Transmitarray for use with a medical radar

Abstract

The disclosure relates to a transmitarray configured to manipulate electromagnetic waves from a medical radar. The transmitarray may have a total thickness of at most 10 mm, and it may have a layered structure comprising two or more layers, such as two to five layers. It typically comprises an array of unit cells. A design of the transmitarray may have been determined by use of computer simulations. The disclosure further relates to a method of manufacturing such a transmitarray, to a system and a method for performing hemodynamic monitoring on a person, and to the use of such a transmitarray in different healthcare applications.

Description

[0001] TRANSMITARRAY FOR USE WITH A MEDICAL RADAR

[0002] TECHNICAL FIELD

[0003] The present disclosure relates to a transmitarray for use with a medical radar. It further relates to a method of manufacturing such a transmitarray, a system comprising such a transmitarray, and a method of performing hemodynamic monitoring on a person.

[0004] BACKGROUND

[0005] Monitoring vital signs consistently plays a critical role in promptly identifying heart rate variability (HRV), which holds clinical significance when diagnosing cardiovascular conditions. Traditional non-invasive contact devices such as phonocardiogram (PCG), photoplethysmograph (PPG), ultrasound cardiography (UCG), electrocardiography (ECG) and impedance cardiography (ICG) are commonly used for this purpose. However, these devices require direct skin contact, which causes discomfort and inconvenience for users. The integration of electromagnetic sensors into wearable devices offers the opportunity to revolutionize health monitoring by allowing continuous and non-invasive monitoring of biological information such as blood pressure, respiratory rate, and heart rate to be monitored non-invasively.

[0006] In recent years, wearable radar systems that use different approaches, such as ultra-wideband (UWB), frequency modulated continuous wave (FMCW), continuous wave, and self-injection locking (SIL), have been proposed for physiological information detection. SIL-based radars offer inherent advantages in mitigating internal reflection and antenna transmit-receive coupling clutter, making them well-suited for integration into wearable devices. However, the duration of operation for such wearables is heavily dependent on the battery capacity. An alternative approach involves the use of passive nonlinear tags, such as harmonic-type tags or intermodulation-type tags. The efficiency of these devices is significant even when equipped with one antenna. Nonetheless, the harmonic tag necessitates dual-band operation of its antenna, while the intermodulation-type tag's transponder necessitates high selectivity diplexers, both presenting challenges in design and integration. Another technique involves leveraging RFID tags for heartbeat monitoring, but it requires close proximity between the sensor reader and the tag; also in it does not explain in detail the information about heart rate monitoring in longer terms.

[0007] In the realm of vital sign monitoring, traditional non-invasive contact devices necessitate direct skin contact, often leading to user discomfort. Recent wearable radar systems, although promising, grapple with issues ranging from battery longevity to design and integration complexities. Additionally, the use of rigid materials in wearable sensors not only causes discomfort during extended use but may also compromise the accuracy and reliability of the collected data. This is exacerbated by the bulkiness of newer devices that incorporate flexible transmitarray lenses. It is crucial to tackling these issues to guarantee that wearable health monitoring devices are not only easy to use and accurate, but also do not require direct contact with the skin.

[0008] OBJECT OF THE DISCLOSURE

[0009] It is an object of the present disclosure to provide a transmitarray with which it is possible to perform non-contact medical measurements in a manner where random body movements do not significantly influence the accuracy of the measurements.

[0010] It is another object of the present disclosure to provide a transmitarray with which a higher sensitivity and thereby more precise measurements can be obtained during medical monitoring than with known systems used for similar purposes.

[0011] It is an object of at least some embodiments of the present disclosure to provide a system with which it is possible to perform hemodynamic monitoring on a person, the monitoring preferably comprising measuring one or more of the following values for the person: wrist pulse, heart rate, beat-by-beat interval, heart rate variability, respiratory rate, and blood pressure. It is also an object of at least some embodiments of the present disclosure to provide a system, which can be used for other radar applications within healthcare.

[0012] It is a further object of the present disclosure to provide an alternative to the prior art.

[0013] In particular, it may be seen as an object of the present disclosure to provide a transmitarray that solves the above-mentioned problems of the prior art.

[0014] SUMMARY

[0015] The above-described objects and several other objects are intended to be obtained in a first aspect of the disclosure by providing a transmitarray configured to manipulate electromagnetic waves from a medical radar. The transmitarray could also be referred to as "metasurface", "metasurface transmitarray", "transmitarray antenna", "transmitarray lens", "flexible lens" or "metasurface lens". A transmitarray can be defined as a phase-shifting surface composed of numerous unit cells arranged in an array. Each unit cell works to focus the wavefronts emitted by a feeding antenna, effectively narrowing the beamwidth. By implementing a progressive phase shift across the transmitarray's aperture, it becomes possible to precisely focus and direct the beam of electromagnetic waves towards a specific target direction. This capability allows for enhanced control and efficiency in directing the signal.

[0016] What is referred to as "manipulate" here and in the following could also be referred to as "adjust".

[0017] The medical radar could use both near-field and far-field radar technology.

[0018] The transmitarray may have a total thickness of at most 10 mm, such as at most 5 mm, such as at most 1 mm, such as at most 0.2 mm, such as a total thickness between 50 and 155 microns. The transmitarray, with a maximum thickness of 10 mm and potentially as thin as 50 to 155 microns, is significantly thinner than those used in traditional applications. This reduced thickness enables the creation of a flexible transmitarray, ideal for integration into textiles worn during monitoring activities. The flexibility of the transmitarray is influenced by various factors, including its in-plane dimensions and the elasticity of its constituent materials, enhancing its suitability for wearable technology applications.

[0019] There are at least the following advantages of providing a flexible transmitarray e.g. by using flexible materials.

[0020] Comfort and Ergonomics: Flexible substrates can conform to the body's contours, making the wearable device more comfortable for continuous use. This is crucial in healthcare monitoring where user compliance is key to collecting consistent and reliable data.

[0021] Durability and Resilience: Such substrates are typically more durable and resistant to wear and tear compared to rigid materials. They can withstand repeated bending and flexing, which is inevitable in wearable devices.

[0022] Lightweight Design: Flexibility often comes with the advantage of being lightweight, which is less obtrusive and more acceptable for users to wear for extended periods, thereby improving patient compliance.

[0023] Integration with Textiles: Flexible antennas can be easily integrated into textiles, allowing for seamless incorporation into everyday clothing. This integration can make health monitoring unobtrusive and more convenient for the user.

[0024] Improved Signal Quality: The close conformity of flexible antennas to the body can result in better signal quality. This is especially important in health monitoring where accurate data collection is essential.

[0025] Adaptability to Movement: In wearable healthcare, it's essential that the device adapts to the user's movements. Flexible substrates can maintain functionality and performance even when the body is in motion, ensuring continuous and reliable monitoring. Customizability: Flexible substrates can be easily customized to fit different body shapes and sizes, as well as to accommodate specific medical monitoring needs.

[0026] Reduced Skin Irritation: Compared to rigid materials, flexible substrates are less likely to cause skin irritation or discomfort, which is particularly important for devices that are worn for long periods.

[0027] Aesthetic Appeal: Flexible antennas can be designed to be visually appealing or even invisible within clothing, which can be a significant factor in user acceptance, especially in consumer healthcare products.

[0028] Innovative Application Possibilities: The flexibility opens possibilities for innovative applications, such as smart patches, integrated sensors in sportswear, or even in advanced medical devices for real-time monitoring of vital signs.

[0029] In summary, flexible substrates in the creation of antennas or transmitarrays for wearable healthcare devices offer a combination of comfort, durability, functionality, and aesthetic appeal, making them highly suitable for continuous health monitoring and patient compliance.

[0030] The transmitarray may have a layered structure comprising two or more layers, such as two to five layers. In the work leading to the present disclosure, transmitarrays with three layers were designed, manufactured, and tested as will be described in further detail below.

[0031] The transmitarray may comprise an array of unit cells, such as an array of at least 150 unit cells. A unit cell may also be referred to as an element. In transmitarrays designed and tested during the development of the present disclosure, the transmitarray has 13 x 13 = 169 unit cells for use with a 2.4 and 5.8 GHz radar technology and 37 x 37 = 1369 unit cells for use with a 24, 60, and 77 GHz radar technology. The unit cells are typically sub-wavelength in size and are responsible for the desired manipulation of the electromagnetic field waves. In some embodiments of the disclosure, the unit cells are square in form and have side lengths between 3 mm and 20 mm, such as between 5 mm and 12 mm, preferably between 7 mm and 8 mm.

[0032] In transmitarrays comprising an array of unit cells, the layered structure may comprise at least a first layer type and a second layer type, the first and second layer types having different in-plane configurations, and the first and second layer types preferably being alternately arranged.

[0033] In such embodiments with first and second layer types, the first layer type may comprise a plurality of unit cells each comprising a cross-shaped metal layer arranged on a polymer substrate, such as on a polyimide substrate, and the second layer type may comprise a plurality of unit cells each comprising a circular-shaped metal layer arranged on a polymer substrate, such as on a polyimide substrate. An example of such a design is shown in the figures.

[0034] In some embodiments of the disclosure, the thickness of the polymer substrate between two neighbouring layers is between 10 microns and 100 microns, such as between 25 microns and 75 microns, preferably between 48 microns and 52 microns.

[0035] In some embodiments of the disclosure, the length of each of the two crossing arms in the cross-shaped metal layer of the first layer type is between 2 mm and 18 mm, such as between 3 mm and 10 mm, preferably between 3.5 mm and 4.5 mm.

[0036] In some embodiments of the disclosure, the width of each of the two crossing arms in the cross-shaped metal layer of the first layer type is between 0.2 mm and 4 mm, such as between 0.5 mm and 2 mm, preferably between 0.8 mm and 1.2 mm.

[0037] In some embodiments of the disclosure the radius of the circle in the crossshaped metal layer of the second layer type is between 1 mm and 8 mm, such as between 2 mm and 5 mm, preferably between 2.5 mm and 3.5 mm. In the latter definition of the transmitarray, "unit cell" refers to each layer, but it will also be possible to define a unit cell as extending through the thickness of the transmitarray so that each unit cell spans all the layers of the transmitarray and thereby also has a layered structure.

[0038] The transmitarray may be provided with an uppermost and / or a lowermost layer which is not divided into sub-units. Such layers may be used to protect the transmitarray e.g. from mechanical damage or moisture.

[0039] In the work leading to the present disclosure, polyimide has been used as substrate material due to its permittivity being found advantageous. However, other polymers with corresponding permittivity could have been used instead. Such possible materials include FR-4, Rogers, Permalloy (Ni80Fe20), Teflon, Arion, Mylar, PTFE (Polytetrafluoroethylene), and quartz. In future designs, it may also turn out as more advantageous to select the material for the substrate based on other parameters than the permittivity.

