Power management system for aircraft container tracking device

An RF asset tracking device for cargo containers that has an extended operational life, due to a power management system and multiple power sources. The device has a solar cell and high capacity supercapacitor as a principal power source and a rechargeable battery as an auxiliary power source. Control circuitries manage and regulate the usage of the primary and secondary sources. Together, these power sources provide sufficient power for the tracking device to operate for an extended period of time, thus increasing the period between needed maintenance and decreasing downtime and thus cost.

FIELD OF THE DISCLOSURE

The present disclosure is directed to wireless asset tracking devices and systems. More particularly, the present disclosure is directed to features configured to extend the battery life of the tracking device.

BACKGROUND

Many freight logistic companies attach tracking devices to airline containers to track their geographic location. This allows the logistic company to determine the geographic location of the container as it moves between the origination and destination point(s), to determine whether the goods inside the container are on time, late, or somehow misplaced. For example, by tracking the movement of the container, the logistic company will quickly know if the container has been misrouted or been placed on the incorrect transport. The advantages of tracking the position of the goods are many and therefore asset tracking has become commonplace throughout the shipping industry.

The tracking devices associated with the container transmit and receive various types of communication signals for determining the geographic position of the tracking device and thus the container. A problem occurs when the tracked container is loaded onto a transportation vessel, such as an aircraft, as the communication signals may potentially cause interference with the vessel systems. Regulatory agencies, such as the Federal Aviation Administration (FAA), place restrictions on communications signals due to their potential interference with flight systems and communications. Therefore it is necessary that the tracking device be deactivated when the cargo container is on board an aircraft.

The experience has been that it is inadequate to rely on a manual switch to deactivate the tracking device when the container is placed on the aircraft. For instance, human operators may merely forget to deactivate the tracking device. Additionally, these containers are normally tightly packed into the transportation vessel cargo hold in such a manner that they are not easily accessible once the container has been placed in the hold, and even less accessible if the hold has been completely loaded. One container with a tracking device still activated that is loaded onto a transportation vessel may require that the entire transportation vessel be unloaded to access and deactivate the tracking device.

Additionally, manual switches are also inconvenient if they have been properly deactivated, for after the container is removed from the transportation vessel at the end of its journey, the tracking device must be reactivated so the container can again be adequately tracked.

In addition to requiring activation and deactivation on a regular basis, aircraft cargo tracking devices need to have long operation or life. Because the devices travel around the world, it may be an extended period of time before the device is at a location that is equipped to service the battery that operates the tracking device.

SUMMARY

The present disclosure provides an asset tracking device for cargo containers that has an extended operational life, thus increasing the duration between battery replacement or maintenance. The asset tracking device is provided with a power management system and with multiple power sources. Together, these power sources provide sufficient power for the tracking device to operate for an extended period of time, thus increasing the period between needed maintenance and decreasing downtime and thus cost.

The device has a solar cell and high capacity supercapacitor as a principal power source and a (rechargeable) battery as an auxiliary power source. Control circuitries manage and regulate the usage of the primary and secondary sources.

This disclosure provides, in one particular embodiment, a wireless RF transmitter device having a GPS positioning element, an RF communication module having an RF operating frequency, the operating frequency having an operating wavelength, a primary power source comprising a solar cell and a supercapacitor, a secondary power source comprising a battery, and a power management system operably connected to the primary power source and the secondary power source.

In another particular embodiment, this disclosure provides a wireless RF transmitter device having a GPS positioning element, a sensor array comprising at least one motion sensor and at least one machine vision sensor, an RF communication module and a cellular communication module, each configured to deactivate and activate based on data detected by the sensor array, a primary power source comprising a solar cell and a supercapacitor, a secondary power source comprising a battery, and a power management system operably connected to the primary power source and the secondary power source.

The tracking devices can be housed or present in an enclosure constructed with a structure that allows passage of visible light (UV) and RF signal therethough. Such a structure can be a perforated metallic material with aperture centers spaced apart uniformly by less than half the wavelength of the RF energy to be passed therethrough, or, by a periodic pattern of slits in the metallic material.

