| 摘要 |
An aperture unit includes a transparent cylindrical member, a magnetic fluid, and a magnetic field generator. The cylindrical member includes a cylindrical chamber. A light input end portion of the cylindrical member is transparent, and an opposite light output end portion of the cylindrical member is transparent. The magnetic fluid is received in the cylindrical chamber. The magnetic fluid includes a transparent solvent, a surfactant, and nano-magnetic particles dispersed substantially evenly in the solvent. Each of the magnetic nano-particles is enveloped by a surfactant. The magnetic field generator is positioned outside the cylindrical chamber. The magnetic field generator is configured for generating a magnetic field applied to the chamber and attracting and clustering the nano-particles, such that an annular nano-particle opaque layer is formed on an inner surface of the cylindrical member.
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