The seven types of electromagnetic waves are radio (1mm-100km wavelengths), microwaves (1mm-1m), infrared (700nm-1mm), visible light (400-700nm), ultraviolet (10-400nm), X-rays (0.01-10nm), and gamma rays (<0.01nm). Each has unique uses, like Wi-Fi, remote controls, and medical imaging.
Table of Contents
Radio Waves
Radio waves are a significant part of life, normally with frequencies below 300 GHz and wavelengths from a few millimeters up to thousands of meters. Because of the low frequency and long wavelength, they serve very well in many applications that demand long-distance transmission. Radio waves, depending on frequency and their use, could be categorized into classes, which have different functions in the field of broadcasting, telecommunications, remote controls, and satellite communications.
One of the more common uses of radio waves is in broadcasting. AM radio, in the frequency range from 535 kHz to 1605 kHz, can cover quite long distances, especially during nighttime when wave propagation improves due to better conditions in the atmosphere. For example, AM radio waves reflecting from the ionosphere can easily cover several hundred kilometers to reach rural or even relatively inaccessible areas. While FM radio has a higher frequency, between 88 and 108 MHz, it has a high sound quality with a more limited radius of no more than 50 to 100 kilometers depending on the landscape and the power of the transmitting station. In cities, FM is great for music and talk shows due to its high fidelity, while AM, which covers a much wider radius, is often used for news and emergency broadcasts in more peripheral areas.
Other very important applications of radio waves include Wi-Fi, which uses two different frequencies: either 2.4 GHz or 5 GHz. The 2.4 GHz has a longer wavelength and hence can penetrate through walls and other obstacles much better to serve larger areas in your house or office. However, its popularity among other household devices, including microwaves and cordless phones, results in interference. The frequency of 5 GHz allows higher speeds for data transfer but has a shorter radius and should be used in smaller areas where speed is prioritized over the range. For example, indoors, a Wi-Fi network at 2.4 GHz can reach up to 45 meters, while with a network at 5 GHz, the same area would go down to just 15 meters. That makes 2.4 GHz Wi-Fi ideal for general connectivity, while the 5 GHz is a better choice for high-speed activities such as video streaming or gaming within close proximity to the router.
Radio waves are also at the core of radar systems in meteorology and in navigation. Weather radars, which usually function at microwave frequencies between 1 and 30 GHz, employ radio waves in detecting precipitation, wind speed, and other atmospheric phenomena. For example, the WSR-88D series of weather radar used throughout the United States by the National Weather Service has a frequency of about 2.7 to 3.0 GHz and range of 460 kilometers. Doppler radar sends out radio waves that return with a frequency shift indicative of the velocity of the precipitation particles, thus estimating storm movement. This information, thus gained, is very useful for issuing early warnings during adverse weather conditions. This allows people to take well in advance precautions against adverse weather conditions.
Radio waves in satellite communication provide GPS, where navigational signals are transmitted from orbiting satellites to receivers on the ground. Usually, GPS satellites operate at two frequencies: 1.57542 GHz known as L1 and 1.2276 GHz known as L2. These frequencies enable GPS devices to calculate the coordinates of a place with high accuracy, which becomes vital in navigation, surveying, and even in the military. The accuracy of GPS technology rests on precise timing of radio wave signals, whereby a difference of a billionth of a second corresponds to several meters of location error. This allows users to navigate anywhere in the world — from finding directions in a city to real-time tracking of vehicles.
Microwaves
Microwaves have lengths of 1 millimeter to 1 meter and frequencies of about 300 MHz to 300 GHz. Due to the fact that microwaves have short wavelengths with higher frequencies compared to radio waves, they are employed in a great number of applications. This part of the spectrum plays an important role in technologies for communication, radar systems, and some appliances for cooking; thus, it affects both industrial applications and daily life. Knowing about the things microwaves can and cannot do will give insight into what they are capable of doing and not capable of while implementing their use in different areas.
One of the most well-known microwave applications is that of microwave ovens operating at around 2.45 GHz. At this frequency, water molecules are very efficiently heated because microwave energy excites the molecules to create heat inside the food. Studies have shown that this is the frequency used in microwave ovens because it penetrates foods to a depth of about 2.5 centimeters, which provides an efficient method for heating in a relatively short period of time. For example, it takes only about two minutes for a microwave oven to take a cup of water to its boiling point, while the stovetop would usually take about twice as long to do the same task. This is the reason why microwaves are used for fast cooking, whereby much time is saved and energy conserved.
