Abstract:
A sensor incorporating a phased heater array structure with a concentrator, separator and detectors for sensing the presence, identity and concentration of a mixture of fluids in a sample or other place. It may utilize an array of gas discharge devices, of chemi-sensors and of photo ionization sensors. The sensors may have control logic for the selection of variable portions and types of the heater elements for the concentrator and the separator. Detectors, the concentrator and separator along with the phased heater array may be integrated on a chip. Registers and the control logic may be integrated in a chip connectable to the chip containing the phased heater array structure via wire-bonds or solder bumps or z-axis conductive elastomers.

Description:
[0001]    This application claims priority under 35 U.S.C. § 119(e)(1) to co-pending U.S. Provisional Patent Application No. 60/440,108, filed Jan. 15, 2003, and entitled “PHASED-III SENSOR”, wherein such document is incorporated herein by reference. This application also claims priority under 35 U.S.C. § 119(e)(1) to co-pending U.S. Provisional Patent Application No. 60/414,211, filed Sep. 27, 2002, and entitled “PHASED SENSOR”, wherein such document is incorporated herein by reference. 
     
    
     
       BACKGROUND  
         [0002]    The present invention pertains to detection of fluids. Particularly, the invention pertains to a phased heater array structure, and more particularly to application of the structure as a sensor for the identification and quantification of fluid components. The term “fluid” may be used as a generic term that includes gases and liquids as species. For instance, air, gas, water and oil are fluids.  
           [0003]    Aspects of structures and processes related to fluid analyzers may be disclosed in U.S. Pat. No. 6,393,894 B1, issued May 28, 2002, to Ulrich Bonne et al., and entitled “Gas Sensor with Phased Heaters for Increased Sensitivity,” which is incorporated herein by reference; U.S. Pat. No. 6,308,553 B1, issued Oct. 30, 2001, to Ulrich Bonne et al., and entitled “Self-Normalizing Flow Sensor and Method for the Same,” which is incorporated herein by reference; and U.S. Pat. No. 4,944,035, issued Jul. 24, 1990, to Roger L. Aagard et al., and entitled “Measurement of Thermal Conductivity and Specific Heat,” which is incorporated herein by reference.  
           [0004]    Presently available gas composition analyzers may be selective and sensitive but lack the capability to identify the component(s) of a sample gas mixture with unknown components, besides being generally bulky and costly. The state-of-the-art combination analyzers GC-GC and GC-MS (gas chromatograph—mass spectrometer) approach the desirable combination of selectivity, sensitivity and smartness, yet are bulky, costly, slow and unsuitable for battery-powered applications. In GC-AED (gas chromatograph—atomic emission detector), the AED alone uses more than 100 watts, uses water cooling, has greater than 10 MHz microwave discharges and are costly.  
           [0005]    The phased heater array sensor initially consisted of separate chips for the concentrator, the separator, as well as for an off-chip flow sensor. These may be integrated onto one chip and provide improvements in the structural integrity and temperature control while reducing power consumption. The next phased heater array sensor involved an addition of integratable, micro-discharge devices for detection, identification and quantification of analyte. However, short of the full integration of the FET switches and shift register(s) onto the chip, there still was a need to wire-bond, route, connect and route about 110 wires from a daughter-board to mother-board with its micro-processor-controlled FET switches, which caused bulk and labor cost. In addition, the phased heater array sensor analyzers and conventional GCs seem to lack flexibility to change preconcentration and separation capabilities on-line.  
           [0006]    Detection, identification and analysis of very small amounts of fluids in a more inexpensive, efficient and inexpensive manner are desired.  
         SUMMARY  
         [0007]    The present invention is a design and operation of a sensor system/analyzer consisting of an array of selective, sensitive, fast and low-power phased heater elements in conjunction with an array of compact, fast, low-power, ambient pressure, minimal pumping spectral analysis devices to achieve fluid component presence, identification and quantification.  
           [0008]    Additionally, flexibility low cost and compactness features are incorporated via FET switches, shift registers and control logic onto the same or a separate chip connected to the phased heater array sensor chip via wire-bonds or solder-bumps on the daughter-PCB (printed circuit board connected to the mother-PCB via only about ten leads) and providing the user flexibility to be able select the fraction of total heatable elements for preconcentration and separation; and selection of analysis logic.  
           [0009]    Multi-fluid detection and analysis may be automated via affordable, in-situ, ultra-sensitive, low-power, low-maintenance and compact micro detectors and analyzers, which can wirelessly or by another medium (e.g., wire or optical fiber) send their detection and/or analysis results to a central or other manned station. A micro fluid analyzer may incorporate a phased heater array, concentrator, separator and diverse approaches. The micro fluid analyzer may be a low-cost approach to sense ozone with a 50 part-per-billion (ppb) maximum emission objective. The analyzer may be capable of detecting a mixture of trace compounds in a host or base sample gas or of trace compounds in a host liquid.  
           [0010]    The fluid analyzer may include a connective configuration to an associated microcontroller or processor. An application of the sensor may include the detection and analyses of air pollutants in aircraft space such as aldehydes, butyric acid, toluene, hexane, and the like, besides the conventional CO 2 , H 2 O and CO. Other sensing may include conditioned indoor space for levels of gases such as CO 2 , H 2 O, aldehydes, hydrocarbons and alcohols, and sensing outdoor space and process streams of industries such as in chemical, refining, product purity, food, paper, metal, glass and pharmaceutical industries. Also, sensing may have a significant place in environmental assurance and protection. Sensing may provide defensive security in and outside of facilities by early detection of chemicals before their concentrations increase and become harmful.  
