Dielectrophoretic Force in Practice
Dielectrophoresis describes the motion of a polarizable particle in a nonuniform electric field. The particle does not need a net charge. The field induces dipoles inside the particle and the surrounding medium. When the field strength changes with position, the dipole feels a net force. This effect is useful in microfluidics, lab on chip devices, cell sorting, particle trapping, and sensor design.
Why Frequency Matters
The response depends on the complex permittivity of the particle and medium. Complex permittivity includes dielectric storage and electrical loss. Conductivity becomes important when frequency is low. At higher frequency, permittivity often dominates. The Clausius Mossotti factor combines these effects into one contrast term. Its real part decides the direction of motion. Positive values pull particles toward stronger fields. Negative values push particles away from stronger fields.
Important Input Choices
Radius has a cubic effect on force. A small change in particle size can cause a large change in force. Medium permittivity also scales the answer directly. The gradient of the squared electric field is the main field term. It is not the same as electric field alone. Sharp electrode edges, small gaps, and high voltage can create large gradients. The calculator lets you enter this gradient directly or estimate it from field and length scale.
Interpreting Results
The signed force shows direction along the chosen gradient axis. The magnitude shows strength without direction. The Stokes velocity estimate assumes creeping flow around a spherical particle. It is most useful for small particles moving slowly in a Newtonian liquid. Real devices may need correction for walls, Brownian motion, heating, electrode polarization, and non spherical shapes.
Good Modeling Habits
Use measured material values when possible. Conductivity and permittivity can change with temperature, buffer concentration, and particle composition. Treat estimated gradients as early design values, not final verification. Compare several frequencies to find positive, negative, or near zero DEP behavior. A near zero real Clausius Mossotti factor may mark a crossover region. Use exports to document assumptions and repeat tests. For best results, record electrode spacing, voltage waveform, buffer conductivity, and temperature. These details make comparisons fair. They also help you rebuild the same DEP condition later during testing, validation, reporting, or design review.