Mettler Electronics Sonicator 740, Инструкция по эксплуатации

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Mettler Electronics Corp. — Rev.G_06/28/12
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Ult
ras
ound Rem
a
ining
P
e
r Cent
Tissue Depth
Centimeters
3.3 MHz 1 MHz
Figure 7.4—Ultrasound Absorption, Bone
The physics of ultrasound and audible sound are similar, except for frequency. Both travel as longitudinal
waves through a conducting medium. Ultrasound waves can be propagated in a gaseous, liquid, or solid
medium, but not in a vacuum.
High frequency sound waves are formed by areas of compression
and rarefaction of the molecules. Ultrasound exhibits certain
beaming properties and can be reflected, refracted, scattered or
absorbed. In passing through media, it is attenuated and the
absorbed energy is transformed into heat. The attenuation
coefficient for longitudinal waves in liquid and soft tissues is high,
producing the phenomenon at bone surfaces known as selective
heating.
Figure 7.5—High Frequency Sound Waves
Clinical ultrasound is produced through the reverse piezoelectric effect. Electricity is carried from a radio
frequency source to an electrode in contact with the surface of a specially cut crystal. The electrical charges
applied to the crystal surface produce mechanical vibrations, or the so-called reverse piezoelectric effect.
The crystal may be natural or synthetic and may be salt, quartz, polycrystalline or ceramic. When this crystal
is in resonance with the driving oscillator, optimum conversion from electrical to mechanical energy is
achieved. The Sonicator 740 uses a barium titanate ceramic for all of its transducers.
Ultrasonic power is expressed in watts (W), or watts per square centimeter (W/cm²). Average intensity
(W/cm²) is obtained by measuring the total output of the applicator (in watts) and then dividing it by the
size of the effective radiating area of the applicator. The effective radiating area is different from the overall
dimension of the applicator face.
Ultrasound waves need a medium for their transmission and that is accomplished by using a proper
coupling agent. This coupling layer between the transducer and body surface will assist in the propagation
of the mechanical vibrations and prevent loss of transmission.
Once the coupling agent is applied to the body surface, the applicator placed in contact, and the desired
output selected in total watts, or watts per square centimeter, the technique of application is by means of
circular or stroking movement. In the circular method, the sound head of the applicator is moved in slow
and circular overlapping movements. In the stroking, or “paintbrush” method, slow back and forth strokes
are used, again with slight overlapping. Motion with either technique should be slow enough to insure
proper energy absorption yet fast enough to eliminate excessive amounts of absorption that could produce
periosteal pain. Some references recommend that the treatment area covered by this moving technique be
two to three times the effective radiating area of the transducer for every five minutes of exposure.
Compression
Rarefaction