Before diving into microwaves, we must study a few basic concepts about the electromagnetic spectrum. As you might be aware, light behaves like a wave in certain situations. Not only that, but it is also an electromagnetic wave, which means it carries both electric as well as magnetic components.
Naturally, if the light is a wave, then it must have properties that define its wave-like behavior. For instance, all light waves must be defined by frequency and wavelength. And as it turns out, they are. This gives rise to what is known as the electromagnetic spectrum.
The spectrum of a quantity is its range of values. Unlike digital values which are quantized, values in a spectrum are continuous and do not vary in steps. In this article, we will discuss the electromagnetic spectrum and a band inside it known as the microwave region.
We have just defined what a spectrum is. Now, let us discuss the electromagnetic spectrum, which refers to the range of frequencies that electromagnetic (light) waves can have. This spectrum is enormous, ranging from as low as 1 Hz to $\mathrm{10^{25}}$ Hz.
Naturally, with such a wide range, light waves have such an enormous difference in their properties in different parts of the spectrum that very few of them can be generalized. Thus, scientists have divided this spectrum into several bands of frequencies. Light waves that belong to a particular band share similar properties. For instance, all the frequencies belonging to the visible region are visible to the naked eye, even though they have different colors.
Microwaves are a class of electromagnetic radiation whose frequencies lie even below the infrared region. That said, their frequencies still belong to the ultra-high frequency or the extremely high-frequency range. Different definitions exist, but most commonly, light waves with frequencies in the range of 300 MHz to 300 GHz are classified as microwaves. Radio engineers use a slightly shorter range of 1 GHz to 300 GHz.
One point you should note is that the “micro” part in “microwave” does not arise out of their wavelengths. Microwave wavelengths top up at around a millimeter. Instead, they are called microwaves since their wavelengths are shorter than those of radio waves, which were commonly used before the discovery of microwaves.
Microwaves are artificially produced using a wide range of apparatuses. The most common ways are to use specialized vacuum tubes which can emit high-power microwaves. Inside these vacuum tubes, clumps of electrons are accelerated by electric or magnetic fields, which generate microwaves.
Semiconductor devices like tunnel diodes and field-effect transistors are used to generate low-power microwaves. These are used in benchtop instruments. At the same time, there are natural sources of microwaves as well. All black bodies emit low levels of microwave radiation at certain temperatures, but it is generally quite small. Similarly, celestial objects also release low-level microwaves, which are used to study them.
Microwaves cannot ionize matter. This makes them particularly safe as compared to their counterparts like ultraviolet and gamma rays. However, since they are electromagnetic waves, they carry energy and heat and cause a heating effect. This can be dangerous upon overexposure.
Like most light waves, microwaves can be reflected and refracted quite easily. However, not all substances can absorb microwaves. This is why microwave ovens are always operated with their doors closed since the doors prevent microwaves from escaping.
Microwaves have a wavelength that is particularly suited for heating substances that have a moisture content. Thus, microwave ovens are commercially used in kitchens. The microwaves heat the water content inside the food. This makes them a safe and rapid alternative to gas-based cooking and heating.
Celestial objects generate microwaves. These are received via large antennas on Earth and can be analyzed to study celestial objects. Further, microwaves sent from Earth and reflected from distant stars can be used to map their targets.
Global Positioning Systems use frequencies in the microwave range. Further, the Wi-Fi routers you have in your home also operate in the microwave region only. Some radar applications also utilize microwave frequencies.
Microwaves have a heating effect that is not quite unlike infrared rays. However, microwaves affect areas with moisture content more drastically. Thus, microwave exposure can increase the chances of cataracts in the eye since they can denature the proteins in our eyes.
Most studies have shown that there is no direct link between microwave exposure and the risk of cancer. Interestingly, though, exposure to microwaves causes clicking or buzzing sounds in the ear due to thermal expansion inside the ear. You would have to be exposed significantly for this to happen.
Dangers associated with microwaves include risks of burns that do not become instantly visible since microwaves affect the tissues which are situated a little deeper inside our body. Thus, no microwave oven should ever be operated with its door open.
spectrum is a range of continuous values that a certain quantity can take. For instance, the colors of the rainbow are a spectrum that ranges from violet to red. Since light travels as an electromagnetic wave across space, it must have an associated frequency. The range of frequencies that light waves can have, is referred to as the electromagnetic spectrum. Due to its vastness, the properties of light waves cannot be generalized across the entire spectrum. Instead, it is divided into various bands. The frequencies inside a single band have similar properties. This article discusses microwaves, which have frequencies between 300 MHz to 300 GHz.
Microwaves are generated naturally by black bodies at certain temperatures and can be artificially produced via vacuum tubes or specialized diodes like tunnel diodes. Vacuum tubes generate microwaves via accelerating clumps of electrons using electric or magnetic fields. The uses of microwaves span scientific as well as commercial applications, with the most common example being that of microwave ovens. Other uses include radio astronomy and radio communication via Wi-Fi.
Q1. If Wi-Fi and radio communications use microwaves, aren’t they dangerous?
Ans. The level of radiation emitted by cell phones and Wi-Fi routers is so insignificant that exposure to it does not cause any harm.
Q2. Is it true that 5G communication is harmful?
Ans. No. These are just misconceptions. As previously stated, microwaves emitted by these towers aren’t harmful. However, they do increase heat around them and thus, the area near the towers tends to become hotter in summers.
Q3. Which materials block microwaves?
Ans. Metals are the best way to block microwaves. Out of metals, silver is an incredible conductor and thus, even a coating of silver that is 3 $\mathrm{\mu m}$ thick can block microwaves with remarkable efficiency.
Q4. The doors of microwave ovens are a bit transparent. How can they absorb microwaves?
Ans. The body of microwave ovens is made of metal and thus, blocks microwaves. The door itself has a glass panel. But behind that glass panel is a metallic mesh, which prevents microwaves from escaping through.
Q5. Why can’t we put metal in the microwave oven?
Ans. Since metal has no moisture content, it cannot use the energy provided by the microwaves effectively. Thus, it starts to become increasingly hot, and can even cause sparks, which can cause burns. Not only is metal inside microwaves pointless, it is also dangerous.
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