Microwave Heater Frequency Sweeping for Uniform Heating
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Solution Overview
Problem
Conventional microwave ovens fail to provide uniform heating for irregularly shaped objects, such as organs or foods, due to limitations in frequency range, cavity structure, and coupling between microwave inputs, leading to hotspots and inefficient heating processes.
Innovation Solution
The use of multiple microwave feeds with varying frequencies, adjustable field elements, and advanced antenna designs to distribute electromagnetic energy uniformly across irregularly shaped objects, allowing for frequency sweeping and power adjustment to optimize heating efficiency and uniformity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional microwave ovens are used for heating, then heating speed is improved, but temperature uniformity deteriorates resulting in hotspots
Solution Approach 1:
The patent applies dynamics by making the microwave frequency variable rather than fixed. The system continuously sweeps through a range of frequencies (e.g., 2.4-2.5 GHz) during the heating process, dynamically adjusting the operating frequency to track the peak absorption frequency of the material as it changes with temperature and moisture content. This dynamic frequency adjustment prevents stationary hotspots while maintaining rapid heating.
Solution Approach 2:
The patent changes the parameter of microwave frequency from a fixed value to a variable parameter that sweeps through a frequency range. By varying the frequency parameter during heating, the system adapts to changing material properties (dielectric constant, loss tangent) as temperature and moisture change, thereby maintaining uniform energy distribution and preventing hotspots while preserving fast heating.
2Temperature
If heating power is reduced to prevent hotspots, then temperature uniformity is improved, but heating time increases significantly
Solution Approach 1:
The system uses dynamic frequency sweeping to maintain high power levels throughout the heating process. Instead of reducing power to prevent hotspots, the frequency is continuously adjusted to track peak absorption, allowing the system to operate at high power while maintaining temperature uniformity. This dynamic approach eliminates the need for slow, low-power heating.
Solution Approach 2:
The patent implements feedback control by monitoring the material's absorption characteristics (through sensors detecting temperature, moisture, or dielectric properties) and using this information to adjust the microwave frequency in real-time. This feedback loop ensures that the system operates at peak efficiency throughout the heating process, maintaining both speed and uniformity without requiring reduced power levels.
3Device complexity
If single frequency microwave heating is used, then device complexity is reduced, but heating uniformity for irregular shapes deteriorates
Solution Approach 1:
The patent changes the microwave frequency parameter during operation rather than using a fixed single frequency. The frequency sweeps through a range (e.g., 2.4-2.5 GHz) to account for variations in material properties and geometry. This parameter variation approach maintains relatively simple device architecture while significantly improving heating uniformity for irregularly shaped objects compared to single-frequency systems.
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
Achieves uniform temperature distribution within ±10°C to ±30% across 80% or 90% of the object's volume, improving heating efficiency and preventing hotspots, as demonstrated by successful thawing and cooking of complex shapes like cow liver and eggs.
Implementation Method 1
a controller that determines an amount of energy that is absorbed by the object and adjusts the heating when a desired amount of energy is absorbed
Implementation Method 2
Electromagnetic heating
Data Source
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.