Gas concentration sensor with a suspended structure

Patent metadata

Field	Value
Publication number	US-9733223-B2
Application number	US-201514619656-A
Country	US
Kind code	B2
Filing date	Feb 11, 2015
Priority date	Feb 13, 2014
Publication date	Aug 15, 2017
Grant date	Aug 15, 2017

Abstract

A concentration sensor for at least one given gas comprising at least one suspended structure ( 2 ) with respect to a support, said suspended structure ( 2 ) being of an electrically conductive material and said structure having a low heat response time, means for biasing said suspended element ( 2 ) and means ( 8 ) for measuring the variation of the electric voltage at the terminals of the suspended structure ( 2 ), the biasing means ( 6 ) being formed by an alternating current source the intensity of which heats the suspended structure ( 2 ) and the frequency of which gives rise to a phase shift between a signal of the biasing means and a signal measured by the measuring means, and means for determining a phase shift variation due to a gas concentration variation and means for determining the concentration variation of said gas from the phase variation.

First claim

The invention claimed is:

1. A concentration sensor for at least one gas species comprising:
at least one suspended structure in a gas environment with respect to a support, said at least one suspended structure being of an electrically conductive material;
a biasing circuit configured to bias said at least one suspended structure by providing an alternating current to a first terminal of said at least one suspended structure at a first end thereof and a second terminal of said at least one suspended structure at a second end thereof opposite the first end;
a measuring circuit configured to measure variation of electric voltage at the first and second terminals of said at least one suspended structure;
a first determination circuit configured to determine a variation of a phase shift between a signal generated by the biasing circuit to bias said at least one suspended structure and a signal measured by the measuring circuit that corresponds to the variation of the electric voltage at the first and second terminals, the variation of the phase shift being due to a concentration variation of the at least one gas species; and
a second determination circuit configured to determine the concentration variation of the at least one gas species from the determined variation of the phase shift,
wherein the biasing circuit includes an alternating current source configured to provide the alternating current, an intensity of which provides heating of said at least one suspended structure by Joule effect, and a frequency of which is such that it gives rise to the phase shift between the signal generated by the biasing circuit to bias said at least one suspended structure and the signal measured by the measuring circuit that corresponds to the variation of the electric voltage at the first and second terminals.

2. The concentration sensor according to claim 1 , wherein the signal measured by the measuring circuit is equal to a 3ω component.

3. The concentration sensor according to claim 2 , wherein the 3ω component is equal to V 3ω =1/2R 0 I 0 ·TCR·ΔT d cos(3ωt+φ).

4. The concentration sensor according to claim 1 , wherein said at least one suspended structure has a heat response time lower than 100 ms.

5. The concentration sensor according to claim 1 , wherein the frequency of the biasing circuit is fixed.

6. The concentration sensor according to claim 5 , wherein the frequency of the biasing circuit is close to or equal to half a cut-off frequency of a heat transfer function of the concentration sensor in the gas environment.

7. The concentration sensor according to claim 6 , wherein the frequency of the biasing circuit is close to or equal to half the cut-off frequency of the heat transfer function of the concentration sensor in the gas environment in the absence of the at least one gas species, a concentration of which is desired to be measured.

8. The concentration sensor according to claim 1 , further comprising a phase locked loop in which a phase shift value is set,
wherein a value of the variation of the phase shift due to the concentration variation of the at least one gas species is measured, and
wherein the frequency of the biasing circuit is changed such that the measured phase shift is equal to the set phase shift, the change in the frequency being used to determine the concentration variation.

9. The concentration sensor according to claim 1 , wherein said at least one suspended structure includes at least one nanowire.

10. The concentration sensor according to claim 9 , wherein the at least one nanowire has a length lower than 1 mm and a cross-section lower than 1 μm×1 μm.

11. The concentration sensor according to claim 1 , wherein said at least one suspended structure includes several suspended structures, each of the suspended structures being biased, and a signal being measured at the first and second terminals of each of the suspended structures by the measuring circuit, whereupon these signals are averaged.

12. A device for measuring a concentration of the at least one gas species contained in the gas environment comprising:
a chromatography column; and
at least one concentration sensor according to claim 1 , said at least one concentration sensor being disposed at an output of or within the chromatography column.

13. The concentration sensor according to claim 1 , wherein the at least suspended structure consists of a single conductive material.

14. The concentration sensor according to claim 1 ,
wherein the at least suspended structure is not configured to vibrate, and
wherein the phase shift variation is caused by the concentration variation of the at least one gas species and not vibration of the at least one suspended structure.

15. The concentration sensor according to claim 1 , wherein the variation in the phase shift constitutes a variation in cut-off frequency.

16. A method for measuring the concentration of at least one gas species using a suspended structure in a gas environment, said method comprising:
applying a biasing signal to the suspended structure, which comprises an electrically conductive material, at a given frequency so as to heat the suspended structure and so as to create a phase shift between the biasing signal and a temperature variation of the suspended structure;
measuring a variation of the phase shift; and
determining a concentration variation of the at least one gas species,
wherein the biasing signal is an alternating current signal applied to a first terminal of the suspended structure at a first end thereof and a second terminal of the suspended structure at a second end thereof opposite the first end.

17. The method for measuring the concentration of at least one gas species according to claim 16 , wherein the suspended structure includes a biasing circuit, a frequency of the biasing circuit being set to half a cut-off frequency of a heat transfer function characteristic of heat exchanges of the suspended structure with the gas environment for a given gas environment.

18. The method for measuring the concentration of a gas species according to claim 17 , wherein in the given gas environment, the concentration of the at least one gas species is null.

19. The method for measuring the concentration of at least one gas species according to claim 16 ,
wherein the phase shift is set to a control value,
wherein variations of the phase shift relative to the control value are measured during the concentration variation of the at least one gas species, and
wherein the given frequency is changed so as to bring the phase shift closer to the control value.

20. The method for measuring the concentration of at least one gas species according to claim 16 , wherein the at least one gas species is in a mixture with a carrier gas so as to form the gas environment, the carrier gas being selected so as to have a heat propagation time different from a heat propagation time of the at least one gas species.

Assignees

• Commissariat A L'Energie Atomique Et Aux Ene Alt
• Commissariat L Energie Atomique Et Aux Energies Alternatives

Inventors

• Ruellan Jeremie
• Duraffourg Laurent

Classifications

• G01N27/18 Primary

  caused by changes in the thermal conductivity of a surrounding material to be tested (G01N27/20 takes precedence) · CPC title

• G01N30/62 Primary

  Detectors specially adapted therefor · CPC title

• B01D53/02

  by adsorption, e.g. preparative gas chromatography {(solid sorbent compositions B01J20/00, preparation of inorganic compounds or elements C01)} · CPC title