# Patent

## Title
Electronic device protection

## Abstract

Apparatus, systems and methods for electronic device protection are provided. A particular apparatus includes a non-conductive substrate and a plurality of cells including conductive members coupled to the non-conductive substrate. The conductive members are arranged to form a first discontinuous mesh, where each conductive member of a cell is separated from conductive members of adjacent cells by a gap and a cavity is defined in the non-conductive substrate at a location of each gap.

## Background
FIELD OF THE DISCLOSURE
The present disclosure is generally related to apparatus, systems and methods for electronic device protection.
BACKGROUND
Low-noise amplifiers in antennas and direction arrival estimation systems may be susceptible to high-power microwave attacks or interference from other devices located near the low-noise amplifiers. In phased array antenna systems and certain other communication systems, silicon carbide (SiC)-based limiters may be placed in-line to provide protection against high-power signals. For example, the SiC-based limiters may be placed between an antenna and the low-noise amplifiers to reduce the amount of power that goes through the low-noise amplifiers. The SiC-based limiters may be integrated at each element of a phased array antenna. Since phased array antennas may include thousands of elements, placing limiters at each element may introduce significant costs and complexity.
Another method of protecting electronic devices, such as low-noise amplifiers, from exposure to high-power electromagnetic radiation, e.g., high-power microwave radiation, may be to place a switchable transistorized mesh system in front of an antenna array. The switchable transistorized mesh system may include conductors arranged in a mesh with discontinuities. A transistor may be present at each discontinuity. When the transistors are off (i.e., behaving like an open switch), electromagnetic energy may pass through the mesh. When the transistors are on (i.e., behaving like a closed switch), the mesh is effectively continuous, and electromagnetic energy may be reflected from the mesh. Since each transistor is provided with power for switching, significant complexity may be added by using such a switchable transistorized mesh system. Further, switching time of the transistors may add an unacceptable delay.
SUMMARY
Apparatus, systems and methods for electronic device protection are provided. A particular apparatus includes a non-conductive substrate and a plurality of cells including conductive members coupled to the non-conductive substrate. The conductive members are arranged to form a first discontinuous mesh where each conductive member of a cell is separated from conductive members of adjacent cells by a gap and a cavity is defined in the non-conductive substrate at a location of each gap.
Another particular apparatus includes a non-conductive substrate and a plurality of conductive members coupled to the non-conductive substrate. The plurality of conductive members are arranged to form a discontinuous mesh defining gaps between adjacent conductive members. A cavity including a gas is defined at each gap. The gas forms a plasma that electrically bridges the gaps to form an electrically continuous mesh in response to electromagnetic radiation.
A particular system includes an electronic device and a protection device to protect the electronic device by selectively blocking electromagnetic radiation. The protection device includes a non-conductive substrate and a plurality of cells including conductive members coupled to the non-conductive substrate. The conductive members are arranged to form a discontinuous mesh where each conductive member of a cell is separated from conductive members of adjacent cells by a gap and a cavity is defined in the substrate at a location of each gap.
A particular method includes permitting a first signal having a first electromagnetic waveform to pass through an apparatus. The apparatus includes a non-conductive substrate and a plurality of cells including conductive members coupled to the non-conductive substrate. The conductive members are arranged to form a discontinuous mesh, where each conductive member of a cell is separated from conductive members of adjacent cells by a gap and a cavity is defined in the substrate at a location of each gap. The method also includes blocking a second signal having a second electromagnetic waveform at the apparatus. The second electromagnetic waveform is different than the first electromagnetic waveform.
The features, functions, and advantages that have been described can be achieved independently in various embodiments or may be combined in yet other embodiments, further details of which are disclosed with reference to the following description and drawings, which are not to scale.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1A is a plan view of a particular embodiment of an apparatus to protect an electronic device;
FIG. 1B is a closer view of a particular portion of the apparatus of FIG. 1A;
FIG. 2 is a sectional view of a gap between cells of the apparatus of FIG. 1A in a first operational state;
FIG. 3 is a sectional view of a gap between cells of the apparatus of FIG. 1A in a second operational state;
FIG. 4 is a perspective view of a first particular embodiment of a system to protect an electronic device in a first operational state;
FIG. 5 is a perspective view of a second particular embodiment of a system to protect an electronic device in a second operational state;
FIG. 6 is a perspective view of a third particular embodiment of a system to protect an electronic device;
FIG. 7 is a flow chart of a particular embodiment of a method to protect an electronic device;
FIG. 8 is a graph of simulated scattering parameters of a particular embodiment of a protection device in a first operational state;
FIG. 9 is a graph of simulated scattering parameters of a particular embodiment of a protection device in a second operational state;
FIG. 10 is a graph of simulated electric field characteristics across half of a gap of a discontinuous mesh according to a first particular embodiment;
FIG. 11 is a graph of simulated electric field characteristics across half of a gap of a discontinuous mesh according to a second particular embodiment;
FIG. 12 is a graph of simulated electric field characteristics across half of a gap of a discontinuous mesh according to a third particular embodiment; and
FIG. 13 is a graph of estimated turn on time of a protection device according to a particular embodiment.



