GB2436634A

GB2436634A - Machine readable code system

Info

Publication number: GB2436634A
Application number: GB0606189A
Authority: GB
Inventors: Kjell Nybergh; Tom Ahola; Jukka Salminen; Marco Sandrini; Martin Zilliacus
Original assignee: Avantone Oy
Current assignee: Valmet Technologies Oy
Priority date: 2006-03-28
Filing date: 2006-03-28
Publication date: 2007-10-03
Also published as: GB0606189D0; WO2007110485A1

Abstract

The invention relates to machine readable codes, to devices for reading such codes and to the systems for creating such codes. The machine readable code 3 comprises a two dimensional array of code elements 9 distributed over a conductive layer (28, figure 3a) in accordance with an associated code value. In one embodiment, the code elements 9 are formed over the conductive layer (28, figure 3a) and, in use, are pressed into the surface of the conductive layer to deform the conductive layer. In another embodiment, the code elements are defined by recessed portions of the surface of the conductive layer (67, figure 7b). A capacitive sensing transducer 13 senses the surface of the conductive layer to generate signals that vary with the distribution of the code elements 9. The signals are processed to determine the code value associated with the machine readable code. The invention may be used to print a two dimensional code on skin 5, the lower layers of skin 28 acting as a conductive layer when the code on the skin are scanned by the sensing transducer 13.

Description

MACHINE READABLE CODE SYSTEM

The present invention relates to a system for reading machine readable codes using a capacitive sensing transducer and in particular to machine readable codes having non-conductive code elements distributed over a conductive substrate.

It is well known to provide machine readable codes on product packaging for stock control and product identification purposes at retail checkouts. It is also known to encode links to remote servers in such machine readable codes so that further information about a product can be obtained.

The present invention aims to provide an alternative machine readable code structure and method for reading the code.

According to one aspect, the present invention provides a system comprising a machine readable code which has an array of code elements geometrically distributed over a conductive layer in accordance with an associated code value and being arranged so that, in use, a surface of said conductive layer is deformed in accordance with the geometrical distribution of the code elements. The system includes a computer device comprising a capacitive sensing transducer which capacitively couples to the conductive layer and which senses the profile of the deformed surface of the conductive layer to generate signals that vary with the geometrical distribution of said code elements.

The computer device also comprises a code reader module which processes the signals generated by the sensing transducer to determine the code value associated with the machine readable code.

According to another aspect, the present invention provides a system comprising a machine readable code which has an array of code elements geometrically distributed over a conductive layer in accordance with an associated code value, where each code element is defined by a recessed portion of the surface of the conductive layer. The system includes a computer device comprising a capacitive sensing transducer which capacitively couples to the conductive layer and which senses the recessed portions of the conductive layer to generate signals that vary with the geometrical distribution of said code elements. The computer device also comprises a code reader module which processes the signals generated by the sensing transducer to determine the code value associated with the machine readable code.

These and other features and aspects of the present invention will become apparent from the following detailed description of embodiments which are given by way of example only and which are described with reference to the accompanying figures in which: Figure 1 is a schematic diagram illustrating a two dimensional machine readable code printed on a user's arm and a portable device having a capacitive sensing transducer for sensing the 2D code and for sensing characteristic features of the user's fingerprint; Figure 2 is a block diagram illustrating the main components of the capacitive sensing transducer shown in Figure 1; Figure 3a is a schematic diagram illustrating the principle of operation of the capacitive sensing transducer used in this embodiment to sense the machine readable code; Figure 3b illustrates the way in which signals are coupled between the conductive substrate and the sensor electrodes of the capacitive sensing transducer; Figure 4 is a schematic block diagram illustrating the main components of the capacitive sensing transducer shown in Figure 1; Figure 5 illustrates an alternative arrangement of sensor electrodes and drive electrode for sensing the presence of code elements of a machine readable code; Figure 6 illustrates a further alternative arrangement of the drive electrode and sensor electrodes that may be used for reading machine readable codes; and Figure 7, which comprises Figures 7a and 7b, illustrates an alternative machine readable code structure.

OVERVIEW

Figure 1 is a schematic diagram illustrating the components of a system 1 that allows users (such as nurses) to obtain further information relating to, for example, a hospital patient by reading a two dimensional (2D) code 3 that is printed on an area of the patient's skin 5 (in this example, on the back of the patient's hand).

The system 1 includes a pager 11 having a capacitive sensing transducer 13 which can read the 2D code 3 printed on the patient's skin 5. In this embodiment, the sensing transducer 13 comprises a commonly available fingerprint sensor such as those provided by AuthenTec Inc., Melbourne, Florida, USA or Fingerprint Cards AB, Gothenburg, Sweden. As shown in the close-up view of the sensing transducer 13, the transducer 13 includes a sensing area 17 comprising a plurality of sensor electrodes 15 arranged in a two-dimensional array and a drive electrode 19 that surrounds the sensing area 17.

