According to the structure and scale of microfluidic chips, their modeling methods can be divided intoSystem level designandDevice level design.

System level design, also known as macro model design, specifically refers to the systematic design of inputs, outputs, and controls based on the entire chip structure as the modeling object. Common system level design methods includeModeling method、Equivalent circuit method、Direct reduction method、Lumped parameter reduction methodWait.

1. Behavioral modeling method

Behavioral modeling method refers to decomposing the entire microfluidic chip into multiple functional components and modeling each functional component. Then, the interface signal is processed using Fourier series to achieve the modeling of the entire chip. This method has problems such as over simplification and low accuracy. When designing complex microfluidic systems, if there are too many simplified parts, errors will accumulate and cannot truly reflect physical laws.

2. Equivalent circuit method

The equivalent circuit method, also known as the node analysis method, is a method that simulates the mathematical model of non electrical components using physical quantities of electrical characteristics based on the similarity between the studied object and the circuit. It represents the physical quantities of the studied problem as physical parameters such as resistance, capacitance, inductance, etc., and then constructs an "equivalent circuit" to solve it.

3. Direct reduction method

The direct reduction method uses trajectory approximation method, orthogonal decomposition method, etc. to directly reduce the partial differential equation system describing the physical phenomena of chips to an ordinary differential equation system, which is then simplified to an algebraic equation system and solved. The direct reduction method can reduce the order of more complex components to obtain simplified macro models. Due to the need to abandon some information that describes the internal physical characteristics of the chip in order to perform order reduction, there may be some deviation between the model and the real model.

4. Lumped parameter reduction method

The lumped parameter reduction method refers to the polynomial curve fitting of simulation results based on static simulation, in order to obtain a system lumped parameter macro model, such as a system lumped mass macro model, a lumped damping macro model, etc.

Device level design is a design aimed at studying the evolution law of a key link in a chip. Device level design is mainly implemented using numerical simulation methods, including finite element method, finite difference method, finite volume method, spectral method, and other numerical simulation methods.

With the help of the above methods, a microfluidic chip operation evolution model can be established using professional software or programming, in order to demonstrate, evaluate, and optimize specific solutions. Currently, the use of professional software for computer-aided design of microfluidic chips (or MEMS) is a major modeling method, with programming mainly applicable to theoretical mechanism research. Common professional software includes COMSOL Multiphysics (finite element method), CFD-ACE+(finite volume method), CoventorWare (finite element method), etc. These types of software are not only designed for MEMS design, but also for functional modules in other research fields. In addition, there are some software specifically designed for microfluidic chip design, such as IntelliSuite, MEMS Pro, TannerPro, HFSS, etc. among which,IntelliSoutNot only can it be used for optimizing chip structure design, but it also includes functions such as parameter analysis, system simulation, and packaging analysis.

Device level design follows physical laws such as mechanics, flow, and heat transfer, with high accuracy. However, due to the large computational complexity, it is generally impossible to achieve numerical simulation of the entire system. System level design is a coarse-grained method for describing the physical laws of microfluidic chip structures as a whole, with relatively low accuracy but fast computational speed. Therefore, the advantages of the above two methods can be integrated by adopting device level design in critical parts of the chip and system level design in non critical parts, forming a macro micro design method.

Macro Micro Design MethodThe basic idea is:

(1) Divide complex microfluidic systems into simple units and complex units.

(2) For simple geometric topological structures such as straight passages, storage tanks, and bends with large scales in a certain direction, analytical solutions can be obtained by modeling using methods such as variable separation or basis function superposition.

(3) For complex geometric topological structures (such as three-dimensional chaotic mixed elements), numerical simulation methods are used to solve them.

(4) Using data fitting and discretization methods to bridge between simple and complex elements. Then, the same method is used to bridge all units and solve the entire system through iterative calculations.