Triboelectric device and corresponding method

Abstract

The first and second layers (110, 120) comprise first (113) and second (123) ridged surfaces respectively. A third layer (131) sandwiched between and in physical contact with the first and second ridged surfaces (113, 123). The third layer (130) is elastically deformable and comprises a second triboelectric material (131). The first triboelectric material (111, 121) has an opposite charge type to the second triboelectric material (131). In a compressed state the first and second ridged surfaces (113, 123) are adapted to cooperatively deform the third layer (130). In a released state the first and second ridged surfaces (113, 123) provide a separation between the first ridged surface (113) and the third layer (130) and between the second ridged surface (123) and the third layer (130). Each layer (110, 120, 130) further comprises an electrode (114, 124, 134).

Description

[0001] TRIBOELECTRIC DEVICE AND CORRESPONDING METHOD

[0002] Field

[0003] Example embodiments relate to electronic devices and methods.

[0004] Background

[0005] Electronic devices such as physical activity monitors (e.g. smart watches), physiological signal sensors (e.g. heart rate sensors, breath rate sensors) and implantable devices (e.g. hearing aids, pacemakers) may be used in the health, sports and lifestyle sectors. There remains a need for further developments in this field.

[0006] Summary

[0007] The scope of protection sought for various embodiments of the invention is set out by the independent claims. The embodiments and features, if any, described in this specification that do not fall under the scope of the independent claims are to be interpreted as examples useful for understanding various embodiments of the invention.

[0008] According to a first aspect, there is described an electronic device comprising: first and second layers each comprising a first triboelectric material, wherein the first and second layers comprise first and second ridged surfaces respectively, a third layer sandwiched between and in physical contact with the first and second ridged surfaces, wherein the third layer is elastically deformable and comprises a second triboelectric material, wherein the first triboelectric material has an opposite charge type to the second triboelectric material; wherein in a compressed state the first and second ridged surfaces are adapted to cooperatively deform the third layer; wherein in a released state the first and second ridged surfaces provide a separation between the first ridged surface and the third layer and between the second ridged surface and the third layer; and wherein each layer further comprises an electrode.

[0009] The electronic device may further comprise an output terminal connected to the electrodes.

[0010] The output terminal may be configured to provide a voltage pulse in response to a transition from the released state to the compressed state or vice versa.

[0011] One of the first and the second triboelectric material may be a negative charge type and the other of the first and the second triboelectric material may be a positive charge type.

[0012] The negative charge type triboelectric material may comprise a silicone elastomer. The positive charge type triboelectric material may comprise a thermoplastic polyurethane.

[0013] The first and second layers may further comprise a planar surface adjacent to their respective ridged surfaces.

[0014] The electrodes of the first and second layer may be provided on the planar surfaces of the first and second layer respectively.

[0015] The electronic device may further comprise fourth and fifth layers arranged to cover the electrodes of the first and second layer.

[0016] The electrode of the third layer may be provided within the third layer.

[0017] The electrodes may comprise a stretchable material.

[0018] The stretchable material may be a silver ink.

[0019] The first and second ridged surfaces may each comprise ridges defined by protrusions and recesses.

[0020] The protrusions of the first ridged surface may be capable of receiving the recesses of the second ridged surface in the compressed state.

[0021] The protrusions and recesses maybe sinusoidal, triangular or square peaks and troughs in a given plane.

[0022] The electronic device may be, or may form part of, a force sensor.

[0023] According to a second aspect, there is described a method comprising: providing first and second layers each comprising a first triboelectric material, wherein the first and second layers comprise first and second ridged surfaces respectively, providing a third layer that is elastically deformable and comprises a second triboelectric material, wherein the first triboelectric material has an opposite charge type to the second triboelectric material; providing an electrode on or within each layer; sandwiching the third layer between and in physical contact with the first and second ridged surfaces, such that in a compressed state the first and second ridged surfaces cooperatively deform the third layer, and such that in a released state the first and second ridged surfaces provide a separation between the first ridged surface and the third layer and between the second ridged surface and the third layer.

[0024] The method may further comprise providing an output terminal connected to the electrodes.

[0025] The output terminal may be configured to provide a voltage pulse in response to a transition from the released state to the compressed state or vice versa.

[0026] The method may further comprise providing one of the first and the second triboelectric material as a negative charge type and the other of the first and the second triboelectric material as a positive charge type.

[0027] The method may further comprise providing a silicone elastomer as the negative charge type triboelectric material.

[0028] The method may further comprise providing a thermoplastic polyurethane as the positive charge type triboelectric material.

[0029] The method may further comprise providing a planar surface on the first and second layers adjacent to their respective ridged surfaces.

[0030] The method may further comprise providing the electrodes of the first and second layer on the planar surfaces of the first and second layer respectively.

