LASERS FOR CONDENSATION PARTICLE COUNTERS

In general, some embodiments include an apparatus, as well as methods and systems thereof, that can detect particles using a condensation particle counter having a laser configured to produce a laser beam. The apparatus can also include a photodetector configured to detect light scattered from the laser beam after the beam hits a particle in a test fluid. More specifically, in some embodiments, the apparatus can detect particles using a fixed laser within the condensation particle counter. Also, in some embodiments, the apparatus can detect particles using a laser configured to produce a focused laser beam that is focused along at least two axes. And, more specifically, in some embodiments, the apparatus can detect particles using a fixed laser within the condensation particle counter that is configured to produce a focused laser beam that is focused along at least two axes.

FIELD

Generally, the present disclosure relates to techniques for detecting particles using lasers. Specifically, the present disclosure relates to techniques for detecting particles using lasers with condensation particle counters.

BACKGROUND

Laser particle counters are known to count particles in an airstream as small as 300 to 500 nanometers (nm) as a consequence of the light scattering signal available for these particle sizes. The ability to measure particles smaller than 300 nm, which are often called ultrafine particles (UFP), is needed as there is mounting evidence that exposure to UFP's can result in endothelial dysfunction, vascular inflammation, and atherosclerosis. Thus, given these example issues, it would be beneficial to characterize airstreams with respect to the concentration of UFPs. This is just one example of the many technical problems solved by the technical solutions described herein.

SUMMARY

In general, some embodiments include an apparatus, as well as methods and systems thereof, that can detect particles using a condensation particle counter having a laser configured to produce a laser beam. The apparatus can also include a photodetector configured to detect light scattered from the laser beam after the beam hits a particle in a test fluid. More specifically, in some embodiments, the apparatus can detect particles using a fixed laser within the condensation particle counter. Also, in some embodiments, the apparatus can detect particles using a laser configured to produce a focused laser beam, wherein the focused laser beam is focused along at least two axes. And, more specifically, in some embodiments, the apparatus can detect particles using a fixed laser within the condensation particle counter that is configured to produce a focused laser beam. In some cases, the beam diameter of the focused laser beam is smaller than the width or the diameter of the opening or the stream diameter of the stream of the test fluid as the laser beam intersects the stream.

In some examples, an apparatus includes a detection chamber and a conduit configured to convey a test fluid to the detection chamber. The apparatus also includes a nozzle at an end of the conduit including an opening and is configured to eject the test fluid into the detection chamber via the opening. The apparatus also includes a detection system configured to monitor at least one characteristic of the test fluid when it is ejected from the opening of the nozzle. And, the detection system, includes a laser, configured to produce a focused laser beam, and a photodetector, configured to detect light scattered from the focused laser beam after the beam hits a particle in the test fluid as the fluid is ejected from the opening of the nozzle. In some cases, the laser is a fixed laser configured to produce a laser beam in general that is not necessarily focused. And, in some cases, the laser is not fixed in that it can be adjusted in an operation of the apparatus. Also, in some examples, the laser is both a fixed laser and configured to produce a focused laser beam. In some examples, the laser is not necessarily fixed or configured to produce a focused laser beam; however, the location of the nozzle is adjustable, in an operation of the apparatus, to align the opening of the nozzle with the laser beam produced by the laser.

In some examples wherein the laser beam is focused, the opening of the nozzle is circular and the beam diameter of the focused laser beam is smaller than the diameter of the opening. In some examples wherein the laser is focused, the opening of the nozzle is oval and the beam diameter of the focused laser beam is smaller than the largest diameter of the opening. In some examples wherein the laser is focused, the opening of the nozzle is oval and the beam diameter of the focused laser beam is smaller than the smallest diameter of the opening.

In some examples wherein the laser beam is focused, the beam diameter of the focused laser beam is smaller than the largest width across the opening of the nozzle. Also, the beam diameter of the focused laser beam can be smaller than the smallest width across the opening of the nozzle. Also, in some examples, the beam diameter of the focused laser beam is smaller than the stream diameter of the stream of the test fluid as the laser beam intersects the stream. Also, in some examples, the beam cross-section area of the focused laser beam, at the intersection of the stream, is smaller than the cross-section area of the stream of the test fluid.

In some examples, the photodetector includes a lensless light scatter collection system, configured to receive the scattered light. And, in some cases, the lensless light scatter collection system is integrated with the photodetector and the apparatus. In some cases, the scattered light collection system is configured to use forward scattered light collection. And, in some examples, the azimuthal collection angles of the light collection are one or more values or in a range of degrees such as 6 to 45 degrees. In some examples, the photodetector includes a lensless scattered light collection system and an integrated beam stop.

In some examples, the detection system is configured to adjust the intensity of the laser beam based on the detection of scattered light by the photodetector. In some cases, the opening and at least another part of the nozzle is in the detection chamber. In some examples, the conduit configured to convey the test fluid to the detection chamber is coupled to a particle growth stage conduit that is upstream of the detection chamber.