[0040] In presently preferred embodiments of the disclosure, a design of the transmitarray has been determined by use of computer simulations. More details will be given below as well as in the detailed description of the disclosure.

[0041] In some embodiments of the disclosure, the transmitarray is configured in such a way that functioning thereof does not require supply of electricity during use. Hereby the total size and weight can be minimized, and there is no need to replace e.g. a battery. This may e.g. be relevant when the transmitarray is designed to be built into a device or textile to be worn by the person on which the measurements are to be made as will be described below.

[0042] In some embodiments of the disclosure, the transmitarray is configured to manipulate electromagnetic waves from a medical radar working at frequencies between 0.1 GHz and 50 GHs, such as between 2 GHz and 30 GHz.

[0043] In particular, the transmitarray may be configured to manipulate electromagnetic waves from a medical radar using 5.8 GHz self-injection locked (SIL) radar technology and a frequency-modulated continuous wave (FMCW) radar. The disclosure may also be used for other types of radar, such as pulse doppler radar, continuous wave radar, FMCW radar, or doppler radar.

[0044] In a second aspect, the disclosure relates to a method of manufacturing a transmitarray according to the first aspect of the disclosure, the method comprising the steps of:

[0045] - determining one or more of the following characteristics: an intended use of the transmitarray, required specifications of the transmitarray, operating frequency range, gain, required efficiency, human tissue performance metrics for the intended use, beamforming and focusing, directivity, power handling capability, bandwidth, and imaging resolution,

[0046] - modelling, by use of the computational electromagnetics tool, a design of the transmitarray,

[0047] - simulating the interaction of electromagnetic waves with the modelled transmitarray to ensure that it meets the required specifications,

[0048] - optionally optimizing the design of the transmitarray with respect to performance, manufacturing feasibility, and cost,

[0049] - optionally checking that the design is scalable to a required size,

[0050] - selecting materials for the further manufacturing based on the operating frequency, environmental conditions, and available manufacturing capabilities, and

[0051] - manufacturing the transmitarray by providing a substrate and applying metal thereon in a pattern determined by the previous steps.

[0052] The disclosure has been developed with the purpose of beam focusing and polarization control as will be described in the detailed description.

[0053] Examples of computational electromagnetic tools that can be used to model the transmitarray are Matlab, Python, CST Microwave Studio, ANSYS HFSS, or COMSOL Multiphysics. However, the scope of protection covers any type of computational electromagnetic tools which are configured to perform the required step of modelling.

[0054] These simulations allow for optimising the structure by adjusting various parameters, such as the geometry and material properties, to achieve the desired electromagnetic response. Typically, the interactions of the metasurface with incident waves is modelled, and the design is iteratively refined based on performance criteria like absorption, reflection, or transmission across specific frequency bands.

[0055] When the method comprises the step of optimizing, this step typically involves iterating the unit cell design.

[0056] The step of simulating the interaction of electromagnetic waves with the modelled transmitarray may be performed by use of the computational electromagnetic tools.

[0057] In the work leading to the present disclosure, polyimide has been used for the substrate, and copper metals have been used for the conductive elements formed thereon. However, the scope of protection covers any suitable materials.

[0058] The step of manufacturing the transmitarray may be performed by any suitable technique, such as photolithography, 3D-printing, or laser etching.

[0059] In some embodiments of the disclosure, the step of modelling comprises designing unit cells that are configured to form the transmitarray when assembled, and the step of manufacturing comprises manufacturing a plurality of unit cells, and assembling the unit cells into the transmitarray. The step of assembling the unit cells may comprise incorporating essential components for the different layers and combining the stacked layers into a unified structure.

[0060] In some embodiments of the disclosure, the step of modelling comprises:

[0061] - using one or more of the following parameters as input parameter(s): number of layers, required precision, X and Y periods (spatial periodicity along a horizontal X-axis and a vertical Y-axis, respectively) of each unit cell when present, the required frequency range, the polarization, and

[0062] - performing a simulation, in which one or more of the following design parameters of the transmitarray is optimized: required phase, specific phase distribution, the materials of substrate and metal, a dielectric constant, a tangent loss, and a layer thickness.

[0063] In this context, the "X and Y periods" are defined as the distances between adjacent repeating unit cells of the metasurface along an X-axis and a Y axes, respectively. The X and Y periods may scale with the number of layers to ensure proper stacking and interaction across the system. The values of X and Y may be fine-tuned to ensure accuracy in periodicity, affecting simulations or manufacturing tolerances. The choice of X and Y periods is typically influenced by the desired frequency range to meet specific resonance or wave propagation characteristics. As polarisation impacts how electromagnetic fields interact with the structure, X and Y periods may be aligned to optimise for linear, circular, or elliptical polarisation.

[0064] In an embodiment designed and tested as part of the development of the present disclosure, the following characteristics were obtained by the simulation and fabrication: required phase = 360°, specific phase distribution = focusing beam to 0° but also possible to focus to specific phase 30°, 45°, 50°, 90°, the substrate between the metal layers is made of polyimide (PI), a dielectric constant of £r= 3.5, a tangent loss of tan 5=0.0027, and a layer thickness =50.8pm. The total substrate thickness with stacked layers = 152.4 pm.

[0065] In a third aspect, the disclosure relates to a system for performing hemodynamic monitoring on a person, the system comprising:

[0066] - a transmitarray according to the first aspect of the disclosure,

[0067] - a medical radar, and

[0068] - a controller configured to control at least the medical radar and to store measured data for later or simultaneous analyses.

[0069] The controller is configured to manage and regulate the operation of the system through manipulation of electromagnetic waves by adjusting properties, such as phase, amplitude, or polarization for applications like beamforming or signal direction. The controller ensures that the transmitarray performs its primary functions, such as directing signals efficiently, and may optionally control additional components within the system, such as power supplies, receiver arrays, or other auxiliary mechanisms. This design allows for flexible and efficient operation, enabling the system to adapt to various requirements or environmental conditions. The controller refers to the radar system, which is the "brain" of the system and is responsible for managing and regulating the operation of the transmitarray.

[0070] Traditionally, the transmitarray is a passive component composed of unit cells made from alternating layers of metal and substrate, designed to manipulate electromagnetic waves through their fixed geometry and material properties without involving active electronics. In such cases, the radar, acting as the controller, does not directly control the transmitarray but could manage auxiliary factors like the input signal properties (e.g., frequency, phase, or polarization) or the physical positioning of the array.

[0071] However, in more modern systems, transmitarrays may incorporate active or reconfigurable elements, such as tunable diodes, liquid crystals, or other metamaterials, which enable dynamic control of their behavior. In these advanced configurations, the radar can actively adjust the transmitarray's properties in real time, allowing for adaptive beam steering, frequency tuning, or other functionalities.

[0072] In some embodiments of the disclosure, the medical radar works at frequencies between 0.1 GHz and 50 GHs, such as between 2 GHz and 30 GHz.

[0073] In particular, the medical radar may use 5.8 GHz self-injection locked (SIL) radar technology and a frequency-modulated continuous wave (FMCW) radar.

[0074] In a fourth aspect, the disclosure relates to a method of performing hemodynamic monitoring on a person by use of a system according to the third aspect of the disclosure.

[0075] The method of performing hemodynamic monitoring may comprise the step of: - measuring one or more of the following values for the person: heart rate, beat- by-beat interval, heart rate variability, Pulmonary Artery Pressure, wrist pulse, respiration, and blood pressure. In some embodiments of the disclosure according to the fourth aspect of the disclosure, the values are output as real-time data. Hereby it is possible to monitor the conditions of a person e.g. dependent on a given activity being performed, and it is possible to take immediate action, if required.

[0076] The method of performing hemodynamic monitoring may further comprise the steps of:

[0077] - comparing at least one of the measured one or more parameters with a predetermined threshold value, and

[0078] - providing an alarm signal when the threshold value is reached.

[0079] The parameters that may trigger the alarm generally includes values such as electromagnetic field strength, frequency shifts, or changes in the phase that deviates from expected norms. The system compares these values with predetermined thresholds, which are based on safety limits or operational requirements.

[0080] In some embodiments of a transmitarray according to the first aspect of the disclosure or of a system according to the second aspect of the disclosure, the transmitarray or the system, respectively, is built into a wearable device configured to be temporarily fastened to the person, such as to a person's wrist and cloth. It may e.g. be built into a Smartwatch or a similar device.

[0081] In some embodiments of a transmitarray according to the first aspect of the disclosure or of a system according to the second aspect of the disclosure, the transmitarray or the system, respectively, is built into or configured to be built into a piece of textile, such as a t-shirt or jacket that can be worn by the person on which the monitoring is to be performed. By only integrating the transmitarray into a wearable textile, any common medical radar can be focused which can lead to higher signal strength, less motion artifacts, and / or more hemodynamic related signal content.

[0082] The method of manufacturing a transmitarray, as outlined above, encompasses a series of comprehensive steps. These include: • Identifying one or more key characteristics relevant to the transmitarray's intended application. This process involves determining the specific purpose or use-case for which the transmitarray is being designed.

[0083] • Establishing the required specifications for the transmitarray. This step involves defining the essential parameters and performance criteria that the transmitarray must meet to be effective in its intended role.

[0084] • Determining the operating frequency range. This involves specifying the range of frequencies over which the transmitarray must perform optimally, considering the application for which it is being designed.

[0085] • Establishing the required efficiency levels. This step involves setting targets for the energy efficiency of the transmitarray, which can be crucial for its functionality, especially in power-sensitive applications.

[0086] • Evaluating human tissue performance metrics for the intended use. For transmitarrays designed for applications involving close proximity to or interaction with the human body, such as in medical or wearable technology, it's important to assess how the device will perform in relation to human tissue, including safety and efficacy considerations.

[0087] These steps ensure a comprehensive and tailored approach to the design and manufacture of a transmitarray, addressing all critical aspects from its intended use and technical specifications to its operational efficiency and human compatibility.

[0088] In a fifth aspect, the disclosure relates to the use of a transmitarray or a system as described herein in healthcare applications, such as

[0089] • non-invasive vital signs monitoring (heart rate, respiration),

[0090] • sleep apnoea detection and respiratory disorders,

[0091] • imaging for early detection of tumours,

[0092] • brain activity and stroke detection,

[0093] • fall detection and posture monitoring,

[0094] • blood flow and cardiovascular monitoring,

[0095] • gestural control and rehabilitation monitoring,

[0096] • neonatal and infant monitoring, tissue differentiation and diagnostics, and monitoring mental health and cognitive functions.

