System for electromagnetic signal channelling through an aerial vehicle

Abstract

A system 500 for electromagnetic signal channelling through an aerial vehicle comprises a first electromagnetic element 504 configured to receive electromagnetic waves 106, a second electromagnetic el

Description

CROSS-REFERENCE TO RELATED APPLICATIONS 5 This application claims priority from United Kingdom patent application number 2311157.8 filed on 20 July 2023, which is incorporated by reference herein. FIELD 10 The present disclosure relates to a system for electromagnetic signal channelling through an aerial vehicle. BACKGROUND 15 Achieving low visibility or low detectability of an object may be desirable for many military and civilian applications. For example, there may be a particular desire to reduce the visibility or detectability of objects such as aerial vehicles. 20 Aerial vehicles have numerous functions, including, but not limited to, transport of people and cargo, surveillance, monitoring of any environment, policing, military operations, and reconnaissance. In some instances, for example in military operations or reconnaissance, it is advantageous for such aerial vehicles to have reduced visibility or detectability. 25 Stealth technology refers a set of techniques that aim to make an object less visible or undetectable by radar, infrared, sonar, or other detection methods. Stealth technology can enhance the survivability and effectiveness of aircraft and spacecraft by reducing their chances of being detected and engaged. Aerial vehicles that are less visible or undetectable by radar, infrared, sonar, or other detection methods can avoid or delay being tracked, targeted, or 30 engaged. Designing and implementing stealth technology may pose many challenges and trade-offs. Specifically, with reference to aerial vehicles, implementing such stealth technologies can be disadvantageous in that the aerodynamics and structural performance of the aerial vehicles may 35 be compromised as a result thereof. One method of implementing stealth technology involves shaping the vehicle body to deflect or 19 09 25 scatter radar waves away from the source. This method has the disadvantage that the aerodynamic performance or payload capacity of the aerial vehicle may be compromised. A further method comprises applying radar-absorbing materials or coatings to the vehicle surface. 5 The application of this method of implementation of stealth technology is limited as radarabsorbing materials or coatings may degrade over time or under harsh environmental conditions. Alternate methods may involve the use of active or passive electronic countermeasures to jam or deceive radar signals, to thereby reduce the detectability of the aerial vehicle by radar. However, 10 these countermeasures may be ineffective against advanced radar systems. Furthermore, active electronic countermeasures may require additional power sources which will increase costs and weight of the aerial vehicle. A further method may involve deploying decoys or chaff to create false targets or clutter. However, 15 the application of this method of stealth technology in aerial vehicles may be ineffective as decoys or chaff may be easily distinguishable from the real target. Additionally, the use of this method may cause collateral damage. Furthermore, stealth technology may be applied to aerial vehicles by generating ionization clouds 20 in the vicinity of the aerial vehicle to refract or absorb radar waves. This method is disadvantageous in that these ionization clouds may interfere with the aerial vehicle’s own communication or navigation systems. Finally, another method of implementing stealth technology in aerial vehicles may involve the use 25 of reflector antennas with adaptive nulling assemblies to produce high-quality nulls in the sidelobe region. However, such reflector antennas may be bulky, complex or costly. There is accordingly scope for improvement. 30 The preceding discussion of the background is intended only to facilitate an understanding of the present disclosure. 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. 35 SUMMARY 19 09 25 In accordance with an aspect of the disclosure there is provided a system for electromagnetic signal channelling through an aerial vehicle, the system comprising the aerial vehicle and: a first electromagnetic element comprising one or more transducer configured to receive electromagnetic waves; 5 a second electromagnetic element comprising one or more transducer configured to emit the electromagnetic waves; and a channel connecting the first electromagnetic element and the second electromagnetic element configured to transmit the electromagnetic waves from the first electromagnetic element to the second electromagnetic element; 10 wherein the channel at least partially includes a material with one or both of a refractive index or electric permittivity which are near zero, which substantially traverses a length of the channel; and wherein the first electromagnetic element is positioned at or near a first side of the aerial vehicle and the second electromagnetic element is positioned at or near a second side of the 15 aerial vehicle. One or both of the permittivity or refractive index may be configurable. The material within the channel may be either or both of a metallic wire or an epsilon-near-zero 20 (ENZ) material. The first side of the aerial vehicle may be positioned at a substantially opposite side of the second side of the aerial vehicle. 