U.S. patent application number 17/681437 was filed with the patent office on 2022-09-22 for personal electronic device emp protective enclosure.
This patent application is currently assigned to Softronics, Ltd.. The applicant listed for this patent is Softronics, Ltd.. Invention is credited to Robert H. STERNOWSKI.
Application Number | 20220302948 17/681437 |
Document ID | / |
Family ID | 1000006164847 |
Filed Date | 2022-09-22 |
United States Patent
Application |
20220302948 |
Kind Code |
A1 |
STERNOWSKI; Robert H. |
September 22, 2022 |
PERSONAL ELECTRONIC DEVICE EMP PROTECTIVE ENCLOSURE
Abstract
A Faraday cage enclosure for a mobile device with a portion that
aligns with a display of the mobile device simultaneously
substantially attenuate EM radiation to non-damaging amplitudes and
is transparent to visible light in an optical spectrum, an EMP
protection circuit electrically connected between the external
charging and data port and the internal charging and data port, and
a passive repeater configured to EM-couple with an antenna of the
mobile device and relay signals to and from the antenna of the
mobile device.
Inventors: |
STERNOWSKI; Robert H.;
(Cedar Rapids, IA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Softronics, Ltd. |
Marion |
IA |
US |
|
|
Assignee: |
Softronics, Ltd.
Marion
IA
|
Family ID: |
1000006164847 |
Appl. No.: |
17/681437 |
Filed: |
February 25, 2022 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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17483294 |
Sep 23, 2021 |
11290143 |
|
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17681437 |
|
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63162298 |
Mar 17, 2021 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01Q 1/12 20130101; H05K
9/0081 20130101; H02H 9/04 20130101; H04B 1/3888 20130101 |
International
Class: |
H04B 1/3888 20060101
H04B001/3888; H02H 9/04 20060101 H02H009/04; H01Q 1/12 20060101
H01Q001/12; H05K 9/00 20060101 H05K009/00 |
Claims
1. A case for a mobile device, comprising: an enclosure selectively
operable to open and receive the mobile device therein and to
substantially attenuate electro-magnetic (EM) radiation in a radio
spectrum to non-damaging amplitudes wherein a portion of the
enclosure that aligns with a display of the mobile device
simultaneously substantially attenuate EM radiation to non-damaging
amplitudes and is transparent to visible light in an optical
spectrum; wherein the enclosure comprises of a bottom portion for
cradling the mobile device therein and a top cover connected to the
bottom portion by an electrically-conductive hinge to both
selectively open and close the enclosure and provide a
low-impedance electrical path between bottom portion and the top
cover of the case.
2. The case of claim 21, and further comprising a passive repeater
configured to EM-couple with an antenna of the mobile device and
relay signals to and from the antenna of the mobile device.
3. The case of claim 2, and further comprising an EMP limiter
connected to the passive repeater to attenuate voltages above a
threshold.
4. The case of claim 2, wherein the passive repeater further
comprises: an internal repeater antenna inside the enclosure and
configured to EM-couple with an antenna of the mobile device, an
external repeater antenna positioned outside of the enclosure, and
a transmission line extending between the internal repeater antenna
and the external repeater antenna.
5. The case of claim 4, wherein the internal repeater antenna and
the external repeater antenna each inherently comprise band
limiting properties reducing coupled EMP energy.
6. The case of claim 22, wherein the EMP protection circuit further
comprises of a low pass filter to pass a dc charging voltage and
data signal to the mobile device.
7. The case of claim 22, wherein the EMP protection circuit further
comprises a voltage suppressor connected in shunt across the
internal charging and data port.
8. The case of claim 22, wherein the EMP protection circuit further
comprises a voltage suppressor connected in shunt across the
external charging and data port.
9. The case of claim 8, wherein the voltage suppressor further
comprises of a gas discharge tube.
10. The case of claim 9, wherein the voltage suppressor is
connected to the outside of the enclosure which functions as a
ground plane.
11. The case of claim 1, wherein the enclosure further comprises of
a bottom portion for cradling the mobile device therein and a top
cover connected to the bottom portion by an electrically-conductive
hinge to both selectively open and close the enclosure and provide
a low-impedance electrical path between bottom portion and the top
cover of the case.
12. The case of claim 11, wherein the top cover has orthogonal
sidewalls extending downward that overlap orthogonal sidewalls of
the bottom portion to reduce a radiation leakage path.
