WO2014032984A1

WO2014032984A1 - Hand-held security scanning device

Info

Publication number: WO2014032984A1
Application number: PCT/EP2013/067072
Authority: WO
Inventors: Ralf Boehnke; Shin Saito
Original assignee: Sony Corporation; Sony Deutschland Gmbh
Priority date: 2012-09-03
Filing date: 2013-08-15
Publication date: 2014-03-06

Abstract

The present invention relates to a handheld security scanning device for scanning a scene. The device comprises a mechanical frame, an antenna holder arrangement, at least one transmit antenna, and at least one receive antenna. The at least one transmit antenna and the at least one receive antenna are arranged on or within the antenna holder arrangement. The antenna holder arrangement extends substantially along a first direction and is mechanically guided within the mechanical frame along a movement axis that is oriented transverse to the first direction. The at least one transmit antenna is configured to transmit electromagnetic radiation towards the scene during a movement of the antenna holder arrangement along the movement axis. The at least one receive antenna is configured to receive reflected electromagnetic radiation from said scene during said movement of the antenna holder arrangement to generate a scanning signal. During this movement the mechanical frame ensures an exact and controlled movement of the antenna holder arrangement.

Description

HAND-HELD SECURITY SCANNING DEVICE

BACKGROUND

Field of the Disclosure

[0001] The present disclosure relates to a hand-held security scanning device for scanning a scene. Further, the present disclosure relates to a security scanning system comprising such a hand-held securing scanning device using electromagnetic waves.

Description of Related Art

[0002] In the past decade airport and inflight security has become more and more important. Several terror acts, such as hijacked airplanes, have not only led to a massive increase and improvement of security checks at and around airports, but also at other public places and venues of public events (e.g. public sport events). This has also led to an increased demand for security scanning methods and corresponding security scanning devices.

[0003] Besides traditional X-ray scanners that are still in use on almost every airport in the world new security scanning devices have been developed. Well-known examples are millimeter-wave scanners (MMW scanners) that are able to create an image of a person's body through the clothes, i.e. to image the body surface of the person without having to unclothe the person. This allows visualizing and detecting hidden objects, such as concealed weapons, concealed fluids, drugs or any other concealed object. In general the millimeter- wave scanners can reveal objects that do not necessarily need to be made of metal (i.e. objects made out of wood, plastics, organic compounds, etc.). These MMW body scanners have shown to meet the need for an efficient, reliable and safe security scanning technique. One such high-resolution body scanner has been presented by Hantscher, S. et al: "94 GHz person scanner with circular aperture as part of a new sensor concept on airports", Radar Symposium (IRS), 2010 11th international, 16-18 June 2010. The body scanner proposed by Hantscher et al. makes use of the so-called Synthetic Aperture Radar (SAR) and allows the detection of concealed objects with a resolution of 3 mm in azimuth and 3 cm in range direction.

[0004] SAR is a radar technique that has originally been developed for military and non-military airborne systems, e.g. air- and spacecrafts. The SAR principle specifically makes use of the relative motion between a moving radar antenna and its target region to provide distinctive long-term coherent-signal variations that are exploited to obtain a finer spatial resolution than conventional beam-scanning radar systems. The SAR-principle requires a single antenna or an array of multiple antennas that repeatedly illuminate a target scene with pulses of radio waves at wavelengths in the range of one meter down to several millimeters or even lower. During scanning the antenna array is moved perpendicular to the scanning direction. The movement direction of the antenna array is usually denoted as azimuth direction, whereas the perpendicular coordinate is denoted as range. During the movement of the radar antenna array reflected radar radiation (echo waveforms) is successively received at different antenna positions, which are finally used to reconstruct a radar image of the target scene based on joint processing of the obtained information (by the distributed measurements). Due to the movement of the radar antenna array the aperture is therefore "synthetically" prolonged compared to Real Aperture Radar systems (RAR) with still-standing radar antenna arrays.

[0005] For further information related to the technical principle of SAR it is referred to Chan, Y. K. et al: "An Introduction to Synthetic Aperture Radar (SAR)", Progress in Electromagnetics Research B., Vol. 2, 27-60, 2008, which shall be herein fully incorporated by reference.

[0006] Most of today's known body scanners exploiting the SAR-principle are designed as large stationary devices that generate a three-dimensional human body representation. Most of them make use of two independent arrays of antennas: A vertical linear antenna array arranged parallel to the body and rotating around the body, and a horizontal circular antenna array surrounding the person's body and moving in a linear fashion parallel to the person's body from the top to the bottom. Even though this type of body scanner has shown a very good imaging resolution, it is, especially due to its design as stationary device, inflexible in its usage. Apart from that such stationary body scanners are very expensive and therefore in many situations not suitable.

[0007] On the other hand, so far known hand-held security scanning devices have not shown to meet the very high technical expectation, especially not in terms of image resolution. Hand-held devices making use of the above-mentioned SAR principle have in most of the cases shown a very poor imaging quality so that they have so far only been used in fields other than security scanning that eventually have lower security requirements or lower requirements with regard to the imaging resolution. The most common problem of these mobile or hand-held SAR imaging devices is the need to precisely control or track the movement of the antenna arrays during the measurement process to obtain "known" positions of the individual snapshot measurements used in the joint SAR processing. If the positions are not well controlled or tracked a SAR image reconstructions shows very poor image quality or even becomes impossible. Investigations have shown that this SAR reconstruction problem is even more pronounced at higher frequencies (due to short wavelengths) and if in addition to the known position the orientation of the antenna (i.e. tilt, roll and yaw angle) is changing as well.

