Inductive Humidity Sensor Using Moisture-Absorbing Core
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Solution Overview
Problem
Semiconductor-based relative humidity sensors often suffer from hysteresis and long-term drift, limiting their accuracy in measuring environmental humidity.
Innovation Solution
A humidity sensor apparatus and method utilizing a resonant circuit with a capacitor and an inductor having a moisture-absorbing core, where the magnetic properties of the core vary with moisture levels, allowing for accurate humidity measurement through an AC excitation signal and sense circuit analysis.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If semiconductor-based resistive or capacitive humidity sensors are used, then the sensor can detect humidity by measuring dielectric constant or resistivity changes, but the sensor suffers from hysteresis and long-term drift reducing measurement accuracy
Solution Approach 1:
The patent replaces semiconductor-based resistive or capacitive sensing mechanisms with an inductive sensing mechanism using a resonant circuit. The inductor's magnetic core absorbs moisture from the environment, changing its magnetic properties (permeability, loss tangent) which alters the resonant frequency and Q-factor of the circuit. This inductive approach eliminates the hysteresis and drift issues inherent in semiconductor materials while maintaining humidity detection capability.
Solution Approach 2:
The patent utilizes changes in magnetic parameters (permeability μ and loss tangent tanδ) of the core material in response to moisture absorption. As the core absorbs water vapor, its magnetic properties change, which directly affects the inductance and resonant characteristics of the circuit. By monitoring these parameter changes through frequency or Q-factor measurements, the system achieves accurate humidity sensing without the reliability problems of semiconductor sensors.
2Reliability
If a resonant circuit with moisture-absorbing core is used, then hysteresis and drift are reduced improving reliability, but the device complexity increases due to additional circuit components
Solution Approach 1:
The resonant circuit serves multiple functions: it provides the sensing mechanism through its frequency response to core moisture absorption, acts as a signal generation source, and enables measurement through Q-factor detection. The microcontroller integrates signal processing, frequency measurement, and humidity calculation functions, consolidating what could be separate components into a unified system that achieves high reliability without excessive complexity.
Solution Approach 2:
The system uses the natural resonant properties of the LC circuit and the inherent changes in the core's magnetic properties to self-generate the sensing signal. The microcontroller automatically measures the resonant frequency and Q-factor, processes the signals, and converts them to humidity readings without requiring external complex instrumentation. The system is self-contained and self-measuring, reducing overall device complexity.
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
The solution provides a more accurate and stable measurement of relative humidity by leveraging the core's variable magnetic properties, reducing hysteresis and drift issues in semiconductor-based sensors.
Implementation Method 1
The core is exposed to an environment and has a magnetic property that is variable in response to a level of humidity in the environment
Implementation Method 2
an inductor with a core that absorbs moisture from its environment and has a magnetic property that is variable in response to a level of humidity
Implementation Method 3
a resonant circuit with a capacitor and an inductor... provide an AC excitation signal to the resonant circuit... determine an inductance of the inductor according to a sense signal from the resonant circuit
Implementation Method 4
provide an AC excitation signal to the resonant circuit... sense circuit to determine an inductance of the inductor according to a sense signal from the resonant circuit
Data Source
AI summary
Described examples include devices and methods for measuring relative humidity of an environment using inductance. The devices can include a resonant circuit, including a capacitor and an inductor. The inductor includes a moisture-absorbing core with at least a portion thereof exposed to an environment, with at least one magnetic property of the core being variable in response to changing levels of moisture in the environment. An excitation circuit provides an AC excitation signal to the resonant circuit. A sense circuit determines an inductance of the inductor according to a sense signal from the resonant circuit. The sense circuit is coupled to generate an output signal that indicates a humidity level of the environment according to the sense signal.