           [0011]    A vast portion of the sensor may be integrated on a chip with conventional semiconductor processes or micro electromechanical system (MEMS) techniques. This kind of fabrication results in small, low-power consumption, and in situ placement of the micro analyzer. The flow rate of the air or gas sample through the monitor may also be very small. Further, a carrier gas for the samples is not necessarily required and thus this lack of carrier gas may reduce the dilution of the samples being tested, besides eliminating the associated maintenance and bulk of pressurized gas-tank handling. This approach permits the sensor to provide quick analyses and prompt results, may be at least an order of magnitude faster than some related art devices. It avoids the delay and costs of labor-intensive laboratory analyses. The sensor is intelligent in that it may have an integrated microcontroller for analysis and determination of gases detected, and may maintain accuracy, successfully operate and communicate information in and from unattended remote locations. The sensor may communicate detector information, analyses and results via utility lines, or optical or wireless media, with the capability of full duplex communication to a host system over a significant distance with “plug-and-play” adaptation and simplicity. The sensor may be net-workable. It may be inter-connectable with other gas sample conditioning devices (e.g., particle filters, valves, flow and pressure sensors), local maintenance control points, and can provide monitoring via the internet. The sensor is robust. It can maintain accuracy in high electromagnetic interference (EMI) environments having very strong electrical and magnetic fields. The sensor has high sensitivity. The sensor offers sub-ppm (parts-per-million) level detection which is 100 to 10,000 times better than related art technology, such as conventional gas chromatographs which may offer a sensitivity in a 1 to 10 ppm range. The sensor is, among other things, a lower-power, faster, and more compact, more sensitive and affordable version of a gas chromatograph. It may have structural integrity and have very low or no risk of leakage in the application of detecting and analyzing pressurized fluid samples over a very large differential pressure range.  
           [0012]    In the sensor, a small pump, such as a Honeywell MesoPump™, may draw a sample into the system, while only a portion of it might flow through the phased heater sensor at a rate controlled by the valve (which may be a Honeywell MesoValve™ or Hoerbiger PiezoValve™). This approach may enable fast sample acquisition despite long sampling lines, and yet provide a regulated, approximately 0.1 to 3 cm 3 /min flow for the detector. The pump of the sensor may be arranged to draw sample gas through a filter in such a way as to provide both fast sample acquisition and regulated flow through the phased heater sensor.  
           [0013]    As a pump draws sample gas through the sensor, the gas may expand and thus increase its volume and linear velocity. The control circuit may be designed to compensate for this change in velocity to keep the heater “wave” in sync with the varying gas velocity in the sensor. To compensate for the change in sample gas volume as it is forced through the heater channels, its electronics may need to adjust either the flow control and/or the heater “wave” speed to keep the internal gas flow velocity in sync with the heater “wave”.  
           [0014]    During a gas survey operation, the sensor&#39;s ability (like any other slower gas chromatographs) may sense multiple trace constituents of air such as about 330 to 700 ppm of CO 2 , about 1 to 2 ppm of CH 4  and about 0.5 to 2.5 percent of H 2 O. This may enable on-line calibration of the output elution times as well as checking of the presence of additional peaks such as ethane, possibly indicating a natural gas, propane or other gas pipeline leak. The ratio of sample gas constituent peak heights thus may reveal clues about the source of the trace gases, which could include car exhaust or gasoline vapors.  
           [0015]    The sensor may have the sensitivity, speed, portability and low power that make the sensor especially well suited for safety-mandated periodic leak surveys of natural gas or propane gas along transmission or distribution pipeline systems and other gas in chemical process plants.  
           [0016]    The sensor may in its leak sensing application use some or all sample gas constituents (and their peak ratios) as calibration markers (elution time identifies the nature of the gas constituents) and/or as leak source identifiers. If the presence alone of a certain peak such as methane (which is present in mountain air at about one to two ppm) may not be enough information to indicate that the source of that constituent is from swamp gas, a natural or pipeline gas or another fluid.  
           [0017]    The sensor may be used as a portable device or installed at a fixed location. In contrast to comparable related art sensors, it may be more compact than a portable flame ionization detector without requiring the bulkiness of hydrogen tanks, it may be faster and more sensitive than hot-filament or metal oxide combustible gas sensors, and much faster, more compact and more power-thrifty than conventional and/or portable gas chromatographs.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0018]    [0018]FIG. 1 is a diagram of a sensor system.  
         [0019]    [0019]FIG. 2 shows details of a micro gas apparatus;  
         [0020]    [0020]FIG. 3 is a layout of an illustrative phased heater mechanism;  
         [0021]    [0021]FIG. 4 is a length-wise sectional view of a heater elements on a streightened channel;  
         [0022]    [0022]FIG. 5 is a length-wise sectional view of a twin-film heater elements on a streightened channel;  
         [0023]    [0023]FIGS. 6 a ,  6   b  and  6   c  show a cross-section end views of the twin-film heater element and single film element.  
         [0024]    [0024]FIG. 7 is a graph illustrating heater temperature profiles, along with corresponding concentration pulses produced at each heater element of the sensor apparatus;  
         [0025]    [0025]FIG. 8 is a graph showing several heater elements to illustrate a step-wise build-up on an analyte concentration;  
         [0026]    [0026]FIG. 9 is a graph showing a concentration pulse that reaches about 100 percent concentration level;  
         [0027]    [0027]FIG. 10 is a table showing detection limits and selectivities for various elements;  
         [0028]    [0028]FIG. 11 shows chromatograms of a multielement test mixture;  
         [0029]    [0029]FIG. 12 is a graph of the relative intensity, discharge versus pressure for a gas;  
         [0030]    [0030]FIG. 13 shows sectional views of an array of light source and detector (MDD) pairs for gas sensing.  
         [0031]    [0031]FIG. 14 is a graph of a spectral responsivity comparison between an MDD and a Si-photo diode.  
