مواد نیمه رسانا

Semiconducting Materials

مواد نیمه رسانا

ABSTRACT

Semiconductors are materials which have resistivities between the extremes of metallic conductors and insulators. A typical scale of conductivity of materials is depicted in Figure 10.1 . Semiconductors lie approximately between conductors ( with σ > 10⁵ siemen/meter ) and insulators (with σ < 10^-10 siemen/meter ) . Semiconductors are materials with filled valence bands and have a small forbidden energy gap between the upper-filled band and the overlapping vacant energy band . The electric conduction in Semiconductors is effected by two types of charge carriers namely . electrons ( negative charge carriers ) and holes ( positive charge carriers ) .

مواد فروالکتریک

Ferroelectric Materials

مواد فروالکتریک

ABSTRACT

Ferroelectric materials are typically nonlinear dielectrics with the following characteristics :

• They exhibit distinct dependency of permittivity on the intensity of an applied electric field
• The dielectric displacement versus applied electric field follows hysteresis loop characteristics
• The dielectric constant of these materials are invariably very high , on the order of thousands to tens of thousands .
• The dielectric parameters are pronouncedly dependent on temperature and the ferroelectric properities are observed only within a definite range of temperature
• There is presence of spontaneous dielectric polarization in the absence of external electric field And this polarization can be switched in direction by applying an electric field

مواد الکترولیت جامد

Solid Electrolytic Materials

مواد الکترولیت جامد

ABSTRACT

Also known as superionic conductors solid electrolytes are ionic materials which exhibit high electrical conductivity ( in comparsion whit liquid electrolytes ) above a certain critical temperature . They are also termed as fast-ion conductors . A solid electrolytes has the following characteristics .

• It is crystalline with ionic bonding
• Its electrical conductivity ( over a specified temperature is high ( 10-10-2 siemen/meter ) .
• Its principal charge carriers are ions . Hence , the fractional contribution of the ionic conductivity to the total conductivity ( termed as ionic transference number ) is almost equal to one .
• Its electronic conductivity is small . The corresponding electronic transference number is less than 10-4

مواد فریتی

Ferrites Materials

مواد فریتی

ABSTRACT

Ferrites are mixed crystals of various metallic oxides and may be considered to consist of oxygen ions in a closed-packed structure with cations filling the interstices . They have a general formula : MOFe₂O₃ , xH₂O where M is a divalent metallic ion such as Mn²⁺ , Fe²⁺ , Co²⁺ , Ni²⁺ , Zn²⁺ , Mg²⁺ , and Cd²⁺ . In general , the magnetic satruration intensity to ferrites is lower than that of various metallic magnetic alloys , but the ferrites have very high resistivity and as such are insulator-like . Therefor , the power loss in ferrites is very small especially at high frequencies . Further , ferrites have a narrow hysteresis (BH) loop and can be made with square-loop characteristics .

مواد فرومغناطیسی

Ferromagnetic Materials

مواد فرومغناطیسی

ABSTRACT

Ferromagnetic materials have the ability to carry high magnetic flux . Ferromagnetism refers to the property of increasing the magnetic flux associated with the material when a magnetizing force is applaid , but there exists a saturation point for most of the magnetic materials beyond which the associated magnetic flux does not increase . This condition is referred to as magnetic saturation . Ferromagnetic materials can be distinctly classified into two groups the magnetically soft and magnetically hard . The distinguishing properties are having high permeability and having easy to magnetize for soft materials and hard materials having high coercivity so that once magnetized the materials must be able to resist demagnetizing forces due to any appleid or stary magnetic fiels .

مواد کامپوزیتی پیزوالکتریک

Piezoelectric Composite Materials

مواد کامپوزیتی پیزوالکتریک

ABSTRACT

A piezoelectric Composite is a combination of a piezoelectric ceramic and/or polymer and a nonpiezoelectric polymer constituting a new version of piezoelectric material . In general terms , piezoelectric composite applies to any piezoelectric material resulting from combining a piezoelectric  polymer or ceramic with other nonpiezoelectric materials including air-filled voids . Earlier versions of piezoelectric  composite synthesized include barium titanate embedded polymer matrix and lead zirconate- titanate (PZT) ceramic Powder dispersed in a polymeric receptacle .Subsequent development are : (i)  Flexible piezoelectric composites using PbTiO₃ or PZT plus synthetic rubber ; (ii) PVD-based pyroelectric composites ; (iii) woven PZT ceramic/polymer composites

 

مواد هوشمند الکترو مغناطیس

Electromagnetic smart Material

مواد هوشمند الکترو مغناطیس

ABSTRACT

smart materials refer to a class of materials and/or composite media having inherent intelligence together with self-adaptive capabilities to external stimuli . Also known as intelligent materials they constitute a few subsets of the material family that “ manifest their own functions intelligently depending on environmental changes” . Electromagnetic (EM) smart materials are specific subsets of smart materials wich can adaptively change their EM characteristics when an external stimulus is applied proportional to a sensed EM response.Classically such intelligent material systems have been conceived in the development of mechanical structures which contain their own sensors actuators and self-assessing computational feasibilities so as to modify their structural (elastic) behavior via feedback control capabilities .

مواد جاذب امواج الکترومغناطیسی

Electromagnetic wave Absorbing Materials

مواد جاذب امواج الکترومغناطیسی

ABSTRACT

For specific application there is a need for materials which absorb the electromagnetic energy incident on them . These nonreflective electromagnetic wave (EM) absorbing materials are useful as radar absorbing materials (RAMs) as surface coverings in electromagnetic anechoic chambers etc . Their primary function is to absorb and dissipate the electromagnetic energy to which they are exposed so that the reflected and/or scattered electromagnetic component is significantly small. In RAM applications when a target is surface-treated with an absorbing material the radar echo is minimized facilitating an electronic countermeasure technique of low probability of detection of the target by the radar.

مواد الکترو اپتیک

Electrooptic Materials

مواد الکترو اپتیک

ABSTRACT

The term electrooptic effect refers  to a change in the refractive index of a transparent substance induced by an applied electric field , usually at a frequency below the optic vibrational resonance of the lattice or the molecules involved . the linear and quadratic electrooptic effects are known as the Pockels and kerr effects, respectively . The linear electrooptic ( or Pockels ) effect refers to a change in relative optical dielectric impermeability (B_ij) proportional to an applied electric field E_k whos highest frequencies are below the lattice resonance of a crystal .Refractive index of a crystal : Considering light propagation through a crystal the electromagnetic energy stored in a unit volume of dielectric is represented by an ellipsoid whit a geometry that reflects the symmetry of the crystal .

مواد هوشمند الکترو مغناطیس

Electromagnetic smart Material

مواد هوشمند الکترو مغناطیس

ABSTRACT

smart materials refer to a class of materials and/or composite media having inherent intelligence together with self-adaptive capabilities to external stimuli . Also known as intelligent materials they constitute a few subsets of the material family that “ manifest their own functions intelligently depending on environmental changes” . Electromagnetic (EM) smart materials are specific subsets of smart materials wich can adaptively change their EM characteristics when an external stimulus is applied proportional to a sensed EM response.Classically such intelligent material systems have been conceived in the development of mechanical structures which contain their own sensors actuators and self-assessing computational feasibilities so as to modify their structural (elastic) behavior via feedback control capabilities .