Apparatus and method for thermal and electromagnetic dosimetry

Abstract

The invention relates to a device and a method for measuring an electromagnetic dosimetric amount received by an object irradiated by an electromagnetic field (23) emitted by an electromagnetic (EM) source (2), said device comprising:-a barrier (3) comprising a top surface (31) facing said electromagnetic source (2) and a bottom surface (32) opposite said top surface (31), said barrier (3) being adapted to absorb at least a portion of said EM field emitted by said electromagnetic source (2); -said barrier comprises a plurality of unit cells (33); -at least one thermal sensor (5) arranged relative to the bottom surface of the barrier (3) and configured to measure a physical quantity relating to a thermal distribution along the surface of the barrier induced by the absorption of the electromagnetic field in the barrier medium; -a processing unit (6) linked to the at least one thermal sensor (5) and configured to calculate the electromagnetic dosimetric quantity as a function of the measured thermal distribution, information relating to the EM field emitted by the EM source and predetermined EM and thermal properties of the barrier.

Description

Technical Field

[0001] The present invention relates to a device and a method for electromagnetic dosimetry, and more precisely to a device for measuring thermal and electromagnetic information in a synchronous manner and retrieving electromagnetic dosimetry quantities induced in a thermal medium (e.g. biological tissue) by an electromagnetic field emitted by an electromagnetic source. Background Art

[0002] With the development of wireless technologies, such as cellular phones and various consumer wireless devices used in contact with the human body, accurately measuring the exposure level of electromagnetic (EM) wave radiation in the human body has become a critical factor.

[0003] There are various devices that reproduce the electromagnetic properties of biological tissue, collectively referred to as "phantoms" for assessing the exposure of the human body to electromagnetic waves: liquid phantoms, semi-solid phantoms, solid phantoms, and hybrid phantoms. Liquid phantoms include a plastic part or a solid shell filled with a gel or liquid having EM properties similar to those of human biological tissue, and the measurement frequency is usually set due to the higher water content, just like in biological tissue. These devices are usually used in the frequency range of 30MHz to 6GHz. These devices have several problems: the liquid needs to be replaced frequently due to evaporation of the liquid and / or degradation of the dielectric properties over time. These devices require special test equipment to support their weight. Due to the strong absorption of EM fields by water molecules, the penetration depth of the EM field is very shallow and the signal-to-noise ratio (SNR) of the embedded sensor is therefore insufficient, so these devices cannot be used at frequencies above 6GHz. The composition of a semi-solid phantom is similar to that of a liquid phantom, and a gelling agent is usually used instead of a liquid to maintain the shape of the phantom without using a solid shell. The main disadvantage of semi-solid phantoms is their limited service life (usually limited to a few days or weeks). Solid phantoms are solid pieces made of solid dielectric materials such as plastics, polymers, ceramics or synthetic rubbers doped with conductive particles such as graphite, carbon or metals. The main advantage of solid phantoms is that their dielectric properties are reliable and constant over time. However, these devices are quite complex and costly to manufacture. In addition, the devices also suffer from high EM losses, and measurements above 10 GHz cannot be performed due to the frequency-dependent EM properties of the phantom material. For example, at 60 GHz, the penetration depth of electromagnetic radiation in human tissue is about 0.5 mm, and the absorption of radiation is essentially limited to the surface layers of the body. This results in a very low signal-to-noise ratio (SNR) for any sensor embedded in a phantom that reproduces the EM properties of the biological tissue.

[0004] From this point of view, due to the peculiarities of the frequency-dependent interaction between the human body and wireless devices, which results in lower reflections and at the same time stronger EM losses, and compliance testing of 5G and later generations of wireless devices operating at frequencies above 6 GHz, the new dosimetry standards and guidelines imply the use of new dosimetry quantities, namely the average absorbed power density (APD) in a specific area, instead of the average RF energy absorption rate (SAR) in a specific volume used at frequencies below 6 GHz. Moreover, given the possible strong mutual influence of the human body on the performance characteristics of 5G devices (and therefore the user exposure level), the new guidelines also imply testing these devices under realistic conditions, taking into account the presence of the human body. These two requirements make the existing EM dosimetry devices used for testing 3G / 4G devices obsolete.

[0005] In addition, to meet the ever-increasing demand for data rates and traffic, 5G and next-generation wireless communication systems will adopt new frequency bands in the frequency range of approximately 24 GHz to 300 GHz, thanks to new wireless access technologies developed for millimeter wave (mmWave) bands, broadband spectrum signals, beamforming, multiple-input multiple-output (MIMO), and dynamic resource allocation in the time, frequency and spatial domains.

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

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

[0008] The higher propagation losses of mmWave are compensated by higher antenna gains achieved through the use of compact antenna arrays and multiple-input multiple-output (MIMO) technology. The beamforming capabilities enabled in 5G devices are used to multiplex parallel data streams to communicate with multiple spatially separated users, or to mitigate dynamic blocking of a single user propagation channel. Portable and wearable devices often contain 4 to 8 antenna elements, which allow support for at least two different beams characterized by different shapes / widths, gains and / or spatial orientations.

[0009] As a result, recent wireless communication devices have more than one antenna and are able to operate in multiple frequency bands and modes, supporting various wireless access technologies. In the case of 5G devices, an additional degree of complexity will be added due to dynamic resource allocation in the time, frequency and space domains. Existing methods of electromagnetic (EM) dosimetry developed for compliance testing of 3G / 4G devices operating below 6 GHz cannot be applied to 5G mmWave devices because all existing technologies have fundamental limitations related to their inability to reproduce realistic use case conditions (given the dynamic resource allocation) or because of the extremely low SNR caused by the high material and propagation EM losses of mmWave. This requires the development of new dosimetry systems that can overcome these limitations.

[0010] Document WO2017 / 0173350 and Figure 1 The reference proposes a device that has both human tissue characteristics and is capable of measuring electromagnetic waves at frequencies greater than 6 GHz. The device includes a layer of dielectric material (S), a semi-transparent metal shield (MSH) with a through hole (OSH), and a sensor array (SENS) placed under the through hole. The sensor is configured to measure an electromagnetic field emitted by an electromagnetic source (EMS).

[0011] Although the device proposed in this article provides reliability and constancy of dielectric properties and may allow electromagnetic dosimetry at frequencies exceeding 6 GHz, the proposed solution does not teach how to reduce or limit significant losses in electromagnetic field intensity during propagation through composite dielectric materials doped with conductive particles (such as carbon), which can lead to strong absorption of electromagnetic fields at high frequencies (especially above 6 GHz).

[0012] Furthermore, similar to other prior art solutions, the measurement procedure used in WO2017 / 0173350 relies on sampling the transmitted field in a number of spatial points defined by the positions of the sensors in the sensor array (SENS). This can lead to inaccuracies because the sensor topology array dictates a fixed grid of sampling points and / or because of additional post-processing steps of digitally integrating the measured quantities in order to compute a dosimetric quantity defined for a given surface area or volume.

[0013] High EM losses may sacrifice measurement accuracy and reduce the signal-to-noise ratio (SNR). In order to increase the SNR, a key parameter for low-power measurements, it is necessary to increase the sensitivity of the sensor or the level of the transmitted electromagnetic signal. Increasing the level of the transmitted electromagnetic signal is generally preferred because it can cope with higher noise levels. However, for low-power devices operating in the millimeter wave frequency range, this is not feasible because standard dielectric materials have limited power at these frequencies and high material losses. These limitations can be critical to the accuracy and cost of dosimetry devices for compliance testing of 5th and later generations of wireless devices.

[0014] In addition, the prior art devices proposed in this document do not take into account the particularity of 5G devices for dynamic resource allocation in the time, frequency and spatial domains, which may cause exposure conditions to change rapidly.

[0015] Therefore, there is a need for an improved apparatus and method for electromagnetic dose determination that can take into account the particularities of 5G devices for dynamic resource allocation (by considering the complex time and frequency resource allocation implemented by 5G and future xG devices, resulting in non-constant exposure conditions), and by developing methods and techniques that are not based on direct EM measurements to improve the signal-to-noise ratio (SNR) of the measurement signal, thereby achieving a more accurate, reliable and rapid method and apparatus for user exposure compliance testing of 5G / xG wireless devices under realistic exposure conditions.

[0016] Another object of the invention is to propose a device allowing to transform the unavoidable electromagnetic losses in the phantom material into a measurable physical quantity, namely the local heat related to the sought dosimetry quantity, thus offering an alternative solution for building EM dosimetry systems.

[0017] Another object of the present invention is to provide a device that is easier and less expensive to manufacture. Summary of the invention

[0018] The present disclosure improves the described situation.

[0019] A device for measuring electromagnetic dosimetry received by an object irradiated by an electromagnetic field emitted by an electromagnetic (EM) source is proposed, comprising:

[0020] - a barrier comprising a top surface facing said electromagnetic source and a bottom surface opposite said top surface, said barrier being adapted to absorb at least a portion of said EM field emitted by said electromagnetic source;

[0021] - the barrier comprises a plurality of unit cells;

[0022] - at least one thermal sensor arranged relative to said bottom surface of said barrier and configured to measure a physical quantity related to the heat distribution along the surface of said barrier induced by absorption of said electromagnetic field in the barrier medium;

[0023] - a processing unit coupled to said at least one thermal sensor and configured to calculate said electromagnetic dosimetry quantity based on the measured heat distribution, information related to said EM field emitted by said EM source and predetermined EM and thermal properties of said barrier.

