WO2015020611A1

WO2015020611A1 - A multi-mode mems aerosol detecting device

Info

Publication number: WO2015020611A1
Application number: PCT/SG2014/000373
Authority: WO
Inventors: Campanella HUMBERTO; Narducci MARGARITA S; Cheam DAW DON
Original assignee: Agency For Science, Technology And Research
Priority date: 2013-08-06
Filing date: 2014-08-06
Publication date: 2015-02-12

Abstract

A multi-mode MEMS aerosol detecting device for detecting aerosol particles, the device comprising a chamber having an inlet, the inlet being configured to allow a gas to enter the chamber; a light source configured to illuminate the gas in the chamber with a light; and a MEMS resonator configured to detect the presence of aerosol particles in the gas based on a characteristic of the aerosol particles related to absorbing the light from the light source, wherein the multi-mode MEMS aerosol detecting device is selectable between at least a first mode and a second mode, the second mode being different from the first mode and one of the first and second mode being a photo-acoustic mode for detecting aerosol particles.

Description

A Multi-mode MEMS Aerosol Detecting Device

PRIORITY CLAIM

[1] The present application claims priority of Singaporean Patent Application No. 201305976-1 , filed on 6 August 2013.

FIELD OF INVENTION

[2] The present invention relates broadly to a multi-mode MEMS aerosol detecting device and a method using thereof.

BACKGROUND

[3] An aerosol emission is a suspension of fine solid particles or liquid droplets in a gas. Examples of aerosol emissions include clouds, and air pollution such as smog and smoke. Recently, combustion and industry-generated gases caused by aerosol emission have reached unsustainable levels.

[4] In order to address the problem of aerosol emission, in-situ environmental monitoring networks have to be deployed to offer real-time data of air quality in major cities. Conventionally, aerosol detectors have been used to monitor the presence of aerosol particles.

[5] However, the conventional aerosol detectors suffer from several limitations in detecting aerosol particles. For example, photo-acoustic detectors are generally bulk, lab-oriented instruments that use cavity resonators. Hence, it is impossible to offer an aerosol detector that is portable and is capable of doing real-time monitoring. Other detection techniques that make use of silicon MEMS photo-acoustic detectors and a capacitive MEMS microphone have been proven to be non-portable and cumbersome. [6] Furthermore, the conventional devices are single-mode detectors. In other words, they are only capable of carrying out acoustic pressure detection or aerosol- dependent temperature detection at radio frequencies. Each of these modes of detecting has its own limitations.

[7] Thus, what is needed is a method and device for detecting aerosol particles in more than one mode which allows exploiting the advantages and avoiding the limitations of each mode. It will also be beneficial to present a solution that is compact and non- cumbersome. Furthermore, other desirable features and characteristics will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and this background of the disclosure.

SUMMARY

[8] According to the Detailed Description, a multi-mode MEMS aerosol detecting device for detecting aerosol particles, the device comprising a chamber having an inlet, the inlet being configured to allow a gas to enter the chamber; a light source configured to illuminate the gas in the chamber with a light; and a MEMS resonator configured to detect the presence of aerosol particles in the gas based on a characteristic of the aerosol particles related to absorbing the light from the light source, wherein the multi- mode MEMS aerosol detecting device is selectable between at least a first mode and a second mode, the second mode being different from the first mode and one of the first and second mode being a photo-acoustic mode for detecting aerosol particles.

[9] In accordance with another aspect, a method of detecting aerosol particles comprising allowing a gas to enter a chamber via an inlet; illuminating the gas in the chamber with a light from a light source; and detecting the presence of aerosol particles in the gas based on a characteristic of the aerosol particles related to absorbing the light from the light source, wherein the detection of the presence of aerosol particles is selectable between at least a first mode and a second mode, the second mode being different from the first mode and one of the first and second mode being a photo- acoustic mode.

BRIEF DESCRIPTION OF THE DRAWINGS

[10] The accompanying figures where like reference numerals refer to identical or functionally similar elements throughout the separate views and which together with the detailed description below are incorporated in and form part of the specification, serve to illustrate various embodiments and to explain various principles and advantages in accordance with a present embodiment.

[11] Figure 1 shows a block diagram of a multi-mode MEMS aerosol detecting device for detecting aerosol particles in accordance with an embodiment.

