This article will address the topic of Acoustic radiation force, a key concept in the current context that covers various aspects of daily life. Acoustic radiation force has become a topic of growing interest due to its relevance in different areas, from science and technology to culture and society. Throughout this exploration, the many facets of Acoustic radiation force will be analyzed, from its origin and evolution to its implications and applications in the modern world. Its impact in different contexts, as well as the perspectives and debates surrounding this topic, will be examined in detail. Through an exhaustive analysis, we will seek to shed light on the importance and complexity of Acoustic radiation force today.
Acoustic radiation force (ARF) is a physical phenomenon resulting from the interaction of an acoustic wave with an obstacle placed along its path. Generally, the force exerted on the obstacle is evaluated by integrating the acoustic radiation pressure (due to the presence of the sonic wave) over its time-varying surface.
The magnitude of the force exerted by an acoustic plane wave at any given location can be calculated as:
where
is a force per unit volume, here expressed in kg/(s2cm2);
The effect of frequency on acoustic radiation force is taken into account via intensity (higher pressures are more difficult to attain at higher frequencies) and absorption (higher frequencies have a higher absorption rate). As a reference, water has an acoustic absorption of 0.002 dB/(MHz2cm).(page number?) Acoustic radiation forces on compressible particles such as bubbles are also known as Bjerknes forces, and are generated through a different mechanism, which does not require sound absorption or reflection. Acoustic radiation forces can also be controlled through sub-wavelength patterning of the surface of the object.
When a particle is exposed to an acoustic standing wave it will experience a time-averaged force known as the primary acoustic radiation force (). In a rectangular microfluidic channel with coplanar walls which acts as a resonance chamber, the incoming acoustic wave can be approximated as a resonant, standing pressure wave of the form:
.
where is the wave number.
For a compressible, spherical and micrometre-sized particle (of radius ) suspended in an inviscid fluid in a rectangular micro-channel with a 1D planar standing ultrasonic wave of wavelength , the expression for the primary radiation force (at the far-field region where )becomes then :
^McAleavey, S. A.; Nightingale, K. R.; Trahey, G. E. (June 2003). "Estimates of echo correlation and measurement bias in acoustic radiation force impulse imaging". IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control. 50 (6): 631–641. doi:10.1109/tuffc.2003.1209550. PMID12839175. S2CID12815598. (subscription required)