A device for electromagnetic characterization of the internal features of an object and a method for manufacturing the device.

Abstract

An apparatus for electromagnetically characterizing the internal features of an object includes a lens disposed between a source of electromagnetic energy and the object. The lens is made of a first material having a first dielectric constant. An opening is formed in the first material, the opening containing or configured to receive one or more second materials having a corresponding second dielectric constant different from the first dielectric constant. The opening is configured such that the lens has a gradient refractive index when the opening contains one or more second materials. An electromagnetic wave generated by the source and incident as a spherical wave onto a first surface of the lens exits a second surface of the lens substantially as a plane wave. The second surface of the lens contacts a receiving surface of the object, and the refractive index of the lens at the second surface of the lens substantially matches the refractive index of the object at the receiving surface to increase the penetration of the plane wave into the object.

Description

Technical Field

[0001] This invention relates to electromagnetic characterization of materials, and more particularly to an apparatus for electromagnetic characterization of the internal features of an object, and a method for manufacturing the apparatus. Background Technology

[0002] The term "non-destructive testing (NDT)" refers to methods for evaluating the characteristics of a material or object without damaging it. NDT is widely used in many different industries, including, for example, gas and oil, aerospace, agriculture, and healthcare. For instance, NDT can be used to image the internal materials of glass fiber reinforced polymers, detect defects inside railway wheels, assess the condition of non-metallic pipes, diagnose breast cancer, brain injuries, or for routine human imaging. Specifically, these methods can diagnose defects and / or assess changes in an object by analyzing the behavior of waves reflected from (or transmitted through) internal features of the object. Equipment used for NDT typically consists of hardware and software components. The hardware components may include a single antenna or an array of antennas (sensors) that emits waves (electromagnetic or acoustic waves) toward a medium and captures the emitted or reflected waves. Any changes in the amplitude or phase of the signal (e.g., a shift in resonant frequency) are measured and processed by the software components to detect anomalies in the object.

[0003] Ultrasonic testing (UT) is considered the most widely used nondestructive testing method, involving the scattering of high-frequency waves. While effective, UT suffers from several drawbacks, including: 1) requiring probe replacement to probe deeper features within an object, increasing the cost of UT equipment; 2) UT requires a matching medium (e.g., a water-based gel) to avoid mismatches between the transmission characteristics of air and the transmitted characteristics of the object being tested (incorrect or insufficient application of the matching gel is one of the main reasons for poor performance of UT systems); and 3) UT operators need to maintain a constant beam along the detection direction, limiting the feasibility of evaluating objects with curved surfaces. These challenges of UT and other industrial NDT systems are primarily due to a lack of consideration for the properties of the object being tested. For example, the same ultrasonic probe is used to detect decay in wood, cracks in ceramics, and cementum cancer. However, these materials have very different and unique material characteristics, leading to variable mismatches between the probe and the medium under investigation, resulting in reduced transmission power / penetration depth. To mitigate this problem, higher power signals are used, which increases detection costs and noise levels.

[0004] Electromagnetic medical imaging, a healthcare subcategory of the NDT industry, attempts to mitigate this problem by using a custom-designed matching medium between the antenna and the human body, which is highly lossy. However, the addition of a matching medium increases system complexity in terms of weight, fluid leakage, and cumbersome antenna placement. Therefore, the feasibility of this approach is limited to a very small number of relatively simple applications, such as breast cancer, where the imaging object is directly within the matching medium. As an alternative solution, body-coupled and biomatched antennas have been proposed. Unlike conventional antennas designed in free space, these antennas are designed for direct contact with the human body to minimize the mismatch between the antenna and the body. While effective, these antennas have compact apertures, thus limiting the energy they can radiate. Increasing the antenna size to increase penetration depth also increases the radiating area, causing the signal to propagate into undesirable neighboring areas.

[0005] In view of the above, the inventors have identified a general need for a structure capable of bridging the gap between the antenna and the object being detected without complicating the detection device or limiting its detection capabilities. Therefore, it is desirable to overcome or mitigate one or more difficulties of the prior art, or at least provide a useful alternative. Summary of the Invention

[0006] According to some embodiments of the present invention, an apparatus for electromagnetically characterizing the internal features of an object is provided. The apparatus includes a lens disposed between a source of electromagnetic energy and the object. The lens is made of a first material having a first dielectric constant. An opening is formed in the first material, the opening containing one or more second materials or configured to receive one or more second materials. The second materials have a corresponding second dielectric constant different from the first dielectric constant. The opening is configured such that the lens has a graded refractive index when the opening contains one or more second materials. An electromagnetic wave generated by the source and incident as a spherical wave onto the first surface of the lens exits the second surface of the lens approximately as a plane wave. The second surface of the lens contacts a receiving surface of the object, and the refractive index of the lens at the second surface of the lens approximately matches the refractive index of the object at the receiving surface to increase the penetration of the plane wave into the object.

