WO2016105555A1 - Portable airborne particle counting systems and methods - Google Patents

Abstract

Particle counting devices and methods. A particle counting device includes a housing structure defining an enclosed flow path and having an air inlet region and an air outlet region, a light source that emits a beam of light, and a photodetector having a sensing region that intersects the beam of light. In operation, an air flow received at the inlet region is directed (pushed or pulled) towards the outlet region through the sensing region, wherein particles in the air flow scatter the beam of light when in the sensing region, and wherein the photodetector detects scattered light and produces a detection signal representative of airborne particles detected, such as sizes and counts.

Description

PORTABLE AIRBORNE PARTICLE COUNTING SYSTEMS AND METHODS INTERNATIONAL PATENT APPLICATION

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH AND DEVELOPMENT

[0001] This invention was made with government support under Grant Number IS-121 1047 awarded by the National Science Foundation. The government has certain rights in the invention.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This patent application claims the benefit of U.S. Provisional Patent Application No. 62/096,371, filed December 23, 2014, which is incorporated by reference.

BACKGROUND

[0003] Low-cost air quality sensing often consists of some form of gas sensor, typically a thermal conductivity based detector tuned to respond to carbon monoxide, ozone, nitrogen oxides, or other gases. However, these devices do a poor job of accurately measuring the actual gas concentrations due to sensor response selectivity and gas interaction problems. Furthermore, these gas sensors are high-power due to their thermal heating requirements. Most importantly, these gas sensors do not measure the primary air pollutant in regards to human health which is airborne particles.

BRIEF SUMMARY

[0004] To address the above problems, the present disclosure advantageously provides airborne particle counting systems and methods. The various embodiments of a novel, functional, low-cost laser air particle counter. The device embodiments demonstrate a signal response consistent with highly calibrated particle sensors. Also, because of the smaller, flexible form factor, and low-power usage, a wide variety of embedded applications, data logging, and wireless applications are possibilities for these sensor embodiments.

[0005] According to an embodiment, a particle counting device is provided that includes a housing structure defining an enclosed flow path and having an air inlet region and an air outlet region, a light source that emits a beam of light, and a photodetector having a sensing region that intersects the beam of light. In operation, an air flow received at the inlet region is directed (pushed or pulled) towards the outlet region through the sensing region, wherein particles in the air flow scatter the beam of light when in the sensing region, and wherein the photodetector detects scattered light and produces a detection signal representative of airborne particles detected, such as sizes and counts..

[0006] In certain aspects, the light source includes a laser. In certain aspects, the housing structure is configured with at least one bend or turn between the inlet region and the sensing region to direct the air flow from the inlet region. In certain aspects, the device further includes a fan that pulls air from the inlet region to the outlet region. In certain aspects, the detection signal represents numbers and sizes of particles detected in the air flow. In certain aspects, the device further includes a communication module adapted to provide the detection signal to an external device. In certain aspects, the communication module implements a wireless protocol for communicating with the external device. In certain aspects, the wireless protocol is a Bluetooth protocol. In certain aspects, the device further includes a straightener module positioned proximal the inlet region, wherein the straightener module reduces an amount of ambient light entering the flow path. In certain aspects, the device further includes a light trap structure or region that traps light from the light source after impinging on the sensing region

[0007] Reference to the remaining portions of the specification, including the drawings and claims, will realize other features and advantages of the present invention. Further features and advantages of the present invention, as well as the structure and operation of various

embodiments of the present invention, are described in detail below with respect to the accompanying drawings. In the drawings, like reference numbers indicate identical or functionally similar elements. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 shows an air particle counter device according to an embodiment.

[0009] Figure 2a shows a piece-wise perspective view of the device of Figure 1.

[0010] Figure 2b shows top, bottom and perspective views of the device of Figure 1.

[0011] Figure 3 shows a still frame of a smoke test video of the device of Figure 1.

[0012] Figure 4 shows results of a series of side by side tests conducted with a calibrated etOne HPPC-6 particle sensor across fifteen locations such as indoor offices, restaurants, subways, and bus stations.

