U.S. patent application number 11/287725 was filed with the patent office on 2007-11-22 for direct conversion system for security standoff detection.
Invention is credited to Florian Krug.
Application Number | 20070267574 11/287725 |
Document ID | / |
Family ID | 38711170 |
Filed Date | 2007-11-22 |
United States Patent
Application |
20070267574 |
Kind Code |
A1 |
Krug; Florian |
November 22, 2007 |
DIRECT CONVERSION SYSTEM FOR SECURITY STANDOFF DETECTION
Abstract
A security detection system is presented. The system includes a
radiation source configured to generate and direct terahertz
radiation onto an object. Further, the system also includes a
detector module configured to detect and process radiation from the
object, the detector module comprising a parallel arrangement of at
least two low noise amplifiers, each operable in a respective
frequency band.
Inventors: |
Krug; Florian; (Munich,
DE) |
Correspondence
Address: |
GENERAL ELECTRIC COMPANY (PCPI);C/O FLETCHER YODER
P. O. BOX 692289
HOUSTON
TX
77269-2289
US
|
Family ID: |
38711170 |
Appl. No.: |
11/287725 |
Filed: |
November 28, 2005 |
Current U.S.
Class: |
250/341.1 |
Current CPC
Class: |
G01N 33/227 20130101;
G01N 21/3563 20130101; G01J 9/04 20130101; G01N 21/3581
20130101 |
Class at
Publication: |
250/341.1 |
International
Class: |
G01J 5/02 20060101
G01J005/02 |
Claims
1. A security detection system, comprising: a radiation source for
generating and directing terahertz radiation onto an object; and a
detector module for detecting and processing radiation from the
object, the detector module comprising a power splitter for
splitting the detected radiation into at least two component
signals, each of the at least two component signals being
attenuated to a different level.
2. The security detection system of claim 1, wherein the detector
module comprises a receiver front end configured to receive the
radiation from the object.
3. The security detection system of claim 1, wherein the detector
module comprises a parallel arrangement of at least two low noise
amplifiers, each operable in a respective frequency band and
configured to process a respective one of the at least two
component signals.
4. The security detection system of claim 1, wherein the detector
module comprises at least two processing channels configured to
process a respective one of the at least two component signals to
generate a respective processed signal.
5. The security detection system of claim 4, wherein the at least
two processing channels each comprises: a first limiter configured
to process a respective component signal to generate a respective
first limited signal; a low noise amplifier configured to amplify
the respective first limited signal to generate a respective
amplified signal; a second limiter configured to process the
respective amplified signal to generate a respective second limited
signal; and an analog-to-digital converter configured to process
the respective second limited signal to generate a respective
digital output signal representative of the respective processed
signal.
6. The security detection system of claim 4, wherein the detector
module comprises a digital signal processing module for combining
the at least two processed signals to generate a composite signal
representative of the detected radiation.
7. The security detection system of claim 6, comprising an analysis
module for analyzing the composite signal to determine if one or
more predetermined features of an explosive material exist.
8. The security detection system of claim 7, comprising a display
module for facilitating display of the one or more predetermined
features.
9. A security detection system, comprising: a radiation source
configured to generate and direct terahertz radiation onto an
object; a receiver front end configured to receive radiation from
the object; a power splitter operatively coupled to the receiver
front end and configured to split the detected radiation signal
into at least two component signals, wherein each of the at least
two component signals is attenuated to a different level; at least
two processing channels in operative association with the power
splitter, wherein each of the at least two processing channels is
configured to process a respective one of the at least two
component signals to generate a respective processed signal; and a
digital signal processing module operatively coupled to the at
least two processing channels and configured to combine the
processed signals to generate a composite signal representative of
the detected radiation.
10. The security detection system of claim 9, wherein the at least
two processing channels each comprises: a first limiter operatively
coupled to the power splitter and configured to process a
respective component signal to generate a respective first limited
signal; a low noise amplifier in operative association with the
first limiter and configured to amplify a respective first limited
signal to generate a respective amplified signal; a second limiter
operatively coupled to the low noise amplifier and configured to
process the respective amplified signal to generate a respective
second limited signal; and an analog-to-digital converter in
operative association with the second limiter and configured to
process the respective second limited signal to generate a
respective digital output signal representative of the respective
processed signal.