         [0032]    [0032]FIG. 15 is an illustration of an integrated layout for the phased heater array structure that includes sensors, a concentrator and a separator;  
         [0033]    [0033]FIG. 16 is a schematic of the logic heating element selection for concentrator and separator portions of a sensor. 
     
    
     DESCRIPTION  
       [0034]    Detection and analysis by sensor  15  of FIG. 1 may include detection, identification and quantification of fluid components. That may include a determination of the concentration of or parts-per-million of the fluid detected. Sensor  15  may be used to detect fluids in the environment. Also, sensor  15  may detect miniscule amounts of pollutants in ambient environment of a conditioned or tested space. Sensor  15  may indicate the health and the level of toxins-to-people in ambient air or exhaled air.  
         [0035]    [0035]FIG. 1 reveals an illustrative diagram of a low-power sensor system  11 . A sample fluid  25  from a process stream, an ambient space or volume  61  may enter a conduit or tube  19  which is connected to an input  34  of a sensor or micro gas apparatus  15 . Fluid  25  may be processed by sensor  15 . Processed fluid  37  may exit output  36  of sensor  15  and be exhausted to volume  61  or another volume, wherever designated, via a conduit or tube  39 .  
         [0036]    Sensor  15  results may be sent to microcontroller/processor  29  for analysis, and immediate conclusions and results. This information may be sent on to observer stations  31  for review and further analysis, evaluation, and decisions about the results found. Data and control information may be sent from stations  31  to microcontroller/processor  29 . Data and information may be sent and received via the wireless medium by a transmitter/receiver  33  at sensor  11  and at stations  31 . Or the data and information may be sent and received via wire or optical lines of communication by a modem  35  at monitor  11  and station  31 . The data and information may be sent to a SCADA (supervisory control and data acquisition) system. These systems may be used in industry (processing, manufacturing, service, health) to detect certain gases and provide information relating to the detection to remote recipients.  
         [0037]    Microcontroller or processor  29  may send various signals to analyzer  15  for control, adjustment, calibration or other purposes. Also, microcontroller/processor  29  may be programmed to provide a prognosis of the environment based on detection results. The analysis calculations, results or other information may be sent to modem  35  for conversion into signals to be sent to a station  31  via lines, fiber or other like media. Also, such output to modem  35  may be instead or simultaneously sent to transmitter  33  for wireless transmission to a station  31 , together with information on the actual location of the detection obtained, e.g., via GPS, especially if it is being used as a portable device. Also, stations  31  may send various signals to modem  35  and receiver  33 , which may be passed on to microcontroller or processor  29  for control, adjustment, calibration or other purposes.  
         [0038]    In FIG. 1, space  61  may be open or closed. Sensor system  11  may have a hook-up that is useable in a closed space  61  such as an aircraft-cabin, machinery room, factory, or some place in another environment. Or it may be useable in an open space  61  of the earth&#39;s environment. The end of input tube or pipe  19  may be in open space  61  and exhaust of exit tube  37  may be placed at a distance somewhat removed from a closed space  61 . System  11  for space  61  may itself be within space  61  except that tube  39  may exit into space  61 , especially downstream in case space  61  is a process stream.  
         [0039]    [0039]FIG. 2 reveals certain details of micro gas apparatus  15 . Further details and variants of it are described below in conjunction with subsequent figures. Sample stream  25  may enter input port  34  from pipe or tube  19 . There may be a particle filter  43  for removing dirt and other particles from the stream of fluid  25  that is to enter apparatus  15 . This removal is for the protection of the apparatus and the filtering should not reduce the apparatus&#39; ability to accurately analyze the composition of fluid  25 . Dirty fluid (with suspended solid or liquid non-volatile particles) might impair proper sensor function. A portion  45  of fluid  25  may flow through the first leg of a differential thermal-conductivity detector (TCD, or chemi-sensor (CRD), or photo-ionization sensor/detector (PID), or other device)  127  and a portion  47  of fluid  25  flows through tube  49  to a pump  51 . By placing a “T” tube immediately adjacent to the inlet  45 , sampling with minimal time delay may be achieved because of the relatively higher flow  47  to help shorten the filter purge time. Pump  51  may cause fluid  47  to flow from the output of particle filter  43  through tube  49  and exit from pump  51 . Pump  53  may effect a flow of fluid  45  through the sensor via tube  57 . Pump  51  may now provide suction capacity of 10-300 cm3/min at less than 1 psi pressure drop (Δp) and low-flow-capacity pump  53  may provide 0.1-3 cm3/min at up to a Δp of 10 psi). There may be additional or fewer pumps, and various tube or plumbing arrangements or configurations for system  15  in FIG. 2. Data from detectors  127  and  128  may be sent to control  130 , which in turn may relay data to microcontroller and/or processor  29  for processing. Resultant information may be sent to station  31 .  
         [0040]    Pumps  51  and  53  may be very thrifty and efficient configurations implemented for pulling in a sample of the fluid being checked for detection of possible gas from somewhere. Low-power electronics having a sleep mode when not in use may be utilized. The use of this particularly thrifty but adequately functional pump  51  and  53 , which may run only about or less than 1-10 seconds before the start of a concentrator and/or measurement cycle of analyzer system  11 , and the use of low-power electronics for control  130  and/or microcontroller/processor  29  (which may use a sleep mode when not in use) might result in about a two times reduction in usage of such power.  
