NDAP Electrode Driving for Digital Microfluidic Droplet Velocity
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Solution Overview
Problem
Digital microfluidic systems face limitations in droplet transportation velocity, which is crucial for high-throughput applications like cell sorting and drug screening, due to constraints in actuation voltage and electrode design, leading to compromised reliability and chip lifetime.
Innovation Solution
The introduction of a control-engaged electrode-driving method, specifically the Natural Discharge after Pulse (NDAP) technique, which involves a sequence of voltages and pulses to optimize droplet movement by managing the electric field and reducing RMS voltage, combined with Cooperative Electrodes (CE) for real-time feedback and efficient droplet positioning.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the actuation voltage is increased to enhance droplet transportation velocity, then the droplet velocity is improved, but the chip lifetime is compromised due to dielectric breakdown
Solution Approach 1:
The patent applies periodic action by using pulsed DC voltage sequences instead of continuous voltage application. The electrode voltage is cycled through specific patterns (e.g., 0V-15V-0V-15V) to create intermittent electric fields that propel droplets while allowing dielectric recovery, thereby reducing cumulative stress and extending chip lifetime while maintaining high droplet velocity
Solution Approach 2:
The patent changes the voltage parameters by introducing time-dependent voltage sequences rather than static voltage levels. The voltage magnitude and duration are optimized (e.g., 15V for 100ms, then 0V for 100ms) to achieve the minimum necessary actuation force for high velocity while limiting peak stress on the dielectric layer, thus resolving the contradiction between speed and reliability
2Speed
If the actuation voltage is increased to accelerate droplet movement, then the droplet velocity is improved, but the cost of electronics increases due to voltage affordability constraints
Solution Approach 1:
The patent uses periodic voltage pulsing to achieve high droplet velocity without requiring continuously high voltage supply. The intermittent nature of the voltage sequence (on for 100ms, off for 100ms) allows the use of lower-voltage, lower-cost electronics while still achieving the desired acceleration and maintenance of droplet speed through repeated cycles
3Speed
If DC voltage is used to maintain droplet movement, then the droplet velocity is improved, but the RMS voltage remains high causing dielectric breakdown
Solution Approach 1:
The patent replaces continuous DC voltage with periodic pulsed DC sequences. The voltage is applied only during specific time windows (e.g., 100ms on, 100ms off), which reduces the RMS voltage by a factor of √2 compared to continuous application at the same peak voltage. This periodic action maintains droplet velocity while significantly reducing energy loss and dielectric stress
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enhances droplet transportation velocity while extending the electrode lifetime, achieving higher average velocities and longer device durability compared to conventional methods, with NDAP+CE demonstrating a 26.8% to 49.5% increase in velocity and potentially tripling electrode lifespan.
Implementation Method 1
Under the principle of electrowetting-on-dielectric (EWOD), vdroplet is determined by the following parameters: (1) surface roughness and hydrophobicity of the fabricated chip; (2) hydro-dynamics of droplets that can be chemical reagents- or biological species with very different compositions; (3) strength of the electric field for surface-tension modulation
Implementation Method 2
A few attempts have been made to address the problems based on hardware. One hardware solution is using the co-planar electrodes as a top-plate-less DMF system to reduce the viscous drag forces between the liquid-solid interfaces
Implementation Method 3
viscous mediums causing drag forces that increase the power required to manipulate the droplets
Data Source
AI summary
According to one aspect of the present disclosure, a control-engaged electrode-driving method for droplet actuation is provided. The method includes, a first voltage is provided to a first electrode for licking off a droplet. A second voltage is naturally discharged to a third voltage for maintaining a droplet movement. A fourth voltage is provided to the first electrode for accelerating the droplet. Naturally discharging from the second voltage to the third voltage and providing the fourth voltage to the first electrode are repeated. The first voltage is provided to a second electrode when a centroid of the droplet reaching a centroid of the first electrode. Naturally discharging from the second voltage to the third voltage and providing the fourth voltage to the second electrode are repeated.