11. The security detection system of claim 9, comprising an
analysis module in operative association with the digital signal
processing module, wherein the analysis module is configured to
analyze the composite signal to determine if one or more
predetermined features of an explosive material exist.
12. The security detection system of claim 11, comprising a display
module operatively coupled to the analysis module, wherein the
display module is configured to facilitate displaying the
identified one or more predetermined features.
13. A method for processing radiation, the method comprising:
irradiating an object with terahertz radiation; detecting radiation
from the object; and processing the detected radiation via a
detector module having a distributed arrangement of low noise
amplifiers, wherein processing comprises splitting the detected
radiation into at least two component signals attenuated to
different levels.
14. The method of claim 13, wherein said irradiating the object
comprises generating and directing terahertz radiation onto the
object.
15. The method of claim 13, wherein said processing the detected
radiation comprises: processing the at least two component signals
via a respective processing channel to generate a respective
processed signal; and combining each of the processed signals to
generate a composite signal representative of the detected
radiation.
16. The method of claim 15, wherein said processing the at least
two component signals comprises: processing each of the at least
two component signals via a first limiter to generate a respective
first limited signal; amplifying each of the first limited signals
to generate a respective amplified signal; processing each of the
amplified signals via a second limiter to generate a respective
second limited signal; and processing each of the second limited
signals via an analog-to-digital converter to generate a respective
digital output signal representative of the respective processed
signal.
17. The method of claim 15, further comprising analyzing the
composite signal to determine if one or more predetermined features
of an explosive material exist.
18. The method of claim 17, further comprising displaying the
identified one or more predetermined features.
19. A method for processing radiation, the method comprising:
irradiating an object terahertz radiation; detecting radiation from
the object; splitting the detected radiation into at least two
component signals, wherein each of the at least two component
signals is attenuated to a different level; processing each of the
at least two component signals via a first limiter to generate a
respective first limited signal; amplifying each of the first
limited signals to generate a respective amplified signal;
processing each of the amplified signals via a second limiter to
generate a respective second limited signal; processing each of the
second limited signals via an analog-to-digital converter to
generate a respective digital output signal representative of the
respective processed signal; and combining each of the processed
signals to generate a composite signal representative of the
detected radiation.
20. The method of claim 19, wherein said irradiating the object
comprises generating and directing terahertz radiation onto the
object.
21. The method of claim 19, further comprising analyzing the
composite signal to determine if one or more predetermined features
of an explosive material exist.
22. The method of claim 21, further comprising displaying the
identified one or more predetermined features.
23. A security detection system, comprising: a radiation source
configured to generate and direct terahertz radiation onto an
object; a detector module configured to detect and process
radiation from the object, wherein the detector module comprises a
receiver front end configured to receive radiation from the object
and a power splitter in operative association with the receiver
front end and configured to split the detected radiation signal
into at least two component signals; a system controller configured
to acquire one or more sets of detected radiation data from the
detector module; and a computer system operationally coupled to the
radiation source and the detector module, wherein the computer
system is configured to facilitate receiving the one or more sets
of detected radiation data.
24. The security detection system of claim 23, wherein the detector
module comprises: at least two processing channels operatively
coupled to the power splitter and configured to process a
respective component signal to generate a respective processed
signal the at least two processing channel comprising a parallel
arrangement of at least two low noise amplifiers operable in
respective frequency bands; and a digital signal processing module
operatively coupled to the at least two processing channels and
configured to combine the processed signals to generate a composite
signal representative of the detected radiation.
25. The security detection system of claim 24, further comprising
an analysis module configured to analyze the composite signal to
determine if one or more predetermined features of an explosive
material exist.
26. The security detection system of claim 25, further comprising a
display module configured to facilitate displaying the identified
one or more predetermined features.
Description
BACKGROUND
[0001] The invention relates generally to apparatus and methods for
imaging in the Terahertz (THz) frequency range, and more
specifically to examining a sample containing an explosive
material.
