System and method for radiofrequency stealth in unmanned aerial vehicles

Abstract

An apparatus comprises a capacitive power module 11 and a controller 15. The capacitive power module includes a capacitive element 12 having a pair of opposing conductive plates 13 and is connected to

Description

CROSS-REFERENCE(S) TO RELATED APPLICATIONS This application claims priority from United Kingdom patent application number 2311153.7 filed on 20 July 2023, which is incorporated by reference herein. FIELD OF THE INVENTION The present disclosure relates to unmanned aerial vehicles (UAV). More specifically, although not exclusively, the present disclosure relates to in-body capacitor storage for UAVs and related devices. The disclosure further relates to providing backup power storage to UAVs and masking the detectability of UAVs. BACKGROUND TO THE INVENTION With advancements in the monitoring, surveillance, and transportation industry, UAVs or drones have become increasingly beneficial to facilitate daily operations. Nowadays, drones find their potential application in areas like aerial photography and videography, search and rescue operations, infrastructure inspection, environmental monitoring, and delivery services. Drones gain importance because of their versatility and capability to access remote areas. For rescue operations, surveillance, and aerial photography they assist in the cause of inspecting the area regarding specific parameters like thermal or optical imaging. Similarly, an infrastructural inspection of far-off areas where manual inspection cannot be done is required to be conducted via drones. UAVs in general and drones in specificity have recently found their use in applications like weather monitoring and delivery services. Integration of drones with contemporary applications is based on the inability of the workforce to reach specific areas which may be congested or remote. Irrespective of ground vehicles, batteries cannot simply add to increase the available power and hence the overall flight time. The time-of-flight exponentially drops with an increase in the number of batteries due to their weight. Efficient time of flight is one of the major parameters to gauge the performance of a drone. It allows the UAV operator to complete a certain expedition in one go. In this regard, different hybrid solutions have been a topic of research for the last few decades. Fuel Cell powered solutions, solar and similar have been proposed but each has its challenges, of which weight constraints are at the top. A solution is to use a small battery and recharge it during operation times. To do this a sophisticated charging mechanism is required which results in high cost. So far, lithium batteries are considered one of the potential power storage sources. However, the operation time requirement extended beyond the capacity of lithium batteries and the industry is looking for other solutions as primary or in parallel with lithium batteries. The use of supercapacitor-based electrical power storage in vehicles has paved a new path in the realm of automobiles and UAVs. Nowadays they are famous for short charging time and large power backup. Another issue, especially with multi-propeller drones, is a buzzing sound they produce. Mostly the sound is caused by the propellers cutting the air and it directly contributes to noise pollution. It can also disturb a mission if stealth mode is required as in the case of wildlife surveillance. In this regard, many noise-free UAV designs are already available in the market. Mostly the noise of the propeller is reduced by making special geometry, but the cost is a reduction in efficiency. Other components which produce noise are motors, frames, and sometimes electronics. In some applications, it is desired to extend a drone’s stealth mode to prevent location sensing and tracking devices, such as radar or lidar, from detecting the drone’s presence. Hiding a drone’s location includes masking the location, or exact location, of the drone. In this manner, a radar system, for example, may be able to detect a device in a certain area but may not be able to determine the exact location of the drone. Hiding a UAV in this way is beneficial as the radar system will not be able to determine the drone’s parameters or specifications, such as size, shape, and travelling speed. Therefore, the radar system will not be able to determine what type of UAV is present and what it is used for. The preceding discussion of the background to the invention is intended only to facilitate an understanding of the present invention. It should be appreciated that the discussion is not an acknowledgment or admission that any of the material referred to was part of the common general knowledge in the art as at the priority date of the application. SUMMARY OF THE INVENTION In accordance with an aspect of the invention there is provided an apparatus comprising: a capacitive power module including a capacitive element having a pair of opposing conductive plates and being connected to an electrical power sink / source; and, a controller configured to switch an operating mode of the capacitive power module between: an energy providing mode in which electrical energy is provided from the capacitive element to the electrical power sink / source; and, an ionization mode in which a potential difference is applied across the pair of opposing conductive plates of the capacitive element, wherein a magnitude of the potential difference applied across the pair of opposing conductive plates is sufficient so as to ionize surrounding air molecules, wherein the controller is configured to select the ionization mode in response to a first instruction. The electrical power sink / source may include a battery which may be configured to: store energy provided by the capacitive element when the capacitive power module operates in the energy providing mode; and, supply electrical energy to the capacitive element when the capacitive power module operates in the ionization mode. The apparatus may be an unmanned aerial vehicle. The unmanned aerial vehicle may have a plurality of arms extending from a body and supporting rotors. The capacitive power module may include a plurality of capacitive elements. The capacitive elements may be disposed in or provide the arms. Each arm may be provided by a capacitive element. One or more capacitive elements may be disposed on each arm. The opposing plates may be provided by a set of concentric, nested tubes separated by a tubular dielectric substrate. The tubes and tubular dielectric substrate may be perforated. The perforations provided in the tubes may be