[0024] In an embodiment, the device further comprises at least one electromagnetic sensor configured to measure said information related to said EM field emitted by said EM source.

[0025] In a preferred embodiment, said processing unit is configured to temporally correlate said information regarding said EM field measured by said at least one electromagnetic sensor and said thermal distribution measured by said at least one thermal sensor to calculate said electromagnetic dosimetry.

[0026] In another embodiment, said processing unit is configured to analyze signals transmitted from said at least one electromagnetic sensor to retrieve said information related to said EM field emitted by said EM source.

[0027] In an embodiment, said at least one electromagnetic sensor is coupled to said electromagnetic source via a control link.

[0028] 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 related to the EM field emitted by the EM source.

[0029] In an embodiment, the at least one thermal sensor is a thermal sensor positioned at a distance from the bottom surface of the barrier and aligned relative to a barrier center, relative to a unit cell center and / or along a direction of EM wave propagation.

[0030] In yet another embodiment, the at least one thermal sensor comprises a plurality of thermocouples attached to or embedded in the bottom surface of the thermal barrier.

[0031] In an embodiment, the at least one thermal sensor comprises at least one thermal element attached to the bottom surface of the barrier.

[0032] In an embodiment, the at least one electromagnetic sensor is an electromagnetic sensor operating in a frequency range at least partially overlapping with an operating frequency range of the electromagnetic source.

[0033] In another embodiment, said at least one electromagnetic sensor is configured to measure said incident EM field from said EM source, said EM field reflected from said top surface of said barrier, or said EM field transmitted through said barrier.

[0034] In an embodiment, the barrier comprises at least one first dielectric layer, the at least one first dielectric layer comprising a top surface facing the electromagnetic source and a bottom surface opposite the top surface;

[0035] - said top surface is at least partially transparent to said electromagnetic field emitted by said source;

[0036] - said bottom surface at least partially reflects said electromagnetic field transmitted through said at least one first dielectric layer;

[0037] - the at least one first dielectric layer is characterized by a complex permittivity and a thickness jointly selected so as to reproduce the electromagnetic response of a reference object, such as biological tissue, human skin tissue.

[0038] In another embodiment, the thermal barrier comprises two dielectric layers, the first dielectric layer having a top surface facing the electromagnetic sensor and the second dielectric layer having a bottom surface facing the thermal sensor, each layer being characterized by a complex dielectric constant and a thickness commonly selected so as to reproduce the electromagnetic response of a reference object, each layer comprising a plurality of unit cells.

[0039] In another embodiment, the thermal barrier comprises two dielectric layers, the first dielectric layer having a top surface facing the electromagnetic sensor and the second dielectric layer having a bottom surface facing the thermal sensor, each layer being characterized by a complex dielectric constant and a thickness commonly selected so as to reproduce the electromagnetic response of a reference object, each layer comprising a plurality of unit cells separated by grooves filled with or made of a dielectric material having a thermal conductivity less than the thermal conductivity of the dielectric material of the second dielectric layer.

[0040] In yet another embodiment, the barrier comprises a first dielectric layer, a second dielectric layer and a third layer, the second layer being made of 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 jointly selected so as to reproduce the electromagnetic response of a reference object, each layer comprising a plurality of unit cells, the unit cells of the third layer being separated by grooves filled with or made of a dielectric material having a thermal conductivity less than that of the dielectric material of the third dielectric layer.

[0041] In another embodiment, the barrier comprises a first dielectric layer, a second dielectric layer and a third layer, each layer being characterized by a complex dielectric constant and a thickness jointly selected so as to reproduce the electromagnetic response of the reference object, each layer comprising a plurality of unit cells, the unit cells of the second layer being separated by grooves, the grooves being filled with or made of a dielectric material having a thermal conductivity less than the thermal conductivity of the dielectric material of the second dielectric layer, and the third layer being made of a thermosensitive material.

[0042] In another aspect, a method of detecting electromagnetic dosimetry received by an object irradiated by an electromagnetic field emitted by an electromagnetic (EM) source is provided, the method comprising:

[0043] - irradiating the surface of the thermal barrier using an EM source;

[0044] - converting the EM field incident on the surface of the thermal barrier into heat induced in the thermal barrier;

[0045] - measuring information related to the induced heat by means of at least one thermal sensor;

[0046] - using said information about said induced heat by a processing unit to determine a time interval [τ 1, A set of moments τ in τ2] i The distribution of temperature rise over time;

[0047] - calculating said electromagnetic dosimetry quantities from said temporal temperature rise distribution, said information about said EM field emitted by said EM source and predetermined EM and thermal properties of said barrier.

[0048] In another aspect, a method of detecting electromagnetic dosimetry received by an object irradiated by an electromagnetic field emitted by an electromagnetic (EM) source is provided, the method comprising:

[0049] - irradiating the surface of the thermal barrier using an EM source;

[0050] - converting the EM field incident on the surface of the thermal barrier into heat induced in the thermal barrier;

[0051] - measuring information related to the induced heat by means of at least one thermal sensor;

[0052] - measuring, by an EM sensor, information related to said EM field emitted by said EM source;

[0053] - using the information about the induced heat by the processing unit to determine the self-time interval [τ 1, A set of moments τ in τ2] i The distribution of temperature rise over time;

[0054] - temporally correlating said information about said temperature rise distribution over time and said information about said EM field emitted by said EM source;

[0055] - calculating said electromagnetic dosimetry using time dependent information about said temperature rise profile over time and said EM field emitted by said EM source and predetermined information about EM and thermal properties of said barrier.

[0056] In an embodiment, the method further comprises the following steps:

[0057] - comparing the signal-to-noise ratio (SNR) of the temperature rise distribution over time with a predetermined threshold;

[0058] - Improving the SNR by using the information about the EM field.

[0059] In another embodiment, completion of the measurement procedure is defined with respect to convergence of numerical solutions of time-reversal EM and thermal models used to calculate said EM dosimetry quantities. BRIEF DESCRIPTION OF THE DRAWINGS

[0060] Other features, details and advantages will be seen in the following detailed description and in the accompanying drawings, in which:

[0061] Figure 1

[0062] [ Figure 1 ] Figure 1 is a schematic illustration of a cross-sectional view of a prior art electromagnetic dosimetry device.

[0063] Figure 2

[0064] [ Figure 2 ] Figure 2 is a schematic illustration of a cross-sectional view of an embodiment of an electromagnetic dosimetry device.

[0065] Figure 3

[0066] [ Figure 3 ] Figure 3 Non-limiting examples of a barrier configured to absorb at least a portion of the electromagnetic power radiated by an electromagnetic source at a given operating frequency of the electromagnetic source are represented: a single layer (a), which includes a plurality of unit cells; two layers (b), which include a plurality of unit cells; two dielectric layers (c), wherein the second layer includes a plurality of unit cells separated by grooves; three layers (d), which include an intermediate layer having a thermal conductivity lower than the thermal conductivity of the bottom layer; three layers (e), which include a bottom layer made of a thermosensitive material.

[0067] Figure 4

[0068] [ Figure 4 ] Figure 4 is a schematic illustration of a cross-sectional view of another embodiment of an electromagnetic dosimetry device.

[0069] Figure 5

[0070] [ Figure 5 ] Figure 5 Schematic illustration of a cross-sectional view of one embodiment of an electromagnetic dosimetry device for use in measuring user exposure levels in a barrier illuminated by two differential spatial beams of electromagnetic radiation emitted by an electromagnetic source.

[0071] Figure 6

[0072] [ Figure 6 ] Figure 6 Schematic illustration of an exemplary temperature rise distribution at the bottom surface of the barrier after a brief exposure along the ξ coordinate, ξ being x or y: Measured temperature profile (thick line, G Σ (ξ)), the temperature pattern associated with two overlapping hot spots induced by the absorbed electromagnetic field retrieved by decomposing the measured temperature profile (thin dashed lines, G1(ξ), G2(ξ)), and the estimated temperature pattern in a barrier with zero thermal conductivity (thin solid lines, F1(ξ), F2(ξ)).

[0073] Figure 7

[0074] [ Figure 7 ] Figure 7 For use according to the embodiment Figure 2 Illustration of a method for calculating dosimetry quantities implemented by a device.

[0075] Figure 8

[0076] [ Figure 8 ] Figure 8 For use according to the embodiment Figure 4 Illustration of different time intervals of the main steps performed in a method implemented by an apparatus for calculating dosimetry quantities by measuring thermal and EM information in a correlated manner.

[0077] Fig. 9

[0078] [ Fig. 9 ] Fig. 9 To describe the use according to the embodiment Figure 4 A flow chart of the steps of a method for calculating a dosimetry amount implemented by a device.

[0079] Fig.10

[0080] [ Fig.10 ] Fig.10 To describe the use according to another embodiment Figure 4 A flow chart of the steps of a method for calculating a dosimetry amount implemented by a device. DETAILED DESCRIPTION

[0081] The terms "top", "bottom", "above", "below", "between", "on", and other similar terms used herein refer to relative positions. The relative positions of the terms do not define or limit a layer to a vector space orientation.

[0082] To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements disclosed in one embodiment may be beneficially utilized on other embodiments without specific recitation.

[0083] In the present disclosure, the term "layer" refers to a structure having a constant thickness or a variable thickness. The layer may be flat or curved. Specifically, the layer may be shaped into a 3D form that reproduces a part of a human body, such as a head or a hand. The layer may be shaped to form a closed surface, such as the surface of the side wall of a cylindrical object.

