Particle Sensor

Abstract

According to an exemplary aspect of the present invention, a device is provided, comprising: a micro-electromechanical (MEMS) capacitor, the MEMS capacitor comprising two plates and a gap between the two plates; a gas conveyor, the gas conveyor being configured to flow a gas through the gap; and a readout circuit, the readout circuit being configured to measure the capacitance of the MEMS capacitor.

Description

Technical Field

[0001] The present invention relates to capacitance-based particle detection. Background Art

[0002] In urban areas, poor air quality due to chemical and particle pollutants is harmful to health. According to the World Health Organization (WHO), exposure to air pollutants caused 7 million deaths in 2012, accounting for one in eight deaths worldwide. In addition to the effects of air pollutants on the human respiratory system, strong links have been established between exposure to air pollution and many other medical conditions, cardiovascular diseases and cancer.

[0003] The negative health effects of air pollutants vary and depend on their composition and state, e.g., gaseous or solid. Therefore, monitoring of the various air pollutants, their concentrations and spatiotemporal distribution is important not only on a global scale, but also on a more localized basis within regions and districts to localize the sources of pollution and the geographical extent of the pollution. In order to measure the transport of pollutants and predict the evolution of the pollution spread, measurements can be made frequently and preferably on a dense spatial grid.

[0004] Filter-based air pollutant monitoring involves the use of filters that are selective for target particles. Once the filter has been exposed to air passing across the filter, the particles captured in the filter can be evaluated to estimate the concentration of particles in the air or more generally in a gas.

[0005] Particle pollutants have a wide range of particle sizes. For example, smoke particles can range from 0.01 to 1 micron, fly ash particles range from 1 to 100 microns, pollen particles range from 10 to 100 microns, heavy dust ranges from 100 to 1000 microns, and cat allergens range from 0.01 to 3 microns. Therefore, using filters, a stack of filters with different selectivities can be used to obtain an estimate of the particle size distribution of particles in a gas such as air. The particle size distribution can include multiple estimates of the concentration of particles of a specific particle size in the gas. Summary of the invention

[0006] According to some aspects, the subject matter of the independent claims is provided. Some embodiments are defined in the dependent claims.

[0007] According to a first aspect of the present invention, a device is provided, comprising: a micro-electromechanical (MEMS) capacitor, the MEMS capacitor comprising two plates and a gap between the two plates; a gas conveyor, the gas conveyor being configured to flow a gas through the gap; and a readout circuit, the readout circuit being configured to measure the capacitance of the MEMS capacitor.

[0008] Various embodiments of the first aspect may include at least one feature from the following bulleted list:

[0009] The gas transporter comprises at least one of a mechanism for generating a pressure difference across the gap and a thermophoresis device configured to generate a temperature gradient across the gap

[0010] The readout circuit is configured to detect changes in the capacitance of the MEMS capacitor caused by particles flowing through the gap along with the gas

[0011] MEMS capacitors consist of multiple gaps connected in parallel, each with its own readout electronics

[0012] Gap width adjustable

[0013] The width of the gap can be adjusted by applying a voltage across the two plates so that the electrostatic force moves at least one plate

[0014] The width of the gap is between 0.05 and 2.00 microns.

[0015] According to a second aspect of the present invention, a device is provided. The device includes at least one processing core and at least one memory including computer program code. The at least one memory and the computer program code are configured to, with the at least one processing core, cause the device to at least: guide a gas conveyor configured to flow gas through a gap between plates of a micro-electromechanical MEMS capacitor to convey the gas through the gap; receive input from a readout circuit configured to measure the capacitance of the MEMS capacitor; and derive a particle concentration in the gas from the input.

[0016] Various embodiments of the second aspect may include at least one feature from the following bulleted list:

[0017] The gas transporter comprises at least one of a mechanism for generating a pressure difference across the gap and a thermophoresis device configured to generate a temperature gradient across the gap

[0018] The device is further configured to adjust the width of the gap

[0019] The device is configured to adjust the width of the gap by applying an adjustable voltage to the plates

[0020] The apparatus is configured to sequentially use a plurality of gap widths to obtain a particle size distribution of particles in a gas.

