GB2555855A

GB2555855A - Short-range radio frequency communication device

Info

Publication number: GB2555855A
Application number: GB1619254.4A
Authority: GB
Inventors: Whelan Sean; Forsythe Dan; Mccarthy Niall; Doust Alexander
Original assignee: Sumitomo Chemical Co Ltd
Current assignee: Sumitomo Chemical Co Ltd
Priority date: 2016-11-14
Filing date: 2016-11-14
Publication date: 2018-05-16
Also published as: WO2018087514A1

Abstract

A short-range radio frequency (e.g. RFID or NFC) communication device 5 includes an antenna 7 configured for short-range radio frequency communications. The device also includes one or more electroluminescent elements 8, and has a driving circuit 9 configured to harvest power from a radio frequency signal 4 received by the antenna 7, and convert the harvested power into a driving signal 14 for the electroluminescent elements. The electroluminescent elements (e.g. organic LEDs) are configured to emit light in response to receiving the driving signal. The device could also control the light emission of the electroluminescent element in dependence on external data received via the antenna and/or locally stored data. The device could be a payment card and the display could show transaction amounts or a remaining balance on the card. Such a card could also be read by a holders mobile phone, and may have an additional input device such as a touchpad.

Description

(54) Title of the Invention: Short-range radio frequency communication device

Abstract Title: Device for short-range RF communications having power harvesting and a display (57) A short-range radio frequency (e.g. RFID or NFC) communication device 5 includes an antenna 7 configured for short-range radio frequency communications. The device also includes one or more electroluminescent elements 8, and has a driving circuit 9 configured to harvest power from a radio frequency signal 4 received by the antenna 7, and convert the harvested power into a driving signal 14 for the electroluminescent elements. The electroluminescent elements (e.g. organic LEDs) are configured to emit light in response to receiving the driving signal. The device could also control the light emission of the electroluminescent element in dependence on external data received via the antenna and/or locally stored data. The device could be a payment card and the display could show transaction amounts or a remaining balance on the card. Such a card could also be read by a holder’s mobile phone, and may have an additional input device such as a touchpad.

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- 1 Short-range radio frequency communication device

Field of the invention

The present invention relates to a short-range radio frequency communication device 5 including an electroluminescent element which is powered by harvesting power radio frequency signals.

Background

Short-range radio frequency communication reading devices and corresponding radio frequency identity (RFID) tags may be useful for several applications. One type of short-range radio frequency communication is referred to as near field communication (NFC) and RFID tags for use with NFC communications may be referred to as NFC tags. NFC readers and NFC tags have been deployed in mass transit systems in which users may pay for travel by simply holding a card including a NFC tag near to a reader on a bus, a train, a train platform and so forth. Contactless payment systems also use NFC. NFC tags may be included in paper or cardboard packaging to assist in stock or cargo tracking by an operative using a handheld NFC reading device. Similarly, NFC tags may be included in shipment labels affixed to parcels or other mail items to assist in tracking and tracing mail items in transit.

RFID tags may be active or passive. Active RFID tags are connected to a power source such as a battery, and may transmit signals even in the absence of an RFID reader. Passive RFID tags do not include a battery or similar power source, and operate using power harvested from signals transmitted by an RFID reader using an embedded antenna. Passive RFID tags have the advantage of not requiring a separate power source such as a battery.

In some applications, operation of an RFID system may not be transparent to a user. Displays have been added to items including passive RFID tags to provide increased feedback to a user. For example, US 2010/0052908 At, US 2011/0279242 At and

CN 104167160 A describe passive, stable display elements, for example electrophoretic, electrochromic or cholesteric liquid crystal displays, operated using power harvested from signals transmitted by an RFID reader. US 2010/0052908 Al also describes RFID tags including batteries for powering active devices.

- 2 Summary

According to a first aspect of the invention there is provided a short-range radio frequency communication device including an antenna configured for short-range radio frequency communications. The short-range radio frequency communication device also includes one or more electroluminescent elements. The short-range radio frequency communication device also includes a driving circuit configured to harvest power from a radio frequency signal received by the antenna, and to convert harvested power into a driving signal for the electroluminescent elements. The electroluminescent elements are configured to emit light in response to receiving the 10 driving signal.

Thus, one or more electroluminescent elements may be powered without the need for a battery, supercapacitor, external wired connection or any other power source.

The antenna, the one or more electroluminescent elements and/or the driving circuit may be supported by a substrate. The substrate may be a flexible substrate. The antenna, the one or more electroluminescent elements and/or the driving circuit may be capable of bending with the flexible substrate. Flexible may mean the capacity to be bent to a radius of curvature of 50 mm or less, 40 mm or less, 30 mm or less, 20 mm or less, 10 mm or less, or 5 mm or less, without experiencing permanent deformation or damage.

Thus, the device may be incorporated into and/or applied to a wide variety of objects. The device maybe applied to a curved surface and remain operational.

Short-range radio frequency communications may include near field communications. Near field communication devices and signals include devices and signals complying with the requirements of ISO/IEC 14443 and/or ISO/IEC 18000-3.

The driving circuit may include a rectifier. The driving circuit may include one or more diodes. The driving circuit may comprise one or more capacitors.

The, or each, electroluminescent element may be configured to emit light in response to a driving signal having an amplitude of less than or equal to 3.5 V. The, or each, electroluminescent element may be configured to emit light in response to a driving signal having an amplitude of no more than 5 V.

-3The short-range radio frequency communication device may have a threshold distance within which a short-range radio frequency communication transmitter should be placed in order for the power harvested from radio frequency signals to be sufficient to cause the electroluminescent elements to emit light.

The device may also include a controller. The controller may be supported by the substrate. The controller may be configured to receive radio frequency signals from the antenna. The controller may be configured to control light emission of the, or each, electroluminescent element by connecting the, or each, electroluminescent element to the driving signal.

