Abstract:
One embodiment of the present invention provides a system for ionizing airborne particulates. The system includes an insulating substrate and a first electroplated structure on the insulating substrate. This first electroplated structure includes an anchor and a probe structure on the anchor that is separate from the insulating substrate. A second electroplated structure is included on the insulating substrate. The first electroplated structure and the second electroplated structure form a unipolar corona discharge based ionizer

Description:
RELATED APPLICATION 
     This application hereby claims priority under 35 U.S.C. §119 to U.S. Provisional Patent Application No. 60/536,935, filed on 16 Jan. 2004, entitled “A Microfabricated Ionizer structure Based on Unipolar Corona Discharge,” by inventors Beelee Chua, Norman C. Tien, Anthony S. Wexler, and Debbie A. Niemeier, which is incorporated herein by reference. 
    
    
     BACKGROUND 
     1. Field of the Invention 
     The present invention relates to an airborne particulate analyzer. More specifically, the present invention relates to a microfabricated device for selectively removing and analyzing airborne particulates from an air stream. 
     2. Related Art 
     A number of techniques are presently used to separate airborne particulate matter from an air stream in order to determine the size and possibly type and quantity of particulates in the air stream, and to filter the air stream. These particulates can include environmental pollution and pathogens, such as bacteria and viruses. 
     Current approaches to separating airborne particulate matter involve using large devices, some of which require a radio-active ionization source. This is particularly true for devices used for separating particulates smaller than 100 nm in size. These devices typically grow particulates to an optimal size after separation to facilitate optical counting. Handheld devices do not exist that are capable of separating and counting particulates smaller than 100 nm. Detection of particulates smaller than 100 nm is advantageous because it includes airborne pathogens such as viruses. 
     The techniques used to detect particulates optically are limited to discrete size bins. These devices are only capable of detecting specific size particulates (i.e. 100 nm, 300 nm, 500 nm, etc). They cannot, however, be re-configured to give values for 150 nm, 180 nm, etc. This is because a specific wavelength that is equivalent to the particulate size is required for their detection. In order to count all particulates, a laser source or array of laser sources to give a continuous wavelength spectrum is required. This is prohibitively expensive. 
     Current portable devices are not able to determine the composition of the particulates, and hence provide little benefit in detecting chemical and/or biological agents. On the other hand, devices which are able to detect these chemical and biological agents are typically laboratory devices, which are unsuitable for field work. 
     The size of current particulate analyzers that are able to detect particulates smaller than 100 nm precludes using them in portable devices, and the substantial price of these particulate analyzers makes ubiquitous positioning within an urban area prohibitively expensive. 
     Hence, what is needed is a portable apparatus, which can effectively size and count particulates smaller than 100 nm in an air stream without the drawbacks cited above. Determining the actual size of the particulates is advantageous because it can possibly lead to determining the source of the particulates. 
     SUMMARY 
     One embodiment of the present invention provides a system for ionizing airborne particulates. The system includes an insulating substrate with a first electroplated structure which resides on the insulating substrate. This first electroplated structure includes an anchor with a probe structure that is separate from the insulating substrate. A second electroplated structure also resides on the insulating substrate. The first electroplated structure and the second electroplated structure are configured to collectively form a unipolar corona discharge based ionizer. 
     In a variation of this embodiment, the second electroplated structure forms a collection grid. 
     In a further variation, the second electroplated structure is comprised of parallel structures, wherein the probe structure is centered between the parallel structures, so that an electrical field formed between the probe structure and the parallel structures is perpendicular to the air flow through the apparatus. 
     In a further variation, the system additionally includes differential mobility separator plates, which are configured to allow selected particles to be passed to a Faraday&#39;s cup for counting. 
     In a further variation, the system includes differential mobility separator plates, which are configured to collect selected particles for counting. 
     In a further variation, the system includes segmented differential mobility separator plates, wherein each segment of the segmented differential mobility separator plates collects a different mobility particle for counting. 
     In a further variation, the system includes differential mobility separator plates, which are configured to separate particulate matter from an air flow, whereby the apparatus forms a filter mechanism. 
     In a further variation, the probe structure is isolated from the main air flow through the apparatus, thereby providing ozone to the main air flow. 
