Optical Current Transducer for Laser Doppler Blood Flowmeter Signal Detection
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Solution Overview
Problem
Existing light detecting apparatuses for laser Doppler blood flowmeters face challenges in accurately detecting signal light components due to their lower intensity compared to fixed light components, leading to difficulties in signal extraction and noise interference.
Innovation Solution
A light detecting apparatus is designed with an optical current transducer unit comprising first and second photoelectric conversion elements that output a differential current, and a current/voltage converting unit that amplifies and standardizes this current to enhance signal detection, reducing noise and saturation issues by canceling DC components and amplifying AC components corresponding to the signal light.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a single photoelectric conversion element is used to detect light from a living body, then the device structure is simple, but the signal light component cannot be accurately detected due to its lower intensity compared to the fixed light component
Solution Approach 1:
The light detecting apparatus is segmented into multiple functional units: a photoelectric conversion element for converting light to electrical signals, a signal separation unit for separating the fixed light component from the signal light component, and a detection unit for detecting the separated signal light component. This segmentation allows accurate detection of the weak signal light component while maintaining reasonable structural complexity through modular design.
Solution Approach 2:
The signal separation unit extracts the fixed light component from the total light signal received by the photoelectric conversion element. By taking out and removing the dominant fixed light component, the weaker signal light component becomes detectable without being overwhelmed by the stronger fixed light component, thereby improving measurement precision.
2Measurement precision
If the fixed light component is not removed, then the detection circuit is simple, but the signal light component is obscured by the stronger fixed light component
Solution Approach 1:
The signal separation unit extracts and removes the fixed light component from the composite light signal. This extraction process isolates the signal light component, enabling accurate detection without the obscuring effect of the stronger fixed light component, thus improving measurement precision despite increased circuit complexity.
Solution Approach 2:
The signal separation unit acts as an intermediary between the photoelectric conversion element and the detection unit. It processes the electrical signals by separating the fixed light component from the signal light component, allowing the detection unit to focus on detecting only the signal light component with improved accuracy.
3Measurement precision
If ambient light background is not compensated, then the detection system is simpler, but the signal-to-noise ratio deteriorates due to ambient light interference
Solution Approach 1:
The signal separation unit removes not only the fixed light component from the laser source but also compensates for ambient light background. By extracting and eliminating these unwanted components, the signal-to-noise ratio is improved, enabling more precise detection of the signal light component despite the added complexity of the compensation mechanism.
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
This approach improves the signal-to-noise ratio and enables accurate detection of signal light components, avoiding saturation and enhancing the gain of the amplification process, thus providing a more reliable measurement of fluid information in the test object.
Implementation Method 1
first and second photoelectric conversion element units each converting the input light to an electric current
Implementation Method 2
current/voltage converting units configured to amplify the detected current, convert it to a voltage signal
Data Source
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AI summary
A light detecting apparatus includes: a first photoelectric conversion element unit (110) and a second photoelectric conversion element unit(120) each of which converts input light to an electric current and output it; an optical current transducer unit (100) for outputting, as a detected current, a differential current between an electric current outputted by the first photoelectric conversion element unit and an electric current outputted by the second photoelectric conversion element unit; and a first current/voltage converting unit (200) for amplifying the detected current outputted from the optical current transducer unit, converting it to a voltage signal, and outputting the voltage signal.