[0031] The method may further comprise providing fourth and fifth layers arranged to cover the electrodes of the first and second layer.

[0032] The method may further comprise providing the electrode of the third layer within the third layer.

[0033] The method may further comprise providing electrodes comprising a stretchable material.

[0034] The method may further comprise providing the stretchable material as a silver ink.

[0035] The method may further comprise providing the first and second ridged surfaces with ridges defined by protrusions and recesses. The method may further comprise providing the protrusions of the first ridged surface to be capable of receiving the recesses of the second ridged surface in the compressed state.

[0036] The method may further comprise providing the protrusions and recesses as sinusoidal, triangular or square peaks and troughs in a given plane.

[0037] The method may further comprise providing the electronic device as, or part of, a force sensor.

[0038] It is to be understood that what is described above is what is presently considered the preferred embodiments. However, it should be noted that the description of the preferred embodiments is given by way of example only and that various modifications may be made without departing from the scope as defined by the appended claims.

[0039] Brief Description of the Drawings

[0040] Example embodiments will now be described by way of non-limiting example, with reference to the accompanying drawings, in which:

[0041] FIG. 1 is a schematic diagram showing an example embodiment of an electronic device in cross section;

[0042] FIG. 2 illustrates an example embodiment of an electronic device transitioning between a fully compressed state and a fully released state;

[0043] FIG. 3 illustrates an example embodiment of an electronic device in perspective view;

[0044] FIG. 4 illustrates an example embodiment of an electronic device in an expanded perspective view;

[0045] FIG. 5(a) illustrates an example embodiment of an electronic device in cross section;

[0046] FIG, 5(b) to (d) are examples of plots showing the open circuit voltage, short circuit charge and short circuit current respectively;

[0047] FIG. 6 is an example of a plot showing the relationship between the theoretically calculated maximum contact area and normal stress with peak height; FIG. 7 is an example of a plot showing the relationship between contact force and peak height, in accordance with an example embodiment;

[0048] FIG. 8 (a to c) are examples of plots showing the output voltage, charge and current respectively as a function of compression force in accordance with an example embodiment;

[0049] FIG. 8(d) is an example of a plot showing the output current as a function of force frequency in accordance with an example embodiment;

[0050] FIG. 9 is an example of a plot showing the relationship between the theoretically calculated maximum contact force and applied force for various example embodiments with different ridge shapes;

[0051] FIG. io is an example of a plot showing the relationship between the theoretically estimated ridge deformation and contact force for various example embodiments with different ridge shapes;

[0052] FIG. n(a) is an example of a plot showing the output voltage and current as a function of resistance in accordance with an example embodiment;

[0053] FIG. n(b) is an example of a plot showing the output power density as a function of resistance in accordance with an example embodiment;

[0054] FIG. 11(c) is an example of a plot showing the output power density as a function of resistance for various force frequencies in accordance with an example embodiment;

[0055] FIG. n(d) is an example of a plot showing the output voltage stability as a function of the number of force cycles in accordance with an example embodiment;

[0056] FIG. 12 illustrates an electronic device directly powering a set of LEDs according to an example embodiment;

[0057] FIG. 13 illustrates an electronic device powering a calculator via a rectifier and capacitors according to an example embodiment;

[0058] FIG. 14(a) illustrates an electronic device employed as a breath monitoring force sensor according to an example embodiment; FIG. 14(b) illustrates an example of a sensing signal from the electronic device of FIG. 14(a) in use;

[0059] FIG. 15(a) illustrates an electronic device employed as a pulse monitoring force sensor according to an example embodiment;

[0060] FIG. 15(b) illustrates an example of a sensing signal from the electronic device of FIG. 15(a) in use;

[0061] FIG. 16(a) illustrates an electronic device employed as a pressure sensing shoe sole for gait analysis according to an example embodiment;

[0062] FIG. 16(b) illustrates an example of a sensing signal from the electronic device of FIG. 16(a) in use;

[0063] FIG. 16(c) illustrates examples of sensing signals from the electronic device of FIG. 16(a) in use;

[0064] FIG. 17 illustrates a method to develop the first and second layer of an electronic device, in accordance with an example embodiment;

[0065] FIG. 18 illustrates a method to develop third or sandwich layer of an electronic device, in accordance with an example embodiment.

[0066] Detailed Description

[0067] Electronic devices such as physical activity monitors (e.g. smart watches), physiological signal sensors (e.g. heart rate sensors, breath rate sensors) and implantable devices (e.g. hearing aids, pacemakers) generally require power sources. A common power source includes commercial batteries, which can provide a limited amount of energy and are dependent on charging sources for their continuous use.

[0068] An electronic device maybe powered by an electromechanical energy harvester such as an electromagnetic, piezo-electric or triboelectric nanogenerator.