DETAILED DESCRIPTION
Embodiments disclosed herein include an inexpensive low-loss, wide-bandwidth, radio frequency (RF) shutter for use in protecting electronic devices, such as low-noise amplifiers and other communication systems. The RF shutter may include conductive elements arranged in a mesh. The conductive elements of the mesh may have a plurality of intersections and microgaps at points between the intersections. The microgaps are discontinuities in the conductive elements which enable the mesh to be transparent to certain electromagnetic waves (e.g., relatively low-power, low-frequency signals). However, in the presence of other electromagnetic waves (e.g., relatively high-power or high-frequency signals), a plasma may be formed in each microgap. The plasma is conductive and electrically bridges the microgap causing the mesh to behave as a continuous mesh and to reflect the electromagnetic waves. In a particular embodiment, the plasma may be a cold plasma. A cold plasma may be only partially ionized. For example, in a cold plasma a little as about 1% of a gas may be ionized. This is in contrast to a thermal or hot plasma, in which a much higher proportion of the gas may be ionized. Thus, electronic devices protected by the RF shutter may retain normal operation (e.g., transmission and reception of relatively low-power, low-frequency signals) during periods between exposures to relatively high-power or high-frequency signals. However, during exposure to the high-power or high-frequency signals, the RF shutter may respond quickly and with little complexity to protect the electronic devices.
When a high-power or high-frequency signal is received at the RF shutter, a large electric field may be generated in each microgap. The electric field may be sufficient to form an atmospheric pressure plasma. However, the electric field may not be sufficient to cause damaging dielectric breakdown or coronal discharge in the microgap. The plasma is electrically conductive and bridges the microgap causing the RF shutter to behave as though it were a continuous mesh. Thus, the mesh acts like a ground plane and reflects the high-power or high-frequency signal to protect the electronics behind it. Accordingly, a passive RF shutter can protect electronics from high-power and high-frequency signals when in an “on” state and allow transmission and reception of lower power, lower frequency signals when in an “off” state. A power level and a frequency of an incoming signal may determine whether the RF shutter is on or off.
FIG. 1A is a plan view of a particular embodiment of an apparatus 100 to protect an electronic device, and FIG. 1B is a closer view of a particular portion of the apparatus 100. The apparatus 100 includes a non-conductive substrate 102 and a plurality of conductive members 106. The conductive members 106 are arranged to form a discontinuous mesh 104. For example, the conductive members 106 may be arranged in cells, two of which are illustrated in FIG. 1B, with a gap 110 between adjacent cells. For example as shown in FIG. 1B, two cells including conductive members 106 and 107 are separated by the gap 110 having a width 112. Each of the cells has a characteristic dimension 114, such as width from center to center of adjacent gaps or a width from center to center of the conductive members 106 and 107. In a particular embodiment, the cells are approximately square and the characteristic dimension 114 is selected based on a first wavelength of a first signal to be allowed to pass through the apparatus 100 and a second wavelength of a second signal that is to be blocked by the apparatus 100. For example, the characteristic dimension 114 may be much smaller than the first wavelength, e.g., approximately one twenty-fifth of the first wavelength. In another example, the characteristic dimension 114 may be smaller than but closer to the second wavelength, e.g., approximately one half of the second wavelength. However, other proportions between the characteristic dimension 114 and the wavelength of the first signal and the second signal may also be used.
The width 112 of the gap 110 is related to electric field strength present in the gap 110 when the conductive elements 106 and 107 are subjected to electromagnetic radiation. For a particular frequency of electromagnetic radiation, a smaller gap width leads to a stronger electric field in the gap 110 and a larger gap width provides a weaker electric field in the gap 110.
The non-conductive substrate 102 may include a ceramic material, a polymer material, or another material that is not conductive or is dielectric. The non-conductive substrate 102 may be substantially transparent to electromagnetic energy in a particular range of concern. For example, the non-conductive substrate 102 may be transparent to a wavelength of signals intended to be transmitted and received through the apparatus 100 (e.g., relatively low-power, relatively low-frequency signals). The non-conductive substrate 102 may also be substantially transparent to signals to be blocked from transmissions through the apparatus 100 (e.g., relatively high-power or relatively high-frequency signals). The non-conductive substrate 102 may have a thickness sufficient to provide desired structural stability. In a particular embodiment, the non-conductive substrate 102 may be formed of a material that facilitates removal of heat that may be built up by the apparatus 100 during use. For example, the non-conductive substrate 102 may be formed of aluminum nitride, which is electrically insulating but may have suitable thermal conductivity.
