Optical Microphone Cavity Layout for Ultrasonic Sound Sensitivity
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Solution Overview
Problem
Conventional optical microphones are low sensitive to sound pressure and struggle to detect ultrasonic sounds above 100 kHz, limiting their frequency detection capabilities.
Innovation Solution
A sound measuring device with a frame that includes reflective surfaces to multiply reflect and cross a laser beam within a predetermined space, increasing the optical path length without enlarging the space, and incorporating a collimating lens to maintain beam alignment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional optical microphone directly captures sound waves using a laser beam, then the upper limit of frequency band exceeds 100 kHz, but the sensitivity to sound pressure is low
Solution Approach 1:
The patent transforms the one-dimensional direct laser path into a multi-dimensional multiply reflected optical path within a cavity. The laser beam reflects multiple times between opposing reflective surfaces, creating an extended optical path that interacts with sound waves from multiple angles and positions, thereby enhancing sensitivity without limiting frequency response
Solution Approach 2:
The patent introduces a cavity with reflective surfaces as an intermediary between the laser beam and the sound waves. This intermediary structure allows the laser beam to indirectly interact with sound pressure variations through multiple reflections, amplifying the detection effect while maintaining broadband frequency capability
2Measurement precision
If the optical path length is increased to improve sensitivity, then the sound pressure sensitivity improves, but the device size increases
Solution Approach 1:
The patent uses multiple reflections between opposing surfaces to create a folded optical path. Instead of extending the physical distance linearly, the laser beam bounces back and forth between reflective surfaces separated by a relatively small distance, effectively multiplying the optical path length within a compact volume
Solution Approach 2:
The continuous multiply reflected optical path allows the laser beam to interact with sound waves repeatedly along its path. Each reflection provides additional interaction opportunities with sound pressure variations, effectively accumulating the detection effect without requiring proportional increases in device size
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 device enhances sound pressure sensitivity by improving the optical path length and reducing beam loss, enabling effective detection of ultrasonic sounds.
Implementation Method 1
a frame including at least one reflective surface that faces a predetermined space through which sound travels... the at least one reflective surface is disposed to multiply reflect and cross the laser beam in the predetermined space
Implementation Method 2
an optical microphone that measures high-speed micro vibration using light as represented by a laser beam... directly capturing a change in refractive index of air caused by sound waves using a laser Doppler vibrometer
Data Source
AI summary
A sound measuring device includes: a light source that emits a laser beam; a frame including at least one reflective surface that faces a predetermined space through which sound travels, and transversely surrounds the predetermined space with respect to a sound propagation direction; and a light receiver that receives the laser beam multiply reflected by the at least one reflective surface. The at least one reflective surface is disposed to multiply reflect and cross the laser beam in the predetermined space as viewed from the sound propagation direction.