Mooron's winter project
Thanx Bob.... but... what music will drive him crazy???
Abba at ultra sonic???
CM
"Bob Crantz" wrote in message
nk.net...
It's all pure crap.
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Attenuation
Most engineers and scientists working in the ultrasound characterize
attenuation as the "half-value layer," or the "half-power distance." These
terms refer to the distance that ultrasound will travel in a particular
tissue before its amplitude or energy is attenuated to half its original
value.
Attenuation
Divergence of the wavefront
Elastic reflection of wave energy
Elastic scattering of wave energy
Absorption of wave energy
Ultrasound Attenuation
Material Half-power distance (cm)
Water 380
Blood 15
Soft tissue 5 to 1
except muscle 1 to 0.6
Bone 0.7 to 0.2
Air 0.08
Lung 0.05
Attenuation in Tissue
Ultrasound energy can travel in water 380 cm before its power decreases to
half of its original value.
Attenuation is greater in soft tissue, and even greater in muscle.
Thus, a thick muscled chest wall will offer a significant obstacle to the
transmission of ultrasound.
Attenuation in Tissue
Non-muscle tissue such as fat does not attenuate acoustic energy as much.
The halfpower distance for bone is still less than muscle, which explains
why bone is such a barrier to ultrasound.
Air and lung tissue have extremely short half-power distances and
represent severe obstacles to the transmission of acoustic energy.
Attenuation
As a general rule, the attenuation coefficient is doubled when the
frequency is doubled.
Beam Forming
Ultrasound beam can be shaped with lenses
Ultrasound transducers (and other antennae) emit energy in three fields
Near field (Fresnel region)
Focused field
Far field (Fraunhofer region)
Diagnostic scanning modes
Usually pulse-echo mode
Further classification depends on how information is displayed
A mode
Amplitude of pressure wave displayed with regard to position
Thickness of cornea
B mode
Amplitudes are represented as pixels (images)
Brightness of pixels - signal strength (Brightness mode)
256 brightness levels/256 gray scales
Shift beam after each transmission to get 2D image
M mode
M (motion) mode
Beam held in fixed position
Measure very fast motions
Heart valves
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Here's typically ultrasound numbers:
In .08cm the ultrasound in air is 1/2 power. It looses 1/2 power every
.031 inches or 25 dB per foot due to spreading. The claims Joe pointed out
nearly match RB's claims about his boat or stereo.
Glory!
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