A CAPACITIVE TOUCH AND PRESSURE SENSOR

A method detects a pressure and a touch and/or presence in a vicinity. A capacitive layered sensor structure includes an electrically permeable and conductive layer, an electrode layer having a first electrode. Between these layers is a first insulating layer. The capacitive layered sensor structure includes a compressible insulating layer between the electrode layer and an electrically conductive layer. The method measures a first capacitance value of the first electrode using the capacitive layered sensor structure, and a second capacitance value of the first electrode using the capacitive layered sensor structure. A determination is made whether the first value is at most equal to a first threshold and at least equal to a second threshold that is greater than the first threshold. An arrangement includes the capacitive layered sensor structure and an electronic arrangement to perform the method. A computer program causes a computer to perform the method.

TECHNICAL FIELD

The invention relates to sensors for sensing touch and pressure. The invention relates to tactile sensors. The invention relates to pressure sensors. The invention relates to capacitive sensors for sensing touch and pressure. The invention relates to methods for capacitively measuring touch and pressure. The invention relates to computer programs used in connection with measuring touch and pressure.

BACKGROUND

Many user interfaces require sensing touch without a pressure and pressure separately. For example a user may move his/her finger on a surface, whereby a touch with the surface indicates a location of the finger. This kind of touch is made substantially without pressing the surface. Moreover, to make a selection, the user may press the surface e.g. by his/her finger. This implies a pressure applied onto the surface. Moreover, from a measured signal, the occurrences of only touch and pressing should be separable. More preferably, the pressure applied should be measurable at least with some accuracy, i.e. better accuracy than a binary application of pressure or not. A capacitive sensor for measuring pressure is known e.g. from the applicant's international publication WO 2018/011464.

Often a sensor for measuring both a touch and a pressure is complex, whereby such a sensor is also expensive. In practice, complexity of such sensors is a hindrance for their wide applicability.

For these reasons, a purpose of the present application is to present a simple sensor arrangement for sensing both touch and pressure. More specifically, to present a simple sensor arrangement for sensing, at a first instance of time, a touch substantially without application of pressure, and at a second instance of time, an application of a pressure. An operating principle of the sensor arrangement is capacitive.

SUMMARY

As gist of the invention is the use of a capacitive layered sensor structure comprising an electrode layer comprising a first electrode and an electrically permeable and conductive layer. Touch and pressure can be determined from capacitances of the first electrode relative to the surroundings. A first purpose of the electrically permeable and conductive layer, related in particular to the permeability of the layer, is to pass an electric field through the electrically permeable and conductive layer so as to capacitively sense, by the first electrode that is located on a first side of the electrically permeable and conductive layer, an object that is located on a second, opposite, side of the electrically permeable and conductive layer. A second purpose of the electrically permeable and conductive layer, related in particular to the conductivity of the layer, is to form a capacitance in between the electrode and the electrically permeable and conductive layer itself. The capacitive layered sensor structure can be used for such measurements. E.g. an electronic arrangement can be configured to measure a capacitance of the first electrode indicative of a touch (or presence in a vicinity) and another capacitance of the first electrode indicative of a pressure.

A less complex sensor arrangement for the purpose is presented in independent claim1of the present application as filed. That sensor arrangement comprises a capacitive layered sensor structure as detailed in the claim1. Moreover, such a capacitive layered sensor structure can be used to measure both a touch and a pressure as detailed in an independent method claim13or the application as filed. Moreover, the method can be run on a computer by running a computer program on a computer. Such a computer program is detailed in claim16of application as filed.

In the figures, the direction Sz indicates a direction of a thickness of the capacitive layered sensor structure. The directions Sx and Sy are perpendicular to each other and to Sz.

DETAILED DESCRIPTION

FIG. 1ashows, in a side view, an arrangement100for capacitively detecting touch at a first time and pressure at a second time. The arrangement100comprises a capacitive layered sensor structure110(on the left hand side of theFIG. 1a) and an electronic arrangement120(on the right hand side of theFIG. 1a). The electronic arrangement120is configured to capacitively detect touch at a first time and pressure at a second time by using the capacitive layered sensor structure110.

The capacitive layered sensor structure110comprises an electrode layer300comprising a first electrode301and a first wire351attached to the first electrode301. To measure touch or pressure, a capacitance of the first electrode301is measured. The capacitance of the first electrode301is measured relative to surroundings, e.g. relative to at least the electrically permeable and conductive layer410. The first wire351connects the first electrode to measurement electronics, e.g. the electronic arrangement120. The electrode layer300may comprise a substrate390(seeFIGS. 1a, 1b, 2a, and2b), onto which the first electrode301and the first wire351may have been printed. In the alternative, the first electrode301may be arranged (e.g. by printing) onto a first insulating layer210(as inFIG. 1c) or a second insulating layer220(seeFIG. 2c). Thus, the first electrode301and the first wire351may constitute the electrode layer300; or electrodes and wires may constitute the electrode layer300; or the electrode layer300may further comprise a substrate. As indicated inFIGS. 1aand 2a, the electrode layer300may comprise a second electrode302. If the electrode layer300comprises the second electrode302, the second electrode is arranged a distance apart from the first electrode301. As an example, the second electrode302may be arranged at least 0.5 mm apart from the first electrode301.

As indicated inFIG. 3a, an electrode layer300may comprise e.g. twenty-five electrodes. As indicated inFIG. 3b, an electrode layer may comprise e.g. sixteen electrodes. For clarity,FIGS. 3aand 3bdo not show the layers above the electrode layer300. A purpose of the electrode layer300is to provide the electrode(s) of the capacitive layered sensor structure110. Circles shown on the electrodes inFIGS. 3aand 3bindicate examples of locations for wires, if wires are connected to the electrodes by conductive adhesive. As an alternative, wires may be arranged (e.g. printed) directly on the same substrate as the electrodes.

Referring toFIGS. 1ato 1c, the capacitive layered sensor structure110comprises a first insulating layer210. The first insulating layer210is arranged in between the electrode layer300and an electrically permeable and conductive layer410in the direction Sz of the thickness of the capacitive layered sensor structure110.

As for the direction Sz of thickness of the capacitive layered sensor structure110, Sz may refer to the direction of the thickness of a planar capacitive layered sensor structure110. The structure110is preferably deformable. Therefore, in use, the structure110needs not to be planar. However, a non-planar sensor structure110may be deformable to a planar shape. In non-planar structures, the direction Sz of the thickness of the structure depends on the point of observation. Moreover, the term thickness of a planar structure refers to the smallest of three orthogonal dimensions of the planar structure.

A first purpose of the of the first insulating layer210is to electrically insulate the electrode(s)301,302, from the electrically permeable and conductive layer410in order to form a capacitance in between the first electrode301and the electrically permeable and conductive layer410. The capacitive layered sensor structure110may comprise a second insulating layer220arranged such that the electrode layer300is arranged in between the first210and second220insulating layers in the direction of thickness of the thickness of the capacitive layered sensor structure110. A second purpose of the first insulating layer210and the second insulating layer220, in combination, is to act as a compressible layer (or as compressible layers), i.e. a layer that is deformed by application of pressure. As known e.g. from the prior art publication mentioned above, a change in a distance between the first electrode301and another conductor (e.g. layer400,410) changes the capacitance therein between. For this functionality, it suffices that only one of the insulating layers210,220is compressible, however, both of them may be compressible. Therefore, at least one of the first insulating layer210and the second insulating layer220is compressible. In other words, at least one of the first insulating layer210and the second insulating layer220is configured to be compressed and deform by such a pressure that is to be detected by the capacitive layered sensor structure110.