The device may also include one or more transistors arranged to connect the, or each electroluminescent element to the driving signal in response to receiving a control signal from the controller. The device may include transistors arranged to connect a group of electroluminescent elements to the driving signal in response to receiving a control signal from the controller. Transistors arranged to connect the, or each electroluminescent element to the driving signal may be included in the driving circuit.

The driving circuit may provide the driving signal to the controller. The controller may directly drive the, or each electroluminescent element using the driving signal.

The controller may be configured to receive a radio frequency signal encoding external data from the antenna.

The controller may be configured to transmit a signal encoding external data using the antenna. The controller may be configured to transmit a signal by varying the electrical loading represented by the antenna. The controller may be configured to transmit a signal based on backscattering of radio frequency signals by the antenna.

The controller may be configured to transmit a radio frequency signal using the antenna.

The controller may include a non-volatile storage element configured to store local data. External data may be written to the non-volatile storage element. The local data may be modified and/or overwritten by the external data.

-4The controller may be configured to control the light emission of the, or each, electroluminescent element in dependence upon the external data and/or local data. Each electroluminescent element may be an organic light emitting diode. The, or each, organic light emitting diode may include an electron injection layer comprising an n5 doped polymer, the polymer comprising one or more arylene repeat units. The electron injection layer may include one or more repeat units selected from fluorene, phenylene and anthracene. The electron injection layer may be doped with 2,3-dihydro-iHbenzoimidazoles. The electron injection layer may be doped with i,3-Dimethyl-2phenyl-2,3-dihydro-iH-benzoimidazole (DMBI). The electron injection layer may be doped with 4-(2,3-Dihydro-i,3-dimethyl-iH-benzimidazol-2-yl)-N,Ndimethylbenzenamine (N-DMBI).

The electron injection layer may be in direct contact with an aluminium electrode.

The, or each, organic light emitting diode may include a layer of sodium fluoride. The layer of sodium fluoride may be provided between the electron injection layer and the aluminium electrode.

The device may include one or more input devices. Input devices may be supported on the substrate. The input devices may be capacitive touch pads. The device may be incorporated within, or applied to, a debit or credit payment card. The device may be incorporated within, or applied to, a pre-payment card. The device may be incorporated within, or applied to, a business card. The device may be incorporated within, or applied to, a game card, game piece or game board. The device may be incorporated within, or applied to, a lottery ticket. The device may be incorporated within, or applied to, a scratch game card.

The antenna may be produced by printing on the substrate. The, or each, electroluminescent element may be produced by printing on the substrate. The driving circuit may be produced by printing on the substrate. The controller may be produced by printing on the substrate. Input devices may be produced by printing on the substrate. Transistors maybe produced by printing on the substrate.

According to a second aspect of the invention there is provided a method for a short35 range radio frequency communication device comprising an antenna configured for short-range radio frequency communications, one or more electroluminescent

-5elements, and a driving circuit configured to harvest power from a radio frequency signal received by the antenna, and to convert harvested power into a driving signal for the electroluminescent elements. The method includes, in response to receiving radio frequency signals from a short-range radio frequency transmitter which is sufficiently close to the short-range radio frequency communication device, supplying the driving signal to at least one electroluminescent element to cause the electroluminescent element to emit light.

-6Brief Description of the Drawings

Certain embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings in which:

Figure l is a schematic view of a short-range radio frequency communication system including a reading device and a short-range radio frequency communication device; Figure 2 illustrates a short-range radio frequency communication device incorporated within a pre-payment card;

Figure 3 is a cross-sectional view of packaging for an organic light emitting diode; Figure 4 is a cross-sectional view of an organic light emitting diode;

Figure 5 shows luminance-voltage characteristics for organic light emitting diodes; Figure 6 illustrates an method of interaction between the reading device and shortrange radio frequency communication device shown in Figure 1; and

Figure 7 is a schematic view of a modified short-range radio frequency communication device.

Detailed Description of Certain Embodiments

In the following, like parts are denoted by like reference numbers.

Passive, stable (for example bi-stable) display elements which do not emit light such as, for example, electrophoretic displays or electrochromic displays only require energy in order to switch the state of a display element. This can allow the displayed information to be retained even when no power is available. However, electrophoretic or electrochromic displays can have slow response times. Furthermore, in some applications it maybe undesirable for information to remain on display when a device is not being actively used. For example, a user of a debit or credit payment card may appreciate being able to see their remaining account balance or credit at the time of, or just after, completing a transaction. However, for reasons of privacy a user may not want to have their remaining account balance or credit viewable on their card at all times. Moreover, a passive non-emitting display requires ambient light in order to be viewed.

Electroluminescent displays typically have faster response times than electrophoretic displays or electrochromic displays. Furthermore, because an electroluminescent display does not display information when unpowered, the privacy issues arising from passive non-emitting display types are not a concern. Moreover, an electroluminescent display may be viewed in conditions where there is little or no ambient light.

-ΊThere are several barriers to providing an electroluminescent display which can be powered by a short-range radio frequency signals. For example, electroluminescent displays typically require power densities and voltages which may be difficult to supply from commonly used short-range radio frequency communication systems such as

NFC.

The present disclosure is concerned with a device including one or more electroluminescent elements which can be powered using short-range radio frequency signals. For example, the electroluminescent elements may be organic light emitting diodes (OLEDs) which can be powered using short-range radio frequency signals. Devices described herein may include organic light emitting diodes (Figure 4) which are capable of operating with sufficient current efficiency in a low-voltage drive regime.

Referring to Figure 1, a short-range radio frequency communication system 1 is shown.