[0007] The device may include a source of electromagnetic energy.

[0008] The opening may contain one or more second materials.

[0009] In some embodiments, the second surface of the lens has a non-planar shape that conforms to the receiving surface of the object.

[0010] In some embodiments, one or more second materials include at least one material having a dielectric constant greater than that of the first dielectric constant.

[0011] In some embodiments, one or more second materials include at least one material having a dielectric constant smaller than that of the first dielectric constant.

[0012] In some embodiments, a second material is arranged in the opening such that the plane wave is deflected from the incident direction at the receiving surface of the object and travels in different directions within the object.

[0013] The object can be a part of the human body.

[0014] In some embodiments, the first material is a 3D printing material, and one or more second materials include water.

[0015] In some embodiments, the openings in the first material are arranged in multiple layers.

[0016] In some embodiments, the opening is a cylindrical opening, and the cylindrical openings in each layer have the same corresponding radius, while the cylindrical openings in different layers have correspondingly different radii.

[0017] According to some embodiments of the present invention, a method for manufacturing an apparatus for electromagnetically characterizing the internal features of an object is provided. The method includes forming a body made of a first material having an opening, the first material having a first dielectric constant, and the opening being configured such that when the opening contains one or more predetermined second materials having a corresponding second dielectric constant different from the first dielectric constant, the resulting spatial configuration having a dielectric constant forms a gradient refractive index lens, wherein an electromagnetic wave incident as a spherical wave on a first surface of the lens departs from a second surface of the lens substantially as a plane wave, the second surface of the lens is in contact with a receiving surface of the object, and the refractive index of the lens at the second surface of the lens substantially matches the refractive index of the object at the receiving surface, such that a matching medium is not required.

[0018] This method may include a source that provides electromagnetic energy.

[0019] The method may include introducing one or more predetermined second materials into an opening in a first material.

[0020] The method may include introducing one or more predetermined second materials into a selected corresponding opening in an opening in a first material to guide a plane wave along a specific direction within the object.

[0021] In some embodiments, the method includes dynamically controlling the introduction of one or more predetermined second materials into a selected corresponding opening in an opening in a first material, and the removal of one or more predetermined second materials from a selected corresponding opening in an opening in the first material, to dynamically guide plane waves in different directions within the object.

[0022] In some embodiments, the body made of the first material is formed such that the second surface of the lens has a non-planar shape that conforms to the receiving surface of the object.

[0023] In some embodiments, the forming step includes 3D printing a body made of a first material having openings.

[0024] In some embodiments, the method includes: applying an optimization method that maximizes the transmission coefficient of the lens while minimizing the reflection coefficient of the lens to determine the structure of the opening.

[0025] An apparatus for electromagnetic characterization of the internal features of an object is also described herein, the apparatus comprising:

[0026] (i) The source of electromagnetic energy; and

[0027] (ii) A lens disposed between a source and an object and in contact with the object, the lens being made of a first material having a first dielectric constant, the first material having an opening that contains one or more second materials or is configured to receive one or more second materials, the second materials having a corresponding second dielectric constant different from the first dielectric constant, the opening being configured such that: the lens has a gradient refractive index when the opening contains one or more second materials, wherein an electromagnetic wave generated by the source and incident as a spherical wave onto the first surface of the lens leaves the second surface of the lens as a plane wave, and the corresponding refractive index of the lens at the second surface of the lens matches the corresponding refractive index of the corresponding surface of the object receiving the plane wave, to increase the penetration of the wave into the object.

