Devices and methods for thermal and electromagnetic dosimetry

Abstract

The present invention relates to a device and method for measuring electromagnetic dosimetry received by an object irradiated with an electromagnetic (EM) field (23) emitted by an electromagnetic wave source (2), the device comprising: a screen (3) having a top surface (31) facing the electromagnetic wave source (2) and a bottom surface (32) opposite the top surface (31), said screen (3) being adapted to absorb at least a portion of the EM field emitted by the electromagnetic wave source (2); the screen comprises a plurality of unit cells (33), and the device further comprises: - at least one thermal sensor (5) arranged with respect to the bottom surface of the screen (3) and configured to measure a physical quantity related to the heat distribution along the surface of the screen induced due to absorption of the electromagnetic field in the screen medium; - a processing unit (6) linked to the at least one thermal sensor (5) and configured to calculate electromagnetic dosimetry quantities from the measured thermal distribution, information about the EM field emitted by the EM source, and predetermined EM and thermal properties of the screen; Includes.

Description

[Technical Field]

[0001] The present invention relates to a device and method for electromagnetic dosimetry, more particularly to a device for measuring thermal and electromagnetic information in a synchronous manner and extracting an electromagnetic dosimetry quantity induced in a thermal medium, e.g., biological tissue, by an electromagnetic field emitted by an electromagnetic wave source. [Background technology]

[0002] With the development of wireless technologies, such as mobile phones and various user wireless devices that come into contact with the human body, accurately measuring the exposure levels of electromagnetic (EM) radiation within the human body has become an important factor.

[0003] There are various categories of devices, commonly referred to as "phantoms," that mimic the electromagnetic properties of biological tissues for assessing human exposure to electromagnetic fields. These include liquid phantoms, semi-solid phantoms, solid phantoms, and even hybrid phantoms. Liquid phantoms contain plastic parts or a solid shell filled with a gel or liquid whose EM properties resemble those of human tissue at the measurement frequency, typically due to its high water content, as found in biological tissue. These devices are typically used in the frequency range from 30 MHz to 6 GHz. These devices have several issues: the liquid evaporates over time and / or its dielectric properties deteriorate, requiring frequent replacement. These devices require special test equipment to support their weight. Use of such devices at frequencies higher than 6 GHz is not possible due to the strong absorption of EM fields by water molecules, resulting in a very shallow penetration depth and an insufficient signal-to-noise ratio (SNR) for implanted sensors. The composition of semi-solid phantoms is similar to that of liquid phantoms; a gelling agent is typically used instead of the liquid to maintain the phantom's shape without the use of a solid shell. Its main drawback is its limited lifespan (typically limited to a few days or weeks). A solid phantom is a solid piece made from a solid dielectric material, such as plastic, polymer, ceramic, or synthetic rubber doped with conductive particles such as graphite, carbon, or metal. Its main advantage is the reliability and constancy of its dielectric properties over time. However, these devices are extremely complex to manufacture and expensive. Furthermore, due to the frequency-dependent EM properties of the phantom material, these devices suffer from high EM losses that do not allow measurements above 10 GHz. For example, at 60 GHz, the penetration depth of electromagnetic radiation in human tissue is on the order of 0.5 mm, and radiation absorption is essentially limited to the surface layers of the body. This results in a prohibitively low signal-to-noise ratio (SNR) for any sensors incorporated into a phantom that replicates the EM properties of the tissue.

[0004] In this regard, due to the peculiarities of the frequency-dependent interaction between the human body and wireless devices, which result in reduced reflections and simultaneously stronger EM losses, compliance testing for 5G and later generation wireless devices operating at frequencies above 6 GHz, new dosimetry standards and guidelines imply the use of a new dosimetry quantity, namely, absorbed power density (APD) averaged over a fixed area, instead of the specific absorption rate (SAR) averaged over a fixed volume used for frequencies below 6 GHz. Furthermore, given the potentially strong interactive influence of the human body on the performance characteristics of 5G devices (and therefore on the user's exposure level), the new guidelines also imply testing such devices under realistic conditions, taking into account the presence of the human body. These two requirements render obsolete existing EM dosimetry devices used to test 3G / 4G devices.

[0005] Furthermore, to meet the demand for increased data rates and traffic volumes, new frequency bands in the frequency range of approximately 24 GHz to 300 GHz will be adopted in 5G and upcoming generations of wireless communication systems thanks to the development of new radio access technologies such as millimeter wave frequency bands, wideband spectrum signals, beamforming, multiple input multiple output (MIMO), and dynamic resource allocation in the time, frequency, and space domains.

[0006] The mmWave spectrum allocated in different countries for 5G and future 6G wireless systems includes multiple sub-bands in licensed (e.g., 24-28 GHz, 37-39 GHz, 47 GHz) and unlicensed (e.g., 60 GHz) spectrum, the bandwidth of which may vary from country to country.

[0007] The available spectrum within each band is divided into multiple channels with standardized carrier sizes for the lower mmWave sub-bands, such as 50 MHz, 100 MHz, 200 MHz, and 400 MHz. The allocation of frequency and time resources can be done in a centralized or distributed mode, with specific schemes that may also differ for different types of 5G wireless devices. Channel capacity can be further increased by frequency reuse and / or multiplexing in the time, space, and polarization domains.

[0008] Higher propagation losses at mmWave are compensated for by higher antenna gains achieved using small antenna arrays and multiple-input, multiple-output (MIMO) techniques. Beamforming capabilities enabled by 5G devices are used to multiplex parallel data streams to communicate with multiple spatially separated users or to mitigate dynamic blockages of the propagation channel by a single user. Portable and wearable devices often house four to eight antenna elements, enabling them to support at least two distinct beams characterized by different shapes / widths, gains, and / or spatial orientations.

[0009] Thus, modern wireless communication devices have multiple antennas, can operate in multiple frequency bands and modes, and support a variety of radio access technologies. For 5G devices, dynamic resource allocation in the time, frequency, and spatial domains adds another layer of complexity. Existing methods for electromagnetic (EM) dosimetry developed for compliance testing of 3G / 4G devices operating at frequencies below 6 GHz cannot be applied to 5G mmWave devices due to the inherent limitations of all existing technologies, either related to an inability to replicate realistic use-case conditions or to an inability to consider dynamic resource allocation, or due to the prohibitively low SNR caused by high material and propagation EM losses at mmWave. This necessitates the development of new dosimetry systems that can overcome these limitations.

[0010] International Publication No. WO2017 / 0173350 proposes a device capable of measuring electromagnetic waves at frequencies higher than 6 GHz while retaining the characteristics of human tissue, with reference to Figure 1. The device comprises a layer of dielectric material (S), a semi-permeable metal shield (MSH) with through-holes (OSH), and an array of sensors (SENS) placed under the through-holes. The sensors are configured to measure the electromagnetic field emitted by an electromagnetic wave source (EMS).

[0011] Although the device proposed in WO2017 / 0173350 provides reliable and consistent dielectric properties, potentially enabling electromagnetic dosimetry at frequencies above 6 GHz, the proposed solution does not teach how to reduce or limit the significant loss in electromagnetic field strength that occurs when propagating through composite dielectric materials doped with conductive microparticles (e.g., carbon), which results in strong absorption of the electromagnetic field at high frequencies, especially above 6 GHz.

[0012] Furthermore, like other prior art solutions, the measurement procedure used in WO 2017 / 0173350 relies on sampling the transmitted electromagnetic field at multiple spatial points defined by the positions of sensors in an array of sensors (SENS), which can give rise to inaccuracies due to the fixed mesh of sampling points defined by the topology of the array of sensors and / or due to additional post-processing steps involving digital integration of the measured quantities to calculate dosimetric quantities defined for a given surface area or volume.

[0013] High EM losses can compromise measurement accuracy and reduce the signal-to-noise ratio (SNR). To increase the SNR, a key parameter for low-power measurements, one needs to increase either the sensor's sensitivity or the level of the transmitted electromagnetic signal. The latter is usually preferable because it allows for higher noise levels to be addressed. However, for low-power devices operating in the millimeter-wave frequency range, this is not possible due to the power limitations and high material losses at these frequencies for standard dielectric materials. These limitations can be significant with regard to the accuracy and cost of dosimetry devices for compliance testing of 5th generation and beyond wireless devices.

[0014] Additionally, the prior art device proposed in WO2017 / 0173350 does not take into account the specificities of 5G devices with regard to dynamic resource allocation in the domains of time, frequency and space, which may result in rapid changes in exposure conditions. [Prior art documents] [Patent documents]

[0015] [Patent Document 1] International Publication No. WO2017 / 0173350 Summary of the Invention [Problem to be solved by the invention]

[0016] Therefore, there is a need for improved devices and methods for electromagnetic dosimetry that take into account the specificities of 5G devices with regard to dynamic resource allocation (by considering the sophisticated time and frequency resource allocation enabled by 5G and future xG devices that result in non-constant exposure conditions), as well as improve the signal-to-noise ratio (SNR) of the measurement signal by developing methods and techniques that are not based on direct EM measurements, thereby enabling the use of more accurate, reliable and fast methods and devices for user exposure compliance testing of 5G / xG wireless devices under realistic exposure conditions.

[0017] Another object of the present invention is to propose a device that makes it possible to convert the unavoidable electromagnetic losses in the phantom material into a measurable physical quantity, i.e., local heat that correlates with the sought-after dosimetric quantity, thereby providing an alternative approach to building EM dosimetry systems.

[0018] Another object of the present invention is to provide a device that is easier and cheaper to manufacture. [Means for solving the problem]

[0019] The present invention improves this situation.

[0020] A device has been proposed for measuring electromagnetic dosimetry received by an object irradiated with an electromagnetic (EM) field emitted by an electromagnetic source, the device comprising: a screen having a top surface facing the electromagnetic wave source and a bottom surface opposite the top surface, said screen being adapted to absorb at least a portion of the EM field emitted by the electromagnetic wave source; the screen includes a plurality of unit cells, and the device further comprises: - at least one thermal sensor arranged with respect to the bottom surface of the screen and configured to measure a physical quantity related to the heat distribution along the surface of the screen induced due to absorption of the electromagnetic field in the screen medium; - a processing unit linked to the at least one thermal sensor and configured to calculate electromagnetic dosimetry quantities from the measured thermal distribution, information about the EM field emitted by the EM source, and predetermined EM and thermal properties of the screen; Equipped with.

