An electromagnetic transducer which generates signals on the basis of the Barkhausen effect under periodically alternating externally applied magnetic switching fields. Prior to use, the magnetic sensor element, for example a ferromagnetic wire, is pre-magnetized by undergoing a program which subjects the wire to a coercive applied field substantially higher than the alternating interrogation field. The coercive field places different zones of the wire into magnetic saturation with varying relative polarity, thereby creating two or more zones of different magnetization. When subjected to the alternating, low intensity interrogation field, sensor coils detect a high level, bipolar output signal.
A pulse signal generator comprising a magnetic element able (1) to cause a large Barkhausen jump; a detection member (2) for detecting a magnetic change in the magnetic element to generate a pulse signal; and a pair of magnetic field sources (3, 4, 6, and 7) provided in parallel to each other on both sides of the magnetic element such that their poles (3A, 4A) are opposed to each other so that when an object (5A) advances from one of opposite poles to the other of the magnetic field sources, a magnetic field applied to the magnetic element changes, causing a large Barkhausen jump in the magnetic element, thus causing the detection member to generate a pulse signal.