[0084] In this disclosure, the term "dosimetric quantity" or "physical quantity" refers to any metric used to quantify electromagnetic exposure, including power density, energy density, radio frequency energy absorption rate, specific energy absorption, electric field strength, magnetic field strength, voltage or current, and their derivatives defined with respect to average surface area or volume.

[0085] In the present disclosure, the term "information of the EM field" refers to any information related to the resource allocation used by a source in the frequency domain, time domain and / or space domain, for example, channels and frequency bands used for transmission, waveforms and time blocks for scheduling transmissions, radiated power, radiation patterns, polarization, phase center positions, antenna architectures, etc.

[0086] In this disclosure, the term "thermal medium" or "thermal barrier" refers to a medium designed to convert an electromagnetic field incident on the surface of the medium into heat in a controlled manner. The thermal medium acts as a spatial transformer of the EM field, converting the EM field into heat induced in the volume of the medium due to absorption of a portion of the EM power transmitted through the thermal medium.

[0087] In the present disclosure, the term "conductive layer" refers to a layer having a conductivity σ≥10 3 Layers made of materials of S / m.

[0088] In this disclosure, the term "dielectric layer" refers to a dielectric layer having an electrical conductivity σ strictly less than 10 3 Layer of thermally conductive and electrically insulating material of S / m.

[0089] refer to Figure 2 , a dosimetric electromagnetic device 1 according to an embodiment of the present disclosure will now be described. In this embodiment, the proposed device combines thermal measurements and specific thermal barriers with predetermined thermal and known electromagnetic parameters to retrieve electromagnetic quantities related to the exposure level of an electromagnetic source.

[0090] The device 1 is placed in an orthogonal spatial coordinate system (XYZ).

[0091] The thermal barrier of the 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, the device may be designed to provide low reflection to allow a greater portion of the incident power to penetrate inside the thermal barrier. Alternatively, it may be configured to reproduce the electromagnetic response of a reference object (e.g. a human anatomical part) when this reference object is illuminated by an electromagnetic source; specifically, the reflection characteristics at the air / skin interface, and measure a physical quantity representative of the reference object related to the electromagnetic field incident on the thermal barrier. The measured physical quantity may be the amplitude of the EM field, the intensity and / or the power density of the EM field incident on the air / dielectric interface or transmitted through the air / dielectric interface.

[0092] The device 1 comprises a thermal barrier 3 extending visibly 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). Figure 2 The device is shown placed in a test configuration. An electromagnetic source 2 is placed at a distance D1 from the device 1 .

[0093] Electromagnetic source

[0094] The electromagnetic field source 2 may be a mobile phone or any other wireless device that is fixed, portable or wearable. This distance D1 is preferably greater than Figure 2 R represented by the wavefront NF The near-field region of the antenna is characterized by . For small electrical antennas, the reactive near-field region is approximately defined with respect to wavelength as R NF =λ0 / 2π, where λ0 is the wavelength in vacuum. For example, at 60 GHz, the distance R NF It is about 0.8mm.

[0095] A person skilled in the art will readily adapt the value of this distance D1 to ensure accurate compliance testing that represents a realistic use case scenario, 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 expected use cases defined by the manufacturer of the wireless device and / or the mobile operator. For example, the distance can vary from a few millimeters (for a smartphone close to the head) to tens of millimeters (for a handheld device).

[0096] The electromagnetic source 2 may include one or more antennas connected to or embedded in the body of the source for transmitting and / or receiving electromagnetic signals.

[0097] like Figure 2 , the electromagnetic field source 2 comprises a single antenna 21 which emits an electromagnetic field represented by a wavefront line 22. The center of the wavefront line coincides with the phase center of the antenna 21. A portion of the electromagnetic wave emitted by the source 2 illuminates a surface 31 of the thermal shield 3 of the device 1. This surface illuminated by the EM wave emitted by the source 2 is referred to as the top surface. The surface of the thermal shield 3 of the device 1 opposite to the EM source is referred to as the bottom surface 32.

[0098] The EM source 2 may operate at a frequency in a band within the frequency range of about 6 GHz to about 300 GHz allocated for 5G and 6G wireless networks, however, due to the scalability of Maxwell equations, the teachings of the present invention may be extended to other frequency bands.

[0099] like Figure 2 , an EM wave emitted by source 2 is incident on top surface 31 of thermal barrier 3. The incident EM wave is denoted by numerical reference 23. The incident wave is partially reflected by top surface 31 of barrier 3 ( Figure 2 3). A portion of the EM wave that is not reflected at the air / barrier interface associated with top surface 31 propagates through barrier 3, from top surface 31 to bottom surface 32, and is partially absorbed by the medium of barrier 3. The EM wave that is transmitted through barrier 3 induces a temperature rise within barrier 3.

[0100] The electromagnetic source 2 may operate with a single antenna that produces a single beam that is fixed in time, space, and frequency. In another embodiment, the electromagnetic source may include more than one antenna and be adapted to operate in multiple frequency bands, thereby allowing dynamic resource allocation in the time, frequency, and space domains. Dynamic resource allocation may involve temporal allocation variations of communication resources (frequency-time blocks and transmission power), and using one of at least two predetermined spatial patterns of radiated power implemented by a beamforming mechanism. For example, an EM source may use only one of a plurality of frequency channels, and its transmissions may be scheduled in the time domain. Thus, the beams produced by each source may be variable in time and frequency.

[0101] Thermal barrier

[0102] The thermal barrier 3 acts as a spatial transformer of the EM field, transforming the EM field into heat induced in the barrier volume due to the absorption of a portion of the EM power of the barrier in the medium transmitted through the barrier. In one embodiment, the barrier may 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 source. As a non-limiting example, the barrier structure may 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. A person skilled in the art will readily adapt different values ​​of the complex permittivity and thickness of the at least one dielectric layer to the embodiments described with respect to the present invention.

[0103] The thermal barrier 3 is adapted to absorb at least a portion of the EM power radiated by the EM source, said EM power being incident on the barrier and transmitted through its surface.

[0104] The thermal barrier 3 comprises a structure extending in a horizontal plane (XY). The structure defines two main surfaces, a top surface 31 facing the electromagnetic source and a bottom surface 32 opposite with respect to the electromagnetic source 2.

[0105] The barrier can be made of a dielectric material that absorbs at a 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 between 24 and 28 GHz, or between 37 and 39 GHz, or between 57 and 71 GHz, or in another sub-band in the frequency range exceeding 6 GHz.

[0106] The thickness of the heat barrier along the z-axis orthogonal to the heat barrier is preferably between λ1 / 10 and 10×λ1, where λ1 is the wavelength of the EM field in the medium of the dielectric layer 3 at frequency F1. For example, at 60 GHz, the thickness T1 of the dielectric layer may be about 1 mm.

[0107] The thermal barrier 3 is preferably positioned at a predetermined distance D1 from the electromagnetic source in such a way that an air gap is provided between the electromagnetic source and the barrier. For example, D1 is selected to be greater than λ1 / 100, λ1 being the wavelength of the EM field in free space at frequency F1. This distance may also be defined according to the intended use of the EM source 2. For example, in the case of a smartphone, this distance may be defined as 5 mm, which is a typical distance for a smartphone when placed close to a user's head.

[0108] In one embodiment, the barrier forms Figure 2, which has a larger dimension in the xy plane, e.g. much larger than the thickness Ts extending along the z-axis. The overall size of the barrier may be defined according to the intended use of the EM source 2. For example, the overall size may be chosen to be equal to the head or hand of a user. Alternatively, the size may be chosen according to the radiation pattern of the source 2 or the expected near or far field distribution in the plane of the barrier produced by the source 2, to allow the size to be characterized with a minimum number of measurements at a fixed relative position of the source 2 and the barrier 3.

[0109] In another embodiment, the barrier forms a complex 3D shape, thereby reproducing the shape of a part of the human body. In other words, a single dielectric layer 3 forms a closed or partially closed shell filled with a medium (e.g., a liquid, gel, foam, or gas). This 3D structure is particularly suitable for simulating a part of the human body, such as a head-like phantom. The medium can be selected as a brain, and the top surface can present a concave surface in the form of a simulated head shape. Alternatively, the medium can be used alone as a mechanical support and / or host medium for at least one thermal sensor 5 placed under the dielectric layer 3.

[0110] In another example, the barrier 3 may include a layer of amorphous and gel-type dielectric material doped with a conductive filler to form a suspended composite material. The percentage of the conductive filler may be varied to reproduce the electromagnetic response of a reference object, such as the reflection characteristics at the air-dielectric interface of human skin tissue.

[0111] The barrier is divided into a plurality of adjacent unit cells 33. In one embodiment, these cells may all be identical. The dimensions of the unit cells are identical. Each unit is characterized by the same electromagnetic and thermal characteristics. In other words, the unit cells are made of the same material and have the same configuration.

[0112] In another embodiment, the unit cells may not be uniform. Each unit cell is characterized by a specific size, its own electromagnetic signature, and its own thermal signature. In other words, the unit cells may be made of different dielectric materials and may have different sizes and / or shapes. The electromagnetic and / or thermal properties and dimensions of each unit cell are adjusted to account for different illumination conditions of each unit by the electromagnetic field emitted by source 2. The unit cells are designed to improve the efficiency of the EM field for heat conversion under different illumination conditions, and / or to prevent heat diffusion in the plane of the barrier.

