An indoor antenna radome with attenuating function, and an indoor radio unit comprising such an antenna radome

Abstract

The present disclosure relates to an indoor antenna radome (102) that is adapted to cover an antenna arrangement (122, 123), where the antenna radome (102) comprises an electrochromic material (150) that is adapted to be connected to a controllable voltage source (111). The electrochromic material (150) is adapted to provide a degree of attenuation to radio frequency, RF, signals (130, 131) when a voltage is applied to the electrochromic material (150), said degree of attenuation exceeding the degree of attenuation provided to RF signals (130, 131) when no voltage is applied to the electrochromic material (150). The present disclosure also relates to an indoor radio unit that comprises a radio arrangement (120, 121) an antenna arrangement (122, 123) and the antenna radome (102).

Description

[0001] TITLE

[0002] An indoor antenna radome with attenuating function, and an indoor radio unit comprising such an antenna radome

[0003] TECHNICAL FIELD

[0004] The present disclosure relates to an indoor antenna radome that is adapted to cover an antenna arrangement. The present disclosure also relates to an indoor radio unit comprising a radio arrangement, an antenna arrangement and the antenna radome.

[0005] BACKGROUND

[0006] Today indoor radio base stations are becoming more and more common, and can often be seen in office buildings, factory buildings and at public places and buildings, for example stadiums, campuses, large office buildings, etc., to deliver high-capacity wireless coverage across the venue. These base stations are normally of a type that emit a relatively low level of radiated Radio Frequency (RF) power and are safe to approach according to different compliance standards e.g. EN 50385 and IEC 62232 stating safe exposure limits.

[0007] It can, however, be desired to minimize radiated RF power affecting a human approaching and / or touching an indoor radio base station. One example of how to achieve this is to attach a snap-on cover or to power off the radio base station. This, however, requires certain measures that may be regarded as cumbersome, and also affects the availability of the wireless services provided by means of the radio base station, and is therefore not desired. There also exist backoff power techniques where the radiated RF power is reduced or turned off, but this is rather challenging as these techniques require additional software algorithms to be added, which adds complexity.

[0008] It is therefore desired to provide means and methods for reducing or minimizing the level of radiated RF power when a human is approaching and / or touching an indoor radio base station.

[0009] SUMMARY

[0010] It is an object of the present disclosure to provide means and methods for reducing or minimizing the level of radiated RF power when a human is approaching and / or touching an indoor radio base station.

[0011] This object is obtained by means of an indoor antenna radome that is adapted to cover an antenna arrangement, where the antenna radome comprises an electrochromic material that is adapted to be connected to a controllable voltage source. The electrochromic material is adapted to provide a degree of attenuation to radio frequency (RF) signals when a voltage is applied to the electrochromic material, said degree of attenuation exceeding the degree of attenuation provided to RF signals when no voltage is applied to the electrochromic material. In this manner, the antenna radome 102 is enabled to provide a lowered degree of transmitted RF power that may affect a human approaching and / or touching, for example, an indoor radio unit that comprises the antenna radome.An electrochromic material can thus work in an antenna radome to control signal propagation in dynamic and selective ways, providing an additional layer of adaptive performance for specific use cases.

[0012] According to some aspects, the antenna radome is constituted by a radome base material and the electrochromic material is applied to the radome base material as a film or gel or is embedded in the radome base material. This means that the electrochromic material can be applied to the radome base material in many different manners.

[0013] This object is also obtained by means of an indoor radio unit comprising a radio arrangement, an antenna arrangement and the antenna radome according to the above. The radio base station further comprises a proximity sensor, a control unit and a controllable voltage source that is connected to the electrochromic material. The control unit is adapted control the voltage source to output a predetermined voltage, corresponding to an electric current that is fed to the electrochromic material via a connecting conductor, when the proximity sensor detects the presence of a person, such that the electrochromic material provides a degree of attenuation to RF signals when a person is within a detection range of the proximity sensor.

[0014] Using the electrochromic material for controlling attenuation of transmitted RF signals and received RF signals passing the antenna radome is a robust and very uncomplicated implementation that provides numerous functional and safety opportunities. Since no advanced software control is needed for controlling the function of the electrochromic shielding function, it is not subject to software faults or malicious attacks, and is therefore uncomplicated to realize.

[0015] According to some aspects, when the voltage source outputs a predetermined voltage, a first electric current is fed to the electrochromic material, the degree of attenuation corresponds to that incoming RF signals mainly are attenuated by the electrochromic material. According to some further aspects, all incoming RF signals are attenuated by the electrochromic material.

