Non-contact microwave test system and method for through-sheet imaging

Abstract

The present invention describes a non-contact system and method for microwave-based imaging means for non-destructive testing (NDT) and evaluation of areas under test (AUT) of assets such as facades, cladding systems, concrete columns, concrete walls, bridges, tunnels, dams, etc. The system is composed of a combination of various subsystems including, but not exclusively, a front-end subsystem, a system-in-package (SiP) subsystem, and a signal processing subsystem responsible for 3D imaging and detection of defects in the asset.

Description

Technical Field

[0001] (Cross - reference to related applications) This application claims the priority of Singapore Patent Application No. 10202004777Y filed on May 21, 2020, the entire content of which is incorporated herein by reference for all purposes.

[0002] The present invention relates to a non - contact microwave - based test or evaluation system and method for inspecting composite structures, and more specifically, to a system and method for non - contact, through - the - sheath deep - penetration inspection of structures with high - resolution image reproduction.

Background Art

[0003] Non - destructive testing and evaluation (NDT&E) is an implementation means in which the area under test (AUT) and its usefulness are not directly affected by the above - mentioned test and evaluation procedures. All major infrastructure assets need to undergo regular NDT&E to confirm their value and avoid serious accidents that may damage the assets and safety. In the field of the built environment, various assets that require regular NDT include: 1) buildings with facade structures, 2) concrete columns and walls that support the structural integrity of buildings, dams, and bridges, and 3) indoor mechanical, electrical, and plumbing fixtures hidden behind walls and ceilings. Assets undergo various defects / anomalies through the process of natural aging over time. If left undetected, these defects can damage the asset's condition, ultimately leading to asset failure and potentially causing accidents. Examples of various defects / anomalies or information by asset type are listed below. (1) Facade structure: · Glass curtain wall: Cracks, corrosion, and delamination in the metal brackets holding the glass curtain wall · Tiled wall: Loose tiles, cracks, delamination · Natural stone exterior cladding: Cracks, corrosion, and delamination in the metal brackets holding the exterior cladding · Metal brackets holding various exterior cladding systems: Position, presence, and shape of the metal brackets (2) Concrete columns and walls · Detection of the position, presence, and size of reinforcing bars to facilitate repair work involving drilling · Monitoring of cracks and corrosion levels in the reinforcing bar structure embedded in concrete · Spalling and endangerment of concrete in the structural integrity of assets · Voids (voids) embedded in concrete structures introduced during the construction phase (3) Indoor mechanical, electrical, and plumbing (MEP) hidden behind walls and ceilings · Detection of the position, presence, and size of reinforcing bars to facilitate repair work involving drilling · Detection of utilities and electrical wiring embedded in walls and other structures · Cracks and corrosion in pipes causing leakage / leaching, wiring disconnection, delamination (4) Detection of water leakage / leaching · Detection of moisture in infrastructure elements for water leaching detection

[0004] Several currently commonly used NDT&E systems and technologies include the following. · Visual / optical camera inspection: This identifies anomalies that have reached the stage of appearing on the external surface of the asset, involving the use of a camera or visual inspection of the asset. Such inspection systems are reactive rather than proactive and do not have the ability to identify defects embedded in the asset that are not visually recognizable. · Infrared (IR)-based inspection: Other fast inspection methods employ IR-based imaging of the asset. This provides a fast inspection scheme that can detect surface and subsurface defects such as delamination and water leaching (embedded defects). However, such inspection techniques are highly dependent on external environmental conditions for their proper operation and provide reliable results. · Ultrasonic NDT: This inspection method is used for through-the-thickness inspection of assets to identify defects such as cracks and corrosion in the reinforcing bars under concrete walls and columns. The inspection process requires a scanning system that physically contacts the asset being inspected. This makes the inspection process time-consuming and a cumbersome process. · Microwave ground penetrating radar (GPR) NDT: This is an alternative inspection method that uses electromagnetic waves to explore assets and identify hidden and embedded defects. For efficient operation, such a scanning system does not need to physically contact the asset being inspected.

[0005] Patent Document 1 discloses a method for testing a substantially concrete structure using ground penetrating radar (GPR) technology, comprising the steps of receiving a plurality of computer-readable data signals, each data signal representing an electromagnetic signal detected from a region of a concrete structure, the one or more detected electromagnetic signals including electromagnetic energy reflected from the concrete structure as a result of corresponding electromagnetic signals transmitted to the concrete structure; selecting one of the data signals, the selected data signal corresponding to a first reinforcing bar; and determining a first distance of the first reinforcing bar from a first side of the substantially concrete structure based only on the selected data signal among the plurality of data signals.

[0006] Patent Document 2 discloses an airborne launch antenna GPR system and method, comprising the steps of calibrating a ground penetrating radar system: reflecting an ultra-wideband signal from a homogeneous material using an airborne transceiver; blocking the selection of frequencies in the reflected signal based on expected interference from external signals using an in-line analog blocking filter; shaping the reflected signal with a digital filter to at least partially restore the ultra-wideband signal; and shaping the reflected light of the ultra-wideband signal from a heterogeneous material using the cross-sectional coefficient determined in the shaping step.

[0007] Patent Document 3 discloses a portable microwave device for evaluating the characteristics of structural members, including a microwave energy source, a transmitter coupled to the microwave energy source for transmitting a microwave signal in the structural member, and a receiver positioned on the same side as the transmitter of the structural member and arranged to receive the microwave signal reflected by the structural member. This is a handheld portable device that can evaluate structural members such as building walls and determine the characteristics of these structures. The device uses low-power microwave energy and differential phase detection to characterize the size of blocks in the wall, the position of voids, etc. The handheld device for microwave NDT consists of a display and control module and a probe module. The display of the indicator is similar to that of eddy current testing.

[0008] Conventionally, to scan a specific asset, the scanner is moved / rotated over the area that needs to be scanned. Such a process is usually manual, time-consuming, and redundant. Therefore, conventional scanners have two major problems to address. · Synthesizing a larger aperture to cover a wide area and generate high-resolution scan results, and · Designing signal processing algorithms for the same type of medium rather than layered media.

[0009] Therefore, there is a need to provide a portable system and method for inspecting and testing various asset structures that integrate innovative technical solutions to have the following capabilities: non-contact and high-speed scanning means; deep penetration for identifying various defects in facade structures, structural solids (concrete columns and concrete walls), indoor MEP condition monitoring, etc.; being mountable / fixable on various platforms such as UGVs, drones, and robotic arms; an intuitive user interface for easy use in efficient and high-speed data interpretation (automated by manual and AI algorithms); and improved inspection efficiency, reduced safety risks for inspectors, time savings, and reduced labor costs.

Prior Art Documents

Patent Document

[0010]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

[0011] The present invention describes microwave-based imaging means for non-destructive testing (NDT) and systems and methods for evaluating areas associated with various assets. The various assets include, but are not limited to, facades and cladding systems, structural bodies such as concrete columns and concrete walls, bridges, tunnels, and dams. The system can operate in a frequency range that varies from 0.1 GHz to 10 GHz. However, the defined concepts and implementation methods of the present invention are not specific to the frequency range and can encompass a wider range of operating frequencies.

[0012] Thus, in one aspect, the present invention is a non-contact microwave test system for through-sheet imaging of a test area, comprising a front-end subsystem for transmitting and receiving electromagnetic waves with the test area, a system-in-package (SiP) subsystem comprising a transmitter and a receiver radio frequency (RF) chain, and a signal processing subsystem for performing reproduction of the spatial reflectivity of heterogeneous multilayer media in the test area.

[0013] In one embodiment, the front-end subsystem comprises at least one transmitter antenna and at least one receiver antenna.

[0014] In one embodiment, the front-end subsystem comprises at least one transceiver.

[0015] In one embodiment, each antenna or transceiver is integrated with a metamaterial lens that enables sub-wavelength high-resolution imaging.

[0016] In one embodiment, a system-in-package (SiP) subsystem generates a stepped-frequency continuous waveform (SFCW).

[0017] In one embodiment, the signal processing subsystem comprises a backpropagation algorithm for reproducing the spatial reflectivity suitable for a multilayer medium and an SFCW waveform.

[0018] In one embodiment, the system further comprises a position confirmation subsystem and an interface subsystem for reproducing a high-resolution image.

[0019] In one embodiment, the position confirmation subsystem comprises an optical flow sensor, an inertial measurement unit (IMU), and an atmospheric pressure sensor.

[0020] In one embodiment, the interface subsystem transfers data from the signal processing subsystem to a cloud server or a local tablet PC for reproducing a high-resolution image.

[0021] In one embodiment, the front-end subsystem is a beamforming MIMO front-end subsystem comprising an array of transmitter antennas multiplexed in time division and an array of receiver antennas constituting a virtual antenna array based on the physical arrangement of the transmitter and receiver antennas, the system-in-package (SiP) subsystem is a MIMO SiP subsystem comprising transmitter and receiver RF chains for generating a stepped-frequency continuous waveform, and the position confirmation subsystem provides the position information of the system for the signal processing subsystem to synthesize a large synthetic aperture for 3D image reproduction.

