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| Amplitude is the maximum displacement from equilibrium. The units are any units of length. |
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What is period (T)?
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The time it takes to complete one cycle.
The units are units of time: sec, min, hours, years. The period for weekly quizzes is every 7 days or 1 week. |
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What is frequency (f)?
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The number of cycles per unit of time.
The unit is Hertz (cycles/sec). The frequency of weekly quizzes is once per week. |
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| How are frequency and period related? |
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| They are inversely proportional. |
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What is angular frequency?
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| Angular frequency is the equivalent of frequency in radians per units of time. The units are radians/sec or rads/sec for short. Rads/sec = 1/sec. |
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| What are the two types of waves as far as as matter is concerned? |
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1) Mechanical (particles of matter oscillate) (sound for example)
2) Electromagnetic (photons oscillate) (X-ray for example) |
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| What are the two different types of wave as far as direction is concerned? |
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1) Longitudinal (particles move parallel to the direction of travel)
2) Transverse (particles move perpendicular to the direction of travel) |
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| What is the difference between compression and rarefaction? |
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Compression is when the particles are all bunched together in a wave during particle oscillations. Rarefaction is when they are not all bunched together.
::::: :: ::::: :: :::::
::::: :: ::::: :: :::::
C---R |
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| What type of wave is sound? |
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| Sound is a mechanical longitudinal wave. |
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| What are the Acoustic Variables? |
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(Put That Drink Down)
Pressure
Temperature
Density
Distance
They are all proportional to one another:
P~T~D~D |
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| What are the characteristics of a sound wave? |
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- Period and frequency
- Velocity and Wavelength
- Power, Intensity, and Amplitude |
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| What is the sound frequency for infrasound? |
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| < 20 Hz (less than 20 Hz) |
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| What is the sound frequency for Audible sound? |
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| What is the sound frequency for Ultrasound? |
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| What is the frequency range for diagnostic ultrasound? |
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| What is the frequency range for Therapeutic US? |
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| What is the frequency range for HIFU US? |
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| What is the frequency range for Intravascular US? |
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| What is the frequency range for medical US? |
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| How are period and frequency determined in ultrasound and how can a technologist change them? |
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| Period and frequency are determined by the crystals in the probe. The only way to change it is to use a different probe. |
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| How high should the frequency be if you're trying to image something deep? |
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| Low. Low frequency means more depth. |
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| How high should the frequency be if you want a clear, nice image? |
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| High. Higher frequency means clearer image, at the cost of not being able to go very deep. |
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| What is the units for period in regards to ultrasound? |
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| What is wavelength and what are its units? |
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Wavelength is the amount of space that occupies 1 cycle.
The units are generally mm in US. |
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| What does wavelength depend on? |
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- The propagation speed of the US in the medium
(V depends on the medium)
- The frequency that is determined by the crystals in the probe. |
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| In, Ultrasound, what is wavelength important for? |
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| Getting images in long axis. Which helps you distinguish between two objects in the scanning line. |
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| How big should your wavelengths be if you want a clear resolution? |
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| Small Wavelength = smaller details seen = better image. |
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What is propagation speed?
What is propagation speed not?
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- Propagation speed is the speed at which a WAVE moves through a medium.
- Propagation speed is NOT the speed at which particles move back and forth.
Units are m/sec, mm/microsec, etc. |
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| Speed is determined by the characteristics of the MEDIUM ONLY. |
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| What will be the speed difference in a medium being hit with a lower frequency and a higher frequency? |
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| There won't be any difference. They will both move through the medium at the SAME speed, because frequency has no affect on propagation speed. Only characteristics of the medium will determine speed. |
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| How can a technologist adjust propagation speed? |
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| They can't, it's a constant that depends on the medium. |
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| The ability to decrease volume when pressure is applied. |
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| The ability to return to original shape after being deformed. |
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| What does velocity greatly depend on? |
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| Velocity greatly depends on compressibility (the inverse of the bulk modulus) and to a lesser degree, density. |
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| Velocity is a property of what? |
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| Velocity is a property of the medium. |
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| What is the range of comparative sound velocities in different mediums? |
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| Air > Lung > Fat > Soft Tissue > Muscle > Bone |
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| What is the propagation speed of air? |
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| What is the propagation speed of lungs? |
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| What is the propagation speed of fat? |
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| What is the propagation speed of soft tissue? |
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| What is the propagation speed of muscle? |
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| What is the propagation speed of bone? |
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| What happens to frequency and propagation speed as ultrasound moves from one medium to the next? |
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- Frequency stays constant, because 's a property of the sound source.
- Propagation speed changes as the characteristics of the medium changes. |
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What does amplitude describe when regarding sound waves?
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| Amplitude describes the magnitude of the sound wave. The units are any units of acoustic variables. So any units of pressure, temperature, density, and particle displacement. |
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| What is amplitude originally determined by? |
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| The sound source, and can be adjusted by the technologist. |
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| What happens as amplitude propagates through tissue? |
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| It steadily decreases, this is known as attenuation. |
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| What is amplitudes relation with frequency? |
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| Amplitude is independent of frequency and vice versa. |
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| When two waves interlap at the same time and place, and create a new wave with the combination of the waves. |
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| What is constructive interferance? |
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| When there is an increase in overall amplitude. |
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| What is destructive interferance? |
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| When there is a decrease in overall amplitude. |
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Power is the amount of work done by the wave per unit of time.
The unit is watt. |
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| Power is also the rate at which energy is transferred into the medium, usually in the form of heat. |
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| Can power be adjusted by the technologist? |
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| Why is it recommended to keep power setting on low? |
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| To avoid over heating tissues from energy transfer. |
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| What happens as power propagates through tissues? |
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| Similarly to amplitude, power decreases as it propagates through tissue because it transfers energy as it goes in the form of heat. |
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Intensity is related to the loudness of the sound. It is the concentration of energy in the US beam.
The units are Watt/cm^2 |
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| What is the maximum intensity for a unfocused transducer? |
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| What is the maximum intensity for a focused transducer? |
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