GB2510636A

GB2510636A - Multi-frequency non-linear junction detector

Info

Publication number: GB2510636A
Application number: GB1302432.8A
Authority: GB
Inventors: Andrew Barry Stephen
Original assignee: Audiotel International Ltd
Current assignee: Audiotel International Ltd
Priority date: 2013-02-12
Filing date: 2013-02-12
Publication date: 2014-08-13
Anticipated expiration: 2033-02-12
Also published as: GB2510636B; GB201302432D0

Abstract

A non-linear junction detector (NLJD) for detecting and locating concealed electronic devices or devices which contain metal contacts or metal junctions has a multi-frequency transmitter configured to illuminate a sweep area with a plurality of RF illumination signals at different frequencies and a receiver configured to receive a return signal from target objects within the sweep area. The return signals are provided to a processor configured to: determine amounts of energy in the return signal within predetermined frequency bands; and compare the amounts of energy in the predetermined frequency bands with a database of signatures each indicative of a specific target object or class of target objects; and provide an indication of likely target object or class of target objects corresponding to the return signal. The RF illumination signals may be predetermined set of frequencies (e.g. GSM, 3G, 4G, WiFi, Bluetooth, NFC) selected according to a target type and corresponding to known frequencies of weakness in the RF screening of the target type.

Description

NON LINEAR JUNCTION DETECTOR

The present invention relates to methods and apparatus for detecting and locating concealed electronic devices or devices which contain metal contacts or metal junctions.

Such devices which are the target of surveillance or sweep operations may also be referred to herein as target objects.

A non-linear junction detector (NLJD) is a device which can be used to detect semiconductor junctions in, for example, electronic devices or to detect metal-to-dissimilar metal junctions. The NLJD operates by illuminating a target junction or object with energy at a fundamental radio frequency (RF). Distortions within and reflections from the non-linear junction can then be analysed to determine the type of junction detected. The reflections from the non-linear junction are usually at twice the illuminating frequency (second harmonic) and three times the illuminating signal frequency (third harmonic).

In general a semiconductor junction will return predominantly second harmonic frequencies, whereas metal-to-dissimilar metal junctions will return higher levels of third harmonic frequencies or very similar levels of second and third harmonic frequencies together but predominantly third harmonic frequencies.

In order for an NLJD to work, the illuminating signal must first enter the target non-linear junction and the generated harmonics must then re-radiate away from the junction back to the NLJD receiver. For this reason, electronic devices that are well screened against RF radiation will be more difficult to detect than poorly screened or unscreened devices.

Until now there have been two main ways in which an NLJD may overcome improved RF screening in target devices. In a first approach, the effective radiated power (ERP) of the illuminating transmitter signal is increased. In a second approach, the NLJD receiver sensitivity is increased. A combination of both is also possible.

Both of these methods of improvement can introduce further problems, the main one being an increased tendency for the WLJD to self-detect. Self-detection occurs when the NLJD detects junctions within the fabric of the NLJD implementation itself, rather than in an intended illuminated target.

I

Further, operating a very high performance NLJD, capable of defeating well RE screened target devices, can become increasingly difficult due to the numerous false positive detections that will exist in modern search environments, e.g. a modern office. A false positive is a detected target which, whilst presenting a real non-linear junction to the MUD, is simply an innocent target within the search environment. Examples can include computers, telephones, lighting units, false ceiling support fixings, electrical wiring etc. It is an object of the present invention to provide an improved MUD capable of better overcoming RF screening protecting many modern day targets, e.g. mobile phones, whilst still maintaining usability by reducing or minimizing the required power in the illuminating signal and reducing or minimizing MUD receiver sensitivity. It is therefore a further object of the invention to provide a NJLJD capable of reducing or minimizing false positive detections within modern search environments.

According to one aspect, the present invention provides a non-linear junction detector comprising: a multi-frequency transmitter configured to illuminate a sweep area with a plurality of RE illumination signals at different frequencies; a receiver configured to receive a return signal from target objects within the sweep area; a processor configured to: determine amounts of energy in the return signal within predetermined frequency bands; and compare the amounts of energy in the predetermined frequency bands with a database of signatures each indicative of a specific target object or class of target objects; and provide an indication of likely target object or class of target objects corresponding to the return signal.