[0069] A triboelectric nanogenerator utilises the triboelectric effect. The triboelectric effect is based on the principle of contact electrification and electrostatic induction that occurs in between the surfaces of two different triboelectric materials, when they come into contact with each other, under an applied mechanical force. The mechanical contact harvests the electrical energy due to the difference of electrostatic charges on the surfaces of the contacting materials.

[0070] FIG. 1 is a schematic diagram showing an electronic device in cross section, indicated generally by reference numeral to, in accordance with an example embodiment. The electronic device to comprises a first layer no and a second layer 120 sandwiching a third layer 130.

[0071] Each of the first no and second 120 layers comprise a first triboelectric material; labelled 111 and 121 respectively. The triboelectric material 111 of the first layer 110 comprises a flat / planar surface 112 and a first ridged surface 113. The first ridged surface 113 comprises a substantially sinusoidal cross section comprising peaks and troughs. Similarly, the triboelectric material 121 of the second layer 120 comprises a flat / planar surface 122 and a second ridged surface 123. The second ridged surface 123 comprises a substantially sinusoidal cross section comprising peaks and troughs. The peaks and troughs of first ridged surface 113 are arranged to cooperate with the peaks and troughs of the second ridged surface 123 when the first 110 and second 120 layers are compressed together. In other words, the troughs of the first ridged surface 113 are capable of receiving the peaks of the second ridged surface 123. Similarly, the troughs of the second ridged surface 123 are capable of receiving the peaks of first ridged surface 113.

[0072] The third layer 130 is sandwiched between and in physical contact with the first and second ridged surfaces 113 and 123. The third layer 130 is elastically deformable and comprises a second triboelectric material 131. The first triboelectric material 111, 121 has an opposite charge type to the second triboelectric material 131; for example the first triboelectric material 111 may comprise a negative charge type and the second triboelectric material 131 may comprise a positive charge type or vice-versa. The third layer 130 is elastically deformable and comprises two flat surfaces arranged on either side of the third layer 130. The first and second ridged surfaces 113 and 123 are in contact with the opposing flat surfaces of the third layer 130. In some embodiments, the third layer 130 may comprise a soft, stretchable and / or viscoelastic material.

[0073] Each of the first, second and third layers 110, 120, 130 comprise an electrode indicated by reference numerals 114, 124 and 134 respectively. The triboelectric charges generated by the device flow through the electrodes to / from an external circuit connected to the electronic device. In some embodiments, the electrodes comprise a stretchable material. In some embodiments, the electrodes comprise a stretchable silver ink. The electrodes 114, 124 of the first and second layers 110, 120 are provided on planar surfaces 112, 122 respectively and covered by fourth and fifth additional layers of the first triboelectric material in for protection of the electrodes 114, 124. The electrode 134 of the third layer 130 is provided inside the second triboelectric material 131 of the third layer 130.

[0074] FIG. 2 illustrates an electronic device 201 transitioning between a fully compressed state 210 and a fully released state 220, in accordance with an example embodiment. The electronic device 201 maybe the same or similar to electronic device 100 in relation to FIG. 1.

[0075] The flowchart comprises four steps corresponding to the states of the electronic device 201 following application and release of a compressive force; the steps are labelled: i) fully compressed state, ii) releasing state, iii) fully released state and iv) compressing state. As previously described, the electronic device 201 comprises a first layer 202 and a second layer 203 sandwiching an elastically deformable third layer 204. The first and second layers 202, 203 comprise a negative triboelectric material and the third layer 204 comprises a positive triboelectric material. The first layer 202 comprises a flat surface 211 and a first ridged surface 212. Similarly, the second layer 203 comprises a flat surface 213 and a second ridged surface 214. The first 212 and second 214 ridged surfaces are substantially sinusoidal in cross section and arranged such that the peaks and troughs of the first ridged surface 212 are aligned to mate with the troughs and peaks of the second ridged surface 214 when compressed together. The third layer 204 comprises a natural substantially flat shape (but is deformable) having opposing surfaces 215 and 216. In all steps, the first ridged surface 212 is in physical contact with surface 215 and the second ridged surface 214 is in physical contact with surface 216. Each layer 202, 203, 204 comprises an electrode 217, 218, 219 respectively. Each electrode 217, 218, 219 is connected to an output terminal 221 via cables.

[0076] In a fully compressed state (step i), a compression force is applied to the (outer) flat surfaces 211, 213 thus compressing the third layer 204 between the first and second ridged surfaces 212, 214. The peaks and troughs of the first and second ridged surfaces 212, 214 cooperatively deform the elastically deformable third layer 204. The opposing surfaces 215, 216 of the third layer 204 therefore deform; taking a substantially sinusoidal shape corresponding broadly to the peaks and troughs of the first and second ridged surfaces 212, 214. In this condition, the first 212 and second 214 ridged surfaces may be at the maximum contact (or friction) with the opposing surfaces 215, 216 of the third layer 204. This may result in the generation of equal and opposite triboelectric charges between surfaces 212 and 215 (negative on surface 212 and positive on surface 215) and likewise between surfaces 214, 216 (negative on surface 214 and positive on surface 216); owing to triboelectrification. Hence the surface charges maybe completely neutralized, and result in no current flow from the electrodes to the output terminal 221.

