Medical Design Briefs - August 2024 - 9
By using piezoceramic
ultrasonic transducers,
minimally or noninvasive and
gentle treatment methods,
with improved therapy
success, can be realized.
(Credit: PI)
Therapeutic
Ultrasound:
Ther
Ult
Contactless Drug Delivery and Treatment
Enabled by Piezo Transducers
I
f an external force with changing amplitude acts on an elastic
medium such as a gas, a liquid or a solid, an undulating propagation
of pressure and density fluctuation occurs in space
and time, starting from the point where the force is applied.
This is known as sound. The frequency of sound waves ranges
from a few hertz (Hz) up to several gigahertz (see Figure 1).
Infrasound, the sound humans cannot hear, lies at frequencies
below 16 Hz. It is followed by the hearing range, which
reaches up to 20 kHz. Ultrasonic waves, which cannot be
heard, lie in the frequency range from 20 kHz to 1.6 GHz,
which equals 16 billion cycles per second. A prominent application
example in medical technology is the use of ultrasound
for diagnostic imaging techniques. In industry and research,
ultrasound is mainly used in measurement technology, where
sound waves with low power are used. The intensity of the
sound describes the power that hits a certain surface. If it exceeds
10 W/cm2, we speak of power ultrasound, which often
shows frequencies in the range of 20-800 kHz.
Medical Design Briefs, August 2024
Power Ultrasound in Medicine
Piezo ceramics generate power ultrasound by using the
piezoelectric effect to transform high-frequency electric energy
into mechanical and vice versa. The ultrasonic waves
generated by a piezoelectric transducer can be used in fluids
to generate so-called cavitation bubbles. These are created
when acoustic sound waves generate rarefaction and compression
zones with locally higher and lower material densities
in a medium. The resulting high tensile and shear forces
between the zones cause the fluid medium to be ripped
apart creating gas-filled cavities.
Depending on the frequency and sound force of the applied
ultrasonic sound waves, two different states can occur
for the cavitation: 1) a stable cavitation with small oscillating
gas bubbles; i.e., they pulsate with the rhythm of the ultrasonic
sound frequency and with that increase or decrease in size;
and 2) an instable cavitation, where such a high ultrasound
power is used that the cavitation bubbles expand so much that
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Medical Design Briefs - August 2024
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Medical Design Briefs - August 2024 - CvrFlap1
Medical Design Briefs - August 2024 - CvrFlap2
Medical Design Briefs - August 2024 - Cover1
Medical Design Briefs - August 2024 - Cover2
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