WO2023182977A1

WO2023182977A1 - Radiation dose rate detectors

Info

Publication number: WO2023182977A1
Application number: PCT/US2022/021282
Authority: WO
Inventors: Arun Virupaksha Gowda; Sergei Ivanovich Dolinsky; Cheng-Po Chen; Adrian Ivan; Liang YIN; Biju Jacob
Original assignee: General Electric Company
Priority date: 2022-03-22
Filing date: 2022-03-22
Publication date: 2023-09-28

Abstract

A sensor includes a casing. The sensor also includes an ionization chamber encapsulated within the casing and configured to measure radiation. The sensor further includes readout circuitry configured to be periodically connected to the ionization chamber to measure a radiation dose in an electrometer mode.

Description

RADIATION DOSE RATE DETECTORS

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH & DEVELOPMENT

[0001] This invention was made with Government support under contract number HDTRA121C0016 awarded by the United States Defense Threat Reduction Agency (DTRA). The Government has certain rights in the invention.

BACKGROUND

[0002] The subject matter disclosed herein relates to radiation sensors.

[0003] For several decades, commercial direct reading dosimeters (electroscopes) have been successfully used for monitoring personnel working at reactors and other sites with significant radiation fields. This type of dosimeter, which is based on a carbon-fiber electrode in an ion chamber, is still in use due to its simple operation, ability to provide direct readout to a user, compactness, and reusability. A line of commercially available direct reading dosimeters, with different exposure ranges from 200 mR up to 100 R (Roentgens), are widely available. Disadvantages of direct reading dosimeters are sensitivity of the fiber-electrode to mechanical shock and the only way to readout is by visually looking into the scope.

[0004] To address the disadvantages of direct reading dosimeters, several new designs of electronic alarming dosimeters (EAD) using silicon diode technology have begun to replace the direct reading dosimeters in some application spaces. Some EADs may measure dose rates from 0.1 mR/hr to 100 R/hr. However, these dosimeters are not designed for long term field operation without user intervention, nor for deployment from vehicles and lack wireless communication. BRIEF DESCRIPTION

[0005] Certain embodiments commensurate in scope with the originally claimed subject matter are summarized below. These embodiments are not intended to limit the scope of the claimed subject matter, but rather these embodiments are intended only to provide a brief summary of possible embodiments. Indeed, the invention may encompass a variety of forms that may be similar to or different from the embodiments set forth below.

[0006] In one embodiment, a sensor is provided. The sensor includes a casing. The sensor also includes an ionization chamber encapsulated within the casing and configured to measure radiation. The sensor further includes readout circuitry' configured to be periodically connected to the ionization chamber to measure a radiation dose in an electrometer mode.

[0007] In another embodiment, a radiation monitoring system is provided. The system includes a plurality of sensors configured to be deployed from a vehicle in an area and to monitor radiation. Each sensor includes a casing. Each sensor also includes an ionization chamber encapsulated within the casing and configured to measure radiation. Each sensor further includes readout circuitry configured to be periodically connected to the ionization chamber to measure a radiation dose in an electrometer mode.

[0008] In a further embodiment, a sensor is provided. The sensor includes a casing shaped as molded sphere and including multiple layers configured to absorb and dissipate impact energy through their deformation and damage. The sensor also includes an ionization chamber encapsulated within the casing and configured to measure radiation. The sensor further includes readout circuitry coupled to the ionization chamber within the casing, wherein the readout circuitry is configured to operate at low' pow'er in an electrometer mode to readout a radiation measurement from the ionization chamber. The sensor even further includes an isolation switch coupling the ionization chamber to the readout circuitry. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] These and other features, aspects, and advantages of the present subject mater will become beter understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:

[0010] FIG. 1 is a partial cut-away view of a radiation sensor node (e.g., having a spherical shape), in accordance with aspects of the present disclosure;

[0011] FIG. 2 is a perspective view of a radiation sensor node in FIG. 1;

[0012] FIG, 3 is a cross-sectional view of an ionization chamber of an air-deployable passive radiation sensor node, in accordance with aspects of the present disclosure;

[0013] FIG, 4 is a cross-sectional view of an ionization chamber of a radiation sensor node (e.g., having a taller side wall), in accordance with aspects of the present disclosure;

[0014] FIG. 5 is a partial cut-away view of a radiation sensor node (e.g., having a cylindrical shape), in accordance with aspects of the present disclosure;

[0015] FIG. 6 is a block diagram of functional components disposed within a radiation sensor node, in accordance with aspects of the present disclosure;

[0016] FIG. 7 is a schematic diagram of a readout circuit or sensing circuit coupled to an ionization chamber of a radiation sensor node, in accordance with aspects of the present disclosure;

[0017] FIG. 8 are graphs illustrating a measured waveform matches a simulated waveform, in accordance with aspects of the present disclosure;

[001S] FIG. 9 is a flow chart of a method for detecting and broadcasting utilizing a radiation sensor node, in accordance with aspects of the present disclosure; [0019] FIG. 10 is a schematic diagram of a radiation sensor node self-orienting itself, in accordance with aspects of the present disclosure; and

[0020] FIG. 11 is a schematic diagram of a core of a radiation sensor node, in accordance with aspects of the present disclosure.

