KR20040046754A - RFID device and method reducing the interference of metals and the material for the same use - Google Patents

Abstract

PURPOSE: A device and a method for an RFID(Radio Frequency Identification) reducing interference of metal, and a material used for the same are provided to reduce the interference of the metal by installing a transmitting material passing a magnetic field generated from an antenna without scattering by absorbing the magnetic field before the reflection from a surface of the metal. CONSTITUTION: Ni-Zn ferrite(300) is interposed between an internal antenna(60) and the metal surface(1000) of an RFID device. If the Ni-Zn ferrite of 125 transmittance is installed by facing to the metal surface on a system using a 13.56 MHz main frequency, the Ni-Zn ferrite uniformly passes the induced magnetic flux(200) by absorbing the induced magnetic flux before the reflection from the metal surface and by absorbing the induced magnetic flux reflected from the metal surface.

Description

RFID device and method reducing the interference of metals and the material for the same use

The present invention relates to an RFID (wireless recognition) device and method, and to a material used for the use thereof, and more particularly, RFID (wireless recognition) including a material capable of eliminating interference due to metal interference in an RFID system. ) Apparatus and method and materials used for the purpose.

In recent years, the RFID (Radio Frequency IDentification) system which automatically recognizes an object and even authenticates and pays for the object has been in the spotlight. RFID, that is, wireless recognition refers to a system that can transmit and receive various data in a wireless manner using a predetermined frequency band. In the case of magnetic and barcodes, a specific external display is required and the recognition rate gradually decreases over time due to damage or damage, whereas an RFID system can overcome such disadvantages. RFID systems are emerging as new solutions, such as those used in various automation projects, distribution, livestock management, access control, time and attendance, logistics, and parking management. Specifically, for example, prepaid / postpaid, including credit / debit cards. It can be used for buses, subway cards, parking lot access cards, department store cards, manufacturing processes on conveyor belts, postal delivery systems, identification tags that record animal information. In an object recognition system, an object containing object recognition information is called a tag, and a device that reads the information recorded on the tag is called an identifier (e.g., a magnetic strip or a barcode display is attached to the tag). Magnetic reader or barcode reader corresponds to reader)

In the past, a magnetic system or a bar code system was mainly used for object recognition. However, magnetic systems (such as card reader systems) read through the data recorded on the magnetic strip of the card as a frictional contact, which causes damage to the magnetic strip of the card and shortens the life of the card. When the card is passed through the card at a speed beyond the reference speed, scanning too late or too fast causes an inconvenience in that a card data reading error occurs, and the magnetic strip has a problem in that its magnetization is weakened over time. In addition, the bar code system also has a problem that the bar code must exist on the surface of the object, thereby preventing the object recognition when the bar code is damaged. This is because the semiconductor laser emitted from the barcode reader can be recognized by being absorbed / reflected by the black / white band of the barcode. In addition, the magnetic or bar code system has a problem that the communication speed is also very slow, it is not suitable when a fast recognition speed is required, such as a bus / subway card.

RFID (radio recognition) system has emerged as a system that can solve the problems of the magnetic or barcode system as described above. The RFID system can be seen as a combination of a tag + identified object with a tag and an external identifier that can recognize the tag from the outside. The RFID system targeted in the present invention is an electronic object identification system using radio frequency, and includes an active RFID in which a power source exists in an identified object and a passive type that receives magnetic energy from the outside as a power source. Passive) There is RFID.

In the present invention, in order to clarify and avoid confusion about the external recognizer and the tag and the recognition object, unless otherwise stated, the RFID device includes only the tag and the recognition object and excludes the external recognizer. The external recognizer has a relatively large antenna (hereinafter referred to as an external antenna) to transmit and receive a radio frequency toward the RFID device, and the RFID device is formed by receiving the radio frequency through a relatively small antenna (hereinafter referred to as an internal antenna). It receives energy and outputs identification data. To this end, the RFID device includes an internal antenna, a coder / decoder, a controller, and a memory.

