Wearable antenna assembly for electromagnetic head imaging

Abstract

A wearable antenna assembly for cross-sectional brain imaging of a subject, the antenna assembly comprising: an elastic cap worn on the head of the subject whose brain is to be imaged; an array of antennas at least partially embedded in the cap at corresponding mutually spaced positions so that when the cap is worn by the subject, the antennas are arranged around the subject's brain; wherein the cap has a multilayer structure including layers consisting of graphite and aluminum oxide powders dispersed in PDMS to improve the matching of dielectric properties with the dielectric properties of the subject's head.

Description

[0001] background

[0002] Stroke is one of the leading causes of disability and death worldwide. According to the Australian Stroke Foundation, in 2017, approximately 55,831 Australians suffered a life-threatening stroke every nine minutes, and this number will increase to one stroke every four minutes by the end of 2050 if no action is taken. The time for diagnosis and treatment is critical for a quick and complete recovery. Therefore, a fast, portable, on-site and accurate detection tool is needed to save thousands of lives. Although there are several existing imaging technologies, such as x-ray mammography, computerized and positron emission tomography, and magnetic resonance imaging (MRI), these technologies are difficult to obtain in rural hospitals and are in any case almost unaffordable for low-income patients. Most importantly, the large size of such systems makes it almost impossible for a team of paramedics to carry and use them on site for rapid diagnosis. In addition, these technologies are either based on ionizing radiation or require bulky static structures that are expensive to use; therefore, it is impractical to use these existing tools for continuous monitoring.

[0003] Previous studies have demonstrated the feasibility of using low-power electromagnetic (EM) waves to detect and diagnose abnormalities within the human brain. This technology was introduced as a complementary low-cost, rapid and non-ionizing method compared to the above-mentioned standard technologies. The EM imaging system consists of a low-power antenna array and a simple transceiver operating in the low microwave frequency band. Therefore, it provides a low-cost, reliable system that can be used as a field diagnostic tool.

[0004] EM image reconstruction is based on the contrast in the dielectric properties of healthy and unhealthy tissues inside the human head. Because the scattering, penetration and absorption of EM signals depend on these properties, the differences in these properties can be used to detect abnormalities by reconstructing useful images. Several types of EM head imaging systems have been proposed for stroke and cancer detection and diagnosis. However, these systems are not easily adaptable for clinical use due to several difficulties that need to be solved. The main limitations of existing systems are their size and limited compatibility with the human head, the penetration depth of electromagnetic signals into the head, the mismatch of antennas with head tissues, and air-skin interface reflections, which cause interference with the useful reflected signals, resulting in inaccurate and low-resolution images.

[0005] It would therefore be desirable to overcome or alleviate one or more difficulties of the prior art, or at least provide a useful alternative.

[0006] Overview

[0007] The inventors have discovered that imaging antenna arrays play a key role in the performance (e.g., image accuracy, detection capabilities) and physical characteristics (e.g., portability, flexibility, weight) of EM head imaging systems. For an efficient and portable EM head imaging system, a lightweight wearable platform and a broadband low-profile unidirectional and efficient antenna array are needed. However, obtaining an antenna array with such characteristics is very challenging due to size constraints when operating in the low microwave frequency band, high mutual coupling between adjacent antennas, and the complexity / high attenuation of human head tissue that inhibits the penetration of EM waves. Prior art EM head imaging systems use conventional imaging antennas on rigid dielectric printed circuit boards (PCBs) or based on ceramic loaded waveguide manufacturing. The reliance on rigid conventional PCB boards limits the ability to improve performance and control the size, compatibility, flexibility and portability of such systems.

[0008] According to some embodiments of the present invention, there is provided a wearable antenna assembly for cross-sectional brain imaging of a subject, the antenna assembly comprising:

[0009] an elastic cap for placement on the head of a subject whose brain is to be imaged;

[0010] an array of antennas at least partially embedded in the cap at respective mutually spaced locations such that when the cap is worn by the subject, the antennas are arranged about the subject's brain;

[0011] The cap has a multilayer structure including layers composed of graphite and alumina powder dispersed in PDMS to improve the matching of dielectric properties with those of the subject's head.

[0012] In some embodiments, the composition of the layer provides a relative dielectric constant of about 20 and a loss tangent of about 0.016 at 1 GHz.

[0013] In some embodiments, graphite and alumina powders are dispersed in PDMS in a ratio of about 0.2:1.8:10 by weight.

