Field of the Invention

The present invention relates to a packaging object comprising at least one radio frequency identification (RFID) tag, said RFID tag is formed in a pattern to function as a frequency lens, which responds to emitted radiation .

Background Art It is well known to print concentric circular "barcodes", where the width of the printed circles encode for a logic content, for instance by means of the 7 module system used in UPC and EAN codes for example. According to this protocol two black bars separated by two white bars represent each digit. Each digit takes up the space of 7 evenly spaced so-called modules . By selecting the number of adjacent modules printed in black in each of the two bars printed, some 30 characters can be encoded. This application is strictly meant for optical read- ing. There must be optical line of sight to the symbol, which is scanned by means of a laser dot moving over the symbol surface. The intensity variation of the reflected light is picked up by a PIN diode and the video signal after processing is translated into a numerical value. Due to the fact that this application is using optical reading several disadvantages occur, for instance the barcode may be placed or printed onto the object with a high accuracy which often not is the case and the barcode have to, during the reading, be directed against scanner. This is a time-consuming process, especially when a high number of objects are to be read.

¹ The use of RFID tags is well known. The Radio Frequency Identity Tag can be passive or active. Passive tags consist of an antenna, which picks up the readers

radio signal, manipulates it in some well-defined way, and reemits a coded signal. The advantage of the RFID is, that optical sight is not needed. In some instances the RFID tag can be read at a distance of 30 meters. The RFID tag often consists of a printed pattern of electrically conducting ink (today often based on colloidal silver, but cheaper organic conductors are ascending) , the so- called antenna, and a very small integrated circuit bonded in a conductive fashion to the antenna. This bond- ing process is expensive and results typically in a tag cost of USD 0.30 per piece. Therefore, there is a need for providing a simpler RFID, which merely consists of an antenna with a limited frequency response.

Summary of the Invention

An object of the present invention is to wholly or partly overcome the above disadvantages and drawbacks of the prior art. More specifically, it is an object to provide a RFID tag which is inexpensive to manufacture as well as apply to an object.

It is furthermore an object to provide an RFID tag which may be used in connection with packaging objects.

In addition it is an object of the present invention to provide a RFID tag which may encode for an alphanu- meric value.

The above objects, together with numerous other objects, advantages and features, which will become evident from the below description, are accomplished by a solution in accordance with the present invention by the RFID tag is a zone plate.

Hereby a barcode which is simple and very cost efficient as well as useful as a RFID tag obtained. The barcode or RFID tag may easily be applied to a packaging object whereby the object may be identified without being visible. This may especially be advantageous at supermarkets or stores where a high number of objects are to be identified during the day.

The matter is that the specific pattern of the zone plate acts as a lens for a specific frequency. When for instance a grid dip meter sweeps a relevant frequency band and the zone plate is in the vicinity of this meter, the meter will observe a sharp decline in the intensity of the electromagnetic field strength at a well defined frequency and its harmonics, whereby the object bearing the zone plate is identified.

Further embodiments of the invention appear from the appended sub-claims as well as the below description.

Description of Preferred Embodiments

According to the invention, if the "Barcode" is printed according to a special protocol it may act as a simple and very cost efficient RFID tag. Such a protocol is the Zone plate. Where the black and white concentric circles reduce in width proportional to the square root of the respective radii. The zone plate is known in optics as the "hologram of a point source" and is fre- quently used in microwave technology as a "lens". The execution of a zone plate, where perfectly white circles alternate with perfectly black circles is known as a Fresnel zone plate. If the contrast variation is graduated in a sinusoidal manner the zone plate is known as a Gabor zone plate, and if the black areas are replaced by zones of a material of a thickness, which retards half a wavelength then we have a phase reversal zone plate also known as a Wood zone plate. This latter execution has the advantage that the "black" zones by constructive inter- ference also contribute to the field strength at the focal point. It is loss free, whereas the ordinary zone plates looses half the electromagnetic radiation. On the other hand printing of or ablation to such a half wave structure is not a trivial task. It is well known that for instance certain cellulosic esters do possess the property of birefringence (for instance Cellophane®) , so

it is perfectly feasible to devices such a Wood zone plate .

According to the invention the zone plate may act as a lens for a specific frequency and focus that radiation into a point. If the focal point is located inside an electric conductor such as water, beer, any soft drinks, potion, lotion or other liquids, the electromagnetic energy at that particular frequency - and its harmonics - will be dissipated as heat in the focal point. As described above if for instance a grid dip meter is used to sweep the relevant frequency band, and held in the vicinity of the zone plate with conducting focal point, one will observe a sharp decline in the intensity of the electromagnetic field strength at a well defined frequency and its harmonics .