[0016] According to some aspects, when the voltage source outputs a predetermined voltage, a second electric current is fed to the electrochromic material, the degree of attenuation corresponds to that incoming RF signals are partially attenuated by the electrochromic material. According to some further aspects, a main part of incoming RF signals are admitted to pass the electrochromic material,

[0017] This means that the electrochromic material can be controlled to any desired degree of attenuation, which of course is advantageous, since the present disclosure thus can be used for different purposes and needs

[0018] According to some aspects, the radio unit comprises a transmitter radio arrangement and a receiver radio arrangement, where the antenna arrangement comprises a set of transmitter antenna devices that are connected to the transmitter radio arrangement, and a set of receiver antenna devices that are connected to the receiver radio arrangement.According to some aspects, the control unit is adapted control the voltage source to stop applying a voltage to the electrochromic material when the presence of a person is not detected. This means that unnecessary attenuation of RF signals is avoided, such that normal function of the radio unit is maximized.

[0019] This object is also obtained by means of methods, control units and computer program products that are associated with the above advantages.

[0020] BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The present disclosure will now be described more in detail with reference to the appended drawings, where:

[0022] Figure 1 shows a schematic perspective view of an indoor radio unit;

[0023] Figure 2 shows a schematic cut-open side view of an indoor radio unit in a first mode of operation;

[0024] Figure 3 shows a schematic cut-open side view of an indoor radio unit in a second mode of operation;

[0025] Figure 4 shows a schematic cut-open side view of an indoor radio unit in a third mode of operation;

[0026] Figure 5 shows a schematic cut-open side view of an indoor radio unit in a fourth mode of operation;

[0027] Figure 6 shows a flowchart for methods according to the present disclosure;

[0028] Figure 7 schematically illustrates a control unit; and

[0029] Figure 8 shows a computer program product.

[0030] DETAILED DESCRIPTION

[0031] Aspects of the present disclosure will now be described more fully hereinafter with reference to the accompanying drawings. The different devices, systems, computer programs and methods disclosed herein can, however, be realized in many different forms and should not be construed as being limited to the aspects set forth herein. Like numbers in the drawings refer to like elements throughout.

[0032] The terminology used herein is for describing aspects of the disclosure only and is not intended to limit the invention. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.

[0033] In the following it is referred to Figure 1 that shows a perspective view of an indoor radio unit 100, Figure 2 that shows a cut-open view of the indoor radio unit 100 in an idle state and Figure 3 that shows a cut-open view of the indoor radiounit 100 in a normal operational state. The indoor radio unit 100 comprises a radio arrangement 120, 121, an antenna arrangement 122, 123 and an indoor antenna radome 102.

[0034] The present disclosure relates to the indoor antenna radome 102 that is adapted to cover an antenna arrangement 122, 123. According to the present disclosure, the antenna radome 102 comprises an electrochromic material 150 that is adapted to be connected to a controllable voltage source 111.The electrochromic material 150 is adapted to provide a degree of attenuation to radio frequency (RF) signals 130, 131 when a voltage is applied to the electrochromic material 150. Said degree of attenuation exceeds the degree of attenuation provided to RF signals 130, 131 when no voltage is applied to the electrochromic material 150.

[0035] Electrochromic materials, particularly polymers and composites, can be engineered to attenuate electromagnetic signals, such as RF signals, by altering their dielectric properties and conductivity under an applied voltage. An electrochromic material can thus work in an antenna radome to control signal propagation in dynamic and selective ways, providing an additional layer of adaptive performance for specific use cases.

[0036] Electrochromic materials are previously known and are described in the literature, for example in US 10033080 B2, and can filter and block light / radiation up to the IR Spectrum, thus engineering a transmission coating / filter to manage midband to highband radio base station operational frequencies, and providing the opportunity for an uncomplicated and robust protection mechanism for RF signals 130, 131.

[0037] When a voltage is applied to the electrochromic material 150, it undergoes a change, for example oxidation / reduction, that causes the electrochromic material 150 to attenuate more RF power by means of absorption and / or reflection. The specific change depends on the electrochromic material 150 itself, the RF frequency and on the amount of voltage applied. This means that the electrochromic material 150 can transition from being RF-transparent to being more or less RF opaque, thus blocking RF signals to a certain degree. In this manner, the antenna radome 102 is enabled to provide a lowered degree of transmitted RF power that may affect a human approaching and / or touching an indoor radio unit that comprises the antenna radome.

