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Sound Waves

Chapter 3 in Edelman

QuestionAnswer
The 7 parameters that characterize a sound wave Period, frequency, amplitude, power, intensity, wavelength, and speed
The parameters of sound wave are determined by 2 things The source of the sound wave and the medium it is traveling through
Definition of period The time it takes a wave to vibrate a single cycle, or the time from the start of one cycle to the the start of the next cycle. Reported in units of time
Typical ultrasound period 0.06 to 0.5 microseconds
Characteristics of a period Period is determined by the sound source only, not by the medium and is NOT adjustable
Definition of frequency The number of particular events that occur in a specific duration of time. Reported in units per second
Typical ultrasound frequency 2 Mhz to 15 Mhz or 2 million to 15 million per second
Characteristics of frequency Frequency of a sound wave is determined by the sound source only, not by the medium and is NOT adjustable
Audible sound frequency 20 Hz to 20,000 Hz
Infrasonic frequency or infrasound Lower than 20 Hz
Ultrasonic frequency or ultrasound Higher than 20,000 Hz (20 kHz)
How are period and frequency related? Inversely; as frequency increases, period decreases; as frequency decreases, period increases. They are also reciprocal
3 parameters describe the size, magnitude or strength of a sound wave Amplitude, power & intensity. These are the only parameters of the 7 that the sonographer can adjust.
Definition of amplitude Amplitude is the "bigness" of a wave. It is the difference between the maximum (or minimum) value and the average or undisturbed value of an acoustic variable. Reported in pascals
Typical ultrasound pressure amplitude 1 million pascals to 3 million pascals or 1 Mpa to 3 Mpa
Characteristics of pressure amplitude Amplitude is determined initially by only the sound source, however, amplitude decreases as sound propagates through the body. Amplitude is adjustable
Definition of power Power is the rate of energy transfer or the rate at which work is performed. Like amplitude, it describes the "bigness" of a wave. Reported in watts
Typical ultrasound power 0.004 to 0.090 watts (4 to 90 milliwatts)
Characteristics of power Initial power is determined by the sound source, but power decreases as sound propagates through the body. Power is adjustable
How are power and amplitude related? Power is proportional to amplitude squared
Definition of intensity Intensity is the concentration of energy in a sound beam. Intensity describes the "bigness" of a wave. Intensity relates to how the power in a wave spreads or is distributed in space. Reported in watts per cm squared (W/cm squared)
Typical ultrasound intensity 0.01 to 300 W/cm squared
Characteristics of intensity Initial intensity is determined by only the sound source, but intensity changes as sound propagates through the body. Intensity is adjustable by
How are intensity and power related? Intensity (W/cm squared) = power (W)/area (cm squared)
How are power, amplitude and intensity related? They are directly related. Therefore when one increases, the others increase. Intensity is proportional to power. Intensity is proportional to amplitude squared. Power is proportional to amplitude squared.
Definition of wavelength Wavelength is the distance or length of one complete cycle. Reported in mm
Typical ultrasound wavelength 0.1 to 0.8 mm
Characteristics of wavelength Wavelength is the only parameter determined by BOTH the source and the medium and is NOT adjustable
The wavelength in soft tissue In soft tissue, sound with a frequency of 1MHz has a wavelength of 1.54 mm
How are frequency and wavelength related? Wavelength (mm) = 1.54 mm/microsecond/frequency (MHz)
Propagation speed The rate at which a sound wave travels through a medium. Measured in m/s or mm/microsec
Characteristics of propagation speed Speed is the only parameter determined by the medium ONLY and is NOT adjustable by the sonographer. The Stiffness and density of an object affect the speed of sound.
Speed of sound in soft tissue 1540 m/s or 1.54 mm/microsec or 1.54 km/s
Stiffness The ability of an object to resist compression. Speed and stiffness are directly related. Also known as bulk modulus. Elasticity and compressibility are the opposite of stiffness.
Density The relative weight of a material. Speed and density are inversely related.
Created by: gillybruursema
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