
1-31
Chapter 1 Safety
Terms and Symbols Related to Acoustic Output and Measurement
The terms and symbols used in the acoustic output tables are dened in the following paragraphs.
A
aprt
-12dB OUTPUT BEAM AREA, ultrasonic beam area induced by -12dB output
beam size (unit: cm
2
)
d
eq
at max. I
pi
EQUIVALENT BEAM DIAMETER, the acoustic beam’s diameter at the location
where the PULSE-INTENSITY INTEGRAL is maximal, expressed as an equivalent
beam area (unit: cm)
d
eq(
z
b)
EQUIVALENT BEAM DIAMETER, the acoustic beam’s diameter at Zb location,
expressed as an equivalent beam area (unit: cm
2
)
Dim of A
aprt
-12dB OUTPUT BEAM DIMENSIONS, the dimensions of an ultrasound
beam (whose pulse beam width is -12dB) from a specic direction that is
perpendicular to the transducer output plane and the beam alignment axis
(unit: cm)
f
awf
ACOUSTIC WORKING FREQUENCY, the arithmetic average of f1 and f2 that are
farthest from each other among the frequencies of the pressure spectrum of
the acoustic signal whose amplitudes are lower than the peak amplitude, i.e.
maximum amplitude, by 3dB (unit: MHz)
Focal Length The focal length in a direction parallel to the beam alignment axis in the dened
operational state of the ultrasound system (unit: cm).
I
pa,
a at max. MI The average attenuated pulse strength at the location where Mechanical Index
(MI) is maximal (unit: W/cm
2
)
I
ta,
a
(z)
Attenuated time average strength at a specic focal length (z) (unit: mW/cm
2
)
MI MECHANICAL INDEX, a variable representing potential cavitations within the
human body (unit: N/A)
P OUTPUT POWER, time average power of an ultrasonic transducer’s emissions
into a free eld through specied media such as water (unit: mW)
P
α
(z)
ATTENUATED OUTPUT POWER, the power of ultrasonic output calculated at a
specic distance from the transducer after attenuation occurs (unit: mW)
P
r,α
ATTENUATED PEAK-RAREFACTIONAL ACOUSTIC PRESSURE, the peak
rarefactional acoustic pressure calculated at a specic distance after attenuation
occurs (unit: MPa)
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