[0002] Over the past several years, there has been an emerging
interest in the potential of THz detection for security related
applications such as imaging of concealed weapons, explosives and
chemical and biological weapons. Terahertz radiation is readily
transmitted through most non-metallic and non-polar media, which
advantageously enables the THz systems to "see through" concealing
barriers such as packaging, clothing, shoes, book bags, for
example, in order to probe any potentially dangerous materials
contained within. Additionally, many materials of interest for
security applications including explosives and chemical and
biological agents have characteristic THz spectra that may be used
to fingerprint and thereby identify these concealed materials.
Thus, the combination of transparency to clothing and packaging
combined with spectroscopy of illicit materials such as narcotics,
biological weapons or explosives may facilitate detection and
identification of many different types of materials. Furthermore,
THz radiation is believed to pose no more than minimal health risks
to either a person being scanned or the operator of the system.
[0003] Presently available THz imaging techniques employ receivers
that can be operated in a super-heterodyne configuration. The
super-heterodyne approach is a relatively simple and low-cost
approach that uses a single low noise amplifier (LNA) gain stage, a
mixer, a local oscillator (LO) source and an intermediate frequency
(IF) block. However, due to the relatively large number of receiver
channels required, time synchronization of the local oscillation
distribution may be critical. Direct-detection architectures may be
employed to overcome the shortcomings of the super-heterodyne
receivers. The direct-detection architecture entails use of a high
gain LNA cascade, bandpass filtering, a high sensitivity detector
and direct current (DC) electronics for noise voltage
amplification. Unfortunately, these direct-detection receivers
require a high level of gain in the low noise amplification stages
with a flat gain response in order to amplify the scene noise floor
above the noise floor of a detector diode. Furthermore, controlling
this level of gain at the module level may be an onerous task as
oscillation and unwanted feedback may occur especially as the
operating frequency is increased.
[0004] There is therefore a need for a THz imaging system capable
of real-time imaging. In particular, there is a significant need
for a design of a THz imaging system for real-time imaging for use
in security standoff detection applications. Also, it would be
desirable to develop a simple and cost-effective method of
fabricating a THz imaging system capable of real-time
three-dimensional imaging.
BRIEF DESCRIPTION
[0005] Briefly, in accordance with aspects of the invention, a
security detection system is presented. The system includes a
radiation source configured to generate and direct terahertz
radiation onto an object. Further, the system also includes a
detector module configured to detect and process radiation from the
object, the detector module comprising a parallel arrangement of at
least two low noise amplifiers, each operable in a respective
frequency band.
[0006] In accordance with further aspects of the invention, a
security detection system is presented. The system includes a
radiation source configured to generate and direct terahertz
radiation onto an object. Furthermore, the system includes a
receiver front end configured to receive radiation from the object.
The system also includes a power splitter operatively coupled to
the receiver front end and configured to split the detected
radiation signal into at least two component signals, wherein each
of the at least two component signals is attenuated to a different
level. In addition, the system includes at least two processing
channels in operative association with the power splitter, wherein
each of the at least two processing channels is configured to
process a respective one of the at least two component signals to
generate a respective processed signal. Also, the system includes a
digital signal processing module operatively coupled to the at
least two processing channels and configured to combine the
processed signals to generate a composite signal representative of
the detected radiation.
[0007] In accordance with yet another aspect of the invention, a
method for processing radiation is presented. The method includes
irradiating an object with terahertz radiation. Additionally, the
method includes detecting radiation from the object. The method
also includes processing the detected radiation via a detector
module having a distributed arrangement of low noise
amplifiers.
[0008] In accordance with further aspects of the invention, a
method for processing radiation is presented. The method includes
irradiating an object with terahertz radiation. Additionally, the
method includes detecting radiation from the object. The method
also includes splitting the detected radiation into at least two
component signals, wherein each of the at least two component
signals is attenuated to a different level. Furthermore, the method
includes processing each of the at least two component signals via
a first limiter to generate a respective first limited signal,
amplifying each of the first limited signals to generate a
respective amplified signal. The method also includes processing
each of the amplified signals via a second limiter to generate a
respective second limited signal and processing each of the second
limited signals via an analog-to-digital converter to generate a
respective digital output signal representative of the respective
processed signal. In addition, the method includes combining each
of the processed signals to generate a composite signal
representative of the detected radiation.