[0022] In one embodiment, the front-end subsystem is a beam-steering antenna front-end subsystem with a single transceiver, the system-in-package (SiP) subsystem is a monostatic reflectometer array SiP subsystem with a transmitter and a receiver RF chain for generating stepped-frequency continuous waveforms, the signal processing subsystem is a digital beamforming signal processing subsystem, and the position confirmation subsystem is equipped on a mobile platform and provides the position information of the system for the signal processing subsystem to synthesize a large synthetic aperture for 3D image reconstruction.

[0023] In one embodiment, each antenna element or transceiver operates in a frequency range of 0.1 GHz to 10 GHz, preferably 0.1 GHz to 6 GHz.

[0024] In one embodiment, the metamaterial lens is made of a double-negative material (DNG) having a negative refractive index property enabling sub-wavelength high-resolution imaging.

[0025] In one embodiment, the metamaterial lens includes variable-size concentric periodic split-ring resonators (SRRs) and concentric circular trace lines extending to the lowermost layer of the lens.

[0026] In one embodiment, the lens is disposed above the antenna element or transceiver for long-distance non-penetrating scanning.

[0027] In one embodiment, the system is configured to be integratable with other mechanical / electrical devices for combined operation.

[0028] In one embodiment, the system is configured as a handheld type, a payload-carrying / mounting type, an autonomous / semi-autonomous / remotely controlled system selected from unmanned ground vehicles (UGVs), drones, robotic arms, crawler robots, and / or combinations thereof for non-destructive inspection of facilities such as facade structures, exterior cladding systems, concrete columns and walls, indoor mechanical, electrical, and plumbing (MEP) fixtures, water, oil, and gas pipelines, metal parts, roads, tree trunks, tunnels, dams, bridges, medical imaging, security monitoring, and inventory sorting.

[0029] In one embodiment, the system is configured to be of the handheld type, and the front-end subsystem comprises a single-input single-output (SISO) configuration consisting of a single transceiver broadband antenna element, a monostatic array of antenna elements, or a MIMO array of antenna elements.

[0030] In one embodiment, the system is a payload-carrying / mounting type, an autonomous / semi-autonomous / remotely controlled system selected from unmanned ground vehicles (UGVs), drones, robotic arms, and crawler robots, and the front-end subsystem comprises a beam-forming antenna subsystem having a single transceiver, a MIMO subsystem having multiple transceivers, or a monostatic array of reflectometers.

[0031] In another aspect of the present invention, a method for non-contact through-sheath imaging of a test area using the system disclosed herein is provided. The method comprises generating electromagnetic waves by the SiP subsystem, transmitting the generated electromagnetic waves to the front-end subsystem via an RF interface, transmitting a backscattered signal to and receiving it from the front-end subsystem from the test area, and routing the received RF signal to the signal processing subsystem by the SiP subsystem for signal processing and reproduction of the spatial reflectivity of the heterogeneous multi-layer medium in the test area.

[0032] In one embodiment, the method further comprises synthesizing, by a signal processing subsystem, data from the SiP subsystem and the position confirmation subsystem to execute a 3D image reproduction algorithm and a data interpretation scheme routed to an interface subsystem, and routing, by the interface subsystem via wired or wireless transmission, the data interpretation and reproduced 3D image to a cloud server or a local tablet PC for the user to visually recognize an image of the test area.

[0033] In one embodiment, the stepped frequency continuous wave (SFCW waveform) is generated by the SiP subsystem.

[0034] In one embodiment, the backscattered signal from the test area is directly sampled at the aperture of the front-end subsystem by a reflectometer that utilizes a Schottky diode at the aperture of an antenna having a metamaterial-based lens.

[0035] In one embodiment, a dead reckoning algorithm for the IMU is combined with an optical flow sensor to recover accurate coordinate information from the position confirmation subsystem.

[0036] In one embodiment, the transmission means is selected from USB, Ethernet, WiFi, Bluetooth®, ZigBee® based on the scenario of the use case.

[0037] In one embodiment, the data stored in the cloud server or the local tablet PC can be accessed using a web application in any computing system such as a workstation / PC, a tablet PC, or a mobile phone.

[0038] In one embodiment, for 3D imaging of the test area, additional phases are individually added one layer at a time to the collected frequency spectrum.

[0039] In one embodiment, the dyadic green function (DGF) of a multilayer medium is used to incorporate layer attenuation and characteristics.

[0040] In one embodiment, an inverse scattering method is used to identify a 3D quantitative image of a test region including parameters such as permittivity and conductivity.

[0041] The above and other objects, features, and other advantageous effects of the present invention should be more clearly understood from the following detailed description in conjunction with the accompanying drawings. For the purpose of explaining the present disclosure, an exemplary configuration of the present disclosure is illustrated. However, the present disclosure is not limited to the specific methods and apparatuses disclosed herein.

Brief Description of the Drawings

[0042]

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[0043] For the purpose of providing an understanding of the principles of the present invention and the scope of the claims included therein, the embodiments shown in the drawings are herein referred to and specific language is used to describe it. Nevertheless, it is understood that the scope of the invention is not thereby intended to be limited. Any changes or further modifications in the described embodiments and any further applications of the principles described herein are considered to be those that can be commonly conceived by those skilled in the art.

[0044] In the following description, in order not to obscure the present invention with unnecessary details, algorithms and functions may be shown in block diagrams. On the other hand, the specific application examples illustrated and described are for illustrative purposes only and should not be construed as the only mode for carrying out the present invention without specific notice herein. Furthermore, the logical block definitions and delimitations between various blocks are examples of specific embodiments. It should be readily apparent to those skilled in the art that many other delimitation means can implement the present invention. For the most part, details regarding timing considerations and the like are omitted when the details are not necessary for a complete understanding of the present invention and are within the capabilities of those skilled in the art.

[0045] The present invention describes a microwave test system for realizing non-contact, non-destructive, deep penetration, through-sheet imaging radar means using electromagnetic waves propagating in the microwave frequency regime. The test system according to the present invention may have applicability in various industries, including, but not limited to, the architectural and construction (indoor and outdoor) industries. Thereby, the systems disclosed herein can be used to test and evaluate assets such as dams, bridges, tunnels, etc. for monitoring the structural state of each asset. To achieve non-contact imaging using microwaves, a number of component-level, system-level, and application-level innovations are applicable. Non-destructive testing of structures in assets refers to the ability of the systems disclosed herein to image and evaluate the structure without damaging the structure or requiring any disassembly of the structure. In the context of the present invention, "high resolution" shall refer to any achieved image resolution less than lambda / 4 (λ / 4) for a particular subset of the operating frequencies.

[0046] For example, the test systems disclosed herein can be used to test and evaluate facades and claddings to detect defects such as cracks and corrosion in metal brackets hidden behind the cladding, thereby preventing delamination of the facade structure. In other embodiments, the system can be used to test and evaluate the condition (cracks and corrosion in the rebar structure) of metal reinforcement structures embedded within concrete columns that make up the structural blocks of those buildings. In other embodiments, the system can be used to detect defects in mechanical, electrical, and plumbing (MEP) fixtures inside buildings, detect cracks and corrosion in pipes, water leakage from pipelines, water infiltration in concrete, and detect the presence of rodents. In other embodiments, the system can be used to test and evaluate the condition (cracks and corrosion in the rebar structure) of metal reinforcement structures embedded within concrete columns and concrete walls. In this regard, the systems disclosed herein can be used to identify and quantify cracks and corrosion (spalling) in the rebar structure, chloride penetration in the concrete, and identify / quantify cracks and voids inside the concrete structure.

[0047] To image and test specific assets, conventional scanner systems are brought into contact and moved / rotated across that area. This is usually manual, time-consuming, and redundant. The system disclosed herein aims to at least solve two main problems in conventional scanners related to, firstly, synthesizing a large aperture that covers a large test area to generate a high-resolution scan result, and secondly, designing signal processing algorithms for heterogeneous layered media rather than homogeneous media.

[0048] To achieve a larger aperture, digital beamforming, a monostatic array, or multiple-input multiple-output (MIMO) beamforming / virtual monostatic array can be employed. These methods may be used in parallel with moving the scanner to achieve a larger aperture more quickly. However, even then, if the scan process is performed manually, it will take time to inspect a large area of the asset. To address this problem, it may be appropriate to mount the scanner on an automated platform such as a drone, UGV, and robotic arm for scanning a larger area of the asset. However, for compatibility with the automated platform, it is ideal for the scanner to possess non-contact scanning capabilities.

[0049] Signal processing algorithms for non-contact scanning and inspection means can take into account the nature of different media layers in front of the scanner, including free space and the layered media of the asset (air + concrete, air + outer surface, etc.). Conventional signal processing algorithms consider the media in front of the scanner as a homogeneous medium (e.g., only a continuous concrete layer). Thus, in one embodiment, the system disclosed herein can scan the AUT of an asset that includes a homogeneous multi-layered media.

[0050] The systems disclosed herein can be configured and adapted to be equipped in various modalities such as handheld, payload-carrying mounted / fixed type, autonomous / semi-autonomous / controlled systems, etc. In one embodiment, the systems disclosed herein can be configured and adapted for mounting / fixing to drones, unmanned ground vehicles (UGVs), robotic arms or crawler robots, and / or combinations thereof by a mounting interface / frame.

