Variable Resistor Gas Sensor Phase Delay Measurement
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Solution Overview
Problem
Existing MEMS micro-sensor devices face inaccuracies in pressure readings due to temperature fluctuations and require integration with CMOS processes and MEMS micro-devices, while lacking the capability to measure gas composition effectively.
Innovation Solution
A method using a variable electrical resistor with a readout circuit that measures the phase delay between modulated electrical excitation and thermal response to determine gas composition and pressure, leveraging thermal conductivity and capacity of the surrounding gas.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional pressure sensors (Pirani gauge) are used to achieve wide dynamic range and low cost, then manufacturing cost and simplicity are improved, but integration with CMOS processes and MEMS micro-devices becomes difficult
Solution Approach 1:
The patent combines the pressure sensing function with standard CMOS fabrication processes and MEMS micro-device structures. The sensor integrates multiple functional elements (heating element, sensing elements, readout circuitry) into a single CMOS-compatible device, enabling simultaneous fabrication with other MEMS components like bolometers, gyroscopes and accelerometers.
Solution Approach 2:
The sensor design achieves multi-functionality by incorporating both pressure sensing and gas composition detection capabilities within the same device structure. The sensor can operate across a wide dynamic range while maintaining compatibility with standard manufacturing processes, serving multiple application needs.
2Ease of manufacture
If MEMS micro-sensor devices are used to achieve low cost and CMOS-compatible integration, then ease of manufacture and integration are improved, but measurement accuracy deteriorates due to temperature fluctuations
Solution Approach 1:
The patent implements temperature compensation through feedback mechanisms. Temperature-sensitive and temperature-insensitive elements are coupled to a bridge readout circuit that provides real-time compensation for temperature-induced resistance changes, maintaining measurement accuracy despite temperature fluctuations.
Solution Approach 2:
The sensor utilizes changes in electrical resistance parameters of the variable resistor in response to temperature and pressure variations. By monitoring resistance changes and applying compensation algorithms, the system maintains accurate pressure readings across varying temperature conditions.
3Measurement precision
If temperature compensation is achieved using temperature-sensitive and temperature-insensitive elements with bridge readout circuit, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The temperature compensation functionality is merged into the standard CMOS fabrication process. The temperature-sensitive and temperature-insensitive elements are integrated alongside the main sensing elements using the same manufacturing steps, eliminating the need for separate compensation circuits and reducing overall device complexity.
4Device complexity
If absolute voltage reading is used for pressure measurement, then device simplicity is improved, but measurement precision deteriorates due to fabrication errors
Solution Approach 1:
The patent employs a bridge readout circuit that provides differential voltage readings instead of absolute voltage measurements. This differential approach cancels out common-mode errors including fabrication variations, providing more accurate pressure measurements while maintaining reasonable circuit complexity.
5Ease of manufacture
If miniaturization is attempted to address high-performance micro-packaging markets, then ease of manufacture and integration are improved, but measurement capability deteriorates
Solution Approach 1:
The miniaturized sensor maintains universal measurement capability by integrating both pressure sensing and gas composition detection functions within the small MEMS structure. The sensor can simultaneously measure multiple parameters despite its reduced size, addressing the needs of high-performance micro-packaging applications.
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 real-time gas composition and pressure measurements over a wide dynamic range, compatible with standard CMOS fabrication processes, and provides relative immunity to temperature fluctuations.
Implementation Method 1
When the variable resistor is electrically excited and heated by the readout circuit, its temperature at equilibrium is a function of applied electrical power and of thermal transfer to the environment and to the surrounding gas
Implementation Method 2
its temperature at equilibrium is a function of applied electrical power and of thermal transfer to the environment and to the surrounding gas
Implementation Method 3
measuring its dynamic thermal response. In the thermal domain, the resistor has a low-pass characteristic, whose phase delay is determined by the thermodynamic characteristics of the surrounding gas such as composition and pressure
Implementation Method 4
measuring its dynamic thermal response. In the thermal domain, the resistor has a low-pass characteristic, whose phase delay is determined by the thermodynamic characteristics of the surrounding gas such as composition and pressure
Data Source
AI summary
A method for sensing gas composition and gas pressure, based on the thermal constants of a variable electrical resistor, is presented. The method for sensing gas composition and pressure includes monitoring a variable electrical resistor whose dynamic thermal response is determined by the thermal conductivity and thermal capacity of the surrounding gas of a given atmospheric environment. In the thermal domain, the sensor has a low-pass characteristic, whose phase delay is determined by the thermodynamic characteristics of the surrounding gas such as composition and pressure. The method can be used for sensing gas composition and can also be used for sensing gas pressure.