slotted. The perforations in the tubular dielectric substrate may be circular. The opposing plates may be provided by semi-circular interlaced ribs which may be extending alternatively from opposing spines and surrounding a cylindrical dielectric substrate. The spines may be moveable towards and away from each other. The opposing plates may be provided by interlaced plates which may be extending alternatively from opposing support members. A slotted dielectric substrate having slots corresponding to positions of the plates may be disposed between the support members. The support members may be moveable towards and away from each other. The first instruction may be generated in response to a detection alert. The detection alert may alert of possible radar-based detection. In accordance with a further aspect of the invention there is provided a capacitive electric storage means for an unmanned aerial vehicle (UAV), comprising: a capacitive unit located near a connector connecting an UAV propelling means to an UAV body, the capacitive unit including two electrodes and a dielectric medium; wherein the capacitive unit is configured to generate an electric field having a first electric field strength. The electric field generated by the capacitive unit may ionise air surrounding the capacitive unit. A distance between the electrodes of the capacitive unit may be adjusted with an adjustment means such that the electric field may have a second electric field strength. The second electric field strength may be stronger than the first electric field strength. An electric potential supplied to the electrodes may be adjusted such that the electric field has a third electric field strength. The third electric field strength may be stronger than the first electric field strength. The third electric field strength may be equal to the second electric field strength. The capacitive unit may have a cross-capacitive effect on another capacitive unit. The capacitive unit may have a perforated geometry configured to reduce noise created by the UAV propelling means. The perforated geometry of the capacitive unit may increase an aerodynamic efficiency of the UAV. The capacitive unit may include an interlocking arrangement which may be configured to increase an effective capacitive surface area of the electrodes of the capacitive unit. The interlocking arrangement may be defined by multiple sections of the electrodes overlapping without contacting. The dielectric medium may be a relatively lightweight dielectric medium and may have multiple perforations configured to decrease the effective capacitive surface area of the electrodes. The adjustment means may be a distance control means including a screw and tread arrangement configured to control the distance between the electrodes. The dielectric medium may mimic support structures or the connectors of the unmanned aerial vehicle. The capacitive unit may have a maze-like geometry configured to reduce noise created by the UAV propelling means. The interlocking arrangement and the maze-like geometry may be complementary. There may be an external ignition circuit which may be configured to supply a potential difference to the capacitive unit such that the electric field has a second electric field or third electric field. The ignition circuit may include a power source module configured to power a high-voltage generator module. The power source may be configured to activate a feedback control loop which may be configured to keep the ignition circuit active until the second electric field or third electric field is generated. A current supplied to the electrodes may be adjusted such that the electric field has a fourth electric field strength. The fourth electric field strength may be equal to the second electric field strength or the third electric field strength. In accordance with an aspect of the present invention there is provided a capacitive charge storage for a UAV, comprising, body capacitive arms between a propeller and a central control unit, wherein the capacitive arms include recurrent capacitive units which includes conductor plates made up of an intrinsic material or include a support geometry which aids in noise reduction and dampening produced by the propeller and a motor unit, wherein a capacitive arm has a parallel plate, inter-lockable, slidable multi-cylindrical, or the like, configured such that between two perforated conductor plates a perforated, lightweight, and compressible dielectric substrate is located which includes almost zero mass density so that an effective distance between the two plates is decreased for increased capacitance generation. In the recurrent parallel plate configuration of the capacitive arm, each wall may have a conductive plate with a respective distance from each other such that cross-capacitance may exist between adjacent plates. Different arrangements may be disclosed which may be used for capacitor storage. The noise reduction purpose of this body capacitive arm may be fulfilled in such a way that when an incoming noise wave with an increased amplitude passes through the capacitive arms due to repetitive striking within the structure of the capacitive arm, the noise wave may lose all its energy and go out of the arm with reduced amplitude. The body’s capacitive arms may be capable of ionising surrounding air due to a strong electric field generation in each arm. Generation of a strong electric field may be achieved either by decreasing the distance between the two conductor plates of the capacitor or increasing a potential provided to them. An external ignition circuit may also achieve ionisation of surrounding air molecules. By generating very high voltages, a strong field between the body’s capacitive arms may be created via the ignition circuit ionising air molecules around it. Ionisation of air molecules around the drone may be helpful in such a way that a returning radio wave coming from an intercepting base station may experience a change in the permittivity of an ionised air zone. Due to the change in the permittivity of the ionised air zone, an incident radio wave may partially reflect or refract into that zone. Therefore, a drone's exact location may be obscured due to a changing magnitude and strength of the returning radio wave. The ionisation of air molecules through the external ignition circuit may be achieved by incorporating ignition wires into the drone’s body through a circular spider-web configuration so that the surrounding air may be ionised uniformly. Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS In the drawings: Figure 1 is a schematic diagram which illustrates an example apparatus according to aspects of the invention; Figure 2 is a three-dimensional view of an example embodiment of an unmanned aerial vehicle (UAV) incorporating a capacitive unit; Figure 3A includes a top view of an example embodiment of a capacitive unit; Figure 3B is a three-dimensional view of another exemplary embodiment of a capacitive unit; Figure 3C is a three-dimensional view of yet another exemplary embodiment of a capacitive unit; Figure 4A is an exemplary embodiment of a connector of the UAV illustrated in Figure 2 including a plurality of capacitive units; Figure 4B is a schematic diagram which illustrates cross-capacitance; Figure 5A includes a side view of an exemplary capacitive unit including an interlocking arrangement; Figure 5B, is a three-dimensional view of another exemplary capacitive unit including another interlocking arrangement and an adjustment means; Figure 6 is a three-dimensional view of another exemplary capacitive unit including another interlocking arrangement and another adjustment means; Figure 7 is a three-dimensional view of another exemplary capacitive unit including perforations and a dielectric medium; Figures 8A-8B are example embodiments of capacitive units having maze-like geometries; Figure 9 is an exemplary perspective view illustrating ionisation of air surrounding a plurality of UAVs of Figure 2; Figure 10 is a schematic diagram illustrating an example of a radio-wave meeting a medium; Figure 11 is an example representation of adjusting a potential difference across two electrodes of a capacitive unit; Figure 12 is a schematic diagram illustrating components of an ignition circuit according to aspects of the present disclosure; Figure 13 is an exemplary representation of an effect the ignition circuit of Figure 12 has on air; and Figure 14 is a top view of the UAV of Figure 2 ionising surrounding air. DETAILED DESCRIPTION WITH REFERENCE TO THE DRAWINGS An apparatus including a capacitive electric storage means having a capacitive effect used for storage of electrical power and / or stealth operation is provided. The capacitive electric storage means may include one or more capacitive units (or “capacitive elements”) which may include two or more electrodes (e.g. in the form of opposing conductive plates) and a dielectric medium. The capacitive electric storage means may include a capacitive power module including the capacitive element having a pair of opposing conductive plates. The capacitive power module may be connected to an electrical power sink / source. The capacitive power module may be switchable between: an energy providing mode and an ionization mode. In the energy providing mode, electrical energy is provided via or from the capacitive element to the electrical power sink / source. The electrical power sink / source may include a power source of the UAV, such as a battery, operating as at least an electrical power source and in some examples as an electrical power sink. The electrical power sink / source may further optionally include (as electrical power sinks) one or more of: electronics (such as a central control unit), one or more motors, or the like. An electrical power sink may receive electrical power for storage and / or consumption. An electrical power source may provide electrical power. In the ionization mode, a potential difference sufficient so as to ionise surrounding air molecules is applied across the pair of opposing conductive plates of the capacitive element. The apparatus includes a controller, which may be provided by a central control unit, configured to switch the capacitive power module between the energy providing mode and the ionization mode. The controller may further be configured to select the ionization mode in response to a first instruction and to select the energy providing mode in response to a second instruction. The capacitive element may, in the ionization mode, ionise surrounding air particles or molecules, and may effectively ionise air molecules surrounding the apparatus. The air may be ionised by an electric field generated by the capacitive element. The greater a strength of the electric field, the greater the reach of the surrounding ionised air molecules may be. The strength of the electric field between the opposing plates may be increased exponentially by decreasing the distance between the two adjacent and / or consecutive plates on the one hand and increasing the potential difference on the other hand. The capacitive electric storage means may be configured to discharge electrical power for use by an unmanned aerial vehicle (UAV). The capacitive electric storage means may be powered or charged together with or separate from a UAV power source. The UAV power source may include any power source, such as a battery. The battery may, for example, be a lithium-based battery. The capacitive electric storage means may be able to ionise air particles surrounding the UAV. The UAV may include a body which may include a central control unit, which may include or provide the controller described above, and the electrical power sink / source. The battery may be configured to: store energy provided from the capacitive element when the capacitive power module operates in the energy providing mode; and, supply electrical energy to the capacitive element when the capacitive power module operates in the ionization mode. The battery may further provide electrical power for other purposes, such as propelling the UAV, powering electronics of the UAV and the like. The UAV may further include a connector which may be configured to connect the body to a propelling means. The propelling means may be a rotor or propeller. The capacitive unit may be located near or on a surface of the connector. The UAV may have multiple propellers and, therefore, multiple connectors, each with one or more capacitive units. The capacitive electric storage may be used to extend a battery’s life and the flight time of the UAV. Thereby, the capacitive electric storage or capacitive power module may be used as an auxiliary power source for the UAV which may provide energy to the electrical power sink / source during the energy providing mode. A larger UAV may be associated with a larger connector or connectors having a greater surface area for integration of the capacitive unit, resulting in a greater capacitive power supply. The terms “unmanned aerial vehicle”, “UAV” and “drone” as used herein should be broadly construed to include any aircraft without any human pilot, crew, or passengers on board and may include any remote-controlled pilotless aircraft or small flying device. The terms “UAV” and “drone” as used herein may be synonymous and may be used interchangeably. In one embodiment, the apparatus may be used in conjunction with a UAV. In such an embodiment the apparatus may be retrofitted to attach to the UAV such that the capacitive power module can connect to the UAV’s electrical power sink / source. In other embodiments, the apparatus may be in the form of or may be integrally formed with a UAV. In some embodiments, the apparatus may include both the capacitive power module and the power sink / source. The UAV may have a plurality of arms which may extend from a body and may support propelling means. Each of the arms may be in the form of or may include a connector which may be configured to connect the body to the propelling means. As mentioned, the capacitive elements may be located on the surface of a connector or arm of the UAV. The capacitive power module may include a plurality of capacitive elements which may be disposed in or provide at least one of the arms. Therefore, the arms may be referred to as “capacitive arms”. Each arm may be provided by at least one capacitive element. In other words, these capacitive arms are composed of capacitive units, or capacitive elements, throughout the arms' length, which may provide power backup to a central control unit. In some examples, the arms may provide an intrinsic geometry and / or may be formed from a material selected or suitable for aiding noise reduction and / or dampening. At the same time, the capacitive arm may make the drone capable of hiding itself from intercepting radio waves based on the ionization of air molecules that pass through it because of the generation of a very high electric field and capacitance. The generation of a very high capacitance changes the permittivity of the region where the drone exists. The capacitive unit may ionise air particles or molecules surrounding the capacitive unit, and may effectively ionise air molecules surrounding the UAV. The air may be ionised by an electric field generated by the capacitive units. The greater a strength of an electric field, the greater the reach of the surrounding ionised air molecules may be. Ionised air molecules may cause detection systems, such as radar, to inaccurately locate the UAV. This may be because the radar detector may detect the ionised air particles and associate them with a foreign object, which may be associated with the UAV, and the detected area or zone may be larger than the zone of the UAV. The electric field may have a first electric field strength which may or may not be strong enough to ionise the surrounding air particles. The electric field strength of the electric field may be dependent on the distance between the electrodes, the potential difference across the electrodes, or the current supplied to the electrodes. There may be an adjustment means which may be configured to adjust the distance between the electrodes which may cause the electrodes to generate a second electric field strength. The adjustment means may be a distance control means including a screw and thread arrangement configured to control the distance between the electrodes. The second electric field strength may ionise air molecules surrounding the capacitive unit. The adjustment means may be configured to adjust the potential difference of the electrodes such that the electric field may have a third electric field strength. The adjustment means may, furthermore, adjust the current supplied such that the electric field may have a fourth electric field strength. The first electric field strength may be different from the second, third, and / or fourth electric field strengths. However, the second, third, and / or fourth electric field strength may be equal. In some instances, the second, third, and fourth electric field strengths may be different. The capacitive unit may have a perforated geometry configured to reduce noise created by the LIAV propelling means. The perforations may be configured to allow noise waves to partially pass through it, thereby obstructing the noise wave which may result in weakened noise waves. The perforated geometry of the capacitive unit may also aid in increasing an aerodynamic efficiency of the unmanned aerial vehicle. The aerodynamic drag and wind resistance may be reduced by the perforations as the perforations may create openings for wind or air to pass through. Furthermore, perforations may be located over the entire connector connecting the body to the propelling means. The capacitive unit may include an interlocking arrangement configured to increase an effective capacitive surface area of the electrodes of the capacitive unit. The interlocking arrangement may be formed by interlocking formations defining the electrodes (or opposing plates) of the capacitive unit. For instance, a first electrode may have a pyramid shape and a second electrode may have an inverse pyramid shape complementary to the first electrode’s pyramid shape. The pyramid shapes of both electrodes may have a larger surface area compared to an electrode having a flat shape expanding over similar dimensions to the bases of the pyramid and inverse pyramid shapes. Furthermore, an effective capacitive area may be a first surface area of the first electrode overlapping with a second surface area of a second electrode, the overlapping surface areas facilitating a capacitive effect. The interlocking arrangement may be defined by multiple sections of the electrodes overlapping without contacting. Furthermore, the capacitive unit may have a maze-like geometry configured to reduce noise created by the UAV propelling means. The interlocking arrangement and the maze-like geometry may be substantially similar. In accordance with another aspect of the disclosure, there may be a hybrid charging mechanism based UAV. The UAV may be an octocopter drone. It should be appreciated that the UAV should not be limited to octocopter drones and that it may be any variant of drones or unmanned aerial vehicles. The drone may include a body including body capacitive arms and body capacitive landing gear, and an external ignition circuit. The body capacitive arms may be similar to the connector described above. The landing gear may be a landing arrangement which may be configured to support the UAV when the UAV is in a landed condition. The landed condition may be a stationary condition in which the UAV is not flying or hovering. The body capacitive arms and landing gear may have an intrinsic geometry or may be made of a material which may aid in unwanted noise reduction and mitigation, the unwanted noise may be caused by a propelling means and motor unit. The