25 The first and second electromagnetic elements may each comprise one or more waveguide. The first electromagnetic element may comprise one or more waveguide together with one or more transducer and the second electromagnetic element may comprise one or more waveguide together with one or more transducer. 30 The transducers may be antennas. A direction of the emitted electromagnetic waves may be controlled by adjusting a radiation pattern of the second electromagnetic element. 35 The system may include a means of generating an electric field. The generated electric field may be configured to modulate one or both of the permittivity or refractive index. The channel may be at least partially constructed from metal oxides and / or polymers. Embodiments of the technology will now be described, by way of example only, with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS In the drawings: 10 Figure 1 illustrates a first embodiment of a system for electromagnetic signal channelling including incident EM waves and emitted EM waves; 15 Figure 2 illustrates a second embodiment of a system for electromagnetic signal channelling for electromagnetic stealth of an object including incident EM waves and emitted EM waves; 19 09 25 Figure 3 illustrates a third embodiment of a system for electromagnetic signal channelling for electromagnetic stealth of an aerial vehicle; 20 Figure 4 is a schematic showing a surface of an electromagnetic element comprising an array of antennas, waveguides, or any other suitable device; 25 Figure 5 is a schematic showing a surface of an electromagnetic element comprising an array of antennas, waveguides, or any other suitable device; Figure 6 is a schematic diagram showing the use of variable capacitors on a surface of an electromagnetic element including array elements; Figure 7 illustrates a waveguide setup including a conductive wire; 30 Figure 8 illustrates two patch antennas connected by ENZ material or a microstrip line; Figure 9 illustrates a radiation pattern of an antenna array; 35 Figure 10A illustrates an example implementation in which waveguides are linked by an ENZ channel; Figure 10B illustrates an example implementation in which waveguides are linked by a conductive wire; Figure 11 5 illustrates how incident EM waves can be used internally for RF harvesting or other appropriate purposes; and Figure 12 illustrates an example system for electromagnetic signal channelling for electromagnetic stealth of an aerial vehicle. 19 09 25 10 DETAILED DESCRIPTION WITH REFERENCE TO THE DRAWINGS Aspects of the present disclosure provide a system for electromagnetic signal channelling through an aerial vehicle. Aspects of the present disclosure provide for such a system to comprise a first electromagnetic element configured to receive electromagnetic waves, a second electromagnetic 15 element configured to emit the electromagnetic waves, and a channel connecting the first electromagnetic element and the second electromagnetic element configured to transmit or convey the electromagnetic waves from the first electromagnetic element to the second electromagnetic element. The first electromagnetic element is positioned near a first side of the aerial vehicle and the second electromagnetic element is positioned at a second side of the aerial 20 vehicle. The channel at least partially includes a material with one or both of a refractive index or electric permittivity which are near zero, which substantially traverses a length of the channel. One or both of the permittivity or refractive index may be configurable. The material within the channel may be either or both of a metallic wire or an epsilon-near-zero (ENZ) material. 25 The channel can transmit or convey the electromagnetic (EM) waves from the first electromagnetic element, which may be defined as being the ‘source’, to the second electromagnetic element, which may be defined as being the ‘sink’, without reflection since EM waves’ phase velocity and wavelength inside the material having near-zero electric permittivity is 30 infinite. The channel may be constructed from metal oxides or polymers, or any other suitable material or combination of materials. The first side of the aerial vehicle may be positioned at a substantially opposite side of the second side of the aerial vehicle such that the first electromagnetic element is positioned at an opposite 35 end of the aerial vehicle to the second electromagnetic element. 19 09 25 The electromagnetic elements may be in the form of transducers, such as antennas, or waveguides. The electromagnetic elements may each comprise one or more of such articles, and may also comprise a combination of transducers, antennas, such as patch antennas, and waveguides. It should be noted that the electromagnetic elements may be any suitable device 5 that can capture and transmit EM waves, for example by converting propagating electromagnetic waves to and from conducted electrical signals. The direction of the electromagnetic waves that are emitted from the second electromagnetic element may be controllable by adjusting a radiation pattern of the second electromagnetic 10 element. The system may include a means of generating an electric field. Additionally, or alternatively, the channel may include an active device capable of generation of an electric field. One or both of the permittivity or refractive index may be modulated by the generated electric field. Modulation 15 of the permittivity of the material or refractive index thereof may be used to generate spurious signals from the aerial vehicle. The spurious signals may mimic characteristics of other aerial vehicles or create false returns from and / or trajectories and locations of the aerial vehicle. The system for electromagnetic signal channelling through an aerial vehicle may be utilised to 20 cloak such an aerial vehicle from radar, for the deception of missiles, to prevent the aerial vehicle from being tracked, and any other suitable application. The process of receiving, transmitting and emitting the EM waves may be effective in reducing or elimination the reflection of the EM waves back to the source, which may be radar, a missile, or any other suitable device. 