendicular to the joining direction of said first sensing plate to said first connecting plate and said third connecting plate coincides with the center line equally dividing the plane surface of said second sensing plate and perpendicular to the joining direction of said second sensing plate to said second connecting plate and said fourth connecting plate; 
 the direction of the extension of said center line is parallel to the direction where said first connecting plate and said second connecting plate sandwich said first diaphragm, and the direction where said third connecting plate and said fourth connecting plate sandwich said second diaphragm; and  
 said resonating portion has a shape symmetrical about each of said center line, and the line orthogonal to said center line and passing through the centers of said first diaphragm and said second diaphragm.  
 
     
     
         12 . The double-headed mass sensor according to any one of claims  1  through  11  characterized in that, 
 each of said main elements and/or each of said subsidiary elements is a piezoelectric element consisting of at least a first electrode, a second electrode, and a piezoelectric film,  
 said piezoelectric element has a laminated structure in which said piezoelectric film is sandwiched between said first electrode and said second electrode, or  
 a structure in which a comb-shaped electrode consisting of said first electrode and said second electrode facing to each other on the plane surface of said piezoelectric film or between said piezoelectric film and a sensing plate on which said piezoelectric film is provided, or  
 a structure in which a said piezoelectric film is provided in the gap between said first electrode and said second electrode forming the comb-shaped electrode.  
 
     
     
         13 . The double-headed mass sensor according to  claim 12  characterized in that the direction of polarization of said piezoelectric film in each of said main elements is opposite to the direction of polarization of said piezoelectric film in each of said subsidiary elements.  
     
     
         14 . The double-headed mass sensor according to  claim 12  or  13  characterized in that said piezoelectric film is formed from a material consisting mainly of lead zirconate, lead titanate, and lead magnesium niobate.  
     
     
         15 . The double-headed mass sensor according to any one of claims  12  through  14  characterized in that the available electrode area of said piezoelectric element is adjusted by removing a part of said first electrode and/or said second electrode with laser processing or machining.  
     
     
         16 . The double-headed mass sensor according to any one of claims  1  through  15  characterized in that each of said diaphragms, each of said connecting plates, and each of said sensing plates form the even plane surface through joining to each other.  
     
     
         17 . The double-headed mass sensor according to any one of claims  1  through  16  characterized in that each of said sensing plates is fitted in and joined to the concave portion formed by each of said connecting plates and said sensor substrate.  
     
     
         18 . The double-headed mass sensor according to any one of claims  1  through  17  characterized in that each of said diaphragms, each of said connecting plates, and each of said sensing plates are integrally formed from a vibrating plate, and 
 said sensor substrate is integrally formed by laminating said vibrating plate and a base plate.  
 
     
     
         19 . The double-headed mass sensor according to any one of claims  1  through  18  characterized in that spring plates are joined to a plane surface in the same direction of each of said connecting plates, or on both plane surfaces of each of said connecting plates, and 
 each of said spring plates is joined to said sensor substrate or a spring plate reinforcing member.  
 
     
     
         20 . The double-headed mass sensor according to  claim 19  characterized in that each of said spring plates is integrally formed with an intermediate plate which is integrally fitted between said vibrating plate and said base plate, or integrally formed with said spring plate reinforcing member integral with said vibrating plate, and formed also integrally with each of said connecting plates.  
     
     
         21 . The double-headed mass sensor according to  claim 19  or  20 , comprising a reinforcing plate join to each of said spring plates, and joined to said sensor substrate.  
     
     
         22 . The double-headed mass sensor according to  claim 21  characterized in that said reinforcing plate is formed integrally with each of said spring plates and said sensor substrate.  
     
     
         23 . The double-headed mass sensor according to any one of claims  1  through  22  characterized in that a catching substance, which reacts only with a substance to be sensed and catches said substance to be sensed, is applied to the surface of at least one of said first diaphragm and said second diaphragm, or to at least a part of the surface of said resonating portion.  
     
     
         24 . The double-headed mass sensor according to any one of claims  1  through  23  characterized in that each of said main elements, each of said subsidiary elements and electrode leads electrically connected to electrodes forming each of said main elements and/or each of said subsidiary elements are insulated by an insulation coating layer consisting of a resin or glass.  
     
