Elliptical Biosensor Ring for Stable Pulse Wave S/N Ratio
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Solution Overview
Problem
Existing pulse wave sensors face challenges in maintaining optimal distance between light-emitting and light-receiving elements due to finger thickness variations, leading to decreased signal-to-noise (S/N) ratio, especially when the sensor ring has a circular cross-section and is non-flexible, or when the material is flexible, causing gaps and improper contact.
Innovation Solution
A sensing device with a non-flexible body having an inner peripheral surface configuration where the distance between the pad and back surfaces is shorter than between the outer and inner side surfaces, ensuring close contact with the finger, particularly the pad, to improve S/N ratio, and the light-emitting and light-receiving elements are positioned symmetrically with respect to the short axis of an elliptical cross-section to maintain optimal distance regardless of finger thickness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a circular cross-section with non-flexible material is used, then structural stability is improved, but a gap is generated between the worn portion and the finger causing decreased S/N ratio
Solution Approach 1:
The patent applies asymmetry by changing the cross-section from a circular shape to an elliptical shape. The elliptical cross-section has a longer axis in the width direction (outer side surface to inner side surface) and a shorter axis in the thickness direction (pad to back), allowing the sensor to maintain close contact with the finger pad while preserving structural stability.
2Measurement precision
If flexible material is used, then close contact with the finger is improved, but the distance between light-emitting and light-receiving elements varies with finger thickness
Solution Approach 1:
The patent uses an elliptical cross-section where the width (along the finger) is greater than the thickness (across the finger). This asymmetric geometry ensures that the distance between the light-emitting and light-receiving elements remains consistent regardless of variations in finger thickness, as the measurement is taken along the width dimension rather than the thickness dimension.
3Ease of manufacture
If the cross-section is circular, then manufacturing simplicity is improved, but the sensor cannot maintain optimal distance for all finger thicknesses
Solution Approach 1:
The patent transitions from a circular cross-section to an elliptical cross-section. While this requires slightly more complex manufacturing, it provides superior adaptability to different finger thicknesses. The elliptical shape with width greater than thickness ensures the sensor maintains optimal measurement geometry across various user populations.
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 configuration enhances the S/N ratio by ensuring consistent and optimal contact between the biosensor and the finger, stabilizing performance across different finger sizes and shapes, and maintaining the distance between light-emitting and light-receiving elements within an optimal range for accurate pulse wave measurement.
Implementation Method 1
a photoplethysmographic sensor that measures a pulse wave signal by using a photoplethysmography method has been put into practical use. The photoplethysmographic sensor includes a light-emitting element that emits light of a specific wavelength to the body surface of a user and a light-receiving element that receives light that has been reflected by or passed through the body of the user.
Data Source
AI summary
A sensing device is provided that includes a non-flexible body that is wearable on a user's finger and a biosensor that measures biological information through the finger. The body has an inner peripheral surface facing a pad, a back, an outer side surface, and an inner side surface. The biosensor is on the inner peripheral surface to face the pad when the body is worn on the finger. In a cross-section of the inner peripheral surface, a first distance between a portion of the inner peripheral surface that faces the pad of the finger and a portion of the inner peripheral surface that faces the back of the finger is shorter than a second distance between a portion of the inner peripheral surface that faces the outer side surface of the finger and a portion of the inner peripheral surface that faces the inner side surface of the finger.