As an example of a patent for a bus / subway pass card equipped with an RFID device and a payment system using the same, there is a Korean Patent No. 2001-287012 (Publication No. 1997-2743) of a C & C Enterprise (National Credit Card Company) application. 1 is a perspective view of a bus / subway pass card provided with an RFID device as a drawing of the patent application, and FIG. 2 shows a circuit block diagram of the integrated circuit of the RFID. Inside the pass card, ie, between the front portion 20 and the back portion 30 on which the magnetic strip 32 is formed, the antenna coil 60 is wound several times along the outer periphery of the card with a thin line, and the antenna coil 60 An integrated circuit 50 is provided inside the. The integrated circuit 50 is divided into an RF interface unit 51, a control unit 56, and a memory unit 58. The RF interface unit 51 includes a rectifier 52 rectifying a induced voltage induced in the antenna 60. A demodulator 53 for modulating and demodulating data transmitted to and received from the antenna 60, a voltage stabilizer 54 for supplying a stable voltage to each component, and a clock generator 55 for clocking an operation controller. The controller 56 includes an operation controller 57 having a data serial-to-parallel conversion circuit, a RAM, and a ROM therein. The operation controller 57 controls the operation of each component in the integrated circuit according to the stored instruction of the ROM. The memory unit 58 includes an EEPROM 59 that can electrically write and delete data, and dedicate a portion of the memory area of the EEPROM 59 to a prepaid micropayment storage area to provide a prepaid card function to the pass card. It can be given, and can be used as a basis for calculating the transportation fare by storing information (such as ticket gates and ticket gates) about a train station entering a part of the memory area.

As such, the system incorporating the RFID device records information such as credit / debit cards, prepaid / postpaid buses, subway pass cards, parking lot access cards, department store cards, manufacturing processes on conveyor belts, postal delivery systems, and animal information. It can be a very simple, semi-permanent tag-recognizer system such as a tag.

However, in the RFID system using the radio frequency or the induction magnet as described above, there is a problem in that the metal surface does not operate when the metal surface is present between the RFID device and the external antenna. In addition to contactlessness and reflection, the advantage of RFID is that, unlike conventional magnetic or barcode systems, a tag (containing information about an object such as a magnetic, barcode or integrated circuit for wireless recognition) needs to be present on the surface of the recognition object. It is not. However, when there is a metal in the recognition object, there is a problem in that it is difficult to use an RFID device using radio frequency or inductive magnetism using the modulated back scatter technology. This is because the induced current is not properly formed due to the phenomenon that the induced magnetic field that is to be received from the external antenna is reflected and scattered by the metal surface.

In an effort to solve this problem, the present inventors have inserted a foamable material disclosed in WO2202 / 25584 between an RFID device and a metal to generate a volume of the foamed material when induced magnetism is generated. Increasingly, the RFID device is moved away from the metal surface to reduce the interference of the metal. That is, a method of adding a foam layer material between the RFID device and the metal, wherein the foam layer material is activated when various stimuli (shock, sound, light, electromagnetic wave induction, etc.) are applied from the outside world and the density decreases. Will have.

However, according to the above method, not only the volume of the recognition object (pass card, parking lot card, etc.) including the RFID device changes depending on the induced magnetism, but also a considerable time is required for the volume change, which requires rapid processing. In this case, the bus / subway pass card requires a high-speed processing of less than 0.1 second.

Therefore, in view of the above problems, the present inventors consider a method of reducing the influence from interference of the metal through the installation of a transmissive material which can absorb and pass without scattering the magnetic field generated from the antenna before reflecting off the metal surface. It is.

Accordingly, an object of the present invention is to provide an RFID device and method for reducing the influence from interference of nearby metals in an RFID device using radio frequency or induction magnetism.

It is also an object of the present invention to provide a material for use in reducing an influence from interference of nearby metals in an RFID device using radio frequency or induction magnetism.

In addition, it is an object of the present invention to provide an RFID system that reduces the influence from interference of nearby metals while maintaining the speed, reflectivity, and advantages of an RFID device.

1 is a perspective view of a bus / subway pass card installed with an RFID device,

2 is a circuit block diagram of an integrated circuit of the RFID of FIG.

3 is a diagram illustrating a distribution of an induction magnetic field formed around an RFID device interposed between a general external antenna,

4 is a diagram illustrating scattering and interference when a metal surface is present on an outer surface of an article including an RFID device;

Fig. 5 is a diagram showing the distribution of induced magnetic fields when a metal surface is present on the outer surface of an article for an RFID device provided with a transmittance material according to the present invention.