body capacitive arm and landing gear may have any aerodynamically optimised geometric configuration along their length. More specifically, the body capacitive arm may have any one of an array of parallel-plate configurations, a cylindrically interlock-able configuration, a cylindrical slidable configuration, a bio-inspired configuration, or fractal and chiral configurations. Figure 1 shows an exemplary schematic diagram of an apparatus (10) including a capacitive power module (11) including a capacitive element (12) having a pair of opposing conductive plates (13) and being connected to an electrical power sink / source (20). The apparatus further includes a controller (15) configured to switch an operating mode of the capacitive power module between: an energy providing mode in which electrical energy is provided via or from the capacitive element to the electrical power sink / source; and, an ionization mode in which a potential difference is applied across the pair of opposing conductive plates of the capacitive element. A magnitude of the potential difference applied across the pair of opposing conductive plates is sufficient so as to ionise surrounding air molecules (e.g., 10,000 V per inch or more). The controller may be configured to select the ionization mode in response to a first instruction. The electrical power sink / source (20) may include or be in the form of a battery (21). The capacitive element (12) may, in addition to the opposing plates (13), include a dielectric substrate (14). The capacitive element (12) may be any one or any combination of concentric, nested tubes separated by a tubular dielectric substrate, ribs and spine, or interlaced plates. The concentric, nested tubes separated by a tubular dielectric substrate may be similar to that shown in Figure 7. The ribs and spine may be similar to that shown in Figure 6. The interlaced plates may be similar to that shown in Figures 8A or 8B. The apparatus may be used in conjunction with an unmanned aerial vehicle (40), as explained earlier. However, it could very well be that the apparatus may be integral to the UAV (40), or that the apparatus is the UAV itself, as explained earlier. Air molecules may penetrate through the capacitive arms and may be ionised by a strong electric field resulting in a change of permittivity thereof. The air molecules may be the air molecules of air surrounding the body capacitive arms. The change of permittivity of surrounding air due to its ionisation may assist in masking the exact location of the UAV. A dielectric substrate between conductive plates may have zero mass density, may be lightweight, and may be compressible such that an effective overlapping area between the plates may be decreased efficiently. The dielectric substrate may be similar to the dielectric medium as described above. The body capacitive arms may aid in uniform weight distribution of the drone’s body by making the body become a backup power source rather than adding extra weight to the body. The intrinsic geometry of the body capacitive arms of the drone may efficiently optimise the aerodynamics of the drone. The external ignition circuit may be inculcated through ignition wires and may assist to ionise the surrounding air molecules to hide the drone's location. The UAV can switch from being battery power to auxiliary power when a battery is depleted. The auxiliary power may be the capacitive body, which may be able to mitigate unwanted noise generation via the intrinsic geometry of capacitive arms and may be able to mask the exact location of the drone. A three-dimensional view of an example UAV (in the illustrated embodiment being an octocopter drone) is illustrated in the embodiment (100) of Figure 2, showing an intrinsic hybrid charging mechanism for drones. A body capacitive arm (102) may contain a certain configuration of capacitors (104) embedded along the body capacitive arm (102). In the illustrated example, the UAV includes a plurality of arms extending from a body and supporting propelling means, in this case being rotors. Each arm may be a body capacitive arm. For instance, for an octocopter drone there may be eight arms and, therefore, eight body capacitive arms (102). For a quadcopter drone there may be four arms and, therefore, four body capacitive arms. The capacitors’ configuration (104) in the capacitive arms (102) complements dry lithium-based batteries of the drone in case of battery depletion, for an increased flight time of the drone, by providing a hybrid or backup charging mechanism to a central control unit (106) of the drone. The capacitive arm of the UAV may also be capable of ionising the air molecules around it due to the generation of a strong electric field. The central control unit (106) of the drone and a landing gear (108, 110) are also shown in Figure 2, where the vertical part of the landing gear (108) may be capacitive such that it may resemble the body capacitive arms (102). A schematic depiction of a parallel plate capacitor (200) is demonstrated in Figures 3A-3C. In the parallel plate configuration, there may be two or more adjacent plates (202, 204) which may have an electric field of a certain strength between them based on the distance between the two plates (202, 204) and their respective overlapping area. As mentioned earlier, the capacitive element or capacitive unit has a pair of opposing plates, therefore, the parallel plate configuration may be viewed as two plates being opposite relative to one another. A number of capacitor units may be formed from such a configuration and the number may increase up to an N number by forming an assembly (206) horizontally along the arm of the drone and increasing the number of conductor plates. The conductive plates of assembly (206) may be placed at a distance (208) from one another. The N numbers formation of capacitive units may also give rise to parasitic capacitive units (210) which may have parasitic capacitances (212, 214, 216, 218, 220, 222). The parasitic capacitances (212, 214, 216, 218, 220, 222) formed on sides of the conductive parallel plates may benefit an overall capacitance formation. It should be appreciated that the parallel plates may be or at least similar to electrodes typically used in capacitor configurations. The plates may, therefore, be similar to the electrodes mentioned in the previous embodiments and description of the invention. An electric field strength between the two plates may be increased exponentially by decreasing the distance between the two adjacent and consecutive plates. Furthermore, the electric field strength between the two plates may also be increased exponentially