DISCUSSION OF THE INVENTION

In the following description, reference is made to the accompanying drawing that forms a part hereof and in which are shown by way of illustration at least one specific embodiment. The following description provides additional specific embodiments. It is to be understood that other embodiments are contemplated and may be made without departing from the scope or spirit of the present disclosure. The following detailed description, therefore, is not to be taken in a limiting sense. While the present disclosure is not so limited, an appreciation of various aspects of the disclosure will be gained through a discussion of the examples provided below.

Unless otherwise indicated, all numbers expressing feature sizes, amounts, and physical properties are to be understood as being modified by the term “about.” Accordingly, unless indicated to the contrary, the numerical parameters set forth are approximations that can vary depending upon the desired properties sought to be obtained by those skilled in the art utilizing the teachings disclosed herein.

A wireless tracking system is highly beneficial in knowing the physical location of an asset at a set point in time. A “tracking system” and variations thereof includes at least one tracking or transmitter device, and a receiver for receiving the location signal from the tracking transmitter device(s). A “tracking device,” “transmitter device,” and variations thereof, is a signal emitting device configured for placement in or on an asset to be tracked, such as a container of goods.

Tracking is particularly beneficial for aircraft cargo, as it is not uncommon for cargo to be moved several times prior to be loaded on to the aircraft for its transport. Additionally, unlike over-the-road cargo, which can be quickly retrieved if placed on the wrong truck, an aircraft cargo container, if loaded on the wrong aircraft, will typically not be retrieved for an extended time period, because typically the aircraft will not be recalled or make an unscheduled landing merely because of one erroneously loaded container. When at the incorrect destination, the container will have to wait to find a return flight or an alternate flight to its desired destination. Because of the larger possibility of lost aircraft cargo containers, it is particularly desirable to know the immediate location of these containers.

As indicated above, the present disclosure provides an asset tracking system for cargo containers. The asset tracking device of the system has a power management system and multiple power sources that provide the device with extended operation time, thus increasing the period between needed maintenance and decreasing downtime and thus cost.

Prior to this invention, asset tracking devices were either powered by an AC main power source, optionally with a rechargeable battery, or by a DC main power battery (the battery being rechargeable or single use). These devices, in general, have short life span and a high maintenance cost. Conversely, the asset tracking device of this disclosure, having a power management system and multiple power sources, has a longer operational life and lower maintenance costs.

Aircraft transport is a highly common mode of transport for cargo containers, and because most airplanes fly across countries where basic cellular infrastructure may vary from CDMA to GSM to 2G to 4G cellular, the tracking device is preferably configured to operate on a global basis regardless of cellular infrastructure. In some embodiments, the tracking device features LTE communication device(s) with a global roaming SIM card to realize true global operations to support GSM, CDMA, and other mobile environment seamlessly. The communication device(s) provide long range and bi-directional wireless communication and cellular communication; both technologies are technically mature and have global coverage. The tracking device also includes an internal antenna system to transmit and receive communication signals. Further, because of possible changes in the route and future business environment, in some embodiments, the device requires no infrastructure such as WiFi routers and/or relays in each destination (e.g., airport).

The container-tracking device is equipped with a location system such as a GPS/GLONASS system, and a communication system that can include ZigBee, WiFi, and CDMA/GSM communication device. The tracking device can be equipped with sensors, such as vision sensors (e.g., primary and secondary), a temperature sensor and motion sensors. A tamper switch, and indicators such as 3 LED and 2 buttons can be part of the tracking device. The tracking device includes a computer processor (e.g., a 16 bit MCU) and non-volatile memory (NVM).

The tracking devices of this invention are ZigBee and/or WiFi enabled providing communication with WiFi and ZigBee routers/receivers. ZigBee and/or WiFi are used as a communication mechanism to send data (ping) between the tracking device and the router. In most situations, the tracking device is constantly in a listening mode. The router/receiver constantly broadcasts a beacon with secure encrypted signature packets that only the tracking device can decode and understand. When the tracking device comes within range of a router's beacon, it decodes the beacon signature. If the signature is correctly decoded, it wakes up and, using secure encrypted packets, broadcasts back its unique ID along with other sensory information (as well as historical information that the tracking might have gathered in its travels including GPS/GLONASS location should the tracking device be so enabled). If the router/receiver receives the secure information from the tracking device, and can decode the information, it sends a specific handshake packet back to the tracking device indicating successful receipt of the information.