In some examples wherein the laser is fixed, the location of the nozzle is adjustable to align the opening of the nozzle with the laser beam of the fixed laser. Also, in some examples, the location of the nozzle is adjustable via an eccentric mechanism including an attachment part attaching the nozzle to the eccentric mechanism and fixed to a rotating axle with the center or a midpoint of the attachment part offset from that of the axle. Also, in some examples, the attachment part is a portion of the nozzle.

These and other important aspects of the invention are described more fully in the detailed description below. The invention is not limited to the particular apparatuses and systems described herein. Other embodiments can be used and changes to the described embodiments can be made without departing from the scope of the claims that follow the detailed description. Within the scope of this application, it should be understood that the various aspects, embodiments, examples, and alternatives set out herein, and individual features thereof can be taken independently or in any possible and compatible combination. Where features are described with reference to a single aspect or embodiment, it should be understood that such features are applicable to all aspects and embodiments unless otherwise stated or where such features are incompatible.

DETAILED DESCRIPTION OF THE DRAWINGS

Details of example embodiments of the invention are described in the following detailed description with reference to the drawings. Although the detailed description provides reference to example embodiments, it is to be understood that the invention disclosed herein is not limited to such example embodiments. But to the contrary, the invention disclosed herein includes numerous alternatives, modifications, and equivalents as will become apparent from consideration of the following detailed description and other parts of this disclosure.

FIG.1Aillustrates a perspective view of a portion of a laser beam102and a portion of a nozzle104of a particle counter, in accordance with some known examples of the prior art and in accordance with some embodiments of the present disclosure.FIG.1Billustrates a cross-sectional view of the laser beam102shown inFIG.1Ainteracting with the nozzle exit106of the nozzle104shown inFIG.1A. Whereas,FIG.2Aillustrates a perspective view of a portion of a focused laser beam202and a portion of a nozzle204of a particle counter, in accordance with some embodiments of the present disclosure.FIG.2Billustrates a cross-sectional view of the focused laser beam202shown inFIG.2Ainteracting with the nozzle exit206of the nozzle204shown inFIG.2A. The focused laser beam202is an example of a two-axis focused laser beam. Whereas the laser beam102is actually a single-axis focused laser beam.

As shown, the width108of the laser beam102is greater than the width or diameter110of the nozzle exit106. The laser beam102shown inFIGS.1A and1Bis a single-axis focused beam for the purposes of this disclosure and it has a width108that is greater than the width or diameter110of the nozzle exit106. Contrary toFIGS.1A and1B,FIGS.2A and2Bshow an example of a two-axis focused laser beam (e.g., see focused laser beam202) in which the focused laser beam has a width (e.g., see width208) that is less than the width or diameter210of the nozzle exit206. Thus, the beam202is a focused laser beam or a two-axis focused laser beam for the purposes of this disclosure. With that said, the focused laser beam202is just one example of how a laser can be focused for the purposes of this disclosure. For example, in some example embodiments where the laser beam is focused, the opening of the nozzle is circular and the beam diameter of the focused laser beam is smaller than the diameter of the opening. Also, in some examples wherein the laser is focused, the opening of the nozzle is oval and the beam diameter of the focused laser beam is smaller than the largest diameter of the opening. Also, in some examples wherein the laser is focused, the opening of the nozzle is oval and the beam diameter of the focused laser beam is smaller than the smallest diameter of the opening.

It is to be understood, for the purposes of this disclosure, that any laser beam that is referred to herein as unfocused or not focused is actually a single-axis focused laser beam in that it is focused along one axis. And, it is to be understood, for the purposes of this disclosure, that any laser beam that is referred to herein as a “focused laser beam” is actually a two-axis or multiple-axis focused laser beam in that it is focused along multiple axes.

In some examples wherein the laser beam is focused, the beam diameter of the focused laser beam is smaller than the largest width across the opening of the nozzle (e.g., see width208and diameter210shown inFIG.2B). Also, in some examples, the beam diameter of the focused laser beam can be smaller than the smallest width across the opening of the nozzle. Also, in some examples, the beam diameter of the focused laser beam is smaller than the stream diameter of the stream of the test fluid as the laser beam intersects the stream. Also, in some examples, the beam cross-section area of the focused laser beam, at the intersection of the stream, is smaller than the cross-section area of the stream of the test fluid.

FIGS.1A,1B,2A, and2Bshows an example difference in optical beam paths between a single-axis focused laser beam of many known optical counters used within condensation particle counters (seeFIGS.1A and1B) and a two-axis focused laser beam used of optical counters used within some of the novel condensation particle counters described herein (seeFIGS.2A and2B). In some embodiments, an elliptical laser beam is used that is wider than the nozzle or the nozzle hole or exit and that has an aspect ratio such that the beam is relatively thin, obtained by the focus of the laser in only a single-axis. This reduction in beam thickness reduces the volume of optically illuminated particles and helps reduce the probability that two particles are in the laser beam at the same time, which is often called coincidence. The single-axis focused laser beam limits the possibility of a particle exiting the nozzle without intersecting the beam. With the single-axis focused beam, the beam is wide like a ribbon or sheet, and the nozzle opening providing a test fluid stream intersect in a region where the intensity is relatively uniform resulting in a scattered light signal that also is relatively uniform in amplitude.