     In a further variation, the apparatus is configured so that the main air flow (including ozone) is bubbled through water, wherein the ozone kills nano-organisms such as bacteria and viruses in the water. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGS. 
         FIG. 1A  presents a top view of a microfabricated corona ionizer in accordance with an embodiment of the present invention. 
         FIG. 1B  presents a side view of a microfabricated corona ionizer in accordance with an embodiment of the present invention. 
         FIG. 1C  presents an orthogonal view of a microfabricated corona ionizer in accordance with an embodiment of the present invention. 
         FIG. 2  illustrates a microfabricated corona ionizer with parallel plates in accordance with an embodiment of the present invention. 
         FIG. 3  illustrates a particulate sensor in accordance with an embodiment of the present invention. 
         FIG. 4  illustrates a segmented particulate sensor in accordance with an embodiment of the present invention. 
         FIG. 5  illustrates a filter mechanism in accordance with an embodiment of the present invention. 
         FIG. 6  illustrates using a filter mechanism in conjunction with a segmented particulate sensor in accordance with an embodiment of the present invention. 
         FIG. 7  illustrates an ozone generator in accordance with an embodiment of the present invention. 
         FIG. 8  illustrates the process of diffusing ozone into an air flow in accordance with an embodiment of the present invention. 
         FIG. 9  illustrates an alternate method of diffusing ozone into an air flow in accordance with an embodiment of the present invention. 
         FIG. 10  illustrates purifying water in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     The following description is presented to enable any person skilled in the art to make and use the invention, and is provided in the context of a particular application and its requirements. Various modifications to the disclosed embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be applied to other embodiments and applications without departing from the spirit and scope of the present invention. Thus, the present invention is not intended to be limited to the embodiments shown, but is to be accorded the widest scope consistent with the principles and features disclosed herein. 
     Corona Ionizer 
       FIG. 1A  presents a top view of a microfabricated corona ionizer in accordance with an embodiment of the present invention. The components of the microfabricated corona ionizer are deposited on an insulating substrate  102 . One possible material for insulating substrate  102  is glass. Anchors  104  and  110  (see  FIG. 1C ) are deposited on substrate  102 . A typical material for anchors  104  and  110  is copper. 
     Probe  106  is deposited with anchor  104  but is undercut so that it is suspended above substrate  102 . The radius of the tip of probe  106  is less than approximately 20 μm, while the suspension height of probe  106  above substrate  102  is typically less than 500 μm. Collection grid  108  extends from anchor  110  and is typically spaced less than 3 mm from the tip of probe  106 . 
     During operation, a voltage is applied between probe  106  and collection grid  108 . This voltage is typically in the range of two kilovolts. In this configuration, the ionizer uses less than 150 milliwatts and has a footprint of approximately 1 centimeter square. The ionizer is able to charge more than 6 million nanoparticulates per second per device. Note that the inception voltage is dependent only upon the inter-electrode spacing and is independent of the radius of curvature of the tip of probe  106 . 
       FIG. 1B  presents a side view of a microfabricated corona ionizer in accordance with an embodiment of the present invention. The view presented in  FIG. 1B  clearly shows how probe  106  is suspended above substrate  102  and the relationship between probe  106  and collection grid  108 . 
       FIG. 1C  presents an orthogonal view of a microfabricated corona ionizer in accordance with an embodiment of the present invention. This view is presented to further clarify the relationships among the components of the microfabricated corona ionizer. 
     Corona Ionizer with Parallel Plates 
       FIG. 2  presents a microfabricated corona ionizer with parallel plates in accordance with an embodiment of the present invention. Anchor  202  and probe  204  are deposited on a substrate (not shown) using techniques similar to those described above for anchor  104  and probe  106 . Grids  206  and supporting anchors are deposited on the substrate such that they are parallel to probe  204  and equidistant from probe  204 . In this configuration, the corona ionizer forms a flow-through ionizer, which is useful for creating microfabricated particulate sensors. 