Because the tracking device must be able to be powered in all environments (e.g., high humidity, low temperatures, high temperatures, etc.), the device of this disclosure has a primary and secondary power source, so that the tracking device does not rely on an AC main power, as in a fully battery-powered device. The power system provides enough power to operate the tracking device without needing any replacement or maintenance for at least one year, in some embodiments at least 18 months. The physical placement, dimensions, and combination of the power system are optimized for overall performance, and for operation under harsh environmental requirements.

FIG. 1illustrates one embodiment of a tracking or transmitter device100that, together with a router/receiver (not shown), forms a tracking system. The particular device100is configured for use on an aircraft or in another location that must comply with FAA regulations; tracking device100has automatic on-off capabilities during transit in order to comply with FAA regulations, and utilizes both RF and cellular communication modes. Transmitter device100deactivates and reactivates, and switches between RF and cellular communication networks, depending on the status of the aircraft, in compliance with FAA regulations and other regulatory requirements. For example, RF communications are not allowed, at least, during takeoff and landing and at cruise altitude, and cellular communications are not allowed during taxiing, takeoff, and at cruise altitude.

Device100includes a multi-source power source, having a primary power source102and a secondary power source103. Primary power source102includes a photovoltaic solar cell block with high capacity supercapacitor, and secondary power source103is a rechargeable battery. Both sources102,103are operably connected to a power management system104.

The solar cell block may be a single solar cell or may be a plurality of cells, arranged in parallel or in series. Electrically connected thereto is the high capacity supercapacitor, which could be a double-layer capacitor, a pseudocapacitor, or a hybrid capacitor.

Examples of suitable batteries for secondary power source103include NiCad, lithium, lithium-ion, zinc-carbon, and alkaline batteries. For example, a 3.7V battery could be used, although it is understood that other voltage batteries could be used. In addition to the solar power recharging batter103, other power source rechargers or regenerators could be utilized, such as an inductive coil, a USB power-line, and mechanical energy harvesting mechanisms.

Electrically connected to power sources102,103is power management system104that includes a battery level monitor and a power control, which in turn is operably connected to a computer chip or CPU106. Power management system104manages and regulates the usage of the primary and secondary power sources102,103. For example, if the available power (e.g., current) from primary source102is low, power management system104may activate secondary power source103, thus either supplementing or replacing the power being used from primary source102. As another example, when primary source102has sufficient available power, yet the sun is shining, power management system104can authorize secondary power source103to draw power from primary source102and recharge.

In some embodiments, CPU106also manages primary and secondary power sources102,103. Additionally, CPU106activates and deactivates various elements of device100, based on the status or location of device100.

Transmitter device100also includes a positioning element, in this embodiment a GPS/GLONASS positioning element108connected to an antenna109, which may be an internal antenna or an external antenna, and may be embedded into a housing encasing the elements of device100. Antenna109may be, for example, a planar inverted F antenna, an inverted L antenna, or a monopole antenna. Antenna109may be a multi-band antenna, one that can transmit and receive signals in multiple frequency bands. Positioning element108provides data to transmitter device100regarding its physical location.

Transmitter device100transmits information or data, such as its location, in the form of a “ping” to the remote receiver via a wireless network, such as ZigBee and/or WiFi. In some embodiments, transmitter device100has two-way communication with the receiver. That is, transmitter device100transmits information (i.e., a ping) and also receives information from the receiver. Further, transmitter device100may receive instructions, such as to acknowledge that device100is active and ready and to transmit the location information. Having received those instructions, device100can send back to the receiver acknowledgement that the communication was received and acted on.

As indicated, the transmitter device is configured to send and optionally receive data via a wireless network. Device100ofFIG. 1is configured with a ZigBee/WiFi module112to connect to the receiver via a ZigBee network or a WiFi network and communicate data (e.g., position data). An alternate embodiment of a transmitter device can utilize a ZigBee/LBT module and a corresponding ZigBee/LBT network. Additionally, transmitter device100may include a data receiver (not shown), such as an infrared data link (IrDA), to provide a second communication means to device100, as an alternate or back-up to module112.

