BACKGROUND OF THE INVENTION

1 . Field of the Invention

[0001] The present invention is directed to radon detectors, and more particularly to a printed film based electrostatic concentrator for radon detection using an electronic sensor.

2. Description of the Related Art

[0002] Radon is a naturally occurring clear, colourless, odorless, tasteless, radioactive noble gas that is produced during the radioactive decay sequence of uranium ( ²³⁸ U). Alpha particles emitted during radon or progeny decay can be very damaging to living tissue. Radon decay products tend to be charged, which results in the progeny (polonium-218) attaching readily to dust, thereby increasing the likelihood of inhalation. If inhaled, radon and radon progeny pose a significant risk to lung tissue, and long-term exposure may lead to lung cancer. Radon exposure is the second leading cause of lung cancer, second only to smoking. Consequently, there exists a need for a cost-effective radon monitor that can be widely deployed.

[0003] A variety of radon detectors exist on the market, most of which detect radon indirectly by sensing radioactive decay. The most common and inexpensive detectors are track-etch detectors, which are typically limited to one-time use for measuring a long-term average radon concentration. Track-etch detectors require specialized equipment for readout in a laboratory setting.

[0004] Another class of radon detector is of the“direct reading” variety, which operate continuously and report the results directly to the user. These direct systems operate by concentrating radon, and/or radon progeny, onto/near a sensor for detecting radioactive decay. Concentration can be achieved in one of two ways:“active concentration” uses calibrated fans to move a known volume of air through a filter, from the surface of which radioactive decay is detected, or“passive concentration” which uses electrostatic fields to concentrate charged radon progeny directly onto a sensor. In general, systems employing active concentration are fast, require calibration, consume significant power, and are expensive. Systems employing passive concentration are slower, require little to no maintenance, require less power to operate, and are more affordable than systems using active concentration.

[0005] One prior art electrostatic concentrator for radon detection is built from a polyethylene cone having a conductive inside surface and separated into two sections to create a strong electrostatic field inside the cone (see R. H. Griffin, H. Le, D. T. Jack, A. Kochermin, and N. G. Tarr,“Radon monitor using custom alpha-detecting MOS 1C,” in Sensors, 2008 IEEE , Oct 2008, pp. 906-909).

[0006] Passive electrostatic radon detectors are well suited to consumers due to their ease of use, direct reporting, and low-cost relative to“active” detectors. Nonetheless, even lower cost passive direct reading radon detectors are not inexpensive and are of limited functionality, which has led to limited public acceptance.

SUMMARY OF THE INVENTION

[0007] It is an aspect of the present invention to provide an electrostatic concentrator for radon detection that overcomes at least some of the disadvantages of prior art electrostatic

concentrators.

[0008] In one aspect, an electrostatic concentrator is set forth for use in radon detection, comprising a plastic sheet having conductive electrodes patterned onto the surface. The sheet is patterned and cut in such a way that it can be assembled into a three-dimensional shape (e.g. a cone), such that when a voltage is applied to the electrodes an electrostatic field is created for propelling radon progeny towards a sensor on which it can be detected.

[0009] According to another aspect, low-cost printed electronics are used to replace polyethylene cones, conductive coatings and metal structures of prior art electrostatic concentrators. The use of printers allows electrodes to be printed using inexpensive conductive carbon inks on thin substrates, such as plastic sheets/films, for easy assembly by a

manufacturer or end user. This also reduces manufacturing costs by minimizing the materials required and leverages the enormous speed and throughput of printing. Minimizing weight also lessens transport and shipping costs, particularly having regard to the potential for shipping and distributing flat packed consumer radon detectors that can be assembled by the end user.

[0010] The above aspects can be attained by an electrostatic concentrator for use in radon detection by a sensor, comprising: a flexible substrate formable into a shape and having at least one opening for air to enter; a shape retaining mechanism for retaining the shape of the flexible substrate when formed into said shape; and a conductive pattern on said flexible substrate forming at least one electrode, such that when the flexible substrate is positioned close to the sensor and voltage is applied to the electrode an electrostatic field is created for propelling radon progeny toward the sensor. [0011] Another aspect can be attained by a method of manufacturing an electrostatic concentrator for use in radon detection, comprising: printing at least one electrode on a flexible substrate; cutting the flexible substrate to form a blank; and assembling the blank to form a dome portion and a cone portion.