Thus, in an embodiment, the first insulating layer210is compressible. In another or the same embodiment, the capacitive layered sensor structure110comprises a second insulating layer220that is compressible. In an embodiment, the first insulating layer210is not compressible and the capacitive layered sensor structure110comprises a second insulating layer220that is compressible. In an embodiment, the first insulating layer210is compressible and the capacitive layered sensor structure110comprises a second insulating layer220that is compressible. In an embodiment, the first insulating layer210is compressible and the capacitive layered sensor structure110comprises a second insulating layer220that is not compressible. In an embodiment, sensor structure110does not comprise the second insulating layer220. The insulating layer that is compressible (i.e. deformable) is arranged in between the electrode layer300and an electrically conductive layer. The first insulating layer is arranged in between the layers300and410; while the second insulating layer220, if present, is arranged in between the layers300and400. In this way, the capacitive layered sensor structure comprises an insulating layer (210,220) that is compressible and that is arranged in between the electrode layer300and an electrically conductive layer (410,400). The electrically conductive layer (410,400) may be electrically permeable.

As indicated inFIG. 1d, also the conductive parts of the electrically permeable and conductive layer410may be printed onto a substrate212. In such a case, also the substrate212may be arranged in between the electrically permeable and conductive layer410and the electrode layer300in the direction of thickness Sz. However, if a substrate212is used, it may be used to cover the electrically permeable and conductive layer410, i.e. it may be used as the third insulating layer230ofFIG. 1b.

If the electrode layer300comprises the substrate390, as inFIGS. 1aand 1b, the first electrode301may be arranged in between the substrate390and the first insulating layer210in the direction of thickness Sz (not shown).

The capacitive layered sensor structure110comprises the electrically permeable and conductive layer410. A first purpose of the electrically permeable and conductive layer410, related in particular to the permeability of the layer410, is to pass an electric field through the electrically permeable and conductive layer410so as to capacitively sense, by the first electrode301, which is located on a first side of the electrically permeable and conductive layer410, an object (e.g.600, seeFIG. 3a) that is located on a second, opposite, side of the electrically permeable and conductive layer410. A second purpose of the electrically permeable and conductive layer410, related in particular to the conductivity of the layer410, is to form a capacitance in between the electrode and the electrically permeable and conductive layer itself.

The electrically permeable and conductive layer410increases the capacitance of the first electrode when compared to situation without layer410, but reduces the amount of capacitance that a touch event is able to generate. Thus, a purpose of the electrically permeable and conductive layer410is to reduce the capacitance that a touch event generates. It has been noticed that without the electrically permeable and conductive layer410a touch could generate so large signals that it could be even greater than a small pressure. It is noted that a touch or a pressure may be made e.g. by a finger or by a whole hand, which affects the magnitude of the observed signal. Thus, a pressure with a finger could, without the electrically permeable and conductive layer410, imply a similar signal as a touch with a whole hand. Therefore, for purposes of reliably distinguishing touch and pressure, the electrically permeable and conductive layer410is applied. In particular, the electrically conductive property of the layer410reduces the signal level generated by a touch.

Moreover, it has been noticed that without the electrical permeability of the layer410, a layer that is only conducting would reduce the effect of touch to such a degree that touch could not be measured at all. The electrical permeability of the layer410has the effect that the touch affects the capacitance of the first electrode301. Thus, even if a purpose of the electrically permeable and conductive layer is to reduce the capacitance of the first electrode when touch is to be measured, a purpose is to reduce the capacitance only to a measurable level; i.e. not completely remove an effect of the touch on the capacitance.

With reference toFIGS. 4a1,4b1, and4d1, the pressure and touch by an object600are sensed in such a case that a part of the first insulating layer210and a part of the electrically permeable and conductive layer410are arranged in between the object600and the first electrode301. This applies also inFIGS. 4a2,4b2, and4d2.

Referring toFIGS. 1ato 1c, as well as to2ato2c, the arrangement100for capacitively detecting touch and pressure further comprises an electronic arrangement120. The electronic arrangement120is electrically coupled to the first electrode301in order to measure the capacitance of the first electrode301. The electronic arrangement120is coupled to the first electrode301via the first wire351. The first wire351may be seen as part of the electronic arrangement120or as part of the capacitive layered sensor structure110. In such a case, the first wire351of the electronic arrangement120is electrically coupled to the first electrode301.

Referring toFIGS. 2ato 2c, in an embodiment, the capacitive layered sensor structure110comprises a second insulating layer220. In such an embodiment, the electrode layer300is arranged in between the first insulating layer210and the second insulating layer220in the direction Sz of the thickness of the capacitive layered sensor structure110. As indicated above, in such an embodiment, at least one of the insulating layers210,220is compressible. Even if not shown inFIGS. 2ato 2c, also in embodiments comprising the second insulating layer, the electrically permeable and conductive layer410may be made onto a substrate212or comprise a substrate212as discussed above in connection withFIG. 1d.

A purpose of the of the second insulating layer220is to electrically insulate the electrode(s)301,302from environment. Electrical contacts to the electrodes in use might cause malfunction of the sensor arrangement100. Moreover, when the sensor structure comprises a first electrically conductive layer400, a purpose of the second insulating layer220is to insulate the electrode(s)301,302from the first electrically conductive layer400and in this way form a capacitance in between the first electrode301and the first electrically conductive layer400. As indicated above, a purpose of the second insulating layer220may be to act as the compressible layer or as one of the compressible layers, i.e. as a layer that is deformed by application of pressure.

As indicated by these functions, even if not shown in the Figures, the capacitive layered sensor structure110may comprise the second insulating layer220even if it does not comprise the first electrically conductive layer400.

With reference toFIGS. 1band 2b, in an embodiment, the capacitive layered sensor structure110comprises a third insulating layer230. In such a case, the electrically permeable and conductive layer410is arranged in between the third insulating layer230and the first insulating layer210. A purpose of the third insulating layer230is to insulate the electrically permeable and conductive layer410from the object600, of which touch or pressure is sensed. This improves the sensitivity of the arrangement100. As indicated inFIG. 1b, the capacitive layered sensor structure110may comprise the third insulating layer230even if it does not comprise the second insulating layer220. As indicated inFIG. 2a, the capacitive layered sensor structure110may comprise the second insulating layer220even if it does not comprise the third insulating layer230. As indicated above, the third insulating layer230may be a substrate212of the conductive parts of the layer410. A substrate212, if used at all, may also be arranged on the other side of the layer410(seeFIG. 1d). In such a case a third insulating layer230may be applied even if not shown inFIG. 1d. The conductive parts of the layer410may be directly printed on the first insulating layer210. Thus the layer210(or layers210,212,390) in between the electrically permeable and conductive layer410and the first electrode layer300may comprise multiple materials e.g. layers of different material. At least one of the materials is dielectric (i.e. electrically resistive); preferably all the materials are dielectric.

The different layers may be attached to each other with adhesive as known per se. However, for clarity, adhesive is not shown in the figures.