With a two-axis focused laser beam, in some embodiments, circular beam is used and the beam is focused down in both directions such that a small and focused spot intersects the nozzle exit or hole. Using the focused beam results in a region with much higher intensity due to the small beam area, and the resulting beam width is now smaller than the nozzle diameter. Thus, with the focused beam, some of the particles may exit the nozzle without having passed through the laser beam. Or, such an occurrence is more likely using the two-axis focused beam compared to the single-axis focused beam. One advantage to the two-axis focused beam is the small spot size, and that it further reduces coincidence as the optically illuminated area is much smaller than a single-axis focused beam. In some embodiments, an elliptical beam can be focused and used with the counter. And, in some embodiments, a circular beam can be single-axis focused in that it is wider than the nozzle or the nozzle hole or exit.

FIG.3illustrates a view of an example condensation particle counter302with parts broken away to show parts in the interior of the counter, in accordance with some embodiments of the present disclosure. The condensation particle counter302includes a nozzle304and a nozzle exit306(such as the nozzle exits shown inFIGS.1A,1B,2A, and2B) as well as a two-axis focused laser beam303shown emitting from a laser module307(such as the focused beam shown inFIGS.2A and2B). The laser module307emits the laser beam303such that it is focused to a tight spot at a working distance from the end of the laser module. The condensation particle counter302also includes an optics housing312that holds at least the optical components of the counter302including holding the laser module307, the nozzle304, an eccentric adjustment mechanism305, and a photodiode314. In some embodiments, the housing312is pneumatically sealed relative to the ambient to ensure that any fluid flow in the optical system only comes from the nozzle exit306. In some embodiments, the nozzle304and then the nozzle exit306are downstream of a conduit in a condenser portion of a condensation particle counter or a conduit providing a barrier fluid flow.

Referring back to the focused laser beam303, the laser beam passes through an aperture316in the housing312. In some examples, the aperture316is integrated into the housing312such that they are one part (e.g., one molded or fabricated part). The aperture316limits stray light from entering the scattered light collection area317of the counter302. A focal point of laser of the laser module307is configured such that the beam emitted intercepts at the center of the exit306of the nozzle304. Particles exiting the nozzle intersect the laser beam303and the intersection of the beam and the particles causes the beam to transform into scattered light318. The scattered light318enters the scattered light collection area317after the intersection of the beam and the particles. As shown, the beam303and the nozzle exit306intersect at a beam waist319of the beam. The beam waist319, in some embodiments, is the part of the beam that has a narrower width than the width of the nozzle or the nozzle hole or exit. The beam waist319can include a focus point of the laser beam303. The scattered light318can be emitted from the intersection of the beam303and the exit306at a forward scattered angle320. The forward scatter angle320can include a group of angles, such as a group of angles ranging between seven and thirty degrees in some examples, relative to the collection of the light318by the photodiode314. An active area322of the photodiode314captures the scattered light318. After the scattered light318is received by the active area322of the photodiode314, the corresponding signal derived from the capturing of the light can be amplified and processed, such as processed by at least an analog-to-digital converter (ADC).

In addition to the scattered light318, the remainder of the light from the beam303continues past the nozzle and strikes a first surface reflector324. The first surface reflector324, as shown inFIG.3, is an un-active area of the photodiode314. The inactive area of the photodiode314can be a part of or include the housing of the photodiode. The first surface reflector324is arranged to reflect the beam303into a beam stop326. The beam stop326is configured to receive the reflection of the light from the non-active area of the photodiode or the reflector324such that all reflection from the surface remains within the beam stop and cannot exit the beam stop. This beam stop326is used in the counter302to prevent stray light from reflecting inside the housing312and into the scattered light collection area317. This way the reflected light that is not scattered at the nozzle exit306by the flowing particles is not collected by the active area322of the photodiode314. Stray light can limit the amplification levels of the photodiode314, as a constant input light represents a DC bias in the amplification circuit and can limit the dynamic range of the amplifier circuit. The internal reflections within the beam stop326can also be reduced in amplitude by the use of optically absorbing material in some embodiments. Also, in some examples, the reflector324includes an absorbing material for the wavelength of the laser beam303.

In some embodiments, the housing312includes a simple plastic housing fabricated from 3D printing. In some examples, the housing312fully integrates the features of the counter302necessary to hold the components internal to the housing such as the laser module307, the nozzle304and nozzle holder325with the eccentric adjustment mechanism305, and the forward scattered light collection optics board that includes the photodiode314. The counter302as a system is designed to be airtight in some examples. This ensures no outside particles enter into the system and only the primary flow from streamed from the nozzle304enters the counter302. This facilitates the optical counting of particles as they exit nozzle304after being grown in a prior condensation growth stage. In some examples, the system of the counter302is designed with considerations that typically come with a condensation particle counter including the capability to operate with a flow of air exiting the condensation growth stages that is at near saturation vapor point of the condenser portion of the growth stage of the particles.

