Patent ID: 8176773

Claim:
A piezoelectric sensor sensing a substance to be sensed in a sample fluid based on a change in natural frequency of a piezoelectric piece by making an adsorption layer formed on an electrode provided on the piezoelectric piece adsorb the substance to be sensed, the piezoelectric sensor comprising: a first electrode for measurement and a second electrode for reference provided apart from each other on one surface side of the piezoelectric piece; a common electrode provided on an opposite surface side of the piezoelectric piece commonly for said first electrode and said second electrode to face said first electrode and said second electrode; an adsorption layer formed on an area, of said common electrode, to which said first electrode is faced across the piezoelectric piece, to adsorb the substance to be sensed; and connecting mutually the area of said common electrode to which said first electrode is faced across the piezoelectric piece and an area of said common electrode to which said second electrode is faced across the piezoelectric piece electrically so that these areas are same electric potential.