Transistors that operated at microwave frequencies were developed in the Seventies. The semiconductor gallium arsenide has a much larger electron mobility than silicon, so units fabricated with this materials can function at 4 instances the frequency of comparable devices of silicon. Beginning within the Seventies GaAs was used to make the first microwave transistors, and it has dominated microwave semiconductors ever since. Another household of transistors with the next frequency restrict is the HEMT , a field effect transistor made with two completely different semiconductors, AlGaAs and GaAs, using heterojunction know-how, and the similar HBT .
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The word “radiation” refers to energy radiating from a source and not to radioactivity. The main effect of absorption of microwaves is to heat materials; the electromagnetic fields trigger polar molecules to vibrate. It has not been shown conclusively that microwaves (or different non-ionizing electromagnetic radiation) have important opposed biological effects at low ranges. Some, however not all, studies recommend that long-term exposure might have a carcinogenic effect. Microwaves emitted by astronomical radio sources; planets, stars, galaxies, and nebulas are studied in radio astronomy with large dish antennas known as radio telescopes.