[0113] Advantageously, the size of the unit cells in the middle of the barrier and on its periphery may vary to account for different illumination conditions depending at least on the angle of incidence, power density and / or polarization of the electromagnetic field on the top surface of the barrier.

[0114] For example, the peripheral unit cells have a larger size to compensate for the difference in reflection / transmission coefficients of TE and TM polarized EM waves at lower incident power densities and / or grazing angles. The minimum size of the unit cell may vary from a fraction of the wavelength in the barrier medium to several of the wavelengths at frequency F1. The minimum size of the unit cell may also depend on the type of thermal sensor used. For example, for thermocouples it may be about 100 microns (for ease of integration) and in the case of infrared imaging sensors about one micron (to match their resolution limit). The maximum size may be defined as practically arbitrary. For example, the size may advantageously be defined as 10×10 mm or 20×20 mm, which are the average surface areas defined in the ICNIRP (International Commission on Non-Ionizing Radiation Protection) recommendations for EM dosimetry at millimeter waves.

[0115] In a configuration where the device includes multiple electrothermal sensors or electro-optical sensors, the total number of units may be equal to the number of thermal sensors. In another embodiment 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 of the thermal infrared image sensor.

[0116] Due to this special honeycomb architecture of the barrier, multiple unit cells characterized by anisotropic thermal conductivity can help mitigate the heat conduction phenomenon in the barrier plane, thus resulting in better resolution and lower distortion in measuring the temporal thermal distribution.

[0117] exist Figure 2 In an embodiment of the invention, the barrier is used to convert absorbed electromagnetic power into heat when the EM waves propagate through the layer 3. The device of the invention comprises a thermal sensor to measure the heat distribution along the surface of the barrier to determine the absorbed EM power. The device further comprises a processing unit 6 (PU) configured to calculate the sought dosimetric quantity, such as the user exposure level, by correlating the absorbed EM power, known EM and thermal characteristics of the barrier and known irradiation conditions defined by the relative position of the source 2 and information about the electromagnetic field emitted by the source 2.

[0118] Thermal Sensor

[0119] The thermal sensor 5 is positioned below the bottom surface 32 of the thermal barrier 3, at a distance D2 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 barrier medium due to the absorbed EM power.

[0120] In an embodiment, the device comprises a single thermal sensor 5, which is aligned relative to the barrier along the direction of electromagnetic wave propagation. The thermal sensor is centrally located and faces the bottom surface 32 of the barrier. The thermal sensor 5 may be an image sensor, such as an infrared or visible light image sensor.

[0121] The image sensor is configured to have a field of view covering at least a portion of the bottom surface of the barrier. In other words, the thermal sensor may have a field of view covering at least one unit cell.

[0122] The thermal image sensor is configured to operate in a spectral range that includes at least a portion of the EM spectrum emitted by the barrier's bottom surface 32. For example, this may be a portion of the infrared spectrum emitted by the heating medium or a portion of the visible spectrum emitted or reflected by the heat sensitive medium.

[0123] The thermal sensor 5 is configured to measure the temperature rise distribution on the barrier. This temperature rise distribution is related to the heat induced by the electromagnetic power partially absorbed by the barrier medium during the exposure duration. The barrier can act as both a phantom structure to simulate the EM response and a thermal conversion element that absorbs the EM power and converts it into heat that is re-emitted as infrared radiation measured by the thermal sensor 5.

[0124] 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 barrier. A thermocouple is an electrical device consisting of two different electrical conductors forming an electrical junction that generates a temperature-dependent voltage due to the Seebeck effect.

[0125] In yet another embodiment, the thermal sensor 5 comprises a plurality of thermal sensitive elements, such as liquid crystals or GaAs semiconductor crystals, attached to the bottom surface of the barrier. These thermal sensitive elements are suitable for converting heat into a measurable physical quantity, such as a spectral shift of the emitted or reflected light.

[0126] The thermal sensor 5 may be any other sensor capable of measuring a physical quantity related to the heat induced in the barrier.

[0127] Processing Unit

[0128] like Figure 2 , the signals captured by the thermal sensor 5 are transmitted to the processing unit 6. Knowing the electromagnetic properties of the barrier and the information about the EM field emitted by the source 2, the processing unit 6 is able to calculate the sought dosimetric quantity related to the EM radiation absorbed by the barrier during the predetermined exposure duration. The processing unit 6 is configured to calculate the heat distribution at the bottom surface 32 of the thermal barrier 3 by processing the information about the induced heat at different moments during the exposure, hereinafter referred to as the "temporal heat distribution". It may be further configured to calculate the sought dosimetric quantity (e.g. transmitted or absorbed power density) by applying Maxwell and heat conduction equations in the medium of the barrier using predetermined electromagnetic and thermal properties.

[0129] Memory unit

[0130] The processing unit 6 is in communication with a memory unit 7 and an interface unit 8. The memory unit 7 is configured to store data related to the signals acquired by the thermal sensors, information related to the EM fields emitted by the source, and processed data. The memory unit 7 may store thermal profiles over time from the thermal sensors, information about the thermal and electromagnetic properties of the barrier, illumination conditions for each unit cell of the barrier, and processed data, such as transmitted and / or absorbed power density averaged per surface area and per time unit.

[0131] Interface unit

[0132] The interface unit 8 is configured to receive data and transmit the data to a user. The interface unit may further include a display unit that allows display of a thermal profile over time. The interface unit 8 may transmit the data to another device equipped with a display unit. The interface may typically be a computer console. The user interface may monitor the operations performed by the different elements of the device by activating and / or controlling the different elements of the device, and exchange information with the different elements. It may therefore determine initialization and calculations to define the irradiation conditions, thereby displaying the retrieval results for visualization.

[0133] Figure 7 A method 100 for detecting dosimetry received by an object irradiated by an electromagnetic (EM) source from an emitted EM field is depicted. Using the above described Figure 2 The method 100 is implemented by means of a device, and therefore the following reference is made to Figure 2 The method is described.

[0134] The method comprises a first phase corresponding to a measurement phase comprising the following steps.

[0135] At step 101, an EM field 23 is emitted by a source 2 in the direction of the top surface of the thermal barrier. In this embodiment, the EM field is generated using known resource allocations in the time, frequency and spatial domains from the source 2 specifications.

[0136] At step 102 , the EM field 23 emitted by the source is converted into heat due to absorption of a portion of the EM field in the medium of the barrier 3 .

[0137] At step 103, the thermal sensor 6 acquires information related to the heat induced in the barrier at different times. This step may include the step of 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 barrier. In another embodiment, the bottom surface 32 is covered by a thermosensitive material, and 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 barrier. In yet another embodiment, the thermal sensor 5 includes a plurality of thermocouples attached to or embedded in the bottom surface 32 of the barrier, and the physical quantity may be a voltage measured by a voltmeter. The information related to heat may be stored in the memory unit 7 and / or displayed by the interface unit 8.

[0138] The second phase includes the following steps.

[0139] At step 104, the processing unit calculates the thermal distribution over time at a set of moments by processing the time series of multiple thermal distributions for each measurement point, pixel or unit cell. Depending on the type of thermal sensor used, this step may include the following intermediate steps:

[0140] - time averaging over the time period Δτ;

[0141] - spatially averaging the unit cell surface area of ​​the bottom surface 32;

[0142] - Converting the physical quantity measured by the thermal sensor into a thermal distribution along the bottom surface 32 of the thermal barrier, the thermal distribution being defined in terms of an absolute temperature or a relative temperature rise at a set of moments during the exposure.

[0143] The third phase includes the following steps.

[0144] At step 105, the processing unit reconstructs the illumination conditions for each pixel (or unit cell) based on the information about the EM field emitted by the source 2 and its relative position. Thus, knowing the electromagnetic and thermal properties of the barrier and the parameters of the electromagnetic wave incident on each pixel (unit cell) of the barrier at each moment, the processing unit 6 calculates the dosimetric quantity associated with the EM radiation incident on the barrier, transmitted through the barrier and / or absorbed by the barrier at each measurement point, pixel or unit cell by using the information about the temporal thermal distribution calculated at step 104 and the known information about the EM field incident on the barrier.

[0145] Figure 3represents a non-limiting example of a thermal barrier 3 configured to measure the thermal profile required to retrieve a dosimetric amount of the barrier plane exposed by the EM field emitted by the EM source 2. In one embodiment, the reflection of the EM field emitted by the source from the top surface of the thermal barrier can be tailored to reproduce the electromagnetic response from a reference object (e.g., a human body).

[0146] Figure 3 The barrier (a) comprises a single layer 3 characterized by a particular combination of complex permittivity and thickness, e.g. to produce a desired electromagnetic response from the surface of the layer as desired to reproduce a 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 this single layer is selected to be at least equal to 1 / 4 of the wavelength of the EM wave in the medium of the single layer, said medium being characterized by a predetermined complex permittivity, whose modulus is smaller than the modulus of the medium of the reference object. Alternatively, this single layer may be represented by a thin film having a thickness much smaller than the wavelength of the EM wave in the medium of the single layer, said bulk medium being characterized by a predetermined complex permittivity, whose modulus is larger than the modulus of the medium on the reference object. These selected equivalence criteria may be defined for at least a portion of the spectrum, at least one polarization, and at least a range of angles of incidence of the EM field radiated by the EM source and incident on the top surface of the barrier.