In an embodiment, the electronic arrangement120is electrically coupled to the electrically permeable and conductive layer410in order to measure the capacitance of the first electrode301relative to the electrically permeable and conductive layer410. A common potential, e.g. a ground potential, may be conducted to the electrically permeable and conductive layer410at least when measuring the capacitance of the first electrode301relative to the layer410. However, the electronic arrangement120need not be electrically coupled to the electrically permeable and conductive layer410. A capacitance that depends on the degree of deformation can be formed in between the first electrode301and a first electrically conductive layer400(seeFIGS. 2ato 2c) for measuring pressure, when the electronic arrangement120is not electrically coupled to the electrically permeable and conductive layer410.

Referring toFIGS. 4a1and4a2, the electronic arrangement120is configured to, at a first instance of time t1, measure a first value v1indicative of a first capacitance of the first electrode301. Moreover, the electronic arrangement120is configured to determine that the first value v1is at most equal to a first threshold thf. As indicated above and inFIGS. 4a1and4a2, when (i) only touch of an object600, or (ii) such a small pressure that is classifiable as being indicative of touch (the pressure being generated by the object600), or (iii) the presence of the object600in a vicinity of the first electrode301is being measured, a value v1of a signal measurable from the first electrode301is reasonable small, i.e. at most equal to a first threshold thf. This is in contrast to measuring pressure (or a higher pressure), which results in a greater value of the signal. Thus, the first value v1being at most equal to the first threshold thfis indicative of an object not pressing (not at all or not hard) the layered sensor structure110(i.e. touching). The value may be a value of a voltage or a current, if the capacitance of the first electrode is sent as an analogue signal. In the alternative, the value may be a digital value of the capacitance.

However, since the touch of an object600, or such a small pressure that is classifiable as being indicative of touch (the pressure being generated by the object600), or the presence of the object600in a vicinity of the first electrode301is being measured, the signal is somewhat higher than in case nothing is measurable. In particular, in such a case, the value v1measurable from the first electrode301is at least equal to a second threshold tht. The second threshold can be called a touch limit. Such a touch limit (i.e. second threshold) can be used to differentiate a touch (as inFIG. 4a1or4a2) from the absence of the object600(FIG. 4c1or4c2). The first value v1being at least equal to a second threshold thtis indicative of an object being present (i.e. touching). As indicated above the term “touch” may therefore refer to the three cases:a contact of an object600with the layered sensor structure110without any pressure being applied, orsuch a small pressure that is classifiable as being indicative of touch (the pressure being generated by the object600), orthe presence of the object600in a vicinity of the first electrode301without a physical contact in between the object600and the layered sensor structure110.

Determining that the first value v1is at most equal to the first threshold thfand at least equal to the second threshold thtmay take place at the first time t1, or the determining may take place later, e.g. in a computer. However, preferably, determining that the first value v1is at most equal to the first threshold thfand at least equal to the second threshold thttakes place when the object600is touching (or mildly pressing) the capacitive layered sensor structure110, as indicated inFIGS. 4a1and4a2.

Referring toFIGS. 4b1and4b2, the electronic arrangement120is configured to, at a second instance of time t2, measure a second value v2indicative of a second capacitance of the first electrode301. Moreover, the electronic arrangement120is configured to determine that the second value v2is more than the first threshold thf. As indicated above, such large values are indicative of a pressure (possibly reasonable high pressure) being applied at a surface of the sensor structure110at a location L that overlaps with the first electrode301.

Determining that the second value v2is more than the first threshold thfmay take place at the second time t2, or the determining may take place later, e.g. in a computer. However, preferably, determining that the second value v2is more than the first threshold thftakes place when the object600is pressing the capacitive layered sensor structure110, as indicated inFIGS. 4b1and4b2.

As detailed above, in this way, the first value v1is indicative of a touch (or being in a vicinity or a mild pressure) and the second value v2is indicative of application of a pressure (e.g. a higher pressure).

Referring toFIGS. 2ato 2cand 4a2,4b2,4c2, and4d2, preferably, the capacitive layered sensor structure110comprises a first electrically conductive layer400. In such a case, the second insulating layer220is arranged in between the first electrically conductive layer400and the electrode layer300, to insulate the electrode layer300from the first electrically conductive layer400. A purpose of the first electrically conductive layer400is to reduce disturbances measurable by the first electrode301. Since the determination of both a touch and a pressure requires a reasonably accurate result, reduction of disturbances, and hence the presence of the first electrically conductive layer400, is preferable.

The first electrically conductive layer400need not be electrically permeable, since, in general, touch is not sensed from the other side of the capacitive layered sensor structure110. However, at least in case touch should be sensed from both sides, also the first electrically conductive layer400could be made also electrically permeable. For manufacturing reasons, the first electrically conductive layer400may be electrically permeable even if touch is not sensed from the other side.

When the capacitive layered sensor structure110comprises the first electrically conductive layer400, the electronic arrangement120may be electrically coupled also to the first electrically conductive layer400in order to measure the capacitance of the first electrode301relative to the first electrically conductive layer400. As indicated above, measuring in particular the capacitance of the first electrode301relative to the first electrically conductive layer400improves accuracy. A common potential, e.g. a ground potential, may be conducted to both the first electrically conductive layer400and the electrically permeable and conductive layer410at least when measuring the capacitance of the first electrode301relative to the layers400,410.

When the capacitive layered sensor structure110comprises the first electrically conductive layer400, the electronic arrangement120may be, but need not be, coupled to the first electrically conductive layer400. If coupled, a capacitance in between the first electrode301and the first electrically conductive layer400may be formed. If not coupled, the first electrically conductive layer400acts mainly as a shield to reduce disturbances.

The electronic arrangement120may be configured to send an output signal Sout. In an embodiment, the output signal Soutis indicative ofthe first value v1being at most equal to the first threshold thf,the first value v1being at least equal to the second threshold tht, andthe second value v2being more than the first threshold thf.

In many applications it may be feasible to have information also about the value of the pressure applied on the first electrode301, not just the information that a pressure is applied. Therefore, in an embodiment, the output signal Soutis indicative of the second value v2.

As indicated above, both touch and pressure can be measured using the capacitive layered sensor structure110. When using the capacitive layered sensor structure110as indicated above, a method for detecting a touch and a pressure is performed. Such a method for detecting a touch and a pressure comprises arranging available a capacitive layered sensor structure110, of which details have been given above.

Referring toFIGS. 4a1and4a2, in an embodiment, the method comprises, at least at a first time t1, when an object600having a volume of at least 1 (cm)3and a dielectric constant of at least 10 is arranged in the vicinity of the first electrode301or touches a surface of the capacitive layered sensor structure110at such a location L that overlaps with the first electrode301such that a part of the first insulating layer210and a part of the electrically permeable and conductive layer410are arranged in between the object600and the first electrode301, and when a pressure is not applied on the first insulating layer210or at most a mild pressure is applied on the first insulating layer, measuring a first value v1indicative of a first capacitance of the first electrode301using the capacitive layered sensor structure110. This may take place at the first time t1, as discussed above and indicated inFIG. 4a2. The embodiment further comprises determining that the first value v1is at most equal to a first threshold thfand at least equal to a second threshold tht.

The size of the object600, as detailed above, corresponds a reasonable small finger of a typical user. The dielectric constant of the object600, as detailed above, corresponds to a dielectric constant of a part of a finger.

