Patent ID: 7053533

Claim:
Measuring apparatus for determining a chemical or physical property in a liquid carrier medium, or of the interaction of that substance with a selective binding layer, the apparatus comprising a piezoelectric resonator element of point group 32 , the selective binding layer being attached to a surface of the element which, in use, is in contact with said liquid carrier medium, the piezoelectric resonator element having a resonance frequency, when operated as a thickness shear resonator, which provides a measure of the property or interaction to be determined, wherein the element is formed from a non AT cut of the crystal, said cut being a rotated Y-cut which is rotated through an angle φ about the crystallographic x-axis, wherein said cut has a negative temperature dependence of resonance frequency in a predetermined temperature range between 10° C. and 40° C. when there is no contact with said carrier medium, and wherein, when the resonator element is in contact with the carrier medium the element has a linear temperature coefficient of resonance frequency, in the temperature range, which is less than that of a pure AT cut under the same conditions.