Evanescent-wave QEPAS Sensor Using Fiber-taper and Micro-resonators

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Solution Overview

Problem

Traditional photoacoustic gas sensors using quartz tuning forks are sensitive to environmental noise and require complex optical alignment and high spatial radiation quality, while evanescent-wave sensors suffer from low sensitivity due to fragility and the need for long microfibers.

Innovation Solution

Combining fiber-taper based evanescent fields with quartz tuning forks and micro-resonators to enhance acoustic signal detection, reducing system size and simplifying optical alignment while achieving high sensitivity.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If traditional open-path QEPAS sensors are used, then detection sensitivity is improved, but optical alignment complexity and system size increase

Engineering Contradiction:

Improvedetection sensitivityVSAvoidoptical alignment complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent combines the optical fiber evanescent field interaction mechanism with the quartz-enhanced photoacoustic spectroscopy detection method, merging two separate techniques into a unified sensor system. This integration allows the sensor to achieve high detection sensitivity through evanescent field absorption while using the quartz tuning fork for acoustic detection, eliminating the need for complex open-path optical alignment systems

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The patent introduces an optical fiber as an intermediary element that mediates between the light source and the gas sample. The evanescent field generated by the optical fiber interacts with the gas molecules, converting optical energy to acoustic signals that are then detected by the quartz tuning fork. This intermediary approach simplifies the optical path while maintaining high sensitivity

Inventive Principle:

Principle #24Intermediary (Mediator)

2Measurement precision

If microfibers are used for evanescent-wave sensing, then sensitivity is improved, but mechanical fragility increases

Engineering Contradiction:

ImprovesensitivityVSAvoidmechanical strength

Core Design Contradiction:

Measurement precisionVSReliability

Solution Approach 1:

The patent employs an optical fiber with a modified cladding structure (D-shaped or with removed cladding) to create a flexible yet mechanically robust evanescent field interaction region. This approach maintains the high sensitivity of microfiber-based evanescent wave sensing while providing the mechanical strength and flexibility of a protected optical fiber, avoiding the fragility of bare microfibers

Inventive Principle:

Principle #30Flexible shells and thin films

3Device complexity

If bare quartz tuning fork is used, then device simplicity is improved, but detection sensitivity decreases

Engineering Contradiction:

Improvedevice simplicityVSAvoiddetection sensitivity

Core Design Contradiction:

Device complexityVSMeasurement precision

Solution Approach 1:

The patent creates a composite sensor system that combines the quartz tuning fork (for acoustic resonance and piezoelectric detection) with the optical fiber evanescent field interaction region. This composite structure integrates the mechanical resonance properties of quartz with the optical interaction capabilities of the fiber, achieving enhanced detection sensitivity while maintaining relative device simplicity

Inventive Principle:

Principle #40Composite materials

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

The solution results in ultra-sensitive, compact, and low-cost gas sensors with a normalized noise equivalent absorption coefficient competitive with traditional open-path QEPAS systems, improving detection sensitivity by over 20 times compared to bare quartz tuning fork sensors.

Implementation Method 1

Gas absorption by an evanescent field has been demonstrated with a palladium film deposited at a core-exposed fiber

Methodology Applied

Scientific EffectEvanescent wave absorption: Absorption (EM radiation)

Implementation Method 2

Photoacoustic gas sensors operate by detecting acoustic vibrations induced by the modulated optical radiation in an analyzed gas sample

Methodology Applied

Scientific EffectPhotoacoustic effect: Photoacoustic Effect

Implementation Method 3

Quartz-enhanced photoacoustic spectroscopy (QEPAS) is one of the most sensitive photoacoustic detection techniques using an oscillator like a quartz tuning fork as the sharply resonant acoustic transducer

Methodology Applied

Scientific EffectPiezoelectric effect: Piezoelectric Effect

Data Source

PatentUS10444199B2Evanescent-wave quartz-enhanced photoacoustic sensor with resonator elements

Publication Date: 2019.10.15 THE CHINESE UNIVERSITY OF HONG KONG

AI summary

A novel evanescent-wave quartz-enhanced optical microfiber photoacoustic gas sensor is provided for detecting trace amounts of gas. Both fiber-taper based evanescent field and photoacoustic spectroscopy can be used to exploit the merits of both technologies. The use of a fiber half-taper into the tuning fork and microresonator tubes can result in reduced system size, simplified optical alignment, and high sensitivity. The techniques described can be used in chemical, biological and environmental sensing applications.