[0038] It should be noted that the main function of an antenna radome normally is to protect an antenna arrangement from physical damage, weather conditions and corrosion, and to basically enhance structural integrity. This helps to ensure that the antenna arrangement remains functional and effective over time, especially in outdoor and / or harsh environments. A well-designed antenna radome should have minimal impact on the performance of the antenna arrangement. Specifically, it should not block, reflect, or absorb RF signals significantly. It should ideally be transparent to RF signals in the frequency range the antenna is designed to operate.

[0039] Here, on the other hand, the antenna radome may be electrically transformed to act in a more or less opposite manner, being enabled to attenuate RF signals on demand, but otherwise acting as a traditional antenna radome.According to some aspects, the antenna radome 102 is constituted by a radome base material 105 and the electrochromic material 150 is applied to the radome base material 105 as a film or gel, or is embedded in the radome base material 105.

[0040] This means that the electrochromic material 150 can be applied to the radome base material 105 in many different manners. The electrochromic material 150 may be comprised of an oxide of tungsten, molybdenum, or niobium, or a combination thereof. The electrochromic material 150 may be based on nano-structured electrochromic and nanocomposite organic or inorganic 'smart' materials.

[0041] The present disclosure also relates to the indoor radio unit 100 according to the above, further comprising the antenna radome 102 as described above. The radio base station 100 further comprises a proximity sensor 103, a control unit 110 and a controllable voltage source 152 that is connected to the electrochromic material 150. When the proximity sensor 103 detects the presence of a person 200, the control unit 110 is adapted control the voltage source 152 to output a predetermined voltage corresponding to an electric current h, i2 that is fed to the electrochromic material 130 via a connecting conductor 104. Then the electrochromic material 150 provides a degree of attenuation to RF signals 130, 131 when a person 200 is within a detection range R of the proximity sensor 200.

[0042] Using the electrochromic material 130 for controlling attenuation of transmitted RF signals 130 and received RF signals 131 passing the antenna radome 102 is a robust and very uncomplicated implementation that provides numerous functional and safety opportunities. Since no advanced software control is needed for controlling the function of the electrochromic shielding function, it is not subject to software faults or malicious attacks, and is therefore uncomplicated to realize. The proximity sensor 103 can act as a power switch for outputting the predetermined voltage.

[0043] The detection range R of can be adapted for different mounting positions and other circumstances, the proximity sensor 103 can even be adapted for two or more different detection ranges R. Then different degrees of attenuation to RF signals 130, 131 for different detection ranges R. It should be noted that, according to some aspects, when no person 200 is detected by the proximity sensor 200, the applied voltage is disengaged such that the antenna radome 102 again becomes transparent to the RF signals 130, 131. The RF signals 130, 131 are only attenuated when a person is detected by the proximity sensor 200, or is within a certain detection range R of the proximity sensor 200, not otherwise. There can also be time delays for applying a voltage to the electrochromic material 150 after detection of a person, and / or for disengaging an applied voltage to the electrochromic material 150 when a person 200 is no longer detected and / or is considered to have left.

[0044] Consequently, according to some aspects, the control unit 110 is adapted control the voltage source 152 to stop applying a voltage to the electrochromic material 150 when the presence of a person 200 is not detected. A time delay may be applied as discussed above. This means that unnecessary attenuation of RF signals is avoided, such that normal function of the radio unit 100 is maximized.It should be noted that the indoor radio unit 100 also comprises further electronic active and passive elements and PCBs, within its envelope, but these are considered well-known to the skilled person and are omitted in this description.

[0045] According to some aspects, as illustrated in Figure 4, when the voltage source 152 outputs a predetermined voltage, a first electric current is fed to the electrochromic material 150, the degree of attenuation corresponds to that incoming RF signals 130, 131 mainly are attenuated 132, 133 by the electrochromic material 150. In this context, incoming RF signals are constituted by RF signals that are incoming towards the antenna radome 102 from any direction. In this example, both the transmitted RF signals 130 from inside of the radio base station 100, and the received RF signals 131 that come from an external source and are intended to be received at the radio base station 100, constitute incoming RF signals.

[0046] For example, all incoming RF signals 130, 131 may be attenuated 132, 133 by the electrochromic material 150, as is the case in Figure 4, where all transmitted RF signals 130 are attenuated 132, and all received RF signals 131 are attenuated 133 as well. This means that the received RF signals 131 are in fact not received at the radio base station 100 at all, but are still originally intended to be received at the radio base station 100.