An embodiment of the method comprises, at least at a second time t2, when the object600is compressing at least one of the first and the second insulating layers210,220at such a location that overlaps with the first electrode301such that a part of the first insulating layer210and a part of the electrically permeable and conductive layer410are arranged in between the object600and the first electrode301, measuring a second value v2indicative of a second capacitance of the first electrode301using the capacitive layered sensor structure110. This may take place at the second time t2, as discussed above and indicated inFIGS. 4b1and4b2. The embodiment further comprises determining that the second value v2is more than the first threshold thf. As detailed below, some small pressures may be classified as touch. Thus, at some other point of time (not shown), the object600may be mildly compressing at least one of the first and the second insulating layers210,220and the resulting capacitance may remain below first threshold thf.

This method may be reflected in the arrangement100. In particular, in an embodiment of the arrangement100, the capacitive layered sensor structure110and the electronic arrangement120are, in combination, configured in the following way:

[A] when the object600having a volume of at least 1 (cm)3and a dielectric constant of at least 10 is arranged in the vicinity of the first electrode301or touches a surface of the capacitive layered structure at such a location L that overlaps with the first electrode301such that a part of the first insulating layer210and a part of the electrically permeable and conductive layer410are arranged in between the object600and the first electrode301, and when neither the first insulating layer210nor the second insulating layer220is compressed, a value v1indicative of the capacitance of the first electrode301as measurable from the capacitive layered sensor structure110by the electronic arrangement120is at most equal to the first threshold thfand at least equal to the second threshold the. Moreover,

[B] at least one of the first insulating layer210and the second insulating layer220is compressible by the object600at such a location L that overlaps with the first electrode such that a part of the first insulating layer210and a part of the electrically permeable and conductive layer410are arranged in between the object600and the first electrode301, in such a way that a value indicative of the capacitance of the first electrode301as measurable from the capacitive layered sensor structure110by the electronic arrangement120is more than the first threshold thf. It is also noted that all compressions need not imply a capacitance above the first threshold thf, but at least a sufficiently high compression will result in the exceeding the first threshold.

As for the features [A] and [B] hereinabove, naturally the arrangement100does not necessarily measure these values at all times. But if, in the situations indicated inFIGS. 4a2and4b2, the value indicative of the capacitance would be measured by the electronic arrangement120, its magnitude would be as described above.

Examples of properties of the object600will be discussed below in connection with the method.

As indicated above and inFIGS. 4a2and4b2, touching (as opposed to pressing) can be determined from a reasonably small value of the signal. In addition and with reference toFIGS. 4a2and4c2, touching (as opposed to absence of both touching and pressing) can be determined from a reasonably large value of the signal. The reasonably large value may be e.g. larger than typical noise. Typically measurement results include noise. This is particularly true in capacitive measurements, since they are sensitive to disturbances in the measurement environment.

Referring toFIGS. 4c1and4c2, typically measurements are made also when no object600is touching or compressing the capacitive layered sensor structure110, in order to determine whether there is such an object600or not. Thus, an embodiment of the method comprises, when an object600having a volume of at least 1 (cm)3and a dielectric constant of at least 10 is not arranged in the vicinity of the first electrode301, measuring a third value v3of a third capacitance of the first electrode301. The method further comprises determining that the third value v3is less than the second threshold tht.

The meaning of the term “vicinity” may dependent on the user needs. In some measurements, a lack of touching may be determined, e.g. when the object600is not closer than 15 cm to the electrode. However, in some other measurements, a lack of touching may be determined, e.g. when the object600is not closer than 1 cm to the electrode. The value of the second threshold thtcan be used to define the meaning vicinity. It may be useful to define the second threshold thtin such a way that when a distance between the object600and the first electrode301is less than a one dimensional size (e.g. length or width) of the first electrode301, the resulting signal is at least equal to the second threshold tht. As an example, an object600having a volume of at least 1 (cm)3and a dielectric constant of at least 10 is not arranged in the vicinity of the first electrode301, when no object600having a volume of at least 1 (cm)3and a dielectric constant of at least 10 is arranged closer than 3 cm (or another distance discussed above, depending on needs) to such a part of a surface of the capacitive layered sensor structure110that overlaps with the first electrode301. Herein the term overlaps means that the overlapping parts are on top of each other in the direction Sz of thickness of the capacitive layered sensor structure110. Correspondingly, for purposes of definition, an object600having a volume of at least 1 (cm)3and a dielectric constant of at least 10 is arranged in the vicinity of the first electrode301, when the object600having a volume of at least 1 (cm)3and a dielectric constant of at least 10 is arranged at most 3 cm (or another distance discussed above, depending on needs) apart from such a part of a surface of the capacitive layered sensor structure110that overlaps with the first electrode301(i.e. the location L).

In an embodiment of the arrangement100, the capacitive layered sensor structure110and the electronic arrangement120are, in combination, configured to function in a corresponding manner. This manner is discussed above for the object600, and the aforementioned properties of the object600are also applicable for the capacitive sensor structure discussed above.

Correspondingly, in an embodiment of the arrangement100, the electronic arrangement120is configured, at a third instance of time t3, measure a third value v3indicative of a third capacitance of the first electrode301and determine that the third value t3is below the second threshold tht. In this way, the third value v3is indicative of absence of both a touch and an application of a pressure. This has been indicated inFIGS. 4c1and4c2as well as inFIGS. 8aand8b.

To summarize the situations indicated inFIGS. 4a1to4d2and8aand8bthe following is noted:(i) when a pressure is applied by the object600at the location L (see above andFIGS. 4a1,4b1,4a2,4b2) a value of the signal is more than the second threshold tht, and may be more than the first threshold thf.(ii) when a pressure is not applied by the object600(seeFIGS. 4c1,4c2,8a,8b), a value of the signal is at most equal to the first threshold thf, and may be more than the second threshold tht.

To further clarify the situation (i) the following is noted:(i,a) when a large pressure is applied by the object600at the location L (see above andFIGS. 4a1,4b1,4a2,4b2) a value of the signal is more than the first threshold thfand(i,b) even if a small, but a positive and non-zero, pressure is applied by the object600at the location L (see above andFIGS. 4a1,4b1,4a2,4b2) a value of the signal may be less first threshold thf.

In this way, the actual value of the first threshold thfmay be used to fine-tune the pressure required for determining a pressure. Referring to the point (i,b), depending on the application, it may be feasible that very small (but greater than zero) pressures are indicative of a touch rather than a pressure. However, referring to the point (i,a) above, at least one of the first and second insulating layers210,220is compressible by the object600such that a value indicative of the capacitance of the first electrode301as measurable from the capacitive layered sensor structure110by the electronic arrangement120is more than the first threshold thf, when the structure110is compressed as indicated in the point (i,a). A reasonable large force may be needed for the value indicative of the capacitance of the first electrode301to exceed the first threshold thf, depending on the value of the first threshold thf.

To further clarify the situation (ii) the following is noted:(ii,a) when a pressure is not applied by the object600(seeFIGS. 4c1,4c2,8a,8b), but the object600touches the capacitive layered structure at the location L or is in a vicinity thereof, a value of the signal is at most equal to the first threshold thfand at least equal to the second threshold thtand(ii,b) when the object600is far away from the first electrode (i.e. neither touching, nor in the vicinity; seeFIGS. 4c1,4c2,8a, and8b), a value of the signal is less than the second threshold tht.

In this way, the actual value of the second threshold thtmay be used to fine-tune the distance required for determining a touch. Depending on the application, it may be feasible that only very small distances are considered to indicate a touch; however, in some applications presence in a vicinity may be indicative of a touch.