Device100also includes a cellular communication module114, which may be CDMA (Code Divisional Multiple Access) and/or GSM (Global System for Mobile Communication) module, configured to connect to the receiver via either a CDMA or GSM network and communicate data to the receiver.

Modules112,114, respectively, have an antenna113,115, one or both of which may optionally include a power amplifier (e.g., power amplifier111) to extend the range of the signal from modules112,114. In some embodiments, modules112,114may be combined into a single physical module rather than two separate or distinct modules. Together, modules112,114provide the communication basis for transmitter device100to the receiver. Module112, which connects device100a wireless RF network, is utilized when FAA regulations allow use of RF communications, and module114, which connects device100to a cellular network, is utilized when FAA regulations do not allow the use of RF communications yet do allow cellular communications.

Any of the data or information regarding device100, such as its position as determined by positioning element108, power level or usage information as determined by power management system104, alarm information, etc., can be stored in a memory116of device100, which may be a permanent memory or a rewritable, nonvolatile memory. Data from memory116may be transmitted to the receiver or may be retained in memory116until manually retrieved.

Transmitter device100includes an array of sensors to determine the location of device100in relation to an aircraft and to determine the status or mode of the aircraft, in order to determine when to activate and deactivate the device. The sensor array includes at least one motion sensor120and at least one machine vision sensor122. In some embodiments, two vision sensors122are present.

Motion sensor(s)120can be, for example, a three-degree of freedom (DOF) device that has a 3-axis accelerometer or can be a six-degree of freedom (DOF) device that includes a 3-axis gyroscope and a 3-axis accelerometer. Other examples of suitable configurations for motion sensor120include a 9-DOF device that includes a 3-axis gyroscope, a 3-axis accelerometer and a 3-axis magnetometer, and a 10-DOF device that includes a 3-axis gyroscope, 3-axis accelerometer, 3-axis magnetometer, and an altitude sensor. Other embodiments of motion sensor(s)120may be used. With the various multiple degrees of freedom, device100can distinguish among various movements, orientations and locations, such as lateral motion, acceleration, inclined or declined motion, and altitude. With this information, device100can determine the aircraft's status, e.g., idle, taxiing, takeoff, cruising at altitude, landing, etc.

Vision sensor(s)122(e.g., a machine vision sensor) determine the curvature of the tagged container's surroundings, such as the interior wall of the cargo hold or the door of the cargo hold. With this information, tracking device100can determine whether it and the tagged container are inside a cargo hold or proximate to the door so that the tracking device can be deactivated.

Motion sensor(s)120can be used to wake up vision sensor(s)122and also to provide secondary information (e.g., lifting onto a conveyer, ramping onto an airplane, ascending, descending, landing, takeoff, touchdown, taxi, etc.) For situations when vision sensor(s)122may fail under extreme conditions, motion sensor(s)120act as a back up. For situations where motion sensor(s)120take over, the solar cell from the primary power source102can be used to detect light signals and determine the light source. The information from motion sensor(s)120, vision sensor(s)122, and from the solar cell is used for decision making during deactivation/reactivation of device100, which is described in more detail below.

Device100may also include an indicator console124having various operational switches, gauges, buttons, and/or lights (e.g., LED lights); in the particular embodiment shown, indicator consul124has 3 LED lights and 2 buttons. Console124may include any number of optional features, such as an audio alarm to indicate any number of problems or malfunctions, such as low battery level, unauthorized movement (as sensed by motion sensor120), or tampering with device100in any manner, as sensed by tamper switch118. Device100may optionally include a temperature sensor121.

The various elements that compose transmitter device100may be housed in an RF and/or cellular transmissive enclosure or housing126, preferably one that is at least water resistant. Additional details regarding enclosure or housing126are provided below. In some embodiments, one or both of power sources102,103may be physically removed from the rest of device100. For example, the solar cell of primary power source102may be physically positioned separate from device100but electrically connected thereto.