13. The case of claim 11, wherein the top cover further comprises
the portion of the enclosure that aligns with the display on the
mobile device, wherein such portion further comprises of a metallic
mesh that simultaneously substantially attenuates EM radiation and
is transparent to visible light in an optical spectrum.
14. The case of claim 13, where the metallic mesh of the top cover
is oriented with its threads at a 45 degree angle to an x-y
orientation of a display of the mobile device for preventing Moire
patterns and enhancing clarity of the display.
15. A case for a mobile device, comprising: an enclosure
comprising: a bottom portion for cradling the mobile device
therein; atop cover; and an electrically-conductive hinge
connecting the bottom portion to the top cover to both selectively
open and close the enclosure and provide a low-impedance electrical
path between bottom portion and the top cover of the case.
16. The case of claim 15, wherein the top cover further comprises
of a portion that aligns with a display on the eon-mobile device
that substantially attenuates EM radiation to non-damaging
amplitudes and is transparent to visible light in an optical
spectrum.
17. The case of claim 16, wherein the portion of the top cover
comprises of a metallic mesh that simultaneously substantially
attenuates EM radiation and is transparent to visible light in an
optical spectrum, wherein the metallic mesh is oriented with its
threads at a 45 degree angle to an x-y orientation of the display
of the mobile device for preventing Moire patterns and enhancing
clarity of the display.
18. The case of claim 15, wherein the top cover has orthogonal
sidewalls extending downward that overlap orthogonal sidewalls of
the bottom portion to reduce a radiation leakage path.
19. The case of claim 15, and further comprising an external
charging and data port on the outside of the enclosure; an internal
charging and data port on the inside of the enclosure configured to
receive the charging and data port of the mobile device; and an EMP
protection circuit electrically connected between the external
charging and data port and the internal charging and data port.
20. The case of claim 19, and further comprising: a passive
repeater configured to EM-couple with an antenna of the mobile
device and relay signals to and from the antenna of the mobile
device; an EMP limiter connected to the passive repeater to
attenuate voltages above a threshold, wherein the passive repeater
further comprises: an internal repeater antenna inside the
enclosure and configured to EM-couple with an antenna of the mobile
device, an external repeater antenna positioned outside of the
enclosure, and a transmission line extending between the internal
repeater antenna and the external repeater antenna.
21. The case of claim 1, and further comprising an external
charging and data port on the outside of the enclosure; and an
internal charging and data port on the inside of the enclosure
configured to receive the charging and data port of the mobile
device.
22. The case of claim 21, and further comprising an EMP protection
circuit electrically connected between the external charging and
data port and the internal charging and data port.
Description
PRIORITY CLAIM
[0001] This application is a division of U.S. patent application
Ser. No. 17/483,294 filed Jan. 23, 2021 which claims the benefit of
U.S. Provisional Patent Application No. 63/162,298 filed on Mar.
17, 2021, the contents of which are hereby incorporated by
reference herein.
TECHNICAL FIELD
[0002] The present invention relates generally to mobile cellular,
wireless or Wi-Fi device accessories, and more particularly to a
protective enclosure capable of protecting the device from an
electro-magnetic pulse.
BACKGROUND INFORMATION
[0003] It is well understood that a high intensity electromagnetic
wavefront generated by a nuclear detonation (or alternatively by
special non-nuclear means) contains sufficient energy to induce
destructive currents in conductive materials as it flows through
and around them. Such a pulse is typically 100-200 nanoseconds in
duration, with intensities on the order of 50 KV/m to 1 MV/m with
the majority of energy concentrated in the 10-1000 MHz spectrum. In
particular, in the case of electronic equipment, EMP generates
currents in microelectronic components, wires, printed circuit
traces, etc., sufficient to vaporize or fuse those electronic
elements, rendering them inoperative. One of the most fearsome
threats to the United States is detonation of a low yield,
EMP-optimized nuclear device in low earth orbit (approx. 200400 km)
over the geographic center of the United States, producing an EMP
wave that will sweep across all of the continental U.S. and fully
disable the power and communications grids. Multiple nation-states
are capable of carrying out such an indirect attack. The resulting
damage would be permanent, and leave the US with its industrial
base also disabled and unable to repair or replace damaged
electronics.
[0004] It is obvious that, in the face of such threats the US
government, and the Department of Defense in particular, have a
serious need for communications equipment that can survive such an
event, and allow intra-government (at a minimum) communications to
defend and recover from such an episode. The driving impetus for
the disclosed invention is the protection and survival of cellular
telephones and handheld radio transceivers. These are complex
assemblies of miniature electronic components and interconnecting
metal wires of various kinds, all of which are subject to damage by
induced currents from a high-power EMP electromagnetic
wavefront.
