Title: Particle detection system and method
Abstract: An apparatus and method for detecting particles. A flow tube is surrounded by eight off-axis ellipsoidal mirrors all having a common first focus coincident with a portion of the flow tube and each having a distinct second focus. In one embodiment, sources of radiation are arranged coincident with exit ports in the mirrors that are also coincident with the respective distinct second foci. These radiation sources are momentarily energized in sequence (or simultaneously), causing light to illuminate a corresponding ellipsoidal mirror. This light strikes the common first focus within a portion of the flow tube. Any particles within the first focus will then scatter the light, and depending upon the source wavelength and the particle, may also provide some amount of fluorescence. This energy is captured by detectors and analyzed to determine the type, size and quantity of particles at the first focus.
Patent Number: 7,009,189 Issued on 03/07/2006 to Saccomanno
| Inventors:
|
Saccomanno; Robert J. (Montville, NJ)
|
| Assignee:
|
Honeywell International, Inc. (DE)
|
| Appl. No.:
|
109682 |
| Filed:
|
April 20, 2005 |
| Current U.S. Class: |
250/461.1 |
| Current Intern'l Class: |
G01N 21/64 (20060101) |
| Field of Search: |
250/4611
|
References Cited [Referenced By]
U.S. Patent Documents
| 4573796 | Mar., 1986 | Martin et al.
| |
| 4651010 | Mar., 1987 | Javan.
| |
| 4702598 | Oct., 1987 | Bohmer.
| |
| 4893928 | Jan., 1990 | Knollenberg.
| |
| 5475487 | Dec., 1995 | Mariella et al.
| |
| 5561515 | Oct., 1996 | Hariston et al.
| |
| 5684587 | Nov., 1997 | Naqwi.
| |
| 5701012 | Dec., 1997 | Ho.
| |
| 5876960 | Mar., 1999 | Rosen.
| |
| 5895922 | Apr., 1999 | Ho.
| |
| 5999250 | Dec., 1999 | Hariston et al.
| |
| 6016195 | Jan., 2000 | Peters.
| |
| 6118532 | Sep., 2000 | Peters.
| |
| 6154276 | Nov., 2000 | Mariella, Jr.
| |
| 6165740 | Dec., 2000 | Fukuda et al.
| |
| 6428198 | Aug., 2002 | Saccomanno et al.
| |
| 6618140 | Sep., 2003 | Frost et al.
| |
| 6870165 | Mar., 2005 | Amirkhanian et al.
| |
| 2002/0118362 | Aug., 2002 | Saccomanno.
| |
Other References
International Search Report; PCT/US2004/004200; Jul. 9, 2004, not a publication.
Hamamatsu Photonics "Si APD S5343, S5344, S5345", Mar. 2001.
Vishay Semiconductor, "Silicon PN Photodiode", Document No. 81619, Rev. 2, May
20, 1999.
Hamamatsu Photonics, "Characteristics and use of Si APD (Avalanche Photodiode)",
Jul. 2001.
Hamamatsu Photonics, "Si photodiode array S4111/S4114 Series," Mar. 2001.
Kartin Kneipp, "Basic of single molecule experiments under ambient conditions,"
M.I.T. Course 6.975, Spring, 2001.
Hamamatsu Photonics, "Multianode PMT With Band Press Filters R5900F-L16 Series",
Apr. 2000.
Roithner Lasertechnik, "RLT370-10 Technical Data", Undated.
CREE, G-SiC® Technology MegaBright LEDs CXXX-MB290-EXXX Undated.
Hamamatsu Photonics, "Xenon Flash Lamps", Apr., 1999.
|
Primary Examiner: Hannaher; Constantine
Attorney, Agent or Firm: Pillsbury Winthrop Shaw Pittman LLP
Parent Case Text
This application is a continuation of application Ser. No. 10/367,331, filed
Feb. 14, 2003.
Claims
What is claimed is:
1. An apparatus for detecting particles, comprising:
a passage through which particles to be detected travel;
a detector assembly through which the passage passes; and
an analyzer in communication with the detector assembly,
the detector assembly comprising a waveguide that receives light emitted or scattered
by the particles and at least two bandpass filters disposed inline with the waveguide;
at least two photodetectors, respectively arranged to detect light passing though
each of the bandpass filters;
an ultraviolet (UV) light source for illuminating the particles; and
a UV light transmitting mirror that allows UV light to reach the passage.