(Explanation of symbols for the main parts of the drawing)

20 ... front

30.Back

50 ... integrated circuit

60 ... internal antenna coil

100 ... RFID device

110 ... external antenna

200 ... magnetic flux

300 ... NiZn Ferrite

1000 ... Metal

According to an aspect of the present invention, there is provided an RFID device for receiving input data by an induced current excited to an internal antenna by a radio frequency supplied from an external antenna, and transmitting output data through the internal antenna. A method and a material as a use thereof.

A first aspect of the present invention is an RFID device for receiving input data by an induced current excited to an internal antenna by a radio frequency supplied from an external antenna and transmitting output data through the internal antenna, wherein the main of the radio frequency is provided. A transmissive material selected according to frequency is installed between the internal antenna and an external metal surface.

An external antenna is an transceiver for transmitting and receiving an identifier, for example, an antenna for transmitting and receiving embedded in a bus / subway ticket gate. When the subway user boards, the ticket gate sends the location and entrance time toward the RFID device, and the RFID device receives the data through the internal antenna, demodulates it, stores it in memory, and stores information on the owner of the RFID device. Modulate and transmit the signal from the internal antenna toward the external antenna. When the subway user gets off, the ticket gate sends a signal requesting information to the RFID device, and the RFID device owns the boarding information (such as the boarding place and entry time) previously stored in the memory according to the signal and the owner of the RFID device. Transmit information about the internal antenna from the internal antenna to the external antenna. Through this process, payment of the fare of the subway can be made.

However, when metal is present in the vicinity of the RFID device, the radio frequency from the external antenna reflects on the metal surface and causes interference. For example, there is a case in which a business card made of metal is contained in the wallet and thus the radio frequency reception of the pass card is interrupted, or a metal part is added to the recognition object including the RFID device.

In the present invention, the reflection of magnetic flux from the metal surface is reduced by providing a transmittance material between the internal antenna and the external metal surface. Such transmittance material should have an appropriate transmittance according to the main frequency. For example, a material with a transmittance of 125 (± 20)%, 2560 or 860 (± 20)% for a main frequency of 13.56 MHz is effective. By installing a material with an appropriate transmittance, the induced magnetic flux is absorbed and passed before it is reflected on the metal surface, and the magnetic flux reflected from the metal surface is absorbed and transmitted without scattering so that disturbance of the magnetic flux with respect to the internal antenna is allowed. This can be reduced.

In this case, uniform control is not possible because the magnitude and the magnetic flux direction of the reflection action of the magnetic flux from the metal surface also vary irregularly in accordance with the frequency of the induced magnetic field received from the external antenna. Therefore, there is a need to separately deal with the reflection from the metal surface according to the frequency used. The frequencies used in passive RFID devices that receive an induced magnetic field from a ticket gate and use it as an energy source, such as a bus / subway pass card, do not include an independent power source. 13.56 MHz, 123 kHz, 125 kHz, 134 kHz, and so on.

Of these, especially for the commonly used main frequency of 13.56 MHz, it is best to use NiZn ferrite (transmittance 125 (± 20)%) as the transmittance material to be installed between the internal antenna and the metal surface. It was. At this time, examples of the product using a material having a transmittance of 125 (+/- 20)% practically include, for example, ferrite 4C65 from Philips Co., Ltd. or ferrite Q5B from TDK Co., Ltd.

In addition, in the use of a material having a transmittance that differs depending on the main frequency used, according to experiments, a material having a transmittance of 125 (± 20)% is suitable for the main frequency of 13.56 MHz as described above. In addition, a material having a transmittance of 2560 (± 20)% or 860 (± 20)% may be used to show good results. In addition, for main frequencies such as 123 kHz, 125 kHz, and 134 kHz, good results are obtained when a material having a transmittance of 860 (± 20)% or 2000 (± 20)% is used.

The second aspect of the present invention is an RFID device for receiving input data from an induced current excited to an internal antenna by a radio frequency supplied from an external antenna and transmitting output data through the internal antenna. The surface comprises a metal, and the transmissive material selected according to the main frequency of the radio frequency is mixed with the metal, the RFID device against interference of metal.