25 Radar and missiles work on the principle of obtaining data about the target from the reflection of the EM waves that they transmit. Therefore, by eliminating or reducing such reflection, cloaking of aerial vehicles may be achieved. In other words, the method may make the aerial vehicle appear invisible or indistinguishable from its surroundings to radar or missiles. 30 In the various embodiments of the present disclosure, the behavior of the material in the channel may be varied. This may be achieved by applying an external electric field or any other suitable method or by using active devices such as amplifiers, resistors, capacitors, or any other suitable device. By varying the behavior of the material in the channel, the reflection and absorption of the incident waves on the waveguide, antenna, traducer, or any other suitable element, may be 35 controlled. This may be used to generate spurious signals for deceiving missiles. By disturbing the matching 19 09 25 between the waveguide and the channel, the amount of reflection can be controlled, which can be used for generating spurious signals, thereby deceiving missiles. The term “epsilon-near-zero” as used herein should be broadly construed as to mean a material 5 or structure with a permittivity value close to zero within a specific frequency range, exhibiting specific electromagnetic properties or effects. Examples of these specific electromagnetic properties or effects may include one or more of: wavelength stretching (very low wave number); enhanced electric field strength; and, unusual wave propagation and tunneling effects. These effects may become more pronounced as the permittivity approaches zero, but they can still be 10 observed and utilized with small, non-zero values. An epsilon-near-zero (ENZ) material may be characterized by a permittivity value which is close to, but not exactly, zero. In some examples, values of about 0.1 or less (but not exactly 0) are considered "near-zero" for permittivity. In other examples, permittivity values of about 0.001 are considered “near-zero”. In further examples, permittivity values of about 0.00001 are considered “near-zero”. The specific value required to 15 achieve "near-zero" behavior may vary depending on the frequency of operation and material composition. Further, in some examples, actual values may depend on the ratio of two permittivities at a boundary, such as at a boundary between an electromagnetic element and free space. In some examples, ENZ behaviour may be achieved by operating an electromagnetic element at or below the cut-off frequency. Thus, in some examples, “near-zero” permittivity is in 20 the range between 0.1 and 0.00001. In some examples, “near-zero” permittivity is less than 0.00001. In the foregoing description, reference to an ENZ material may be understood to be interchangeable with a material having a near-zero refractive index (NZRI) in alternate embodiments. Refractive index is the square root of the permittivity and is directly proportional thereto. 25 The term “cloaking” with reference to electromagnetic cloaking, as used herein should be broadly construed as to mean the act of making an object invisible for electromagnetic radiation. The term “tunneling” as used herein should be broadly construed as to mean the process whereby 30 electromagnetic waves propagate through barriers or channels. The term “electromagnetic element” as used herein should be broadly construed as to mean any suitable transducer or waveguide, including antennas. 35 The term “electromagnetic signal channeling” as used herein should be broadly construed as to mean the transmission of electromagnetic waves through a pathway, channel, or tunnel. 19 09 25 Figures 1 to 12 illustrate example embodiments of the above-described system for electromagnetic signal channelling for cloaking an aerial vehicle according to aspects of the present disclosure. 5 Figure 1 illustrates a first embodiment of a system (500) for electromagnetic signal channelling including incident EM waves and emitted EM waves. The system (500) comprises two waveguides (504, 506) connected by a narrow ENZ channel (502). When the EM wave (106) enters the first waveguide (504), it tunnels through the ENZ channel (502) and appears at the second waveguide (506), irrespective of the shape and size of the ENZ channel (502). This is 10 because the ENZ channel supports a mode with an infinite phase velocity and a very large wavelength, which allows it to couple efficiently with the modes of waveguides. The EM wave (108) is then emitted from the second waveguide (506). The cross sections (508, 510) of the waveguides (504, 506) must be equal to avoid mismatch resulting in the reflection of EM waves from the interface of the waveguides and the ENZ channel. Under the EM wave incidence, the 15 reflection coefficient is given by the formula: _ (a! - a2) + ikp^pAp P (ai + a2) - ikonr,pAp Where k0 = is the free space wave number, nr