WO2012165939A1

WO2012165939A1 - Micropump with integrated gas sensing system and method thereof

Info

Publication number: WO2012165939A1
Application number: PCT/MY2012/000111
Authority: WO
Inventors: Lee Hing WAH; Daniel Bien Chia Sheng; Masuri Othman
Original assignee: Mimos Berhad
Priority date: 2011-05-27
Filing date: 2012-05-23
Publication date: 2012-12-06
Also published as: MY186461A

Abstract

The present invention provides a micro-gas sensor comprises a micropump having an inlet and an outlet, wherein the micropump is operable to pump gas through a gas passage therein; and a sensor having a sensor element disposed along the gas passage, wherein the sensor element is suspended within the gas passage. A method of sensing gas is also provided herewith.

Description

MICROPUMP WITH INTEGRATED GAS SENSING SYSTEM AND METHOD THEREOF

Field of the Invention

[0001] The present invention relates to a sensing system. In particular, the present invention relates to a micropump gas sensing system and a method of sensing 5 gas.

Background

[0002] Chemical gas detection or sensing has an increasing demand in many sectors such as agricultural, environmental monitoring, biomedical and other industrial processes. In general, gas sensor or detector requires good contact of the gas particles

10 to the sensing element. Conventionally, gas sensor device utilizes the pressure gradient through passive or natural characteristics in the gas flow for the gas particles to come into contact with sensing elements of the gas sensor. FIGs. 1A-1C exemplify a various gas sensor system that functioned based on the aforementioned principle. These gas sensor systems are fabricated using micromachining technology, where 5 FIG. 1A is a micro-hotplate sensor, FIG. IB is a hot wire sensor and FIG. 1C is an

integrated gas sensor.

[0003] There are known issues with these sensors: the sensor response is slow; the gas particles that are in contact with the sensing elements are limited in mass and relatively lower concentration. Conventional sensing devices are made with sensing

20 materials incorporated within the sensing devices with a small sensing area exposed on

a side of the devices' surface and the rest of the sensing materials embedded within the

SUBSTITUTE SHEET sensing devices. Hence, the limited area for gas particles detection resulting in lower or limited device sensitivity.

[0004] Further, gas suction for micro-gas sensors is accomplished naturally through diffusion of gas particles resulting in slower rate of gas detection. There is also no assurance as to the gas particles are appropriately directed across the sensing contact area for carrying out the gas sensing.

[0005] US 6,889,576 relates to an integrated mesopump-sensor suitable for disposition in 2D and 3D arrays. The mesopump sensor comprises multiple compartments that are fluidly connected in series, an inlet and an outlet. A sensor element is mounted along the inlet path, undisruptively, for sensing fluid. The sensor element comprises sensors that are disposed on the walls of narrow channels so as to maximize the surface-to-volume ratio to maximize the interaction between the fluid and the sensor material.

[0006] US 2010/0154519 relates to a micro-electro-mechanical system of MEMS type allowing fluid to flow through therein. The system comprises a piezoelectric micropump for pumping fluid across the system, and sensors disposed along the fluid path. The fluid path can be channeled into multiple paths with different types of sensors disposed at the respective path. The multiple paths are ultimately joined up to the outlet. Summary

[0007] In one aspect of the present invention, there is provided a micro-gas sensor comprises a micropump having an inlet and an outlet, wherein the micropump is

SUBSTITUTE SHEET operable to pump gas through a gas passage therein; and a sensor having a sensor element disposed along the gas passage, wherein the sensor element is suspended within the gas passage.

[0008] In one embodiment, the micro-gas sensor may further comprise another sensor having a sensor element suspended within the gas passage at a different location. The sensors may be disposed at the inlet and another sensor may be disposed at the outlet. Further, both sensors may be disposed at respective downstream spout of the inlet and the outlet. Preferably, the sensors are hinged to suspend in the gas passage through contact pad. [0009] In another embodiment, the micropump may be a diaphragm pump, a piezoelectric pump, a electrostatic pump, a thermo thermo-pneumatic pump, a bimetallic pump or a shape memory alloy-based pump. On the other hand, the sensor may be a MEMS-based gas sensor. Possibly, the sensor is an active-type gas sensor such as a micro-hotplate platform sensor. Alternatively, the sensor may be a passive- type gas sensor such as a resistive sensor or a capacitive-sensor.