The conductive members 106 and 107 may include any suitable conductor, such as silver, gold, copper, aluminum, or another metal or conductor selected for a particular application. In a particular embodiment, materials used to form the non-conductive substrate 102 and the conductive members 106 and 107 may be selected to facilitate low cost manufacturing of the apparatus 100. For example, the materials may be selected to facilitate manufacturing of the apparatus 100 using relatively inexpensive fabrication techniques that are commonly employed to manufacture integrated circuits and other electronic devices. For example, the materials may be selected to enable manufacturing the apparatus 100 using wet etch, dry etch, deposition, photolithography, imprint lithography, chemical mechanical polishing, printing, or other inexpensive additive or subtractive processes that are used to manufacture electronics and integrated circuits. For purposes of simulations discussed herein the conductive members were simulated to be formed of copper. The conductive members 106 and 107 may have a thickness of as little as a few skin depths. For example, for copper conductive members the skin depth may be approximately 3 microns, so a thickness of several skin depths, e.g., about 10 microns, may be sufficient.
In a particular embodiment, a cavity 116 may be present in the non-conductive substrate 102 at each of the gaps 110, as illustrated further in FIGS. 2 and 3. In FIG. 2, the cavity 116 is formed in the non-conductive substrate 102 at the gap 110 between the adjacent conductive members 106 and 107. The cavity 116 may undercut a portion of the adjacent conductive members 106 and 107. The cavity 116 may have a depth of a same order of magnitude as the width 112 of the gap 110. For example, when the width 112 of the gap 110 is about 20 μm, the cavity 116 may have a depth of about 10 μm to about 40 μm.
The cavity 116 may include a gas that forms a plasma when the gas is excited by particular electromagnetic waveforms. In a particular embodiment, the gas is retained by an overlaying substrate 103. In yet another embodiment, the overlaying substrate 103 may be large enough to encapsulate the whole mesh array 100 rather than at individual gap areas 110. The overlaying substrate 103 may be formed of the same material as the non-conductive substrate 102. For example, the conductive members 106 and 107 may be substantially encased or embedded within the non-conductive substrate 102 and the overlaying substrate 103. In another particular embodiment, the overlaying substrate 103 may not be present. For example, an upper surface 108 of the apparatus 100 may be exposed to air, and the air may be used to form the plasma. In another example, the upper surface 108 of the apparatus 100 may be covered to retain the gas that forms the plasma. The gas may include air, a noble gas (e.g., Argon), or another gas that has an acceptable operating range between an electric field strength that causes the gas to generate a plasma and an electric field strength that causes dielectric breakdown of the gas, as described further below. For example, for air the dielectric breakdown field strength is about 60 times the plasma generation field strength, providing a dynamic operating range of about 18 decibels.
As illustrated in FIG. 2, a first signal having a first waveform 120 may be received at the apparatus 100 and may be transmitted or permitted to propagate through the apparatus 100 as illustrated in FIG. 2. Referring to FIG. 3, a second signal having a second waveform 122 may be received at the apparatus 100 and may cause the gas in the cavity 116 to form a plasma 130. The plasma 130 provides a conductive path across the gap 110. The plasma 130 may be electrically conductive enough to bridge the gap 110 to cause the discontinuous metal mesh formed by the conductive members 106 and 107 to behave as a continuous mesh. For example electron density in the gap 110 may range from about 10^13 electrons per cubic centimeter to as much as 10^17 electrons per cubic centimeter, with a conductivity measuring from about 10^2 Siemens per meter (S/m) to about 10^4 S/m. Thus, the second signal having the second waveform 122 stimulates formation of the plasma 130 and thereby causes the discontinuous mesh to be continuous, blocking or inhibiting transmission or propagation of the second signal.
Accordingly, the apparatus 100 may selectively inhibit transmission of electromagnetic radiation based on characteristics of the electromagnetic radiation. For example, the gas may form the plasma 130 that electrically bridges the gap 110 to form an electrically continuous mesh in response to electromagnetic radiation having first characteristics (e.g., the second waveform 112). When the plasma 130 electrically bridges the gaps, the electromagnetic radiation having the first characteristics is inhibited from passing through the apparatus 100. However, the apparatus 100 allows electromagnetic radiation that has second characteristics (e.g., the first waveform 120) to pass through the apparatus 100.
FIG. 4 is a perspective view of a first particular embodiment of a system to protect an electronic device in a first operational state. The system includes an electronic device 404 coupled to an antenna 402 and protected by the apparatus 100. The electronic device 404 may include one or more low-noise amplifiers or other devices to be protected from high-power or high-frequency signals.
A first signal having a first waveform 420 may be transmitted by a transmitter 406 and received at the antenna 402. The first waveform 420 may have characteristics (such as a wavelength 408) that do not stimulate formation of the plasma in gaps of the apparatus 100. Thus, the first signal is able to pass through the apparatus 100, to be received at the antenna 402, and to be sent as a signal 410 to the electronic device 404.