[0097] The first, second, third, fourth, and fifth aspects of the present disclosure may each be combined with any of the other aspects. These and other aspects of the disclosure will be apparent from and elucidated with reference to the embodiments described hereinafter.

[0098] BRIEF DESCRIPTION OF THE FIGURES

[0099] The transmitarray and system according to the disclosure will now be described in more detail with regard to the accompanying figures. The figures show one way of implementing the present disclosure and is not to be construed as being limiting to other possible embodiments falling within the scope of the attached claim set.

[0100] Figure 1A schematically shows a unit cell architecture of the transmitarray lens.

[0101] Figures IB and 1C schematically shows an even-layer and an odd-layer, respectively, of a unit cell according to the disclosure.

[0102] Figure ID schematically shows an electromagnetic setup using a HFSS floquet port.

[0103] Figure 2 is a schematic representation of Bessel beam generation using axicon.

[0104] Figure 3A shows a metasurface optimization using Matlab. Figure 3B shown a printed flexible transmitarray lens.

[0105] Figure 4 shows a comparison of the vital sign waveforms obtained by using SIL Radar with and without a Flexible Lens.

[0106] Figure 5 shows a comparison of the extracted heartbeat signal using EEMD with the R wave locations of the reference ECG signal.

[0107] Figure 6 is a schematic representation of heart rate detection technique with a flexible transmitarray lens and a remote SIL radar.

[0108] Figure 7 schematically shows a simplified equivalent circuit model employed for a four-layer copper flexible transmitarray, where the values are normalized.

[0109] Figure 8 shows measured radiation patterns of the flexible transmitarray at 10°, 20°, 30°, 40° bending conditions in anechoic chamber.

[0110] Figure 9A shows the portrayal of the transmitarray is contoured along the E-plane on a cylindrical surface, delineated by means of a geometric model. Figure 9B shows a principal perspective, presenting a graphical exposition of its tangible arrangement and configuration.

[0111] Figure 10 shows measuring the focusing effect of the transmitarray lens. Figure 10A shows the measurement setup. Figure 10B shows simulated received power distribution on the focal plane. Figure 10C shows measured received power distribution on the focal plane. Figure 10D shows simulated and experimental received powers transmitarray at 5.8 GHz.

[0112] Figure 11 shows an illustration method for hand grip and ice-cold pressure test challenge.

[0113] Figure 12 shows the estimated normalized heartbeat wave from the self-injection locked (SIL) radar and comparing them with the peaks of the reference electrocardiogram (ECG) signal. Figure 12 shows the extracted heartbeat waveform from SIL radar with and without flexible lens.

[0114] Figure 13 shows performance comparison beat-to-beat peak interval HR values between Radar and ECG using Bland-Altman plot. Figure 13A is for hand-grip test challenge, and figure 13B is for ice cold test challenge.

[0115] Figure 14 shows the power spectrum distribution of HRV using SIL radar and the reference ECG signal. Figure 14A shows handgrip test challenge, and figure 14B shows ice test pressure challenge. DETAILED DESCRIPTION OF AN EMBODIMENT

[0116] The following is a description of an embodiment of the disclosure in the form of a flexible transmitarray designed for focusing electromagnetic waves beam in the far-field for healthcare radar. The flexible transmitarray is manufactured with a substrate of polyimide, and it has a dielectric substrate of Er = 3.5, tangent loss tan 5 = 0.0027 and thickness = 152.54 pm with a transmission coefficient around 0.9. It comprises three dielectric substrates and four copper layers where the odd layers are printed with a circular shape and the even layers are printed with a cross shape. The proposed structure has been found to outperform known solutions for remote detection in healthcare radar when evaluated with different focal lengths and bending conditions.

[0117] The utilization of electromagnetic sensors in wearable devices to continuously monitor biological information, including heart rate, respiratory rate, and blood pressure, has significant potential to revolutionize health monitoring. Unlike traditional medical equipment, wearable devices can provide real-time data that is easily accessible to patients and healthcare providers while also more comfortable and convenient to wear. They can also provide precaution alerts for individuals at risk for specific medical conditions and promote healthy lifestyles through fitness tracking.

[0118] However, there are also limitations to consider. One major limitation is the dependence on battery power, which can limit the duration of monitoring. The frequency band restrictions of electromagnetic sensors can also narrow the operating frequency range and make it challenging to capture a wide range of physiological data. The rigidity of traditional materials used in sensors can also limit their applicability in certain contexts, such as physical activity or for individuals with certain body types.

[0119] To address these limitations, the studies leading to the present disclosure explored the potential of a flexible transmitarray lens for vital signs using 5.8 GHz self-injection locked (SIL) radar technology. The flexible transmitarray lens was made of polyimide flex substrates, which are lightweight, have a low dielectric constant, and are ultrathin and flexible. The lens was tested under various conditions, proving stable in both flat and bent positions. The work also included a 60 mm thick muscle layer in the simulation setup for computational performance analysis. The findings overcome limitations associated with rigid materials and enable more comfortable and accurate heart rate monitoring in wearable devices.

[0120] Figures 1A-1C illustrate the proposed structure of the transmitarray lens according to an embodiment of the disclosure within a square area with a side length of 7 mm (0.11 A at 5.8 GHz). Figure 1A schematically shows the unit cell 2 architecture of the transmitarray lens. Figure ID schematically shows the electromagnetic setup using a HFSS floquet port with air 6, muscle 7 and reference planes 8. As shown in Figure 1A, the lens comprises four metallic copper-layers 3, 4 for better control over the electromagnetic properties and enhanced performance compared to single-layer substrates. The even-layers 3 have a cross pattern (cross arm width 1 mm, total cross arm length 4 mm), and the odd-layers 4 have a circular pattern with a radius of 3 mm. The substrate 5 between the metal layers is made of polyimide (PI). It has a dielectric constant of Er = 3.5, a tangent loss tan 5 = 0.0027, and a thickness = 50.8 pm. The thickness of each of the metal layers being 0.035 pm, the total thickness of the unit cell is (4 * 0.035 pm + 3 * 50.8 pm) = 152.54 pm.

[0121] The proposed transmitarray lens needs to have a specific phase distribution cp to achieve a focusing effect as described by the Bessel beam equation. The equation is given as:

[0122] Figure 2 is a representation of Bessel beam generation from an incident Gaupssian beam using an optical element called an axicon. Such non-diffracting Bessel beams are useful in optical trapping, microscopy, and precision cutting, and they are ideal for scenarios requiring long-range, stable beam profiles or selfreconstruction after obstruction.

[0123] The Gaussian input beam is characterized by a bell-shaped intensity profile represented by the dashed curve in the left side of the figure. The beam initially has a waist radius Wo, which is the radius of the Gaussian beam at its narrowest point (beam waist) and determines the initial beam width before it encounters the axicon. The beam radius R refers to the radius of the Gaussian beam as it interacts with the axicon.

[0124] The axicon is a conical optical element, which plays a pivotal role in converting the Gaussian beam into a Bessel beam by refracting the light into concentric rings.

[0125] The apex angle a of the axicon, which is the angle at the tip of the conical axicon, determines the degree to which the beam is refracted and is critical in determining the beam angle 3, which is the angle of the Bessel beam's propagation in relation to the Z-axis.

[0126] The Bessel beam's intensity pattern includes a central peak surrounded by rings. The width of the central peak and the spacing between rings are determined by the input beam parameters and the axicon properties. Bessel beams exhibit the property of being self-reconstructing and nondiffracting over a certain propagation range Zmax. Zmax is the distance along the propagation axis (Z-axis), i.e. the direction of beam propagation, over which the beam maintains its Bessel profile. Beyond this range, the beam begins to diverge, resulting in an intensity profile like the one represented by the dashed curve in the right side of the figure.

[0127] The distance Zmax depends on the initial beam parameters Wo, R, the apex angle a, and the wavelength of the light. A smaller apex angle a or narrower beam waist Wo leads to a longer Zmax. The propagation range Zmax extends from the Bessel beam region start (A), which is the region where the Gaussian beam begins transforming into a Bessel beam after passing through the axicon, to the Bessel beam region end (B), which is the point where the Bessel beam structure deteriorates due to diffraction or other effects.

[0128] TABLE I

[0129] TRANSMISSION COEFFICIENTS OF A UNIT CELL WITH DIFFERENT DIMENSIONS

[0130] Dimensions. Transmission coeff.

[0131] Table I presents the optimized design of the transmitarray lens obtained using floquet port ANSYS HFSS software. To ensure the practicality of the transmitarray, the simulation was conducted with a 60 mm thick muscle layer with dielectric constant Er = 48.8, as shown in Figure ID. In Figure 3A, the phase distribution of the transmitarray lens is shown, which was optimized using Matlab. Figure 3B shows the final design of the transmitarray, which is a printed flexible polyimide transmitarray comprising 12x12 elements. It can be shown that the theoretical computation of Zmax is 90 mm or 2.12 Ao, assuming a base angle of P = 30° to achieve the desired energy distribution in a human heart valve.

[0132] The electric field distribution of a y-polarized incident wave has not undergone significant scattering when normally illuminated at Z = -10 mm has significant non-scattered aspects. The simulated focusing distance (Zmax) is 80 mm (2.02 Ao), which is lower than the theoretically computed value but still suitable for remote vital radar applications using a Gaussian beam within the Rayleigh distance. The simulated value 3, which is the angle between the incident wave and the surface of the lens is 29.6° and is in close agreement with the theoretical prediction. When the simulations are performed in different planes at distances of Z = +10 mm, +30 mm, +60 mm, +90 mm, the focusing efficiencies are 39.5%, 49%, 42%, 27%, respectively.

[0133] Therefore, the proposed transmit array is consistent with the theoretical expectations and exhibits high efficiency at a distance of Z = Zmax / 2. Knowing the efficiency of the energy distribution in different planes can improve the accuracy of the actual implementation and enable it to function correctly even if the flexible transmit array is floating, bending, or unsteady at the desired distance. The design also considers bending conditions, and it has been found that the stretch on the unit cell and contraction of the substrate are negligible. Moreover, the dielectric effects of the material remain constant.

[0134] In a simplified model of the flexible structure under various bending angles, the boundary conditions are met to obtain the electric field in different E-plane bending angles such as 10°, 20°, 30°, and 40°.

[0135] Considering the gain calculated by the aperture cross-section dimension, the focusing efficiency is 53.3%. The energy transmission of the non-diffracting Bessel beam should remain constant within the focusing range, both in the flat and bent conditions.