To read the 2D code 3, the nurse scans or swipes their pager 11 over the surface of the patient's skin 5 until the sensing transducer 13 is swiped over the area of the patient's skin 5 carrying the 2D code 3.

When the code 3 is read, the information contained in the code is determined. The information obtained from the 2D code 3 may, for example, be the personal identification of the hospital patient and other information, such as the patient's medical history and any medicinal allergies that the patient may have. The information is output to the nurse on, for example, a display 12 of the pager 11. In addition or alternatively, the pager 11 may transmit the information obtained from the 2D code 3 to a receiver 22 of a remote personal computer 20 via a communications link 23, which can be for example, a mobile telephone network or a wireless communications link (e.g. Bluetooth). The personal computer 20 then outputs the received information to the nurse on a display 21 of the personal computer 20.

In this embodiment, the pager 11 also includes a fingerprint sensing module that can use the same sensing transducer 13 for sensing the fingerprint of the hospital patient for authentication purposes.

This is important in situations where it is vital for a user to verify that the information obtained from the 2D code relates to the correct hospital patient so that, for example, the nurse does not issue medication to the wrong patient. In this way, the same sensor 13 can be used to sense different things for different purposes. In this embodiment, the nurse manually specifies (via a keypad (not shown) of the pager 11) whether a fingerprint is to be scanned or if a 2D code 3 is to be scanned. Alternatively, the pager 11 may be arranged to automatically detect whether a fingerprint is being sensed or if a 2D code 3 is being sensed (from the variation in the signal levels that are obtained) A more detailed description will now be given of the 2D code 3 used in this embodiment and of the various components of the pager 11.

2D CODE As is well known, 2D codes 3 such as the one shown in Figure 1 represent information by the presence or absence of code elements 9 within the 2D array of possible code element positions. In the Figures, the presence of a code element 9 is represented by a black square and the absence of a code element is represented by a white square. The way in which the information is represented and encoded within the 2D array is defined by an appropriate standard or by a proprietary encoding scheme. In this embodiment, the 2D code 3 that is used is based on a conventional "Data Matrix" type two-dimensional code. An L-shaped frame 25 borders the array of code elements 9 and is provided so that the reading device (i.e. the pager 11) can determine the relative orientation between the 2D code 3 and the capacitive sensing transducer 13 and hence where the 2D code 3 begins and where it ends.

In this embodiment, the code elements 9 are formed from conventional printing ink which is substantially non-conductive (at least when dry).

In this embodiment, the 2D code 3 has dimensions of 1cm x 1cm and the code elements 9 and non-conductive skin elements 10 have dimensions 0.2mm x 0.2mm. This means that in this embodiment, the 2D code 3 can represent about 2.4kbits of data. As mentioned above, the way in which this data is represented in the geometrically distributed array of code elements 9 is defined by the standard code type used (in this case by the Data Matrix standard).

PAGER

Figure 2 is a block diagram illustrating in more detail the main components of the user's pager 11. As shown, the pager 11 includes a transceiver circuit 31 9 -and an antenna 33 for transmitting signals to and for receiving signals from the personal computer 20. As shown in Figure 2, the pager 11 also includes a processor 41 which controls the operation of the pager 11 under control of various software modules stored within memory 43. In this embodiment, the memory 43 includes a control module 44, a fingerprint sensing module 45, a code reader module 47 and a working memory area 51. The processor 41 is connected to the transceiver circuit 31 which allows the control module 44 to transmit information (e.g. obtained from the code reader module 47 or the fingerprint sensing module 45) to the remote personal computer 20 via communications link 23.

Figure 2 also shows the capacitive sensing transducer 13 which forms part of the pager 11 and which is used to read the 2D codes 3 or the user's fingerprint. In this embodiment, the capacitive sensing transducer 13 is normally powered down to save battery power.

Therefore, in this embodiment, when the user wishes to scan a fingerprint or a 2D code 3, they must press an appropriate button or buttons on a keypad 53 to cause the processor 41 to power-up the sensing transducer 13. The signals obtained from the sensing transducer 13 are then passed to the processor 41 which stores the data in the working memory 51. In response, the processor 41 (running under control of the control module 44) initiates the fingerprint sensing module 45 if a fingerprint is being scanned or the code reader module 47 if a 2D code 3 is being scanned. The appropriate module then processes the sensor values stored in the working memory area 51.

