Patent Application
20070097366
Optical systems and methods are useful in detecting particles. One type of optical system is a fluorescent biological particle detection system. Particulate detection has certain security-related uses, such as, for example, ascertaining the introduction of potentially hazardous air-borne biological particles to an environment. Determining the size of air-borne particles can assist in identifying whether the particles are respirable or not. Further, air-borne particles may be subjected to a light source capable of inducing an emission of fluorescence from the particles. For example, fluorescence detected in the 400 to 540 nanometer (nm) range signals the presence of nicotinamide adenine dinucleotide hydrogen, which is indicative of biological activity or viability. See, for example, U.S. Pat. Nos. 5,701,012 and 5,895,922.
Optical particle detection also is used in commercial smoke detectors, where optical scatter detection is used to signify the presence of an airborne particle. Particle counters also are used in the semiconductor industry to monitor air cleanliness for the particle-sensitive photolithography step. By measuring the absorption of certain optical wavelengths, one also can measure the presence of specific chemicals, such as NOx, CO2, or carbon monoxide. Fourier-transform infrared spectroscopy (FTIR) detection can be used to identify the presence of ice and water vapor. In this sense, the term “particle” refers to any individual mass or collection of masses that can interact with energy—most typically electromagnetic energy.
Disadvantages have been noted in known particle detector systems. One disadvantage is that known detector systems have high noise to signal ratios, due primarily to stray light and a low particle detection cross-section. Known particle detector systems may utilize lasers or laser diodes as light emitting sources. Known fluorescent particle detector systems utilize a collimating lens prior to striking the target particles. Also, known particle systems utilize conduits that are not fully optically transparent.
One embodiment of the invention described herein is directed to a particle detection system that includes at least one light emitting source for generating light, a non-collimating reflector for redirecting the generated light, an area through which a particle stream may be transmitted and into which the generated light is redirected, a collimating reflector, and at least one detector. At least a portion of energy formed by the redirected generated light striking one or more particles in the particle stream is directed to the collimating reflector and redirected to the detector(s).
Another embodiment of the invention is directed to an optical system for detecting particles that includes an air-sheath inlet through which a curtain of air is introduced, a conduit radially interior to the air-sheath inlet through which a particle stream is transmitted, and a pumping system consisting of a single pump positioned downstream of the air-sheath inlet and the conduit and configured to enable transmission of the particle stream and introduction of the curtain of air.
Another embodiment of the invention is an optical system for detecting particles that includes a plurality of light emitting sources for generating light and a light redirecting system consisting of a single reflector for redirecting the generated light. Each of the light emitting sources transmits generated light at the single reflector that redirects the generated light toward a stream of particles.
Another embodiment of the invention is a method for detecting particles. The method includes introducing a stream of particles into an enclosed container, transmitting light at a non-collimating reflector, redirecting the light to a focal point within the stream of particles, collecting incident light formed by the striking of the generated light upon at least one particle within the stream of particles, and transmitting the incident light to at least one detector.
These and other advantages and features will be more readily understood from the following detailed description of preferred embodiments of the invention that is provided in connection with the accompanying drawings.
a illustrates a particle detection system constructed in accordance with an exemplary embodiment of the invention.
b is a partial view of a portion of the particle detection system of
a is a schematic view illustrating generated light being transmitted into an excitation zone within the particle detection system of
b is a schematic view illustrating fluorescent light being transmitted from the excitation zone and reflected light being transmitted to a detector within the particle detection system of
Referring specifically to
The intake mechanism 113 includes a pair of concentric inlets. Specifically, the intake mechanism 113 includes a particle inlet 114 having an opening 116 extending through a cover plate 120 and into the interior 130 of the enclosure 102 and concentric air inlet 122 disposed radially exterior to the particle inlet 114. The cover plate 120 is attached to a surface of the enclosure 102 in such a way as to enclose the air inlet 122 underneath. An air filter 124 is attached to an open end 121 of the cover plate 120 to allow for filtered air to be transmitted through the air inlet 122.
