Optical Diode Temperature Sensing for Wearables Under Skin Contact Variations
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Solution Overview
Problem
Temperature sensors on wearable devices often suffer from errors due to poor skin contact and mechanical strain, leading to inaccurate temperature estimation of users.
Innovation Solution
Utilizing LEDs and PDs for both biometric sensing and temperature estimation by applying different bias currents to calculate diode base-emitter voltages (VBE) and compensating for skin contact and mechanical strain through averaging and calibration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If dedicated temperature sensors are used to measure absolute temperature, then temperature measurement capability is provided, but measurement precision deteriorates due to poor skin contact and mechanical strain
Solution Approach 1:
The patent replaces mechanical contact-based temperature sensors with optical sensors (LEDs and photodiodes) that measure temperature through light emission and detection. This substitution eliminates the need for direct mechanical contact with skin, thereby avoiding errors caused by poor skin contact while maintaining temperature measurement capability through optical properties that have known temperature coefficients
Solution Approach 2:
The patent changes the measurement parameter from direct thermal contact to optical property changes (light emission intensity and wavelength) that are temperature-dependent. By measuring how optical parameters change with temperature, the system achieves accurate temperature sensing without relying on mechanical skin contact quality
2Measurement precision
If temperature sensors are installed into the wearable electronic device, then temperature sensing capability is provided, but measurement precision deteriorates due to coupling forces and mechanical strain
Solution Approach 1:
The patent replaces mechanically-mounted temperature sensors with optically-coupled sensors that are not subjected to the same mechanical strains. The optical sensors are positioned to detect light from LEDs without experiencing the coupling forces that affect traditionally mounted temperature sensors, thereby eliminating strain-induced measurement errors
Solution Approach 2:
The patent introduces an optical intermediary (light) between the temperature measurement process and the sensor. Instead of directly measuring temperature through mechanical contact, the system uses light as a mediator that carries temperature information from the LED to the photodiode, isolating the measurement process from mechanical strain
3Measurement precision
If multiple LEDs and PDs are used for temperature sensing, then measurement precision improves through averaging, but device complexity increases
Solution Approach 1:
The patent makes the LED and photodiode components serve dual functions: biometric sensing and temperature measurement. The same optical components used for one purpose are configured to perform the other, eliminating the need for separate dedicated temperature sensor arrays and reducing overall device complexity while maintaining measurement precision
Solution Approach 2:
The patent merges the temperature sensing function with the existing biometric sensing optical components. By combining these functions into a single integrated system, the patent avoids the complexity of adding separate temperature sensor arrays while achieving improved temperature measurement through the optical properties of the combined components
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
Accurately estimates user temperature by minimizing errors from skin contact quality and mechanical strain, enhancing the reliability of temperature sensing.
Implementation Method 1
By biasing the LEDs and PDs with different bias currents and obtaining different diode base-emitter voltages (VBE) having known negative temperature coefficients, changes in VBE (ΔVBE) can be computed and used to estimate the temperature of the user
Data Source
AI summary
This relates to using light emitting diodes (LEDs) and/or photodiodes (PDs) on a device intended to come in contact with a user for temperature sensing. In some examples, the LEDs and PDs can be used for both biometric sensing and user temperature sensing. By biasing the LEDs and PDs with different bias currents and obtaining different diode base-emitter voltages (VBE) having known negative temperature coefficients, changes in VBE (ΔVBE) can be computed and used to estimate user temperature. In particular, a measurement circuit including a current source or sink, an amplifier, and an analog to digital converter (ADC) can be connected to each LED and PD. Different bias currents can be applied to the LEDs and/or PDs (the PDs being forward-biased instead of their normal reverse-biased mode for biometric sensing) to obtain different VBE measurements, and those differences can be used in equations to estimate the temperature of the user.