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JP-7854713-B2 - Method for extracting gas characteristics by acoustic measurement and apparatus for the same purpose

JP7854713B2JP 7854713 B2JP7854713 B2JP 7854713B2JP-7854713-B2

Inventors

  • ユルドゥルム タンジュ
  • 吉川 元起

Assignees

  • 国立研究開発法人物質・材料研究機構

Dates

Publication Date
20260507
Application Date
20221018

Claims (10)

  1. In a method for extracting gas characteristics using acoustic measurements, The casing and An acoustic wave output means attached to one end of the housing, Using an acoustic resonator having sound pressure measuring means arranged inside the housing, The steps include: introducing a target gas into the acoustic resonator while emitting an acoustic wave excited by a specific signal from the acoustic wave output means into the acoustic resonator, and measuring the sound pressure caused by the acoustic wave in both the frequency domain and the time domain using the sound pressure measuring means; A method comprising the step of extracting the characteristics of the target gas from the results obtained in the measurement step.
  2. In the measurement step, The measurement in the frequency domain includes measuring the signal output from the sound pressure measuring means using an acoustic wave excited by 1/f noise with constant energy per octave, and obtaining the frequency response function of the sound pressure acting on the sound pressure measuring means. The measurement in the time domain includes measuring the time variation of the signal output from the sound pressure measuring means using an acoustic wave excited by a fixed-frequency sine wave. The method according to claim 1.
  3. The extraction step described above is: This includes obtaining the physical parameters of the target gas from the frequency response function obtained from the measurement in the aforementioned frequency domain, This includes extracting feature quantities from the time evolution of the output signal obtained by the measurement in the aforementioned time domain, The method according to claim 2.
  4. The measurement in the aforementioned frequency domain is performed as follows: The signal output from the sound pressure measuring means when the acoustic resonator is filled with the target gas is measured, and a first frequency response function is obtained. This includes measuring the signal output from the sound pressure measuring means when the acoustic resonator is filled with purge gas, and obtaining a second frequency response function. In the extraction step, the physical parameters of the target gas are obtained based on the selected resonance peak obtained by comparing the first and second frequency response functions. The method according to claim 3.
  5. The measurement in the time domain includes introducing the target gas and the purge gas alternately into the acoustic resonator and measuring the time change of the signal output from the sound pressure measuring means. In the extraction step, feature quantities are extracted from the time change of the output signal. The method according to claim 3.
  6. The method according to claim 3, further comprising applying principal component analysis or linear discriminant analysis to a data set obtained in the extraction step, which consists of physical parameters of the target gas from measurements in the frequency domain and feature quantities from measurements in the time domain.
  7. The method according to any one of claims 1 to 6, wherein the acoustic resonator is a single-ended tube with one end open and the other end closed, and is a resonator with a wavelength of (1/4 + 2n/4) wavelengths (where n is an integer greater than or equal to 0), or a double-ended tube with both ends open, and is a resonator with a wavelength of (1/2 + 2n/2) wavelengths (where n is an integer greater than or equal to 0).
  8. The method according to claim 7, wherein the acoustic resonator is the one-sided open tube and is a resonator with a wavelength of (1/4 + 2n/4) wavelengths (where n is an integer greater than or equal to 0).
  9. The method according to claim 8, wherein the acoustic resonator is a quarter-wavelength resonator.
  10. An apparatus for extracting gas characteristics by acoustic measurement, The casing and An acoustic wave output means attached to one end of the housing, The acoustic resonator comprises a sound pressure measuring means arranged within the housing, The aforementioned acoustic resonator has an introduction section for introducing the target gas into its interior, and an exhaust section for discharging the internal gas to the outside. The system is configured such that an acoustic wave excited by a specific signal is emitted from the acoustic wave output means into the acoustic resonator, while a target gas is introduced into the acoustic resonator, and the sound pressure due to the acoustic wave can be measured by the sound pressure measuring means in both the frequency domain and the time domain. Device.