[0021] According to a third aspect of the present invention, a method is provided, comprising: directing a gas conveyor to cause a gas to flow through a gap between plates of a micro-electromechanical (MEMS) capacitor; receiving an input from a readout circuit configured to measure the capacitance of the MEMS capacitor; and deriving a particle concentration in the gas from the input.

[0022] Various embodiments of the third aspect may include at least one feature corresponding to a feature from the preceding bulleted list arranged in connection with the second aspect.

[0023] According to a fourth aspect of the present invention, there is provided an apparatus comprising: means for directing a gas conveyor configured to cause a gas to flow through a gap between plates of a micro-electromechanical (MEMS) capacitor to convey the gas through the gap; means for receiving an input from a readout circuit configured to measure the capacitance of the MEMS capacitor; and means for deriving a particle concentration in the gas from the input.

[0024] According to a fifth aspect of the present invention, there is provided a non-transitory computer-readable medium having a computer-readable instruction set stored thereon. The computer-readable instruction set, when executed by at least one processor, causes an apparatus to at least: direct a gas conveyor configured to flow a gas through a gap between plates of a micro-electromechanical MEMS capacitor to convey the gas through the gap; receive an input from a readout circuit configured to measure the capacitance of the MEMS capacitor; and derive a particle concentration in the gas from the input.

[0025] According to a sixth aspect of the present invention, there is provided a computer program configured to execute the method according to the third aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 An example system is shown in accordance with at least some embodiments of the present invention;

[0027] Figure 2 Two graphs are included in accordance with at least some embodiments of the present invention.

[0028] Figure 3 An example apparatus capable of supporting at least some embodiments of the present invention is shown;

[0029] Figure 4 shows signaling according to at least some embodiments of the present invention;

[0030] Figure 5 is a flow chart of a method according to at least some embodiments of the present invention; and

[0031] Figure 6Concepts according to at least some embodiments of the present invention are illustrated. DETAILED DESCRIPTION

[0032] Micro-electromechanical (MEMS) capacitors can be used to detect particles in a gas flowing between the plates of the capacitor. Particles flowing through the gap between the plates of the capacitor cause a momentary change in the capacitance of the capacitor. This change can be detected by a suitable readout circuit.

[0033] The thickness of the gap in a MEMS capacitor can be adjustable, thereby obtaining selectivity regarding the particle size that can pass through the gap. In detail, particles with a diameter larger than the gap width cannot pass. By varying the thickness of the gap, the distribution of particle sizes can be determined.

[0034] Figure 1 An example system according to at least some embodiments of the present invention is shown. The MEMS capacitor 100 includes two plates 110, 120, which may be made of or coated with a metallic substance, for example. For simplicity and clarity, the plates 110, 120 need not have the same Figure 1 The MEMS capacitor 100 has a housing 130 on which the other components of the MEMS capacitor 100 are mounted. The plate 120 is mounted on the housing 130 using a spring mount 140 so that the distance between the plates 110 and 120 is adjustable, for example by applying a selectable bias voltage to the plates 110 and 120 to generate an electrostatic attraction force of selectable strength. The spring mount 140 is arranged at Figure 1 1 and 2. It is shown schematically in FIG. 1 and many mechanical variations of spring mechanisms may be employed, or other means may be employed additionally or alternatively to adjust the distance between plates 110 and 120. The distance between plates 110 and 120 defines the width of the gap.

[0035] Although this article mainly discusses one gap and two plates, in general, the MEMS capacitor 100 can include multiple gaps connected in parallel, each gap having its own readout electronics, each gap between two plates. Thus, in this general form, the number of plates can be greater than two.

[0036] The readout circuit 150 is configured to measure the capacitance of the MEMS capacitor 100. The readout circuit 150 is enabled to detect relatively rapid changes in capacitance, as will be described below. The readout circuit 150 is operably coupled to the control device 160 via a connection 156. In some embodiments, the connection 156 traverses the housing 130. The readout circuit 160 can be configured to measure the capacitance of the MEMS capacitor 100 by determining the response of the MEMS capacitor 100 to a square wave, or by measuring the capacitance of the MEMS capacitor 100, such as by resonance measurement, as is known in the art.