FIG. 5 is a perspective view of a second particular embodiment of the system of FIG. 4 in a second operational state. In FIG. 5, a second transmitter 506 may transmit a second signal having a second waveform 522. The second waveform 522 may be characterized by particular parameters, such as a second wavelength 508, an amplitude, a signal strength, and so forth. When the second signal is received at the apparatus 100, the second signal may stimulate formation of the plasma in the gaps of the apparatus 100. Accordingly, the apparatus 100 in FIG. 5 is illustrated as continuous (i.e., without gaps) due to the presence of the plasma between the gaps. The apparatus 100 may act as a ground plane to reflect or block transmission of the second signal, resulting in the second signal not being received at the antenna 402. As illustrated in FIG. 5, no second signal 510 is received at the electronic device 404, and the electronic device 404 is protected from harm as a result of the second signal.
Thus, the apparatus 100 acts as a passive RF shutter to that allows some signals to pass through and blocks or reflects other signals. Put another way, the apparatus 100 has a first operational state in which the apparatus 100 is substantially transparent to a first electromagnetic waveform and a second operational state that is engaged when the apparatus is exposed to a second electromagnetic waveform that is different than the first electromagnetic waveform. In the second operational state, the apparatus 100 may be substantially opaque to the first electromagnetic waveform and to the second electromagnetic waveform. The apparatus 100 is able to block certain signals quickly, with little added complexity, and without the use of external control systems and power systems. Rather, the signal to be blocked itself stimulates formation of the plasma and causes the signal to be blocked. Accordingly, the switching time required to switch the apparatus 100 from the first operational state (where signals are allowed to pass through) to the second operational state (where signals are not allowed to pass through) may be about 2 nanoseconds or less.
FIG. 6 is a perspective view of a third particular embodiment of a system to protect the electronic device 404. The system of FIG. 6 illustrates an active protection system for the electronic device 404. The system includes a third transmitter 626 that sends a third signal having a third waveform 622. The third waveform 622 may include particular characteristics, such as a third wavelength 624, an amplitude, and signal strength when received at the apparatus 100. As previously described, the apparatus 100 is discontinuous and substantially transparent to signals having certain waveforms, which enables those signals to be received at the antenna 402. In a particular embodiment, the third waveform 622 is selected to stimulate formation of the plasma at gaps of the apparatus 100. For example, the third transmitter 626 may be a relatively low power, high frequency transmitter located relatively near the antenna 402.
In a particular embodiment, the third transmitter 626 is under control of a controller 640 associated with the electronic device 404. The third transmitter 626 may be used to turn on protective characteristics of the apparatus 100 in response to the controller 640. For example, a fourth transmitter 606 may be a perceived threat to the electronic device 404. That is, the fourth transmitter 606 may be capable of transmitting a fourth signal 620 that may be harmful to the electronic device 404. The controller 640 may engage the third transmitter 626 to stimulate formation of the plasma in gaps of the apparatus 100 when the perceived threat is near the electronic device 404. In another example, the fourth transmitter 606 may be a relatively high-power transmitter that is collocated with the electronic device 404. The fourth transmitter 606 may periodically or occasionally transmit signals that could be harmful to the electronic device 404. The controller 640 may selectively engage the third transmitter 626 to stimulate formation of the plasma in gaps of the apparatus 100 when the fourth transmitter 606 is transmitting or is about to transmit the potentially harmful fourth signal 620. In yet another example, the third transmitter 626 may send the third signal to stimulate formation of the plasma all of the time except for when the electronic device 404 is to send or receive signals via the antenna 402. To illustrate, the third transmitter 626 may leave the apparatus 100 “on” (i.e., with plasma in the gaps of the apparatus 100) to block signals from being received at the electronic device 404 until a particular time when the signals are expected or desired, at which point the third transmitter 626 may cease sending the third signal to turn the apparatus 100 “off” (i.e., with no plasma in the gaps).
In a particular embodiment, the system includes the first apparatus 100 and a second apparatus 650. The second apparatus 650 may be included as a layer over or under the first apparatus 100. The second apparatus 650 may include a second discontinuous mesh formed by second conductive members spaced apart by second gaps. The second gaps may have a different widths than the gaps of the discontinuous mesh of the apparatus 100. The width of the gap may be related to the electric field strength in the gap when a mesh is exposed to electromagnetic radiation. For example, smaller gaps may exhibit a stronger electric field than larger gaps. Accordingly, the larger gaps of the second apparatus 650 may experience smaller electric fields than the smaller gaps of the apparatus 100 when both are subjected to the fourth signal.
When the fourth signal 620 is a relatively high-power signal, the smaller gaps of the apparatus 100 may have a strong enough electric field to exceed a dielectric breakdown threshold of the gas in the gaps of the apparatus 100. Thus, the gaps of the apparatus 100 may experience damaging arching or coronal discharge. The second gaps of the second apparatus 650 are larger and have a smaller electric field. When the apparatus 100 and the second apparatus 650 use the same gas in their respective gaps, the second gaps can endure a stronger signal than the gaps of the apparatus 100 without exceeding the dielectric breakdown threshold of the gas. In a particular embodiment, the apparatus 100 and the second apparatus 650 may use different gases with different dielectric breakdown threshold to provide protection against signals with different signal strengths.