In particular, when a fingerprint is being scanned, the fingerprint sensing module 45 processes the sensor data values stored within the working memory area 51 to identify the characteristic features of the fingerprint which it compares with stored fingerprint data for the user (obtained in a prior registration process) for authentication purposes. When a 2D code 3 is being scanned, the code reader module 47 processes the sensor data values stored within the working memory area 51 to recover the information defined within the 2D code 3. As discussed above, the pager 11 may output the information to the user via the display 55 or transmit the information to the remote personal computer 20 using the transceiver circuit 31.

CAPACITIVE SENSING TRA1TSDUCER -PRINCIPLE OF OPERATION Figure 3a is a schematic diagram illustrating the way in which the capacitive sensing transducer 13 used in this embodiment detects the 2D code 3. (As will be apparent to those skilled in the art, where other types of capacitive sensing transducer 13 are used, these may operate under different principles.) Figure 3a shows the structure of the capacitive sensing transducer 13 and illustrates the array of sensor electrodes 15 and the drive electrode 19. As shown, the drive electrode 19 is connected to an AC source 61 which is also connected to a grounded reference electrode 63 located under the sensor electrodes 15.

As shown in Figure 3a, the drive electrode 19 and the sensor electrodes 15 are provided beneath a protective layer 14 which protects the electrodes from the environment.

Figure 3a also shows the user's skin 5 which carries the code elements 9 of the 2D code 3. As shown, in this embodiment, when the capacitive sensing transducer 13 is brought into contact with the patient's skin 5, the printed code elements 9 are pushed into the skin 5 by the protective layer 14 until the portions 10 of the skin between the code elements 9 also touch the surface of the protective layer 14. In this way, the surface of the skin 5 is deformed in accordance with the geometrical distribution of the code elements.

As those skilled in the art will appreciate, human skin 5 includes a surface layer 27 of dead dry skin having low electrical conductivity and, beneath that, a layer 28 of live skin. The boundary region 29 between this 27 layer of dead skin and the layer 28 of live skin is where the live cells begin turning into "keratinised" skin, which is moist and electrically conductive.

In operation, when the AC source 61 generates an AC drive signal, it is applied between the drive electrode 19 and the reference electrode 63. The AC drive signal capacitively couples to the conductive boundary region 29 through the protective layer 14.

This causes an electric field 65 to be generated

between this boundary region 29 and the reference electrode 63. As a result of the deformation of the boundary region 29 by the code elements 9, the electric field 65 which is generated spatially varies in accordance with the geometric distribution of the code elements 9.

In this embodiment, the frequency of the AC drive signal applied to the drive electrode 19 is approximately ioo kHz, which means that the wavelength

of the electric field 65 is much larger than all

dimensions of the code elements 9 and of the sensor area 17 of the transducer 13. As a result, the

electric field 65 generated between the conductive

boundary region 29 and the reference electrode 63 will be purely electric with no magnetic components and no electromagnetic effects. Consequently, the electric

field 65 can be treated as a quasi-static electric

field whose field strength varies with the geometric distribution of the code elements 9. Thus, the array of sensor electrodes 15 placed in the electric field will acquire voltages that represent the spatial

variation of the electric field 65, from which the

spatial distribution of the code elements of the 2D code 3 can be determined and hence the information contained within the 2D code 3.

Another way to consider the operation of the capacitive sensing transducer 13 is to consider the difference in the admittance between the conductive skin 5 and the sensor electrodes 15 that are adjacent the code elements 9 and the admittance between the conductive skin 5 and the sensor electrodes 15 that are adjacent the gaps between the code elements 9.

Figure 3b schematically illustrates part of the capacitive sensing transducer 13 when the user's skin carrying the 2D code 3 is pressed against the protective layer 14 of the transducer 13. Figure 3b illustrates more accurately the thickness of the protective layer 14 compared to the thickness of the code elements 9. In particular, the protective layer 14 is typically about 0.2 micrometres and the thickness of the code elements 9 is typically between 1 and 2 micrometres (The thickness of the protective layer 14 is exaggerated in Figure 3a in order to illustrate the spatially varying electric field 65.) As shown in Figure 3b, the distance between the conductive skin 5 and the sensor electrode 1513 where there is no code element is much smaller than the distance between the conductive skin 5 and the electrode l5 when there is a code element 9. As a result, the admittance (opposite of impedance) in the direction perpendicular to the patient's skin 5 is much lower in the positions where the code elements 9 are present than the corresponding admittance at the positions in the 2D code 3 where there are no code elements 9. As a result of this difference in admittance, the signal levels output from the sensor electrodes l5 that are positioned adjacent the positions in the 2D code 3 where there is no code element 9 will be greater than the signal levels output from the other sensor electrodes which are positioned adjacent code elements 9 of the 2D code 3.

Therefore, by suitable processing of the signal levels obtained from the sensor electrodes, the code reader module 47 can identify positions in the 2D code 3 where there are code elements 9 (and positions where there are not) and hence can recover the information encoded by the 2D code 3.

