JP2008510143A - Micro discharge sensor system - Google Patents

Abstract

  A microplasma sensor system comprising a glow discharge gap formed by an electrode (53). The fluid to be sensed can be sent near the discharge (56) in the gap. The light from the discharge can be coupled to a spectroscopic analyzer or processor to determine the properties of the fluid. The coupling may comprise a waveguide (63) near the discharge gap. The cleanliness of the window and the electrical separation of the electrodes can be maintained by the discharge. The optical analyzer may comprise a filter (22) for one or more optical channels for the detector (23). The detector can output an electrical signal to be processed. The electrode (53) includes an optical waveguide (63) between the electrodes. Alternatively, the electrode (53) is formed concentrically around the optical waveguide (63) and forms an annular discharge gap with the other electrodes. The optical waveguide (63) may be one or more optical fibers.

Description

  This application claims priority as a continuation-in-part of U.S. Ser. No. 10 / 749,863, filed on Dec. 31, 2003 under the title “Microplasma Sensor System”. This US application is hereby incorporated by reference. The present invention relates to fluid detection. In particular, the present invention relates to a plasma structure, and more particularly to the application of this structure as a sensor for the identification and quantification of fluid components. The term “fluid” is used as a generic term that includes gases and liquids as species. For example, air, gas, water and oil are fluids.

  The structure and method features relating to fluid analyzers are described in US Pat. No. 6,393,894 issued to Ulrich Bonne et al. On May 28, 2002, entitled “Gas Sensor with Phase Heater to Increase Sensitivity”. This US patent is incorporated herein by reference. Related art fluid component analyzers are selective and sensitive, but lack the ability to identify one or more components of a sample mixture with unknown components, and are generally bulky and expensive. The state of the art coupled analyzers GC-GC and GC-MS (Gas Chromatograph-Mass Spectrometer) attempt to combine selectivity, sensitivity and sophistication, but are still bulky, expensive and speedy. Slow and unsuitable for battery powered applications. In a GC-AED (gas chromatograph-atomic emission detector), the AED uses 100 watts or more alone, uses water cooling, uses a microwave discharge of 10 MHz or more, and is expensive.

  Micro gas chromatography (μGC) detectors are fast responsive (<1 ms) to specific components, sensitive, non-selective, simple in construction, inexpensive, compact and also low It needs to be electric power (~ mW). The μGC detectors available or conceived today are extremely insensitive (≧ 10-100 ppm of analyte) as thermal conductivity sensors and are too selected for specific components such as fluorescence and electron capture detectors In the case of many GC detectors, it is relatively expensive so that in 2003 the usual price is about $ 600, $ 3000 and more, and through spectral analysis The micro-discharge device (MDD) monitored in this manner is susceptible to drift due to contamination of the optical element, or the power is relatively high like an AED (atomic emission detector) that consumes 100 W or more.

Related art NOx (and even NH ₃ , SOx, COx, O ₂ , VOC, etc.) sensors monitor and / or regulate the release of this material from the combustion process (external and internal), but uncontrolled stationary or automotive combustion Not suitable for use in system sensors. These sensors are very expensive (chemiluminescence (CL) and multilayer ZrO ₂ sensors) and very bulky (chemiluminescence (CL) and IR absorption when the detection limit is close to 5 ppm) It is very fragile (CL and IR long pass cells) or not stable enough (SnO ₂ / WO ₂ and wet electrochemical sensors) and is too expensive to apply especially to automobiles. Another known problem with optical sensors is the high maintenance costs required to keep the optics clean and the short life of electrical contacts to any motorized center that is exposed to harsh combustion exhaust conditions.

Related art optical gas sensors (NO, CO, NH ₃ , SO ₂ , CH ₄ , ..., CWA) based on spectroscopic analysis of glow discharge radiation are not rugged, low cost and compact multi-channel analyzers Therefore, it is not suitable for a package type system that is compact, inexpensive, and has a wide wavelength range. These sensors are too expensive and bulky (eg FTIR or conventional dispersive spectrometers or new compact palm top size spectrometers), too fragile (spectrometers) and not sufficiently conductive (Narrow bandpass filters require a fairly good collimation of light to avoid widening the band, i.e. require low aperture operation resulting in low photoconductivity) or are not flexible enough (individual narrow (The number of channels in the band pass filter is small.) Also, the problem with these optical sensors is that the maintenance cost for keeping the optical system clean is high.

  The present invention resides in a sensor system having a discharge gap formed by a plurality of electrodes. The fluid to be sensed enters near the discharge in the gap. The optical coupling includes a waveguide proximate the discharge gap. The optical coupling and the cleanness of the one or more electrodes are maintained by the discharge. A processor is coupled to the waveguide. Electrodes and waveguides take various forms and configurations.