[0005] It is well-known to those skilled in the art that the
simplest and most effect method for protection of such devices from
high-intensity electromagnetic fields is to 100% contain them in a
Faraday cage. A Faraday cage is simply a sealed conductive box with
the device to be protected located inside of it. With the device
installed inside of a sealed box with no openings, the device is
obviously non-functional without a means for a user to physically
or remotely access it. Such a Faraday cage is, on the other hand, a
useful means of storing a vulnerable item protected from EMP
damage. After the episode, the cage/packaging can be opened and the
undamaged device removed and used. The physics principle in action
is the conductive metal comprising the walls of the Faraday cage.
Electromagnetic waves cannot penetrate metal, and hence a powerful
EMP wavefront will harmlessly induce high currents in the surface
of the Faraday cage, which will be harmlessly dissipated as heat as
they flow about the cage's surface.
[0006] Government and defensive units, however, have a need to be
able to communicate before, during and after a nuclear attack
(commonly referred to as pre-, trans- and post-attack periods).
Thus the government has a serious need for protected devices that
will both survive and operate during all three phases.
[0007] The prior art is full of cases to protect a user of a mobile
device from perceived harmful electro-magnetic frequency (EMF)
radiation. These cases operate on a similar principal of
incorporating a Faraday cage around the device, but all of the
prior art cases leave portions of the case radio-transparent in
order to maintain functionality of the device. While such cases may
block a large portion of the EMF radiation from device while still
allowing functionality for the user, having any
radiation-transparent surface on the case leaves the mobile device
susceptible to damage from an EMP.
[0008] What is disclosed is protective enclosure for a personal
communication device to be protected and operated during an EMP
event; conversely, the enclosure can also be used to provide a
general consumer with a case that provides superior protection
against EMF radiation from the personal communication device.
SUMMARY
[0009] In accordance with one aspect of the present invention,
disclosed is a case for a mobile device. The case comprises of an
enclosure that has a bottom portion for cradling the mobile device
therein, a top cover, and an electrically-conductive hinge
connecting the bottom portion to the top cover to both selectively
open and close the enclosure and provide a low-impedance electrical
path between bottom portion and the top cover of the case.
[0010] In an embodiment, the top cover further comprises of a
portion that aligns with a display on the on mobile device that
substantially attenuates EM radiation to non-damaging amplitudes
and is transparent to visible light in an optical spectrum. The
portion of the top cover comprises of a metallic mesh that
simultaneously substantially attenuates EM radiation and is
transparent to visible light in an optical spectrum. The metallic
mesh is oriented with its threads at a 45 degree angle to an x-y
orientation of the display of the mobile device for preventing
Moire patterns and enhancing clarity of the display. The top cover
has orthogonal sidewalls extending downward that overlap orthogonal
sidewalls of the bottom portion to reduce a radiation leakage path
by.
[0011] The case can also have an external charging and data port on
the outside of the enclosure. An internal charging and data port on
the inside of the enclosure is configured to receive the charging
and data port of the mobile device. An EMP protection circuit is
electrically connected between the external charging and data port
and the internal charging and data port.
[0012] A passive repeater configured to EM-couple with an antenna
of the mobile device and relay signals to and from the antenna of
the mobile device can be provided. An EMP limiter can be connected
to the passive repeater to attenuate voltages above a threshold.
The passive repeater can further comprise an internal repeater
antenna inside the enclosure and configured to EM-couple with an
antenna of the mobile device. An external repeater antenna can be
positioned outside of the enclosure with a transmission line
extending between the internal repeater antenna and the external
repeater antenna.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] These and other features and advantages of the present
invention will be better understood by reading the following
detailed description, taken together with the drawings wherein:
[0014] FIG. 1 shows a front-side perspective view of a protective
case for a mobile device according to this disclosure.
[0015] FIG. 1A is a close-up view of area 1A of FIG. 1.
[0016] FIG. 2 shows a back-side perspective view of the protective
case of FIG. 1
[0017] FIG. 3 shows a cross-sectional view of the case of FIG. 1
taken along the line A-A.
[0018] FIG. 4 shows a front-side perspective view of the case of
FIG. 1 with the front cover open.
[0019] FIG. 5 shows a front perspective of the case of FIG. 1 with
the top cover removed.
[0020] FIG. 6 shows an electrical schematic for protecting a mobile
device from an electromagnetic pulse according to this
disclosure.