[0147] The single layer 3 comprises 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 a conductive filler, such as particles or a material comprising inclusions of another material characterized by different values ​​of the complex dielectric constant. For a given thickness T of the layer 3 S The material, type of doping and volume ratio of the layer are selected to have a desired complex dielectric constant to reproduce a desired electromagnetic response, such as a complex reflection coefficient or its magnitude, from the top surface 31 of the layer 3. For example, the reference object is human skin tissue, and the complex dielectric constant and thickness T of the dielectric layer 3 can be selected to be s The magnitude of the complex reflection coefficient reproduced from the human skin surface has typical values ​​ranging from 0.75 to 0.4 in the frequency range of 6 GHz to 300 GHz.

[0148] Figure 3 The barrier (b) comprises a first dielectric layer 41 and a second dielectric layer 42. Each layer comprises a plurality of unit cells. Each dielectric layer is characterized by its own thickness, its own complex dielectric constant and its own thermal conductivity. This second layer allows adjustment at the first layer-second layer interface depending on the ratio between the dielectric constant of the medium of the first layer 41 and the dielectric constant of the medium of the second layer 42 to increase or decrease the reflection of the bottom surface of the first layer.

[0149] Figure 3The barrier (c) comprises a first dielectric layer 51 and a second dielectric layer 52. Each layer comprises a plurality of unit cells. Each dielectric layer is characterized by its own thickness, its own complex dielectric constant and its own thermal conductivity. In addition, the unit cells of the second layer 52 are separated by grooves. The grooves are filled with or made of another dielectric material having a thermal conductivity less than that of the material of the second layer 52 to mitigate heat diffusion in the xy plane, resulting in thermal crosstalk between adjacent cells.

[0150] Figure 3 The barrier (d) comprises 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 less than that of the third layer. Each layer comprises a plurality of unit cells. The unit cells of the third layer are separated by grooves 64, which are filled with or made of a dielectric material having a thermal conductivity less than that of the dielectric material of the third dielectric layer 63. The lower thermal conductivity of the second layer 62 allows for mitigation of heat diffusion along the z-axis (between the third and first layers), as well as heat diffusion along the xy plane in the medium of the first layer, which is thermally isolated from the third layer by the second layer.

[0151] Figure 3 The barrier (e) comprises a first dielectric layer 71, a second dielectric layer 72 and a third layer 73. Each layer is characterized by a complex permittivity and a thickness selected in common so as to reproduce the electromagnetic response of a reference object. Each layer comprises a plurality of 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 having a thermal conductivity less than that of the dielectric material of the second dielectric layer 72 to mitigate heat diffusion along the xy plane. The third layer 73 is made of a thermosensitive material.

[0152] Figure 4 is a schematic illustration of another embodiment of an EM dosimetry device 10 combining at least one electromagnetic sensor 11 for obtaining information about the EM field emitted by the source 2 and a thermal sensor 5 for measuring a physical quantity related to the heat induced in the barrier medium.

[0153] Figure 4 The device enables obtaining information related to the EM field emitted by the EM source 2 by real-time monitoring of the EM field at at least one spatial point and a set of time points within the exposure time [τ1, τ2], so as to determine the time / frequency / space resource allocation used by the electromagnetic source 2 at each moment in the test time, and the illumination conditions for each pixel (or unit cell) of the barrier at each moment.

[0154] The information about the EM field emitted by the source 2 may include any part of the information about the allocation of wireless resources used by the source 2 in the frequency domain, the time domain and / or the spatial domain. In one embodiment, it may at least relate to the frequency channel used for transmission, which is basic information for determining the corresponding values ​​of the frequency-dependent EM properties of the barrier, such as the complex permittivity. It may further relate to the amplitude and phase of the incident EM field in the location of at least one EM sensor 11, to allow the determination of the EM source 2 position and orientation required for calculating the wavefront and polarization of the incident field at each point of the barrier surface or each unit cell. In yet another embodiment, it may relate to the waveform in the time domain.

[0155] Information related to the heat induced in the barrier 3 measured by the thermal sensor 5 can then be synchronized with EM information related to the EM field incident on the top surface of the thermal barrier, which is determined based on information obtained by the electromagnetic sensor 11 regarding the time / frequency / space resource allocation used by the electromagnetic source 2 during the test, so as to enable post-processing and retrieval of dose measurements based on the measured thermal distribution of an unknown EM source (i.e., without preliminary knowledge of the resource allocation used by the source 2, or in the case where the source 2 uses a dynamic time-varying resource allocation).

[0156] The step of collecting information about the heat induced in the barrier starts simultaneously with the step of collecting information about the EM field emitted by the source. In other words, the thermal sensor and the EM sensor start measuring at the same time.

[0157] and Figure 2 Similar to the device 1 of , the device 10 comprises a thermal barrier 3 extending visibly 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). Figure 4 The device is shown placed in a test configuration. The electromagnetic source 2 is placed at a distance D1 from the device 10. In addition, the device 10 comprises an electromagnetic sensor 11.

[0158] The proposed device allows characterization of wireless devices with limited or no information about the number of antennas, their position and orientation inside the electromagnetic source, their radiation pattern, their phase center position and operating frequency, and time / frequency / space resource allocation that can be dynamically changed during testing.

[0159] Previously referenced Figure 2 A thermal barrier 3, an EM source 2 and a thermal sensor 5 are depicted.

[0160] The electromagnetic sensor 11 may include at least an RF front end and an RF receiver, and is configured to receive electromagnetic waves emitted by the electromagnetic source 2 to determine parameters of the incident EM field in the location of the EM sensor 11. It may be further configured to convert the information carried by it into a usable form. The EM sensor 11 is configured to detect at least one of the parameters of the incident electromagnetic field: power density, amplitude and phase of the E and / or H field, polarization, frequency and waveform. The EM sensor 11 is configured to detect any additional parameters related to the time and frequency resource allocation of the electromagnetic source 2. In addition, the EM sensor may be capable of detecting parasitic EM fields emitted by other EM sources than the electromagnetic source 2 used for dosimetry testing. Information related to parasitic EM fields can be used to correct data related to heat induced by the EM field received by the barrier.

[0161] like Figure 4 As shown in , the EM sensor 11 is arranged relative 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 for reliable detection of the EM field in line-of-sight mode. This allows obtaining information related to the EM field emitted by the EM source 2, which may include the intensity of the EM field radiated by the EM source 2 or the magnitude and phase of the E and / or H field defined at any set of moments during the test. In addition, this information may include any part of the information related to the wireless resource allocation of the source in the frequency domain, time domain and / or space domain. This information may include, for example, the channel and resource blocks used for transmission, the waveform and time block for the scheduled transmission. This information may be further post-processed by the processing unit 6 to retrieve information about the illumination conditions for each measurement point, the pixel (or unit cell) of the barrier 3 at different moments.

[0162] In one embodiment, the EM sensor 11 may be attached to or embedded in the top surface of the barrier 3 . Figure 4 The configuration shows the EM sensor 11 positioned at a given distance from the EM source and the barrier.

[0163] In another embodiment, the EM sensor is arranged relative to the barrier to capture the EM field reflected from the top surface of the barrier in a multipath mode. In this embodiment, the EM sensor 11 may be positioned at a distance from the barrier 3. Alternatively, it may be attached to the top surface of the barrier 3 or embedded in the top surface.

[0164] In yet another embodiment, the EM sensor is arranged below the bottom surface of the barrier to capture the EM field transmitted through the barrier. In this embodiment, the EM sensor may be placed below the barrier, or alternatively, attached to or embedded in the bottom surface of the barrier 3.

[0165] The device 10 may include more than one EM sensor. The additional EM sensors are configured to detect complementary portions of information related to the EM field emitted by the EM source, such as to cover complementary portions of a frequency range of the operating frequency of the EM source 2, a sub-range of angles of incidence of the incident EM field, one of two polarizations. This embodiment is particularly applicable when the EM source includes more than one antenna. For example, each EM sensor is associated with an antenna to measure the EM field emitted under certain illumination conditions (e.g., angle of incidence, frequency, polarization, modulation). The use of multiple EM sensors covering only a portion of the information allows the architecture of the RF front end to be simplified by reducing the operating bandwidth of the RF front end and / or limiting the measurements to only one polarization.

[0166] In yet another embodiment, the apparatus comprises at least three EM sensors distributed in the 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 transmitting antenna and thus detect switching between different beams generated by the antenna in case the EM source is equipped with a beamforming and / or MIMO antenna system, or detect switching between different antennas in case the EM source is equipped with more than one antenna.

[0167] In yet another embodiment, the EM sensor 11 is integrated in an EM source 2 operable as an EM receiver. For example, the source 2 with two RF front ends uses a first antenna for transmission and a second antenna for detecting the EM field reflected from the barrier. In other words, the EM source is configured to support two operating modes simultaneously, such as transmitting an EM field towards the top surface of the barrier and receiving the EM field reflected from the top surface of the barrier. Information related to the EM field emitted by the source (retrieved from the EM signal received by the second antenna) can be further delivered to the processing unit 6 via a control link 26. In one embodiment, this control link can be a wireless link established by the EM sensor 11. Alternatively, the control link can be established through the application layer, as long as both the processing unit 6 and the source 2 can be configured to support these connections. Depending on the source PHY, MAC and APP layer architecture, the information related to the EM field emitted by the source during the test time can be directly accessed by the processing unit 6 through a common protocol.

[0168] 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 EM source operating frequency range to allow detection of parasitic EM waves.

[0169] like Figure 4 , the output of the thermal sensor is connected to the input of the processing unit 6. The input of the memory unit is connected to the processing unit 6.

