Capacitive Temperature Sensing Using Ferroelectric Ceramic
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Solution Overview
Problem
Monitoring the temperature of high voltage power cables, especially at splices and junctions, is challenging due to their insulation and burial or suspension, which requires a non-invasive and effective sensing method that can operate without an internal power source and maintain accuracy over a wide temperature range.
Innovation Solution
A capacitive sensing composition using a ferroelectric ceramic material with a Curie temperature below 30 degrees C, exhibiting a negative slope of capacitance versus temperature from 30 to 150 degrees C, integrated into an L-C circuit that changes resonant frequency in response to temperature changes, allowing for non-contact temperature monitoring.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If conventional temperature sensing methods are used on high voltage power cables, then temperature monitoring is possible, but the sensing apparatus requires internal power sources and physical connections that are difficult to implement on buried or suspended cables
Solution Approach 1:
The patent replaces conventional electronic temperature sensors requiring power sources and physical connections with a capacitive sensing element that utilizes the cable's existing electric field. The sensing element forms a capacitor where the cable acts as one electrode and the sensing element as the other, eliminating the need for mechanical power connections while enabling temperature monitoring through capacitance measurements.
Solution Approach 2:
The high voltage power cable itself serves dual purposes: it provides both the electric field necessary for capacitive sensing and the thermal path for temperature measurement. The cable's own electric field powers the capacitive sensing operation without requiring external power sources, making the system self-sufficient.
2Measurement precision
If standard capacitive sensing materials are used, then capacitance changes can be detected, but the sensing accuracy deteriorates at high temperatures due to positive temperature coefficients
Solution Approach 1:
The patent changes the temperature coefficient parameter of the capacitive sensing material from positive to negative. By selecting a ferroelectric ceramic material with a Curie temperature below 30°C, the material exhibits negative capacitance temperature coefficients in the 30-150°C range, reversing the typical behavior and enabling accurate high-temperature sensing where conventional materials fail.
Solution Approach 2:
The patent utilizes the phase transition characteristics of ferroelectric materials near their Curie temperature. The material undergoes a phase transition from ferroelectric to paraelectric state at the Curie point, creating a measurable capacitance change that is highly sensitive to temperature variations. By positioning the Curie temperature below 30°C, the material operates in the paraelectric phase at sensing temperatures, providing stable negative temperature coefficients.
3Reliability
If ferroelectric materials with Curie temperature below 30°C are used, then negative capacitance temperature coefficients are achieved, but the material stability may be compromised
Solution Approach 1:
The patent employs composite material strategies by combining ferroelectric ceramic particles with a polymer matrix or using doped ceramic compositions. The composite structure provides both the desired low Curie temperature for negative temperature coefficients and enhanced structural stability. The polymer matrix or dopants help stabilize the ceramic grain structure, preventing degradation during high-temperature aging while maintaining the ferroelectric properties.
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 solution enables accurate, passive temperature monitoring of high voltage power cables with enhanced resistance to high-temperature aging and electric field effects, maintaining reliability over extended periods.
Implementation Method 1
capacitive sensing composition that includes a ferroelectric ceramic material and exhibits a measurable electrical Curie temperature
Implementation Method 2
a ferroelectric ceramic material that exhibits a measurable electrical Curie temperature that is below 30 degrees C, and wherein the capacitive sensing composition exhibits a negative slope of capacitance versus temperature
Implementation Method 3
integrated into an L-C circuit that changes resonant frequency in response to temperature changes, allowing for non-contact temperature monitoring
Data Source
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AI summary
A passive temperature-sensing apparatus, which includes a capacitive sensing element that includes a capacitive sensing composition that includes a ferroelectric ceramic material that exhibits a measurable electrical Curie temperature that is below 30 degrees C. The capacitive sensing composition exhibits a negative slope of capacitance versus temperature over the temperature range of from 30 degrees C to 150 degrees C.