The system 1 includes a reading device 2 which includes a short-range radio frequency communication transmitter 3 configured to transmit radio frequency signals 4. The radio frequency signals 4 may encode data, for example by modulating a carrier signal.

The transmitter 3 operates at a low power level and has a short effective range. In other words, the power level of the transmitter 3 is such that a receiver will be unable to reliably detect the radio frequency signals 4 unless the distance separating the transmitter 3 and such a receiver is short. Short range may be in the range of up to 10 cm. The transmitter 3 may be a near field communication (NFC) transmitter, for example conforming to ISO/IEC 14443, and/or ISO/IEC 18000-3 standards. The transmitter 3 periodically transmits polling signals (also sometime as referred to as “interrogation” signals) and monitors for replies from any RFID tags which have moved into the transmitter 3 interrogation range.

The reading device 2 may be housed within a mobile communications terminal (not shown). The reading device 2 may be statically mounted at a location such as, for example, at or near a bus stop, train platform, advertising poster, point of sale display and so forth. The reading device 2 may be mounted to a vehicle such as, for example, a bus, train, tram and so forth.

-8The system l includes a short-range radio frequency communication device 5 which includes a substrate 6. An antenna 7, one or more electroluminescent elements 8, a driving circuit 9 and a controller 10 are supported by the substrate 6.

The substrate 6 is preferable flexible. A flexible substrate 6 is made of a material which maybe bent to a radius of curvature of 100 mm or less without undergoing permanent deformation or damage. Substrates 6 with greater flexibility may be used such as, for example, substrates 6 capable of bending to radii of 50 mm or less, 40 mm or less, 30 mm or less, 20 mm or less, 10 mm or less, or 5 mm or less without experiencing permanent deformation or damage. For example, a flexible material may be capable of withstanding bending to a bend radius of 10 mm for at least one thousand cycles of bending and unbending without experiencing permanent deformation or damage. The substrate 6 need not be a single piece of material, and the substrate 6 may be made up or two or more separate substrates joined, bonded or laminated to one another. A separate substrate 6 need not always be used, and the antenna 7, electroluminescent element(s) 8, driving circuit 9 and optionally controller 10 may be supported directly on, or embedded within, an item incorporating the device 5.

When the substrate 6 is flexible, the minimum bend radius of the device 5 overall may be less than the minimum bend radius of the substrate 6 alone, because the minimum bend radius of the device 5 also depends on the bend radius of the substrate 6 which the antenna 7, electroluminescent element(s) 8, driving circuit 9 and/or controller 10 can sustain without damage. Preferably the device 5 overall is flexible, and may be bent to a radius of curvature of 100 mm or less without undergoing permanent deformation or damage to the antenna 7, electroluminescent element(s) 8, driving circuit 9 and/or controller 10. In some examples, the device 5 may be bent to radii of 50 mm or less, 40 mm or less, 30 mm or less, 20 mm or less, 10 mm or less, or 5 mm or less without radii of 50 mm or less, 40 mm or less, 30 mm or less, 20 mm or less, 10 mm or less, or 5 mm or less without experiencing permanent deformation or damage. For example, a flexible element such as a flexible electroluminescent element 8 in the form of a flexible organic light emitting diode, may be capable of withstanding bending to a bend radius of 10 mm for at least one thousand cycles of bending and unbending, without experiencing permanent deformation or damage.

The antenna 7 is formed by a conductive track 11 disposed on a surface of the substrate

6. The antenna 7 geometry is configured to receive radio frequency signals 4

-9originating at short-ranges. For example, the antenna 7 maybe configured to couple to coils (not shown) of a transmitter 3. The antenna 7 may be configured for NFC, for example to conform to ISO/IEC 14443 and/or ISO/IEC 18000-3 standards. When the antenna 7 receives radio frequency electromagnetic signals 4, corresponding radio frequency electronic signals 12 are induced in the antenna 7 conductive track 11. The antenna 7 is connected to both the driving circuit 9 and the controller 10.

The controller 10 receives and processes electronic radio frequency signals 12 and extracts data encoded in the corresponding electromagnetic radio frequency signals 4.

In some examples the device 5 and controller 10 only receive radio frequency signals 4. However, in other examples the device 5 and controller 10 may use the antenna 7 to send signals encoding data back to the reading device 2. The mechanism by which the device 5 sends signals to the reading device 2 typically depends on the frequency of electromagnetic radio frequency signals 4 which the transmitter 3 is configured to use.

For low to high radio frequency signals 4, the separation between the transmitter 3 and antenna 7 may be considerably less than one wavelength. The antenna 7 of the device 7 maybe inductively coupled to an antenna (not shown) of the transmitter 3. As a result of such coupling, modulating the electrical loading of the transmitter 3 by the antenna 7 can be detected by the transmitter 3. For ultra-high radio frequency signals 4 the separation between transmitter 3 and antenna 7 may correspond to one or more wavelengths. When the transmitter 3 uses ultra-high radio frequency signals 4, the device 5 may send signals encoding data to the reading device 2 using a backscattering mechanism. The controller 10 may simply drive the antenna 7 to emit electromagnetic radio frequency signals 4, however, this may require a prohibitive amount of power for a passive device 5.

In addition to external data received encoded by radio frequency signals 4, the controller 10 may also include non-volatile storage 13 for storing local data. Local data may include, for example, information for uniquely identifying the device 5. Local data may include authentication information in the form of queries and corresponding responses which allow the reading device 2 and the device 5 to authenticate one another. Local data may include information about an object in which the device 5 is incorporated, or to which the device 5 has been attached or applied. The controller 10 may store external data received from the reading device 2 directly into the non-volatile storage 13. The controller 10 may modify and/or overwrite some or all of the local data

- 10 stored in the non-volatile storage 13 based on external data encoded by radio frequency signals 4.

