# Material, Sensors, Actuators and Fabrication Lesson 1

ME5410 - Lesson 2, Topic 1 - Introduction to Robotic Materials

why metal is good conductor? Because the the core of the atom for a structure, but the electron is not associated with one atom, but can move freely

most of the time, pure metal is better than alloy in terms of conductivity, but alloy is better in terms of strength, so we need to balance the two in the design of long distance power line (p25)

## Electrical Properties - Ohm's Law: $V=I*R$ - Resistivity($\rho, \Omega.cm$): $\rho = (A/L)*R$ - Conductivity($\sigma, \Omega^{-1} {cm}^{-1}$): $\sigma = 1/\rho$ - Electirc power loss($P, W$): $P = V*I = I^2R$ - Another form of Ohm's Law: $J = \frac{I}{A} = \sigma \frac{V}{l} = \sigma\xi$ J is current density ($A/cm^2$), $\xi$ is electric field ($V/cm$) ### Material by conductivity - Conductor: $C > 10^3 \Omega^{-1} cm^{-1}$ or $R < 10^{-3} \Omega cm$ - Dielectric or Insulator: $C < 10^{-12} \Omega^{-1} cm^{-1}$ or $R > 10^{12} \Omega cm$ - Dielectric: store electrical charge - Insulator: stop current flow - Semiconductor - Intrinsic: result from the band structure of a pure element or compound - Extrinsic: result from the addition of impurities - Superconductor - Ionic conductor - Electronic conductor