Nanotechnology-Enabled Sensors

56 Chapter 2: Sensor Characteristics and Physical Effects
Fig. 2.27 Rotation of the polarization plane on a magnetized surface as a result of
the magneto-optic Kerr effect.
The Kerr effect can be used to fabricate sensors for various applications.
For instance, Karl et al 86 developed a pressure sensor based on a micromembrane
coated with a magnetostrictive thin-film. The pressure difference
across the diaphragm causes deflection and thus stress in the
magnetostrictive layer. This leads to a change in the magnetic properties of
the thin-film, which can be measured as a change in the MOKE properties.
It is widely utilized for determining the magnetization of materials. MOKE
can also be used to study the magnetic anisotropy of deposited ferromagnetic
thin films. Magnetic properties of such films are closely related to
their morphology and micro/nano structures. 87
2.3.20 Kerrand Pockels Effects
Discovered by John Kerr in 1875, it is an electro-optic effect in which a
material changes its refractive index in response to an electric field. Here,
birefringence is induced electrically in isotropic materials. 88 When an electric
field is applied to a liquid or a gas, its molecules (which have electric
dipoles) may become partly oriented with the field. 5 This renders the substance
anisotropic and causes birefringence in the light traveling through it.
However, only light passing through the medium normal to the electric