[0013] Figure 5 shows examples of user interfaces on a smart phone device according to an embodiment.

DETAILED DESCRIPTION

[0014] The present disclosure relates generally to airborne particle detection and counting systems and methods.

[0015] Figure 1 shows an air particle counter device 10 according to an embodiment. Device 10 includes a light source 5, such as a laser source, and a light detector or

photodetector 6, such as a photodiode, arranged orthogonally such that the focal point of the laser is located in a sensing region of detector 6, e.g., proximal light detector 6. For example, the light source 5 may include a laser and detector 6 may include a photodiode, wherein the laser and photodiode are arranged orthogonally such that the focal point of the laser 5 is located directly above the photodiode 6 as shown in Figure 1. Air is drawn through the system from inlet region 9 across the detection region of photodiode 6 using a small fan positioned or located within the device so as to create a negative pressure at inlet region 9 and draw air with any particulate matter into the inner portion of device 10. Particles in the air stream that intersect the path of the laser light scatter light onto the photodiode, and the resulting photodiode voltage signal is amplified, e.g., by an op-amp circuit, and sampled by a microcontroller, e.g. with a 10 bit ADC. The data is analyzed for peaks, which indicate that a particle has been detected. [0016] Figures 2a shows a piece-wise perspective view of device 10 and Figure 2b shows top, bottom and perspective views of device 10.

[0017] The light source 5 may include a diode laser, or other laser. Alternatively, a coherent light source other than a laser may be used, or a LED or other source may be used. Also, detector 6 may include any optical detector or any device that converts an optical signal into an electrical signal may be used. Examples of useful detectors might include PIN photodiodes and avalanche photodiodes.

[0018] In certain embodiments, special considerations are made in the mechanical design of device 10, e.g., design of housing structure of device 10, to minimize the amount of ambient light that enters the system. This allows the device to remain accurate in a variety of lighting environments. In certain embodiments, these design features include one or more of the following: (1) a specially shaped air passage which minimizes the amount of ambient light that reaches the detection or sensing region, while still allowing for laminar flow across the sensing region of the photodiode, (2) the use of a centrifugal fan for additional ambient light rejection at the flow outlet, and (3) the selection of materials which have high absorption rates for the visible wavelengths of light. Examples of such materials might include materials having matted finishes or selective coatings (e.g., black paint).

[0019] For example, the flow of air over the detector 6 should be non-turbulent and of a constant rate to allow for accurate calculation of particle density. Second, a large percentage of ambient light should be shielded from the detector 6 such that changing light conditions will not affect the calibration of the sensor device. No existing sensor device has addressed both of these issues simultaneously. For example, existing devices typically should not be operated in direct sunlight or other bright light source as this could affect count accuracy in such devices. This is a significant limitation for air particle sensors or monitors if they are to be portable and functional across a wide range of environments where people go, including outdoors.

[0020] To maximize the ambient light rejection, in one embodiment, the air channels leading to and from the detector 6 include one or multiple turns to prevent ambient light from illuminating the photodiode. Figure 1 shows an embodiment with a single turn 12 in the air channel. In addition, a flow straightener 8 at the inlet 9 and a centrifugal fan 7 at the outlet (not shown) may be used to further prevent light from entering the system or reduce the amount of light entering the system. Simple calculations of the Reynold's number were performed to guide the design of the flow channel to ensure non-turbulent flow. Because of the complex channel geometry, qualitative smoke tests (Figure 3) were conducted to confirm the absence of turbulence and other detrimental effects, such as eddies which may recirculate particles and decrease the responsiveness and accuracy of the sensor.

[0021] In one embodiment, a light trap region 13 is provided to prevent source light and/or stray reflected light from returning to the sensing region. The light trap region 13 may include a light absorptive material (e.g., coating) and have a configuration that results in multiple reflections, and hence multiple absorptions, to thereby reduce or eliminate any light entering the light trap region from exiting the light trap region.