[0136] In an experimental setup used to monitor the vital signs of a seated subject wearing the flexible transmitarray lens, along with an ECG on the wrists and an ankle following Einthoven's triangle, the SIL radar system emits and receives a 5.8 GHz Doppler radar beam at a distance of 100 cm, with a transmit power of 2 dBm and power consumption of 330 mW. The SIL radar system consists of an array antenna, a SIL oscillator (SILO), and a frequency demodulator for efficient signal acquisition. Notably, the transmitarray lens is attached to the subject's clothing near the aorta.

[0137] Figure 4 demonstrates the sensitivity for capturing vital sign information that was improved by using the flexible lens. It focuses the beam signals on the heart valve, giving clearer vital sign information. The normalized spectrum frequencies for respiration (0.3 Hz) and heartbeat (1.51 Hz) can be identified using the flexible lens. In contrast, without the flexible lens, the measured respiration amplitude is smaller (0.38 Hz), and the measured heartbeat frequency is lower (around 1.3 Hz) due to reduced signal clarity, accuracy and / or focus of the reflected signals.

[0138] Figure 5 compares the heartbeat signal obtained from the SIL radar using the flexible lens and the reference ECG signal using ten consecutive samples. The EEMD (Ensemble Empirical Mode Decomposition) method extracts the heartbeat signal from the radar by adding IMF3 and IMF4 (third and fourth Intrinsic Mode Functions obtained by the EEMD) directly in the time domain.

[0139] Thus, in summary the present disclosure introduces a new technique that utilizes flexible transmitarray lens SIL radar technology to detect vital signs. The disclosure offers high accuracy and sensitivity, enabling real-time remote healthcare radar applications. Additionally, the method provides the ability to focus the beam from the transmit antenna to a specific heart area, thus improving the precision of the detection process. The technique is expected to be useful in remote sensor systems for pulse detection, with the detected heart rate showing a moderate correlation to the reference values.

[0140] The following is a more detailed description of the disclosure, and there may be some overlap with the above description. As described above, the transmitarray lenses are designed for medical radar systems, enhancing the direction of electromagnetic beams in the far-field. However, the scope of protection also covers near-field applications. The near-field region is typically within a distance of approximately one wavelength of the electromagnetic source.

[0141] In practical terms, this is the area where the electromagnetic fields are still closely linked to the source and have not yet transitioned fully into freely propagating waves.

[0142] In this context, near-field applications could include imaging, sensing, or medical diagnostics where high spatial resolution or localized interaction with tissues is required. For instance, near-field systems might be used to achieve better detail in radar-based medical imaging due to the stronger, non-propagating fields interacting with objects in close proximity. While the transmitarray lenses are designed primarily for far-field beam shaping, their ability to manipulate electromagnetic waves could also enhance performance in the near-field. For instance, they could focus or shape the fields more effectively in the near-field for specialized medical applications.

[0143] Its exceptional precision and sensitivity render it an ideal tool for real-time remote health monitoring systems, particularly in pulse detection. The research findings consistently aligned the heart rates detected by this innovative method with standard reference rates, reaffirming its reliability and accuracy. This consistency highlights the potential of the transmitarray lenses as a valuable advancement in medical radar systems. The study not only validates the effectiveness and reliability of the lenses but also lays a solid foundation for further research and development in this field. The insights garnered are expected to significantly bolster the progression of radar technologies in healthcare, leading to more accurate, efficient, and non-invasive health monitoring solutions, thereby enhancing patient care and outcomes.

[0144] To overcome the limitations of known techniques as described in the section "Background", the study leading to the present disclosure explores the potential of a flexible transmitarray lens to monitor vital signs using SIL radar technology at 5.8 GHz. In such applications, the lens serves to focus the beam of the transmitter antenna through the human heart. Experimental tests have been conducted to assess the stability of the lens in both flat and bent positions. Additionally, we have incorporated simulated skin and muscle layers to assess lens performance under realistic conditions. Our findings demonstrate that the use of flexible transmitarray lenses can overcome the limitations associated with rigid materials and wearable radar devices. Utilizing flexible substrates allows wearable devices to achieve both more comfortable and precise heart rate monitoring. This research marks a significant step forward in enhancing the user experience and accuracy of health monitoring devices, making them more convenient, low cost, and efficient for daily use, even over extended periods, without the need for direct skin contact.

[0145] The radar system, as schematically depicted in Figure 6, is an innovative assembly designed to operate at a frequency of 5.8 GHz. Within this system, an individual carries a flexible transmitarray, carefully positioned near their aorta on the chest. On the opposite side of the individual stands the Self-Injection Locking (SIL) radar, stationed at a strategic location to ensure optimal reception and transmission of signals. The radar's core functionality revolves around a delay line frequency demodulator. This demodulator is tasked with interpreting the transmitted signals emanating from the Self-Injection Locking Oscillator (SILO). During this demodulation phase, the system is adept at extracting pivotal information: the Doppler phase shift, a consequence of the natural movement of the chest wall. This phase shift becomes the precursor for the derivation of the heartbeat signal, a vital metric that offers information on real-time physiological responses, especially during physical exertion.

[0146] The flexible transmitarray is not merely an accessory; it serves a pivotal role in the radar structure. This pliable lens, when integrated, meticulously focuses the frequency-modulated (FM) signals that the SIL radar emits. Moreover, it has the capability to inject the Doppler-shifted echo signals back into the SILO, amplifying the system's precision and efficiency.

[0147] The FM signal, represented as SFM(t) in Equation (1), is formulated based on the amplitude A0Sc and frequency CDosc intrinsic to the SILO.

[0148] Equation (2) delves deeper into the dynamics of frequency modulation, elucidating how variables such as the locking range CDLR, the inherent distance Rc and the relative motion xc(t) between the transmitter and the chest-mounted apparatus interact. The locking range, as defined by CDLR finds its theoretical foundation in Adler's equation.

[0149] In the given context, Q represents the quality factor of the (SILO), while Aec signifies the echo's signal amplitude Sec(t) that has undergone Doppler shifting. SILO circuits employ a clapp structure, wherein the injection port is intricately linked to the transistor gate. This setup has a 200 MHz bandwidth and produces 0.5 dBm output power. The specialized antenna of the SIL radar receives the FM signal SFM(t) that is injected into the SILO of the system. Subsequently, the signal undergoes low-noise amplification using a low-noise amplifier (LNA) with a very narrow bandwidth. After amplification, the signal is directed to the delay line frequency demodulator. We obtain the frequency modulation Aco(t) by computing the arctangent of the in-phase (I(t)) and the quadrature component (Q(t)) that are extracted from the demodulator.

[0150] The symbol Td signifies the temporal delay introduced by the delay line present within the demodulator. When the electrical altitude of xc(t) at (Dose is insignificant, equation (2) can be used to make an approximation.

[0151] Consequently, the movement of the chest, denoted as xc(t), is calculated using Equations (4) and (5). This derived movement signal is then subjected to additional processing to extract the heartbeat signal. The heartrate signal extraction enables the assessment of variations in the intervals between consecutive heartbeats, providing valuable insight into the autonomic nervous system's functioning and cardiovascular health. However, the implementation of heart rate variability (HRV) investigation is an essential instrument for the identification and monitoring of various cardiovascular diseases.

[0152] The following is a description of a multiband radar antenna.

[0153] The SIL Doppler radar antenna is specifically designed for a 3-8 GHz bandwidth, featuring a smaller beamwidth of less than 17°. This design incorporates high gain, narrow beamwidth, sensitivity, and excellent efficiency to optimize the power of the radar system. By focusing the transmitted and received electromagnetic waves in a specific direction, it maximizes the system's capabilities. The array antenna is designed with a three-band structure, providing multiple operating frequencies. Its input impedance ranges from 150 to 337 ohms, allowing flexibility and compatibility with various systems. The proposed configuration of the antenna array has overall dimensions of 52 x 44 mm. It utilizes a dielectric substrate with a 1.6 mm thickness, a relative permittivity (Er) of 3.5, loss tangent (tan 5) of 0.02, and relative permeability of 1.

[0154] The offered antenna array consists mainly of two identical pairs of U-slots. One substrate contains four radiating elements in the upper layer, while another substrate comprises the ground and the feed line in the bottom layer. An impedance SMA connector 50 is used at the termination of the antenna feed line to transmit the input RF signal (Figure 6), minimizing signal reflections, and improving power transfer efficiency. Incorporating multilayer designs into antenna arrays aims to enhance bandwidth and radiation patterns by leveraging differences in layer thicknesses and dielectric constants to achieve desired features. The inclusion of an air gap in the antenna array design offers several advantages. First, it provides isolation between elements, reducing mutual coupling and interference, thus improving the integrity of the signal and the overall performance. Secondly, the air gap minimizes crosstalk, resulting in cleaner signals and reduced interference. Moreover, it provides the ability to accurately regulate the radiation pattern of each element, and the overall matrix contributes to superior overall performance.

[0155] The proposed antenna array architecture consists of square patches with 2 x 2 radiating elements and two U-slots in the upper layer. Vias with a diameter of 0.8 mm are utilized to establish the connection between the feed line in the bottom layer and the four radiating elements. The feeding network consists of a one-to-four power divider and a transmission line that is soldered to the 50-ohm coaxial SMA connector. Table II shows the parameters of the proposed construction, including specifics on its size and geometric features.

[0156] Implementing the two U-slots in the antenna array improves return loss and bandwidth. This corresponds to a bandwidth enhancement of 50%, indicating the achievement of enhanced gain and bandwidth in the desired frequency band. Considering the unpredictable characteristics of the FR4 laminate and the influence of SMA connectors, the results obtained from simulations and measurements are deemed satisfactory.

[0157] A return loss of the simulations and measurements with the visual expression of the physical implementation of the U-shape design of 27.151 dB, 32.243 dB and 24.017 demonstrates favourable values at frequencies of 3.8, 5.8 and 8.8 GHz. Additionally, the antenna has a bandwidth of 113, 403.7, and 500.88 MHz in a frequency range of 3.65-3.85, 5.5-5.9, and 8.4-8.8 GHz. Significantly, the measured reflection coefficient closely corresponds to the simulated results, providing further validation for the accuracy of the calculations. To enhance isolation performance, a cutting-edge dual U-slot patch metamaterial is seamlessly integrated at the focal point of the antenna elements. This arrangement significantly improves isolation, exceeding -20 dB in the three operating bands, mitigating interference. The decoupling element can be seen as a type of electromagnetic bandgap (EBG) structure, which occupies minimal space compared to previously reported designs.

[0158] As a result, the proposed technique offers a compact and efficient solution, allowing an increase in the packing density of the antenna system, and the antenna array performs effectively within the desired frequency range for radar communication applications.