2. The apparatus of claim 1, wherein the UV light transmitting mirror reflects
visible light into the waveguide and towards the bandpass filters.
3. The apparatus of claim 1, wherein the waveguide is comprised of non-fluorescing
UV light absorbing glass.
4. The apparatus of claim 1, wherein one of the photodetectors is a fluorescence detector.
5. The apparatus of claim 1, wherein one of the photodetectors is a background
floor detector.
6. The apparatus of claim 1, wherein at least one of the photodetectors is a
non-pixellated detector.
7. The apparatus of claim 1, wherein at least one of the photodetectors is a
pixellated detector.
8. The apparatus of claim 1, wherein the detector comprises a plurality of ports
and the waveguide is disposed to receive light from one of the plurality of ports.
9. The apparatus of claim 1, further comprising a laser excitation source aimed
at the passage.
10. The apparatus of claim 1, further comprising a display for providing information
to a user of the apparatus regarding a nature of the particles being detected.
11. The apparatus of claim 1, further comprising a plurality of light sources
surrounding the passage.
12. A method of detecting particles, comprising the steps of:
passing said particles past a plurality of sources of illumination that are arranged
to illuminate said particles from different vantage points;
energizing the plurality of sources in a predetermined sequence and in separate
groups thereof;
detecting at least one of scattering and fluorescence energy generated by the
particles in response to each of said illumination sources; and
processing the scattering and fluorescence energy and determining at least one
of a type, a size and a quantity of the particles to be detected.
13. The method of claim 12, wherein at least one of the plurality of sources
of illumination comprises an ultraviolet (UV) light source.
14. The method of claim 12, wherein at least one of the plurality of sources
of illumination comprises a laser light source.
15. The method of claim 12, further comprising sequentially energizing respective
ones of the plurality of sources of illumination.
16. The method of claim 12, further comprising receiving fluorescence energy
into a waveguide.
17. The method of claim 16, further comprising filtering the fluorescence energy
into at least two bands.
18. The method of claim 17, further comprising separately detecting energy in
each of the at least two bands.
19. A method of analyzing particles, comprising the steps of:
causing said particles to be analyzed to pass through a passageway;
irradiating the passageway with ultraviolet (UV) light from a plurality of UV
light sources surrounding the passageway, wherein the plurality of UV light sources
are energized in separate groups;
receiving fluorescence energy generated by the particles within a waveguide;
bandpass filtering the fluorescence energy in the waveguide to obtain filtered
fluorescence energy; and
detecting the filtered fluorescence energy using a photodetector that is responsive
to a band corresponding to that of the filtered fluorescence energy.
20. The method of claim 19, further comprising sequentially energizing respective
ones of the plurality of UV light sources.
21. The method of claim 19, further comprising determining at least one of a
type, a size and a quantity of the particles to be analyzed.
22. A method of detecting particles, comprising the steps of:
passing said particles past a plurality of sources of illumination that are arranged
to illuminate said particles from different vantage points;
energizing the plurality of sources in a predetermined sequence;
detecting at least one of scattering and fluorescence energy generated by the
particles in response to each of said illumination sources; and
processing the scattering and fluorescence energy and determining at least one
of a type, a size and a quantity of the particles to be detected,
wherein said processing detects particles in shadow.
Description
BACKGROUND
1. Field of the Invention
The present invention relates to systems and methods for detecting and classifying
particles through optical means.
2. Background of the Invention
It has been a longstanding desire to provide systems and methods for accurately
detecting particle size, quantities, and whether the particles are biological or
not. The detection and categorization of biological particles, in particular, is
generally referred to as cytometry. Accurate and portable cytometry equipment is
presently of critical importance to detect biological pathogens, such as anthrax,
or other pathogens that may impact public health.
Known cytometry methodologies make use of fluorescence, often initiated by
laser light, to identify particles. In this particular methodology, a laser wavelength
is selected to be near or at the peak of an absorption resonance in the particle,
trace gas, compound or chemical element to be detected. This absorption resonance
is selected to be one that causes strong fluorescence. In one such known cytometry
system, described in U.S. Pat. No. 4,651,010 to Javan, laser light illuminates
air drawn through a duct, which may bear the particles to be detected, such light
having a wavelength near or at the peak of an absorption resonance in the trace
gases or chemical elements to be detected. A photodetector responds to the resulting
radiation of fluorescent light caused by the laser induced biochemical fluorescence.