[0012] A further aspect can be attained by a method of manufacturing a blank for assembly into an electrostatic concentrator for use in radon detection, comprising: printing top and bottom electrodes on a flexible substrate; and cutting said flexible substrate to form a shape having at least one opening and a plurality of tabs and slots.

[0013] These together with other aspects and advantages which will be subsequently apparent, reside in the details of construction and operation as more fully hereinafter described and claimed, reference being had to the accompanying drawings forming a part hereof, wherein like numerals refer to like parts throughout.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 is a perspective view of an exemplary passive direct reading radon detector incorporating an electrostatic concentrator according to an embodiment of the invention;

[0015] Figure 2A is a schematic representation of a cross section through the electrostatic concentrator depicted in Figure 1 ;

[0016] Figure 2B is a schematic representation of an electric field distribution within the electrostatic concentrator of Figure 2A;

[0017] Figure 3 is a schematic diagram of a charge pump for creating an electrostatic field within the electrostatic concentrator depicted in Figures 1 and 2A;

[0018] Figure 4 is a flowchart of a method for manufacturing the electrostatic concentrator depicted in Figures 1 and 2A;

[0019] Figure 5 is an illustration of a sheet of plastic on which a pattern of conductive ink is printed, according to an embodiment of the invention;

[0020] Figure 6 shows a pattern for cutting the plastic sheet of Figure 5;

[0021] Figure 7 shows the electrostatic concentrator of Figures 1 and 2A in an unassembled state following cutting of the sheet of plastic of Figure 5 according to the pattern of Figure 6; and

[0022] Figure 8 shows the electrostatic concentrator of Figures 1 and 2A assembled according to the method of Figure 4.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] With reference to Figure 1 , a passive concentrator based direct reading radon detector 100 is shown comprising an electrostatic concentrator 110 positioned over a sensor such as an alpha particle-detecting integrated circuit (IC) 120. The concentrator 110 and IC 120 are enclosed within a cylindrical protective housing 130 having apertures 140 for receiving ambient air. A microcontroller (not shown) drives the IC 120 and transmits data, as is known in the art.

[0024] As discussed above, passive direct reading radon detectors such as detector 100 measure radon levels by detecting radioactive decay, such as alpha particles emitted during the decay of radon or its progeny. However, since alpha particles travel at most a few centimeters in air, radon or its progeny must be brought close to the alpha-detecting IC 120. Therefore, electrostatic concentrator 110 is used to concentrate charged radon progeny, polonium-218, onto the surface of the IC 120. As discussed in greater detail below, electrostatic concentrator 1 10 is preferably fabricated from a thin flexible substrate, such as a plastic sheet, onto which at least one electrode is printed using conductive material such as carbon ink. Alternatively, other conductive material may be used, such as silver, conductive polymers or conductive paint. The flexible substrate is cut to form a top dome portion and bottom body portion, as described in greater detail below, and a shape retaining mechanism is provided for retaining the shape of the electrostatic concentrator 1 10 upon assembly. In one embodiment the shape retaining mechanism comprises tabs and slots and/or adhesives. The flexible substrate is cut via at least one of a mechanical (e.g. die cut), optical (e.g. laser cut), thermal, or water based cutting method.

[0025] Figure 2A is a schematic representation of a cross section through the electrostatic concentrator 1 10 of Figure 1 . When assembled, the electrostatic concentrator 1 10 forms a body portion 200 and a dome portion 210. One or both of the body portion 200 and dome portion 210 may include one or more openings (not shown) for air to enter the concentrator. Top and bottom electrodes 220 and 230 are fabricated from conductive carbon ink (or other suitable conductor) that separates the electrostatic concentrator 1 10 into two sections to create a strong sweep field inside the body portion, such that when voltage is applied an electrostatic field is created for propelling radon progeny toward opening 240, as shown in Figure 2B. Although the exemplary concentrator comprises a hemi-sphere (dome) and a body portion, other shapes are

contemplated. For example, the body portion may be conical or in the shape of a funnel (as illustrated) or may be cylindrical. Also, the body portion may be dispensed with entirely, leaving only the dome portion or a box shape with the 1C 120 positioned at the bottom thereof. An opening 240 is provided at the bottom of the electrostatic concentrator 1 10 for deposition of the progeny across the IC 120. In one embodiment, IC 120 may be disposed inside the

concentrator 1 10. A potentials of 2500 V and 2120 V are applied to the top and bottom electrodes, respectively, for electrostatically concentrating the radon progeny onto the surface of IC 120, which is held at ground potential.

