Inductive Input Device

The following invention relates to an input device, which input device controls an external device by the movements of an activation unit, which input device comprises a plurality of inductor units, which inductor unit comprises a plurality of planar coils, which input device further comprises an activation unit.

The following invention relates further to a method for a control system for an external device, where an input device is activated by an activation unit, where movement of the activation unit in relation to a number of coils placed in the input device is analysed, and a signal is transmitted to the external device.

Input devices are used to provide data and control signals to an information processing system. In particular, when operating as part of a human-machine interface, the input device provides data and control signals corresponding to the activation of the input device by a user. Examples of such input devices for human-machine interfaces are pointing devices for entering substantially continuous spatial information and keyboards for entering discrete spatial information. Such input devices for human-machine interfaces may be used for controlling external devices, such as computers, consumer electronics, or aids for the disabled, such as wheelchairs or prostheses.

An important part within such an input device is the interface between the user and the pointing device converting the user's gestures to machine readable signals in an analogue or digital form. The gestures are detected by interaction with a sensor arrange- ment that in operation generates signals in response to the gestures performed by the user. Gestures may be all kinds of movements or displacements of body parts, such as movements of a finger, head, eyes or the tongue.

One kind of input device, such as a touch panel, comprises a sensor arrangement that di- rectly interacts with the body part creating the gesture for generating signals.

A different kind of input device requires an activation unit, such as a stylus, interacting with a sensor arrangement adapted to generate signals in response to the interaction between the activation unit and the sensor arrangement.

The sensor arrangement according to this kind of input device has an interaction surface on which the activation unit is placed and/or moved by the user's gestures. The sensor arrangement comprises a plurality of sensor elements, typically distributed over the interaction surface just beneath a protective layer covering the interaction surface. The sensor elements detect the proximity of the activation unit and, based on a given sensor principle, generate a corresponding signal. Support electronics is provided for driving and reading the sensor elements of the sensor arrangement and generate a signal corresponding to the placement and/or movement of the activation unit on the interaction surface. The support electronics may be an integrated part of the sensor arrangement or may be provided as a separate unit in communication with the sensor arrangement.

Numerous sensor principles may be employed for generating signals from the interaction between the sensor elements of the sensor arrangement and the activation unit comprising pressure sensors, force sensors, optical sensors, capacitive sensors and inductive sensors. In the case where the interaction between the activation unit and the sensor arrangement is induction, the sensor elements are induction coils.

Many applications require more and more miniaturisation of the sensor arrangement in order to enhance the functionality provided by the sensor arrangement and/or due to very stringent spatial constraints on the overall dimensions of the sensor arrangement for a given application. At the same time, it is important to provide reliably detectable signals. Miniaturisation typically quenches signal levels drastically affecting the signal- to-noise level and thereby detect ability of the signal in a maybe equally miniaturised power supply, driver, read-out and signal processing electronics.

A typing device comprising an activation unit, where the sensor principle is based on inductive interaction between induction coils arranged in an inductor unit and a metallic activation unit is known from WO 2006 105 797 A2. WO 2006 105 797 A2 discloses a method and system for tongue based control of computers and/or aids, particularly for

severely disabled persons. The system disclosed comprises a mouth cavity arrangement with at least one coil and an activation unit fixed to the user's tongue, wherein the mouth cavity arrangement by inductive interaction with the activation unit provides signals with information identifying the coil in the arrangement generating the signal as an on/off switch for a keyboard depending the position of the activation unit. The sensor coils according to WO 2006 105 797 A2 are produced by winding wire on a winding support, removing the wound coils from the winding support and moulding the coils into a biocompatible polymer material.

Signal levels due to inductive interaction between a sensor coil and the activation unit decay very rapidly with increasing distance between the activation unit and the coil. Signal levels of inductive sensor arrangement are therefore very sensitive to variations in the shape of the sensor coils and the flatness of the interaction surface. Both the production of such sensor arrangements on an industrial scale as well as the possibilities for miniaturisation of such a sensor arrangement are currently limited by the technology known in the art.

Therefore, there is a need for providing an improved inductive sensor arrangement that is easily produced on an industrial scale, adapted to be miniaturised and that satisfies the needs for generating reliable signals from the inductive interaction between an inductor unit and an activation unit.

JP 2004117052 describes a thin film sensor for detecting the position of a movable element with high precision. The film sensor is provided with a sensor substrate and mag- nets fitted to the moving member which travels in two dimensions along the direction of the surface of the sensor substrate. The sensor substrate is a film substrate on which a large number of coils are arranged into a matrix shape in the whole moving region of the moving member. Accordingly, induced electromotive forces are generated in the coils by electromagnetic induction action of the moving magnetic member, and the po- sition of the moving member is detected by a controller.

EP0500367 relates to an inductive coil arrangement for measuring the physical characteristics of a token. The coil arrangement comprises a plurality of inductors, each indue-

tor being formed out of at least two superposed planar spiral tracks separated by an insulating layer of a multi-layer electrical device, such as a plurality of printed circuit boards which are laminated together. Conductive paths extend axially between the tracks. The invention extends to a method of manufacturing the inductive coil arrange- ment, as well as to a token validation device incorporating the inductive coil arrangement.

NL 1032211 describes a control apparatus for use by disabled persons and involves one or more pointers connected with a fixed position of the tongue, in conjunction with one or more detection apparatuses connected with a fixed position with the upper jaw.

The object of the invention is to provide an input device activated by movements of an activation unit which can be used as a pointing device.

A further object of the invention is to control computers and electronic devises by use of the pointing devices.

It is also an object of the invention to uses an input device as a pointing device.

It is also an object of the invention to control a wheelchair by the pointing device.