With reference toFIGS. 8aand 8b, when the signal is below the second threshold tht, there are at least two options. First, as indicated inFIG. 8a, a fourth value v4indicative of the capacitance of the first electrode, which fourth value v4is less than the second threshold tht, may be greater than a detection limit thdet. In this case the signal is indicative that an object600is within a detectable distance from the first electrode301, however, not in a vicinity of the first electrode301. Second, as indicated inFIG. 8b, a fifth value v5indicative of the capacitance of the first electrode301, which fifth value v5is less than the second threshold tht, may be less than a detection limit thdet. In this case the signal is indicative that nothing is within a detectable distance from the first electrode301. The detection limit thdetis related to noise levels within the measurements, as detailed below.

Thus, to further clarify the situation (ii,b) as indicated above, the following is noted:(ii,b,1) when the object600is only reasonably far away from the first electrode301, however, neither touching, nor in the vicinity; seeFIG. 8a, a value v4of the signal may be determinable, i.e. distinguishable from noise and thus more than a detection limit thdet.(ii,b,2) when the object600is very far away from the first electrode301, seeFIG. 8b, a value v5of the signal is indistinguishable from noise and thus less than a detection limit thdet.

Thus, in an embodiment, the electronic arrangement120is configured toat a fourth instance of time t4, measure a fourth value v4indicative of a fourth capacitance of the first electrode301, anddetermine that the fourth value v4is more than a detection limit thdetand less than the second threshold tht.

A corresponding embodiment of the method comprisesat a fourth instance of time t4, measuring a fourth value v4indicative of a fourth capacitance of the first electrode301, anddetermining that the fourth value v4is more than a detection limit thdetand less than the second threshold tht.

Moreover, in an embodiment, the electronic arrangement120is configured toat a fifth instance of time t5, measure a fifth value v5indicative of a fifth capacitance of the first electrode301, and determine that the fifth value v5is less than the detection limit thdet.

A corresponding embodiment of the method comprisesat a fifth instance of time t5, measuring a fifth value v5indicative of a fifth capacitance of the first electrode301, anddetermining that the fifth value v5is less than the detection limit thdet.

As indicated above, the touch can be differentiated from the pressing by using a proper electrically permeable and conductive layer410and a proper first threshold thf, in combination. If the first threshold thf, is too large, information related to the value of the pressure is lost. If the first threshold thf, is too small, some touch, even without pressing, could be incorrectly determined as being indicative of application of pressure. These situations, however, depend on the use of the sensor arrangement100. A typical use is a user interface, wherein a user operates the sensor arrangement100by a finger or fingers. Pressure in such an application is typically some hundreds of grams per square centimetre (i.e. some tens of kPa). Therefore, in an embodiment, the sensor arrangement100is configured such that when at least one of the first insulating layer210and the second insulating layer220is compressed by the object600having a volume of at least 1 (cm)3and a dielectric constant of at least 10 with a pressure of 10 kPa such that a part of the first insulating layer210and a part of the electrically permeable and conductive layer410are arranged in between the object600and the first electrode301, a value indicative of the capacitance of the first electrode301as measurable from the capacitive layered sensor structure110by the electronic arrangement120equals a use value vuse. Such a use value vuseis shown inFIGS. 4d1and4d2. This value corresponds to a typical value indicative of the capacitance, when a pressure is applied to the capacitive layered sensor structure110, the value being measurable by the electronic arrangement120. In order for meaningful pressure data to be measurable, in an embodiment, the first threshold thfis at most 95% of the use value vuse. More preferably, the first threshold thfis at most 75% of the use value vuse, such as at most 50% of the use value vuse.

As indicated above, the touch can be differentiated from absence of touching and pressing by using a proper electrically permeable and conductive layer410and a proper second threshold tht, in combination. If the second threshold tht, is too large, some forms of touch are not necessarily identified. If the first threshold thf, is too small, incorrect indication of a touch may be measured.

Moreover, typically measurements include noise. Therefore, even if there is not object600in a vicinity of the first sensor301, a signal measured therefrom is not constant. Thus, the signal measured in such case has a mean (<v>) and a deviation (stdv). In order not to make meaningless measurement, a detection limit thdetmay be set to a value equalling the mean added by the deviation (i.e. thdet=<v>+stdv); or to a value equalling the mean added by two deviations (i.e. thdet=<v>+2×stdv). Thus, all signal values that are less than the detection limit thdetmay be considered meaningless.

For completeness it is noted that the detection limit thdetis at most equal to the second threshold tht. Typically, the detection limit thdetis less than the second threshold tht. Moreover, the second threshold thtis less than the first threshold thf. Preferably, the second threshold thtis less than the first threshold thfby at least a noise level stdv(discussed in detail above), i.e. preferably, tht<thf−stdv. The first threshold thfmay correspond to a situation wherein the compressible layer (210and/or220) is compressed to some extent. The first threshold thfmay correspond to a situation wherein the compressible layer (210and/or220) is fully compressed. In such an extreme case, the presence of pressure would be determined only when the compressible layer (210and/or220) is fully compressed, and other compressions would be classified as a touch.

As for the second threshold (i.e. touch limit) tht, what has been said above about the object600and the vicinity, applies.

Referring toFIG. 1a, 1b, 1c, 1d, 2a, 2b, 2c, 5aand 5b, in an embodiment of the arrangement100, the electronic arrangement120is configured to send an output signal Sout, wherein the output signal Soutis indicative of [i] the first value v1being in between the second threshold thtand the first threshold thf, and [ii] the second value v2being above the first threshold thf. Preferably the output signal Soutis also indicative of the second value v2itself. As indicated in these figures, multiple implementations of the sensor arrangement100are possible.

As indicated inFIGS. 1a, 2a, and 5a, the electronic arrangement120may be an integral part of the arrangement100for capacitively detecting touch and pressure. The electronic arrangement120may perform the measurements as indicated above, and send an output signal Soutindicative of the first value v1being in between the second threshold thtand the first threshold thf, and of the second value v2being above the first threshold thf. As indicated above, preferably the output signal is indicative of the second value v2. The output signal Soutmay be used according to needs. As indicated inFIGS. 1aand 2a, a circuit board500, e.g. a flexible circuit board500, may be electrically coupled to the first electrode301. Moreover, a microchip510attached to the circuit board500may be configured to measure the capacitance of the first electrode as indicated above. Referring toFIGS. 1aand 2a, the microchip510may be configured to send an output signal Soutas indicated above. Referring toFIG. 5a, the microchip510and another chip520(hereinafter referred to as a computer520) may be attached to the circuit board, and the computer520may be configured to send an output signal Soutas indicated above. Moreover, the microchip510may send a signal Sinto the computer520e.g. via a wire. The signal Sinmay be indicative of the first and second values v1and v2.

However, comparison of these values with the first threshold thfneed not be done in microchip510, but may be done in the computer520. In addition, comparison of these signal value with the second threshold thtneeds not be done in microchip510, but may be done in the computer520. However, preferably, comparison of signal value with the second threshold thtis done in the microchip510. Thus, the signal Sinneeds not be indicative of absence of the object600. Even if the microchip510may be configured to determine also a third value v3that is below the second threshold v2(seeFIG. 4c2), the microchip510needs not to send such data to the second part of the electronic arrangement120(e.g. the computer520). E.g. the microchip510may send the signal Sinonly when a signal as measured from the first electrode301at least equals the second threshold tht.