[0051] In some embodiments, the test system can be configured to be integrated into other mechanical / electrical equipment for combined system operation in a collaborative manner to achieve the required functions. Figure 3 shows an embodiment of the present invention in which the test system can be mutually integrated into a UGV and a Cobot for collaborative functions. As can be readily understood, the systems disclosed herein can generally be used as sensor inputs for mutually compatible mechanical / electrical equipment.

[0052] The systems disclosed herein can be configured and adapted for use in non-contact, non-destructive inspection of assets and the area under test (AUT) of the asset. The assets can include, but are not limited to, the following. 1. Facade structures (detection of cracks and corrosion in metal brackets holding the structure, delamination of glass curtain walls or natural stone facades, detection of loose tiles, cracks, delamination, etc. in tiled walls) 2. Cladding systems (detection of the position, presence, and shape of metal brackets holding various cladding systems) 3. Concrete columns and walls (detection of the position, presence, and size of steel bars to facilitate repair work with perforations, monitoring of the degree of cracks and corrosion in steel bar structures embedded in concrete, detection of spalling and endangering of concrete in the structural integrity of the asset, detection of voids (voids) embedded in concrete structures introduced during the construction phase) 4. Indoor MEP hidden on the back side of walls and ceilings (detection of the position, presence and size of steel bars, detection of utilities and electrical wiring embedded in walls and other structures, detection of cracks and corrosion in pipelines causing leakage / leakage, detection of wiring breaks, delamination, to facilitate repair work with perforations) 5. Pipelines (detection of scratches and damages in pipes causing water leakage, moisture detection of infrastructure elements for water leakage detection, corrosion of the insulation layer under in oil and gas pipelines, detection of corrosion of the concrete refractory layer under the legs of large spherical tanks / containers / pipes, inspection of composite wraps used for pipeline repair) 6. Aircraft fuselage (inspection of cracks and corrosion in the paint layer under metal parts of the aircraft fuselage, inspection of composite parts for interfacial delamination and internal defects) 7. Product packaging (detect the interior of the product without opening the package and test for cracks or damages) 8. Infrastructure (roads, tunnels, dams and bridges, inspection of tree trunks for cavitation, decay, confirmation of surface defects or corrosion without disassembling surrounding structures) 9. Biomedical imaging (non-invasive methods for disease detection or imaging of body parts) 10. Automotive parts (detection of tire tread size) 11. Security, surveillance and warehousing (inspection of metallic and non-metallic materials in buildings, airports, offices and public places)

[0053] In one embodiment, the system disclosed herein can penetrate and see through various different materials that make up the asset being inspected and the AUT. The materials that the system can penetrate or see through can be, but are not limited to, non-metallic materials including concrete, bricks and mortar, ceramic facades, exterior stone, and glass facades. In one embodiment, the system may be capable of performing through-thickness inspection of any non-metallic material and surface level imaging of metallic materials.

[0054] The system disclosed herein may comprise a number of subsystems including, but not limited to, a front-end subsystem, a system-in-package (SiP) subsystem, a signal processing subsystem, a location confirmation subsystem, and an interface subsystem.

[0055] The front-end subsystem can be responsible for the transmission and reception of RF signals and the propagation between the SiP subsystem. The SiP subsystem can be responsible for the control of the RF subsystem, waveform synthesis, and data collection. The signal processing subsystem can be responsible for the image reproduction (3D) of the backscattered signal (electromagnetic wave) from the AUT. The location confirmation subsystem can be responsible for identifying the exact coordinate (x, y, z) information for each response (t) for accurate 3D image reproduction. The interface subsystem can be responsible for transferring data and control information from the test system to the end user.

[0056] In one embodiment, the system disclosed herein may comprise a front-end subsystem for transmitting and receiving electromagnetic waves to and from a test area, a system-in-package (SiP) subsystem comprising a transmitter and receiver radio frequency (RF) chain, and a signal processing subsystem for reproducing the spatial reflectivity of a heterogeneous multilayer medium in the test area. In the context of the present invention, spatial reflectivity refers to the 3D image reproduction of the backscattered signal from the AUT, whereby the spatial reflectivity may have an amplitude component and a phase component for each x, y, and z coordinate.

[0057] In one embodiment, the system disclosed herein may further comprise a location confirmation subsystem and an interface subsystem for high-resolution image reproduction.

[0058] In one embodiment, the system disclosed herein may comprise a front-end subsystem, a system-in-package (SiP) subsystem, a signal processing subsystem, a location confirmation subsystem, and an interface subsystem.

[0059] In one embodiment, the system may further comprise a processing subsystem.

[0060] The system disclosed herein may include generating electromagnetic waves by a SiP subsystem, transmitting the generated electromagnetic waves to a front-end subsystem via an RF interface, transmitting and receiving a backscattered signal from the test area to the front-end subsystem, and routing the received RF signal to a signal processing subsystem by the SiP subsystem for signal processing and reproduction of the spatial reflectivity of the heterogeneous multilayer medium in the test area. It can be used in a method for non-contact through-sheet imaging of a test area.

[0061] The method disclosed herein may further include synthesizing data from a SiP subsystem and a position confirmation subsystem by a signal processing subsystem to execute an image reproduction algorithm and a data interpretation scheme routed to an interface subsystem, and routing the data interpretation and reproduced image to a cloud server or a local tablet PC via wired or wireless transmission by the interface subsystem so that a user can view an image of the test area.

[0062] In one embodiment, the system disclosed herein may include a front-end subsystem for transmitting and receiving electromagnetic waves with a test area, a system-in-package (SiP) subsystem including a transmitter and a receiver radio frequency (RF) chain for generating a stepped frequency continuous waveform (SFCW), a signal processing subsystem including a backpropagation algorithm for reproduction of spatial reflectivity suitable for a multilayer medium and an SFCW waveform, a position confirmation subsystem including an optical flow sensor, an inertial measurement unit (IMU), and an atmospheric pressure sensor, and an interface subsystem for transferring data from the signal processing subsystem to a cloud server or a local tablet PC for reproduction of a high-resolution image.

[0063] The test system disclosed herein can synthesize a large synthetic aperture to cover a large area under test (AUT) by utilizing aperture synthesis techniques such as digital beamforming, multiple-input multiple-output (MIMO) beamforming, virtual monostatic array, monostatic array configuration, etc., and / or by moving the system over a region with non-uniform motion. In the context of the system disclosed herein, "non-uniform" refers to any motion that is irregular and not "regular motion", and regular motion is, for example, raster motion following a regular path on the x-axis and y-axis.

[0064] The field of view of the test system can depend on a combination of factors including the synthetic aperture generated by moving the test system according to the invention and / or the array generated by the configuration of the transmitter and receiver in the front-end subsystem. In particular, the test system can be physically movable to obtain a larger synthetic aperture, or digital beamforming techniques can be used in an antenna array for directional signal transmission and reception (to steer the beam in the intended direction). In this regard, the size of the aperture can be increased due to the system being stationary and / or due to the operation of beamforming in a system comparable to a system without beamforming technology.

[0065] In one embodiment, the field of view of the test system can depend on the rectangular grid generated in time-division multiplexing mode and the synthetic aperture generated by moving the test system in a virtual array. In one embodiment, the field of view of the test system can depend on the monostatic reflectometer array employed in the system.

[0066] Conventional test systems can use ground penetrating radar (GPR) technology. GPR (step frequency continuous wave (SFCW) or pulsed) typically operates in a frequency range extending from 0.1 GHz to 6 GHz. The frequency range is selected according to the scenario of the use case and the application requirements. When the detection application requires deeper penetration, lower frequency values are selected. The attenuation of lower frequency electromagnetic (EM) signals is less than that of higher frequency signals. However, for such applications, the resolution is compromised, and as a result, the cross-range resolution of the radar at lower frequencies is limited by the diffraction limit. To overcome the diffraction limit, the lens method can be adopted. Conventional dielectric lenses can be achieved by designing a curved dielectric structure that increases the gain and reduces the power half-value width of the antenna's transmission and reception. However, conventional lenses cannot overcome the diffraction limit because they do not amplify the evanescent mode, resulting in a loss of near-field information. Theoretically, it is possible to use double-negative materials (DNG) to design flat lenses to overcome the diffraction limit. DNG materials have a negative effective permittivity and a negative permeability. These metamaterials do not exist in nature. However, they can be realized using periodic structures. These periodic structures usually have narrow-band characteristics. For scanning means with a large bandwidth, broadband DNG needs to be designed to achieve focusing and overcome the diffraction limit. Such means can potentially increase the gain of the Tx / Rx antenna and enable the scanning of assets from a long distance in a non-contact manner.

[0067] Thus, in one embodiment, each antenna or transceiver can be integrated with a lens that enables sub-wavelength high-resolution imaging. In one embodiment, the lens can be a metamaterial-based lens that enables sub-wavelength high-resolution imaging of large AUTs by overcoming the diffraction limit.

[0068] In one embodiment, the metamaterial-based lens can include concentric periodic split ring resonators (SRRs) of variable size and concentric circular trace lines extending to the bottom layer of the lens.