In the present invention, the magnetic flux reflection from the metal surface is reduced by mixing the transmittance material on the metal surface. Such transmittance material should have an appropriate transmittance according to the main frequency. In this case, uniform control is not possible because the magnitude and the magnetic flux direction of the reflection action of the magnetic flux from the metal surface also vary irregularly in accordance with the frequency of the induced magnetic field received from the external antenna. Therefore, there is a need to separately deal with the reflection from the metal surface according to the frequency used. For the main frequency of 13.56 MHz, which is particularly commonly used in passive RFID devices, it is recommended to use NiZn ferrite (transmittance 125 (± 20)%) as the transmittance material to be installed between the internal antenna and the metal surface. The best results were shown. At this time, examples of the product using a material having a transmittance of 125 (± 20)%, which are practically available, include, for example, Ferrite 4C65 manufactured by Philips Co., Ltd. or Ferrite Q5B manufactured by TDK Co., Ltd.

In addition, in the use of a material having a transmittance that differs depending on the main frequency used, according to experiments, a material having a transmittance of 125 (± 20)% is suitable for the main frequency of 13.56 MHz as described above. In addition, a material having a transmittance of 2560 (± 20)% or 860 (± 20)% may be used to show good results. In addition, for main frequencies such as 123 kHz, 125 kHz, and 134 kHz, good results are obtained when a material having a transmittance of 860 (± 20)% or 2000 (± 20)% is used.

Therefore, a material having a suitable transmittance depending on the main frequency used can be used to reduce the adverse effect of reflection from the metal surface.

Other features of the present invention are the same as those of the first aspect, and thus duplicated description thereof will be omitted.

The third aspect of the present invention provides a method for the induction magnetic field in an RFID system that receives input data from an induced current excited to an internal antenna by a radio frequency supplied from an external antenna and transmits output data through the internal antenna. As a method of overcoming interference,

A method of overcoming metal interference with an induced magnetic field in an RFID system, wherein a transmissive material selected according to the main frequency of the radio frequency is provided between the internal antenna and an external metal surface. Since the features of the present invention are the same as those of the first aspect of the present invention, redundant descriptions thereof will be omitted.

In addition, the fourth aspect of the present invention, in the RFID system for receiving the input data from the induced current excited to the internal antenna by the radio frequency supplied from the external antenna, and transmits the output data through the internal antenna, the induction magnetic field In the method of overcoming the interference of metals for

A method of overcoming metal interference with an induction magnetic field in an RFID system, characterized in that a transmittance material having a transmittance selected according to the main frequency of the radio frequency is mixed with the metal. Since the features of the present invention are the same as those of the second aspect of the present invention, redundant descriptions thereof will be omitted.

The fifth aspect of the present invention provides a method for the induction of a magnetic field in an RFID system that receives input data from an induced current excited to an internal antenna by a radio frequency supplied from an external antenna and transmits output data through the internal antenna. A transmissive material provided for overcoming interference, the material selected according to the main frequency of the radio frequency; It is a transmittance material, characterized in that provided between the internal antenna and the external metal surface.

In addition, a sixth aspect of the present invention is directed to the induction magnetic field in an RFID system that receives input data from an induced current excited to an internal antenna by a radio frequency supplied from an external antenna and transmits output data through the internal antenna. A transmissive material installed to overcome metal interference, the material selected according to the main frequency of the radio frequency; It is a transmittance material characterized in that it is mixed with an external metal.

Products using such materials include ferrite 4C65 from Philips, Inc. or ferrite Q5B from TDK, Inc., as mentioned above. In addition, the material may be applied by varying the transmittance according to the main frequency.

Hereinafter, with reference to the drawings will be described an embodiment of the present invention.

3 illustrates an RFID device interposed between a general external antenna and an induction magnetic field formed around the RFID device. For example, in the case of an antitheft device, if an induced magnetic field formed at a predetermined frequency in an external antenna spans an RFID device (or an antenna therein), the RFID device responds at a predetermined response frequency, and the response frequency is zero. In case of one frequency, the signal is passed, but in case of the second frequency, the burglar alarm is activated to indicate that the article containing the RFID device or the tag is stolen. However, as described above, in the presence of metal, the magnetic flux is irregularly reflected from the surface thereof, so that the RFID device or the tag cannot recognize the induced magnetic field from the external antenna properly. In addition, even when the response is made, it is difficult to properly recognize whether the external antenna is the first frequency or the second frequency due to the reflection of the metal surface.

