GB2321551A - Reading smartcards - Google Patents

Abstract

An active VHF transmitter/receiver unit and a card interact at radiation frequencies above 100 MHz across a fairly small distance. In order to avoid a change of transfer efficiency due to subtle alterations in antenna attitudes relative to each other, or in the spacing from each other, or in other modifications of the environment affecting the radiation resistance of the antennae the primary frequency of the oscillator source fluctuates, and is self-adapting to said random conditions.

Description

Power Transfer between at variable distance coupled VHF antennas, and oscillator drive circuit for same.

In most countries of the world there are watchdog institutions to ensure that neither industry nor private citizens use electrical equipment which, either singly or in aggregation,produce electronic space pollution in excess of prescribed limits and criteria. In the scientific world many are anxious to introduce as little man-made radiation noise as possible.

On the other hand, there are newly developing techniques about to be introduced - such as the use of miniature computers contained in credit-and money cards interfacing with terminals via RF-coupled circuits. If millions of these device are in daily use, background noise is bound to increase.

My three patent applications as hereunder cited GB 9605050.4 of March 22,1996 GB 9606764.0 " " 29,1996 and GB 9609102.O " May 1, 1996 address the problem of powering a microprocessor chip from an antenna placed into a portable pocketsize component. The twin objective has been (a) reducing the radiation at distances beyond five or six inches from the card terminal so that confidential data cannot be picked up by unauthorized persons (b) drastically improving the ratio of usefully transferred power to total radiated power.

Whereas the means suggested in the above cited papers have in tests proven to be very effective in achieving the first-named objective, the second one could not be said to have been reliably achieved because of the sensibility of VHF antennas to environmental conditions and the inherent narrowness of the bandwidth in the matched condition. There was a preponderant uncertainty as to whether optimum transfer conditions can be reliably repeated even with the best of precautions t this point it was important to realize that it was quite irrelevant for the transfer of energy and even less so for the transfer of data, at which precise carrier frequency it is tazing place. Therefore, the idea of employing a rigidly fixed farrier frequency could be abandoned. Instead, theVHF generaor may be allowed at any moment to adjust its frequency to that Dne at which (as a result of all the contributive factors present) free oscillation would happen; this would automatically unsure that also the coupled antenna is optimally matched irres deceive of the distance between the sending and receiving anten zas.(i.e. within the reduced range geometry due to the said T-shaped or twin-loop antenna elements as described in the cited Patent applications).

Uhis is the essence of the present patent application which can readily be added to the principles described in the cited three earlier patent applications, and the implementation of which nay be achievable by a variety of circuits and antenna layouts.

En the drawings which give specific examples of execution ig. 1 shows an electric circuit closely connected to a VHF ansenna. A coaxial feed line is deliberately avoided as its inerent impedance would reduce the adaptability of the circuit.

ig. 2 shows two versions of encoding digital data for modulaing the power output of the circuit of Fig. 1, by way of example.

ig. 3 shows the inherent simplicity of the card antenna circuit sing conductive laminates and small discrete capacitors.

ig. 4 illustrates with some exaggeration the kind of frequency variation that might occur when the card antenna is gradually Drought near to the Reader antenna. The aim is to get reasonably onstant power betweenfour and zero inch spacing while beyond our inches spacing a rapid reduction of the power transfer mould take place.A negative feedback circuit also reduces the radiating wattage at higher frequences, thus compounding the Primary effect.

ig. 5 gives an indication of the possibility of producing a ompact component made up of the VHF compartment and the lamiate antenna.

Fig. 6 shows the twin-loop arranged in such a way that the connections and 0 with the VHF drive circuit, come conveniently to be placed fairly in the middle of the cardlike surface.

Figure 7 shows an arrangement of an outdoor terminal which may be either a fixed terminal or a light portable one powered by a battery.

