Ferrite Bead EMI Suppression on Isolated Microwave Cables
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Solution Overview
Problem
Medical microwave delivery systems face challenges in suppressing electromagnetic interference (EMI) due to unwanted radiation emissions, particularly when the chassis ground is isolated from patient-contacting parts, as existing filtering schemes can create leakage current issues and reduce output power.
Innovation Solution
Incorporating a ferrite element around the coaxial cable to suppress unwanted currents and emissions, which acts as an antenna, without introducing DC blocking elements that reduce output power, thereby meeting EMC regulations and maintaining patient safety isolation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If DC blocking elements and filtering schemes are used to provide patient isolation and suppress EMI, then electrical isolation and EMI suppression are improved, but output power is reduced and leakage current increases
Solution Approach 1:
The patent extracts the EMI suppression function from the traditional DC blocking capacitor and filtering circuit combination, implementing it separately through ferrite beads placed on the coaxial cable. This allows the main power transmission path to remain unobstructed while EMI is suppressed at the cable level, avoiding power loss through capacitive reactance and leakage current issues
Solution Approach 2:
Ferrite beads are introduced as intermediary elements on the coaxial cable to suppress EMI. These beads act as magnetic lossy materials that attenuate high-frequency EMI signals without blocking the microwave power transmission, serving as a mediator between power transmission and EMI suppression requirements
2Reliability
If DC blocking elements are used to maintain patient isolation, then electrical isolation is improved, but leakage current increases
Solution Approach 1:
The patent separates the patient isolation function (maintained through floating ground architecture) from EMI suppression, implementing the latter through ferrite beads on external cables. This extraction eliminates the need for large DC blocking capacitors that would otherwise be required, thereby reducing leakage current while maintaining isolation
Solution Approach 2:
The patent replaces the traditional electrical isolation mechanism (DC blocking capacitors in filtering circuits) with a magnetic isolation approach using ferrite beads on cables. This substitution reduces leakage current because ferrite beads suppress EMI through magnetic losses rather than requiring capacitive blocking paths
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 ferrite element effectively attenuates high-frequency electromagnetic currents, reducing unwanted radiation emissions to below the threshold value, ensuring compliance with electromagnetic compatibility standards while maintaining electrical isolation and patient safety.
Implementation Method 1
The geometry and/or a material of the ferrite element may be selected to provide suppression of electromagnetic radiation within the desired suppression band
Data Source
AI summary
A medical microwave delivery system comprises a microwave generator for providing microwave energy, wherein the microwave generator is electrically isolated from an electrical earth of the medical microwave delivery system, a coaxial cable configured to transfer microwave energy from the microwave generator, and a ferrite element configured to at least partially surround at least part of the coaxial cable.