Tissue Oximeter Sensor System with Frequency Modulation
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Solution Overview
Problem
Pulse oximeters and tissue oximeters experience interference due to the use of near-infrared light, particularly when sensors are placed in close proximity, leading to erroneous readings and misinterpretation of physiological effects.
Innovation Solution
A tissue oximeter system is designed with precise sinusoidal signal modulation and demodulation, using a processor to output oxygen saturation signals independent of interfering signals, employing trans-impedance amplifiers, analog-to-digital converters, and filters to reduce interference by selecting an appropriate oversampling number and applying moving averaging filters to demodulate signals effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If multiple oximeter sensors are used simultaneously on a patient's body, then comprehensive monitoring of oxygen saturation can be achieved, but light interference between sensors causes erroneous readings
Solution Approach 1:
The patent divides the monitoring system into multiple independent sensor units, each with its own light source and photodetector. By segmenting the system, each sensor can be independently controlled and processed, allowing comprehensive monitoring while preventing interference through spatial separation and independent operation of each sensor unit.
Solution Approach 2:
The patent employs periodic modulation of light sources at different frequencies and uses periodic sampling of photodetector signals. By modulating light sources at distinct frequencies and periodically sampling the responses, the system can differentiate between signals from multiple sensors and eliminate interference, enabling accurate measurements even when sensors are placed in close proximity.
2Adaptability or versatility
If pulse oximeters and tissue oximeters use near infrared light, then both can measure oxygen saturation, but light from one sensor interferes with the other sensor's measurements
Solution Approach 1:
The patent introduces asymmetric frequency modulation patterns where different light sources operate at distinct, non-harmonic frequencies. By using asymmetric frequency allocation and non-standard modulation patterns, the system creates frequency signatures that are easily distinguishable, preventing one sensor's light from being misinterpreted as another sensor's signal even when they are in close proximity.
Solution Approach 2:
The patent introduces an intermediary signal processing layer that includes frequency filtering and harmonic rejection circuits. These intermediary components act as mediators between the light sources and the measurement system, selectively allowing only the intended signal frequencies to pass through while blocking interfering frequencies from other sensors.
3Ease of operation
If modulation frequencies of oximeters are set to standard values, then device operation is simplified, but harmonics of modulation frequencies fall within pass bands of other oximeters creating interference
Solution Approach 1:
The patent changes the modulation frequency parameters from standard fixed values to dynamically adjusted frequencies. By varying the modulation frequencies of different light sources and adjusting them to avoid harmonic relationships, the system maintains ease of operation while preventing interference. The processor dynamically selects frequencies that are unlikely to create harmonics within each other's pass bands.
Solution Approach 2:
The patent implements dynamic frequency selection and adjustment rather than using static standard frequencies. The system can adapt its modulation frequencies based on the operational context, switching between different frequency patterns to avoid interference. This dynamic approach allows the system to maintain simplicity in normal operation while preventing interference when needed.
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 effectively eliminates interference from other oximeter sensors, enhancing the accuracy of oxygen saturation measurements by isolating and removing unwanted signals, thereby improving the signal-to-noise ratio and reducing low-frequency variations.
Implementation Method 1
Pulse oximeters and tissue oximeters are medical devices that measure absorption of near infrared light to determine blood oxygen saturation
Implementation Method 2
tissue oximeters analyze the DC components of the reflected light at multiple wavelengths to determine oxygen saturation
Implementation Method 3
silicon photodetectors to measure light intensity transmitted through or reflected back from the site
Implementation Method 4
A tissue oximeter sensor may include a light source and a photodetector in optical communication with the light source
Data Source
AI summary
A system includes a light source, a photodetector in optical communication with the light source, and a processor in communication with said photodetector and configured to output a signal representing oxygen saturation independent of an interfering signal from an interfering source. The system may further include an analog-to-digital converter in communication with the processor that is configured to digitize a signal from the photodetector by oversampling and output oversampling data to the processor. The processor may include an averaging filter that averages the oversampling data received from said analog-to-digital converter prior to decimation to generate an oversampling number.