[0021] In one embodiment, the device further comprises at least one electromagnetic sensor configured to measure information about the EM field emitted by the EM source.

[0022] In a preferred embodiment, the processing unit is configured to calculate electromagnetic dosimetry quantities by temporally correlating information about the EM fields measured by the at least one electromagnetic sensor and the thermal distribution measured by the at least one thermal sensor.

[0023] In another embodiment, the processing unit is configured to analyze signals transmitted from the at least one electromagnetic sensor to derive information about the EM field emitted by the EM source.

[0024] In one embodiment, at least one electromagnetic sensor is linked to the electromagnetic wave source by a control link.

[0025] In a further embodiment, the processing unit is configured to use a lock-in technique to post-process the thermal distribution over time by using a predetermined lock-in frequency and waveform for the EM field emitted by the EM source.

[0026] In one embodiment, the at least one thermal sensor is positioned a fixed distance from the bottom surface of the screen and is aligned with respect to the center of the screen, with respect to the center of the unit cell, and / or along the direction of EM wave propagation.

[0027] In yet another embodiment, the at least one thermal sensor includes a plurality of thermocouples attached to or embedded in the bottom surface of the thermal screen.

[0028] In one embodiment, the at least one thermal sensor comprises at least one heat-sensitive element attached to the bottom surface of the screen.

[0029] In one embodiment, the at least one electromagnetic sensor is an electromagnetic sensor that operates in a frequency range that at least partially overlaps with an operating frequency range of the electromagnetic wave source.

[0030] In another embodiment, the at least one electromagnetic sensor is configured to measure an incident EM field from an EM source, an EM field reflected from the top surface of the screen, or an EM field transmitted through the screen.

[0031] In one embodiment, the screen includes at least one first dielectric layer having a top surface facing the electromagnetic wave source and a bottom surface opposite the top surface; - the top surface is at least partially transparent to an electromagnetic field emitted by an electromagnetic wave source; - the bottom surface is at least partially reflective to an electromagnetic field transmitted through the at least one first dielectric layer; - said at least one first dielectric layer is characterized by a complex permittivity and a thickness which are together selected to reproduce the electromagnetic response of a reference object, for example biological tissue, such as human skin tissue;

[0032] In another embodiment, the thermal screen comprises two dielectric layers, a first dielectric layer having a top surface facing the electromagnetic sensor and a second dielectric layer having a bottom surface facing the thermal sensor, each layer characterized by a complex permittivity and a thickness that are jointly selected to replicate the electromagnetic response of a reference object, and each layer comprising a plurality of unit cells.

[0033] In another embodiment, a thermal screen comprises two dielectric layers, a first dielectric layer having a top surface facing the electromagnetic sensor and a second dielectric layer having a bottom surface facing the thermal sensor, each layer characterized by a complex permittivity and a thickness that are together selected to replicate the electromagnetic response of a reference object, each layer including a plurality of unit cells separated by grooves, the grooves filled with or made from a dielectric material having a thermal conductivity that is less than the thermal conductivity of the dielectric material of the second dielectric layer.

[0034] In yet another embodiment, the screen comprises a first dielectric layer, a second dielectric layer, and a third layer, the second layer being made from a dielectric material having a thermal conductivity less than that of the third layer, each layer being characterized by a complex permittivity and a thickness that are together selected to replicate the electromagnetic response of a reference object, each layer including a plurality of unit cells, the unit cells of the third layer being separated by grooves, the grooves being filled with or made from a dielectric material having a thermal conductivity less than that of the dielectric material of the third dielectric layer.

[0035] In another embodiment, the screen comprises a first dielectric layer, a second dielectric layer, and a third layer, each characterized by a complex permittivity and a thickness jointly selected to replicate the electromagnetic response of a reference object, each layer including a plurality of unit cells, the unit cells of the second layer being separated by grooves, the grooves being filled with or made from a dielectric material having a thermal conductivity less than that of the dielectric material of the second dielectric layer, and the third layer being made from a heat-sensitive material.

[0036] In another aspect, a method is provided for detecting electromagnetic dosimetry received by an object irradiated with an electromagnetic (EM) field emitted by an electromagnetic source, the method comprising: - irradiating a surface of a thermal screen using an EM source; - converting EM fields incident on the surface of the thermal screen into heat induced within the thermal screen; - measuring information about the induced heat by at least one thermal sensor; - the processing unit uses the information about the induced heat to calculate the time τ within the time interval [τ1, τ2] i determining a temperature rise distribution over time in the set of - calculating electromagnetic dosimetry quantities from the temperature rise distribution over time, information about the EM field emitted by the EM source, and predetermined EM and thermal properties of the screen; Includes.

[0037] In another aspect, a method is provided for detecting electromagnetic dosimetry received by an object irradiated with an electromagnetic (EM) field emitted by an electromagnetic source, the method comprising: - irradiating a surface of a thermal screen using an EM source; - converting EM fields incident on the surface of the thermal screen into heat induced within the thermal screen; - measuring information about the induced heat by at least one thermal sensor; - measuring, by an EM sensor, information about the EM field emitted by the EM source; - the processing unit uses the information about the induced heat to calculate the time τ within the time interval [τ1, τ2] i determining a temperature rise distribution over time in the set of - temporally correlating information about the temperature rise distribution over time and information about the EM field emitted by the EM source; - calculating electromagnetic dosimetry quantities using time-correlated information about the temperature rise distribution over time and the EM field emitted by the EM source, and predetermined information about the EM and thermal properties of the screen; Includes.

[0038] In one embodiment, the method comprises: - comparing the signal-to-noise ratio (SNR) of the temperature rise distribution over time with a predetermined threshold; - Improving the SNR by using information about the EM field Further includes:

[0039] In another embodiment, completion of the measurement procedure is defined in terms of convergence of the numerical solution of the time-reverse EM and thermal models used to calculate the EM dosimetry quantities.

[0040] Other features, details, and advantages are set forth in the detailed description and figures that follow. [Brief explanation of the drawings]

[0041] [Figure 1] 1 is a schematic cross-sectional view of a prior art device for electromagnetic dosimetry; FIG. [Figure 2] 1 is a schematic cross-sectional view of an embodiment of a device for electromagnetic dosimetry. [Figure 3] FIG. 1 illustrates non-limiting examples of screens configured to absorb at least a portion of the electromagnetic power radiated by an electromagnetic wave source at a given operating frequency of the source, including (a) a single layer including a plurality of unit cells, (b) two layers including a plurality of unit cells, (c) two dielectric layers with a second layer including a plurality of unit cells separated by a groove, (d) three layers including a middle layer having a lower thermal conductivity than the bottom layer, and (e) three layers including a bottom layer made of a heat-sensitive material. [Figure 4] FIG. 10 is a schematic cross-sectional view of another embodiment of a device for electromagnetic dosimetry. [Figure 5] 1 is a schematic cross-sectional view of an embodiment of a device for electromagnetic dosimetry applied to measure user exposure levels within a screen illuminated by two differential spatial beams of electromagnetic radiation emitted by an electromagnetic wave source; FIG. [Figure 6] Schematic diagram of an exemplary temperature rise distribution at the bottom surface of a screen after a short exposure along the ξ coordinate, where ξ is either x or y, showing the measured temperature profile (thick line, GΣ(ξ)), the temperature patterns associated with two overlapping hot spots induced by absorbed electromagnetic fields extracted through decomposition of the measured temperature profile (thin dotted lines, G1(ξ), G2(ξ)), and the estimated temperature pattern in a screen with zero thermal conductivity (thin solid lines, F1(ξ), F2(ξ)). [Figure 7] 3 illustrates a method for calculating dosimetry quantities implemented using the device of FIG. 2 according to one embodiment. [Figure 8] 5 illustrates different time intervals of the main steps performed in a method for calculating dosimetry quantities by measuring thermal and EM information in a correlation manner, implemented using the device of FIG. 4 according to one embodiment. [Figure 9] 5 is a flowchart illustrating steps of a method for calculating dosimetry quantities implemented using the device of FIG. 4 according to one embodiment. [Figure 10] 5 is a flowchart illustrating steps of a method for calculating dosimetry quantities implemented using the device of FIG. 4 according to another embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0042] As used herein, terms such as "top," "bottom," "above," "below," "between," "above," and other similar terms refer to relative positions that do not define or limit the layers to vector spatial orientations.

[0043] For ease of understanding, identical reference numerals will be used to designate identical elements common to the figures wherever possible. It is contemplated that elements disclosed in one embodiment may be beneficially utilized on other embodiments without specific recitation.

[0044] In this disclosure, the term "layer" refers to a structure having a constant or variable thickness. A layer may be planar or curved. In particular, a layer may be shaped to replicate the 3D shape of a part of the human body, such as a head or hand. A layer may be shaped to form a closed surface, such as the surface of a sidewall of a cylindrical object.

[0045] In this disclosure, the term "dosimetry quantity" or "physical quantity" refers to any metric used to quantify electromagnetic exposure, including power density, energy density, specific absorption rate, specific energy absorption, electric field strength, magnetic field strength, voltage or current, as well as their derivatives defined with respect to average surface area or volume.

[0046] In this disclosure, the term "EM field information" refers to any information related to resource allocation used by an electromagnetic source in the frequency, time, and / or space domains, such as frequency channels and frequency bands used for transmission, waveforms and time blocks used for scheduled transmissions, radiated power, radiation pattern, polarization, phase center location, antenna architecture, etc.

[0047] In this disclosure, the term "thermal medium" or "thermal screen" refers to a medium designed to convert electromagnetic fields incident on the surface of the medium into heat in a controlled manner. The thermal medium acts as a spatial converter of EM fields into heat that is induced within the volume of the medium due to absorption of a portion of the EM power transmitted through the thermal medium.

[0048] In this disclosure, the term "conductive layer" refers to a layer having a conductivity of σ≧10 3 Refers to a layer made of a material with S / m.

[0049] In this disclosure, the term "dielectric layer" means exactly 10 3 It refers to a layer made of a thermally conductive and electrically insulating material with a conductivity σ smaller than S / m.