[0037] The control device 160 can be configured to record the capacitance measurement signal from the readout circuit 150. The control device 160 can be further configured to change the gap width between the plates, for example by changing the bias voltage. The control device 160 can be configured to perform a series of measurements using the MEMS capacitor 100. The series of measurements includes multiple measurements with different gap widths. The connection 161 can connect the control device 160 to other nodes, for example via the Internet, the Internet of Things, or a sensor network. The connection 161 can be wired or at least partially wireless.

[0038] The gas conveyor 170 is configured to flow a gas, such as air, through the gap between the plates 110, 120. For example, the gas conveyor may be arranged to create a pressure gradient across the length of the gap. The gas conveyor 170 may be provided by installing at least one fan to create a negative pressure (e.g., Figure 1 as shown) and / or by creating an overpressure between the gas conveyor 170 and the gap to create a pressure gradient.

[0039] Another possibility is to use thermophoretic forces, also known as heat diffusion, whereby a temperature gradient is created across the length of the gap, causing the gas to flow through the gap. While the width of the gap is the distance between the plates 110 and 120, the length of the gap is perpendicular to the width, so that as the gas flows along the length of the gap, the gas flows from one side of the MEMS capacitor 100 to the other through the gap separating the plates 110, 120. For example, a temperature gradient can be induced across the length of the gap by using a heatable grid or plate.

[0040] Existing fine particle detection solutions are usually bulky, i.e. not portable and expensive, with their prices ranging in the tens of thousands of Euros. On-chip solutions will have several advantages over existing solutions, such as their small size, low cost and low power consumption. Miniaturized particle sensor platforms are the key engine for air quality monitoring sensor networks. Sensor networks can be formed by introducing sensors into basic infrastructure or even into mobile devices. Air quality data together with pressure information can be collected and reported, for example, to cloud services and used for air quality prediction and / or monitoring. Forecasts can further enable early warning systems for air pollution levels. Similarly, mobile fine particle sensors can be used as personal dosimeters to measure cumulative fine particle hazard exposure. Such sensor networks have a significant impact on society and the economy due to reduced mortality and healthcare costs. For example, users may wear protective masks to respond to alerts about particulate pollution.

[0041] In use, the gas conveyor 170 pushes or pulls the gas 102 (e.g., air) through the gap between the plates 110 and 120, and the readout circuit 150 measures the capacitance of the MEMS capacitor 100. If particles are conveyed through the gap, the capacitance of the MEMS capacitor 100 changes, in other words, the capacitance of the MEMS capacitor 100 is different depending on whether there is only gas or both gas and particles in the gap. The instantaneous change in capacitance can be counted as a particle that has flowed through the gap. In fact, when a particle is between the two plates, the capacitance will increase instantaneously, because the relative dielectric constant of the particle is generally greater than the relative dielectric constant of the air.

[0042] The readout circuit 150 or the control device 160 can be configured to assign an estimated size to a particle passing through the gap based on the size of the transient effect on the capacitance. The width of the gap defines an upper limit on the diameter of the particles passing through. A mapping from the size of the transient change in capacitance to an estimate of the particle size can be prepared. Before taking a measurement, the mapping can be prepared experimentally or according to first principles. Since the gap in an actual MEMS capacitor 100 can be relatively narrow, on the order of 0.1 to several microns, it is relatively unlikely that two particles are in the gap at the same time, which enables more reliable counting of single particles.

[0043] During the measurement, the control device 160 can compile statistics on the number and size of particles passing through the gap. As described above, the size of each particle can be estimated based on the gap width and the size of the capacitance change.

[0044] The control device 160 may be arranged to make a series of measurements at different gap widths, for example starting with a narrow gap and gradually extending to a wider gap width. Alternatively, the series of measurements may start with a wider gap and then proceed to a narrower gap width. Since the gap width serves as a natural cutoff for particle size, this type of measurement may be used to derive a particle size distribution of particles present in a gas (e.g., which may be air).

[0045] To make a series of measurements, control device 160 may direct the gap between plates 110 and 120 to first take an initial value, and then collect measurements sufficient to characterize the concentration of particles in the gas that can pass through the gap when the gap is at the initial value width. Control device 160 may then cause the gap to take a second width, such as wider than the initial value, and collect sufficient measurements to characterize the concentration of particles in the gas that can pass through the gap when the gap takes the second width.