Fig. 8 shows a portable terminal that provides a switch with the option to communicate with a card either at a fixed high frequency, or with a card at a variable frequenc- This does not duplicate notes in one of the earlier(cited)patent applications on the choice of a carrier frequency which would affect the antenna system only by causing in it a unison linear resonance which, too, can drive the card chip and would be effective over relatively larger distances.between a terminal and a chip card.

Description of the Drawings. (Please note:The figures on sheet I are being re-drawn spreading them over two sheets to comply better with regulations. They will be forwarded to the Patent Office on receipt of a request to do so).

Figure 1 shows a high-speed NPN transistor 4 which is over the shortest possible path connected to the twin-loop antenna with its center branch la and its two side branches lb. In this example, this is done via coupling capacitors 2, with the center branch la connected to the collector, and the outer branches via a voltage divider to the base of the transistor. When power is switched on a pulse applied to branch la travels via the two outer branches reaching the base of the transistor reduced in--agplitudefafter a definite delay period. This causes an increase in transistor current and a voltage drop at the collector, i.e. a negative going pulse applied to center branch la.

This in turn will appear at the transistor base after the said delay period and cause an increase of voltage at the collector point, i.e. a positive going pulse to the branch la. The condition for the build-up of an oscillation are given and this continues until radiation and other losses equal tht power introduced.

Ef the antenna branches la, ib extend over the full length )f a standard credit card, the resonance frequency would be Ln the order of o,9 gigahertz (GHz). For the purpose of sending digital data, various forms of amplitude modulation may be used lnd figure 2 shows an inverted pulse length modulation for input 0 the base of transistor 5. When the Reader antenna listens to ard data, the input to gate or base 5 must be kept low.This weeps the transistor 5 in the conductive state with the antenna La, ib radiating.

Dig. 3 shows an example of a card antenna with built-in chip 9.

ks explained in the priority applications, the antenna strips 8a 3b, and connecting links would consist of thin metal folio or plastic folio with deposited metal film. The metal need not be )f the inert ones such as gold,platin or the like since the conduc ors would not be exposed to the athmosphere.Small lumped capaci ors cl and c2 may be placed into each loop path so as to lower the iatural resonance frequency of the card antenna. Their purpose is :o lower the mutual resonance point when the card is presented 0 the Reader antenna.

ig. 4 gives an idea of the frequency changes of the Reader-Card )oscillator system as the spacing between Reader and card is re Ruced. The figures entered into the diagram are not derived from neasurements. Frequences will be lowered inverse proportional as -he root of the mutual inductance increases.

ig. 5 is a side view of the integrated component according to -he invention. It consists of a shielded soace inside a metal ;hell 3 which contains the VHF circuitry. Also shown are the flange portion 3a, a lid plate 11, a ferrite plate 12 which conpentrates the forward-directed electromagnetic flux, and final Ly the laminated sheet 1 containing the Reader Antenna of Fig. 1 'he metal container 3 may also contain a compartment for a batte :y (not shown).

{returning to Fig. 4, it can be seen that a steep fall in flux energy is expected in the transition from an antenna spacing at inches. This would be due partly to the antenna configuration 1S shown, partly by the introduction of a negative feedback nto the emitter of the transistor 4 (fig. 1), by means of a 6 coaxial resonator/representing the ground connection for the said transistor. This resonator may be tuned to about 0.9GHz of and would already at/frequency below that value represent a negatively acting impedance thereby reducing the oscillator power very rapidly if no card is nearer than 5 to 6 inches from the transaction point. For card distances below 5 inches the natural resonance frequences are not affected by the coaxial resonator 6 which then simssy acts as a ground connection.

Figs 6 and 7 show the front and side elevations of a card terminal which feasibly may be used for outdoor installations, or as a mobile outdoor unit. In Fig. 6 it will be observed that the antenna layout is modified, mainly to get the endpoints for the twin loops into the center of the antenna area. (and).

From these points, metallic connecting pins may reach into the space 15 (Fig. 7) for easy plug connection to the circuitry placed into that space.

In Figure 7, one can again distinguish the laminated antenna sheet 1, the ferrite insulator plate 12, and the sturdy lid 3a. A threaded tubular handle or support tube 16 furnishes an airtight closure to prevent humidity from entering into space 15.