  The present NO (and other chemical) sensor system based on the present optical spectrum / molecular radiation is low power, low mass and compact (the radiant glow discharge plasma of each element is 10-100 μ in diameter) . The plasma of this system operates at about 1100 ° C. The system is also low cost, rugged (no need for precise optical alignment), and maintains various types of stable operating environments. With proper air filtration, the sensor system can operate without high-temperature plasma self-cleaning, signal processing and advantageous low-cost, compact and rugged packaging, as well as no rare gas purge operations as in the case of exhaust gas component measurements. Done.

  MDD is used to clean the optical transmission surface and to maintain electrode separation when applied to MDD detectors. That is, the same plasma discharge is used to keep the observation window clean by plasma etching any combustion product deposits such as condensable tar and carbon soot. The same or similar glow discharge maintains cleanliness and (more importantly) the required electrical isolation of the soot sensor electrodes of the soot sensor. Spectral radiation and soot sensors can be placed together in one package. In other words, it is compatible and can be easily integrated with the soot sensor system.

  The silica tip can be omitted and a discharge acts between the two free standing electrodes. The same plasma discharge maintains the necessary electrical insulation of the ungrounded micro-discharge electrode (an enlarged view of the electrode tip in the example of FIG. 2), or does not cause a pause in the measurement and self-check cycle Such insulation can be achieved with a simple power cleaning cycle. With little power, the electrostatic field across the impactor “baffle” or between the “fins” of the cyclone element improves the capture and retention of relatively small particles. Housings with louvers (and cyclonic and impactor particle separators) are less expensive than sensor system frit. The removal of the bound particles through the cyclone and impactor plate occurs with low Δp versus sample gas flow (FIG. 14).

Refined positioning between the end of the optical fiber and the photodiode is used to detect small angle optical fiber light components as required by the width of the selected bandpass filter. The system is more compact, sophisticated and less expensive than chemiluminescence based sensor systems. The system is more stable than conventional optical sensor systems based on metal oxides or catalysts and consumes less energy than a sensor system based on ZrO2. The system is more tolerant of temperature changes than other sensor systems and is easier to manufacture than sensor systems based on ZrO ₂ , metal oxides or catalysts.

  This system is less expensive than a conventional MDD-based NOx sensor system. The system can observe NO spectral emissions in the IR. The system can also design one MDD as a source and another MDD as a detector in the same plane. Water condensation is removed by stripping or preferably rendered harmless by sensor heating. Another sensor is packaged in the same housing of the system to reduce cost and overall bulk and incorporate plasma cleaning synergy. MDD emission spectroscopy relies on a scanning narrow bandpass MEMS Fabry-Perot (FP) filter, which is compact, versatile (with multiple channels), and very effective in light intensity (When a large number (100 to 1000) of MDDs operate in parallel, the mirror / etalon reflectivity is high), but maintenance is not time-consuming. This is because the FP filter operates in a closed environment and other optical surfaces exposed to the sample gas are self-cleaned by the MDD.

A microdischarge device (MDD) 11 is shown in the systems 10, 20 and 30 of FIGS. 1, 4 and 6, respectively. The device 11 has one electrode 31 and another electrode 32, and the ends of these electrodes face each other to form a gap that generates the micro glow discharge 18. This gap is surrounded by a glass tube or hollow pipe 33. The device 11 comprises a soot electrode and is kept without soot formation. The glow of device 11 has a UV / visible spectrum as shown in the graph of FIG. This graph shows the relationship between the relative intensity versus wavelength (nm) in the spectral emission of a glow discharge using 22.9 ppm NO for N2 in an environment of 700 Toor. To date, noble gases (N ₂ , Ar, He) have been used to consider the characteristics of such microdischarges.

  The glow discharge device 11 is part of the system 10 as shown in FIG. This system consists of the building blocks shown schematically in FIGS. 1, 11, 12 and 13 (similar to FIG. 3). The system 10 includes a sample gas filter 13 that is connected to the opening 15 of the exhaust pipe 14. The sample gas filter 13 can remove PM (particulate matter) and condense the exhaust sample 16 from the exhaust 17. The sample 16 flows into the vicinity of the glow discharge 18 located in the glass tube 33 and affects the discharge light emission according to the composition of the sample 16. Light 27 from the discharge 18 propagates through the fiber 21 to the filter 22 and is converted to an electrical signal by the detector 23. The electrical signal thus obtained is sent to the amplifier and microprocessor 24 where it is processed and becomes an output signal representing the composition of the sample 16.

  The glow discharge 18 is about 10 to 500 microns in diameter. The discharge is initiated and maintained by an AC / DC power supply of about 100-400 volts in series with a resistor 19 of about 1-15 MΩ, resulting in the spectral band emission shown in FIG. The power source 28 is connected to the metal electrode 31 and the metal electrode 32 through the resistor 19. The glow discharge 18 is started and maintained between the electrodes 31 and 32 by application of a voltage from the power source 28. The electrodes 31 and 32 are covered with an insulating material 46 such as MgO.