Microwaves also play a very significant role in communication, especially when it comes to cellular and satellite communications. Microwaves of frequencies between 1 and 40 GHz are employed in a mobile network such as 4G and 5G for data carriage over long distances at wide bandwidth. While 4G LTE operates, for example, over the spectrum of 700 MHz up to 2.7 GHz, 5G goes up to 28 GHz and even higher in certain markets. Faster data transfer speed or higher network capacity enabled by the use of high-frequency spectrum allows for streaming high-definition video or support for massive data communication in highly populated areas. However, the higher frequencies within the microwave range—especially those above 6 GHz—tend to have smaller transmission ranges, and interference with buildings and other obstacles is more possible; therefore, a much denser network of antennas is required in order to provide reliable connectivity.
Radar relies heavily on microwaves for accurate observation that reaches very far, especially in weather observation, aviation, and even military operations. In fact, it detects precipitation and the movement of weather fronts because the frequency of weather radar is around 2.7 to 3.0 GHz within the microwave range. For instance, a Doppler radar for the detection of a storm pattern sends microwaves and measures the return time and frequency shift of those waves once they are reflected by precipitation particles. With this information, meteorologists can forecast the intensity and movement of storms over an area as big as 250 kilometers. It is in aviation that the microwave radar, within the range of 9 to 10 GHz, functions for monitoring aircraft positions with accuracy within a distance of several hundred kilometers for safety and efficient routing of air traffic.
Microwaves find their important application in space communication, especially within the frequency range between 1 and 30 GHz, also called the C, X, and Ku bands. That is why these bands are suitable for carrying signals from Earth to Satellites and vice-versa, as they can travel through the atmosphere of Earth with minimal attenuation. The Ku band, if taken, for instance, provides frequency between 12 and 18 GHz; it is quite common in satellite TV broadcasting to make high-definition television signals available around every home on Earth. X-band frequency ranges from 8 to 12 GHz, have been the most utilized for military satellite communications, due to their high reliability even in bad weather conditions. Microwaves utilized for such satellite applications ensure uniformity in quality signal transmission over very long distances—from broadcasting television programs across continents to enabling global positioning systems across the globe.
Infrared Waves
Infrared waves occupy the spectrum just below that of visible light, with wavelengths from about 700 nanometers to 1 millimeter, and are associated primarily with heat. These waves are not visible to the human eye; however, we feel their presence around us every day in the form of heat from the sun, heating devices, or electronic sensors. Applications may range from great thermal imaging or remote sensing to communication devices and domestic technology.
Infrared waves have a wide application in thermal imaging based on the principle of the detection of infrared radiation emitted by objects. This becomes rather important in applications involving night-vision equipment, firefighting, and search-and-rescue missions. For instance, using an infrared thermal camera can detect as small a temperature difference as 0.1 degrees Celsius; this enables firefighters to visualize through smoke or to locate hotspots within a burning building. Typically, such cameras work within the middle-wave infrared range—between 3 and 5 micrometers. This is a quite good wavelength range for picking up heat signatures emitted from objects at temperatures common in industrial and natural settings, and this makes it highly valuable for the detection of changes in temperatures and for the movement of objects under conditions of low visibility.
Infrared waves also play an important role in remote controls and wireless communication. Most remote controls to televisions, fans, and air conditioners operate within the near-infrared range from 700 nanometers to 1.4 micrometers. A remote, upon being used, sends pulses of infrared light that encode the gadget-specific instructions, which, in turn, are decoded by an IR sensor into commands. Typically, these pulses operate at a frequency of about 38 kHz and allow high-speed data transfer without interference from any other light sources. In practice, this would mean the IR remote can send information across distances of up to 10 meters, given open lines of view, for ease in managing many devices in a house efficiently.
