RF Heating Impedance Network Tuning Using Phase Detection

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Solution Overview

Problem

Capacitive food heating systems face inefficiencies due to dynamic changes in food load impedance during heating, leading to uneven and reduced heating efficiency.

Innovation Solution

A variable impedance matching network is employed, which uses a unique searching algorithm to rapidly determine optimal impedance matching states by measuring phase angles between forward and reflected RF signals, allowing for efficient tuning and adjustment of series and shunt inductances to maintain efficient RF energy transfer.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Loss of energy

If a fixed impedance matching network is used in the RF heating system, then the device complexity is reduced, but the heating efficiency deteriorates due to impedance mismatch as food load changes during heating

Engineering Contradiction:

Improveheating efficiencyVSAvoidimpedance matching network complexity

Core Design Contradiction:

Loss of energyVSDevice complexity

Solution Approach 1:

The patent applies the Dynamics principle by implementing a variable impedance matching network that can dynamically adjust its parameters during the heating process. The network transitions from a fixed configuration to a dynamic one that adapts to changing food load impedance, thereby maintaining optimal power transfer efficiency throughout the heating cycle without requiring overly complex real-time control systems.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The patent employs theParameter changesprinciple by modifying the impedance parameters of the matching network in response to detected phase angles. The system changes inductance or capacitance values within the matching network to compensate for load variations, ensuring consistent heating efficiency across different heating stages while avoiding the need for complete system reconfiguration.

Inventive Principle:

Principle #35Parameter changes

2Loss of energy

If the impedance matching network is continuously adjusted during heating, then the heating efficiency is maintained, but the device complexity and control system complexity increase

Engineering Contradiction:

Improveenergy loss during heatingVSAvoidcontrol system complexity

Core Design Contradiction:

Loss of energyVSDevice complexity

Solution Approach 1:

The patent implements theFeedbackprinciple by using phase angle detection between forward and reflected RF signals to monitor impedance matching conditions in real-time. This feedback mechanism enables the control system to make targeted adjustments to the matching network parameters, maintaining high heating efficiency with a relatively simple control architecture that only intervenes when phase angle deviations indicate mismatch conditions.

Inventive Principle:

Principle #23Feedback

3Measurement precision

If a simple impedance matching approach is used, then the device complexity is low, but the measurement precision of phase angle detection and impedance matching deteriorates

Engineering Contradiction:

Improvephase angle detection precisionVSAvoidimpedance matching network complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent applies theMechanics substitutionprinciple by replacing complex mechanical or manual impedance tuning mechanisms with electronic phase angle detection and automated control. The system uses electrical signal processing to precisely measure phase angles between forward and reflected signals, enabling accurate impedance matching without requiring complex mechanical adjustment mechanisms or manual intervention.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

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 ensures consistent and efficient heating by continuously matching the impedance of the heating system to the changing load, reducing energy loss and maintaining high power absorption by the food load throughout the heating process.

Implementation Method 1

electromagnetic energy is supplied to the electrodes to provide warming of the food load

Methodology Applied

Scientific EffectDielectric heating: Dielectric Heating

Implementation Method 2

measuring phase angles between forward and reflected RF signals

Methodology Applied

Scientific EffectPhase angle detection:

Data Source

PatentUS10771036B2RF heating system with phase detection for impedance network tuning

Publication Date: 2020.09.08 NXP USA INC

AI summary

A system and method for tuning an impedance network of a device is provided. An RF signal is provided through a transmission path connected to an impedance matching network that includes a first variable component and a second variable component. A phase angle between a forward signal and a reflected signal along the transmission path is determined. Based on the phase angle between the forward signal and the reflected signal, the first variable component is modified to improve an impedance match between the RF signal source and the electrode. After modifying the first variable component, a ratio of a power of the reflected signal to a power of the forward signal is determined, and an inductance of the second variable component is modified to reduce the ratio of a power of the reflected signal to a power of the forward signal.