Multilayer Detector Shield for Pulse Oximetry EMI Noise
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Solution Overview
Problem
Conventional electromagnetic shields, such as those made of copper, reflect light unevenly, affecting the wavelengths reaching photodiodes in pulse oximetry devices and introducing background noise due to their reflective properties, which can distort the light signal detected.
Innovation Solution
A multilayered detector shield comprising a copper EMI shield with a shiny, reflective nickel or nickel alloy layer that reflects light evenly across a predetermined band of wavelengths, minimizing the impact of copper's uneven reflectivity and allowing unobstructed passage of desired wavelengths to the photodiode.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a copper EMI shield is used to block electromagnetic interference, then the shielding effectiveness is improved, but the light signal accuracy deteriorates due to uneven wavelength reflection
Solution Approach 1:
The patent applies composite materials by combining copper EMI shield with a nickel or nickel alloy reflective layer. The copper layer provides electromagnetic interference shielding, while the nickel layer provides uniform optical reflection across the spectral band of interest (600-1100 nm). This composite structure resolves the contradiction by integrating two materials with complementary properties: copper for EMI blocking and nickel for wavelength-neutral light reflection, thereby maintaining both shielding effectiveness and light signal accuracy.
2Object-affected harmful factors
If a conductive EMI shield is placed over the photodiode, then electromagnetic interference is reduced, but background noise increases due to parasitic coupling and light reflection
Solution Approach 1:
The composite structure of copper EMI shield with nickel reflective coating addresses this contradiction by providing EMI shielding through the copper layer while the nickel layer minimizes parasitic light reflection that would create background noise. The nickel's uniform reflectivity across the measurement spectrum ensures that reflected light does not introduce wavelength-dependent noise, thus reducing overall background noise while maintaining EMI protection.
Solution Approach 2:
The nickel or nickel alloy layer is selected specifically for its optical properties - its color and reflective characteristics cause it to reflect substantially equal amounts of light across the predetermined spectral band (600-1100 nm). This color/reflectivity property of the nickel layer reduces wavelength-selective background noise while the copper underlying layer provides EMI shielding, resolving the contradiction between EMI reduction and noise generation.
3Ease of manufacture
If copper is used as the EMI shield material, then cost and conductivity are improved, but optical signal fidelity deteriorates due to wavelength-dependent reflection
Solution Approach 1:
The patent uses a composite material system where copper provides the base EMI shielding structure (maintaining cost-effectiveness and conductivity) while a nickel or nickel alloy reflective layer is applied over the copper. This composite approach preserves the manufacturing advantages of copper while adding the optical properties of nickel that ensure faithful spectral response. The nickel layer costs more than plain copper but the overall solution remains cost-effective compared to using expensive optically-neutral materials alone.
Solution Approach 2:
The nickel reflective layer is applied locally on the surface of the copper EMI shield, specifically on the side facing the photodiode where light interaction occurs. This local application of different material properties (copper bulk for EMI shielding, nickel surface for optical reflection) resolves the contradiction by providing wavelength-neutral reflection only where needed for light interaction, while maintaining the cost-effective copper structure throughout the rest of the shield.
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 multilayered shield effectively blocks electromagnetic interference while maintaining the accuracy of light signals by ensuring that only the desired wavelengths reach the photodiode, improving the spectral response and reducing noise in pulse oximetry measurements.
Implementation Method 1
a layer of shiny, lustrous material (such as Nickel) is placed over a copper EMI shield... this layer of material will reflect substantially equal amounts of light within a predetermined band of desired wavelengths
Implementation Method 2
an electromagnetic shield is utilized as an effective method of reducing the effect of EMI-induced noise... surrounding potentially affected parts with a 'Faraday cage' of electrically conducting material
Implementation Method 3
The detector detects the attenuated light and sends a signal indicative of the detected light to a patient monitor for analysis
Data Source
AI summary
An improved photodiode detector shielding apparatus and method are provided which shield a photodiode detector from electromagnetic interference and ambient light, without affecting the wavelengths of light that reach the photodiode. The improved photodiode detector shield has two layers. A bottom layer is substantially made from an electrically conducting material and is fixed over a photodiode in order to shield it from EMI and ambient light. A top layer is substantially made from a lustrous, shiny, reflective material that reflects an equal amount of light across a band of wavelengths. Both layers have areas with optically transmissive openings, which are aligned to allow for the unobstructed passage of light of a band of wavelengths to the photodiode. Light within a band of wavelengths is evenly reflected off the top of the first surface and also reaches the photodiode. In this regard, the detector shield blocks EMI and ambient light without affecting the wavelengths of light desired to reach the photodiode.