[0069] In one embodiment, the metamaterial lens may be disposed on top of the transmitter antenna and the receiver antenna. In one embodiment, the lens may be an electromagnetic metamaterial lens. Electromagnetic metamaterials are artificially designed periodic structures that exhibit physical properties such as a negative refractive index not exhibited by naturally occurring materials. These electromagnetic metamaterials are sometimes referred to as negative index materials (NIMs).

[0070] In one embodiment, the metamaterial lens may be a flat lens made of a double negative material (DNG) having the property of a negative refractive index that enables sub-wavelength high-resolution imaging.

[0071] Figure 1 shows an overview of the portable microwave test system disclosed herein. The imaging system may operate in the electromagnetic wave frequency spectrum in the range of 0.1 GHz to 10 GHz, preferably 0.1 GHz to 6 GHz. This frequency spectrum is selected to be suitable for applications that require deeper penetration inside non-metallic materials including, but not limited to, concrete, brick and mortar, ceramic facades, exterior stone, and glass facades.

[0072] In one embodiment, the system disclosed herein can achieve a penetration depth of at least 0.20 m or 0.30 m in non-metallic materials, which may vary depending on the material that the test area is composed of. In one embodiment, the system disclosed herein can achieve a penetration depth of at least 0.20 m to 1 m, more preferably at least 0.50 m, in non-metallic materials.

[0073] All different modalities of the test system are non-contact with the asset being tested. In the context of the present disclosure, "non-contact" means that there is no physical contact between the system and the asset, thereby resulting in a gap / space or stand-off distance of at least 1 lambda (λ) therebetween. The space or stand-off distance between the asset (e.g., the building or structure in FIG. 1) and the test system may depend on the use case and application scenario.

[0074] In one embodiment, the stand-off distance can be at least 1 lambda. In one embodiment, the stand-off distance can be at least about 0.01 m, 0.02 m, 0.03 m, 0.04 m, 0.05 m, 0.1 m, 0.2 m, 0.3 m, 0.4 m, 0.5 m, 1 m, 1.5 m or 2 m. In one embodiment, the stand-off distance can be in the range of 0.05 m to 5 m. In one embodiment, the stand-off distance can be in the range of 0.5 m to 1 m. In one embodiment, the stand-off distance can be in the range of 2 m to 3 m.

[0075] In one embodiment, the systems disclosed herein can distinguish two separate objects when they are separated by at least about 0.02 m. This refers to the system range resolution and cross-range resolution of the objects when scanning the test area. In one embodiment, the system can have a range resolution and cross-range resolution of at least about 0.01 m. In one embodiment, the system can have a range resolution and cross-range resolution of about 0.02 m. In one embodiment, the system can have a distance resolution and cross-range resolution of about 0.025 m.

[0076] In certain embodiments, a cross-range resolution and distance resolution of 0.003 m to 0.0075 m can be achieved using advanced electromagnetic techniques.

[0077] As will be appreciated, the distance resolution and penetration depth of the systems disclosed herein can vary depending on the test area and the stand-off distance from the asset. The distance resolution can depend on the bandwidth used.

[0078] In one embodiment, the system-in-package (SiP) subsystem can generate a stepped-frequency continuous waveform (SFCW) of distance resolution defined as R res = c / 2B. Here, B is the bandwidth of the SFCW waveform used, and c is the speed of light. The cross-range resolution is related to the wavelength, the aperture being scanned, and the stand-off distance: δx = λz0 / 2Dx may depend on. Here, λ is the wavelength, z0 is the stand-off distance, and D x is the aperture size. The maximum scanned range may depend on the amount of transmitted power and the frequency step size.

[0079] Figures 2A - E represent various modalities of the test system according to the present invention. 1A shows an embodiment in which the test system is a hand-held device, the hand-held device is portable and non-contact, and can be held at a predetermined distance from the test area. 1B shows an embodiment in which the test system is the hand-held device according to 1A and is mounted on a wheel that rotates on the surface of the asset to be inspected. 1C shows an embodiment in which the test system is mounted on a drone. 1D shows an embodiment in which the test system is mounted on a ground robot platform. 1E shows an embodiment in which the test system is equipped on a wall-climbing robot.

[0080] In one embodiment 1A, the test system is equipped in a hand-held non-contact mode. In one embodiment 1B, the test system is the hand-held device according to 1A and is equipped on a wheel that rotates on the surface of the asset to be inspected. In another embodiment 1C, the test system is mounted on a drone. In a further embodiment 1D, the test system is equipped on an unmanned ground robot such as a robotic arm. In another embodiment 1E, the test system is the hand-held device according to 1A and is equipped on a wall-climbing robot.

[0081] The standard stand-off distances (100A, 100B) for 1A and 1D are at least 1λ at the center operating frequency, and can vary from about 0.5 m to 1 m at a distance resolution of 0.02 m and a cross-range resolution, with a penetration depth of at least about 0.5 m inside concrete (3) and 0.6 m inside exterior stone (5).

[0082] The standard stand-off distance (100C) for 1C can be about 2m - 3m at a distance resolution and cross-range resolution of 0.02m, at a penetration depth of about 0.2m inside the concrete (3) and 0.2m inside the facade stone (5).

[0083] In Figure 1, the arrow (2) indicates the passage of electromagnetic waves through the facade stone (5) for inspecting the condition of the metal bracket, and the passage of electromagnetic waves through the concrete (3) for inspecting the mesh structure condition of the structural steel bars (4). This electromagnetic-based non-contact through-sheet test system serves to identify defects in concealed structures such as cracks and corrosion in the metal brackets behind the facade, and to evaluate the structural integrity of the assets and the area under test (AUT) by monitoring the condition of the steel bars (4) embedded inside the concrete (3).

[0084] Figure 3 shows an embodiment in which the test system (301) is integrated into an unmanned ground vehicle (302) by a manipulator such as a robotic arm (303). The robotic arm has an other end to which other instruments such as a drilling machine (304) and any other specific electrical / mechanical equipment can be integrated. Such an embodiment of the scanner system can be used to scan and identify the positions of the steel bars / utilities embedded inside infrastructure elements such as walls, ceilings, floors, and columns, and to handle target use cases such as restoration / repair and drilling for layout work by combining the functions of various sensors and devices in a closed-loop configuration.

[0085] Figure 4 shows a test system (401) operating in a non-contact mode, where the front-end subsystem and the radar antenna (405) transmit and receive electromagnetic waves. The test system is at a standoff distance (407) from the area under test (AUT) (406). The AUT can include a multi-layer medium having multi-layer non-metallic materials such as an exterior material system including glass, ceramic, stone, concrete layer, brickwork, etc. The standoff distance includes the air medium that separates the system from the area under test of the asset. The scanning system in a particular embodiment can be used to test for the presence of metallic reinforcing bars (408) in the multi-layer medium. In one embodiment, the test system can be used to explore the presence of defects (409, 410) (cracks, deterioration) in fixtures on the back side of a facade (411) made of materials such as glass, ceramic, and stone. In one embodiment, the test system can be used to inspect the corrosion state and degree of a reinforcing structure (408). In one embodiment, the test system can be used to inspect for defects such as cracks and voids (409, 410) in a concrete multi-layer. In one embodiment, the test system is used to explore the presence of moisture inside an infrastructure element to detect water seepage (412).

[0086] Figure 5 shows various appearances of an enclosure or housing (501) of a test system suitable for stand-alone operation or operation by integration / mounting / fixing with other mechanical / electrical equipment for autonomous / semi-autonomous / controlled inspection. The test system can include inserts (502) on the outer surface of the enclosure suitable for instantaneous integration / mounting / fixing with other equipment for cooperative operation. LEDs (503) can be provided on the enclosure side to indicate the status of the operation of the test system, together with a power socket (505) and a switch (504) for on / off operation. On the other side, there may be ports for digital input / output (506).

[0087] In one embodiment, the enclosure or housing of the test system may include a front-end subsystem, a SiP subsystem, a signal processing subsystem, a positioning subsystem, and an interface subsystem. In other embodiments, the enclosure or housing may include a processing subsystem. The enclosure or housing may be made of any suitable material that is suitable for operation in the desired modality of the system. As will be readily understood by those skilled in the art, the enclosure or housing may be made of any material that does not affect the performance of the electrical device and does not interfere with electromagnetic waves.

[0088] The enclosure or housing of the system may be of any suitable shape or size according to the mode of use. In one embodiment, the enclosure or housing may be of any suitable size in the range of about 5×5×2.5 cm to about 75×75×75 cm. In other embodiments, the enclosure or housing may be of any suitable size in the range of about 10×10×5 cm to about 50×50×50 cm.

[0089] Two alternative embodiments of the test system according to the present invention having various subsystems are provided in FIGS. 6 and 7.

[0090] In the following description, the overall workflow for the scanning means will be described, followed by a detailed description of the subsystems in the scanner, and then the implementation of the described subsystems to achieve various modalities 1A, 1B, 1C, 1D, or 1E.