FIG.4illustrates a view of another example condensation particle counter402with parts broken away to show parts in the interior of the counter, in accordance with some embodiments of the present disclosure. The counter402shares similar parts to the counter302, except the housing412is configured differently from housing312in that it holds the photodiode314differently and includes the first surface reflector424instead of the first surface reflector being part of an un-active area of the photodiode. Also, as shown the beam stop426of the counter402has a different design from the beam stop326of the counter302. The beam stop426is integrated into the housing412and is shown including a primary reflecting surface428that is integrated into the housing too. This primary reflective surface428can include a light-absorbing material too. Additionally, the surfaces within the beam stop426(as well as the beam stop326) can be coated with such a material to ensure that further reflections and any scattered light are further attenuated to reduce scattered light from entering the viewing area of the photodiode (e.g., see scattered light collection area317). The design of the beam stop426may also include topography and geometry that further help reduce internal reflections. As shown, this can include a saw-tooth-like profile at the primary reflective surface428, or a variety geometry to ensure incoming light is captured. Such features can also be used by the beam stop326.

Similarly, in some embodiments, the housing412includes a simple plastic housing fabricated from 3D printing. In some examples, the housing412fully integrates the features of the counter402necessary to hold the components internal to the housing such as the laser module307, the nozzle304and nozzle holder325with the eccentric adjustment mechanism305, and the forward scattered light collection optics board that includes the photodiode314. Similarly, the counter402as a system is designed to be airtight in some examples. This ensures no outside particles enter into the system and only the primary flow from streamed from the nozzle304enters the counter402. This facilitates the optical counting of particles as they exit nozzle304after being grown in a prior condensation growth stage. In some examples, the system of the counter402is designed with considerations that typically come with a condensation particle counter including the capability to operate with a flow of air exiting the condensation growth stages that is at near saturation vapor point of the condenser portion of the growth stage of the particles.

In some examples, the nozzle304and the beam303may not align such that the beam waist319and particles released from the nozzle exit306intersect. To overcome such misalignment, the nozzle304is attached to the nozzle holder325which is part of the eccentric adjustment mechanism305. Rotation of part of the eccentric adjustment mechanism305results in an arc sweep of the nozzle304. Thus, the nozzle304can be adjusted by the eccentric adjustment mechanism305to intercept the laser beam303by rotating the nozzle holder325via the eccentric adjustment mechanism.

FIG.5illustrates a view of the condensation particle counter302with parts broken away to show parts in the interior of the counter and zoomed in on the nozzle304of the counter to show an adjustment mechanism305of the nozzle, in accordance with some embodiments of the present disclosure.

The center502of the adjustment mechanism305and the nozzle holder325lies on the laser beam axis504of the laser beam, and an angular or positional error can be adjusted out by a nozzle motion path506resulting from the rotation about the center502of the nozzle holder325. The rotation and adjustment of the nozzle304ensures optical alignment between the nozzle exit306and the beam303. The alignment of the laser beam303to the nozzle304is critical in the counters302and402since the particles exiting the nozzle must intersect the laser beam to scatter the light of the beam to be captured by the photodiode314and then the corresponding signal eventually being transformed into information including a particle count.

In general, some embodiments include an apparatus, as well as methods and systems thereof, that can detect particles using a condensation particle counter (e.g., see counter302or402) having a laser (e.g., see laser module307) configured to produce a laser beam (e.g., see laser beam303). The apparatus can also include a photodetector (e.g., see photodiode314) configured to detect light scattered from the laser beam after the beam hits a particle in a test fluid. More specifically, in some embodiments, the apparatus can detect particles using a fixed laser within the condensation particle counter (e.g., see laser module307). Also, in some embodiments, the apparatus can detect particles using a laser configured to produce a focused laser beam (e.g., see focused laser beam303), wherein the focused laser beam is focused along at least two axes. And, more specifically, in some embodiments, the apparatus can detect particles using a fixed laser within the condensation particle counter that is configured to produce a focused laser beam (e.g., see laser module307and focused laser beam303). In some cases, the beam diameter of the focused laser beam is smaller than the width or a diameter of the opening or the stream diameter of the stream of the test fluid as the laser beam intersects the stream (e.g., see beam waist319which is narrower than the nozzle exit306).