The air inlet 122 is concentric with the opening 116 of the particle inlet 114. The particle inlet 114 may be attached to the cover plate 120, in which case the air inlet 122 may extend completely around the particle inlet 114. In other embodiments, and as illustrated in
Particles are introduced into the interior 130 of the enclosure within a particle stream 118 (
The air-sheath 132 serves as an optically transparent conduit serving to isolate the particle stream 118 from the remainder of the interior 130. It should be appreciated that other optically transparent conduits may be utilized to isolate the particle stream 118, such as, for example, poly ether ether ketone (PEEK), Teflon AF, fused silica, quartz, sapphire, or other transparent, low auto-fluorescent media capable of being formed into a conduit.
As the air-sheath 132 and the particle stream 118 extend closer to the pump 136, the air-sheath 132 begins to collapse radially inwardly toward the particle stream 118, and both streams 118, 132 exit the interior 130 through an outlet 134, which is in fluid connection with the pump 136. Through the use of the air-sheath 132, the particle stream 118 is isolated from the environment through an optically transparent mechanism, thereby enabling a more accurate optical measurement of particles within the particle stream 118.
An additional benefit of the air-sheath 132 is that it can assist in cleaning the interior walls of the enclosure 102. Further, by ramping up the pump 136 intermittingly, a turbulent regime can be initiated to clean the interior 130 of the optical detection system 100. Optionally, ultrasonic waves may be used to clean the interior walls of the enclosure 102.
With specific reference to
As illustrated, the first light emitting source 142 emits a light 146 which strikes the coated surface of the first reflector 106 and bounces into the excitation zone 150 at a focal spot 148. The second (optional) light emitting source 242 emits a light 246 which strikes the coated surface of the first reflector 106 and reflects into the excitation zone 150 at a focal spot 248. It should be appreciated that any suitable light emitting source 142, 242 may be utilized, such as, for example, light emitting diodes, including surface-emitting light emitting diodes, ultraviolet light emitting diodes, edge-emitting light emitting diodes, resonant cavity light emitting diodes, flip-chipped light emitting diodes, gas-discharge lamps, mercury lamps, filament lamps, black-body radiators, chemo-luminescent media, organic light emitting diodes, phosphor upconverted sources, plasma sources, solar radiation, sparking devices, vertical light emitting diodes, and wavelength-specific light emitting diodes, lasers, and laser diodes, and any other suitable light emitting device capable of emitting a sufficiently high intensity light of the desired wavelength. By “sufficiently high intensity light” is meant a light of sufficient intensity to induce an effective optical signal, such as particle fluorescence. The term “wavelength” should be understood to encompass a range of wavelengths and to refer to a spectral range of electromagnetic energy. Furthermore, the light emitting source 142, 242 may be pulsed to achieve the desired intensity of light without sacrificing reliability or lifetime. Another advantage of a very fast pulsed source, such as an LED, would be to synchronize the detector to the source for the purpose of improving the signal to noise ratio. A heat sink may be attached to the light-emitting source 142, 242 to enhance heat dissipation.
An optically transparent window 144 may be positioned between the first reflector 106 and the interior 130 of the enclosure 102. The optically transparent window 144 may include an optical filter for lessening the amount of parasitic light that is in the range of the detection spectrum from entering the interior 130 of the enclosure and producing parasitic signals in the form of scattered light.
A particle 152 traveling within the particle stream 118 enters the excitation zone 150. As the particle 152 encounters the focal spot 148, 248, the redirected generated light 146, 246 strikes the particle 152, creating an optical signal 154, 254. It should be appreciated that the optical signal may be fluorescence, absorption, transmission, reflectance, and/or scattering. For ease of description, the optical signals 154, 254 will be described herein as being fluorescent in nature. Most of the fluorescent light 154, 254 scatters throughout the interior 130 of the enclosure 102. This backscattered light eventually dissipates into a beam dump 138. The backscattered light may be used to detect dirtiness within the interior 130 of the enclosure 102. For example, a predetermined intensity of backscattered light may represent a certain threshold level of cleanliness within the enclosure 102, and any backscattered light lacking that predetermined intensity to a certain degree may represent a dirtier interior 130.