The optical fiber 21 is connected to the glow discharge device 11 at an optical interface or window 25 and is used for a NO filter 22, 336.9 or 357.5 ± 2 nm reference N2 with 247.2 or 258.8 ± 1.4 nm. Filter, optionally used with other bandpass filters for O ₂ , CH, C ₂ , CO, SO ₂ and 251.2 ± 2.5 and 362.3 ± 4 nm off-NO and N2 filters, respectively To do. The optical filter 22 is provided at the flat end of the optical fiber 21 having a narrow bandpass half-width of about 3 nm (matching the NO emission half-bandwidth (HBW) of ˜2.8 nm) to 20 nm. As shown in FIGS. 1, 11, and 12, a photo detector 23 (Si diode sensitive to UV, Si phototransistor) is provided near the filter 22. The output of the photo detector 23 is sent to an amplifier and signal processor 24 which outputs related signals for NO, VOC, CO, SOx, etc. in the sample 16 with its ppm output signal at its output 35.

  In operation, the apparatus 11 is configured to cause the microdischarge 18 to grow close to the observation fiber 21 side and strike the observation fiber 21 side, as shown in FIG. The spattering action of the mild discharge 18 maintains the optical transparency of the window 25 of FIG. 1 at a high level, even though the combustion exhaust gas tends to contact the optical surface and darken the optical surface in a short time. . However, the cleaning action of the window 25 is due to the plasma of the discharge 18. The electrodes are also kept clean.

1 and other systems described herein include a fiber optic cable 21 having a filter 23 at one end and a glow discharge 18 at the other end, and one or more. PM filter 13 is included. These fibers and filter materials are inexpensive, heat resistant (cool sample gas temperature, no need for intermediate PM filter 13) and high to minimize the angular sensitivity of the bandpass filter 22. In some filter examples, including those of refractive index, the relationship between the peak transmission wavelength λ0 and the deflection angle ψ of incident light from those parallel to the fiber axis is expressed as follows.
λ _ψ = λ ₀ (ne ² -sin ² ψ) 0.5 / ne
This effect of the refractive index n at λ _ψ is represented in the table of FIG. 8 by data for λ ₀ = 250 nm, ψ = 10 ° and 20 °.

The highest refractive index of the listed materials, ie sapphire with n = 1.845 at 250 nm, still shifts by about 5 nm when ψ = 20 °, but from window 25 when ψ = 10 ° (φ ≦ 10 °). It is only about 1.5 nm for positioning the fibers 21 at a distance (see FIGS. 2 and 14), which is one approach. Another approach is based on using a wide bandpass filter with a full width at half maximum of 23 nm and covering all bands of NO with λ ₀ = 247.2 ± 12 nm. The down-side of this approach is This is a loss of almost 5 times the NO sensitivity and a large probability of cross sensitivity to other gases that emit spectrum in the same band. If this approach is chosen, the filter manufacturability, price, and shifts due to angular and temperature fluctuations become less important.

Regarding the effect of temperature, λ0 tends to shift to a relatively long wavelength with increasing temperature (and decreasing temperature) due to thermal expansion of the coating material as proposed here.
λ _T = λ ₀ + αΔT, α˜0.01−0.2 nm / ° C.
This is because if the temperature is simply raised by 100 ° C., λ ₀ is shifted by 10 nm, and α = 0.1 nm / ° C. if the above information is correct. Values of α ′ to 10 ⁻⁶ −10 ⁻⁵ / ° C. or α to 2 · 10 ⁻⁴ nm−2 · 10 ⁻³ nm / ° C. are expected.

It is useful to calculate the maximum diameter d possible for a single mode optical fiber that has a relatively limited tolerance angle and can keep the bandpass half width of the associated interference filter small. For single-mode fiber operation, the quantity V <2.405, where V = (πd / λ) {n (core) ² −n (clad) ² )} ^0.5 , and therefore d <2.405 · λ · {n (core) ² −n (clad) 2)} ^0.5 , and in the example based on sapphire (n = 1.6) optical fiber, the operation is near 300 nm, and Δn to 0.3 needs to be d <673 nm. For single-mode fibers, the numerical aperture (= the sine value of the maximum allowable angle, which is the half angle of a cone where light is totally internally reflected at the fiber core) NA is 0.15 for single-mode fibers, and In the case of multimode fiber, it is 0.3.
NA = sin (qmax) = (n1 ² −n2 ² ) ^0.5

  Manufacturing costs are low because they are inexpensive parts and assemblies as previously described herein. These components include one grounded wire and one insulated wire in a tube 33 (glass, quartz, sapphire) to support plasma in the spark plug enclosure 44, as shown in FIG. Optical fiber 21, provided with interference filter 22, two to four photodiodes 23, power supply 28 equipped with DC-DC converter (100-400V), amplifier 24 for photodiode 23, signal processing and logic function It includes a microprocessor 24, a PM filter 13 and a sample gas flow path. It also performs automated assembly and calibration to reduce costs. There is almost no scrap in manufacturing the microplasma sensor system 10.

