Abstract: An ultrasound device sends and guides ultrasonic waves to a part surface through a fluid in laminar flow along a curved path, and then receives the reflected and/or scattered waves from that surface in the mode of a sensor. The received signal yields information about the part surface topography such as roughness, scratches, and dents. Since the device can operate in real-time in situ on moving, as well as on stationary parts, the received ultrasonic signal may be used to monitor tool wear during part fabrication, and even provide feedback information for machine control.