[0008] WO 2005/044085 A2, for example, discloses such a hand-held device exploiting the SAR principle, which is mainly used for detecting foreign objects within the body after a surgery. The radar antenna arrays are thereby integrated in a hand-held detector, which an operator may freely move over a target region of the patient's body. It becomes clear that an inaccurate movement of the detector handle results in the above- mentioned problem of a non-precise control and tracking possibility of the antenna positions as well as a limited control of the antenna orientation. Even though statistical filtering algorithms are proposed according to WO 2005/044085 A2 an imaging resolution of such a device would clearly not be enough for a security scanning application, while it might be sufficient to at least roughly detect a foreign object within the body (without accurately imaging it) as proposed therein.

[0009] The "background" description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventor(s), to the extent it is described in this background section, as well as aspects of the description which may not otherwise qualify as prior art at the time of filing, are neither expressly or impliedly admitted as prior art against the present invention.

SUMMARY

[0010] It is an object to provide an improved hand- held security scanning device that is more practical in terms of function and use and serves for a more reliable detection of hidden objects. Particularly, it is an object to provide a hand-held security scanning device that serves for an enhanced imaging resolution compared to state of the art devices of this type. It is a further object to provide a corresponding security scanning system including such a hand-held security scanning device that is suitable for the daily use and may be applied in a variety of different security scanning applications including airport security as well as in other public security appliances where a stationary unit is typically not used due to its inflexibility, power requirements or cost.

[0011] According to an aspect, there is provided a hand-held security scanning device for scanning a scene, comprising: a mechanical frame, an antenna holder arrangement, at least one transmit antenna, and at least one receive antenna, wherein the at least one transmit antenna and the at least one receive antenna are arranged on or within the antenna holder arrangement, wherein the antenna holder arrangement extends substantially along a first direction and is mechanically guided within the mechanical frame along a movement axis that is oriented transverse to the first direction, wherein the at least one transmit antenna is configured to transmit electromagnetic radiation towards the scene during a movement of the antenna holder arrangement along the movement axis, and wherein the at least one receive antenna is configured to receive reflected electromagnetic radiation from said scene during said movement of the antenna holder arrangement to generate a scanning signal.

[0012] According to a further aspect, there is provided a security scanning system comprising: a handheld security scanning device according to claim 1 , a processing unit that processes the scanning signal generated by said scanning device to reconstruct an image of the scene, and an imaging unit that illustrates the image of the scene.

[0013] Preferred embodiments are defined in the dependent claims. It shall be understood that the claimed security scanning system has similar and/or identical preferred embodiments as the claimed security scanning device and as defined in the dependent claims.

[0014] One of the aspects of the present disclosure is the usage of a mechanical frame that serves as a mechanical support structure to assist and control the movement of the antenna holder arrangement on or within which the at least one transmit antenna and the at least one receive antenna is arranged. Compared to a most probably unconstrained movement of the transmit and receive antenna array as this is the case in an unguided hand device without constraints as proposed in WO 2005/044085 A2, the movement of the transmit and receive antenna array is due to the provided mechanical guiding frame much more controlled and predictable. In other words, the mechanical guiding frame reduces the degree of freedom for the movement of the transmit and receive antenna array, since it only allows a movement of the antenna array along the predefined movement axis. Independent on how the movement of the antenna holder arrangement including the transmit and receive antenna array is activated (e.g. either by hand or by an electric actuator) the mechanical frame exactly guides the movement along the movement axis, i.e. it forces the antenna holder arrangement including the antenna arrays to perform an exact and controlled movement which may no longer be unconstrained.

[0015] One of the basic ideas of the present disclosure is thus to constrain the movement of the transmit and receive antenna array by the mechanical frame. The mechanical frame thereby confines the movement to follow a desired trajectory that is preferably perpendicular to the first direction along which the antenna holder arrangement extends. It shall be understood that the movement of the antenna holder arrangement is still not exactly constrained, as an operator of the device may still slightly move the hand-held security scanning device during the scanning procedure.

[0016] However, a first difference is that an exactly perpendicular movement of the antenna holder array with respect to its lateral dimension is assured, which is a mandatory condition when making use of the SAR principle. Secondly, it is much easier for the operator of a device to keep the mechanical frame at a desired position and in a desired orientation with respect to the scene to be scanned, instead of having to move the antenna holder arrangement including the transmit and receive antenna arrays by hand along a desired trajectory (as this is necessary according to the prior art device known from WO 2005/044085 A2). Even if the operator may unintentionally move or tilt the scanning device (the mechanical frame) during the scanning procedure, the unintentional movement or tilting of the mechanical frame may be measured and recorded, for example by using an inertial sensor that may be integrated into the mechanical frame.

[0017] In summary this means that a specific movement direction (up/down or left/right) is predefined through the mechanical frame in which the antenna holder arrangement is mechanically guided. Apart from that, a specific movement speed of the antenna holder arrangement relative to the mechanical frame, that is either constant, uniform or at least predictable, may be foreseen and a predefined orientation of the transmit and receive antenna arrays may be easily controlled. These constraints are especially of importance in case the presented hand-held security scanning device is configured to reconstruct an image of the scanned scene according to the Synthetic Aperture Radar (SAR) principle.