  NOx sensing via MDD can be done in other ways by a noble gas purge in one microchannel leading to MDD, but without this purge, only the sample gas is directed to MDD. The sensing system of FIG. 1 is characterized by operating MDD without a noble purge gas, using MDD to clean windows and maintain electrode insulation in MDD detector applications, not observing spectral emissions in IR, Constructing a co-planar MDD as another source MDD, such as a detector, and placing spectral radiation and, for example, a sputum sensor together in one package. The optical surface 33 on the MDD side facing the optical fiber, that is, the window 25 of FIGS. 1, 2, 4 and 6 is self-cleaned. Noble gas purge cleaning is required.

  The sensor system 10 uses a plasma discharge device 11 to measure exhaust gas components without a noble gas purge, and observes the plasma by etching any combustion product deposits such as condensable tar and carbon-soot. Using plasma discharge 18 to keep the surface clean, using plasma discharge to maintain the necessary electrical insulation of the ungrounded micro-discharge electrode (see enlarged view of an example electrode tip in FIG. 2), Using plasma discharge to maintain electrical insulation in the need of ungrounded electrodes with additional periodic power cleaning cycles, with or without pause in measurement and self-check cycles, temperature induced wavelengths in bandpass filters After wrinkle detection and before spectral MDD detection to minimize shift Using the associated PM filter 13 to cool and clean the sample gas, the end of the optical fiber and the photodiode to detect only the small angle optical fiber light component required by the chosen bandpass filter width The same or similar glow to maintain the cleanness of the soot sensor electrode (not shown in FIGS. 1-3) and (more importantly) the necessary electrical insulation. Using the discharge 18.

  Additional structural features of the Art Pseudostate PM filter solve the water condensation challenges (sensor removal or detoxification by heating) and reduce cost, overall bulk and plasma cleaning synergy Includes a mechanism for packaging the soot sensor electrode in the same housing.

  Another configuration of the glow discharge device 11 is a system 20 shown in FIG. The scanning Fabry-Perot filter 26 shown in more detail in FIG. 5 is adapted to the desired bandwidth and wavelength range for the desired application. The PM filtered gas 16 enters the glow discharge device 11 and enters the vicinity of the glow discharge 18. The glow discharge 18 is surrounded by a glass capillary or tube 33. The discharge 18 is initiated and maintained by a voltage of about 100-400 volts from the power supply 28 connected to the electrodes 31, 32, and a discharge is generated from these electrodes. The light tube 34 or other optical transmission mechanism is optically connected to the glass tube 33 at the window 25 and transmits the discharge light 27 to a non-divergent Fabry-Perot narrow bandpass scanning filter 26. The filter 26 performs spectral analysis of the light 27.

  The filter 26 is a MEMS spectrometer based on a Fabry-Perot (FP) for MDD emission analysis. The light tube 34 is optically coupled to a Pyrex or quartz glass window 36 of the filter 26. The window 36 is a UV blocking filter. As shown in FIG. 5, light 27 propagates through a window 36 into an FP cavity with a high cavity 37 of about 5 mils (25 microns), which is particularly important to pass or filter. An etalon 38 that moves up and down is provided to adjust the cavity 37 to a suitable frequency. The movement of the etalon 38 is performed by the control signal line 45. This adjustment determines the wavelength of light 27 to be passed or blocked. The cavity 37 includes a sapphire base 38, and the window 36 includes a peripheral sealing seal 39 formed around the periphery of the cavity 37 to form a space within the cavity, and a window 36 and sapphire to seal the cavity from the periphery. And a seal between the base 38.

  The portion of light 27 that passes through cavity 37 is sensed by an array of detectors 41. The detector 41 is linear or in the form of another type of array, or is made of AlGaN / GaN or other suitable or operable material. The detector 41 converts the optical signal 27 into an electrical signal, and this electrical signal is input to the readout integrated circuit 42. The circuit 42 includes a processor that analyzes the signal and provides information about the sample gas 16. Package 43 is utilized to enclose at least a portion of filter 26 throughout. The output of circuit 42 provides spectroscopic analysis of light 27. This analysis implies the composition of the sample gas 16 passing through the glow discharge 18.

  During the operation of the filter 26, a single tine (= transmission peak of the Fabry-Perot comb filter) with a half-width of about 1 nm to 3 nm is scanned, and the others are in the scanning region. Imagine being configured to be on the outside. The table of FIG. 9 shows the parameters of wavelength modulation based on the FP for gas sensing. Some examples of FP filter design parameters required to perform this and other applications of MDD (CO and O2 sensing) are shown. The parameters shown in FIG. 9 include sensed gas, band center, tine spacing, line width, ν / Δν, FP spacing, dither, band limit and definition, among many other parameters.

