UCSB ECE 594 - Overview of RF Sensors (15 pages)

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Overview of RF Sensors



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Overview of RF Sensors

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Pages:
15
School:
University of California, Santa Barbara
Course:
Ece 594 - High Speed Mixed Signal & Communications IC design

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Notes 2 ECE594I Fall 2009 E R Brown Overview of RF Sensors Definition an RF system designed to detect the presence of objects or materials through their electromagnetic reflection or emission Hierarchy RF Sensors Proximity to Target Transmitter Remote Passive Receiver Point Active Coherent Coherent Active Incoherent Incoherent An active sensor detects radiation reflected from an object that the sensor system itself transmits The paradigm active sensor is the radar an acronym for radio detection and ranging A passive sensor detects thermal radiation emitted by an object or environmental radiation reflected by the object The paradigm passive sensor is the radiometer Coherent receivers are often based on heterodyne down conversion more later Incoherent receivers are often based on square law detection more later 39 Notes 2 ECE594I Fall 2009 E R Brown Review of Classical Electromagnetics Maxwell s Equations r r E 0 Constitutive Relations Coulomb s r r r D E r 0 E In free space r B 0 r r r E B t r v v B H r 0 H Z o 0 0 377 Faraday s r r v v v H J C D t D t generalized Ampere s In free space Take curl of Faraday s r r r r r r r r r r r r E 2 E E B t H t In free space r r r r r r r r 2 E E 2 E 0 D t t r 0 0 2 E t 2 r r2 r 2 E 0 0 E t 2 0 And we get the vector wave equation Sinusoidal solutions r r r r E r t Re E r e j t r r 2 r 2 Vector Helmholtz Eqn for E E 0 0 E 0 r r 2 r 2 Analogous Eqn for H H 0 0 H 0 r Radiation always entails two degrees of freedom E 40 and r H Notes 2 ECE594I Fall 2009 E R Brown Simplest solution Plane Wave r r r jkr rr r jk x E r E0e E0e For propagation along x axis Substitution back into vector Helmholtz eqn yields r r 2 2 2 2 k E 0 0 E 0 k 0 0 2 c 2 This is called the dispersion relation a very important kinematic relationship for all wave phenomena Poynting s and Sensor Power Theorem r r From plane wave propagation we know that E H is a vector that always points in the direction propagation To understand what the magnitude means operate on this



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