         [0041]    [0041]FIG. 3 is a schematic diagram of part of the sensor apparatus  10 ,  15 , representing a portion of concentrator  124  or separator  126  in FIG. 2. The sensor apparatus may include a substrate  12  and a controller  130 . Controller  130  may or may not be incorporated into substrate  12 . Substrate  12  may have a number of thin film heater elements  20 ,  22 ,  24 , and  26  positioned thereon. While only four heater elements are shown, any number of heater elements may be provided, for instance, between two and one thousand, but typically in the 20-100 range. Heater elements  20 ,  22 ,  24 , and  26  may be fabricated of any suitable electrical conductor, stable metal, or alloy film, such as a nickel-iron alloy sometimes referred to as permalloy having a composition of eighty percent nickel and twenty percent iron; platinum, platinum silicide and polysilicon. Heater elements  20 ,  22 ,  24 , and  26  may be provided on a thin, low-thermal mass, low-in-plane thermal conduction, support member  30 , as shown in FIGS. 4 and 5. Support member or membrane  30  may be made from Si 3 N 4  or other appropriate or like material. The heater elements may be made from Pt or other appropriate or like material.  
         [0042]    Substrate  12  may have a well-defined single-channel phased heater mechanism  41  having a channel  32  for receiving the sample fluid stream  45 , as shown in FIG. 4. FIG. 5 reveals a double-channel phased heater design  41  having channels  31  and  32 . Substrate  12  and portion or wafer  65  may have defined channels  31  and  32  for receiving a streaming sample fluid  45 . The channels may be fabricated by selectively etching silicon channel wafer substrate  12  beneath support member  30  and wafer or portion  65  above the support member. The channels may include an entry port  34  and an exhaust port  36 .  
         [0043]    The sensor apparatus may also include a number of interactive elements inside channels  31  and  32  so that they are exposed to the streaming sample fluid  45 . Each of the interactive elements may be positioned adjacent, i.e., for closest possible contact, to a corresponding heater element. For example, in FIG. 4, interactive elements  40 ,  42 ,  44 , and  46  may be provided on the lower surface of support member  30  in channel  32 , and be adjacent to heater elements  20 ,  22 ,  24 , and  26 , respectively. In FIG. 5, additional interactive elements  140 ,  142 ,  144 , and  146  may be provided on the upper surface of support member  30  in second channel  31 , and also adjacent to heater elements  20 ,  22 ,  24 , and  26 , respectively. There may be other channels with additional interactive film elements which are not shown in the present illustrative example. The interactive elements may be formed from any number of films commonly used in liquid or gas chromatography, such as silica gel, polymethylsiloxane, polydimethylsiloxane, polyethyleneglycol, porous silica, Nanoglass™, active carbon, and other polymeric substances. Furthermore, the above interactive substances may be modified by suitable dopants to achieve varying degrees of polarity and/or hydrophobicity, to achieve optimal adsorption and/or separation of targeted analytes.  
         [0044]    [0044]FIG. 6 a  shows a cross-section end view of two-channel phased heater mechanism  41 . The top and bottom perspectives of portions in FIGS. 6 a ,  6   b  and  6   c  may not necessarily appear to be the same. An end view of a single channel phased heater mechanism  41  may incorporate the support member  30  and substrate  12  and the items between them, in FIGS. 6 b  and  6   c . FIG. 6 b  shows a version of the phased heater mechanism  41  having an exposed 1 micron membrane. Shown in FIG. 6 b  is open space  392 . FIG. 6 c  shows a ruggedized, low power version having a small closed space  394 . Support member  30  may be attached to top structure  65 . Anchors  67  may hold support member  30  in place relative to channel  31 . Fewer anchor  67  points minimize heat conduction losses from support  30  to other portions of structure  41 . There may be a heater membrane that has a small number anchor points for little heat conduction from the heater elements. In contrast to a normal anchoring scheme, the present example may have a reduction of anchor points to result in the saving about 1.5 times of the remaining heater element input power.  
         [0045]    The heater elements of a phased heater array may be coated with an adsorber material on both surfaces, i.e., top and bottom sides, for less power dissipation and more efficient heating of the incoming detected gas. The heater elements may have small widths for reduced power dissipation.  
         [0046]    Interactive film elements may be formed by passing a stream of material carrying the desired sorbent material through channel  32  of single-channel heating mechanism  41 . This may provide an interactive layer throughout the channel. If separate interactive elements  40 ,  42 ,  44 ,  46  are desired, the coating may be spin-coated onto substrate  30  attached to the bottom wafer  12 , before attaching the top wafer  65  in FIG. 6 a , and then selectively “developed” by either using standard photoresist masking and patterning methods or by providing a temperature change to the coating, via heater elements  20 ,  22 ,  24  and  26 .  
         [0047]    The surfaces of inside channel of the heater array, except those surfaces intentionally by design coated with an adsorber material, may be coated with a non-adsorbing, thermal insulating layer. The thickness of the adsorber coating or film may be reduced thereby decreasing the time needed for adsorption and desorption. As in FIG. 6 a , coating  69  of a non-adsorbing, thermal insulating material may be applied to the inside walls of channel  31  in the single-channel heater  41 , and the wall of channels  31  and  32  in the dual-channel heater mechanism  41 , except where there is adsorber coated surfaces, by design, such as the interactive elements. Coating  69  may reduce the needed heater element power by about 1.5 times. The material should have thermal conduction that is substantially less than the material used in the channel walls. The latter may be silicon. Alternative materials for coating  69  may include SiO 2  or other metal oxides. Coating  69  may reduce power used for the heater elements in support  30 . A minimizing or reduction of the size (width, length and thickness) of the heater element membranes as well as the adsorber film, while retaining a reasonable ratio of mobile/stationary phase volume, may result in about a four times power reduction. The minimized or reduced adsorber film thickness may reduce the time needed for adsorption-desorption and save about 1.5 times in energy needed per fluid analysis.  
