Alignment direction detection device

An alignment direction detection device that detects an alignment direction of fibers in a test object including one or more sheets of electrically conductive composite materials each containing electrically conductive fibers, comprising:

• an excitation coil to apply an AC magnetic field to the test object;
• one or more magnetic field sensors arranged at positions maintaining a fixed positional relationship with the excitation coil, each of which detects an inductive magnetic field caused by the AC magnetic field and outputs voltage corresponding to the inductive magnetic field;
• a conveyance device to move at least one of the test object and a sensor unit including the excitation coil and the one or more magnetic field sensors;
• and
• processing circuitry to control the excitation coil, the one or more magnetic field sensors, and the conveyance device,
• wherein the processing circuitry
• calculates a radial direction space frequency as a function of (i) a size of the magnetic field sensor and (ii) a distance between the magnetic field sensor and the test object,
• performs a band limitation on a distribution of the voltage outputted from each magnetic field sensor included in the one or more magnetic field sensors based on the calculated radial direction space frequency,
• transforms the band-limited voltage distribution into an output intensity waveform with respect to a space angle at the radial direction space frequency, and
• calculates a peak angle that is a peak position of the output intensity waveform as an alignment angle representing the alignment direction.