[0050] A device 1 for electromagnetic dosimetry according to an embodiment of the present disclosure will now be described below with reference to Figure 2. In this embodiment, the proposed device combines thermal measurements with a specific thermal screen having predetermined thermal and known electromagnetic parameters to extract electromagnetic quantities related to the level of exposure from an electromagnetic source.

[0051] The device 1 is placed in a Cartesian spatial coordinate system (XYZ).

[0052] The thermal screen of device 1 is advantageously designed to have a predetermined EM response to an incident EM field characterized by a predetermined frequency, polarization, and angle of incidence. In one embodiment, it may be designed to provide low reflection, allowing a greater portion of the incident power to penetrate the thermal screen interior. Alternatively, it may be configured to reproduce the electromagnetic response of a reference object, such as an anatomical part of the human body, when the reference object is illuminated by an electromagnetic source, particularly the reflection characteristics at the air / skin interface, and measure a physical quantity related to the electromagnetic field incident on the thermal screen representing the reference object. The measured physical quantity may be a function of the EM field amplitude, the strength and / or power density of the EM field incident on or transmitted through the air / dielectric interface.

[0053] The device 1 comprises a thermal screen 3, a thermal sensor 5 and a processing unit 6 (PU) extending substantially along a plane (XY). The device further comprises a memory unit 7 (MU) and an interface unit 8 (IU). Figure 2 shows the device placed in a test configuration. An electromagnetic wave source 2 is arranged at a distance D1 relative to the device 1.

[0054] Electromagnetic wave source The electromagnetic field source 2 may be a mobile phone or any other wireless device, fixed, portable or wearable. This distance D1 is preferably within the range R represented by the wavefront line in FIG. NF For electrically small antennas, the reactive near-field zone is larger than the antenna near-field zone, which is characterized by R NF =λ / 2π, where λ is the wavelength in vacuum. For example, at 60 GHz, the distance R NF is about 0.8 mm.

[0055] Those skilled in the art can easily adapt this distance D1 value to ensure accurate compliance testing representative of realistic use-case situations, such as a mobile phone close to a user's head. The distance D1 and the location of the wireless device under test depend on the intended use-case defined by the wireless device manufacturer and / or mobile phone operator. For example, the distance can vary from a few millimeters (for a smartphone close to the head) to tens of centimeters (for a handheld device).

[0056] The electromagnetic source 2 may include one or more antennas connected to or incorporated into the body of the electromagnetic source for transmitting and / or receiving electromagnetic signals.

[0057] As shown in Figure 2, electromagnetic field source 2 includes one single antenna 21 that emits an electromagnetic field represented by wavefront line 22. The center of the wavefront line coincides with the phase center of antenna 21. A portion of the electromagnetic waves emitted by electromagnetic wave source 2 illuminates surface 31 of thermal screen 3 of device 1. The surface illuminated by the EM waves emitted by electromagnetic wave source 2 is referred to as the top surface. The surface of thermal screen 3 of device 1 facing the EM source is referred to as the bottom surface 32.

[0058] EM source 2 may operate at a frequency within a band within the frequency range from about 6 GHz to about 300 GHz allocated to 5G and 6G wireless networks, although thanks to the scalability of Maxwell's equations, the teachings of the present invention may be scaled to other frequency bands.

[0059] As shown in FIG. 2, EM waves emitted by electromagnetic source 2 are incident on top surface 31 of thermal screen 3. The incident EM waves are indicated by numeral reference 23. The incident waves are partially reflected by top surface 31 of screen 3 (not shown in FIG. 2). The portion of the EM waves that is not reflected at the air / screen interface associated with top surface 31 propagates through screen 3 from top surface 31 to bottom surface 32 and is partially absorbed within the medium of screen 3. The EM waves that are transmitted through screen 3 induce a temperature rise within screen 3.

[0060] The electromagnetic source 2 may operate with a single antenna generating a single beam fixed in time, space, and frequency. In another embodiment, the electromagnetic source may be equipped with multiple antennas and adapted to operate in multiple frequency bands, allowing dynamic resource allocation in the time, frequency, and space domains. Dynamic resource allocation may involve variation in the time allocation of communication resources (frequency-time blocks and transmission power) and even the use of one of at least two predetermined spatial views of radiated power enabled by a beamforming mechanism. For example, an EM source may use only one of multiple frequency channels, and its transmission may be scheduled in the time domain. Thus, the beam generated by each electromagnetic source may vary in time and frequency.

[0061] thermal screen The thermal screen 3 acts as a spatial converter of the EM field into heat induced within the volume of the screen due to the absorption of a portion of the EM force transmitted through the screen in the medium of the screen. In one embodiment, the screen can represent a phantom structure that reproduces the electromagnetic response of a reference object made of an electromagnetic lossy medium, such as biological tissue, when its surface is illuminated by electromagnetic waves emitted by an electromagnetic wave source. As a non-limiting example, the screen structure can include at least one dielectric layer made of any solid dielectric material characterized by a complex permittivity, such as plastic, polymer, ceramic, glass, resin, or paper. Those skilled in the art will easily adapt different values ​​of the complex permittivity and thickness of the at least one dielectric layer to the embodiments described for the present invention.

[0062] The thermal screen 3 is adapted to absorb at least a portion of the EM power emitted by the EM source that is incident on the screen and transmitted through its surface.

[0063] The thermal screen 3 comprises a structure extending in a horizontal plane (XY) that defines two main surfaces: a top surface 31 facing the source of electromagnetic waves and a bottom surface 32 facing away from the source 2.

[0064] The screen may be made from a dielectric material that absorbs at frequency F1, which is the operating frequency of the electromagnetic source 2 under test and varies between a minimum value of F1 and a maximum value of F2, for example, 24-28 GHz, 37-39 GHz, or 57-71 GHz, or within another sub-band within the frequency range above 6 GHz.

[0065] The thickness T of the thermal screen along the z-axis perpendicular to the thermal screen S is preferably between λ / 10 and 10×λ, where λ is the wavelength of the EM field in the medium of the dielectric layer 3 at frequency F. For example, the thickness T of the dielectric layer may be about 1 mm at 60 GHz.

[0066] The thermal screen 3 is preferably positioned a predetermined distance D1 from the electromagnetic wave source to form an air gap between the electromagnetic wave source and the screen. For example, D1 is selected to be greater than λ / 100, where λ1 is the wavelength of the EM field in free space at frequency F1. This distance may be defined depending on the intended use of the EM source 2. For example, in the case of a smartphone, it may be defined as 5 mm, which is a typical distance for a smartphone when placed near a user's head.

[0067] In one embodiment, the screen forms a 2D planar structure as shown in FIG. 2, with a large dimension in the xy plane, e.g., significantly larger than the thickness Ts extending along the z-axis. The overall size of the screen may be defined according to the intended use of the EM source 2. For example, it may be selected to be equal to the user's head or hand. Alternatively, it may be selected according to the radiation pattern of the electromagnetic source 2 or the expected near or far field distribution in the plane of the screen generated by the electromagnetic source 2, allowing characterization with a minimum number of measurements under fixed relative positions of the electromagnetic source 2 and the screen 3.

[0068] In another embodiment, the screen forms a complex 3D shape that replicates the shape of a part of the human body. In other words, the single dielectric layer 3 forms a closed or partially closed shell filled with a medium, such as a liquid, gel, foam, or gas. This 3D structure is particularly suitable for simulating the case of a part of the human body, such as a head-shaped phantom. The medium is selected to act as the brain, and the top surface may exhibit a concave shape in a manner that simulates the morphology of the head. Alternatively, the medium may be used solely as a mechanical support and / or host medium for at least one thermal sensor 5 placed under the dielectric layer 3.

[0069] In another example, the screen 3 may include layers of amorphous and gel-type dielectric material doped with conductive fillers to form a suspended composite. The percentage of conductive fillers can be varied to replicate the electromagnetic response of a reference object, such as the reflective characteristics at the air-dielectric interface of human skin tissue.

[0070] The screen is divided into a number of adjacent unit cells 33. In one embodiment, these cells may all be identical. The unit cells have the same dimensions. Each cell is characterized by the same electromagnetic and thermal characteristics. In other words, the unit cells are made from the same material and have the same configuration.

[0071] In another embodiment, the unit cells may be non-identical. Each unit cell is characterized by a specific size, its own electromagnetic characteristics, and its own thermal characteristics. In other words, the unit cells may be made of different dielectric materials and may have different sizes and / or shapes. The dimensions and electromagnetic and / or thermal properties of each unit cell are adjusted to account for the different illumination conditions of each cell due to the electromagnetic field emitted by the electromagnetic wave source 2. The unit cells are designed to improve the efficiency of EM field-to-heat conversion under different illumination conditions and / or to prevent heat diffusion within the plane of the screen.

[0072] Advantageously, the size of the unit cells in the middle and periphery of the screen can be varied to account for different illumination conditions that depend on at least the angle of incidence, power density, and / or polarization of the electromagnetic field on the top surface of the screen.

[0073] For example, the peripheral unit cells have larger sizes to compensate for the difference in reflection / transmission coefficients for TE and TM polarized electromagnetic waves at lower incident power densities and / or elevation angles. The minimum size of the unit cells can vary from a fraction of a wavelength in the screen medium at frequency F1 to several times that wavelength. The minimum size of the unit cells can also depend on the type of thermal sensor used. For example, this can be on the order of 100 microns for thermocouples (to facilitate integration) or 1 micron for infrared imaging sensors (to match resolution limits). The maximum size can be defined rather arbitrarily. For example, it can be usefully defined as 10 × 10 mm or 20 × 20 mm, the average surface area defined in the ICNIRP (International Commission on Non-Ionizing Radiation Protection) recommendations for EM dosimetry at millimeter waves.

[0074] In configurations where the device includes multiple electro-thermal or electro-optical sensors, the total number of cells may be equal to the number of thermal sensors. In other embodiments where the device includes a thermal infrared image sensor, the total number of unit cells may be less than or equal to the number of pixels in the thermal infrared image sensor.

[0075] Thanks to the particular cell architecture of this screen, the multiple unit cells characterized by anisotropic thermal conductivity help to mitigate heat conduction phenomena in the plane of the screen, thus increasing the resolution and reducing distortions of the measured thermal distribution over time.