[0010] In a further embodiment, the sensor may comprise any of metal oxides selected from a group consisting of tin oxide (Sn0₂), tungsten oxide (WO_x), tantalum pentoxide (Ta₂05), aluminium oxide (AI2O3) copper oxide (CuO), iron oxide (Fe₂0₃), titanium oxide (TiO), Neodymium Oxide (Nd₂0₃), indium oxide (In?0₃), copper oxide (CuO), vanadium pentoxide (ν¾0₅) and zinc oxide (ZnO).

SUBSTITUTE SHEET [0011] In another aspect of the present invention, there is provided a method of sensing gas through the aforesaid micro-gas sensor. The method may comprise pumping gas into the micropump through the inlet and the outlet; sensing the gas that passed through the sensor element suspending within the gas passage; and acquiring signals from the sensor element.

Brief Description of the Drawings

[0012] This invention will be described by way of non-limiting embodiments of the present invention, with reference to the accompanying drawings, in which:

[0013] FIGs. 1A-1C exemplifies a various type of known sensing elements; [0014] FIG. 2 illustrates an integrated micropump gas sensing system in accordance with one embodiment of the present invention;

[0015] FIG. 3 A illustrates a MEMS-based gas sensor adapted for the integrated micropump gas sensing system of FIG. 2 in accordance with an embodiment of the present invention; [0016] FIG. 3B exemplifies a sensing element adapted for the integrated micropump gas sensing system in accordance with another embodiment of the present invention.;

[0017] FIGs. 4A-4C illustrate various types of MEMS-based gas sensors which can be integrated on in the micropump of FIG. 2;

SUBSTITUTE SHEET [0018] FIG. 5 illustrates an operation flow of the integrated micropump gas sensing system of FIG. 2 in accordance with one embodiment of the present invention; and

[0019] FIGs. 6A-6B illustrates a gas sensing operation through the gas sensing system of FIG. 2.

Detailed Description

[0020] In line with the above summary, the following description of a number of specific and alternative embodiments is provided to understand the inventive features of the present invention. It shall be apparent to one skilled in the art, however that this invention may be practiced without such specific details. Some of the details may not be described at length so as not to obscure the invention. For ease of reference, - common reference numerals will be used throughout the figures when referring to the same or similar features common to the figures.

[0021] The present invention offers a gas sensor or detector that optimizes sensing areas of the sensing elements adapted within sensor, gas flow rate and density of gas particles in contact with the sensing contact area.

[0022] For that purpose, this invention proposes an integrated micropump gas sensing system which consists of a micropump for suction of the gas particles, a double-sided sensing element MEMS-based gas sensor and nozzle elements as gas flow passage. The integrated micropump gas sensing system comprises sensors integrated within a micropump. In particular, the micropump having an inlet, an outlet and two sensing elements that are disposed along fluid path of the inlet and the outlet

SUBSTITUTE SHEET respectively. The micropump can be a piezo-disc pump, and the sensor elements may be MEMS-based gas sensors.

[0023] Operationally, the micropump is actuated to pump gases into the micropump through the inlet and out from the micropump through the outlet. As the gas flows across the fluid path, the sensors mounted along the inlet and the outlet respectively are therefore able to provide gas sensing and detection. In an embodiment, it is desired that the gas sensing elements have an aerodynamic shape to minimize the flow disruption when the gas flows through the fluid path. As the two sensing elements are exposed on the fluid path, and not embedded within the surfaces of the sensor body, the two sides of each sensor are utilized for sensing as the gas passes through micropump. Such sensor is relatively more effective because it optimizes the overall exposed surface areas of the sensor to the gas to be detected. As the micropump is used, it further increases the rate of gas detection. It increases the sensing efficiency and sensitivity of a gas-sensing device.

[0024] FIG. 2 illustrates an integrated micropump gas sensing system 100 (or gas sensing system in short) in accordance with one embodiment of the present invention. The gas sensing system 100 comprises a micropump 102 and gas sensors 104. The micropump 102 can be a diaphragm micropump 105 comprises a pump body 112, an inlet 114, an outlet 116, a diaphragm element 118 and a Piezo-disk 120. The pump body 112 is formed by two attached substrates 122 with a top substrate defining a recess area and the bottom substrate having two through holes defining the inlet 114 and the outlet 116 respectively. When the top substrate and the bottom substrate are attached together, the recess area forms a pump cavity 124. Accordingly, the inlet 114,

SUBSTITUTE SHEET the pump cavity 124 and the outlet 116 forms a gas flow passage of the gas sensing system 100. The inlet 114 and 116 may further provided with check valve or the like for restricting the fluid flow in unidirectional only.