Since the FP spacing layer 38 of the cavity 37 is dithered by a given amount, the Δλ linewidth bandpass is
Scan around the band center with a cm-1 or nm tine spacing or between the illustrated band limits in nm. The calculated Fabry-Perot bandwidth and spectral position (including AlGaN detector array response) in the last column of the table of FIG. 9 are shown in FIG. 10 for the minimum, center and maximum wavelength positions, respectively, with the corresponding etalon mirror spacing. . FIG. 10 shows the ratio of the relationship between transmission and wavelength with respect to wavelength scanning of the MEMS FP filter. The wavelength position is limited by the available wavelength sensitivity range of the AlGaN detector, which is approximately 290-360 nm in the example calculation of FIG.

  The system 20 of FIG. 4 is characterized by the following measurement performance (λ and ± Δλ / 2): 247.2 or 258.8 ± 1.4 nm for NO, 336.9 or 357.5 ± 2 nm for reference N2, and Off-NO and N2 are taken as typical emission bands where the scanning FP filter and detector 26 are required to achieve 251.2 ± 2.5 nm and 362.3 ± 4 nm, respectively. Consider the known effect of the f number on the fineness of the achievable FP filter 26, which here is further suppressed. However, the FP filter 26 is configured to be hardly sensitive to drift depending on the temperature of the wavelength bandpass, but is limited by the temperature range rating of the discharge device 11.

The sensor system 20 includes: non-dispersive (based on Fabry-Perot) spectroscopic analysis (other than dispersive spectroscopic analysis) or plasma microdischarge for gas sensing by spectral emission analysis of unknown gas mixture samples As an instrument (MDD), a Fabry-Perot (FP) wavelength scan performed via a MEMS-based FP filter configuration, a fast gas chromatography peak (GC) analyzer and independently, NO, O ₂ , SO ₂ ,. . . . New use of the above-mentioned assembly (spectral filter based on MDD and FP) in a single unit as a stand-alone gas sensor for use in a micro GC or μGC-μGC or μGC-μGC with a low false positive probability (Pfp) of GC -Based on the new use of the above assembly (MDD + FP + GC), MDD gas mixture analyzer, and the configuration of MDD where the discharge self-cleans window 25 and operates without a noble gas purge.

Due to the successful configuration of the systems 10, 20, a low false positive probability can be achieved when using the discharge device 11 and detector as part of a GC-CG-MDD microanalyzer, denoted as PHASED. The sensing systems 10 and 20 have the following advantages over the conventionally proposed exhaust gas composition sensing system. The system is more compact, robust and less expensive than a sensor system based on chemiluminescence. The system is more stable than conventional optical sensors based on metals, oxides or catalysts. This system consumes less energy than NO and O ₂ sensor systems based on ZrO ₂ and is more tolerant of temperature changes than other ZrO ₂ —NO / O ₂ sensor systems. The system is also easier to manufacture than sensor systems based on multilayer ZrO ₂ , metal oxides or catalysts. The system is also flexible and can be easily integrated with the soot sensor system.

  The system 30 of FIG. 6 includes the discharge gap device 11 as in the systems 10 and 20, but the light 27 is connected to the discharge 18 via the light tube 34 to reveal information about the sample gas 16. Transmitted to a dispersive spectrometer 47 that analyzes the radiation. The light 27 is transmitted to an optical grating 48 that reflects the various wavelengths of the light 27 to various pixels of the CCD light detection array 49, respectively. Electrical signals from array 49 are sent to processor 51 for analysis and interpretation.

  One sensor system is shown in FIGS. 11, 12, 13, 14 and 14A, and the other system is shown in FIGS. The MDD 60 of FIG. 11 generates optical emission 56, which is an enclosure that at least partially contains a plurality of electrodes and one or more optical waveguides. Since it is protected from particulate matter in the exhaust gas by a screen or stainless steel frit 55 that is considered a housing, it is characteristic of the gaseous environment around the electrode 53 supported by a ~ 2x2 mm silica chip. The exhaust gas 65 is turbulent and reaches temperatures up to 1100 ° C. (2012 ° F.). As shown in FIG. 13, the MDD 60 is accommodated in a spark plug type package, that is, a housing 57. The housing 57 is screwed into a fitting member 58 having an M14 thread 61, for example. Alternatively, the fitting member 58 is formed or welded to the exhaust pipe 59 or other fixed member that receives the fluid to be tested. The package or housing 57 may include hexagonal mating members such as nuts and bolts so that the housing and package can be screwed and unscrewed with a tool like a wrench.

  Light is transmitted from the discharge 56 through the fiber 63 to the optical filter 22. The fibers 63 can be silica fibers having an outer diameter of about 20 to 200 microns. Filter 22 may have a delta wavelength of about 2-5 nm. The filtered light is processed to be detected by a photodiode, a phototransistor, or generally a “photodetector” 23, each based on one filter pair detector. The electrical conductor connects the detector 23 to the terminal 115 of the connector 64. Terminal 115 connects to processor 24 (not shown in FIGS. 11 and 12, but as shown in FIG. 1).