         [0048]    Heater elements  20 ,  22 ,  24  and  26  may be GC-film-coated on both the top and bottom sides so that the width and power dissipation of the heater element surface by about two times. The fabrication of these heater elements involves two coating steps, with the second step requiring wafer-to-wafer bonding and coating after protecting the first coat inside the second wafer and dissolving the first wafer.  
         [0049]    Another approach achieving the desired ruggedness (i.e. not expose a thin membrane  20 ,  22 ,  24 , . . . to the exterior environment) but without the need to coat these both top and bottom, is to coat only the top and reduce the bottom channel  32  to a small height, see FIG. 6 a , so that the volumetric ratio (air/film) is of a value of less than 500.  
         [0050]    The micro gas analyzer may have heater elements  40 ,  42 , . . . ,  44 ,  46  and  140 ,  142 , . . . ,  144 ,  146  fabricated via repeated, sequentially spin-coated (or other deposition means) steps, so that a pre-arranged pattern of concentrator and separator elements are coated with different adsorber materials A, B, C, . . . (known in GC literature as stationary phases), so that not only can the ratio of concentrator/separator elements be chosen, but also which of those coated with A, B, C and so forth may be chosen (and at what desorption temperature) to contribute to the concentration process and electronically be injected into the separator, where again a choice of element temperature ramping rates may be chosen for the A&#39;s to be different for the B, C, . . . elements; and furthermore adding versatility to this system in such a way that after separating the gases from the group of “A”-elements; another set of gases may be separated from the group of “B” elements, and so forth. The ratio of concentrator to separator heater elements may be set or changed by a ratio control mechanism  490  connected to controller  130 .  
         [0051]    Controller  130  may be electrically connected to each of the heater elements  20 ,  22 ,  24 ,  26 , and detector  50  as shown in FIG. 3. Controller  130  may energize heater elements  20 ,  22 ,  24 , and  26  in a time phased sequence (see bottom of FIG. 7) such that each of the corresponding interactive elements  40 ,  42 ,  44 , and  46  become heated and desorb selected constituents into a streaming sample fluid  45  at about the time when an upstream concentration pulse, produced by one or more upstream interactive elements, reaches the interactive element. Any number of interactive elements may be used to achieve the desired concentration of constituent gases in the concentration pulse. The resulting concentration pulse may be provided to detector  50 ,  128 , for detection and analysis. Detector  50 ,  127 , or  128  (FIGS. 2 and 3) may be a thermal-conductivity detector, discharge ionization detector, CRD, PID, MDD, or any other type of detector such as that typically used in gas or fluid chromatography.  
         [0052]    [0052]FIG. 7 is a graph showing illustrative relative heater temperatures, along with corresponding concentration pulses produced at each heater element. As indicated above, controller  130  may energize heater elements  20 ,  22 ,  24 , and  26  in a time phased sequence with voltage signals  71 . Illustrative time phased heater relative temperatures for heater elements  20 ,  22 ,  24 , and  26  are shown by temperature profiles or lines  60 ,  62 ,  64 , and  66 , respectively.  
         [0053]    In the example shown, controller  130  (FIG. 3) may first energize first heater element  20  to increase its temperature as shown at line  60  of FIG. 7. Since first heater element  20  is thermally coupled to first interactive element  40  (FIGS. 4 and 5), the first interactive element desorbs selected constituents into the streaming sample fluid  45  to produce a first concentration pulse  70  (FIG. 7) at the detector  128  or  50 , if no other heater elements were to be pulsed. The streaming sample fluid  45  carries the first concentration pulse  70  downstream toward second heater element  22 , as shown by arrow  72 .  
         [0054]    Controller  130  may next energize second heater element  22  to increase its temperature as shown at line  62 , starting at or before the energy pulse on element  20  has been stopped. Since second heater element  22  is thermally coupled to second interactive element  42 , the second interactive element also desorbs selected constituents into streaming sample fluid  45  to produce a second concentration pulse. Controller  130  may energize second heater element  22  such that the second concentration pulse substantially overlaps first concentration pulse  70  to produce a higher concentration pulse  74 , as shown in FIG. 7. The streaming sample fluid  45  carries larger concentration pulse  74  downstream toward third heater element  24 , as shown by arrow  76 .  
         [0055]    Controller  130  may then energize third heater element  24  to increase its temperature as shown at line  64  in FIG. 7. Since third heater element  24  is thermally coupled to third interactive element  44 , third interactive element  44  may desorb selected constituents into the streaming sample fluid to produce a third concentration pulse. Controller  130  may energize third heater element  24  such that the third concentration pulse substantially overlaps larger concentration pulse  74  provided by first and second heater elements  20  and  22  to produce an even larger concentration pulse  78 . The streaming sample fluid  45  carries this larger concentration pulse  78  downstream toward an “Nth” heater element  26 , as shown by arrow  80 .  
         [0056]    Controller  130  may then energize “N-th” heater element  26  to increase its temperature as shown at line  66 . Since “N-th” heater element  26  is thermally coupled to an “N-th” interactive element  46 , “N-th” interactive element  46  may desorb selected constituents into streaming sample fluid  45  to produce an “N-th” concentration pulse. Controller  130  may energize “N-th” heater element  26  such that the “N-th” concentration pulse substantially overlaps larger concentration pulse  78  provided by the previous N-1 interactive elements. The streaming sample fluid carries “N-th” concentration pulse  82  to either a separator  126  or a detector  50  or  128 , as described below.  
         [0057]    As indicated above, heater elements  20 ,  22 ,  24 , and  26  may have a common length. As such, controller  130  can achieve equal temperatures of the heater elements by providing an equal voltage, current, or power pulse to each heater element. The voltage, current, or power pulse may have any desired shape including a triangular shape, a square shape, a bell shape, or any other shape. An approximately square shaped voltage, current, or power pulse is used to achieve temperature profiles  60 ,  62 ,  64 , and  66  shown in FIG. 7. The temperature profiles look like that, and note that the desorbed species are generated with a small time delay, relative to the voltage pulses.  