FIG. 2shows a schematic diagram of the power management scheme of tracking device100. Power management system140has a circuit142connecting a specially designed solar cell144, a high capacity supercapacitor145and a (rechargeable) battery146. In the illustrated embodiment, all elements144,145and146are arranged in parallel; other configurations could of course be used. Together, solar cell144and high capacity supercapacitor145are a principal power source (i.e., primary power source102fromFIG. 1). A first control circuitry148senses current flowing from the principal power source, i.e., from solar cell144and supercapacitor145. Circuitry148operates and manages system140under usual conditions. When circuitry148senses that sufficient power (current) is not available from solar cell144and supercapacitor145, a second control circuitry149activates available power from battery146. Together, control circuitries148,149regulate the current from and voltage across system140.

In system140, (rechargeable) battery146is a back-up power source to solar cell144and supercapacitor145, and is typically only activated when the principal power source (i.e., solar cell144and supercapacitor145) is unable to provide enough current. Secondary control circuitry149manages the current from battery146so that it does not excess, or shortage. Control circuitry149also senses the power of battery146, and warns tracking device100if battery146needs to be replaced or recharged, or is otherwise malfunctioning. Both first and second control circuitries148,149also manage draining process of unused charge from system140at the end of life or as requested by the user, without recalling device100to a maintenance facility.

In addition to the power management system described above, with primary solar cell power source102and the secondary battery power source103, additional battery charging techniques can be incorporated into device100, such as the techniques disclosed in U.S. Patent Application Publication 2013/0324059 titled “Wireless Device with Hybrid Energy Charging,” the entire disclosure of which is incorporated herein by reference.

All components of the power sources (e.g., of primary solar power source102(including solar cells144and supercapacitor145), battery power source103(battery146) and power management system104) are environmentally friendly (e.g., RoHS, REACH, UN, UL, FM, FDA compliant). Additionally, they can operate at temperatures between −20° C. and 60° C. and can be stored at temperatures between −55° C. and 85° C.

For example, battery146is made from non-explosive, and non-toxic material; it has a low leakage current, a rated capacity between 500 mAh and 1000 mAh, and a long shelf life. High capacity supercapacitor145is also made from non-explosive and non-toxic material; it has a high energy density, high capacitance up to 100 Farads, a high peak current up to 1 A, low impedance (ESR), rapid charging and discharging; it has a long life (little or no degradation over hundreds of thousands of cycles, and not subject to the wear and aging). Solar cells144can be formed from semiconductor materials that meet RoHS, REACH, FIPS-140-2, CE, FM, FDA, UN, UL compliance, and that are some of the most benign materials. All control circuitry148,149is also made of industrial grade semiconductor components, and thus considered benign.

Further, tracking device100and its power sources102,103are IP67 compliant to protect against humidity and dust and will operate successfully during exposure to humidity between 30% and 95% RH and temperatures between −20° C. and 85° C.

As indicated above, device100can be particularly configured for tracking aircraft cargo; device100can be configured to activate and deactivate its various communication modules112,114depending on the relation of device100to the aircraft and the status of the aircraft. In general, device100is configured to operate on RF communication when the container is outside of the aircraft, and either communicate via cellular or to be silent while in the aircraft, depending on the aircraft's status. For example, when the cargo container and device100are outside of an aircraft, device100transmits its data (e.g., the container's location) via an RF signal. As the container passes through a door into the aircraft cargo hold, the data is transmitted by a cellular signal. When the container is in the cargo hold, including during taxiing, flight, and landing, both RF module112and cellular module114deactivate. After flight, as the container passes through the door out from the aircraft cargo hold, device100transmits the data via a cellular signal. Once the container is outside of the aircraft, device100transmits the data via RF signal. Additional details regarding deactivating and reactivating device100based on its relation to an aircraft and the aircraft's status can be found in U.S. Patent Application Publication 2013/0321122 titled “Method and System for Airplane Container Tracking,” which is incorporated herein by reference in its entirety.