[ 2] Figure 2 shows a schematic diagram of the multi-mode MEMS aerosol detecting device in a photo-acoustic mode in accordance with an embodiment.

[13] Figure 3 illustrates steps of detecting aerosol particles in the photo-acoustic mode based on the multi-mode MEMS aerosol detecting device shown in Figure 2.

[14] Figure 4 shows a schematic diagram of the multi-mode MEMS aerosol detecting device in a bulk acoustic wave (BAW) resonance frequency mode in accordance with an embodiment.

[15] Figure 5 illustrates steps of detecting aerosol particles in the BAW resonance frequency mode based on the multi-mode MEMS aerosol detecting device shown in Figure 4.

[16] Figure 6 shows a cross sectional view of the multi-mode MEMS aerosol detecting device at a wafer level in accordance with an embodiment. [17] Figure 7 shows a schematic diagram of a resonator used in the multi-mode MEMS aerosol detecting device of Figure 2.

[18] Figure 8 shows an analytical model of the thermal-excitation sensitivity and the acoustic-excitation sensitivity for the resonator used in the multi-mode MEMS aerosol detecting device of Figure 2.

[19] Figure 9 shows a tabular pipe that is modeled to analyze the BAW resonance frequency mode.

[20] Figures 10(a)-10(b) show two stages used for the tabular pipe of Figure 9 for analyzing the results of the BAW resonance frequency mode.

[21] Figure 11 shows results of the heat transfer analysis of the tabular pipe of Figure 9.

[22] Figure 12 shows results of the frequency shift analysis of the tabular pipe of Figure 9.

DETAILED DESCRIPTION

[23] It should further be appreciated that the exemplary embodiments are only examples, and are not intended to limit the scope, applicability, operation, or configuration of the invention in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing an exemplary embodiment of the invention, it being understood that various changes may be made in the function and arrangement of elements and method of operation described in an exemplary embodiment without departing from the scope of the invention as set forth in the appended claims.

[24] Figure 1 shows a block diagram of a multi-mode MEMS aerosol detecting device 100 for detecting aerosol particles in accordance with an embodiment. In a specific implementation, the multi-mode MEMS aerosol detecting device 100 includes an inlet port 04 and an outlet port 106 in a chamber 122. The inlet port 104 is configured to allow a fluid such as a gas to enter the chamber 122. The outlet port 106 is configured to allow the fluid such as the gas to exit the chamber 122.

[25] The multi-mode MEMS aerosol detecting device 100 is further configured to communicate with an air flow controller 102 which is configured to introduce the gas into the inlet port 104. The air flow controller 102 could be arranged to be integral with or separate from the multi-mode MEMS aerosol detecting device 100.

[26] Further, the multi-mode MEMS aerosol detecting device 100 is configured to communicate with a light source 112 which is configured to illuminate the gas in the chamber 122 with a light. The light source 1 12 is configured to receive a light control signal and output the light to illuminate the chamber 122 via a light input port 110. This will cause a scattered light path which will be sent to a power meter port 1 16. In an embodiment, the power meter port 1 6 is configured to detect a characteristic of the scattered light path. Further, the power meter port 1 16 is configured to communicate with an external optical power meter 120. The external optical power meter 120 is configured to receive the detected characteristic of the scattered light path from the power meter port 1 16 and output a signal.

[27] The multi-mode MEMS aerosol detecting device 100 also includes a MEMS resonator 108 that is configured to detect the presence of aerosol particles in the gas based on the light absorbing characteristics of the aerosol particles. The MEMS resonator 108 is comprised of a suitable material such as aluminum nitride (AIN) that facilitates the function of detecting aerosol particles. The MEMS resonator 108 is configured to detect the aerosol particles in two modes. The two modes may be a photo-acoustic mode and a bulk acoustic wave (BAW) resonance frequency mode. The MEMS resonator 108 is also configured to convert the reading (e.g. an amplitude of an acoustic pressure wave or temperature variations) of the aerosol particles into an electrical signal indicative of a concentration of the aerosol particles in the chamber 122.

[28] The MEMS resonator 108 is configured to communicate with a signal processing unit 118. The electrical signal from the MEMS resonator 108 is fed into a signal processing unit 118. The signal processing unit 1 18 is configured to calculate the concentration of aerosol particles based on the electrical signal. The signal processing unit 1 18 may be included in the chamber 122 or arranged outside the chamber 122. In an embodiment, the signal processing unit 118 is configured to calculate the concentration of aerosol particles based on the electrical signal from the MEMS resonator 108 and the signal from the external optical power meter 120.

