Piezoelectric resonator and sensing sensor

A sensing device, comprising:

• a piezoelectric resonator comprising:
• a piezoelectric piece made from an AT cut crystal and having a first surface side and a second surface side;
• a first oscillation area which is provided in the piezoelectric piece for taking out a first oscillation frequency under a predetermined reference temperature atmosphere;
• a second oscillation area, which is provided in the piezoelectric piece in an area different from said first oscillation area, for taking out a second oscillation frequency different from the first oscillation frequency under the reference temperature atmosphere;
• and
• an elastic boundary area which is provided in the piezeoelectric piece between said first oscillation area and said second oscillation area;
• the sensing device further comprising:
• a first excitation electrode provided on said first surface side of the piezoelectric piece in said first oscillation area;
• a second excitation electrode provided on said first surface side of the piezoelectric piece in said second oscillation area;
• at least one third electrode formed on said second surface side of the piezoelectric piece;
• a first oscillator circuit for taking out said first oscillation frequency from said first oscillation area;
• a second oscillator circuit, different from said first oscillation circuit, for taking out said second oscillation frequency from said second oscillation area;
• and
• a processing unit which calculates a difference between said second oscillation frequency and said first oscillation frequency and cancels out an oscillation variation component included in said second oscillation frequency corresponding to a change in temperature of said piezoelectric resonator;
• wherein an adsorption layer that adsorbs a sensed substance is not formed on said first excitation electrode;
• wherein an adsorption layer that adsorbs the sensed substance is formed on said second excitation electrode;
• wherein a frequency difference between the first oscillation frequency and the second oscillation frequency, in said reference temperature atmosphere, is not less than 0.2% nor greater than 1.1% of the first and second oscillation frequencies;
• and
• wherein the frequency difference is adjusted by making values of at least one of the following (i) and (ii) different between said first oscillation area and said second oscillation area:
• (i) masses of said first excitation electrode and second excitation electrode;
• and
• (ii) thickness of the piezoelectric piece in said first oscillation area and said second oscillation area.