[0025] Still referring to FIG. 2, the diaphragm element 118 is provided on the top substrate, sealing the cavity beneath. The Piezo-disk 120 is further attached on top of the diaphragm element 118. The diaphragm element 118 operationally moves in a reciprocating action causing the volume of the pump cavity to increase and decrease to pump air in and out of the micropump through the inlet 114 and the outlet 116. The diaphragm element's 118 can be actuated by any known actuating principle, such as piezoelectric, electrostatic, thermo-pneumatic, bimetallic actuation and shape memory alloy, etc. In the present embodiment, the Piezo-disk 120 attached thereto is selected herewith, by way of non-limiting example, for actuating the diaphragm element 118. Such configuration may have similar configuration to any piezoelectric-based pumps that are well known in the art, and therefore, no further details is provided in the present description.

[0026] As shown in FIG. 2, the two gas sensors 104 are respectively disposed at the inlet 114 and the outlet 116. Each of the gas sensors 104 comprises a sensing element 125. Preferably, the sensing elements 125 are floating along the gas flow passage such that the sensing elements are entirely exposed for sensing the gas. In the present embodiment, the sensing elements 125 are configured at the respective downstream spout of the inlet 114 and the outlet 116.

[0027] FIG. 3A illustrates a MEMS-based gas sensor 300 adapted for the integrated micropump gas sensing system 100 of FIG. 2 in accordance with an

SUBSTITUTE SHEET embodiment of the present invention. The MEMS-based gas sensor 300 comprises a contact pad 302 and a sensing element 304. The MEMS-based gas sensor 300 is adapted for disposed along the gas passage of the gas sensing system 100. As aforementioned, it is preferred that the gas sensor is floating along the gas passage. In the present embodiment, the sensing element 304 is hinged on the substrate 122 via the contract pad 302. More specifically, the sensing element 304 is hinged across the opening of the inlet or outlet on the substrate 122. An insulating layer 320 may further be provided between the contact pad 302 and the substrate 122. Accordingly, the sensing element 304 is suspended across the inlet/outlet opening. In the present embodiment, the contact pad 302 embraces the perimeter of the sensing element 304.

[0028] FIG. 3B exemplifies a gas-sensing element 310 in adapted for the integrated micropump gas sensing system 100 in accordance with another embodiment of the present invention. The gas-sensing element 310 has contact pads 315 extended from its sides and attached to the substrate 318 for hinging the sensing element across the gas passage.

[0029] FIGs. 4A-4C illustrate various types of MEMS-based gas sensors, which can be integrated on in the micropump 102 of FIG. 2. The MEMS-based gas sensors can be of an active-type gas sensor such as micro-hotplate platform shown in FIG. 4A or in the form of a passive-type gas sensor such as a resistive or capacitive- type platform shown in FIG. 4B and FIG. 4C respectively.

[0030] By way of illustrations, not limitation, the sensing elements incorporated for the gas sensor of the present invention may include metal oxide types sensing elements. The metal oxide may be selected from a group consisting and not

SUBSTITUTE SHEET limited to tin oxide (Sn02), tungsten oxide (WO_x), tantalum pentoxide (Ta₂0₅), aluminium oxide (AI2O3) copper oxide (CuO), iron oxide (Fe2(¾), titanium oxide (TiO), Neodymium Oxide (Nd203), indium oxide (Ιη2θ₃), copper oxide (CuO), vanadium pentoxide (V^Os), zinc oxide (ZnO) and others. [0031] FIG. 5 illustrates an operation flow of the integrated micropump gas sensing system 100 of FIG. 2 in accordance with one embodiment of the present invention. For clarity, some steps of the operation flow are illustrated in conjunctions with FIGs. 6A-6D. The operation flow starts with actuating micropump at step 502 such that the diaphragm element moves in a reciprocating motion. When the diaphragm element is moving up as shown in FIG. 6 A, which increases the volume of the pump cavity, gas particles are drawn towards the gas sensor disposed at the inlet at step 504. As the pump cavity increases its volume, the gas particles are accelerated and directed to pass through the inlet into the pump cavity as shown in FIG. 6B at step 504. The gas particles bombard both sides of the sensing surface of the gas-sensing element in higher concentration resulting in higher signal sensitivity at step 506. The gas sensing commences at step 508 to generate the relevant electrical signals. The gas particles continue to enter the pump cavity as shown in FIG. 6C at step 510. At step 512, the diaphragm element displaces to move in an opposing direction causing the volume of the pump cavity to decrease as shown in FIG. 6D. The gas particulars within the pump cavity are therefore pumped out from the pump cavity through the outlet at step 514. As the gas particles exit the pump cavity, the gas particles come in contact with both sides of the sensing element disposed at the outlet at step 516. At step 518, the gas sensing at the outlet commences as well as the gas particles exits the gas sensor system at step 520.