DETAILED DESCRIPTION

[0021] One or more specific embodiments will be described below'. In an effort to provide a concise description of these embodiments, not all features of an actual implementation are described in the specification. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions must be made to achieve the developers’ specific goals, such as compliance with system-related and business-related constraints, which may vary from one implementation to another. Moreover, it should be appreciated that such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure.

[0022] When introducing elements of various embodiments of the present subject matter, the articles “a,” “an,” “the,” and “said” are intended to mean that there are one or more of the elements. The terms “comprising,” “including,” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements. Furthermore, any numerical examples in the following discussion are intended to be nonlimiting, and thus additional numerical values, ranges, and percentages are within the scope of the disclosed embodiments.

[0023] The present disclosure provides systems and methods for long term monitoring of radiation in the field. In particular, disclosed embodiments include a passive radiation sensor node that is configured to be deployed by ground or air into the field as part of a radiation detection system that includes a plurality of the passive radiation sensor nodes (e.g., 1000s radiation sensor nodes). Each passive radiation sensor node includes deployment flexibility (e.g., by air or ground vehicle), an unattended field life of greater than a year, a communication range of greater than one kilometer, and can be manufactured at a low cost. Each passive radiation sensor nodes includes a low’ leakage ionization chamber (with leakage in the order of femtoamperes (fA), preferably significantly less than the ionization current) and low' power electronics (e.g., including readout circuitry) disposed within a casing or packaging configured to provide ingress protection and drop survivability. The disclosed embodiments provide small, low-cost sensors that are disposable and that can be utilized over a long period in the field (e.g., under varying conditions).

[0024] FIG. 1 is a partial cut-away view of a sensor node (e.g., passive radiation sensor node) 10 (e.g., having a spherical shape). As depicted in FIG. 1 (and FIG. 2), the sensor node 10 has a spherical shape. The sensor node 10 may have a compact size ranging from approximately 200 to 1,000 cm³. The overall mass of the sensor node 10 may range from approximately 200 to 500 grams (g). The sensor node 10 may have a diameter ranging from approximately 100 to 2.00 mm.

[0025] The sensor node 10 includes sensor components and associated electronics fully encapsulated within a protective casing or packaging 12. The protective casing 12 may be made of low moisture permeability’ organic materials and coatings to provide ingress protection against dust and water damage. Although not required, in the illustrated embodiment, the protective casing 12 is a double layer casing including a first layer 14 and a second layer 16. In certain embodiments, the layers 14, 16 may be made of different materials. The first layer 14 (e.g., a pre-molded inner shell) is disposed about (e.g., encapsulating) the sensor components and associated electronics to secure them from shock and vibration. The first layer 14 may be molded using a low-pressure polyamide. The first layer 14 may be disposed about a conforming layer (not shown) disposed about the sensor components and associated electronics for moisture protection and surface insulation resistance. For example, conformal coating of the sensor components (e.g., ionization chamber) may consist of poly(p-xylene) polymer to provide moisture and dielectric barrier properties. Conformal coating of a printed circuit board (PCB) assembly may include acrylic, urethane, or epoxy materials for additional protection and surface insulation and protection. The second layer 16 is a pre-molded 360 degree outer shell disposed about (e.g., encapsulating) the first layer 14. The second layer 16 is configured to provide impact absorbing properties (i.e., drop shock survivability) and environmental protection for at least one year of operation life. The second layer 16 may be molded using epoxy or viscoelastic polymers or other moldable materials.

[0026] An outer surface 18 of the second layer 16 may include a plurality of surface features 20 (e.g., protrusions or knobs) extending away (e.g., outward) from the second layer 16. The surface features 20 are configured for shock or impact energy absorption. The surface features 20 and layers 14, 16 are configured to absorb and dissipate impact energy through their deformation and damage. In particular, surface features 20 act as crumple (sacrificial) structures for consumption of the drop shock energy. The crumple zone increases the stopping distance and reduces the stress transferred to the enclosed components. In addition, the surface features 20 increase drag and act as grippers to enable the sensor node 10 to remain in its deployed location. The sensor node 10 may thus be configured to survive drops from an air vehicle from tens of meters in the air. The sensor node 10 may also be configured to survive drops from a ground vehicle moving up to 50 km/hr.