The driving circuit 9 is configured to harvest power from electronic radio frequency 5 signals 12, and to convert harvest power into a driving signal 14 for driving the electroluminescent element(s) 8. The driving signal 14 does not include power from any source other than the harvested power. The driving circuit 9 also provides the driving signal 14 to the controller 10. Preferably, the driving signal 14 is a DC voltage having sufficient amplitude to exceed a voltage threshold V_T of the electroluminescent elements 8. The voltage threshold Vt of an electroluminescent element 8, for example an organic light emitting diode 21 (Figure 3), is the minimum voltage which must be applied across an electroluminescent element 8 to cause emission of photons, i.e. to illuminate the electroluminescent element 8. The driving circuit 9 includes at least a rectifier (not shown), for example one in the form of more diodes. The driving circuit 9 may also include one or more capacitances arranged to reduce oscillations (also referred to as ripples) in the driving signal 14.

In order to harvest sufficient power to cause the electroluminescent element(s) 8, for example an organic light emitting diode(s) 21 (Figure 3), to emit light, the device 5 will need to be within a threshold distance of the transmitter 3. The threshold distance will typically be less than a maximum range of the transmitter 3. The threshold distance maybe 2 cm or less.

In some examples, whether or not the electroluminescent elements 8 emit light can be controlled by the controller 10 using control signals 15. For example, each electroluminescent element 8 may be connected to the driving circuit 9 via a transistor (not shown) which is controlled by a corresponding control signal 15 from the controller 10. The controller 10 maybe configured to control the light emission of each electroluminescent element 8 in dependence on external data encoded by radio frequency signals 4 and/or local data stored in the non-volatile storage 13.

Preferably, an organic thin film transistor (not shown) is used to control illumination of one or more corresponding electroluminescent elements 8. One or more organic thin film transistors (not shown) may be supported by the substrate 6. One or more organic thin film transistors (not shown) may be integrally formed with one or more electroluminescent elements, for example integrally formed with one or more organic

- 11 light emitting diodes 8. Alternatively, one or more transistors or organic thin film transistors (not shown) maybe included in the driving circuit 9.

The device 5 may include any number of electroluminescent elements 8. Preferably, the voltage threshold V_T of the electroluminescent elements 8 is less than or equal to

3.5 V. Preferably the voltage threshold of the electroluminescent elements 8 is no more than 5 V. Electroluminescent elements 8 in the form of flexible organic light emitting diodes 21 (Figure 3) which are operable in this low voltage driving regime are described further hereinafter (see Figures 3 and 4). A low voltage threshold V_T is important because the peak voltage induced in the antenna 7 is typically quite low. For example, the peak voltage induced in an NFC antenna during operation can be of the order of 3 to 5 V. Although the driving circuit 9 can be configured to increase the voltage, some power will be lost in the conversion and the current for driving the electroluminescent element(s) 8 (which is typically expected to be proportional to the illumination intensity) would be decreased even if the power could be kept constant.

In some examples, the device 5 may include a single electroluminescent element 8. Individual electroluminescent elements 8 maybe of any shape, for example, electroluminescent elements 8 may take the shape of letters, numerals or other symbols. Alternatively, the device 5 may include a number of electroluminescent elements 8 in the form of pixels arranged to form an array. The electroluminescent elements 8 may be addressable by the control signals 15 individually, in groups, or in a combination of individual and group addressing.

Preferably, the antenna 7 and the electroluminescent element(s) 8 are printed onto the substrate 6. Alternatively, the electroluminescent element(s) 8 may be printed onto a separate substrate which is then bonded to the substrate 6. The substrate 6 may take the form of one or more thin and flexible polyimide layers. The conductive tracks 11 forming the antenna 7, and other conductive tracks connecting the driving circuit 9, electroluminescent element(s) 8 and controller 10 may also be printed using conductive inks such as, for example, metal based or polymer based conductive inks. Transistors (not shown) for receiving control signals 15 and switching the driving signal 14 to electroluminescent elements 8 on and off maybe provided by organic thin-film transistors printed on the substrate 6. The driving circuit 9 and controller 10 may be provided as discrete components mounted on the substrate 6, may be entirely printed

- 12 onto the substrate 6, or may each include a mixture of mounted discrete components and printed components.

The device 5 does not need to include a controller 10. For example, a device 5 omitting 5 the controller 10 may be placed close to the transmitter 3 of a reading device 2, whereupon the antenna 4 receives radio frequency signals 4 from the transmitter 3, the driving circuit 9 converts the corresponding electronic radio frequency signals 12 into a driving signal 14, and the driving signal 14 is supplied to the electroluminescent element(s) 8 which start emitting light. When the device is moved away from the transmitter 3, the electroluminescent element(s) 8 will stop emitting light once the amplitude of the driving signal 14 drops below the voltage threshold of the electroluminescent element(s) 8.

The driving circuit 9 need not provide the same driving signal 14 to the controller 10.

Instead, the driving circuit 9 may be configured to harvest power from electronic radio frequency signals 12 and to convert some of the harvested power into the driving signal 14 for the electroluminescent element(s) 8, and to convert some of the harvested power into a second, different driving signal (not shown) for the controller 10. For example, the controller 10 and electroluminescent element(s) 8 maybe powered by different DC voltages.

The driving signal 14 has been described as provided directly from the driving circuit 9 to the one or more electroluminescent elements 8. However, in other examples the driving circuit 9 may provide the driving signal 14 only to the controller 10 and the controller 10 may drive the electroluminescent elements 8 directly.

In some examples, the driving circuit 9 and controller 10 may be integrated as a single element such as, for example, a single integrated circuit.