[0009] In accordance with further aspects of the invention, a
security detection system is presented. The system includes a
radiation source configured to generate and direct terahertz
radiation onto an object. Furthermore, the system includes a
detector module configured to detect and process radiation from the
object, wherein the detector module comprises an parallel
arrangement of at least two low noise amplifiers, wherein each low
noise amplifier is configured to be operable in a respective
frequency band. The system also includes a system controller
configured to acquire one or more sets of detected radiation data
from the detector module. Additionally, the system includes a
computer system operationally coupled to the radiation source and
the detector module, wherein the computer system is configured to
facilitate receiving the one or more sets of detected radiation
data.
DRAWINGS
[0010] These and other features, aspects, and advantages of the
invention will become better understood when the following detailed
description is read with reference to the accompanying drawings in
which like characters represent like parts throughout the drawings,
wherein:
[0011] FIG. 1 is a block diagram of an exemplary security standoff
detection system, in accordance with aspects of the invention;
[0012] FIG. 2 is a block diagram of an exemplary detector module
for use in the security standoff detection system illustrated in
FIG. 1, in accordance with aspects of the invention;
[0013] FIG. 3 is a flow chart depicting an exemplary process for
security standoff detection, in accordance with aspects of the
invention;
[0014] FIG. 4 is a flow chart depicting an exemplary process for
detecting radiation and processing detected radiation, in
accordance with aspects of the invention;
[0015] FIG. 5 is a flow chart depicting an exemplary process for
processing detected radiation, in accordance with aspects of the
invention; and
[0016] FIG. 6 is a flow chart depicting an exemplary process for
processing detected radiation via the detector module illustrated
in FIG. 2, in accordance with aspects of the invention.
DETAILED DESCRIPTION
[0017] Security detection systems for imaging in the THz frequency
range are being increasingly employed in various applications. For
example, security detection systems are utilized to detect
materials of interest, such as, but not limited to, concealed
weapons and/or explosives by scanning persons and/or objects in
open areas such as airports and stations. Current THz imaging
techniques employ receivers arranged in a super-heterodyne
configuration. However, these super-heterodyne receivers suffer
from drawbacks associated with time synchronization of local
oscillation distribution. Direct-detection architectures have been
used to mitigate the problems associated with the super-heterodyne
receivers. Unfortunately, these direct-detection based systems
require a high level of gain in the LNA stages. It may therefore be
desirable to develop a robust technique that advantageously
facilitates real-time imaging for use in security standoff
detection applications. The techniques discussed herein address
some or all of these issues.
[0018] Although, the exemplary embodiments illustrated hereinafter
are described in the context of a security detection system for use
in detecting concealed explosives and/or weapons on a person, it
will be appreciated that use of the security detection system in a
variety of security applications, such as, but not limited to,
detection of explosives in parcels and luggage are also
contemplated in conjunction with the invention.
[0019] FIG. 1 is a block diagram of an exemplary system 10 for use
in security standoff detection in accordance with aspects of the
invention. As will be appreciated, in a standoff detection system,
a THz transmitter and a detector may be spaced at a distance of
greater than three meters. Additionally, the standoff detection
system may be gainfully employed for long-range screening and
detection, and potentially offers a solution for scanning people in
open areas such as airports and stations.
[0020] In the illustrated embodiment, the exemplary security
standoff detection system 10 may be configured to facilitate
detection of a material of interest on a person or in a parcel or
luggage. As used herein, a "material of interest" may include
concealed weapons, an explosive material, narcotics, biological
agents or chemical agents. It may be noted that figures are drawn
for illustrative purposes and are not drawn to scale. In the
illustrated embodiment the exemplary security standoff detection
system 10 is shown as including a radiation source 12. In one
embodiment, the radiation source 12 may be a terahertz (THz)
source, for example. In accordance with aspects of the invention,
the THz source 12 may be configured to generate and direct THz
radiation onto an object 20. Further, in certain embodiments, the
radiation generated by the THz source 12 may be in a range from
about 0.1 THz to about 10 THz. In a presently contemplated
embodiment of the security standoff detection system 10, the
radiation source 12 is shown as being in operative association with
a transmitter 14. The source 12 may be configured to transmit THz
radiation onto the object 20 via the transmitter 14. Also, the
transmitter 14 is operatively coupled to a transmitting antenna 16.