Gaps widths, characteristic dimensions, gases, or any combination thereof of the apparatus 100 and the second apparatus 650 may be selected to cause the apparatus 100 and the second apparatus 650 to provide different protection characteristics. For example, the second apparatus 650 may have a different characteristic dimension than the characteristic dimension 114 of the apparatus 100. Thus, the apparatus 100 and the second apparatus 650 may turn on (i.e., generate a plasma) in response to different waveforms and may be able to endure different waveforms without being overpowered (e.g., before a dielectric breakdown threshold is reached). Further, although only the apparatus 100 and the second apparatus 650 are illustrated, the system may include more than two layers. Any number of layers may be provided and each layer may include characteristic dimensions, gases and gaps selected to provide desired protection characteristics. Additionally, although the second apparatus 650 is only shown in the active system illustrated in FIG. 6, the second apparatus 650 or other layers may be used with a passive system, such as the system illustrated in FIGS. 4 and 5.
FIG. 7 illustrates a first particular embodiment of a method of protecting an electronic device. The method includes, at 702, permitting a first signal having a first electromagnetic waveform to pass through an apparatus. For example, the apparatus may be a protection device, such as the apparatus 100, that includes a discontinuous mesh of conductive members separated by gaps. The apparatus may include a non-conductive substrate and a plurality of cells including conductive members. Conductive members may be arranged to form the discontinuous mesh. Each conductive member of a cell is separated from conductive members of adjacent cells by a gap. A cavity may be defined in the non-conductive substrate at each gap. In response to exposure to particular electromagnetic waveforms, a plasma may be formed in the cavity at each gap.
The method also includes, at 704, blocking a second signal having a second electromagnetic waveform at the apparatus. The second electromagnetic waveform may be different than the first electromagnetic waveform. For example, the second electromagnetic waveform may cause a material present in the cavity at each gap to be ionized to form a plasma, at 706. To illustrate, a wavelength of the second electromagnetic waveform may be smaller than a wavelength of the first electromagnetic waveform, at 708. The wavelength of the second electromagnetic waveform may stimulate or excite the material present in the cavity to form the plasma. In another illustrative example, the power of the second signal may be greater than the first signal, at 710. The plasma may be stimulated in the cavity at each gap in response to the second signal due to the signal strength.
The method may also include, at 712, applying an activation signal to the apparatus to cause the second signal to be blocked. For example, a transmitter, such as the second transmitter 626 of FIG. 6, may be used to selectively turn the apparatus “on,” so that signals are blocked, or “off,” so that signals can pass through. In a particular embodiment, the activation signal may have a first polarization and an incoming signal may have a second polarization that is different from the first polarization. The incoming signal may be blocked based on first polarization of the activation signal, at 714.
Simulations were conducted to characterize performance of a protection device, such as the apparatus 100 of FIGS. 1A, 1B and 2-6. For purposes of the simulations, the conductive members 106 and 107 of the apparatus 100 were simulated as 70 μm wide copper traces with gaps midway between intersections of vertical and horizontal traces. For a first simulation, the gaps 110 were simulated as having a width 112 of approximately 20 μm, and the cell size or characteristic dimension 114 of the cells was simulated as about 5 mm. For a second simulation, the gaps 110 were simulated as having a width 112 of approximately 80 μm, and the cell size or characteristic dimension 114 of the cells was simulated as about 5 mm.
FIG. 8 is a graph of scattering parameters of the simulated protection device in a first operational state that simulates no plasma being present (i.e., the gaps are discontinuities in the conductive members). As shown in FIG. 8, when subjected to a 2.45 gigahertz signal, substantially all of the signal is transmitted through the apparatus, with less than a 30 decibel reflection at 2.45 gigahertz.
FIG. 9 is a graph of simulated scattering parameters of a particular embodiment of a protection device in a second operational state that simulates the plasma being present in the gaps (i.e., no discontinuities in the conductive members). FIG. 9 shows that with the gaps bridged, the apparatus 100 acts as an effective ground plane and reflects most of the incoming signal with less than 12 decimals getting through at 2.45 gigahertz. It is noted that performance of the apparatus 100 may be improved by adjusting a size of the mesh (i.e., a distance between intersection points or approximate size of the cells) to be more sub-wavelength. The performance of the apparatus 100 may also be improved by using several layers of mesh with different characteristics.