[0046] When increasing the gap width, it is possible to identify transient changes in capacitance that are caused by particles that were too large to be present in earlier measurements taken when the gap was narrower. Thus, as the change in capacitance is greater, the larger the particle. Therefore, when using a wider gap width, particles that were already considered in the measurement using the narrower gap width can be eliminated from the statistics, which can help to derive the size distribution of the particles.

[0047] The control device 160 can be configured to dynamically determine when to end a measurement using a particular gap width. For example, once a predetermined number of particles are detected passing through the gap, the control device 160 can determine that enough data has been collected to characterize the particles using a particular gap width. The gap width can then be changed, or if a measurement series has only one measurement with one gap width, the measurement series can be performed. For example, 40 or 80 particles may be sufficient. Alternatively or additionally, the measurement can be ended after a predetermined time has passed, during which the measurement is valid. For example, in the case where there are no or only a few particles in the gas, it may be difficult or even impossible to detect a predetermined number of particles.

[0048] To determine the concentration of particles, the control device 160 can estimate how much gas is passing through the gap. This can be known in advance using a gas flow rate meter, using the gas conveyor 170, as a function of the gap width.

[0049] Figure 2 Two graphs are included according to at least some embodiments of the present invention. In the upper graph, the relative change in capacitance is plotted against particle size. The relative change in diameter is on the vertical axis, and the particle size is on the horizontal axis. The width G of the gap between the plates is 1 micron. The height H of the plates is 2 microns. The width W of the plates is 10 microns. Both axes are logarithmic. For example, a particle with a diameter of 0.2 microns results in a relative change in capacitance of 1...4 x 10 -4 , while a particle with a diameter of 0.9 μm results in a relative change in capacitance of 3x 10 -2 ...1x 10 -1 .

[0050] In the graph below, particle frequency is plotted against particle concentration. Frequency is plotted on a logarithmic scale on the vertical axis, and particle concentration is plotted on the horizontal axis in micrograms per square meter, also on a logarithmic scale. The top curve represents particles with a diameter of 0.1 micrometers. The middle curve represents particles with a diameter of 0.5 micrometers. The bottom curve represents particles with a diameter of 1 micrometer. The plate dimensions and gap are the same as in the graph above, and the gas velocity is one meter per second. As shown in this graph, less than one particle per second is expected in most cases, with only the smallest particles at the highest concentration representing about five particles per second. Given the size of the MEMS capacitor and the gas velocity of 1 m / s, even under these conditions, it is rare for two particles to be in the gap at the same time.

[0051] Figure 3 An example apparatus capable of supporting at least some embodiments of the present invention is shown. Device 300 is shown, which may include, for example Figure 1 The control device 160 of the present invention is provided. The processor 310 is included in the device 300, and the processor 310 may include, for example, a single-core or multi-core processor, wherein the single-core processor includes one processing core and the multi-core processor includes more than one processing core. The processor 310 may generally include a control device. The processor 310 may include more than one processor. The processor 310 may be a control device. The processing core may include, for example, a Cortex-A8 processing core manufactured by ARM Holdings or a Steamroller processing core manufactured by Advanced Micro Devices Corporation. The processor 310 may include at least one Qualcomm Snapdragon and / or Intel Atom processor. The processor 310 may include at least one application-specific integrated circuit (ASIC). The processor 310 may include at least one field programmable gate array (FPGA). The processor 310 may be a device for performing the method steps in the device 300. The processor 310 may be configured at least in part by computer instructions to perform actions.

[0052] Device 300 may include memory 320. Memory 320 may include random access memory and / or permanent memory. Memory 320 may include at least one RAM chip. Memory 320 may include, for example, solid-state, magnetic, optical and / or holographic memory. Memory 320 may be at least partially accessible to processor 310. Memory 320 may be at least partially included in processor 310. Memory 320 may be a device for storing information. Memory 320 may include computer instructions that processor 310 is configured to execute. When computer instructions configured to cause processor 310 to perform certain actions are stored in memory 320 and device 300 as a whole is configured to run under the guidance of processor 310 using computer instructions from memory 320, processor 310 and / or at least one of its processing cores may be considered to be configured to perform the certain actions. Memory 320 may be at least partially included in processor 310. Memory 320 may be at least partially external to device 300 but accessible to device 300.