[0027] The sensor nodes 10 require minimal power for operation and thus may be configured to be operational for more than one year in the field after being deployed. Locations of deployment could range from hot to severe cold climatic conditions. The sensor nodes are configured to operate in hot, basic, and cold climates, which would subject them to induced temperature extremes of -46 °C to 49 °C and relative humidity tending towards 100 percent. In addition to these climatic conditions, the sensor nodes 10 may experience stresses during transportation and storage and mission/sortie use. The sensor nodes 10 may experience thermal shock, high and low' temperatures, sand/dust, rain/hail, solar radiation, fungus growth, random vibration, salt fog, and other conditions. In certain embodiments, additional coating layers may be added to provide water ingress protection.

[0028] The sensor node 10 may form a sensing system with a plurality of sensor nodes 10. The sensor nodes 10 may be deployed in the 1000s in an area from air or ground vehicles. The sensors nodes 10 are configured to survive a drop impact when deployed. The sensor nodes 10 having a spherical shape as in FIG. 1 and the dimensions noted above has a terminal velocity of approximately 30 m/s. In a drop event, the ground combined with the protective casing 12 act together as a cushion to the electronic assembly inside of the spherical sensor node 10. Less electronic assembly deformation/stress and longer impact duration is expected for a soft ground (e.g., grass or sand). On the other hand, for a harder ground such as rock, more casing deformation occurs. Similarly, less electronic assembly stress and longer impact duration are expected for a soft or energy absorbing enclosure as depicted in FIG. 1.

[0029] The sensor node 10 includes internally includes an ionization chamber 22, readout and communication electronics 24, an on-board battery 26, and an antenna 28 (e.g., long range antenna for communication of greater than 1 km). The ionization chamber 22 is configured to sense radiation. The ionization chamber 22 is a gas-filled detector (e.g., air). Normal operation of the ionization chamber 22 is based on the collection of all the charges created by ionization of the gas through the application of an electric field. The ionization chamber 22 is configured to have a relatively flat response to a wide range of gamma and x-ray energies (typically from tens of keV to nearly 10 MeV) and, thus, is suited to measure x-ray and gamma radiation. The ionization current is proportional to the volume of the chamber 22 and the exposure rate.

[0030] Turning to FIG. 3, the ionization chamber 22 is of compact size (e.g., having a volume of approximately 1 to 100 cm³). The ionization chamber 22 is in the form of a cylinder or cuboid or sphere. The ionization chamber 22 includes an insulator tube or spacer 30 disposed (e.g., sandwiched) between two metal electrodes 32, 34 (which are parallel with respect to each other). An adhesive seal 36 couples the insulator tube 30 to the electrodes 32, 34. The adhesive seal 36 also acts as a seal. The electrodes 32, 34 are made of copper or aluminum and may be of a thickness of approximately 1 mm. The tube 30 may be made of low-cost materials (e.g., low permeability plastics) having very low electrical leakage (e.g., less than one fA) and high intrinsic resistance (e.g., greater than 1 X 10¹⁵ ohms). The low-cost materials may be polycarbonate, quartz, or polytetrafluoroethylene (PTFE) .

[0031] The ionization chamber 22 is filled with dry air or dry nitrogen at approximately 1 atmosphere. The gas pressure within the ionization chamber may be kept at slightly higher than 1 atmosphere (approximately 1.2 to 1.5 atmospheres) to keep moisture from entering the ionization chamber 22 and to reduce the possibility of condensation. The volume within the ionization chamber 22 is of a volume to provide sufficient signal (e.g., ionization current voltage discharge) compared to the leakage current of the ionization chamber 22 and the isolation switch for the readout circuitry, while still enabling the compact size of the ionization chamber 22.

[0032] A voltage 37 of approximately 10-100 volts (V) may be used to charge the ionization chamber 22, which is high enough to prevent recombination of the ion pairs and efficiently collect ionization charges. In one embodiment, the ionization chamber 22 includes a gap 40 (Li) between the electrodes 32, 34. The ionization chamber 22 may have chamber volume of approximately 30 cm³. The ionization current corresponding to 2 mR/hour and 30 cnf volume is approximately 6 fA. The total charge lost every 10 minutes would be approximately 3 pC, which will be converted into voltage by connecting a charge sensitive amplifier to the ionization chamber 22. In other embodiments, the dimensions of the ionization chamber 22 may vary. The sensing charge is collected from the electrode 32.