As mentioned in the patent to Javan, it is also known to pulse the illuminating
laser beam and gate the receiver coupled to the photodetector to cause it to respond
in a delayed manner during a short period following each laser illumination pulse.
The delay is fashioned to take advantage of the fluorescence decay time of the
agent to be detected, so as to discriminate against false ambient illumination.
In addition to fluorescence techniques, particle geometry can be characterized
by illuminating the particles with an excitation source and recording the scattering
profiles. Such a system is described in U.S. Pat. No. 5,561,515 to Hairston et al.
Despite the availability of advanced apparatuses in the field of particle
detection & classification, such as those described in the patents to Javan and
Hairston et al., there is nevertheless a need for improved systems and methods.
SUMMARY OF THE INVENTION
In accordance with the present invention, a flow tube carrying a fluid is passed
through a detector assembly. The detector assembly is configured such that the
flow tube is surrounded by eight off-axis ellipsoidal mirrors, all having a common
first focus coincident with a portion of the flow tube, and each having a distinct
second focus. At one or more of the second foci there is coupled therethrough one
or more sources of radiation, and in addition one or more high-gain optical sensors.
In one embodiment all sources of energy are simultaneously energized, in an other
embodiment selected sources are energized and in yet another embodiment each source
(or groups thereof) is momentarily energized in sequence, causing light to illuminate
(underfill) its corresponding ellipsoidal mirror. The light reflected from each
mirror will strike the common first focus within a portion of the flow tube. Any
particles suspended in the fluid and within the first focus will then scatter the
light, and depending upon the source wavelength and the particle, may also provide
some amount of fluorescence (either inherent to the particle or through fluorescent
dye staining as is known in the art). This energy is captured by sensors coupled
to each of the second foci for each of the eight mirrors, thereby defining, to
at least a rough order, the scattering profile relative to the direction of the
incident light from one of the ellipsoidal mirrors. The recorded energy distributions
are then processed from all the mirrors in order to determine the type, size and
quantity of particles at the first focus. The apparatus and method in accordance
with the present invention also helps to determine if one particle is shadowing another.
The foregoing and other features of the present invention, along with the attendant
advantages thereof, will be apparent to those skilled in the art upon reading the
following detailed description in conjunction with the drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is schematic representation of an exemplary system in accordance with
the present invention.
FIGS. 2A, 2B, 2C and 2D are, respectively, assembly, isometric
and side elevation views of the exemplary detector assembly in accordance with
the present invention.
FIG. 3 illustrates an arrangement including a UV LED for exciting and detecting
a sample in accordance with the present invention.
FIG. 4 illustrates a detector assembly having a laser excitation source, in
accordance with the present invention.
FIG. 5 depicts an elevation view of an embodiment of the present invention.
FIG. 6 illustrates a cross sectional view of the detector assembly, including
ray traces, in accordance with the present invention.
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 shows an exemplary component arrangement in accordance with the present
invention including a nozzle
12 into which is provided a fluid with known
properties by way of pipe
13. Particles to be detected are delivered to
nozzle
12 through input tube
15. The fluid and the particles to be
detected flow together, preferably such that the particles to be detected are distributed
evenly throughout the fluid. Nozzle
12 is preferably arranged to generate
droplets of the resulting fluid/particle mixture or to generate a stream of fluid
with the particles to be detected suspended throughout. Nozzle
12 feeds
flow tube
16, which is arranged to pass through detector assembly
20
(described in detail below). Flow tube
16 (or at least a portion thereof
that passes through detector assembly
20) is preferably comprised of a transparent
material (e.g., glass or plastic) with optical characteristics that do not inhibit
or detrimentally effect light detection and reflection in accordance with principles
of the present invention that are described later herein.
Those skilled in the art will appreciate that the "fluid" provided through
pipe
13 in the context of the present invention includes both liquids and/or
gases. Also, to the extent that the addition of a fluid-through pipe
13
is unnecessary (e.g., when the particles to be detected are already suspended in
a gas, or it is a gas itself that is to be detected), then nozzle
12 and
pipe
13 may be eliminated altogether.
After passing through detector assembly
20, material in flow tube
16
is either passed as waste
17 through flow tube portion
16a,
or is cycled through pump/fan unit
18 (the selection of a pump or fan depends,
of course, on the nature of the material inside flow tube
16) through flow
tube portion
16b, and back to an input end of flow tube
16.
The general direction of fluid flow through the exemplary apparatus of FIG. 1 is
shown by arrow A.