In this embodiment, the sensor electrodes 15 are square having a size of approximately 50 microns by 50 microns and have a pitch also of about 50 microns, so the sensor electrodes 15 are very close to each other relative to their dimensions. As discussed above, the sensing transducer 13 is intended to be swiped across the 2D code 3 to be read. Therefore, as shown in Figure 1, the sensing area 17 is elongate with the longer edge being slightly larger than the width of the 2D code 3 to be read. In this embodiment, the sensing area 17 has dimensions 12 mm x 2 mm and includes approximately 9600 sensor electrodes 15.

Although it would be possible to detect and read the 2D code 3 using a single column of sensor electrodes 15, in this embodiment, several columns of sensor electrodes 15 are provided within the sensing area 17 along the swipe direction, which allows the code reader to determine the speed at which the sensing transducer 13 is swiped over the 2D code 3.

As discussed above, the 2D code 3 has dimensions of 1cm x 1cm and the code elements 9 have dimensions 0.2mm x 0.2mm. With the size of the sensor electrodes 15 used in this embodiment, it would be possible to reduce the size of the code elements 9 and hence increase the amount of data that can be stored in the 2D code 3. However, as the size of the code elements 9 is reduced, the more unreliable the sensing becomes as fewer measurements will be obtained from each code element 9.

The operating principal of the capacitive sensing transducer 13 is the same when sensing a fingerprint.

In this case, there will be no code elements 9 to deform the surface of the patient's skin. However, as the structure of the ridges and grooves which define the patient's fingerprint extends through to the boundary region 29 between the layer 27 of dead skin and the layer 28 of live skin, the electric field that is generated between the patient's finger and the sensor electrodes is will also vary with the grooves and ridges of the fingerprint. Consequently, by suitable processing of the signal levels obtained from the sensor electrodes 15, the fingerprint sensing module 45 can extract characteristic features of the patient's fingerprint which it can then compare with stored fingerprint data in order to confirm the identity of the patient.

CAPACITIVE SENSING TRANSDUCER -COMPONENT STRUCTURE

Figure 4 is a schematic block diagram illustrating the main components of the capacitive sensing transducer 13 used in this embodiment. As shown, the transducer 13 includes the array of sensor electrodes 15 and the drive electrode 19. The drive electrode 19 is connected to a drive amplifier 71 which amplifies a drive signal generated by a drive signal generator 73.

In this embodiment, the drive signal generator 73 only generates the drive signal when instructed to do so by the processor 41. Figure 4 also shows that, in this embodiment, each of the sensor electrodes 15 is coimected to a respective high impedance amplifier 75 which amplifies the signal from that sensor electrode 15. High impedance amplifiers 75 are required as the sensor electrodes 15 have characteristic impedances in the Teraohm range.

As discussed above, in this embodiment, the source 61 (i.e. the drive signal generator 73) generates an AC

drive signal. Therefore, the electric field 65

generated between the conductive skin 5 and the reference electrode 63 will also be an AC electric

field at the drive frequency. Consequently, the

output from each high impedance amplifier 75 will also be an AC signal at the drive frequency whose peak amplitude depends on the presence or absence of a code element 9 adjacent the corresponding sensor electrode 15. As shown in Figure 4, the outputs from the high impedance amplifiers 75 are demodulated and filtered by a respective demodulation and filtering circuit 77 to obtain a DC voltage level that depends upon the peak amplitude of the AC signal output by the corresponding amplifier 75. The output from each demodulation and filtering circuit 77 is then input to a respective sample and hold circuit 79 which samples the voltage level when triggered to do so by the processor 41.

As discussed above, in this embodiment, the dimensions of the sensing area 17 are such that to read the 2D code 3, the capacitive sensing transducer 13 has to be scanned across the 2D code 3 (or the 2D code 3 has to be scanned across the sensing transducer 13) Therefore, in this embodiment, the processor 41 causes the sample and hold circuits 79 to sample the output from the demodulation and filtering circuit 77 at a sampling rate that ensures that sufficient samples are obtained to allow the detection of the code pattern for some maximum speed at which the sensing transducer 13 is likely to be scanned across the 2D code 3.

As shown in Figure 4, the voltage levels held by the sample and hold circuits 79 are digitised by an analogue to digital converter 81 and then stored in the working memory area 51 for processing by the code reader module 47 or the fingerprint sensing module 45.

The way in which these modules process the digitised voltage levels to determine the characteristics of the fingerprint or to determine the 2D code value are well known to those skilled in the art and will not, therefore, be described in further detail here.

ALTERNATIVE SENSING TRANSDUCERS

In the embodiment described above, a separate drive electrode 19 was provided around the outside of the sensor electrodes 15. An alternative form of sensing transducer 13 will now be described in which the drive electrode is distributed over the sensing area 17 to surround the sensor electrodes.