[0033] The ionization chamber 22 is sealed utilizing low permeability organic materials (e.g., liquid crystal polymer or benzo-cyclo-butene). The low permeability organic materials provide a near-hermetic seal that provides protection from moisture permeation for a period of months to years depending on the seal thickness. As noted above, the ionization chamber 22 will be coated with a conformal coating (e.g., a chemical vapor deposited poly(p-xylene) polymer) that acts as a moisture protective and dielectric barrier.

[0034] The electric field (E) within the ionization chamber 22 is equivalent to the applied bias voltage (V) divided by the height 40 (Li) of a side wall 42 of the tube 30. E is greater than Emin (which is the minimum field required to ensure maximum ionization current). In certain embodiments, a height 44 (L2) of the side wall 42 of the tube 30 may be increased relative to the distance (Li) between the electrodes m a central region of the ionization chamber 22, as depicted in FIG. 4, while maintaining the same volume for the ionization chamber 22. A taller side wall 42 provides higher resistance and, thus, lower electrical leakage. In addition, a taller side wall 42 reduces the E for the same fixed applied bias V. In certain embodiments, the ionization chamber 22 may include a reference resistor configured to measure leakage. The reference resistor would have the same equivalent resistance as the ionization chamber 22.

[0035] Returning to FIG. 1, the on-board battery 26 is disposed on the side of the ionization chamber 22 opposite from the readout and communications electronics 24 and the antenna 28. The battery 26 is configured to provide power to enable the sensor node 10 to operate for over a year. The battery 26 may have a total battery capacity of 1,200 mAh or greater. In one embodiment, the battery 26 may be a lithium com cell batery. Prior to activation of the sensor node 10, the standby current is minimal. Over one year of shelf life (prior to activation), the sensor node 10 use about 26 mAh of battery’ capacity’. When the sensor node 10 is activated, it may measure the dose rate every 1 hour (or another interval). The longer the measurement interval, the longer the battery life. Once the sensor node 10 detects radiation and sends alarms over a radio (not numbered in FIG. 1, part of readout and communications circuitry’ 24), assuming a message from the radio message is sent once every' minute, the current used is greater than the current, utilized for measuring the dose rate. Once the sensor node 10 begins transmiting a signal, the battery 26 should last for a number of weeks. The operational time trades off with the sensing and alarm message duty cycle (period between inactivity). The operating parameters can be programmed or changed prior to deployment via a radio channel of the radio. In certain embodiments, a larger capacity battery or multiple bateries distributed in parallel can be used if both short measurement interval and longer operation time is required.

[0036] The readout and communication electronics 24 are low power. Low power means a device can operate for greater than 1 year with approximately 2000 to 4000 mAh of battery capacity. The readout electronics of the readout and communication electronics 24 are configured to take dose rate readings at periodic intervals by integrating charge and recharging the chamber to the operational voltage. The measured recharge is directly related to the dose rate. The measurements may be done periodically (e.g., every 1-10 minutes), and between measurements, the ionization chamber 22 will be disconnected from the readout electronics using a high isolation switch (e.g., relay switch or MEMS switch) with very low off-state leakage (e.g. less than 1 fA) and high off-state resistance (e.g., greater than 1 X 10ⁱ³ ohms). In this mode (electrometer mode), the sensor does not consume power and the readout electronics will be powered off during the measurement period and is active only for a fraction of a second during readout and recharging of the ionization chamber 22. This operational approach will significantly increase the life of the batery 26.

[0037] The antenna 26 may be a low-cost single band antenna. The antenna 26 may work in a frequency range of 868 to 928 MHz. In certain embodiments, the antenna 26 is a monopole antenna. The antenna 26 may be a long range (LoRa) antenna. The antenna 26 may be a flexible PCB, surface mounted, insulated copper wire, or printed. As depicted in FIG. 1, antenna 26 is oriented perpendicular to the electrodes (e.g., electrodes 32, 34 in FIGS. 3 and 4) of the ionization chamber 22. In certain embodiments, the antenna 26 may be printed on an outer surface of the first layer 14 to improve coverage. As depicted in FIGS. 1 and 5, the antenna 26 is a helical antenna.