[0014] In some embodiments, the antennas are arranged in two rows around the subject's brain.

[0015] In some embodiments, the cap includes a PDMS layer between the subject's head and the transceiver elements of each antenna.

[0016] In some embodiments, the ground planes of the antennas are spaced apart from one another to allow for flexibility and resiliency of the cap.

[0017] In some embodiments, the transceiver element of each antenna is configured with multiple openings and multiple pins shorting the transceiver element to corresponding ground planes so that the antenna supports multiple resonances and its output is substantially unidirectional and broadband when coupled to the subject's head.

[0018] In some embodiments, the cap includes two spaced apart halves formed from a first elastic material and connected by a second elastic material that is more extensible than the first elastic material, such that the cap is wearable by subjects having a wider range of head sizes.

[0019] In some embodiments, each antenna is electrically connected by a respective RF cable to a common multi-pin connector that is attached to the cap.

[0020] In some embodiments, each antenna includes an integral coaxial connector having a signal pin that connects directly to the transceiver element of the antenna and a ground portion that connects directly to the ground plane of the antenna.

[0021] According to some embodiments of the present invention, there is provided a method of forming a wearable antenna assembly for cross-sectional brain imaging of a subject, the method comprising the following steps:

[0022] An elastic cap is formed for wearing on the head of a subject whose brain is to be imaged, comprising at least partially embedding an array of antennas in the cap at corresponding mutually spaced positions so that when the cap is worn by the subject, the antennas are arranged around the subject's brain; wherein the elastic cap has a multilayer structure including a matching material layer composed of graphite and aluminum oxide powders dispersed in PDMS to improve the matching of dielectric properties with the dielectric properties of the subject's head.

[0023] According to some embodiments of the present invention, there is provided a method of forming a wearable antenna assembly for cross-sectional brain imaging of a subject, the method comprising the following steps:

[0024] forming a first PDMS layer;

[0025] forming a substantially planar transceiver element and a corresponding substantially planar ground plane;

[0026] Arranging the transceiver elements at corresponding positions spaced apart from each other on the PDMS layer;

[0027] forming a matching material layer composed of graphite and aluminum oxide powder dispersed in PDMS on the transceiver element and the first PDMS layer to improve the matching of dielectric properties with the dielectric properties of the subject's head;

[0028] disposing ground planes on the matching material layer at respective mutually spaced locations aligned with locations of the transceiver elements; and

[0029] forming a second PDMS layer on the ground plane and the matching material layer to encapsulate the ground plane;

[0030] The resulting assembly is in the form of an elastic cap to be worn by a subject whose brain is to be imaged, the transceiver elements and corresponding ground plane forming a corresponding antenna embedded within the cap.

[0031] In some embodiments, the method includes forming a matching material by mixing graphite and alumina powders with PDMS in colloid form and allowing it to harden.

[0032] In some embodiments, the composition of the matching material is graphite:alumina powder:PDMS in a ratio of about 0.2:1.8:10 by weight.

[0033] In some embodiments, the method includes connecting the antennas to a common multi-pin connector by respective RF cables and attaching the multi-pin connector to the cap.

[0034] According to some embodiments of the present invention, there is provided a method for determining the relative spatial position and orientation of antennas of an antenna array arranged around a head of a subject whose brain is to be imaged using electromagnetic signals emitted by the antennas and scattered from the subject's brain, the method comprising the following steps: providing the antennas with corresponding reference markers; using a 3D imaging camera to automatically identify the reference markers, determine the spatial position and orientation of the reference markers, and process the spatial position and orientation of the reference markers and data representing the outer surface of the subject's head to determine the orientation of the antenna relative to the subject's head and the distance of each antenna from the subject's head.

[0035] According to some embodiments of the present invention, there is provided an antenna for an antenna array arranged around a body part of a subject, the body part to be imaged using electromagnetic signals emitted by the antenna and scattered from the body part, the antenna comprising a substantially planar transceiver element and a corresponding substantially planar ground plane aligned with the transceiver element, the transceiver element being configured with a plurality of openings and a plurality of pins shorting the transceiver element to the ground plane, such that the antenna supports multiple resonances and its output is substantially unidirectional and broadband when coupled to the body part of the subject.

[0036] According to some embodiments of the present invention, a method is provided of using magnetic materials to improve matching, bandwidth, and signal penetration inside the human head in addition to reducing antenna size and enabling the use of a greater number of antennas for better image quality.