Figure 5 schematically illustrates the form of the drive electrode 131 and the two-dimensional array of sensor electrodes 133 used in this embodiment. As shown, in this embodiment, the sensor electrodes 133 are arranged in four rows with the positions of the sensor electrodes 133 in each row being staggered relative to the positions of the sensor electrodes 133 in the other rows. As those skilled in the art will appreciate, by staggering the rows of sensor electrodes 133 in this way, it is still possible to obtain an accurate picture of the geometrical arrangement of the code elements 9 even when the code elements 9 have a similar size to the size of the sensor electrodes 133. The lines 135 shown in Figure indicate different directions of swiping the sensor relative to the 2D code 3. As can be seen, the layout of the sensor electrodes 133 serves to minimise the redundant readings from them, assuming of course that the sensing transducer 13 is swiped along a straight line.

As can be seen from Figure 5, in this embodiment, the drive electrode 131 is formed from a substantially planar uniform layer of conductor which extends over the entire sensing area 17 where the sensor electrodes 133 are located. With this arrangement, there will be a direct coupling between the drive electrode 131 and the portions 10 of the patient's skin 5 formed between the code elements 9 of the 2D code 3.

Various manufacturing techniques can be used to manufacture the drive electrode 131 and the array of sensor electrodes 133 shown in Figure 5. For example, a continuous layer of conductor may be provided on an insulating base and then a ring 137 surrounding each sensor electrode 133 may be etched away, thereby insulating each sensor electrode 133 from the drive electrode 131. This technique would be particularly suitable where the electrodes are made using printed circuit boards. Other manufacturing techniques could of course be used. For example, the electrodes may be formed as conductive layers on a silicon substrate, which are formed through different deposition techniques.

In the above embodiment, the drive electrode 131 was formed as a substantially planar layer of conductor.

In an alternative embodiment, the drive electrode may be formed from a plurality of connected ring portions which surround the individual sensor electrodes 133.

Such an arrangement is illustrated in Figure 6. As the ring portions 139 are connected together, the drive electrode 141 shown in Figure 6 only needs a single connection point (not shown) to the excitation source 61. If the individual ring portions 139 are electrically disconnected from each other then separate connections would have to be provided to each drive electrode. As those skilled in the art will appreciate, this is not preferred as it increases the complexity of the wiring arrangement for connecting the source 61 to the drive electrodes.

ALTERNATIVE 2D CODE STRUCTURES In the above embodiment, the 2D code 3 is formed by printing conventional ink on the surface of a non-rigid substrate, in particular, the surface of the patient's skin 5 (although the invention is equally applicable to an animal's skin). The capacitive sensing transducer 13 is able to distinguish between positions in the 2D code 3 where there are code elements 9 and positions in the 2D code where there are no code elements because the code elements 9 are pressed into the skin when the sensing transducer 13 is brought into contact with the code elements 9, and

this changes the electric field pattern that is

generated when the drive electrode is driven with the drive signal.

As those skilled in the art will appreciate, the 2D code 3 could be formed on a rigid conductive substrate, such as a rigid layer of metal. As shown in Figure 7a, in such an embodiment, the 2D code can be formed by stamping a pattern of the 2D code 3 into the surface of a rigid conductive substrate 67 so that the 2D code 3 is impressed into the conductive substrate 67. In this embodiment, the code elements 9 of the 2D code 3 are formed by air (which is non-conductive) that is located in the recessed portions of the conductive substrate. Alternatively, the recesses formed by the stamping can then be filled with a non-conductive material (such as ink) to prevent the build up of dirt affecting the reading and/or to render the 2D code 3 visible to the eye. In such an embodiment, the code elements 9 of the 2D code 3 can be formed by a suitable engraving technique (such as carving or etching) instead of stamping them.

Additionally, in such an embodiment, the rigid conductive substrate 67 can be a substantially planar surface (as shown in Figure 7a) or it can be formed by a surface which is curved, such as the circumferential surface of an aluminium can.

In yet another alternative structure, as shown in Figure 7b, code elements 9 of the 2D code 3 can be formed by recesses impressed or engraved in a layer of conductive material 67 which is provided between a substrate 68 and a protective layer 69 (preferably of insulating material).

With these alternative arrangements, the capacitive sensing transducer 13 will operate in the same way as discussed in the first embodiment to read the 2D code 3 because the portions of the conductive substrate (layer) which are located between the code elements impressed or engraved into the substrate will be closer to the sensor electrodes than the other portions of the substrate In other words, in this embodiment, the surface of the conductive surface is permanently deformed in accordance with the geometrical distribution of the code elements. As a result, the electric field generated between the rigid conductive substrate and the referenceelectrode will vary with the positions of the engraved code elements of the 2D code and hence with the information defined by the 2D code.

