Microwave Energy Control System for Impedance Mismatch Compensation

Solution Overview

Problem

During medical procedures like microwave ablation, energy transfer through transmission lines is hindered by impedance mismatches and line losses, which are difficult to accurately compensate due to the small wavelength of microwaves relative to the transmission line length.

Innovation Solution

A measurement and control system that includes a directional coupler to sample output signals, a calibration unit to store and generate calibration signals based on transmission line loss information, and a control unit to adjust the energy source, ensuring accurate energy delivery by compensating for impedance mismatches and line losses.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If conventional impedance matching circuits with capacitors and inductors are used, then impedance compensation is attempted, but accurate measurements cannot be obtained due to the small wavelength of microwaves relative to transmission line length

Engineering Contradiction:

Improveimpedance measurement accuracyVSAvoiddifficulty of obtaining accurate impedance measurements

Core Design Contradiction:

Measurement precisionVSDifficulty of detecting and measuring

Solution Approach 1:

The system performs preliminary calibration by measuring the transmission line's electrical characteristics (such as S-parameters) before the actual medical procedure. This preliminary measurement captures the line's impedance and loss characteristics, which are then stored and used to generate compensation parameters. By performing this measurement action before the procedure when tissue impedance changes have not yet occurred, the system establishes a baseline for accurate energy delivery compensation.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The system implements a feedback mechanism where the measured transmission line characteristics are used to generate compensation parameters that are applied to the microwave generator. The control system continuously monitors and adjusts the energy delivery based on the stored calibration data, creating a closed-loop system that compensates for impedance mismatches and maximizes power transfer to the treatment site.

Inventive Principle:

Principle #23Feedback

2Length of stationary object

If the transmission line is long relative to the microwave wavelength, then energy delivery distance is sufficient, but transmission line losses and impedance mismatches increase

Engineering Contradiction:

Improvetransmission line lengthVSAvoidtransmission line power loss

Core Design Contradiction:

Length of stationary objectVSLoss of energy

Solution Approach 1:

The system performs preliminary calibration by measuring the transmission line's electrical characteristics (such as S-parameters) before the actual medical procedure. This preliminary measurement captures the line's impedance and loss characteristics, which are then stored and used to generate compensation parameters. By performing this measurement action before the procedure when tissue impedance changes have not yet occurred, the system establishes a baseline for accurate energy delivery compensation.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The system changes the electrical parameters (magnitude and phase) of the microwave signal based on the stored calibration data. The control system adjusts these parameters in real-time to compensate for transmission line losses and impedance variations, thereby maximizing power transfer efficiency despite the long transmission line length.

Inventive Principle:

Principle #35Parameter changes

3Device complexity

If impedance matching is not achieved, then system complexity is reduced, but reflected waves create standing waves that contribute to power loss

Engineering Contradiction:

Improvesimplicity of system configurationVSAvoidpower loss from standing waves

Core Design Contradiction:

Device complexityVSLoss of energy

Solution Approach 1:

The system implements a feedback mechanism where the measured transmission line characteristics are used to generate compensation parameters that are applied to the microwave generator. The control system continuously monitors and adjusts the energy delivery based on the stored calibration data, creating a closed-loop system that compensates for impedance mismatches and maximizes power transfer to the treatment site.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The control system acts as an intermediary between the microwave generator and the transmission line, using stored calibration parameters to mediate the energy transfer. By processing the calibration data and generating appropriate compensation signals, the control system eliminates the need for complex hardware impedance matching networks while minimizing standing wave effects.

Inventive Principle:

Principle #24Intermediary (Mediator)

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 system effectively maximizes energy transfer to the patient by accurately measuring and adjusting for transmission line losses and impedance changes during procedures, enhancing the efficiency of energy delivery.

Implementation Method 1

The measurement system may include a directional coupler. The directional coupler may be configured to sample the output signal generated by the energy source.

Methodology Applied

Scientific EffectElectromagnetic coupling: Electromagnetic Induction

Implementation Method 2

the energy generated may be a microwave having a frequency and a wavelength associated therewith. During the microwave ablation surgical procedure, the microwave may be transmitted to the patient via a transmission line.

Methodology Applied

Scientific EffectElectromagnetic wave propagation: Electromagnetic Induction

Implementation Method 3

If the line and load impedances do not match (i.e. impedance mismatch) a reflected wave may be created, which can generate a standing wave that can contribute to the power loss associated with the impedance mismatch.

Methodology Applied

Scientific EffectImpedance mismatch reflection: Reflection

Implementation Method 4

In a microwave ablation surgical procedure the energy generated may be a microwave having a frequency and a wavelength associated therewith.

Methodology Applied

Scientific EffectDielectric heating: Dielectric Heating

Implementation Method 5

the impedance at the surgical site changes as the microwave ablation procedure progresses. This is because of tissue necrosis associated with the microwave ablation surgical procedure.

Methodology Applied

Scientific EffectTissue necrosis: Ablation

Data Source

PatentUS9861424B2Measurement and control systems and methods for electrosurgical procedures

Publication Date: 2018.01.09 COVIDIEN LP

AI summary

An energy delivery system for use in performing a medical procedure is provided. The medical procedure can employ an energy source, the energy source can be connected to an energy delivering device via a transmission line. The energy delivery system can include a measurement system, the measurement system can be configured to sample an output signal generated by the energy source. The energy delivery system includes a control system, which includes a calibration unit. The calibration unit can be configured to generate a calibration signal. The calibration signal can have a magnitude and phase, wherein the magnitude and phase is representative of the output signal and the transmission line loss information. The energy delivery system can also include a control unit, the control unit being configured to receive the calibration signal and adjust the energy source as needed.