What is the difference between wave and microwave

Microwaves

The applications of microwaves are diverse; They range from warming up ready meals to radar and satellite television to accelerating electrons in the radiation sources of the future, the X-ray lasers.

Heinrich Hertz created the first microwaves in 1886, six years after creating the first radio waves. However, technical applications of microwaves took longer to emerge than had been the case with radio waves.

Microwaves, like radio waves, are created by vibrations of electrons in metals. So-called klystrons or magnetrons are used as powerful sources today. The wavelengths of microwaves are between around 30 centimeters and one millimeter.

The microwave oven

A microwave oven

The best known application of microwaves is the microwave oven, which defrosts, heats or cooks food with the help of microwave radiation. It was invented by Percy Spencer in 1947.

In a microwave oven, food is irradiated with microwaves with a wavelength of about 12 centimeters. Water molecules in the food absorb the radiation, start to vibrate and heat is generated through friction. The food is heated in the microwave oven from the inside instead of the heat - as with normal cooking - first having to be conducted from the outside in.

Intense microwaves, such as those used for cooking, can also damage human tissue and are particularly dangerous to the eyes as they contain a lot of water. This is why microwave ovens are always shielded with a metal grille through which no radiation can escape.

radar

Radar has become an indispensable part of today's aviation. During the Second World War, in the Battle of Britain, the British knew of imminent attacks by the Germans even before their bombers could be seen in the sky. The technology for this was only developed in the 1930s. Today speed traps put motorists all over the world on the brakes. The name Radar (Radio Detection and Ranging) comes from the early days of technology when radio waves were used instead of microwaves.

Radar tower at the Hamburg Landungsbrücken

Radar beams consist of short pulses of microwaves. They are reflected from objects such as cars. The reflected pulses are received by the radar device and the distance can be calculated from the time that has elapsed between transmission and reception. A phenomenon called the Doppler effect also ensures that the frequency of the microwaves changes depending on whether the car is approaching or moving away. The speed can be calculated from these changes.

Satellite television

Satellite dishes receive microwaves from space and thus bring TV broadcasts to the screen. Special satellites are used to send the signals from the ground stations to the home receiving dishes. At an altitude of 36,000 kilometers, these rotate around the earth's axis just as quickly as the earth itself and therefore seem to hang constantly in the same place in space. These satellites are therefore called geostationary. They are, so to speak, microwave mirrors with a fixed position in the sky.

Microwaves for powerful X-ray lasers

As the X-ray sources of the future, powerful X-ray lasers such as the European XFEL X-ray laser planned in Hamburg will open up completely new research opportunities. In such X-ray lasers, the ultra-short flashes of light are generated by high-energy electrons that are accelerated to almost the speed of light with the help of microwaves. Microwave generators, so-called klystrons, are also used - a total of 38 for the European XFEL.