Patent ID: 7114373

Claim:
An apparatus for measuring the viscosity and temperature of a fluid comprising: a transducer arranged to vibrate when provided with a drive signal of a given frequency to produce an ultrasonic shear wave; an impedance matching layer that is inserted into said fluid and which couples at least a first portion of said ultrasonic shear wave produced by said transducer into said fluid and from which at least a second portion of said ultrasonic shear wave is reflected back to said transducer; a detector which is operative to detect a measurement signal produced by said transducer when said second reflected portion of wave is incident upon said transducer; a control circuit which varies said frequency of said drive signal applied to said transducer and hence the frequency of said ultrasonic shear wave; a processor which determines an optimum frequency of said drive signal at which said measurement signal produced by said transducer has its minimum amplitude; and a temperature determining means which estimates the temperature of said fluid as a function of said optimum frequency.