  The failure mode may be due to contact problems between the conducting wire 62 through or around the silica chip 54 and the conducting wire 62 embedded in the spark plug package 57. Alternatively, a single spark plug-like housing package 57 may be provided, in which case a pair of self-supporting discharge electrodes 53 are provided, or the ends of the conducting wires 62 form electrodes, and the discharge 56 is the entrance surface of the optical fiber 63. 64 can be kept clean and without the MDD silica chip 54. The electrodes are also kept clean. This cleaning of the surface 64 and the electrode occurs without the presence of a noble gas. The conductive wire 62 extends from the connection body 64 to the electrode 53. The length of the conducting wire 62 and the waveguide 63 is about 10 to 40 cm.

  To avoid contact problems between the electrode 53 and the conductor 62, FIG. 12 shows another sensor package structure, the silica chip 54 is omitted, the conductor 62 passes through the spark plug housing 57, and the sensor exhaust gas. Extend in the side. The leads 62 are strong enough to retain their position and shape without the need for the silica chips 54 to support them. An alumina insulator 69 is provided around the conductor 62 and the waveguide 63 in the package, housing or structure 57. A separate discharge electrode 53 made of a deposited thin film metal material is provided at the end of the conductor 62, and the conductor is regarded as an alternative electrode 53. The shape and space between these electrodes is not different from the self-supporting spark plug electrodes, but is formed by mechanical cutting, shaping and bending to achieve typical electrode shapes and 10-30 micron spacing. The silica chip 54 is formed, the lead wire 62 is passed through the silica chip, the electrode (the end of the lead wire 62) is deposited by a contact metal, the chip is diced, and the positioning and fixing through the spark plug-like housing 57 are performed. The cost to do can be reduced. The end of the conductor is regarded as the electrode 53 or 62.

  Potential performance problems caused by an ideal and unclean optical interface between the silica chip 54 and the optical fiber 63 can be eliminated, and transmission loss through the interface between the silica chip 54 and the optical fiber 63 can be reduced.

  During operation, a successful system configuration creates a micro-discharge 56 near the viewing optical surface, such as that of silica fibers 63, chips and / or windows, and strikes this optical surface. Due to the mild discharge sputtering action, the combustion exhaust gas has a known tendency to darken the optical surface in contact with the combustion exhaust gas in a short time due to the deposition of tar and soot-containing materials, but the optical transmission surface Keep optical transmission at a high level. This function is a discharge plasma cleaning action. Excessive discharge action causes glow discharge action to etch material on the surface adjacent to the glow discharge, but insufficient discharge action (ie power) causes deposition.

Capillary electrode discharge (CED) methods generate atmospheric pressure plasma and are used for surface cleaning, such as removal of organic material on a glass substrate. Helium or hydrogen (He or H ₂ ) is used as the starting and discharge gas, and oxygen (O ₂ ) is added as the reactive gas. A low frequency AC power source with a sinusoidal voltage (20 kHz to 20 GHz) is used to generate plasma under atmospheric pressure. The electrode is composed of a 10 micron thick capillary dielectric, and the electrode has a diameter of about 300 microns. The He / O ₂ plasma generated at a distance of several mm between the capillary electrode and the substrate (ground) is uniform and very stable. Spectroscopic methods and the IV characteristics of the discharge are used to characterize the capillary electrode discharge. In addition to the He / O ₂ plasma, other gas effects similar to the effects of He-added gases such as CF ₄ , Ar, and N ₂ are used to remove organic materials such as photoresist. After exposure to He / O ₂ plasma, observe the cleaning rate of the organic material in the glass at 1000 Å / min or more. As measured by X-ray photoelectron spectroscopy, there are several effects of various gas mixtures in addition to the effect of He / O _{2 on} the cleaning rate of the organic and remaining residue surface chemical compositions.

  FIG. 14 shows a sensor system 80 having a housing or enclosure 66 that includes a particle suppression structure 67 that is a louver, sample gas input / output, and swirl and cyclone separator. Is provided. A housing or enclosure 66 at least partially houses the electrode and one or more optical waveguides. The particle suppression structure 67 includes an impactor plate 68 that assists in separating particles of the fluid 65. The flow of exhaust 65 through structure 67 is caused by head pressure and venturi action, and the enclosure 66 is inserted into the fluid or exhaust gas 65 flow or has a 0.3 mm opening at the top of the structure. Assisted with components. Also, the fluid or exhaust gas 65 is rather turbulent in the tube or carrier 59, and the structure 67 does not break the microdischarge 56 for accurate reading by the sensor system 80. Provides a way to sample the exhaust 65.

  The electrode 53 forms the basis of the microdischarge 56. The response of the discharge 56 to the sensed fluid 65 is optically transmitted by the optical fiber 63 to a photodetector that converts it into an electrical signal. The signal is digitized for computer processing and analysis of the fluid. The light transmitted from the discharge 56 can be IR, visible and / or UV. Conductor or electrode 62 and fiber 63 are housed in a housing 57 with ceramic insulator 69 and structurally supported. The electrode 62 is attached to a connector pin 71 having a dimension of 0.3 mm. The discharge 56 keeps the electrode and waveguide input surfaces clean without the need for purging with noble gases. Filters, detectors, power supplies and processors associated with system 80 are similar to those of systems 60 and 70.