[0028] A method for manufacturing an apparatus for electromagnetic characterizing the internal features of an object is also described herein, the method comprising:

[0029] (i) A source that provides electromagnetic energy; and

[0030] (ii) A body is formed from a first material having an opening, the first material having a first dielectric constant, and the opening is configured such that when the opening contains one or more predetermined second materials having a corresponding second dielectric constant different from the first dielectric constant, the resulting spatial configuration with dielectric constant forms a gradient refractive index lens, wherein an electromagnetic wave, as a spherical wave, is incident on the first surface of the lens and leaves the second surface of the lens as a plane wave, and the corresponding refractive index of the lens at the second surface of the lens matches the corresponding refractive index of the corresponding surface of the object receiving the plane wave, such that no matching medium is required. Attached Figure Description

[0031] The following description, with reference to the accompanying drawings, illustrates some embodiments of the invention by way of example only, in which:

[0032] Figure 1 This is a schematic diagram of a graded index (GRIN) lens according to an embodiment of the present invention, which is arranged between a radiating antenna and an object or medium to be evaluated or imaged.

[0033] Figure 2 This explains Figure 1 A schematic diagram illustrating the working principle of a GRIN lens that converts electromagnetic waves from spherical waves into plane waves;

[0034] Figure 3 This is a schematic diagram showing a GRIN lens initially formed (right) as a body made of a matrix material with empty (i.e., air-filled) cylindrical openings of different radii, and (left) a GRIN lens after the openings are filled with a liquid (e.g., water) having a dielectric constant different from that of the matrix material.

[0035] Figure 4 This is a schematic cross-sectional side view of a multilayer GRIN lens with N different layers, each layer having a corresponding thickness (corresponding to a distance d from the lens surface). i and dielectric constant ε i ;

[0036] Figure 5 and Figure 6 These are corresponding cross-sectional side views of simulated models of a 250mm thick concrete slab radiated by a 1GHz electromagnetic wave emitted from an antenna, with and without a double-layer GRIN lens arranged between the antenna and the slab (configured to match the dielectric constant of the concrete), respectively. The electric field intensity within the concrete slab is represented by grayscale levels.

[0037] Figure 7 It is in having Figure 6 GRIN lenses and those without Figure 6 In the case of a GRIN lens, the reflected wave coefficient (S) 11 According to the electromagnetic wave frequency curve;

[0038] Figure 8 It is in having Figure 6 GRIN lenses and those without Figure 6 A graph showing the electric field strength within a concrete slab in the case of a GRIN lens, based on the distance between the slab and the antenna.

[0039] Figure 9 and Figure 10 It is a corresponding cross-sectional side view of a simulated model of a sandy body radiated by 1 GHz electromagnetic waves emitted from the antenna and passing through three layers of GRIN lenses, wherein most of the openings in the lens matrix material are empty, and only the openings located at the left and right ends of the lens are filled with water to guide the waves toward that side of the lens.

[0040] Figure 11 and Figure 12 The images are cross-sectional side views of a simulated human torso radiated by 1 GHz electromagnetic waves emitted from a human body-matched antenna and a multi-layered GRIN lens, illustrating how the GRIN lens can generate relatively uniform plane waves that propagate through the human body, in contrast to the rapidly decaying spherical waves from the human body-matched antenna.

[0041] Figure 13 It is a schematic cross-sectional side view of a model of a human torso, in which a curved “human-fit” GRIN lens is conformally arranged on the human torso and located between the torso and the antenna.

[0042] Figure 14 yes Figure 13 The corresponding simulation of the arrangement shows a relatively constant electric field strength within the portion of the torso directly aligned with the antenna.

[0043] Figure 15 It is in having Figure 13 and Figure 14 The reflected wave coefficient (S) in the case of a curved GRIN lens and a corresponding flat GRIN lens with a matching refractive index. 11 Based on the electromagnetic wave frequency curve; and

[0044] Figure 16 This is a flowchart of a method for electromagnetically characterizing the internal features of an object according to an embodiment described in the present invention, the method including the steps of a method for manufacturing an apparatus for electromagnetically characterizing the internal features of an object. Detailed Implementation

[0045] Embodiments of the present invention include an apparatus for electromagnetically characterizing the internal features of an object, and a method for manufacturing such an apparatus. The apparatus includes a lens made of a first material having an opening in the first material containing a second material (in some embodiments, multiple second materials). These materials have different dielectric constants, and the opening and dielectric constants are configured such that the lens has a graded refractive index, wherein an electromagnetic wave incident as a spherical wave on a first surface of the lens exits the second surface of the lens substantially as a plane wave, and the corresponding refractive index of the lens at the second surface of the lens matches the corresponding refractive index of the object's receiving plane wave surface ("receiving surface") to increase the penetration of the plane wave through the object.