In some examples, an apparatus includes a detection chamber (e.g., see the scattered light collection area317and the immediate surrounding area within the housing312) and a conduit configured to convey a test fluid to the detection chamber (e.g., see nozzle304which is at the downstream end of a conduit configured to convey a test fluid to the detection chamber). The apparatus also includes a nozzle (e.g., see nozzle304) at an end of the conduit including an opening (e.g., see nozzle exit306) and is configured to eject the test fluid into the detection chamber via the opening. The apparatus also includes a detection system configured to monitor at least one characteristic of the test fluid when it is ejected from the opening of the nozzle. And, the detection system, includes a laser (e.g., see laser module307), configured to produce a focused laser beam (e.g., see laser beam303), and a photodetector (e.g., see photodiode314), configured to detect light scattered from the focused laser beam after the beam hits a particle in the test fluid as the fluid is ejected from the opening of the nozzle. In some cases, the laser is a fixed laser configured to produce a laser beam in general that is not necessarily focused. And, in some cases, the laser is not fixed in that it can be adjusted in an operation of the apparatus. Also, in some examples, the laser is both a fixed laser and configured to produce a focused laser beam. In some examples, the laser is not necessarily fixed or configured to produce a focused laser beam; however, the location of the nozzle is adjustable, in an operation of the apparatus, to align the opening of the nozzle with the laser beam produced by the laser (e.g., see eccentric adjustment mechanism305, nozzle holder325, center502of the adjustment mechanism305, the laser beam axis504of the laser beam303, and the nozzle motion path506shown inFIG.5).

In some examples, the photodetector includes a lensless light scatter collection configured to receive the scattered light (e.g., see photodiode314). And, in some cases, the lensless light scatter collection is integrated with the photodetector and the apparatus. In some cases, the light collection system is configured to use forward scattered light collection. And, in some examples, the azimuthal collection angles of the light collection are 6 to 45 degrees. In some examples, the photodetector includes a lensless scattered light collection system, first surface reflector, and an integrated beam stop.

In some examples, the detection system is configured to adjust the intensity of the laser beam based on the detection of scattered light by the photodetector. In some cases, the opening and at least another part of the nozzle is in the detection chamber. In some examples, the conduit configured to convey the test fluid to the detection chamber is coupled to a particle growth stage conduit that is upstream to the detection chamber (e.g., see optical counter portion602and the incoming flow of particles at flow604of the illustrative flowchart600depicted inFIG.6).

In some examples wherein the laser is fixed, the location of the nozzle is adjustable to align the opening of the nozzle with the laser beam of the fixed laser (e.g., see the laser module307and the nozzle304shown inFIGS.3and4). Also, in some examples, the location of the nozzle is adjustable via an eccentric mechanism including an attachment part attaching the nozzle to the eccentric mechanism and fixed to a rotating axle with the center or a midpoint of the attachment part offset from that of the axle (e.g., see eccentric adjustment mechanism305, nozzle holder325, center502of the adjustment mechanism305, the laser beam axis504of the laser beam303, and the nozzle motion path506shown inFIG.5). Also, in some examples, the attachment part is a portion of the nozzle.

In some embodiments, in a condensation particle counter (such as counter302or402), the counter uses a specially designed growth section to aerosol particles from their original size of 10-1000 nm(0.01-1 um) to 5000-10,000 nm(5-6 um). This growth mechanism is used, because traditional optical detection of particles by light scattering has a rough scaling factor of dp{circumflex over ( )}4 power, meaning the scattered light intensity for a 100 nm particle is roughly 1/10,000th of that of a 1 um particle. Thus the only practical way to optically detect a particle that is 10 nm in diameter, is to enlarge enough to easily optically detect it. This is done using condensation to grow the particles, which the initial state of a particle acts as seed nuclei to the condensation growth process. Once the particles have grown to sufficient size they are passed into the optical counting portion of the system. The optical counting device of the system can use forward light scattering for the optical detection of particles, due to the larger forward light scattering lobe of particles. To generate the light scattering signal, a focused laser beam is formed from a laser diode, and is passed over a nozzle (e.g., see laser module307and nozzle304). The nozzle acts to both physically constrain the particles to a much smaller region, allowing for the final laser beam width to be smaller and at a higher intensity, and also has the effect of accelerating the particles so that they are further separated in distance in an axial direction corresponding to the beam helping ensure only one particle at time passes through the beam.

In some example systems, the forward light scattering collection or capturing uses a pair of large aspheric lenses, with a focal location set at the intercept of the laser beam and nozzle. The area in which the aspheric collection and laser beam area is often called the viewing volume, and represents the area in which particle scattered light can be collected. To ensure a uniform signal from the scattered light the laser beam is typically much wider than the nozzle (e.g., seeFIGS.1A and1B). In such cases, the laser beam has a Gaussian beam profile to ensure a relatively uniform intensity and only 10% of the beam width is often used; thus, for example, for a nozzle that may be 0.35 mm in diameter, the laser beam width(1/e{circumflex over ( )}2) may be 1.3 mm. This use of a wide beam, such as shown inFIGS.1A and1B, provides a relatively uniform signal at the tradeoff for beam intensity. In such examples and others, in the axial direction, the beam is focused down in terms of thickness, which has the benefits of both increasing the intensity and reducing the transit time into the beam to reduce the probability of more than one particle being present in the beam, often called coincidence. Overall, this design functions well but requires a significant number of components including precision alignment features to align the laser diode to the beam shaping optics and also to ensure that the laser beam passes over the nozzle. Precision assembly is also required to ensure that the beam stop, which prevents the laser beam from shining directly into the photodiode that collects the scatted light. The large lenses, typically of an aspheric type for the scattered light collection, can both be expensive but also must have good alignment to the nozzle and viewing volume to ensure the scattered light is collected within the collection angles of the optics. This all adds up to many precision machined components, precision assembly steps to ensure alignment, and this all adds to the considerable cost associated with such designs.