[0021] FIG. 7A shows an electrical schematic for the power EMP
protection circuit.
[0022] FIG. 7B shows another electrical schematic for the power EMP
protection circuit.
[0023] FIG. 8 shows an electrical schematic for a passive radio
relay with EMP protection according to this disclosure.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0024] FIGS. 1-5 show a case 100 for protecting a mobile device 200
from an electromagnetic pulse (EMP) or, conversely, for protecting
a user from electromagnetic frequency (EMF) radiation from mobile
device 200. This disclosure will be directed to describing case 100
from the point of view of protecting mobile device 200 from EMP,
but those skilled in the art will recognize that case 100 provides
superior protection from EMF. Reference to EMP and EMF radiation
refers to that portion of the EM-spectrum referred to as the "radio
spectrum." Importantly, case 100 can protect mobile device 200 from
harmful radiation in the radio spectrum without having to
disassemble or modify mobile device 200 in any way and without
attenuating radiation in the optical spectrum, which makes case 100
easily adaptable for any user. Case 100 also allows the user to
place and receive cellular calls (voice, data, text, or any other
standard capabilities of an unprotected cellphone), read the
display, manipulate the touchscreen and tactile controls, charge
the cellphone's battery, and use the data and headphone port signal
lines all while installed in the EMP protective enclosure of case
100.
[0025] To provide this superior protection, case 100 is implemented
as a modified Faraday cage to enclose and protect mobile device 200
from the EMP while allowing a user access to needed functionality,
as described above. Case 100 simultaneously permits mobile device
200 to survive and be usable before, during and after a nuclear
attack. Case 100 allows for sound transmission, light transmission,
tactile motion (e.g., access to pushbuttons, knobs, etc.), primary
power and other electrical signals through case 100 to the
circuitry of mobile device 200.
[0026] Generally, a passive repeater is used to apply external
radio signals to the internal antenna of mobile device 200. A
limiter circuit can prevent excessive EMP energy from entering an
internal antenna of mobile device 200. Similarly, an external
charging and data port 103 (USB, Lightning, or the like) on case
100 connects to an external charger, routes the charging current
through a lowpass filter and limiter circuit inside case 100 to an
internal charging and data port 106 (USB, Lightning, or the like)
that connects to a charging and data port 201 of mobile device 200.
Generally, charging and data port 201 of mobile device 200 is a
female connecting port which connects to a male connecting port of
internal charging and data port 106 inside enclosure 101 while
external charging and data port 103 is a female connecting port to
connect with the male end of the external charging cable.
[0027] All limiter and lowpass circuits are implemented on a small
interface board inside case 100 where the ground plane layer serves
as part of the Faraday cage surface. A small radio-transparent
elastomer radome covers the external antenna, primarily for
aesthetic and shock protection purposes. An electrically-conductive
hinged metal visor with the protective mesh bonded to it allows
reading the LCD display of mobile device 200 with the EMP
protection in place. To enter data via the touchscreen of mobile
device 200, the visor must be temporarily opened (exposing the
device to EMP damage unless the user physically protects the device
from EMP exposure via other means). Case 100 provides all of this
functionality without need to modify mobile device 200. Mobile
device 200 simply mounts and plugs into case 100 in a manner
similar to standard protective cases with built in spare batteries.
This provides case 100 with a level of familiarity that inhibits
any misuse or operator error.
[0028] Case 100 comprises of an enclosure 101 with a hinged "visor"
that completely surrounds mobile device 200. This hinged "visor"
mechanically and electrically connected to the Faraday cage of
enclosure 101 has a portion that aligns with the display where
there is a cutout which fully reveals the display of mobile device
200. The cutout contains an optically-transmissive fine wire mesh
which provides 80 db of radio attenuation. The mesh is sandwiched
between two sheets of transparent plastic for damage and wear
protection, with the mesh bonded to the grounded visor frame.
Because the standard input entry touchscreen for mobile device 200
is capacitive, it will not function through a grounded mesh screen.
Therefore, the user must open the visor to use the touchscreen of
mobile device 200. Opening the visor, however, exposes mobile
device 200 to EMP damage, requiring the user to take care where and
when he opens it. This tradeoff recognizes that most use in
emergency conditions is receiving or sending audio or receiving
text/data.