[0076] In the embodiment of Figure 2, the screen is used to convert absorbed electromagnetic power into heat as the EM waves propagate through layer 3. The device of the present invention comprises a thermal sensor that measures the heat distribution along the surface of the screen to determine the absorbed EM power. The device further comprises a processing unit 6 (PU) configured to calculate a sought dosimetry quantity, e.g., user exposure level, by correlating the absorbed EM power, known EM and thermal characteristics of the screen, and known exposure conditions defined by information related to the relative position of the electromagnetic wave source 2 and the electromagnetic field emitted by the electromagnetic wave source 2.

[0077] Thermal sensor The thermal sensor 5 is positioned a distance D2 below the bottom surface 32 of the thermal screen 3 on the opposite side relative to the electromagnetic source 2. The thermal sensor 5 is configured to measure the temperature or heat induced in the screen medium due to the absorbed EM power.

[0078] In one embodiment, the device comprises a single thermal sensor 5 aligned with respect to the screen along the direction of electromagnetic wave propagation. The thermal sensor is located in the center of the screen and faces towards the bottom surface 32 of the screen. The thermal sensor 5 may be an image sensor, such as an infrared image sensor or a visible light image sensor.

[0079] The image sensor is configured to have a field of view that covers at least a portion of the bottom surface of the screen, or in other words, the thermal sensor may have a field of view that covers at least one unit cell.

[0080] The thermal image sensor is configured to operate within a spectral range that includes at least a portion of the EM spectrum emitted by the bottom surface 32 of the screen. For example, this may be the portion of the infrared spectrum emitted by the heated medium, or the portion of the visible spectrum emitted or reflected by the heat-sensitive medium.

[0081] The thermal sensor 5 is configured to measure the temperature rise distribution on the screen, which is related to the heat induced by the electromagnetic force partially absorbed in the screen medium during the exposure duration. The screen can simultaneously act as a phantom structure simulating the EM response and as a thermal transducer that absorbs the EM force and converts it into heat that is re-radiated as infrared radiation measured by the thermal sensor 5.

[0082] In another embodiment, the thermal sensor 5 comprises a plurality of thermoelectric elements, commonly referred to as thermocouples, embedded in or attached to the bottom surface of the screen. A thermocouple is an electrical device consisting of two dissimilar electrical conductors forming an electrical junction that generates a temperature-dependent voltage as a result of the Seebeck effect.

[0083] In yet another embodiment, the thermal sensor 5 comprises a plurality of heat-sensitive elements, such as liquid crystals or GaAs semiconductor crystals, attached to the bottom surface of the screen, adapted to convert heat into a measurable physical quantity, such as a spectral shift in emitted or reflected light.

[0084] The thermal sensor 5 may be any other sensor capable of measuring a physical quantity related to the heat induced in the screen.

[0085] Processing Unit As shown in Figure 2, the signals captured by the thermal sensor 5 are transmitted to a processing unit 6. Knowing information about the electromagnetic properties of the screen and the EM field emitted by the electromagnetic source 2, the processing unit 6 can calculate the desired dosimetric quantities related to the EM radiation absorbed by the screen during a predetermined exposure duration. The processing unit 6 is configured to calculate the heat distribution at the bottom surface 32 of the thermal screen 3 by processing information about the heat induced at different times during the exposure, hereinafter referred to as the "thermal distribution over time". It may further be configured to calculate the desired dosimetric quantities (e.g., transmitted or absorbed power density) by applying Maxwell's equations and the heat conduction equation in the medium of the screen having predetermined electromagnetic and thermal properties.

[0086] memory unit The processing unit 6 communicates with a memory unit 7 and an interface unit 8. The memory unit 7 is configured to store data relating to the signals acquired by the thermal sensors, information about the EM fields emitted by the electromagnetic source, and processed data. The memory unit 7 can store processed data such as thermal profiles from the thermal sensors over time, information about the thermal and electromagnetic properties of the screen, irradiation conditions for each unit cell of the screen, and transmitted and / or absorbed power densities averaged per surface area and per time unit.

[0087] Interface Unit The interface unit 8 is configured to receive and transmit data to a user. The interface unit may further include a display unit that allows displaying the thermal profile over time. The interface unit 8 may transmit data to another device equipped with a display unit. The interface may typically be a computer console. The user interface allows monitoring and exchanging information with the device by initiating and / or controlling the operations performed by the different elements of the device. This therefore allows determining initialization and calculations, defining irradiation conditions, and displaying the retrieved results for visualization.

[0088] 7 illustrates a method 100 for detecting dosimetry received by an object irradiated with an electromagnetic (EM) field emitted by an electromagnetic wave source. The method 100 is implemented using the device of FIG. 2 described above, and therefore will be described below with reference to FIG. 2.

[0089] The method comprises a first phase corresponding to a measurement phase comprising the following steps:

[0090] In step 101, an EM field 23 is emitted in the direction of the top surface of the thermal screen by an electromagnetic source 2. In this embodiment, known resource allocations in the domains of time, frequency, and space from the specifications of the electromagnetic source 2 are used to generate the EM field.

[0091] In step 102 , the EM field 23 emitted by the electromagnetic source is converted into heat as a result of absorption of a portion of the EM field in the medium of the screen 3 .

[0092] In step 103, the thermal sensor 6 acquires information about heat induced in the screen at different times. This step may include measuring a physical quantity proportional to the induced heat by at least one thermal sensor 5. In one embodiment, the thermal sensor may be an infrared image sensor, and the physical quantity may be the intensity of infrared radiation emitted from the bottom surface 32 of the thermal screen. In another embodiment, the bottom surface 32 is covered with a heat-sensitive material, the thermal sensor is an image sensor, and the physical quantity may be the intensity of visible light emitted or reflected by the bottom surface 32 of the screen. In yet another embodiment, the thermal sensor 5 includes multiple thermocouples attached to or embedded in the bottom surface 32 of the screen, and the physical quantity may be a voltage measured by a voltmeter. The heat-related information may be stored in the memory unit 7 and / or displayed by the interface unit 8.

[0093] The second phase includes the following steps:

[0094] In step 104, the processing unit calculates the thermal distribution over time at a set of time points by processing the time series of multiple thermal distributions for each point of the measurement, pixel or unit cell. Depending on the type of thermal sensor used, this step may include the following intermediate steps: - time averaging over a period of Δτ; - spatially averaging the unit cell surface area of ​​the base 32; - converting the physical quantities measured by the thermal sensors into a heat distribution along the bottom surface 32 of the thermal screen defined in terms of absolute temperature or relative temperature rise at a set of time points during exposure; may include:

[0095] The third phase includes the following steps:

[0096] In step 105, the processing unit reconstructs the irradiation conditions for each pixel (or unit cell) based on information about the EM field emitted by the electromagnetic source 2 and its relative position. Thus, by knowing the electromagnetic and thermal properties of the screen and the parameters of the electromagnetic waves incident on each pixel (cell unit) of the screen at each time, the processing unit 6 calculates the dosimetry quantities associated with the EM radiation incident on, transmitted through and / or absorbed by the screen at each point of measurement, pixel or cell unit, by using the information about the thermal distribution over time calculated in step 104 and the known information about the EM field incident on the screen.

[0097] 3 depicts a non-limiting example of a thermal screen 3 configured to measure the thermal distribution required to extract a dosimetric quantity in the plane of the screen exposed to the EM field emitted by the EM source 2. In one embodiment, the reflection of the EM field emitted by the electromagnetic source from the top surface of the thermal screen can be adjusted to replicate the electromagnetic response from a reference object, for example, a human body.

[0098] The screen (a) of FIG. 3 includes a monolayer 3 characterized by a particular combination of complex permittivity and thickness required to generate a desired electromagnetic response from the surface of the layer, e.g., to replicate the corresponding electromagnetic response from the upper surface of a reference object, e.g., biological tissue such as human skin. In one embodiment, the thickness of the monolayer is selected to be at least equal to one-quarter of the wavelength of the EM wave in the medium of the monolayer, the medium being characterized by a predetermined absolute value of the complex permittivity being smaller than the absolute value of the complex permittivity of the medium of the reference object. Alternatively, the monolayer may be represented by a thin film having a thickness significantly smaller than the wavelength of the EM wave in the medium of the monolayer, the bulk medium being characterized by a predetermined absolute value of the complex permittivity being larger than the absolute value of the complex permittivity of the medium above the reference object. These selected equivalence criteria may be defined for at least a portion of the frequency spectrum, at least one polarization, and at least a range of angles of incidence of the EM field emitted by the EM source and incident on the top surface of the screen.

[0099] The single layer 3 includes a plurality of unit cells. In one embodiment, the layer is made of a dielectric material. The dielectric layer 3 may be made of a dielectric material doped with conductive fillers, such as a material containing particles or inclusions of another material characterized by a different value of complex permittivity. The layer materials, the type of doping, and their volume ratios are determined for a given thickness T of the layer 3 to reproduce a desired electromagnetic response, such as a complex reflection coefficient or its magnitude, from the top surface 31 of the layer 3. s For example, the reference object is a human skin tissue, and the complex permittivity and thickness T of the dielectric layer 3 are selected. s may each be selected to reproduce the magnitude of the complex reflection coefficient from the surface of human skin, whose typical values ​​range from 0.75 to 0.4 within the frequency range of 6 GHz to 300 GHz.

[0100] The screen (b) of FIG. 3 includes a first dielectric layer 41 and a second dielectric layer 42. Each layer includes a plurality of unit cells. Each dielectric layer is characterized by its own thickness, its own complex permittivity, and its own thermal conductivity. This second layer allows adjusting, increasing, or decreasing the reflection from the bottom surface of the first layer at the first-second layer interface, depending on the ratio between the permittivity of the medium of the first layer 41 and the permittivity of the medium of the second layer 42.

[0101] Screen (c) of FIG. 3 includes a first dielectric layer 51 and a second dielectric layer 52. Each layer contains a plurality of unit cells. Each dielectric layer is characterized by its own thickness, its own complex permittivity, and its own thermal conductivity. Additionally, the unit cells of the second layer 52 are separated by grooves. The grooves are filled with or made of another dielectric material with a thermal conductivity smaller than that of the material of the second layer 52, reducing heat diffusion in the xy plane that causes thermal crosstalk between adjacent cells.

