# Infrared Radiation - Electromagnetic Waves

Infrared radiation or IR also referred to as infrared, is a region of the electromagnetic radiation spectrum where the range of wavelengths is from about 700 nanometers to 1 millimetre. It is a type of radiant energy that is invisible to human eyes but that we can feel as heat. Depending on the wavelength and frequency, infrared is commonly divided into five categories: near-wavelength, short-wavelength, mid-wavelength, long-wavelength and far-infrared.

Electromagnetic radiation spectrum which has the wavelengths between 700 nanometers to 1 millimeter.

The word infrared means below red. Red light has the longest wavelength that our eyes can see but infrared waves cannot be seen by the eye.

• Infrared radiations are also referred to as heat or thermal waves or electromagnetic waves. This is because they have a heat-inducing property. Sometimes infrared rays are used in applications where heat production is required like in infrared heaters or for therapeutic purposes where a patient requires physical therapy.
• Sometimes infrared rays themselves are classified as near infrared and far infrared rays.
• Near-infrared rays are used in electronic applications like TV remote sensors and photography. Their applications can be somewhat similar to visible light applications since their wavelength ranges are close.
• Far infrared rays are more thermal in nature. Anything generating heat gives out far infrared radiation. Even the human body (at $37^{\circ}C$ ) gives off infrared radiations of around 800 nm wavelength.

We already know that the wavelength of the infrared radiation is between 700 nm to 1 mm, which is between the red limit of the visible spectrum. But following is the classification of bands based on the spectral range 1µm and 50µm:

• 1µm to 3µm which is known as the band I or Short Wave Infrared
• 3µm to 5µm which is known as the band II or Middle Wave Infrared
• 8µm to 14µm which is known as the band III or Long Wave Infrared

## Properties of Infrared Waves

### Transverse Waves

Infrared waves consists of transverse waves. According to Serway’s College Physics, infrared wave is said to be transverse wave when the displacement of wave is right angle to the direction in which the wave’s energy is travelling.

### Wavelength

The wavelengths of infrared waves is unique and are usually measured in microns. A micron is defined as one millionth of a metre. The shortest wavelength of infrared wave is about 0.7 microns. The longest wavelength of infrared wave is 350 microns. According to studies, the upper limit of any infrared wave is 1000 microns.

### Speed

The speed at which infrared waves travels is 299,792,458 m.s-1.

### Particles

According to quantum theory, infrared waves can exist as either wave or as a particle at the same time.

### Absorption and Reflection

The absorption and reflection of infrared waves depends on the nature of the substance that the waves are made to strike. Materials such as ozone, carbon dioxide, and water vapour absorb infrared radiation. Snow and aluminum foil are the materials that reflect the infrared radiation.

### Refraction and Interference

Infrared waves exhibit the property of refraction making the waves experience slight change in direction when the wave passes from one medium to another. Refraction property of infrared wave can be noticed in earth’s atmosphere. When two infrared waves with same wavelength meet each other, they will interfere with one another.

### Thermal Properties

Infrared radiation can be the source of heat as they have thermal properties. When the infrared radiation strikes the oxygen or nitrogen molecules, the radiation makes the molecules move faster as they gain more energy. So it can be concluded that infrared radiation makes materials hotter and therefore can be used as a heat source.

## Infrared Rays Uses

Following are the uses of infrared rays:

•  Communications: Infrared lasers are used for free space optical communications as these are relatively inexpensive. These also find applications in the areas that are densely populated.
• Spectroscopy: Infrared vibrational spectroscopy is used for identifying the molecules by analyzing their bonds as the molecule vibrates at different frequencies. The unit used to express the radiation is cm-1.
• Astronomy: Optical components like mirrors, lenses and digital detectors are used to study the objects that are in space. These objects glow when they are exposed to the radiated heat.

## Applications of Infrared Waves

Following are the areas of use of infrared waves:

### Heat Source

There are two different industries that use infrared radiation as heat source and they are:

• Medical uses: Infrared radiation finds application as a heating source. There are infrared saunas which are used for treating high blood pressure, rheumatoid arthritis, and high blood pressure which are chronic health problems. Infrared radiation is considered to be one of the safest methods of physiotherapy.
• Manufacturing industries: Industries which concentrate on manufacturing processes such as forming of plastics, curing of coatings, plastic welding, etc use infrared heaters in place of contact heating and convection ovens.

### Cosmetology Application

Infrared rays are widely used for cosmetic applications such as for treating skin injuries, smoothing of wrinkles, reducing the occurrence of dandruff, blackheads, etc. The reason why infrared rays are used is because they can penetrate through the skin up to 3-4 mm. They also warm the skin resulting in improved blood circulation, continuous supply of oxygen and other nutrients to the skin.

### Astronomy

Astronomers use optical devices such as mirrors, solid state digital detectors, lenses to study objects from space with the help of infrared waves. The images from these optical devices are obtained with the help of infrared telescope.

### Massage Therapy

Infrared rays are used for warming the skin and for relaxing the muscles. Infrared rays are preferred because of their penetration quality through skin.

### Infrared Photography

Infrared filters are used for capturing pictures in infrared photography. This imaging is done for objects that are placed in near-infrared spectrum. Most of digital cameras use infrared blockers making the near-infrared appear as purple-white color in the final image.

### Infrared Communication

Data transmission with the help of infrared radiation is very common in short-range communication. For encoding the data infrared light-emitting diodes are used which emit infrared radiation and is focused into a narrow beam with the help of plastic lens. At the receiver end, a photodiode is placed for converting infrared radiation into electric current.

### List a few properties of infrared radiation.

Following are a few properties of infrared radiation:

1. Infrared radiation, like all radiation, travels at a speed of 299,792,458 meters per second.
2. Infrared light can exhibit both wave and particle nature at the same time.
3. Depending on the nature of the material that infrared radiation strikes, it can either be absorbed or reflected.
4. Infrared radiation increases the thermal energy in particles.

### List a few medicinal effects of infrared radiation.

A few medicinal effects of infrared radiation are as follows:

• Used to reduce the inflammation of throat, ear and nose
• Used as an aid in stress management
• Reduces pain arthritis
• It eases kidney function

### How do we experience infrared radiation on a daily basis?

Infrared is a type of radiant energy that is invisible to the eyes and we can only feel it in the form of heat. All objects in the universe emit some level of IR radiation. Sun and fire are among the most obvious source of infrared radiation.