FIG. 10 is a graph of simulated electric field characteristics across half of a gap of a discontinuous mesh according to a first particular embodiment. Magnitude of the electric field is shown along the y-axis. A location along the gap is shown along the x-axis, starting at distance 0, which is the edge of a conductive member, and extending to a distance 10 μm from the edge of the conductive member, which is approximately a center of the gap. The electric field across the gap is believed to be approximately symmetric about the center of the gap; thus, only half of the gap was simulated. The graph in FIG. 10 shows the electric field strength at points in the gap when the conductive members are exposed to a 2.45 GHz signal at various incident power levels. For example, at an incident power of about 1 watt/cm^2, the electric field strength inside the gap ranges from about 3.5×10^5 volts per meter to about 6×10^5 volts per meter, as shown by line 1004. At an incident power of 0.1 watt/cm^2, the electric field strength ranges from about 1×10^5 volts per meter to about 1.9×10^5 volts per meter, as shown by line 1008. Both of these incident power levels produce sufficient electric field strength to initiate plasma in the gap. That is, both incident power levels exceed a plasma threshold 1010 of air. Yet both of these incident power levels remain safely below air dielectric breakdown field strength 1002.
Different gap sizes may accommodate different incident power levels without exceeding the dielectric breakdown field strength 1002. Additionally, different gases may have different plasma thresholds and dielectric breakdown thresholds. Accordingly, a gap size and a gas may be selected to provide protection for particular incident power levels of particular frequencies of electromagnetic radiation.
FIG. 11 is a graph of simulated electric field characteristics across half of a gap of a discontinuous mesh according to a second particular embodiment. As in FIG. 10, only a half-gap is illustrated. The gap simulated for FIG. 11 has a width of gap at 80 μm. Since the electric field strength is believed to be symmetrical in the gap, the x-axis shows the distance from the edge of a conductive member at 0 to the midpoint of the gap at 40 μm. The graph in FIG. 11 also shows the dielectric breakdown threshold of air 1002 and the plasma threshold of air 1010. The graph shows electric field strength for a 2.45 GHz signal at various incident power levels.
The electric field strength in the gap for a 1 watt/cm^2 incident power is shown by line 1108. Thus, for the 80 μm gap, 1 watt/cm^2 incident power is sufficient to surpass the plasma threshold 1010 but remains below the dielectric breakdown threshold 1002. The electric field strength in the gap for a 5 watt/cm^2 incident power is shown by line 1106, and the electric field strength in the gap for a 10 watt/cm^2 incident power is shown by line 1104. Both the 5 watt/cm^2 incident power and the 10 watt/cm^2 incident power are sufficient to surpass the plasma threshold 1010 but remain below the dielectric breakdown threshold 1002. Thus, by widening the gap from the 20 μm gap simulated in FIG. 10 to the 80 μm gap simulated in FIG. 11, a higher incident power level signal can be blocked. For example, the 80 μm gap can withstand at least a 10 watt/cm^2 incident power level without reaching the dielectric breakdown threshold 1002.
FIG. 12 is a graph of simulated electric field characteristics across half of a gap of a discontinuous mesh according to a third particular embodiment. For FIG. 12, the gap was simulated as having a width of 20 μm, with half of the gap shown in FIG. 12. FIG. 12 shows how a higher frequency signal with a lower incident power level affects the electric field in the gap. Specifically, FIG. 12 shows the electric field in the gap for various incident power levels of a 30.6 GHz signal, as compared to the 2.45 GHz signal used for FIG. 10 with the same gap width. The plasma threshold 1010 and the dielectric breakdown point of air 1002 are also shown in FIG. 12.
The higher frequency signal used for FIG. 12 may provide better coupling across the gap using less power. To illustrate, line 1206 shows the electric field across the gap at a 1 mW/cm^2 incident power level. Thus, using a 30.6 GHz signal, an incident power level as low as 1 mW/cm^2 is sufficient to generate a plasma in the gap. The line 1204 shows the electric field across the gap at a 10 mW/cm^2 incident power level.
While the simulations described above illustrate effects of frequency of a received signal and gap width on generation of a plasma, another consideration is response time. That is, how long it takes for the mesh to switch from an inactive state (i.e., without plasma) to an active state (i.e., with plasma). The switching response time is approximately the plasma initiation time, i.e., how much time is required to initiate the plasma. The plasma is initiated when electrons of the gas in the gap become ionized. Thus, a time required for an electron to achieve ionization energy in response to an electric field is an estimate of the plasma initiation time.
FIG. 13 is a graph of estimated turn on time of a protection device according to a particular embodiment. FIG. 13 graphs an approximation of the time required for an electron in an electric field to gain enough energy for ionization neglecting electron energy lost during inelastic collisions with gas molecular species. This graph demonstrates that for various electric field strengths, the time required for an electron to become ionized is less than about two nanoseconds. Accordingly, the turn on response time of the apparatus 100 of FIG. 1 is expected to be about two nanoseconds or less.