[0077] In a releasing state (step ii), the compression force (applied during step i) is released thus the deformed third layer 204 begins to elastically reform, i.e. return to its default (substantially flat) shape (or a similar shape to the default shape) forcing the first and second layers 202, 203 apart from the third layer 204. As the first and second layers 202, 203 separate from the third layer 204, gaps form between the surfaces 212, 215 and 214, 216. The gaps / separation between surfaces 212, 215 and surfaces 214, 216 disturbs the equilibrium of charges on their respective surfaces. These disturbed surface charges create a negative polarity on the electrode 219 and a positive polarity on the electrodes 217 and 218. The polarity results in a voltage pulse and flow of current from the negative electrode 219 to the positive electrodes 217 and 218.

[0078] In the fully released state (step iii), the third layer 204 is completely relaxed and has returned to the substantially flat shape or a similar shape. The surface charge distribution of the layers 202, 203 and 204 are in equilibrium and hence no flow of current from the respective electrodes 217, 218, 219.

[0079] In the compressing state (step iv), the compressive force is applied again to the (outer) flat surfaces 211, 213 thus compressing and deforming the third layer 204 between the first and second ridged surfaces 212, 214. The equilibrium of surface charge distribution is again disturbed. Thus, to restore the surface charge equilibrium, the first and second layers 202, 203 collect the electrons from the third layer 204 through the passage of current from electrodes 217 and 218 to electrode 219 via the output terminal 221.

[0080] In some embodiments, the third layer elastically reforms to its original state once the pressure is released in a repeatable manner.

[0081] In some embodiments, under the continuous compression and releasing pressure cycles, the third layer deforms and reforms by the first and second ridge surfaces, and these processes are repeatable in cyclic manner.

[0082] In some embodiments, during the continuous cyclic contact and separations between the third layer and other first and second layers generates the charges across their surface owing to triboelectric effect. Continuous cyclic compressive forces applied and released on the electronic device 201 can result in the generation of alternating current (AC) from the electrodes 217, 218, 219 to the output terminal 221 as the electronic device 201 transitions from a compressed state to a released state and vice versa. The compressed state maybe a fully compressed state as described above or a partially compressed state. In a partially compressed state, the ridged surfaces 212, 214 are not in full contact with the third layer 204 thus some gaps remain. The released state may be a fully released state as described above or a partially released state. In a partially released state, the third layer 204 is not completely relaxed and is still under some stress from the ridged surfaces 212, 214. The magnitude of the output signal from the device 201 may be lower if the device cycles through partially compressed and / or partially released states compared to fully compressed or fully released states.

[0083] FIG. 3 illustrates an electronic device in perspective view, indicated generally by reference numeral 300, in accordance with an example embodiment. The electronic device 300 maybe the same or similar to electronic device too or 201 in FIGs. 1 and 2. The electronic device 300 comprises first and second layers 310 and 320 each comprising a first triboelectric material 301. The first and second layers 310 and 320 comprise first and second ridged surfaces 311 and 321 respectively. A third layer 330 is sandwiched between and in physical contact with the first and second ridged surfaces 311 and 321. The third layer 330 comprises a second triboelectric material 302. The first triboelectric material 301 has an opposite charge type to the second triboelectric material 302.

[0084] The first and second ridged surfaces 311 and 321 comprises ridges defined by protrusions and recesses. The protrusions of the first ridged surface 311 are arranged to cooperate with the recesses of the second ridged surface 321 (and vice versa) to deform the third layer 330 when the electronic device 300 is in a compressed state. In other words, the recesses of the second ridged surface 321 are arranged to receive the protrusions of the first ridged surface 311 and vice versa. In some embodiments, the protrusions and recesses form substantially sinusoidal peaks and troughs in cross section. In some embodiments, first and second ridged surfaces 311 and 321 comprise a plurality of sinusoidal peaks and troughs. In some embodiments, the peaks are symmetrical about a centre axis. In some embodiments, the plurality of peaks and troughs are arranged in a two dimensional lattice (such as an equilateral triangular lattice). It should be noted that the substantially sinusoidal arrangement of peaks and troughs provided by the ridged surfaces of the electronic device 300 are not essential to all example embodiments. In some embodiments, ridges comprising triangular, square, or other shapes (in cross section) may be used. In some embodiments, the shape and / or dimensions of the ridges may depend on the input compression force applied on the electronic device 300. As described in relation to FIG. 2, the electronic device 300 maybe compressed and released in a continuous cycle to generate an alternating current.