[0029] More specifically, enclosure 101 can comprise a bottom
portion 102 and a top cover 104 connected together by a hinge 106
which provides a low-impedance electrical path between bottom
portion 102 and top cover 104 of enclosure 101. Mobile device 200
fits into bottom portion 102. In this arrangement, bottom portion
102 can be configured as a cradle with a back side 107 and four
side walls 108a, 108b, 108c, and 108d that extend upward and inward
from back side 107 to provide protection for the sides of mobile
device 200. Inward portion 109 of side walls 108a, 108b, 108c, and
108d overlap mobile device 200 for reasons discussed below. The
bottom side wall 108a is considered the side corresponding to the
charging ports and the top side wall 108b corresponds to the
opposite side.
[0030] Side wall 108d can further comprise a button extender 110
that extends perpendicularly outward with a through hole extending
there through for receiving a pin 111 to connect top cover 104 to
bottom portion 102 to create hinge 106, which allows enclosure 101
to be opened and closed to insert and remove mobile device 200.
Various arrangements of enclosure 101 that allows for the insertion
and removal of mobile device 200 are contemplated herein. The
important feature of all such arrangements is that enclosure 101
completely surrounds mobile device 200 with no gaps larger than
one-tenth of a wavelength in size over the frequency range of the
threat energy, which is primarily 10 MHz (100 feet wavelength) to
1000 MHz (12 inch wavelength).
[0031] Enclosure 101 comprises of a high conductivity material
(e.g., metal, metallic foil, metallic film, metallic mesh, metallic
fabrics, metallic coatings, metal nanoparticles, etc.) that allows
continuous electrical conductivity over all of its surfaces to
dissipate induced currents. This means enclosure 101 can be
constructed in a variety of ways, including, but not limited to,
metal shells, plastic shells with metallic coatings, or even
transparent coverings made from metallic film, mesh, fabrics or
nanoparticles that provide high conductivity with visible light
transparency.
[0032] Top cover 104 of enclosure 101 allows for transmission of
visible light. A high conductivity yet visible light transparent
plastic cover 115 overlaid a mesh screen 114, as shown in FIG. 1A
and FIG. 3, is combined to top cover 104 and is configured to
overlay the display of mobile device 200. Mesh screen 114 is
configured with holes no larger than one-tenth the wavelength of
the EM waves from an EM pulse through which the light from the
display can shine and be reflected. In one implementation, mesh
screen 114 comprises of a fine metallic mesh of 50-200 threads/inch
with 0.001-0.002 inch diameter with spacing between the threads for
openings that are typically 0.020 to 0.004 inches. This allows
enough light through for reading the display via light transmission
between the threads of the metallic mesh. Mesh screen 114 can be
bonded to between two layers of plastic, a plastic cover 115a and a
plastic cover 115b, which allows mesh screen 114 to dissipate
surface currents induced by an EMP while providing clear protective
layers on each side. To prevent more patterns from occurring when
mesh screen 114 is overlaid on the x-y linear pixel LCD screen of
mobile device 200, mesh screen 114 is oriented with its threads
running at a 45 degree angle to the x-y pixel grid (see FIG. 1A)
for preventing Moire patterns and enhancing clarity of the
display.
[0033] One shortcoming of case 100 is that the capacitive
touchscreen now commonly found in most mobile devices 200
implemented as cellphones and personal electronics will not operate
with a conductive mesh screen 114 installed over the top. The
capacitive charge of a fingertip is evenly distributed over the
protective mesh, and becomes roughly equivalent to pressing the
palm of your hand to the entire touchscreen simultaneously. This
provides no useful function. If the touchscreen is to be used, mesh
screen 114 must be removed for the duration of the input
operations. For this reason, enclosure 101 configured with a top
cover 104 connected to a bottom portion 102 by a hinge 106 that
allows top cover 104 to be temporarily lifted for access to the
touchscreen display of mobile device 200 may be preferred. The
user, however, would be cautioned that mobile device 200 would not
be protected from EMP with top cover 104 opened.
[0034] As can be seen in FIG. 3, a z-shaped joint is formed by the
overlay of top cover 104 on bottom portion 102 to create a
circuitous path to reflect EM waves off the corners of the joint in
enclosure 101. Vertical sides 105 of top cover 104, when closed,
extend downward to overlap side wall 108c and side wall 108d of
bottom portion 102. This flange created by vertical sides 105
forces a circuitous radio energy path between top cover 104 and
bottom portion 102 that enhances the rejection of damaging radio
power entering the Faraday cage of enclosure 101.
