Patent Application
20140292592
The present invention relates to communications equipment in an annular vehicle.
An annular vehicle typically has an outer hull which defines a hull axis and appears substantially annular when viewed along the hull axis, the interior of the annulus defining a duct which is open at both ends.
The annular vehicle may be a submersible vehicle. When the vehicle is submerged in water (or any other liquid), the liquid may flood the duct. The term submersible is used here to refer to surface vehicles which are only partly submerged, as well as vehicles which are fully submerged in the liquid. A submersible annular vehicle is described in WO 2007/045887. It is desirable to provide a wireless communications system for an annular vehicle.
Underwater communications systems have traditionally been based on acoustic techniques, typically using hydrophones. Underwater communications are generally more difficult than land-based communications for several reasons. Underwater communications can be subject to significant multi-path propagation, leading to interference and phase shifting. The underwater signal can also be subject to strong attenuation over longer distances. Acoustic underwater communications are generally unsuitable for high data rates. The underwater channels also typically provide small exploitable bandwidths, and these channels can exhibit time variations and Doppler effects due to motions in the water medium, e.g. the moving surface. Furthermore, the high latency of underwater communications makes some tasks, e.g. synchronisation of clocks, difficult.
A first aspect of the invention provides an annular vehicle having a body which defines a body axis and appears substantially annular when viewed along the body axis, the interior of the annulus defining a duct which is open at both ends, and an electric field coupled dipole antenna arrangement for electro-magnetic communications which includes at least one dipole antenna.
A second aspect of the invention provides an underwater communications system comprising a plurality of nodes, wherein each node is an annular vehicle in accordance with the first aspect of the invention, and wherein each node is operable to communicate with at least one other node using their electric field coupled dipole antenna arrangements.
A third aspect of the invention provides a method of operating an underwater communications system comprising a plurality of nodes, at least some of the nodes being annular vehicles in accordance with the first aspect of the invention, the method comprising making electro-magnetic communications between the nodes using their electric field coupled dipole antenna arrangements.
The invention is advantageous in that the electric field (EF) coupled dipole antenna arrangement can provide communications with lower latency than systems employing acoustic communications. For example, the latency of the communications (i.e. the time from when a first node transmits and a second node receives the transmission) can be reduced by up to around 200 times as compared with traditional acoustic communications. This is particularly beneficial where the communications may be used to transfer synchronisation signals, as communications with high latency would be unsuitable for this purpose. The data transfer rate achievable using EF communications may also be higher than with acoustics, although this increase may be marginal in some circumstances.
Use of the EF coupled dipole antenna arrangement provides excellent synergy with the annular vehicle. The annular body may provide good separation for electrodes of the EF coupled dipole antenna arrangement disposed around the body. Although means for propulsion, for example, may be disposed within the duct there may also be regions free of electro-magnetic sources within the duct. By positioning the electrodes around the annular body with a region substantially free of electro-magnetic sources between the electrodes, the antenna arrangement may be designed to avoid electro-magnetic interference effects.
Preferably, the vehicle is a submersible and is configured such that when the vehicle is submerged in a liquid, the liquid floods the duct. The liquid may be water. The reduced wavelength in water makes low frequency (of the order of 10 kHz) more practical underwater due to the reduced separation distance required between nodes. Fresh water has a higher impedance than sea water and so the communications may be more reliable in fresh water. However, the annular vehicle may have particular aptitude for deep sea water operations. Alternatively, the vehicle may be an airborne vehicle in which case the fluid filling the duct would be air.
At least one dipole antenna may have separated electrodes disposed on opposite sides of the duct. In this context ‘opposite’ is not intended to be limited to diametric opposition, although the electrodes may, of course, be arranged diametrically opposed. The electrodes separation is preferably at least 120 degrees with respect to the vehicle axis.
The vehicle preferably has no electronics equipment disposed directly between the electrodes. Any such equipment could be an electro-magnetic source which could interfere with the antenna reception/transmission.
The electrodes of the at least one dipole antenna may be conformal with the vehicle body. Conformal electrodes would reduce drag of the moving vehicle, as compared with electrodes projecting outwardly from the vehicle body shape.