[0085] FIG. 4 illustrates an electronic device in an expanded perspective view, indicated generally by reference numeral 400, in accordance with an example embodiment. The electronic device 400 may be the same or similar to electronic device 300 in relation to FIG. 3. The electronic device 400 comprises first and second layers 410 and 420 sandwiching a third layer 430; as previously described.

[0086] The first layer 410 comprises an electrode 412 laminated on a layer of a silicone elastomer (such as Ecoflex® (00-30)) 413. The electrode 412 may comprise a sheet of a stretchable silver ink. The silicone elastomer is a negative triboelectric material. The silicone elastomer 413 comprises a flat / planar surface and a first ridged surface (similar to surface 311 as described in relation to in FIG. 3). An additional layer of silicone elastomer 411 is coated on top of the electrode 412 to protect the electrode 412 from mechanical wear. The electrode 412 is thus enclosed within the first layer 410.

[0087] Similarly, the second layer 420 comprises an electrode 422 laminated on a layer of a silicone elastomer (such as Ecoflex® (00-30)) 423. The electrode 422 may comprise a sheet of a stretchable silver ink. The silicone elastomer is a negative triboelectric material. The silicone elastomer 423 comprises a flat / planar surface and a second ridged surface (similar to surface 311 as described in relation to in FIG. 3). An additional layer of silicone elastomer 421 is coated on top of the electrode 422 to protect the electrode 422 from mechanical wear. The electrode 422 is thus enclosed within the second layer 420.

[0088] The third layer 430 comprises an electrode 432 sandwiched between two thin layers of a thermoplastic polyurethane (TPU) 431 and 433. The electrode 432 may comprise a sheet of a stretchable silver ink. The TPU is a positive triboelectric material. The top TPU layer 431 is in physical contact with the first ridged surface 413 and the bottom TPU layer 433 is in physical contact with the second ridged surface 423.

[0089] FIG. 5(a) illustrates an electronic device 400 in cross section, in accordance with an example embodiment. As previously described, the electronic device 400 comprises first and second silicone elastomer layers 410, 420 sandwiching a TPU layer 430. The silicone elastomer layers 410, 420 comprise first and second ridged surfaces which are substantially sinusoidal in cross section, having peaks and troughs. The width of the peaks (and troughs) 52 and the height of the peaks 51 is indicated with arrows.

[0090] FIG, 5(b) to (d) are plots showing the open circuit voltage, short circuit charge and short circuit current respectively as a function of time following a cyclic compressive force of 30N at a 1Hz rate for six embodiments of electronic device 400. The six embodiments correspond to peak heights 51 of omm (i.e. flat), 0.25mm, 0.5mm, imm, 2mm and 3mm respectively. Each embodiment has the same peak width 52 of 4mm. Thus, the six embodiments provide ridged surfaces having surface areas of 1600mm2(flat), 1603mm2(0.25mm), 1614mm2(0.5mm), 1658mm2(imm), 1831mm2(2mm) and 2120mm2(3mm) respectively. The maximum voltage, charge and current is achieved for a peak height 51 of imm as this configuration provides the maximum contact area between the first and second ridged surfaces and the TPU layer 430. Increasing the peak height 51 beyond imm for a peak width 52 does not substantially increase contact area because the peaks are unable to deform the TPU layer 430 any further (due to the stiffness of the TPU layer 430) and therefore the peaks themselves begin to in compress. This is due to the viscoelasticity of the elastomeric material. In theory, the peaks on the silicone elastomer layers 410, 420 are able to exert the pressure on TPU layer 430 and push it up to a certain level, after which the stiffness of the TPU layer 430 causes the increase in normal stress on the ridged surfaces and ultimately resulting in the compression of viscoelastic Eco-flex peaks rather than further pushing the TPU layer 430. To validate this, a mechanical structural simulation was performed on the design structure of the electronic device 400. The material properties of both silicone elastomer layers 410, 420 and TPU layer 430 are given in Table 1.

[0091] Model Properties

[0092] C, = 17 KPa

[0093] CB= -0.2 KPa

[0094] Silicone Rubber Yeoli C3 = 0.023 KPa

[0095] Ecoflex 00-30 3rdDj = 15

[0096] Ds= 20

[0097] Ds= 10

[0098] C10= -1.1 MPa

[0099] C01= 5.2 MPa

[0100] TPU Mooney-Rivlm CJJ = -846.5 MPa

[0101] 5thCm = 451.7 MPa

[0102] C02= 398.7 MPa

[0103] Di = 10

[0104] Table 1

[0105] To depict real-world conditions, the 3D structures of the electronic device 400 with different peak heights 52 were subjected to the incremental compressive forces from o- 70 N. The increase in force applied on the electronic device 400 resulted in the increase of electrical output. Similarly, the increase in force applied on the contact area (i.e., Contact Force) results in increased electrical performance. To validate this theory, we derived the values of contact area between the two triboelectric layers and normal stress exerted on the TPU layer 430 at 30 N for all the ridge sizes.