Also shown in FIG. 1 is an analyzer
30, which will be described later
herein, and an optional display device
32, including one that might be connected
to a general purpose computer (not shown) that is programmed to function in accordance
with the principles of the present invention. Display
32 may also be, for
example, a more simple LED or liquid crystal read out, or any other form of device
that provides visual output to a user to indicate to the user the nature of the
particles being detected.
Generally speaking, the particles to be detected are passed via flow tube
16 through detector assembly
20 wherein the particles to be detected
are analyzed using one or more of several techniques that employ radiant energy,
typically in the form of ultra violet radiation, laser light and/or non-collimated
or non-coherent light.
FIGS. 2A,
2B,
2C and
2D illustrate a basic structure for
an exemplary detector assembly
20 in accordance with the present invention.
A similar structure, albeit used for an entirely different purpose, is described
in detail in U.S. Pat. No. 6,428,198 B1, which is incorporated herein in its entirety.
At a high level, detector assembly
20 is designed to receive a source (or
sources) of radiant energy that is directed towards flow tube
16, which
preferably passes substantially through a central longitudinal axis of detector
assembly
20. Resulting reflected light and fluorescence effects are thereafter
monitored via a plurality of detectors that are positioned at exit ports and that
are connected, via optical fibers or lightguides
61, to analyzer
30
as shown in FIG. 1. In one preferable implementation, detector assembly
20
is approximately 3" by 4" by 3.6" high and comprises a plurality of ellipsoidal
mirrors
10.
Ellipsoidal mirrors
10 are supported by a plurality of L-shaped
support brackets
115. Each wing of the "L" is approximately 0.9" wide and
2.25" high. The isometric view of FIG. 2D shows three L-shaped support brackets
115, with the fourth one hidden behind detector assembly
20 in that
view. Each bracket
115 preferably has a pair of clearance through-holes
(one on each side of the "L")
117, to which lightguides
61 can be
connected, and a pair of tapped holes
119 for securing each lightguide
61
to its respective adjuster
120 by means of thumb screw clamp
18.
Through-hole
117 is approximately 0.36" in diameter and tapped hole
119
is approximately 0.19" in diameter. Ellipsoidal mirrors
10 are preferably
supported by top and bottom hub plates
116,
114 each having approximate
dimensions of 3" by 3.9" by 0.25" thick and having a diameter of 4.93". The height
from the top of top hub plate
116 to the bottom of bottom hub plate
114,
when supporting mirrors
10, is approximately 2.75".
To ensure that ellipsoidal mirrors
10 and mirror edge slots
112,
which form exit port holes for detector assembly
20, are properly aligned,
it is desirable (but not essential) to build a suitable set of accurate datum surfaces
into the design of the assembly. Efficient light transmission and extraction can
depend on such proper alignment. Details of possible datum surfaces are described
in detail in U.S. Pat. No. 6,428,198 B1 and may be employed to the extent desired.
Referring still to FIGS. 2A-D, the top and bottom of the four ellipsoidal
mirrors
10 preferably have cylindrical surfaces that engage cylindrical
hubs of hub plates
116 and
114, respectively. In a preferred implementation,
ellipsoidal mirrors
10 are securely held against hub plates
114 and
116 by means of garter springs (not shown, but see U.S. Pat. No. 6,428,198
B1) that engage matching torroidal grooves
127 ground into the backs of
ellipsoidal mirrors
10.
Clocking alignment of each ellipsoidal mirror
10 about the hub axis
is provided by notches
140 in the top corner edges of each mirror section.
Notches
140 preferably have accurate reference datum surfaces that are normal
to the bottom face of hub plate
116. The four L-shaped support brackets
115 and their eight through-holes
117 are accurately positioned with
respect to the hub plate
116 so as to ensure proper alignment of through-holes
117 with mirror edge slots
112. Thus, as can be readily gleaned from
FIGS. 2A-D (and other figures), the mirrors
10 (and mirror section
110
described below) are arranged along a circumference of a circle, which is coaxial
with detector assembly
20, whose center is penetrated by flow tube
16
such that the mirrors (
10,
110) surround flow tube
16.
In regard to fabrication, the unit cost of molding accurate glass surfaces is
less than the cost of grinding them (and, of course, less than the cost of grinding
and polishing them). Therefore, the critical surfaces of ellipsoidal mirrors
10
are preferably molded.