[0037] Also described herein is a wearable antenna assembly for cross-sectional brain imaging of a subject, the antenna assembly comprising:

[0038] an elastic cap for placement on the head of a subject whose brain is to be imaged;

[0039] an array of antennas at least partially embedded in the cap at respective mutually spaced locations such that when the cap is worn by the subject, the antennas are arranged around the subject's brain,

[0040] Each antenna includes a generally planar transceiver element and a corresponding generally planar ground plane aligned with the transceiver element, wherein a matching material having a relative dielectric constant of at least 10 is disposed between the transceiver element and the ground plane.

[0041] Also described herein is a method of forming a wearable antenna assembly for cross-sectional brain imaging of a subject, the method comprising the steps of:

[0042] forming a first PDMS layer;

[0043] forming a substantially planar transceiver element and a corresponding substantially planar ground plane;

[0044] Arranging the transceiver elements at corresponding positions spaced apart from each other on the PDMS layer;

[0045] forming a matching material layer having a relative dielectric constant of at least 10 on the transceiver element and the first PDMS layer;

[0046] disposing ground planes on the matching material layer at respective mutually spaced locations aligned with locations of the transceiver elements; and

[0047] forming a second PDMS layer on the ground plane and the matching material layer to encapsulate the ground plane;

[0048] The resulting assembly is in the form of an elastic cap to be worn by a subject whose brain is to be imaged, the transceiver elements and corresponding ground plane forming a corresponding antenna embedded within the cap.

[0049] In order to solve the difficulties of the prior art, the inventors have developed a wearable broadband and lightweight antenna assembly for EM head imaging and stroke detection based on polymer composite technology. This improves the physical compatibility, portability and performance of the EM imaging system. In the work gradually leading to the present invention, the inventors developed a multi-layer customized flexible polymer composite substrate material. The multi-layer composite substrate material consists of polydimethylsiloxane (PDMS) polymer, micron-sized graphite, iron oxide (FeO.Fe2O3), aluminum oxide (Al2O3), and powder. In the described embodiment, each antenna element is etched and embedded inside the flexible substrate layer. With the ability to significantly reduce the physical size of the imaging system and improve the performance of the imaging system, three aspects of the wearable antenna assembly are summarized as follows:

[0050] a) Development of flexible multilayer polymer composite substrate materials for imaging antennas and EM head imaging system platforms: PDMS is used as a substrate material for antennas and platforms. It has very suitable mechanical and electrical properties, including high flexibility, durability, transparency, and low dielectric loss. In addition, PDMS has a high volume resistivity (about 2.9×10 14 Ω-cm), which helps prevent the generation of parasitic currents in the substrate that would degrade antenna performance. Another substrate material is a mixture of PDMS with micron-sized alumina and graphite powders, which provide good dielectric properties, including high dielectric constant, stability and reasonable losses. These additive materials possess excellent dispersion and solubility properties with PDMS. The electrical properties of the developed structure, adjusted by the concentration ratio of alumina and graphite to PDMS, have been characterized to obtain dielectric properties that meet the performance requirements of EM head imaging systems, including enhancing the matching of the antenna to human tissue and the size of the antenna. In addition, the described multilayer structure is highly flexible and compatible with the human head, allowing the antenna assembly to be worn like a swimming cap.

[0051] In addition, magnetite iron oxide (FeO.Fe2O3), which has good magnetic properties such as low loss, high stability, and excellent dispersion and dissolution properties with many other materials, can also be synthesized with PDMS, and Al2O3 as a second version of the substrate being developed. Such a magnetic-based substrate possesses promising RF properties due to its magnetic permeability greater than 1. Magnetite iron oxide will be mixed with PDMS and Al2O3 in different ratios to obtain the best electromagnetic properties that will help the antenna match the human head. It will improve the penetration of electromagnetic waves inside the head, widen the bandwidth of the antenna, and reduce its physical size.

[0052] b) Imaging Antenna Array: As mentioned above, antennas are key elements of EM imaging systems, as the detection capabilities, image resolution and accuracy of the system are mainly based on the performance of these antennas. The compactness and portability of the system depends on the size and weight of the imaging antenna array. The most important characteristics of each antenna element to achieve an efficient and compact EM head system are broadband, unidirectional, high front-to-back ratio (FTBR) EM performance as well as low profile and compact mechanical characteristics. Broadband, unidirectional and high FTBR characteristics are required to ensure high penetration depth of EM waves into human head tissue, which results in high signal-to-noise ratio (SNR) that enhances useful reflected signals from stroke or other abnormalities inside the brain. An array of imaging antennas that meets the above mentioned requirements is described herein based on a developed tunable flexible substrate and is embedded inside a cap-like support structure having an elliptical shape around the head.