[0047] According to some aspects, as illustrated in Figure 5, when the voltage source 152 outputs a predetermined voltage, a second electric current i2 is fed to the electrochromic material 150, the degree of attenuation corresponds to that incoming RF signals 130, 131 are partially attenuated 134, 137 by the electrochromic material 150. This may be sufficient for the desired effect to be achieved, and does not need to impair the normal operation of the radio base station 100 more than necessary. This is illustrated in Figure 5, where transmitted RF signals 130 are partially attenuated 134, and are partially admitted to pass 135. Furthermore, received RF signals 131 are partially attenuated 136, and are partially admitted to pass 137.

[0048] According to some aspects, a main part of the incoming RF signals 130, 131 are admitted to pass 135, 137 the electrochromic material 150. If this still achieves the desired effect, the normal operation of the radio base station 100 will be affected as little as possible.

[0049] The examples above illustrate that the electrochromic material 150 can be controlled to any desired degree of attenuation, which of course is advantageous, since the present disclosure thus can be used for different purposes and needs. Either the electrochromic material 150 can be controlled one predetermined degree of attenuation, or alternatively the electrochromic material 150 can be controlled to several predetermined degrees of attenuation. The amount of attenuation can for example be regulated from 100 % or lower to about 10 % depending on the current need. The higher the applied voltage is, the less transparent the electrochromic material 150 material is.

[0050] According to some aspects, as depicted in the illustrated examples, the radio unit 100 comprises a transmitter radio arrangement 120 and a receiver radio arrangement 121, where the antenna arrangement comprises a set of transmitter antenna devices 122 that are connected to the transmitter radio arrangement 120, and a set of receiver antennadevices 123 that are connected to the receiver radio arrangement 121. The transmitter radio arrangement 120 may comprise a first number of radio chains, and the receiver radio arrangement 121 may comprise a second number of radio chains, where the first number and the second number may be the same or mutually different.

[0051] According to some aspects, transmitter antenna devices 122 and the receiver antenna devices 123 are in practice constituted by the same antenna devices, acting as duplex antenna devices.

[0052] Alternatively, the radio unit 100 comprises only a transmitter radio arrangement 120 and a set of transmitter antenna devices 122 that are connected to the transmitter radio arrangement 120, no receiver radio arrangement 121 and receiver antenna devices 123.

[0053] The present disclosure sets out to provide competitive solutions for RF exposure compliance avoiding sophisticated software triggering power control structures which may require increased processing power which is detrimental to power consumption and product complexity.

[0054] With reference also to Figure 6, the present disclosure also relates to a method in an indoor radio unit 100. The method comprises transmitting S100 radio frequency, RF, signals 130 via a radome 101 with an electrochromic material 150, detecting S200 the presence of a person 200, and controlling S300 a controllable voltage source 111 to apply a voltage to the electrochromic material 150 such that the electrochromic material 150 provides a degree of attenuation to the transmitted RF signals 130.

[0055] According to some aspects, the method further comprises controlling S310 a controllable voltage source 111 to apply a voltage to the electrochromic material 150 such that a first electric current is fed to the electrochromic material 150, where the degree of attenuation corresponds to that incoming RF signals 130, 131 mainly are attenuated 132, 133 by the electrochromic material 150.

[0056] According to some aspects, all incoming RF signals 130, 131 are attenuated 132, 133 by the electrochromic material 150.

[0057] According to some aspects, the method further comprises controlling S320 a controllable voltage source 111 to apply a voltage to the electrochromic material 150 such that a second electric current i2 is fed to the electrochromic material 150, where the degree of attenuation corresponds to that incoming RF signals 130, 131 are partially attenuated 134, 137 by the electrochromic material 150.

[0058] According to some aspects, incoming RF signals 130, 131 are mainly admitted to pass 135, 137 the electrochromic material 150.According to some aspects, the method further comprises controlling S400 the controllable voltage source 111 to stop applying a voltage to the electrochromic material 150 when the presence of a person 200 is not detected. Here, a time delay may be applied as discussed previously.