[0018] According to an embodiment, the electromagnetic radiation transmitted by the at least one transmit antenna and the reflected electromagnetic radiation received by the at least one receive antenna is radar radiation and the generated scanning signal is a radar signal, wherein the scanning device further comprises a processing unit that processes the radar signal to reconstruct an image of the scene according to the SAR principle. Especially in this case, the problem to precisely control and/or track the movement of the transmit and receive radar antennas during the measurement process is solved in an intelligent way by use of the mechanical guiding support that is provided by the mechanical frame. The position of the individual SAR measurement points may therefore be well- controlled or is at least traceable. As the antenna orientation (i.e. roll, tilt, pointing direction etc.) may be defined and/or controlled, or is at least traceable during the SAR scan, a superior SAR image result is ensured.

[0019] The inventors have therefore found an intelligent way of providing a hand-held security scanning device that may make use of the SAR principle, which is easy to use for an operator, may be implemented in a variety of different situations, and finally still serves for a good image resolution that could even be compared with the image solution of a stationary scanning device. Since the proposed scanning device is designed as a hand-held device, it is much more flexible to use than a stationary scanning device.

[0020] It shall be pointed out that the terms "transmit antenna" and "receive antenna" according to the present disclosure refer to any type of antenna, preferably to a radar antenna. Even though it is preferred that according to the present disclosure an array of a plurality of transmit and receive antennas is used, it is generally conceivable that the security scanning device comprises only one transmit and only one receive antenna. It shall be also noted that the term "scene" refers to any object or subject or a group of objects and subjects that are scanned or imaged with the security scanning device according to the present disclosure. The term "electromagnetic radiation" shall refer to electromagnetic radiation preferably in the spectral range of radar radiation. The "mechanical frame" proposed according to the present disclosure may have various shapes and sizes as long as it guarantees a guidance along a movement axis that is transverse, preferably exactly perpendicular to the first direction along which the antenna holder arrangement substantially extends.

[0021] It is to be understood that both the foregoing general description of the invention and the following detailed description are exemplary, but not restrictive, of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] A more complete appreciation of the disclosure and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:

Fig. 1 schematically shows a first embodiment of a hand-held security scanning device according to the present disclosure,

Fig. 2 shows a schematic block diagram principally illustrating mandatory and non-mandatory parts of the security scanning device according to the present disclosure,

Figs. 3a, b schematically show practical appliances of the hand-held security scanning device according to the present disclosure,

Fig. 4 shows a schematic back view of the first embodiment of the hand-held security scanning device according to the present disclosure,

Fig. 5 schematically shows a second embodiment of the hand-held security scanning device according to the present disclosure,

Figs. 6a-c schematically show a third embodiment of the hand-held security scanning device according to the present disclosure,

Fig. 7 schematically shows a fourth embodiment of the hand-held security scanning device according to the present disclosure,

Fig. 8 schematically shows a fifth embodiment of the hand-held security scanning device according to the present disclosure, Figs. 9a,b schematically show a sixth embodiment of the hand-held security scanning device according to the present disclosure, and

Figs 10a,b schematically show a seventh embodiment of the hand- held security scanning device according to the present disclosure.

DESCRIPTION OF THE EMBODIMENTS

[0023] Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views, Fig. 1 schematically shows a first embodiment of a hand-held security scanning device 10 according to the present disclosure in a front view. The security scanning device comprises a mechanical frame 12 and an antenna holder arrangement 14, which is mechanically guided within the mechanical frame 12 along a movement axis 16. The antenna holder arrangement 14 comprises an antenna array of at least one transmit antenna 18 and at least one receive antenna 20. In the illustrated example a plurality of transmit antennas 18 and receive antennas 20 (eight transmit antennas 18 and five receive antennas 20) are arranged on or within the antenna holder arrangement 14. It is to be noted that the number of transmit and receive antennas 18, 20 may of course differ from the illustrated example.

[0024] The antenna holder arrangement 14 substantially extends along a first direction that is indicated by the arrow 22. The guidance of the antenna holder arrangement 14 within the mechanical frame 12 is chosen such that this first direction 22 is oriented transverse, preferably perpendicular, to the movement axis 16. Due to said guidance the antenna holder arrangement 14 may thus only be moved up and down along the movement axis 16 (i.e. no other transverse movements are possible relative to the mechanical frame 12). The mechanical frame 12 therefore constraints the movement of the antenna holder arrangement 14 and accordingly also the movement of the transmit and receive antennas 18, 20. In other words, the mechanical frame 12 confines the movement of the antenna array to follow a desired trajectory (a straight up and down movement) that is indicated by the arrow 24. Depending on the spatial orientation of the mechanical frame 12 the antenna holder arrangement 14 may therefore only move up and down or left to right along the trajectory 24. The mechanical frame 12 in this way provides an exact, controlled or at least predictable movement of the antenna array 18, 20. The movement of the antenna holder arrangement 14 including the transmit and receive antennas 18, 20 may be realized in many ways, e.g. by a mechanical actuator, an electrical actuator or manually, as this will be presented further below.

[0025] In order to reconstruct an image of a scene 26 the hand-held security scanning device 10 according to the present disclosure preferably exploits the principle of a Synthetic Aperture Radar (SAR). Thereto, the transmit antennas 18 are configured to transmit electromagnetic radiation 28 towards the scene 26 while the antenna holder arrangement 14 is moved (up and down) along the movement axis 16. The receive antennas 20 are configured to receive electromagnetic radiation 30 that is reflected/scattered back from the scene 26, wherein said reflected electromagnetic radiation 30 is also received during the movement of the antenna holder arrangement 14 along the movement axis 16.

