Difference Between Attenuation and Absorption

Main Difference – Attenuation vs Absorption

Attenuation is an important term used especially in physics, radiotherapy, telecommunication, and electrical engineering when dealing with waves and signals whereas the term absorption is used in various fields of study including physics, chemistry, biology, mathematics, engineering, medicine, and economics. Even though the two concepts have a relationship in some cases, they have different and specific meanings. This article describes the difference between attenuation and absorption in detail. In Physics, the main difference between attenuation and absorption is that attenuation is the gradual reduction in the intensity of a signal or a beam of waves which is propagating through a material medium whereas the absorption is the way in which the energy of a photon is taken up by matter.

This article covers,

1. What is Attenuation?

2. What is Absorption?

3. What is the Difference Between Attenuation and Absorption 

What is Attenuation

In physics / engineering, the gradual reduction in the intensity of a signal (beam of waves) which is propagating through a material is known as the attenuation. It is a common phenomenon experienced by any kind of wave or signal propagating through a medium. For example, acoustic waves are attenuated by water, X- rays are attenuated by lead, and seismic waves are attenuated as they propagate through the Earth. Normally, attenuation is an exponential function of the path length through the medium. In other words, the extent of the attenuation of a wave through a given medium depends on the path length. In addition, the attenuation of a wave or beam depends on the frequency of the wave and the medium through which the wave propagates. The units of measuring attenuation are dB/m, dB/cm or dB/km (decibels per unit path length)

The extent of the attenuation of electromagnetic waves depends on the medium through which the waves propagate. For instance, the extent of attenuation of a given EM wave through water and a plasma is very different. The attenuation of EM waves occurs due to both absorption and scattering of photons. The absorption of EM waves in a matter is a result of several types of interactions (photoelectric effect, Compton effect, pair production) take place between EM waves and matter.

Attenuation is a very important factor in telecommunication as the attenuation limits the effective range of signals. In fiber optics, the attenuation of signals through the medium is commonly known as the transmission loss. Fiber optic technology is widely being used for long- range communication as the attenuation in optical fibers is notably low compared to other communication technologies.

Attenuation of ultrasound waves in a given medium is the reduction in amplitude of the waves traveling through the medium and, depends on the medium, the path length and the frequency of the waves. The extent of the attenuation determines the quality of images. Therefore, attenuation of ultrasound waves is a very important factor in ultrasound imaging.

Frequency dependent attenuation of electromagnetic radiation in standard atmosphere

What is Absorption

The term Absorption is used in different fields of study with different meanings. In electromagnetism, the absorption of energy of EM waves by a material is commonly referred to as the absorption. In this process, the absorbed energy appears as the heat of the medium or another form of energy such as the vibrational and rotational energy of the atoms or molecules of the medium. The absorption of EM waves depends on several factors such as the frequency of EM waves, the medium, path length, and concentration of the absorbing medium. Light waves can propagate through a perfectly transparent material without any reduction in the amplitude. In practice, transparent glasses permit the light waves to pass through them with a relatively low reduction in the amplitude. However, light waves passing through highly opaque mediums lose their total amount of energy and eventually disappear.

In acoustic physics, the absorption of sound waves by a material medium is commonly referred to as absorption. Absorption of sound waves is a popular area of study, especially in sound proofing. Normally, soft, flexible, porous materials are good sound absorbers whereas hard, heavy materials reflect sound waves. The absorbed sound energy is mainly converted into heat of the absorbing medium.

In chemistry, absorption is mainly used to refer the absorption of particles by solid or liquid mediums. For instance, the absorption of carbon dioxide by calcium hydroxide is an absorption of gas molecules by a liquid medium.

Difference Between Attenuation and Absorption

Definition:

Attenuation: Attenuation is the gradual reduction in the intensity of a signal or a beam of waves which is propagating through a material medium.

Absorption: The term absorption is defined in different ways in different fields of study. For instance, in electromagnetism, the absorption is the way in which the energy of a photon is taken up by matter whereas, in chemistry, absorption of particles by a liquid or solid is commonly known as the absorption.

Application:

Attenuation: The concept of attenuation is used in radiotherapy, ultrasound imaging, communication, etc.

Absorption: The concept of absorption is used in  soundproofing, absorption spectroscopy, etc.

Image Courtesy:

 “Micrwavattrp.”By. Dantor assumed (based on copyright claims). –  Own work assumed (based on copyright claims).(CC BY-SA 2.5) via Commons Wikimedia

 “Absorption or emission spectroscopy”By Mysterioso – Own work (CC BY-SA 3.0) via Commons Wikimedia 

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