p is the relative permeability of the ENZ material, and Ap is the total area of the transverse cross-section of channel. It shows that when the two 20 waveguides have the same cross section, a = ar = a2, the reflection coefficient can be made arbitrarily small by making the channel narrower. In Figure 2 a second embodiment of a system (600) for electromagnetic signal channelling including incident EM waves and emitted EM waves is illustrated. The system (600) is used in a 25 method of cloaking an object (104) through the phenomena of energy tunneling is disclosed. The system may have a first waveguide, patch antenna, or any other suitable device (504) at a first side of the object (104). The incident EM wave (106) tunnels through the narrow ENZ channel (502) without reflection, bypassing the object (104) and exiting the system at a second waveguide, an antenna, or any other suitable device (506). The EM waves are then emitted (602) at the 30 second waveguide (506). Figure 3 depicts a third embodiment of a system (700) for electromagnetic signal channelling. The system (700) is utilized for the cloaking of aerial vehicles wherein the aerial vehicle (702) is cloaked by exploiting the energy tunneling using an ENZ channel (706), which is connected to a 35 first electromagnetic element (708), which may be a patch antenna, flexible antenna, paint resonator, or any other suitable device and a second electromagnetic element (704), which may 19 09 25 also be a patch antenna, flexible antenna, paint resonator or any other suitable device, through which the transmitted EM waves are emitted from the system (700). The EM waves incident on the first electromagnetic element (708) are transmitted through the ENZ channel (706), bypassing the aerial vehicle (702) and leaving the system (700) through the second electromagnetic element 5 (704), thereby eliminating any reflection of incident EM waves from the surface of the aerial vehicle (702) and achieving cloaking thereof. The transmission of the EM wave through the second electromagnetic element (704), the ENZ channel (706), and the first electromagnetic element (708) may be disturbed to achieve a controlled reflection of the incident EM waves, which may be used for spurious signal generation for deceiving missiles, radars, or any other suitable 10 device. Figure 4 illustrates a front view of a surface (800) including a plurality of either one of the first (708) or the second electromagnetic elements (704) of the system shown in Figure 3. The surface (800) provides for a special type of array (703) of patch antennas, flexible antennas, waveguides, 15 or any other suitable devices (705). Each element of the array (703) may have a corresponding element on the other side of the aerial vehicle connected by a narrow ENZ channel to the respective element (705) on the first side, thereby achieving energy tunneling and cloaking of the aerial vehicle, on whose surfaces these arrays (703) may be printed. As such, for example, an element of the array (703) being the first electromagnetic element (708) will correspond to a 20 further element on another array being the second electromagnetic element (704) of the system, connected by a narrow ENZ channel. Figure 5 is a further exemplary front view of a surface (7000) including a plurality of differently sized electromagnetic elements (such as being differently sized variants of either one of the first 25 (708) or the second electromagnetic element (704) of the system shown in Figure 3). This surface (7000) provides for individual elements (705) having different sizes to take into account a scenario wherein EM waves have variable frequencies, such as in the case of frequency hopping. Frequency hopping refers to a technique used in wireless communication systems where a carrier frequency of a signal changes or “hops” over a wide range of frequencies according to a 30 predetermined pattern. This may be achieved by of designing patch antennas, waveguides, and the like, for different frequencies. Figure 6 illustrates a further exemplary front view of a surface (7001) including a plurality of electromagnetic elements. This exemplary surface (7001) includes an array (7003) comprising 35 individual elements (705), having a number of tunable capacitors (7005, 7007) for achieving tunability of the elements (705) to the desired frequencies. The elements (705) of the system (7001) may have n capacitors (7005) for achieving tunability to the desired frequencies. Each 19 09 25 element (705) of the array (7003) may be connected to a similar element on a second, opposite side through an ENZ channel. In some embodiments, this ENZ channel may be a narrow ENZ channel. Alternatively, the whole array (7003) may be connected to a single tunable element (705) having a capacitor (7005) achieving the configuration n to 1. 5 Figure 7 shows a fourth embodiment of a system (900) for electromagnetic signal channeling including two electromagnetic elements, specifically, two waveguides (504, 506), one acting as an inlet (504) (or source) for an incident EM wave (106) and the second one as an outlet (506) (or sink) from where the EM wave (602) exits. The two waveguides (504, 506) are connected by 10 a thin conducting wire (902), and the channel may be filled with a dielectric (904), while the outer boundaries of the channel (906) may be of PEC. The conducting wire is a metallic wire, but any other suitable conducting wire may be used in further embodiments of such a system. Energy tunnelling can be achieved in this system (900) as the thin metallic wire acts as a resonator that create a high-intensity electromagnetic field around it when it is excited by an external source. 