Sub-micron Fiber Optic Hydrophone for High-Frequency Acoustic Sensing
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Solution Overview
Problem
Current hydrophone devices face challenges with high temperature and cavitation issues due to High Intensity Focused Ultrasound (HIFU) fields, leading to device failure, and suffer from spatial averaging and phase fluctuations, resulting in poor spatial resolution and sensitivity, especially in detecting acoustic pressure amplitudes above 3 MHz.
Innovation Solution
A fiber optic hydrophone system with an optical fiber core diameter of less than 10 μm and a thin layer of material (2-10 nm thick) on the immersion surface contact, which measures changes in pressure based on intensity, phase, and wavelength of Fresnel back reflections, minimizing spatial averaging and phase fluctuations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If existing hydrophone probes with aperture diameters of about 500 μm or more are used, then the device can detect acoustic pressure amplitude, but spatial averaging occurs beyond 3 MHz leading to poor spatial resolution
Solution Approach 1:
The patent changes the critical parameter of aperture diameter from 500 μm to sub-micron dimensions (less than 10 μm), enabling the hydrophone to resolve acoustic fields beyond 3 MHz without spatial averaging while maintaining detection capability
Solution Approach 2:
The patent replaces traditional piezoelectric mechanical sensing elements with fiber optic-based sensing, eliminating the need for large aperture piezoelectric crystals while achieving superior spatial resolution through optical field interactions at sub-micron scales
2Measurement precision
If phase modulated fiber optic sensors are used, then acoustic pressure can be sensed, but optical phase fluctuations cause higher amplitude noise and measurement errors
Solution Approach 1:
The patent extracts and eliminates the phase modulation mechanism that causes noise, opting instead for direct intensity-based or wavelength-based detection that does not suffer from optical phase fluctuations, thereby removing the source of measurement errors
Solution Approach 2:
The patent employs a simple fiber tip structure with basic optical detection rather than complex interferometric phase modulation systems, reducing sensitivity to environmental phase disturbances and simplifying the overall sensing mechanism
3Measurement precision
If wavelength modulated fiber optic hydrophones with sensing dimensions of about 600 μm to 3 mm are used, then acoustic sensing is achieved, but poor spatial resolution limits the resolution bandwidth
Solution Approach 1:
The patent dramatically reduces the sensing dimension parameter from millimeter-scale (600 μm to 3 mm) to sub-micron scale (less than 10 μm), enabling high spatial resolution acoustic sensing that supports bandwidths beyond 3 MHz without the spatial averaging problems of conventional sensors
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 system achieves high sensitivity and sub-micron resolution, enabling accurate characterization of acoustic fields up to 100 MHz without spatial averaging, thus improving detection accuracy and reliability in harsh environments.
Implementation Method 1
detecting changes in the intensity, phase, and/or wavelength in back reflected optical signal
Data Source
AI summary
A sensing method is based on using a special fiberoptic probe for detection of acoustic/ultrasound pressure in an immersion medium. The developed system is highly sensitive in detecting ultrasound waves up to 100 MHz, for imaging of micro structures and more. For applications up to 100 MHz, without spatial averaging corrections, the probe tip is modified by reducing the fiber diameter to 7 um or less. Also, to maximize acousto-optic interaction, the probe tip, not just its end face, may be coated with a thin layer of metallic material. This thin film coating satisfies partial transparency of the metallic coating. The coating thickness may range from 2 nm to 10 nm or others depending on the type of the coating material. The probe detects the pressure of acoustic and/or ultrasound waves propagating within an immersion medium, whenever the probe tip is immersed inside the medium, and having a reasonable immersion contact surface.