A device for inspecting a workpiece surface includes a sensor, a sonotrode having a sound-emitting surface and rigidly connected to the sensor to form a sensor unit, and a movable positioning device coupled with the sensor unit to position the sensor unit in a position opposite to the workpiece surface. The positioning device includes a force-applying member to urge the sensor unit in a direction of the workpiece or strip material surface by applying a predefined urging force or using gravity as the urging force. The sound-emitting surface of the sonotrode generates ultrasonic oscillations to produce an ultrasonic levitation force field in the presence of a gaseous medium between the workpiece surface and the sound-emitting surface to thereby generate a counterforce in opposition to the urging force so that the sensor unit is held hovering at a distance to the workpiece or strip surface.