[0022] In one embodiment, an optional light baffle module 4 is included to contain the source light and further prevent unwanted light from traversing the interior of the device. For example, the light baffle 4 may include a series of one or more plates with pinholes arranged along the direction of the source beam.

[0023] In one embodiment, an integrated photodiode and amplifier (OPT101) is used to simplify the electronics design of the system. The output of the OPT101 can be further amplified and attenuated in multiple, e.g., three, stages using a low power operational amplifier.

[0024] For example, in one embodiment, the analog signal is sampled by a processor, e.g., an ARM Cortex M4 based processor at 12 bits at 200 kHz. A mostly interrupt driven system calculates when particles of two different size ranges have been detected during a time window, and stores a buffer of counts during previous time windows. The data can be logged on the device and/or transmitted wirelessly, e.g., using Bluetooth Low Energy (BLE) to a nearby device. In certain embodiments, a small form-factor battery such as a small 400m Ah LiPo battery, may be used which allows for taking multiple, e.g., 120, distinct readings, or 8 hours of data when sampled every 6 minutes. The sampling parameters can of course be adjusted or varied to suit particular applications or power requirements.

[0025] Research was conducted against a MET- ONE HPPC-6 device (a highly calibrated $4000 particle counter used in clean room applications) at different locations of varying ambient light intensity and air quality, resulted in a correlation between the present embodiment as shown in Figure l and the MET-ONE device. The cost for producing certain embodiments, on the other hand, can be quite low, e.g., on the order of $25 USD.

[0026] Two validation studies were conducted to confirm the accuracy of the present embodiment. First, the sensor device was exposed to particles of known origin to characterize its response characteristics against accurate, calibrated hardware using a $4,000 MetOne HPPC-6 particle counter. The signal response to two types of particles were used to guide the cutoffs for fine (<2.5 micron) and coarse (2.5-10 micron) particles. Strong differences are easily observed in the signal produced by wood smoke and household dust. These tests provided the data needed to program the sensor device to distinguish both fine and coarse particles. Next, a series of side by side tests were conducted with the calibrated MetOne HPPC-6 particle sensor across fifteen locations such as indoor offices, restaurants, subways, and bus stations (Figure 4). The data shows strong correlation with the $4,000 HPPC-6 across this entire range.

[0027] The devices according to the present embodiments can be used for sensing air quality. Because they are generally of low cost and size they can be used to allow a user to capture, log, and view their daily exposure. Using a networked device such as a mobile phone embodiments can allow for crowd sourced applications of citizen data collection of health issues around air particles or pollen counts throughout indoor and outdoor locations. Such devices can also be embedded into a watch form factor or attached to a skateboard, bike, car, etc. Such devices can also be used to determine location such as indoor or outdoor and can be used to help other communities or agencies marshal resources by helping inform where higher concentrations of air pollutants are located. Such devices can help build maps of clean routes for jogging, the least polluted parks to visit, the healthiest path to bike through a city, etc. Use of such devices also raises general awareness about air quality and

environmental issues particularly when combined with persuasive interfaces and/or pervasive games.

[0028] While the present embodiments can operate standalone and log data, their usage may be more persuasive and compelling when the data is experienced real-time through a user interface, e.g., through a mobile phone interface. For example, using Bluetooth, e.g., Bluetooth Low Energy (BLE), live particle count data can be transmitted to a handheld device such as an Apple iPhone running an iOS App (Figure 5).

[0029] The interface, in certain aspects, supports scaffolding a user into the data— from a compelling real-time visualization that invites curiosity into a deeper exploration of the rich particle dataset with time and location patterns. In one embodiment, a user interface is composed of three screens: (1 ) an animated, ambient display that allows users to easily visualize the air quality, (2) a bar graph view that communicates precise particle counts and corresponding health related information, and (3) an interactive stacked graph view that displays historical readings across time and location.

[0030] The initial screen of the application may display animated particles as colorful circles that move and interact as a particle simulation system on the screen. The two sizes of particles (e.g., small and large) are distinguished by their color (e.g., blue/purple), size, and movement (e.g., fast/slow). Updates to this screen are deliberate, with particles slowly fading in and out such that the user is made aware of changing air quality conditions. This screen is unique in that it is factual, yet playfully aesthetic.

