![]() ![]() Ultrasound-operated tools make this minimally- or non-invasive surgery technique, which is often also called incisionless, possible today. It is possible to selectively remove certain tissue areas with the help of focused ultrasound – and with a completely contactless procedure (Figure 3). Further application examples using therapeutic ultrasound are cartilage therapy, the administration of drugs through the skin and cosmetic treatments. These include methods which use focused, but also unfocused, ultrasound – for example tissue ablation, targeted drug delivery, the ultrasound-assisted dissolution of blood clots (thrombolysis), or the fragmentation of kidney stones (lithotripsy). By using piezoceramic ultrasonic transducers, minimally- or non-invasive and gentle treatment methods, with improved therapy success, can be realized. In this case, therapeutic ultrasound refers to a group of methods in which ultrasound is not only a means of diagnosis but also the core element of therapy itself. Ultrasound opens new and innovative therapeutic possibilities that improve or even substitute many established procedures: Minimally invasive, and gentle treatment methods with improved therapy success and fewer side effects, can be realized using piezo components. In addition to cavitation, power ultrasound can cause changes in material or even destroy it, which is used, for example, in medical applications, but also in industrial material processing or ultrasonic cleaning. For example, the stable cavitation is applied in medical imaging when gas-filled microspheres are used as an ultrasound contrast medium. These physical effects of cavitation are used for various medical applications. © PI | Figure 2: Cavitation in liquids caused by ultrasonic waves. In this case, very high forces and pressures are released in the form of shock waves and extremely high temperatures of several 1,000☌, as well as flashes of light can occur temporarily (Figure 2). The resulting high tensile and shear forces between the zones cause the fluid medium to be ripped apart creating gas-filled cavities.ĭepending 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 they finally implode. These are created when acoustic sound waves generate rarefaction and compression zones with locally higher and lower material densities in a medium. The ultrasonic waves generated by a piezoelectric transducer can be used in fluids to generate so-called cavitation bubbles. Piezo ceramics generate power ultrasound by using the piezoelectric effect to transform high frequency electric energy into mechanical and vice versa. If it exceeds 10W/cm 2, we speak of power ultrasound, which often shows frequencies in the range of 20kHz to 800kHz. The intensity of the sound describes the power that hits a certain surface. ![]() In industry and research, ultrasound is mainly used in measurement technology, where sound waves with low power are used. A prominent application example in medical technology is the use of ultrasound for diagnostic imaging techniques. Ultrasonic waves, which cannot be heard, lie in the frequency range from 20kHz to 1.6GHz, which equals 16 billion cycles per second. It’s followed by the hearing range, which reaches up to 20kHz. Infrasound, the sound humans cannot hear, lies at frequencies below 16Hz. © PI | Figure 1: Frequency range of sound.
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