[0053] c) Hardware Architecture of a Portable and Wearable EM Head Imaging System: The described antenna assembly is based on a multi-layer flexible support structure or "cap" that can be worn in the same way as a swimming cap. Although the developed materials based on PDMS are very flexible, their ability to stretch is limited. In order to make the cap conform to different head shapes, the two halves of the cap are formed from a flexible substrate and then connected to each other by a thin stretchable and flexible silicone membrane. As a low-cost structure, the cap can be formed in different sizes to accommodate extremely different head sizes. An antenna array with optimized performance is embedded in the cap to achieve effective scanning inside the head. The antenna array is shielded by an array of conductive copper patches that act as a ground plane for the antenna array. These conductive patches are spaced with small gaps to ensure the flexibility of the cap and to ensure that all layers of the structure are fixed together.

[0054] For successful image reconstruction, the exact position of each antenna around the head needs to be known to determine the corresponding time delay of the scattered signal that conveys useful information. The exact position and geometric arrangement of the imaging antennas are critical to the imaging processing algorithm. Because the antenna assembly is conformal to the wearer's head, the inward-facing structures of the assembly and the antenna point inward at different angles to the head. This produces unequal distances and asymmetric angles among the antenna elements in the array, and it is difficult to directly determine the exact position of each antenna. For different human heads, the antennas of the array will have different positions. To overcome these challenges, 3D depth camera technology can be used to determine the exact position of each antenna, in particular the excitation port of each imaging antenna. This information is then included as a priori information in the image processing algorithm.

[0055] When in use, the imaging antenna is connected to a high dynamic range VNA (or microwave transceiver) via an RF coaxial cable. Calibration of the VNA and RF cable is performed to eliminate noise that may affect the accuracy of the results. The VNA then generates and transmits and receives signals via the imaging antenna. Reflected signals from stroke or other abnormalities are collected by the VNA and simultaneously sent to a computer for signal processing and image reconstruction using appropriate processing algorithms (e.g., based on radar or tomography techniques). The entire system is low cost, portable, and lightweight. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] Some embodiments of the invention are described below by way of example only with reference to the accompanying drawings, in which:

[0057] Figure 1 including a schematic cross-sectional side view of an antenna component of an antenna assembly according to an embodiment of the invention, a plan view of an antenna structure of the antenna component (left hand side) and an alternative antenna structure of an alternative embodiment (right hand side), and an exploded view showing the arrangement of layers of the antenna component;

[0058] Figure 2 includes a cross-sectional side view of the antenna assembly worn by a subject whose brain is to be imaged and a plan view of the antenna assembly;

[0059] Figure 3 is a schematic diagram of a system for brain tomography (including a wearable antenna assembly) according to an embodiment of the present invention;

[0060] Figure 4 is a flow chart of a process for determining the spatial position and orientation of an antenna relative to a subject's head;

[0061] Figure 5 is a schematic diagram of the manufacturing process of the composite substrate;

[0062] Figure 6 is a graph of measured values ​​of dielectric properties (dielectric constant and loss tangent) of the composite substrate; and

[0063] Figure 7 is a graph of simulated and measured reflection coefficient (S11) for a single antenna element.

[0064] Detailed Description

[0065] like Figure 3 As shown, the electromagnetic medical imaging system for detecting brain injury includes an antenna assembly 102, a vector network analyzer (VNA) 204, and an analysis component 206. The antenna assembly 102 is wearable and Figure 1 1 is shown as being worn on the head of a human subject whose brain is to be imaged. Antenna assembly 102 includes an array of antennas arranged around the subject's head so that each antenna of the array can be selectively energized to radiate a signal of an electromagnetic wave or microwave frequency into the subject's brain to be scattered, and the corresponding scattered signal is detected by all antennas of the array (including the antenna that transmits the corresponding signal). For ease of reference, the overall process of sequentially causing each antenna of the array to transmit a corresponding microwave signal and using the antenna to receive the corresponding scattered signal is referred to herein as "scanning".