[0170] The processing unit 6 is configured to process the EM signals transmitted from the at least one EM sensor to retrieve information related to the EM field emitted by the source 2 to reconstruct the illumination conditions at the top surface 31 of the thermal barrier during the exposure.

[0171] The processing unit 6 is configured to calculate dosimetry using information about the induced heat from the thermal sensor 5 and information about the EM field and information about the thermal barrier 3 by correlating the thermal distribution over time with information about the irradiation conditions for each pixel (or unit cell) of the top surface 31 of the thermal barrier. Information about the EM field predetermined or detected by the EM sensor temporally correlated with the information about the heat detected by the thermal sensor allows to retrieve dosimetry related to the exposure level of the object by the EM source averaged per predetermined duration and / or surface area. The step of temporal correlation between the thermal distribution over time and the information about the EM field acquired by the EM sensor allows for more accurate and reliable post-processing and retrieval of dosimetry from the measured thermal distribution during testing.

[0172] In one embodiment, Figure 4 The apparatus 10 comprises an EM transmitter configured to actively control the operation of the EM source in a manner that imposes a given time / frequency / space resource allocation during testing.

[0173] The EM transmitter is arranged within the radio coverage area relative to the source 2. In another embodiment, the EM transmitter is embedded in or attached to the top surface of the barrier.

[0174] 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 a transceiver capable of operating in half-duplex or full-duplex mode. Figure 4 , the EM sensor 11 is connected to the EM source 2 through a control link 26. Alternatively, for high-end wireless devices, the control link 26 may be organized through an APP layer.

[0175] The use of control link 26 allows processing unit 6 to actively control resource allocation of source 2 via EM sensor 11. This may involve selection of communication parameters of time / frequency blocks and adaptive power levels, as well as beam switching and MIMO schemes.

[0176] In this configuration, the EM transmitter may direct the EM source to adjust information related to the EM field, such as transmitted power, frequency, polarization, waveform of the EM field, thereby resulting in an optimal signal-to-noise ratio of the thermal distribution measured by the thermal sensor 5 .

[0177] In a preferred embodiment, the processing unit 6 is configured to use a transient thermography technique (which is a known technique based on periodic pulse excitation) to retrieve low amplitude temperature distributions masked by ambient thermal noise. In this configuration, the processing unit 6 is configured to determine the optimal parameters of the transient technique (i.e., the waveform and locking frequency of the periodic pulses), which translate into optimal information about the EM field emitted by the source 2. This optimal information is transmitted via the control link 26 to the EM transmitter that controls the EM source.

[0178] In this way, the processing unit 6 can configure the source 2 to generate a modulated input signal having a predetermined locking frequency and waveform. Knowing this information, the processing unit 6 applies a Fourier transformation to the measured thermal distribution over time and transforms the signal into the spectral domain, and then filters the thermal noise from the spectral frequency components located at the predetermined locking frequency.

[0179] The temporal correlation between the exposure conditions retrieved from the EM signal detected by the EM sensor 11 or applied by the processing unit 6 through the control link 26 or through the APP layer and the thermal signal detected by the thermal sensor allows the implementation of a transient thermal imaging technique (also called "lock-in technique") in the post-processing of the measured heat distribution in the barrier. This technique allows reliable detection of the heat induced in the barrier, with a magnitude comparable to or even below the thermal noise level.

[0180] refer to Figure 5 and 6 , as detailed below Figure 2 and Figure 4 operation of the device.

[0181] During the test, the EM source 2 is placed at a distance D1 from the barrier. The EM source 2 has a frequency divided among a plurality of channels having a predetermined bandwidth. The EM source is capable of multiplexing in the frequency, time and space domains by dynamically changing the channel, time and space modulation schemes and / or radiation patterns. The EM source comprises a single antenna configured to emit at least two different radiation beams characterized by angular radiation patterns, gain and main beam direction. The angle of incidence θ of the EM field radiated by the EM source and incident on the top surface of the barrier can be estimated based on the relative position of the transmitting antenna and the distance D1.

[0182] Barrier 3 can be Figure 3 Any of the structures described in . The device comprises thermal sensors placed on opposite sides of the barrier at a certain distance D2 defined with respect to their field of view, said field of view covering at least a portion of the bottom surface of the barrier.

[0183] exist Figure 5In the embodiment, the first beam and the second beam are incident on the top surface 31 of the barrier at tilt angles θ1, θ2, respectively. The thermal sensor 5 is placed in such a way as to cover at least a part of the area illuminated by the EM source.

[0184] When the top surface 31 of the barrier is illuminated by the EM field emitted by the source 2, a portion of the EM wave is reflected from the upper surface 31 of the dielectric layer 3, and a portion of the EM wave is transmitted through the interior of the barrier and is at least partially absorbed along the propagation path inside the barrier. The absorbed portion of the EM wave induces a temperature rise in the barrier, resulting in the generation of a heat distribution at the bottom surface of the barrier.

[0185] Figure 6 shows an exemplary temperature distribution profile or thermal pattern G induced at the bottom surface of the barrier after a short exposure time. Σ (ξ,τ), whose duration is defined by τ measured in time units. The spatial parameter ξ may represent an x ​​or y coordinate in the bottom surface of the barrier. The thermal sensor 5 may be used to detect at any time τ i ∈(0,τ) measures this pattern. In a preferred embodiment, the thermal sensor 5 is an IR image sensor.

[0186] Thick solid curve G Σ represents the measured temperature profile. The two thin dashed curves G1, G2 represent the temperature pattern associated with two overlapping hot spots induced by the absorbed EM field retrieved by decomposing the measured profile. The two thin solid curves F1, F2 represent the estimated temperature profile that would be induced in a barrier with zero thermal conductivity.

[0187] Knowing the relative positions of the transmitting antennas attached to or embedded in the EM source 2, the distances D1 and D2, the physical parameters of the barrier (e.g., the shape of the barrier medium at the operating frequency of the EM source, the thickness T s and effective complex permittivity) as well as thermal properties of the barrier (e.g. thermal conductivity, heat capacity, and IR emissivity). A person skilled in the art, by applying Maxwell and heat equations, can calculate the EM power absorbed locally in the barrier as a function of the thermodynamics measured at the corresponding surface area (e.g. defined by a unit cell area). This embodiment allows estimating the exposure level caused by EM radiation absorbed in the barrier over a predetermined duration of the test assuming that the EM resource allocation remains fixed and unchanged. The retrieved dosimetric quantity (e.g. absorbed power density) can then be calculated for any surface area. The obtained data can be further used to retrieve the exposure level that a user may receive under the same exposure conditions by scaling.

[0188] The scaling factor can be determined by comparing the magnitude of the EM reflectance of the surface and the absorptivity in the barrier medium and the biological tissue (e.g. human skin tissue). The former can be defined analytically, numerically (by full-wave EM simulations), or experimentally. The latter (EM properties of biological tissue at different frequencies) is known from the scientific literature or can be measured using commercially available EM characterization techniques (e.g. coaxial probes).

[0189] In another embodiment, the EM source 2 is capable of multiplexing in the frequency domain, time domain, and space domain by dynamically changing the channel and waveform of the transmitted signal. Figure 4 The device can be used to determine the exposure level of a reference object represented by the barrier.

[0190] The EM sensor measures the incident EM field, such as its incident power, the amplitude and / or the phase of the 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 source by a post-processing procedure. This information may relate, for example, to the frequency channels used by the EM source, time domain multiplexing information and / or the incident power density in a specific position of the EM sensor. These data may then be used to determine, at each moment of the test, at least a portion of the information about the EM field emitter by the EM source. For example, it may be used to determine at which time interval (within the test duration) the barrier was exposed by the first and second beams, at what frequency, and with what incident power (absolute or relative). This information may then be used to estimate the partial contribution of the different EM source operation modes to the overall thermal distribution measured by the thermal sensor. Furthermore, the knowledge about time domain multiplexing may be used to explain the thermal dynamics, taking into account the heat diffusion along the bottom surface of the barrier due to the finite thermal conductivity of the barrier 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], then due to the longer time between excitation and IR measurement, it can be expected that the first beam will cause a stronger distortion of the measured temperature distribution due to heat diffusion.

[0191] Finally, the processing unit 6 is configured to process the data from the thermal sensor and the data from the EM sensor 11, taking into account the temporal correlation between the exposure conditions detected based on the information obtained by the EM sensor and the thermodynamics measured by the thermal sensor. Thus, the information related to the EM field detected by the EM sensor and the information related to the rising temperature distribution detected by the thermal sensor can be correlated to retrieve dosimetric quantities related to the user's exposure level to the EM source.

[0192] See also Figure 8 and 9, the following describes a method 200 for detecting a dose measurement amount received by an object irradiated by an electromagnetic field emitted by an electromagnetic (EM) source. Figure 4 The device implements method 200.

[0193] The method comprises a first phase corresponding to a measurement phase comprising the following steps.

[0194] At step 201 (S1), an EM field 23 is emitted by a source 2 in the direction of the top surface of the thermal barrier. In this embodiment, at least a portion of the information about the allocation of resources used by the source 2 to generate the EM field is unknown.

[0195] At step 202 ( S2 ), the EM field 23 emitted by the source is converted into heat due to absorption of a portion of the EM field in the medium of the barrier 3 .