[0102] Screen (d) of FIG. 3 includes a first dielectric layer 61, a second dielectric layer 62, and a third layer 63. The second layer 62 is made of a dielectric material having a thermal conductivity lower than that of the third layer. Each layer includes a plurality of unit cells. The unit cells of the third layer are separated by grooves 64, which are filled with or made from a dielectric material having a thermal conductivity lower than that of the dielectric material of the third dielectric layer 63. The lower thermal conductivity of the second layer 62 allows for reduced heat diffusion along the z-axis (between the third layer and the first layer) and also along the x-y plane in the medium of the first layer, which is insulated from the third layer by the second layer.

[0103] Screen (e) in FIG. 3 includes a first dielectric layer 71, a second dielectric layer 72, and a third layer 73. Each layer is characterized by a complex permittivity and thickness that are jointly selected to replicate the electromagnetic response of a reference object. Each layer includes multiple unit cells. The unit cells of the second layer 72 are separated by grooves 74. The grooves are filled with or made of a dielectric material that has a thermal conductivity less than that of the dielectric material of the second dielectric layer 72, reducing heat diffusion along the xy plane. The third layer 73 is made of a heat-sensitive material.

[0104] FIG. 4 is a schematic diagram of another embodiment of an EM dosimetry device 10 that combines at least one electromagnetic sensor 11 for obtaining information about the EM field emitted by an electromagnetic source 2 and a thermal sensor 5 for measuring a physical quantity related to heat induced in the screen medium.

[0105] The device of Figure 4 makes it possible to obtain information about the EM field emitted by EM source 2 through real-time monitoring of the EM field at at least one spatial point and a set of time instants within the exposure time [τ1, τ2], thereby determining the allocation of time / frequency / spatial resources used by electromagnetic source 2 at each time instant within the test duration, as well as the illumination conditions for each pixel (or unit cell) of the screen at each time instant.

[0106] The information about the EM field emitted by the electromagnetic source 2 may include any piece of information related to the radio resource allocation used by the electromagnetic source 2 in the frequency, time, and / or space domains. In one embodiment, this may concern at least the frequency channel used for transmission, which is information essential for determining the corresponding values ​​of the frequency-dependent EM properties of the screen, such as the complex permittivity. It may also concern the amplitude and phase of the incident EM field at the location of the at least one EM sensor 11, allowing for the determination of the position and orientation of the EM source 2 necessary to calculate the wavefront and polarization of the incident EM field at each point or each unit cell on the screen surface. In yet another embodiment, it may concern waveforms in the time domain.

[0107] The information about the heat induced in the screen 3 measured by the thermal sensor 5 may then be synchronized with EM information about the EM field incident on the top surface of the thermal screen, determined based on information obtained by the electromagnetic sensor 11 about the time / frequency / space resource allocation used by the electromagnetic source 2 during the test, allowing post-processing and retrieval of dosimetric quantities from the measured heat distribution for an unknown EM source (i.e., when we do not have prior knowledge about the resource allocation used by the electromagnetic source 2, or when the electromagnetic source 2 uses a dynamic time-varying resource allocation).

[0108] The steps of collecting information about the heat induced in the screen and collecting information about the EM field emitted by the electromagnetic source start simultaneously, in other words the thermal sensor and the EM sensor start measuring at the same time.

[0109] Similar to device 1 of Fig. 2, device 10 comprises a thermal screen 3 extending substantially along a plane (XY), a thermal sensor 5, and a processing unit 6 (PU). The device further comprises a memory unit 7 (MU) and an interface unit 8 (IU). Fig. 4 shows the device placed in a test configuration. An electromagnetic wave source 2 is disposed at a distance D1 relative to device 10. In addition, device 10 comprises an electromagnetic sensor 11.

[0110] The proposed device makes it possible to characterize wireless devices with limited or no information about the number of antennas, their location and orientation inside the electromagnetic source, their radiation pattern, their phase center location, and operating frequency, as well as the time / frequency / space resources that can change dynamically during the test.

[0111] The thermal screen 3, EM source 2, and thermal sensor 5 have been previously described with reference to FIG.

[0112] The electromagnetic sensor 11 may include at least an RF front end and an RF receiver and is configured to receive the electromagnetic waves emitted by the electromagnetic wave source 2 and determine parameters of the incident EM field at the location of the electromagnetic sensor 11. It may further be configured to convert the information carried therein into a usable form. The EM sensor 11 is configured to detect at least one of the following parameters of the incident electromagnetic field: power density, amplitude, and phase, polarization, frequency, and waveform of the E and / or H fields. The EM sensor 11 is configured to detect additional parameters related to the allocation of time and frequency resources of the electromagnetic wave source 2. Furthermore, the EM sensor may be capable of detecting parasitic EM fields emitted by other EM sources different from the electromagnetic wave source 2 used for the dosimetry test. Information about the parasitic EM fields may be used to correct data related to the heating induced by the EM fields received by the screen.

[0113] As shown in FIG. 4 , the EM sensor 11 is arranged with respect to the EM source 2 to detect the EM field 23 emitted by the EM source. The EM sensor is aligned with the EM source to ensure reliable detection of the EM field in line-of-sight mode. This allows obtaining information about the EM field emitted by the EM source 2, which may include the intensity of the EM field emitted by the EM source 2, or the magnitude and phase of the E and / or H fields defined at any set of time points during the test. In addition, this information may include any part of information related to the allocation of radio resources by the electromagnetic source in the frequency, time, and / or space domains. This information may include, for example, the frequency channels and resource blocks used for transmission, the waveforms and time blocks for scheduled transmissions, etc. This information may be further post-processed by the processing unit 6 to extract information about measurements of the screen 3 at different time points and the illumination conditions for each point on the pixel (or unit cell).

[0114] In one embodiment, the EM sensor 11 may be attached to or embedded in the top surface of the screen 3. The configuration of Figure 4 shows the EM sensor 11 positioned at a given distance from the EM source and the screen.

[0115] In another embodiment, the EM sensor is arranged with respect to the screen to capture the EM field reflected from the top surface of the screen in multi-pass mode. In this embodiment, the EM sensor 11 may be located at a fixed distance from the screen 3. Alternatively, it may be attached to or embedded in the top surface of the screen 3.

[0116] In yet another embodiment, the EM sensor is positioned below the bottom surface of the screen, thereby capturing the EM field transmitted through the screen. In this embodiment, the EM sensor is located below the screen, or alternatively, is attached to or embedded in the bottom surface of the screen 3.

[0117] The device 10 may include multiple EM sensors. The additional EM sensors are configured to detect complementary portions of the information related to the EM field emitted by the EM source, e.g., covering complementary portions of the frequency range of the operating frequency of the EM source 2, a subrange of the angle of incidence of the incident EM field, or one of two polarizations. This embodiment is particularly useful when the EM source includes multiple antennas. For example, each EM sensor is associated with an antenna to measure the EM field emitted under several illumination conditions, e.g., angle of incidence, frequency, polarization, modulation. The use of multiple EM sensors covering only a portion of the information can simplify the architecture of the RF front end by reducing the operating bandwidth and / or limiting measurements to only one polarization.

[0118] In yet another embodiment, the device comprises at least three EM sensors distributed in space around the EM source. The EM sensors are configured to measure the amplitude and / or phase of the incident EM field. Information about the phase of the EM field collected by these EM sensors can be used to determine the phase center position of the radiating antenna, thereby detecting switching between different beams generated by the antenna if the EM source comprises a beamforming and / or MIMO antenna system, or detecting switching between different antennas if the EM source comprises multiple antennas.

[0119] In yet another embodiment, the EM sensor 11 is integrated into the EM source 2, which can operate as an EM receiver. For example, the electromagnetic source 2 has two RF front ends, using a first antenna for transmission and a second antenna for detecting the EM field reflected from the screen. In other words, the EM source is configured to simultaneously support two operating modes, such as emitting an EM field toward the top surface of the screen and receiving the EM field reflected from the top surface of the screen. Information about the EM field emitted by the electromagnetic source can be extracted from the EM signal received by the second antenna and further transmitted to the processing unit 6 via the control link 26. In one embodiment, this control link can be a wireless link established through the EM sensor 11. Alternatively, the control link can be established through the application layer, provided that both the processing unit 6 and the electromagnetic source 2 can be configured to support such a connection. Depending on the electromagnetic source PHY, MAC, and APP layer architecture, the information about the EM field emitted by the electromagnetic source during test time can be directly accessible to the processing unit 6 through a common protocol.

[0120] The operating frequency range of the EM sensor may cover at least a portion of the operating frequency range of the EM source. In another embodiment, the operating frequency range of the EM sensor may be wider than the operating frequency range of the EM source, thereby allowing for detection of parasitic EM waves.

[0121] 4, the output of the thermal sensor is linked to the input of the processing unit 6. The input of the memory unit is linked to the processing unit 6.

[0122] The processing unit 6 is configured to process the EM signals transmitted from the at least one EM sensor to extract information about the EM field emitted by the electromagnetic source 2 and to reconstruct the illumination conditions at the top surface 31 of the thermal screen at a point in time during exposure.

[0123] The processing unit 6 is configured to calculate dosimetric quantities by using the information related to the induced heat from the thermal sensors 5, the information related to the EM fields, and the information related to the thermal screen 3 to correlate the thermal distribution over time with information related to the irradiation conditions of each pixel (or unit cell) of the top surface 31 of the thermal screen. The information related to the EM fields predetermined or detected by the EM sensors, correlated over time with the information related to the heat detected by the thermal sensors, allows for retrieval of dosimetric quantities related to the exposure level of the object by the EM source averaged over a given duration and / or surface area. The step of time correlation between the thermal distribution over time and the information related to the EM fields acquired by the EM sensors during the test allows for more accurate and reliable post-processing and retrieval of dosimetric quantities from the measured thermal distribution.

[0124] In one embodiment, device 10 of FIG. 4 comprises an EM transmitter configured to actively control the operation of an EM source under test in a manner that imposes a given time / frequency / spatial resource allocation.