Each ellipsoidal mirror
10 comprises two ellipsoidal mirror sections
110, which is a preferable configuration for ease of manufacture. In a preferred
implementation, each ellipsoidal mirror section
110 is positioned in such
a way so as to have a first focal point common to all eight mirror sections
110,
namely substantially centered on flow tube
16. Further, each ellipsoidal
mirror section
110 preferably has a second unique focal point, each of which
is substantially centered on or near a respective mirror edge slot
112 that
provides a cylindrical exit port
125 for a corresponding cylindrical rod
138 (to be described in detail below). Thus, each ellipsoidal mirror section
110 focuses reflected light from flow tube
16 on a corresponding
exit port
125 located at or near the second focal point of a given mirror
section
110. Note that each mirror edge slot
112 is aligned with
a respective L bracket port through hole
117. Each exit port
125
is on the order of, e.g., 4 mm in diameter. Note that the aforementioned dimensional
characteristics are based upon a flow tube
16 having an inside diameter
of about 1.5 mm.
There are preferably eight mirror edge slots
112 (one for each ellipsoidal
mirror section
110) and thus eight corresponding clearance through-holes
117. Note that each mirror edge slot
112 is formed by a half-hole
in a mirror edge. Each ellipsoidal mirror section
110 preferably has two
half-holes, one on each side, thus providing four holes
112 and eight positions
for cylindrical rods
138. In some implementations it may be desirable to
enlarge the diameters of each cylindrical rod
138 to capture more reflected
light. However, such enlargement typically requires a corresponding enlargement
of each mirror edge slot
112, which reduces the area of the ellipsoidal
mirror section
110 surfaces which, in turn, can actually reduce light collection
efficiency. The efficiency loss attributable to this reduction in mirror area is
significant when, e.g., the mirror edge slot
112 area is large enough to
become a significant fraction of the mirror section
110 area. Note that
detector assembly
20 can be scaled in size around the desired diameter of
flow tube
16. The scaling is based upon the optical magnification of the
design, which is on the order of 2.3, visually evident by the ratio of the length
of the light rays shown in FIG. 4. Therefore, a larger diameter flow tube will
generate a larger image at the second focus, thereby requiring a larger mirror
edge slot. In order to maintain a high degree of collection efficiency for light
scattered from the flow tube, the slot area should be small in relationship to
the area of the ellipsoidal mirror surface, and therein lies the desire to scale
the design in relation to the diameter of the flow tube. Such tradeoffs to maximize
S/N can be optimized, in part, through use of optical simulation software such
as ASAP manufactured by Breault Research Organization (Tucson, Ariz.).
While the illustrated detector assembly
20 design comprises four ellipsoidal
mirrors
10 formed from eight ellipsoidal mirror sections
110, other
alternative design configurations are contemplated by the present invention. For
example, detector assembly
20 could comprise a greater or a lesser number
of ellipsoidal mirrors disposed about flow tube
16 that would all have a
common first focal point. As in the illustrated configuration, the second focal
point of each mirror would preferably be unique and would be paired with a corresponding
unique exit port for light egress. The greater the number of mirrors in the detector
assembly
20, the smaller would be the solid angle intercepted by each mirror
as seen from flow tube
16 or from the corresponding exit port. This assumes,
of course, that the mirrors surrounding flow tube
16 are all identical.
Ellipsoidal mirrors
10 may be fabricated from materials such as
metal, glass or plastic. Preferably the bulk materials do not exhibit fluorescence.
Metal mirrors may be fabricated from, e.g., diamond-turned aluminum or electro-formed
nickel. Glass mirrors can employ such materials as Schott B270 or Duran (borosilicate).
Plastic mirrors can employ materials such as acrylic, polycarbonate or cycloolefin
copolymer (COC) such as Topas from Ticona. Mirrors preferably use first-surface
specular coatings such as aluminum, dielectric thin films, or other highly-reflective
coatings of a non-fluorescing nature. The coating preferably reflects both the
LED/laser light (e.g. UV) and the scattered light (UV and fluorescence). The coating
may also comprise notch filter characteristics as desired to increase S/N. An additional
benefit of the first-surface coating is to preclude light from entering the bulk
material, minimizing the potential for any residual fluorescence effects in the
bulk material, should it exist. Of course the surface of edge slots
125
and inside surfaces of hub plates
114 and
116 are exposed to light
scatter from flow tube
16, and must be considered for fluorescence properties
as well.
