Sensing device

A sensing device that passes, on one surface side of a piezoelectric piece, a fluid containing a sensing object from a front side to a rear side and that makes an adsorption layer on a surface of a common electrode formed on the one surface side of the piezoelectric piece adsorb the sensing object to sense the sensing object, the sensing device comprising:

• the common electrode containing a first electrode portion and a second electrode portion which are separated from each other in a left and right direction, and each of said first and second electrode portions extends along a front and rear direction, the first electrode portion and the second electrode portion being connected to a common ground electrode;
• the first electrode portion being sectioned to a first adsorption region located in the front side and a reference region located in the rear side, a first adsorption layer being formed on a surface of the first electrode portion in the first adsorption region, an adsorption layer being not formed on a surface of the first electrode portion in the reference region,
• the second electrode portion being sectioned to a reference region located in the front side and a second adsorption region located in the rear side, the second adsorption layer being formed on a surface of the second electrode portion in the second adsorption region, an adsorption layer being not formed on a surface of the second electrode portion in the reference region located in the front side;
• when the reference region of the second electrode portion is referred to as a first reference region, and the reference region of the first electrode portion is referred to as a second reference region, first opposite electrodes which are individually formed on the other surface side of the piezoelectric piece so as to be opposite the first adsorption region and the first reference region, respectively;
• second opposite electrodes which are individually formed on the other surface side of the piezoelectric piece so as to be opposite the second adsorption region and the second reference region, respectively;
• a flow path formation member for passing, on the one surface side of the piezoelectric piece, the fluid containing the sensing object from the front side to the rear side;
• an oscillation circuit for oscillating the piezoelectric piece;
• a frequency measurement portion for measuring an oscillation frequency of the oscillation circuit;
• and
• a control portion for determining:
• a first difference between an oscillation frequency of the piezoelectric piece between the first adsorption region and the first opposite electrode and an oscillation frequency of the piezoelectric piece between the first reference region and the first opposite electrode, and
• a second difference between an oscillation frequency of the piezoelectric piece between the second adsorption region and the second opposite electrode and an oscillation frequency of the piezoelectric piece between the second reference region and the second opposite electrode, so as to calculate a sum value of the first difference and the second difference.