SAW Microsystem for Low-Pressure Gas Measurement
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Solution Overview
Problem
Existing pressure sensors, particularly those using surface acoustic wave (SAW) and bulk acoustic wave (BAW) technologies, lack sensitivity in low and very low pressure ranges, making them unusable for precise measurements below 1 mbar, and are also affected by the thermal conductivity of gases, leading to measurement uncertainty when the gas composition is unknown.
Innovation Solution
A microsystem incorporating an elastic wave device with a radiofrequency wave generator operating above 200 MHz, capable of self-calibration based on gas composition, and featuring means to modify temperature, such as a heating resistor, to enhance sensitivity and precision by analyzing frequency variations induced by pressure changes in a gas, while minimizing heat loss and optimizing temperature coefficients for precise pressure measurement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional SAW or BAW pressure sensors are used, then the device structure is simple, but the sensitivity in low and very low pressure ranges is insufficient
Solution Approach 1:
The patent changes the operating parameters of the elastic wave device by applying it to a heated body, utilizing temperature-induced frequency shifts to enhance pressure measurement sensitivity in the low pressure range. This parameter change approach allows the sensor to achieve high sensitivity without complicating the basic device structure.
Solution Approach 2:
The patent replaces direct mechanical pressure detection with a thermal field-based measurement approach. By measuring frequency variations caused by temperature changes (which are themselves influenced by pressure through thermal conductivity), the system achieves sensitive pressure detection without complex mechanical structures.
2Measurement precision
If thermal pressure gauges are used, then the measurement can be performed, but the sensitivity to gas nature is high leading to measurement uncertainty
Solution Approach 1:
The patent employs feedback mechanisms to compensate for gas nature effects. By continuously monitoring frequency variations and comparing them against reference values, the system can identify and correct for thermal conductivity variations caused by different gas compositions, thereby maintaining measurement accuracy.
Solution Approach 2:
The patent utilizes temperature as a controlling parameter to standardize measurement conditions. By operating the sensor at controlled temperatures and using temperature-induced frequency shifts as a reference, the system can compensate for variations in gas thermal conductivity and achieve consistent pressure measurements across different gas types.
3Loss of time
If the response time is reduced to tens of seconds or less than 100 milliseconds, then the measurement speed increases, but the energy consumption increases
Solution Approach 1:
The patent employs periodic heating cycles rather than continuous heating to achieve rapid response. By applying heat in controlled pulses and utilizing the thermal mass of the body, the system achieves fast response times (tens of seconds or less than 100 milliseconds) while reducing overall energy consumption compared to continuous operation.
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 system achieves high precision in the range of 10^-3 mbar to 10^-1 mbar, with the ability to operate across a wider pressure range, and reduces response time and energy consumption, enabling accurate pressure measurement and self-calibration independent of gas composition.
Implementation Method 1
Devices of the 'elastic wave' type (SAW or BAW) exploit the electro-acoustic properties of piezoelectric substrates such as quartz, lithium niobate (LiNbO3) or zinc oxide to generate surface or volume.
Implementation Method 2
The mechanical vibration generated propagates at frequencies depending on the crystallographic direction, the dimensions of the crystal lamina and the electromechanical conversion factor of the material.
Implementation Method 3
the thermal conductivity of a gas is a function of both the pressure and its chemical nature
Data Source
Figure 1~2B
Figure 3~4
Figure 5
AI summary
The system (1) has a radiofrequency signal wave generator (8) for generating the radiofrequency wave of 2.5 gigahertz (GHz), and a heating resistor (11) arranged above or below a surface acoustic wave device (2) for modifying the temperature of the surface acoustic wave device. A comparator (9) is provided for comparing the operating frequency of the surface acoustic wave device with the reference frequency. The surface acoustic wave device comprises an acoustic wave emitter (3) connected to the generator, and an acoustic wave receiver (5) connected to the comparator. An independent claim is also included for a method for measuring a gas pressure using a gas pressure measuring system.