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Microwaves

The existence of electromagnetic waves was predicted by James Clerk Maxwell in 1864 from his equations. 

James Clerk Maxwell

In 1888, Heinrich Hertz was the first to demonstrate the existence of electromagnetic waves by building an apparatus that produced and detected microwaves in the UHF region. The design necessarily used horse-and-buggy materials, including a horse trough, a wrought iron point spark, Leyden jars, and a length of zinc gutter whose parabolic cross-section worked as a reflection antenna.

 Heinrich Hertz

 In 1894 J. C. Bose publicly demonstrated radio control of a bell using millimeter wavelengths, and conducted research into the propagation of microwaves

 J. C. Bose

The microwave oven was invented as an accidental by-product of war-time (World War 2) radar research using magnetrons (vacuum tubes that produce microwave radiation, a type of electromagnetic radiation that has a wavelength between 1 mm and 30 cm).

Dr. Percy LeBaron Spencer

In 1946, the engineer Dr. Percy LeBaron Spencer, who worked for the Raytheon Corporation, was working on magnetrons. One day at work, he had a candy bar in his pocket, and found that it had melted. He realized that the microwaves he was working with had caused it to melt. After experimenting, he realized that microwaves would cook foods quickly - even faster than conventional ovens that cook with heat.

The Raytheon Corporation produced the first commercial microwave oven in 1954; it was called the 1161 Radarange. It was large, expensive, and had a power of 1600 watts.

1161 Radarange

 The first domestic microwave oven was produced in 1967 by Amana (a division of Raytheon).

 1967, Amana, a division of Raytheon, introduced its domestic Radarange microwave oven

In 1967, Amana, a division of Raytheon, introduced its domestic Radarange microwave oven, marking the beginning of the use of microwave ovens in home kitchens. Although sales were slow during the first few years, partially due to the oven’s relatively expensive price tag, the concept of quick microwave cooking had arrived. In succeeding years, Litton and a number of other companies joined the countertop microwave oven market. By the end of 1971, the price of countertop units began to decrease and their capabilities were expanded.

 

The radio range showing the radar bands L,S,C,X,K (from L to R).

Microwaves are electromagnetic waves with wavelengths ranging from as long as one meter to as short as one millimeter, or equivalently, with frequencies between 300 MHz (0.3 GHz) and 300 GHz.

Microwaves have wavelengths that can be measured in centimeters. The longer microwaves, those closer to a foot in length, are the waves which heat our food in a microwave oven. Image of child putting a dish in a microwave oven.

Microwaves are good for transmitting information from one place to another because microwave energy can penetrate haze, light rain and snow, clouds, and smoke.

Shorter microwaves are used in remote sensing. These microwaves are used for radar like the doppler radar used in weather forecasts. Microwaves, used for radar, are just a few inches long.

A red tower with round microwave antennae on it.
This microwave tower can transmit information like telephone calls and computer data from one city to another.

How do we "see" using Microwaves?

Radar is an acronym for "radio detection and ranging". Radar was developed to detect objects and determine their range (or position) by transmitting short bursts of microwaves. The strength and origin of "echoes" received from objects that were hit by the microwaves is then recorded.

Because radar senses electromagnetic waves that are a reflection of an active transmission, radar is considered an active remote sensing system. Passive remote sensing refers to the sensing of electromagnetic waves which did not originate from the satellite or sensor itself. The sensor is just a passive observer. Doppler radar weather map.

 

What do Microwaves show us?

Satellite image of Alaskan shores D Because microwaves can penetrate haze, light rain and snow, clouds and smoke, these waves are good for viewing the Earth from space.

The ERS-1 satellite sends out wavelengths about 5.7 cm long (C-band). This image shows sea ice breaking off the shores of Alaska.

The Amazon River D The JERS satellite uses wavelengths about 20 cm in length (L-band). This is an image of the Amazon River in Brazil.
Salt Lake City, UtahD This is a radar image acquired from the Space Shuttle. It also used a wavelength in the L-band of the microwave spectrum. Here we see a computer enhanced radar image of some mountains on the edge of Salt Lake City, Utah.

In the 1960's a startling discovery was made quite by accident. A pair of scientists at Bell Laboratories detected background noise using a special low noise antenna. The strange thing about the noise was that it was coming from every direction and did not seem to vary in intensity much at all. If this static were from something on our world, like radio transmissions from a nearby airport control tower, it would only come from one direction, not everywhere. The scientists soon realized they had discovered the cosmic microwave background radiation. This radiation, which fills the entire Universe, is believed to be a clue to it's beginning, something known as the Big Bang.

Image of the cosmic microwave background.

The image above is a Cosmic Background Explorer (COBE) image of the cosmic microwave background, the pink and blue colors showing the tiny fluctuations in it.

Credit:NASA,ESA