  FIG. 14A shows a sensor 81 with the same type of structure and electrical components as the sensor system 80, but the housing of the sensor 81 is somewhat different. The structure 82 has inputs of fluid 65 from the sides, the fluid advances through the multiple impactor plates to the region of the microdischarge 56, and exits through the end or top of the housing or structure 82. . On the other hand, the structure 82 is configured to have both fluid input and output at the top thereof. The systems 60, 70, 80, 81 are used to sense other gases than the exhaust gas 65.

  A robust MDD sensor system is provided. 16, FIG. 17, FIG. 18A and FIG. 18B show a sensor configuration in which the one shown in FIG. 14 and FIG. 14A is expanded. A preferred range for the gap 83 of the surrounding MDD electrode 62 is 30-70 microns. FIG. 15 shows in detail the region of the electrode gap 83 shown in FIG. Due to the shape of the two electrodes 62 at the discharge location, the spacing between the two electrodes can be within a desired range, and then the spacing is maintained by the cladding of the thick optical fiber 63. However, the “hook” at the tip of the electrode 62 adds unacceptable cost during manufacture, and the cavity becomes clogged with deposits during use in the automotive exhaust environment.

  FIG. 16 shows an apparatus 113 that avoids clogging and spacing problems by using a tubular bottom electrode 84 and a (grounded) top electrode 85 with a tip 86, where the tip 86 of the top electrode 85 is thin (≦ λ / 2) Align with cladding 88. The diameter of the fiber with the cladding is about 70 microns. The risk of upsets in the 30-70 micron discharge gap is high, and this is probably the cost to solve. The gas discharge area is represented by two oval shaded areas 89.

  FIG. 17 shows a device 114 having a qualitative (not to scale) side of the tubular optical fiber 91, with a discharge (oval shape) on the top rim of the tubular “fiber” between the center electrode 93 and the outer electrode 94. Region 92 represents a ring-shaped or annular micro-discharge cross section). The tubular fiber 91 may be replaced with a number of optical fibers adjacent to each other in parallel to the electrode. The overall diameter of the device 114 is about 3 mm. The diameter of the center electrode 93 is about 0.5 mm. The outer diameter of the tubular fiber or optical fiber 91 is about 0.6 mm.

  18A and 18B show devices 111 and 112, respectively, which includes a single optical fiber 95 with a diameter of 40-70 microns with a thin cladding, and device 112 has a diameter of about 300-500 microns. It has four fibers 95 positioned and fixed between two large-diameter metal electrodes 96 and 97 (0.3 to 0.5 mm). Both electrodes 96 and 97 are fixed in the same ceramic block 69 as shown in FIG. The discharge light 56 is aligned with the optical fiber 95, and the assembly can be manufactured relatively easily. In addition to providing mechanical flexibility, the use of separate fibers 95 provides design flexibility in the manner of separation into various wavelength channels (via the bandpass filter 22 or the dispersive element of FIG. 1). .

  19A and 19B provide discharge light 103, ease of manufacture (gap adjustment and stability through a common ceramic fixture block despite temperature variations) and design flexibility. In that regard, two forms 101, 102 of the sensor system with respect to FIGS. 17, 18A and 18B are shown. In the form 101, a fiber 106 that transmits light from the discharge 103 of the assembly 101 is provided between the electrodes 104 and 105. The tubular optical fiber 107 in FIG. 19B is replaced with a large number (10-20) of individual fibers 108, which are positioned along a circle or path around the central electrode 109. A circular discharge 103 starts between the center electrode 109 and the surrounding electrode 110. Circular fiber devices 107, 108 transmit light from the discharge 103 of the assembly or device 102. The device 102 is very similar to the device 114 of FIG. 17, but the tubular fiber 91 of the device 114 is provided in place of the plurality of fibers 108 in the device 102.

  The devices 112 and 102 shown in FIGS. 18B and 19B, respectively, have sufficient area for the discharges 92 and 103, and optics to transmit the discharge light from the device to the appropriate optical and electrical mechanisms for signal processing and analysis. Fibers 91, 107, 108 are provided. While the invention has been described with respect to at least one exemplary embodiment, many variations and modifications will become apparent to those skilled in the art upon reading this specification. Therefore, the claims should be interpreted as broadly as possible from the viewpoint of the prior art so as to include all of the modifications and changes.

