Capacitively Isolated Physiological Sensor Reducing EMI
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Solution Overview
Problem
Near-infrared spectroscopy sensors in medical applications are sensitive to electromagnetic interference from devices like electrosurgical equipment and electrocardiogram devices, leading to false oxygen saturation readings due to voltage potential differences between the patient and the sensor pad, and existing solutions like Faraday shields are expensive and reduce sensitivity.
Innovation Solution
The sensor employs capacitively isolation of the sensor pad from the patient and signal ground from the monitor, using conductive and pressure-sensitive adhesives to reduce voltage potential and electromagnetic interference, while minimizing electromagnetic field generation from the printed circuit board traces.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a Faraday shield is used to reduce electromagnetic interference sensitivity, then the sensor's resistance to electromagnetic interference improves, but the sensor's sensitivity to near-infrared light decreases and manufacturing cost increases
Solution Approach 1:
The patent introduces an intermediary substance (conductive adhesive or gel) between the sensor pad and patient skin that serves dual functions: it provides capacitive coupling to reduce electromagnetic interference while allowing near-infrared light to pass through to the photodiode. This intermediary layer acts as a mediator that reconciles the conflicting requirements of EMI shielding and light transmission.
Solution Approach 2:
The patent changes the electrical parameters of the sensor interface by introducing capacitive coupling through conductive adhesives or gels with specific dielectric properties. This parameter change allows the system to achieve electromagnetic interference rejection through capacitive isolation while maintaining optical transparency for near-infrared spectroscopy measurements.
2Object-affected harmful factors
If a Faraday shield is used to reduce electromagnetic interference sensitivity, then the sensor's resistance to electromagnetic interference improves, but the sensor flexibility decreases
Solution Approach 1:
The conductive adhesive or gel layer serves as a flexible intermediary that provides capacitive coupling without requiring rigid Faraday shield structures. This intermediary approach maintains sensor flexibility and conformability to patient skin while achieving electromagnetic interference rejection through capacitive isolation.
Solution Approach 2:
The patent replaces the mechanical Faraday shield structure with an electrical/capacitive isolation mechanism. Instead of using physical metallic shielding that would reduce flexibility, the system uses capacitive coupling through conductive adhesives or gels to achieve electromagnetic interference rejection, thereby substituting a mechanical solution with an electrical field-based solution.
3Object-affected harmful factors
If capacitively isolated design is used to reduce electromagnetic interference, then electromagnetic interference sensitivity decreases, but device complexity increases
Solution Approach 1:
The sensor pad's conductive adhesive or gel layer performs multiple functions simultaneously: it provides electrical isolation for capacitive coupling, maintains optical transparency for light transmission, ensures mechanical adhesion to skin, and creates the necessary capacitive interface for EMI rejection. This self-service approach reduces overall device complexity by integrating multiple functions into existing sensor 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 approach effectively reduces electromagnetic interference, maintaining sensor sensitivity and flexibility without the added expense of Faraday shields, ensuring accurate oxygen saturation readings.
Implementation Method 1
the sensor employs capacitively isolation of the sensor pad from the patient and signal ground from the monitor
Implementation Method 2
electronic devices such as electrosurgical generators, electrocardiogram devices, power sources, or any other medical or non-medical devices near the sensor pad may interfere with the light received by the light detector
Implementation Method 3
using conductive and pressure-sensitive adhesives to reduce voltage potential and electromagnetic interference
Implementation Method 4
A physiological sensor employing near-infrared spectroscopy may be used to detect characteristics of various body tissues by transmitting and receiving near-infrared light through the body tissue
Data Source
AI summary
A physiological sensor having reduced sensitivity to interference includes a light source, a light detector in optical communication with the light source, and a sensor pad at least partially housing the light source and the light detector. The sensor pad is configured to be capacitively isolated from a patient. Moreover, the physiological sensor may be electrically connected to an amplifier having a signal ground and a monitor.