Q15Micro and Smart System Technology

Coupled Electro-Mechanics and Capillary Electrophoresis

A coupled electro-mechanical system in MEMS refers to any microstructure in which electrical and mechanical energy domains interact bidirectionally through a coupling field (commonly electrostatic, piezoelectric, or piezoresistive), such that an electrical input (voltage or charge) produces a mechanical output (displacement or force), and conversely a mechanical input (displacement or strain) produces an electrical output (capacitance change or induced charge) - this bidirectional coupling is the fundamental operating principle underlying most MEMS actuators and sensors, and accurate modeling requires solving the electrical and mechanical domain equations simultaneously (coupled-field analysis) rather than independently, since the mechanical deformation itself alters the electrical field distribution (and hence the force), which in turn affects the deformation, in a mutually dependent feedback loop.

A canonical example is the electrostatically-actuated parallel-plate microstructure, where applying a voltage V between a fixed and a movable (compliant, spring-suspended) electrode generates an attractive electrostatic force proportional to V-squared and inversely proportional to the square of the gap, causing the movable electrode to deflect; this deflection changes the gap, which changes the electrostatic force for the same applied voltage, requiring the coupled system of the mechanical spring equation (force balance between electrostatic force and spring restoring force) and the electrical field equation to be solved together - a coupling that famously produces the 'pull-in' instability phenomenon (where, beyond a critical voltage, no stable equilibrium deflection exists and the movable electrode snaps down to contact the fixed electrode) central to the design of many electrostatic MEMS actuators and switches.

Capillary Electrophoresis

Capillary electrophoresis (CE) is a microfluidic separation technique used in lab-on-chip and biomedical MEMS devices to separate charged molecular species (such as DNA fragments, proteins, or ions) based on their differing electrophoretic mobility when subjected to an electric field along a narrow capillary channel. A sample is introduced into one end of a micromachined capillary channel filled with a buffer electrolyte, and a high-voltage DC field is applied along the channel's length, causing charged analyte molecules to migrate at velocities determined by their charge-to-size ratio, so different species separate into distinct, spatially resolved bands as they travel along the channel, which are then detected (commonly by optical fluorescence or UV absorbance) as they pass a fixed detection point near the channel's outlet.

Miniaturized, MEMS-based CE devices additionally exploit electro-osmotic flow (the bulk fluid motion induced by the electric field acting on the electric double layer at the channel wall) alongside electrophoretic migration to achieve fast, efficient separation within a very small, integrated microfluidic chip footprint, making capillary electrophoresis a key enabling separation technique for portable, point-of-care diagnostic lab-on-chip systems, DNA sequencing microsystems, and other biomedical microsystem applications requiring rapid, high-resolution separation of small sample volumes without the bulky equipment and large reagent volumes needed by conventional bench-scale electrophoresis apparatus.