[0091] When implementing the embodiment according to the block diagram shown in FIG. 6, the test system may include the following subsystems. · A beamforming MIMO front-end subsystem (10) comprising an array of time-division multiplexed transmitter antennas and an array of receiver antennas that form a virtual antenna array based on the physical arrangement of the transmitter and receiver antennas. Each antenna element operates over a wide frequency range of 0.1 GHz to 10 GHz, preferably 0.1 GHz to 6 GHz, and is integrated with a metamaterial-based lens that enables sub-wavelength high-resolution imaging. · A MIMO SiP subsystem (11) comprising a transmitter and receiver RF chain for generating a stepped frequency continuous waveform in a frequency spectrum in the range of 0.1 GHz to 10 GHz, preferably 0.1 GHz to 10 GHz · A signal processing subsystem (12) that performs reproduction of the spatial reflectivity (3D image) of the asset under inspection by adopting various backpropagation algorithms suitable for multilayer media and SFCW waveforms · A position confirmation subsystem (13) that provides the position information of the scanner useful for the signal processing subsystem 12 to synthesize a large synthetic aperture for 3D image reproduction · An interface subsystem (14) responsible for transferring the data after signal processing to a cloud server or a local tablet PC (15). 3D processed data visualization of the AUT occurs. This visualization may be via a user interface (GUI), and the user (17) can interact with the system by modifying specific interaction elements on the GUI

[0092] The SiP subsystem (11) can generate an SFCW chirp and transmit it to the front-end subsystem (10) via an RF interface (18). The front-end subsystem (10) can transmit and receive electromagnetic waves (backscattered signals) via an air medium (22). The analog-digital converter (ADC) data received RF signal is routed by the SiP subsystem (11) to the signal processing subsystem (12) via a baseband interface (19) for signal processing and reproduction. The signal processing subsystem (12) synthesizes the data from the SiP subsystem (11) and the data from the positioning subsystem (13) from the interface (20) and executes a 3D image reproduction algorithm and a data interpretation scheme routed to the interface subsystem (14) via the interface (26). Interfaces (26), (18), (19), and (20) are all within the test system and are mostly via printed circuit board (PCB) traces in either a microstrip configuration or a coplanar waveguide (CPW) configuration. For the RF interface (18), the PCB trace line has a 50-ohm line impedance that minimizes reflections. A balun can be used to convert a single-ended to a differential line and vice versa. Since the data throughput for the interface (19) must be high, a parallel interface scheme including, but not limited to, a camera serial interface (CSI) and a low-voltage differential signaling (LVDS) interface is used. The interface subsystem (14) routes the data interpretation and reproduced 3D image to a cloud server or a local tablet PC (15) via a wired or wireless transmission means (21). The transmission means (21) can be selected to be wired (USB, Ethernet, etc.) or wireless (WiFi, Bluetooth®, ZigBee®, etc.) based on the scenario of the application and use case.

[0093] The front-end subsystem (10) consists of an array of broadband antenna elements operating in the frequency range of 0.1 GHz to 10 GHz, preferably 0.1 GHz to 6 GHz, and is integrated with a metamaterial-based lens to improve antenna gain and reduce the power half-value width. The metamaterial-based lens can also enable sub-wavelength high-resolution imaging by overcoming the diffraction limit. FIG. 10 shows a focused image (54) of a broadband spiral antenna element (46), the radiation pattern (52) of the antenna element, and a metal bracket (55) having a number of holes. Since the gain of the antenna is not very high (about 5 dBi) and the holes are significantly smaller than the wavelength, (54) is not very clear, indicating that sub-wavelength imaging is not very accurate.

[0094] Electromagnetic metamaterials are artificially designed periodic structures that exhibit physical properties such as a negative refractive index not shown by naturally occurring materials. These materials are sometimes referred to as negative refractive index materials (NIMs). Electromagnetic lenses are generally designed to achieve focusing by increasing the gain and decreasing the power half-width. Lenses designed using NIMs are different from those designed using positive refractive index materials (PIMs). Ordinary materials with a positive refractive index need to be curved to function as lenses. One of the important differences between them is that flat lenses designed using NIMs can be used to focus electromagnetic waves. Due to the property of negative refractive index, sub-wavelength high-resolution imaging becomes possible, which is not achievable using positive refractive index materials. NIMs achieve this by extracting and amplifying the decaying evanescent modes that carry information about the near field. The negative refractive index is achieved by using variable-sized concentric periodic split-ring resonators (SRRs) and concentric circular trace lines extending in the bottom layer, as shown in (47A) and (47B) of FIG. 10. This unique design helps to achieve NIMs with a large bandwidth in the range of 0.1 GHz to 10 GHz, preferably 0.1 GHz to 6 GHz. The SRRs help to achieve negative transmittance, and the concentric circular trace lines help to achieve negative permittivity. From the radiation patterns (53) and (52), it can be seen that the gain of the antenna increases by 3 dB and the power half-width decreases by 40 degrees. (56) of FIG. 10 shows a reproduced image of the metal bracket (55). It can be seen that the reproduced image (56) becomes significantly clearer compared to the focused image (54) due to being measured by the presence of the metamaterial-based lens.

[0095] As described above, the test system and method according to the present invention can achieve deep penetration imaging in the microwave frequency range of 0.1 GHz to 10 GHz, preferably 0.1 GHz to 6 GHz, without sacrificing sub-wavelength resolution by using a specially designed metamaterial-based planar lens.

[0096] A MIMO system has an array of antenna elements associated with a transmitter known as a transmit (Tx) array and an array of antenna elements associated with a receiver known as a receive (Rx) array. The increment of the Tx array pattern and the Rx array pattern results in the equivalent radiation pattern of the MIMO radar. It is well known that the radiation pattern of an array is the Fourier transform of the array distribution. The convolution of the Tx array and the Rx array in space results in a virtual array. The Fourier transform results in the radiation pattern of the virtual array and, similarly, gives the radiation pattern of the MIMO system. Some of the significant parameters that help to identify the MIMO system include (but are not limited to) the range or distance, velocity, and angle of arrival of the object under inspection. The arrangement of the Rx array, similar to the Tx array, is a factor in the accuracy of various estimated values of the above parameters. Generally, when N antennas are equally spaced in a linear arrangement, the angular resolution (Δθ) of the MIMO system in the direction in which the antennas are arranged is given by the following formula: Δθ = λ / Nd. Here, λ is the operating wavelength, and D is the element spacing in the equally spaced linear array. The above formula shows that the angular resolution is inversely proportional to the total number of antenna elements in the transmitter and the receiver. The cascaded MIMO system with a large number of Tx and Rx channels provides a very high angular resolution in both the azimuth and elevation planes based on the arrangement of the Tx array and the Rx array. The number of Tx and Rx arrays depends on the frequency range selected for a particular application of the test system. In the frequency range of 0.1 GHz to 10 GHz, the Tx×Rx elements can be up to 10×10 at most in the least single transceiver or single antenna and receiver. The arrangement of the Tx array and the Rx array in the MIMO configuration can be represented by (57) in FIG. 11. The resulting virtual array is a 16-element square array shown by (58) in FIG. 11.

[0097] FIG. 8 shows a detailed view of the transmitter (35) and receiver (36) blocks / chains in a system-in-package (SiP) subsystem (11, 24) according to the present invention. The number of transmitter and receiver blocks depends on the requirements of the application as well as the required accuracy and resolution of the estimated parameters. The transmitter block consists of a 16-bit DAC (35A) that converts a baseband signal from an LVDS interface by a field programmable gate array (FPGA) block (37) into an analog signal. The signal from the DAC serves as an input for an IQ modulator that generates an RF signal operating at any frequency from 0.1 GHz to 10 GHz, preferably from 0.1 GHz to 6 GHz. The frequency is controlled by an SPI interface from (37) that controls (35D), (35E) and (35F). The RF signal is amplified by an RF amplifier block and input to a beam focusing transmitter antenna having a metamaterial lens in the front-end subsystem (10, 23). The received RF signal from the front-end subsystem is input to an IQ demodulator (36A) that demodulates the signal, and further amplification is performed at (36B) and input to an analog-to-digital converter (ADC) (36C) that interfaces to the FPGA block (37) via an LVDS interface. In a MIMO configuration, multiple transmitter and receiver blocks exist with the local oscillator and digital clocks (35D, 35E, 35F) synchronized.

[0098] FIGS. 12 and 13 give an overview of the overall test method and the signal processing subsystem (12) responsible for image reproduction and data interpretation. At each point within the source aperture, a stepped frequency continuous wave (SFCW waveform) is generated by the SiP subsystem (11) and transmitted by the front-end subsystem (10). The frequency is incremented in 0.1 MHz steps from 0.1 GHz to 6 GHz as shown in FIG. 13 and data is recorded. The range resolution of the SFCW system is R res = c / (2Nf step ), where c is the speed of light, N is the total number of frequency steps, and f stepis the frequency step. Therefore, the frequency range extended to 0.1 GHz to 6 GHz corresponds to a range resolution of 2.5 cm. Therefore, the test system disclosed herein means that two separate objects can be distinguished when the object is separated at a distance of at least 2.5 cm. One of the important advantages of an SFCW-based system is that Nf step while widening the entire bandwidth given by, the absolute bandwidth of each channel can be made narrow. The overall operation of the SFCW system is as follows. (a) The transceiver transmits and receives signals at increasing frequencies (one frequency at a time). (b) For each frequency, received baseband IQ data is recorded. In one embodiment, an inverse Fourier transform (IFFT) is executable to obtain a range profile.