[0053] Device 300 may include a transmitter 330. Device 300 may include a receiver 340. Transmitter 330 and receiver 340 may be configured to transmit and receive information, respectively, according to at least one cellular or non-cellular standard. Transmitter 330 may include more than one transmitter. Receiver 340 may include more than one receiver. Transmitter 330 and / or receiver 340 may be configured to operate according to standards such as, for example, Global System for Mobile Communications (GSM), Wideband Code Division Multiple Access (WCDMA), 5G, Long Term Evolution (LTE), IS-95, Wireless Local Area Network (WLAN), Ethernet, and / or Worldwide Interoperability for Microwave Access (WiMAX).

[0054] The device 300 may include a user interface (UI) 360. The UI 360 may include at least one of a display, a keyboard, a touch screen, a vibrator arranged to signal a user by vibrating the device 300, a speaker, and a microphone. The user may be able to operate the device 300 via the UI 360, for example to configure a particle detection measurement.

[0055] The processor 310 may be equipped with a transmitter arranged to output information from the processor 310 to other devices included in the device 300 via electrical leads inside the device 300. Such a transmitter may include a serial bus transmitter arranged to output information, for example, via at least one electrical lead connected to the memory 320 for storage therein. As an alternative to a serial bus, the transmitter may include a parallel bus transmitter. Similarly, the processor 310 may include a receiver arranged to receive information from other devices included in the device 300 to the processor 310 via electrical leads inside the device 300. Such a receiver may include a serial bus receiver arranged to receive information from a receiver 340, for example, via at least one electrical lead, for processing in the processor 310. As an alternative to a serial bus, the receiver may include a parallel bus receiver.

[0056] The device 300 may include Figure 3 Other devices not shown in the figure. For example, where the device 300 comprises a smartphone, it may include at least one digital camera. Some devices 300 may include a back camera and a front camera, wherein the back camera may be used for digital photography and the front camera may be used for video calling. The device 300 may include a fingerprint sensor arranged to at least partially authenticate a user of the device 300. In some embodiments, the device 300 lacks at least one of the above devices.

[0057] The processor 310, the memory 320, the transmitter 330, the receiver 340 and / or the UI 360 may be interconnected in a variety of different ways via electrical leads inside the device 300. For example, each of the aforementioned devices may be connected to a main bus inside the device 300, respectively, to allow the devices to exchange information. However, as will be appreciated by those skilled in the art, this is only one example, and depending on the embodiment, various ways of interconnecting at least two of the aforementioned devices may be selected without departing from the scope of the present invention.

[0058] Figure 4 0010 shows signaling according to at least some embodiments of the present invention. Figure 1 On the left side is the MEMS capacitor 100. Figure 1 In the centre is the control device 160, and on the right is a separate control entity CTRL which may correspond to, for example, a meteorological agency or a civil protection control centre. Time advances from top to bottom.

[0059] In phase 410, the control entity CTRL requests measurements from the control device 160. Phase 410 may include instructing the control device 160 about the requested series of measurements. In response, the control device 160 instructs the MEMS capacitor 100 to perform measurements with a first gap width between the plates 110, 120. The gap width may be identified in phase 420, or phase 420 may include the control device 160 controlling the MEMS capacitor 100 to take the desired gap width between the capacitor plates. Phase 430 includes the MEMS capacitor 100 performing the measurements requested in phase 420. Once the MEMS capacitor 100 takes the measurement results with the first gap width, it returns the results to the control device 160 in phase 440. Subsequently, in phase 450, the control device 160 instructs the MEMS capacitor 100 to perform measurements with a second gap width between the plates 110, 120. Phase 460 includes the MEMS capacitor 100 performing the measurements requested in phase 450. Once the MEMS capacitor 100 has taken the measurement result of the second gap width, it returns the result to the control device 160 in stage 470. Figure 4 Two measurements are shown in , but more than two measurements may be requested and performed. As soon as the control device 160 has the results of the series of measurements, it informs the control entity CTRL thereof in a step 480 .