[0066] As known to those skilled in the art, the vector network analyzer (VNA) 110 supplies antenna energy over a frequency band of 0.5 to 2 GHz as described above, and records the corresponding signal from the antenna as data (referred to herein as "scattering" data) that represents the amplitude and phase of the scattered microwaves in the form of what are referred to in the art as "scattering parameters" or "S parameters." The VNA 110 sends the data to the analysis component 206 for processing to generate images of internal features of the subject's head (e.g., brain blood clots, hemorrhage sites, and other features), and classify these features (e.g., into brain blood clots or hemorrhage sites).

[0067] According to the described embodiment of the present invention, the antenna assembly includes an antenna array embedded in a flexible and elastic composite material so that the assembly can be stretched over the head of a human subject and worn like a swimming cap. The antenna array is a compact, lightweight, portable broadband antenna array, which makes it suitable for portable electromagnetic medical imaging systems.

[0068] A. Antenna assembly

[0069] Antenna arrays are a way to improve the physical compatibility, portability and performance of the system. Figure 3 A portion of a wearable, broadband, compact and lightweight antenna assembly is shown. The antenna assembly ( Figure 3 ) is in the general form of a flexible and elastically deformable and resilient wearable cap (similar to a swim cap) in which an antenna array is embedded, allowing the antenna array to be aligned with and secured in close proximity to the subject's head. The cap is composed of a composite material, which is a mixture of polydimethylsiloxane (PDMS), micron-sized graphite (G), and aluminum oxide (Al2O3) powders selected to increase the relative dielectric constant of the composite material from the pure PDMS value of 2.9 to a value greater than 10, thereby improving the match with the dielectric properties of the human head, which generally has a relative dielectric constant of about 45. On the other hand, magnetite iron oxide (FeO.Fe2O3) can also be mixed with PDMS and Al2O3 to form a magnetic-based composite substrate. The magnetic-based substrate is developed to enhance antenna matching, bandwidth, penetration on the head, and reduce the physical size of the antenna.

[0070] For ease of reference, the first composite material is referred to herein as "PDMS-G-Al2O3", and the magnetic-based substrate material is PDMS-FeO.Fe2O3-Al2O3. The first developed substrate was manufactured as follows. First, the PDMS polymer elastomer consists of two components: a base resin and a curing agent. The base resin is mixed with the curing agent in a weight ratio of 10:1. Then microparticles of graphite and alumina are dispersed in the PDMS elastomer in different ratios as described below. A magnetic stirrer is used to stir the mixed solution to ensure that the resulting structure is homogeneous. The mixture is then cured in a cap mold by placing the mixture in an oven dryer at 55°C for 3-4 hours. A cap mold with the anatomical shape of a human head is manufactured using a 3D printer. The dielectric properties of the composite PDMS-G-Al2O3 mixture are then characterized and evaluated using a dielectric probe kit and a vector network analyzer 110. Based on the results, the optimal ratio of the mixed components can be determined and used for antenna optimization.

[0071] In particular, pure PDMS has a relative dielectric constant of 2.9 and a loss tangent of 0.013 at 1 GHz. By mixing PDMS, micronized graphite, and alumina (PDMS-G-Al2O3) in a weight ratio of 10:0.2:1.8, respectively, the relative dielectric constant is increased to 20 and the loss tangent is 0.016 at 1 GHz. Because the average dielectric constant of the human head is about 45, this significantly improves the matching of the antenna to the human head while limiting the dielectric losses of the antenna element. The PDMS-G-Al2O3 material is very flexible; for example, a full bend of 180° (U-bend) is possible for a sheet thickness of up to at least 10 mm.

[0072] The magnetic based substrate was formed from a composition of PDMS, micron-sized iron oxide and aluminum oxide in a weight ratio of 10:2:2 respectively. The fabrication process of this substrate was as described above for the first substrate, except that the graphite was replaced by iron oxide.

[0073] B. Antenna Array

[0074] like Figure 1 and 2 As shown, each antenna of the antenna array includes a conductive copper sheet serving as an antenna ground plane 103, a conductive multi-slot radiating element 106, and conductive pins 107 connecting the ground plane 103 to corresponding positions of the radiating element 106. In the described embodiment, the radiating element 106 includes four conductive short-circuit pins 107, such as Figure 1 However, in other embodiments this need not be the case; for example, Figure 1 The center row of the right-hand column of shows an alternative embodiment in which the radiating element 106 includes six shorting pins 107 .