[0099] FIG. 14 shows the range profiles obtained when the test system is used to explore two objects at two different distances. FIG. 14 shows that there are two peaks (140 and 141) corresponding to the two objects. The real part of the range profile can be used to estimate the electrical properties of the material based on the characteristics (142 and 143) of the obtained waveform.

[0100] In certain embodiments according to modalities 1A, 1B, 1C, 1D or 1E, the test system can move in the source plane (59) along the x and y directions as shown in FIG. 9 to form an aperture much larger than the aperture of an individual antenna element or the aperture of a virtual array composed of MIMO transmitters and receivers. The larger aperture improves the cross-region resolution of imaging and a sufficiently focused image can be obtained. The position of the scanner is calculated by the position confirmation subsystem (13). The position confirmation subsystem (13) in 1A and 1B can be implemented using a combination of sensors such as an optical flow sensor, an inertial measurement unit (IMU) and an atmospheric pressure sensor for accurate position confirmation with a resolution of 0.5 cm or less. In embodiments of 1C, 1D and 1E, the position confirmation subsystem (31) may be present inside a moving platform such as a drone or a ground robot / crawler.

[0101] Apart from physically moving the test system to obtain a larger synthetic aperture, digital beamforming technology (63) can be used. Beamforming is a signal processing technique used in antenna arrays for directional signal transmission and reception (steering the beam in the intended direction). There are two main types of beamforming methods: analog beamforming (ABF) method and digital beamforming (DBF) method. In analog beamforming, a single signal is supplied to each antenna element in the array by passing it through an analog phase shifter where the signal is amplified and directed towards the desired receiver. Amplitude / phase variations are applied to the analog signal at the transmitter end where signals from different antennas are added before ADC conversion. Digital beamforming is based on the conversion of the RF signal at each antenna element into two streams of binary baseband signals representing the cosine and sine channels. These two digital baseband signals can be used to recover both the amplitude and phase of the signals received at each element of the array. The process of digital beamforming means that weighting is performed by a complex weighting function and then added together to form the desired output. Beam steering in DBF can be easily achieved by using signal processing techniques in the digital domain, thereby reducing the need for components such as phase shifters, time delay lines, and attenuators used in ABF.

[0102] Among others, there are a number of different digital beamformers that can be equipped in a system, including phase shift beamformers, minimum variance distortionless response (MVDR) beamformers, and linearly constrained minimum variance (LCMV) beamformers. Conventional beamformers delay the received signal at each antenna (delay-and-sum beamforming). In the case of narrowband, it is equivalent to multiplying the signal at each antenna by a phase coefficient.

[0103] The phase shift beamformer approximates the time delay beamformer for narrowband signals by phase-shifting the incoming signals. The phase shift beamformer belongs to the category of conventional beamformers.

[0104] The MVDR beamformer is a beamforming method that overcomes the problem of interference associated with conventional delay-and-sum beamforming. It preserves the signals from a specific desired direction and suppresses all signals incoming from other directions. The beamformer weighting is calculated by using W MVDR =R n -1 a / (a´R n -1 a). Here, R n is the noise + interference covariance matrix.

[0105] The LCMV beamformer is useful in dealing with the obvious self-nulling problem in the MVDR scheme. With this beamformer, it becomes possible to input multiple constraints with respect to the desired direction (target direction). The beamformer weighting is calculated by W LCMV =R n -1 C(CR n -1 C´) -1 d. Here, C is the constraint matrix, and d represents the signal gain due to the constraint. The LCMV beamformer algorithm can be used due to its significant benefits. Depending on the definition of the 2D or 3D matrix of element positions (in our case, 2D), the steering angle must be defined. The maximum and minimum limits (degrees) must be set with an angular step size that increases with each iteration. By defining the steering angle vector, each antenna element is digitally steered along its angular direction with a given angular step size. The sensor covariance matrix is defined based on the antenna element positions and the maximum allowable azimuth and elevation limits. Once the sensor covariance matrix and the steering vector are obtained, the gain for the weighting vector is determined. Then, the weighting vector is multiplied by the received data from each of the virtual channels to P DBF (x, y) = S L (k x , k y ) × w LCMV Obtain the digitally steered backscatter data given by using

[0106] At each point (59A) in FIG. 12, the recorded frequency spectrum is combined with the position information from the position confirmation subsystem (13 / 31) to obtain S(x, y, z, f). Here, (x, y, z) refers to the source aperture. S(x, y, z, f) represents the raw data or scattered data obtained by the test system.

[0107] In one embodiment according to FIG. 7, the test system may include the following subsystems. · A beam focusing antenna front-end subsystem (23) with a single transceiver. The antenna elements operate over a wide frequency range of 0.1 GHz to 10 GHz, preferably 0.1 GHz to 6 GHz, and are integrated with a metamaterial lens (47) enabling sub-wavelength high-resolution imaging. · A monostatic reflectometer array SiP subsystem (24) equipped with a transmitter and receiver RF chain for generating a stepped frequency continuous waveform in the frequency spectrum range of 0.1 GHz to 10 GHz, preferably 0.1 GHz to 6 GHz · A digital beamforming signal processing subsystem (25) that performs the reproduction of the spatial reflectivity (3D image) of the asset under inspection by adopting 31 multilayer media and various backward propagation algorithms suitable for the SFCW waveform · A position confirmation subsystem (31) on a moving platform that provides the position information of the system useful for the signal processing subsystem 25 to synthesize a large synthetic aperture for 3D image reproduction · An interface subsystem (27) that transfers the data after signal processing to a cloud server or a local tablet PC (15) and visualizes AUT. This visualization can be via a user interface (GUI). The user (9) can interact with the system by modifying specific interaction elements of the GUI.

[0108] In embodiments according to modalities 1A, 1B, 1C, 1D, and 1E, S(x, y, z, f) can be configured by using a monostatic array of reflectometers (23) (comprising antenna elements having metamaterial lenses) and associated reflectometer SiPs (24) instead of moving the test system at the source aperture or using digital beamforming. In the context of the systems disclosed herein, a reflectometer refers to a transmitting radar antenna element having a Schottky diode incorporated therein.

[0109] The monostatic array of reflectometers (23) and associated reflectometer SiPs (24) is shown in FIG. 7, which is an alternative upper architecture for a non-contact microwave test system. Each individual element in the monostatic array can be composed of antenna elements having metamaterial lenses (47) arranged in a rectangular array configuration. The output is directly obtained from the aperture of the antenna shown by (47C) in FIG. 10 instead of using a normal homodyne / heterodyne transceiver architecture. The output can be phase-referenced by integrating a zero-biased Schottky diode (43) at the aperture of the antenna. In this case, an external phase reference source is not required.

[0110] The monostatic reflectometer array SiP subsystem (24) according to the embodiment of FIG. 7 can be implemented as shown in FIG. 9. In FIG. 9, the SiP subsystems (11, 24) can consist of a digital - analog converter (DAC) controlled by a signal processing subsystem (12, 25). The DAC is used to control a voltage - controlled oscillator (VCO) (39). A number of SP4T switches (40) can be used to switch to different elements in the antenna array (42). The Schottky diodes (43) are routed through a multiplexer (44) and mixed with the transmit - receive signals to provide a real - value output that is sampled by an analog - digital converter (ADC) (45) and input to the signal processing subsystem (25). S(x,y,z,f), where (x,y,z) refers to the source aperture, is captured in a single shot in the architecture as its real - value output captured by the ADC (45) at various frequencies controlled by the VCO (39).

[0111] In all embodiments of the systems disclosed herein, an object in front of the system can be considered to consist of a number of point targets. If a point target is at position (x´,y´,z´), the reflectivity (qualitative image) function τ(x´,y´,z´,f) is related to the characteristics of the medium as indicated by the recorded frequency spectrum and the two - way dyadic Green's function (DGF) G RT (x,y,z;x´,y´,z´,f). The relationship is S(x,y,z,f)=τ(x´,y´,z´,f)×G RT (x,y,z;x´,y´,z´,f) given by. The G of the medium RT (x,y,z;x´,y´,z´,f) is G RT (r;r´,f)=G R (r;r´,f)×G R (r´;r,f). Note that r = (x,y,z) and r´=(x´,y´,z´).

[0112] In an air medium, the reflectance function can be calculated using the following procedure. a) The 2D fast Fourier transform (FFT) of S(x, y, z, f) is calculated as S(k x , k y , z, f). The wave number k is related to the frequency f by using the relation: k = c / f. b) Phase compensation is performed by multiplying S(k x , k y , k z , f) by a coherence filtering multiplier

Number

Number

[0113] The overall procedure of image reproduction can be condensed by the following equation.

Number

[0114] In one embodiment 65A: 65, to focus on a specific layer z´ = 0 to z´ max , an additional phase can be individually added to the collected frequency spectrum one layer at a time. This method can include the electrical, magnetic, and physical properties of different layers. In the spectral domain, the equation governing the focusing from the source aperture at z = 0 to the object in layer M at z´ = 0 to z´ max is given by [Equation] where d i represents the distance value of the interface separating layers i and i + 1, [Equation] and [Equation] is the permittivity of layer i.

[0115] The overall procedure of the individual algorithm can be reduced using the following equation: [Equation] .