In some other example systems, such as in lower-cost optical counters used outside of condensation particle counters, take a different approach to particle detection. The use of low cost and focused laser beam modules can be used along with an integrated beam stop to produce a high-intensity focused beam design. In some of such examples, a 90-degree scattered light collection can be used due to the different requirements of a simple optical particle counter. However, in such simple designs, since a nozzle may not be used, the electronics required to amplify the signal may have much fewer bandwidth limitations when compared to the high speed of the typical condensation particle counter. Thus, the use of focused beams to get high intensity at the focus area provides a technical way of eliminating a wide range of scattered light collection optics in a particle counter design.

Some optics systems disclosed herein, such as the ones shown inFIGS.3and4, provide for the optical counting of particles as they exit a nozzle of a condensation particle counter. Such a system is designed with considerations that typically come with a particle counter including the capability of it to work with a flow of air exiting the condensation growth stages that is at near saturation vapor point of the condenser portion of the growth stage. In such systems, such as the systems shown inFIGS.3and4, many of the shortcomings and design challenges are overcome in the attempt to make a device for lensless light scattering collection. Large aspheric collection lenses provide a significant amount of scattered light collection, and simply removing them from the system and using a large format photodiode alone would not have enough scattered light to be compatible with a high-speed amplification circuit. To overcome this, the amount of scattered light generated must be significantly increased. One way to do this is to increase the intensity of the light in which the particles intersect the laser beam (e.g., see the focused beams ofFIGS.2A,2B,3,4, and5). To do this, the laser providing the laser must use a module for the generation of a focused laser beam that can provide a beam with a spot size of 0.035×0.035 mm (in contrast to typical designs that would have 1.3 mm×0.035 mm spot size). This increases the beam intensity; and thus, scattered light intensity is increased as well. In some cases, the scattered light intensity is increased by a magnitude of fifty times that of a single-axis focused beam. This significant increase in scattered light allows for the removal of the lenses (which can be very costly) and transition to a simple flat photodiode to collect the forward scattered light (which is shown in the counters302and402).

Some example systems use raw laser diodes and then discrete optic components to generate the desired laser beam profile. This has resulted in complex alignment mechanics. In some embodiments, to avoid complications, the optics system uses a preassembled laser drive module that includes lenses and is integrated within the sealed housing of the counter (e.g., see counters302and402). Some example counters are sealed to the inner flow cavity to prevent particles from entering into the optics system and contaminating them. To improve upon such a design, the laser module in some embodiments is sealed into the housing with no seals between the particle flow coming out of the nozzle and the optics of the system. In such examples, it can be useful to use a sheath or bypass flow, which acts to reduce the vapor pressure of the final mixture below the saturation point and also acts as a barrier to prevent particles from floating around in the optics system and depositing on components of the optics system (e.g., see the second fluid conduit132in fluid communication with the detection chamber102—which is carrying a barrier fluid134and is independent of the first fluid conduit106that carries the test fluid—illustrated in FIG. 1 of U.S. patent application Ser. No. 18/428,986, filed on Jan. 31, 2024, and entitled “CONDENSATION PARTICLE COUNTERS”, the entire disclosure of which application is hereby incorporated herein by reference).

In some embodiments, the use of a laser module along with the less complex system design has enabled a counter that does not require difficult laser alignment. In the designs shown inFIGS.3,4, and5, the housings can be 3D printed all in one piece and no alignment step (or difficult laser alignment) is needed to align the beam with the beam stop. The beam stop can use the edge of the photodiode packaging as a first surface reflector, as shown with the counter302, in which the beam is then reflected into an integrated beam stop where the internal reflection within the beam stop prevents the light from ever exiting the beam stop. The beam stop can also be fabricated into the same portion of the housing that holds the laser and provides the internal flow into the optics chamber of the particle counter.

In some examples, where misalignment sometimes occurs, the nozzle providing the stream of particles can be attached to a part that can be rotated on an eccentric path, so that the nozzle can be rotated to bring into the intersection of the laser beam (e.g., see counters302and402as well as the alignment mechanism emphasized inFIG.5). In some examples, using the particle count and amplitude of scattered light pulses allows for alignment to occur. As the nozzle is rotated, the recorded number increases as the laser begins to intercept the nozzle, and the change in concentration flattens out as the flow of particles sweeps across the beam and then falls off again if the alignment is off. Such a design can provide for an automated process, where the alignment does not require manual adjustment. Feedback from the counter counting the particles can provide for enhancing the alignment of the nozzle with the laser beam.

