Mettler Electronics Sonicator 740 - Theory of Operation

Sonicator 740 Instruction Manual— Rev.G_06/28/12
27
Section 7—Theory of Operation
7.1 Introduction to Ultrasound
Ultrasound is a form of acoustical vibration occurring at frequencies too high to be perceived by the human
ear. The limit for the audible range is at about 20 kHz. Frequencies above this level are considered
ultrasound. The range 700 kHz to 1, 1 MHz appeared during early investigative work to be best suited to
clinical applications. Most therapeutic ultrasound devices operate at frequencies within this range. Recent
studies have been conducted utilizing a frequency of 3 MHz. Since 3 MHz allows ultrasound transmission
only 1/3 the depth of 1 MHz, it has been used for the treatment of more superficial structures.
Figures 7.1, 7.2, 7.3 and 7.4 illustrate the relative depths of penetration of 1 and 3.3 MHz. Since the body is
actually composed of a variety of tissues, the depth of penetration will depend on the amount of each tissue
in the path of the ultrasound beam. Quite frequently, the presence of bone in the ultrasound beam will be
the limiting factor in determining the actual depth to which the ultrasound beam will reach. This is best
illustrated in Figure 7.4. In the fingers and toes, ultrasound can pass around the bone to the opposite surface
of the digit. In this case, if the intensity is high enough, the patient may report heat or discomfort on the
surface opposite the ultrasound application.
012345
0
10
20
30
40
50
60
70
80
90
100
Ultrasound Remaining
Per Cent
Tissue Depth
Centimeters
3.3 MHz 1 MHz
Figure 7.1—Ultrasound Absorption, Skin
012345
0
10
20
30
40
50
60
70
80
90
100
Ultrasound Remaining
Per Cent
Tissue Depth
Centimeters
3.3 MHz 1 MHz
Figure 7.2—Ultrasound Absorption, Fat
0
1
2
3
4
5
0
10
20
30
40
50
60
70
80
90
100
Ultrasound Remaining
Percent
Tissue Depth
Centimeters
3.3 MHz 1 MHz
Figure 7.3—Ultrasound Absorption, Muscle with the Ultrasound Beam Perpendicular to the Muscle Fibers