[0196] At step 203a (S3a), the thermal sensor 6 acquires information related to the heat induced in the barrier at multiple moments. This step may include the step of 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 barrier. In another embodiment, the bottom surface 32 is covered with a thermosensitive material, and 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 barrier. In yet another embodiment, the thermal sensor 5 includes a plurality of thermocouples attached to or embedded in the bottom surface 32 of the barrier, and the physical quantity may be a voltage measured by a voltmeter. The information related to heat may be stored in the memory unit 7 and / or displayed by the interface unit 8.

[0197] At step 203b (S3b), the EM sensor 11 continuously acquires information related to the EM field emitted by the source 2 at the same time as the thermal sensor 5. The information related to the EM field emitted by the source may include any part of the information related to the wireless resource allocation by the source in the frequency domain, time domain and / or space domain.

[0198] like Figure 8 As shown in the figure, the duration of this first phase is determined by the time interval [τ 1,τ3] limit, where τ3 is the switch-off time of the source 2. In one embodiment, this termination time can be defined based on feedback from the processing unit 6 signaling the successful termination of the calculation process. Steps S3a and S3b of measuring information related to the thermal field and the EM field are also performed within the same time interval [τ1, τ3]. The measured raw data (regarding physical quantities related to the induced heat) and the post-processed data (relating to the distribution of the temperature rise over time and the EM field incident on the barrier) are stored in the memory unit 7. A portion of this information, which lasts for a period of time [τ1, τ2], is used to calculate the sought dosimetry quantity by the processing unit 6. The duration of this time interval can be continuously increased depending on the success of the calculation procedure, which requires a sufficient SNR for thermal measurements and sufficient information related to the EM field. Step S3a and step S3b are synchronized in time. Both steps should start at the same time τ1, corresponding to the same moment in the same time interval.

[0199] The second stage corresponds to the post-processing stage and includes the following steps.

[0200] At step 204a (S4a), the processing unit 6 calculates information related to the induced heat to reconstruct the heat distribution at the bottom surface 32 of the thermal barrier 3 at different moments in the time interval [τ1, τ2], referred to as the temporal heat distribution at a set of moments. Depending on the type of thermal sensor used, this step may include the following intermediate steps:

[0201] - time averaging over the time period Δτ;

[0202] - spatial averaging of the unit surface area of ​​the bottom surface 32;

[0203] - Converting the physical quantity measured by the thermal sensor into a thermal distribution along the bottom surface 32 of the thermal barrier, the thermal distribution being defined in terms of an absolute temperature or a relative temperature rise at a set of moments during the exposure.

[0204] At step 204b (S4b), the processing unit 6 calculates information related to the EM field emitted by the source 2 to reconstruct the time instant τ associated with the temporal thermal measurement. i Illumination conditions at the top surface 31 of the barrier 3 at ∈[τ1,τ2].

[0205] Depending on the part of the information available, this step may include the following intermediate steps:

[0206] - calculating the barrier medium EM characteristics at the operating frequency of source 2 defined with respect to the frequency resource allocation;

[0207] - Calculate the propagation path and losses between source 2 and thermal barrier 3:

[0208] - Calculate the reflection / transmission of the top surface of the barrier 3 for a given polarization and angle of incidence defined by the relative position of the source 2;

[0209] - Temporal / spatial averaging of incident power density per unit surface area and per unit time interval.

[0210] Phase 2 can start at any time τ2 (τ1<τ2≤τ3). Fig. 9 In an embodiment of the present invention, the start time is fixed and predetermined.

[0211] The duration of the post-processing of the heat-related information and the EM field-related information may be different and is determined by τ h and τ em Therefore, the breaking time of source 2 is defined as follows: τ3 = τ2 + max(τ h ,τ em )+τ c .

[0212] The third phase includes the following steps.

[0213] At step 205, the processing unit 6 calculates dosimetry using the information about the induced heat, the information about the EM field, and predetermined thermal and electromagnetic properties about the barrier 3 at the frequency of the source 2. The processing unit temporally correlates the temporal thermal distribution calculated in step 204a and the information about the irradiation conditions of the top surface of the barrier calculated in step 204b, and calculates an EM dosimetry associated with the EM radiation incident on and absorbed by the barrier at each measurement point, pixel, or cell unit.

[0214] The calculated data with a time stamp comprising at least the exposure duration defined by the time interval [τ1, τ2] may be stored by the memory unit 7 and / or displayed by the interface unit 8 .

[0215] refer to Figure 8 and 10 , a method 300 for detecting a dose measurement amount received by an object irradiated by an electromagnetic field emitted by an electromagnetic (EM) source according to another embodiment is described below. Figure 4 The device implements method 300.

[0216] The method comprises a first phase corresponding to a measurement phase comprising the following steps.

[0217] At step 301 (S1), an EM field 23 is emitted by source 2 in the direction of the top surface of the thermal barrier. In this embodiment, at least a portion of the information regarding the allocation of resources used by source 2 to generate the EM field is unknown.

[0218] At step 302 ( S2 ), the EM field 23 emitted by the source is converted into heat due to absorption of a portion of the EM field in the medium of the barrier 3 .

[0219] At step 303a (S3a), the thermal sensor 6 acquires information related to the heat induced in the barrier at different times. This step may include the step of 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 barrier. In another embodiment, the bottom surface 32 is covered with a thermosensitive material, and 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 barrier. In yet another embodiment, the thermal sensor 5 includes a plurality of thermocouples attached to or embedded in the bottom surface 32 of the barrier, and the physical quantity may be a voltage measured by a voltmeter. Information related to heat may be stored in the memory unit 7 and / or displayed by the interface unit 8.

[0220] At step 303b (S3b), EM sensor 11 acquires information related to the EM field emitted by source 2. The information related to the EM field emitted by the source may include any portion of information related to wireless resource allocation by the source in frequency, time and / or spatial domains.

[0221] like Figure 8 As shown in , the duration of this first phase is limited by the time interval [τ1, τ3], where τ3 is the switch-off time of the source 2. In one embodiment, this termination time can be defined based on feedback from the processing unit 6, signaling the successful termination of the calculation process. Steps S3a and S3b of measuring information related to the thermal field and the EM field are also performed within the same time interval [τ1, τ3]. The measured raw data (regarding physical quantities related to the induced heat) and the post-processed data (relating to the distribution of the temperature rise over time and the EM field incident on the barrier) are stored in the memory unit 7. A portion of this information, which lasts for a period of time [τ1, τ2], is used to calculate the sought dosimetric quantity by the processing unit 6. 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 and sufficient information related to the EM field. Step S3a and step S3b are synchronized in time. The steps should start at the same time τ1, corresponding to the same moment in the same time interval.

[0222] Advantageously, in this embodiment, the duration of this phase can be adjusted in real time depending on the success of phases 2 and 3. The termination criteria of this phase can be defined with respect to a predetermined value of τ3 or based on successful termination of phase 3.

[0223] The second stage corresponds to the post-processing stage and includes the following steps.

[0224] At step 304a (S4a), the processing unit 6 calculates information about the induced heat to reconstruct the heat distribution at the bottom surface 32 of the thermal barrier 3 at different moments in the time interval [τ1, τ2], referred to as the temporal heat distribution at a set of moments. Depending on the type of thermal sensor used, this step may include the following intermediate steps:

[0225] - time averaging over the time period Δτ;

[0226] - spatial averaging of the unit surface area of ​​the bottom surface 32;

[0227] - Converting the physical quantity measured by the thermal sensor into a thermal distribution along the bottom surface 32 of the thermal barrier, the thermal distribution being defined in terms of an absolute temperature or a relative temperature rise at a set of moments during the exposure.

[0228] At step 304b (S4b), the processing unit 6 calculates information related to the EM field emitted by the source 2 to reconstruct the time instant τ associated with the temporal thermal measurement. i Illumination conditions at the top surface 31 of the barrier 3 at ∈[τ1,τ2].

[0229] Depending on the part of the information available, this step may include the following intermediate steps:

[0230] - calculating the barrier medium EM characteristics at the operating frequency of source 2 defined with respect to the frequency resource allocation;

[0231] - Calculate the propagation path and losses between source 2 and thermal barrier 3:

[0232] - Calculate the reflection / transmission of the top surface of the barrier 3 for a given polarization and angle of incidence defined by the relative position of the source 2;

[0233] - Temporal / spatial averaging of incident power density per unit surface area and per unit time interval.

[0234] In a similar manner, phase 2 can be started at any moment and this start time τ2 can be fixed and predetermined or iteratively increased until the third phase is successfully terminated or until it becomes equal to the total duration of phase 1. The increase in the start time allows increasing the interval of the exposure time considered and therefore achieving a higher temperature rise in the heating zone, which may be necessary to achieve a desired threshold value of the signal-to-noise ratio (SNR) defined with respect to the thermal noise and / or sensitivity of the thermal sensor 5.

[0235] The duration of post-processing of the heat-related information and the EM field-related information may be different and is determined by τ h and τ em definition.

[0236] The success criteria of step 304a can be defined in terms of an SNR level, which is defined relative to an acceptable threshold that can guarantee a reliable interpretation of the measured thermal data. In case of insufficient SNR (SNR<threshold), additional steps for improving SNR can be applied, such as transient thermal imaging, as described below. Fig.10 In FIG. 5 , this optional step is depicted by a box surrounded by a dashed line.