An optical fiber, such as a solid core fiber lightguide
61, is connected
to cooperate with a corresponding exit port
125. This can be accomplished
with or without a cylindrical rod
138 (described below). The position of
each fiber
61 may be adjusted by a respective adjuster
120 to ensure
proper alignment with the exit port
125. Note that each adjuster
120
is aligned with a corresponding fiber adjustment through hole
117.
Cylindrical rods
138 may be fabricated from solid glass (e.g.,
LaSFN31) having a high refractive index or from fused silica having a low refractive
index. An exemplary cylindrical rod
138 is 13 mm in length and 4 mm in diameter.
Such a rod
138 provides an optically transmissive element or light pipe,
which can be air-spaced or bonded to its corresponding fiber
61.
Note that each of mirror section
110 is an ellipsoid of revolution about
the ellipsoid major axis. Accordingly, detector assembly
20 has eight ellipsoidal
mirrors sections
110 having a first common focal point at the center of
the assembly's cavity and a second unique focal point, not shared with any other
ellipsoid, which is at one of the eight mirror edge slots
112 located near
the edge of each adjacent ellipsoidal mirror section
110. The second focus
is preferably located such that light rays reflecting from the ellipsoidal mirror
avoid intersecting flow tube
16, again with the intent of maximizing S/N.
Mirror edge slots
112 can preferably interface with a respective transmissive
element (e.g., element
51 shown in FIG. 3) or an optical light pipe such
as solid cylindrical rod
138 or a rod that morphs from round to a polygonal
shape over its length to efficiently couple to an equivalently shaped waveguide
(e.g., element
51). Note that the second focus from ellipsoidal mirrors
can be designed such that it lies beyond slots
125, thereby precluding the
need for rods
138, for example, coupling directly from an ellipsoidal mirror
to element
51. This would, however, require a slighty larger slot diameter
to preclude shadowing by the ellipsoidal mirror surrounding the edge slots.
There are two primary ways to irradiate the substance flowing in flow tube
16 to achieve the desired fluorescent response from the particles to be
detected. A first way is to have each (or at least a subset) of the exit ports
125 function as combined input and output ports. FIG. 3 shows an arrangement
in which an ultra violet (UV) LED (laser diode, or a UV-carrying fiber from a remote
source of UV)
49 is positioned on one side of a UV transmitting mirror
50
that is located adjacent at least one of the exit ports
125. The divergence
of UV from the LED is preferably chosen to slightly underfill the opposing ellipsoidal
mirror
10. The geometry of the ellipsoid mirrors
10 is design to
substantially concentrate all of the UV light across the inside diameter of flow
tube
16. Thus, as shown, radiation emitted by UV LED
49 is transmitted
through UV transmitting element
50 and a particle to be detected in flow
tube
16 is "illuminated". Upon this illumination, the particle to be detected
may absorb the UV radiation thereby causing fluorescent light to be generated.
This fluorescent light is then received at one or more of the exit ports
125,
as a result of the unique locations of the focal points of the several ellipsoidal
mirror sections
110 disposed around flow tube
16 in detector assembly
20. In a preferred embodiment, the generated (non-UV) fluorescent light
thus falls on UV transmitting element
50 and is reflected up through a UV
absorbing glass (non-fluorescing) trapezoidal waveguide
51. Preferably,
one or more bandpass filters
52a,
52b are placed in
line with waveguide
51 such that one or more photo detectors
53a,
53b (in this case avalanche photo detectors, APDs) can detect the
appropriate band of radiation. Thus, according to the first primary way to irradiate
the substance flowing in flow tube
16, exit ports
125 can be utilized
as combination input and output channels via which UV radiation and returning fluorescent
radiation is passed. It should be noted that this embodiment has been described
with non-imaging optics arranged at exit ports
125. However, imaging optics
could be utilized at one or more exit ports
125, as desired.
Advantages of the foregoing arrangement include the fact that the source
need not contain additional optics, since the ellipsoidal mirror will focus the
expanding UV beam onto flow tube
16 at a point (as shown in FIG. 3). Also,
this arrangement allows detection of particles in shadow, especially in the case
where a UV source is placed at more than one port. On the other hand, one disadvantage
of this configuration is it complicates the assembly at each exit port
125.
In accordance with a second primary way to irradiate the substance flowing in
flow tube
16, a laser
60 (shown in FIG. 4) is employed. While this
laser could be arranged to be co-located with the individual detecting apparatus
arranged at each exit port
125, it is also possible to locate the laser
(or other excitation source that has a small beam width and that is collimated)
at a separately provided aperture placed into one or more mirror sections
110.