[0059] In Figure 7 it is schematically illustrated, in terms of a number of functional units, the components of the control unit 110 according to embodiments of the discussions herein. Processing circuitry 115 is provided using any combination of one or more of a suitable central processing unit CPU, multiprocessor, microcontroller, digital signal processor DSP, etc., capable of executing software instructions stored in a computer program product, e.g. in the form of a storage medium 116. The processing circuitry 115 may further be provided as at least one application specific integrated circuit ASIC, or field programmable gate array FPGA. The processing circuitry thus comprises a plurality of digital logic components.

[0060] Particularly, the processing circuitry 115 is configured to cause the control unit 110 to perform a set of operations, or steps to control the operation of the indoor radio unit 100 including, but not being limited to, controlling the proximity sensor 103 and the controllable voltage source 152. For example, the storage medium 116 may store the set of operations, and the processing circuitry 115 may be configured to retrieve the set of operations from the storage medium 116 to cause the control unit 110 to perform the set of operations. The set of operations may be provided as a set of executable instructions. Thus, the processing circuitry 115 is thereby arranged to execute at least parts of the methods as herein disclosed.

[0061] The storage medium 116 may also comprise persistent storage, which, for example, can be any single one or combination of magnetic memory, optical memory, solid state memory or even remotely mounted memory.

[0062] According to some aspects, the control unit 110 further comprises an interface 117 for communications with at least one external device. As such, the interface 117 may comprise one or more transmitters and receivers, comprising analogue and digital components and a suitable number of ports for wireline communication. The interface 117 can be adapted for communication with other devices, such as other indoor radio units. Examples of such wireless communication devices are Bluetooth®, WiFi® (IEEE802.11b), Global System Mobile (GSM) and LTE (Long Term Evolution), to name a few.

[0063] With continued reference to Figure 7, the present disclosure also relates to a control unit 110, such as the above control unit 110, that is adapted to execute the methods described herein, and which may be comprised in the indoor radio unit 100.

[0064] With reference to Figure 8, the present disclosure also relates to a computer program product 300 comprising computer executable instructions 310 stored on media 320 to execute the methods described herein.As indicated in Figure 2, according to some aspects, the control unit 110 may be adapted to be in contact, suitably by means of wireless communication 241, with external units, for example a communication system 240. This may, e.g., be a third generation partnership program (3GPP) defined access network like the fourth generation (4G) or the fifth generation (5G) access networks or a satellite system such as GPS. The access network may provide access to remote networks and other resources such as, e.g., the Internet. According to some aspects, the remote server can be a part of a cloud service 242 and be adapted to communicate 241 via a communications system 240.

[0065] It is also appreciated that some processing functions may be performed by resources in a remote network 242, such as a remote server 243, where the remote network 242 can be a cloud service.

[0066] The control unit 110 may be constituted by one or more control unit parts that can be separate from each other. Some or all control unit parts may be comprised in a control unit arrangement 110 and / or a remote server 243.

[0067] The present disclosure is not limited to the above, but may vary freely within the scope of the appended claims. For example, the antenna devices 122, 123 may comprise antenna elements that can be arranged in many different way to confer desired radiation properties, for example in a circumferential manner. When antenna elements are placed at the perimeter of the radio unit 100 they may confer an omnidirectional coverage. The antenna elements can be of many types, such as for example dipole antenna elements, slot antenna elements and patch antenna elements, as well as combinations thereof. The antenna elements can for example be formed in PCB technology as well as formed in metal sheets.

[0068] The indoor radio unit 100 may be placed in many different indoor positions, such mounted on a wall or on a ceiling.

[0069] The proximity sensor 200 can be of any suitable kind, for example a passive infrared (IR) sensor, ultrasonic sensor, capacitive sensor, radar-type senor, etc., having one or more detection ranges R.

[0070] The attenuated RF signals 132, 133; 134, 136 are for example attenuated by means of reflection and / or by means of absorption.

[0071] The voltage can be applied to the electrochromic material 150 in many different ways, for example by means of electrodes that are in contact with the electrochromic material 150.

[0072] According to some aspects, the indoor radio unit 100 is applicable for so-called low power radios, which in practice means an RF power that falls below 2W for each RF port at the transmitter radio arrangement 120.

[0073] In the examples, the indoor radio unit 100 is shown to have a circular shape. This is of course only an example, according to some aspects, the indoor radio unit 100 may be square or have any other polygonal gorm. Other types of shapes are also conceivable, such as for example oval and spherical.