[0035] Enclosure 101 of case 100 can be provided with one or more
hole patterns 116 for sound transmission to and from speakers and
microphones. Each hole pattern 116 is configured to align with a
corresponding hole pattern on mobile device 200, and is less than
one-tenth of the EMP wavelength, which is on the order of 0.010
inch diameter.
[0036] Turning to FIG. 4, shown is case 100 with top cover 104 of
enclosure 101 opened. Bottom portion 102 of enclosure 101 is
revealed to show a top covering portion 118 and a bottom covering
portion 120 each of which extend from perpendicular inward from the
top of side wall 108d and 108c, respectively, to cover portions of
the corresponding top and bottom of mobile device 200,
respectively. In this way one or more hole patterns 116 are placed
in each of top covering portion 118 and bottom covering portion 120
to align with speaker and microphone holes on mobile device
200.
[0037] In an embodiment, a small hole sufficient for the front
camera lens typical of mobile devices 200 can be placed on top
portion aligned with the camera lens location on mobile device 200.
Such a hole is only protected against EMP while the top cover 104
is closed. A rear camera lens opening may also be provided in back
side 107 of bottom portion 102, but doing so places a significant
aperture in the Faraday cage which may result in damage to mobile
device 200. One skilled in the art will observe that a pivoted or
hinged metal cover may be installed to cover such an aperture when
not in use, preserving the integrity of the Faraday cage of
enclosure 101. However, similar to opening the top cover 104, the
protected device is susceptible to damage while the protective
cover is open.
[0038] Accessing pushbuttons typical of mobile device 200 while
mounted in case 100 requires button extender 110. Button extender
110 comprises of a T-shaped plunger with the "head" of the "T"
resting on the button of mobile device 200 inside enclosure 101
with the shaft of the plunger passing through a hole in side wall
108d of enclosure 101 of case 100 with 0.001-0.003 inch clearance
and protruding a distance and in a location where the user can
easily press button extender 110 and indirectly press the button on
mobile device 200. The narrow tolerance gap around the button
extender 110 meets the one-tenth wavelength criterion for any holes
in case 100 for EMP protection. Simultaneously, the "T" head of
button extender 110 inside the case provides a circuitous radio
energy path to enhance rejection of damaging power. Button extender
110 can be provided for all of the physical buttons on mobile
device 200, including the volume up, volume down, and power
buttons. A similar button extender 110 can be provided in any of
side walls 108a, 108b, 108c, or 108d or in top cover 104 to engage
any button on mobile device 200. If mobile device 200 is
implemented as a cellular phone with a tactile, physical keyboard
for inputs, the foregoing button extenders 110 can be provided for
every input to provide mobile device 200 with full functionality
inside enclosure 101 without opening top cover 104 of enclosure
101.
[0039] Mobile device 200 also has vibration from an internal
vibrator motor in mobile device 200 which can be transmitted
through case 100 without an impact to EMP protection. Enclosure 101
can comprise a shock-absorbing elastomer 112 on the inside to
protect mobile device 200 from falls and other impacts.
[0040] Case 100 also comprises electronic circuitry to allow mobile
device 200 to communicate with cellular towers, charging and access
to peripherals. This circuitry can all be located on a small
printed circuit board 113 inside enclosure 101. For mobile device
200 to function properly while in case 100, primary power and
digital signals through enclosure 101 to the circuitry must be
allowed. Damaging signals will be conducted over any/all wires
penetrating a Faraday cage and entering the volume of space where
the protected device is located, which means protection circuits
must be installed to shunt any damaging energy from an EMP.
[0041] Turning to FIG. 6, shown is block diagram of mobile device
200 inside case 100. As illustrated, an EMP protection circuit 130
and an EMP limiter 140 in a passive relay are each installed in
series with each signal conductor to shunt the damaging energy to
the Faraday cage surface (i.e. surface of enclosure 101) of case
100 for dissipation along with the circulating surface currents. A
filter implemented as EMP protection circuit 130 and EMP limiter
140 that attenuate all interfering energy (primarily 10-1000 MHz
for EM pulse) by at least 80 decibels and pass only the desired
signals are disclosed.
[0042] FIG. 7A shows a schematic of EMP protection circuit 130.
Side wall 108a of enclosure 101 comprises of external charging and
data port 103, which comprises of a power input port 124, which
further comprises of positive and negative terminals. A gas
discharge tube 132 is connected in shunt across the positive and
negative terminals of power input port 124 outside of the Faraday
cage created by enclosure 101. Gas discharge tube 132 is capable of
withstanding thousands of volts and thousands of amperes for the
duration of an EMP pulse. The excessively high voltage and amperage
induction is presumed due to the long charging cables most users
use, which also would induce a large EMP voltage spike. With gas
discharge tube 132 connected to ground 131 and to enclosure 101 of
case 100, damaging energy from an EMP is dissipated along with
circulating surface currents on enclosure 101.