The security detection system 10 may be configured to transmit the
THz radiation generated by the THz source 12 via the transmitting
antenna 16.
[0021] Additionally, reference numeral 18 represents THz radiation
that is incident on the object 20. Furthermore, in the illustrated
embodiment, reference numeral 22 is indicative of an explosive
material that may be concealed on the person 20. As previously
noted, although the embodiments illustrated are described in the
context of a security detection system used to detect hidden
weapons and/or explosives 22 on a person 20, detection of weapons,
explosives and/or chemical and biological agents in parcels and
luggage are also contemplated in conjunction with the
invention.
[0022] The security detection system 10 may include a receiving
station 26. As used herein "receiving station" 26 refers to a
module that includes a receiving antenna 28, a receiver front-end
30 and an exemplary direct conversion detection module 32. In
accordance with aspects of the invention, the receiving station 26
may be configured to detect and process radiation 24 from the
object 20. It may be noted that the radiation 24 may include
radiation transmitted through the object 20, reflected from the
object 20 or combinations thereof. The receiving antenna 28 may be
configured to facilitate receiving the THz radiation 24. Moreover,
the receiver front-end 30 may be configured to receive the
radiation 24 from the receiving antenna 28.
[0023] Further, the exemplary direct conversion detection module 32
may include a parallel arrangement of at least two low noise
amplifiers (LNAs), where each of the at least two LNAs are operable
in a respective frequency band. This exemplary parallel arrangement
of LNAs will be described in greater detail with reference to FIG.
2. In addition, the direct conversion detection module 32 may be
configured to generate a processed signal representative of the
detected radiation 24.
[0024] The processed signal generated by the direct conversion
detection module 32 may then be analyzed by an analysis module 34.
For example, the analysis module 34 may be configured to facilitate
detection of an explosive material via analysis of the processed
signal. The explosive material, if any, may then be displayed on a
display module 36, for instance.
[0025] As previously noted, presently available THz imaging
techniques employ receivers that may be operated in a
super-heterodyne configuration. The super-heterodyne approach is a
relatively simple and low-cost approach that uses a single LNA gain
stage, a mixer, a local oscillator source and an intermediate
frequency block. Due to the relatively large number of receiver
channels required, time synchronization of the local oscillation
distribution may be critical. The drawbacks associated with the
super-heterodyne receivers may be circumvented by employing
direct-detection architectures. The direct-detection architecture
entails use of a high gain LNA cascade, bandpass filtering, a high
sensitivity detector and direct current electronics for noise
voltage amplification. Unfortunately, these direct-detection
receivers require a high level of gain in the low noise
amplification stages with a flat gain response in order to amplify
the scene noise floor above the noise floor of a detector diode.
Furthermore, controlling this level of gain at the module level may
be a tedious task.
[0026] In accordance with aspects of the invention, an exemplary
direct conversion detection module that circumvents the drawbacks
of the currently available direct-detection architectures is
presented. FIG. 2 illustrates an exemplary embodiment of an
architecture 38 of the direct conversion detection module 32 of
FIG. 1 in greater detail. The exemplary direct conversion detection
module 38 may be configured to facilitate processing detected
radiation to detect and identify presence of a material of
interest, where the direction conversion detection module 38 may
include a parallel arrangement of at least two LNAs. It should be
noted that each of the at least two LNAs is operable in a
respective frequency band.
[0027] As will be appreciated, presently available ADCs are
incapable of processing relatively high frequencies typically
encountered in THz radiation. Additionally, current THz imaging
techniques are known to employ a cascade of high gain LNAs. These
shortcomings may be overcome by splitting the high frequency
detected radiation signal into a plurality of component signals
having relatively low frequencies. In other words, in accordance
with aspects of the invention, these component signals may be
simultaneously processed in a parallel fashion employing the
currently available LNAs and ADCs.
