Resonant CO2 sensing with mitigation of cross-sensitivities

Patent metadata

Field	Value
Publication number	US-9778238-B2
Application number	US-201414480986-A
Country	US
Kind code	B2
Filing date	Sep 9, 2014
Priority date	Sep 9, 2014
Publication date	Oct 3, 2017
Grant date	Oct 3, 2017

Abstract

Various exemplary embodiments relate to a device to measure carbon dioxide (CO 2 ) levels, including a first oscillator group comprising a first sensor to measure air pressure, where the first sensor comprises a first sealed membrane, and where the first sealed membrane overlays a sealed first cavity; a second oscillator group including a second sensor to measure the resonance frequency of a second unsealed oscillating membrane, and where the second unsealed membrane overlays a second cavity in contact with the air outside of the second sensor; and a mixer accepting as input a first frequency measurement output from the first oscillator group and a second frequency measurement output from the second oscillator group, outputting the difference of the first frequency measurement and the second frequency measurement, and computing a carbon dioxide measurement based on the difference.

First claim

What is claimed is:

1. A device to output a difference of frequency measurements, comprising:
a first oscillator group comprising a first sensor to measure air pressure, wherein the first sensor comprises a first sealed membrane, wherein the first sealed membrane overlays a sealed first cavity;
a second oscillator group comprising a second sensor to measure the resonance frequency of a second unsealed oscillating membrane, wherein the second unsealed membrane overlays a second cavity in contact with the air outside of the second sensor; and
a mixer accepting as input a first frequency measurement output from the first oscillator group and a second frequency measurement output from the second oscillator group, and outputting a difference of the first frequency measurement and the second frequency measurement.

2. The device of claim 1 , wherein the first sealed membrane and the second unsealed oscillating membrane measure 200×200 μm 2 .

3. The device of claim 1 , wherein the first sealed membrane is hermetically sealed and deflects under a pressure gradient.

4. The device of claim 3 , wherein deflecting under a pressure gradient comprises deflecting under a pressure difference between inside the membrane and outside the membrane.

5. The device of claim 1 , wherein the second oscillator group further comprises a first top electrode and a second bottom electrode.

6. A device to output a difference of frequency measurements, comprising:
a first sensor to measure air pressure, wherein the first sensor comprises a sealed membrane, wherein the sealed membrane overlays a sealed first cavity;
a second sensor to measure the resonance frequency of an unsealed oscillating membrane, wherein the second sensor comprises a heater, wherein the unsealed membrane overlays a second cavity in contact with the air outside of the second sensor, and wherein the heater is in contact with the interior surface of the second cavity; and
a mixer accepting as input a first frequency measurement output from the first sensor and a second frequency measurement output from the second sensor, and outputting a difference of the first frequency measurement and the second frequency measurement.

7. The device of claim 6 , wherein the sealed membrane and the unsealed oscillating membrane measure 200×200 μm 2 .

8. The device of claim 6 , wherein the sealed membrane is hermetically sealed and deflects under a pressure gradient.

9. The device of claim 6 , wherein the second sensor further comprises a first top electrode and a second bottom electrode.

Assignees

• Ams Int Ag

Inventors

• Van Der Avoort Casper
• Besling Willem

Classifications

• G01N29/2406

  Electrostatic or capacitive probes, e.g. electret or cMUT-probes · CPC title

• G01N2291/0255

  (Bio)chemical reactions, e.g. on biosensors · CPC title

• G01N2291/02818

  Density, viscosity · CPC title

• G01N2291/021

  Gases · CPC title

• G01N2291/0256

  Adsorption, desorption, surface mass change, e.g. on biosensors · CPC title