Microwaves Science

What are bands?
Different wavelengths of microwaves are grouped into sub-bands.

How are they useful?
They provide different information to scientists.

What are medium length waves called? C-band. They can penetrate through clouds, dust, smoke, snow and rain to reveal the earth’s surface. Eg: Ice breaking off shores in Alaska are viewed.

What are L-bands? These are used by GPS receiver in the car and can penetrate through canopy cover of forests and measure the soil moisture of rain forests. Eg: Amazon river in Brazil can be viewed.

What specific band is used to measure the condition beneath clouds in a storm? Ku-band. Scatterometer measures changes in energy of microwave pulses and can determine speed and direction of wind near ocean surface.

Explain Radar technology. It works by sending a microwave impulse and senses the energy reflected by it. It works actively as a remote sensing agent sending impulse every moment. Doppler Radar, Scatterometer, Radar Altimeter are few active remote sensing agents that use microwave frequencies.

How do scientists measure the amount of heat stored in oceans? By measuring the sea surface height around the world they predict global weather and climate events. The concept used is that warm water is less dense than cold water and therefore areas with higher sea surface temperature tend to be warmer than lower areas.

What is passive remote sensing? This refers to sensing of EM waves which did not originate from the satellite or instrument itself. It is merely a passive observer collecting EM radiation. They have revolutionized weather forecasting by providing global view of weather patterns and surface temperatures.

How the idea of ‘BIG BANG’ did bang the imagination of scientists? In 1965 using L-band scientists at Bell Labs found by accident a background noise using a special low-noise antennae. The strange thing about this noise was that it was coming from every direction and did not seem to vary in intensity much at all.

What is strange? It may have come from planet earth, wouldn’t it? If it were from earth such as radio transmissions from nearby airport tower it would come from one direction and not everywhere. They soon realized that they had serendipitously discovered the cosmic background radiation. This radiation fills the universe and is in fact a clue to its bang bang!


How does a microwave oven work? It works by passing microwave radiation, usually at a frequency of 2450 MHz (a wavelength of 12.24 cm), through the food.

Name the principle involved. Water, fat, and sugar molecules in the food absorb energy from the microwave beam in a process called dielectric heating.

How is motion cum heating created in oven? Many molecules (such as those of water) are electric dipoles, meaning that they have a positive charge at one end and a negative charge at the other, and therefore rotate as they try to align themselves with the alternating electric field induced by the microwave beam.
This molecular movement creates heat as the rotating molecules hit other molecules and put them into motion.

How efficient is microwave heating on fats and sugars? It is most efficient on liquid water, and much less so on fats and sugars (which have less molecular dipole moment), and frozen water (where the molecules are not free to rotate).

Microwave frequency bands: 0.3 GHz [10cm] to 300 GHz [1mm]
Designation	Freq range [GHz]	Wavelength range	Typical uses
L band	1 – 2	15 - 30 cm	military telemetry, GPS, mobile phones (GSM), amateur radio
S band	2 – 4	7.5 - 15 cm	weather radar, surface ship radar, sAcO (Mw ovens, Mw devices/comm, radio astronomy, mobile phones, wireless LAN, Bluetooth, ZigBee, GPS, amateur radio)
C band	4 – 8	3.75 - 7.5 cm	long-distance radio telecomm.
X band	8 – 12	25 - 37.5 mm	sAcO, radar, tB, space comm, amateur radio
Ku band	12 – 18	16.7 - 25 mm	sAcO
K band	18 – 26.5	11.3 - 16.7 mm	sAcO, radar, astronomical observations, ar
Ka band	26.5 – 40	5.0 - 11.3 mm	sAcO
Q band	33 - 50	6.0 - 9.0 mm	sAcO, terrestrial mw comm., radio astronomy, ar
U band	40 – 60	5.0 - 7.5 mm
V band	50 – 75	4.0 - 6.0 mm	mm wave radar & scientific research
W band	75 – 110	2.7 - 4.0 mm	sAcO, mm-wave radar research, military radar t&t
F band	90 – 140	2.1 - 3.3 mm	wireless LAN, most modern radars, sAcO
D band	110 – 170	1.8 - 2.7 mm	amateur radio, directed-energy weapon, mm wave scanner

*sAcO: Comm. Satellite; *mm: millimeter; *Mw: Microwave; *tB: terrestrial broadband; *ar: automotive radar; *t&t: targeting and tracking;

Microwaves are strongly absorbed at wavelengths shorter than about 1.5 cm (above 20 GHz) by water and other molecules in the air. When radars were first developed at K band during World War II, it was not known that there was a nearby absorption band (due to water vapor and oxygen in the atmosphere). To avoid this problem, the original K band was split into a lower band, Ku, and upper band, Ka.

P band is sometimes used for Ku Band. "P" for "previous" was a radar band used in the UK ranging from 250 to 500 MHz and now obsolete per IEEE Std 521.


Source: wikipedia, sciencedaily.com, missionscience.nasa