Device100can be configured to have its data collection or ping event be event-based or time-based, or based on any other protocol. Examples of various event-based protocols, identified as SMART Ping™ events, such as described in U.S. Patent Application Publication 2013/0321211 titled “Asset Tracking System with Adjusted Ping Rate and Ping Period,” U.S. Patent Application Publication 2013/0324151 titled “Asset Tracking System with Data Ping Based on Asset Movement,” U.S. Patent Application Publication 2013/0324152 titled “Asset Tracking System Activated by Predetermined Pattern of Asset Movement,” and U.S. patent application Ser. No. 14/038,341 filed Sep. 26, 2013 titled “Pattern Recognition Based Motion Detection for Asset Tracking System,” all which are incorporated herein by reference in their entirety, can further be used to optimize power consumption. Another method, which stores multiple data points and sends it once, described in U.S. patent application Ser. No. 14/140,330 filed Dec. 24, 2013 titled “Methodology to Extend Battery Power in Asset-Tracking Device” and also incorporated herein by reference in its entirety, can additionally or alternately be used.

Device100, with the power management system described herein, can be used in combination with sensors, positioned in or on the container, that provide information regarding the location of the container, particularly, if the container is proximate to, being loaded into, or already loaded in a transportation vessels, so that the tracking device can be deactivated so as to not interfere with the communications systems of the transportation vessel, such as an aircraft. Examples of tracking systems that include such sensors include those described in U.S. patent application Ser. No. 14/140,304 filed Dec. 24, 2013 titled “Method and Apparatus for Activation and Deactivation of Aircraft Container Tracking Device” and also incorporated herein by reference in its entirety.

Device100can be placed into or on a cargo container (either the exterior or interior). Alternately, device100may be formed into the wall of a cargo container, thus being integral with the container. No matter where or how installed, tracking device100is installed or attached in such a manner that it does not interfere with cargo handling equipment; this includes placement of transmitting device100and the power sources, if removed from the device, in a location such that neither the cargo handling equipment (e.g., fork truck or the like) nor a turbulent aircraft ride readily can damage the devices or power sources.

In optimum conditions, the transmission of RF signals and cellular signals, both to and from the device, is uninhibited. To collect as much energy as possible for tracking device100, device100, or at least the photovoltaic portion102of device100, is exposed to visible light, either directly or through housing or enclosure126.

For embodiments where tracking device100is mounted on the exterior of a cargo container, enclosure126of device100can be constructed from a shielded structure and material adapted to withstand severe environment conditions involving high thermal and mechanical stress while providing light (UV) and RF transparency. The UV transparency allows sufficient photons to reach photovoltaic device102to reliably power tracking device100and the RF transparency attenuates less transmitted/received cellular signals at specific frequency bands. Examples of suitable materials for enclosure126include polymeric materials such as polycarbonate and polyethylene. For embodiments where tracking device100is present in or on the interior of the cargo container, in addition to or alternately to enclosure126being transparent, the entire cargo container can be light (UV) and RF transparent or only a portion thereof, such as a window or one wall.

A particular embodiment of a light (UV) and RF transparent structure that can be used for enclosure126or the cargo container is illustrated inFIGS. 3 and 4. The structure includes a perforated metallic material with a periodic pattern of apertures sandwiched with a glass or dielectric plate. The glass or dielectric plate not only provides structural support, but also is protective against severe environments.

Turning toFIG. 3, an enclosure200is shown formed from a perforated metallic material. Enclosure200, in this embodiment, is a cuboid (rectangular) and includes a plurality of walls202(i.e.,202a,202b,202c, etc.), at least one of which includes the perforated metallic material. Enclosure200may be a cargo container or may be enclosure126of device100.

Wall202is constructed from a metallic material204perforated with a periodic pattern of apertures206adjacent to a dielectric plate208. Although not required, dielectric plate208is in contact with metallic material204and may be secured (e.g., adhered) thereto. The entire wall202may have the pattern of apertures206thereon, or only a portion of wall202may have apertures206. Metallic material204can be any metal such as iron, steel (e.g., stainless steel), titanium, aluminum, copper, molybdenum, or brass. Metallic material204may be a metal alloy or an alloy of metal with a non-metallic material; for example, metallic material204may be a reinforced metal and/or composite material. In some embodiments, a highly electrical conductive metal such as copper, beryllium copper, or aluminum is desired for metallic material204. The thickness of metallic material204is selected based on the dielectric constant of dielectric plate208, the dimensions (e.g., diameter) of apertures206, and the operating wavelength, since each of these parameters affect the equivalent electrical length of the waveguide formed by aperture206through metallic material204.