This can be achieved by the preamble to claim 1 if further modified by forming the coils in a plurality of layers of a multilayer printed circuit, which plurality of layers form a number of planar turns, which planar turns are coupled serially for forming the coils, which coils are connected to an AC source for generating an oscillating magnetic field, which activation unit is formed of a material that has influence of the oscillating magnetic field generated by the coils.

Hereby, it is achieved that a highly efficient indication of movement of an activation unit can be achieved, with the possibility of achieving a number of different activation signals. The use of oscillating AC voltage at the coil leads to an oscillating magnetic field. The influence of an oscillating magnetic field can be achieved by many different materials as long as the materials have influence of the magnetic fields such as magnetic

or electric conductivity. As the activation unit has influence on the magnetic field, it is relatively easy, by measuring the oscillating voltages or current at the coils, to indicate current or voltage change because of the influence of the magnetic field has increased or decreased the measured current or voltage. In this way, it is possible to build an input device where an activation unit can be indicated even if the activation unit is in some distance from a coil. Therefore, by using a number of coils, the exact position of the activation unit can be indicated. This can be achieved because the activation unit will probably influence the magnetic field in more coils at the same time.

In a possible embodiment for the invention the input device can be integrated in a mouth cavity, which input device is activated by the activation unit, which activation unit is fastened to the tongue. Hereby, it can be achieved that a person can use his or her tongue as an activation tool for an external device. That can be derived if a person is trained to use his/her tongue. It is possible to find materials which can be used at the tongue of a human being, which materials are biocompatible.

The multilayer printed circuit board can comprise a stack of layers, which layers comprise a substrate layer covered with a first conducting coating layer on a first side and with a second conducting coating layer on a second side, which conducting layers are forming the turns, which adjacent printed circuit board layers are bonded together by a bonding layer, wherein electrical connections between conducting coating layers are provided by interlayer connection means, preferably as conducting through plated holes and/or through plated blind holes. By using a multilayer printed circuit board for forming the coils, it is possible to achieve a large number of turns in a relatively small coil. The production of multilayer circuit boards is well-known, and it is also well-known how to produce coils by forming a number of inner layers with the turns. These inner layers are interconnected by wire holes which can be formed in two different ways. Thus, there may be connection holes which are relatively large or blind wire holes under the surface of the printed board, to which blind wire holes there is no access from the outside. The number of turns of the coils and also the size of the coils can be decreased in the future when new technology for producing printed circuit boards is developed. Otherwise, if a smaller coil has to be used, this coil might be produced as an integrated

circuit because in an integrated circuit, conductive tracks of three microns with three microns isolation are state-of-the- art.

At least one coil can comprise a total number of turns of at least 20, preferably more than 50. The number of turns has direct influence on the size of the measured signal. Therefore, by developing a good input device, a skilled man would go for the highest number of turns. Using a low number of turns will give a relatively weak signal, and the signal would then have to be selected from noise picked up by the coils. The electronic device receiving the signals from the coils can of course use noise reduction circuits. Particularly if the activation of the coils is performed by a specific frequency, it is possible to use frequency filters for filtering out noise having different frequencies. For a skilled man, it is always the best solution to reach as many turns in the coils as possible to get the highest level of signal output from the coils.

At least two coils out of the plurality of coils can be arranged laterally offset so that turns thereof overlap. Operating with partly offset of some of the turns, it is possible to increase the area in which the activation unit can be detected. Operating with two coils which are both laterally offset in a direction to each other, it is probably possible to in- dicate the position of an indicating unit on a relatively long line between the two coils.

The coils can be arranged laterally offset in a non-overlapping arrangement. It is also possible to use the invention with non-overlapping of the coils in order to get clear signal difference from the activation of each of the coils. The use of non-overlapping or overlapping coils depends on the actual use.

The overlapping coils can be interlaced. If the coils are formed in a multilayer printed circuit, it is possible that some of the inner layers have a larger coil diameter than other layers. In that way, it is possible that the neighbour coil has the opposite design for achieving interlaced coils. This can be efficient for achieving information about the exact position of the activation unit.

The planar spirals of at least one of the coils can have an oblong shape. The use of coils having oblong shape also gives a position indication of the activation unit for the length of the oblong coil. Even outside the coil, some indication will be possible.

Four coils of oblong shape can form a first cross of coils, in which first cross of coils the smaller part of the oblong shaped coil is orientated towards a centre of the first cross. As the coils are oblong, it is possible to indicate the actual position of the activation unit. Therefore, movement in two axes can be indicated.

The first cross of coils can further comprises four circular coils placed between the oblong shaped coils, which first cross of coils forms a first pointing device. By using a cross of oblong shaped coils, it is possible to indicate movement in four different directions.. If further, four circular coils are placed between the oblong shaped coils, it is possible to indicate the position of the activation unit around a circle, and it is possible to indicate the distance from the centre. In that way, both the size of movement and the direction of movement can be indicated. An input device can be placed in the mouth of a human being, and the input device is generating a pointing device for a computer. Instead of controlling a computer pointing device, these signals could also be used for driving a wheelchair or for activating other kinds of electronic devices.

In an alternative embodiment for the invention four coils of oblong shape can form the first cross of coils, in which first cross of coils the smaller part of the oblong shaped coil is orientated towards a centre of the first cross, which first cross of coils further comprises a second cross of coils comprising further four oblong coils placed between the oblong shaped coils of the first cross of coil, which first cross of coils in combination with the second cross of coils forms a second pointing device. Placing further oblong coils between the first cross of coils will give that result by using the activation unit that there will be no areas between the coils where the activation unit is not detected. By using only the four coils in the pointing device, there will be a space between the coils where the activation unit will be difficult to detect but maybe not impossible as long as the activation unit is covering at least part of one of the coils. Placing extra coils between the existing coils, the activation unit will always be detected even with a better

signal noise representation so a more precise indication of the actual placement of the activation unit is achieved.

