Wireless Surface Wave Temperature Sensing for High-Heat Appliances
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Solution Overview
Problem
Existing temperature measurement methods in household appliances, particularly at high temperatures, are complex and prone to failure due to the limitations of LC resonant circuits and require more complex circuitry, making them unsuitable for elevated temperatures.
Innovation Solution
A method using a surface wave device with a high-frequency electromagnetic excitation wave transmitted wirelessly, measuring signal levels across a frequency band to determine the current temperature by selecting the transmit frequency with the highest signal level, which simplifies circuitry and reduces failure susceptibility, and can be used at elevated temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If LC resonant circuits are used for temperature measurement, then temperature-dependent resonant frequency can be measured, but the system becomes unsuitable for high temperatures and requires complex circuitry
Solution Approach 1:
The patent replaces the mechanical/electrical LC resonant circuit system with an acoustic resonance system using a speaker and microphone. The speaker generates acoustic waves that resonate with the cavity at temperature-dependent frequencies, and the microphone detects these resonances. This substitution eliminates the high-temperature limitations and circuitry complexity of LC resonant circuits while maintaining the ability to measure temperature through resonant frequency detection.
2Measurement precision
If LC resonant circuits are used for temperature measurement, then temperature can be determined through resonant frequency, but the system is prone to failure at elevated temperatures
Solution Approach 1:
The patent changes the physical parameter domain from electrical (LC resonant circuits) to acoustic (cavity resonance). Acoustic resonance in a sealed cavity is not affected by high temperatures in the way that electrical components are, as it depends on the speed of sound in the gas filling the cavity and the geometric dimensions, which remain stable at elevated temperatures. This parameter change enables reliable temperature measurement in high-temperature environments.
3Temperature
If surface wave devices are used for temperature measurement, then high temperature suitability is achieved, but the evaluation process requires complex signal analysis
Solution Approach 1:
The patent replaces the surface wave device (which requires complex signal evaluation through phase shift analysis or Fourier transformation) with a simple acoustic resonance system using a speaker and microphone. The resonance frequencies can be directly identified from the frequency spectrum without requiring complex mathematical transformations, thereby reducing signal evaluation complexity while maintaining high-temperature suitability.
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 results in a more reliable, cost-effective temperature measurement system suitable for high temperatures, with reduced manufacturing costs and improved accuracy through recalibration and averaging signal levels, enabling precise temperature control and display.
Implementation Method 1
a pre-defined transmit frequency is selected from a frequency band containing the temperature-dependent resonant frequencies that occur in an LC resonant circuit incorporated in a temperature measuring probe
Implementation Method 2
During a first phase, the excitation wave is wirelessly transmitted to the LC resonant circuit of the temperature measuring probe. As a result, an electromagnetic response wave is generated in the LC resonant circuit
Data Source
AI summary
A method for temperature measurement in a household appliance includes generating a high-frequency electromagnetic excitation wave of a predefined transmit frequency. The transmit frequency is selected from a frequency band including temperature-dependent resonant frequencies that occur in a surface wave device incorporated in a temperature measuring probe and which respectively correspond to temperatures expected at the temperature measuring probe during operation of the household appliance. During a first phase, the excitation wave is wirelessly transmitting to the surface wave device. During a second phase following the first phase, an electromagnetic response wave generated by the excitation wave in the surface wave device is wirelessly transmitting to a processing unit. Signal levels of response signals generated from response waves of different transmit frequencies are measured and compared to determine the current temperature of the surface wave device based on the transmit frequency associated with the highest signal level.