The multi-frequency transmitter may be configured to illuminate the sweep area with a predetermined set of frequencies selected according to a target type selected. The predetermined frequencies may correspond to frequencies related to radio communication channels. The predetermined frequencies may correspond to one or more of mobile telecommunications device channels, near field communications channels, and short range radio network channels. The predetermined frequencies may correspond to frequencies related to any one or more of GSM, 3G, 4G, WiFi, Bluetooth, and NFC communication channels. The non-linear junction detector may include a signature database comprising a plurality of signatures, each signature comprising an indication of energy amounts found in plural different frequency bands for different target objects and/or different classes of target object. The non-linear junction detector may include a user interface and the processor may be configured to use the indication of likely target or class of targets corresponding to the return signal to select a detected object for output by the user interlace, or to deselect the detected object for output by the user interface, the user interlace being configured to give said output as a visible, audible or haptic indication to a user. The non-linear junction detector may include: a user interface configured to receive a user input indicating one or more target object types selected, a database indicating a plurality of illumination signal frequencies required as a function of target type, and the processor may be configured to select the plurality of RF illumination signals at different frequencies based on the one or more target object types selected.

According to another aspect, the present invention provides a method of operating a non-linear junction detector comprising the steps of: illuminating a sweep area with a plurality of RF illumination signals at different frequencies; receiving a return signal from target objects within the sweep area; using a processor to: determine amounts of energy in the return signal within predetermined frequency bands; and compare the amounts of energy in the predetermined frequency bands with a database of signatures each indicative of a specific target object or class of target objects; and provide an indication of likely target object or class of target objects corresponding to the return signal.

Embodiments of the present invention will now be described by way of example and with reference to the accompanying drawings in which: Figure 1 shows a schematic functional block diagram of a multi-frequency non-linear junction detector; and Figure 2 shows a process flow of an exemplary method executed by the non-linear junction detector of figure 1.

Figure 1 shows an implementation of a high performance non-linear junction detector (NLJD) for use in detecting and locating a wide range of concealed and RF screened electronic devices. This implementation, and other implementations, may be used in, for example, (i) counter-surveillance environments to detect and locate hidden surveillance devices, (ii) electronic ordinance detection (EOD) environments to detect and locate certain components within ordinance devices; and (iii) secure environments to detect prohibited devices such as mobile telephones.

The NLJD of figure 1 allows the system to maintain a high detection probability of screened targets without increasing the illuminating signal or system receive sensitivity to a point which makes the system unusable due to high levels of false positives in a modern search environment.

Figure 1 shows a multi-frequency NLJD 100 capable of covering a frequency range approaching or exceeding an octava The NLJD 100 includes a wideband transmit module 101 comprising: a wideband transmit antenna 7; a low passive intermodulation (PIM) RF switch I combiner 6; two or more transmit harmonic suppression filters 4, 5; a low PIM RE switch / splitter 3; an RE power amplifier 2; and a variable RE frequency transmit source 1.

The multi-frequency NLJD 100 further includes a wideband receive module 102 comprising a second harmonic receive channel 103 and a third harmonic receive channel 104. The second harmonic receive channel comprises a receive antenna 8; a low PIM RE input switch I splitter 9; multiple receive filters 10, 11; an RE switch I combiner 12; a low noise amplifier 13; and a variable RE frequency NLJD receiver 14 Similarly, the third harmonic receive channel comprises a receive antenna 17; a low PIM RE input switch / splitter 18; multiple receive filters 19, 20; an RF switch / combiner 21; a low noise amplifier 22; and a variable RF frequency NLJD receiver 23.

The multi-frequency NLJD 100 also includes control and processing circuitry 15, which is used to control the variable RE frequency operation of the system and to process recovered responses from the receivers.

The multi-frequency NLJD 100 also includes a user interface 16 which is used to inform the user of the level and type of target detected and also allow the user to select different set-up configurations to optimise performance for certain types of target.

The system also includes a database 24 for storing and retrieving target signatures' to allow the multi-frequency MUD 100 to identify target types and learn new target types as they become available.

Where the multi-frequency NLJD 100 is implemented over a range of RF frequencies which is less than an octave it may be possible to replace the multiple filter banks 4, 5, 10, 11 and 19, 20 with single filters, e.g. 4,10 and 19. In this scenario, it may also be possible to omit the low PIM RF switches / combiners 6, 12 and 21 and also omit the low PIM RF switches! splitters 3, 9 and 18. Where the multi-frequency NLJD is implemented over wide frequency ranges, it may be desirable to include more than two filters in each bank.

