Electromagnetic fields and applications

Dr. Jonathan Bredow

Fields and their applications• A field relates to the spatial distribution of some quantity of

interest• The field may be described by a scalar, or it may be described

by a vector • Pressure example (scalar field)

http://www.usairnet.com/weather/maps/current/barometric-pressure/

Fields and their applications• Wind direction example

http://www.ambientweather.com/cuunstwimap.html

• Wind direction and barometric pressure are related by the gradient operator

Common fields in electrical engineering

• An Electric Field is produced by charges, and influences other charges (single charge example)

http://www.google.com/search?q=electric+field+lines&hl=en&prmd=imvnsfd&tbm=isch&tbo=u&source=univ&sa=X&ei=id5pT6vhIqapsQKStvmOCQ&sqi=2&ved=0CCwQsAQ&biw=1027&bih=521

Common fields in electrical engineering

• A Magnetic Field is produced by charges in motion, and influences other charges in motion

http://www.google.com/search?q=magnetic+field&hl=en&prmd=imvns&tbm=isch&tbo=u&source=univ&sa=X&ei=jttpT665D-LQsgLX4dikCQ&ved=0CF8QsAQ&biw=1027&bih=521

Applications involving electric/magnetic fields

• Influence position or motion of charges by producing fields (CRT, MRI)

• Sense information about the surrounding electric/magnetic environment from the fields being produced (Power line monitoring, Hall-effect detectors), or from how fields are disturbed (Metal detection, MRI)

• Energy storage (Capacitor – electric field, inductor – magnetic field)

• Energy conversion – transformers, motors, relays• Many applications for waves involving electric and magnetic

fields (more coming on this)

Waves

• Wave - a disturbance or variation that transfers energy progressively from point to point in a medium and that may take the form of an elastic deformation or of a variation of pressure, electric or magnetic intensity, electric potential, or temperature

• http://www.acs.psu.edu/drussell/Demos/waves-intro/waves-intro.html

• Time varying electric fields couple with (result in) time varying magnetic fields and vice-versa leading to a wave of energy referred to as an electromagnetic (EM) wave which propagates away from the source at the speed of light (in open air or vacuum).

• For practical applications EM waves may propagate in free space, or they may be confined to structures referred to as transmission lines.

Transmission lines

• Circuit models

http://www.google.com/search?q=transmission+lines&hl=en&prmd=imvnsb&tbm=isch&tbo=u&source=univ&sa=X&ei=zyNqT8i1IbHLsQKH_8WVCQ&ved=0CHgQsAQ&biw=1097&bih=535

Practical transmission lines

• Coaxial line

• Twisted pair

• Microstrip

• Waveguide

• Fiber optics

• Optical lens systems (wave beam modes)

Applications of transmission lines

• Microwave circuits

http://www.google.com/search?q=microwave+circuits&hl=en&prmd=imvns&tbm=isch&tbo=u&source=univ&sa=X&ei=ByhqT7e-JoHctgeTibTkCA&sqi=2&ved=0CFUQsAQ&biw=1097&bih=535

Applications of transmission lines (2)

• Optical lens systems

http://www.google.com/search?q=compound+lens&hl=en&prmd=imvns&tbm=isch&tbo=u&source=univ&sa=X&ei=mClqT9bmLtLqtgfL1OWPCQ&sqi=2&ved=0CFAQsAQ&biw=1097&bih=535

Applications of transmission lines (3)

• Other – What do you think?

Applications of free space EM waves – communications

• Broadcast radio/television– Radio and television (Analog and HD)– Analog and Digital, AM, FM, SW & Satellite

• Two-way radio communication– Point-to-point (Family radio, emergency communications)– Wire replacement (Bluetooth)– Networked (internet, 802.11)– Cellular (CDMA, GSM, 3G, 4G)

Radar: determining range to objects

http://www.radartutorial.eu/01.basics/rb04.en.html

t = 2R/c, where R is range to the object 1 msec corresponds to 150 m

Doppler Shift- Relationship between wavelength, l, and frequency, f, is c= fl

- Distance traveled during one period of the waveform is x= v/f

-The apparent wavelength is thus l’=l – x, or l’ = (c-v)/f

- Hence, the apparent frequency is f’ = c/l’ = f(1/(1-v/c))

- The Doppler shift is then fd=f’-f

‘

http://imagine.gsfc.nasa.gov/YBA/M31-velocity/Doppler-shift-2.html

Radar applications

• Weather monitoring• Speed monitoring• Aircraft monitoring• Surveillance• Remote sensing from space

UTA anechoic chamber – purpose?

Radiometry

• All objects emit EM energy according to Planck’s Law

• Radiometry applications

– Assessing heat leakage (for example, in a home)– Assessing heating/overheating in devices and systems– Radioastronomy– Night vision

Antennas

• Antennas are designed to efficiently radiate or capture radio frequency energy – cellular basestation example

http://www.google.com/search?q=antenna+images&hl=en&prmd=imvns&tbm=isch&tbo=u&source=univ&sa=X&ei=7jJqT6WmJOyGsALe6oyjCQ&ved=0CD4QsAQ&biw=1097&bih=535