Microwave Stray Field Sensor for Moisture Measurement
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Solution Overview
Problem
Existing methods for measuring moisture content using microwave stray field sensors are limited to around 20% accuracy due to sensitivity issues and ambiguity in resonance frequency shifts, leading to reduced measurement precision beyond this range.
Innovation Solution
The solution involves determining product properties by analyzing the damping of at least two working modes in a microwave stray field sensor arrangement, which allows for a monotonic dependence on humidity, enabling accurate measurements beyond 20% moisture content without significant loss of accuracy. This is achieved by using frequencies above 10 MHz and specific design features that minimize radiation losses and maximize microwave attenuation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If resonance frequency shift is used for moisture measurement, then measurement accuracy is improved for low moisture content, but measurement becomes ambiguous for moisture content above 20%
Solution Approach 1:
The patent transitions from single-frequency resonance measurement to multi-frequency attenuation measurement. By measuring attenuation at multiple frequencies (e.g., 2.1 GHz and 2.6 GHz) and using the ratio or difference of these measurements, the system creates a new dimensional approach that eliminates the ambiguity present in single-frequency methods while extending the measurable moisture range beyond 20%.
Solution Approach 2:
The patent changes the measurement parameter from resonance frequency shift to attenuation (damping) measurement. This parameter change allows the system to maintain monotonic dependence on moisture content across a wider range. By operating in the attenuation domain rather than frequency shift domain, the system achieves both high accuracy and extended measurement range.
2Measurement precision
If microwave radiation losses are reduced, then measurement accuracy is improved, but device complexity increases
Solution Approach 1:
The patent introduces a dielectric material as an intermediary between the microwave source and the product being measured. This dielectric layer serves multiple functions: it confines the microwave fields to reduce radiation losses, it provides a controlled electromagnetic environment, and it enhances the interaction between microwaves and the product. This intermediary element achieves the dual goal of reducing losses and maintaining relatively simple device architecture.
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 extends the measurement range for moisture content beyond 20% with maintained accuracy, allowing for precise determination of product properties like moisture, density, and mass, even at higher humidity levels, and can be applied to various product forms and treatment processes.
Implementation Method 1
determine a density-independent measured variable dependent only on the material moisture from the frequency shift and the change in quality or damping of an examined resonance curve of the loaded resonator compared to the unloaded resonator
Implementation Method 2
measuring device for measuring a product property (10) using at least one microwave stray field sensor arrangement (25) having at least one microwave resonator (7)
Implementation Method 3
the change in attenuation over the frequency depends very sensitively on the humidity
Implementation Method 4
measured values associated with the damping of the working modes
Data Source
Figure 1~2
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Figure 5~6
AI summary
The device has a micro-wave scatter field sensor arrangement i.e. micro-strip conductor arrangement, comprising a product chamber arranged outside a microwave- scatter field resonator. A micro-wave generation device generates a micro-wave field in the resonator. An evaluation unit evaluates a signal for determination of product characteristics. The evaluation device is arranged for determination of the characteristics in dependent upon measurement values (G1, G2), which are associated with micro-wave damping of operating modes, whose resonance frequency ranges to three giga-hertz. An independent claim is also included for a method for measuring the characteristics of the product.