Apparatus and method for noninvasive particle detection using doppler spectroscopy

An apparatus for noninvasively detecting at least one particle suspended in a fluid flowing in a pipe having an axis and a wall, comprising:

• a first transducer in vibrational communication with an outside surface of said pipe at a chosen position along the axis thereof;
• a signal generator for providing a chosen signal having at least one selected frequency to said first ultrasonic transducer, wherein vibrations are generated in said fluid at least a portion of which vibrations are in the direction of flow of said fluid;
• a second transducer in vibrational communication with an outside surface of said pipe disposed alongside said first transducer at the chosen position along the axis for detecting a scattered vibration signal from said at least one particle;
• and
• means for monitoring a Doppler frequency shift between the detected scattered signal from said at least one particle and the chosen vibration signal generated by said first transducer;
• whereby said at least one particle is detected.