Claims

CLAIMS1. An indoor antenna radome (102) that is adapted to cover an antenna arrangement (122, 123), where the antenna radome (102) comprises an electrochromic material (150) that is adapted to be connected to a controllable voltage source (111), where the electrochromic material (150) is adapted to provide a degree of attenuation to radio frequency, RF, signals (130, 131) when a voltage is applied to the electrochromic material (150), said degree of attenuation exceeding the degree of attenuation provided to RF signals (130, 131) when no voltage is applied to the electrochromic material (150).

2. The antenna radome (102) according to claim 1, wherein the antenna radome (102) is constituted by a radome base material (105) and the electrochromic material (150) is applied to the radome base material (105) as a film or gel or is embedded in the radome base material (105).

3. An indoor radio unit (100) comprising a radio arrangement (120, 121), an antenna arrangement (122, 123) and the antenna radome (102) according to any one of the claims 1 or 2, the radio base station (100) further comprising a proximity sensor (103), a control unit (110) and a controllable voltage source (152) that is connected to the electrochromic material (150), where the control unit (110) is adapted control the voltage source (152) to output a predetermined voltage, corresponding to an electric current (h, i2) that is fed to the electrochromic material (130) via a connecting conductor (104), when the proximity sensor (103) detects the presence of a person (200) such that the electrochromic material (150) provides a degree of attenuation to RF signals (130, 131) when a person (200) is within a detection range (R) of the proximity sensor (200).

4. The indoor radio unit (100) according to claim 3, wherein, when the voltage source (152) outputs a predetermined voltage, a first electric current (h) is fed to the electrochromic material (150), the degree of attenuation corresponds to that incoming RF signals (130, 131) mainly are attenuated (132, 133) by the electrochromic material (150).

5. The indoor radio unit (100) according to claim 4, wherein all incoming RF signals (130, 131) are attenuated (132, 133) by the electrochromic material (150).

6. The indoor radio unit (100) according to claim 3, wherein, when the voltage source (152) outputs a predetermined voltage, a second electric current ) is fed to the electrochromic material (150), the degree of attenuation corresponds to that incoming RF signals (130, 131) are partially attenuated (134, 137) by the electrochromic material (150).

7. The indoor radio unit (100) according to claim 6, wherein a main part of incoming RF signals (130, 131) are admitted to pass (135, 137) the electrochromic material (150),8. The indoor radio unit (100) according to any one of the claims 3-7, wherein the radio unit (100) comprises a transmitter radio arrangement (120) and a receiver radio arrangement (121), where the antenna arrangement comprises a set of transmitter antenna devices (122) that are connected to the transmitter radio arrangement (120), and a set of receiver antenna devices (123) that are connected to the receiver radio arrangement (121).

9. The indoor radio unit (100) according to any one of the previous claims, wherein the control unit (110) is adapted control the voltage source (152) to stop applying a voltage to the electrochromic material (150) when the presence of a person (200) is not detected.

10. A method in an indoor radio unit (100), the method comprisingtransmitting (S100) radio frequency, RF, signals (130) via a radome (101) with an electrochromic material (150);detecting (S200) the presence of a person (200);controlling (S300) a controllable voltage source (111) to apply a voltage to the electrochromic material (150) such that the electrochromic material (150) provides a degree of attenuation to the transmitted RF signals (130).

11. The method according to claim 10, further comprising controlling (S310) a controllable voltage source (111) to apply a voltage to the electrochromic material (150) such that a first electric current (h) is fed to the electrochromic material (150), where the degree of attenuation corresponds to that incoming RF signals (130, 131) mainly are attenuated (132, 133) by the electrochromic material (150).

12. The method according to claim 10, wherein all incoming RF signals (130, 131) are attenuated (132, 133) by the electrochromic material (150).

13. The method according to claim 10, further comprising controlling (S320) a controllable voltage source (111) to apply a voltage to the electrochromic material (150) such that a second electric current ) is fed to the electrochromic material (150), where the degree of attenuation corresponds to that incoming RF signals (130, 131) are partially attenuated (134, 137) by the electrochromic material (150).

14. The method according to claim 13, wherein incoming RF signals (130, 131) mainly are admitted to pass (135, 137) the electrochromic material (150).

15. The method according to any one of the claims 9-14, further comprising controlling (S400) the controllable voltage source (111) to stop applying a voltage to the electrochromic material (150) when the presence of a person (200) is not detected.

16. A control unit (110) adapted to execute the methods according to any one of the claims 9-15.

17. A computer program product (300) comprising computer executable instructions (310) stored on media (320) to execute the methods according to any one of the claims 9-15.

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