[29] Figure 2 shows a schematic diagram of the multi-mode MEMS aerosol detecting device 200 in a photo-acoustic mode in accordance with an embodiment. The multi- mode MEMS aerosol detecting device 200 comprises an air inlet 202 and an air outlet 204. The air inlet 202 and the air outlet 204 function similar to the inlet port 104 and the outlet port 106 shown in Figure 1. In other words, the air inlet 202 is configured to allow a fluid such as a gas to enter the multi-mode MEMS aerosol detecting device 200. The air outlet 204 is configured to allow the fluid such as the gas to exit the multi-mode MEMS aerosol detecting device 200.

[30] In the photo-acoustic mode/ the multi-mode MEMS aerosol detecting device 200 exploits the photo-acoustic or thermo-acoustic effect. The photo-acoustic effect is a physical phenomenon in which a periodically interrupted beam of light generates sound waves in a gas through which it is passing; this results from energy in the interrupted light beam being transformed first into internal motions of the gas molecules, then into random translational motions of these molecules, or heat, and finally into periodic pressure fluctuations or sound. [31] As shown in Figure 2, a pulsed light signal 210 is fed into the multi-mode MEMS aerosol detecting device 208. The multi-mode 208 includes a MEMS resonator 204 for measuring the formed sound waves. The photo-acoustic effect is quantified by measuring the formed sound (or acoustic pressure wave) with the MEMS resonator 204. Time variations of the electric output (current or voltage) detected by the MEMS resonator 204 are the photo-acoustic signals. These measurements are useful to determine certain properties of the sample. For example, the photo-acoustic signals are used to obtain the actual absorption of light in either opaque or transparent objects. Transparent objects are typically not suitable for common absorption spectroscopy because of the scattering of light. Photo-acoustics is impervious to this scattering since absorbed light alone can create a signal. Advantageously, this is useful for detecting substances in extremely low concentrations, because very strong pulses of light from a laser can be used to increase sensitivity and very narrow wavelengths can be used for specificity.

[32] In the multi-mode MEMS aerosol detecting device 200, the MEMS resonator 204 is used to detect the suspended aerosol particles in an air sample. The MEMS resonator 204 and the particles are enclosed in the same chamber, whereas a pulsed light source illuminates the aerosol. The pulsed light causes oscillatory particle scattering and absorption leading to oscillatory heating convection and radiation. Then, an acoustic pressure wave of the same pulse frequency starts traveling in the chamber. With the appropriate design, the MEMS resonator 204 picks up the acoustic wave which elicits its flexural resonance. The quality factor or vibration intensity is thus proportional to the aerosol concentration. As such, the MEMS resonator 204, which comprises at least AIN, can be used to detect aerosol particles 208 accurately even when they are in extremely low concentrations in the chamber. Advantageously, this provides a compact and non-cumbersome solution to detecting aerosol particles. This is in contrast to the conventional silicon photo-acoustic detectors that have been proven to be non-portable and cumbersome. More details on how the MEMS resonator 204 functions in the photo- acoustic mode will be shown in Figure 7. [33] Figure 3 shows a flow chart 300 illustrating a method of detecting aerosol particles in the photo-acoustic mode based on the multi-mode MEMS aerosol detecting device 200 shown in Figure 2. Here, the MEMS resonator 204 operates in the photo- acoustic mode even though it is capable to operable in the BAW resonance frequency mode. At step 302, a gas input is injected into the chamber of the multi- mode MEMS aerosol detecting device. At step 304, the gas in the chamber is illuminated with a pulsed light from a light source. The light source may be internal or external to the multi-mode MEMS aerosol detecting device. At step 306, an acoustic pressure wave is detected by the MEMS resonator based on the light absorption of the aerosol particles.

[34] To detect an amount of the aerosol particles, at step 308, the acoustic (or mechanical) signal is converted into an electrical signal proportion to the amount of aerosol particles in the multi-mode MEMS aerosol detecting device 200. At step 310, a concentration of the aerosol particles is calculated from the converted electrical signal. Calibration is carried out at step 312.