The remaining fluorescent light 154, 254 strikes the coated surface of the second reflector 110. The second reflector 110 may be a collimating reflector. Reflected light 156, 256 is directed toward the detector 104. The detector 104 may be a photoconductor, a photodiode, a photomultiplier tube, or an avalanche photodiode, or any photo detector capable of detecting single photons or collections of single photons. An optional optical filter 140 may be positioned between the second reflector 110 and the detector 104. The optical filter 140 may be filtered to specific wavelengths, thus serving to eliminate one or more portions of the light spectrum to decrease the noise to signal ratio.
The first reflector 106, the second reflector 110 and the detector 104 are all shown to be orthogonal to each other. Such an arrangement is advantageous in that neither reflector is in direct sight of the other, thereby lessening the reflection of direct light 146, 246 into the detector 104. It should be appreciated, however, that absolute orthogonality may not be required, and the first reflector 106 may be somewhat less than or more than ninety degrees offset from the second reflector 110, which in turn may be somewhat less than or more than one-hundred and eighty degrees offset from the detector 104.
The light emitting sources 142, 242 and the detectors 104 may be tuned to the absorption and emission profiles of various particles. For example, at least one light emitting source 142, 242 may emit light at a first wavelength at which a predetermined particle fluoresces while another of the light emitting sources 142, 242 may emit light at a second wavelength at which a second predetermined particle fluoresces. It should be appreciated that certain particles fluoresce at more than one wavelength, and thus the first and second predetermined particles may indeed be the same particles. Alternatively, each of the light emitting sources 142, 242 may emit light at a wavelength at which several types of particles fluoresce and each of the detectors 104 is tuned to detect the fluorescent light at wavelengths differing from the other of the detectors 104.
When several excitation wavelengths are employed and corresponding emission spectra are collected, this collection of spectra constitutes an excitation-emission map. Suitable methods for determination of fluorescence-excitation maps are provided in, for example, U.S. Pat. Nos. 6,166,804 and 6,541,264. Fluorescence excitation-emission maps are useful because they provide a more comprehensive spectral signature for a single species and provide a more detailed capability to reveal if more than one fluorescent species are present in a measured sample.
For example, a 280 nm UV source and 365 nm UV source can be turned on alternately such that an incoming particle stream is hit with one UV wavelength at a time. Bacteria will fluoresce primarily in the 340 nm range, due to protein fluorescence, upon exposure to 280 nm UV radiation. Bacteria will fluoresce primarily in the 430-550 nm range upon excitation with 365 nm UV light, due to NADH and flavin fluorescence. In contrast, many common fluorescent interferents, such as diesel soot and many vegetable oil aerosols, show significant fluorescence at only one of these excitation wavelengths. Thus, with one photo detector optically filtered at 340 nm and another photo detector optically filtered at 430-550 nm, a sufficient algorithm can be developed for discriminating airborne bacteria from common interferents. Table 1 provides a summary of fluorescence ranges for bio-agents and common interferents exposed to light at various wavelengths.
With specific reference to
At Step 205, a pair of reflectors, such as reflectors 106, 110, is located within an enclosure 102. The reflectors are placed relative to one another such that direct light from the first reflector 106 does not impinge directly upon the second reflector 110. For example, the reflectors 106, 110 may be placed orthogonal to one another. At Step 210, at least one detector, such as detector 104, is located relative to the two reflectors. Specifically, the detector 104 is placed so as to receive light directly from the second reflector 110 but be out of direct sight of the first reflector 106. For example, the detector 104 may be placed directly opposite the second reflector 110 and orthogonal to the first reflector 106.
At Step 215, a pump, such as pump 136, is engaged to induce a pressure differential within the enclosure 102. At Step 220, a particle stream is introduced into an environmentally isolated location. As described with reference to
While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. For example, while the enclosure 102 is illustrated as being cubic, it should be appreciated that the enclosure 102 may take any suitable configuration. Further, while optional optical filters have been described with reference to the detector 104 and the window 144, it should be appreciated that each light emitting source may itself incorporate an optical filter. Also, while the velocity of the illustrated air-sheath 132 is described as being greater than the velocity of the particle stream 118, it should be understood that the velocity of the air-sheath 132 can be any velocity relative to the particle stream 118 velocity. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.