[0075] As in Figure 1As shown in the top portion of , each antenna also includes a corresponding coaxial connector 104, which includes a hollow cylindrical Teflon insulating sleeve 104A surrounding an inner pin 104B connected to the corresponding position of the radiating element and a shell 104C connected to the ground plane 103. The conductive ground plane 103 and the radiating element 106 are attached to the opposite surfaces of the flexible composite PDMS-G-Al2O3 layer 102, which acts as the antenna substrate. The high dielectric constant of the composite substrate material allows significant miniaturization of the antenna elements. Each antenna is configured as a modified multi-slot planar magnetoelectric (ME) dipole antenna. The electric dipole is generated by the double-sided multi-slot radiating patch 106, while the magnetic dipole is introduced by the parallel and side shorting pins 107. The magnetic dipole and the electric dipole together form a planar ME pole. Such a configuration allows for further miniaturization and broadband performance due to the increase in electrical length caused by the multiple slots 108 in the patch and the multiple resonances created by the shorting pins 107 of each radiating element. Figure 7 The simulated and measured reflection coefficient (S11) of a single element (with four shorting pins) 108 is shown in FIG.

[0076] Two pure PDMS layers 101, 105 are attached to the exposed face of the ground plane 103 and the radiating element 106, so that each antenna comprises a stack consisting of an outer PDMS layer 105, a ground plane 103, a composite PDMS-based material as either PDMS-G-Al2O3 or PDMS-Fe2O3-Al2O3 layer 102, a radiating element 106 and an inner PDMS layer 101. Due to its low dielectric constant (which can reduce signal penetration in the subject's head), the inner PMDS substrate layer 101 disposed between the radiating element 106 and the subject's head is relatively thin, 1 mm in the described embodiment. In contrast, the thickness of the outer PDMS layer 105 above the ground plane 103 is not critical in terms of system performance and is selected to be 1 mm to simply reduce the weight of the wearable antenna assembly. The radiating element 106 and ground plane 103 are embedded between the PDMS layers 101 , 105 , protecting the antenna array from dust, corrosion, water and rust, and allowing the antenna assembly to be robust in challenging environments.

[0077] In the described embodiment, each antenna element has lateral dimensions of 2.5 cm x 2.8 cm and a thickness of 0.025 mm. Figure 2As shown, the antennas are arranged around the subject's head as two roughly concentric elliptical rings 204, 205. The lower outer ring 204 includes 16 antennas, while the upper inner ring 205 includes 8 antennas. The ground plane 103 acts as an electromagnetic shield for the system. In order to maintain the flexibility of the wearable antenna assembly, a fully solid conductive ground plane is not used. Instead, a limited number of copper sheets separated by small gaps are used. This configuration ensures a light-weight, compact assembly, and in fact only negligible electromagnetic power leaks through the gaps between the ground plane sheets 103.

[0078] The wearable antenna assembly is configured as a stretchable and flexible cap to be worn by a subject. Although the PDMS and PDMS-G-Al2O3 materials are very flexible, they still have a limited ability to stretch. Therefore, in order to allow the cap to fit different head sizes and shapes, in some embodiments the cap is formed into two halves 203A and 203B, which are then interconnected by a thin and highly stretchable and flexible membrane 201, such as Figure 2 As shown. The thicknesses of the outer PDMS layer 105, the ground plane 103, the composite PDMS-G-Al2O3 layer 102, the radiating element 106, the inner PDMS layer 101 and the cap interconnect film 201 are 1 mm, 0.012 mm, 3.5 mm, 0.012 mm, 1 mm and 3.5 mm respectively. For extreme head sizes, caps of different sizes can be produced at low cost.

[0079] C. Manufacturing Process

[0080] refer to Figure 5 , the manufacturing process of the complete 3D multilayer wearable component is summarized as follows. First, a 1 mm inner PDMS layer 101 is produced. Once this layer hardens, the antenna element 106 is formed in a second step (by stamping and etching a 0.012 mm copper sheet) and Figure 2 The general arrangement shown is attached to one side of the inner PDMS layer 101 at the corresponding positions. Then, a composite PDMS-G-Al2O3 layer 102 with a thickness of 3.5 mm is produced and hardened on the radiating element 106, and attached to the inner PDMS layer 101. In the next step, a 0.012 mm thick copper sheet is cut to form the ground plane 103 of the antenna and attached to the composite PDMS-G-Al2O3 layer 102 at the corresponding positions so that they are aligned with the corresponding antenna elements 106. Finally, a 1 mm PDMS layer is attached to form an outer PDMS layer 105 covering the ground plane 103. Finally, all the layers are bonded together to form a composite structure because when the PDMS is in the form of a colloid, it is highly sticky. In the Figure 6 The dielectric properties of several PDMS-G-Al2O3 samples with different concentrations are shown in FIG.

