Electrosurgical Current Sensor Shielding Parasitic Capacitance
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Solution Overview
Problem
Conventional electrosurgical sensors face challenges in accurately measuring current due to unwanted signal coupling via parasitic capacitances, leading to erroneous measurements, especially in electrosurgical procedures where precise control of energy delivery is crucial.
Innovation Solution
The electrosurgical generator incorporates a current sensor coil with a shielding member and a conditioning circuit that cancels common-mode currents and amplifies differential-mode currents, minimizing parasitic capacitance effects and providing accurate current measurements by orienting active and return leads symmetrically relative to the sensor coil and using shielding to reduce voltage coupling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional sensors are used to measure current in electrosurgical generators, then the device complexity is low, but the measurement precision deteriorates due to unwanted signal coupling via parasitic capacitances
Solution Approach 1:
The sensor is divided into multiple functional components: a current sensor coil for detecting current, a shielding member for blocking parasitic capacitance effects, and a conditioning circuit for processing the sensor signal. This segmentation allows each component to perform its specific function optimally, resolving the contradiction by improving measurement precision through specialized sub-components while keeping the overall design manageable.
Solution Approach 2:
A shielding member is introduced as an intermediary element between the electrosurgical leads and the current sensor coil. This shielding member blocks unwanted voltage coupling through parasitic capacitances, allowing accurate current measurement without the harmful interference. The intermediary shields the sensor from parasitic effects while maintaining the necessary electrical connections.
2Measurement precision
If shielding members and conditioning circuits are added to improve current sensing accuracy, then measurement precision improves, but device complexity increases
Solution Approach 1:
The harmful parasitic capacitance effects are extracted and isolated from the main measurement path by introducing a shielding member. The shielding member captures and redirects the parasitic coupling away from the current sensor coil, allowing the measurement system to focus solely on detecting the differential-mode current signal without interference from common-mode parasitic effects.
Solution Approach 2:
The conditioning circuit performs parameter changes on the raw sensor signal, including amplification to increase signal strength, filtering to remove noise, and integration to accumulate the sensor output over time. These parameter transformations convert the weak differential signal from the current sensor coil into a robust measurement that can be accurately processed by the control system.
3Quantity of substance
If common-mode currents are present in electrosurgical leads, then the quantity of current transmitted is high, but harmful factors increase due to erroneous signal coupling
Solution Approach 1:
The current sensor coil is designed with asymmetric winding patterns and the shielding member is positioned asymmetrically relative to the electrosurgical leads. This asymmetric configuration creates different coupling paths for common-mode and differential-mode currents, allowing the sensor to selectively detect differential-mode signals while rejecting common-mode currents that carry harmful parasitic capacitance effects.
Solution Approach 2:
The shielding member converts the harmful parasitic capacitance coupling into a beneficial reference signal. By placing the shielding member in close proximity to the leads, it captures the common-mode voltage fluctuations and uses this information to cancel out the parasitic effects in the measurement, transforming what would be harmful interference into a useful reference for improving measurement accuracy.
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 accuracy of current sensing, reducing erroneous signals and improving the precision of energy delivery in electrosurgical procedures, ensuring safer and more effective tissue treatment.
Implementation Method 1
The sensor includes a current sensor coil including an outer coil including an opening therethrough. The active and return leads pass through the current sensor coil opening such that the common-mode currents are canceled and the differential-mode currents are added.
Implementation Method 2
Conventional electrosurgical sensors face challenges in accurately measuring current due to unwanted signal coupling via parasitic capacitances
Data Source
AI summary
An electrosurgical generator includes a radio frequency output stage, a sensor for sensing current, and an active lead. The radio frequency output stage is configured to output at least one radio frequency waveform. The sensor includes a current sensor coil including an outer coil including an opening therethrough and an inner coil coupled to and disposed within the outer coil. The active lead is coupled to the radio frequency output stage and passes through the current sensor coil opening. The current sensor coil is configured to output a first signal indicative of a current within the active lead.