The device 5 may be incorporated within, attached to, or applied to a wide variety of different objects. For example, the device 5 maybe incorporated into a debit or credit payment card. Payment cards increasingly include NFC chips to allow contactless payments. Using the device 5, payment cards may be provided with further functionality such as, for example, an electroluminescent element display 8 to show the user of the payment card their remaining account balance or credit after completing a

-13transaction. The electroluminescent element display 8 may take the form of an organic light emitting diode 21 (Figure 3) display.

The device 5 may be incorporated into a pre-payment card such as a public transport 5 card to pay for buses, trams, trains and the like. The controller 10 of a pre-payment card may store a unique identifier in the non-volatile storage 13. When a user wishes to pay for a ticket, for example a bus ticket, they may place the pre-payment card or or near to a reading device 3 on the bus or at a bus stop. The reading device 2 reads the unique identifier (subject to authentication) and deducts the cost of the ticket from an account corresponding to the pre-payment card. Typically, the balance associated with each pre-payment card will be stored on a server (not shown) for security reasons. However, the reading device 2 could transmit the remaining balance after paying for a ticket to the device 5, which can display the remaining balance to the user using an electroluminescent element display 8. The electroluminescent element display 8 may take the form of an organic light emitting diode 21 (Figure 3) display.

The device 5 may be incorporated within a business card. When a receiver of the business card scans the business card using a NFC reader built into their mobile phone, the controller 10 may send contact information of the business card provider to the mobile phone and may illuminate an electroluminescent element 8 in the shape of a business logo or name. In this way, a business card maybe provided with a memorable “stand-out” effect. The electroluminescent element 8 may take the form of an organic light emitting diode 21 (Figure 3).

The device 5 may be incorporated into a lottery ticket. For example, a user may select numbers at a vendor site and the vendor can use a reading device 2 to store the selected numbers into the non-volatile memory 13 of a device 5 incorporated in the ticket, in addition to printing the numbers on the ticket. After the lottery draw, the ticket holder could check whether they have won a prize by placing the ticket on or next to a reading device 2 a vendor site. The reading device 2 can read the stored numbers, check them against the winning numbers, and send data to the device 5 indicating whether the ticket has won a prize. If the ticket has won a prize then this may be indicated to the ticket holder by illuminating one or more electroluminescent elements 8. The electroluminescent elements 8 may take the form of organic light emitting diodes 21 (Figure 3).

-14The device 5 may be incorporated within playing cards, models and/or boards for playing a game. The device 5 may be incorporated into a label for products and/or produce. The preceding examples are non-exhaustive.

Referring also to Figure 2, an example of a pre-payment card 16 incorporating the device 5 is shown.

The substrate 6 of the device 5 is encapsulated by, or laminated between layers of, a protective polymer exterior layer 17. The exterior layer 17 is shown peeled back in

Figure 2. The exterior layer 17 covers and conceals the antenna 7, driving circuit 9 and controller 10. A region of the exterior layer 17 is transparent and provides a window 18 through which the electroluminescent elements 8 can emit light. The device 5 incorporated into the pre-payment card 16 is an NFC device. The electroluminescent elements 8 take the form of organic light emitting diodes arranged in the form of a seven-segment display 19 for displaying numerals. The exterior layer 17 may be decorated with indicia 20 indicating the purpose of the pre-payment card 16 and other contextual information, graphics, logos and so forth.

The pre-payment card 16 shown in Figure 2 is a pre-payment card 16 for a public transportation network. A user of the pre-payment card 16 can place the pre-payment card 16 proximate to reading devices 2 located on buses, trains, trams, bus stops, train platforms and so forth. The reading device 2 reads the identity of the pre-payment card 16 and the cost of a ticket is deducted from an account associated with the pre-payment card 16. At the same time, the seven segment display 19 is illuminated to indicate to the user of the pre-payment card the amount of their remaining balance. The balance of an account is typically held on a server (not shown) which is in communication with the reading device 2 for security reasons. However, account balance information may also be duplicated in the non-volatile storage of the controller 10. This can allow a user to check their balance even when they are not close to a reading device 2 associated with the public transportation network. For example, a user may use an NFC reader built into their mobile phone to power the pre-payment card 16 so that they may view their remaining balance on the display 19. In this way, the user can avoid unnecessary queuing to check their balance at a counter or card top-up payment machine, or embarrassment from boarding a bus or train, or reaching a barrier, without having sufficient balance to pay for a ticket.

-15The system 1 can be made secure and private. For example, the device 5 and the reading device 5 may perform an authentication when NFC communication is initiated.

If the reading device 2 is authenticated as belonging to the public transportation network, then the controller 10 may permit write access to the non-volatile storage 13 so that the local copy of the balance information may be updated. If the reading device is not authenticated as belonging to the public transportation network, then the controller 10 may restrict access to the non-volatile storage 13 to read-only. The prepayment card 16 may also be paired with a users’ mobile telephone, so that the balance is only displayed in response to an authenticated communication with the users’ mobile telephone. In this way, the users’ balance can be viewed using an NFC reader in a way which preserves the users’ privacy. Similar authentication methods are preferable when the device 5 is incorporated into a debit or credit payment card.

Further details of communications between a device 5 and a reading device 2 are explained hereinafter (Figure 6).

In the example shown in Figure 2, the pre-payment card 16 includes a single window

18. However, an exterior layer 17 may include more than one window 18, for example an exterior layer 17 may include as many windows 18 as there are electroluminescent elements 8. Windows 18 need not be transparent, and may instead be provided as through holes of the exterior layer 17. Electroluminescent elements 8 need not be grouped in one region of the substrate 6, and maybe distributed across front and/or reverse faces of the substrate 6, either individually or in groups.

Organic light-emitting diodes

Organic light emitting diodes 21 (Figure 3) are an example of a suitable electroluminescent element 8.

Referring also to Figure 3, an organic light emitting diode 21 which maybe powered using short-range radio frequency signals 4 is shown.