[0038] In certain embodiments, as depicted in FIG. 5, the sensor node 10 includes a cylindrical or hockey puck shape. The components of the sensor node 10 are the same as FIG. 1 except the antenna 26 is oriented in a direction parallel to the electrodes (e.g., electrodes 32, 34 in FIGS. 3 and 4) of the ionization chamber 22,

[ 0039 ] FIG. 6 is a block diagram of functional components disposed within the radiation sensor node 10 (e.g., within the protective casing 12 in FIG. 1). These functional components are configured to operate under low power. These functional components may be integrated on a PCB. In certain embodiments, these functional components may be distributed on 2 to 3 PCBs interconnected via flexible interconnects to enable strain relief during drop impact. The radiation sensor node 10 includes a dose rate sensor 22 (e.g., ionization chamber) coupled to a switch 46 (e.g., high isolation switch such as a relay switch or a MEMS switch) with very low off-state leakage (e.g. less than 1 fA) and high off-state resistance (e.g., greater than 1 X 10¹⁵ ohms). In certain embodiments, where the switch 46 is a MEMS switch, it may be utilized in a wafer level package. Although a MEMS switch needs a high activation voltage, the switch 46 will be only be actuated for 1ms per measurement, thus, enabling voltage boosting circuit to be powered off most of the time to conserve energy. The switch 46 is coupled to charge sensing circuitry 48 (e.g., readout circuitry) which is coupled to digitization circuitry 50 (e.g., analog to digital converter). The digitization circuitry 50 provides the digitized sensor signal to a microcontroller 52. The antenna 28 (e.g., long range antenna) is coupled to a radio transceiver 54 (e.g., long range radio transceiver) that is coupled to the microcontroller 52. The battery 26 (e.g., power management battery) is also coupled to the microcontroller 52. Further, an activation switch 56 is coupled to the microcontroller 52.

[0040] The sensor node 10 is configured to wirelessly communicate via beacon broadcasting (e.g., beaconing to a distance of greater than 1 km). Utilization of the LoRa radio transceiver 54 (and LoRA antenna 28) provides low power consumption and the use of sub-GHz industrial, scientific, and medical (ISM) bands. In addition, the LoRa radio transceiver 54 has a range of up to 15 km in free space and up to 2 km in urban areas. LoRa is a spread spectrum modulation technique derived from Chirp Spread Spectrum (CSS) technology. LoRa also provides secure communication (e.g., via end-to-end AES 128 encryption), mutual authentication, integrity protection, and confidentiality. LoRa also provides the ability to geolocate the sensor node 10 without using any GPS receiver. The sensor node 10 may communicate sensor data, with a device (e.g., drone flown into the field where the sensor nodes 10 are deployed) having a receiver with a LoRa Gateway at its end.

[0041] The activation switch 56 is configured to configure the sensor node 10 and to begin dose rate detection with the sensor node 10. The sensor node 10 is powered at a very low power state (e.g., standby current of approximately 3 pA or less), waiting for an activation signal. In certain embodiments, the activation switch 56 is a magnetic reed switch. Sensors nodes 10 with magnetic reed switches are activated individually. In certain embodiments, the activation switch 56 is a LoRa module (e.g. the radio transceiver 54 and the antenna 28) receiving a signal from a LoRa transmitter that causes the microcontroller 56 to provide the activation signal. In this embodiment, multiple sensors nodes 10 may be activated via an activation signal from the LoRa transmitter. Once activated, the sensor node 10 makes its radio channel active for a short time (e.g. 2 seconds). Within this short window, the operator can interrogate, configure, and activate the sensor node 10 for dose rate monitoring. If within the activation window, no radio communication is received, or an incorrect protocol is followed, then the sensor node 10 goes back to a low power idle state. Once activated, the sensor node 10 will begin periodic measurement of dose rate and is ready to be deploy ed.

[0042] The microcontroller 52 includes a processor and a memory'’. The processor 24 may include multiple microprocessors, one or more “general-purpose” microprocessors, one or more special-purpose microprocessors, and/or one or more application specific integrated circuits (ASICS), system-on-chip (SoC) device, or some other processor configuration. For example, the processor may include one or more reduced instruction set (RISC) processors or complex instruction set (CISC) processors. The processor 24 may execute instructions to carry out the operations of the sensor node 10. These instructions may be encoded in programs or code stored in a tangible non-transitory computer-readable medium (e.g., an optical disc, solid state device, chip, firmware, etc.) such as the memory . The microcontroller 52 manages the sensor initiation, sensor measurement, the switch 46, power management (sleep/wake up), alarm threshold decision, and drives the radio transmission. The microcontroller 52 is configured to begin alarming (via the transceiver 54 and the antenna 28) when the detected radiation passes 2mR/hr or other set alarm threshold.

[0043] In certain embodiments, the sensor node 10 may include other components. For example, the sensor node 10 may include a GPS positioning system. The sensor node 10 may also include other sensors such as an accelerometer, temperature sensor, humidity sensor, and so forth.