[0125] The EM transmitter is arranged within the zone of radio coverage relative to the electromagnetic source 2. In another embodiment, the EM transmitter is embedded in or attached to the top surface of the screen.

[0126] The EM transmitter may be combined with an EM sensor. In this configuration, the EM sensor may include at least one RF front end and one transceiver capable of operating in half-duplex or full-duplex mode. As shown in FIG. 4, the EM sensor 11 is linked to the EM source 2 by a control link 26. Alternatively, in high-end wireless devices, the control link 26 may be organized through the APP layer.

[0127] The use of the control link 26 allows the processing unit 6 to actively control the resource allocation of the electromagnetic wave source 2 through the EM sensor 11. This may involve the selection of communication parameters of time / frequency blocks and adaptive power levels, as well as beam switching and MIMO schemes.

[0128] In this configuration, the EM transmitter may control the EM source to adjust information about the EM field, such as the radiated power, frequency, polarization, and waveform of the EM field, that provides an optimal signal-to-noise ratio for the heat distribution measured by the thermal sensor 5.

[0129] In a preferred embodiment, processing unit 6 is configured to use transient thermography, a known technique based on periodic pulse excitation, to extract low amplitude temperature distributions buried by ambient thermal noise. In this configuration, processing unit 6 is configured to determine optimal parameters of the transient technique (i.e., waveform and lock-in frequency of the periodic pulses) that are converted into optimal information about the EM field emitted by electromagnetic source 2. This optimal information is transmitted over control link 26 to an EM transmitter that controls the EM source.

[0130] As such, processing unit 6 can configure electromagnetic wave source 2 to generate a modulated input signal having a predetermined lock-in frequency and waveform. Knowing this information, processing unit 6 applies a Fourier transform to the measured thermal distribution over time to convert the signal into the spectral domain, and then filters out thermal noise from the spectral frequency component that lies at the predetermined lock-in frequency.

[0131] The time correlation between the exposure conditions, derived from the EM signals detected by the EM sensors 11 or imposed by the processing unit 6 through the control link 26 or through the APP layer, and the thermal signals detected by the thermal sensors allows the implementation of a transient thermography technique (also called "lock-in technique") in the post-processing of the measured heat distribution in the screen. This technique allows reliable detection of heat induced in the screen with a magnitude comparable to or lower than the thermal noise level.

[0132] The operation of the devices of FIGS. 2 and 4 is described in more detail below with reference to FIGS.

[0133] During testing, EM source 2 is placed at a distance D1 from the screen. EM source 2 emits a frequency F1 divided into multiple frequency channels with a predetermined bandwidth.

[0134]

number

[0135] The EM source operates in a frequency, time, and spatial domain. The EM source can be multiplexed in the frequency, time, and spatial domains by dynamically changing frequency channels, time, and spatial modulation schemes and / or radiation patterns. The EM source comprises a single antenna configured to radiate at least two distinct radiation beams characterized by angular radiation patterns, gains, and main beam directions. The angle of incidence θ of the EM field radiated by the EM source and incident on the top surface of the screen can be estimated as a function of the relative position of the radiating antenna and the distance D1.

[0136] The screen 3 may be any one of the structures described in Figure 3. The device comprises a thermal sensor placed a certain distance D2 away from the opposite side of the screen, with the field of view defined to cover at least part of the bottom surface of the screen.

[0137] In Figure 5, the first and second beams are incident on the top surface 31 of the screen at oblique angles θ1 and θ2, respectively. The thermal sensor 5 is positioned in a manner that covers at least a portion of the area illuminated by the EM source.

[0138] When the top surface 31 of the screen is irradiated with the EM field emitted by the electromagnetic wave source 2, part of the EM wave is reflected from the upper surface 31 of the dielectric layer 3, and part of the EM wave is transmitted along a propagation path inside the screen and is at least partially absorbed along the propagation path. The absorbed part of the EM wave induces a temperature rise within the screen, causing the formation of a heat distribution on the bottom surface of the screen.

[0139] FIG. 6 shows an exemplary temperature distribution profile or thermal pattern G induced at the bottom surface of the screen after a short exposure time defined by τ whose duration is measured in hours. Σ (ξ,τ). The spatial parameter ξ can represent the x or y coordinate in the bottom plane of the screen. This pattern is detected by the thermal sensor 5 at any instant τ i ∈(0,τ). In a preferred embodiment, the thermal sensor 5 is an IR image sensor.

[0140] Thick solid line G Σ The curve indicated by G represents the measured temperature profile. The curves indicated by the two thin dotted lines G1 and G2 represent the temperature pattern associated with two overlapping hot spots induced by absorbed EM fields extracted through decomposition of the measured profile. The curves indicated by the two thin solid lines F1 and F2 represent the estimated temperature profile that would be induced in a screen with zero thermal conductivity.

[0141] the relative positions of the radiating antennas attached to or embedded in the EM source 2, the distances D1 and D2, the physical parameters of the screen, e.g., shape, thickness T s, and the effective complex permittivity of the screen medium at the operating frequency of the EM source, as well as the thermal properties of the screen, such as thermal conductivity, heat capacity, and IR emissivity, can be known by those skilled in the art by applying Maxwell's equations and the heat equation to calculate the EM power locally absorbed within the screen as a function of the measured thermodynamics at the corresponding surface area, defined, for example, by the unit cell area. This embodiment allows for estimating the level of exposure caused by absorbed EM radiation within the screen during a given duration of the test, under the assumption that the EM resource allocation remains fixed and unchanged. The retrieved dosimetry quantities (e.g., absorbed power density) can then be calculated for any surface area. The acquired data can further be used, by scaling, to retrieve the exposure level a user may have experienced under the same exposure conditions.

[0142] This scaling factor can be determined by comparing the magnitude of the EM reflection coefficient from the surface and the magnitude of absorption for the screen medium and biological tissue (e.g., human skin tissue). The former can be defined analytically, numerically (through full-wave EM simulations), or experimentally. The latter (the EM properties of biological tissue at different frequencies) can be known from the scientific literature or measured using commercially available EM property measurement techniques (e.g., coaxial probes).

[0143] In another embodiment, the EM source 2 can be multiplexed in the frequency, time, and spatial domains by dynamically changing the frequency channel and waveform of the emitted signal. The device of Figure 4 can be used to determine the exposure level of a reference object represented by a screen.

[0144] The EM sensor measures the incident power, amplitude, and / or phase of the incident EM field, e.g., E or H field. The received signal is then transmitted to a processing unit 6, which retrieves information about the EM field emitted by the electromagnetic source through a post-processing procedure. For example, this information may relate to the frequency channel used by the EM source, time-domain multiplexing information, and / or the incident power density at the specific location of the EM sensor. These data can then be used to determine at least some of the information about the EM field emitter by the EM source at each time point of the test. For example, they can be used to determine which time intervals (during the test) the screen was exposed to by the first and second beams, at which frequencies, and with which incident powers (absolute or relative). This information can be used to estimate the partial contributions of different EM source operating modes to the overall heat distribution measured by the thermal sensor. Furthermore, knowledge of the time-domain multiplexing can be used to interpret thermodynamics by taking into account heat diffusion along the bottom surface of the screen due to the finite thermal conductivity of the screen medium. For example, if the first and second spatial beams are used sequentially in time, such that the first beam is used within the time interval t∈[0,τ0] and then the second beam is used within the time interval t∈[τ0,τ], a stronger distortion of the measured temperature distribution due to thermal diffusion can be expected for the first beam, due to the longer time between excitation and IR measurement.

[0145] Finally, the processing unit 6 is configured to process the data from the thermal sensors and the data from the EM sensors 11, taking into account the time correlation between the exposure conditions detected based on the information obtained by the EM sensors and the thermodynamics measured by the thermal sensors. Thus, information about the EM fields detected by the EM sensors can be correlated with information about the elevated temperature distribution detected by the thermal sensors to derive dosimetry quantities related to the user exposure level from the EM source.

[0146] 8 and 9, a method 200 for detecting dosimetry experienced by an object irradiated with an electromagnetic (EM) field emitted by an electromagnetic source is described below. Method 200 is implemented using the device of FIG. 4 described above.

[0147] The method comprises a first phase corresponding to a measurement phase comprising the following steps:

[0148] In step 201 (S1), an EM field 23 is emitted in the direction of the top surface of the thermal screen by an electromagnetic source 2. In this embodiment, at least some of the information regarding the resource allocation used by the electromagnetic source 2 to generate the EM field is unknown.

[0149] In step 202 (S2), the EM field 23 emitted by the electromagnetic source is converted into heat as a result of absorption of part of the EM field in the medium of the screen 3.

[0150] In step 203a (S3a), the thermal sensor 6 acquires information about heat induced in the screen at multiple time points. This step may include measuring a physical quantity proportional to the induced heat by at least one thermal sensor 5. In one embodiment, the thermal sensor may be an infrared image sensor, and the physical quantity may be the intensity of infrared radiation emitted from the bottom surface 32 of the thermal screen. In another embodiment, the bottom surface 32 is covered with a heat-sensitive material, the thermal sensor is an image sensor, and the physical quantity may be the intensity of visible light radiation emitted or reflected by the bottom surface 32 of the screen. In yet another embodiment, the thermal sensor 5 includes multiple thermocouples attached to or embedded in the bottom surface 32 of the screen, and the physical quantity may be a voltage measured by a voltmeter. The heat-related information may be stored in the memory unit 7 and / or displayed by the interface unit 8.

[0151] In step 203b (S3b), the EM sensor 11 continuously acquires information about the EM field emitted by the electromagnetic source 2 at the same time as the thermal sensor 5. The information about the EM field emitted by the electromagnetic source may include any piece of information related to radio resource allocation by the electromagnetic source in the domains of frequency, time, and / or space.

[0152] As shown in FIG. 8, the duration of this first phase is limited by a time interval [τ1, τ3], where τ3 is the switch-off time of the electromagnetic wave source 2. In one embodiment, this end time can be defined based on feedback from the processing unit 6, which signals the successful completion of the calculation process. Steps S3a and S3b for measuring information about the thermal and EM fields are also performed within the same time interval [τ1, τ3]. The measured raw data (related to physical quantities related to the induced heat) and post-processed data (related to the temperature rise distribution over time and the EM fields incident on the screen) are stored in the memory unit 7. Part of this information for the time period [τ1, τ2] is used by the processing unit 6 to calculate the desired dosimetric quantities. The duration of this time interval can be continuously increased depending on the success of the calculation procedure, which requires a sufficient SNR for the thermal measurements as well as sufficient information about the EM fields. Steps S3a and S3b are synchronized in time. These two steps start at the same time τ1, which corresponds to the same point in time in the same time interval.