OTHER MODIFICATIONS AND ALTERNATIVES

In the first embodiment, the capacitive sensing transducer 13 included a drive electrode 19 that was provided around the periphery of the sensing area 17.

Further, in the first embodiment, the sensing transducer 13 was arranged so that it had to be swiped (scanned) across the fingerprint or the 2D code to be sensed. As those skilled in the art will appreciate, the surface area of the 2D array of sensor electrodes may be made considerably larger so that it corresponds at least to the surface area of the 2D code 3 to be read. In this way, it is not necessary to swipe the sensing transducer 13 across the 2D code or across the fingerprint to be able to read the same.

The use of such an "area" transducer will reduce the complexity of the detection software modules that are used to detect the 2D code and the characteristics of the fingerprint but will require a larger and more expensive sensing area 17. It will also require the position of the 2D code 3 to be known so that the sensing transducer 13 can be placed over the 2D code 3.

In the first embodiment described above, a separate electrical connection was provided from each sensor electrode to a corresponding high impedance amplifier.

As those skilled in the art will appreciate, it is not essential to have a separate processing channel (comprising the high impedance amplifier, demodulator and filter circuit and sample and hold circuit) for each sensor electrode. Instead, the signals from the different sensor electrodes may be multiplexed through a smaller number, or even a single processing channel.

In the above embodiments, the 2D code was based on a Data Matrix type code in which the code elements 9 are arranged in a two-dimensional Cartesian array and bordered by an L-shaped frame 25. As those skilled in the art will appreciate, it is possible to apply the invention to other types of codes, such as to conventional lD or 2D barcodes, Maxicodes, Code one type codes, QR codes, Aztec codes etc. or to 2D codes in which the positions of the code elements are defined in polar coordinates.

In the above embodiment, a user's pager included a capacitive sensing transducer which could be used for both fingerprint sensing and 2D code reading. As those skilled in the art will appreciate, the above- described capacitive sensing transducer and the above-described fingerprint sensing and code reader modules may be provided in any type of computer device, such as a personal (laptop) computer, a mobile (cellular) telephone, a portable digital assistant, etc. In the above embodiments, the fingerprint sensing module and the code reader module operated substantially independently of each other. However, in some applications, these two modules may cooperate.

For example, in the hospital application discussed above, the data encoded in the 2D code may include fingerprint data identifying the patient to which the remaining data in the body of the 2D code relates.

Therefore, when the nurse uses the pager 11 to read the 2D code 3, he/she can also take a fingerprint reading from the patient and the pager can compare the fingerprint data obtained from the fingerprint scan with the fingerprint data obtained from the 2D code, in order to verify that the information obtained from the 2D code belongs to the patient under test.

In the above embodiment, the 2]J code was printed on the back of a hospital patient's arm and provided additional information relevant to that patient. As those skilled in the art will appreciate, the use of such codes can be used in a number of different applications For example, the codes can be used to control access to venues such as nightclubs and amusement parks. With such applications, the 2D codes can be used to store various information such as the user's age, the type of ticket purchased etc. As those skilled in the art will appreciate, the use of such codes in these applications offers a number of advantages over the existing techniques used to control access as it reduces the likelihood of users being able to duplicate the stamped code.

In the above embodiments, the sensing transducer was arranged to provide a drive signal to the conductive substrate via a drive electrode. However, as those skilled in the art will appreciate, other capacitive type sensing systems may be used. For example, instead of coupling the conductive substrate to the drive electrode, the conductive substrate may be coupled to a ground electrode of the sensing transducer. In this case, the sensing electrodes may each be arranged to sense the local capacitance in its vicinity, which will vary depending on whether or not there is a code element in its vicinity.

Additionally, it is not essential to use an AC drive signal. A DC drive signal may be used instead.

In the above embodiments, the sensor electrodes were square or circular. As those skilled in the art will appreciate, the sensor electrodes may be arranged to have any convenient shape. For example, in other embodiments, the sensor electrodes may be hexagonal in shape.

In the first embodiment described above, the drive electrode was provided below the protective layer. As those skilled in the art will appreciate, the drive electrode could instead be provided above the protective layer so that it comes into direct contact (galvanic) with the conductive layer.

In the first embodiment described above, an array of sensor electrodes was provided with a drive electrode mounted around the outside of the array. As those skilled in the art will appreciate, the sensor could also work by making the drive electrode the sensor electrode and by making the sensor electrodes individual drive electrodes. In this case, the individual drive electrodes could be driven sequentially, with the output from the sensor electrode being processed through a single processing channel to provide the corresponding voltage level.

