EM Waves & Optical Behaviors

Comms 4 EM Waves

Radiation

The process where waves and energy particles travel through free space

Emission

The process of intentionally releasing radiation

Electromagnetic Wave

A wave composed of two components, the magnetic field (H) and the electric field (E), which vary sinusoidally in time and are perpendicular to the direction of propagation (transverse)

Wave Velocity

The speed of an EM wave, which depends on the medium it travels through; it travels fastest in free space (speed of light, c)

Wave Velocity Formula

v = c / squareroot(epsilonr), where c is the speed of light (3 x 10^8 m/s) and epsilon_r is relative permittivity

Frequency

The number of cycles an electromagnetic wave completes in one second; expressed in Hertz (Hz)

Wavelength

The distance that the radio wave travels in the time of one cycle; expressed in meters (m)

Polarization

The physical orientation or direction of the electric field (E field) in space

Linear Polarization

A type of polarization where the E field has a particular fixed direction in space (e.g., Vertical or Horizontal)

Circular Polarization

A type of polarization where the E field rotates about the axis of the direction of propagation

Elliptical Polarization

Similar to circular polarization, but the electric (E) and magnetic (H) fields are unequal

Random Polarization

A polarization state with no fixed pattern

Ray

A line drawn along the direction of propagation of the wave

Wavefront

A surface representing a constant phase of the wave

Refraction

The bending of a radio wave as it passes from one medium to another at an angle, involving a change in direction and speed

Index of Refraction (n)

The ratio of the speed of a radio wave in free space to the speed of the radio wave in a specific medium

Index of Refraction Formula

n = c / v = squareroot(epsilonr)

Snell's Law

A law relating the indices of refraction and angles of incidence and refraction: n1 * sin(thetai) = n2 * sin(thetar)

Reflection

Occurs when an incident wave strikes the boundary of two media and some or all of the incident power does not enter the second material

Reflection Coefficient

The ratio of the electric intensity of the reflected wave to that of the incident wave

Diffuse Reflection

Reflection that occurs at irregular and rough surfaces

Specular Reflection

Mirror-like reflection that occurs at very smooth surfaces

Rayleigh Criterion

States that a semi-rough surface will reflect as if it were a smooth surface if cosine(theta_i)

Diffraction

The redistribution of energy within a wavefront when it passes near the edge of an opaque object, allowing secondary waves to enter the shadow zone

Huygen's Principle

The principle stating that any point on a wavefront of light may be regarded as the source of secondary waves

Interference

The phenomenon that occurs when two waves that left one source and traveled by different paths arrive at a point