As indicated inFIG. 5b, the electronic arrangement120may comprise separate parts. For example, a first part of the electronic arrangement120may comprise a circuit board500, e.g. a flexible circuit board500, electrically coupled to the first electrode301; and a microchip510attached to the circuit board500. However, the microchip510may be configured to only determine the values v1, v2(and optionally v3, v4, and v5) of the capacitance of the first electrode301and send a signal Sinto a second part of the electronic arrangement120. The signal Sinis indicative of the values v1and v2. Then, a second part of the electronic arrangement120, such as a computer520may receive the signal Sinand determine how the signal Sinis indicative of a touch and a pressure following the principles indicated above. The second part (e.g. computer520) may e.g. determine the values v1and v2from the signal Sinand determine (a) that the value v1is at most equal to the first threshold and at least equal to the second threshold thtand (b) that the second value v2is more than the first threshold thf. The signal Sinmay be sent to the computer520via a wire as inFIG. 5aor wirelessly, as inFIG. 5b.

When the second part of the electronic arrangement120(e.g. computer520) is used, a computer program may run on the computer520. Such a computer program, when run on the computer520, is configured to cause the computer520to (a) receive information indicative of the first threshold thf, (b) receive information indicative of the second threshold tht, and (c) receive a signal Sinindicative of a first capacitance and a second capacitance measured by a capacitive layered sensor structure110. The computer program, when run on the computer520, is further configured: to cause the computer520to determine, from the signal Sina first value v1indicative of the first capacitance and a second value v2indicative of the second capacitance; to determine that the first value v1is at most equal to the first threshold thf; to determine that the second value v2is more than the first threshold thf; and to generate an output signal Sout. The output signal Soutis indicative of the first value v1being at most equal to the first threshold thfand the second value v2being more than the first threshold thf. Unlike the arrangement100, the computer520needs not to determine that the first value v1is at least equal to the second threshold tht, since such information may have been taken account in the signal Sinas detailed above. Naturally, the computer program, when run on the computer520, may be further configured: to cause the computer520to determine that the first value v1is at least equal to the second threshold tht. Moreover, the output signal Soutmay be indicative of the first value v1being at least equal to the second threshold tht.

As indicated above, the electronic arrangement120may be configured to send an output signal Sout, wherein the output signal Soutis also indicative of the second value v2. Correspondingly, the computer program, when run on the computer520, may be configured to cause the computer520to generate such an output signal Sout, that the output signal Soutis also indicative of the second value v2.

As indicated above, the electronic arrangement120, e.g. the microchip510and the computer520in combination, may be configured to determine also a third value v3that is below the second threshold tht(seeFIG. 4c2). Moreover, the microchip510may send such data to the second part of the electronic arrangement120(e.g. computer520). The electronic arrangement120, e.g. the microchip510and the computer520in combination, may be configured to determine also a fourth value v4that is below the second threshold thtand above the detection limit thdet. (seeFIG. 8a). The electronic arrangement120, e.g. the microchip510and the computer520in combination, may be configured to determine also a fifth value v5that is below the detection limit thdet. (seeFIG. 8b).

Thus, an embodiment of a computer program, when run on the computer520, is configured to cause the computer520to receive such a signal Sinthat is indicative of also a third capacitance measured by a capacitive layered sensor structure110. Moreover, the embodiment of the computer program, when run on the computer520, is configured to cause the computer520to determine from the signal Sina third value v3indicative of the third capacitance; to determine that the first value v1is at least equal to the second threshold tht; and to determine that the third value v3is less than the second threshold tht.

An embodiment of a computer program, when run on the computer520, is configured to cause the computer520to receive information indicative of the detection limit thdetand to receive such a signal Sinthat is indicative of also a fourth capacitance measured by a capacitive layered sensor structure110. Moreover, the embodiment of the computer program, when run on the computer520, is configured to cause the computer520to determine from the signal Sina fourth value v4indicative of the fourth capacitance; and to determine that the fourth value v4is less than the second threshold thtand more than the detection limit thdet.

An embodiment of a computer program, when run on the computer520, is configured to cause the computer520to receive information indicative of the detection limit thdetand to receive such a signal Sinthat is indicative of also a fifth capacitance measured by a capacitive layered sensor structure110. Moreover, the embodiment of the computer program, when run on the computer520, is configured to cause the computer520to determine from the signal Sina fifth value v5indicative of the fifth capacitance; and to determine that the fifth value v5is less than the detection limit thdet.

Referring toFIGS. 7ato 7e, in an embodiment, the electrically permeable and conductive layer410comprises a conductive area412and a non-conductive area414. As indicated inFIG. 7b, the electrically permeable and conductive layer410may comprise multiple non-conductive areas414(e.g. apertures or holes) separated from each other by parts of the conductive area412. In a similar manner, the electrically permeable and conductive layer410may comprise multiple conductive areas412separated from each other by parts of the non-conductive area414(not shown). Referring toFIG. 7e, the conductive area412of the electrically permeable and conductive layer410may be a meandering line, whereby the electrically permeable and conductive layer410may comprise only one conductive area412and only one non-conductive area414.

Referring toFIGS. 7ato 7d, in a preferable embodiment, a conductive area412limits a non-conductive area414or non-conductive areas414. In other words, in that embodiment, the conductive area412laterally surrounds a non-conductive area414or non-conductive areas414. Thus, the non-conductive area414or non-conductive areas414form(s) an aperture or apertures to the conductive area412. In a preferable embodiment, a cross sectional area A414of the non-conductive area414is from 0.01 (mm)2to 100 (mm)2. Herein the unit (mm)2stands for square millimetre. In case there are multiple non-conductive areas, preferably, a cross sectional area A414of at least one of the non-conductive areas414is from 0.01 (mm)2to 100 (mm)2. Herein the cross sectional area A414is an area of the cross section of the non-conductive area414, wherein the cross section is defined on a plane having a normal to the direction Sz of thickness of the capacitive layered structure110. The aforementioned area has been found to be sufficiently large for determining a touch caused by a finger of the user by the first electrode301through the electrically permeable and conductive layer410. The aforementioned area has been found to be sufficiently small for sufficiently reducing disturbances to the capacitance of the first electrode301. In particular, the aforementioned areas have been found suitable, regarding a total area of overlapping parts of first electrode301and the non-conductive area(s)414. Referring toFIGS. 7eand 7f, the conductive area412need not limit an aperture.

Preferably the non-conductive area414(or at least one such area414) is arranged at a location of the first electrode301. More specifically, preferably, the non-conductive area414or at least one of the non-conductive areas414overlaps with the first electrode301. As above, also herein the term overlaps means that the overlapping parts are on top of each other in the direction Sz of thickness of the capacitive layered sensor structure110.

Referring toFIGS. 7aand 7b, the conductive area412and the non-conductive area(s)414may be manufactured e.g. by first forming a uniformly conductive layer412, and then removing conductive material to form the non-conductive area(s)414. More preferably, the conductive area412may be printed onto a non-conductive substrate212(FIG. 1d) by using conductive ink or paste in such a manner that the ink or the paste is not printed to the non-conductive area(s)414. For example, conductive polymer-based material may serve as the material for the conductive area(s)412. Such conductive polymer-based material typically comprises conductive particles. Such conductive particles may be particles of some metal (e.g. copper, aluminium, silver, gold) or carbon (including, but not limited to graphene and carbon nanotubes). In addition, conductive polymer-based materials include polyaniline, a polyvinyl (e.g. polyvinyl alcohol or polyvinyl chloride), and PEDOT:PSS (i.e. poly(3,4-ethylenedioxythiophene) polystyrene sulfonate), which may be used as the material for the conductive area(s)412.