         [0058]    [0058]FIG. 8 is a graph showing a number of heater elements to illustrate, first, how the concentration increases stepwise as the desorption of subsequent elements is appropriately synchronized with the streaming sample fluid velocity and, second, how the lengths of individual elements are matched to the expected increased rate of mass diffusivity flux as the concentration levels and gradients increase. It should be pointed out here that prior to the elements shown in FIG. 8, the analyte concentration may have been already magnified by a factor, F, by virtue of pulsing an initial element with a length F-times longer than the one shown as element  100  (H 1 ) or, alternatively by simultaneously pulsing elements  1 ,  2 , . . . , F and collecting all the desorbed analyte with the still cool element  100  (H 1 ), before pulsing it. It is recognized that each of the concentration pulses may tend to decrease in amplitude and increase in length when traveling down channel  32  due to diffusion. To accommodate this increased length, it is contemplated that the length of each successive heater element may be increased along the streaming sample fluid. For example, a second heater element  102  may have a length W 2  that is larger than a length W 1  of a first heater element  100 . Likewise, a third heater element  104  may have a length W 3  that is larger than length W 2  of second heater element  102 . Thus, it is contemplated that the length of each heater element  100 ,  102 , and  104  may be increased, relative to the adjacent upstream heater element, by an amount that corresponds to the expected increased length of the concentration pulse of the upstream heater elements due to diffusion. However, in some cases in which the target analyte concentrations are very small or the adsorbing film capacities are very large, it may be possible and advantageous to significantly decrease the length of subsequent or last heater elements in order to achieve maximum focusing performance of the concentrator function, which is based on minimizing the film volume into which we can adsorb a given quantity of analyte(s) from a given volume of sample gas pumped (pump  51  in FIG. 2) through the concentrator during a given time, and thus increase the analyte(s) concentration by the same ratio of sample volume/film volume (of the last heater element).  
         [0059]    To simplify the control of the heater elements, the length of each successive heater element may be kept constant to produce the same overall heater resistance between heater elements, thereby allowing equal voltage, current, or power pulses to be used to produce similar temperature profiles. Alternatively, the heater elements may have different lengths, and the controller may provide different voltage, current, or power pulse amplitudes to the heater element to produce a similar temperature profile.  
         [0060]    [0060]FIG. 9 is a graph showing a concentration pulse  110  that achieves a 100 percent concentration level. It is recognized that even though concentration pulse  110  has achieved a maximum concentration level, such as 100 percent, the concentration of the corresponding constituent can still be determined. To do so, detector  50 ,  128 ,  164  may detect the concentration pulse  110 , and controller  130  may integrate the output signal of the detector over time to determine the concentration of the corresponding constituent in the original sample of stream  45 .  
         [0061]    In “GC peak identification”, it is desired to associate unequivocally a chemical compound with each gas peak exiting from a gas chromatograph (GC), which is a tool to achieve such separations of individual constituents from each other. There are several approaches for identifying components of a gas. In a GC-MS combination, each GC-peak is analyzed for its mass, while processing the molecular fragments resulting from the required ionization process at the MS inlet. In a GC-GC combination, different separation column materials are used in the first and second GC, in order to add information to the analysis record, which may help with compound identification. In a GC-AED combination, a microwave-powered gas discharge may generate tell-tale optical spectral emission lines (atoms) and bands (molecules) to help identify the gas of the GC-peak in the gas discharge plasma. In the GC-MDD or GC-GC-MDD configurations, the micro discharge device (MDD) may emit spectra of the analyte peaks as they elute from the GC or GC-GC, and reveal molecular and atomic structure and thus identification of the analyte peaks.  
         [0062]    An example of how the selective wavelength channels of an AED can identify the atomic makeup of a compound separated by GC is illustrated in FIG. 11, which shows separate channels for C, H, N, O, S, Cl, Br, P, D, Si and F atomic emissions, with a corresponding list of channels in the table of FIG. 10. FIG. 11 shows chromatograms of a multielement test mixture with various peaks that may indicate the element and its approximate amount. Peak  301  indicates 2.5 ng of 4-fluoroanisole; peak  302  indicates 2.6 ng of 1-bromohexane; peak  303  indicates 2.1 ng of tetraethylorthosilicate; peak  304  indicates 1.9 ng of n-perdeuterodecane; peak  305  indicates 2.7 ng of nitrobenzene; peak  306  indicates 2.4 ng of triethyl phosphate; peak  307  indicates 2.1 tert-butyl disulfide; peak  308  indicates 3.3 ng of 1,2,4-trichlorobenzene; peak  309  indicates 170 ng of n-dodecane; peak  310  indicates 17 ng of n-tridecane; and peak  311  indicates 5.1 ng of n-tetradecane. For such chromatograms, the GC conditions may include a column flow of 3.3 mL/min, a split ratio of 36:1, and an oven program from 60 degrees to 180 degrees Centigrade (C) at 30 degrees C./min. Part of a UV spectrum of neutral and ionized emitters of Ne, generated with low-power microdischarges are shown in FIG. 12. Also shown in this figure is that the spectral species change in intensity as the “Ne” pressure changes. The optical output may depend on several parameters such as discharge cavity geometry, applied voltage and pressure. Molecular bands are emitted and may even be used for “NO” measurements of such gases as in the hot exhaust of jet engines.  
