Note: Descriptions are shown in the official language in which they were submitted.
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APPARATUS FOR MONITORING OPENING OF SEALED CONTAINERS
DESCRIPTION
TECHNICAL FIELD:
The invention relates to apparatus for monitoring opening of sealed containers
and
is especially, but not exclusively, concerned with monitoring for unauthorized
access to
vaults, safes, strongboxes, and sealed containers for goods-in-transit, such
as goods
vehicles, box trailers or shipping/transport containers of the kind carried by
tractor-
trailers, trains, aeroplanes or ships.
BACKGROUND ART:
As a result of introducing so-called "Just-in-Time" manufacturing systems, and
"Inventory-on-wheels" systems which use global positioning systems (GPS), many
companies now have more products in transit than in their warehouses.
Consequently,
thefts of and from tractor-trailers, shipping containers and the like are
increasingly a
major security problem.
Security devices for tractor-trailers and transportation containers are known.
For
example, US patent number 5,475,362 discloses an alarm system for tractor-
trailers
which employs sensing switches which trigger the alarm when actuated, such as
by the
unauthorized opening of a door, and may also disable the vehicle. US patent
number
5,615,247 discloses a security device for cargo transport containers which
employs a pair
of cables threaded through the door handles of the container. If the cables
are cut or
disconnected, the security device uses a cellular radio network to send an
alarm signal
to a security company. A disadvantage of these arrangements is that they
protect only
against conventional access, such as through doors, and are visible from
inside or outside
the container.
For one aspect of the present invention, an object is to mitigate this problem
and
provide a security device for sealed enclosures or containers which is capable
of
detecting access by any route. For another aspect of the invention, an object
is to provide
covert apparatus for monitoring opening of sealed enclosures.
DISCLOSURE OF INVENTION:
According to one aspect of the present invention, apparatus for monitoring
opening of an electromagnetically shielded enclosure, such as a shipping
container, box
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trailer, vault, and so on, comprises a radio receiver unit having at least one
antenna for
reception of radio signals, the receiver unit to be housed within the
enclosure and
comprising means for scanning a predetermined band of radio frequencies,
periodically
or continuously, and detecting a predetermined radio signal level; and means
operable
in dependence upon such radio signal level detection to generate a signal
indicating
opening of the enclosure.
The receiver may detect the predetermined radio signal level by determining
that
the signal energy in the predetermined band inside the enclosure increased
abruptly to
exceed a preset reference level.
Alternatively, the receiver may detect the radio signal as a difference
between
internal and external radio signal levels.
Trailers and transport containers used for valuable products usually have
metal
panels, typically steel or aluminum, to make entry more difficult.
Consequently, they are
enclosures which are shielded against ingress of electromagnetic radiation
(Faraday
cages). Whether thieves steal the entire trailer or container, or break into
it while it is
parked or stored, at some point they will need to gain access to the contents
by opening
the door or cutting a hole in a side panel or roof panel, the latter approach
sometimes
being used when a trailer has been parked with its rear door against a wall.
When this
happens, electromagnetic radiation enters the enclosure and is detected by the
receiver
unit.
The receiver unit may be connected to an antenna for transmitting an alarm
signal
to a remote location, conveniently by cellular telephone, radio or satellite
communications, either directly or by way of an existing system with which the
vehicle
is equipped.
Determining when and where the theft occurred often is particularly difficult,
since it is known for thieves to replace customs or other door seals. Shipping
of a
container from one country to another might entail transport by tractor-
trailers, storage
in customs depots, and transportation on board ship. If, upon arrival of the
container
at its destination, it is discovered that it has been opened and the contents
stolen or
tampered with, it is very difficult to determine where and when this occurred,
which
hampers investigations by police officers and may also affect insurance
claims.
Accordingly, the receiver may be provided with means for recording the times
of all
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events involving opening or closing of the container, to provide a record for
checking
when the container reaches its destination.
Preferably, when an intrusion occurs, the receiver captures and stores the
frequency spectrum. Each city has its own particular FM frequency spectrum so
the
captured spectrum can be compared with known city spectra to identify the city
in which
the or each intrusion took place.
The receiver may also include means for activating a local audible and/or
visual
alarm, such as a siren, vehicle horn, vehicle lights, and so on. In some
cases, however,
it may be preferable to record the opening/closing of the enclosure without
generating
an alarm.