[0106] FIG. 6 is a plot showing the relationship between the theoretically analyzed maximum contact area and normal stress with peak height 51, in accordance with an example embodiment. It can be observed that, the normal stress increases with the increase of the peak height 51 while the maximum contact area is 100% up to imm ridge size. After that, the maximum contact area starts decreasing, implying that the maximum contact area is achieved with a 1 mm peak height 51.

[0107] FIG. 7 is a plot showing the relationship between the theoretically analyzed contact force and peak height 51, in accordance with an example embodiment. The maximum values of contact force is achieved with a 1 mm peak height 51. Increasing contact force increases power output of the electronic device 400 as shown in FIG. 5b to 5d.

[0108] The ability of the electronic device 400 to respond to various forces is relevant to possible practical applications. Thus, to study the relationship between the external mechanical loadings and electrical output performance of the electronic device 400, the output (VOC, QSC and ISC) of the six embodiments described above were measured by applying compressive forces from 5 N to 70 N.

[0109] The performance of the electronic device 400 was analysed by applying the distinct range of compressive forces and frequencies, using the bespoke linear motor based customized dynamic mechanical setup. The electrical output performance including the VOC, ISC and QSC under distinct compression conditions are measured using the electrometer 6514 (Keithley instruments) and low-noise preamplifier integrated with the digital phosphor oscilloscope DPO-4104 (Tektronix Inc.).

[0110] FIG. 8 (a to c) are plots showing examples of the output voltage, charge and current respectively of the six embodiments as a function of compression force. The output magnitude for all embodiments may increase with the increase in compressive forces. This may be because a greater contact force increases the triboelectric surface charge densities and hence the output performance increases. Furthermore, after 30 N of compressive force, the VOC and QSC may start saturating. This maybe because a 30N compressive force may be sufficient to push the maximum number of charge on the contacting surfaces. The output current may be a function of the force frequency because the current depends on the rate of flow of charge. Therefore, if the force frequency is increased, the charge movement may also increase; which may result in the increase of the output current.

[0111] FIG. 8(d) is a plot showing the output current of the six embodiments as a function of force frequency. The substantially sinusoidal ridges arrangement with the 1 mm peak height embodiment with the surface area of 1658mm2may provide the highest current value for all the different frequencies and forces used.

[0112] The above examples describe embodiments in which the ridged surfaces comprise substantially sinusoidal ridges. It will be understood that this is not intended to be limiting and other ridge shapes could be used. For example triangular and square ridge shapes may be used.

[0113] In some embodiments, the ridge shape and dimensions may be designed to suit specific uses of the electronic device. In some embodiments, the ridge shape and dimensions may be designed to suit specific ranges of compression forces expected to be applied to the electronic device.

[0114] FIG. 9 is an example of a plot showing the relationship between the theoretically calculated maximum contact force and applied (compression) force for various example embodiments with different ridge shapes. The example embodiments include substantially sinusoidal ridges, substantially triangular ridges and substantially square ridges (in cross section). FIG. 9 shows that embodiments comprising square ridges may provide a higher contact force at applied forces greater than approximately 30N when compared to embodiments with sinusoidal or triangular ridges. Whereas, at the lower to mid applied forces (in the range of 10N to 30N), embodiments comprising sinusoidal ridges may provide a higher contact force than embodiments comprising square ridges. Embodiments comprising triangular ridges may provide a lower contact force than embodiments comprising sinusoidal or square ridges at all applied force values. Thus in some embodiments, square ridges maybe preferable where the device maybe subject to higher applied forces. Similarly, in some embodiments sinusoidal ridges may be preferable where the device is subject to low and medium applied forces for example in biomedical applications in which the device is subject to low pressures from the body. FIG. 10 is an example of a plot showing the relationship between the theoretically estimated ridge deformation and contact force for various example embodiments with different ridge shapes. The results indicate that triangular shaped ridges may deform at a quicker rate than sinusoidal or square shaped ridges. Thus, square and sinusoidal shaped ridges may provide a slower rate of deformation. Furthermore, the deformation for the sinusoidal shaped ridges may be less than the deformation for square shaped ridges for all applied forces in some embodiments. In some embodiments, sinusoidal ridges may provide more contact force while maintaining the integrity of the structure than embodiments comprising square shaped ridges. FIG. 10 shows that generally, the rate of deformation of embodiments comprising sinusoidal shaped ridges may be lower than embodiments comprising triangle or square shaped ridges. Therefore, embodiments comprising sinusoidal ridges may provide improved structural integrity than embodiments comprising triangle or square shaped ridges.