Dielectric plate208provides structural support to wall202and also protects enclosure200and its contents against environmental elements (e.g., rain, humidity, dust, etc.). Dielectric plate208maybe a conventional dielectric material such as quartz, boron nitride, silicon nitride, beryllium oxide, aluminum oxide, or glass and is transmissive and at least partially transparent (preferably, fully transparent) to visible light. Preferably, dielectric plate208is not opaque. In some embodiments, a second dielectric plate may be present on the other side of metallic material204, thus forming a sandwich construction of metallic material204between two glass or dielectric plates208. In most embodiments, the thickness of dielectric plate208is less than 10 times the thickness of metallic material204.

Metallic plate204includes apertures206configured to allow the passage of RF and visible light therethrough. Apertures206may be referred to as waveguides, directing the passage of RF and visible light through metallic plate204. RF energy, in general, has a frequency of 3 kHz to 300 GHz, which corresponds to a wavelength of 10 km to 1 cm. For most RF tracking systems, the RF frequency used is 0.4 to 7.2 GHz, which corresponds to a wavelength of 4 to 70 cm. Visible light includes wavelengths of about 390 to 700 nm, and near infrared (NIR) includes wavelengths of about 700 nm to 1 mm.

The frequency behavior of enclosure200can be designed by altering the shape, size and orientation of apertures206and also the thickness of metallic plate204. Examples of suitable shapes for apertures206include circular, oval/elliptical, rectangular (including square), other polygonal, and irregular shapes. In most embodiments, all apertures206on container200or at least on wall202will have the same shape and size, although in some embodiments, the multiple shapes and/or sizes may be used to allow different wavelengths of energy to pass therethrough. Apertures206may be arranged in a regular, orderly pattern or may be randomly positioned. They may be arranged in parallel rows, with apertures in adjacent rows aligned to form columns orthogonal to the rows, or the rows may be offset.

In one embodiment, the aperture shape is circular, as shown inFIG. 4. A plurality of apertures306is shown, each having a diameter “d” equal to or less than half (½) the wavelength and more than quarter (¼) of the wavelength of the RF energy to be transmitted and/or received. This diameter “d” is both a length and a width or height for circular apertures306. Apertures306in adjacent rows are spaced a distance “a” (between apertures centers) and apertures306in a row are spaced a distance “b” (between adjacent aperture centers), where both “a” and “b” are less than half (½) the wavelength of the RF energy to be passed. In this embodiment, apertures306form adjacent equilateral triangles, the centers of apertures306in adjacent rows/columns forming an angle “theta” (θ) of 60°, and thus “a” and “b” being equal. Particular examples of circular aperture patterns include: d=8 cm, a/b=16 cm, and theta=60 degrees, for RF energy having a wavelength of 33.31 cm; d=2.9 cm, a/b=5.85 cm, and theta=60 degrees, for RF energy having a wavelength of 11.71 cm; and d=1 cm, a/b=2 cm and theta=60 degrees, for RF energy having a wavelength of 4.16 cm.

Other embodiments of perforated metallic structures are provided in U.S. Patent Application Publication 2014/0018023 (Lee et al.), titled “Light and RF Transparent Enclosure for Use with Asset Tracking Device,” the entire disclosure of which is incorporated herein by reference.

The perforated structure should have sufficient integrity so that the container conforms to National Aerospace Standard (NAS) NAS3610 and FAA Technical Standard Order (TSO) No. C90c; these specifications dictate the compression and rigidity strength of the container, in addition to the external and interface geometries of the container. International Air Transport Association (IATA) unit load device (ULD) Technical Manual, 20th edition, may also be used for operational specifications.

Thus, various embodiments of the POWER MANAGEMENT SYSTEM FOR AIRCRAFT CONTAINER TRACKING DEVICE are disclosed. The implementations described above and other implementations are within the scope of the following claims. One skilled in the art will appreciate that the present invention can be practiced with embodiments other than those disclosed. The disclosed embodiments are presented for purposes of illustration and not limitation, and the present invention is limited only by the claims that follow.