[0026] The 2500 V and 2120 V potentials may be generated by a Cockcroft- Walton charge pump 300, such as shown in Figure 3, which utilizes a series of capacitors and diodes to convert a 5 V peak-to-peak square wave from a timer 310 into the 2500 V DC voltage connected to the top electrode 220 at connection 340 and the 2120 V DC voltage connected to the bottom electrode 230 at connection 320. Although the exemplary embodiment uses voltage values of 2500 V and 2120 V and the IC 120 at ground potential, other values may be used. Also, in one embodiment a transformer may be used to achieve the first step-up in voltage.

[0027] According to another aspect of the invention, the electrostatic concentrator of Figures 1 and 2A may be manufactured according to the exemplary method shown in Figure 4. At step 400, a conductive pattern 500, preferably formed of ink, is printed on to the flexible substrate which, according to an exemplary embodiment is a sheet of plastic 510, as shown in Figure 5. Plastic sheet 510 can, for example, be manufactured from polyethylene terephthalate, polyimide, polypropylene, etc. Next, at step 410, the sheet 510 is cut (e.g. laser cut, die cut, etc.) according to the pattern 600 shown in Figure 6, to create a blank 700 having a disc shaped portion (assembled to form a dome) connected to an arcuate portion (assembled to form a cone), both of which include a plurality of tabs 710 and slots 720, as shown in Figure 7, although, as discussed above the plurality of tabs 710 and slots 720 may in some embodiments be replaced by or supplemented by adhesives or other shape retaining mechanism (e.g. a limited number of tabs/slots may be incorporated for initial assembly in order to hold the desired shape of the electrostatic concentrator while adhesive cures are applied).

[0028] The blank 700 is then assembled, at step 420, in the style of origami, to form the final assembled electrostatic concentrator 1 10, as shown in Figure 8 (i.e. the blank 700 is formable into the shape of the electrostatic concentrator 1 10). Specifically, tabs 710 circumscribing the dome portion of the blank 700 are inserted in corresponding slots 720 circumscribing the top of the cone portion 200 of the blank. Likewise, tabs 710 along the edges of the cone portion 200 of the blank are inserted in corresponding slots extending radially across the cone portion. Radial slots 720 in the disc shaped dome portion allow the printed plastic to fold radially during assembly so as to create the domed top 210 while also creating openings 800 for the ingress of air, as shown in Figure 8. Additional tabs extend from the top and bottom electrodes for connection to the charge pump 300, at 320 and 340.

[0029] The present invention has been described with respect to the exemplary embodiment shown in the Figures. However, a person of ordinary skill in the art may conceive of alternatives and variations. For example, it is contemplated that the natural rebound of the plastic may be used to form the concentrator once the flat system is unpacked (e.g. the dome can be flattened for delivery and then rebound to the domed shape once the concentrator is unpacked). Also, whereas the embodiment described above incorporates top and bottom electrodes, it is contemplated that a single or more than two electrodes may be utilized as an alternative. For the single electrode embodiment, it is contemplated that the electrode can be printed on one of either the body portion 200 and a dome portion 210, with a bottom electrode disposed on a printed circuit board (PCB) to which IC 120 is mounted. In other embodiments, whether single electrode or multi-electrode, the IC 120 can function as an electrode.

[0030] The many features and advantages of the invention are apparent from the detailed specification and, thus, it is intended by the appended claims to cover all such features and advantages of the invention that fall within the true spirit and scope of the invention. Further, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation illustrated and described, and accordingly all suitable modifications and equivalents may be resorted to, falling within the scope of the invention.