[35] Figure 4 shows a schematic diagram of the multi-mode MEMS aerosol detecting device a bulk acoustic wave (BAW) resonance frequency mode in accordance with an embodiment. BAW devices are used for radio frequency selectivity in mobile communication system and other wireless applications. BAW has several advantages as they are remarkably small in size, have better power handling abilities and better frequency sensitivity. For example, any small stimulus can lead to significant shifting of the resonant frequency for a BAW resonator (even for a BAW resonator which had low TCFs). Examples of such stimuli are thermal excitation and heating produced by the aerosol particles after being excited by the light source. This is different from lower frequency technologies. Advantageously, a BAW device is one that provides a high spectral purity resonator in the radio frequency and microwave frequency ranges. Such BAW devices may be coupled together to form filters or other frequency selective devices. [36] The multi-mode MEMS aerosol detecting device 400 comprises an air inlet 402 and an air outlet 406. The air inlet 402 and the air outlet 406 function similar to the inlet port 104 and the outlet port 106 shown in Figure 1. In other words, the air inlet 402 is configured to allow a fluid such as a gas to enter the multi-mode MEMS aerosol detecting device 400. The air outlet 404 is configured to allow the fluid such as the gas to exit the multi-mode MEMS aerosol detecting device 400.

[37] In the BAW resonance frequency mode, the multi-mode MEMS aerosol detecting device 400 exploits the radio frequency selectivity effect. The radio frequency selectivity effect is a phenomenon in which a continuous-wave light source illuminates the aerosol and causes a light-aerosol interaction. The light-aerosol interaction causes particle scattering, absorption, collision which leads to heat transfer such as convection and radiation. Heat transfer proportional to the particle concentration then occurs to the MEMS resonator, thus causes a change of temperature of the resonator and a subsequent shift of its BAW resonance frequency.

[38] As shown in Figure 4, a continuous wave light 410 is fed into the multi-mode MEMS aerosol detecting device 400. The multi-mode MEMS aerosol detecting device 400 includes a MEMS resonator 404 for measuring the shift of its resonance frequency. The BAW resonance frequency is quantified by measuring the resonance frequency with the MEMS resonator 404. Advantageously, it is possible to predict a concentration of aerosol particles in an enclosed environment based on the expected frequency shift of the MEMS resonator 404 in proportion to its temperature coefficient of frequency (TCF) response. Further, by selecting a particular frequency range, the MEMS resonator 404 functions as a highly reliable device leading to a more stable solution.

[39] Figure 5 shows a flow chart 500 illustrating a method of detecting aerosol particles in the BAW resonance frequency mode based on the multi-mode MEMS aerosol detecting device 400 shown in Figure 4. Here, the MEMS resonator operates in the BAW resonance frequency mode. At step 502, a gas input is injected into the chamber of the multi-mode MEMS aerosol detecting device. At step 504, the gas in the chamber is illuminated with a continuous-wave light from a light source. The light source may be internal or external to the multi-mode MEMS aerosol detecting device. At step 506, a change in the temperature of the aerosol particles is detected by the MEMS resonator based on the light absorption of the aerosol particles.

[40] At step 508, the MEMS frequency shift due to heating the chamber is analyzed through the temperature coefficient of frequency (TCF) response. At step 510, the concentration of the aerosol particles is calculated from the converted electrical signal. Calibration is carried out at step 512.

[41] Figure 6 shows a cross sectional view of the multi-mode MEMS aerosol detecting device 600 at a wafer level in accordance with an embodiment. The multi-mode MEMS aerosol detecting device 600 is a miniaturized aerosol detecting device that uses a MEMS resonator 602 to carry out in-situ, real-time detection of suspended aerosol particles.

[42] The multi-mode MEMS aerosol detecting device 600 includes a first device wafer 604 and a second device wafer 612. The first device wafer 604 and/or the second device wafer 612 may be at least one or more of a silicon wafer, silicon-on- insulator wafer, silicon carbide wafer, or any other substrate wafer suitable for micro-fabrication or MEMS technologies.

[43] A MEMS resonator 602 that is configured to function as a sensor component is fabricated onto the first device wafer 604. The first device wafer 604 further comprises a top bump or a top under-bump metallization (UBM) 606, 608. The UBM typically is a patterned, thin-film stack of material that provides an electrical connection from the silicon die to a solder bump or a barrier function that limits unwanted diffusion from the bump to the silicon die; and a mechanical interconnection of the solder bump to the die through adhesion to the die passivation and attachment to a solder bump pad. The first device wafer 604 may comprise the MEMS resonator 602 embedded in a polymer dielectric. Subsequently, the MEMS frequency shift due to heating is analyzed through the TCF response.