Coils of the first cross can be interlaced with the coil of the second cross. Further im- provements can be achieved if the coils are interlaced which is especially effective if a relative small activation unit is used.. By the interlaced coils, there will always be a response from both coils if the activation unit is placed there between.

In an alternative embodiment, only four interlaced coils can form a cross. This cross can then as well as already described measure the actual position of the activation unit both in terms of direction and size. Therefore, in this way, a kind of pointing device for activation is possible.

Two oblong shaped coils are formed along a common axis, which oblong shaped coils are orientated with the smallest diameter towards each other. Hereby, a caterpillar pointing device is formed. In this caterpillar pointing device, only a positive and negative direction can be indicated. But in use, one direction can be used for indicating size, and moving the caterpillar pointing device in the opposite direction could instead adjust a circular movement. In this way, it is possible to achieve vector information to a com- puter system. This vector information could as already described be used for controlling electronic devices, or it could be used for controlling a wheelchair.

A matrix of coils can form a keyboard, which coils are formed in rows. By an alternative embodiment, a matrix pad is formed which could be used as a keyboard e.g. for writing. The number of pads used at a time is relatively small, but e.g. sending a text message over a mobile phone only requires a small number of electric contacts. Using e.g. 10 different coils, it is possible to send a SMS message in this way.

The material of the activation unit can be formed of a biocompatible metal selected from the group of platinum, titanium, gold, stainless steel or any similar alloy. There are many different materials which can be used for the activation unit. The only limitation for the material is that it must have positive or negative influence of a magnetic field.

The object of this invention can also be fulfilled by the preamble to claim 14 if further modified by the input device where the coils can be under influence of an oscillating voltage for generating a oscillating magnetic field, which oscillating magnetic field is changed by movement of an activation unit near the coils, where the coils of the input device are forming a pointing device, by which pointing device at least two signals are achieved, representing a first and a second parameter.

The input device can be placed in a mouth cavity, where an activation unit (15) is attached to the tongue.

Within this application, it is understood that the planar coils are formed on the printed circuit board by conducting tracks extending from an external connection point to an internal connection point, the tracks forming a number of turns of the respective spiral. The principal axis of the coil formed by the at least one spiral is oriented essentially perpendicular to the plane of the printed circuit board intersecting the plane of the coil at a central point enclosed by the turns of the coil.

The input device comprises one or more sensor coils, i.e. inductors adapted to provide a signal in response to the proximity of an activation unit of magnetic or conductive mate- rial.

An input device according to the invention may be used as a device for entering spatial information in a discrete mode, such as with a keyboard, in a substantially continuous mode, such as with a pointing device, or a combination of these, wherein the mode may be selected according to the location of the activation unit on the interaction surface or by the gesture performed.

During operation, the input device generates signals corresponding to a signal response of the at least one coil to the proximity of the activation unit. The activation unit may be of a magnetic or a conductive material. The magnetic material may be a material having the properties of a magnet or may be a material capable of being magnetised or attracted by a magnet. Preferably, the magnetic material is merely capable of being magnetised or

attracted by a magnet as for example a soft ferromagnetic material. The signal response may be detected by variable inductance techniques.

The activation unit may be made of a soft ferromagnetic material (paramagnetic) that increases the inductance of the coil (positive activation). In principle, it is also possible to activate the coil with an activation unit made from a permanent magnet, also providing a positive activation. However, depending on the application, this may not be practical. For example, when using an input device according to the invention in a tongue control system, a permanently magnetic activation unit may be irritating in daily use, due to interference with magnetic items that a user might have to put into the mouth on a daily basis. Alternatively, the activation unit may be made of a conductive material (diamagnetic) that decreases the inductance of the coil (negative activation).

The signal response from the at least one coil is a maximum when the activation unit is placed at the centre of the coil. The signal response decreases with increasing distance between the activation unit and the centre of the coil.

For lateral movements of the activation unit on the interaction surface, three characteristic regions may be distinguished. In a core region close to the principal axis, the signal response is a maximum and varies only slightly with displacements of the activation unit. In a transition region, the signal response decreases with increasing distance between the activation unit and the principal axis of the coil. In a remote region at distances beyond the transition region, the activation unit is too far away from the principal axis to bring about a detectable signal response.

The input unit may be operated by applying an alternating current or voltage of constant amplitude to the at least one coil, thereby generating an alternating magnetic field depending on the inductance of the coil. An alternating voltage occurring over the coil may be measured according to Faraday's law V _em f = -L di/dt, where L is the inductance of the coil. Proximity of the activation unit to the coil may be detected by a change in the amplitude of the alternating current or voltage over the coil for a constant applied current, due to the inductive interaction between the coil and the material of the activation unit.

Producing the coils of the inductor unit by known pattern transfer techniques on a printed circuit board as the carrier for the at least one coil has the advantage of high reproducibility and control of the coil dimensions and shape both if there are several coils in the same inductor unit and when producing large numbers of identical inductor units.

Furthermore, a well-defined flat surface of the inductor unit is easily obtained when using printed circuit board for the carrier also in the case where the carrier is further encapsulated by a biocompatible or otherwise protective material. Thereby, an unob- structed movement of the activation unit over the interaction surface becomes possible and the distance between the activation unit and the coils is well-defined, thereby generating a reproducible and reliable signal according to the placement of the activation unit on the interaction surface.

A further important advantage of the input device according to the invention is that for the fabrication of the inductor coils of the inductor unit tedious winding of wires on a winding support is avoided. The coils are formed by conductive tracks provided on the printed circuit board acting as the wire support. Thereby, the need for a winding support of a given shape is eliminated, and a variety of coil shapes is easily obtained already at the design stage by merely drawing the layout of the pattern to be transferred to the printed circuit board.