by increasing a potential across the plates. An isometric view of the capacitive arm (102) having embedded capacitive units is depicted in embodiment (300) of Figure 4A. The arm (102) may contain an arrangement of conductive plates (302, 304, 306) placed periodically in such a way that a cross-capacitance (310) may exist between the adjacent faces, of one unit, placed at a specific distance (308), as illustrated in Figure 4B. The arrangement may also have supporting structures and a geometry which may increase the strength of the capacitive arm, improve aerodynamics along the arm and incorporate noise reduction mechanisms into the drone. A recurrent presence of the capacitive units in one arm (102) may increase a backup charging capacity of the drone which may increase the time of flight. The capacitive unit may also dampen unwanted noise generated by the propelling means and a motor through its perforated geometry. The capacitive units may further improve the aerodynamic efficiency along the arm (102). An efficient configuration to exponentially increase the overlapping area of the two conductive and opposing plates of the capacitive unit or capacitive element is displayed in the embodiments (400A, 400B) of Figure 5A and Figure 5B. The opposing plates may be provided by interlaced plates extending alternatively from opposing support members. A slotted dielectric substrate (406) having slots corresponding to positions of the plates may be disposed between the support members. The dielectric substrate may be a lightweight dielectric substrate. Such an interlocking arrangement may allow the adjacent conductive plates (402,404) to be engaged into one another by efficiently increasing a surface area utilised for capacitor formation, which may increase the capacitance generation. The opposing plates may be moveable towards one another. More specifically, the support members may be moveable towards each other by way of a distance control means. Having moveable opposing members, or support members, efficiently decreases or increases the surface utilised by the capacitive unit or capacitive element. The lightweight substrate may be made up of perforated and / or compressible materials so that the effective surface area between the two plates may be decreased. This arrangement for the capacitive arm of the UAV may be implemented with the help of an adjustment means which may be configured to control the distance between the plates. The adjustment means may be similar to the adjustment means previously mentioned above and may be a distance control means. The distance control means may include insulator screws (408) which may be configured to control the distance between the two plates (410, 412). Similarly, a novel thoracic-cage configuration for capacitance generation is depicted in embodiment (500) of Figure 6. Two conductive and opposing plates (502, 504) may be included which may be similar to the plates (202, 204) of the capacitive unit. The conductive plates (502, 504) may comprise projected cylinder-shaped extrudes which may extend over a base cylinder (506), the base cylinder (506) serving as a dielectric substrate and mimicking the arms of a drone for capacitance formation. Thereby, the opposing plates may be provided by semi-circular interlaced ribs, which may be referred to as the projected cylindrical-shaped extrudes, extending alternatively from opposing spines and surrounding a cylindrical dielectric substrate. The spines may be moveable towards and away from one another to increase or decrease the distance between them. For example, the distance between the two plates may be controlled via controlling screws (508). Between the two plates of the interlock-able capacitor may be a dielectric substrate which may be made from perforated and / or compressible materials which may have zero mass density so that the effective surface area between the two plates may be decreased effectively for capacitance generation. Another configuration for capacitance formation within the arms between the central control unit (106) and propelling means of embodiment (100) is depicted in the embodiment (600) of Figure 7. As mentioned earlier, the capacitive element or capacitive unit has a pair of opposing plates (602, 604). The opposing plates (602, 604) may be provided by a set of concentric, nested tubes (602, 604) separated by a tubular dielectric substrate (606). The plates (602, 604) and the dielectric substrate (606) between them may be cylinder-shaped. The cylinder-shaped conductor plates (602, 604) may be similar to the conductive plates (502, 504) of embodiment 500 and the plates (202, 204) of the capacitive unit. Each cylindrical layer may slide in and out of one another so that each layer may have perforations and geometries which may support a noise-reduction mechanism. Thereby, the tubes (602, 604) and the tubular dielectric substrate (606) may be perforated. More specifically, the perforations provided in the tubes may be slotted. Even more specifically, the perforations in the tubular dielectric substrate may be circular. It should be appreciated that the perforations of tubes and the tubular dielectric substrate may have any shape and / or pattern. It may very well be that they have the same type of perforations or even different types of perforations. However, in the preferred embodiment, the tubes have similar perforations, and the tubular structure has differently shaped perforations compared to that of the tubes. Each possible configuration depicted previously may be embedded in the arms of the drone so that the battery life in one flight may be increased. The capacitive arms of the drone, under the generation of a higher electric field, may also be able to ionize air molecules around the drone to evade detection. Similarly, each capacitor plate's intrinsic geometry or material may be in such a way that the noise reduction and damping mechanism is incorporated too. A simplified depiction demonstrating the noise reduction mechanism through the capacitive arm of the drone is depicted in the embodiments (700A, 700B) of Figures 8A and 8B. The embodiment displays an incoming noise wave (702) from the propeller and motor unit into the drone's capacitive arm block (704). In the capacitive block (704), the adjacent sides of the capacitor unit may be made up of porous material and / or may have a maze-like geometry which may be porous and / or perforated but solid at the same time. In this manner, the capacitor unit may support unwanted noise-dampening. The body capacitor block (704) may have multi-dimensional maze geometry on each wall. The noise reduction mechanism