[0046] In some embodiments, the lens is in the form of a flat plate or "plate" made of a first material having cylindrical openings arranged in multiple layers within the first material. However, typically, the lens and the openings within the lens can have arbitrary shapes. The dielectric properties of each layer of the lens are controlled by filling the openings with one or more selected materials (typically fluids) and / or by selecting the size and / or spatial arrangement of the openings (e.g., by selecting the radius of the cylindrical openings) to achieve a gradual transition of electromagnetic waves from air to a non-air medium while calibrating the waves along a desired direction. Typically, the effective dielectric constant of a layer (or other region) of the lens can be controlled by appropriately selecting the dielectric constant of the first material, the dielectric constant of the second material (or, in the case of multiple second materials, multiple dielectric constants), and the spatial configuration of one or more second materials within the first material. Typically, the dielectric constants of the first material and the second material are chosen to be completely different. For example, the first material may be a high dielectric constant material and the second material may be a low dielectric constant material, or the first material may be a low dielectric constant material and the second material may be a high dielectric constant material. According to this disclosure, the appropriate selection of the first and second materials will be apparent to those skilled in the art.

[0047] Gradient-index (GRIN) lenses are formed by designing a refractive index gradient within the lens. Unlike conventional lenses, GRIN lenses can be designed with a flat shape and are tailored to convert incident waves into plane waves that travel in the desired direction. Previously, GRIN lenses were typically constructed using stacks of dielectric materials with different dielectric constants selected based on radiation requirements. However, GRIN lenses have not previously been used for dielectric matching constructions for NDT (including electromagnetic medical diagnostic applications) for several reasons. In particular, NDT applications typically operate at low microwave frequencies, requiring physically large lenses, which is impractical for compact systems or situations with limited workspace. Therefore, NDT applications are considered useless at frequencies below 10 GHz, and to compensate for the high absorption rates at higher frequencies, electromagnetic sources operate at increased power to achieve the desired penetration of electromagnetic waves into the object being analyzed. However, high power cannot be used in some NDT applications that require shielding and compliance with safety regulations, such as medical diagnostic applications. Furthermore, lens structures are generally considered to be focusing structures and are thought to be meaningful only for frequencies at and above the K-band (i.e., above 18 GHz).

[0048] The embodiments described in this invention include a GRIN lens having a lens layer, the GRIN lens being configured to maximize signal transmission from an antenna to the object under study by causing a spherical wave to gradually transform from air through a gradient dielectric constant layer into a plane wave at the object, as in... Figure 1 and Figure 2 It is shown schematically in the diagram.

[0049] As in Figure 16 The method for electromagnetically characterizing the internal features of an object includes the steps of fabricating a specific lens structure / construction for a given electromagnetic wave frequency and the object, and the steps of analyzing or imaging these features using the resulting device. In the described embodiment, the lens structure is fabricated using 3D printing technology and takes the form of a planar sheet having multiple openings at one end in the form of cylindrical openings, as shown in... Figure 3As shown in the diagram. To reduce manufacturing costs for mass production applications, the lens can be formed from 3D printing materials. It will be apparent to those skilled in the art that the lens structure can be formed from low-dielectric-constant or high-dielectric-constant materials. The resulting "perforated" structure allows for the grading and control of the lens's dielectric constant by filling the holes with a high-dielectric-constant filling material (e.g., water) to increase the dielectric constant, or by filling the holes with a low-dielectric-constant material (e.g., glycerol) to decrease the dielectric constant (relative to the lens material), or by leaving the holes empty (i.e., filling them with air). Furthermore, the perforated structure also aids in the formation of GRIN lenses by independently designing gradients in the dielectric properties of different layers of the lens. This can be easily achieved by changing the size of the openings (in this example, by changing the radius of the cylindrical opening) and / or the filling material, which can be solid, liquid, or gas.

[0050] To design medium-matched GRIN lenses, it is essential to understand wave propagation behavior within multilayer media with varying dielectric properties. The general form of multilayer wave propagation theory is detailed in Chew, Weng Cho's "Waves and fields in inhomogeneous media," IEEE Press, 1995 ("Chew"), and analysis is performed using generalized reflection and transmission coefficients. To utilize this theory and develop design methods, multilayer structures, such as those in… Figure 4 As shown in the figure. This structure consists of N layers, where the dielectric constant of each layer is ε. i d i It is the distance from the surface of the structure to the interface between layer i and layer i+1. Figure 4 In the diagram, region 1 represents air, and region N represents the object or medium being detected. To simplify the analysis of wave behavior, it is assumed that the incident wave has TE polarization and a normal incident angle.