Guiding means may be provided on the interaction surface marking selected regions on the interaction surface and/or the location of specific coils, thereby facilitating the local- isation and controlled placement of the activation unit by the user.

Further according to one embodiment of an input device according to the invention, the at least one coil comprises a first planar spiral and a second planar spiral arranged in different layers of the printed circuit board being a multilayer printed circuit board.

A coil may thus be build up of a plurality of spirals, each spiral comprising a number of turns, wherein different spirals are placed in different layers of the multilayer printed circuit board. By stacking a number of spirals in different layers of the multilayer

printed circuit board, the number of turns in the coil may be increased while keeping the footprint, i.e. the lateral extension of the coil in the plane of the input device small, thereby allowing to substantially increasing the sensitivity of the coils for a given footprint.

Further according to another embodiment of an input device according to the invention, the first and the second planar spirals are connected in series.

The spirals arranged in different layers of the multilayer printed circuit board are elec- trically connected to each other by interlayer connections. By way of example, a first spiral being wound inwardly starting from an external connection point towards an internal connection point may be connected to the internal connection point of a second spiral that is arranged in a second layer of the multilayer printed circuit board beneath or above the first spiral. The second spiral is wound outwardly starting from the internal connection point towards an external connection point, where the second spiral via an interlayer connection may be connected to a further spiral in a further layer of the multilayer printed circuit board.

In practice, the sense of curling of the first spiral is opposite to the sense of curling of the second spiral, so that the sense of the current around the principal axis of the coil is the same for both spirals. A coil comprising more than two spirals may be constructed as a stack of alternating first and second spirals having mutually opposite sense of curling and alternating being connected at internal and external connection points. Thereby it is achieved that the magnetic field generated by the current in all turns of the coil adds up constructively and that the signal response from each of the turns of the coil adds up to a correspondingly increased total signal response.

Further according to one embodiment of an input device according to the invention, the multilayer printed circuit board is a stack of a number of layers, each layer comprising a substrate layer partly covered with a first conducting coating layer on a first side and with a second partly conducting coating layer on a second side, adjacent printed circuit board layers being bonded together by a bonding layer, wherein electrical connections

between conducting coating layers are provided by interlayer connection means, preferably as conductively plated thru-holes and/or blind-holes.

The substrate layers may be made of a known printed circuit board material, such as FR4 or alike, or of a ceramic material. The substrate layer may be covered with a conducting coating, such as copper which may be patterned using known patterning techniques. In the current state-of-the-art, a typical resolution for patterning the conductive coating layers is achieved allowing for a conducting track width and isolating space width of 75 μm, respectively.

A number of substrate layers with the patterned conducting coating on either side may then be stacked, aligned with respect to each other and bonded together by an isolating bonding layer. Interlayer connections may be provided by wire holes through the stacked layers, wherein the interior side of the holes is plated with a conducting layer in electrical contact with connection points of the layers to be connected. The substrate layers may for some of the interconnections be designed as buried wire holes, which connect inner layers without any connection to the surface of the printed board.

On the outermost layers, the multilayer printed circuit board may be provided with spaces for attaching electronic components and/or microelectronic circuits, processors or alike.

Further according to one embodiment of an input device according to the invention, the at least one coil has a total number of turns of at least 20, preferably more than 50.

A coil with an increased number of windings may provide an increased magnetic field and consequently an increased signal response level. In practice, it has been shown that at least 20 turns may be required for achieving a detectable signal, and preferably more than 50 turns are required to achieve an acceptable signal-to-noise level.

Miniaturisation constraints may determine the lateral dimensions of the coil, while the patterning resolution of the employed patterning technology may determine the number of windings that may be provided in a planar spiral within given lateral dimension. Ac-

cording to the invention as mentioned above, the windings of the coil may be provided in different layers in a stacked arrangement of a plurality of planar spirals. Thereby, an increased number of windings is achieved while fulfilling the lateral dimension constraints of the miniaturisation requirements.

Further according to one embodiment according to the invention, an input device comprises a plurality of coils being arranged parallel to the interaction surface.

By providing a plurality of coils, the functionality of the input device may be enhanced. Depending on their arrangement, the coils may be independent or mutually coupled. The signal response from each of the coils may be used isolated, for example when using individual coils as the keys in a keypad. Alternatively, the signal response from a given coil in combination with the signal response from other coils in the vicinity can be detected, for example when determining the position of the activation unit using signals from at least two coils, where the signal levels depend on the distance between the activation unit and the respective coil generating the signal.

Typically, the coils are addressed and read out individually using switch arrays, but a large variety of multiplexing and de-multiplexing schemes may be conceived for driv- ing the plurality of coils and reading the signal response there from.

Further, according to one embodiment of an input device according to the invention, the coils are arranged laterally offset in a non-overlapping arrangement. According to this embodiment, a number of coils may be arranged on the carrier adjacent to each other.

According to one possible embodiment, all the coils on a carrier have essentially the same shape and dimensions, wherein the coils are arranged adjacent to each other on a regular grid, so as to essentially cover the interaction surface only leaving small areas uncovered which may be used e.g. for providing interlayer connections. The grid may for example be a rectangular grid, or a triangular grid. The coils arranged on that grid may have a circular, elliptic, triangular, rectangular, hexagonal or otherwise polygonal shape.

By arranging the coils in a non-overlapping arrangement on a multilayer printed circuit board carrier, each of the coils may comprise spirals in all layers to the full extent of the footprint available for that coil. Thereby, each of the coils may be provided with a maximum of windings and the signal response from that coil is maximised for the given footprint when the activation unit is placed near the principal axis of the coil.