[0159] The estimated radiation patterns at the specified design frequencies of 3.81, 5.8, and 8.8 GHz in the cp = 0° and cp = 90° planes exhibit symmetrical features, focusing on a specific and narrow direction. Across a range of frequencies, the simulated and measured results display a notable level of agreement, signifying a strong consistency between the two sets of data. The proposed antenna exhibits a measured H-plane 3-dB beamwidth of 45°, 39°, and 42.5° at frequencies of 3.81, 5.8, and 8.8 GHz. With their expansive H-plane radiation patterns, it provides comprehensive coverage of the azimuth plane when multiple panels are utilized.

[0160] According to the findings, the measured gain and efficiency of the array antenna is 5.6 dB at 3.81 GHz, with an accompanying efficiency of 62%. Within the 5.8 GHz band, the measured gain exceeds 10.2 dB, and the productivity reaches 73%. At 8.8 GHz, the quantified improvement is 9.33 dB, while the efficiency is 51%. These results clearly indicate that high gain is present across all three desired frequency bands, thereby ensuring excellent sensing directivity and sensitivity.

[0161] In conclusion, the U-shaped patches in the antenna design significantly enhance gain, providing a focused and directed radiation pattern ideal for precise and sensitive signal detection, crucial for healthcare radar systems. These characteristics ensure accurate monitoring of biological signals such as breathing or heartbeats, with minimal interference. Additionally, the U-shaped patches' design attributes make the antenna compatible with our suggested flexible transmitarrays lens, offering directional transmission, flexibility, and improved bandwidth, essential for various wireless applications.

[0162] The following is a description of a single-band flexible transmitarray lens.

[0163] The proposed layout of the transmitarray lens is shown in Figure 1 and was described above.

[0164] The optimized design of the unit cells, achieved through simulation using ANSYS (HFSS) software, is outlined in Table I shown above. The simulation considered a practical scenario with a 50 mm air gap and employed Floquet port excitation. To ensure the real-world applicability of the transmitarray, additional factors were taken into account. Specifically, the simulation incorporated a 60 mm thick muscle, 20 mm fat, and 10 mm thick skin layer, both characterized by dielectric constants of Er = 47.715, Er = 4.9549 and Er = 34.0914, respectively. Figure ID provides a visual representation of this setup. By considering these practical aspects in the simulation, the optimized design of the transmitarray lens enhances the accuracy and reliability of the design, ensuring its feasibility and performance in real-world scenarios.

[0165] A simplified circuit representation of each cell, as illustrated in Figure 7, can effectively model the behaviour of the cell. In this circuit, the metalized layers are represented by the shunt admittances on the transmission lines, with normalized values denoted as bi and b2. Then, in a proportional four-layer arrangement, the unit-cell elements in layers 2 and 4 demonstrate equal admittances. The circuit's termination is accomplished by using a normalized free-space characteristic admittance set to 1. The sections of the transmission line with lengths of d represent the spacing between layers. This length takes into account the physical distance between the layers, along with an empirical correction for the substrate (in this case, the substrate thickness is 50.8 pm).

[0166] The phase distribution of the transmitarray lens, which underwent optimization using Matlab with reference to the values provided in Table I, is depicted in Figure 3A which was described above. Figure 3B presents an ultimate configuration of the transmitarray, showcasing a printed flexible polyimide design comprising 12x12 elements and a total square of 110 mm x 110 mm. The theoretical computation of Zmax is 90 mm or 2.12 Ao, assuming a base angle of P = 30° to achieve the desired energy distribution in a human heart valve.

[0167] Taking into account the equivalent circuit depicted in Figure 7, yin was set to 1 and the equation was rearranged to express b2 in terms of bi.

[0168] 62 — —

[0169] 612

[0170] To achieve a desired phase shift in a transmitarray, the process involves varying bi as an odd layer and calculating the corresponding b2 as an even layer for different transmission phase values d. The transmission phase of the circuit is dictated by the transmission matrix, as indicated in Table I. Once bi is determined, the susceptibility value of b2 is calculated using equation (6) to ensure proper match. Regardless of the shape of the elements, these two curves are influenced by the total layers, the physical partition, and the substrate thickness. The same approach can be used for transmitarray cells with either two or four layers, although the matching conditions for b2 will differ from equation (6).

[0171] Using an equivalent circuit represented in Figure 7, the given equation derives the relationship between b2 and bi. Here, P represents the phase constant, which is determined by the operating frequency and the speed of light, bi and b2 are normalized complex admittance values that characterize the behaviour of the transmitarray cell. Their purpose is to accomplish the desired phase shift within the cell. The term (|3d)2+ bi2in the equation represents a combination of the phase shift presented by the physical segregation between the layers (d) and the normalized admittance bi. It affects the overall phase response of the transmitarray cell. By manipulating bi and calculating the corresponding b2 for different values of d, the transmission phase can be controlled and adjusted accordingly. It is necessary to note that the values of bi and b2 are obtained by analysis and optimization, considering various factors such as the number of layers, partition in the physical layer, substrate thickness, and the desired phase shift in the transmitarray cell. These parameters are essential in designing efficient and effective transmitarray systems. The proposed transmitarray lens needs to have a specific phase distribution cp to achieve a focusing effect, as described by the Bessel beam equation. The equation is given as:

[0172] Here, ko represents the wave number, which is equal to 2n divided by the free- space wavelength Ao. As illustrated in Figure 2, which was described above, the axicon base angle is denoted by P, and x and y specify the horizontal and vertical distances from the focal point (xo, yo, z) and a position on the transmitarray lens (xo, yo, 0). The focal length is equivalent to the non-diffracting distance z. An important observation is that as the axicon base angle increases, there is a corresponding decrease in the maximum non-diffracting distance z, and vice versa, resulting in a closer focusing area to the lens. The optimal focusing distance is at Zmax / 2, where Zmax is the maximum distance of the focusing area. Increasing the radius R of the axicon's surface increases the maximum distance Zmax, which can be computed by Z max — R / tan p.

[0173] Comparing the penetration of the electric field into the chest with and without the use of a flexible transmitarray lens, it is found that the electric field distribution does not converge at the focal point (0,0,90) mm without a flexible transmitarray. With a flexible transmitarray, on the contrary, the electric field penetrates successfully at the focal point (0,0,90) mm. Furthermore, the electric field distribution of a y-polarized incident wave has been studied when the transmitarray lens is illuminated at Z = -10 mm with significant non-scattered aspects. The simulated focusing distance (Zmax) is 80 mm (2.02 Ao), which is lower than the theoretically calculated value, but still suitable for remote vital radar applications using a Gaussian beam within the Rayleigh distance. The simulated value p is the angle between the incident wave and the lens surface, which is 29.6° and is in close agreement with the theoretical prediction. When simulations are performed in different planes at distances of Z = +10 mm, +30 mm, +60 mm, +90 mm, the focusing efficiencies are 39.5%, 49%, 42%, 27%.

[0174] In real implementations, the target orientation may vary, necessitating the derivation of the transmitarray beam deflection formula based on the generalized refraction law. This formula can be expressed as follows:

[0175] Here, the incident angle symbolized by 0i, 0t denotes the refraction angles, while the refractive index symbolized by m and nt characterizes the refracted medium. Given the vertical incidence of the beam from the air, it traverses the transmitarray and subsequently refracts into the human body, leading to 0i = 0 and ni = nt = 1. This condition applies to the x and y directions, thus allowing us formulating the deflection equation as follows: ip2 — A'o sin ( ) x + Aig sin (^2 ) V (9)

[0176] In this scenario, 0i and 02 represent the refraction angles in the x and y directions. Maintaining consistent energy transmission efficiency for Bessel beams within the focusing range is highly important. The following equation is required for efficiency computation: where q = represents the average power or energy transmission efficiency, Re represents the real part of the quantity within parentheses. In this case, we have the cross product of two vectors "E and "H* representing the electric field and the complex conjugate of the magnetic field, respectively, d representing an infinitesimal area vector. The integral is taken over Si and S2, which represent the cross-sectional regions of the focusing region. Theoretically, the optimal focusing plane is found at Z = Zmax / 2, where the greatest focusing diameter is reached with a radius of R. Thus, the focusing efficiency is determined by comparing the circular area of the focusing zone (Si) with a diameter of R to the square area of the complete plane (S2) with a side length of 2R. Both surfaces are identical to the metasurface size. By adhering to these design considerations, the proposed transmitarray aligns with the anticipated theoretical outcomes and exhibits high efficiency at a distance of Z = Zmax / 2. Understanding the energy distribution efficiency in different planes facilitates the accurate implementation and to ensure proper functionality, even if the flexible transmit array experiences floating, bending, or unsteadiness at the desired distance. Moreover, it is crucial to note that, within the focusing range, the energy remains confined to the specific plane of that size, maintaining the desired characteristics. The design also accounts for bending conditions, and it has been observed that the unit cell experiences minimal stretching, while the substrate undergoes negligible contraction. Furthermore, the dielectric effects of the material remain consistent.

[0177] Figure 8 exhibits the acquired radiation beam orientations, and the measured radiation patterns exhibit a remarkable agreement with the simulated results for both the E-plane and H-plane radiation patterns at 5.8 GHz, even when subjected to diverse bending conditions. The transmitarray exhibits a peak gain of 26.63 dB, and the 3-dB gain bandwidth spans 16.9% of the operating frequency. The antenna efficiency, taking into account the gain calculated by the aperture crosssection size, is determined to be 85.3%. The radiation patterns exhibit stability across the 5.8 GHz band. In terms of polarization performance, the measured cross-polarization level at 5.8 GHz is observed to be -29.8 dB, indicating a good level of cross-polarization suppression. The maximum sidelobe level is measured to be -13.4 dB.

