What's Your Frequency?
As far back as the late 19th century, the visionary Nikola Tesla was predicting fantastic ideas and technologies that wouldn’t come into widespread use until over 100 years later. Tesla was a pioneer in research on radio and wireless communications. In 1898 he built and demonstrated a remote-controlled model boat. This was only a few years after Guglielmo Marconi had successfully sent the first wireless radio communication. Tesla was fond of pointing out that the transmission was only accomplished by using several of his own patents.
In those early days, the atmosphere would’ve been relatively devoid of human-generated radio waves (there are still plenty of natural causes of radio waves). Today we are bathed in radio waves almost everywhere we go. Our cell phones, our wifi, our bluetooth headsets…it’s all possible because of radio. When we talk about radio though, we’re talking about a very specific subset of a much larger spectrum called electromagnetic radiation.
Electromagnetic radiation refers to the waves of the electromagnetic field that propagate from sources of electromagnetic energy. The entire grouping of all electromagnetic radiation is called the electromagnetic spectrum. Because it is composed of waves we classify electromagnetic radiation based on its frequency. The lowest frequencies (and longest wavelengths) include things like ELF (Extremely Low Frequency) waves that are used to communicate with deeply submerged submarines. ELF waves have a frequency of 3-30Hz and a wavelength between 100 megameters and 10 megameters. As you increase in frequency, you start to encounter what we commonly refer to as radio waves (AM/FM broadcast radio as well as broadcast TV). These waves range in frequency from about 300kHz to 300MHz. Wavelengths are significantly shorter now too ranging between one kilometer and one meter.
For wifi, cellular and other modern wireless communications we use higher frequency radio waves which are often also referred to as microwaves (because their wavelengths are so short). If you have a wireless router at home, you might have seen it can transmit the signal and either 2.4GHz or 5GHz. Cordless telephones also transmit in roughly this frequency range. Cell phones transmit in discrete bands ranging from about 800MHz to almost 2GHz. It’s less common today, but cell phones used to be categorized as being tri-band or quad-band phones. Almost all cell phones made today are capable of accessing all common bands available in the market for which they are designed.
What many people don’t realize is that visible light (ROYGBIV) is also part of the electromagnetic spectrum. After microwaves we get into infrared just below the bottom of the visible light spectrum. The frequencies of these waves are now much higher with infrared ranging from 300GHz to 430THz (that’s terahertz). The visible spectrum starts at around 430THz and goes up to 790THz and has wavelengths ranging from about 400 to 700 nanometers. Red colors will have the lowest frequencies and the blue and violet colors will have the highest.
Just beyond the visible spectrum we have ultraviolet which starts to really peg the frequency scales at 790THz to 30PHz (petahertz, 10 to the 15th power). Beyond ultraviolet still we first encounter x-rays (between 30PHz and 30EHz, exahertz, 10 to the 18th power) and finally, at the top of the scale, with wavelengths less than 0.01 nanometers and a frequency above 30EHz we have gamma rays.
Still with me? One of the things some people wonder about is if all of this radiation is bad for us. X-rays and gamma rays certainly are. X-rays will penetrate soft tissue but not bone (hence why we use them to look for broken bones). They can damage cellular structures including DNA, which can result in health risks. This is why medical staff will wear some kind of dosimeter to know how much of this kind of radiation they’ve been exposed to. Gamma rays will generally penetrate a human body completely, easily causing major cellular damage and DNA degradation. X-rays and gamma rays aren’t typically found on earth’s surface and those rays originating off the planet are mostly blocked by the earth’s magnetosphere and atmosphere. When people talk about radiation exposure after a nuclear blast or from nuclear waste, they’re typically talking about the damage done by gamma radiation emitted as the result of radioactive material. It’s radioactive because it decays and emits gamma rays in the process.
The lowest energy electromagnetic radiation that can hurt you is ultraviolet. This is what causes sunburns. Lower energy electromagnetic radiation cannot cause major harm to humans because it cannot penetrate cellular membranes. However, lower energy radiation can cause damage in other ways. For example, so-called directed-energy weapons have been tested that use microwaves to actually heat the target just like a microwave oven. These devices are often declared to be “non-lethal” but that’s just a matter of degree. Research is also being conducted into possible negative effects from ELF waves. Common radio and even microwave radiation are not typically considered harmful as they are unable to penetrate cellular membranes (such radiation would be termed non-ionizing). However, research in this area is highly contentious and concrete answers on safety are hard to find. That said, you’re more likely to injure yourself from superheated water in a microwave oven rather than the radiation itself.
Bonus mind-blowing fact: Quickly unrolling a roll of ordinary scotch tape inside a vacuum will actually generate x-rays.