[0081] Layers are formed and assembled on a 3D cap mold with adjustable thickness. In the described embodiment, a 3D printer technology is used to manufacture the mold. The 3D mold is used to form the anatomical shape of the human head and ensure that there is no noticeable air gap between the wearable cap and the skin of the subject's head.

[0082] Each antenna element is associated with a corresponding RF connector 104. In the depicted embodiment, the RF connector 104 is a 50Ω coaxial connector for energizing the antenna and is connected to a short length of high quality RF cable 302 routed along the outer PDMS layer 105, such as Figure 3 As shown, the antenna assembly is connected to a common multi-pin terminal 301 located on the top of the cap. In other embodiments, the cables can be replaced by low-loss transmission lines that form part of the flexible substrate. These lines can be integrated with the switch matrix on the flexible substrate, and thus only one RF cable and one control line are required to connect the antenna assembly to an external transceiver and processing unit.

[0083] C. Antenna array position and 3D depth camera

[0084] For successful image reconstruction, the relative positions of the antennas arranged around the subject's head need to be known to determine the corresponding time delays of the scattered microwave signals. When the cap is worn by the subject, the antenna array generally becomes conformal to the subject's head, but the antennas can still have different orientations and distances relative to the subject's head. In view of this, a 3D camera and image processing can be used to determine the spatial position and orientation of each antenna (particularly the excitation port of each imaging antenna).

[0085] The process used to locate the antenna position is as follows Figure 4 The step 402 shown starts by performing a labeling and scanning of the antenna array placed on the head surface. The scanning is to acquire the 3D structure of the antenna array, while different labels (each label is in the form of an Aruco mark - a square mark composed of a wide black border and an identifier in the form of a small square white shape represented by an internal binary matrix) are attached; next, the antenna port 302 is used as an anchor point for detecting the antenna position. The scanned image contains information on the spatial distribution of the array as well as the encoded label of each antenna. In order to ensure that the antenna position is represented in the same coordinate system as the imaging system, the scanned structure is aligned with a standardized coordinate system in step 404.

[0086] In step 406, the antenna position is determined using information from the scanning process (i.e., the aligned structure and the mark). In one embodiment, a click and collect method 406A is used. The aligned structure containing the mark is imported and visually represented. The position of the antenna is manually determined by clicking on the corresponding mark, and its position (antenna position) is recorded and calculated accordingly by using the developed code. In an alternative embodiment, a mark detection algorithm 406B is used. The system automatically identifies the position of each antenna by utilizing an open source computer vision library (Opencv). The process includes two main steps: detecting marker candidates and classifying marker candidates. In the first step, the scanned image is analyzed to find square shapes (in black and white), which are candidates for the mark. In the next step, the marker candidates are classified to confirm whether they are real markers by analyzing their internal coding, which is represented by a white square shape containing a unique binary matrix for each marker. This involves extracting and analyzing the marker bits of each marker, wherein the image of the marker is thresholded and divided to determine and separate the black and white bits. These bits are then analyzed to confirm whether the tag is known (e.g., whether it belongs to the system's library of tags). In addition, this step also confirms which tag represents which antenna based on the unique code of each tag. When the tags are confirmed, their spatial positions are stored and used to determine the positions of the antennas (by taking into account the known offsets between each tag position and the position of its corresponding antenna).

[0087] In step 410, the system calculates the relative distance between each antenna and the head surface using the detected antenna positions and the 3D head surface 408 of the subject's head. In addition, by using the antenna positions and the subject's head surface, the orientation of each antenna toward the head surface can also be determined.

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

Claims

1. A wearable antenna assembly for cross-sectional brain imaging of a subject, the antenna assembly comprising: an elastic cap for placement on the head of a subject whose brain is to be imaged; an array of antennas at least partially embedded in the cap at respective mutually spaced locations such that when the cap is worn by the subject, the antennas are arranged about the subject's brain; The cap has a multi-layer structure including layers composed of graphite and alumina powder dispersed in PDMS to improve the matching of dielectric properties with those of the subject's head.

2. The antenna assembly of claim 1, wherein the composition of the layer provides a relative dielectric constant of approximately 20 and a loss tangent of approximately 0.016 at 1 GHz.

3. The antenna assembly of claim 1 or 2, wherein the graphite and alumina powders are dispersed in the PDMS in a ratio of about 0.2:1.8:10 by weight.