[0026] The reflected electromagnetic radiation 30 induces or generates a scanning signal at the receive antennas 20. Said generated scanning signal, which is preferably a radar signal, may then be taken to reconstruct an image of the scene 26 according to the SAR principle. As the SAR principle is generally known in the prior art, a high resolution radar image may be generated by exploiting the movement of the transmit and receive antennas 18, 20 and by using dedicated mathematical algorithms to form the radar image based on joint processing of the obtained information/the obtained scanning signal (by the distributed measurements).

[0027] In other words, imaging the scene 26 according to the SAR principle takes place during the movement of the antenna holder arrangement 14 along the movement axis 16 in both directions (up or down). In this way a sequence of images is taken at each up or down movement of the antenna holder arrangement 14 along the movement axis 16. In SAR- specific terms the direction along or parallel to the movement axis 16 is thus denoted as SAR dimension or azimuth dimension. [0028] In order to establish the SAR principle with the hand-held scanning device 10 the electromagnetic radiation 28 transmitted by the at least one transmit antenna 18 and the reflected electromagnetic radiation 30 received by the at least one receive antenna 20 is an electromagnetic radiation in the radar frequency spectrum. Preferably the at least one transmit antenna 18 transmits frequency-modulated continuous wave (FMCW) radar signal or stepped frequency continuous wave (SFCW) radar signal with a frequency that is selected from a range between 1 GHz and 300 GHz, in particular in a range between 10 GHz and 150 GHz. Typical values used in the system 10 according to the present disclosure are around or at 30 GHz, 60 GHz, 80 GHz, 90 GHz or even near 140 GHz. As it is for example depicted in Fig. 1 the system 10 is preferably realized as a multiple-in multiple- out (MIMO) radar system with multiple transmit antennas 18 and multiple receive antennas 20 that are arranged next to each other on the antenna holder arrangement 14 along the first direction 22.

[0029] As it is known from other SAR systems, an exactly controlled movement of the transmit and receive antennas 18, 20 is one of the most important requirements, since the SAR algorithm may otherwise not work and SAR image reconstruction is almost impossible without a precisely controlled movement or a movement that is tracked precisely during a SAR radar scan and the trajectory is later on used in the SAR reconstruction process. The precision of the movement control needed in a SAR system is typically in the order of +/- 0,5 x wavelength at maximum. In case of a radar system operating at 30 GHz and an according wavelength of 1 cm this means that the accuracy of the movement must be in the order of 5 mm. For higher frequencies the situation is even worse. At an operating frequency of for example 150 GHz, the wavelength is only 2 mm and therefore a movement precision is needed that is in the order of 1 mm or even below. This consideration shows that a very precise movement of the antenna holder arrangement 14 is absolutely crucial during scanning. The position of the transmit and receive antennas 18, 20 therefore needs to be exactly controllable, traceable and known at each specific point in time during scanning. [0030] According to the present disclosure, this precision is guaranteed by the mechanical support frame 12 that assists and controls the movement of the antenna holder arrangement 14 and therefore also the movement of the transmit and receive antennas 18, 20 in the SAR dimension (azimuth dimension). The mechanical frame 12 in other words forces the antenna array 18, 20 to perform an exact and controlled movement as desired by the operator during the SAR measurement.

[0031] The mechanical guidance of the antenna holder arrangement 14 within the mechanical frame 12 may be realized in many ways. Preferably, a guiding rail may be used in which the antenna holder arrangement 14 is guided at each of its lateral sides. Roller or slide bearings may also be integrated into the mechanical frame 12 in order to guide the antenna holder arrangement 14 along the movement axis 16.

[0032] An operator using the device 10 only has to point with the device 10 towards the scene 26 to be scanned (i.e. to hold the frame 12 towards the scene 26) and has to keep it still during the scanning procedure. As explained above, the antenna holder arrangement 14 in this time moves up and down along the movement axis 16, while the scene 26 is scanned by the antenna array 18, 20 using the SAR principle.

[0033] Two exemplary scenarios of such a scanning procedure are schematically shown in Fig. 3a and Fig. 3b. As the device 10 makes use of millimeter wave technology it may be used as a body scanner to screen persons in order to identify hidden objects, for example under the clothes. As it is known from other state of the art body scanners the device 10 may be used to visualize the top surface (i.e. the contours of the skin of the body). A typical scenario is depicted in Fig. 3a. Here, the operator holds the device 10 in front of the person 34 to be screened and a scanned portion 36 (or Field of View (FOV)) is visualized by the SAR radar. Typically the scanning range (i.e. the distance between the scanning device 10 and the person 34) is limited between 30 cm and 3 m. It is to be noted that the scanned portion 36 (or FOV) depends not so much on the distance between the person 34 and the frame 12, but rather on the chosen SAR topology and the antennas 18, 20 used. Since the image in the FOV is reconstructed via the SAR principle, it relies on the fact that the FOV is somehow covered by the radiation and reception via the transmit and receive antennas 18, 20, which have a certain antenna pattern themselves. It shall also be understood that the hand- held security scanning device 10 according to the present disclosure may not only be used as a human body scanner, but also for other applications. Another exemplary scenario is schematically depicted in Fig. 3b, which shows a screening scenario wherein the device 10 is used to inspect the content of a bag without opening or unpacking the bag. Similar objects can be screened as well, e.g. briefcases, carton boxes, back packs, etc. The screening device 10 is also useful to identify hidden objects in a head- wrap (turban). As the device 10 is portable and may be operated in a short distance (e.g. at a distance of around 1 m to the scene to be scanned 26), the device 10 may be used in a very flexible and practical manner.