Further according to one embodiment of an input device according to the invention, at least two coils out of the plurality of coils are arranged laterally offset so that turns thereof overlap.

By overlapping the coils, the transition region is extended, i.e. the activation unit may be detected at larger distances from the principal axis of the coil than with comparable non-overlapping coils. Furthermore, a distance-dependent signal response is provided over a larger range of distances as compared to non-overlapping coils. This is particu- larly advantageous for providing substantially continuous signals, for example when using the input device as a pointing device when controlling external devices, such as a pointer on a computer screen, prosthesis or a wheelchair.

The activation unit may be detected in the transition region of more than one coil, and the position and movements of the activation unit in a pre-determined coordinate system may be determined from the distance-dependent signals of the involved coils.

Further according to one embodiment of an input device according to the invention, the overlapping coils are interlaced. In an interlaced arrangement of coils, turns of the first planar spiral of one coil are arranged overlapping with and sandwiched between turns of first and second planar spirals of another coil. By this arrangement, the coupling between the overlapping coils may be increased as compared to non-interlaced overlapping coils of essentially the same geometry. Furthermore, the interlaced arrangement is particularly advantageous for coils that are built up from more than two spirals each, because the difference in distance in axial direction between the coil and the interaction surface is reduced to a minimum.

Further according to one embodiment of an input device according to the invention, the planar spirals of at least one of the coils have an oblong shape. Thereby, a larger transition region is achieved in the direction of the elongation as compared to a circular coil of comparable dimensions. An example of an oblong shape is an oval shape. Another example of an oblong shape is a drop like shape. As explained above, an enlarged transition region provides an extended range of distances between the activation unit and the principal axis, in which range the activation unit is detectable, and the signal response from the coil is distance dependent.

According to a further aspect of the invention, an inductor unit for an input device according to the invention is provided.

According to yet another aspect of the invention, a tongue control system is provided for controlling an external device by the movements of a tongue, the tongue control sys- tern comprising an input device according to any of the claims 1-12, wherein the inductor unit is integrated in a mouth cavity arrangement of the tongue control system, preferably as a palatal arrangement, and the activation unit is attached to the tongue.

An input device according to the invention is well suited to fulfil the requirements with respect to functionality and miniaturisation of an inductive tongue control system. A tongue control system comprising the input device according to the invention furthermore has the advantage that a user is provided with a smooth interaction surface with high sensitivity which can be fabricated with high precision at an industrial level.

Further according to one embodiment of a tongue control system according to the invention, the material of the activation unit is a biocompatible metal selected from the group of platinum, titanium, gold, stainless steel or any similar alloy or a biocompatible conductive polymer.

The invention is explained in detail below with reference to the drawings. The drawings show in

Fig. 1 shows a schematic view of a coil for an input device according to one embodiment of the invention comprising four spirals connected in series,

Fig. 2 shows a sectional perspective view of a multilayer circuit board for a carrier in an inductor unit according to another embodiment of the invention,

Fig. 3 shows an arrangement of test coils on a multilayer printed circuit board carrier,

Fig. 4 shows a schematic view of a coil and an activation unit in proximity of the coil,

Fig. 5 shows a graph of the relative activation signal as a function of the lateral offset of the activation unit with respect to the principal axis of three coils,

Fig. 6 shows an inductor unit for a tongue control system according to an embodi- ment of the invention comprising five printed circuit board carriers, and

Fig. 7 shows a schematic view of an input device according to one embodiment of the invention.

Fig. 8 shows a pointing device with a concentric level of activation.

Fig. 9 shows an example of a pointing device.

Fig. 9 shows an example of a pointing device with interlaced coils.

Fig. 10 shows an example of a caterpillar pointing device with two coils.

Fig. 11 shows a pointing device with the function of interpolation of directions of a ten coil keyboard.

Fig. 12 shows an example of a keyboard with eight coils.

Fig. 13 shows a possible embodiment for the invention by using a cross made of four longitudinal coils.

Fig. 14 shows an alternative embodiment to the invention shown in Figure 13.

Fig. 15 shows a possible embodiment of the invention.

Fig. 1 shows a coil 1 that is built from four or more planar spirals 2a, 2b, 2c, and 2d each having an internal connection point 3a-3b and an external connection point 4. The spirals are arranged in a stack of different layers of a multilayer printed circuit board and connected in series by interlayer connections 5a, 5b, 5c.

Starting from external connection point 4a, a first spiral 2a winds inwardly towards an internal connection point 3 a, which via an interlayer connection 5 a is connected to the internal connection point 3b of a second spiral 2b. The spiral is formed by a conductive track 7 patterned in a conductive coating layer on a substrate material of the printed circuit board. Adjacent turns are separated by a spacing 8 between tracks 7.

From point 3b, the second spiral 2b winds outwardly towards the external connection point 4b of the second spiral 2b, where the second spiral via a further interlayer connection 5b is connected to a further spiral 2c, via a further connection 5 c being connected to spiral 2d.

The sense of curling of the first spiral 2a is opposite to the sense of curling of the sec- ond spiral 2b, so that the sense of the current around the principal axis 9 of the coil 1 is the same for both spirals 2a, 2b. Accordingly, when following the path of the current through the coil further down in the stack, the sense of curling of adjacent spirals alternates, thus maintaining the sense of the current around the principal axis 9 of the coil 1.

According to one embodiment, the at least one coil 1 is provided on a multilayer printed circuit board 20, the coil 1 comprising a number of spirals 2 arranged in different layers 21 - 25 of the multiple layer printed circuit board 20.