Where the enclosure is a trailer of a tractor-trailer unit or other vehicle
equipped
with a transmitter for use with a global positioning system (GPS), the
receiver unit may
comprise means for interfacing to the GPS receiver to provide a record of the
location
of the container at the time it was opened.
Preferably, the monitoring apparatus is not readily apparent to a potential
intruder. The apparatus may be hidden from view or camouflaged. Many shipping
containers and the like have door seals which comprise a tubular seal of
rubber or other
flexible material. According to another aspect of the invention for use with
such
containers the antenna is filamentary, conveniently a length of leaky cable
(open
transmission line) and is disposed inside the tubular door seal. The receiver
unit itself
may be housed in a slim cylindrical housing and also disposed inside the door
seal.
An advantage of disposing the antenna inside the door seal is that the close
proximity to the metal of the door and/or surrounding end wall effectively
short-circuits
the antenna and hence the radio receiver signal when the door is closed.
Alternatively, the antenna or/and receiver unit may be camouflaged as a
reinforcing strip or other feature of the container interior.
According to another aspect of the invention, a method of monitoring for
opening
of an electromagnetically shielded enclosure using a radio receiver unit
having at least
one antenna for reception of radio frequency signals, includes the steps of
housing the
receiver unit within the enclosure, operating the receiver unit to scan a
predetermined
band of radio frequencies, periodically or continuously, detecting a
predetermined radio
signal level; and, in dependence upon such radio signal level detection,
generating a
signal indicating opening of the enclosure.
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Preferred embodiments of the invention will now be described, by way of
example only, with reference to the accompanying drawing.
BRIEF DESCRIPTION OF THE DRAWING:
The attached drawing is a block schematic diagram of the monitoring apparatus
including a scanning FM receiver unit shown in more detail.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
An electromagnetically-shielded enclosure, which could be a shipping container
or the box trailer of a tractor-trailer vehicle, houses an electromagnetic
field disturbances
volumetric sensor comprising a radio receiver unit which is connected to an
antenna.
The antenna comprises a leaky cable located around the door of the container,
housed
within a door seal. Preferably, the radio receiver unit is capable of
operating throughout
the broadcast FM radio band from 88 MHz. to 108 MHz.
Referring to the drawing, in the receiver unit 11, the radio frequency signal
received from the associated antenna 12 is coupled to a bandpass filter 14
which restricts
the radio signal to the FM spectrum from 88 MHz. to 108 MHz. and passes it to
a low
noise amplifier 15. The amplified signal from amplifier 15 is down-converted
to an
intermediate frequency (IF) signal of 10.7 MHz. by a mixer 16 which derives
its local
oscillator signal (LO) from a phase-locked loop oscillator (PLO) 17. The PLO
17 is
controlled, via bus 18, by a microcontroller 19 which causes the local
oscillator
frequency to scan the spectrum in steps of 200 kHz. which is the usual spacing
between
FM radio stations.
The microcontroller 19 monitors continuously the signal strength inside the
enclosure. For each frequency step, the down-converted IF signal from mixer 16
is
filtered by a second bandpass filter 20 having a bandwidth of 300 kHz.
centered upon
the IF frequency. The magnitude of the output from second bandpass filter 20
is
measured using a logarithmic amplifier 21. The analog signal from the
logarithmic
amplifier 21 represents the amplitude of the radio frequency signal for a
selected station
and is filtered by a low pass filter 22 having a cut-off of 80 Hz. The
filtered signal Ar
from low pass filter 22 is converted to an eleven bit digital signal by analog-
to-digital
(A-to-D) converter 23 within the microcontroller 19. The digital signal from A-
to-D
converter 23 is processed by a signal processor 24 of the microcontroller 19.
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D.C. power for the receiver is provided from an internal battery.
The microprocessor 19 causes the receiver to scan the FM radio band
continuously. During each scan, the microcontroller 19 accumulates the power
levels
detected at each frequency step, (as derived from the signals from the A-D
converter 23)
5 and calculates the total accumulated power or energy of the received signals
in the band
for each 200 kHz. increment in frequency. The microcontroller 19 compares this
energy
level with a preset reference level and also compares the time in which the
signal
increased. If the signal energy increased to greater than the threshold within
a
predetermined time, e.g. 0.5 seconds, the microcontroller 19 generates an
"Enclosure
opened" ALARM signal on line 25. The preset reference level is set so that, so
long as
the container has not been opened, it will be greater than the signal level
inside the
enclosure. Conversely, when the energy level returns to its previous value,
i.e. that
prevailing before the container was opened, the microcontroller 19 will
generate an
"Enclosure closed" signal on line 26.