Alternatively, the drive electrodes may be driven simultaneously with a respective drive signal at a respective different drive frequency. In this case, the signals obtained from the common sensor electrode would have to be frequency analysed to obtain the relevant voltage levels for each frequency and hence the signal levels associated with each drive electrode. The way in which such frequency analysis can be carried out will be apparent to those skilled in the art and will not be described further here.

In the first embodiment, the 2D code was formed by printing ink onto a conductive substrate. As those skilled in the art will appreciate, different print material could be used other than ink. For example, toner could be used instead. Additionally, the 2D code can be formed on the substrate, for example, by stamping the 2D code onto the substrate with ink or by laying a mask of the 2D code over the substrate and then spraying paint or ink over the mask so that the 2D code is formed on the substrate.

In the embodiments described above, the 2D codes are preferably formed with a non-conductive material.

However, as those skilled in the art will appreciate, it is not essential that the material is non-conductive. The code elements could instead be formed with a conductive material, provided that the admittance of the conductive substrate in the direction perpendicular to the substrate at positions where there is a code element is different from the admittance of the conductive substrate at positions where there is no code element, so that the capacitive sensing transducer can detect the positions in the 2D code where there are code elements.

Further, as those skilled in the art will appreciate, it is not essential to form the 2D code on the substrate by printing. Alternatively, the 2D code may be formed by gluing or attaching the code elements onto the conductive substrate. In such a case, the code elements may be individually attached to the conductive substrate or a layer of material may be attached to the conductive substrate and then portions of it etched or milled away to define the 2D code.

In the first embodiment the 2D code was formed on the surface of human skin. As those skilled in the art will appreciate, the 2D codes may be formed on non-rigid substrates made of soft metals such as aluminium or flexible compounds such as conductive rubber. As another alternative, a layer of non-rigid material, such as aluminium, could be provided on a substrate formed from a deformable material, such as plastic, rubber, foam, etc. In the above embodiments, the capacitive sensing transducer was formed integrally within the housing of the pager 11. As those skilled in the art will appreciate, the capacitive sensing transducer 13 may be provided in a separate housing and connected to the appropriate computer device via an appropriate wired or wireless link.

As those skilled in the art will appreciate, the various embodiments and modifications described above are given by way of example only. Various other embodiments and modifications will be apparent to those skilled in the art.

Claims

Claims: 1. A system comprising: a machine readable code having a

plurality of code elements geometrically distributed over a conductive layer in accordance with an associated code value, the machine readable code being arranged so that, in use, a surface of said conductive layer is deformed in accordance with the geometrical distribution of the code elements; and a computer device comprising: a capacitive sensing transducer arranged, in use, to capacitively couple to said conductive layer and to sense said deformed surface of the conductive layer to thereby generate signals that vary with the geometrical distribution of said code elements; and a code reader module operable to process the signals generated by said sensing transducer, to determine the code value associated with the machine readable code.

2. A system according to claim 1, wherein said code elements are formed on the surface of skin and wherein said conductive layer is provided beneath the surface of the skin.

3. A system according to claim 2, wherein, in use, the code elements are impressed into the surface of the skin which causes the deformation of said conductive layer.

4. A system comprising: a machine readable code having a plurality of code elements geometrically distributed over a conductive layer in accordance with an associated code value, each code element being defined by a recessed portion of a surface of said conductive layer; and a computer device comprising: a capacitive sensing transducer arranged, in use, to capacitively couple to said conductive layer and to sense the recessed portions of said surface of the conductive layer to thereby generate signals that vary with the geometrical distribution of said code elements; and a code reader module operable to process the signals generated by said sensing transducer, to determine the code value associated with the machine readable code.

5. A system according to claim 4, wherein said machine readable code further comprises a substrate layer and a protective layer, and wherein said conductive layer is arranged between the substrate layer and the protective layer.

6. A system according to claim 4, wherein said recessed portions defining said plurality of code elements are filled with a non-conductive material.

7. A system according to claim 6, wherein said non-conductive material comprises non-conductive ink.

8. A system according to any preceding claim, wherein the capacitive sensing transducer comprises: i) a plurality of electrodes arranged over a sensing area of the transducer; ii) drive circuitry operable to generate a drive signal and to apply the drive signal to a first subset of the plurality of electrodes; and iii) sensor circuitry operable to sense signals obtained from a second subset of the plurality of electrodes, and wherein the capacitive sensing transducer and said machine readable code are arranged so that when the machine readable code is placed over said capacitive sensing transducer and upon the application of said drive signal to said first subset of electrodes, said signals which vary with the geometrical distribution of said code elements are generated in the second subset of electrodes.

9. A system according to claim 8, wherein said first subset of electrodes comprises an electrode provided around a periphery of said sensing area of the transducer.