15 The electromagnetic waves travel through the waveguide channel with almost no propagation losses in cases where the source frequency matches the resonant frequency of the wires, guiding the EM wave from one waveguide (504) to another (506) and vice versa. The energy tunneling phenomenon occurs when the frequency of the electromagnetic waves matches the resonant frequency of the wire, which is given by: c a / b\ fr = T~ 271 Je0 W Where c is the speed of light, e0 is the permittivity of free space, and b is the width of the waveguide channel. In Figure 8, an exemplary embodiment (1000) of a system for achieving coupling between two resonators (1002,1004) is illustrated. The resonators (1002,1004) are connected by a thin channel (1006), enabling coupling or tunneling between the resonators. 30 Figure 9 shows an exemplary radiation pattern (1104) of an array (1102) which includes elements (1106), which may be patch antennas, flexible antennas, waveguides, and the like. The directivity associated with the radiation pattern of the array (1102) may be controlled and can be adjusted as is required. The radiation pattern (1104) of a patch antenna depends on the shape, size, and position of the patch on the ground plane. The higher the directivity, the more focused the beam 35 is. 19 09 25 Figure 10A shows an example implementation of the system of any one of the first, second, or third embodiments of the disclosed system which includes waveguides (504, 506) having cross sections (508, 510) connected by a narrow channel of ENZ material (502). By varying the ratio of cross sections (508, 510) of the waveguides (504, 506), tunnelling efficiency may be adjusted. A 5 larger cross-section may increase the transmission coefficient of an EM wave by allowing more modes to propagate, while a smaller cross-section may decrease the EM wave by causing more reflection and scattering. Referring now to Figure 10B, the same phenomena may be observed in waveguides (1504,1506) having thin metallic wire (902) in the channel instead of ENZ material (502), as described above with reference to the fourth embodiment of the disclosed system. By 10 varying the ratio of the cross-sections (1202) and (1204), the efficiency of the tunneling may be controlled as per requirements. In Figure 11, a further embodiment of a system (1300) which can be implemented to perform a method of damping or utilizing incident EM waves internally in an aerial vehicle is illustrated. The 15 EM waves (106) incident on a first waveguide (504) may tunnel through an ENZ channel (502) and exit through a second waveguide (506) in the form of an emitted EM wave (1304). In the system (1300) illustrated and described, a radio frequency (RF) load (1302), which may be an RF harvester or any other suitable device, may be present, thereby, eliminating the incident EM waves (106) internally. 20 Figure 12 shows an example system for electromagnetic signal channelling for electromagnetic stealth of an aerial vehicle (1404) using the electromagnetic signal channelling, as described in the foregoing, in use. An incident EM wave (106) may tunnel through the environment around the aerial vehicle, which may be made epsilon-near-zero (ENZ) material (1402). The EM wave may 25 exit the setup without reflection (602). The aerial vehicle (1404) may effectively be hidden from the EM wave. A system for electromagnetic signal channeling for electromagnetic stealth of an object is provided. The described system may find application in stealth technology for aerial vehicles. The 30 described system may reduce the radar cross-section of an aerial or space vehicle. Aspects of the present disclosure provide for printing or placing a source EM element that receives incident EM waves and a sink EM element on another side that emits or repropagates the incident EM waves. The system comprises a first transducer configured to receive electromagnetic waves, a second transducer configured to emit the electromagnetic waves, and a channel connecting the 35 first transducer and the second transducer configured to transmit the electromagnetic waves from the first transducer to the second transducer. The first transducer is positioned near a first side of the object and the second transducer is positioned at a second side of the object. 19 09 25 The described system may shield a vehicle from a broad spectrum of frequencies and for a wide range of incident angles. Similarly, the ENZ channel can be made from inexpensive and light materials, such as metal oxides or polymers, that are suitable for practical applications. Moreover, 5 it can easily fit with existing aerial vehicles without compromising their aerodynamics or performance. The method can effectively protect the aerial vehicle from radar detection and missile tracking, enhancing its stealth and survivability. The foregoing description has been presented for the purpose of illustration; it is not intended to 10 be exhaustive or to limit the technology 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 15 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 present disclosure be limited not by this detailed description, but rather by any claims that issue on an application based hereon. Accordingly, the present disclosure is intended to be illustrative, but not limiting, of the scope of any accompanying claims. 20 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. 25 19 09 25

