Can we use sound energy to turn noise into forms of energy? Sounds crazy, but we discover different types of energy all the time — especially when it comes to renewables — and sound energy is just another kind.
Around the world, it’s hard to find somewhere that noise is not part of the landscape. From the roar of traffic to the sound of musical instruments, humans make a lot of noise. There are many different types of sound ranging from the audible to the inaudible.
Sound sources may be pleasant or unpleasant to the human ear, depending on loudness, different pitches, types of sound, sound source, and sound intensity. Regardless, sound energy travels and depending on the sound source and the intensity, sound can sometimes be considered a pollutant.
So what is sound energy, exactly? Sound energy is turning sound into electricity. Though the science of turning sound energy into electricity is still emerging, it has been done. For example, microphones and speakers are examples of sound becoming electrical energy.
In fact, a group of young high-school students figured out how to produce enough electricity with sound energy to turn on a light bulb. Admittedly, that’s a long way from generating enough electricity to power a home or an entire city. But it’s a beginning and the science behind it is developing. Let’s learn more about the intriguing world of sound, including sound energy examples.
The mechanics of hearing demonstrate some of the mechanics of sound energy.
When we hear a sound, we are experiencing sound waves funneling into the ear canal and moving the eardrum, much like a drum head vibrates when struck. Different sounds make different vibrations that affect how the eardrum moves.
The vibrations travel from the eardrum via ossicles to the cochlea (a fluid-filled organ), causing surface waves that strike hair cells. Depending on the location of the hair cells in the cochlea, the brain “hears” high- or low-pitched sounds via the auditory nerve. It then translates the initial vibrations of the air molecules in the sound wave into sounds we understand.
In physics, the study of sound is known as acoustics and includes all constructs of sound.
In simple terms, sound energy comes from vibrations moving through something. Solids, liquids, and gases all transmit sound as energy waves.
Sound energy is the result when a force, either sound or pressure, makes an object or substance vibrate. That energy moves through the substance in waves. Those sound waves are called kinetic mechanical energy.
Sound waves are sometimes called mechanical waves because sound waves require a physical medium to propagate. Liquids, gases, or solid materials transfer the pressure variations, creating mechanical energy in waves.
Like all waves, sound waves have peaks and valleys. The peaks are called compressions, while rarefaction is the term used for the lows.
The oscillations between compression and rarefaction move through gaseous, liquid, or solid media to produce energy. The number of compression/rarefaction cycles in a given period determines the frequency of a sound wave.
Scientists measure sound energy’s intensity and pressure in Pascals and decibels. Sound waves are also sometimes called pressure waves because the pressure of the sound wave moves the particles through which it passes.
Wavelength, period, amplitude, and frequency are the four primary parts of a sound wave, regardless of the wave type and the medium through which the sound travels.
When energy can do work but isn’t actively applying force, it’s called potential energy.
In physics, work is measured by the energy transferred. When something is moved over a distance by an external force, that’s work.
The coiled spring of a Slinky is an example of potential energy. Until the spring is released, it’s not doing work. The work occurs when the spring moves (is released), becoming kinetic energy. Kinetic energy is the energy of motion.
Sound energy can be both: either kinetic energy or potential energy.
An example might be that of a musical instrument. When the instrument is played, it generates sound waves, producing kinetic energy. But when that same musical instrument is at rest, only the potential for energy is there.
In addition to a wave’s primary constituents — frequency, amplitude, wavelength, and frequency — scientists categorize waves based on three distinguishing characteristics: longitudinal, transverse, and surface movement.
Using the movement of a medium’s particles relative to the direction of travel is a standard method for distinguishing the kind of wave.
To understand transverse waves, we’ll talk about the Slinky again. Consider a Slinky’s movement as your hand alternates up and down. The energy of this “activated” Slinky moves vertically along the direction of travel, displacing the coils (which, in this case, represent wave particles) up and down.
Types of transverse waves include:
On the other hand, longitudinal waves move the wave’s energy right or left along the wave’s horizontal axis. So our Slinky, when stretched out horizontally and pulsed horizontally like an accordion, will pulse horizontally along its left-right direction of travel parallel to the wave’s axis.
Sound waves are longitudinal waves, as are ultrasound waves, and seismic P-waves.
The chief characteristic of a surface wave is its particles’ circular motion. Only the particles on the medium’s surface move circularly; the movement decreases as the particles move away from the surface.
Sound energy occurs when an object vibrates. Noise, whether within the human range of hearing or not, is sound energy. Sonar, ultrasonic (greater than 20 kilohertz) music, speech, and environmental noise are all forms of sound energy.
Whether from an inanimate object or a sentient being, sounds come from everywhere. Some are pleasant to our hearing, some are not. Consider these sound energy examples and how they make you feel:
Even when it is seemingly quiet, there is always sound.
Sound vibrations can become electrical energy through the principle of electromagnetic induction. Electromagnetic induction generates electrical current using a magnetic field.
When a magnetic field and a conductor, such as a wire coil, move in relationship to one another, electromagnetic induction occurs. As long as the conductor is in a closed circuit, current flows wherever the conductor crosses the lines of the magnetic force.
Piezoelectricity uses unique crystals to convert mechanical energy — in this case, sound wave energy — into electrical energy.
Under compression, the crystals act as conductors. When crystals are compressed, their structure changes and the crystal acquires a net charge. That charge can be converted to an electrical current.
Other materials, such as bone, special ceramics, and enamel, are also piezoelectric conductors. These materials have in common the ability to produce an internal electrical charge due to applied mechanical stress.
Using very-high-frequency sound waves — frequencies 100 million times higher than people can hear — piezoelectric materials become electrical signals that give off light waves in the terahertz frequency range.
Piezoelectricity unites the electrical and mechanical states of the piezoelectric material. Under compression, the material used has a current flow that changes its polarization to become an electrical charge, known as a net dipole moment.
As we know, sounds constantly fill our acoustic environment. Like all energy, sound energy has the potential to generate electricity. Just like the sun provides unlimited solar energy and the breeze provides wind energy, sound energy is renewable because sentient beings and insentient objects alike constantly produce sound.
While sound waves and energy production principles have long been understood, the technology to convert sound energy to electricity is in its infancy.
However, as scientists and technicians investigate and improve the technologies involved in sound-generated electricity, sound energy may produce mass electricity one day.
If that sounds like a pipe dream, remember solar and wind power were once beyond our grasp too.
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