     Basic Particulate Sensor 
       FIG. 3  illustrates a particulate sensor in accordance with an embodiment of the present invention. Anchor  302 , probe  304 , and grids  306  form a corona ionizer as described above with reference to  FIG. 2 . Differential mobility separator plates  308  and  310  are deposited on the substrate such that airflow passing the ionizer is directed between mobility separator plates  308  and  310 . When a potential difference is applied between mobility separator  308  and  310 , an electric filed is created between them. 
     When charged particulates enter the space between mobility separator plates  308  and  310 , they are deflected by the electric field. The amount of deflection is dependent upon the mobility of the particulates and the strength of the applied field. By varying the voltage applied to mobility separator plates  308  and  310 , particulates of different mobility can be made to impinge on the Faraday&#39;s cup  314 . The current generated by this impingement can be measured to determine the concentration of particulates with a given mobility. Note that particulates of different mobility can also be made to impinge on mobility separator plate  310  and the resultant current can be measured to determine the concentration of particulates with a given mobility. 
     Segmented Particulate Sensor 
       FIG. 4  illustrates a segmented particulate sensor in accordance with an embodiment of the present invention. Ionizer  402  is deposited on the substrate as described above in reference to  FIG. 2 . Each segment of segmented mobility separator plate  406  can be biased to a different voltage. In this configuration, particulates with multiple mobilities can be measured simultaneously. Sheath air  404  is a source of clean air. Note that sheath air  404  can be a clean gas other than air, such as clean nitrogen. 
     Filter Mechanism 
       FIG. 5  illustrates a filter mechanism  502  in accordance with an embodiment of the present invention. Filter mechanism  502  is constructed as described above in conjunction with  FIG. 3  with the addition of flow divider  504 . Flow divider  504  channels filtered air out of portal  506 , while particulates are channeled out of portal  508 . By applying a proper bias to separator electrodes  510 , the ionized particulates are channeled to portal  508 . 
     Combined Filter and Segmented Particulate Sensor 
       FIG. 6  illustrates using a filter mechanism in conjunction with a segmented particulate sensor in accordance with an embodiment of the present invention. Ionizer  604  filters its input air rejecting particulates  606 , thus providing clean air  608  as the sheath air. Ionizer  602  ionizes particulates in the incoming sample. These ionized particulates  512  are selected for measurement by segmented mobility separator plate  610  as described above in conjunction with  FIG. 4 . 
     Ozone Generator 
       FIG. 7  illustrates an ozone generator  700  in accordance with an embodiment of the present invention. Ozone generator  700  includes a high voltage tip  702 , a grounded metal plate  704 , and insulator plate  706 , and an insulator grid  708 . High voltage tip  702  and grounded metal plate  704  form a microfabricated corona discharge ionizer which creates ozone during operation. The ozone diffuses through the insulator grid  708  into the surrounding air. 
     Ozone Diffusing Unit 
       FIG. 8  illustrates diffusing ozone into an air flow in accordance with an embodiment of the present invention. As illustrated in  FIG. 8 , ozone generator  700  is embedded in a pipe or tubing which directs airflow  802  past ozone generator  700 . Ozone  804  diffuses out of ozone generator  700  into airflow  802 . Ozone  802  can kill pathogens such as bacteria and viruses within airflow  802 . 
     Alternate Ozone Diffusing Unit 
       FIG. 9  illustrates an alternate method of diffusing ozone into an air flow in accordance with an embodiment of the present invention. In the configuration illustrated in  FIG. 9 , the ozone generator includes two high-voltage tips  902 , one high voltage tip facing grounded metal plate  902  and one high voltage tip facing grounded metal plate  904 . Ozone  910  diffuses into airflow  908  in the same manner described above in conjunction with  FIG. 8 . 
     Purifying Water 
       FIG. 10  illustrates purifying water in accordance with an embodiment of the present invention. Pump  1002  pumps air through ozone generator  1004  and into water container  1006 . The air with the infused ozone bubbles through water  1008  in water container  1006  killing nano-organisms, such as bacteria and viruses. 
     The foregoing descriptions of embodiments of the present invention have been presented for purposes of illustration and description only. They are not intended to be exhaustive or to limit the present invention to the forms disclosed. Accordingly, many modifications and variations will be apparent to practitioners skilled in the art. Additionally, the above disclosure is not intended to limit the present invention. The scope of the present invention is defined by the appended claims.