A composite magnetic material contains first magnetic particles made of a first magnetic material and second magnetic particles made of a second magnetic material, the first and second magnetic particles being mixed with each other. The filter receives an input signal that includes one or more bands of frequencies. A field lens device is disposed before the mask to direct a light beam through the mask and focus the light beam at a field lens focal point. In some embodiments of the present invention, novel low contrast filters and variable contrast filters are used. Motor terminals protrude from the motor. After the gradation exposure, development processing is performed on the insulating layer such that a recess is formed in a portion of the insulating layer that has been irradiated with the exposure light through the partial light-transmitting region.