I. Principle of Ultrasonic Extraction of Traditional Chinese Medicine: Dominated by the "Cavitation Effect"
The mechanism of ultrasonic extraction of traditional Chinese medicine originates from the cavitation effect induced by ultrasound in a liquid medium, which is the key distinction from traditional extraction methods such as decoction and reflux extraction. When ultrasound (typically at a frequency of 20 kHz) acts on a mixture of traditional Chinese medicine and solvent, it generates a large number of microscopic bubbles ("cavitation bubbles") with diameters of several micrometers within the liquid. These bubbles continuously expand and compress in response to the vibration of the ultrasound waves. When the pressure reaches a critical value, the bubbles collapse instantaneously, releasing intense energy and shockwave pressure. This extreme environment rapidly disrupts the structure of the cell walls of the Chinese herbal material, such as cellulose and hemicellulose, breaking down the cellular "barrier" and directly exposing the active components (e.g., alkaloids, flavonoids, saponins) within the cells to the solvent. This significantly shortens the pathway for component dissolution. The collapse of the bubbles also drives the surrounding liquid to form high-speed microflows, producing intense stirring and impact effects. This prevents the formation of a "concentration difference barrier" between the solvent and the surface of the Chinese herbal particles—a phenomenon in traditional extraction where dissolved active components on the surface create a high-concentration layer that hinders further dissolution of internal components. The microflow disturbance from ultrasound rapidly removes the high-concentration solution from the surface, allowing fresh solvent to continuously come into contact with the interior of the herbal material, thereby enhancing dissolution efficiency.

II. Auxiliary Effects: Synergy of Mechanical Vibration and Thermal Effects

In addition to the cavitation effect, the mechanical vibration and thermal effects of ultrasound also contribute to improving extraction efficiency.

Physical Fragmentation via Mechanical Vibration: During propagation, ultrasound generates periodic mechanical vibrations on the solid particles of the Chinese herbal material, akin to "microscopic grinding." These vibrations can create fissures within the particles and even disperse larger particles into finer powder (without causing excessive fragmentation that would lead to filtration difficulties), further increasing the contact area between the herbal material and the solvent. This provides more "pathways" for the dissolution of active components.

Regulation via Mild Thermal Effects: As ultrasound propagates through the medium, part of its energy is converted into heat, causing a slight increase in system temperature (typically controllable between 40–60°C). This gentle temperature rise not only enhances the movement rate of solvent molecules, improving their penetration and dissolution capabilities, but also avoids the destruction of heat-sensitive active components (e.g., polysaccharides, volatile oils) that can occur in traditional high-temperature decoction methods (e.g., above 100°C). Thus, it balances efficiency with the stability of components.