[0153] The second phase corresponds to the post-processing phase and includes the following steps:

[0154] In step 204a (S4a), the processing unit 6 calculates information about the induced heat in order to reconstruct the heat distribution on the bottom surface 32 of the thermal screen 3 at different times within the time interval [τ1, τ2], referred to as the thermal distribution over time at the set of time points. Depending on the type of thermal sensor used, this step can be divided into the following intermediate steps: - time averaging over a period of Δτ; - spatially averaging over the unit surface area of ​​the base 32; - converting the physical quantities measured by the thermal sensors into a heat distribution along the bottom surface 32 of the thermal screen defined in terms of absolute temperature or relative temperature rise at a set of time points during exposure; may include:

[0155] In step 204b (S4b), the processing unit 6 calculates the time points τ i We calculate information about the EM field emitted by the electromagnetic source 2 to reconstruct the illumination conditions at the top surface 31 of the screen 3 at ∈[τ1, τ2].

[0156] Depending on the piece of information available, this step may include the following intermediate steps: - calculating the EM properties of the screen medium at the operating frequency of the electromagnetic source 2 defined in relation to the frequency resource allocation, - calculating the propagation paths and losses between the electromagnetic wave source 2 and the thermal screen 3; - calculating the reflection / transmission at the top surface of the screen 3 for a given polarization and angle of incidence defined by the relative position of the electromagnetic source 2; - time / space averaging of the incident power density per unit surface area and unit time interval; may include:

[0157] Phase 2 can start at any time τ2 (τ1<τ2≦τ3). In the embodiment of Figure 9, the start time is fixed and predetermined.

[0158] The duration of post-processing of the heat-related information and the EM field-related information may be different, τ h and τ em Therefore, the switch-off time of the electromagnetic wave source 2 is defined as τ3 = τ2 + max(τ h ,τ em )+τ c is defined by

[0159] The third phase includes the following steps:

[0160] In step 205, processing unit 6 calculates dosimetry quantities using information relating to the induced heat, information about the EM field, and predetermined thermal and electromagnetic properties relating to screen 3 at the frequency of electromagnetic source 2. The processing unit temporally correlates the heat distribution over time calculated in step 204a with information relating to the illumination conditions on the top surface of the screen calculated in step 204b, and calculates EM dosimetry quantities associated with the EM radiation incident on and absorbed by the screen at each point of measurement, pixel, or cell unit.

[0161] The calculated data accompanied by time tags including the duration of exposure defined by at least the time interval [τ 1 , τ 2 ] may be stored by the memory unit 7 and / or displayed by the interface unit 8 .

[0162] 8 and 10, a method 300 according to another embodiment for detecting dosimetry experienced by an object irradiated with an electromagnetic (EM) field emitted by an electromagnetic wave source is described below. The method 300 is implemented using the device of FIG. 4 described above.

[0163] The method comprises a first phase corresponding to a measurement phase comprising the following steps:

[0164] In step 301 (S1), an EM field 23 is emitted in the direction of the top surface of the thermal screen by an electromagnetic source 2. In this embodiment, at least some of the information regarding the resource allocation used by the electromagnetic source 2 to generate the EM field is unknown.

[0165] In step 302 (S2), the EM field 23 emitted by the electromagnetic source is converted into heat as a result of absorption of part of the EM field in the medium of the screen 3.

[0166] In step 303 (S3a), the thermal sensor 6 acquires information about heat induced in the screen at different times. This step may include measuring a physical quantity proportional to the induced heat by at least one thermal sensor 5. In one embodiment, the thermal sensor may be an infrared image sensor, and the physical quantity may be the intensity of infrared radiation emitted from the bottom surface 32 of the thermal screen. In another embodiment, the bottom surface 32 is covered with a heat-sensitive material, the thermal sensor is an image sensor, and the physical quantity may be the intensity of visible light radiation emitted or reflected by the bottom surface 32 of the screen. In yet another embodiment, the thermal sensor 5 includes multiple thermocouples attached to or embedded in the bottom surface 32 of the screen, and the physical quantity may be a voltage measured by a voltmeter. The heat-related information may be stored in the memory unit 7 and / or displayed by the interface unit 8.

[0167] In step 303b (S3b), the EM sensor 11 obtains information about the EM field emitted by the electromagnetic source 2. The information about the EM field emitted by the electromagnetic source may include any part of the information about the radio resource allocation by the electromagnetic source in the domains of frequency, time, and / or space.

[0168] As shown in FIG. 8, the duration of this first phase is limited by a time interval [τ1, τ3], where τ3 is the switch-off time of the electromagnetic wave source 2. In one embodiment, this end time can be defined based on feedback from the processing unit 6, which indicates the successful completion of the calculation process. Steps S3a and S3b for measuring information about the heat and EM fields are also performed within the same time interval [τ1, τ3]. The measured raw data (related to physical quantities related to the induced heat) and post-processed data (related to the temperature rise distribution over time and the EM fields incident on the screen) are stored in the memory unit 7. Part of this information for the time period [τ1, τ2] is used by the processing unit 6 to calculate the desired dosimetric quantities. The duration of this time interval can be continuously increased depending on the success of the calculation procedure, which requires a sufficient SNR for the heat measurements and sufficient information about the EM fields. Steps S3a and S3b are synchronized in time. They start at the same time τ1, which corresponds to the same point in time in the same time interval.

[0169] Advantageously, in this embodiment, the duration of this phase may be adjusted in real time depending on the success of phases 2 and 3. The termination criteria for this phase may be defined with respect to a predetermined value of τ or based on the successful termination of phase 3.

[0170] The second phase corresponds to the post-processing phase and includes the following steps:

[0171] In step 304a (S4a), the processing unit 6 calculates information about the induced heat in order to reconstruct the heat distribution on the bottom surface 32 of the thermal screen 3 at different times within the time interval [τ1, τ2], referred to as the thermal distribution over time at the set of time points. Depending on the type of thermal sensor used, this step may be divided into the following intermediate steps: - time averaging over a period of Δτ; - spatially averaging over the unit surface area of ​​the base 32; - converting the physical quantities measured by the thermal sensors into a heat distribution along the bottom surface 32 of the thermal screen defined in terms of absolute temperature or relative temperature rise at a set of time points during exposure; may include:

[0172] In step 304b (S4b), the processing unit 6 calculates the time points τ i We calculate information about the EM field emitted by the electromagnetic source 2 to reconstruct the illumination conditions at the top surface 31 of the screen 3 at ∈[τ1, τ2].

[0173] Depending on the piece of information available, this step may include the following intermediate steps: - calculating the EM properties of the screen medium at the operating frequency of the electromagnetic source 2 defined in relation to the frequency resource allocation, - calculating the propagation paths and losses between the electromagnetic wave source 2 and the thermal screen 3; - calculating the reflection / transmission at the top surface of the screen 3 for a given polarization and angle of incidence defined by the relative position of the electromagnetic source 2; - time / space averaging of the incident power density per unit surface area and unit time interval; may include:

[0174] In a similar manner, phase 2 may be initiated at any time, with this start time τ being fixed and predetermined, or repeatedly postponed until the third phase is successfully completed or equal to the total duration of the first phase. Postponing the start time allows for a larger interval of exposure time to be considered, and thus achieves a higher temperature rise within the heating zone that may be necessary to achieve a desired threshold of signal-to-noise ratio (SNR), defined in terms of thermal noise and / or sensitivity of the thermal sensor 5.

[0175] The duration of post-processing of the heat-related information and the EM field-related information may be different, τ hand τ em is defined by

[0176] The success criteria for step 304a may be defined in terms of an SNR level defined in terms of an acceptable threshold that may ensure reliable interpretation of the measured thermal data. If the SNR is insufficient (SNR<threshold), additional steps to improve the SNR, such as transient thermography, may be applied, as described below. In Figure 10, this optional step is indicated by the dotted box.

[0177] The transient thermography method for improving SNR requires periodic excitation with a predetermined waveform. Once the excitation conditions (i.e., pulse frequency and duration) are known, Fourier-based filtering techniques can be applied to filter out stationary thermal noise. This significantly improves the SNR and enables reliable readout of thermal data buried in thermal noise. However, implementing this method requires control of resource allocation, at least with respect to the operating frequency, waveform, and radiation pattern, which are to be predefined. This can be done through a control link 26 between the processing unit 6 and the electromagnetic wave source 2. In one embodiment, this control link can be represented by a wireless link established through the EM sensor 11. Alternatively, it can be established through the application layer, provided that both the processing unit 6 and the electromagnetic wave source 2 can be configured to support such a connection.

[0178] The third phase (Phase 3) includes the following steps:

[0179] In step 305, processing unit 6 calculates dosimetry quantities using information related to the induced heat, information about the EM field, and the electromagnetic and thermal properties of screen 3 at the frequency of electromagnetic source 2. Processing unit 6 temporally correlates the heat distribution over time calculated in step 304a with information about the illumination conditions on the top surface of the screen calculated in step 304b to calculate EM dosimetry quantities associated with the EM radiation incident on and absorbed by the screen at each point of measurement, pixel, or cell unit.

[0180] The calculated data accompanied by time tags including the duration of the exposure period defined by at least the time interval [τ 1 , τ 2 ] may be stored by the memory unit 7 and / or displayed by the interface unit 8 .