The electrodes of the at least one dipole antenna may be removable. Removable electrodes allow for ease of maintenance and/or repair of the electrodes.
The electrodes of the at least one dipole antenna may be covered by a dielectric material. The dielectric material may have an impedance selected to substantially match an impedance of a medium in which the vehicle is intended to operate. For example, the impedance of sea water varies with salinity. The dielectric material may be a plastics material, for example, and may be provided as a cap, or cover, over the respective dipole electrodes.
The at least one dipole antenna may have a coaxial cable extending substantially circumferentially around the duct. The coaxial cable may be shielded. The coaxial cable connects the electrodes to the antenna transmit/receive electronics.
The dipole antenna arrangement may include a plurality of dipole antennas.
The dipole antenna arrangement may include at least two substantially parallel dipole antennas.
Additionally, or alternatively, the dipole antenna arrangement may include at least two substantially orthogonal dipole antennas. For example, orthogonal dipole receive antennas may provide the capability for three-dimensional EF sensing.
The dipole antenna arrangement may include at least one transmitter antenna, and/or at least one receiver antenna, and/or at least one transceiver antenna, and/or at least one transmitter-receiver antenna.
The dipole antenna arrangement may include one or more dipole antennas disposed at an end of the duct. Mounting the dipole antenna(s) at an end of the duct can be beneficial, particularly where electronics equipment is disposed generally centrally along the body axis of the vehicle. This helps to minimise electro-magnetic interference effects of the electronics equipment on the dipole antenna(s).
Positioning the dipole antenna(s) at an end of the vehicle may be beneficial as it can be desirable to ‘fly’ the vehicle into a soft substrate so as to become partially embedded in the substrate. For example, where the vehicle is a submersible it may be desirable to fly the vehicle into the sea bed (or equivalent in fresh water, e.g. lake bed or river bed). Communications via the dipole antenna arrangement may be made over longer distances through the sea bed channel than through the lossy water channel.
The body axis may define a longitudinal axis in the direction of forward travel of the vehicle, and the dipole antenna arrangement may include one or more dipole antennas disposed at the forward end of the vehicle.
A least part of the vehicle body may be swept with respect to the body axis. The swept body may exhibit improved lift/drag performance as compared with an un-swept vehicle.
The swept annular body may form a pair of diametrically opposed apices at each end of the vehicle. Each pair of diametrically opposed apices may be spaced by a distance of approximately ¼ wavelength. For example, the diametrically opposed apices may be spaced by a distance of approximately 0.1 m to 1 m, preferably approximately 0.5 m.
The apices may provide particularly suitable locations for positioning the electrodes of the dipole antenna arrangement. For example, each dipole of the antenna arrangement may be associated with a respective pair of diametrically opposed apices, such that the separated electrodes of each dipole are disposed at a respective apex of the pair of apices. The electrodes at the diametrically opposed apices are, by definition, separated by the diameter of the duct.
The annular body may be swept such that the diametrically opposed apices at each end of the vehicle are oriented orthogonally. This may be achieved through a ‘double swept’ or ‘chevron’ design of the annular body. At each end of the vehicle, the annular body will define a first and second pairs of diametrically opposed apices. The first pair of apices will have an interior angle less than 180 degrees, whereas the second pair of apices will have an interior angle greater than 180 degrees, i.e. a re-entrant angle such that the apices face inwardly towards the vehicle body. The first and second pairs of apices will be oriented orthogonally. The other end of the annular body will also feature two pairs of orthogonal diametrically opposed apices, such that each inwardly facing apex faces towards an outwardly facing apex at the other end of the vehicle.
The double swept annular body has particular synergy with the electrode positioning of the dipole antenna arrangement, as it becomes possible to arrange two orthogonal dipoles at one end, or at both ends, of the vehicle. The body axial spacing of the apex pairs at each end of the vehicle may beneficially provide sufficient spacing between two dipole antennas disposed at the same end of the vehicle.