Various embodiments disclosed provide protection devices to protect electronics. A protection device includes a discontinuous mesh that can act as a protective screen for communication systems and other electronic systems that may be susceptible to electromagnetic damage due to high-power electromagnetic radiation. The discontinuous mesh may act as a nonlinear element that is substantially transparent to electromagnetic radiation at low powers or particular frequencies and that becomes substantially opaque or reflective to high-power electromagnetic radiation. The protection device may be passive in that it reacts to switch from the transparent state to the opaque state in response to the incident electromagnetic radiation that is to be blocked. The protection device may also be actively controlled by transmitting a signal having a desired modulation toward the discontinuous mesh when it is desired to switch the discontinuous mesh to a protection state. The protection device may include multiple layers of the discontinuous mesh to provide protection at different incident power levels.
The discontinuous mesh may act as an electromagnetic shutter to provide passive protection without requiring sensing systems or other complex circuitry for switching. Characteristics of an incident signal (e.g., the incident power level and frequency) may determine whether the incident signal is allowed to pass through the discontinuous mesh or is blocked by the discontinuous mesh.
Using active modulation, it is possible to illuminate the discontinuous mesh using a relatively high frequency, low power illumination signal in order to activate the protection device. The frequency of the illumination signal may be approximately a resonant frequency of the discontinuous mesh based on cell size (i.e., spacing of conductive members of the discontinuous mesh). Thus, the illumination signal may have a wavelength on an order of about two times the cell size. Since the discontinuous mesh may be designed for a working signal (i.e., a signal that is allowed to pass through) with a wavelength on an order of about twenty-five times the cell size there may be little interference between the working signal and the illumination signal. Frequency of the illumination signal can also be chosen to be between harmonics of operating frequencies of an aperture associated with the protection device to avoid unwanted coupling of the aperture. When active modulation of the discontinuous mesh is used, polarization of the illumination signal may cause the screen to selectively block signals having a particular polarity. For example, depending on polarization of the illumination signal, either vertically or horizontally polarized incoming signals may be blocked.
A unit cell size of the discontinuous mesh may be selected to improve performance for particular incident signals. For example, the unit cell size may be selected to be much smaller than a wavelength of the particular incident signal to increase a reflection coefficient of the discontinuous mesh, A gap width of the discontinuous mesh can be selected to mitigate a specific threshold level of incident power. For example, larger gaps may be used to mitigate higher incident power levels. Additionally, multiple discontinuous mesh layers with varying gap widths can be used to mitigate a broader range of incident power levels. For example, two mesh layers may be used with a first layer having wider gaps than a second layer. The first layer may only turn on for relatively high incident power levels. The second layer may be activated for lower incident power levels, but may be overpowered by the higher incident power levels. Additionally, when the first layer is on top of the second layer, the second layer may be activated by “spill over” from the first layer, providing additional protection. That is, when a relatively high-power signal activates the first layer, a portion of the high-power signal may pass through the first layer. The portion of the high-power signal that passes through the first layer may be sufficient to activate the second layer, enabling the second layer to provide additional protection. Each layer may provide up to about 25 decibels of attenuation and up to about 18 decibels of dynamic operating range of the incident power level.
The illustrations of the embodiments described herein are intended to provide a general understanding of the structure of the various embodiments. The illustrations are not intended to serve as a complete description of all of the elements and features of apparatus and systems that utilize the structures or methods described herein. Many other embodiments may be apparent to those of skill in the art upon reviewing the disclosure. Other embodiments may be utilized and derived from the disclosure, such that structural and logical substitutions and changes may be made without departing from the scope of the disclosure. For example, method steps may be performed in a different order than is shown in the figures or one or more method steps may be omitted. Accordingly, the disclosure and the figures are to be regarded as illustrative rather than restrictive.
Moreover, although specific embodiments have been illustrated and described herein, it should be appreciated that any subsequent arrangement designed to achieve the same or similar results may be substituted for the specific embodiments shown. This disclosure is intended to cover any and all subsequent adaptations or variations of various embodiments. Combinations of the above embodiments, and other embodiments not specifically described herein, will be apparent to those of skill in the art upon reviewing the description.
The Abstract of the Disclosure is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims. In addition, in the foregoing Detailed Description, various features may be grouped together or described in a single embodiment for the purpose of streamlining the disclosure. This disclosure is not to be interpreted as reflecting an intention that the claimed embodiments require more features than are expressly recited in each claim. Rather, as the following claims reflect, the claimed subject matter may be directed to less than all of the features of any of the disclosed embodiments.