Claims

1. A system for electromagnetic signal channelling through an aerial vehicle, the system comprising the aerial vehicle and:5 a first electromagnetic element comprising one or more transducer configured toreceive electromagnetic waves;a second electromagnetic element comprising one or more transducer configured to emit the electromagnetic waves; anda channel connecting the first electromagnetic element and the second 10 electromagnetic element configured to transmit the electromagnetic waves from the first electromagnetic element to the second electromagnetic element;wherein the channel at least partially includes a material with one or both of a refractive index or electric permittivity which are near zero, which substantially traverses a length of the channel; and15 wherein the first electromagnetic element is positioned at or near a first side of theaerial vehicle and the second electromagnetic element is positioned at or near a second side of the aerial vehicle.

2. The system as claimed in claim 1, wherein one or both of the permittivity or refractive 20 index are configurable.

3. The system as claimed in either one of claim 1 or 2, wherein the material within the channel is either or both of a metallic wire or an epsilon-near-zero (ENZ) material.25 4. The system as claimed in any one of the preceding claims, wherein the first side ofthe aerial vehicle is positioned at a substantially opposite side of the second side of the aerial vehicle.

5. The system as claimed in any one of the preceding claims, wherein the first and 30 second electromagnetic elements each comprise one or more waveguide.

6. The system as claimed in any one of the preceding claims, wherein the first electromagnetic element comprises one or more waveguide together with one or more transducer and the second electromagnetic element comprises one or more waveguide 35 together with one or more transducer.LO CXI7. The system as claimed in any one of the preceding claims, wherein the transducersare antennas.

8. The system as claimed in any one of the preceding claims, wherein a direction of 5 the emitted electromagnetic waves is controlled by adjusting a radiation pattern of the second electromagnetic element.

9. The system as claimed in any one of the preceding claims, including a means of generating an electric field.1010. The system as claimed in claim 9, wherein the generated electric field is configured to modulate one or both of the permittivity or refractive index.

11. The system as claimed in any one of the preceding claims, wherein the channel is 15 at least partially constructed from metal oxides and / or polymers.

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