[0051] The generalized reflection coefficient is defined as the ratio of the amplitude of the reflected wave to the amplitude of the incident wave at a distance d1 from the surface, while the generalized transmission coefficient is the ratio of the amplitude of the transmitted wave in region N to the amplitude of the incident wave in region 1. As described in Chew, the generalized reflection coefficient is obtained using the following formula:

[0052]

[0053] Among them, R i，i+1 and R i+1，i R is the Fresnel reflection coefficient at the interface between layer i and layer i+1, and vice versa. i，i+1 and R i+1，i It can be limited to:

[0054]

[0055]

[0056] in

[0057]

[0058] In equation (1), T i，i+1 and T i+1，i It is the Fresnel transmission coefficient at the interface between layer i and layer i+1, and vice versa, T i，i+1 and T i+1，i It can be limited to:

[0059]

[0060]

[0061] The generalized transmittance is defined as:

[0062]

[0063] Wherein, S is given by the following equation:

[0064]

[0065] Design Methodology:

[0066] The ultimate goal of theoretical analysis of the lens structure is to determine d. i and ε i The optimal values ​​are determined to minimize the generalized reflection coefficient at the air-lens interface and maximize the generalized transmission coefficient from air to the target medium (layer N). The first step in the design methodology is to determine the number of layers forming the GRIN lens, as increasing the number of layers provides a smoother transition; therefore, this involves a trade-off between the complexity of the lens and the number of degrees of freedom for designing the matching lens. The next step is to determine the initial values ​​for the dielectric constant and thickness of each layer. At this stage, the dielectric constant (ε) value is set to increase from the dielectric constant of air (ε0 = ε1 = 1) to the dielectric constant of the target medium (i.e., ε1 < ε2 < ... < ε). N The values ​​of ) are determined by using standard optimization methods to optimize the generalized reflection coefficient and generalized transmission coefficient. Although a genetic algorithm is used in the described embodiment, suitable alternative optimization methods will be apparent to those skilled in the art. Since the field emitted by the excitation feed through the antenna is equivalent to a plane wave with different incident angles (see...), Figure 2Therefore, the values ​​under normal incidence are used as initial design parameters. In the following steps, the final values ​​of dielectric constant and layer thickness are optimized by minimizing the antenna's return loss and maximizing penetration into the target object or medium; for example, using simulators such as CST microwave studio or Ansys Electronic Desktop.

[0067] The conventional method for fabricating layers with a desired dielectric constant value is to use existing ceramics or high-dielectric-constant dielectrics. However, this limits the dielectric constant value to that of available prefabricated ceramics / dielectrics. Furthermore, it restricts the feasibility and flexibility of lenses to certain shapes, such as flat surfaces. To mitigate this problem, a dielectric constant value can be obtained by providing openings or holes in other homogeneous media, such as in… Figure 3 As shown in the figure. These holes are filled with water or other suitable materials (most conveniently fluids) to provide the desired dielectric constant value. For example, as described in Mei, Zhong Lei, Jing Bai, and Tie Jun Cui, “Gradient exponential metamaterials realized by a borehole array,” Journal of Physics D: Applied Physics 43.5 (2010): 055404, in Figure 3 The effective dielectric constant of each layer of the structure shown can be approximated as:

[0068] ε eff =ε m f1+ε h f2 (9)

[0069] Where, ε m ε is the dielectric constant of the matrix medium (e.g., polylactic acid). h f1 and f2 are the dielectric constants of the second (introduced) material (e.g., water), and the volume fractions of the matrix material and the second material, respectively.

[0070] The resulting lens can be used to: 1) increase penetration depth, 2) change the intensity of the electric field in a desired direction, and 3) concentrate energy in a specific region within the target object / medium. Furthermore, since the dielectric constant of the layer can be easily controlled using a fluid filler, the exit surface of the lens can be non-planar, allowing the lens to conform to the corresponding complementary non-planar (e.g., curved) receiving surface of the object being detected, thereby avoiding any need for a matching medium between the lens / antenna and the object.