The multilayer printed circuit board 20 shown in Fig. 2 is a stack of five layers 21 - 25, each layer 21 - 25 comprising a substrate layer 10 covered with a first conducting coating layer 11 on a first side and with a second conducting coating layer 12 on a second side, adjacent printed circuit board layers 21/22, 22/23, ... 24/25 being bonded together by a bonding layer 13, wherein electrical connections between conducting coating layers 11,12 are provided by interlayer connection means 5, preferably as conductively plated thru-holes and/or blind-holes.

The spirals 2 may be fabricated in conductive coating layers 11, 12 of about 30μm thickness with a width of the track 7 of down to 75 μm and a width of the spacing 8 of down to 75 μm. These dimensions are close to the patterning resolution currently achieved by the state-of-the-art for multilayer printed circuit board fabrication. Smaller dimensions are contemplated as fabrication technologies are improved to allow for the reliable and cost-effective production at a patterning resolution below 75 μm.

The substrate layers 10 may be made of a known printed circuit board material, such as FR4 or alike. Ceramic materials are also contemplated. The substrate layer 10 may be covered with a conductive coating 11, 12, material, such as copper or gold.

By stacking five substrate layers 10 provided with the patterned conducting coating 11, 12 on either side may then be stacked, aligned with respect to each other and bonded together by a bonding layer 13. Interlayer connections 5 may be provided by holes through the stacked layers, wherein the interior side of the holes is plated with a conducting layer in electrical contact with connection points of the layers to be connected. Alternatively, blind holes and/or so-called buried micro-vias may be used for electrically connecting selected conducting layers with each other.

The at least one coil 1 on the printed circuit board 20 is via leads 31, 33 on either end of the coil 1 connected to connection pads 32, for the connection with driver and read-out electronics (not shown).

On the outermost layers, the multilayer printed circuit board may also be provided with spaces (not shown) for attaching electronic components, such as surface mountable

components and/or microelectronic circuits, such as signal processors, integrated communication circuits or alike, to the multilayer integrated circuit board, thereby integrating at least parts of the required electronics for driving the coils, reading the signal response, processing the signal response to provide optionally amplified and/or digitised signals that can be communicated to the external device controlled by the input device.

Fig. 3 shows a printed circuit board comprising an arrangement of test coils Ll - L12 having different geometries. Table 1 summarises the geometry parameters for the coils Ll - L12. The printed circuit board has five substrate layers 10 (fig 2), each having a thickness of 150μm and being coated on either side with a conductive coating layer of 35μm thick copper. The spirals of the coils Ll - L12 are patterned in the conductive coating layer with a track width of lOOμm and a spacing width of lOOμm, except for the coils L4 and L5 that are patterned with a track width of lOOμm and a spacing width of 120μm. The coils Ll - L8 have ten spirals each, wherein the coils are stacked, curled and connected in series as explained for a coil with four spirals with reference to Fig. 1 above.

Table 1: Geometry for the coils Ll - L9

The test coils Ll, L2, L4, L6, L7, and L8 are examples of circular coil geometry having between 50 (L2) and 120 turns (L8).

The test coils L3 and L5 are examples of an oval shape of the coil.

The test coils L9 - L 12 are circular coils arranged in an overlapping arrangement of multiple coils. The test coils L9 - L12 have five spirals in a stacked arrangement, the spirals being curled and connected in series as explained above with reference to Fig. 1. The five spirals each of the two of the coils L9, Ll 1 are arranged in the first conductive layers 11 (fig 2), and the five spirals of each of the two other coils LlO, L12 are arranged in the second conductive layers 12 (fig 2). The coils overlap pairwise with each other, wherein the spirals of overlapping coils are interlaced with each other. Coil L9 overlaps with the coils LlO and L12, and coil LI l overlaps with coils LlO and L12,

whereas coil L9 does not overlap with coil Ll 1 and coil LlO does not overlap with coil L12.

The current in overlapping coils (L9/L10, L9/L12, L11/L10, L11/L12) is passed counter-rotatingly around the respective principal axes of the overlapping coils (L9/L10, L9/L12, Ll 1/LlO, Ll 1/L12) so that the current in the region of overlap has the same direction in both coils. For the same geometry of the coil if the no of spirals increases by reducing the with of the track and if the thickness of the PCB is reduced then the inductance increases exponently with these changes.

The proximity of the activation unit is detected as illustrated schematically in Fig. 4.

Passing an alternating current i through the coil 1 generates a magnetic field as indicated by flux lines 16. In the absence of an activation unit 15, the coil 1 has an induc- tance L. According to Faraday's law, an alternating voltage Vemf = -L di/dt may be observed on the coil 1, where L is the inductance of the coil. For a given current, the amplitude of the alternating voltage is thus a measure for the inductance of the coil 1.

In the absence of an activation unit 15, the coil 1 has an inductance Lb _ase - Bringing an activation unit 15 close to the coil 1 induces a change in the inductance of the coil 1, due to the inductive interaction between the coil 1 and the material of the activation unit 15. The change in inductance may be measured as a change in the amplitude of the alternating voltage Vemf over the coil for an applied current i with constant amplitude.

The coil 1 may be activated by an activation unit 15 made of a soft ferromagnetic material (paramagnetic) that increases the inductance of the coil (positive activation) or by an activation unit 15 made of a conductive material (diamagnetic) that decreases the inductance of the coil (negative activation). In principle, it is also possible to activate the coil 1 with an activation unit 15 made from a permanent magnet.

The activation effect depends on the conductivity and permeability of the material of the activation unit. Positive activation of approx. 20% can be achieved by a material with relative magnetic permeability higher than or equal to 100 and conductivity lower than

10 ³ S/m. A negative activation of approx. 10% can be achieved by a material with relative magnetic permeability of 1 and conductivity higher than 10 ³ S/m.