[0043] Input port 124 is connected in series to a filter 134 inside
enclosure 101. Filter 134 is tuned to pass or limit the desired
frequencies. A more specific implementation of filter 134 is shown
in FIG. 7B. Filter 134 can be implemented as a low pass filter for
the charging circuit and comprise an LC circuit tuned to pass a DC
charging voltage and 60 Hz AC voltages. Filter 134 implemented as a
low pass filter can comprise an inductor 133 and a capacitor 137 of
the appropriate size for purposes of tuning to the desired
frequencies. A voltage suppressor 139, such as a metal oxide
varistor (MOV) or transient voltage suppressor is connected in
shunt across internal charging and data port 106 (e.g., USB or
Lightning connector) to suppress all over-voltages as secondary
protection to gas discharge tube 132.
[0044] Digital signals are also commonly provided with power
through external charging and data port 103. In the case of digital
signals, lowpass filters are again a useful solution for static or
low frequency signaling. However, when the signal frequency enters
the EMP spectral range (i.e., a 10-100-1000 Mbps Ethernet signal),
the problem becomes more difficult to solve.
[0045] In this case, the circuit of FIG. 7A is again used, but with
the cut-off frequency of the lowpass filter 134 adjusted upward to
the data rate of the data signal. The USB data rate used in mobile
devices rarely exceeds 100 MHz, but this represents approximately
10% of the EMP energy spectrum. In this case, we rely on the TVS
protector to clip any high voltage spikes passing through the
lowpass filter 134 so as not to cause damage to mobile device 200.
This solution may at worst prevent successful data reception for a
few data pulse durations for the direction of an EMP pulse. One
skilled in the art will recognize that EMP protection circuit 130
of FIGS. 7A and 7B can be implemented for each data signal line 125
in external charging and data port 103.
[0046] In many cases, however, the signal requires a wide bandwidth
(Ethernet and USB are examples), which essentially requires passing
the EMP spectrum along with the desired signal spectrum. In this
case, rather than limiting the incoming spectrum, it becomes
necessary to limit the incoming signal amplitude. EMP protection
circuit 130 is designed for shorting out to the surface of the
Faraday cage of enclosure 101 the signal line's induced EM pulse
energy for its 100-200 nanosecond duration. This can be
accomplished with voltage suppressor 139 (e.g., Zener diode, TVS
diode, Metal Oxide Varistor, gas discharge tube, etc.), which is a
high impedance (and hence transparent to normal circuit operations)
when the signal line which it is shunting to ground 131 has less
than the threshold voltage. When an EMP appears, EMP protection
circuit 130 quickly avalanches to a near-zero impedance state,
shunting the pulse energy to the surfaces of case 100. This
protection does disable desired operation of the signal line for
the duration of the EM pulse, but protects the circuitry.
[0047] It is also contemplated that mobile device 200 with wireless
charging capability also functions inside case 100. Wireless phone
chargers operate at very low frequencies, below the spectrum of an
EMP, and are also magnetic fields. This means that wireless
charging would work through case 100, which is a non-magnetic case
(e.g., aluminum) without any protection features.
[0048] Case 100 must also be able to pass communication signals to
and from mobile device 200. It is well known to all skilled in
antenna design and application that all antennas both receive and
radiate electromagnetic energy simultaneously. FIG. 8 shows a
passive radio relay 140 comprising of two identical cellular
antennas connected by a coaxial cable with EMP limiter 140 between
them. One antenna is external repeater antenna 142, and is located
outside the Faraday cage of enclosure 101. The other identical
antenna is internal repeater antenna 146 and is located inside the
Faraday cage of enclosure 101 adjacent to the internal antenna 203
of mobile device 200 and coupling signal power into/out of it. Each
of external repeater antenna 142 and internal repeater antenna 146
inherently comprise band limiting properties reducing coupled EMP
energy.