in the capacitive arm (704) may lower the amplitude of the noise wave (706) going leaving the block (704). The same mechanism may be inculcated into the body capacitive arm (102) through the configuration displayed in the arm's isometric view (708), where the projected fins of each body capacitive arm may aid in noise reduction because of their geometry. The phenomena of the drone’s camouflage because of the ionisation of surrounding air molecules due to the capacitive arms is exhibited in an exemplary embodiment (800) of Figure 9. A base station (802) may send radio waves (804) to intercept the UAV in a specific airspace. The radio waves may experience a change in permittivity between two zones, where one zone may be normal air with a permittivity e1(806), and the other sone may be the ionised air which may have a permittivity e2 (808). Due to the air molecules' ionisation (814), the drone’s location may get obscured (810, 812), whereas the actual location may not be as such. This blanket of ionised air (816) around the drone’s presence may influence the radio waves to transmit delayed data, thereby hiding the actual location of the drone. A simplified conceptual representation of the radio waves is depicted in embodiment (900) of Figure 10. The incident wave (902) with intensity Et may hit the medium (904) with an incident angle di (906) and based on the intrinsic properties of the medium (904), the intensity Er and angle 9r (908) of a reflected ray (910) may change. A part of the incident ray (902) may also refract (912) into the medium where a part of the incident wave’s intensity Et may form a transmittance angle et with the medium (904). The same conceptual phenomena may be translated for the radio waves, where the medium change may be viewed as the change in permittivity of air comprising ionised air molecules. Due to the change in strength Er and angle 6r of the reflected wave (910), an obscured location of the drone may be received. The ionisation of air molecules may be achieved by the generation of a strong electric field by a capacitive unit by decreasing the distance between the two plates of the capacitor (1002, 1004) on the one hand, where on the other hand, the same may be done by increasing the potential (1006) provided to the two plates of the capacitive unit. The phenomena of ionisation of air molecules around the body capacitive arms of the drone, achieved by increasing the potential provided to plates, is depicted in the embodiment (1000) of Figure 11. The increased potential provision to the plates of the capacitor may result in a stronger electric field generation (1008), which may in turn ionise more air molecules. The same phenomena of ionising surrounding air may also be achieved through an external ignition circuit. The simplified block diagram of the ignition circuit is demonstrated in an exemplary embodiment (1100) of Figure 12. The block diagram may include a power source module (1102) which may power up a high-voltage generator module (1104). The high-voltage generator may produce a very high voltage which may be thousands of Volts from a minimal voltage input. At the same time, the power source may also activate a feedback control loop module (1106) and a digital signal processing (DSP) module (1108). The ignition circuit may be activated by a pulse width modulation (PWM) selection module (1110), which may signal the DSP module (1108) when to provide voltage to an ignition mechanism module (1112). The ignition mechanism module (1112) and power source module (1102) may collectively activate the high-voltage generator module (1104). The high-voltage generator (1104) may also be connected to a feedback control loop (1114) which may be tasked to influence the circuit to run until a specific voltage is generated such that the circuit may ionise the air. The feedback control loop may be tasked upon receiving a first instruction. The first instruction may be generated in response to a detection alert. The detection alert may alert of possible radar detection. The detection alert may be transmitted by an external alert-generating component, source, apparatus, server, or the like. The phenomena of ionisation (1202) of air molecules surrounding the capacitive arms (1204) by the generation of a strong electric field (1206) when a specific amount of current (1208) passes through the arm (1202) via an external ignition circuit is demonstrated in an exemplary embodiment (1200) of Figure 13. A top view of an example UAV (1300) according to aspects of the present disclosure is illustrated in Figure 14. Where the drone may comprise capacitive arms (102) for hybrid energy provision to the central control unit (1302) of the drone by also allowing noise reduction and ionisation of air molecules (1304) surrounding the drone for evading detection. The ionisation of air molecules (1304) may also be achieved by a dedicated external ignition circuit incorporated through ignition wires (1306) in a circular spider-web geometry, which may allow the generation of the high electric field around the drone. A system and method for radiofrequency stealth in unmanned arial vehicles is described. A UAV comprises body capacitive arms extend between the propeller and central control unit and are composed of capacitive units throughout the arms' length. The capacitive arms are arranged to generate of a high electric field and capacitance. The generation of a very high capacitance changes the permittivity, which affects the magnitude and angle of reflected radio waves in such a way that detection of the drone is hindered. The foregoing description has been presented for the purpose of illustration; it is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Persons skilled in the relevant art can appreciate that many modifications and variations are possible in light of the above disclosure. The language used in the specification has been principally selected for readability and instructional purposes, and it may not have been selected to delineate or circumscribe the inventive subject matter. It is therefore intended that the scope of the invention be limited not by this detailed description, but rather by any claims that issue on an application based hereon. Accordingly, the disclosure of the embodiments of the invention is intended to be illustrative, but not limiting, of the scope of the invention, which is set forth in the following claims. Finally, throughout the specification and accompanying claims, unless the context requires otherwise, the word ‘comprise’ or variations such as ‘comprises’ or ‘comprising’ will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.