## Claims

1. An apparatus, comprising:
a non-conductive substrate; and
a plurality of cells including conductive members coupled to the non-conductive substrate, wherein the conductive members are arranged to form a first discontinuous mesh, wherein each conductive member of a cell is separated from conductive members of adjacent cells by a gap, and wherein a cavity is defined in the non-conductive substrate at a location of each gap.

2. The apparatus of claim 1, wherein the apparatus permits propagation therethrough of a first electromagnetic waveform having a first wavelength.

3. The apparatus of claim 2, wherein, when the apparatus is subjected to a second electromagnetic waveform having a second wavelength, the apparatus blocks propagation of the second electromagnetic waveform.

4. The apparatus of claim 1, wherein each cavity includes a gas that forms a plasma when the gas is excited by a particular electromagnetic waveform.

5. The apparatus of claim 1, wherein dimensions of the plurality of cells are selected to permit transmission of a first electromagnetic waveform having a first wavelength through the apparatus and to block transmission of a second electromagnetic waveform having a second wavelength through the apparatus, wherein the second wavelength is different than the first wavelength.

6. The apparatus of claim 5, wherein each of the plurality of cells is approximately square and has a length of approximately one-half of the second wavelength.

7. The apparatus of claim 6, wherein the length is approximately one-twenty-fifth of the first wavelength.

8. The apparatus of claim 1, further comprising a plurality of second cells including second conductive members spaced apart by second gaps to form a second discontinuous mesh, wherein the second discontinuous mesh is layered over the first discontinuous mesh, and wherein the second gaps have a different width than a width of the gap of the first discontinuous mesh.

9. A system, comprising:
an electronic device;
a protection device to protect the electronic device by selectively blocking electromagnetic radiation, the protection device comprising:
a non-conductive substrate; and
a plurality of cells including conductive members coupled to the non-conductive substrate, wherein the conductive members are arranged to form a discontinuous mesh, wherein each conductive member of a cell is separated from conductive members of adjacent cells by a gap, and wherein a cavity is defined in the substrate at a location of each gap.

10. The system of claim 9, wherein the electronic device comprises an antenna.

11. The system of claim 9, wherein the electronic device is operable to transmit a signal having a first electromagnetic waveform, and wherein, in a first operational state, the protection device is substantially transparent to the first electromagnetic waveform.

12. The system of claim 11, wherein the protection device operates in a second operational state when exposed to a second electromagnetic waveform that is different than the first electromagnetic waveform, and wherein, in the second operational state, the protection device is substantially opaque to the first electromagnetic waveform and to the second electromagnetic waveform.

13. The system of claim 12, wherein a time required to switch from the first operational state to the second operational state is about 2 nanoseconds or less.

14. The system of claim 9, further comprising a second electronic device, the second electronic device adapted to radiate a third electromagnetic waveform, wherein, when the protection device is subjected to the third electromagnetic waveform, the protection device blocks transmission of the electromagnetic radiation.

15. A method, comprising:
permitting a first signal having a first electromagnetic waveform to pass through an apparatus, the apparatus comprising:
a non-conductive substrate; and
a plurality of cells including conductive members coupled to the non-conductive substrate, wherein the conductive members are arranged to form a discontinuous mesh, wherein each conductive member of a cell is separated from conductive members of adjacent cells by a gap, and wherein a cavity is defined in the substrate at a location of each gap; and

blocking a second signal having a second electromagnetic waveform at the apparatus, wherein the second electromagnetic waveform is different than the first electromagnetic waveform.

16. The method of claim 15, wherein the second electromagnetic waveform causes a material present in the cavity at each gap to be ionized to form a plasma.

17. The method of claim 15, wherein a wavelength of the second electromagnetic waveform is less than a wavelength of the first electromagnetic waveform.

18. The method of claim 15, wherein a power of the second signal when the second signal is received at the apparatus is greater than a power of the first signal when the first signal is received at the apparatus.

19. The method of claim 15, further comprising applying an activation signal to the apparatus to cause the second signal to be blocked.

20. The method of claim 19, wherein the first signal has a first polarization and the second signal has a second polarization that is different from the first polarization, and wherein the second signal is blocked based on a polarization of the activation signal.

21. An apparatus, comprising:
a non-conductive substrate; and
a plurality of conductive members coupled to the non-conductive substrate, the plurality of conductive members arranged to form a discontinuous mesh defining gaps between adjacent conductive members, wherein a cavity including a gas is defined at each gap, wherein the gas forms a plasma that electrically bridges the gaps to form an electrically continuous mesh in response to electromagnetic radiation.

22. The apparatus of claim 21, wherein the gas forms the plasma in response to electromagnetic radiation that has first characteristics, and when the plasma electrically bridges the gaps, the electromagnetic radiation having the first characteristics is inhibited from passing through the apparatus.

23. The apparatus of claim 22, wherein the apparatus allows electromagnetic radiation that has second characteristics that are different from the first characteristics to pass through the apparatus.