[0071] Example I - Industrial Applications

[0072] The simplest case in NDT is when the object under study is radiated by an antenna / sensor and no matching medium is required. This is generally not a problem if the object's dielectric properties are the same as air's. However, if the medium has a high dielectric constant (e.g., concrete has an ε-coulomb at 1 GHz), then... r =4.7), then this difference will cause a matching problem. To demonstrate this phenomenon, the CST microwave studio was used to simulate a 250mm thick concrete slab radiated by a microstrip-fed slot antenna operating at 0.75GHz to 1GHz and located at a distance of 50mm from the concrete slab. Figure 5 As shown, most of the radiated wave is reflected at the air-concrete boundary 502, and only a small portion of the wave penetrates into the concrete. This mismatch is also evident from the antenna's reflection coefficient, as shown in... Figure 7 As shown in the diagram. Instead of using an external matching medium, a matched GRIN lens with 11 openings in each of the two layers is directly placed on the object being detected and radiated by an antenna. Following the design and manufacturing method described above, the resulting optimized dual-layer GRIN lens has aperture diameters of r1 = 2.2 mm and r2 = 3.45 mm, where the spacing between adjacent openings is 6.9 mm and 4.4 mm, respectively. In this example, the ultimate goal of the design is to maximize the electric field strength at the center of the concrete slab, enabling the characterization or imaging of the deepest target features (e.g., cracks) within the slab by applying the GRIN lens to the opposite surfaces of the slab. Dielectric constant values ​​were calculated for each layer, which is composed of perforated polylactic acid, in which the openings are filled with water (see [reference]). Figure 6 (See illustration). A genetic algorithm in CST software is then used to optimize the aperture diameter and the spacing between layers of the apertures. Typically, the number of apertures should be large enough to at least cover the hole of the excitation antenna, such as the width of a slot antenna. (See illustration). Figure 8 As shown, the lens increases the electric field strength at the center of the plate (z = 175 mm) by 8 dB (V / m). Furthermore, Figure 8 It was also shown that the electric field strength within the substrate at a depth of z = 75 mm could be increased by up to 15 dB. This is because the dielectric constant increases from ε in the gradient lens layer. r =1 gradually transforms into ε r =4.7, thus the antenna's reflection coefficient is also improved over a wide operating frequency range of 0.65GHz to 1.4GHz.

[0073] Example II - Beam / Electric Field (E-Field) Guiding

[0074] In any non-destructive testing scenario, the following situation arises: the antenna / sensor beam needs to be guided to radiate in directions other than the aiming direction. In ultrasonic probes, this is accomplished through mechanical / manual movement by the operator, resulting in errors related to both the operator and the mating medium. The operator-related error is caused by natural human movement, while the mating medium-related error is caused by variations in the thickness of the mating medium. For the mating medium to be effective, it needs to have a uniform thickness across all parts of the interface. This is not feasible for planar sensors on curved surfaces, as they create uneven gaps between the contact and non-contact portions of the sensor and the surface of the object under study.

[0075] The GRIN lens structure described herein can be configured to alter the beam direction by changing the gradient of a small portion of the lens through water filling only some of the openings in each layer and leaving the others empty (i.e., containing air) or filled with different materials having a selected dielectric constant. This allows the wave to be statically or dynamically guided to the desired direction. In static mode, the dielectric properties are selected to be specific to each direction. Conversely, in dynamic or reconfigurable mode, a pumping structure is used to dynamically control the flow of water (or other fluid or non-fluid materials). For example, in Figure 9 and Figure 10 The image illustrates a static lens configuration with two scanning modes for analyzing sand. In this example, the lens has three layers with 11 openings, the radii of the openings in each layer being 3.2 mm, 2.65 mm, and 2 mm, respectively, and the spacing between adjacent openings in each layer being 5.1 mm, 6.2 mm, and 7.5 mm, respectively. For dynamic guidance of the planar beam, a standard fluid pump, commonly used in the microfluidics and biotechnology industries, can be used to dynamically fill and empty selected openings within the lens.