The circuit of Fig. 8 shows up the antenna connecting points and ss , but is otherwise very similar to that shown in Fig. 1.

It is here used also to indicate two further features which may be in demand. One is the substS e, or the addition,of analogue communication facilities producing analogue modulation of the field covered by the twin-antenna geometry. Accordingly, the input to the base of transistor 4 consists of a microphone MIC and the digital data output is replaced by a diode controlled detector circuit and earphone 14.

The second feature is a facility to choose between the already described de-emphasis of the short wave spectrum of resonance possibilities (by means of resonator 6 in the emitter to ground connection) and an emphasis for the shortwave or gigahertz region.

A switch handle SWH can externally actuate switches SW1 and SW2 to produce the changeover to a connection where the resonator 6 is replaced by a straight ground connection 18, and the resistor R in the collector of transistor 4 is substituted by another resonator 6a. Similar switches may be provided to produce a changeover from twin-loop to single loop mode, for temporary range extension.

Claims (10)

1. !. A twin-loop antenna configuration capable of electromagnetically oscillating in at least two modes, one in which the antenna loops oscillate in phase opposition and a second mode wherein the antenna currents oscillate linearly in unison even though at a higher frequency, a n d w h e r e i n the oscillator drive circuit is mounted on the same support structure as the antenna conductors, this system further characterized by a high degree of dependence of the oscillating frequency upon the radiation resistance changes of the antenna to which it is linked.
2. 2. A system of energy transfer from a card transaction terminal to a chip card wherein the chip carrier (card) consists of layers of bonded laminates one or more of which carry a twin loop antenna consisting of a middle branch and two side bran ches on either side thereof and are transversally connected to the middle branch, either of which may optionally be inter rupted for the insertion of a capacitive or inductive link element, and wherein the Reader antenna has broadly the same size and shape, and is connected to a transmitter drive cir cuit whose oscillating frequency is strongly co-determined by the mutual inductance and coupling conditions of the card an tenna and Reader antenna when brought into mutual proximity.
3. 3. A system of energy and data transfer as in Claim 2, wherein the by the transmitter circuit produced carrier is amplitude modulated and wherein the data are encoded as pulse or interval length variations or pulses with different rise times to represent binary maqnitudes, for storage in the message receiving data processor unit.
4. 4. A system of energy and information transfer as in Claim 2 wherein the binary data are represented by frequency shifts imposed on the radiated energy.
5. 5. A system of energy and information transfer as in Claim 2 wherein the binary data are represented by phasing shifts imposed on the radiated energy.
6. 6. A system of energy and information transfer as in Claims 1 and 2 w h e r e i n the oscillation drive circuit is modulated by amplified microphone voltages, and the selfsame circuit is also equipped with a detector for such analogue variations as are imposedYradiation resistance changes in the proximity environment sf the said antenna.
7. 7. An oscillator drive circuit as in Claim 1 which also contains connection switching elements accessable to manual operation via electronic or mechanical switches so as to put the said antenna from its normal twin-loop operating mode into a linear or uni-directional oscillation mode.
8. 8. An oscillation drive circuit as in Claim 1 or 7 which also contains switching elements between the circuit and the said antenna accessable to manual operation via electronic or me chanical switches so as to put said antenna temporarily from its normal twin-loop operating mode into a single loop mode.
9. 9. An oscillation drive circuit as in Claim 1 which also con tains means to emphasize the emission of a certain range in the feasible frequency spectrum, such as tuned chokes or filters emphasizing a certain frequency band,with the object of either weakening or strengthening the emission of that range relative to others, and optionally switching elements in said circuit accessable to manual operation via electronic or mechanical switches (SW1, SW2 fig. 8) in order to achieve temporarily a corresppondingly modified performance of the said energy and information transfer arrangement.
10. 10. A system and device for the transfer of energy and signals by prevailingly proximity radiation as illustrated in the drawings and described in the explanatory statement.