Amplitude/Intensity
Height of wave
Function of source (transducer)
Major determinant of power output
Intensity is proportional to amplitude
Intensity = power/area (units = mw/cm2)
Theoretical concern of bioeffects of US mediated by amplitude/power
Physics of sound
Speed of Sound
- Speed of sound in ‘norm‘ tissue:
c = 1540 m/s
- Typical wavelength (f = 1..40 MHz):
λ = c / f λ = 1.54 .. 0.04 mm
- Strong absorption (frequency dependent):
0.5..1.0 dB/cm/MHz
Target Characteristics
- Echogenic (=bright)
- Large reflection component
- Waves returning to transducer
- Anechoic or Hypoechoic (=dark)
- Large attenuation component
- Waves not returning to transducer
- Mixed echogenicity
Transducer Principles: What is Piezoelectric/ Piezoelectricity?
The transducer contains a special type of crystal with in it named piezoelectric crystal.
- In a electric field the alignment of dipole with in the crystal changes, which in turn causes the crystal to change the shape.
- If the voltage is applied in a sudden burst the crystal vibrates and generates sound.
- Piezo-electric crystal
- Converts electric signals to mechanical & vice versa
- Transmits pulses of sound into tissue and listens for echoes
- Most of the time is spent listening for echoes
- Piezoelectricity means pressure electricity, which is used to describe the coupling between a materials mechanical and electrical behaviors.
- Piezoelectric Effect
- when a piezoelectric material is squeezed or stretched, electric charge is generated on its surface.
- Inverse Piezoelectric Effect
- Conversely, when subjected to a electric voltage input, a piezoelectric material mechanically deforms.