4 illustrates scattering and interference when the metal surface 1000 is present on an outer surface of an article (a recognized object) including the RFID device 100. Since the induced magnetic flux 200 of the predetermined frequency flowing from the external antenna 110 is scattered irregularly on the metal surface 1000, an interference phenomenon occurs toward the internal antenna 60 of the RFID, thereby causing inoperation. The RFID device 100 may receive an input signal by demodulating a predetermined amount of magnetic flux and a current induced by a change in the magnetic flux. As illustrated, the magnetic flux 200 may be irregularly reflected from the metal surface 1000. Therefore, a predetermined amount of magnetic flux and a change in the magnetic flux cannot be detected, causing an inoperability.

FIG. 5 illustrates the internal antenna 60 and the metal surface 1000 of the RFID device 100 for the case where the metal surface 1000 exists on the outer surface of the article (recognition object) including the RFID device 100 of FIG. 4. ), And NiZn ferrite 300 is interposed. As shown, in a system using a main frequency of 13.56 MHz, when NiZn ferrite 300 having a transmittance of 125 (± 20)% is installed against the metal surface 1000, the NiZn ferrite 300 is induced magnetic flux (200). ) Is absorbed and passed evenly before being reflected at the metal surface 1000, and absorbs and induces the flux flux reflected at the metal surface and passes evenly.

However, since the magnitude and the magnetic flux direction of the reflection of the magnetic flux from the metal surface vary irregularly according to the frequency of the induced magnetic field received from the external antenna 110, uniform control is impossible. Therefore, there is a need to separately deal with the reflection from the metal surface 1000 according to the frequency used. The frequencies used in passive RFID devices are 13.56 MHz, 123 kHz, 125 kHz, 134 kHz, etc., as set forth by the International Organization for Standardization (ISO), among which the most commonly used main frequencies of 13.56 MHz The use of NiZn ferrite (transmittance 125 (± 20)%) as the transmittance material to be installed between the internal antenna and the metal surface showed the best results.

In addition, in the use of a material having a transmittance that differs depending on the main frequency used, according to experiments, a material having a transmittance of 125 (± 20)% is suitable for the main frequency of 13.56 MHz as described above. In addition, a material with a transmittance of 2560 (± 20)% or 860 (± 20)% was used, which showed good results. In addition, for main frequencies such as 123 kHz, 125 kHz, and 134 kHz, good results were obtained when materials having transmittances of 860 (± 20)% or 2000 (± 20)% were used.

While various aspects of the present invention have been shown with the embodiments, the above embodiments are shown as an example thereof, and an increase of a part of the components corresponding to the technical spirit of the present invention defined by the appended claims, Changes and modifications may not be exceeded within the scope of the present invention.

By using the RFID (radio recognition) device and method according to the present invention and the material used for the purpose, the RFID device, method and method for reducing the influence from interference of nearby metals while maintaining the speed and reflectivity, which are advantages of the RFID system, and A material for that use can be provided.

Claims (24)