[0034] As the scanning speed (i.e. the movement of the antenna holder arrangement 14) is very fast, preferably in the order of below one second (several tenths of a second), the time that the operator has to keep the device 10 still at a fixed position in front of the scene 26 is very short. Handles 32a, b may be provided at each lateral side of the mechanical frame 12 that enable the operator to hold the device 10 by hand. The operator does therefore no longer need to manually move the antenna array in an uncontrolled manner by hand over the scene to be scanned 26 as this has been proposed by WO 2005/044085 A2. The advantages of the system 10 according to the present disclosure should thus be evident.

[0035] Fig. 2 depicts a block diagram illustrating the technical design of the security scanning device 10 according to the present disclosure in a schematic manner. It has to be noted that this block diagram includes mandatory and non-mandatory features of the device 10.

[0036] As already explained above, the device comprises several transmit antennas 18 that are configured to transmit radar radiation 28 towards the scene 26 while the antenna holder arrangement 14 is moved along the movement axis 16. The plurality of receive antennas 20 are configured to receive the radiation 30 that is reflected from the scene 26 at the same time. Both, the transmit antennas 18 and the receive antennas 20, are connected to a central processing unit 38 that processes the radar signal to reconstruct an image of the scene 26 according to the SAR principle. The electronic connection between each of the parts of the device 10 may either be hard- wired or wireless. The processing unit 38 may be realized as any type of computer chip or microchip that has software stored thereon for performing an image reconstruction. The computed/reconstructed image may, for example, be imaged on an imaging unit 40, which may be represented by a screen or small display. It shall be understood that the imaging unit 40 may either be directly integrated into the device 10 or being represented as a screen or display that is locally separated from the device 10. The processing unit 38 itself does also not necessarily need to be directly integrated into the device 10. According to an embodiment, it is also conceivable to integrate a communication interface unit into the device 10 (e.g. a wireless transceiver, WLAN-interface, Bluetooth-interface or an infrared-interface) that transmits the received radar signal to an external computing device, such as a PC or a dedicated SAR processing unit or external dedicated processing unit. In this case the final image reconstruction is processed externally by the external processing unit (i.e. a PC).

[0037] The device 10 may further comprise an actuator 42 that is configured to move the antenna holder arrangement 14 relative to the mechanical frame 12 along the movement axis 16. This actuator 42 may either be realized as a mechanical actuator or as an electronic actuator, e.g. as an electronic motor. The actuator 42 may be integrated into the mechanical frame 12, but may also be arranged within the antenna holder arrangement 14. As it will be explained further below, this actuator 42 is not a mandatory feature. The antenna holder arrangement 14 may in an embodiment according to the present disclosure also be moved by hand.

[0038] An actuator 42 as depicted in Fig. 2 has several advantages. The actuator 42 may first of all guarantee a uniform, homogeneous and predictable movement of the antenna holder arrangement 14. A constant movement speed of the antenna array relative to the mechanical frame 12 may be easily realized in this way. This is especially advantageous in terms of a precise movement control of the antenna array. [0039] Furthermore, the device 10 may also comprise a movement sensor 44 that measures the speed of the movement of the antenna holder arrangement 14 relative to the mechanical frame 12. This movement sensor thus allows to exactly obtain "known" positions of the antenna holder arrangement while the individual snapshot measurements are taken in the joint SAR processing. Since this movement sensor 44 may only detect the position and the movement speed of the antenna holder arrangement 14 relative to the mechanical frame 12, the precision of the detection and therefore also the quality of the image reconstruction may even be increased by providing inertial sensors 46, 48 that measure the acceleration and/or the spatial orientation of the mechanical frame 12. In one embodiment, an accelerometer 46 and a gyroscope 48 may be integrated into the mechanical frame 12. This allows detecting if the frame 12 has unintentionally been moved, tilted or rotated during the scanning procedure. The accelerometer 46 may, for example, be realized as a three-axial-accelerometer measuring the accelerations of the mechanical frame 12 in all three spatial directions. The gyroscope 48 instead measures the angular accelerations in all three angular directions (pitch, yaw and roll angles). It has to be noted that the accelerometer 46 and the gyroscope 48 may also be integrated into one common inertial sensor (IMU: Inertial Measurement Unit).

[0040] The acceleration signals produced by the inertial sensor(s) 46, 48 are delivered to the central processing unit 38. The processing unit 38 is then able to integrate these acceleration signals and adapt or correct the image reconstruction algorithm (SAR algorithm) in order to cancel out smaller measurement errors that could be caused by smaller unintentional hand movements of the operator during the scanning process. By measuring the movement of the frame 12 during scanning, the SAR samples measured at certain positions may be corrected. In particular, the movement may be compensated for by remapping the measurement points onto a desired grid. The inertial sensor signals can also be used for image stitching in case multiple images are taken. Furthermore, the inertial sensor(s) can give feedback to the user (via a pictogram on the screen 40, other optical feedback via lights, tactile feedback such as vibration or sound) how to orientate the device for a certain scan operation. These commands could tell the operator to keep the device 10/mechanical frame 12 horizontal and/or to minimize the movement during a scan. The overall position accuracy of the measurement is thereby significantly increased. Lastly, it shall be noted that the device 10 may also comprise a storage unit 50 that is connected to the central processing unit 38 and stores the radar signals (individual snapshots) that are acquired during scanning.

