Microwave Frequency Sweeping for Uniform Heating of Irregular Objects
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Solution Overview
Problem
Conventional microwave ovens fail to provide uniform heating for irregularly shaped objects due to limitations in frequency range, cavity structure, and coupling issues, leading to hotspots and inefficient heating processes.
Innovation Solution
The use of multiple microwave feeds with varying frequencies, adjustable field elements, and antenna arrays to distribute energy uniformly across irregularly shaped objects, allowing for efficient heating by sweeping frequencies and adjusting power levels based on energy absorption measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional microwave ovens use single frequency heating, then heating speed is fast, but temperature distribution becomes non-uniform with hotspots
Solution Approach 1:
The patent applies parameter changes by varying the frequency of microwave energy across a broad range (e.g., 300 MHz to 3 GHz) during the heating process. By dynamically adjusting the frequency parameter rather than using a fixed single frequency, the system achieves both fast heating rates and uniform temperature distribution, eliminating hotspots while maintaining high productivity.
2Power
If microwave energy is concentrated to heat quickly, then heating efficiency increases, but hotspots and thermal runaway occur
Solution Approach 1:
The patent implements local quality by creating spatially varying heating zones through the use of multiple feeds positioned at different locations and orientations within the cavity. Each feed delivers microwave energy with different characteristics, resulting in locally optimized heating that collectively achieves uniform overall heating without concentrated hotspots, thus maintaining high power efficiency without thermal runaway.
3Temperature
If heating power is reduced to prevent hotspots, then temperature uniformity improves, but heating time increases significantly
Solution Approach 1:
The patent applies periodic action by continuously varying the microwave frequency and power levels throughout the heating process rather than maintaining constant parameters. This dynamic periodic modulation of heating parameters allows the system to achieve uniform temperature distribution while maintaining sufficiently high power levels to complete heating in reasonable time, avoiding the excessive heating times associated with low-power continuous heating.
4Device complexity
If single feed configuration is used, then device complexity is low, but energy distribution uniformity is poor
Solution Approach 1:
The patent implements segmentation by dividing the heating system into multiple independent feeds, each capable of delivering microwave energy with different frequencies, phases, and power levels. This segmentation of the single-feed system into multiple feeds enables superior energy distribution uniformity across the heated object, while the modular nature of the segmented feeds keeps device complexity manageable through independent control of each segment.
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 hotspots and increasing heating efficiency, as demonstrated by successful thawing and cooking of irregularly shaped items like a cow liver.
Implementation Method 1
The frequencies of the energy fed to two of the feeds differs by at least 8 MHz, or 20 MHz... allowing for efficient heating by sweeping frequencies and adjusting power levels based on energy absorption measurements
Implementation Method 2
Electromagnetic heating according to an efficiency of energy transfer... The use of multiple microwave feeds with varying frequencies, adjustable field elements, and antenna arrays to distribute energy uniformly across irregularly shaped objects
Implementation Method 3
One method of providing uniform heating is to allow the heat deposited in a hot spot to diffuse to surrounding regions and heat them by conduction
Implementation Method 4
Due to convection from the object, it is not a serious option for cooking or heating much above room temperature
Data Source
AI summary
A method of delivering energy to an object in a cavity may include transmitting electromagnetic energy to the cavity at a plurality of frequencies. At each of the plurality of frequencies, the method may also include determining an efficiency of energy transfer into the object and adjusting power transmitted at each of the plurality of frequencies such that a multiplicative product of the efficiency and the power transmitted is substantially constant across each of the plurality of frequencies.