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Video: The Perfect Wave
Microfluidic components are the key to many applications, such as lab-on-a-chip sensors for medical diagnostics or cost-effective flow sensors. When developing these products, manufacturers are faced with the challenge of effectively transporting or mixing liquids in the smallest of spaces.
The mechanical properties of liquids within geometries with dimensions of a few 100 µm or smaller can differ from the properties at the macro level. This is due to the fact that the ratio of the liquid surface to its volume is very large with these small dimensions and therefore factors such as surface tension, heat transport and viscosity have a significant influence.
Researchers at the SUNY College of Nanoscale Science and Engineering (CNSE) in Albany, USA, are examining the use of surface acoustic waves (SAWs) as drives for liquid flows. Since the speed of sound in substrates and liquids is different, dispersion leads to the sound wave being introduced into the liquid at a certain angle. The damping of this pressure wave causes an acoustically induced flow (acoustic streaming, at the end of the article you will find an info box about its origin and the effect of surface acoustic waves).
Simulation simplifies design decisions
To effectively develop such devices, understanding the acoustic properties of the piezoelectric material used to create SAWs is a critical first step. In this context, numerical simulation is a powerful tool for e.g. B. to determine the effects of different electrode metals and geometries on acoustic wave propagation. The insights can be used to make better design decisions.
Graham Potter, research associate at CNSE, is investigating the use of various piezoelectric materials for applications using acoustically induced flow. The CNSE is part of a unique university-industrial partnership with Sematech, a global industrial semiconductor research consortium that addresses the challenges of modern manufacturing technologies.
Potter works at CNSE in Professor James Castracane's laboratory. His team designs components that are made of piezoelectric substrates, such as. B. lithium niobate (LiNbO3) with a Y-turned cut at a rotation angle of 128 °. “The angle of the cut is determined in relation to the crystalline axes. This particular orientation has traditionally been used in bandpass filters due to the existence of a Rayleigh wave. The Rayleigh wave is a type of SAW with strong electromechanical coupling that propagates in a single direction along the wafer surface,”explains Potter.
AC voltage generates harmonic vibrations
“For this reason, many studies in which this material was used for acoustically induced flow were limited to linear components with one-way orientation. We are interested in the design of circular or focusing component architectures (see Figure 1A). Therefore, and because of the anisotropy of the crystal, we needed a better understanding of the wave characteristics across the entire surface,”continued Potter. In the experimental setup used, an array of gold electrodes, also known as an interdigitated transducer (IDT), was created on a piezoelectric substrate. An AC voltage is applied to the electrodes, which excites the surface to harmonic vibrations due to the inverse piezoelectric effect,which in turn creates a SAW. "By varying the orientation of these test components across the surface (see Figure 1B), the resonance frequency and acoustic flow response can be determined as a function of the direction of propagation," explains Potter. These components can be used for the test of the acoustic flow effect with selected orientations on the surface and for the experimental validation of simulation results. The 20 µm segment shown corresponds to the size of the modeled area.These components can be used for the test of the acoustic flow effect with selected orientations on the surface and for the experimental validation of simulation results. The 20 µm segment shown corresponds to the size of the modeled area.These components can be used for the test of the acoustic flow effect with selected orientations on the surface and for the experimental validation of simulation results. The 20 µm segment shown corresponds to the size of the modeled area.
Content of the article:
- Page 1: The perfect wave
- Page 2: Understand problems faster thanks to simulation
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