[0116] However, the above model does not consider the discontinuity between different layers. To account for this discontinuity, the Fresnel transmission coefficient can be used. The Fresnel transmission coefficient T i,i+1 from layers i and i + 1 is given by the equation: [Equation] is given by

[0117] The final formula for 3D image reproduction using the individual incorporation of phase changes in each layer and the incorporation of Fresnel coefficients that incorporate the discontinuities of different layers is

Number

[0118] Algorithm (65A) does not consider multiple reflections and attenuations by different layers. To incorporate layer attenuation and different characteristics, the DGF of the stratified layered medium can be used (65B). The recording frequency spectrum S(x, y, z, f) across the source aperture is related to the reflectivity function τ(x, y, z, x´, y´, z´, f) and the two-way DGF of the layered stratified medium G RT (x, y, z; x´, y´, z´, f) by the equation: S(x, y, z, f) = τ(x´, y´, z´, f) × G RT (x, y, z; x´, y´, z´, f) + v(x, y, z, f) where v(x, y, z, f) is additive noise.

[0119] The deconvolution for determining the reflectivity function can be performed by the equation:

Number

Number

[0120] The 3D reconstructed image from the signal processing subsystem 12 / 25 can be input to the interface subsystem 14 / 27, which can be a wired interface. In one embodiment, the interface subsystem 14 / 27 is implemented using an Ethernet interface and a USB interface. In one embodiment, the interface subsystem 14 / 27 is implemented using Bluetooth®, ZigBee®, WiFi, or LTE. In certain examples, 14 / 27 transfers data directly to a tablet / PC, and an application present on the PC / workstation is used to visualize the reflectance function τ(x´, y´, z´ = 0 to z´ m ). In one embodiment, the interface subsystem 14 / 27 transfers data to a cloud server. The data is remotely accessible using a web application in any computing system 15, including but not limited to workstations / PCs, tablet PCs, and mobile phones.

[0121] Figure 12 shows a particular embodiment of the visualization of the 3D reflectance function τ(x´, y´, z´ = 0 to z´ m ). The data calculated by the signal processing subsystem 12 / 25 is read and visualized as a 3D cube 66A. The slider 67 enables the visualization of any necessary slices along the x-axis, y-axis, and z-axis. In other embodiments, the visualization of the recorded reflectance function is performed as 3D voxels that give a realistic representation of the recorded data. In one embodiment, tools 68 are provided for operations such as changing the color scheme, introducing grid lines, introducing axes, and changing the viewpoint / field of view of the 3D cube. In one embodiment, means 66B for visualization in a 2D field of view and manual embedding object tagging are provided. In one embodiment, means 66B for manual tagging of defects identified from the data are provided. In other embodiments, means 66B for automatic tagging of embedded objects identified from the data by an AI-based algorithm operating in the background are provided. In other embodiments, means 66B for automatic tagging of embedded defects identified from the data by an AI-based algorithm operating in the background are provided.

[0122] In the exemplary architectures shown in FIGS. 6 and 7, the various subsystems can be implemented for the various modalities 1A, 1B, 1C, 1D, and 1E. The overall operation of the various modalities will be described as follows.

[0123] In an embodiment of 1A (handheld non-contact microwave test system), the system can be composed of a beam focusing antenna front-end subsystem 23 having a single transceiver. 1A can include a positioning subsystem 13 capable of providing accurate coordinates for processing using a signal processing subsystem 12. 1A can move over an area in a non-uniform manner, and the recorded data is fused with the coordinate information from the positioning subsystem 13 to obtain S(x, y, z, f). The signal processing subsystem 12 can be used to reproduce the reflectivity function τ(x´, y´, z´ = 0 to z´ m ) can be used. τ(x´, y´, z´ = 0 to z´ from the signal processing subsystem 12 m ) is routed by an interface subsystem 14 to a cloud server or a local tablet PC 15 and may be visualized by the aforementioned GUI, and the user 17 can view the GUI and perform data interpretation.

[0124] In one embodiment of 1A, the system can be composed of a MIMO front-end subsystem 10 having a plurality of transceivers and an associated SiP subsystem 11. 1A can move over an area with high-speed non-uniform movement (because a large number of antennas configured virtually cover a larger aperture in a single shot), and the recorded data is fused with the coordinate information from the positioning subsystem 13 to obtain S(x, y, z, f). The signal processing subsystem 12 can be used to reproduce the reflectivity function τ(x´, y´, z´ = 0 to z´ m ) can be used. τ(x´, y´, z´ = 0 to z´ from the signal processing subsystem 12 m) is routed by the interface subsystem 14 to the cloud server or the local tablet PC 15, may be visualized by the aforementioned GUI, and the user 17 can view the GUI and perform data interpretation.

[0125] In one embodiment of 1A, the front-end subsystem may be implemented as a monostatic array of reflectometers 47C and the associated SiP subsystem 24. S(x, y, z, f) can be captured in a single shot without moving the scanner. The signal processing subsystem 12 is used to reproduce the reflectance function τ(x´, y´, z´ = 0 to z´ m ) can be used. τ(x´, y´, z´ = 0 to z´ from the signal processing subsystem 12 m ) is routed by the interface subsystem 14 to the cloud server or the local tablet PC 15, may be visualized by the aforementioned GUI, and the user 17 can view the GUI and perform data interpretation.

[0126] In an embodiment according to 1B (wheel-equipped hand-held non-contact test system), the system may be composed of a beam focusing antenna front-end subsystem 23 having a single transceiver. 1B may include a position confirmation subsystem 13 that can provide accurate coordinates for processing using the signal processing subsystem 12. 1B can move over the area in a uniform manner (because the scanner has wheels), and the recorded data is fused with the coordinate information from the position confirmation subsystem 13 to obtain S(x, y, z, f). The signal processing subsystem 12 is used to reproduce the reflectance function τ(x´, y´, z´ = 0 to z´ m ) can be used. τ(x´, y´, z´ = 0 to z´ from the signal processing subsystem 12 m ) is routed by the interface subsystem 14 to the cloud server or the local tablet PC 15, may be visualized by the aforementioned GUI, and the user 17 can view the GUI and perform data interpretation.

[0127] In one embodiment of 1B, the scanner may be composed of a MIMO front-end subsystem 10 having a plurality of transceivers and an associated SiP subsystem 11. 1B can move over an area with a uniform motion in larger steps, which means a faster scan (because a large number of virtual-sided antennas cover a larger aperture in a single shot), and the recorded data is fused with the coordinate information from the positioning subsystem 13 to obtain S(x, y, z, f). The signal processing subsystem 12 can be used to reproduce the reflectivity function τ(x´, y´, z´ = 0 to z´ m ). The τ(x´, y´, z´ = 0 to z´ m ) from the signal processing subsystem 12 may be routed by the interface subsystem 14 to a cloud server or a local tablet PC 15 and visualized by the aforementioned GUI, and the user 17 can view the GUI and perform data interpretation.

[0128] In one embodiment of 1B, the front-end subsystem may be implemented as a monostatic array of reflectometers 47C and an associated SiP subsystem 24. S(x, y, z, f) can be captured in a single shot without moving the scanner. The signal processing subsystem 12 can be used to reproduce the reflectivity function τ(x´, y´, z´ = 0 to z´ m ). The τ(x´, y´, z´ = 0 to z´ m ) from the signal processing subsystem 12 may be routed by the interface subsystem 14 to a cloud server or a local tablet PC 15 and visualized by the aforementioned GUI, and the user 17 can view the GUI and perform data interpretation.

[0129] In an embodiment related to 1C (a test system mounted on a drone), the system may be composed of a beamforming antenna front-end subsystem 23 having a single transceiver. 1C can determine coordinates from a position confirmation subsystem 31 in the drone that can provide accurate coordinates for processing using a signal processing subsystem 25. 1C can move over the area in a uniform manner or be pre-plannable, and the recorded data is fused with the coordinate information from the position confirmation subsystem 31 to obtain S(x, y, z, f). The signal processing subsystem 25 can be used to reproduce the reflectivity function τ(x´, y´, z´ = 0 to z´ m ). τ(x´, y´, z´ = 0 to z´ m ) from the signal processing subsystem 25 may be routed by an interface subsystem 27 to a cloud server or a local tablet PC 15 and visualized by the aforementioned GUI, and the user 17 can view the GUI and perform data interpretation.

[0130] In one embodiment of 1C, the system may include a MIMO front-end subsystem 10 having a plurality of transceivers and an associated SiP subsystem 11. 1C can move over the area with a uniform movement in larger steps, which means a faster scan (because a multi-sided antenna composed of virtual ones covers a larger aperture in a single shot), and the recorded data is fused with the coordinate information from the position confirmation subsystem 31 to obtain S(x, y, z, f). The signal processing subsystem 12 can be used to reproduce the reflectivity function τ(x´, y´, z´ = 0 to z´ m ). τ(x´, y´, z´ = 0 to z´ m ) from the signal processing subsystem 12 may be routed by an interface subsystem 14 to a cloud server or a local tablet PC 15 and visualized by the aforementioned GUI, and the user 17 can view the GUI and perform data interpretation.