Figure 2 shows a microdischarge device optically coupled to an optical multi-channel analyzer based on light input via an interference filter. FIG. 3 is a detailed view of a discharge gap for an optical fiber interface. The discharge gap housing attached to the exhaust pipe is shown. 1 shows a microdischarge device optically coupled to an optical single channel wavelength modulation analyzer based on a scanning Fabry-Perot filter. It is detail drawing of a Fabry-Perot type | mold analyzer. 1 shows a microdischarge device optically coupled to a spectrometer. ₂ is a graph of the relationship between the relative intensity and wavelength of the spectral emission of a glow discharge with a mixture of NO in N2. 4 is a table of angular sensitivity data for materials of various refractive indices. It is a table | surface of the Fabry-Perot filter design parameter of the wavelength modulation in gas sensing. It is a graph of the wavelength scanning of a Fabry-Perot filter. It is a sensor system provided with the silica chip which supports a micro discharge electrode. It is a sensor system that does not include a silica chip that supports a micro-discharge electrode. A sensor arranged in a spark plug package is shown. It is sectional drawing which opens an electrode enclosure and shows a sensor. It is sectional drawing which opens an electrode enclosure and shows a sensor. It is a fragmentary view of the sensor showing the overlapping edge of the electrode. 1 shows a sensor with electrodes concentric to an optical waveguide. It is a cross-sectional view of concentric electrodes forming an annular discharge gap. It is a top view of an optical filter. It is a top view of a pair of electrode isolate | separated by many optical filters. It is a side sectional view and a top view of two electrodes separated by an optical filter. FIG. 4 is a side sectional view and a top view of two concentric electrodes separated by an optical waveguide.

Claims (32)

A first electrode;
A second electrode proximate to the first electrode and forming a gap with the first electrode;
An optical waveguide having a first end proximate to the gap;
A sensor system comprising a waveguide disposed between a first electrode and a second electrode.   The sensor system of claim 1, wherein the waveguide is at least one optical fiber.   The sensor system according to claim 2, wherein the waveguide is a plurality of optical fibers.   The sensor system of claim 1, wherein the waveguide is a layer formed around the first electrode; and the second electrode is a layer formed around the waveguide.   2. The waveguide according to claim 1, wherein the waveguide is a plurality of optical fibers adjacent to each other and arranged like a layer around the first electrode, and the second electrode is a layer formed around the waveguide. Sensor system.   The sensor system according to claim 5, wherein the first electrode and the second electrode form a concentric gap.   6. The sensor system of claim 5, wherein the concentric gap is an annular microdischarge gap.   The sensor system according to claim 7, wherein the glow gap discharge plasma can be generated at a temperature up to 1100 ° C. _NOx, O _2, NH 3 sensor system of claim 1, wherein configured to sense one of the fluids of the group consisting of, SOx and VOC.   The sensor system of claim 1, further comprising an enclosure that at least partially surrounds the first electrode and the second electrode, the enclosure comprising an input and an output.   The sensor system of claim 1, wherein the enclosure comprises at least one baffle.   The sensor system according to claim 10, wherein the enclosure is a stainless steel frit.   The sensor system according to claim 1, further comprising a spark plug-shaped housing, wherein the housing at least partially accommodates the first electrode, the second electrode, and the optical waveguide.   The sensor system according to claim 13, wherein the first electrode and the second electrode are self-supporting electrodes.   The sensor system according to claim 14, wherein the housing includes an insulator that holds the first electrode and the second electrode.   The sensor system of claim 10, wherein the enclosure comprises a particle suppressor.   The sensor system according to claim 2, wherein the gap is a discharge gap.   18. The sensor system according to claim 17, wherein the first electrode is susceptible to soot generation and is kept clean by a discharge gap.   The sensor system of claim 18, wherein the first electrode is kept clean without a noble gas.   The sensor system according to claim 1, wherein the gap is capable of generating a discharge and keeps the optical surface of the first end of the optical waveguide clean.   21. The sensor system according to claim 20, wherein the optical surface at the first end of the optical waveguide is kept clean without a noble gas.   18. The sensor system of claim 17, further comprising at least one filter near the second end of the optical waveguide.   The sensor system according to claim 22, wherein the at least one filter is a bandpass filter of a wavelength band.   The sensor system of claim 23, further comprising a light intensity indicator connected to the filter.   25. The sensor system of claim 24, further comprising an enclosure that at least partially surrounds the first electrode and the second electrode.   26. The sensor system of claim 25, further comprising a particulate material filter connected to the enclosure.   27. The sensor system of claim 26, further comprising a spark plug package that at least partially accommodates the particulate material filter, the first electrode, the second electrode, and the first end of the optical waveguide.   28. The sensor system of claim 27, wherein the spark plug package is connected to an exhaust system. An optical waveguide;
A first electrode formed concentrically around the optical waveguide;
A second electrode proximate to the end of the first electrode and forming a gap with the concentric end of the first electrode;
A sensor system comprising:   The sensor system according to claim 30, wherein the waveguide is an optical fiber.   The sensor system according to claim 30, wherein the optical fiber comprises a light transmission core; and a clad formed concentrically around the core.   32. The sensor system of claim 31, wherein the gap is an annular discharge gap.

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