Whispering-Gallery-Mode Seismometer Using Microsphere Resonator

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Solution Overview

Problem

Current seismometers face challenges in accurately measuring small motions and accelerations due to limitations in sensitivity and mechanical isolation, particularly in detecting nano-g levels of acceleration and forces.

Innovation Solution

A whispering-gallery-mode-based seismometer is developed, utilizing a micro-optical resonator with a hollow polymer microsphere supported by a compliant spring-mass system, which measures motion through changes in the optical resonant frequency caused by deformation of the microsphere, enabling detection of nano-g accelerations and forces.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If conventional mechanical seismometers are used, then they can measure ground motion, but they suffer from insufficient sensitivity to detect nano-g levels of acceleration

Engineering Contradiction:

Improveacceleration detection sensitivityVSAvoidmechanical isolation system complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent replaces the conventional mechanical sensing system with an optical sensing system. A micro-optical resonator (microsphere) is used to detect proof mass displacement through changes in optical resonant frequency, eliminating the need for complex mechanical isolation and sensing mechanisms while achieving nano-g level sensitivity.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent utilizes mechanical vibration principles by suspending the proof mass on a compliant spring-mass system that allows controlled vibration. The resonant frequency of this mechanical system is designed to be much lower than the measurement bandwidth, enabling effective isolation of high-frequency ground motions while maintaining sensitivity to low-frequency accelerations.

Inventive Principle:

Principle #18Mechanical vibration

2Measurement precision

If the micro-optical resonator is made smaller to improve sensitivity, then detection precision improves, but the resonator becomes more fragile and harder to manufacture

Engineering Contradiction:

Improvedisplacement sensing precisionVSAvoidmicrosphere fabrication difficulty

Core Design Contradiction:

Measurement precisionVSManufacturing precision

Solution Approach 1:

The patent optimizes the size parameter of the microsphere resonator to achieve a balance between sensitivity and manufacturability. The microsphere diameter is selected to provide sufficient optical confinement and sensitivity while remaining within fabrication capabilities. Additionally, the resonant frequency is tuned by adjusting the sphere size to match the desired measurement bandwidth.

Inventive Principle:

Principle #35Parameter changes

3Reliability

If the spring-mass system is made more compliant to improve isolation, then mechanical isolation improves, but the system response time increases

Engineering Contradiction:

Improvemechanical isolation performanceVSAvoidsystem response time

Core Design Contradiction:

ReliabilityVSSpeed

Solution Approach 1:

The patent designs the spring-mass system with dynamic characteristics optimized for the target application. The spring constant and proof mass are selected to achieve a natural frequency much lower than the measurement bandwidth, providing effective isolation. The system response time is managed by ensuring the mechanical time constant is much shorter than the measurement integration time, allowing the system to quickly reach steady state while maintaining isolation performance.

Inventive Principle:

Principle #15Dynamics

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 provides enhanced sensitivity and accuracy in measuring small motions and accelerations, achieving detection of nano-g levels of acceleration and forces with a compact design, suitable for a wide range of seismic measurements.

Implementation Method 1

utilizing a micro-optical resonator with a hollow polymer microsphere supported by a compliant spring-mass system, which measures motion through changes in the optical resonant frequency caused by deformation of the microsphere

Methodology Applied

Scientific EffectWhispering-gallery mode resonance: Resonance

Implementation Method 2

measures motion through changes in the optical resonant frequency caused by deformation of the microsphere

Methodology Applied

Scientific EffectOptical resonant frequency shift:

Implementation Method 3

a hollow polymer microsphere supported by a compliant spring-mass system, which measures motion through changes in the optical resonant frequency caused by deformation of the microsphere

Methodology Applied

Scientific EffectElastic deformation: Elasticity

Data Source

PatentUS8743372B2Whispering-gallery-mode-based seismometer

Publication Date: 2014.06.03 SOUTHERN METHODIST UNIVERSITY

AI summary

A whispering-gallery-mode-based seismometer provides for receiving laser light into an optical fiber, operatively coupling the laser light from the optical fiber into a whispering-gallery-mode-based optical resonator, operatively coupling a spring of a spring-mass assembly to a housing structure; and locating the whispering-gallery-mode-based optical resonator between the spring-mass assembly and the housing structure so as to provide for compressing the whispering-gallery-mode-based optical resonator between the spring-mass assembly and the housing structure responsive to a dynamic compression force from the spring-mass assembly responsive to a motion of the housing structure relative to an inertial frame of reference.