Claims

1. An apparatus comprising:a capacitive power module including a capacitive element having a pair of opposing conductive plates and being connected to an electrical power sink / source; and,a controller configured to switch an operating mode of the capacitive power module between: an energy providing mode in which electrical energy is provided from the capacitive element to the electrical power sink / source; and, an ionization mode in which a potential difference is applied across the pair of opposing conductive plates of the capacitive element, wherein a magnitude of the potential difference applied across the pair of opposing conductive plates is sufficient so as to ionize surrounding air molecules, wherein the controller is configured to select the ionization mode in response to a first instruction.

2. The apparatus as claimed in claim 1, wherein the electrical power sink / source includes a battery configured to: store energy provided from the capacitive element when the capacitive power module operates in the energy providing mode; and, supply electrical energy to the capacitive element when the capacitive power module operates in the ionization mode.

3. The apparatus as claimed in claim 1 or claim 2, wherein the apparatus is an unmanned aerial vehicle having a plurality of arms extending from a body and supporting rotors.

4. The apparatus as claimed in claim 3, wherein the capacitive power module includes a plurality of capacitive elements and wherein the capacitive elements are disposed in or provide the arms.

5. The apparatus as claimed in claim 4, wherein each arm is provided by a capacitive element.

6. The apparatus as claimed in claim 4, wherein one or more capacitive elements are disposed on each arm.

7. The apparatus as claimed in any one of the previous claims, wherein the opposing plates are provided by a set of concentric, nested tubes separated by a tubular dielectric substrate.

8. The apparatus as claimed in claim 7, wherein the tubes and tubular dielectric substrate are perforated.

9. The apparatus as claimed in claim 8, wherein perforations provided in the tubes are slotted.

10. The apparatus as claimed in claim 8 or claim 9, wherein perforations in the tubular dielectric substrate are circular.

11. The apparatus as claimed in any one of the previous claims, wherein the opposing plates are provided by semi-circular interlaced ribs extending alternatively from opposing spines and surrounding a cylindrical dielectric substrate.

12. The apparatus as claimed in claim 11, wherein the spines are moveable towards and away from each other.

13. The apparatus as claimed in any one of the previous claims, wherein the opposing plates are provided by interlaced plates extending alternatively from opposing support members, and wherein a slotted dielectric substrate having slots corresponding to positions of the plates is disposed between the support members.

14. The apparatus as claimed in claim 13, wherein the support members are moveable towards and away from each other.

15. The apparatus as claimed in any one of the previous claims, wherein the first instruction is generated in response to a detection alert.

16. The apparatus as claimed in claim 15, wherein the detection alert alerts of possible radarbased detection.

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