Magnet displacement sensor using MI elements for eyelid movement sensing

An improved magnet-displacement sensor constructed using amorphous magneto-inductive (MI) elements for both-eyelid movement sensing is described. Folded amorphous wires without any coils are fixed on a glass frame and sensitively detect a magnetic field generated from a small magnet which is attached on an upper eyelid. These noncontact field sensors detect an eyelid movement accompanied by eyeball motion of as small as 1 μm by canceling disturbance fields. The changing value of a cross correlation of two time series of both eyelids was measured for two subjects with a time interval of 3 h through 24 h. A relation between the magnitude of the cross correlation and sleepiness was obtained when subjects traced a light spot target which oscillated horizontally with a 0.2 Hz sinusoidal waveform