[0076] Example III - Biomedical Applications

[0077] Electromagnetic imaging / diagnostic systems for biomedical applications are a subcategory of nondestructive testing. Because the detection medium is the human body, these systems differ significantly from those used in industrial applications. Biomedical applications are strictly regulated to ensure safety precautions. Therefore, limitations are imposed on maximum transmittable power levels, the chemicals used in the medium mixture, and any direct contact between metal components and the human body. To achieve meaningful penetration within the human body, which can lead to attrition, the antenna needs to operate at a relatively low microwave frequency of approximately 1 GHz, requiring a large antenna capable of covering a large portion of the body. This presents challenges for imaging algorithms / signal processing techniques that use differential comparison methods and require two different focused beams covering only a small target area of ​​the body (e.g., the left and right lobes of the liver) and a comparison of the behavior of scattered waves. Furthermore, the shape and dielectric properties of different parts of the human body vary significantly, necessitating adjustments to the antenna configuration for optimal operation. Considering the simplicity of adjusting dielectric properties and the flexibility of wave propagation design, the lens structure described herein accommodates all these requirements.

[0078] To demonstrate the effectiveness of the lens structure, a torso-matched four-layer GRIN lens was designed and manufactured using the method described above. Each layer has 11 cylindrical openings, with diameters of r1 = 1.95 mm, r2 = 2.55 mm, r3 = 2.9 mm, and r4 = 3.8 mm, and spacings of the openings in each layer of 4.2 mm, 5.9 mm, 6.6 mm, and 7.8 mm, respectively.

[0079] To highlight the differences in the behavior of propagating waves, in Figure 11 and Figure 12 The performance of the GRIN lens antenna was compared with that of a human-matched / coupled antenna operating in the same frequency band. The human-matched antenna was designed on a printed circuit board (made of FR4 in this example) and simulated near a material similar to the human body. Both antennas were simulated on a two-layer structure, where the first layer represents human skin and the second layer represents the properties of ordinary human tissue within the human torso. Two significant differences were observed; firstly, the penetration depth was significantly greater, and secondly, the strength of the GRIN lens antenna at the center of the structure, at z = 175 mm, was 35 dB (V / m) stronger than that of the human-matched design. Furthermore, compared to... Figure 11 Compared to the spherical radiation generated by the human-matched antenna shown in the figure, in Figure 12 The wave propagation generated by the lens structure occurs as a plane wave. These factors together improve the device's sensitivity and accuracy to any changes in the body's tissues.

[0080] To enhance the performance of the lens structure described herein, the lens, having a curved exit surface, is manufactured to conform to the shape of the torso region of the object, as in... Figure 13 As shown in the diagram. This is done to avoid reflections caused by any gap between the flat lens exit surface and the curvature of the human body. The strength of the electric field of the curved structure (as shown in the diagram) Figure 14 (as shown in) and reflectance (as shown in) Figure 15 (As shown in the image) It remains strong and continuous.

[0081] Based on the above description, it is clear that the medium-matched GRIN lens described herein fulfills the following important requirements for NDT detection:

[0082] (i) Non-destructive systems can be optimized and customized for any application by simply changing the dielectric properties of the lens. This can be easily achieved by changing the number of layers of openings, the size of the openings in the lens medium, the spatial arrangement of the openings, and the volume ratio of air / water (or other material) in each opening.

[0083] (ii) The lenses can be manufactured cheaply and easily using 3D printing technology, which significantly reduces maintenance and replacement costs.

[0084] (iii) As spherical waves gradually transform into plane waves, reflections at the air / medium interface are reduced or eliminated. Therefore, the penetration depth increases without the need for any refractive index matching medium.

[0085] (iv) Due to the calibration of the electromagnetic waves by the lens and the gradually increasing refractive index (matching lens), the intensity of the electric field within the target medium increases. Therefore, the scattered signal from the medium is received with an improved signal-to-noise ratio (SNR).

[0086] (v) Unlike conventional NDT testing devices, the dielectric constant of the lens can be adjusted to maintain the lens's performance on non-flat surfaces and conform to the shape of the target medium.

[0087] (vi) By simply changing the material (e.g., the water-to-air gap) ratio in different directions, the intensity of the electric field within the target medium can be controlled in different directions.

[0088] Many modifications will be apparent to those skilled in the art without departing from the scope of the invention.

Claims

1. An apparatus for electromagnetically imaging internal features of an object including human body parts, comprising a lens disposed between a source of electromagnetic energy and the object, the lens being made of a first material having a first dielectric constant, the first material having an opening, the opening containing or configured to receive one or more second materials, the second materials having a corresponding second dielectric constant different from the first dielectric constant, the opening being configured such that: the lens has a graded refractive index when the opening contains the one or more second materials, wherein... The electromagnetic wave generated by the source and incident as a spherical wave onto the first surface of the lens leaves the second surface of the lens approximately as a plane wave. The second surface of the lens is in contact with the receiving surface of the object, and the refractive index of the lens at the second surface of the lens is approximately matched with the refractive index of the object at the receiving surface to increase the penetration of the plane wave into the object.