The MUD 100 uses a variable, stepped or swept transmit and receive frequency.

Control circuit 15 is configured to control the variable frequency transmit source I to generate a plurality of transmit signals at different frequencies for each detection scan.

The plurality of transmit signals at different frequencies may be discrete signals each at a predetermined centre frequency or a continuous set of signals swept through a predetermined frequency range or series of different frequency ranges.

The transmit signals are amplified by RE power amplifier 2 and fed to filters 4, 5 to suppress any unwanted harmonics in the signal to be transmitted. The filters remove harmonic content that may be introduced by the transmit circuitry. The number of filters required may be determined according to the range of frequencies used. The filtered signals are combined in the low PIM switch I combiner 6 and then transmitted by the transmit antenna 7. Thus, the transmit module 101 is generally configured to illuminate a sweep area that is within range of the transmit antenna with a plurality of RF illumination signals at different frequencies.

The receive module 102 receives return signals from any target objects in the sweep area that contain semiconductor or metal-to-dissimilar-metal junctions by virtue of return radiation at the second or third harmonics of the transmitted signals. Return signals from the antennae 8, 17 are split into relevant frequency bands by the low PIM RF input switches! splitters 9, 18 and fed to respective filters 10, 11, 19, 20 to isolate the selected second and third harmonics and suppress the fundamental frequency. The receive filters 10, 11, 19, 20 thereby also protect the receive circuitry from overload that may be caused by the fundamental transmit (illumination) signal. The resulting filtered signals are combined with second and third harmonic switches I combiners 12, 21 and respectively fed to low noise amplifiers 13, 22 then fed to variable frequency detectors 14, 23. The outputs of the detectors 14, 23 are then analysed by control and processing circuitry 15.

By sweeping or discretely stepping the system frequency over a band, or a number of bands, or a number of discrete frequencies, the NLJD is capable of effectively locating weak spots' in the RE screening of any target devices in the illumination sweep area.

In preferred configurations, the choice of frequencies of the RE illumination signals is particularly chosen in order to maximise the probability of exploiting weaknesses in the RE screening of known types of target devices, thus enhancing the probability of detecting the target devices. In addition, by exploiting specific weaknesses at plural frequencies that are specific to known types of target device, or known classes of target device, the NLJD is able to detect "signatures" of certain target devices or classes of target devices.

Thus, the NLJD is preferably configured to obtain frequency response signatures' for a plurality of targets so that detected targets can be identified to the operator as such, or if the signature' corresponds to known innocent devices or classes of devices, these can be disregarded or categorised by the system to avoid generating many false positive' detection events.

Eor example, devices such as mobile telephones are generally inherently designed such that they have RE screening weaknesses at the frequencies or frequency bands required for communication channels used by the mobile telephone. Thus, the mobile telephone will have a relatively reduced RF screening effectiveness at frequencies corresponding to one or more of: the cellular or mobile telephone network communication bands (e.g. OSM, 3G, 40, DVB-H, SMR etc); wireless LAN communication bands, such as the WiEi 2.4 0Hz bands; short range device-to-device communication bands such as 2.45 GHz used by Bluetooth-enabled devices; and near-field communication channel bands for devices enabled with near field communication systems.

Any or all of these communication frequency bands which are used by any particular electronic device may result in reduced RF screening capability of the device at or around those bands. As such, selection of frequencies at or close to these frequency bands (or sub-harmonics or harmonics thereof) for the illumination signal of the NLJD may provide an increased detectability of the target device by increased penetration of the device by the illumination signal and/or increased emission of second and third harmonics by junctions within the target device.

Thus, in a general aspect, the NLJD 100 may be configured to select frequencies for the illumination signals corresponding to one or more of radio communication channels, mobile telephony communication channels, medium and short range communication

channels and near field communication channels.

In some circumstances, according to local legislation, there may be restrictions on use of transmitter devices (such as MUDs) that transmit at certain reserved frequencies for communications channels. If these coincide with desired frequencies of an RF illumination signal, use of a specific sub-harmonic of those desired frequencies as the illumination signal instead may still exploit the inherent weakness of the RF screening of the target object by more easily allowing any second harmonic or third harmonic return signal from a junction in the object to penetrate the RE screening at the frequency of the communication channel to be thereby detected by the NLJD. Thus, the expression "illumination signals corresponding to one or more communications channels" is intended to also encompass at least sub-harmonics at one-half or one-third of the communication channel frequency.