[0237] The transient thermal imaging method for improving the SNR requires periodic excitation with a predetermined waveform. Knowing the excitation conditions (i.e., the frequency and duration of the pulses), Fourier-based filtering techniques can be applied to filter the steady-state thermal noise. This can significantly improve the SNR and enable reliable readout of thermal data masked by thermal noise. However, the implementation of this method requires control over resource allocation, at least involving the operating frequency, waveform and radiation pattern, which should be predefined. This can be accomplished through a control link 26 between the processing unit 6 and the 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, as long as both the processing unit 6 and the source can be configured to support such a connection.

[0238] The third phase (Phase 3) includes the following steps.

[0239] At step 305, the processing unit 6 calculates dosimetry using the information about the induced heat, the information about the EM field, and the electromagnetic and thermal characteristics of the barrier 3 at the frequency of the source 2. The processing unit 6 temporally correlates the temporal thermal distribution calculated in step 304a with the information about the irradiation conditions of the top surface of the barrier calculated in step 304b, and calculates EM dosimetry associated with the EM radiation incident on and absorbed by the barrier at each measurement point, pixel, or unit cell.

[0240] The calculated data with a time stamp including at least the duration of the exposure period defined by the time interval [τ1, τ2] may be stored by the memory unit 7 and / or displayed by the interface unit 8 .

[0241] The success criterion for completing phase 3 can be defined with respect to the convergence of the numerical solution of the time-reversal EM / thermal model used by the processing unit 6 to calculate the thermal conductivity of the thermal system based on the instant τ in the time interval [τ1, τ2]. i∈[τ1,τ2], the temperature rise distribution determined by the processing unit 6 based on the information related to the induced heat measured by the thermal sensor 5 and processed by the processing unit 6, taking into account the barrier exposure conditions determined by the processing unit 6 within the time interval [τ1,τ2] based on the information related to the EM field determined in advance or acquired by the EM sensor 11 and the predetermined barrier EM / thermal properties. In addition to the known factors related to the convergence of the numerical solution of differential equations (such as Maxwell's equations and the heat equation), the convergence of the time reversal EM / thermal model depends largely on the accuracy of the determination of 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 of the temperature rise distribution calculation can be improved by increasing the incident power density of the EM field, by increasing the exposure time defined by the parameter τ2, and / or by using a predetermined waveform of the excitation signal emitted by the EM source 2 to allow intelligent 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 with respect to a predetermined threshold of the relative change in the value of the dosimetric quantity calculated for iteratively increasing exposure times.

[0242] If the convergence criterion is reached, the measurement procedure can be terminated, where the total execution time τ3 = τ2 + max(τ h ,τ em )+τ c , where τ h is the time required to post-process the information relative to the induced heat, and τ em is the time required to post-process the information relative to the EM field emitted by source 2, and τ c is the time required to complete the third stage 3 of solving the EM / thermal time inversion model.

[0243] If the convergence criteria are not met, the following additional steps can be performed:

[0244] - Longer data sets with information about heat and EM fields corresponding to longer exposure times can be processed. This can be done by increasing the value of parameter t2, or by restarting the measurement with another resource allocation to enable intelligent post-processing of the thermal data, thereby improving the SNR and thus the convergence of the algorithm. The new resource allocation may involve the use of a specific radiation pattern (beamforming) and / or specific frequencies and / or waveforms, resulting in a better SNR of the thermal signal through better EM to heat conversion efficiency or more localized exposure.

Claims

1. A device (1) for measuring electromagnetic dosimetry received by an object irradiated by an electromagnetic (EM) field (23) emitted by an electromagnetic source (2), comprising: - a barrier (3) comprising a top surface (31) facing the electromagnetic source (2) and a bottom surface (32) opposite the top surface (31), the barrier (3) being suitable for absorbing at least a part of the EM field emitted by the electromagnetic source (2); - the barrier comprises a plurality of unit cells (33); - at least one thermal sensor (5) arranged relative to said bottom surface of said barrier (3) and configured to measure a physical quantity related to the heat distribution along the surface of said barrier induced by absorption of said electromagnetic field in the barrier medium; - a processing unit (6) coupled to said at least one thermal sensor (5) and configured to calculate said electromagnetic dosimetry quantity based on the measured heat distribution, information about said EM field emitted by said EM source and predetermined EM and thermal properties of said barrier.

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

3. The device according to claim 2, characterized in that The processing unit (6) is configured to temporally correlate the information related to 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) to calculate the electromagnetic dosimetry.

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

5. The device according to any one of claims 2 to 4, characterized in that The at least one electromagnetic sensor (11) is connected to the electromagnetic source (2) via a control link (26).

6. The device according to any one of claims 1 to 5, characterized in that 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 related to the EM field (23) emitted by the EM source (2).

7. The device according to any one of claims 1 to 6, characterized in that The at least one thermal sensor (5) is a thermal sensor positioned at a distance from the bottom surface of the barrier and aligned relative to the barrier center, relative to the center of the unit cell and / or along the direction of EM wave propagation.

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

9. The device according to any one of claims 1 to 6, characterized in that The at least one thermal sensor (5) comprises at least one heat-sensitive element attached to the bottom surface of the barrier.

10. The device according to any one of claims 2 to 9, characterized in that 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 source (2).

11. The device according to any one of claims 2 to 10, characterized in that The at least one electromagnetic sensor (11) is configured to measure the incident EM field (23) from the EM source, the EM field reflected from the top surface of the barrier, or the EM field transmitted through the barrier.

12. The device according to any one of claims 1 to 11, characterized in that The barrier (3) comprises at least one first dielectric layer (3), the at least one first dielectric layer (3) comprising a top surface (31) facing the electromagnetic source (2) and a bottom surface (32) opposite to the top surface (31); - said top surface (31) is at least partially transparent to said electromagnetic field emitted by said source (2); - said bottom surface (32) at least partially reflects said electromagnetic field transmitted through said at least one first dielectric layer (3); - the at least one first dielectric layer (3) is characterized by a complex permittivity and a thickness jointly selected so as to reproduce the electromagnetic response of a reference object, such as biological tissue, human skin tissue.

13. The device according to any one of claims 1 to 11, characterized in that The thermal barrier comprises two dielectric layers (41, 42), the first dielectric layer (41) having a top surface facing the electromagnetic sensor (2) and the second dielectric layer (42) having a bottom surface facing the thermal sensor (5), each layer being characterized by a complex permittivity and a thickness commonly selected so as to reproduce the electromagnetic response of a reference object, each layer comprising a plurality of unit cells.

14. The device according to any one of claims 1 to 11, characterized in that The barrier comprises two dielectric layers (51, 52), the first dielectric layer (51) having a top surface facing the electromagnetic sensor (2) and the second dielectric layer (52) having a bottom surface facing the thermal sensor (5), each layer being characterized by a complex permittivity and a thickness commonly selected so as to reproduce the electromagnetic response of a reference object, each layer comprising a plurality of unit cells separated by grooves (54) filled with or made of a dielectric material having a thermal conductivity less than that of the dielectric material of the second dielectric layer (52).

15. The device according to any one of claims 1 to 11, characterized in that The barrier comprises a first dielectric layer (61), a second dielectric layer (62) and a third layer (63), the second layer (62) being made of 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 jointly selected so as to reproduce the electromagnetic response of a reference object, each layer comprising a plurality of unit cells, the unit cells of the third layer being separated by grooves (64) filled with or made of a dielectric material having a thermal conductivity less than that of the dielectric material of the third dielectric layer (63).

16. The device according to any one of claims 1 to 11, characterized in that The barrier comprises a first dielectric layer (71), a second dielectric layer (72) and a third layer (73), each layer being characterized by a complex dielectric constant and a thickness jointly selected so as to reproduce the electromagnetic response of the reference object, each layer comprising 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 of a dielectric material having a thermal conductivity less than that of the dielectric material of the second dielectric layer (72), and the third layer (73) being made of a thermosensitive material.

17. A method of detecting electromagnetic dosimetry received by an object irradiated by an electromagnetic (EM) field emitted by an electromagnetic source, the method comprising: - irradiating the surface of the thermal barrier (3) with an EM source (2); - converting the EM field incident on the surface of the thermal barrier (3) into heat induced in the medium of the thermal barrier (3); - measuring information related to the induced heat by means of at least one thermal sensor (5); - using said information about said induced heat by a processing unit (6) to determine a set of moments τ in the time interval [τ1, τ2] i The distribution of temperature rise over time; - calculating said electromagnetic dosimetry quantities from said temporal temperature rise distribution, said information about said EM field emitted by said EM source and predetermined EM and thermal properties of said thermal barrier (3).

18. A method of detecting electromagnetic dosimetry received by an object irradiated by an electromagnetic (EM) field emitted by an electromagnetic source, the method comprising: - irradiating the surface of the thermal barrier (3) with an EM source (2); - converting the EM field incident on the surface of the thermal barrier (3) into heat induced in the thermal barrier (3); - measuring information related to the induced heat by means of at least one thermal sensor (5); - measuring information related to said EM field emitted by said EM source (2) by means of an EM sensor (11); - using the information about the induced heat by the processing unit (6) to determine a set of moments τ in the time interval [τ1, τ2] i The distribution of temperature rise over time; - temporally correlating said information about said temperature rise distribution over time and said information about said EM field emitted by said EM source; - calculating said electromagnetic dosimetry using time-dependent information about said temperature rise distribution over time and about said EM field emitted by said EM source and predetermined information about EM and thermal properties of said thermal barrier (3).

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

20. The method according to claim 18 or 19, characterized in that Completion of the measurement procedure is defined with respect to the convergence of the numerical solutions of the time-reversal EM and thermal models used to calculate the EM dosimetry quantities.

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