         [0063]    One may obtain useful gas composition information by feeding an environmental gas sample to microdischarge devices. In a first approach, one may use one microgas discharge device, the operating parameters (voltage, pressure, flow and possibly the geometry) of which may be changed to yield variations in the output emission spectrum such that after evaluation and processing of such emission data, information on the type and concentration of the gas sample constituents may be made. In a second approach, one may use several micro-gas discharge devices, whereby the operating parameters of each may be changed, for emission output evaluation as in the first approach, and may obtain better results via a statistical analysis. The third approach may be the same as the first one, except that each micro-discharge may be only operated at one condition, but set to be different from that of the set-point of the other microdischarges.  
         [0064]    [0064]FIG. 13 represents the third approach, whereby the gas sample may pass serially from one type of discharge to the next, and the assumption may be that the nature of the gas sample does not change during this process. The figure shows an array  350  of light source—detector pairs for gas composition sensing in a gas  45  stream at various pressures and voltages. The different voltages, +V1, +V2 . . . and pressures P1 and P2 may be marked as such. The plasma of the micro discharges  352  from the light source block  351  are indicated by the ellipsoids between the (+) and (−) electrodes. Opposing source block  351  is a detector block  353  having micro gas discharge devices operating as detectors  354  of the light from the source discharges  352 . There may be filters situated on detectors  354 . The filters may be different and selected for detection and analysis of particular groups of gases. The various lines of emission of the gases from the micro discharges may be detected and identified for determining the components of a detected gas. Array  350  may be connected to controller  130 . A processor may be utilized in the control of the micro discharges and the detection of the effects of the discharges in the flow of gas  45  through array  350 .  
         [0065]    Light source block  351  may be made from silicon. Situated on block  351  may be a wall-like structure  355  of Si 3 N 4  or Pyrex™, forming a channel for containing the flow of gas  45  through device  350 . On top of structure  355  may be a conductive layer of Pt or Cu material  356 . On the Pt material is a layer  357  of Si 3 N 4  that may extend over the flow channel. On top of layer  357  may be a layer  358  of Pt and a layer  359  of Si 3 N 4  as a wall for forming a channel for detectors  354 . The fourth approach may be like the third approach except for the feeding the gas sample to each discharge in a parallel rather than serial fashion.  
         [0066]    A fifth approach may be the same as the fourth or third approach, except that the gas sample may have undergone a separation process as provided, e.g., by a conventional GC. A sixth approach may be the same as the fifth approach, except that prior to the separation process, the sample analytes of interest may be first concentrated by a conventional pre-concentration step.  
         [0067]    The seventh approach may be the same as the sixth approach, except that prior to the separation process, the sample analytes of interest may have been previously concentrated by a multi-stage pre-concentration process and then electronically injected into the separator as offered by the phased heater array sensor.  
         [0068]    In the sixth and seventh approaches with reference to FIG. 2, the idea is to feed individual gas-analyte peaks eluting from the GC column or the phased heater array sensor separator channel to each discharge device in the shown array of discharges.  
         [0069]    Gas flow may be in series as shown in FIG. 13. Or it may be in parallel which may be necessary for an optimal peak identification, whereby (for the sake of minimizing total analysis time) each discharge cell may operate at a fixed condition of applied voltage, gas pressure (determined by the vacuum or suction pump at the exit of the array, e.g., by a Mesopump™). In FIG. 13, only two pressures may be indicated by way of example, as easily achieved by a flow restriction between the 4 th  and 5 th  discharge element. Several changes in the discharge parameter such as flow rate, temperature (via local micro-heaters) or geometry (hollow-cathode or flat-plate discharge, besides simple changes in the identification of cell) are not shown, but may be likewise implemented.  
         [0070]    Due to their typically small size (10-100 μm), these sensors may not appear to use much real estate and may be included in block  128  of FIG. 2.  
         [0071]    Sensor  15  may have a flow sensor  125  situated between concentrator  124  and separator  126 , a thermal-conductivity detector at the input of concentrator  124 . It may have a thermal-conductivity detector between concentrator  124  and separator  126 . There may be a thermal-conductivity detector at the output of discharge mechanism  350 . Sensor  15  may include various combinations of some of the noted components in various locations in the sensor  128  of FIG. 2, depending upon the desired application. The drawing of sensor  15  in FIG. 2 is an illustrative example of the sensor. Sensor  15  may have other configurations not illustrated in this figure.  
         [0072]    The gas micro-discharge cells may offer attractive features, which may significantly enhance the usefulness, versatility and value of the phased heater array sensor. Examples of the features include: 1) low power capability—each discharge operates at 700-900 Torr (0.92-1.18 bar) with as little as 120 V DC, at 10 μm, which may amount to 1.2 mW that appears to be a minimal power not even achieved by microTDCs; 2) ease of building along with a compactness (50×50 μm), shown the insert of FIG. 12; 3) the operability of micro-discharges as photo detectors which may be shown by the spectral responsivity comparison between a 100 μm microdischarge and an Si APD in FIG. 14, which no other light sources such as 100-W microwave driven AEDs (requiring water cooling) are known to do; 4) the integratability and wafer level assembly of the discharge source and photodiodes with a phased heater array structure, without having to resort to Si-doping to manufacture monolithic Si-photodiodes; and 5) the added dimensionality (i.e., selectivity) by varying discharge parameters as noted above.  
         [0073]    The present invention may have gas composition sensing capabilities via micro-discharge having: 1) a combination of phased heater array sensor with micro gas discharge devices; 2) the combination of 1), whereby one set or array of gas discharge devices may provide the spectral emission and another, complementary set (with or without narrow-band band-pass filters or micro spectrometer) may provide the light detection function; 3) the combination of 2) with appropriate permutations of designs described above under the first through seventh approaches; and 4) the flexibility to program heatable elements as additional pre-concentrator or additional separator elements of the phased heater array structure, as needed for a specific analysis, to achieve optimal preconcentration or separation performance.  