The dipole antenna arrangement may be configured for electro-magnetic communications at a carrier frequency in the range 10 kHz to 1000 kHz, preferably in the range 50 kHz to 100 kHz.
The vehicle may further comprise a propulsion system. The propulsion system may be used to drive the vehicle forwards and/or backwards, and/or in rotation about its body axis. The vehicle may be a glider. The glider may be powered or un-powered.
In the underwater communications system of the second aspect of the invention, the plurality of nodes may include at least one static node on the sea bed and/or at least one swimming node.
In the method of operating an underwater communications system according to the third aspect of the invention, the plurality of nodes may include a plurality of static nodes on the sea bed, and the method may further comprise making communications between the static nodes via a signal path predominantly through the sea bed.
The plurality of nodes may include at least one static node on the sea bed and at least one swimming node, and the method may further comprise making communications between the static node and the swimming node via a signal path predominantly through the sea water.
The plurality of nodes may include at least one swimming node and at least one above water surface node, and the method may further comprise making communications between the swimming node and the surface node via a signal path that includes an air propagation path.
The plurality of nodes may include at least one static node on the sea bed, and the method may further comprise positioning the static node on the sea bed by flying the annular vehicle into the sea bed so as to be partially embedded in the sea bed.
The method may further comprise deploying the nodes from a surface vessel, and preferably subsequently recovering the nodes to the vessel.
Embodiments of the invention will now be described with reference to the accompanying drawings, in which:
The annular vehicle 1 defines a bow end 6 and a stern end 7. The fluid-foil profile of the body 2 is arranged to generate lift as the annular vehicle 1 moves through a fluid medium, with the fluid passing through the duct 5 and around the outside of the annular body 2.
The fluid-foil profile, as shown in
In the particular embodiment shown in
The body 2 of the vehicle 1 has an internal volume between inner and outer skins that may be used to house a variety of components, depending on the intended function of the vehicle 1. For example, the body 2 may house batteries, ballast chambers, payload bays, gas storage, electronic equipment, such as wiring routes, processors, data storage devices, communications equipment, etc. These components may be disposed intermediate circumferential structural frames of the body that support the outer skins. The body 2 may be a pressurized or pressurizable hull.
The annular vehicle 1 shown in
Returning to the embodiment shown in
The vehicle 1 includes an electric field (EF) coupled dipole antenna arrangement 20 for electromagnetic communications. The dipole antenna arrangement includes at least one dipole antenna. As is well known, a dipole antenna generally includes a pair of electrodes spaced a distance apart.
In the embodiment shown in
The swept vehicle body 2 defines a first pair of apices at the bow end 6 of the vehicle 1 and a second pair of apices, orthogonal to the first, at the stern end 7 of the vehicle. The pair of apices at the bow 6 provide a particularly suitable location for positioning the electrodes 21a, 21b of the dipole antenna arrangement 20. The electrodes are separated by the diameter of the duct 5, and because the first pair of apices project forwardly it becomes possible to axially separate the electrodes 21a, 21b from electro-magnetic sources within the vehicle along the body axis 3. In particular, the electrodes 21a, 21b may be disposed in a region of the vehicle where interference from devices such as batteries, actuators, control electronics and propulsion systems may be minimised.
In addition, the limited volume available within the leading edge 9 of the fluid-foil profile is well utilised by making the electrodes conformal with the leading edge at each apex. The conformal electrodes will reduce drag of the moving vehicle, as compared with electrodes projecting outwardly from the vehicle body shape. At the same time, the contact surface area of the electrodes 21a, 21b with the surrounding fluid medium remains advantageously large due to the shape of the apices of the vehicle body 2.
In one embodiment, the vehicle 1 is an unmanned underwater vehicle (UUV) and the duct 5 has a diameter of approximately 0.5 m such that the vehicle can be launched from a standard torpedo tube. However, the diameter of the duct may vary widely depending of the intended use of the vehicle, whether for airborne or underwater use, manned or unmanned, type of launch system, etc.