[0115] In some embodiments, the electronic device may be the same or similar to 400 in relation to FIG. 5 and may comprise sinusoidal shaped ridges having a peak height 51 of imm. An example of the output signal from the example electronic device is shown in FIG. n(a to d).

[0116] FIG. 11(a) shows the plot of output voltage of the example electronic device as a function of load resistance in accordance with an example embodiment. The voltage (Vioad) may increase with the increment of the resistance from 1 Mil, reaching the highest value (88 V) at 10 GG, while current (Iioad) showed the opposite trend with the highest value at 10 K£2. These two quantities may cross each other at around 100 Mil, indicating this value as the approximate internal resistance of the electronic device. Since the electronic device has a high internal resistance, it may be utilized as a current source.

[0117] FIG. 11(b) is a plot showing the output power density of the example electronic device as a function of load resistance in accordance with an example embodiment. The power density was investigated by connecting the example device in series with external variable resistors (from 10 K£2 to 10 GG) and testing it at 30N and constant frequency (1Hz). The output power density was calculated by using the formula P = I2R. Where I is the output current at load resistance. The maximum measured output current shown in FIG. 11(b) is 360 mW / m2at 100 Mil. In some embodiments, 100 Mil maybe considered the approximate value of internal resistance of the example electronic device. FIG. 11(c) is a plot showing the output power density as a function of resistance for 1Hz, 5Hz and 7Hz force frequency in accordance with an example embodiment. The output power density may be increased by increasing the frequency of the applied force cycles (360, ~4O6 and 490 mW / m2for 1, 5 and 7 Hz respectively).

[0118] FIG. 11(d) is a plot showing the output voltage stability of the electronic device 400 as a function of the number of force cycles in accordance with an example embodiment. The voltage stability was evaluated by applying the compressive force of 30 N at 1Hz for 1200 cycles. Stable peaks of output voltages (Voc) are observed, demonstrating the practical value of the electronic device 400 for long-term cyclic application.

[0119] The powering capacity of the electronic device 400 was analyzed by powering the commercial Light Emitting Diodes (LEDs) and calculator by applying the compressive force. To power the LEDs, they were simply connected in series with each other and with the electronic device. For powering the calculator, the output of the electronic device was connected to the bridge rectifier IC. Two capacitors of 47 pF were connected in series to store the rectified output. The calculator was then powered by connecting it in parallel with the capacitor.

[0120] FIG. 12 illustrates an electronic device according to an example embodiment. The electronic device is utilized to power a number of commercial LEDs connected in series. The LEDs emit after the electronic device was subjected to the compressive forces of 30 N at 5 Hz.

[0121] FIG. 13 illustrates an electronic device according to an example embodiment. The electronic device is used to power a commercially available digital calculator using compressive forces of 30 N and 5 Hz. The output of the electronic device was first rectified then used to charge a capacitor (23.5 pF) up to 2.2 V. The charged capacitor was then used to power the calculator.

[0122] Data acquisition for breath monitor applications were performed by using DAQ-6510 (Keithley instruments) and integrating it with the customized application developed on LabView platform (National Instruments Corp.). For the breath monitor, the 4x4 cm2electronic device was encased in a 3D printed case which is tied to the lower thoracic region. The breath wave signals from the electronic device were then acquired by the LabView based program. FIG. 14(a) illustrates an electronic device according to an example embodiment. The electronic device is used for a real-time breath monitoring belt. The 3D printed housing along with a textile-based belt was used to hold the electronic device against the lower thoracic region.

[0123] FIG. 14(b) illustrates the output voltage of an example electronic device as a function of time, in accordance with an example embodiment. The example electronic device enables determination of distinct breathing phases such as tachypnea (hyper-breathing), apnea (no breathing) and Eupnea (normal breathing) conditions.

[0124] Data acquisition for pulse detector and gait analysis applications were performed by using USB-DAQ 6343 (National Instruments Corp.) and integrating it with the customized application developed on Lab View platform (National Instruments Corp.). For the pulse sensor realization a 3D printed case was used to place the electronic device in it and tie it against the wrist (As shown in FIG. 15). The pulse signals from the wrist tied electronic device were then acquired by LabView based program. This program processes the acquired signal with peak detection module in real time. For gait analysis application, seven embodiments of the electronic device with the dimensions of i.6xi,6 cm2were placed in the customized shoesole made by the laser cutting the flexible cork sheet (As shown in FIG. 16). LabView based intensity plotting module was used to record, plot the real-time activation, and deactivation of multiple electronic devices.

[0125] FIG. 15(a) illustrates an electronic device employed as a pulse monitoring force sensor according to an example embodiment. The electronic device was sized to the measurements of 12x12 mm2and was utilized as a real-time pulse count monitor. Moreover, 3D printed housing along with a band was utilized to clamp the electronic device to the wrist.