[0049] In transmit, internal antenna 203 of mobile device 200
couples energy into internal repeater antenna 146. That energy
travels through transmission line 147, which can be implemented as
coaxial cable, and limiter circuit 140 (both of which are described
below) to external repeater antenna 142, where it is radiated,
ultimately arriving at a cell tower. In receive, the signal power
from the cell tower is received by external repeater antenna 142,
passes through transmission line 147 through the limiter circuit
140, and is applied to internal repeater antenna 146, where it is
radiated and coupled into the internal antenna 203 of mobile device
200. The inherent resonant nature of the repeater antennas (as well
as the cellphone antenna and its internal bandpass filters in
receive and transmit) further help reduce the spectral content of
EMP energy reaching mobile device 200.
[0050] Because enclosure 101 is conductive, it will block EM waves
from entering the case, except as specifically allowed as described
herein. Case 100 is configured to allow high frequency
electromagnetic energy through enclosure 101 of case 100 to the
radio circuitry of mobile device 200 for sending and receiving
communication signals, so that mobile device 200 continues to
function while inside enclosure 101 of case 100.
[0051] FIG. 8 shows the electrical schematic for EMP limiter 140 of
FIG. 6 implemented in a passive radio relay with EMP protection.
The passive radio relay comprises of external repeater antenna 142
positioned outside enclosure 101 of case 100 connected to a
transmission line 147 that passes through enclosure 101 and is
connected to internal repeater antenna 146. Internal repeater
antenna 146 EM-couples with antenna 203 of mobile device 200 and
relays signals to and from antenna 203 of the mobile device
200.
[0052] An EMP limiter 140 connected in the passive repeater
attenuates voltages above a threshold. EMP limiter 140 can comprise
of a gas discharge tube 143 outside of enclosure 101 connected in
shunt from transmission line 147 to ground 131. Gas discharge tube
143 is capable of withstanding thousands of volts and thousands of
amperes for the duration of an EMP pulse. With gas discharge tube
143 connected to ground 131 and to enclosure 101 of case 100,
damaging energy from an EMP is dissipated along with circulating
surface currents on enclosure 101. EMP limiter 140 also comprise of
an internal resistor 145 to limit the current.
[0053] EMP limiter 140 can be located on a small printed circuit
board along with the printed circuit mounted internal repeater
antenna 146 (discussed below). EMP limiter 140 is designed for the
type of mobile device 200. For mobile device 200 configured to
communicate using narrowband signals, EMP limiter 140 can be
implemented as a bandpass filter. For wideband communication, EMP
limiter 140 can be implemented as an amplitude limiter. If mobile
device 200 only receives signals (e.g., a pager or the like),
amplitude protection necessary for receiving signals is minimal
because the desired signal has microscopic power. For mobile device
200 that transmits signals, however, the amplitude limiter of EMP
limiter 140 becomes more complex as the transmitter power level
rises. When the power level is high enough, the high power
transmitter output circuit alone may be capable of withstanding the
EMP pulse.
[0054] An internal repeater antenna 146 is provided inside
enclosure 101 connected either directly to EMP limiter 140 or
connected to a transient suppression component 148 (e.g., Zener
diode, TVS diode, Metal Oxide Varistor, gas discharge tube, etc.)
with a high impedance when the signal line which it is shunting to
ground has less than the threshold voltage. Particularly noteworthy
is that both internal repeater antenna 146 and external repeater
antenna 142 of this passive repeater utilizes the ground-plane of
the Faraday cage of enclosure 101, which is connected to ground
131.
[0055] In operation, transmit signals are relayed from the antenna
203 internal to mobile device 200 to internal repeater antenna 146
and out of enclosure 101 through transmission line 147 to external
repeater antenna 142. Receive signals are received at external
repeater antenna 142 which are passed through transmission line 147
to internal repeater antenna 146 and then relayed to antenna 203 of
mobile device 200. In an EMP event, excessive signals are
attenuated by protection circuit 144 and transient suppression
component 148.
[0056] One skilled in the art will recognize that case 100 can
protect any device susceptible to neutralization from an EM pulse.
In this regard, mobile device 200 means any type of communication
device such a mobile phone, pager, any type of transmitter, any
type of receiver, etc., and any type of non-radio or
non-communication devices, as well. Also, any of the filters
discussed in reference to a particular embodiment, circuit or
drawing can be used in any other embodiment, circuit or drawing
based on the technical requirements.
[0057] While the principles of the invention have been described
herein, it is to be understood by those skilled in the art that
this description is made only by way of example and not as a
limitation as to the scope of the invention. Other embodiments are
contemplated within the scope of the present invention in addition
to the exemplary embodiments shown and described herein.
Modifications and substitutions by one of ordinary skill in the art
are considered to be within the scope of the present invention,
which is not to be limited except by the following claims.
* * * * *