[0031] The user may swipe in one direction, e.g., left, to access the bar graph view. Here, the individual particles are stacked and viewed as a whole. The precise number of each particle size is displayed along with more information, such as the precise size of the particles, common origins of such particles, and health concerns associated with the current air quality conditions.

[0032] The user can access a final display, such as a stacked line graph, e.g., by rotating their phone into landscape position or otherwise selecting a display option. This graph displays all past readings of the device. A stacked line graph is advantageous as it allows the user to see readings for both sizes of particles, as well as total number of particles. This view is interactive, allowing the user to zoom in/out, scroll forwards and backwards, and learn more about any particular reading; tapping on a specific data point displays the location, date, and precise number of particles for that reading. [0033] An advantage of the present embodiments is the ability to easily be adapted into a variety of form factors and lifestyle application settings. A subset of such exemplary design possibilities include the following:

[0034] Carabiner / Clip On— With the addition of an exterior loop and minor changes in the exterior geometry, this application can be easily implemented enabling air quality measurements from book-bags, purses, etc.

[0035] Bike and Stroller— In this example the device may take on the familiar water bottle like form factor enabling easy integration into biking and stroller activities.

[0036] Watch— The size constraints of the watch form factor are governed in part by the size of the laser. Though proper part selections, one can readily adapt the device to a worn device.

[0037] Children's Toys— the device may be integrated into a toy, e.g., into a toy airplane. The large fuselage affords easy integration of the sensor and enables a new culture of participation into sensing by children.

[0038] All references, including publications, patent applications, and patents, cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein.

[0039] The use of the terms "a" and "an" and "the" and "at least one" and similar referents in the context of describing the disclosed subject matter (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The use of the term "at least one" followed by a list of one or more items (for example, "at least one of A and B") is to be construed to mean one item selected from the listed items (A or B) or any combination of two or more of the listed items (A and B), unless otherwise indicated herein or clearly contradicted by context. The terms

"comprising," "having," "including," and "containing" are to be construed as open-ended terms (i.e., meaning "including, but not limited to,") unless otherwise noted. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or example language (e.g., "such as") provided herein, is intended merely to better illuminate the disclosed subject matter and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention.

[0040] Certain embodiments are described herein. Variations of those embodiments may become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventors expect skilled artisans to employ such variations as appropriate, and the inventors intend for the embodiments to be practiced otherwise than as specifically described herein. Accordingly, this disclosure includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any

combination of the above-described elements in all possible variations thereof is encompassed by the disclosure unless otherwise indicated herein or otherwise clearly contradicted by context.

Claims

CLAIM(S):

1. A particle counting device, comprising:

a housing structure defining an enclosed flow path and having an air inlet region and an air outlet region;

a light source that emits a beam of light,

a photodetector having a sensing region that intersects the beam of light, wherein an air flow received at the inlet region is directed towards the outlet region through the sensing region, wherein particles in the air flow scatter the beam of light when in the sensing region, and wherein the photodetector detects scattered light and produces a detection signal.

2. The device of claim 1 , wherein the light source includes a laser.

3. The device of claim 1 , wherein the housing structure is configured with at least one bend or turn between the inlet region and the sensing region to direct the air flow from the inlet region.

4. The device of claim 1 , further including a fan that pulls air from the inlet region to the outlet region.

5. The device of claim 1 , wherein the detection signal represents numbers and sizes of particles detected in the air flow.

6. The device of claim 1 , further including a communication module adapted to provide the detection signal to an external device.

7. The device of claim 6, wherein the communication module implements a wireless protocol for communicating with the external device.

8. The device of claim 7, wherein the wireless protocol is a Bluetooth protocol.

9. The device of claim 1 , further including a straightener module positioned proximal the inlet region, wherein the straightener module reduces an amount of ambient light entering the flow path.

10. The device of claim 1 , further including a light trap region that traps light from the light source after impinging on the sensing region.