Prior knowledge of the type of target being searched for, e.g. concealed mobile phones, enables the MUD system to be pre-set to frequencies which give the highest probability of detection for that target. Thus the NLJD system can be continually optimised for differing targets, classes of targets and search scenarios.

The processing circuitry 15 in the NLJD 100 is configured to analyse the amounts of energy found in return signals elicited by the illuminatFon signals. The amounts of energy found respectively at each of plural frequency bands is compared with one or more signatures stored in the NUB signature database 24. Each signature in the signature database may be indicative of a specific target, a specific target type or class of targets.

Each signature in the signature database 24 includes an indication of energy amounts found in plural different frequency bands for different target devices andIor different classes of target devices.

The energy amounts may be expressed as an absolute received energy level for each frequency band. The energy amounts may be expressed as an absolute energy level for each frequency band as a function of the transmit power. The energy amounts may be expressed as an energy level for each frequency band as a ratio of transmitted power.

The energy amounts may be expressed in relative terms for each of the frequency bands, e.g. normalised across multiple frequency bands and thereby independent of transmit power and range of the target from the antenna. The energy amounts may be indicated as a simply binary yes/no at many different frequency bands, indicating an energy amount above a simple threshold. The frequency bands used in the signatures may be of any size (i.e. frequency range) including wide bands, narrow bands or even down to effectively single frequencies. The different bands may be of different sizes to one another in any given signature, e.g. depending on the frequency resolution required for any particular interrogated RE screening weaknesses.

By comparing the energy amounts found at plural different frequency bands with signatures in the database 24, the processor 15 is thereby able to provide an indication of likely targets or classes of targets where the return signal matches or is close to a relevant signature.

The signature database 24 may be pre-programmed with signatures of known target devices or classes of device. The NLJD 100 may also have a learning function in which the operator is able to teach the NLJD new signatures of detected and identified target objects when these are found during a sweep.

In another arrangement, the NLJD is configured to be set up by the operator, using the user interface 16, to seek specific target objects or classes of target object. For example, if the user is seeking conceared mobile telephones, the user interface may provide an input to set mobile telephone' as a class of devices sought. The NLJD may retrieve frequency band information from the database 24 indicative of frequencies / frequency bands where mobile telephones can be expected to have RE screening weaknesses. This information is then used by the NLJD to determine the plurality of illumination frequencies required to exploit those weaknesses during a sweep operation.

Thus, in a general aspect, the NLJD may be configured to illuminate the sweep area with a predetermined set of frequencies selected automatically according to a target type selected.

In a further arrangement, the NLJD may use signature information from the database to disregard certain patterns of return signal where these can be attributed to certain target objects or classes of target object which are not of interest to the user. This may avoid the user being swamped with too many false positive results which may otherwise tend to increase the risk of missing a target object during a sweep.

The user interface may include a display indicating identified detected objects and pre-classifying them according to the preferences of the user, e.g. displaying target objects in red and non-target objects in green. Return signals that do not correspond to any known signature in the database could be flagged for further investigation.

Thus it will be understood that the NLJD may be programmed to use the signature database to (i) classify detected objects; (ii) positively identify selected target objects matching signatures in the database while screening out non-selected objects; (iii) screen out selected target objects matching signatures in the database while displaying objects not selected; or (iv) combinations thereof.

Matching of the return signal to signatures in the signature database may be accomplished by comparing energy amounts in the different frequency bands according to a simple binary (yes or no) threshold matching at each frequency band, or may use a more sophisticated pattern matching algorithm.

The NLJD may further be used to identify departures from a normal signature' of an object or class of objects which could be indicative of the object concealing a target object, i.e. acting as a Trojan horse. Thus, for example, a bugging device concealed within an otherwise innocuous object such as a computer, telephone or lighting control, may be more readily detected by virtue of exploitation of the particular RF screening weaknesses of the object.

Although the arrangement shown in figure 1 deploys two receive channels 103, 104 respectively dedicated to second and third harmonic return signals, certain classes of target object may not require detection of one or other of the second or third harmonics and a single receive channel at a specific harmonic may be possible.

The different modules and circuitry arrangements of figure 1 may be provided within a single screened enclosure or housing or may be distributed across two or more separate enclosures or housings.