SUBSTITUTE SHEET [0032] The present invention offers a gas sensing system that senses gas through a forced gas stream formed by the micropump. The gas is sensed twice in one sensing cycle both upstream and downstream of the gas sensing system. Further, as the sensing elements are disposed along the fluid path, the sensing surface of each sensing element is optimized. Signals from the respective gas sensing elements are acquired by an external readout circuitry for further processing. In one embodiment, the signals taken from the two sensing elements can be averaged out as a single reading.

[0033] The use of the micropump, through forced airflow, ensures majorities of the gas particles enter the integrated micropump sensing system with an accelerated flow rate, and hence relatively higher density. Each of the gas sensors is further disposed along the air passage in a floating matter to optimize the surface area of the sensing elements. The gas sensing system further provided the gas sensors at the inlet and the outlet. The overall sensing area provided by each sensor increases thereby increases the efficiency. Further, the sensors are provided at the inlet and outlet allowing gas detection to occur in both pre- and post-entry of the gas particles in the micro gas sensing system.

[0034] While specific embodiments have been described and illustrated, it is understood that many changes, modifications, variations and combinations thereof could be made to the present invention without departing from the scope of the invention.

SUBSTITUTE SHEET

Claims

1. A micro-gas sensor comprising:

a micropump having an inlet and an outlet, wherein the micropump is operable to pump gas through a gas passage therein; and

a sensor having a sensor element disposed along the gas passage, wherein the sensor element is suspended within the gas passage.

2. The micro-gas sensor according to claim 1, further comprising another sensor having a sensor element suspended within the gas passage at a different location.

3. The micro-gas sensor according to claim 2, wherein one of the sensors is disposed at the inlet and another sensor is disposed at the outlet.

4. The micro-gas sensor according to claim 3, wherein both sensors are disposed at respective downstream spout of the inlet and the outlet.

5. The micro-gas sensor according to claim 3, wherein the sensors are hinged to suspend in the gas passage through contact pad.

6. The micro-gas sensor according to claim 1, wherein the micropump is a diaphragm pump.

7. The micro-gas sensor according to claim 1, wherein the micropump is a piezoelectric pump.

SUBSTITUTE SHEET

8. The micro-gas sensor according to claim 1 , wherein the micropump is a electrostatic pump.

9. The micro-gas sensor according to claim 1 , wherein the micropump is a thermo thermo-pneumatic pump.

10. The micro-gas sensor according to claim 1, wherein the micropump is a bimetallic pump.

11. The micro-gas sensor according to claim 1, wherein the micropump is a shape memory alloy-based pump.

12. The micro-gas sensor according to claim 1, wherein the sensor is a MEMS- based gas sensor.

13. The micro-gas sensor according to claim 12, wherein the sensor is an active- type gas sensor.

14. The micro-gas sensor according to claim 13, wherein the sensor is a micro- hotplate platform sensor.

15. The micro-gas sensor according to claim 12, wherein the sensor is a passive- type gas sensor.

SUBSTITUTE SHEET

16. The micro-gas sensor according to claim 15, wherein the sensor is a resistive sensor.

17. The micro-gas sensor according to claim 15, wherein the sensor is a capacitive- sensor.

18. The micro-gas sensor according to claim 1, whereanyin the sensor comprises any of metal oxides selected from a group consisting of tin oxide (Sn(¾), tungsten oxide (WO_x), tantalum pentoxide (TaaOs), aluminium oxide (AI2O3) copper oxide (CuO), iron oxide (Fe203), titanium oxide (TiO), Neodymium Oxide Nd20₃), indium oxide (Ιη2θ3), copper oxide (CuO), vanadium pentoxide Γν¾θ5) and zinc oxide (ZnO).

19. A method of sensing gas through a micro-gas sensor according to claim 1, the method comprises: pumping gas into the micropump through the inlet and the outlet; sensing the gas that passed through the sensor element suspending within the gas passage; and acquiring signals from the sensor element.

SUBSTITUTE SHEET