Surface Plasmon Sensor Ellipticity Detection

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Solution Overview

Problem

Existing surface plasmon sensors face complexity in measuring refractive indices due to the need for precise detection of absorption angles, which complicates the measurement process, especially when small differences in refractive indices are involved.

Innovation Solution

A surface plasmon sensor that measures refractive index by detecting changes in ellipticity of reflected light, allowing for easier and more accurate determination of absorption angles through zero-point detection rather than smallest-point detection, using a metal layer with a periodic structure and a conical mount arrangement.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If smallest point detection is used to measure absorption angle, then measurement precision can be achieved, but device complexity and ease of operation deteriorate

Engineering Contradiction:

Improveabsorption angle measurement precisionVSAvoidmeasurement process complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The invention changes the detection parameter from reflectance (which requires finding the minimum point) to ellipticity (which allows zero-point detection). By measuring the ellipticity of reflected light instead of reflectance intensity, the system transforms the measurement from a minimum-point detection problem to a zero-point detection problem, which is inherently simpler and more precise.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The invention replaces the traditional reflectance-based detection mechanism with an ellipticity-based detection mechanism. This substitution fundamentally changes how the absorption angle is detected, using polarization state changes (ellipticity) rather than intensity changes (reflectance), thereby simplifying the measurement process while maintaining or improving precision.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Measurement precision

If reflectance measurement is used to determine absorption angle, then measurement can be performed, but ease of operation deteriorates due to complicated smallest point detection

Engineering Contradiction:

Improverefractive index measurement precisionVSAvoidmeasurement operation simplicity

Core Design Contradiction:

Measurement precisionVSEase of operation

Solution Approach 1:

Inventive Principle:

Principle #35Parameter changes

3Measurement precision

If traditional surface plasmon sensor is used, then refractive index measurement can be performed, but measurement sensitivity deteriorates for substances with minute refractive index differences

Engineering Contradiction:

Improverefractive index measurement precisionVSAvoidmeasurement sensitivity for minute differences

Core Design Contradiction:

Measurement precisionVSReliability

Solution Approach 1:

The invention changes the detection parameter from reflectance to ellipticity. The ellipticity of reflected light exhibits a sharp transition at the absorption angle, providing a more sensitive indicator for detecting small changes in refractive index. This parameter change enhances the ability to distinguish between substances with minute refractive index differences.

Inventive Principle:

Principle #35Parameter changes

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 straightforward and precise measurement of refractive indices with high accuracy, even for substances with minute refractive index differences, by simplifying the detection process and improving measurement sensitivity.

Implementation Method 1

the reflectance ρ rapidly decreases at a certain angle of incidence (hereinafter referred to as absorption angle θ sp ). This phenomenon is called the plasmon resonance absorption, and is a phenomenon which is associated with electromagnetic wave coupling between an incident light and a surface plasmon excited on a surface of metal.

Methodology Applied

Scientific EffectSurface plasmon resonance absorption: Resonance

Implementation Method 2

a surface plasmon sensor that measures refractive index by detecting changes in ellipticity of reflected light, allowing for easier and more accurate determination of absorption angles through zero-point detection rather than smallest-point detection

Methodology Applied

Scientific EffectEllipticity detection: Polarisation

Data Source

PatentEP2669658B1Surface plasmon sensor and refractive index measurement method

Publication Date: 2019.06.26 NATIONAL INSTITUTE OF TECHNOLOGY

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Figure 2(a)~2(d)
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AI summary

To provide a surface plasmon sensor for measuring a refractive index by which a refractive index can be easily measured with high accuracy without relying on an absorption curve. The surface plasmon sensor includes: a reflection plate which includes a metal layer having a periodic structure and on which a specimen is arranged; a light source which irradiates an incident light to the reflection plate; a light receiving part which receives a reflected light reflected on the reflection plate; and a measurement part which measures a refractive index of the specimen based on phase information on two kinds of waves which are included in reflected light reflected on a periodic structure surface and differ in polarization direction.