[0044] FIG. 7 is a schematic diagram of the readout circuit or sensing circuit 48 coupled to the ionization chamber 22 of the radiation sensor node 10. The switch 46 (isolation switch) in FIG. 7 may be an electromechanical switch such as a relay switch or a (micro- electromechanical systems) MEMS switch. In certain embodiments, the switch 46 may be an electrical switch such as a metal---oxide---semiconductor field-effect transistor (MOSFET). The basic sensing circuit 48 includes the ionization chamber 22 (C), a charge integrating amplifier 58, and the switch 46 (e.g., Switches A and B) connecting the two. When the switch 46 is closed, the chamber 22 is charged to a pre- determined bias voltage, using a lesser positive voltage bias on the positive side and a greater negative voltage bias on the negative side. The voltage bias across the electrodes would be sufficient for dose rate detection. Employing a bipolar voltage supply allows the use of low power, low' voltage supply electronics for the sensing circuit 48. The ionization chamber voltage is charged to the bias voltage. Upon charging the ionization chamber 2.2, the swatch 46 is opened for a given period of time (e.g., 10 minutes) enabling the ionization chamber 22 to discharge. In the presence of ionizing radiation at 2 mR/hour dose rate, the chamber 22 will lose charge. After 10 minutes of this dose rate exposure, the voltage on the chamber 22 drops. When the sensing circuit 46 is connected to the chamber by closing the switch, the amplifier 58 charges the chamber 22 to its initial state and the output voltage of the amplifier 58 is proportional to the amount of charge used to replenish the charge lost in the ionization chamber 22. The output voltage would peak at about 0.3 V above the baseline voltage and reset itself back to the baseline level within 2 seconds through the reset resistor R. The output signal of the detector is proportional to the sensing interval, because the ionization chamber 22 loses more charge with a longer sensing time at a constant dose rate. Due to the noise floor, the detection speed limit for the 2 mR/hour dose rate is to be between 1 to 10 minutes. At the low end of the sensing time of 1 minute, a small voltage drop of is converted to the output. At this level, the signal to noise ratio may be too small to reliably measure the dose rate and make the alarm determination. At the high end of the sensing time of 10 minutes, the expected voltage drop provides a sufficiently large signal to noise ratio.

[0045] FIG. 8 are graphs illustrating a measured waveform matches a simulated waveform. The top graph in FIG. 8 illustrates the actual measurement of a radiation dose in the output voltage signal with the readout circuitry discussed above. The bottom graph illustrates a simulated waveform. The measured output pulse 57 in the top graph matches the simulated output pulse 59 in the bottom graph.

[0046] FIG. 9 is a flow chart of a method 60 for detecting and broadcasting utilizing a radiation sensor node. One or more steps of the method 60 may be performed by the functional components (e.g., microcontroller 52) in FIG. 6 of the sensor node. The method 60 includes receiving an activation signal or wake up signal that activates the sensor node (block 62). The wireless communication system of the sensor node will remain in an inactive state for most of its mission life, once activated and surrounded by normal background radiation. The sensor node will broadcast a periodic signal (for example, 1-4 times a day) to the end user to communicate that the node is still operational. Once activated, the sensor node measures the dose rate (block 64). If the radiation dose remains below the threshold, the sensor node continues periodically measuring the dose rate. If the sensor node has detected a radiation dose above the threshold, a radio message will be transmitted indicating that one detection event has occurred (block 66). In the method 60, the sensor node will continually periodically measure dose rate (block 68). If the next measurement again exceeds the threshold, the radio message will indicate that the radiation dose is over the threshold two consecutive times (block 70). In the method 60, the sensor node will continually periodically measure dose rate (block 72). In particular, the radiation detection and alarm broadcasting continues in this manner for one more cycle (blocks 74 and 76) before the alarm is constantly broadcasted for a period of greater than 1 hour (block 78), until the battery is depleted. While broadcasting the alarm, the dose rate continues to be measured (block 76) to provide additional information to the user on the number of above-threshold measurements. The power consumption of these measurements is significantly smaller than the power used to transmit the alarm. If the dose rate drops between alarms, the alarm message will indicate that the dose rate is below the threshold and communicate the maximum consecutive over-threshold events (block 80). The sensor node will then continue to monitor radiation until readings above the threshold are measured, following the above protocol.