Referring toFIG. 7c, the conductive area412may be formed of conductive lines, filaments, or yarns crossing each other, whereby non-conductive areas414are arranged in between the conductive lines, filaments, or yarns. Referring toFIG. 7d, the electrically permeable and conductive layer410may be a woven layer (i.e. fabric) made of conductive yarn. Such conductive fabric includes the yarns as the conductive areas and non-conductive areas in between the yarns.

The non-conductive area414may be observable on a small scale. For example, a poorly conducting polymer-based layer may serve as the electrically permeable and conductive layer410. Such poorly conductive polymer-based material typically comprises a reasonably small amount of conductive particles. Such conductive particles may be particles of some metal (e.g. copper, aluminium, silver, gold) or carbon (including, but not limited to graphene and carbon nanotubes). In addition, some (reasonably) conductive polymers, such as polyaniline, a polyvinyl, and PEDOT:PSS may comprise non-conductive areas in the microscale, depending on their conductivity. The amount of the particles correlates with conductivity, and the conductivity is low, yet the material is conductive, when the amount of particles is just above a percolation threshold of the particles. Thus, on a large scale, the material seems conductive, since the particles percolate, while, on a smaller scale, the material comprises areas that are not electrically connected to each other, i.e. they are non-conductive. In the non-conductive areas, the particles do not percolate. However, the conductive particles that are not connected to other conductive particles may hinder the electrical permeability of electrically permeable and conductive layer410. Therefore, in a preferable embodiment, the non-conductive area414does not comprise particles of electrically conductive material.

Preferably, a ratio of the area of the non-conductive areas414and the area of the conductive area412is at a proper range. Thus, in an embodiment, the electrically permeable and conductive layer410comprises a conductive area412and at least one non-conductive area414. The conductive area412may limit the non-conductive area(s)414as indicated above. This proper range applies preferably at least nearby the first electrode301.

To this end, in an embodiment, at least a part of the conductive area412overlaps with the first electrode301. The cross sectional area of the part of the conductive area412that overlaps with the first electrode301is denoted by A412,301inFIGS. 7aand 7b. Moreover, at least a part of the at least one non-conductive area414overlaps with the first electrode301. The cross sectional area of the part(s) of the non-conductive area(s)414that overlap(s) with the first electrode301is denoted by A414,301inFIGS. 7aand 7b. Herein the cross sectional areas A412,301and A414,301are areas of the cross section of the conductive area412and non-conductive area414, respectively, overlapping with the first electrode301, wherein the cross section is defined on a plane having a normal to the direction Sz of thickness of the capacitive layered structure110.

Preferably, the cross sectional area A412,301of the part of the conductive area412that overlaps with the first electrode301is at least 5% of a cross sectional area A301of the first electrode. As for a maximum of the cross sectional area A412,301of the part of the conductive area412that overlaps with the first electrode301, the conductive area412may comprise only one aperture having a size within the aforementioned limits, while the first electrode301may be reasonably large. Thus, the upper limit may be at least approximately 100%. Correspondingly, preferably, the cross sectional area A414,301of the part of the non-conductive area(s)414that overlap(s) with the first electrode301may be at most 95% of the cross sectional area A301of the first electrode301.

Moreover, preferably, the cross sectional area A414,301of the part(s) of the non-conductive area(s)414that overlap(s) with the first electrode301is from 0.01 (mm)2to 100 (mm)2. This size range has been found suitable in particular for application where a touch and pressure of a finger of a user is determined.

If a second electrode302is present, preferably the conductive area(s)412and the non-conductive area(s) overlap with the second electrode302in a similar manner mutatis mutandis.

In an embodiment, the electrically permeable and conductive layer410comprises a conductive area412that limits (e.g. surrounds) a non-conductive area414or non-conductive areas414, such that a cross sectional area A412of the conductive area is from 5% to 95% of a total cross sectional area A412+A414of the conductive area412and the non-conductive area414or non-conductive areas414limited by (e.g. surrounded by) by the conductive area412

Preferably, the electrode layer300comprises a second electrode302and a second wire352attached to the second electrode302. This has the effect that the spatial accuracy of the capacitive measurements is improved. Preferably, the first wire351connects only the first electrode301to the electronic arrangement120and the second wire352connects only the second electrode302to the electronic arrangement120. This has the effect that the capacitances of the first and second electrode301,302can be measured without multiplexing, which improves the temporal accuracy of the measurements. Thus, in an embodiment, the electronic arrangement120is configured to measure a capacitance of the whole area of the first electrode301at one instance of time. Correspondingly, in an embodiment, the electronic arrangement120is not configured to measure capacitances of parts of the first electrode301at subsequent instances of time. However, the measurement principle can be applied also with such a layered sensor structure110wherein the first wire351connects both the first electrode301and the second electrode302to the electronic arrangement120, and the electrode (301,302), of which capacitance is measured, is determined by multiplexing. For using multiplexing, at least one of the electrically permeable and conductive layer410and the first electrically conductive layer400may be divided to areas that at least partly overlap with at least one of the first electrode301and the second electrode302, wherein the areas of the layer (410,400) are not electrically connected to each other.

As indicated above and inFIGS. 1band 2b, in an embodiment, the capacitive layered sensor structure110comprises a third insulating layer230. The third insulating layer230is arranged such that the electrically permeable and conductive layer410is arranged in between the third insulating layer230and the first insulating layer210in the direction Sz of thickness of the capacitive layered sensor structure110. A primary purpose of the third insulating layer230is to insulate the electrically permeable and conductive layer410from the object600. This improves sensitivity of the measurements. A secondary purpose of the third insulating layer230is to act as a decorative layer. The capacitive layered sensor structure110may comprise the third insulating layer230even if it does not comprise the second insulating layer220.

Referring toFIG. 6, the capacitive layered sensor structure110may further comprise a fourth insulating layer240and a second electrode layer300b. The capacitive layered sensor structure110may comprise the fourth insulating layer240even if it does not comprise the third insulating layer e.g. ofFIG. 1b. In such an embodiment, the fourth insulating layer240is arranged in between the first electrically conductive layer400and a second electrode layer300b. In case the fourth insulating layer240is compressible and electrodes of the second electrode layer300boverlap with electrodes of the first electrode layer300, a capacitance of an electrode of the second electrode layer300bis less affected by touch only. Therefore, such a structure can be used to measure pressure more accurately than e.g. the structure ofFIG. 1bor2b. However, the capacitive layered sensor structure110ofFIG. 6is more complex than the one ofFIG. 1bor2b, whereby it would be more expensive to manufacture.

As for the materials and thicknesses of the layers of the layered capacitive sensor structure110, the materials and thicknesses are preferably selected such that the layered capacitive sensor structure110is flexible. More preferably, the materials and thicknesses are preferably selected such that the layered capacitive sensor structure110is flexible and stretchable, i.e. conformable.

