Noninvasive Glucose Measurement Using Modulated Laser Interference
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Solution Overview
Problem
Current noninvasive near-infrared human component measurement techniques face challenges such as weak signals due to high water absorption, variability in testing conditions, and human physiological changes, leading to low accuracy and interference in glucose concentration detection.
Innovation Solution
The method employs modulated tunable diode lasers with selectable optical lengths, using interference between measuring and reference beams to enhance signal-to-noise ratio and filter out interference, allowing for real-time, high-speed, and noninvasive measurement of human components by selecting specific optical lengths within human tissue.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If near-infrared spectroscopy is used for noninvasive human component measurement, then noninvasive and real-time measurement is achieved, but signal strength is weak due to high water absorption in tissue
Solution Approach 1:
The patent applies periodic modulation of the laser source at a known frequency and uses lock-in detection to extract the weak periodic signal from the weak periodic signal. This periodic action allows the system to distinguish the weak glucose absorption signal from the strong water absorption background by synchronizing detection with the modulation frequency, thereby improving signal-to-noise ratio without requiring higher illumination intensity.
Solution Approach 2:
The patent introduces an intermediary modulation scheme where the laser wavelength is modulated at a known frequency. This modulation acts as an intermediary that encodes the absorption information in the frequency domain, allowing the weak signal to be extracted through frequency-selective detection. The modulated signal serves as an intermediary carrier that carries the absorption information away from the direct weak optical signal.
2Reliability
If conventional near-infrared measurement is used, then noninvasive testing is achieved, but measurement accuracy is reduced due to variability in testing conditions and physiological changes
Solution Approach 1:
The patent implements feedback mechanisms through real-time monitoring of the modulation depth and wavelength drift. The system continuously adjusts the laser wavelength and modulation parameters based on feedback signals from the detection system. This feedback allows the system to compensate for physiological changes and testing condition variations, maintaining measurement accuracy despite the noninvasive nature of the test.
Solution Approach 2:
The patent changes the measurement parameters by operating in the frequency domain rather than the time domain. By modulating the laser at a known frequency and detecting at that frequency, the system transforms the measurement from a direct intensity measurement to a frequency-based measurement. This parameter change allows the system to distinguish between signal variations due to glucose concentration and variations due to physiological changes, improving measurement precision.
3Productivity
If multiple optical paths are measured simultaneously, then measurement speed is improved, but signal interference and noise increase
Solution Approach 1:
The patent segments the measurement process by measuring multiple optical paths at different depths separately in the frequency domain. Each optical path is identified by its characteristic frequency signature, allowing the system to segment the complex signal into distinct components. This segmentation enables simultaneous measurement of multiple paths while maintaining signal integrity through frequency-based separation, reducing interference between paths.
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 accuracy and reliability of glucose concentration measurement by isolating the signal of interest from tissue scattering, reducing noise and physiological interference, enabling precise and efficient noninvasive monitoring.
Implementation Method 1
based on an interference between measuring beam and reference beam, the interference's beat frequency is proportional to an optical length difference between the measurement light and the reference light
Implementation Method 2
The near infrared absorption, which wavelength range is 780 nm-2500 nm, is mainly caused by frequency doubling of the molecular vibration or combination frequency of several compounds which have the chemical bond X—H, such as C—H, and O—H, and N-H
Implementation Method 3
frequency doubling of the molecular vibration
Implementation Method 4
said laser is modulated, based on an interference between measuring beam and reference beam, the interference's beat frequency is proportional to an optical length difference
Data Source
AI summary
A method and apparatus for noninvasive measurement of a human body component, such as glucose, in vivo, include near infrared spectroscopy based laser sources driven at a carrier frequency lying within the characteristic absorption of the component. The apparatus also drives the laser diodes with a modulation frequency to generate a frequency difference between the measuring light and reference beam, and the interference of the two beams results in a beat frequency signal, which frequency is proportional to the optical path difference between the measuring light and the reference beam. The scattering lights from human tissue with different optical lengths are simultaneously detected and selected based on the beat frequency. The method is a convenient embodiment of the floating reference principle, which takes advantage of optical length selection.