[0047] In certain embodiments, a center of mass of a sensor node may be intentionally biased to one side to define a preferred upright operation to increase exposure of the ionization chamber to radiation and support reliable radio transmissions. However, when the sensor node is deployed from a ground/air vehicle, the local placement of the node relative to the surrounding environment is not controlled. Thus, variations in local conditions may add uncertainty to the measured dose rate. Thus, the sensor nodes may be deployed in large quantities (e.g., 1000s of sensor nodes) to cover an area with sufficient proximity to each other to provide redundancy of measurements at. a local scale to account for any nodes that, are shielded partially from the radiation source(s). In addition, the sensor node’s mechanical design and materials provide line of sight to the sensitive volume of the ionization chamber by using openings in the electronics boards and optimal placement of the components within the package enclosure.

[0048] In certain embodiments, as depicted in FIG. 10, the sensor node 10 may be selforienting. As depicted in FIG. 10, the sensor node 10 may be deployed in a position 82 where the antenna 28 is not. upright (e.g., not at the 12 o’clock position) and a center of mass 84 is not located at the bottom (e.g., at the 6 o’clock position). The sensor node 10 may include a mechanical means (e.g., rollers 86) to position (e.g., rotate) the sensor node 10 to a preferred upright position or orientation 88 (e.g., with the antenna 28 pointing to the 12 o’clock position and the center of mass 84 located near the 6 o’clock position). In certain embodiments, the sensor node 10 may include sensors (e.g., accelerometers) to provide feedback regarding positioning of the sensor node 10.

[0049] FIG. 11 is a schematic diagram of an alternative embodiment of a core 90 of the radiation sensor node 10 that can be disposed within the casing. The core 90 includes a PCB 92 coupled to a cover 94. Within a chamber 96 (e.g., air cavity chamber) formed by the PCB 92 and the cover 94, a plate 98 (e.g., metal plate) forming an electrode of the ionization chamber 22 is centrally located. The plate 98 is centrally located in the chamber 96 via a plastic (e.g., PTFE) support or standoff 100 coupled to the PCB 92, The plate 98 is coupled to the standoff via one or more fasteners and the standoff 100 is coupled to the PCB 92 via one or more fasteners. A metal cap or lid 102 (e.g., forming another electrode of the ionization chamber 2.2.) is disposed about the plate 98. The metal cap 102 is coupled to the PCB 92 to via a plastic (e.g., PTFE) isolation ring 104 and one or more fasteners. The PCB 92 and the metal lid 102 encapsulate the plate 98. The 94 and the PCB 92 encapsulate the ionization chamber 22. The cover 94 forms a hermetic wail. The cover 94 may be 3D printed. The cover 94 may be made of plastic (e.g., acrylonitrile butadiene styrene). A pin or wire connection 106 couples the plate 98 to a relay 108 (e.g., isolation relay). A pin or wire connection 110 couples the metal cap 102 to a relay 112 (e.g., isolation relay). The relays 108, 1 12 are disposed over air isolation cut outs 114 in the PCB 92. The ionization chamber 22 operates as described above.

[0050] On the side of the PCB 92 opposite from the ionization chamber 2.2, a layer 116 may be disposed on the PCB 92 to provide some rigidity. The layer 1 16 may be a molding compound or a rigidizer. A layer 117 (e.g., Kapton tape) may be disposed across the isolation cut outs 114 to keep mold from flowing into the ionization chamber 22. On the side of the PCB 92 opposite from the ionization chamber 22, the antenna 28 is disposed on the PCB 92. The antenna 28 extends parallel to the PCB 92 in a horizontal orientation. In certain embodiments, a cover 118 may be disposed over the antenna 28.

[0051] The cover 94 includes multiple holders or receptacles 120 for bateries 26. The core 90 may include 2 or 3 or more bateries 26 (e.g., buton cell bateries). A wire connection 124 couples the bateries 26 to the various components of the core 90 that need power. The core 90 may include other electronic components (e.g., high voltage booster, low noise amplifier, etc.) disposed on the PCB 92 on the side with the ionization chamber 22.

[0052] The ionization chamber 22 in FIG. 11 lacks the side wall or tube present in the ionization chambers 22 present in FIGS. 1 and 5. This eliminates a dominant leakage pathway. In addition, the entire air cavity volume within the chamber 96 is active and, thus, increases the signal that can be detected. In addition, the PCB 92 is rigidly attached to the chamber 96. The whole core 90 can be sealed and molded to provide ingress protection and drop impact resistance. The ionization chamber 22 in FIG. 11 does not have to be as delicately placed in the casing.

[0053] As noted above, the sensor nodes 10 are utilized to measure radiation and to enable an aerial map of the radiation to be generated. In other embodiments, the sensor nodes 10 may be utilized to measure other parameters (e.g., such as physical parameters or chemical parameters) and to enable an aerial map to be generated for these other parameters. For example, the sensors nodes 10 may be utilized to monitor a chemical spill.

