A method for reducing flux concentrating capacity of a shield in a magnetic readwrite head positioned to read perpendicular residual magnetic fields on a magnetic media. A plurality of flow channels each opened at both end faces are formed in the substrate. The second PCB includes a first surface. The distribution of intensity of the image acquired by utilization of such intensity or image pick-up gain reflects a time lag between the time at which the illumination light is emitted from a light source and the time at which the light reflected from individual points of the object reaches an image pick-up device. The usable rotation speed range of the wind energy installation can be extended to provide a more powerful generator with a higher rating, without changing the converter.