[0041] It is clear that the device 10 may comprise further electronic devices and/or elements, such as filters, amplifiers, integrators, analogue-to-digital converters, etc., that are for simplicity reasons not illustrated in Fig. 2.

[0042] In summary, the following desired features are achieved with the security scanning device 10 according to the present disclosure:

1. The position of the individual SAR measurement points is well controlled and traceable, as a uniform, homogeneous and regular sampling grid may be obtained by a constant movement speed of the antenna array within the mechanical support frame.

2. The antenna orientation (i.e. roll, tilt, pointing direction) is well defined and controlled during the SAR scan. This ensures a superior SAR imaging result.

[0043] Fig. 4 illustrates a further embodiment of the security scanning device 10 according to the present disclosure. The schematic view depicted in Fig. 4 could, for example, represent the back side view of the device 10 (shown from the other side as in Fig. 1). In the example shown in Fig. 4 the imaging unit 40 is directly integrated into the security scanning device 10. The imaging unit 40 therein comprises a main display 40a and a smaller detail display 40b arranged in the lower corner of the main display 40a. The main display 40a is according to this example used to visualize an image of the whole scene 26, while the detail display 40b only illustrates a detailed section of the scanned scene to illustrate specific regions of interest of the scanned scene. Concealed objects 52 (e.g. a weapon) may therefore be inspected in an enlarged view on the detail display 40b. The back side of the device 10 may also comprise one or more control buttons 54 for interac- tion between the operator and the scanning device 10. Buttons like a start button to initialize the scanning process or a stop button to stop the scanning process as well as a restart button to restart or reset the scanning process may be provided. It is to be noted that also other buttons or other means that allow an interaction with the user may generally be provided without departing from the present disclosure.

[0044] The embodiment schematically shown in Fig. 5 shall illustrate that independent of the other parts that are integrated into the device 10, the device 10 may also only comprise one single handle 32c (grip) that is connected to the mechanical frame (instead of two handles 32a, 32b, one at each side of the mechanical frame 12 as this has been shown in Fig. 1 and 2). The single handle 32c has the advantage that the operator may hold the device 10 with only one hand, which increases the flexibility for the operator to use the other hand for other purposes.

[0045] In the following different principles how to move the antenna holder arrangement 14 with respect to the mechanical frame 12 shall be explained with reference to Figs. 6-9.

[0046] A first possibility is shown in Fig. 6a-c. According to this embodiment, the movement of the antenna holder arrangement 14 is caused by gravity. This means that the antenna holder arrangement is either manually or automatically (by a motor) moved to the top position within the mechanical frame 12 (illustrated in Fig. 6a). During scanning the antenna holder arrangement 14 then moves down along the movement axis (indicated by arrow 56 in Fig. 6a) until it reaches its bottom position (illustrated in Fig. 6b). Since the natural gravity is used to accelerate the antenna holder arrangement 14 during the scanning procedure, an extra actuator 42 (as this has been explained with reference to Fig. 2) is not necessarily needed. Besides that, by using the natural gravity to accelerate the antenna holder arrangement 14 higher movement speeds can be realized, in particular in the range of up to 5 m/s. After the antenna holder arrangement has reached its bottom position (see Fig 6b) the whole frame 12/device 10 is turned or rotated by 180° by the operator, so that the antenna holder arrangement 14 including the antenna array 18, 20 is then at its top position again. This turn or rotation is illustrated in Fig. 6b by arrow 58. Another, new scan is now possible (see Fig. 6c).

[0047] As it can be seen from the example illustrated in Fig. 6, the SAR scanning is only provided during the down-movement of the antenna holder arrangement 14 (not during the up-movement of the antenna holder arrangement 14). Independent of using an additional actuator 42 this is anyway a preferred way of scanning as in the down direction the movement is simplified due to smaller forces that are needed to move the antenna holder arrangement 14 (supported by the gravity). According to an embodiment, the device 10 in this case preferably comprises an additional orientation sensor (not shown) that measures the spatial orientation of the mechanical frame 12. It particularly measures which side of the frame 12 is currently on top or on the bottom. One of the above- mentioned inertial sensors 46, 48 may be taken to account for this information. The information is especially needed for the SAR radar image reconstruction and the visualization to the user, so that an image being displayed as upside-down may be prevented. It is to be noted that other markers such as text markers or any alignment markers may be provided as well in order to indicate to the user how the mechanical frame 12 is oriented. Another possibility is to provide differently colored handles 32a, b.

[0048] A further possibility to move the antenna holder arrangement 14 during scanning is depicted in Fig. 7. In this embodiment the antenna holder arrangement 14 is slided manually (by hand) up and down relative to the mechanical frame 12. A mechanical holder (grip) 60 is provided, which is connected to the antenna holder arrangement 14 and allows for moving the antenna holder arrangement 14 by hand.

[0049] The user may thus keep the device 10 with one hand by grabbing the single handle 32c and may use the mechanical holder 60 to slide the antenna holder arrangement 14 including the antenna array 18, 20 up and down relative to the mechanical frame 12. In this case it is especially preferred that the device 10 further comprises a movement limiter that limits the speed of the movement of the antenna holder arrangement 14 along the movement axis 16 to a predefined speed relative to the mechanical frame 12. The movement limiter shall lead to a homogeneous, constant, or at least predictable movement of the antenna holder arrangement 14. It can, for example, be realized as a mechanical brake that is integrated into the guidance of the mechanical frame 12, in which the antenna holder arrangement 14 is guided. The brake then limits the speed of the movement to a maximum speed.