2. The device according to claim 1, wherein, The opening contains one or more of the second materials.

3. The device according to claim 1, wherein, The second surface of the lens has a non-planar shape that conforms to the receiving surface of the object.

4. The device according to claim 3, wherein, The one or more second materials include at least one material having a dielectric constant greater than that of the first dielectric constant.

5. The device according to claim 3, wherein, The one or more second materials include at least one material having a dielectric constant smaller than that of the first dielectric constant.

6. The device according to any one of claims 1-5, wherein, The second material is arranged in the opening such that the plane wave is deflected from the incident direction at the receiving surface of the object and travels in different directions within the object.

7. The device according to any one of claims 1-5, wherein, Electromagnetic radiation includes microwaves.

8. The device according to any one of claims 1-5, wherein, The first material is a 3D printing material, and the one or more second materials include water.

9. The device according to any one of claims 1-5, wherein, The openings in the first material are arranged in multiple layers.

10. The device according to claim 9, wherein, The opening is a cylindrical opening, and the cylindrical openings in each layer have the same corresponding radius, while the cylindrical openings in different layers have correspondingly different radii.

11. A method of manufacturing an apparatus for electromagnetically characterizing internal features of an object including human body parts, the method comprising forming a body made of a first material having an opening, the first material having a first dielectric constant, and the opening being configured such that: when the opening contains one or more predetermined second materials having a corresponding second dielectric constant different from the first dielectric constant, the resulting spatial configuration having a dielectric constant forms a lens with a gradient refractive index, wherein, Electromagnetic waves incident on the first surface of the lens as spherical waves depart from the second surface of the lens approximately as plane waves. The second surface of the lens is in contact with the receiving surface of the object, and the refractive index of the lens at the second surface of the lens is approximately matched with the refractive index of the object at the receiving surface, so that no matching medium is required.

12. The method according to claim 11, further comprising: The one or more predetermined second materials are introduced into the opening in the first material.

13. The method according to claim 11 or 12, further comprising: One or more predetermined second materials are introduced into a selected corresponding opening in the opening in the first material to guide the plane wave in a specific direction within the object.

14. The method according to claim 11 or 12, further comprising: The introduction of one or more predetermined second materials into selected corresponding openings in the openings of the first material, and the removal of one or more predetermined second materials from selected corresponding openings in the openings of the first material, are dynamically controlled to guide the plane wave dynamically in different directions within the object.

15. The method according to claim 11 or 12, wherein, The body, made of the first material, is formed such that the second surface of the lens has a non-planar shape that conforms to the receiving surface of the object.

16. The method according to claim 11 or 12, wherein, The forming step includes 3D printing the body made of the first material having openings.

17. The method according to claim 11 or 12, further comprising: The structure of the opening is determined by applying an optimization method that maximizes the transmission coefficient of the lens while minimizing the reflection coefficient of the lens.

18. An apparatus for electromagnetic imaging of internal features of an object, including human body parts, comprising: A source of electromagnetic energy, wherein the source of electromagnetic energy includes microwaves with a frequency of approximately 1 GHz; and A lens disposed between the source of the electromagnetic energy and the object, the lens being made of a first material having a first dielectric constant, the first material having an opening that contains or is configured to receive one or more second materials having a corresponding second dielectric constant different from the first dielectric constant, the opening being configured such that the lens has a gradient refractive index when the opening contains the one or more second materials, wherein an electromagnetic wave generated by the source and incident as a spherical wave onto the first surface of the lens exits the second surface of the lens approximately as a plane wave, the second surface of the lens being in contact with a receiving surface of the object, and the refractive index of the lens at the second surface of the lens approximately matching the refractive index of the object at the receiving surface, to increase the penetration of the plane wave into the object; The opening includes a cylindrical opening oriented perpendicular to the propagation direction of the electromagnetic wave; and The openings are arranged in multiple layers.

19. The device according to claim 18, wherein, The multilayer comprises four layers with diameters of r1=1.95 mm, r2=2.55 mm, r3=2.9 mm, and r4=3.8 mm.

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