The second major field of application where infrared waves apply is in medical and health sectors, specially in diagnostic imaging and therapeutic treatments. Medical diagnosis uses infrared thermography to detect abnormal temperature patterns on the skin using wavelengths of between 8 and 15 micrometers. This is particularly useful in finding such conditions as inflammation, circulatory problems, or the detection of fevers. For instance, infrared thermometers are able to measure body temperature in less than a second with very accurate readings during a health checkup by detecting infrared radiation emitted from the skin. This technique has attained international importance in the recent health crises, including the COVID-19 pandemic, where non-contact infrared thermometers provided quick and hygienic ways of checking body temperatures in public places.
Infrared waves are also widely applied in astronomy and environmental studies. Infrared telescopes receive heat from distant stars, planets, and galaxies that are usually masked by dust clouds obscuring visible light. Another example is the Hubble Space Telescope, which operates partly in infrared. This opens up a whole new universe for observations that cannot be seen at normal wavelengths. Infrared observation involves wavelengths from 1 to 100 micrometers—a range that enables researchers to study star and galaxy formation since cooler objects emit much more infrared radiation compared to visible light. In addition, Earth surface temperature, vegetation health, and ocean currents are detected by infrared sensors on environmental satellites. For example, the MODIS satellite sensor collects data in wavelengths of thermal infrared, thus enabling the mapping of climate patterns, such as ocean warming, with much greater detail through time and geography.
Visible Light
The visible part of the spectrum is made up of a range of wavelengths, roughly from 400 to 700 nanometers. In this range, each different wavelength corresponds to a specific color, as detected by the human eye: from violet at the short end of the spectrum to red at the long end. It plays an important role in life, for one’s ability to see and distinguish color, and has further very extensive applications within technology, healthcare, and scientific research.
The Sun is the primary source of natural visible light. It emits light at approximately 5,500 Kelvin, with its peak wavelength at approximately 500 nanometers, which actually falls into the green portion of the visible spectrum. It is within this peak sensitivity range that optimum perception of the eye occurs, enabling us to see best in daylight. Sunlight gives roughly 100,000 lux on a sunny day, while artificial indoor lighting, depending on its power, generally gives between 100 to 500 lux. This immense difference in intensities has a great influence on the circadian rhythm in humans, thus affecting sleep and overall health. Studies have shown that the more natural light one is exposed to, particularly in the morning, the more he or she has a constant circadian rhythm. Which would translate to better mood and cognitive functioning. On the other hand, too much exposure to artificial lights, especially blue light from nighttime screen viewing may just disturb the balance in this rhythm. Hence, sleep disturbance occurs when visible lights are not appropriately balanced in photography—made possible by playing with light and color to record images. There are three main colors of light that camera sensors detect: red, green, and blue. These colors are achieved by placing color filters on the sensor pixels. The sensor then changes millions of single points of light into a full-color image. A good quality digital camera sensor may contain approximately 12 million pixels, every one of them able to capture one color at different intensities, which in turn form the picture by putting them together. This allows for the capturing of actual and precise details of any subject, in natural or artificial light, by allowing changes where the lighting is poor or too bright. The principle behind the process is the same in video technology, where each frame represents a set of images that, when run at a specific speed, usually 24 frames per second in movies, create an illusion of movement.
Visible light has been employed in various medical diagnostic and therapeutic uses. For example, a technique that involves illuminating with visible light internal organs by way of endoscopy allows doctors to see the inside of a body without surgical intervention. The endoscope contains a light source and a camera. Images are recorded at captured wavelengths in the visible range, hence allowing good visualization of tissues and organs. Other significant applications are phototherapies, which are used in the treatment of skin disorders, including psoriasis and eczema, where inflammation is reduced by specific wavelengths of visible light. Phototherapy, or blue light therapy, is used around 415 nanometers to treat acne by targeting and destroying bacteria on the skin’s surface. This is the wavelength that has been able to reach even into the skin up to a depth of 2 millimeters and can thus provide surface-level treatments without further damage to deeper tissue.
Visible light plays an important role in scientific research, especially in the fields of astronomy and physics. Telescopes, particularly those that detect visible light, like optical telescopes, have assisted astronomers in learning about stars, planets, and galaxies far, far away for centuries. Observations in the visible provide one way of studying the chemical composition, temperature, and motion of objects in space. The Hubble Space Telescope, for example, has recorded images in visible, ultraviolet and near-infrared light with remarkable resolution of features in galaxies and nebulae. Color is a measure of a star’s temperature, so when astronomers measure color, they are also classifying the star somehow. The example could be that the star appearing blue emits light at shorter wavelengths and hence has a temperature above 10,000 Kelvin, while that of a red star has longer wavelengths, hence cooler, about 3,000 Kelvin. These color differences, as captured through imaging by means of telescopes, provide insights into stellar and galactic life cycles and evolution.