[0028] In the illustrated embodiment, the direct conversion
detection module 38 is illustrated as having a power splitter 42
that is configured to split detected radiation 40 into a plurality
of component signals, wherein each of the plurality of component
signals is attenuated to a different level. The detected radiation
40 is representative of radiation transmitted through the object,
reflected from the object or combinations thereof. In the
illustrated embodiment, the detected radiation 40 is shown as being
split by the power splitter 42 into a first component signal 44, a
second component signal 46 and a third component signal 48, where
each of the component signals is attenuated to a different level.
However, as will be appreciated, the power splitter 42 may also be
configured to split the detected radiation signal 40 into more than
three component signals.
[0029] Furthermore, in one embodiment, each of the three component
signals 44, 46, 48 may be attenuated such that the an attenuation
of the first component signal 44 is relatively less than an
attenuation of the second component signal 46 and an attenuation of
the third component signal 48. For example, the first component
signal may be attenuated by about 20 decibels, the second component
signal 46 may be attenuated by about 40 decibels, while the third
component signal 48 may be attenuated by about 60 decibels.
[0030] Subsequently, each of the component signals 44, 46, 48 may
be simultaneously processed via a respective processing channel.
The processing channels may be configured to generate a respective
processed component signal. In a presently contemplated
configuration, the direct conversion detection module 38 is
illustrated as having a first processing channel 50, a second
processing channel 52 and a third processing channel 54, where each
of the processing channels may be configured to process a
respective component signal. For instance, the first processing
channel 50 may be configured to process the first component signal
44. Similarly, the second processing channel 52 may be configured
to process the second component signal 46, while the third
processing channel 48 may be configured to process the third
component signal 48. It may be noted that the direct conversion
detection module 38 may include a desired number of processing
channels such that the number of processing channels is related to
the number of component signals generated by the power splitter
42.
[0031] As previously noted, each of the component signals generated
by the power splitter 42 may be processed via a respective
processing channel to generate a respective processed component
signal. A limiter 56, a first low noise amplifier (LNA) 58, a
limiter 60, and a first analog-to-digital converter (ADC) 62 may be
serially coupled to form the first processing channel 50. The first
component signal 44 may be processed via the limiter 56 to generate
a first limited signal. In the illustrated embodiment, the first
limiter 56 may be configured to facilitate a good impedance match
between an output of the power splitter 42 and an input of the LNA
58 for a broad frequency spectrum.
[0032] Subsequently, this first limited signal may be amplified via
the first LNA 58. As will be appreciated, the first LNA 58 is
typically a preamplifier that is configured to amplify very weak
first component signal 44. Consequent to amplification by the first
LNA 58, an amplified signal may be generated.
[0033] Following amplification, the amplified signal may be further
processed via the second limiter 60 to generate a second limited
signal. The second limiter 60 may be configured to facilitate a
good impedance match between an output of the LNA 58 and an input
of the ADC 62. An output of the limiter 60, the second limited
signal, may be processed via the ADC 62 to obtain a digital output
signal. This digital output signal may be referred to as a first
processed component signal, where the first processed component
signal is representative of the first component signal 44. The ADC
62 may be configured to aid in broadband conversion and to deliver
the attenuated component signal for signal reconstruction based on
signal processing methods.
[0034] In a similar fashion, a limiter 64, a second LNA 66, a
limiter 68, and a second ADC 70 may be serially coupled to form the
second processing channel 52. As with the first processing channel
50, the second component signal 46 may be processed along the
second processing channel 52 via the limiter 64 and amplified by
the second LNA 66. An output of the second LNA 66, a second
amplified signal, may be further processed via the limiter 68, as
previously described. Furthermore, an output of the limiter 68 may
be converted to a second digital output signal by the second ADC
70. Subsequent to this processing, a second processed component
signal representative of the second component signal 46 is
generated by the second processing channel 52.
[0035] As described with reference to the first and second
processing channels 50, 52, a limiter 72, a third LNA 74, a limiter
76, and a third ADC 78 may be serially coupled to form the third
processing channel 54. The third component signal 48 may be
processed along the third processing channel 54 via the limiter 72
and amplified by the third LNA 74. As previously described, the
amplified signal may be further processed via the limiter 76 and
converted to a digital output signal via the third ADC 78.