Table 2 shows the electrical parameters for the coils Ll - L9 that are shown in Fig. 2 and listed in Table 1. The data comprise the inductance Lb _ase for the non-activated coil

1 , the resistance R of the coil, the inductance L _ste ei and L _cop per for activation with a steel activation unit and a copper activation unit, respectively, as well as the corresponding values for relative activation A _re i(steel) = (L _ste ei - Lbase) / Lb _ase and A _re i(copper) = (L _cop per

- Lbase) / Lbase- The relative activation allows comparison of coils with different number of turns and different geometry.

Table 2: Electrical parameters for the coils Ll - L9

Fig. 5 shows for three of the test coils L3 (squares), L6 (circles), L9 (stars) the relative activation A _re i(steel) as a function of lateral displacement of the activation unit 15 with

respect to the principal axis of the coils L3, L6, L9. The geometrical data and the electrical parameters of the three coils L3, L6, L9 are listed in Tables 1 and 2, respectively.

The activation unit used for the activation was a circular stainless steel puck with a di- ameter of 4 mm.

Measurements for the circular coils L6, L9 were performed from the area of maximal activation (i.e. the centre of the activation unit was on top of the centre of the coil) and ended when the activation unit was externally tangent with the coil edge. For measuring the oval coil L3, the activation unit was displaced laterally along the long axis (axis of symmetry) from the centre towards the pointed end.

Measurement of the inductance and resistance of the coil has been performed with an RLC meter. A voltage output (proportional with the coil inductance) from the RLC me- ter could be monitored on an oscilloscope.

Fig. 6 shows an input device according to one embodiment of the invention for application in a tongue control system. The input device comprises five multilayer printed circuit board carriers 26 - 30 each carrying a different arrangement of coils adapted to per- form different functions. The carriers 26 - 30 are inclined with respect to each other to facilitate the placement of the inductor unit 6 in a user's palate 99. The input device comprises on carrier 30 a rosette coil arrangement 17 for use as a pointing device, on carrier 27 a matrix arrangement 18 of coils that may e.g. be used as a keypad, on each of the two carriers 28, 29 a so-called caterpillar device that is particularly useful for con- trolling movements of two coordinates, and on carrier 26 two circular coils that may be employed as individual switches.

Fig. 7 shows the input device of a possible embodiment for the tongue control unit. An activation unit 15 is attached to the tongue of a user. When the user slides the activation unit 15 over the interaction surfaces of the different carriers 26 - 30, the at least one coil 1 in proximity to the activation unit 15 is activated. In order to detect the activation, driver and read-out electronics 35, 36 may probe one coil 1 at a time, scanning all coils in the inductor unit 6 in a predetermined sequence using a multiplexing switch 37. Each

of the coils 1 may be probed by applying a sinusoidal alternating current with constant amplitude, thereby generating an alternating voltage across the coil 1. The amplitude of the alternating voltage may be measured and compared to a reference value for the amplitude of the voltage of the coil 1 in the absence of an activation unit 15. The proximity of an activation unit 15, and thus the activation of the coil 1, may be detected as a deviation of the voltage amplitude from the reference value. The response signal for each of the coils 1 may be amplified in an amplification stage 38 and processed further in a signal processor 39. Processing may include background removal, filtering and coding the analogue signal into digital data. The signal processor 39 delivers its output to a com- municator unit 40 that may communicate the data, e.g. through a wireless connection, to an external device 42 in the form of data that require conversion at the external device 42 and/or control signals that may be used directly by the external device 42 to be controlled by the input unit according to the invention. Correspondingly, a power supply 41 for the support electronics 35 - 40 may be integrated with the input unit or supplied ex- ternally.

In analogy to the above-described use and operation of an input unit in a tongue control system, input units according to this or other embodiments of the invention may be used and operated in combination with a large variety of external devices including com- puters, consumer electronics, wheelchairs and prostheses.

It should be noted that the above-described driver and read-out electronics may be integrated with an input device according to the invention or provided in separate units in operative connection with the input device.

Without leaving the scope of the present invention, multiple other schemes for driving and reading the coils of the inductor unit may be contemplated regarding both multiplexing and de-multiplexing for probing the inductance of the coils, as well as with respect to amplification, signal processing and communicating the data and control sig- nals to an external unit.

Fig. 8 shows a pointing device with a concentric level of activation 102. The pointing device 102 comprises a cross of longitudinal coils 104, 106, 108 and 110. The pointing

device 102 further comprises circular coils 112, 114, 116 and 118. Furthermore, a number of wire holes 120 are indicated in the printed circuit board which is forming the pointing device 102. Furthermore, connection holes 122 are indicated. The coils are attributed to eight main directions with 45 degrees there between indicated by arrows 124. The coils 104,106,108,110,112,114,116,118 have areas of maximal activation and a transition area. Within a first inner circle 125, pointer translation is obtained when the activation unit slides along the surface of the oval coils 104,106,108,110. If the activation unit is placed between the axes of the two neighbouring oval coils, a variable activation signal is generated in both coils which encodes the direction between the two main directions. Within the bigger circle 126, pointer translation is possible along the eight main directions indicated by arrows 124. If the activation unit is placed between two of the main directions of neighbouring oval coils 104,106,108,110 and round coils 112,114,116,118, a variable activation signal is generated in both coils that encodes the direction between corresponding 90 degrees and 45 degrees main directions.

Fig. 9 shows an example of a pointing device with interlaced coils 132. The pointing device 132 comprises four interlaced coils 134, 136, 138 and 140. Furthermore, wire holes 142 are indicated which perform interconnection between inner layers in the multilayer board. A cross of arrows 144 is also indicated.