Ultraviolet (UV) Light
Ultraviolet can be described as a sort of electromagnetic light lying beyond visible light, within the range of approximately 10-400 nanometres, and consists of three key categories: UVA, UVB, and UVC. Each of these types possesses specific properties and applications based on its wavelength and energy level. Actually, UV light deeply influences both biological systems and technological applications, from medical treatments to the monitoring of the environment.
UVA has the longest wavelength in the UV range and reaches as far as 320-400 nanometres, deeply into the skin, to cause aging and tanning effects. About 95% of the UV radiation that reaches the Earth’s surface is constituted by UVA since most parts of it manage to pass through the atmosphere. UVA is abundantly used in tanning beds since most of the bulbs are made up of about 95% UVA and 5% UVB radiation. Indeed, chronic exposure to UVA has been documented in studies to be associated with an increased risk of skin damage and skin aging, with the cumulative effect possibly not visibly manifesting itself until years later. Still, while it does pose some risks, UVA’s lesser energy compared to UVB and UVC is medically useful, in phototherapies administered for skin diseases such as psoriasis, where the controlled application of UVA can be quite effective in mitigating symptoms.
UVB has between 280 and 320 nanometres, thus it is more energetic than UVA radiation and partly absorbed by the ozone layer; only a small percentage reaches the Earth’s surface. This form of UV is mainly responsible for sunburn and plays the prime role in vitamin D synthesis in human skin. The majority of studies suggest that 10-15-minute midday exposure to UVB, depending on geographic location and skin type, can synthesize quantities of vitamin D adequate for the day. However, there are also significant risks with UVB radiation; longer periods of exposure can cause skin burns and increase the risk of skin cancers. UVB phototherapy is sometimes used in medical applications for vitamin D deficiencies or for specific skin disorders where the amount of exposure must be carefully controlled to balance therapeutic benefits against minimal risk.
UVC has wavelengths between 100 and 280 nanometers and represents the most energetic and dangerous type of UV light. Fortunately, it is almost completely absorbed by the Earth’s atmosphere—by the ozone layer, primarily—before it can reach the surface. UVC light is very effective as a germicide. The UVC lamps emit at about 254 nanometres, a wavelength efficiently destroying the DNA and RNA of the micro-organisms by killing or inactivating them. Indeed, studies have documented that, depending on the dosage, UVC is able to destroy up to 99.9% of the viruses and bacteria on surfaces in a matter of minutes. This makes UVC an important tool in infection control. More recently, UVC has been seized upon as holding particular promise for pathogen control in public spaces during health crises—precautions must be taken to avoid exposure to human skin and eyes.
X-Rays
X-rays fall within the spectrum between the wavelength range of 0.01 to 10 nanometres, thereby placing them between ultraviolet light and gamma rays. Because of their short wavelengths and high frequencies, they are capable of transmission through materials of all types. X-rays find wide applications in medical diagnosis, security checks, and scientific research. The capability of X-rays to delineate structures and details internally, which is beyond human vision, has indeed transformed many fields.
X-ray imaging is one of the most diagnosed tools used in medicine. The energies that medical X-rays operate under range from 20 to 150 keV, depending on the tissue under analysis. For example, dental X-rays use lower energy of about 70 keV because they need only to penetrate pieces of soft tissue and bone in the mouth, while chest X-rays will require higher energies to penetrate larger sections of the body and produce an image of lungs and heart. X-ray images, or radiographs, rely on the principle of differential tissue density; thus, the denser structures—like bones—appear white owing to the greater absorption of X-rays, while softer tissues appear in shades of gray. It aids in the diagnosis of fractures and pathologies such as tumors and infections.