[0178] However, the measured aperture efficiency is negligibly descending compared to the simulated value, with respective values of which are 65% and 78.9%. This discrepancy in aperture efficiencies could be attributed to various factors, including fabrication tolerances or measurement uncertainties. Despite the minor variations, it still demonstrates a reasonable level of efficiency in capturing and utilizing the available electromagnetic energy. The efficiency of the aperture q can be determined using equation:

[0179] In this context, G stands for the approximated gain, Do signifies the maximum directivity, Ao represents the wavelength in free space, while Aedenotes the physical extent of the aperture. Our proposed stacked-layer flexible transmitarray lens has a very good efficiency without the need for holes. The exceptional efficiency can be chiefly attributed to meticulous management of spillover and taper losses, registering at 0.52 dB and 0.41 dB, respectively, as well as transmission loss around 1.25 dB. The illustration of the structured curved transmitarray as a cylindrical-rectangular cavity is presented visually in Figure 9A. The z-direction is confirmed to be the axis of the cylindrical surface where the unit cell is united. L is the transmitarray length L = 110 mm A / 2, W stands for the transmitarray width W = 1.524 pm, substrate thickness is denoted by h, the cylindrical surface radius is Ra, and the estimated bending angle: 20 = L / (Ra + h). To represent different bending configurations, the bending angle 20 and the inner bending radius a are adjusted accordingly. The eigenvalue, k, represents the wave number propagating in the medium, k = 2n / A. In cavity architecture, where different bending angles are considered boundary conditions, the variation in the eigenvalue k signifies a change in the propagation wavelength A within the medium. The phase velocity remains constant when electromagnetic waves propagate at an identical frequency. N = Af = 1 / pe. The cavity structure obeys the Helmholtz equation, with the magnetic vector potential A and the electric vector potential F and fulfilling the equation inside the cavity. The resonant frequencies differ for various modes such as Temli or Tmmli, and can be determined using the following formula:

[0180] The values of kmi are found by solving Equations (15) and (16) for the Tez modes (bending in the E-plane) and the TMz modes (bending in the H-plane):

[0181] The Bessel functions Jv and Yvcorrespond to the first and second categories. The parameter v indicates the Bessel function order, which is defined as v = mn / 20. The prime sign in Equations (13) and (14) represents the derivative of the statement of Bessel functions.

[0182] In the extreme case of a flat substrate, where there is no bending or curvature, the bending angle has a value of 20 = 0°, and the bending radius approaches infinity (a -> oo). in this case, the TE101 eigenfrequency returns to the resonant frequency of the flat configuration, which can be defined as: m7T

[0183] "'mi ~ ■ Jr, mli

[0184] 20a, '

[0185] Equation (13) is satisfied as the order of the Bessel function, denoted as v, tends to a significantly large number. Furthermore, it can be demonstrated that the TMon eigenfrequency also returns to the resonant frequency of the flat configuration. This satisfies Equation (14) when v = 0, which given by:

[0186] The simulation results support these findings by indicating that the resonance frequency of the transmitarray remains largely unaffected by bending in the E- and H-plane. The reason for this is that it has a minimal impact on the existing path for the fundamental resonance. Furthermore, by examining Equation (12) for the fundamental mode TMon(m = 0, I = 1, I = 1), it can be observed that the order of the Bessel function, v = mn / 20, is equal to zero for various bending angles 20. In order to derive the electric field for varying bending angles along the E plane, the boundary conditions are meticulously satisfied such as 10°, 20°, 30°, and 40°. Focusing efficiency is acquired considering the gain determined by the cross-sectional dimension of the aperture, which is 53.3%. The energy transmission of the non-diffracting Bessel beam should remain constant within the focusing range, both under flat and bent conditions. To address the task of evaluating the specific absorption rate (SAR) and its safety aspects through computational and experimental means, which is also safe to wear on the human body, we investigated a streamlined three-layer flexible transmitarray lens constructed from polyimide with Ansys HFSS. This setup featured the flexible transmitarray lens placed on the human chest. The calculated SAR values obtained from this analysis are presented in Table II. The SAR values outlined in Table II confirm that the system adheres to the safety guidelines established by both the Federal Communications Commission (FCC) and the International Commission on Non-Ionizing Radiation Protection (ICNIRP). This underscores that the use of a flexible transmitarray lens structure in SIL radar applications facilitates the attainment of minimal SAR values, for which no detrimental consequences have been identified.

[0187] Figure 10A depicts an experimental setup used to analyse the received power in the focal plane of a transmitarray lens 1, attached to a piece of pork meat (thickness w = 90 mm), which simulates the dielectric properties of human muscle 7. The transmitting antenna Tx, which is connected to a signal generator 10, is arranged at a distance D = 1 m from the transmitarray lens 1, and the receiving antenna Rx, which is connected to a spectrum analyser 9, is arranged at a distance d = 1 mm from the piece of pork meat. Figures 10B and 10C illustrate the comparison between simulated and actual measurements of the normalized received power distribution in the same plane, showing a notable match between them. The recorded contour area of -4 dB is verified to be smaller than 15 mmx l5 mm, which confirms the sufficient focusing ability of the transmitarray lens. Although the received power level is subject to alteration due to the proximity of the pork meat to the receiving antenna, the shift related to the focal point remains approximately consistent. However, Figure 10D illustrates the power received with different separation distances between the transmitting and receiving antennas. The transmitted power was 19 dBm and the antenna array, utilized as a transmitter, was implemented with a frequency of 5.8 GHz and a gain of 13.8 dBi. During the experimental measurements, distances were systematically modified, and the resulting received power was carefully documented. Both experimental and theoretical results showed significant congruence, despite the presence of minor discrepancies attributed to various factors. These factors include environmental conditions, fabrication inconsistencies, SMA losses, RF cable losses, and other associated losses.

[0188] The following is a description of the vital sign monitoring and results.

[0189] The subject is wearing a flexible transmit array lens, and an ECG is placed on the wrists and an ankle according to the Einthoven triangle with an emphasis on lead I. The 5.8 GHz SIL radar system serves as a key component in this configuration, emitting and detecting beams over 100 cm. The radar operates with a transmit power of 2 dBm and consumes 330 mW of power.

[0190] The SIL radar system comprises an array antenna, a frequency demodulator, and a self-injection locked oscillator (SILO), all of which contribute to efficient signal acquisition. The transmitarray lens is meticulously fastened to the individual's garment in proximity to the aorta, facilitating the effective aggregation and analysis of data. It functions to capture and bounce back a radar beam from a 5.8 GHz Doppler radar positioned 1 meter away. Table III conveys details regarding the SIL radar components and specifications.

[0191] Two separate experiments, namely the hand-grip test challenge and the ice-cold test pressure challenge, were meticulously performed to accumulate physiological signals, as illustrated in Figure 11. Throughout these experiments, participants were guided to maintain a relaxed posture and breathe naturally, all while in the vicinity of the SIL Radar and adorned with a flexible lens. The hand grip test required participants to exert pressure with their hands, while the ice-cold test elicited physiological responses by exposing them to cold stimuli. Despite substantial movements from participants, the use of the flexible transmitarray lens effectively mitigated the impact of these movements, ensuring a steadfast focus of the radar beam. Due to variations in human body structure and the lightweight, thin, and flexible nature of our transmitarray lens, it could bend between 5° and 15° without compromising the performance of the antenna or the precision of vital sign detection. A total of four male subjects participated in these experiments (age 31.3 ± 22.4 years, height 165.9 ± 8.8 cm).

[0192] Figure 4, which was described above, emphasizes the improved accuracy in detecting vital sign information using the flexible lens. This advanced lens allows precise targeting of beam signals onto the heart valve, resulting in clearer and more detailed vital sign measurements. When utilizing the flexible lens, the specific spectrum frequencies recorded for breathing stand at 0.3 Hz, while for the heartbeat it is 1.51 Hz. In contrast, without the use of this lens, the frequency for breathing reduces to 0.38 Hz and the heartbeat measurement drops to around 1.3 Hz. This demonstrates the importance of the flexible lens in capturing accurate vital data.

[0193] Figure 12 provides a visual comparison of heartbeat waveforms obtained from the SIL radar, both with and without the application of our adaptable lens. The upper part of the figure presents the standardized heartbeat waveform obtained with our adaptable lens, demonstrating the baseline results. On the other hand, the lower part of the figure depicts the standardized heartbeat waveform captured without our adaptable lens in operation. The data clearly highlight the notable enhancement and stabilization of the heartbeat waveform when using the flexible transmitarray. This improvement is attributed to the increased sensitivity and consistent stability provided by the flexible transmitarray throughout all conducted experiments, confirming its significant impact on the reliability and accuracy of heartbeat waveform detection.

[0194] During the evaluation, the focus was predominantly on the deployment of the innovative adaptable transmitarray, which is meticulously designed for human chest attachment. Despite this primary focus, the application of the flexible transmitarray was extended to two distinct and challenging experimental scenarios: the handgrip test and the ice-cold test pressure. The successful implementation of these diverse tests underscored the transmitarray's robust performance and versatility, confirming its capability to enhance and stabilize heartbeat waveform measurements across a range of conditions. In the course of these experiments, factors such as moving averages and body movements induced by the tests were present, potentially affecting the results. However, the flexible transmitarray proved instrumental in mitigating the impact of body movements, ensuring the reliability of the captured heartbeat waveform data. This effectiveness is largely attributed to the unique properties of a transmitarray according to the present disclosure. It is exceptionally thin, lightweight, and flexible, perfectly conforming to the structure of the human chest when worn. These characteristics not only ensure comfort and convenience for the wearer but also contribute substantially to the accurate and reliable monitoring of heartbeat waveforms, even in the face of external disturbances and movements.

[0195] The effectiveness of the flexible transmitarray according to the present disclosure, employed alongside SIL radar, was rigorously validated by contrasting its performance with the established ECG measurements. A comparison was made, including a detailed and methodical analysis of heart rate (HR) in beats per minute (bpm) during two different experimental scenarios: the handgrip test challenge and the ice-cold test pressure. HR values sourced from both the SIL radar (equipped with the flexible transmitarray) and a reference ECG signal over a one-minute span were analysed. Before the exercise, the radar recorded an average HR value of approximately 76.9605 bpm, closely aligned with the reference ECG average value of 76.3789 bpm. Post-exercise measurements exhibited an increase in HR for both methods, with the radar reporting an average of 79.2819 bpm and the reference ECG indicating an average of 77.5589 bpm. These data underscore a general elevation after exercise in average HR values. Proceeding further, in an HR comparison between the SIL radar heartbeat signal and the reference ECG signal during the ice-cold test challenge, similarly to the observations made in the challenge of the handgrip test, a comparable trend was discerned, albeit with a different group of subjects.

[0196] To assess the agreement between Radar and ECG measurements, Bland-Altman plots were employed in the experiment. Figure 13 presents the Bland-Altman plots for the same beat-beat interval values, which closely reflect the instantaneous heart rate. Figures 13A and 13B are the hand grip test challenge and the ice-cold test challenge, respectively. The Bland-Altman analysis evaluates the differences in BBI values obtained from two distinct measurement techniques relative to their respective mean values. This statistical approach enables the assessment of agreement or discrepancy between the two methods, revealing potential variations in the measurement outcomes. The solid black line in this context represents the average difference between the methods, whereas the dashed black lines delineate the lower and upper limits of agreement (LoA). The limits of agreement (LoA) are estimated by adding and subtracting 1.96 times the standard deviation of the differences from the mean difference. Essentially, the LoA serves as a measure to establish the range within which most of the discrepancies between the two measurement methods are expected to lie. During the analysis, a small, fixed bias of -2.623 ms was observed in the hand-grip test, while a bias of 3.252 ms was observed in the ice-cold test. The calculated LoAs were determined to be -380.48 ms and 375.23 ms for the hand-grip test, and -288.78 ms and 295.29 ms for the ice-cold test.