This latter configuration is depicted in FIG. 4. Those skilled in the art will
appreciate that in the eight mirror version of the present invention described
herein different combinations of sources and detectors can be employed.
Advantages of this second implementation include avoiding consuming any
of the eight port locations for the excitation source and allowing each exit port
125 to have the same configuration of detectors (e.g., a trapezoidal waveguide
or an imaging optic).
Some possible disadvantage of such an arrangement include the fact that the
source possibly needs to have additional optics to collimate the beam, and may
require appropriate alignment structure to ensure it irradiates flow tube
16.
Also, the beam size needs to be small enough to avoid consuming a large fraction
of the ellipsoidal mirror surface(s), which would result in lower sensitivity for
those ports whose associated mirrors have holes in them. A small beam is also desirable
so that it only irradiates a small portion of flow tube
16 so as to minimize
the number of particles it illuminates. Also, a single laser may not be able to
illuminate some particles that are being shadowed by other particles.
FIG. 4 and FIG. 5 show respectively top and elevation views of an embodiment
of the present invention. These figures illustrate, with the several illustrated
ray traces, how light that is scattered by a particle in flow tube
16 is
collected at a selected imaging and/or non-imaging detector
75. An imaging
detector might be, for example, a pixellated array such as intensified CCDs, whereas
a non-imaging detector is intended to include devices such as photo diodes, like
those shown in FIG. 3, or simply transmissive device such as trapezoidal waveguide
51.
In the case of FIG. 4, an angle α (alpha) is presented and in the case
of
FIG. 5 an angle θ (theta) is presented. These angles represent the collection
half-angles in azimuth (alpha) and elevation (theta) for the sectional views of
these figures. If we assume that a particle fluoresces after being irradiated,
and further assuming the fluorescence is isotropic (equal energy radiating per
solid angle), a detector placed at the second focus of each ellipsoidal mirror
section
110 would receive light from all points of the mirror. Since the
mirror is asymmetric, the converging beam is also asymmetric, and can be represented
(roughly) by maximum collection half-angles of alpha and theta. In reality, as
shown in FIG. 2B, the boundary of each mirror section
110 is somewhat complex,
and so, for example, fluorescent light striking a mirror section
110 at
the uppermost and lowermost corners of the mirror might exceed alpha and beta.
Note that the trapezoidal optic
51 shown in FIG. 3 is used to collimate
theta from +/-25 degrees to be equivalent to alpha at +/-12.5 degrees, while leaving
alpha unchanged.
FIG. 6 shows yet another cross sectional top view of detector assembly
20
with several exemplary ray traces. As shown, flow tube
16 is positioned
at a common first focus of all eight ellipsoidal mirror sections
110. Each
ellipsoidal mirror section
110 also has a distinct second focus, mainly
on one of the exit ports
125. Consequently, reflected light beams miss flow
tube
16 thereby achieving high collection efficiency at exit ports
125.
Although it should be apparent to those skilled in the art, it is nevertheless
noted that each detector
75 mounted adjacent an exit port
125 detects
light that arrives from a predetermined one of the corresponding ellipsoidal mirror
sections
110.
Referring to FIG. 3, it should be understood by those skilled in the art
that one or more ports
125 can be equipped with these devices. Specifically,
a trapezoidal non-imaging optic
51 (with appropriate bandpass filters, if
so desired) is provided at the output of an exit port
125. Such an optic
device (which can be fabricated by Mindrum Precision, Rancho Cucamonga, Calif.)
can make the asymmetric angular output (+/-12.5 degrees, +/-25 degrees) to be symmetric
as previously explained. Alternatively, the asymmetry can be advantageous when
trying to couple laser light through one or more ports into detector assembly
20,
since most laser diodes have asymmetric angular spreads. It is also important to
note that if particle geometry is the primary desire (and not biodetection via
fluorescence), then UV LED 49 (e.g., available from Roithner Lasertechnik, Vienna,
Austria) can be replaced by a non-UV light source, of which there are numerous
sources know to those skilled in the art. Further, APD
53b can be
replaced with the source, and APD
53a can employ two or more detectors
in the same device to provide enhanced S/N (e.g. to subtract dark noise) as is
known in the art and described in
Photodiode Amplifiers, Op Amp Solutions, J.
