Acoustic Gas Concentration Sensor Using Multi-Frequency Dispersion
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Solution Overview
Problem
Existing methods for determining the concentration of constituents in fluid mixtures, such as carbon dioxide in combustion engine intake tracts, are often unreliable and costly, particularly when measuring carbon dioxide concentrations using temperature-dependent methods like lambda probes, and lack robustness and independence from mass flow measurements.
Innovation Solution
A method and apparatus utilizing sound conversion units that send and receive sound signals at different frequencies to determine the concentration of constituents in a fluid chamber, leveraging sound dispersion effects to calculate characteristic values representative of concentration and mass flow, with CMUT transducers providing a cost-effective and reliable solution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If temperature-dependent methods like lambda probes are used to determine carbon dioxide concentration, then measurement capability is provided, but reliability and robustness deteriorate due to temperature dependence and mass flow interference
Solution Approach 1:
The patent replaces temperature-dependent electrochemical lambda probes with acoustic measurement methods using sound waves. The system measures the speed of sound and attenuation at different frequencies to determine gas composition, eliminating the temperature dependence and mass flow sensitivity inherent in lambda probes. This substitution provides reliable concentration measurements independent of thermal conditions.
Solution Approach 2:
The system changes the measurement parameter from temperature-based electrochemical response to acoustic velocity and attenuation characteristics. By measuring sound propagation properties at multiple frequencies, the system extracts concentration information that is independent of temperature and mass flow, resolving the reliability issues of traditional methods.
2Device complexity
If single frequency sound measurement is used, then device complexity is reduced, but measurement precision deteriorates due to inability to separate concentration and mass flow effects
Solution Approach 1:
The patent segments the measurement into multiple frequency components, using at least two different frequencies to independently determine concentration and mass flow. This segmentation allows the system to separate the coupled effects of concentration and velocity, achieving precise concentration measurement while maintaining relatively simple device architecture.
Solution Approach 2:
The system adds the frequency dimension to the measurement, using multiple frequencies rather than a single frequency. This dimensional expansion provides additional independent equations to solve for both concentration and mass flow, improving measurement precision without proportionally increasing device complexity.
3Ease of manufacture
If traditional concentration measurement methods are used, then cost is reduced, but adaptability deteriorates due to dependence on mass flow and temperature conditions
Solution Approach 1:
The acoustic measurement system serves multiple functions: it determines gas concentration, measures mass flow, and operates independently of temperature and pressure conditions. This multi-functionality provides adaptability across different operating conditions while maintaining cost-effectiveness compared to multiple specialized sensors.
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
Enables reliable and cost-effective determination of carbon dioxide concentration and mass flow in fluid mixtures, independent of mass flow, facilitating precise exhaust gas recirculation and improving measurement robustness compared to traditional methods.
Implementation Method 1
leveraging sound dispersion effects to calculate characteristic values representative of concentration and mass flow
Implementation Method 2
A first propagation time (L1) of the first sound signal (SS1) is determined and a second propagation time (L2) of the second sound signal (SS2) is determined
Data Source
AI summary
The present disclosure relates to sensors and the teachings may be applied to a method and a corresponding apparatus for determining a concentration of a constituent of a fluid mixture in a fluid chamber. A method may include sending and receiving a first sound signal; sending and receiving a second sound signal; measuring the propagation time of the sound signals; calculating a value based on the propagation times representative of the concentration; sending and receiving a third sound signal with a second sound conversion unit; measuring a third propagation time; and calculating a second characteristic value based on the first propagation time and the third propagation time, representative of a mass flow of the fluid mixture.