[0197] In the research leading to the present disclosure, by precisely targeting the human heart rate, it was possible to extract detailed information from the power spectrum density (PSD). It is typically challenging to discern the PSD, especially when the echo pulse signal waveform is disrupted by noise and the signal is not directly aimed at the human heart. Figures 14A and 14B present an example of the power spectrum density (PSD) of HRV measured from both the SIL radar and the reference ECG. In Figure 14A, before the challenge of hand grip test, the HF range of PSD was relatively high in both the radar and ECG signals. Following the completion of the exercise, there was a slight increase in PSD of HF PSD. Furthermore, the LF range exhibited a notable increase after hand grip challenge, indicating a change in the spectral characteristics associated with the autonomic nervous system activity. Figure 14B depicts the PSD from the ice pressure test challenge. The HF value increased substantially, as well as the LF range increased. This analysis of power spectra provides valuable insight into the dynamic changes in HRV associated with different physiological conditions and interventions. It helps to elucidate the underlying mechanisms and responses of the cardiovascular system, contributing to a deeper understanding of human physiology and potential applications in health monitoring and assessment.

[0198] The power spectrum densities acquired from time series data of heartbeat intervals are examined in the frequency domain of heart rate variability (HRV). This analysis provides valuable information on the distribution of power across different frequency components within the HRV signal and helps identify specific frequency bands associated with physiological mechanisms and autonomic nervous system activity. To perform a spectral analysis of HRV, several steps were followed. Firstly, the beat-by-beat series, representing the time duration between successive heartbeats, were uniformly interpolated at a rate of 5 Hz. This ensured consistent and evenly spaced data points, enabling accurate spectral analysis. The power spectra were then estimated using the Welch periodogram method, which involves dividing the data into overlapping segments and applying a Fourier transform to each segment. A 90% overlap was used to ensure sufficient data overlap for reliable spectral estimation.

[0199] To minimize any linear trends in the data, linear detrending was performed using Hann windows of 300 seconds in length. To enhance the spectral resolution and reduce noise, a broadband smoothing technique was applied. This involved applying a moving average to the power spectra, with the order of the moving average increasing with the spectral frequency. This smoothing process improved the coherence and interpretability of the spectral content. The power spectra obtained were summed within specific frequency bands that are important for analysing heart rate variability (HRV). These bands include the very low frequency (VLF) range from 0.003 to 0.04 Hz, the low frequency (LF) range from 0.04 to 0.15 Hz, and the high frequency (HF) range from 0.15 to 0.4 Hz.

[0200] Tables IV and V provide a comprehensive summary of HRV indices in the frequency domain, also the Bland-Altman plot results, utilizing data from four subjects. The Bland-Altman plot is a valuable tool for detecting systematic errors, such as fixed or proportional biases, in the measurements. The tables also include the natural logarithm of the components of LF and HF, normalized to the square of total power (s2), which aids in the analysis and interpretation of HRV in the frequency domain. The R wave in the ECG waveform represents ventricular depolarization, while the RR interval signifies the duration of a full cardiac cycle. Calculating the average change in duration between successive RR intervals allows us to determine the heart rate variability (HRV). Additionally, the tables present PHF and PLF, representing high-frequency and low-frequency bands in the power spectrum density of heart rate fluctuations, respectively. These frequency bands provide valuable information on the modulation of heart rate by various physiological mechanisms, such as respiratory and autonomic activity.

[0201] The transmitarray and the system describe in the present disclosure may find use in a large number of healthcare applications, of which some are mentioned and described briefly in the following:

[0202] 1. Non-invasive vital signs monitoring

[0203] Microwave radar systems can be used to monitor vital signs such as heart rate and respiration in hospital or home settings by detecting small, periodic movements in the chest cavity.

[0204] The use of beam-focusing metasurfaces enhance the radar's ability to pinpoint the exact area of interest (e.g. the chest), improving the sensitivity and accuracy of the measurements, especially for detecting subtle chest movements in patients, such as during sleep or in patients with respiratory issues like COPD or asthma.

[0205] 2. Sleep apnoea detection and respiratory disorders

[0206] In sleep medicine, microwave radar systems can be used to monitor breathing patterns in both clinical and home environments and detect conditions like sleep apnoea, where breathing stops intermittently during sleep. The use of beam-focusing metasurfaces help concentrate the radar signal on the chest and diaphragm, providing a more accurate assessment of breathing irregularities. This allows for non-intrusive, continuous observations, which are less cumbersome than using traditional devices like CPAP machines or wired sensors, while real-time data with improved accuracy is delivered due to the focused beam control. ging for early detection of tumours

[0207] Microwave radar systems can detect abnormalities in tissue properties, and beam-focusing metasurfaces enhance this capability. By focusing the microwave beam on specific tissue areas, such as breast tissue, the radar can detect subtle changes that indicate the presence of tumours or other abnormalities. This approach is particularly valuable for breast cancer screening.

[0208] Thus, being a safer imaging modality with no radiation exposure, the use of beam-focusing metasurfaces provides a non-ionizing alternative to mammography, potentially allowing for more frequent screenings and earlier detection of abnormalities.

[0209] n activity and stroke detection

[0210] Microwave radar systems enhanced by metasurfaces can penetrate the skull to monitor brain activity and detect strokes or other brain injuries. Focused beams improve the ability to detect subtle differences in tissue properties, such as changes in blood flow that occur during a stroke.

[0211] Thus, the use of beam-focusing metasurfaces allows for real-time non- invasive monitoring of brain conditions without the need for expensive and complex MRI or CT scanners, making it accessible for continuous bedside monitoring in critical care. detection and posture monitoring

[0212] For elderly patients or those with mobility issues, microwave radar systems equipped with beam-focusing metasurfaces can monitor body posture and movements to detect falls or predict their likelihood. By focusing the microwave beam on key joints or the torso, the radar can precisely track how a person is standing, sitting, or moving.

[0213] Such highly accurate fall prediction and detection systems can be used for elderly care or in hospital settings, even through walls or clothing, enabling quick emergency response and reducing fall-related injuries. d flow and cardiovascular monitoring

[0214] Microwave radar systems are sensitive to small movements and can detect variations in blood flow. Metasurfaces improve the radar's focusing capabilities, allowing for a more accurate monitoring of the blood flow in critical areas, such as arteries, veins, or even the heart. This is particularly useful for early detection of cardiovascular issues.

[0215] Thus, the use of metasurfaces provides real-time, contactless monitoring of blood flow in patients with vascular conditions or heart disease allowing continuous observation of hemodynamic changes without the need for Doppler ultrasound or invasive probes. Gestural control and rehabilitation monitoring

[0216] In rehabilitation, microwave radar systems can be used to monitor patient movements, allowing doctors or therapists to track recovery progress, for instance in physical therapy, especially in post-surgical or stroke recovery.

[0217] Beam-focusing metasurfaces enhance the radar's ability to detect fine motor movements or larger gestures, making it an effective tool for monitoring rehabilitation exercises. Thus, precise monitoring of patient movements can be obtained, ensuring that exercises are being performed correctly, and providing data for assessing improvement over time. Neonatal and infant monitoring

[0218] Microwave radar systems can be used for contactless monitoring of vital signs in neonates and infants in NICUs (neonatal intensive care units) without the need for contact-based devices like electrodes or straps.

[0219] The use of beam-focusing metasurfaces enable precise, focused monitoring of an infant's chest to detect respiratory rates, heart rates, and even movement patterns during sleep. Thus, a continuous, real-time monitoring, which is safer and more comfortable for the infant, is obtained with reduced risk of skin irritation or infection. Tissue differentiation and diagnostics

[0220] Microwave frequencies can differentiate between various types of tissues based on their dielectric properties. Beam-focusing metasurfaces enable more accurate detection of differences between healthy and diseased tissue, potentially aiding in diagnostics such as identifying inflammation, tumours, or tissue damage. Thus, non-invasive, contact-free diagnostics for detection of tissue abnormalities may be obtained, which can identify problems earlier than other imaging techniques without exposing patients to harmful radiation.

[0221] 10 Monitoring mental health and cognitive functions

[0222] Microwave radar systems can also track small, involuntary movements, such as facial expressions or tremors, which can be associated with mental health conditions like anxiety, stress, or Parkinson's disease. Beamfocusing metasurfaces can direct the radar beam to the head or specific body parts, improving the sensitivity of the radar to detect subtle physiological responses to stress or cognitive load.

[0223] Thus, contactless, continuous and remote monitoring of physiological signals, such as signals related to stress, anxiety, or neurological disorders, is obtained, providing insights into mental health with the need for invasive or cumbersome devices.

[0224] Hence, as described here-above, beam-focusing metasurfaces in the microwave frequency range offer a transformative approach to radar-based healthcare systems. These systems provide non-invasive, contactless monitoring that is highly precise, making them ideal for detecting and tracking subtle physiological changes, such as heart rate, breathing, and even tissue abnormalities. In healthcare, microwave radar systems with metasurfaces can revolutionize diagnostics, monitoring, and therapeutic tracking, offering real-time, low-risk solutions that improve patient care while reducing the need for invasive procedures and ionizing radiation.

[0225] Transmitarray metasurfaces can manipulate microwave beams to focus energy on specific regions of interest in the patient's body. The frequency of the microwave radar is critical because it determines the depth of penetration, resolution and accuracy of the system. Thus, different healthcare applications require different frequencies depending on the target tissues, the depth of focus, and the need for high-resolution detection. 2.4 GHz - 5.8 GHz:

[0226] These lower microwave frequencies are commonly used in hospitals or home settings for continuously monitoring vital signs, such as detecting heart rate, respiration, and sleep patterns.

[0227] These frequencies provide good penetration into soft tissues, making them ideal for chest monitoring and for tracking small, periodic movements like breathing.

[0228] 10 GHz - 12 GHz:

[0229] Slightly higher frequencies provide better resolution, suitable for tracking smaller physiological movements, such as subtle chest wall motion or cardiac muscle contraction.

[0230] Giving a more detailed measurement of smaller or more specific regions of the body while maintaining adequate penetration, these higher frequencies are particularly applicable for sleep apnoea monitoring, cardiac health tracking, and some imaging applications.