The organic light emitting diode 21 is deposited onto a transparent substrate 22 in the form of a layer of polyethylene naphthalate (PEN) having a thickness of 125 pm (in the z direction shown in Figure 3). The transparent substrate 22 has first and second surfaces 23, 24 and the organic light emitting diode 21 is deposited onto the first surface 23. A foil 25 is laminated over the first surface 23 of the substrate 22 and the

-ι6exemplary organic light emitting diode 21 using a layer of adhesive 26. The foil 25 is in the form of an aluminium foil having a thickness of 20 pm. The foil 25 is provided for the purpose of sealing the organic light emitting diode 21 against the environment, and the foil 25 is not used as an electrode. The adhesive 25 takes the form of a pressure5 sensitive adhesive having a thickness of approximately 25 pm. An outer layer 27 is laminated over the foil 25. The outer layer 27 is in the form of a layer of polyethylene terephthalate (PET) having a thickness of 25 pm. The outer layer 27 maybe chemically or thermally bonded to the foil 25, or alternatively the foil 25 may be deposited onto or chemically/thermally bonded to the outer layer 27 before the foil 25 is adhered to the substrate 22 and organic light emitting diode 21. The organic light emitting diode 21 emits light through the transparent substrate 22, i.e. from the first surface 23 towards the second surface 24 and away from the foil 25 (in the negative z direction shown in Figure 3). A transparent outer layer 28 is laminated covering the second surface 24 of the substrate 22 using a layer of transparent adhesive 29. The transparent outer layer 8 takes the form of a layer of polyethylene terephthalate (PET) having a thickness of 25 pm, and the layer of transparent adhesive 29 takes the form of a pressure-sensitive adhesive having a thickness of approximately 25 pm. In this example, the outer layer 27 and the transparent outer layer 28 are made of the same material and the adhesive layer 26 and transparent adhesive layer 29 are made of the same material. However, only the transparent outer layer 28 and the transparent adhesive layer 29 need to be transparent. The outer layer 27 and adhesive layer 26 maybe opaque.

Transparency is relative to the emission wavelength of the organic light emitting diode

21. A material may be considered transparent if it transmits 70% or more of light at the emission wavelength of the organic light emitting diode 21. In other examples, a material maybe considered transparent if it transmits 50% or more of light at the emission wavelength.

The transparent substrate 22 is typically not provided by the substrate 6. The arrangement of transparent substrate 22, organic light emitting diode 21, adhesive layers 26, 29, foil 25 and outer layers 27,28 maybe bonded to or otherwise supported by the substrate 6. In other examples, the substrate 6 may provide the transparent substrate 22.

The organic light emitting diode 21 comprises an anode, a cathode and an organic lightemitting layer between the anode and the cathode. One or more further layers maybe

-17provided between the anode and cathode including, without limitation, chargetransporting, charge-blocking and charge-injecting layers.

Referring also to Figure 4, the structure of the organic light emitting diode 21 is shown. 5

The anode is provided by a transparent electrode 30 supported on the first surface 23 of the transparent substrate 22. The transparent electrode 30 provides the anode and takes the form of a layer of indium tin oxide (ITO) having a thickness of around 65 nm.

The cathode is provided by an electron injection layer 31 supported directly on a top electrode 32. The top electrode 32 takes the form of an aluminium electrode having a thickness of around 200 nm. The electron injection layer 31 has a thickness of 10 nm and comprises or consists of an n-doped, non-polymeric or polymeric electrontransporting material. The electron-transporting material is preferably a polymer comprising one or more arylene repeat units, optionally one or more repeat units selected from fluorene, phenylene and anthracene. Suitable n-dopants are 2,3dihydro-iH-benzoimidazoles, optionally i,3-Dimethyl-2-phenyl-2,3-dihydro-iHbenzoimidazole (DMBI) and 4-(2,3-Dihydro-i,3-dimethyl-iPf-benzimidazol-2yl)-X,X-dimethylbenzenamine (N-DMBI). The top electrode 32 takes the form of an aluminium electrode having a thickness of around 200 nm. The electron injection layer 31 and top electrode 32 are arranged with the electron injection layer 31 facing the transparent electrode 30.

Alight emitting layer 33 comprising one or more light-emitting materials is arranged between the transparent electrode 30 (anode) and the electron injection layer 31 (cathode). Light-emitting materials maybe fluorescent materials, phosphorescent materials or a mixture of fluorescent and phosphorescent materials. Preferred lightemitting polymers are conjugated polymers, more preferably polyfluorenes, examples of which are described in Bernius, Μ. T., Inbasekaran, M., O'Brien, J. and Wu, W.,

Progress with Light-Emitting Polymers. Adv. Mater., 12 1737-1750, 2000, the contents of which are incorporated herein by reference. The light-emitting layer 33 may comprise a host material and a fluorescent or phosphorescent light-emitting dopant. Preferred phosphorescent dopants are row two or row three transition metal complexes, preferably complexes of ruthenium, rhodium, palladium, rhenium, osmium, iridium, platinum or gold, most preferably complexes of iridium.

-18The particular material selected for the light emitting layer 33 depends on the desired emission wavelength of the organic light emitting diode 21.

A hole injection layer 34 is supported on the transparent electrode 30, between the transparent electrode 30 (anode) and the light emitting layer 33. The hole injection layer 34 takes the form of a layer of a conducting organic material having a thickness of around 50 nm. Preferred conducting organic materials are polyethylenedioxythiophene (PEDOT) doped with a polyacid, for example polystyrene 10 sulfonic acid (PSS); and polythiophenes, for example Plexcore ® available from

Plextronics, Inc.