The reason the microcontroller also determines the rate at which the signal
level
changed is that a sudden change occurring, say, in 0.5 seconds, implies
opening of the
container whereas a more gradual change may result from a change in the
environment
or location of the closed container. The microcontroller 19 will also
determine that the
signal strength has remained above the threshold for a predetermined length of
time, to
avoid recording as an "event", e.g. unauthorized opening, a brief disturbance
of the
signal level without opening of the enclosure.
The user may adjust the threshold, and hence the sensitivity, by means of
control
line "Adjust sensitivity". In addition, the user may select on of three modes
of operation
"Record On-event", "Record Continuously" or "Record On-event and
Continuously".
The apparatus will be provided with outputs for indicating events such as
opening
and closing of the enclosure and tampering with or failure of the monitoring
apparatus,
and battery condition. The microcontroller 19 is shown with an RS232 port
enabling
such data to be transferred, conveniently by means of an infra-red coupling to
enable the
data to be downloaded and the apparatus reconfigured by means of such a laptop
computer equipped with an infra-red I/O interface.
Various modifications are feasible within the scope of the present invention.
Thus, the receiver 11 may be arranged to capture the FM spectrum prevailing
when the
intrusion occurred. In particular, the microcontroller 19 may be programmed to
capture
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the spectrum and store it in the memory of the signal processor 24. Each city
has its
own particular FM frequency spectrum. When subsequently an intrusion is being
investigated, the captured frequency spectrum can be compared with known
spectra for
different cities to identify the city in which the or each intrusion took
place. This
information is crucial to locating the intrusion site and allocating shipper
responsibility.
The monitoring apparatus could comprise two antennas, one inside and the other
outside the enclosure enabling the receiver to monitor the signal levels
inside and outside
the enclosure, determine the difference between them, and indicate opening of
the
enclosure whenever the difference is less than a preset reference.
If cost and simplicity warrant it, a simpler, analog embodiment could be
employed, using an analog sample-and-hold circuit connected to a comparator,
for
example a Schmidt trigger, for comparing the output of the sample-and-hold
circuit with
a preset reference voltage. The reference voltage would be set so that, so
long as the
container was closed, and the electromagnetic shielding intact, it would not
be exceeded
by the output of the sample-and-hold circuit yet, as soon as the enclosure was
opened,
the increase in the radio signal level inside the enclosure would cause the
output of the
sample-and-hold circuit to exceed the reference. When that happened, the
comparator
would generate an alarm signal.
It should be appreciated that other types of radio receiver could be employed
instead of an FM radio receiver, monitoring for example AM bands, cellular
telephone
bands, LORAN-C (trademark) or even cosmic/manmade noise. The antenna would be
selected to suit. For example, a loop antenna might be provided around a door,
a short
dipole might be hidden within a package, a ported coaxial cable might be
disposed along
a long wall. Although, in the described embodiment, the antenna is shown
separate from
the receiver unit, it could be integrated into it.
It should be appreciated that, although the specific implementation described
herein is for a shipping container, the invention is not limited to shipping
containers or
tractor-trailers. Rather, the invention could be applied to any enclosure
which is shielded
against ingress of electromagnetic radiation, whether made of shielding
material, such
as a metal trailer, steel-lined bank vault, metal barrel, steel cabinet or
safe, and so on,
or very thick concrete, such as a bank vault, or made from a material which
does not
itself provide shielding but which is lined with a suitable screening mesh or
film which
comprises the shield.
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Although the specific embodiment has been described with reference to
unauthorized access to shipping containers, it should be appreciated that
embodiments
of the invention may be used for monitoring containers carrying toxic or
radioactive
materials. Although the apparatus primarily monitors for unauthorized opening
of the
enclosure, it would be possible to add other sensors to sense temperature,
pressure,
acceleration, earth magnetic field (e.g. for orientation) and so on and have
the
microcontroller monitor those also by way of suitable additional I/O
interfaces.
It is envisaged that there might be locations, such as in the middle of the
ocean,
where reception of normal FM or other radio signals is very poor. In order to
ensure
proper operation of the monitoring apparatus in such conditions, the carrier
may use a
low power transmitter, for example on board the ship, to radiate a suitable
signal
continuously and ensure that the monitoring apparatus will always be able to
detect a
change in the signal strength when the container is opened.