4. The antenna assembly according to any one of claims 1 to 3, wherein the antennas are arranged in two rows around the subject's brain.

5. The antenna assembly of any one of claims 1 to 4, wherein the cap comprises a PDMS layer between the subject's head and the transceiver element of each antenna.

6. The antenna assembly of any one of claims 1 to 5, wherein the ground planes of the antennas are spaced apart from each other to allow flexibility and elasticity of the cap.

7. An antenna assembly according to any one of claims 1 to 6, wherein the transceiver element of each antenna is configured with a plurality of openings and a plurality of pins short-circuiting the transceiver element to a corresponding ground plane, so that the antenna supports multiple resonances and the output of the antenna is substantially unidirectional and broadband when the antenna is coupled to the subject's head.

8. An antenna assembly according to any one of claims 1 to 7, wherein the cap comprises two spaced apart halves formed from a first elastic material and connected by a second elastic material that is more extensible than the first elastic material, so that the cap can be worn by subjects having a wider range of head sizes.

9. The antenna assembly of any one of claims 1 to 8, wherein each antenna is electrically connected by a respective RF cable to a common multi-pin connector, the multi-pin connector being attached to the cap.

10. The antenna assembly of any one of claims 1 to 9, wherein each antenna includes an integral coaxial connector having a signal pin directly connected to a transceiver element of the antenna and a ground portion directly connected to a ground plane of the antenna.

11. A method of forming a wearable antenna assembly for cross-sectional brain imaging of a subject, the method comprising the steps of: An elastic cap is formed to be worn on the head of a subject whose brain is to be imaged, comprising at least partially embedding an array of antennas in the cap at corresponding mutually spaced positions so that when the cap is worn by the subject, the antennas are arranged around the brain of the subject; wherein the elastic cap has a multi-layer structure, the multi-layer structure including a matching material layer composed of graphite and aluminum oxide powder dispersed in PDMS to improve the matching of dielectric properties with the dielectric properties of the subject's head.

12. A method of forming a wearable antenna assembly for cross-sectional brain imaging of a subject, the method comprising the steps of: forming a first PDMS layer; forming a substantially planar transceiver element and a corresponding substantially planar ground plane; Arranging the transceiver elements at corresponding positions spaced apart from each other on the PDMS layer; forming a matching material layer composed of graphite and aluminum oxide powder dispersed in PDMS on the transceiver element and the first PDMS layer to improve the matching of dielectric properties with the dielectric properties of the subject's head; disposing the ground plane on the matching material layer at respective mutually spaced locations aligned with the locations of the transceiver elements; as well as forming a second PDMS layer on the ground plane and the matching material layer to encapsulate the ground plane; Where the resulting assembly is in the form of an elastic cap to be worn by a subject whose brain is to be imaged, the transceiver elements and corresponding ground planes form corresponding antennas embedded within the cap.

13. A method according to claim 12, comprising forming the matching material by mixing graphite and alumina powders with PDMS in colloid form and allowing it to harden.

14. The method of claim 13, wherein the composition of the matching material is graphite:alumina powder:PDMS in a ratio of about 0.2:1.8:10 by weight.

15. A method according to any one of claims 12 to 14, comprising connecting the antennas to a common multi-pin connector by respective RF cables and attaching the multi-pin connector to the cap.

16. The method according to claim 11 also includes determining the relative spatial position and orientation of the antenna by providing the antenna with corresponding reference markers; using a 3D imaging camera to automatically identify the reference markers, determine the spatial position and orientation of the reference markers, and process the spatial position and orientation of the reference markers and data representing the outer surface of the subject's head to determine the orientation of the antenna relative to the subject's head and the distance of each antenna to the subject's head.

17. The antenna assembly according to claim 1, wherein: Each of the antennas includes a generally planar transceiver element and a corresponding generally planar ground plane aligned with the transceiver element, the transceiver element being configured with a plurality of openings and a plurality of pins shorting the transceiver element to the ground plane such that the antenna supports multiple resonances and the output of the antenna is substantially unidirectional and broadband when the antenna is coupled to a body part of the subject.

18. The method according to claim 11, wherein: Each of the antennas includes a generally planar transceiver element and a corresponding generally planar ground plane aligned with the transceiver element, the transceiver element being configured with a plurality of openings and a plurality of pins shorting the transceiver element to the ground plane such that the antenna supports multiple resonances and the output of the antenna is substantially unidirectional and broadband when the antenna is coupled to a body part of the subject.

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