A hole transport layer 35 is supported on the hole injection layer 34, between the hole injection layer 34 and the light emitting layer 33. The hole transport layer 35 takes the form of a layer having a thickness of 22 nm and comprising or consisting of a polymeric or non-polymeric hole-transporting material. The hole-transporting material is preferably an aromatic amine or a polymer comprising arylamine repeat units. Exemplary hole-transporting polymers are as described in WO 99/54385, WO 2005/049546 and WO 2013/108022, the contents of which are incorporated herein by reference.

The organic light emitting diode 21 is operable in a low drive voltage regime. For example, the voltage threshold V_T is preferably 3.5 V or less, and no more than 5 V. Combined with relatively high current efficiency, the capability to be driven by relatively low voltages enables the organic light emitting diode 21 to be powered using energy from radio frequency signals 4 received by the antenna 7 of the device 5.

In other embodiments, the cathode may be in direct contact with the light-emitting layer. In these embodiments, the cathode may comprise a first layer of a metal compound having a first surface in direct contact with the light-emitting layer and an opposing second surface in direct contact with a second layer comprising or consisting of a conducting material. Preferably, the metal compound is a metal fluoride, more preferably an alkali or alkali earth fluoride, most preferably FiF, NaF or KF.

Preferably, the second layer consists of a metal, more preferably a metal having a work function of more than 3.5 eV, preferably at least 4.0 eV, most preferably aluminium.

-19A third layer comprising or consisting of a metal having a work function of more than 3.5 eV, preferably at least 4.0 eV may be adjacent to the second layer.

Work functions of elemental metals are as given in the CRC Handbook of Chemistry and Physics, 87^th Edition, 12-114. For any given element, the first listed work function value applies if more than one work function value is listed.

A preferred cathode is NaF / Al.

Referring also to Figure 5, first and second luminance-voltage characteristics 36, 37 for exemplary organic light emitting diodes 21 are shown. The first and second luminance10 voltage characteristics 36,37 are plotted against a base ten logarithmic y-axis.

A first luminance-voltage characteristic 36 corresponds to a flexible organic light emitting diode 21 which emits blue light. The first luminance-voltage characteristic 36 has a voltage threshold V_T of around 2.75 V. A second luminance-voltage characteristic

37 corresponds to a flexible organic light emitting diode 21 which emits white light.

The second luminance-voltage characteristic 37 has a voltage threshold V_T of around 2.25 V. The flexibility of the blue and white organic light emitting diodes 21 corresponding to the first and second luminance-voltage characteristics 36, 37 is sufficient to withstand bending to a 10 mm bend radius for one thousand cycles of bending and unbending.

The minimum voltage threshold Vt for light emission typically does not produce sufficient luminance to be easily observed by the human eye, except in dark ambient conditions. A voltage threshold for observable light emissions, V_Obs, may be determined based on a desired luminance value 38. For example the desired luminance value 38 shown in Figure 5 is 400 Cd. nr² (candelas per square meter of organic light emitting diode 21). To reach the desired luminance value 38, the blue organic light emitting diode 21 may be driven at V_Obs ~ 3 V, and the white organic light emitting diode 21 may be driven at V_Obs ~ 4·9 V. Thus, both the blue and white flexible organic light emitting diodes 21 may be driven using voltages in the range of 3 to 5 V. The precise value of the desired luminance value 38 will vary with the application, and need not be 400 Cd.nr². The power density of both the blue and white flexible organic light emitting diodes 21 is less than 50 mW.cnr² (milliwatts per square cm of organic light emitting diode) when the luminance is 400 Cd.nr².

- 20 Method of using the device

In use, the device 5 is both activated and powered by positioning the device 5 close to the transmitter 3 of a reading device 2. The device 5 may need to be closer to the transmitter 3 than would be required for conventional RFID tag interrogation using antenna load coupling or backscattering, in order to provide a sufficient amplitude of radio frequency signals 4 to power the electroluminescent element(s) 8.

As described hereinbefore, some examples of the device 5 may omit the controller 10.

Electroluminescent elements 8 of a device 5 omitting a controller 10 will start emitting light as soon as the antenna 7 is receiving a sufficient amplitude of radio frequency signals 4 from the transmitter 3 to power the electroluminescent elements 8 .

In other examples, illumination of the electroluminescent elements 8 may depend upon authentication, data exchange and/or intermediate processing steps.

Referring also to Figure 6, a method of controlling illumination of the electroluminescent element(s) 8 is shown.

The transmitter 3 of a reading device 2 periodically transmits polling queries in the form of radio frequency signals 4 to determine whether a device 5 or other RFID tagged object is within the interrogation range of the reading device 2 (step Si).

When the device 5 is within interrogation range, the antenna 7 receives the radio frequency signals 4 corresponding to the polling queries, and the device 5 acknowledges the polling query (step S2). The method by which the device 5 provides an acknowledging signal depends on the frequency used and may be, for example, antenna load coupling, backscattering or a separate transmission of radio frequency signals 4 (if the power available to the device 5 is sufficient). In systems 1 which do not use security and which are intended merely to allow a reading device 2 to identify a device 5, the acknowledgement message may take the form of an identifier which uniquely identifies the device 5.

Once the reading device 2 receives an acknowledgement, if the system 1 uses security feature, one or more rounds of authentication queries and responses may be conducted (step S3). For example, the reading device 2 transmits radio frequency signals 4

- 21 encoding a query. The controller 10 of the device 5 checks the non-volatile storage 13 for a reply matching the query and sends the reply to the reading device 2. If the reply received matches a correct reply, then the device 5 and reading device 2 are authenticated and further data exchange may be carried out. The system 1 may use one or more rounds of queries and responses to perform authentication.

The hereinbefore described example of a debit or credit payment card would utilise authentication to confirm that a payment card was a valid payment card.