In some examples, a challenge with using a particle counter where the laser beam has a width that is narrower than the width of the nozzle or nozzle exit, and thus the trajectory of particles, is that because the laser beam includes a Gaussian distribution of light some fraction of particles only hit the edge of the beam resulting in a scattered light signal that is smaller than if the same particle had intercepted the middle portion of the laser beam. This means that a fraction of the particles exiting at the exit of the nozzle correspond with no scattered light and that there is a distribution of scattered light intensity. In designs where the beam is not focused, and in which the laser is much wider than the nozzle exit, the distribution of pulse heights corresponds with only a very small range corresponding to the small variation of laser beam intensity that occurs across the nozzle exit. To overcome the challenge of using a focused laser beam, a correction method can be used (e.g., see the operations shown inFIGS.6and7). The correction method can be used in a way in which each particle's laser-scattered light pulse is collected, the peak of the intensity is determined, and a distribution of pulse amplitude is generated. Then, two threshold levels are used to determine which fraction of particles lie above and below these thresholds, which can be referred to as the threshold count ratio. Because of the Gaussian distribution of the focused laser, it is possible to compute which fraction of the particles were counted based on the threshold count ratio. The process flow for this method includes capturing the raw signal of the scattered light as particles traverse the beam, digitizing the captured signal using at least an analog-to-digital converter, and then computing the peak of the signal. Then, the method can include aggregating signal peak information on a time basis using the produced distribution to compute the threshold count ratio as well as using the threshold count ratio and an empirically determined model to compute a true count of particles exiting the nozzle.

Specifically,FIG.6depicts an illustrative flowchart600that starts with an example generation and outputting of an analog signal produced from the light collection of a photodiode of a condensation particle counter, such as the photodiode314of counter302or402. And, the flowchart600ends with an example determination of the number of particles exiting the nozzle of the counter per unit time.

As shown inFIG.6, an optical counter portion602is in fluid communication with the growth stage of a condensation particle counter (see the incoming flow of particles at flow604). Particles that have been enlarged via condensation growth pass through a nozzle606which both constrains the particles into a smaller area and accelerates them (e.g., also see nozzle304shown inFIGS.3to5). This increases the physical spacing between particles and helps reduce the probability that more than one particle is in the laser beam path simultaneously. In the design shown inFIG.6, a barrier flow is introduced into the optics system at input608, which reduces the vapor pressure of the working fluid used by the condensation growth stage and prevents condensation of the working fluid in the optics housing by diluting the vapor. The laser module, nozzle606, and the photodiode are all contained within pneumatically sealed optics housing similar to the design shown inFIGS.3to5and such that the only inflows into the optics system are those of the barrier flow at input608and incoming flow from the condensation growth stage via the nozzle606and the exit of the nozzle607(e.g., also see the second fluid conduit132in fluid communication with the detection chamber102—which is carrying a barrier fluid134and is independent of the first fluid conduit106that carries the test fluid—illustrated in FIG. 1 of U.S. patent application Ser. No. 18/428,986, filed on Jan. 31, 2024, and entitled “CONDENSATION PARTICLE COUNTERS”, the entire disclosure of which application is hereby incorporated herein by reference).

Particles exiting the nozzle606will intersect the focused laser beam610at its narrowest point (or at the waist of the focused beam), which results in the highest optical flux density and the highest intensity as well as an increased amount of scattered light as the particles traverse the beam at the exit of the nozzle607. The scattered light (such as scatter light318shown inFIGS.3and4) is captured by the photodiode and then the corresponding signal from the captured light is amplified and fed into an analog to a digital converter618via operation620(which can be implemented by a signal amplification circuit or by a computing system such as the one illustrated inFIG.8, or a combination thereof depending on the embodiment).

Next, after the conversion by the digital converter618, a computing system, such as the computing system800depicted inFIG.8, determines the peak amplitude of the pulses along with pulse width and logs and aggregates such parts of the converted signal over a defined time interval. The resulting data, determined and aggregated by the computing system, includes a distribution of pulse amplitude. The distribution of the pulse amplitude can vary significantly because the laser beam is smaller than the nozzle and some particles do not intercept the focused laser beam, some partially intercept the beam but give lower scattered light intensity, and some particles intercept the beam at peak intensity of the beam and give the highest level of scattered light. This also results in a fraction of particles that exit the nozzle in which there is no scattered light as they do not traverse the beam, and some in which the captured scattered light is not sufficient to be seen over the optical and electronic noise in the optical system of portion602. However, this fraction of missed counts can be corrected using computing operations (e.g., see operations of method700depicted inFIG.7) implemented by a computing system such as the computing system800shown inFIG.8.