[0054] Technical effects of the disclosed embodiments include providing small, low- cost sensors (e.g., for measuring radiation) that are disposable and that can be utilized over a long period in the field (e.g., under varying conditions) with minimal long-term environmental impact. The sensors also include a casing or packaging configured to provide ingress protection and drop survivability.

[0055] The techniques presented and claimed herein are referenced and applied to material objects and concrete examples of a practical nature that demonstrably improve the present technical field and, as such, are not abstract, intangible or purely theoretical. Further, if any claims appended to the end of this specification contain one or more elements designated as “means for [perform]mg [a function]... ” or “step for [perform]ing [a function]... ”, it is intended that such elements are to be interpreted under 35 U.S.C. 112(f). However, for any claims containing elements designated in any other manner, it is intended that such elements are not to be interpreted under 35 U.S.C. 112(f).

[0056] This writen description uses examples to disclose the present subject matter, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the subject matter is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.

Claims

CLAIMS:

1. A sensor, comprising: a casing, an ionization chamber encapsulated within the casing and configured to measure radiation; and readout circuitry configured to be periodically connected to the ionization chamber to measure a radiation dose in an electrometer mode.

2. The sensor of claim 1 , comprising an isolation switch configured to connect the ionization chamber to the readout circuitry.

3. The sensor of claim 2, wherein the isolation switch comprises an electromechanical switch or an electrical switch.

4. The sensor of claim 1, wherein the sensor is configured to operate in a low power mode by putting electronics of the sensor in a sleep mode when in a communication mode or when not reading out the ionization chamber.

5. The sensor of claim 1 , wherein the casing comprises a molded sphere.

6. The sensor of claim 1, wherein the casing comprises multiple layers made of different materials,

7. The sensor of claim 1, wherein the casing is configured to provide both ingress protection and drop impact protection to the ionization chamber and the readout circuitry' within the casing.

8. The sensor of claim 1, wherein the casing comprises a plurality of protrusions extending out from an outer surface of the casing, wherein the plurality of protrusions are configured to absorb and dissipate impact energy through their deformation and damage.

9. The sensor of claim 1, wherein the ionization chamber comprises a low electrical leakage insulator tube disposed between a pair of parallel electrodes, and wherein a height of the low' electrical leakage insulator tube is greater than a gap between the pair of parallel electrodes at a central location of the ionization chamber.

10. The sensor of claim 1, wherein the ionization chamber comprises a metal plate centrally located within the ionization chamber and a metal cap disposed over the metal plate, and the metal plate is a first electrode and the metal cap is a second electrode.

11. The sensor of claim 1 , comprising a magnetic activation switch disposed within the casing and configured to activate the sensor to periodically measure radiation.

12. The sensor of claim 1, comprising a transceiver and an antenna disposed within the casing to communicate wireless signals, and wherein the sensor is configured to be activated to periodically measure radiation in response to an activation signal received from a remote transmitter.

13. The sensor of claim 12, comprising a microcontroller configured to cause a warning signal to be transmitted via the transceiver and the antenna when the radiation surpasses a threshold during a measurement cycle.

14. The sensor of claim 13 , wherein the microcontroller is configured to cause an alarm signal to be continuously transmitted via the transceiver and the antenna until the sensor runs out. of power when the radiation surpasses the threshold during multiple measurement cycles.

15. The sensor of claim 1, wherein the ionization chamber is configured to have electrical leakage that is less than an ionization current of the ionization chamber.

16. The sensor of claim 1, comprising an on-board battery .

17. The sensor of claim 1, wherein the sensor is configured to self-orient itself upon being deployed.

18. A radiation monitoring system, comprising: a plurality of sensors configured to be deployed from a vehicle in an area and to monitor radiation, wherein each sensor of the plurality of sensors comprises: a casing; an ionization chamber encapsulated within the casing and configured to measure radiation; and readout circuitry configured to be periodically connected to the ionization chamber to measure a radiation dose in an electrometer mode.

19. A sensor, comprising: a casing shaped as molded sphere and comprising multiple layers configured to absorb and dissipate impact energy through their deformation and damage; an ionization chamber encapsulated within the casing and configured to measure radiation, wherein the ionization chamber comprises a low electrical leakage insulator tube disposed between a pair of parallel electrodes; readout circuitry coupled to the ionization chamber within the casing, wherein the readout circuitry is configured to operate at low power in an electrometer mode to readout a radiation measurement from the ionization chamber; and an isolation switch coupling the ionization chamber to the readout circuitry.

20. The sensor of claim 19, wherein the casing is configured to provide ingress protection to the ionization chamber and the readout circuitry within the casing.