The described preferred arrangements of WLJD exploit screening weaknesses in target objects at frequencies corresponding to the communication channels used by the target objects. However, other specific frequencies may be found to correspond to screening weaknesses of target objects merely by virtue of specific physical structures or layouts of component parts of the target objects. Such weaknesses, when known, can also be defined in the stored signatures corresponding to those objects and used in the predetermined selection of illumination signal frequencies.

A general method of operation of an exemplary NLJD 100 as described above is shown in figure 2. In step 201, a user of the NLJD may select one or more target object types or classes of target object. The NLJD may then automatically select, from a database, a plurality of transmit frequencies with which to illuminate a sweep area (step 202), the transmit frequencies being selected according to known or suspected RF screening weaknesses of the target objects or classes of target object. The NLJD then illuminates a sweep area with the plurality of illumination signals (step 203) using the wideband transmit module 101. In step 204, the NLJD receiver module 102 receives a return signal from the illuminated sweep area. The return signal will potentially include second and/or third harmonics of the illumination signal reflected or re-radiated by non-linear junctions. In step 205, the processing circuitry 15 determines and analyses the amounts of energy in the return signal within frequency bands. The processing circuitry 15 then compares the energy distribution in these frequency bands with templates for known objects or classes of object stored in the signature database (step 206). From this comparison, the processing circuitry 15 provides an indication of likely targets or classes of targets corresponding to the return signal (step 207) Steps 203 to 207 may be performed cyclically, e.g. on a continuous or semi-continuous basis during a sweep operation using the N4LJD to build up a two or three dimensional map of the sweep space. Step 207 may comprise a number of possible modalities discussed earlier, including classifying some or all detected objects for the user, which may be displayed accordingly; positively identifying selected target objects to be output for display to the user; deselecting some target objects identified as innocent targets to suppress display to the user. The NLJD may provide as output (step 208), e.g. via the user interface 16, a map display of objects in the sweep area, a log of detection events, and I or provide a real-time alert to the user each time a target object is detected.

Outputs and alerts can be visible, audible or haptic outputs as well as electronic data outputs, or combinations thereof.

Other embodiments are intentionally within the scope of the accompanying claims.

Claims

CLAIMS1. A non-linear junction detector comprising: a multi-frequency transmitter configured to illuminate a sweep area with a plurality of RF illumination signals at different frequencies; a receiver configured to receive a return signal from target objects within the sweep area; a processor configured to: determine amounts of energy in the return signal within predetermined frequency bands; and compare the amounts of energy in the predetermined frequency bands with a database of signatures each indicative of a specific target object or class of target objects; and provide an indication of likely target object or class of target objects corresponding to the return signal.
2. The non-linear junction detector of claim I in which the multi-frequency transmitter is configured to illuminate the sweep area with a predetermined set of frequencies selected according to a target type selected.
3. The non-linear junction detector of claim 2 in which the predetermined frequencies correspond to frequencies related to radio communication channels.
4. The non-linear junction detector of claim 3 in which the predetermined frequencies correspond to one or more of mobile telecommunications device channels, near field communications channels, and short range radio network channels.
5. The non-linear junction detector of claim 4 in which the predetermined frequencies correspond to frequencies related to any one or more of GSM, 3G, 4G, WiFi, Bluetooth, and NFC communication channels.
6. The non-linear junction detector of claim 1 further including a signature database comprising a plurality of signatures, each signature comprising an indication of energy amounts found hi plural different frequency bands for different target objects and/or different classes of target object.
7. The non-linear junction detector of claim 1 further includhig a user interface and in which the processor is configured to use the indication of likely target or class of targets corresponding to the return signal to select a detected object for output by the user interface, or to deselect the detected object for output by the user interface, the user interface being configured to give said output as a visible, audible or haptic indication to a user.
8. The non-linear junction detector of claim 1 further including a user interlace configured to receive a user input indicating one or more target object types selected, a database indicating a plurality of illumination signal frequencies required as a function of target type, the processor configured to select the plurality of RF illumination signals at different frequencies based on the one or more target object types selected.
9. A method of operating a non-linear junction detector comprising the steps of: illuminating a sweep area with a plurality of RF illumination signals at different frequencies; receiving a return signal from target objects within the sweep area; using a processor to: determine amounts of energy in the return signal within predetermined frequency bands; and compare the amounts of energy in the predetermined frequency bands with a database of signatures each indicative of a specific target object or class of target objects; and provide an indication of likely target object or class of target objects corresponding to the return signal.