Ferrofluid is a three component magnetic colloid that behaves as a homogenous system even in applied magnetic field.γ-Fe₂O₃ water base ferrofluid (maghemite) has a good transmittance at a low magnetic volume fraction (less than 1%)it is possible to obtain good magneto-optic effect and transmittance.

Without any applied field ferrofluids are isotropic. But when a magnetic field is applied ferrofluids acquire an optical anisotropy two cases are possible. Faraday’s rotation of plane polarized light when magnetic field is parallel to the light beam.

Anisotropy is linear in perpendicular configuration.If ferrofluid is placed in a cylinder which acts as an electromagnet producing lines of flux in direction of light, due to attraction of flux linear more fluid is attracted near cylinder wall producing a structure as shown.

This pattern acts as a lens (distance for light to travel varies instantly).And such a pattern can be varied depending upon the field of electromagnet and causing to produce auto focal lens. If ferrofluid added to sol-gel sample to produce sol-gel doped ferrofluid solid structure of ferrofluid with higher transmittance is obtained.

When sol-gel doped ferrofluid produced under zero magnetic field has good transmittance and residual birefrigerence (Δn. ~ 8.8*10^-7, which may be due to earth magnetic field. On eliminating the residual birefringence (equivalent to cello tapes) and on preparing in different shapes gives rise to constant focal length lens.

Uses:

· Transmittance varies with volume fraction for different wavelength and auto focusing can be obtained with wavelet filters.

· Can be auto focused easily to read VCD, DVD, MP3, MP5

· Can be used in focusing of laser with wavelet filter.

· Can be used to develop artificial human eye lens.

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1. Vibration reduction and heat control in AC motors using ferrofluids