Description

This invention relates to a method and apparatus for extracting gas characteristics by acoustic measurement, and more particularly to a method and apparatus for extracting gas characteristics by acoustic measurement in both the frequency domain and the time domain. Measuring, sensing, and extracting gas properties is crucial for identifying chemical species. Gas detectors measure specific properties such as molecular weight, density, volatility, and vapor pressure. Various gas properties can be extracted using analytical models based on the measured signals, or by combining multiple sensors that measure different properties. Such high-precision measurements enable the identification of gas samples based on the properties of gas molecules, and are used in many fields, including agriculture, healthcare, medicine, safety, robotics, and environmental science. Existing gas sensors come in various types, utilizing metal oxides, chemistristors, field-effect transistors, electrochemistry, surface acoustic waves (SAW), cantilevers, films, quartz crystals, and microchannels. When the substance being measured flows around the sensor element, the adsorption of the target molecules onto the sensor element alters its behavior, resulting in a unique signal based on the characteristics of both the sensor element and the target gas. While this type of sensor typically relies on the chemical affinity between the sensor element and the gas molecules, allowing for specific gas species (types of target gas) to be designed with chemical selectivity, determining physical parameters such as gas density (ρ) and vapor pressure, in addition to concentration (C), remains difficult with simple devices. In contrast, gas sensors that measure physical properties do not depend on the chemical affinity between such sensor elements and target molecules, making them applicable to all types of gases and enabling the quantification of physical parameters. Non-patent documents 1-3 describe acoustic gas sensors using solid piezoelectric SAWs. However, these sensors utilize chemoreceptors to induce frequency shifts, meaning their measurement accuracy depends on the performance of the chemoreceptors, and they also require effort for the synthesis and manufacture of these chemoreceptors. X. Qi, J. Liu, Y. Liang, J. Li, S. He, The response mechanism of surface acoustic wave gas sensors in real time, Japanese Journal of Applied Physics, 58(2019) 014001.L. Zhou, Z. Hu, P. Wang, N. Gao, B. Zhai, M. Ouyang, et al., Enhanced NO2 sensitivity of SnO2 SAW gas sensors by facet engineering, Sensors Actuators B: Chemical, 361(2022) 131735.N. Levit, D. Pestov, G. Tepper, High surface area polymer coatings for SAW-based chemical sensor applications, Sensors Actuators B: Chemical, 82(2002) 241-9. A schematic cross-sectional view showing a specific example of the configuration of an acoustic resonator usable in the present invention.This figure shows the numerical simulation results of the resonant frequency f res of the second resonance of the quarter-wavelength acoustic resonator fabricated in the example, using finite element analysis.This figure shows the results of numerically simulating the frequency response function of the sound pressure acting on the microphone for various sound velocities c in the acoustic resonator fabricated in the example, using finite element analysis.A schematic diagram showing the configuration of a measurement system for gas measurement using the acoustic resonator fabricated in the example.This figure shows the frequency response function obtained by introducing the target gas into the measurement chamber during the frequency domain measurement in the example.This figure shows a magnified view of the area enclosed by the dotted line in Figure 5A (the area including the resonance peak of the second resonance).This figure shows a graph plotting the relationship between the resonant frequency f res and the speed of sound c (Y axis) against the gas density ρ (X axis) for the target gas. For both the resonant frequency f res and the speed of sound c, the coefficient of determination of the approximation curve was R² = 1.The figure shows alternating cycles illustrating the frequency and time domain behavior of n-hexane, relating to the measurement results in the frequency and time domains of the embodiment. The frequency response function inserted in the figure is the resonance peak of pure nitrogen and n-hexane in the frequency range of 5.5 to 8.5 kHz for Figure 5A.The figure shows the root mean square values of the microphone output voltage in the time domain for different gases, relating to the measurement results in the frequency and time domains of the example.Regarding the measurement results in the frequency and time domains of the embodiment, Figure 6B shows the microphone output voltage in the third cycle, with the baseline value (ΔV) subtracted.The measurement results in the frequency and time domains of the embodiment are sho