     
         25 . The double-headed mass sensor according to  claim 24  characterized in that said resin is a fluorocarbon resin or a silicone resin.  
     
     
         26 . The double-headed mass sensor according to  claim 24  or  25  characterized in that at least a part of the surface of said insulation coating layer is coated by a shield layer consisting of a conductive material.  
     
     
         27 . The double-headed mass sensor according to any one of claims  1  through  26  characterized in that each of sensor substrates, each of said diaphragms, each of said connecting plates, each of said sensing plates, each of said spring plates, and said spring plate reinforcing member and said reinforcing plate are comprised of stabilized zirconia or partially stabilized zirconia.  
     
     
         28 . The double-headed mass sensor according to any one of claims  1  through  27  characterized in that the shapes of at least some of each of said diaphragms, each of said connecting plates, each of said sensing plates, and each of said spring plates are dimensionally adjusted by trimming with laser processing or machining.  
     
     
         29 . A method for sensing a mass with a double-headed mass sensor in which connecting plates are joined to each of two diaphragms at respective sides, and a sensing plate on which a main element or a subsidiary element is provided as required bridges between said connecting plates, or sandwiches said connecting plates, and at least a part of the side of said connecting plate is joined to a sensor substrate, characterized in measuring with said element the resonant frequency of the resonating portion of said double-headed mass sensor on the basis of at least either one of, 
 the bending-mode oscillation in which said diaphragm, making the face where said connecting plate is joined to said sensor substrate the fixed face, bends in the direction perpendicular to a vertical axis passing through the center of said fixed face vertically, and in the direction perpendicular to the plane surface of said diaphragm;    the axial rotation-mode oscillation in which said diaphragm makes rotational oscillation around said vertical axis making said vertical axis the central axis;    the θ-mode swing oscillation in which said diaphragm makes pendulum-like oscillation centered on said vertical axis in the direction perpendicular to the side of said diaphragm and also perpendicular to said vertical axis; or    the φ-mode swing oscillation in which sad diaphragm makes pendulum-like oscillation centered on said vertical axis with the swing in the direction perpendicular to the side of said diaphragm and also perpendicular to said vertical axis accompanied by the swing in the direction parallel to the side of said diaphragm.    
     
     
         30 . A method for sensing a mass with a double-headed mass sensor in which each of two diaphragms is joined so as to be sandwiched by connecting plates at respective sides, a sensing plate on which a main element or a subsidiary element is provided as required bridges between said connecting plates, or sandwiches said connecting plates, and at least a part of the side of said connecting plate is joined to the sides facing to each other across the gap in the sensor substrate, characterized in measuring with said element the resonant frequency of the resonating portion of said double-headed mass sensor on the basis of at least either one of, 
 the axial rotation-mode oscillation in which said diaphragm, making the face where said connecting plate is joined to said sensor substrate the fixed face, makes rotational oscillation around said vertical axis passing through the center of said fixed face vertically, while making said vertical axis the central axis;    the η-mode plane rotational oscillation in which said diaphragm makes rotational oscillation around the center of said diaphragm in the plane surface of said diaphragm;    the φ-mode swing oscillation in which said diaphragm makes pendulum-like oscillation centered on said vertical axis with the swing in the direction perpendicular to the side of said diaphragm and also perpendicular to said vertical axis accompanied by the swing in the direction parallel to the side of said diaphragm; or    the monoaxial-mode reciprocal oscillation in which said diaphragm oscillates reciprocally in the plane surface of said diaphragm in the direction orthogonal to said vertical axis.    
     
     
         31 . The method for sensing a mass with a double-headed mass sensor according to  claim 29  or  30  characterized in that, by obtaining difference between two resonant frequencies produced by the fact that the masses of one diaphragm and the connecting plate joined to the diaphragm do not change, and the masses of the other diaphragm and the connecting plate joined to the other diaphragm change, change in the masses of said other diaphragm and the connecting plate joined to the other diaphragm is sensed.