Lecture_2

Angleofincidenceangleofreflectedwave incidentwave

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Unformatted text preview: tion Diffraction Reflection Reflection When an electromagnetic wave encounters a conducting surface… Reflected and incident waves travel in directions that make equal angles with the perpendicular line from the surface – Angle of reflection and angle of incidence Reflection Reflection Phase shift = 180 degrees. Angle of incidence = Angle of reflected wave. Incident Wave Reflected Wave Reflection Reflection Reflected wave will be 180 degrees out of phase with the incident wave The only way to get reflected energy back to the source (as needed for radar to work) is to hit the material perpendicular to the surface If the surface is not flat then reflected rays will not go in the same direction (scattering) Many other things besides targets can cause reflections (dust, rain, snow, and water vapor, sandstorms in the Gulf) Refraction Refraction When a wave strikes a boundary between two transparent media in which the velocity of light differs, the incident ray will generally divide into a reflected ray and a refracted ray Snell’s Law n1 sin θ1 = n2 sin θ2 Diffraction Diffraction Causes plane waves traveling in a straight path to bend around a boundary or obstruction Diffraction Diffraction ...plane waves traveling in a straight path bend around a boundary or obstruction. detected island not detected Losses Losses Losses in energy transmission are primarily due to spreading, absorption, and scattering – Spreading: as the wave travels outward from the source, its energy is expanding over an increasingly larger area – Absorption: molecules of the medium will absorb some of the energy as the wave passes by – Scattering: results from reflections off suspended particles within a medium Maxwell’s Theory Maxwell’s Theory An accelerating electric field will generate a time­varying magnetic field A time­varying magnetic field will generate a time­varying electric field ...and so on...and so on...and so on... Maxwell’s Theory Maxwell’s Theory There is an energy transfer taking place between electrical and magnetic fields when changes occur in electrical or magnetic energy – Each affects the other… A changing electrical field produces a changing magnetic field that produces a change in the electrical field... Maxwell’s Theory Maxwell’s Theory Bottom line: – If we produce a varying electrical field we can produce a corresponding varying magnetic field – They will propagate together as electromagnetic waves...
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