[0060] Figure 5 is a flow chart of a method according to at least some embodiments of the present invention. The stages of the method shown may be performed, for example, in the device 110, an auxiliary device or a personal computer, or in a control device installed therein when configured to control its functions.

[0061] Stage 510 includes directing a gas conveyor to flow a gas through a gap between plates of a micro-electromechanical MEMS capacitor. Stage 520 includes receiving an input from a readout circuit configured to measure the capacitance of the MEMS capacitor. Finally, stage 530 includes deriving a particle concentration in the gas from the input.

[0062] Regarding the capacitance of the air gap:

[0063] Figure 6 The detector in consists of two electrodes with air or another gas blown through the gap between them. In the upper part of the figure a stereoscopic view of the detector is shown without particles in the gap, while in the lower part of the figure a schematic view of the detector is shown with particles of diameter d in the gap. A particle in the gap changes the capacitance. This is for Figure 6 The device is calculated based on the cubic particles in the device. If the particle dielectric constant ε r When is close to 1, the gap G is narrow, and the following model is particularly accurate.

[0064]

[0065] This is Figure 2 The amplitude of the capacitance change is roughly the same as ΔC~d 3…4 If the relative resolution of the capacitance change is ΔC / C0=100ppm, the minimum detectable particle size is d≈0.1μm.

[0066] A characteristic of air gap detectors is that they operate slowly. The average transmission frequency of particles through the channel is

[0067]

[0068] Wherein, the gas velocity is v, the mass density of the particles is p, the volume flow rate of air is dV / dt=vWG, the mass concentration of particles is m, and the mass of particles is M=pd 3 , the particle number density is N = m / M. Figure 2 Therefore, the following conditions apply: p = 2000 kg / m 3 , dV / dt=10 -11 m 3 / s.

[0069] One way to increase the frequency of the signal pulses is to increase the pressure difference across the detector. This increases the gas velocity but also shortens the signal pulses. Figure 2 In the lower case, the pulse duration can be t = H / v = 2 μs, thanks to the high-speed capability of the measurement electronics.

[0070] Since the particle-induced pulses are relatively short, a wider bandwidth can be used. With reasonable values ​​of U = 10 V, T = 300 K, B = 1 MHz centered at a drive frequency of 10 MHz, C = 0.09 fF, and Q = 1000, we obtain a noise limit of ΔC = 0.00048 aF or ΔC / C = 5.5 ppm.

[0071] If multiple gaps are connected in parallel, the total capacitance increases, which reduces the relative capacitance resolution. Each gap can be equipped with its own readout electronics to maintain the relative resolution. This can be achieved using, for example, integrated readout electronics.

[0072] It should be understood that the disclosed embodiments of the invention are not limited to the specific structures, processing steps or materials disclosed herein, but extend to their equivalents, as will be recognized by those of ordinary skill in the relevant art. It should also be understood that the terminology employed herein is only used for the purpose of describing specific embodiments and is not intended to be limiting.

[0073] References to one embodiment or one embodiment throughout the specification mean that a particular feature, structure, or characteristic described in conjunction with the embodiment is included in at least one embodiment of the present invention. Thus, the phrases "in one embodiment" or "in an embodiment" appearing in various places throughout the specification do not necessarily all refer to the same embodiment. Where terms such as about or substantially are used to refer to values, the exact value is also disclosed.

[0074] As used herein, for convenience, multiple items, structural elements, constituent elements, and / or materials may be presented in a common list. However, these lists should be interpreted as if each member of the list were individually identified as a separate and unique member. Therefore, based solely on their presentation in a common group without an indication to the contrary, no single member of the list should be interpreted as equivalent to any other member of the same list. In addition, various embodiments and examples of the present invention and alternatives for its various components may be referenced herein. It should be understood that such embodiments, examples, and substitutions should not be construed as being actually equivalent to each other, but rather should be considered as independent and autonomous representations of the present invention.

