Capacitive Droplet Detection in Digital Microfluidic Devices

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

Existing digital microfluidic devices face challenges in detecting droplet positions without substantial modifications to the second substrate or addition of complex circuitry at every pixel, particularly in active matrix electrowetting on dielectric (EWoD) devices, due to the small size of droplets and lack of contrast with the surrounding oil, which complicates optical confirmation and increases fabrication and driver costs.

Innovation Solution

A digital microfluidic device with capacitance measuring means integrated into the source lines to determine the presence or absence of fluid droplets between the first and second electrodes, allowing for electrical detection without additional circuitry at every pixel, using a capacitor connected to the source line to measure the voltage drop across the capacitor and apply an alternating voltage to the second electrode.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If capacitance measuring means is added to detect droplet position, then measurement precision is improved, but device complexity increases

Engineering Contradiction:

Improvedroplet position detectionVSAvoidcircuitry complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The source lines are designed to serve dual functions: driving the first electrodes during normal operation and measuring capacitance during sensing operations. This eliminates the need for separate sensing circuitry at each pixel, reducing device complexity while maintaining measurement precision through the integrated capacitance measuring means.

Inventive Principle:

Principle #6Universality (Multi-functionality)

2Measurement precision

If TFT array is added to second substrate for droplet detection, then measurement precision is improved, but manufacturing precision requirements increase

Engineering Contradiction:

Improvedroplet position detectionVSAvoidalignment precision

Core Design Contradiction:

Measurement precisionVSManufacturing precision

Solution Approach 1:

The sensing function is extracted from the second substrate and implemented through the existing source lines and capacitance measuring means on the first substrate. This eliminates the need for a separate TFT array on the second substrate, thereby removing the alignment precision requirements between two substrates while maintaining droplet detection capability.

Inventive Principle:

Principle #2Taking out (Extraction)

3Measurement precision

If optical detection method is used to confirm droplet position, then measurement precision is improved, but device complexity increases

Engineering Contradiction:

Improvedroplet position detectionVSAvoidoptical system complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The optical detection system is replaced with an electrical sensing system using capacitance measurement. The source lines and capacitance measuring means provide electrical detection of droplet positions, eliminating the need for optical components, light sources, and imaging systems while achieving comparable or superior measurement precision.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

4Measurement precision

If additional circuitry is added at every pixel for sensing, then measurement precision is improved, but ease of manufacture decreases

Engineering Contradiction:

Improvedroplet position detectionVSAvoidfabrication ease

Core Design Contradiction:

Measurement precisionVSEase of manufacture

Solution Approach 1:

Inventive Principle:

Principle #6Universality (Multi-functionality)

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

Enables effective droplet position detection in digital microfluidic devices without the need for extensive modifications to the second substrate or additional circuitry, reducing fabrication and driver costs while maintaining accurate droplet positioning and movement control.

Implementation Method 1

at least one source line is provided with capacitance measuring means arranged to measure the capacitance between at least one of the first electrodes connected thereto and the at least one second electrode, and thereby determine the present or absence of a fluid droplet

Methodology Applied

Scientific EffectCapacitance: Capacitance

Implementation Method 2

U.S. Pat. No. 10,882,042 describes a process for detecting droplet position which relies upon a change in capacitance due to the difference in dielectric constant between the aqueous droplet and the surrounding oil

Methodology Applied

Scientific EffectDielectric: Dielectric

Implementation Method 3

Digital microfluidic devices are alternatively referred to as electrowetting on dielectric, or 'EWoD,' devices to differentiate them from competing microfluidic systems

Methodology Applied

Scientific EffectElectrowetting: Electrowetting

Data Source

PatentUS20240139743A1Digital microfluidic device with capacitive sensing

Publication Date: 2024.05.02 NUCLERA LTD

AI summary

Disclosed are methods and devices for sensing the presence of aqueous droplets on digital microfluidic devices.