Like radiography, computed tomography, also called a CT scan, uses X-rays to take cross-sectional pictures of the body; however, unlike radiography, CT scans enable a more detailed three-dimensional view of internal structures. In a CT scan, the X-ray beams rotate around the body; a computer assembles the resulting multitude of angles into an image. A typical CT scan uses 1-10 mSv of X-rays, depending on the type of scan. For comparison, a typical chest X-ray exposes the patient to 0.1 mSv, whereas an abdominal CT scan may use as much as 8 mSv. Because larger doses of X-ray radiation are used in CT scans than in conventional X-rays, though, its diagnostic benefits outweigh the risks, including the detection of cancers, vascular diseases, and internal injuries. Advances in CT technology continue to reduce radiation doses so that the technique is becoming both safer and more available.
In security applications, such as luggage and cargo inspection, X-ray scanners are widely used at airports and border checkpoints. Lower-energy X-rays are used here, typically from 30 to 140 keV, which penetrate an object to give an image of the interior. X-ray absorption depends on the density and atomic number of the materials; hence, the scanners are able to differentiate between organic and inorganic materials. Items of high density, such as metals, appear darker, while organic items, such as food or clothes, appear lighter on the X-ray images. This technology assists security personnel in that it aids them in quickly identifying possible threats without having to manually search every item physically. This provides good balance in efficiency against security. Higher-energy X-rays can scan larger items with advanced cargo inspection systems, often up to 9 MeV, so shipping containers are thoroughly inspected without disrupting the flow of global trade.
Gamma Rays
Gamma rays are electromagnetic waves with wavelengths smaller than 0.01 nanometers and frequencies above 10 exahertz, or 10¹⁹ Hz. Because of their very small wavelengths, gamma rays are the most energetic form of electromagnetic radiation. This extreme energy allows gamma rays to penetrate almost any material, but that fact also makes them incredibly useful and simultaneously quite dangerous. Gamma rays are produced by nuclear reactions, by radioactive decay, and by astrophysical processes. Applications of gamma rays range from medical treatments and imaging to studies of nuclear science and astronomy.
In medicine, gamma rays are essential in the treatment of cancer radiation treatment. Gamma radiation can target the cancerous cells and actually damage the DNA enough not to reproduce. One of the most utilized sources of gamma rays in treatment is Cobalt-60, which has two major gamma radiation energies of emission at 1.17 and 1.33 MeV (million electron volts). One session of radiation treatment commonly covers dosage in the range of 20 to 80 Gy, usually divided into fractions, and whereby one Gy is defined as one joule of radiation energy absorbed per kilogram of tissue. This was done to minimize the damage in healthy tissues around the tumor, yet effectively targeting the tumor. Medical imaging also makes use of gamma rays through techniques like positron emission tomography scans, wherein gamma rays emitted by a radioactive tracer in the body produce high-resolution images of biological processes at the cellular level — valuable for diagnosis and monitoring of disease.
Gamma rays figure very significantly in sterilization procedures, especially for medical equipment and food products. Gamma rays are favored in sterilization due to their great power of penetration into materials. It must ensure that all microorganisms, including bacteria and viruses, are destroyed. A typical gamma irradiation sterilization facility exposes an item with a dosage quantity between 25 and 50 kGy, where 1 kGy means 1,000 Gy of absorbed radiation. These benefits contrast gamma sterilization to other methods, such as chemical treatments, in that there is no residue left from them, while structural integrity is not compromised, for example, in surgical instruments, syringes, and plastic containers. In the case of food irradiation, gamma rays extend shelf life and decrease foodborne pathogens with a minimal loss of nutritional quality in food, as the radiation does not render the food radioactive.
Material inspection by gamma rays is utilized in the fields of nuclear science and industry to detect structural weaknesses. Gamma-ray radiography allows engineers to study the integrity of metallic structures and welds in pipelines, aircraft, and other critical infrastructure. Using isotopes such as Iridium-192, with gamma radiation emissions over a range of energies at approximately 0.31 to 1.37 MeV, inspectors are able to visualize internal flaws and fractures within materials. This is indeed a priceless non-destructive test that guarantees safety and reliability without the dismantling of equipment. To explain this in more detail, gamma-ray radiography on an oil pipeline could reveal tiny hairline or corrosions that may cause fatal failures if they remain unnoticed. Each inspection requires safety measures with respect to hazards associated with radiation risk to workers. For example, exposure time and shielding are controlled in each inspection, which underlines the need for very stringent safety when working with gamma radiation.