[44] At least one input port 614 is provided on the first device wafer 604. The input port 6 4 is a physical channel for fluid circulation. Examples of the input port 614 include a channel that is micro-machined in the first device wafer 604 or a heterogeneously integrated micro channel. Depending on the channel dimensions, hybridization of the first wafer device 604 is also considered to connect the MEMS resonator to the input port 614.. Similarly, at least one output port 616 is provided on the device wafer 612 to allow a fluid such a gas to exit the multi-mode MEMS aerosol detecting device 600.

[45] An optical waveguide is provided in between the first device wafer 604 and the second device wafer 612. An optical waveguide is a physical structure that guides electromagnetic waves in the optical spectrum. Examples of the optical waveguide include rectangular waveguide and optical fiber. The optical wavelength is configured to allow light to be introduced into the multi-mode MEMS aerosol detecting device 600.

[46] Advantageously, such an integrated device further miniaturizes the aerosol detecting solution into a highly scalable MEMS device and makes it possible for promising applications such as environmental monitoring for air quality control. Similarly, it is also made possible for other gas detection applications such as food quality control or toxic gas detection.

[47] Figure 7 shows a schematic diagram of a resonator used in the multi-mode MEMS aerosol detecting device of Figure 2. A resonator typically is a device that exhibits resonant behavior, that is, it naturally oscillates in some circumstances (e.g., at some frequencies) with greater amplitude. [48] In some embodiments, a cantilever resonator is used as shown in Figure 7. Thermal noise, which is an intrinsic noise source, and acoustic noise coming from environmental vibrations drive the resonator at the ultralow signal limits. The thermal sensitivity is obtained by :

[49] Where <rms_thermai>i is the root mean square deflection value due to thermal noise, K_B is the Boltzmann constant, l is temperature and k_em is the effective cantilever stiffness at the first mode. On the other hand, the acoustic sensitivity is given by :

^•S- acoustic ) _wiB )

[50] Where

is the root mean square deflection value due to acoustic noise expressed in dB referred to 20 μΡθ, W_dB is the acoustic pressure value, w and L are width and length of cantilever, respectively, Qi is the quality factor at the first mode, and k_em is the effective cantilever stiffness at the first mode. It is important to determine a value which dominates the detection sensitivity for a resonator with a given geometry and mechanical stiffness.

[51] Figure 8 shows an analytical model according to "Study of Thermal and Acoustic Noise Interferences in Low Stiffness Atomic Force Microscope Cantilevers And Characterization of Their Dynamic Properties" (published in Review of Scientific Instruments Volume 83, page 013704), which is hereby incorporated herein by reference by its entirety. . Line 802 represents the thermal sensitivity model for the resonator at different pressure values (dB) and temperatures (°C). Line 804 represents the acoustic sensitivity model for the resonator at different pressure values (dB) and temperatures (°C). Figure 8 shows that the thermal sensitivity model dominates for ultra low acoustic pressures, whereas the acoustic sensitivity model dominates above certain pressure value (P0 dB in the example).

[52] A region lies in the middle where there is no clear dominance of one model over the other, namely the noise interference region. This region is then extracted for each resonator design. Finally, the RMS deflection sensitivity value can be used to calculate the RMS voltage sensitivity <rms_acoustic>v, by using the piezoelectric constant d₃i :

[53] Where <rms>s_enSitivity is the minimum value between the thermal and acoustic noise sensitivities. Using <rms>v, the detector sensitivity of the resonator shown in Figure 7 will be determined.

[54] Figure 9 shows a tabular pipe 900 that is modeled to analyze the BAW resonance frequency mode. The tabular pipe 900 is one which heat is transferred with a laminar flow regime. It is assumed that the tabular pipe 900 is an empty pipe through which air may flow in. The amount of heat may be calculated using the following equation:

[55] Where h [W/m^2oK] is the heat transfer coefficient, p [Kg/m³] is the density of the fluid, u [m/s] is the velocity of the fluid, c_p [J/Kg°K] is the heat capacity of the fluid, L [m] is the length where the heat is applied and D [m] is the diameter of the pipe. [56] It is possible to use the tabular pipe 900 in two stages and more details will be given in Figures 10(a) and 10(b). Figures 10(a)- 0(b) show two stages used in the tabular pipe of Figure 9 for analyzing the results of the BAW resonance frequency mode. To do so, a three-step approach is taken:

(1 ) Analyzing the laser to carbon cloud interaction;

(2) Analyzing the carbon cloud to MEMS interaction; and

(3) Analyzing the MEMS frequency shift due to heating through its temperature coefficient of frequency (TCF) response.