[0231] 24 GHz and above:

[0232] These high frequencies are suitable for high-resolution imaging and applications requiring precise detection of tissue characteristics, such as cancer screening and tissue diagnostics.

[0233] As penetration into deep tissues is limited, the system working at these frequencies is more suitable for surface-level imaging or scanning of shallow tissues, such as microwave imaging of tumours, cancer detection (e.g., breast cancer screening), and tissue characterisation.

[0234] The distance between the transmitarray and the patient is a key design consideration, as it affects the system's beam focusing ability, the quality of the received data, and the precision of the radar's measurements. Thus, the distance must be optimised depending on the application to ensure that the radar beam is focused accurately onto the patient's body or the regions being monitored.

[0235] Short-range applications (0.5-2 meters):

[0236] For vital signs monitoring applications, the radar with the transmitarray is typically positioned between 0.5 m and 2 m from the patient. The transmitarray is usually placed directly in front of the radar antenna and manipulates the transmitted microwave signals to precisely focus on the chest or abdomen of the patient.

[0237] This configuration is ideal for bedside monitoring or wearable medical devices, where the radar needs to detect small movements, such as heartbeats or breathing patterns.

[0238] Systems in this configuration typically use a frequency between 2.4 GHz and 10 GHz, balancing penetration depth and resolution for short-distance vital sign detection.

[0239] Medium-range applications (1-3 meters):

[0240] For room-scale applications like fall detection or posture monitoring, the radar system with the transmitarray may be placed at a medium distance of 1-3 meters from the patient. The transmitarray will typically be mounted in a bedside device or on a wall, or it may be integrated into a monitoring system within the patient's room. It focuses the radar beam across the room or towards the patient's body to detect movement or posture changes.

[0241] This range is particularly useful for detecting large movements, such as falls or changes in body position, while the patient is sleeping or moving in a room. Frequencies between 5.8 GHz and 24 GHz can provide higher resolution and sufficient range for room-scale detection, allowing the radar system to monitor the patient without needing to be physically close.

[0242] Long-range applications (3-5 meters or more):

[0243] In cases where a wider area or full-body monitoring is needed, such as in hospital rooms or rehabilitation centres, the radar with the transmitarray can operate at distances up to 3-5 meters. The transmitarray may be placed on the ceiling or mounted on a wall to focus the radar beams across the room. It is positioned strategically to direct the radar beam toward specific regions of the patient's body or the entire room.

[0244] This setup enables the radar to cover a larger area, making it possible to monitor a patient's full-body movements, track fall risks, or assist in physical rehabilitation.

[0245] Higher frequencies around 10 GHz to 24 GHz are ideal for these applications, where high-resolution imaging and body scanning are necessary.

[0246] Thus, in summary, the present disclosure provides a new method that uses SIL radar technology with flexible transmitarray lenses for the detection of vital signs. This methodology offers a significant advantage by enabling the radar wave beam to target a specific area of the thoracic region, thereby yielding a more precise detection of cardiac anomalies. This targeted approach allows for accurate measurement of vital signs while minimizing the impact of random body movements during experiments such as handgrip test and ice-cold test pressure resulting in improved system performance. This increased sensitivity enables more accurate detection of the characteristics of the beat-by-beat interval (BBI) and heart rate variability (HRV), crucial indicators of cardiac activity. These advances contribute to the general precision and reliability of the radar system in capturing and analysing various physiological parameters related to heart activity. In conclusion, the proposed technique offers a valuable approach for remote sensor systems in pulse detection, demonstrating a moderate correlation between the detected heart rate and the reference values. This low-cost transmitarray lens has a potential impact extends to various healthcare and monitoring applications, where real-time and non-contact vital sign detection plays a crucial role.

[0247] Although the present disclosure has been described in connection with the specified embodiments, it should not be construed as being in any way limited to the presented examples. The scope of the present disclosure is set out by the accompanying claim set. In the context of the claims, the terms "comprising" or "comprises" do not exclude other possible elements or steps. Also, the mentioning of references such as "a" or "an" etc. should not be construed as excluding a plurality. The use of reference signs in the claims with respect to elements indicated in the figures shall also not be construed as limiting the scope of the disclosure. Furthermore, individual features mentioned in different claims, may possibly be advantageously combined, and the mentioning of these features in different claims does not exclude that a combination of features is not possible and advantageous.

Claims

CLAIMS1. Transmitarray configured to manipulate electromagnetic waves from a medical radar.

2. Transmitarray according to claim 1, wherein the transmitarray has a total thickness of at most 10 mm, such as at most 5 mm, such as at most 1 mm, such as at most 0.2 mm, such as a total thickness between 50 and 155 microns.

3. Transmitarray according to claim 1 or 2, wherein the transmitarray comprises an array of unit cells, such as an array of at least 150 unit cells.

4. Transmitarray according to claim 3, wherein the unit cells are square in form and have side lengths between 3 mm and 20 mm, such as between 5 mm and 12 mm, preferably between 7 mm and 8 mm.

5. Transmitarray according to any of the preceding claims, wherein the transmitarray has a layered structure comprising two or more layers, such as two to five layers.

6. Transmitarray according to claim 5, wherein the layered structure comprises at least a first layer type and a second layer type, the first and second layer types having different in-plane configurations, and the first and second layer types preferably being alternately arranged.

7. Transmitarray according to claim 6, wherein the first layer type comprises a plurality of unit cells each comprising a cross-shaped metal layer arranged on a polymer substrate, such as on a polyimide substrate, and the second layer type comprises a plurality of unit cells each comprising a circular-shaped metal layer arranged on a polymer substrate, such as on a polyimide substrate.

8. Transmitarray according to claim 7, wherein the thickness of the polymer substrate between two neighbouring layers is between 10 microns and 100 microns, such as between 25 microns and 75 microns, preferably between 48 microns and 52 microns.

9. Transmitarray according to claim 7 or 8, wherein the length of each of the two crossing arms in the cross-shaped metal layer of the first layer type is between2 mm and 18 mm, such as between 3 mm and 10 mm, preferably between 3.5 mm and 4.5 mm.

10. Transmitarray according to any of claims 7-9, wherein the width of each of the two crossing arms in the cross-shaped metal layer of the first layer type is between 0.2 mm and 4 mm, such as between 0.5 mm and 2 mm, preferably between 0.8 mm and 1.2 mm.

11. Transmitarray according to any of claims 7-10, wherein the radius of the circle in the cross-shaped metal layer of the second layer type is between 1 mm and8 mm, such as between 2 mm and 5 mm, preferably between 2.5 mm and3.5 mm.

12. Transmitarray according to any of the preceding claims, wherein the transmitarray is configured in such a way that functioning thereof does not require supply of electricity during use.

13. Transmitarray according to any of the preceding claims, wherein the transmitarray is configured to manipulate electromagnetic waves from medical radars working at frequencies between 0.1 GHz and 50 GHs, such as between 2 GHz and 30 GHz.

14. Transmitarray according to claim 13, wherein the transmitarray is configured to manipulate electromagnetic waves from a medical radar using 5.8 GHz selfinjection locked (SIL) radar technology and a frequency-modulated continuous wave (FMCW) radar.

15. Method of manufacturing a transmitarray according to any of the preceding claims, the method comprising the steps of- determining one or more of the following characteristics: an intended use of the transmitarray, required specifications of the transmitarray, operating frequency range, gain, required efficiency, human tissue performance metrics for the intended use, beamforming and focusing, directivity, power handling capability, bandwidth, and imaging resolution,- modelling, by use of the computational electromagnetics tool, a design of the transmitarray,- simulating the interaction of electromagnetic waves with the modelled transmitarray to ensure that it meets the required specifications,- optionally optimizing the design of the transmitarray with respect to performance, manufacturing feasibility, and cost,- optionally checking that the design is scalable to a required size,- selecting materials for the further manufacturing based on the operating frequency, environmental conditions, and available manufacturing capabilities, and- manufacturing the transmitarray by providing a substrate and applying metal thereon in a pattern determined by the previous steps.

16. Method according to claim 15, wherein the step of modelling comprises designing unit cells that are configured to form the transmitarray when assembled, and the step of manufacturing comprises manufacturing a plurality of unit cells, and assembling the unit cells into the transmitarray.

17. Method according to claim 15 or 16, wherein the step of modelling comprises using one or more of the following parameters as input parameter(s): number of layers, required precision, X and Y periods (spatial periodicity along a horizontal X-axis and a vertical Y-axis, respectively) of each unit cell when present, the required frequency range, the polarization, and performing a simulation, in which one or more of the following design parameters of the transmitarray is optimized: required phase, specific phase distribution, the materials of substrate and metal, a dielectric constant, a tangent loss, and a layer thickness.

18. System for performing hemodynamic monitoring on a person, the system comprising: a transmitarray according to any of claims 1-14, a medical radar, and a controller configured to control at least the medical radar and to store measured data for later or simultaneous analyses.

19. System according claim 18, wherein the medical radar works at frequencies between 0.1 GHz and 50 GHs, such as between 2 GHz and 30 GHz.

20. System according to claim 18 or 19, wherein the medical radar uses 5.8 GHz self-injection locked (SIL) radar technology and a frequency-modulated continuous wave (FMCW) radar.

21. Method of performing hemodynamic monitoring on a person by use of a system according to any of claims 18-20.

22. Method according to claim 21, comprising the step of measuring one or more of the following values for the person: heart rate, beat-by-beat interval, heart rate variability, Pulmonary Artery Pressure, wrist pulse, respiration, and blood pressure.

23. Method according to claim 21 or 22, wherein the values are output as realtime data.

24. Method according to any of claims 21-23, further comprising the steps of- comparing at least one of the measured one or more parameters with a predetermined threshold value, and providing an alarm signal when the threshold value is reached.

25. Transmitarray according to any of claims 1-14 or system according to any of claims 18-20, wherein the transmitarray or the system, respectively, is built into a wearable device configured to be temporarily fastened to the person, such as to a person's wrist and cloth.

26. Transmitarray according to any of claims 1-14 or system according to any of claims 18-20, wherein the transmitarray or the system, respectively is built into or configured to be built into a piece of textile, such as a t-shirt or jacket that can be worn by the person on which the monitoring is to be performed.

27. The use of a transmitarray according to any of claims 1-14 or claims 25-26 or a system according to any of claims 18-20 in healthcare applications, such as non-invasive vital signs monitoring (heart rate, respiration), sleep apnoea detection and respiratory disorders, imaging for early detection of tumours,- brain activity and stroke detection,- fall detection and posture monitoring, - blood flow and cardiovascular monitoring,- gestural control and rehabilitation monitoring, neonatal and infant monitoring,- tissue differentiation and diagnostics, and monitoring mental health and cognitive functions.

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