[0075] In addition, in one or more embodiments, the described features, structures, or characteristics may be combined in any suitable manner. In the foregoing description, many specific details, such as examples of lengths, widths, shapes, etc., are provided to provide a thorough understanding of the embodiments of the present invention. However, those skilled in the relevant art will recognize that the present invention may be practiced without one or more of the specific details, or with other methods, components, materials, etc. In other cases, well-known structures, materials, or operations are not shown or described in detail in order to avoid obscuring various aspects of the present invention. Figure 1 The reference numerals in .

[0076] Although the above examples illustrate the principles of the present invention in one or more specific applications, it is obvious to those skilled in the art that many modifications may be made to the form, use and details of the implementation without paying any creative effort and without departing from the principles and concepts of the present invention. Therefore, it is not intended to limit the present invention except as set forth in the appended claims.

[0077] The verbs "comprise" and "include" are used in this document as open limitations that neither exclude nor require the presence of unrecited features. Unless expressly stated otherwise, the features recited in the dependent claims may be freely combined with each other. Furthermore, it should be understood that the use of "a" or "an" throughout this document, i.e. in the singular, does not exclude a plurality.

[0078] Industrial Applicability

[0079] At least some embodiments of the present invention find industrial application in particle detection.

[0080] List of abbreviations

[0081] MEMS

[0082] Reference numerals list

[0083] 100 MEMS capacitors 110,120 Plates of MEMS capacitor 100 130 case 140 Spring Mounting 150 Readout circuit 160 Control Equipment 156,161 connect 170 Gas transporter 102 gas 300-360 Figure 3 The structure of the device 410-480 Figure 4 Stages of the method 510-530 Figure 5 Stages of the method

Claims

1. A device comprising: - a micro-electromechanical MEMS capacitor comprising two plates and a gap between the two plates; - a gas conveyor configured to cause a gas to flow through the gap; as well as - a readout circuit configured to measure the capacitance of the MEMS capacitor; wherein the readout circuit is configured to detect a change in capacitance of the MEMS capacitor caused by particles flowing through the gap with the gas; Wherein, the width of the gap is adjustable.

2. The device according to claim 1, wherein: The gas transporter includes at least one of a mechanism for generating a pressure differential across the gap and a thermophoretic device configured to generate a temperature gradient across the gap.

3. The device according to claim 1, wherein: The MEMS capacitor includes multiple gaps connected in parallel, each gap having its own readout electronics.

4. The device according to claim 1, wherein: The width of the gap is adjusted by applying a voltage across the two plates such that an electrostatic force is induced to move at least one of the two plates.

5. The device according to claim 1, wherein: The width of the gap is between 0.05 and 2.00 microns.

6. A device comprising: means for directing a gas conveyor configured to flow a gas through a gap between plates of a micro-electromechanical MEMS capacitor to convey the gas through the gap; means for receiving an input from a readout circuit configured to measure a capacitance of the MEMS capacitor, wherein particles flowing through the gap with the gas cause a change in the capacitance of the MEMS capacitor, and means for deriving from said input a concentration of particles in said gas; Wherein, the device is further configured to be able to adjust the width of the gap.

7. The device according to claim 6, wherein: The gas transporter includes at least one of a mechanism that generates a pressure differential across the gap and a thermophoretic device configured to generate a temperature gradient across the gap.

8. The device according to claim 6, wherein: The apparatus is configured to adjust the width of the gap by applying an adjustable voltage to the plates.

9. The device according to claim 6, wherein: The apparatus is configured to obtain a particle size distribution of particles in the gas using a plurality of gap widths in sequence.

10. A method comprising: - directing a gas conveyor to flow a gas through a gap between plates of a micro-electromechanical (MEMS) capacitor; - receiving an input from a readout circuit configured to measure a capacitance of the MEMS capacitor, wherein particles flowing through the gap with the gas cause a change in the capacitance of the MEMS capacitor; as well as - deriving a particle concentration in said gas from said input; - Adjust the width of the gap.

11. The method according to claim 10, wherein: The gas transporter includes at least one of a mechanism for generating a pressure differential across the gap and a thermophoretic device configured to generate a temperature gradient across the gap.

12. The method according to claim 10, wherein: The step of adjusting the width of the gap comprises applying an adjustable voltage to the plates.

13. The method according to claim 10 or 12, further comprising obtaining a particle size distribution of particles in the gas using a plurality of gap widths in sequence.

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