Subsequent to the processing, a third processed component signal,
representative of the third component signal 48, is generated by
the third processing channel 54.
[0036] As previously noted, the direct conversion detection module
38 includes a parallel arrangement of a plurality of LNAs, where
each of the plurality of LNAs is operable in a respective frequency
band. In a presently contemplated configuration, three LNAs 58, 66,
74 are arranged in a parallel arrangement to facilitate parallel
processing of the plurality of component signals 44, 46, 48. It may
be noted that, in one embodiment, each of the three LNAs 58, 66, 74
may be configured such that each of the LNAs has a different gain
to deliver a desired dynamic range and noise performance. For
instance, a gain of the first LNA 58 may be configured to be
relatively greater than a gain of the second LNA 66 and a gain of
the third LNA 74. For example, the gain of the first LNA 58 may be
20 decibels (dB), the gain of the second LNA may be 30 dB, while
the gain of the third LNA 74 may be 40 dB.
[0037] By implementing the LNAs in an exemplary parallel
arrangement as described hereinabove, use of a high gain LNA
cascade typically employed in current THz imaging techniques may be
circumvented. In addition, presently available ADCs may be utilized
to process the individual component signals having relatively low
frequencies.
[0038] Consequent to the processing of the three component signals
44, 46, 48 via respective processing channels 50, 52, 54,
respective digital signals representative of corresponding
component signals are generated. In a presently contemplated
configuration, the direct conversion detection module 38 may
include a digital signal processing (DSP) module 80. The DSP module
80 may be configured to receive the plurality of processed
component signals generated by respective processing channels and
combine the processed component signals to generate a single,
digital composite signal 82. In other words, the DSP module 80 may
be configured to combine the plurality of component signals that
have been attenuated to different levels and amplified to different
levels to reconstruct the detected radiation signal 40.
Accordingly, the composite signal 82 generated by the DSP module 80
is representative of the detected radiation 40.
[0039] This composite signal 82 may then be processed via an
analysis module, such as the analysis module 34 (see FIG. 1). In
one embodiment, the analysis module may be configured to process
the composite signal 82 to facilitate detection of presence of a
variety of materials of interest for security applications, such
as, but not limited to, concealed explosives, weapons, chemical and
biological agents. Each of these materials of interest is known to
exhibit characteristic THz spectra that may be employed to
fingerprint and thereby identify these materials of interest.
Accordingly, predetermined features, such as THz spectra, may be
employed to aid in the detection and identification of materials of
interest. Subsequent to the analysis of the composite signal 82 by
the analysis module, the detected materials of interest, if any,
may be displayed on a display module, such as the display module 36
(see FIG. 1) to facilitate a user to easily visualize any detected
materials of interest, such as concealed weapons and/or explosive
material, for example.
[0040] Turning now to FIG. 3, a flow chart of exemplary logic 84
for processing detected THz radiation is illustrated. In accordance
with exemplary aspects of the invention, a method for processing
detected radiation for use in a security standoff detection system
is presented. The method starts at step 86 where an object may be
irradiated with a THz signal. As previously noted, a THz source
capable of generating and directing THz radiation towards the
object may be utilized to irradiate the object. In one embodiment,
the object may include a person, while in other embodiments, the
object may include a parcel or luggage.
[0041] At step 88, THz radiation from the object may be detected
via an exemplary direct conversion detection module, in accordance
with aspects of the invention. In certain embodiments, THz
radiation transmitted through the object may be detected.
Alternatively, in certain other embodiments, THz radiation
reflected from the object may be detected. However, it may be noted
that a combination of THz radiation transmitted through the object
and THz radiation reflected from the object may also be detected.
Following step 88, the detected radiation signal may be processed
at step 90 to determine if a material of interest exists. The
method of processing the detected radiation to determine if a
material of interest exists will be defined in greater detail with
reference to FIGS. 4-5.
