Microwave Cavity Heating for Uniform Warming of Irregular Objects

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Solution Overview

Problem

Conventional microwave ovens fail to provide uniform heating for irregularly shaped objects, leading to temperature differences and hotspots, which is particularly problematic for defrosting or cooking organs and foods with non-spherical shapes.

Innovation Solution

The use of multiple microwave feeds operating at different frequencies, with adjustable power levels and field adjusting elements within the cavity, allows for sweeping the frequency range to optimize energy absorption and reduce coupling between feeds, ensuring uniform heating across the object.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If conventional microwave ovens are used for heating, then heating speed is fast, but temperature uniformity deteriorates with hotspots and temperature differences up to 100°C

Engineering Contradiction:

Improveheating speedVSAvoidtemperature uniformity

Core Design Contradiction:

ProductivityVSTemperature

Solution Approach 1:

The microwave heating system is divided into multiple independent feeds (at least two feeds), each operating at different frequencies and power levels. This segmentation allows independent control of energy input to different regions of the object, enabling uniform heating across the entire object while maintaining fast heating speeds.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Each feed is assigned different power levels and frequencies tailored to specific regions of the object. Field adjusting elements are positioned to create localized field distributions that match the object's geometry and heating requirements, ensuring uniform temperature distribution without hotspots.

Inventive Principle:

Principle #3Local quality

2Temperature

If multiple microwave feeds operating at different frequencies are used, then temperature uniformity is improved, but device complexity increases

Engineering Contradiction:

Improvetemperature uniformityVSAvoidnumber of feeds and control systems

Core Design Contradiction:

TemperatureVSDevice complexity

Solution Approach 1:

The multiple feeds share common control circuitry and frequency generation resources. The system uses a unified control architecture that manages all feeds through standardized interfaces, reducing the overall complexity despite having multiple feeds operating at different frequencies.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Solution Approach 2:

The system dynamically adjusts frequency and power level parameters of the feeds based on real-time temperature feedback and object characteristics. This adaptive parameter control optimizes heating uniformity while minimizing the need for complex hardware modifications.

Inventive Principle:

Principle #35Parameter changes

3Productivity

If field adjusting elements are positioned to optimize heating, then heating efficiency is improved, but device complexity and adjustment difficulty increase

Engineering Contradiction:

Improveheating efficiencyVSAvoidease of field adjustment

Core Design Contradiction:

ProductivityVSEase of operation

Solution Approach 1:

Temperature sensors are placed at multiple locations within the object to provide real-time feedback on temperature distribution. The control system uses this feedback to automatically adjust the position and power levels of field adjusting elements, optimizing heating efficiency without requiring manual intervention or complex adjustment procedures.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The system performs self-adjustment of field distributing elements based on temperature feedback and pre-programmed algorithms. The control circuitry automatically optimizes the position and configuration of field adjusting elements to achieve uniform heating, eliminating the need for manual adjustment by the operator.

Inventive Principle:

Principle #25Self-service

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 achieves uniform temperature distribution within 50°C across 80-90% of the object's volume, reducing the risk of hotspots and recrystallization, and enabling efficient heating of irregularly shaped objects with minimal temperature variation.

Implementation Method 1

The microwave energy is fed at different frequencies in a small range, normally between 2.4 and 2.5 MHz... sweeping the frequency range to optimize energy absorption

Methodology Applied

Scientific EffectElectromagnetic radiation absorption: Absorption (EM radiation)

Implementation Method 2

The microwave oven is a ubiquitous feature in modern society... electromagnetic heating... UHF or microwave energy is fed into the cavity

Methodology Applied

Scientific EffectDielectric heating: Dielectric Heating

Implementation Method 3

allow the heat deposited in a hot spot to diffuse to surrounding regions and heat them by conduction... heat diffuses before the temperature rise at the hot spot becomes objectionable

Methodology Applied

Scientific EffectThermal conduction: Conduction (thermal)

Implementation Method 4

Due to convection from the object, it is not a serious option for cooking or heating much above room temperature

Methodology Applied

Scientific EffectConvection: Convection

Data Source

PatentUS8941040B2Electromagnetic heating

Publication Date: 2015.01.27 JOLIET 2010 LTD

AI summary

An electromagnetic heater for heating an irregularly shaped object, including:a cavity within which an object is to be placed;at least one feed which feeds UHF or microwave energy into the cavity; anda controller that controls one or more characteristics of the cavity or energy to assure that the UHF or microwave energy is deposited uniformly in the object within ±30% over at least 80% of the volume of the object.