10. A system according to claim 8 or 9, wherein said first subset of electrodes and said conductive layer are arranged so that, in use, they are capacitively or galvanically coupled to each other.

11. A system according to any preceding claim, wherein said plurality of code elements are geometrically distributed over a conductive layer in a two-dimensional array in accordance with the associated code value.

12. A system according to any preceding claim, wherein said capacitive sensing transducer is further operable, in use, to capacitively couple to a finger placed over the capacitive sensing transducer and to generate therefrom signals that vary with identifying characteristics of said finger, and wherein said computer device further comprises a fingerprint sensing module operable to process signals generated by said sensing transducer when a finger is placed over said capacitive sensing transducer to determine the identifying characteristics of said finger.

13. A system according to claim 12, wherein said code value associated with the machine readable code comprises fingerprint data defining identifying characteristics of a finger, and wherein said computer device is operable to compare the fingerprint data of said determined code value with the identifying characteristics of said finger determined by said fingerprint sensing module to determine if there is a match.

14. A system according to claim 12 or 13, wherein said computer device is further operable: to automatically detect if a finger or a machine readable code is placed over said capacitive sensing transducer; and to pass the signals generated by said capacitive sensing transducer either to said fingerprint sensing module or to said code reader module in dependence upon said detection result.

15. A system according to any of claims 12 to 14, wherein said capacitive sensing transducer is operable to sense said finger or said machine readable code when scanned across the finger or machine readable code.

16. In a computer device having a capacitive sensing transducer, a method of reading a machine readable code comprising a plurality of code elements geometrically distributed over a conductive layer in accordance with an associated code value, the method comprising the steps of: positioning said machine readable code over or under the capacitive sensing transducer; deforming the surface of said conductive layer in accordance with the geometrical distribution of the code elements; capacitively coupling the capacitive sensing transducer to said conductive layer to sense said deformed surface of the conductive layer to thereby generate signals that vary with the geometrical distribution of said code elements; and processing the generated signals to determine the code value associated with the machine readable code.

17. In a computer device having a capacitive sensing transducer, a method of reading a machine readable code comprising a plurality of code elements geometrically distributed over a conductive layer in accordance with an associated code value, each code element being defined by a recessed portion of a surface of the conductive layer, the method comprising the steps of: positioning said machine readable code over or under the capacitive sensing transducer; capacitively coupling the capacitive sensing transducer to said conductive layer to generate signals that vary with the geometrical distribution of said recessed portions; and processing the generated signals to determine the code value associated with the machine readable code.

18. A method according to claim 16 or 17, wherein said step of capacitively coupling comprises the sub-steps of: generating a drive signal and applying the drive signal to a first subset of a plurality of electrodes of said capacitive sensing transducer signals so that signals are generated in a second subset of said plurality of electrodes, which signals vary in dependence upon the geometrical distribution of said non-conductive code elements; and sensing said signals generated by the second subset of the plurality of electrodes.

19. A method according to any of claims 16 to 18, wherein said step of capacitively coupling comprises capacitively or galvanically coupling said first subset of electrodes and said conductive layer.

20. A method according to any of claims 16 to 19, further comprising the steps of: capacitively coupling said capacitive sensing transducer to a finger placed over the capacitive sensing transducer; generating therefrom signals that vary with identifying characteristics of said finger; and processing the signals generated when a finger is placed over said capacitive sensing transducer to determine the identifying characteristics of said finger.

21. A method according to claim 20, wherein said code value associated with the machine readable code comprises fingerprint data defining identifying characteristics of a finger, and wherein the method further comprises a step of comparing the fingerprint data of said determined code value with the determined identifying characteristics of said finger to determine if there is a match.

22. A method according to claim 20 or 21, further comprising a step of automatically detecting if a finger or a machine readable code is placed over said capacitive sensing transducer and processing the signals generated by said capacitive sensing transducer in dependence upon said detection result.

23. A method according to any of claims 20 to 22, wherein said signals are generated by the capacitive sensing transducer when scanned across the finger or machine readable code.

24. A method of forming a machine readable code in a conductive layer comprising the steps of: forming a plurality of recessed portions in a surface of the said conductive layer, each of said plurality of recessed portions defining a code element of said machine readable code.

25. A method according to claim 24, wherein said forming step forms said recessed portions in the surface of the conductive layer by stamping a pattern of the machine readable code into the surface of the conductive layer.

26. A method according to claim 24, wherein said forming step forms said recessed portions in the surface of the conductive layer by engraving a pattern of the machine readable code into the surface of the conductive layer.

27. A method according to any of claims 24 to 26, further comprising a step of filling said plurality of recessed portions with a non-conductive material.

28. A method according to claim 27, wherein said non-conductive material comprises non-conductive ink.