Acoustics the Science of Sound Ultrasound and Vibration

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Acoustics is the science that studies the production, transmission, control, reception and effects of mechanical waves and vibrations (sound). The science of acoustics is used in many fields of study, including earth sciences, life sciences, engineering and the arts.  Sound waves propagate as disturbances in the ambient audible to the human ear.  The loudness of these disturbances is known as sound pressure level and is measured in decibels.  The sound spectrum includes infrasonic, audio and ultrasonic sound waves.

Sound waves propagate through air, water and solids; however, during their propagation, sound waves can be refracted, reflected, or attenuated by the medium. Sound waves are measured by their frequency, wavelength and amplitude. Frequency measures the number of sound vibrations per second. The frequencies at which a human being can perceive sound vary between 20 Hertz (20 cycles per second) and 20,000 Hertz. It is within these frequency ranges that people can communicate to each other and listen to music.

Amplitude is the amount of positive or negative change in atmospheric pressure caused by a sound wave. Higher amplitude waves will cause greater changes in atmospheric pressure.  Sound amplitudes can be measured by viewing the form of a wave through an oscilloscope. Wavelength is the distance over which the shape of a wave repeats itself.  Wavelength is inversely proportional to the frequency of a wave. Higher frequency waves have shorter wavelengths and lower frequency waves have longer wavelengths.

The ultrasonic sound waves comprise frequencies above the audible range of human hearing (20,000 Hertz).  Ultrasonic frequencies have shorter wavelengths. Ultrasound waves are used in medical technologies, such as ultrasonography and elastography. On the lower end of the sound spectrum is the infrasonic sound range which comprises frequencies lower than 20 Hertz. This frequency range is used in medicine to study the movements of the body corresponding with the heart beat and to monitor earthquakes, as well.

Transducers (loudspeakers, microphones, hydrophones, sonar) are devices used to convert one form of energy into another form of energy.  Loudspeakers convert electrical signals into sound waves. Microphones convert sound waves into electrical signals. The medical ultrasonic devices utilize piezoelectric transducers to convert sound waves into electrical pulses which are detected by an ultrasonic scanner and converted into a digital image. The frequencies used in diagnostic ultrasound vary from 2 to 18 MHz.

The science of acoustics studies how sound waves behave in the ambient and in the medical industry; however, it also covers a broader range of fields and subfields. The Lindsay´s Wheel of Acoustics describes the scopes of acoustics beginning with four major fields, including Engineering, Earth Sciences, Life Sciences and the arts. These major fields of acoustics are further classified into an array of subfields in the science of acoustics.

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