[0042] Referring now to FIG. 4, a flow chart illustrating exemplary
logic 92 for a method of processing a detected radiation signal 94
via an exemplary direct conversion detection module is depicted. As
previously described, in accordance with exemplary aspects of the
invention, the direct conversion detection module (see FIG. 2) may
include a power splitter that is configured to split the detected
radiation signal in two or more component signals. Accordingly, at
step 96, the detected radiation signal is split into a plurality of
component signals. Further, each of the component signals is
attenuated to a different level, as previously described with
reference to FIG. 2. Subsequently, at step 98, each of these
component signals may be processed via a respective processing
channel to generate a respective processed component signal. The
method of processing each of the component signals will be
described in greater detail with reference to FIG. 5.
[0043] Following step 98, each of the processed component signals
may be combined at step 100 to generate a composite signal, where
the composite signal is representative of the detected radiation
signal. In one embodiment, a DSP module may be employed to
facilitate combining the plurality of processed component signals,
where each of the plurality of processed component signals has been
attenuated to a different level. The combined composite signal may
then be analyzed at step 102 to determine if any material of
interest, such as an explosive material, exists. An image may then
be generated and displayed at step 104. The displayed image may aid
a user in visualizing presence of any explosive material.
[0044] FIG. 5 illustrates exemplary logic 106 for processing each
of the component signals 108 via a respective processing channel.
The method starts at step 110 where the component signal 108 is
processed via a first limiter. The first limiter may be configured
to process the component signal 108 and generate a first limited
signal. At step 112, this first limited signal may be amplified via
a LNA to generate an amplified signal. As will be appreciated, a
LNA may be employed to amplify very weak detected radiation signal
captured by the receiving antenna 28 (see FIG. 1). Consequent to
amplification by the LNA, an amplified signal may be generated. The
amplified signal may then be processed via a second limiter at step
114. A second limited signal may be generated consequent to
processing the amplified signal via the second limiter.
Additionally, at step 116, the second limited signal may be
processed via an ADC to generate a digital output signal. This
digital output signal is representative of a processed component
signal.
[0045] In accordance with exemplary aspects of the invention, each
of the plurality of component signals may be simultaneously
processed via a respective parallel processing channel. In other
words, each of the component signals may be simultaneously
processed via steps 110-116.
[0046] The security standoff detection system 10 illustrated in
FIG. 1 may find application in a variety of security applications.
For example, the security detection system 10 may find application
in detection of concealed weapons and/or explosives on a person, in
luggage or in parcels. As will be appreciated, the use of the
security detection system described hereinabove has given rise to
numerous new possibilities enabling enhanced speed of operation and
overall cost reduction.
[0047] Also, as the high frequency detected radiation signal is
split into a plurality of component signals having relatively low
frequencies, each of the plurality of component signals may be
simultaneously processed via a single respective LNA. By
implementing the direct conversion detection module 38 having a
plurality of LNAs in a parallel arrangement, use of high gain LNA
cascades employed by current techniques may be circumvented.
Furthermore, this exemplary parallel arrangement of LNAs
advantageously enhances stability of the direct conversion
detection module 38 as the present arrangement does not call for
control of LNA gain.
[0048] Additionally, current ADCs are not configured to process
signals having relatively high frequencies typically encountered in
THz radiation. By implementing the direct conversion detection
module 38 such that the detected radiation signal 40 is split into
a plurality of component signals having relatively low frequencies,
currently available ADCs may be employed to process the component
signals having relatively low frequencies. Also, disadvantages
associated with use of local oscillators (LOs) may be mitigated
thereby advantageously reducing cost associated with the security
system 10 (see FIG. 1). Furthermore, the methods of processing
detected radiation described hereinabove advantageously facilitate
real-time imaging of persons, packages and luggage to aid in the
detection of concealed weapons, explosives, biological and chemical
agents.
[0049] While the invention has been described in detail in
connection with only a limited number of embodiments, it should be
readily understood that the invention is not limited to such
disclosed embodiments. Rather, the invention can be modified to
incorporate any number of variations, alterations, substitutions or
equivalent arrangements not heretofore described, but which are
commensurate with the spirit and scope of the invention.
Additionally, while various embodiments of the invention have been
described, it is to be understood that aspects of the invention may
include only some of the described embodiments. Accordingly, the
invention is not to be seen as limited by the foregoing
description, but is only limited by the scope of the appended
claims.
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