Authentication could also be used to confirm that an NFC reader included in a mobile telephone is authorised to display the remaining account balance or credit using an electroluminescent element display 8 of the device 5. If the system 1 is not secured, the authentication step (step S3) may be omitted.

The reading device 2 may transmit radio frequency signals 4 for exchanging data with the device 5 (step S4). Depending upon the system 1, data exchange may be one directional or bi-directional. The reading device 2 may transmit radio frequency signals 4 encoding data. Alternatively, the reading device 2 may simply transmit a radio frequency signal 4 in the form of a carrier wave in order to power the device 5 so that the device 5 can send a reply including data from the non-volatile storage 13. For example, the reading device 2 can transmit radio frequency signals 4 which encode data by modulating a carrier wave, then continue broadcasting the carrier wave to provide power for the device 5 to reply using antenna load coupling, backscattering or by transmitting radio frequency signals 4 (depending on the power available and the frequency of operation). The exchanged data maybe an identifier which uniquely identifies the device 5.

In the hereinbefore described example of a debit or credit payment card, after a vendor reading device 2 has authenticated a transaction, the vendor reading device 2 may send the device an updated balance for displaying to the payment card user.

The controller 10 may perform processing (step S5), for example, to decode the data received from the reading device 2.

The controller 10 causes the driving signal 14 to be supplied to one, some or all of the electroluminescent elements 8 (step S6). The specific electroluminescent elements 8 illuminated in this way may be dependent on data received from the reading device 2

- 22 (step S4), retrieved from the non-volatile storage 13 and/or any intermediate processing (step S5) performed by the controller 10.

Modifications

It will be appreciated that many modifications may be made to the embodiments hereinbefore described. Such modifications may involve equivalent and other features which are already known in the design, manufacture and use of electroluminescent elements and/or short-range radio frequency communication devices, and which may be used instead of or in addition to features already described herein. Features of one embodiment may be replaced or supplemented by features of another embodiment.

Referring also to Figure 7, a modified derice 39 is shown.

The modified device 39 is the same as the device 5 except that the modified device 39 further includes one or more input devices 40 supported by the substrate 6. For example, one or more input devices 40 in the form of capacitive touch pads may be printed onto the substrate 6. Input devices 40 may provide additional functionality to the modified device 39. For example, illumination of the electroluminescent element(s) 8 may be made conditional on a user actuating an input device 40 concurrently with interrogation by the reading device 2. Alternatively, the modified device 39 may be configured such that a user actuating an input device 40 concurrently with interrogation by the reading device 2 suppresses illumination of the electroluminescent element(s) 8. The functions of the input derice(s) 40 need not be linked solely to whether or not to illuminate the electroluminescent element(s) 8. For example, if the modified device 39 is embedded in a payment card, then authorisation of a transaction maybe made conditional upon a user actuating an input device 40. In this way, unauthorised reading of the payment card when stored in a users’ wallet or pocket can be prevented.

Although claims have been formulated in this application to particular combinations of features, it should be understood that the scope of the disclosure of the present invention also includes any novel features or any novel combination of features disclosed herein either explicitly or implicitly or any generalization thereof, whether or not it relates to the same invention as presently claimed in any claim and whether or not it mitigates any or all of the same technical problems as does the present invention. The applicant hereby gives notice that new claims may be formulated to such features

-23and/or combinations of such features during the prosecution of the present application or of any further application derived therefrom.

Claims

1. A short-range radio frequency communication device comprising:

an antenna configured for short-range radio frequency communications;

5 one or more electroluminescent elements; and a driving circuit configured to harvest power from a radio frequency signal received by the antenna, and to convert harvested power into a driving signal for the electroluminescent elements;

wherein the electroluminescent elements are configured to emit light in io response to receiving the driving signal.

2. A device according to claim l, wherein the, or each, electroluminescent element is configured to emit light in response to a driving signal having an amplitude of less than or equal to 3.5 V.

3. A device according to claims 1 or 2, further comprising a controller configured to:

receive radio frequency signals from the antenna; and control light emission of the, or each, electroluminescent element by connecting 20 the, or each, electroluminescent element to the driving signal.

4. A device according to claim 3, wherein the controller is configured to transmit a signal using the antenna.

25

5. A device according to claims 3 or 4, wherein the controller is configured to receive a radio frequency signal encoding external data from the antenna.

6. A device according to any one of claims 3 to 5, wherein the controller comprises a non-volatile storage element configured to store local data.

7. A device according to any one of claims 5 or 6, wherein the controller is configured to control the light emission of the, or each, electroluminescent element in dependence upon the external data and/or local data.

35

8. A device according to any preceding claim, wherein each electroluminescent element comprises an organic light emitting diode.

-259- A device according to claim 8, wherein the, or each, organic light emitting diode comprises an electron injection layer comprising an n-doped polymer, the polymer comprising one or more arylene repeat units.

10. A device according to claim 9, wherein the electron injection layer is in direct contact with an aluminium electrode.

11. A device according to claim any one of claims 8 to 10, wherein the, or each,

10 organic light emitting diode comprises a layer of sodium fluoride.

12. A device according to any preceding claim, further comprising one or more input devices.

15

13. A device according to any preceding claim, wherein the antenna and/or the one or more electroluminescent elements are produced by printing.

14. A method for a short-range radio frequency communication device comprising an antenna configured for short-range radio frequency communications, one or more

20 electroluminescent elements, and a driving circuit configured to harvest power from a radio frequency signal received by the antenna, and to convert harvested power into a driving signal for the electroluminescent elements, the method comprising:

in response to receiving radio frequency signals from a short-range radio frequency transmitter which is sufficiently close to the short-range radio frequency

25 communication device, supplying the driving signal to at least one electroluminescent element to cause the electroluminescent element to emit light.

Intellectual

Property

Office

Application No: GB1619254.4 Examiner: Alan Phipps