[0050] Alternatively or additionally, the device 10 may further comprise a movement speed indicator that provides a visual, tactile or audible command to the operator of the device 10 indicating in what direction and with what kind of speed the antenna holder arrangement 14 shall be moved. In any way, an at least partially constant, homogeneous movement of the antenna holder arrangement 14 is crucial for the SAR algorithm as this has been already explained above. Especially in case of a hand movement of the antenna holder arrangement 14 (as shown in Fig. 7) any deviations from a constant and homogeneous movement should be tracked. Therefore, it is especially in this case desired that the device 10 includes a movement sensor 44 that measures the speed of the movement of the antenna holder arrangement 14 along the movement axis 16 relative to the mechanical frame 12 (as this has been explained above with reference to Fig. 2). The measured, eventually non-constant speed can then be tracked and used in the SAR image reconstruction algorithm as a correction value.

[0051] A further possibility to even more precisely control the movement of the antenna holder arrangement 14 is illustrated in Fig. 9. According to the therein illustrated embodiment the actuator for moving the antenna holder arrangement 14 relative to the mechanical frame 12 is realized by a mechanical spring 62, preferably by two mechanical springs 62 (one on each side), that is arranged on the mechanical frame 12 and connected to the antenna holder arrangement 14. The spring element 62 may be charged (compressed) by the operator, i.e. by moving the antenna holder arrangement 14 down to its bottom position with the mechanical holder 60 (see Fig. 9a). As depicted in Fig. 9b, the mechanical holder 60 may then be released, which leads to a relaxation of the spring element 62 and to a constant acceleration of the antenna holder arrangement 40. In this way, a homogeneous and predictable movement of the antenna holder arrangement 14 is guaranteed. However, even in this example a brake system as explained above may be applied to control the movement speed and to receive an even more homogeneous movement.

[0052] According to a further embodiment, the device 10 includes an initializing sensor 64 that detects a beginning of the movement of the antenna holder arrangement 14 at a predefined starting position and a stop sensor 66 that detects an end of the movement of the antenna holder arrangement 14 when the antenna holder arrangement reaches a predefined end position (see Fig. 9b). In this embodiment the at least one transmit antenna 18 is configured to start transmitting electromagnetic radiation towards the scene 26 when the beginning of the movement is detected and to stop transmitting electromagnetic radiation towards the scene 26 when the end of the movement is detected. Similarly, the at least one receive antenna is configured to start receiving reflected electromagnetic radiation from said scene 26 when the beginning of the movement is detected and to stop receiving reflected electromagnetic radiation from said scene 26 when the end of the movement is detected. In other words, start and stop sensors 64, 66 are used to trigger the transmission and reception of the radar signal, the SAR data recording and the SAR image processing.

[0053] The most automated embodiment of the security scanning device 10 is schematically depicted in Fig. 8. According to this embodiment, the antenna holder arrangement 14 is moved within the mechanical frame 12 by an electric actuator, such as an electric motor. This electric motor or actuator is schematically illustrated in Fig. 8 and referenced with reference numeral 68. This motorized movement system 68 may for example be integrated into the sides of the mechanical frame 12. It may be also integrated directly into the antenna holder arrangement 14. It shall be understood that also other motorized or automated movement systems 68 can be used without departing from the present disclosure. The motorized movement system 68 is not restricted to any type and/or number of motors, placement of the motors or any type of transmission (either direct transmission or a transmission equipped with a number of belts, gear wheels, spindles, etc.). [0054] A last embodiment of the hand- held security scanning device 10 according to the present disclosure is shown in Fig. 10. All above mentioned principles and embodiments that relate to the different movement types of the antenna holder arrangement 14 may also be implemented into the device 10 as illustrated in Fig. 10. The only difference to the embodiments that have been described so far is that the security scanning device 10 according to this embodiment comprises not only one antenna holder arrangement 14 but two antenna holder arrangements 14', 14", wherein each of the antenna holder arrangements 14', 14" comprises an array of transmit antennas 18', 18" and an array of receive antennas 20', 20". In other words, the mechanical frame 12 in this case hosts multiple antenna holder arrangements 14', 14" and multiple antenna arrays 18', 18", 20', 20" which move in opposite direction at the same time. The two topologies (number and arrangement of TX and RX antennas) on the multiple holder arrangements 14', 14" do not need to be identical. The two antenna holder arrangements 14', 14" thus move synchronously from the center of the frame 12 in opposite directions to the border of the frame and vice versa towards the center of the frame 12 again. This does not only reduce the scanning time but also prevents or at least compensates any occurring torque. It is clear that the radar imaging process (the SAR imaging process) is modified accordingly to result in a desired (i.e. uniform) sampling pattern. It shall be also clear that in all embodiments the antenna holder arrangements 14, 14', 14" do not have to move up and down, but may also move left to right if the mechanical frame 12 is turned by 90°. In this case the antenna arrays 18, 20 would move along the horizontal axis.

