Piezoelectric actuators are commonly used in microfluidic systems to control and manipulate fluids at a small scale. These actuators utilize the piezoelectric effect, which is the ability of certain materials to generate an electric charge in response to applied mechanical stress or to deform in response to an applied electric field. In microfluidic systems, piezoelectric actuators are used to generate mechanical vibrations, deformations, or displacements that can manipulate fluids in various ways. Here's how they work:
Mechanical Deformation: Piezoelectric actuators are made from materials that exhibit the piezoelectric effect, such as certain types of ceramics and crystals (e.g., lead zirconate titanate or PZT). When a voltage is applied to the piezoelectric material, it undergoes mechanical deformation due to the induced electric field. This deformation can be in the form of expansion, contraction, bending, or vibration, depending on the design of the actuator.
Vibration and Oscillation: In microfluidic systems, one common application of piezoelectric actuators is generating mechanical vibrations or oscillations. These vibrations can be transferred to the microfluidic device or chamber, causing fluid manipulation. For example, by attaching a piezoelectric actuator to the substrate of a microfluidic channel, the vibrations can lead to mixing, particle trapping, droplet generation, or fluid pumping.
Valve and Pump Control: Piezoelectric actuators can be integrated into microfluidic valves and pumps. When the actuator deforms due to applied voltage, it can physically close or open a valve, regulating the flow of fluids. Similarly, the deformation of an actuator can compress a fluidic chamber, acting as a pump and displacing fluid. This mechanism is particularly useful for creating miniaturized and precise fluidic systems.
Particle Manipulation: Microfluidic systems often involve manipulating particles, cells, or droplets. Piezoelectric actuators can be employed to create acoustic waves or vibrations, which in turn generate acoustic streaming or standing waves. These phenomena can help trap, sort, and move particles within the fluidic channels, enabling precise particle manipulation.
Mixing and Dispersion: Vibrations generated by piezoelectric actuators can induce turbulence and flow patterns in microfluidic channels. This promotes efficient mixing and dispersion of different fluids or reagents, which is crucial in various applications such as chemical reactions, assays, and sample preparation.
Flow Focusing and Droplet Formation: By strategically placing piezoelectric actuators near fluidic junctions or constrictions, the generated vibrations can assist in precise control of fluid flow. This is used, for example, in flow-focusing techniques to create uniform droplets of desired sizes for applications in drug encapsulation, biological assays, and more.
In summary, piezoelectric actuators in microfluidic systems provide a versatile means of controlling fluid manipulation through mechanical deformations and vibrations. Their compact size, rapid response, and precise control make them valuable tools for researchers and engineers working on various applications in the field of microfluidics.