Bio-compatible Resilient Plastic Light Channels for Physiological Sensors
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Solution Overview
Problem
Physiological sensors, such as heart rate sensors, face discomfort and performance degradation due to ambient light and air gaps when worn close to the skin, especially during exercise, as they often rely on hard plastics that allow ambient light to reach the detector and increase optical loss.
Innovation Solution
A light guide system using bio-compatible resilient plastic light channels that transmit optical energy from the emitter and block ambient light, with one channel in optical communication with the emitter and the other with the detector, integrated into wearable forms like eartips or wristbands, utilizing a longpass optical filter to reject shorter wavelengths and maintain contact with the skin.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If hard plastic is used for the sensor housing, then structural strength is improved, but ambient light blocks the detector and causes performance degradation
Solution Approach 1:
The patent applies local quality by using different materials for different parts of the housing: hard plastic for structural components and soft resilient plastic specifically for the light channel portions that contact the skin. This localized material differentiation allows the light channels to conform to skin contours and block ambient light while maintaining overall structural strength of the device housing.
2Measurement precision
If the sensor is positioned close to the skin, then measurement accuracy is improved, but discomfort increases during movement and exercise
Solution Approach 1:
The patent employs flexible shells by using soft resilient plastic for the light channel portions that directly contact the skin. This flexible material conforms to skin contours and moves with the body during exercise, maintaining close contact for accurate measurements while preventing discomfort from rigid pressure points.
3Ease of operation
If air gaps are present between the sensor and skin, then wearability is improved, but optical loss increases and signal quality degrades
Solution Approach 1:
The patent applies preliminary action by pre-forming the light channels with a curved contour that matches the expected skin surface geometry before the sensor is worn. This pre-shaping ensures that when the sensor contacts the skin, the light channels maintain continuous contact without creating air gaps, thereby preventing optical loss while preserving wearability.
4Device complexity
If ambient light reaches the detector, then device simplicity is maintained, but signal-to-noise ratio decreases and performance degrades
Solution Approach 1:
The patent uses the soft resilient plastic light channels as an intermediary element between the external environment and the detector. This material acts as a mechanical and optical barrier that blocks ambient light from reaching the detector while still allowing the emitter's optical energy to pass through to the skin and return to the detector, thereby improving signal-to-noise ratio without adding complex optical filtering 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
This solution enhances signal-to-noise ratio and reduces discomfort by minimizing optical loss and ambient light interference, improving the performance and wearability of physiological sensors.
Implementation Method 1
The bio-compatible resilient plastic has an optical transmission spectrum that transmits the optical energy of the emitter and substantially blocks ambient light
Implementation Method 2
The optical transmission spectrum may define a longpass optical filter where a lowest wavelength of an optical spectrum of the emitter is greater than a transition wavelength of the longpass optical filter
Implementation Method 3
The emitter is disposed in the sensor body and is configured to irradiate a skin of a wearer with an optical beam
Implementation Method 4
The detector is disposed in the sensor body and is configured to receive optical energy from the irradiated skin of the wearer and to generate an electrical signal in response to the received optical energy
Data Source
AI summary
A light guide system for a physiological sensor includes a light channel in optical communication with an emitter and a light channel in optical communication with a detector. The light channels are formed of a bio-compatible resilient plastic, such as a silicone, that is blended with a colorant. Each light channel has an optical transmission spectrum that passes the emitter spectral band and rejects most or all ambient light. The colorant can be a pigment provided as a suspension in a liquid or a dye provided in liquid form. The optical transmission spectrum defines a longpass optical filter where the shortest wavelength of the optical spectrum of the emitter is greater than the transition wavelength of the longpass optical filter. Each of the light channels is configured to be in contact with the skin, thereby reducing or eliminating optical loss due to transmission through an air gap.