[0055] In summary, a hand-held security scanning device is provided, which uses a mechanical support frame for Synthetic Aperture Radar (SAR) imaging. An antenna array with multiple transmit and receive antennas is used for SAR imaging. The mechanical frame is provided for exact and controlled movement of the antenna array. The device according to the present disclosure thus overcomes the problem of non-constant speed, left-to-right deviation, and/or tilt of the scanning device, that could occur in a system that is simply moved by hand without any trajectory assistance or tracking. [0056] Obviously, numerous modifications and variations of the present disclosure are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein.

[0057] In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. A single element or other unit may fulfill the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

Claims

1. A handheld security scanning device for scanning a scene, comprising:

a mechanical frame,

an antenna holder arrangement,

at least one transmit antenna, and

at least one receive antenna,

wherein the at least one transmit antenna and the at least one receive antenna are arranged on or within the antenna holder arrangement,

wherein the antenna holder arrangement extends substantially along a first direction and is mechanically guided within the mechanical frame along a movement axis that is oriented transverse to the first direction,

wherein the at least one transmit antenna is configured to transmit electromagnetic radiation towards the scene during a movement of the antenna holder arrangement along the movement axis, and

wherein the at least one receive antenna is configured to receive reflected electromagnetic radiation from said scene during said movement of the antenna holder arrangement to generate a scanning signal.

2. The handheld security scanning device according to claim 1, wherein the mechanical frame has a rectangular or quadratic shape, and wherein first direction is oriented perpendicular to the movement axis.

3. The handheld security scanning device according to claim 1, wherein the electromagnetic radiation transmitted by the at least one transmit antenna and the reflected electromagnetic radiation received by the at least one receive antenna is radar radiation and the generated scanning signal is a radar signal, and wherein the scanning device further comprises a processing unit that processes the radar signal to reconstruct an image of the scene according to the Synthetic Aperture Radar (SAR) principle.

4. The handheld security scanning device according to claim 1, wherein the at least one transmit antenna transmits a frequency-modulated continuous wave (FMCW) radar signal or a stepped frequency continuous wave (SFCW) radar signal with a frequency of between 1 GHz and 300 GHz, in particular of between 10 GHz and 150 GHz.

5. The handheld security scanning device according to claim 1, further comprising an actuator that is configured to move the antenna holder arrangement relative to the mechanical frame along the movement axis.

6. The handheld security scanning device according to claim 5, wherein the actuator is a mechanical spring that is arranged on the mechanical frame and connected to the antenna holder arrangement.

7. The handheld security scanning device according to claim 5, wherein the actuator is a motor that is configured to move the antenna holder arrangement with a predefined constant speed relative to the mechanical frame.

8. The handheld security scanning device according to claim 1, further comprising a mechanical holder that is connected to the antenna holder arrangement for moving the antenna holder arrangement by hand.

9. The handheld security scanning device according to claim 1, further comprising a movement sensor that measures a speed of the movement of the antenna holder arrangement along the movement axis relative to the mechanical frame.

10. The handheld security scanning device according to claim 1, further including an inertial sensor that measures an acceleration and/or orientation of the mechanical frame.

11. The handheld security scanning device according to claim 1 , further comprising a movement limiter that limits a speed of the movement of the antenna holder arrangement along the movement axis to a predefined speed relative to the mechanical frame.

12. The handheld security scanning device according to claim 8, further comprising a movement speed indicator that provides a visual, tactile or audible command to an operator of the device indicating in what direction and with what kind of speed the antenna holder arrangement shall be moved.

13. The handheld security scanning device according to claim 1, further including an initializing sensor that detects a beginning of the movement of the antenna holder arrangement at a predefined starting position and a stop sensor that detects an end of the movement of the antenna holder arrangement when the antenna holder arrangement reaches a predefined end position, wherein the at least one transmit antenna is configured to start transmitting electromagnetic radiation towards the scene when the beginning of the movement is detected and to stop transmitting electromagnetic radiation towards the scene when the end of the movement is detected, and wherein the at least one receive antenna is configured to start receiving reflected electromagnetic radiation from said scene when the beginning of the movement is detected and to stop receiving reflected electromagnetic radiation from said scene when the end of the movement is detected.

14. The handheld security scanning device according to claim 1, wherein the handheld security scanning device comprises two of said antenna holder arrangements, a first antenna holder arrangement and a second antenna holder arrangement, wherein on or within each of the two antenna holder arrangements at least one of said transmit antenna and at least one said receive antenna is arranged, wherein each of the two antenna holder arrangements extends substantially parallel to said first direction and is mechanically guided within the mechanical frame along the movement axis that is oriented perpendicular to the first direction, wherein each of the at least one transmit antennas is configured to transmit electromagnetic radiation towards the scene during a movement of the two antenna holder arrangements along the movement axis, wherein each of the at least one receive antennas is configured to receive electromagnetic reflected radiation from said scene during said movement of the two antenna holder arrangements, and wherein the two antenna holder arrangements are configured to be moved in opposite directions along the movement axis during scanning.

15. The handheld security scanning device according to claim 1, wherein the antenna holder arrangement is moveable along the movement axis in two opposing directions, wherein the at least one transmit antenna is configured to transmit electromagnetic radiation towards the scene only during a movement of the antenna holder arrangement in one of the two opposing directions, and wherein the at least one receive antenna is configured to receive reflected electromagnetic radiation from said scene only during said movement of the antenna holder arrangement in the one of the two opposing directions.

16. A security scanning system comprising:

a handheld security scanning device according to claim 1 ,

a processing unit that processes the scanning signal generated by said scanning device to reconstruct an image of the scene, and

an imaging unit that illustrates the image of the scene.