Graeme, McGraw-Hill, ISBN 0-07-024247-X. APDs are available in custom arrays from
Pacific Sensors (Westlake Village, Calif.). Suitable bandpass filter technology,
having very high transmittance and extinction ratios can be obtained from Omega
Optical, Inc., (Brattleboro, Vt.). Also note that the spectral transmittance of
elements shown in FIG. 3 are selected to enhance the S/N based on the wavelengths
of interest in such a design. Such materials can be obtained for example, from
Schott Glass Technologies, Inc. (Duryea, Pa.).
In a preferred embodiment, an intensified CCD (e.g. from Hamamatsu, see http://usa.hamamatsu.com/sys-applications/fluorescence.html),
or like imaging device, receives light at-or-projected-from the second focus of
an ellipsoid, and which may be electronically captured such that it can be displayed
on a display
32 and/or saved and/or manipulated electronically with analyzer
30, or more generally, a computer (as is well-known in the prior art).
In view of the configuration of detector assembly
20, the present invention
offers several unique advantages in the art of particle detection. For example,
the configuration of the detector assembly
20 in accordance with the present
invention is much more compact and by substantially (or even completely) surrounding
the flow tube with collection mirrors, much higher in collection efficiency than
conventional particle detectors. Further, the method of irradiating the particles
in the round or in a sequential rotary fashions offers another dimension of functionality.
More specifically, as described above, flow tube
16 is surrounded by
eight off-axis ellipsoidal mirrors, all having a common first focus coincident
with a portion of flow tube
16, and each having a distinct second focus.
At some or all of the second foci, namely exit ports
125, there is placed
one or more sources of radiation, and in addition, one or more high-gain optical
sensors, e.g., detectors
75. In the separately-located laser source embodiment,
the source of radiation may be co-located with exit ports
125 or separately located.
Each source is momentarily and simultaneously energized, energized in groups
(e.g., for irradiation from orthognal directions), or momentarily energized in
sequence, causing light to illuminate (underfill) its corresponding ellipsoidal
mirror section
110. This light strikes the common first focus within a portion
of flow tube
16. Any particles within the first focus will then scatter
the light, and depending upon the source wavelength and the particle, may also
provide some amount of fluorescence. This energy is captured by detectors
75
at each of the second foci, exit ports
125, for each of the eight mirrors,
thereby defining, to at least a rough order, the scattering profile relative to
the direction of the incident light from one of the ellipsoidal mirrors. The recorded
energy distributions are then processed from all the mirrors in order to determine
the type, size and quantity of particles at the first focus. This method of analysis
"in the round" also helps to determine if one particle is shadowing another.
In the case of UV LEDs
49 that may not be fast enough or if the fluorescence
decay times are long (when compared to the velocity of the particles in flow tube
16) then the pulsing sequence can be arranged so that flow tube
16
is irradiated at orthogonal views closest-in-time, which would give the best opportunity
to discern whether one or more particles is being shadowed. It may also be desirable
to pulse all the UV LEDs at the same during at least each recurring measurement
cycle time to maximize signal-to-noise for at least one measurement.
The foregoing disclosure of the preferred embodiments of the present invention
has been presented for purposes of illustration and description. It is not intended
to be exhaustive or to limit the invention to the precise forms disclosed. Many
variations and modifications of the embodiments described herein will be apparent
to one of ordinary skill in the art in light of the above disclosure. The scope
of the invention is to be defined only by the claims appended hereto, and by their
equivalents. For example, the excitation source can be coupled into the flow tube
along the direction of particle flow, using the tube as a light pipe, with one
or more extraction features adjacent to the common first foci. Also, alternate
collection optic geometries can be employed that fully surround the flow tube,
such as ones that include curved or multi-faceted mirrors, ones that include various
arrangements of distribution arrays, as well as arrangements such as those described
in U.S. Pat. No. 6,428,198.
Further, in describing representative embodiments of the present invention,
the specification may have presented the method and/or process of the present invention
as a particular sequence of steps. However, to the extent that the method or process
does not rely on the particular order of steps set forth herein, the method or
process should not be limited to the particular sequence of steps described. As
one of ordinary skill in the art would appreciate, other sequences of steps may
be possible. Therefore, the particular order of the steps set forth in the specification
should not be construed as limitations on the claims. In addition, the claims directed
to the method and/or process of the present invention should not be limited to
the performance of their steps in the order written, and one skilled in the art
can readily appreciate that the sequences may be varied and still remain within
the spirit and scope of the present invention.
*