As for the term flexible, a planar flexible material can be bent to a radius of curvature of 10 mm (or less) without breaking the material at a temperature of 20° C. Moreover, the flexible material can be thereafter turned back to the planar form at a temperature of 20° C. without breaking the material. As for the term stretchable, a stretchable material can be stretched by at least 10% in a reversible manner. In particular, a layer of stretchable material can be stretched by at least 10% in a reversible manner a direction that is perpendicular to the direction of thickness of the layer. The reversibility of the stretching is spontaneous, i.e. elastic. Thus, a planar conformable material is flexible as indicated above and stretchable in a direction of the plane of the planar conformable material. A planar conformable material can be arranged to conform a surface of a hemisphere having a radius of 10 cm (or less) at a temperature of 20° C. without introducing significant plastic (i.e. irreversible) deformations to the material.

As for the term compressible, a compressible material can be compressed by at least 10% in a reversible manner. In particular, a layer of compressible material can be compressed by at least 10% in a reversible manner in the direction of the thickness of the layer. The reversibility of the compression is spontaneous, i.e. elastic. Moreover, a Young's modulus of a compressible layer may be less than 1 GPa.

As for suitable materials for the insulating layers210,220,230, a purpose of the insulating layers is to electrically insulate. Therefore, a resistivity of a material of the first insulating layer210and a material of the second insulating layer220(if present) may be at least 10 Ωm at a temperature of 23° C. This applies also for the third insulating layer230, if present. Typically, a resistivity of a material of the first insulating layer210and a material of the second insulating layer220(if present) is at least 100 Ωm at a temperature of 23° C.

As indicated above, at least one of the first and second insulating layers210,220is compressible; however the second insulating layer220needs not be present in the solution. The meaning of the term compressible has been discussed above. Suitable materials for a compressible layer include materials from a material group A, wherein the material group A consists of polyurethane (such as thermoplastic polyurethane), polyethylene, poly(ethylene-vinyl acetate), polyvinyl chloride, polyborodimethylsiloxane, polystyrene, acrylonitrile-butadiene-styrene, styrene-butadienestyrene, styrene-ethylene-butylene-styrene ethylene propylene rubber, neoprene, cork, latex, natural rubber, siloxane polymer (such as silicone), and thermoplastic elastomeric gel. Moreover, in order to have reasonable deformations, in an embodiment, a thickness of the compressible layer (210and/or220) is at least 0.05 mm, preferably at least 0.3 mm such as at least 0.5 mm. A thickness of the compressible layer (210and/or220) is preferably from 0.05 mm to 5 mm, such as from 0.3 mm to 4 mm, such as from 0.5 mm to 2 mm. A Young's modulus in compression of the compressible layer is preferably from 0.01 MPa to 15 MPa, such as from 0.1 MPa to 5 MPa. A Young's modulus in tension may differ from the Young's modulus in compression. Moreover, a material of the compressible layer has preferably a yield strain of at least 10 percent. This ensures that the material can be sufficiently compressed in use.

Preferably, the first insulating layer210and the second insulating layer220are flexible in the aforementioned sense. Moreover, preferably, a Young's modulus of the first insulating layer210is at most 10 GPa, such as at most 5.0 GPa. Moreover, preferably, a Young's modulus of the second insulating layer220is at most 10 GPa, such as at most 5.0 GPa.

The first insulating layer210or the second insulating layer220may act only as a flexible insulator. Suitable materials for a flexible layer include materials from a material group B, wherein the material group B consists of textile, polyimide, polyethylene naphthalate, polyethylene terephthalate, and polyetheretherketone. Suitable materials for a flexible layer also include materials from the material group A as defined above. However, the first insulating layer210or the second insulating layer220need not be flexible. In such a case, suitable materials further include epoxy and phenolic resin. Examples include FR-4 glass epoxy and cotton paper impregnated with phenolic resin. In particular, the second insulating layer220may be hard and/or stiff, if the sensor structure110needs not be flexible, and the first insulating layer210is compressible.

A thickness of an insulating layer that does not act as a compressible layer may be e.g. up to 5 mm as indicated above. However a thickness of an insulating layer that does not act as a compressible layer may be e.g. less 1 mm, such as less than 0.5 mm, e.g. from 50 μm to 1 mm or from 50 μm to 0.5 mm.

What has been said about the thicknesses and materials of the first and second insulating layers210,220applies to the third insulating layer230. The third insulating layer230needs not to be compressible.

As for the electrode layer300, preferably also the electrode layer is flexible. More preferably flexible and stretchable.

In an embodiment, the first electrode301is made of such material that is stretchable by at least 5% without breaking. Preferably the second electrode302is made of such material that is stretchable by at least 5% without breaking. Such material may be e.g. ink or paste. In an embodiment, the first electrode301comprises electrically conductive particles, such as flakes or nanoparticles, attached to each other in an electrically conductive manner. In an embodiment, the first electrode301comprises electrically conductive particles comprising at least one of carbon (including, but not limited to graphene and carbon nanotubes), copper, silver, and gold. In an embodiment, the first electrode301comprises electrically conductive particles comprising carbon. In an embodiment, the first electrode301comprises electrically conductive polymer-based material, such as at least one of polyaniline, a polyvinyl (e.g. polyvinyl alcohol or polyvinyl chloride), and PEDOT:PSS (i.e. poly(3,4-ethylenedioxythiophene) polystyrene sulfonate). What has been said about the material of the first electrode301applies, in an embodiment, to all electrodes including the second electrode302. What has been said about the material of the first electrode301applies, in an embodiment, to the first wire351. What has been said about the material of the first electrode301applies, in an embodiment, to the second wire352.

The first electrode301may be arranged (e.g. by printing) onto the first insulating layer210or the second insulating layer220(seeFIGS. 1cand 2c). In the alternative, the first electrode301may be arranged (e.g. by printing) onto a substrate390(seeFIGS. 1aand 2a). What has been said about the material of the insulating layers210,220applies to the substrate390.

As for the first electrically conductive layer400, the first electrically conductive layer400may be uniformly conductive, e.g. made using conductive ink or paste a uniform amount on a uniform surface. In the alternative, the first electrically conductive layer400may be a mesh of conductive yarns, e.g. made using conductive ink or paste or filaments. It may also suffice that the first electrically conductive layer400consists of a meandering electrically conductive line. It may also suffice that the first electrically conductive layer400comprises multiple separate electrically conductive lines. In an embodiment, at least a part of the first electrically conductive layer400is made from a conductive ink. In an embodiment the first electrically conductive layer400comprises electrically conductive fabric. In an embodiment, the first electrically conductive layer400comprises electrically conductive polymer. Preferably, the first electrically conductive layer400is uniformly conductive. As for the term conductive, a conductive material has a resistivity of at most 10 Ωm, measured at a temperature of 23° C. and at an internal elastic strain of 0%; i.e. without compression or tension, i.e. at rest.

What has been said about the material of the first electrically conductive layer400applies to the material of the electrically permeable and conductive layer410, in particular to the conductive area(s)412of the electrically permeable and conductive layer410. However, at least one non-conductive area414may be arranged to the electrically permeable and conductive layer410at least if its conductivity would be otherwise uniform and high.

Moreover, preferably [A] a conductivity of the first electrically conductive layer400at a temperature of 23° C. (at rest) is higher than a conductivity of the electrically permeable and conductive layer410at a temperature of 23° C. (at rest) and/or [B] a greater portion of the first electrically conductive layer400than of the electrically permeable and conductive layer410is covered by conductive material.