[57] For the first two steps, the (i) thermodynamics and fluid theories and (ii) COMSOL Multiphysics finite element modeling (FEM) are combined. For the third step, ANSYS for FEM is used.

[58] Figure 10(a) shows the first stage of the tabular pipe 900 that is modeled to analyze the BAW resonance frequency mode. In the first stage, the carbon particles are heated. Figure 10(b) shows the second stage of the tabular pipe 900 that is modeled to analyze the BAW resonance frequency mode. In the second stage, the air between the carbon cloud and the resonator surface is heated.

[59] The temperatures of the carbon particles and the carbon to resonator air interface, in the first and second stage, are calculated using the following equations. m

u =— (5) [60] For the first stage, where m=9.5E-8Kg/s, Air p@293. 15°K=1.14Kg/m^3, A=7 9m² , u is 1.06m/s. For the second stage, where m=9.5E-9Kg/s, p@~370°K=1.008Kg/m³' A=7.8E-9m², u is 1.06m/s.

ReD =— (6)

v

[61] For the first stage, where D=100um, Air v@293.15°K=1 .6E-5m²/s, ReD, the laminar flow is 6.39. For the second stage, where D=100um, Air v@~370°K=2.1 E-5m²/s ReD, the laminar flow is 5.74

Gz = ^{Re Pr Z)} (7)

L

[62] For the first stage, where Air Pr@293.15°K=0.71 , L1 =100um, Gz, the Graetz number, is 4.5. For the second stage, Air Pr@~370°K=0.707, L2=20um, Gz, the Graetz number, is 20.3.

0.0668GZ

NuD = 3.657 + — (8)

0.04 + Gz^"

[63] Where NuD is the Nusset number, NuD =3.9 in the first stage and NuD =4.7 in the second stage.

* = (9)

D

[64] For the first stage, where Air k@293.15°K=0.0268W/m°K, h is 1053W/m2°K. For the second stage, Air k@~370°K=0.02984W/m°K, h is 403W/m2°K.

[65] For the first stage, where Air Cp@293.15°K=1007J/Kg°K, Tboutl is 370.6°K. For the second stage, where Air Cp@293.15°K=1007J/Kg°K, Tbout2 is 312°K. [66] Figure 11 shows results of the heat transfer analysis 1 100 of the tabular pipe in Figure 9. Line 102 shows that as the distance of the resonator increases, the resonator surface temperature reduces. In other words, the resonator surface temperature gets higher if the distance to resonator is shorter.

[67] Figure 12 shows results of the frequency shift analysis 1200 of the tabular pipe in Figure 9. The slopes of line 1202 and line 1204 show the TCF of the BAW resonance frequency used in the BAW operation mode of the sensor. Different slopes show that the TCF can be process-controlled to adjust the sensitivity of the aerosol MEMS detector when operating in the BAW resonance mode. Both line 1202 and line 1204 show that, as for an aluminum nitride (AIN) MEMS resonator sensor with a negative TCF, higher concentration of aerosol particles (in ppm) leading to higher resonator surface temperatures, will cause the BAW resonance frequency to shift to lower values than for lower aerosol particles concentration.

[68] From Figures 1 1 and 12, it can be seen that in the BAW resonance frequency mode, it is possible to predict a frequency shift of the MEMS resonator in proportion to its TCF response, due to laser heating of the carbon particles and the consequent heat transfer to the resonator. Generally, sensitivity of the MEMS resonator depends on the TCF response.

[69] Advantageously, a multi-mode MEMS aerosol detecting device is provided. It leverages on a single AIN acoustic MEMS resonator operating in multiple resonance modes, such as mechanical resonance or photo-acoustic mode, BAW resonance shit detection. A person skilled in the art will also appreciate that a combination of these modes is also possible. [70] Further, a miniaturized aerosol detector instrument based on the single AIN MEMS resonator is also provided. This makes it possible to carry out in-situ, real-time detection of suspected aerosol particles.