         [0074]    The present phased heater array sensor-microdischarge detector combination over previously proposed micro gas analyzers may provide sensitivity, speed, portability and low power of the phased heater array sensor, combined with the selectivity, “peak-identification” capability, low-power, light source and detection capability, integratability, simplicity and compactness contributed by micro gas discharge devices, which no other microanalyzers have been known to achieve.  
         [0075]    [0075]FIG. 15 illustrates the integration of sensors, pre-concentrator and/or concentrator  124  and separator  126  of micro gas apparatus  15  (i.e., the phased heater array structure) on a single chip  401  which would be mounted and connected on a circuit board that also connects with other chips as well. One such other chip may hold FET switches, shift registers and logic. The 401 chip may reside on a daughter board. The 401 chip and the main circuit board were originally connected by about 110 wires. However, after the integration of all of the switches onto the separate chip on the daughter board, the number of printed circuit board routing leads and connector pins was reduced to about 10 (i.e., for differential temperature compensation, flow sensor, switch clock, logic, power and ground). The FET switches, shift registers and control logic located on a separate IC may be connected to the phased heater array structure chip via wire-bonds or solder-bumps. With the new logic of the FETs, a user of sensor system  15  may select the fraction of total heatable elements for operating as preconcentrators versus separators.  
         [0076]    [0076]FIG. 16 is a schematic of an illustrative example 402 of control logic for sensor system  11 . Circuit  410  may be an instance of a logic cell in an array. It may contain D flip-flops  403 , R-S flip-flops  404 , AND gates  405  and  415 , OR gates  406 , FETs  407  and an inverter  408 , plus additional circuitry as needed. A clock line  411  may be connected to a clock input of D flip-flop  403 . A separator enable line  413  may be connected to a first input of AND gate  405 . A data-in line  412  may be connected to a D input of flip-flop  403 . A reset line  414  may be connected to an S input of flip-flop  404  and a reset input of flip-flop  403 . A Q output of flip-flop  404  may be connected to a second input of AND gate  405 . A Q output of flip-flop  403  may be connected to an R input of flip-flop  404  and to a first input of AND gate  415 . Separator enable line  413  may be connected to an input of inverter  408 . An output of inverter  408  may be connected to a second input of AND gate  415 . Outputs of AND gates  415  and  405  may be connected to first and second inputs, respectively, of OR gate  406 . An output of OR gate  406  may be connected to a gate of FET  407 . The other terminals of FET  407  may be connected to a FET common line  416  and a FET output terminal  417 , respectfully. The far right logic cell may have a Q output of flip-flop  403  connected to a data out line  418 .  
         [0077]    This logic may allow the user to pre-select the number of pre-concentrator elements that the circuit will pulse and heat up, before pausing and then ramping up the temperature on all of the remaining heater elements, which then may function as part of the segmented separator. There is an additional dimension of flexibility which may allow for the depositing of different materials on any of the phased heater array sensor elements of chip  401  chip via suitable masking, so that preferential preconcentration, filtering of interference and cascaded separation may be enabled.  
         [0078]    [0078]FIG. 16 further illustrates how up to 50 FET switches may be controlled by on-chip logic, each having an on resistance at or below 0.5 ohms and be able to switch about 12 volt potentials. The on-chip logic may operate in two modes, that is, the concentrator or 1 st  mode and the separator or 2 nd  mode, the respective mode being determined by a control line bit. The 1 st  mode may involve a shift register which, after a reset, sequentially turns on a low resistance FET, and disables a flip-flop associated with that same FET. At the next clock cycle, the first FET turns off, and the next FET turns on and its associated flip-flop is disabled. This sequence may be repeated until some external drive electronics turns off the clock and enables the 2 nd  operating mode. Once the second mode is enabled, all of the FETs where the flip-flop has not been disabled may turn on simultaneously. This 2 nd  mode may stay on until the reset has been triggered and the flip-flops are reset, the FETs are turned off and the process can be repeated.  
         [0079]    Two chips may be used in series to bond to the (up to 50) the phased heater array sensor chip pads on each of its sides, such that the sequential switching will go from the first chip to the second chip. It may be necessary for the signal from the last switch on the first chip to trigger the first switch on the second chip. It is possible that the mode switch from sequential addressing of the remaining FETs in parallel may happen sometime before or after the switching has moved to the second chip.  
         [0080]    One may introduce adsorber coating diversity into the phased heater array sensor heater elements, such as by alternating individual elements or groups of elements in either or both preconcentrator or the separator, with more than one adsorber material, and adjusting the logic program for the switches as in FIG. 16 or to favor (in terms of maximum applied voltage or temperature) certain types of coatings in the preconcentrator and equally or differently in the separator, to achieve the desired analyte preconcentrating, analyte filtering and analysis results which may be the analysis of selected group preconcentrator pulses or cascaded (in time) preconcentrator analyte pulses.  
         [0081]    The user may be enabled with great flexibility to adjust the phased heater array sensor operation and performance to the varying needs imposed by the analysis problem: He can select the number or fraction of total heater array elements to function as pre-concentrators vs. separators, thus varying the concentration of the analyte relative to the separation, i.e., resolution and selectivity of the analyte components, while retaining the ability to design and fabricate low-power, optimally temperature-controlled heater elements, that feature structural integrity, optimal focusing features, analyte selectivity/filtering, and smart integration of preconcentration, separation, flow control and detection technology, such as TC and micro-plasma-discharge sensors. One may integrate the CMOS drive electronics with the phased heater array sensor flow-channel chip.  
         [0082]    Although the invention has been described with respect to at least one illustrative embodiment, many variations and modifications will become apparent to those skilled in the art upon reading the present specification. It is therefore the intention that the appended claims be interpreted as broadly as possible in view of the prior art to include all such variations and modifications.