The sharpness of this resonance absorption peak depends on the loss factor of the circuit, known to those skilled in the art as the "Q". The attainable value of Q depends on the number of concentric circles. This again is limited by the printing precision. It is understood, from the square root function, that the circles become progressively narrower when moving away from the centre. Thus there is a limit given by the printing precision as to how many concentric circles can be rendered without short circuit. The typical zone plate will comprise a max of 250 concentric circles.

The zone plate may according to the invention be printed, engraved, injection moulded or made by laser ablating on a conductively coated insulating substrate. Furthermore, the pattern of the zone plate may be designed to act on a specific frequency, advantageously, the zone plate is adapted to respond in a frequency range from 15 kHz to 30 GHz.

Advantageously according to the invention the zone plate may have a circular form, however, the zone plate may also have an elliptical form, which zone plate may be perceived as off axis circular zone plate, and at a loss

of efficiency even rectangular zone plates may be perceived. This is of cause a trade off between zone plate efficiency and allowable reading distance and Q.

In an expedient embodiment according to the inven- tion a plurality of different patterned zone plates may be applied to the same object so that the different zone plates respond to different frequencies, which may encode for an alphanumeric value.

The rapid evolution of printed electronics ties in very well with this development is so far as the Advent of conducting inks lead to the development of printed field effect transistors and thus logic circuits can be created, which may or may not be placed in the focal point of the zone plate. According to a preferred embodiment according to the invention the packaging object is a food stuff container such as a bottle or a can, said food stuff container being made of glass, plastic, china, paper, wood, ceramic or metal or a combination thereof. The food stuff con- tained in the food stuff container may expedient be an electrical conducting media such as water, beer, wine, alcohol, any soft drink, potion or milk.

Furthermore, the packaging object according to the invention may be a liquid container such as a bottle or a can, said liquid container being made of glass, plastic or metal or a combination thereof. The liquid contained in the liquid container may also be an electrical conducting media such as shampoo or lotion and the like. In addition, the packaging object may be a box, a bag or a crate made of solid board, corrugated board, plastic, paper, wood, china, ceramic, metal or a combination thereof.

Advantageously, the zone plate may be a visible part of the decoration of the packaging object or it is embed- ded under the decoration of the packaging object or reverse printed on a rear side of the substrate.

Furthermore, the substrate may be conducting, in which case the focal point will be located in front of the zone structure (by reflection) . Then, the conducting focal spot by some means have to be supported above the substrate plane. For instance, the zone plate may be placed inside a crate, and the conductive focal spot may be placed on the outside of said crate, for instance in the form of a dot of conducting printing ink or a piece of pressure sensitive tape. A number of such zone plate / focal point combinations may be incorporated into the crate and encoding or reencoding may be obtained by means of ablating / removing conductive spots on the outside. The changeable coding thus obtainable may be utilised to article- / date- or batch-coding. Another embodiment of the invention would be to apply the zone plate pattern to an insulating part of the "body" - for instance the dry part of a bottleneck and diametrically opposite apply or remove an electrically conducting spot. It is understood that several such zone plates can be applied to the neck. If the closure is made out of an insulating polymer the opportunity to apply zone plates to the surface exists, taking advantage of the liquid surface, which the radio frequency can thus "see".

Furthermore, within the inventive idea the zone plate may also be applied instead of an antenna. When using logic from a silicon chip the cost is to high extent determined by the area of the chip. This is due to the fact that the number of chips that can be sawed out of one wafer is inversely proportional to the area of each chip. Extensive work in the line of miniaturization of the transistor functions has supported the Moore's law, packaging twice as many transistor functions per unit area every 18 months. But in a RFID context the small scale is a distinct disadvantage. This is due to the fact that when the chip gets small compared to the wave length of the radiation it is supposed to work with the impedance mismatch, very rapidly leads to a drop in energy

transfer between the chip and the E-field of the electromagnetic radiation. In order to alleviate this mismatch it is common place to design the antenna. The antenna is derived from the classical physics of a dipole, and in some instances enhanced by extra elements according to professor Yagi's antenna principle or a log-period antenna principle. However, this antenna has to be connected to the chip in an electrically conducting manner. This process known as bonding is the biggest source of the direct cost of an intelligent RFID chip, leading to a price tag of USD 0.30.

Bonding and the cost and quality problems associated with it may be avoided if the chip is placed in the focal point of a zone plate, the impedance mismatch being par- tially remedied by the zone plate, typically though at a cost of 6dB .

Although the invention above has been described in connection with preferred embodiments of the invention, it will be evident for a person skilled in the art that several modifications are conceivable without departing from the invention as defined by the following claims .