The computing operations can use the collected and digitized data from converter618, operation620, and derivatives thereof (which can include information on maximum pulse amplitude) and use a correction factor to correct the fraction of missed counts of particles. A two-level discriminator or threshold generator, which is implemented by the computing system, is applied to the data at operation622and a summation of all counts above or below selected thresholds is computed. The first level, the lower count threshold, is derived from the sum of all counts that have a peak amplitude under a lower threshold level. The second level computed is derived from the sum of all peak amplitudes above the higher threshold level, called the upper count threshold. In such examples, a correction is applied in which a predetermined correction is used to account for missed particles using the threshold count ratio—which can be a ratio of the upper count threshold to the lower count threshold (referred to in the drawings as the threshold count fraction). But, first, the ratio is determined at operation624. The corrected count, derived from the ratio, for an estimated true number of particles having exited the nozzle, is determined at operation626. Then, in some examples, the estimated true number of particles can be used to calculate the count rate. Also, given known flow rates, the computing system can determine an estimated true concentration of particles present in the sample fluid. Besides a computing system, such as system800, the operations620,622, and624can be implemented by a set of comparators and simple counters, such that the two levels are summed.

FIG.7illustrates an example method700implemented by a computing system for determining the number of particles exiting a nozzle of a counter per unit time, in accordance with some embodiments of the present disclosure. The method700is a computer-implemented method and, at step702, commences with generating analog information based on analog signal outputted by the counter (e.g., see the output of optical counter portion602shown inFIG.6). At step704, the method700continues with converting the analog information to digital information(e.g., see operation620shown inFIG.6). At step706, the method700continues with determining a lower count threshold and an upper count threshold (e.g., see operation622). At step708, the method700continues with determining a threshold count fraction based at least partially on the determined thresholds (e.g., see operation624). At step710, the method700continues with determining the number of particles exiting in the nozzle of the counter per unit of time based at least partially on the determined threshold count fraction (e.g., see operation626).

FIG.8illustrates example aspects of an example computing system800, in accordance with some embodiments of the present disclosure.FIG.8illustrates parts of the computing system800within which a set of instructions, for causing the machine to perform any one or more of the methodologies discussed herein, can be executed (e.g., see operations of the steps of method700as well as operations of converter618and operations620,622,624, and626of flowchart600). In some embodiments, the computing system800can correspond to a host system that includes, is coupled to, or utilizes memory or can be used to perform the operations of a controller. In alternative embodiments, the machine can be connected (e.g., networked) to other machines in a LAN, an intranet, an extranet, and/or the Internet. The machine can be a personal computer (PC), a tablet PC, a set-top box (STB), a Personal Digital Assistant (PDA), a cellular telephone, or any machine capable of executing a set of instructions (sequential or otherwise) that specify actions to be taken by that machine. Further, while a single machine is illustrated, the term “machine” shall also be taken to include any collection of machines that individually or jointly execute a set (or multiple sets) of instructions to perform any one or more of the methodologies discussed herein.

The computing system800includes a processing device802, a main memory804(e.g., read-only memory (ROM), flash memory, dynamic random-access memory (DRAM), etc.), a static memory1206(e.g., flash memory, static random-access memory (SRAM), etc.), and a data storage system810, which communicate with each other via a bus820. The processing device802represents one or more general-purpose processing devices such as a microprocessor, a central processing unit, or the like. More particularly, the processing device can be a microprocessor or a processor implementing other instruction sets, or processors implementing a combination of instruction sets. The processing device802can also be one or more special-purpose processing devices such as an application-specific integrated circuit (ASIC), a field programmable gate array (FPGA), a digital signal processor (DSP), a network processor, or the like. The processing device802is configured to execute instructions814for performing the operations discussed herein. The computing system800can further include a communications interface device808to communicate over one or more LAN/WAN networks816.

The data storage system810can include a machine-readable storage medium812(also known as a computer-readable medium) on which is stored one or more sets of instructions814or software embodying any one or more of the methodologies or functions described herein (e.g., see operations of the steps of method700as well as operations of converter618and operations620,622,624, and626of flowchart600). The instructions814can also reside, completely or at least partially, within the main memory804and/or within the processing device802during execution thereof by the computing system800, the main memory804and the processing device802also constituting machine-readable storage media. While the machine-readable storage medium812is shown in an example embodiment to be a single medium, the term “machine-readable storage medium” should be taken to include a single medium or multiple media that store the one or more sets of instructions. The term “machine-readable storage medium” shall also be taken to include any medium that is capable of storing or encoding a set of instructions for execution by the machine and that causes the machine to perform any one or more of the methodologies of the present disclosure (e.g., see operations of the steps of method700as well as operations of converter618and operations620,622,624, and626of flowchart600). The term “machine-readable storage medium” shall accordingly be taken to include, but not be limited to, solid-state memories, optical media, and magnetic media.

While the invention has been described in conjunction with the specific embodiments described herein, it is evident that many alternatives, combinations, modifications, and variations are apparent to those skilled in the art. Accordingly, the example embodiments of the invention, as set forth herein are intended to be illustrative only, and not in a limiting sense. Various changes can be made without departing from the spirit and scope of the invention.