Interlaced coils 134,136,138,140 are used in a configuration which represents an alternative to the embodiment for the invention shown at Fig. 8. In operation, the maximum signal can be achieved if an activation unit is placed above the centre of the coils 134,136,138,140. If the activation unit is placed between two of the coils in the transit area, a variable activation signal is generated in both coils that encodes a direction between the corresponding two main directions. The interlaced coils have a larger transition area and a reduced number of coils which allows a more precise translation of the pointer. Movement of the activation unit is performed over a larger area. Depending on the actual use of the pointing device 132, speed can be encoded in the duration of the activation. This design of a pointing device can be extended to a network of a larger number of sensors. Interlacing of coils can be exploited to combine the area of maximal activation with the transition area such that it provides the best signal which may encode both position and speed of the pointer.

Fig. 10 shows an example of a caterpillar pointing device with two coils. Two concentric coils 154 and 156 are pointing towards each other. Wire holes 158 and connection points 160 are also shown at Fig. 10. The pointing device shown at fig. 10 can produce a linear translation of the pointer. The linear translation is fundamental decomposition of the 2D movement. Any points in the two-dimensional space can be reached from the initial position by using this linear translation. Another fundamental decomposition of the 2D movement is the rotation plus linear translation. The caterpillar pointing device uses this type of decomposition.

Fig. 11 shows a pointing device with the function of interpolation of directions of a ten coil keyboard 200. Fig. 11 shows a matrix comprising three rows of coils. The first row is formed of coils 202, 204, 206 and 208. The second, middle row is formed of coils 210,212,214, and the third, upper row is formed of the coils 216,218, and 220.

The keyboard 200 processes the movement of the activation unit along the x- and the y- axis from coil 202 to the coil 214.

Fig. 12 shows an example of a keyboard with eight coils 250. The coils 252,254,256 form a lower row where coils 258, 560,262 form a middle row, and where coils 264 and 266 form an upper row.

Also as shown in Fig. 12, on/off functions could be achieved, or a direction could be indicated starting from one of the coils and ending at one of the other coils. An alternative embodiment for the keyboard shown at Fig. 11 and Fig. 12 is that writing should be possible using the same technology as a SMS technology for a mobile phone. This could be highly efficient for multi-disabled persons if they by a matrix pad placed in their mouth could be able to write a primitive text.

Figure 13 shows a possible embodiment for the invention by using a cross 300 made of four longitudinal coils 304, 306, 308 and 310. The oblong coils are pointing their narrow parts towards each other.

By forming a cross of drop-formed coils as shown at figure 13, it is possible by a relatively large pointing device to read a nearly perfect detection of the pointing device in relation to the coils 304, 306, 308 and 310.

Figure 14 shows an alternative embodiment to the invention shown in Figure 13. Figure 14 shows a cross of coils 320 which comprises as shown at figure 13 the coils 304, 306, 308 and 310. Figure 14 shows a further cross of coils 322, 324, 226 and 328. The coils from the second cross are interlaced with the first set of coils so that if the coils 304, 306, 308, 320 in a multi-layer printed circuit form maybe a first and second layer then the coils 322, 324, 326, 328 can form the second and the third layer. In this way it can be achieved that the coils are interlaced but also totally electrically isolated from each other because a layer of pre-preg will always isolate the two different kinds of coils. Producing a multi-layer of maybe 50 layers or even more, there could be achieved relatively effective signals from the coils if a pointing device is placed near the surface of the coils. By the invention shown at figure 14, even relatively small pointing devices can be indicated highly effective. Thereby a very small but highly effective input device can be achieved which could be used in a lot of different situations.

Figure 15 shows a possible embodiment of the invention 350 which comprises coils 304, 306, 308 and 310 as shown at the figure 13 and 14. Between these coils are placed coils 352, 354, 356 and 358. These coils are placed in a minimal distance to the first set of coils but the coils are not interlaced. Non-interlaced coils could also be produced so that different layers of a multi-layer comprise the different crosses of coils. By placing the coils independently of each other without interlacing the coils, it is possible to achieve a much clearer signal from the coils, so that a more easy and precise detection of a pointing device is possible.

The different pointing devices or matrix pads can be combined in a common input device which could be carried in the mouth of a person. This could be very important for disabled persons, but a mouth input device could also be important in other situations. As already described, it is possible to define a pointing device, and the pointing device could be highly efficient if a person is trained for using it. It should be possible e.g. to use the tongue combined with the input device to control an aeroplane. Typically, e.g. in

military fighters, the pilot have both his hands occupied with e.g. controlling the plane, the radio and weapon systems. Other functions could be controlled by his tongue.

This invention could be used in different critical environments such as e.g. in chemical productions where it is necessary to have access to a computer but where the harsh environment is destroying typical electronic devices. It should be possible by this invention to perform an input device that is totally protected against the harsh environment which could be activated by placing e.g. a pointing device at one or more fingers of glove carried by the personnel who has to operate in the harsh environment. Therefore, this could be very useful in chemical production lines where typical control of production facility takes place from a control system but in some situations you have to go closer to the process and provide a computer with input.

The input device could also be used in submarine environments. Divers, who have to control different electronic equipment, could use pointing devices at their glove and in that way use the pointing device e.g. for controlling a submarine system. Also activation of tools will be possible by using this input device which could be placed at the surface of the equipment and protected in such a manner so that the seawater will not harm the pointing device.

A further use of this input device could be on ships where the input device, well- protected, could be used for controlling different facilities on board a ship but which facilities have to be activated from the outdoor where the equipment now and then is in touch with salt water.

Further embodiments of the design of coils are of course possible. Instead of using printed circuit boards, integrated technology could be used for forming the coils. In that way, much smaller coils could be produced and by integrated coils in the input device, much more information could be achieved.