[0131] In one embodiment of 1C, the front-end subsystem can be implemented as a monostatic array of reflectometers 47C and the associated SiP subsystem 24. S(x, y, z, f) can be captured in a single shot without moving the scanner. The signal processing subsystem 12 can be used to reproduce the reflectance function τ(x’, y’, z’ = 0 to z’ m ). The τ(x’, y’, z’ = 0 to z’ m ) from the signal processing subsystem 12 can be routed by the interface subsystem 14 to a cloud server or a local tablet PC 15 and visualized by the aforementioned GUI, and the user 17 can view the GUI and perform data interpretation.

[0132] In the embodiments of 1D and 1E (test systems mounted on a robotic arm / crawler), the system can include a beam focusing antenna front-end subsystem 23 having a single transceiver. 1D can determine the coordinates from a position confirmation subsystem 31 in a robotic arm that can provide accurate coordinates for processing using the signal processing subsystem 25. 1D and 1E can move over the area in a uniform manner or can be pre-planned, and the recorded data is fused with the coordinate information from the position confirmation subsystem 31 to obtain S(x, y, z, f). The signal processing subsystem 25 can be used to reproduce the reflectance function τ(x´, y´, z´ = 0 to z´ m ). The τ(x´, y´, z´ = 0 to z´ m ) from the signal processing subsystem 25 can be routed by the interface subsystem 27 to a cloud server or a local tablet PC 15 and visualized by the aforementioned GUI, and the user 17 can view the GUI and perform data interpretation.

[0133] In one embodiment of 1D and 1E, the scanner may comprise a MIMO front-end subsystem 10 having a plurality of transceivers and an associated SiP subsystem 11. 1D and 1E can move over the area with a uniform motion in larger steps, which means faster scanning (because the multi-sided antennas, which are virtual, cover a larger aperture in a single shot), and the recorded data is fused with the coordinate information from the positioning subsystem 31 to obtain S(x, y, z, f). The signal processing subsystem 12 can be used to reproduce the reflectivity function τ(x´, y´, z´ = 0 to z´ m ). The τ(x´, y´, z´ = 0 to z´ m ) from the signal processing subsystem 12 may be routed by the interface subsystem 14 to a cloud server or a local tablet PC 15 and visualized by the aforementioned GUI, and the user 17 can view the GUI and perform data interpretation.

[0134] In one embodiment of 1D and 1E, the front-end subsystem may be implemented as a monostatic array of reflectometers 47C and an associated SiP subsystem 24. S(x, y, z, f) can be captured in a single shot without moving the scanner. The signal processing subsystem 12 can be used to reproduce the reflectivity function τ(x´, y´, z´ = 0 to z´ m ). The τ(x´, y´, z´ = 0 to z´ m ) from the signal processing subsystem 12 may be routed by the interface subsystem 14 to a cloud server or a local tablet PC 15 and visualized by the aforementioned GUI, and the user 17 can view the GUI and perform data interpretation.

[0135] Various modalities 1A, 1B, 1C, 1D, and 1E can be used for the inspection of a building, as shown by 71 in FIG. 16. The system can be equipped for the inspection of a tunnel, as shown by 72. The scanning means can be equipped for the inspection of a bridge, as shown by 73. The system is equipped for the inspection at the legs of a spherical tank / container, as shown by 74. These applications are not limited to the use cases described above and may include various applications of this technology in the NDT market.

[0136] Although some exemplary embodiments have been described herein, it should be apparent to those skilled in the art that the foregoing are merely exemplary and not limiting, and are presented by way of example only. Numerous variations and other exemplary embodiments are within the scope of those skilled in the art and are considered to fall within the scope of the present invention. In particular, many of the examples presented herein include specific combinations of method steps or apparatus elements, but it should be understood that those steps and those elements can be combined in other ways to achieve the same purpose. Steps, elements, and features described only in connection with one embodiment are not excluded from a similar role in other embodiments.

Claims

1. A non-contact microwave test system for through-sheath imaging of a test area, the system comprising: A front-end subsystem configured to transmit and receive electromagnetic waves with the test area; A system-in-package (SiP) subsystem comprising a transmitter and a receiver radio frequency (RF) chain, the system-in-package (SiP) subsystem generating a stepped frequency continuous wave (SFCW) waveform; A signal processing subsystem configured to perform reproduction of the spatial reflectivity of a heterogeneous multilayer medium in the test area; Comprising; Configured to operate in a frequency range of 0.1 GHz to 10 GHz; The front-end subsystem comprises at least one transmitter antenna and at least one receiver antenna, or at least one transceiver; Each antenna or transceiver is integrated with a metamaterial-based lens enabling sub-wavelength high-resolution imaging; The metamaterial-based lens is made of a double-negative material (DNG) having a negative refractive index characteristic enabling sub-wavelength high-resolution imaging, and includes a variable-size concentric periodic split-ring resonator (SRR) and concentric circular trace lines extending to the lowermost layer of the lens, the system.

2. The system according to claim 1, configured to acquire recorded broadband frequency domain data over a source aperture represented as S(x, y, z, f).

3. The system according to claim 1, wherein the signal processing subsystem comprises a backpropagation algorithm for reproduction of spatial reflectivity suitable for a multilayer medium and an SFCW waveform.

4. A position confirmation subsystem; An interface subsystem for reproduction of a high-resolution image; The system according to claim 1, further comprising.

5. The system according to claim 4, wherein the position confirmation subsystem comprises an optical flow sensor, an inertial measurement unit (IMU), and an atmospheric pressure sensor.

6. The system according to claim 4, wherein the interface subsystem transfers data from the signal processing subsystem to a cloud server or a local tablet PC for reproduction of the high-resolution image.

7. The front-end subsystem is a beamforming MIMO front-end subsystem comprising an array of transmit antennas and an array of receive antennas that form a virtual antenna array, which are time-division multiplexed based on the physical arrangement of the transmitter and receiver antennas. The system-in-package (SiP) subsystem is a MIMO SiP subsystem comprising the transmitter and receiver RF chains for generating the stepped frequency continuous wave (SFCW) waveform. The position confirmation subsystem is the system according to claim 4, which provides position information of the system for the signal processing subsystem to synthesize a large synthetic aperture for 3D image reproduction.

8. The front-end subsystem is a beamforming antenna front-end subsystem comprising a single transceiver. The system-in-package (SiP) subsystem is a monostatic reflectometer array SiP subsystem comprising the transmitter and receiver RF chains for generating the stepped frequency continuous wave (SFCW) waveform. The signal processing subsystem is a digital beamforming signal processing subsystem. The position confirmation subsystem is deployed on a mobile platform and provides position information of the system for the signal processing subsystem to synthesize a large synthetic aperture for 3D image reproduction, which is the system according to claim 4.

9. The system according to any one of claims 1 to 8, wherein each antenna element or transceiver operates in a frequency range of 0.1 GHz to 10 GHz.

10. The system according to claim 1, wherein the lens is disposed above the antenna element or transceiver for long-distance non-penetrating scanning.

11. Non-destructive inspection of facilities such as facade structures, exterior material systems, concrete columns and walls, indoor mechanical, electrical and plumbing (MEP) fixtures, water, oil and gas pipelines, metal parts, roads, tree trunks, tunnels, dams, bridges, etc., medical imaging, security monitoring, and for inventory sorting, a handheld type, a mounted / fixed type for payload transportation, an autonomous / semi-autonomous / controlled system selected from unmanned ground vehicles (UGVs), drones, robotic arms, crawler robots and / or combinations thereof, which is the system according to claim 1.

12. The system is configured to be handheld, and the front-end subsystem has a single-input single-output (SISO) configuration consisting of a single transceiver broadband antenna element, a monostatic array of antenna elements, or a MIMO array of antenna elements The system according to claim 11, comprising.

13. The system is a mounted / fixed, autonomous / semi-autonomous / controlled system for payload transportation selected from unmanned ground vehicles (UGVs), drones, robotic arms, and crawler robots, and the front-end subsystem has a beamforming antenna subsystem with a single transceiver, a MIMO subsystem with multiple transceivers, or a monostatic array of reflectometers The system according to claim 11, comprising.

14. A method for non-contact through-sheet imaging of a test area using the system according to claim 1, comprising: generating electromagnetic waves by the SiP subsystem, wherein a stepped frequency continuous wave (SFCW) waveform is generated by the SiP subsystem; transmitting the generated electromagnetic waves to the front-end subsystem via an RF interface; transmitting a backscattered signal to the front-end subsystem and receiving it from the test area; routing the received RF signal to the signal processing subsystem by the SiP subsystem for signal processing and reproduction of the spatial reflectivity of the heterogeneous multilayer medium in the test area; executing a 3D image reproduction algorithm and a data interpretation scheme by the signal processing subsystem to synthesize data from the SiP subsystem and the position confirmation subsystem and route it to the interface subsystem; routing the data interpretation and reproduced 3D image to a cloud server or a local tablet PC via wired or wireless transmission by the interface subsystem so that a user can view an image of the test area; A method comprising.

15. The method according to claim 14, wherein the backscattered signal from the test area is directly sampled at the aperture of the front-end subsystem by a reflectometer using a Schottky diode at the aperture of an antenna having a metamaterial-based lens.

16. The method according to claim 14, wherein a dead reckoning algorithm for an IMU is combined with an optical flow sensor to recover accurate coordinate information from the position confirmation subsystem.

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