[71] It should further be appreciated that the exemplary embodiments are only examples, and are not intended to limit the scope, applicability, operation, or configuration of the invention in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing an exemplary embodiment of the invention, it being understood that various changes may be made in the function and arrangement of elements and method of operation described in an exemplary embodiment without departing from the scope of the invention as set forth in the appended claims.

Claims

CLAIMS:

1. A multi-mode MEMS aerosol detecting device for detecting aerosol particles, the device comprising:

a chamber having an inlet, the inlet being configured to allow a gas to enter the chamber;

a light source configured to illuminate the gas in the chamber with a light; and a MEMS resonator configured to detect the presence of aerosol particles in the gas based on a characteristic of the aerosol particles related to absorbing the light from the light source,

wherein the multi-mode MEMS aerosol detecting device is selectable between at least a first mode and a second mode, the second mode being different from the first mode and one of the first and second mode being a photo-acoustic mode for detecting aerosol particles.

2. The multi-mode MEMS aerosol detecting device according to claim 1 , wherein the other mode is a bulk acoustic wave (BAW) resonance frequency mode for detecting aerosol particles.

3. The multi-mode MEMS aerosol detecting device according to claim 1 , wherein the MEMS resonator is composed at least in part of aluminum nitride (AIN).

4. The multi-mode MEMS aerosol detecting device according to claim 1 , wherein when the multi-mode aerosol detecting device is in the photo-acoustic mode, the light source is configured to illuminate the gas with a pulsed light and the MEMS resonator is configured to detect an acoustic pressure wave.

5. The multi-mode MEMS aerosol detecting device according to claim 4, wherein the MEMS resonator is configured to convert an amplitude of the acoustic pressure wave into an electrical signal indicative of a concentration of the aerosol particles in the chamber.

6. The multi-mode MEMS aerosol detecting device according to claim 5, further comprising a signal processing unit coupled to the MEMS resonator, the signal processing unit being configured to calculate the concentration of the aerosol particles based on the electrical signal.

7. The multi-mode MEMS aerosol detecting device according to claim 2, wherein when the multi-mode aerosol detecting device is in the BAW resonance frequency mode, the light source is configured to illuminate the gas with a continuous-wave light and the MEMS resonator is configured to detect temperature variations produced by the aerosol particles.

8. The multi-mode MEMS aerosol detecting device according to claim 7, wherein the MEMS resonator is configured to convert the temperature variations into an electrical signal indicative of a concentration of the aerosol particles in the chamber.

9. The multi-mode MEMS aerosol detecting device according to claim 8, further comprising a signal processing unit coupled to the MEMS resonator, the signal processing unit being configured to calculate the concentration of the aerosol particles based on the electrical signal.

10. A method of detecting aerosol particles comprising: allowing a gas to enter a chamber via an inlet;

illuminating the gas in the chamber with a light from a light source; and detecting the presence of aerosol particles in the gas based on a characteristic of the aerosol particles related to absorbing the light from the light source, wherein the detection of the presence of aerosol particles is selectable between at least a first mode and a second mode, the second mode being different from the first mode and one of the first and second mode being a photo- acoustic mode.

11. The method according to claim 10, wherein the other mode is a bulk acoustic wave (BAW) resonance frequency mode.

12. The method according to claim 11 , wherein the detection of the presence of aerosol particle is carried out by a MEMS resonator.

13. The method according to claim 12, wherein the MEMS resonator is composed at least in part of aluminum nitride (AIN).

14. The method according to claim 10, wherein when the detection of the presence of aerosol particles is in the photo-acoustic mode, the gas in the chamber is illuminated with a pulsed light and an acoustic pressure wave is detected.

15. The method according to claim 14, further comprising converting an amplitude of the acoustic pressure wave into an electrical signal indicative of a concentration of the aerosol particles in the chamber.

16. The method according to claim 15, further comprising calculating the concentration of the aerosol particles based on the electrical signal.

17. The method according to claim 1 1 , wherein when the detection of the presence of aerosol particles is in the BAW resonance frequency mode, the gas in the chamber is illuminated with a continuous-wave light and temperature variations produced by the aerosol particles are detected.

18. The method according to claim 17, further comprising converting the temperature variations into an electrical signal indicative of a concentration of the aerosol particles in the chamber.

19. The method according to claim 18, further comprising calculating the concentration of the aerosol particles based on the electrical signal.