[0181] The success criteria for the completion of Phase 3 were determined by the processing unit 6 based on information about the EM fields and the predetermined screen EM / thermal properties, as determined or acquired by the EM sensors 11 [τ1, τ i a time point τ determined by the processing unit 6 based on the information about the induced heat measured by the thermal sensor 5 and processed by the processing unit 6, taking into account the screen exposure conditions during the time interval iBased on the temperature rise distribution at ∈[τ1,τ2], the convergence criterion can be defined in terms of the convergence of the numerical solution of a time-reversed EM / thermal model used by the processing unit 6 to calculate an EM dosimetric quantity (e.g., absorbed power density or absorbed energy density derived as the time integral of absorbed power density) for the time interval [τ1,τ2]. Apart from known factors related to the convergence of numerical solutions of differential equations, such as Maxwell's equations and the heat equation, the convergence of the time-reversed EM / thermal model strongly depends on the accuracy in determining the temperature rise distribution, which is considered as the initial input data for the time-reversal simulation. For a given level of ambient thermal noise, the accuracy in calculating the temperature rise distribution can be improved by increasing the incident power density of the EM field, increasing the exposure time defined by the parameter τ2, and / or using a predetermined waveform of the excitation signal emitted by the EM source 2, which may enable smart post-processing of the measured thermal data, such as transient thermography with a predetermined lock-in frequency. The convergence criterion of the numerical solution can be defined in terms of a predetermined threshold for the relative change in the value of the calculated dosimetric quantity for iteratively increasing exposure times.

[0182] If the convergence criterion is reached, the measurement procedure reduces the total execution time τ3 = τ2 + max(τ h ,τ em )+τ c can be terminated with, where τ h is the time required to post-process the information about the induced heat, and τ em is the time required to post-process the information about the EM field emitted by source 2, and τ c is the time required to complete the third phase 3 of solving the EM / thermal time-reversal model.

[0183] If the convergence criteria is not reached, the following additional steps may be performed. - Longer data sets of information related to thermal and EM fields, corresponding to longer exposure times, can be processed. This can be done by increasing the value of the parameter τ2 or restarting the measurement using a different resource allocation for enabling smart post-processing of the thermal data, which can improve the SNR and, consequently, the convergence of the algorithm. The new resource allocation can involve a specific radiation pattern (beamforming) and / or the use of specific frequencies and / or waveforms, which can result in an improved SNR for the thermal signal through increased EM-to-thermal conversion efficiency or more localized exposure. [Explanation of symbols]

[0184] 1 device 2. Electromagnetic wave source 3. Thermal Screen 5. Thermal Sensor 6 Processing Unit 7 Memory Unit 8 Interface Unit 10 EM Dosimetry Device 11 Electromagnetic Sensor 21 Single Antenna 22 Wavefront 23 EM World 26 Control Link 31 Surface, upper surface, top surface 32 bottom 33 adjacent unit cells 41 First dielectric layer 42 second dielectric layer 51 First dielectric layer 52 Second Dielectric Layer 61 first dielectric layer 62 Second dielectric layer 63 Third Layer 64 Groove 71 First dielectric layer 72 Second Dielectric Layer 73 Third Layer 74 Groove 100 ways 200 ways 300 ways

Claims

1. A device (1) for measuring electromagnetic dosimetry received by an object irradiated with an electromagnetic (EM) field (23) emitted by an electromagnetic wave source (2), comprising: a screen (3) having a top surface (31) facing the electromagnetic wave source (2) and a bottom surface (32) opposite the top surface (31), the screen (3) being adapted to absorb at least a portion of the EM field emitted by the electromagnetic wave source (2); said screen comprises a plurality of unit cells (33), said device (1) further comprising: at least one thermal sensor (5) arranged with respect to the bottom surface of the screen (3) and configured to measure a physical quantity related to the heat distribution along the surface of the screen induced due to the absorption of an electromagnetic field in the screen medium; a processing unit (6) linked to said at least one thermal sensor (5) and configured to calculate said electromagnetic dosimetry quantities from said measured thermal distribution, information about the EM field emitted by said EM source, and predetermined EM and thermal properties of said screen; A device (1) comprising:

2. The device of claim 1 , further comprising at least one electromagnetic sensor (11) configured to measure the information regarding the EM field emitted by the EM source.

3. 3. The device of claim 2, wherein the processing unit (6) is configured to calculate the electromagnetic dosimetry by temporally correlating information about the EM field measured by the at least one electromagnetic sensor (11) and the thermal distribution measured by the at least one thermal sensor (5).

4. 4. The device according to claim 2 or 3, wherein the processing unit (6) is configured to analyze the signals transmitted from the at least one electromagnetic sensor (11) to retrieve the information about the EM field emitted by the EM source (2).

5. 5. The device according to any one of claims 2 to 4, wherein the at least one electromagnetic sensor (11) is linked to the electromagnetic wave source (2) by a control link (26).

6. 6. The device of claim 1, wherein the processing unit (6) is configured to use a lock-in technique to post-process the thermal distribution over time by using a predetermined lock-in frequency and waveform for the EM field (23) emitted by the EM source (2).

7. 7. The device according to any one of claims 1 to 6, wherein the at least one thermal sensor (5) is a thermal sensor located at a distance from the bottom surface of the screen and aligned with respect to the center of the screen, with respect to the center of a unit cell and / or along the direction of the EM wave propagation.

8. 7. The device according to any one of claims 1 to 6, wherein the at least one thermal sensor (5) comprises a plurality of thermocouples attached to or embedded in the bottom surface of the thermal screen.

9. 7. The device according to any one of the preceding claims, wherein the at least one thermal sensor (5) comprises at least one heat-sensitive element attached to the bottom surface of the screen.

10. 10. The device according to any one of claims 2 to 9, wherein the at least one electromagnetic sensor (11) is an electromagnetic sensor operating in a frequency range that at least partially overlaps with an operating frequency range of the electromagnetic wave source (2).

11. 11. The device of claim 2, wherein the at least one electromagnetic sensor (11) is configured to measure an incident EM field (23) from the EM source, the EM field reflected from the top surface of the screen, or the EM field transmitted through the screen.

12. The screen (3) includes at least one first dielectric layer (3) having a top surface (31) facing the electromagnetic wave source (2) and a bottom surface (32) opposite to the top surface (31); - said top surface (31) is at least partially transparent to the electromagnetic field emitted by said electromagnetic wave source (2); - said bottom surface (32) is at least partially reflective to said electromagnetic field transmitted through said at least one first dielectric layer (3); - A device according to any one of claims 1 to 11, wherein said at least one first dielectric layer (3) is characterized by a complex permittivity and a thickness which are jointly selected to reproduce the electromagnetic response of a reference object, for example biological tissue, human skin tissue.

13. 12. The device of claim 1, wherein the thermal screen comprises two dielectric layers (41, 42), a first dielectric layer (41) having a top surface facing the electromagnetic sensor (2) and a second dielectric layer (42) having a bottom surface facing the thermal sensor (5), each layer characterized by a complex permittivity and a thickness that are jointly selected to reproduce the electromagnetic response of a reference object, and each layer comprising a plurality of unit cells.

14. 12. The device of claim 1, wherein the screen comprises two dielectric layers (51, 52), a first dielectric layer (51) having a top surface facing the electromagnetic sensor (2) and a second dielectric layer (52) having a bottom surface facing the thermal sensor (5), each layer characterized by a complex permittivity and a thickness that are together selected to reproduce the electromagnetic response of a reference object, each layer including a plurality of unit cells, the unit cells being separated by grooves (54), the grooves being filled with or made from a dielectric material having a thermal conductivity that is smaller than the thermal conductivity of the dielectric material of the second dielectric layer (52).

15. 12. The device of claim 1, wherein the screen comprises a first dielectric layer (61), a second dielectric layer (62), and a third layer (63), the second layer (62) being made from a dielectric material having a thermal conductivity smaller than that of the third layer, each layer being characterized by a complex permittivity and a thickness that are together selected to reproduce the electromagnetic response of a reference object, each layer including a plurality of unit cells, the unit cells of the third layer being separated by grooves (64), the grooves being filled with or made from a dielectric material having a thermal conductivity smaller than that of the dielectric material of the third dielectric layer (63).

16. 12. The device of claim 1, wherein the screen comprises a first dielectric layer (71), a second dielectric layer (72), and a third layer (73), each characterized by a complex permittivity and a thickness that are together selected to reproduce the electromagnetic response of a reference object, each layer including a plurality of unit cells, the unit cells of the second layer (72) being separated by grooves (74), the grooves being filled with or made from a dielectric material having a thermal conductivity that is smaller than that of the dielectric material of the second dielectric layer (72), and the third layer (73) being made from a heat-sensitive material.

17. 1. A method for detecting electromagnetic dosimetry received by an object illuminated by an electromagnetic (EM) field emitted by an electromagnetic source, comprising: - irradiating the surface of a thermal screen (3) using an EM source (2); - converting the EM fields incident on the surface of the thermal screen (3) into heat induced in the medium of the thermal screen (3); - measuring information about said induced heat by said at least one thermal sensor (5); - using said information on said induced heat, by a processing unit (6) for a time interval [τ １ , τ ２ ] at time τ ｉ determining a temperature rise distribution over time in the set of - calculating said electromagnetic dosimetry quantities from said temperature rise distribution over time, said information on said EM field emitted by said EM source and predetermined EM and thermal properties of said thermal screen (3); A method comprising:

18. 1. A method for detecting electromagnetic dosimetry received by an object illuminated by an electromagnetic (EM) field emitted by an electromagnetic source, comprising: - irradiating the surface of a thermal screen (3) using an EM source (2); - converting the EM fields incident on the surface of the thermal screen (3) into heat induced in the thermal screen (3); - measuring information about said induced heat by said at least one thermal sensor (5); - measuring said information about said EM field emitted by said EM source (2) by means of an EM sensor (11); - using said information on said induced heat, by a processing unit (6) for a time interval [τ １ , τ ２ ] at time τ ｉ determining a temperature rise distribution over time in the set of - temporally correlating the information about the temperature rise distribution over time and the information about the EM field emitted by the EM source; - calculating said electromagnetic dosimetry quantities using time-correlated information on said temperature rise distribution over time and on the EM field emitted by said EM source, and predetermined information on the EM and thermal properties of said thermal screen (3); A method comprising:

19. - comparing the signal-to-noise ratio (SNR) of said temperature rise distribution over time with a predetermined threshold; improving the SNR by using said information about said EM fields; 20. The method of claim 18, further comprising:

20. 20. The method of claim 18 or 19, wherein completion of the measurement procedure is defined in terms of convergence of a numerical solution of a time-reversed EM and thermal model used to calculate the EM dosimetry quantity.

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