In order to understand what sound energy is, we must first understand what sound is exactly. Sound is defined as a mechanical wave (a wave which cannot travel without some sort of a medium) which travels via a gaseous, liquid, plasmatic or solid medium. This mechanical wave is actually a vibration of pressure and is only classified as a “sound” in its earliest senses if it falls within the audible range of frequencies.
Now that we know what sound is, it would be easier to understand the energy that is present within sound. It can be defined simply as the energy that is present within each of the above mentioned occurrences and is thus achieved via oscillation of matter. The following formula is used to elaborate the concept of sound energy in physics:
In the equation above, P = sound pressure, v = particle velocity, po = density and c = sound speed.
A point to be noted is the fact that sound energy is indeed a form of mechanical energy because the waves of pressure which are exerted upon the medium through which they travel cause compression and rarefaction in them. Sound energy is usually not very prominent under normal circumstances because the energy it contains is not significant enough. Nonetheless, it can do work (causing change) and thus it is a form of energy.
As the energy within a traveling wave of sound is not very prominent, joule is not used to measure sound, unlike other forms of energy. Instead, more emphasis is put on the pressure and intensity of sound, which is why pascals or decibels are the preferred units of measuring sound.
Using the energy in sound
This is a concept which is not as abundant or easily achievable as it sounds. The main difference between the energy in sound and the energy in other alternate sources of energy such as the wind or water is the fact that the amount of energy in sound is far lesser. However, sound energy is constantly being researched upon from different aspects and for various purposes.
1. Military application -– Scientists had found out long ago that sound frequencies can be manipulated to disrupt living cells. Although it is not a use that we should particularly look forward to, weaponization of sound is possible and the detrimental effects of high frequencies on lab animals have confirmed internal bleedings and significant physical damage. The technology is still at its experimental stage though and will take time before maturing into full-fledged weaponry.
2. Alternate source of energy -– Perhaps what most of us look forward to when we discuss the uses of sound energy is the progress we are making in terms of using sound as a source of useable energy. Sound requires closed energy production units to produce useable energy and one such apparatus is the Stirling engine. Simply put, the steam engine’s process of working can be defined in this way; liquid is heated and cooled within the engine in such a way that it turns the piston inside, which generates the necessary energy for locomotion. Sound energy has the potential to do the job within this motor via the application of appropriate frequencies. The excess heat produced as a byproduct of using sound energy is also promising as this model could then not only provide homes with electricity, but with additional water and air heating facilities also.
3. Lift and propulsion -– Another potent aspect of sound energy that the scientists are trying to utilize is its locomotive capabilities. It has been found that sound at ultrahigh frequencies can indeed cause objects to propel forward or lift up. The famous experiment which revealed and confirmed this feature of sound to the world was done by Japanese scientist Yoshiki Hashimoto. He used totally controlled supersonic waves (20,000 vibrations/second) to levitate by one mm, a wafer made out of silicon. This instrument was introduced as the Kaijo Acoustic Levitator by Hashimoto, which can revolutionize the semiconductor industry. While comparing it with other sources of “zero contact” locomotion like electromagnetism, Kaijo Corporation is of the opinion that ultra-frequencies fare a lot better.
4. Sonoluminescence -– This is something that has interested the American scientists more than anything else and has reached prominence outside the planet itself! The absence of weight has made space a perfect backdrop for sonic experiments because they can be carried out better without the interference of gravity. It was in one of such space labs that new and groundbreaking facts about sonoluminiscence (also known as acoustic luminescence) were discovered by Americans.
It was discovered to the amazement of scientists that the proper liquid, when subjected to sound frequencies of high-intensity, produces light. Amazing as this fact is, one should know that this is not a new phenomenon as the same kind of luminescence was seen back in the 1930s, right here on earth. There is however, a significant difference between the two observations. The difference is more of degree than of kind as it was possible to perform the experiment on a single bubble of water; which revealed to the researchers that the luminescence occurs in pulses and each of the pulses has an extremely short duration. The complex experiment, according to Tim Leighton (University of Southampton) is not easy to explain to even an expert who is new to acoustic physics as it crosses the boundaries of standard physics.
5. Virtual sound -– It is now time to discuss a more entertaining use of sound that the researchers are considering as well at Southampton. The technology is known simply as Stereo Dipole and the most basic way to describe it would be to call it a kind of virtual sound system that will accompany virtual reality based entertainment systems. The concept has already won them the “Millennium Product” award from the Design Council, due to its potential to produce absolutely life-like 360° surround sound. The extent of the experience however, may depend on a particular person’s hearing capacities.