An RFID device for receiving input data by an induced current excited to an internal antenna by a radio frequency supplied from an external antenna, and transmitting output data through the internal antenna, A transmissive material selected according to the main frequency of the radio frequency is provided between the internal antenna and the external metal surface. The method of claim 1, When the main frequency of the radio frequency is 13.56 MHz, The transmittance material selected according to the main frequency is at least one selected from the group consisting of transmittance materials of approximately 125 (± 20)%, 2560 (± 20)%, and 860 (± 20)%. RFID device in preparation. The method according to claim 1 or 2, And the transmittance material is NiZn ferrite. The method of claim 1, When the main frequency of the radio frequency is any one of 123 KHz, 125 KHz and 134 KHz, the transmittance material selected according to the main frequency is at least in the group consisting of transmittance material of approximately 860 (± 20)% or 2000 (± 20)% RFID device for the interference of the metal, characterized in that one selected. An RFID device that receives input data from an induced current excited to an internal antenna by a radio frequency supplied from an external antenna, and transmits output data through the internal antenna. The outer surface of the RFID device comprises a metal, The transmittance material selected according to the main frequency of the radio frequency is mixed with the metal. The method of claim 5, When the main frequency of the radio frequency is 13.56 MHz, The transmittance material selected according to the main frequency is at least one selected from the group consisting of transmittance materials of approximately 125 (± 20)%, 2560 (± 20)%, and 860 (± 20)%. RFID device in preparation. The method according to claim 5 or 6, And the transmittance material is NiZn ferrite. The method of claim 5, When the main frequency of the radio frequency is any one of 123 KHz, 125 KHz and 134 KHz, the transmittance material selected according to the main frequency is at least in the group consisting of transmittance material of approximately 860 (± 20)% or 2000 (± 20)% RFID device for the interference of the metal, characterized in that one selected. In an RFID system that receives input data from an induced current excited to an internal antenna by a radio frequency supplied from an external antenna and transmits output data through the internal antenna, a method of overcoming metal interference with the induction magnetic field. , And transmissive material having a transmittance selected according to the main frequency of the radio frequency between the internal antenna and an external metal surface. The method of claim 9, When the main frequency of the radio frequency is 13.56 MHz, The transmittance material selected according to the main frequency is at least one selected from the group consisting of transmittance materials of approximately 125 (± 20)%, 2560 (± 20)%, and 860 (± 20)%. To overcome the interference of metals on induction fields. The method of claim 9 or 10, And said transmittance material is NiZn ferrite. The method of claim 9, When the main frequency of the radio frequency is any one of 123 KHz, 125 KHz and 134 KHz, the transmittance material selected according to the main frequency is at least in the group consisting of transmittance material of approximately 860 (± 20)% or 2000 (± 20)% A method of overcoming interference of metals against inductive fields in an RFID system, characterized in that one is selected. In an RFID system that receives input data from an induced current excited to an internal antenna by a radio frequency supplied from an external antenna and transmits output data through the internal antenna, a method of overcoming metal interference with the induction magnetic field. , The method of overcoming metal interference with an induction field in an RFID system, characterized in that the material is mixed with a transmission material having a transmission selected according to the main frequency of the radio frequency. The method of claim 13, When the main frequency of the radio frequency is 13.56 MHz, The transmittance material selected according to the main frequency is at least one selected from the group consisting of transmittance materials of approximately 125 (± 20)%, 2560 (± 20)%, and 860 (± 20)%. To overcome the interference of metals on induction fields. The method according to claim 13 or 14, And said transmittance material is NiZn ferrite. The method of claim 13, When the main frequency of the radio frequency is any one of 123 KHz, 125 KHz and 134 KHz, the transmittance material selected according to the main frequency is at least in the group consisting of transmittance material of approximately 860 (± 20)% or 2000 (± 20)% A method of overcoming interference of metals against inductive fields in an RFID system, characterized in that one is selected. In an RFID system that receives input data from an induced current excited to an internal antenna by a radio frequency supplied from an external antenna and transmits output data through the internal antenna, to overcome metal interference with the induced magnetic field. As the transmittance material to be installed, Selected according to the main frequency of the radio frequency, Transmittance material between the internal antenna and an external metal surface. The method of claim 17, When the main frequency of the radio frequency is 13.56 MHz, The transmittance material selected according to the main frequency is at least one selected from the group consisting of transmittance materials of approximately 125 (± 20)%, 2560 (± 20)%, and 860 (± 20)%. The method of claim 17 or 18, The transmittance material is NiZn ferrite. The method of claim 17, When the main frequency of the radio frequency is any one of 123 KHz, 125 KHz and 134 KHz, the transmittance material selected according to the main frequency is at least in the group consisting of transmittance material of approximately 860 (± 20)% or 2000 (± 20)% A transmittance material, characterized in that one is selected. In an RFID system that receives input data from an induced current excited to an internal antenna by a radio frequency supplied from an external antenna and transmits output data through the internal antenna, to overcome metal interference with the induced magnetic field. As the transmittance material to be installed, Selected according to the main frequency of the radio frequency, A transmittance material characterized in that it is mixed with an external metal. The method of claim 21, When the main frequency of the radio frequency is 13.56 MHz, The transmittance material selected according to the main frequency is at least one selected from the group consisting of transmittance materials of approximately 125 (± 20)%, 2560 (± 20)%, and 860 (± 20)%. The method of claim 21 or 22, The transmittance material is NiZn ferrite. The method of claim 21, When the main frequency of the radio frequency is any one of 123 KHz, 125 KHz and 134 KHz, the transmittance material selected according to the main frequency is at least in the group consisting of transmittance material of approximately 860 (± 20)% or 2000 (± 20)% A transmittance material, characterized in that one is selected.