FLOATING on SOUND WAVES with ACOUSTIC LEVITATION Sound Is a Formidable Power
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ACOUSTIC LEVITATION | CONTAINERLESS PROCESSING Argonne National Laboratory, IL, USA FLOATING ON SOUND WAVES WITH ACOUSTIC LEVITATION Sound is a formidable power. Under the right conditions, it can manipulate and change the state of matter. The pharmaceutical industry is turning to acoustic levitation to address the ever-present need for high-quality medicine delivery systems, especially as technology for treating patients expands and becomes more customized. BY LAURA BOWEN At Argonne National Laboratory, efficient production and delivery part of the United States Department of pharmaceutical products. In of Energy, Kamlesh Suthar and a controlled environment, the Chris Benmore are hard at work levitator provides a containerless and implementing acoustic technology contaminant-free space for creating to transform the manufacturing of high-purity amorphous chemicals. pharmaceuticals. The team is turning According to the team at Argonne, to multiphysics simulation to improve “Many amorphous drugs are mixed their acoustic levitator—a device that with a polymer to help keep them generates sound waves to lift and stable for a long time.” At the manipulate matter. midpoint of each node of the standing waves in Suthar’s acoustic levitator, ACOUSTICALLY MANUFACTURED molecules gather into droplets and FIGURE 1. The acoustic levitator creates PHARMACEUTICALS form small spheres (see Figure 1). The standing sound waves that allow droplets By mixing chemicals while they droplets float a few millimeters apart of liquid to levitate. The levitator is made of spin and float in the air, Argonne and gently rotate, suspended, between two transducers, each coated with a thin is working to facilitate more two small piezoelectric transducers. layer of foam to control the wave pattern. FIGURE 2. The initial distribution of the particles at t=.001 (left). Particles gather into droplets at t=0.75 and photograph of physical particle distribution (right). 44 | COMSOL NEWS | 2014 ACOUSTIC LEVITATION | CONTAINERLESS PROCESSING A magnitude and frequency slightly above the audible range, 160 dB and 22 KHz, generates standing acoustic waves with pockets of high-pressure zones. The transducers convert electrical energy into acoustic pressure. The method set in place by Suthar and Benmore is a powerful technique for developing medicine. It is easier for human bodies to absorb and process amorphous chemicals because they are more soluble and bioavailable than when in crystalline form. THE LIFTING POWER OF ACOUSTOPHORETIC FORCE Designing the geometry just right to control the movement of the particles was crucial to the function FIGURE 3. Regular sound pressure level generated due to a standing pressure wave at of the levitator. In this experiment, 22 KHz frequency (left) and pressure pockets with alternative pressure value (right). several counterbalancing forces work together to create a phenomenon that allows the particles to float find a foam geometry that allowed droplets are pushed to the center and in a controlled way (see Figure 2). them to control how individual levitate due to the balancing forces The acoustophoretic force, particle- droplets would form. In addition, involved.” particle interaction, drag, gravity, and they considered how changes to The researchers at Argonne surface tension of the droplets need the viscosity and surface tension can solidified their design with the help of to be taken into account. Specific affect their shape. The interference multiphysics simulation. As the scientists patterns of Gaussian profile foam creates droplet structures that continue to hone the designs of their made of polystyrene were designed to Suthar mapped with a fluid structure acoustic levitators, the possibilities for remove any unwanted acoustic waves interaction (FSI) simulation. He innovation are infinite. Pharmaceutical generated by the transducers and considered all of the relevant effects developers will be able to control the act as a filter along the edge of each using the CFD Module and level set concentration, droplet size, and amount one, creating a well-defined standing method, a numerical way to keep of each chemical in medicine. The wave that reflects evenly, with little track of interfaces between different discoveries that Argonne is making have interference. media during the simulation. Using wide applications in the global medical These parameters cause the the level set method to control the community. This is especially true where particles to arrange vertically, then shape of the droplets at various shifts new resources and machinery could rapidly form into droplets. The in acoustic modes helped Suthar to mean truly life-changing advances for droplets stay in the desired vertical achieve a spherical shape and control patients. n position because they are constantly the way the droplets interacted. moving horizontally. When the researchers ran the experiment to verify their design, HOW ACOUSTIC SIMULATION STACKS they discovered that the results of UP AGAINST EXPERIMENTS the simulation were consistent with The team created a COMSOL Multiphysics® the behavior of the droplets in the simulation to verify their synchrotron- high-speed photographs that they based x-ray experiments at APS, the took at APS. The simulation results Advanced Photon Source, a facility showing the acoustic field distribution that holds the brightest storage ring- (see Figure 3) were also similar to the generated x-ray beams in the western experimental results. hemisphere. They used the Acoustics As Suthar explains, “With the Module and Particle Tracing Module, constructive interference of pressure add-ons to COMSOL. They first waves, we get a standing pressure considered the frequency and material wave with positive and negative properties of the piezoelectric pressure pockets. Within these transducers and any thermal effects pockets, the sound reaches roughly The Argonne team, from left to right: that might impact the levitator. They the level of water droplet levitation. Patric Den Hartog, Kamlesh Suthar, and then used a trial-and-error method to So if you sprinkle water mist, the Chris Benmore. COMSOL NEWS | 2014 | 45.