Electric field (EF) coupled dipole antennas can provide communications up to around 200 times faster than traditional underwater acoustic communications. Although the range of EF coupled dipole antennas may be much lower than antennas for acoustic communications, the significantly lower latency of communications possible with EF coupled dipole antennas are particularly suitable for some short range communications, e.g. for transferring synchronisation signals between a plurality of nodes in an underwater communications system.
The dipole antenna 21 may be configured to either transmit or receive electric field communications, or alternatively may be configured for selectively switching between transmit and receive operations.
The dipole antenna 21 is typically operated in the low frequency (LF) range of radio communications, and more particularly may be operated in the 50 kHz to 100 kHz range for underwater communications. However, it is envisaged that the dipole antenna may alternatively be operated in the very low frequency (VLF) range, or the medium frequency (MLF) range, depending on the communications being effected, and the operational situation of the vehicle.
In one embodiment, the electrodes 21a, 21b are spaced apart by a distance approximately equal to ¼ the wavelength of the communications signal. Depending on the diameter of the annular vehicle 1, the frequency of the communications can be tuned within the desired frequency range. Whilst it would be possible to position the electrodes such that they are not diametrically opposed across the annular vehicle, so as to optimise the antenna performance by varying the dipole spacing, this would depend on the vehicle geometry and for instance would not be particularly suitable with the swept vehicle 1 shown in
With the vehicle submerged in a fluid medium such as water, the electrodes will be coupled with the fluid. The power rating of the dipole antenna 21 is therefore relatively low due to the closed path through the fluid and a voltage of approximately 3V, for example, may be appropriate.
The low power requirements of the dipole antenna are not particularly disadvantageous as compared with a loop antenna, for example, which also requires a low power rating to avoid interference with nearby electronic systems. Moreover, a loop antenna would be more susceptible from interference from running motors (such as may be found in the propulsion devices for the vehicle), and loop antennas typically suffer blind spots and have a high space requirement which would not package well with an annular vehicle. These factors have been found to promote particular synergy between an annular vehicle and a dipole antenna arrangement.
The electrodes 21a, 21b are preferably made of brass or bronze but may be made of any other suitable material. Anti-corrosion measures are put in place to mitigate the effects of coupling the electrodes 21a, 21b with the fluid medium. For example, the electrodes are AC coupled rather than DC coupled, and the electrodes may also be covered with a layer of dielectric material. The electrodes 21a, 21b are also made removable from the vehicle 1. This enables easy maintenance and/or repair of the electrodes.
The dielectric material covering the electrodes may have an impedance selected to substantially match the impedance of the fluid medium in which the vehicle is intended to operate. For example, the impedance of sea water varies with salinity, typically between 2 ′Ω to 10 ′Ω. The dielectric material may be made of a plastics material, for example, and may be provided as a cap, or cover, over the electrodes.
The coaxial cables, shown in
The vehicle 1 may be used as a node within a communications system.
Communications predominantly through the sea bed substrate 80 using the “skin effect” compares particularly favourably with a communications path 91 predominantly through the ‘blue water’ alone, such as shown in
It will be appreciated that the exemplary communications between nodes in a communications system shown in
The static node(s) may be positioned on the sea bed by ‘flying’ the annular vehicle into the sea bed so as to be partially embedded in the sea bed. The nodes may be launched from a surface vessel, and subsequently recovered to the vessel.
The direction of the communications between the various nodes will depend on the configuration of each node. For example, each node may include one or more dipole antennas, and each antenna may be configured for transmit or receive operations only, or may be configured for selectively switching between transmit and receive operations using control electronics as described above with respect to
The vehicle 201 illustrated in
The vehicle 301 illustrated in
The vehicle 401 illustrated in
The vehicle 501 illustrated in
The dipole antenna arrangements described above are provided purely as examples and other variants of the antenna arrangements will be appreciated by those skilled in the art.
Although the invention has been described above with reference to one or more preferred embodiments, it will be appreciated that various changes or modifications may be made without departing from the scope of the invention as defined in the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1120350.2 | Nov 2011 | GB | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/GB2012/052887 | 11/22/2012 | WO | 00 | 5/22/2014 |
