Researcher Asier Marzo, affiliated to BIG, is the main author in the recent paper published in Nature Communications “Holographic Acoustic Elements for Manipulation of Levitated Particles”. The research is a collaboration between Bristol University (BIG and uNDT groups), Sussex University (Interact Lab), Ultrahaptics and the Public University of Navarre (TAIPECO group).
In the paper, a method to create acoustic holograms with a phased-array of ultrasonic transducers is presented. These holograms are tridimensional acoustic fields that can be emitted even from a flat surface. Unless the conventional light-holograms, the acoustic holograms cannot be seen but they exert considerable forces on physical objects and can pass through water and human tissue. This enables the creation of tractor beams, tangible displays of levitated pixels or the manipulation of particles inside the human body.
Three holograms were found to be optimum for levitation. The first is an acoustic field that resembles a pair of fingers that pinch the particle. The second is an acoustic tornado that drags the objects to its eye. And the third could be described as a high-intensity cage that surrounds the objects from all directions.
An ultrasonic phased-array is composed of several loudspeakers denominated transducers. Each transducer plays a sinusoidal wave of the same frequency and amplitude but with slightly different offsets (phase-delays). The waves are emitted from a two-dimensional surface yet their interference patterns creates a tri-dimensional shape above.
A canon is a musical composition in which the same melody is played by several instruments but starting at different times. The composition is carefully engineered to create beautiful harmonies at every instant that result from the combination of the same melody played at different points. Similarly, our computer algorithm calculates the phase-delays for each transducer so that the listener, the particle in our case, gets surrounded by the desired acoustic levels.
The authors of the paper are Asier Marzo, Sue Ann Seah, Bruce W. Drinkwater, Deepak Ranjan Sahoo, Benjamin Long and Sriram Subramanian.