[0126] FIG. 15(b) illustrates an example of a sensing signal from the electronic device of FIG. 15(a) in use. The sensing signal shows the pulse rate of the user.

[0127] FIG. 16(a) illustrates an electronic device employed as a pressure sensing shoe sole for gait analysis according to an example embodiment. A plurality of the electronic device (Si to S7) are arranged into an array in a shoe sole for the real-time gait monitoring application. The electronic device allows recording of a pressure map of a human foot in real-time. FIG. 16(b) illustrates an example of a sensing signal from the electronic device of FIG. 16(a) in use. The sensing signal may be used to monitor the pressure distribution on the shoe sole whilst a user steps on it.

[0128] FIG. 16(c) illustrates an example of sensing signals from the electronic device of FIG. 16(a) in use. An example of the sensing signal from the device whilst the user is running is shown. An example of the sensing signal from the device whilst the user is walking is also shown. Since the example sensing signals are different to each other, the sensing signal may be used to monitor the movement of the user.

[0129] In some embodiments, the electronic device may be used for distinct biomedical applications including patients body movement monitoring, dementia patient monitoring by observing the environmental changes and patients daily physical activities, etc.

[0130] In some embodiments, a silicone elastomer with the ridges on its surface and TPU film were used as the negative and positive triboelectric materials, respectively.

[0131] FIG. 17 illustrates a method of manufacturing a silicone elastomer layer with a ridged surface, in accordance with an example embodiment. To produce the ridged surface on the silicon elastomer, firstly, the invert ridged patterned molds were developed by utilizing a 3D printing technique. These molds with the various ridge dimensions were produced with poly-lactic acid (PLA) over an area of 4x4 cm2. Afterward, the mixture of type-A and type-B elastomer components of Ecoflex 00-30 (Smooth-on, Inc.), at equal volume were prepared and poured onto the 3D printed molds, followed by a curing treatment at 600C for 4 hours in an oven. After the curing treatment, silver (Ag) ink (DuPont PE874; Insulectro Printed Electronics) was deposited on its surface by the doctor blade method via 3.6x3.6 cm2mask. Subsequently, another elastomer layer was coated on top, and it was utilized as a protective cover of the Ag electrode followed by the curing treatment at 600C for 4 hrs. The whole stack consists of the ridge-type elastomer along with the Ag electrode and protecting cover was then peeled-off from the 3D printed mold. Such a whole elastomer ridged stack was further heated at 1200C in oven for 20 mins to completely cure the Ag ink.

[0132] FIG. 18 illustrates a method of manufacturing a TPU layer, in accordance with an example embodiment. A commercially purchased TPU layer (Platilon U073 Covestro Ag.; Thickness of too pm) with an area of 4x4 cm2was printed with an Ag ink as an electrode, by the doctor blade method followed by the curing treatment at 1200C for 20 mins. Afterwards, another TPU layer was placed and laminated on top of TPU / Ag, by the hot press technique to attain a unified double sided TPU layers along with the Ag electrode in the middle.

[0133] Ultimately, the as-fabricated TPU / Ag / TPU stack was further sandwiched between two elastomer ridged stacks to realize the electronic device, as shown in FIG. 3.

Claims

Claims1. An electronic device comprising: first and second layers each comprising a first triboelectric material, wherein the first and second layers comprise first and second ridged surfaces respectively, a third layer sandwiched between and in physical contact with the first and second ridged surfaces, wherein the third layer is elastically deformable and comprises a second triboelectric material, wherein the first triboelectric material has an opposite charge type to the second triboelectric material; wherein in a compressed state the first and second ridged surfaces are adapted to cooperatively deform the third layer; wherein in a released state the first and second ridged surfaces provide a separation between the first ridged surface and the third layer and between the second ridged surface and the third layer; and wherein each layer further comprises an electrode.

2. An electronic device according to claim 1, further comprising an output terminal connected to the electrodes.

3. An electronic device according to claim 2, wherein the output terminal is configured to provide a voltage pulse in response to a transition from the released state to the compressed state or vice versa.

4. An electronic device according to any of claims 1 to 3, wherein one of the first and the second triboelectric material is a negative charge type and the other of the first and the second triboelectric material is a positive charge type.

5. An electronic device according to claim 4, wherein the negative charge type triboelectric material comprises a silicone elastomer.

6. An electronic device according to claim 4 or claim 5, wherein the positive charge type triboelectric material comprises a thermoplastic polyurethane.

7. An electronic device according to any preceding claim, wherein the first and second layers further comprise a planar surface adjacent to their respective ridged surfaces.

8. An electronic device according to claim 7, wherein the electrodes of the first and second layer are provided on the planar surfaces of the first and second layerrespectively. An electronic device according to claim 8, further comprising fourth and fifth layers arranged to cover the electrodes of the first and second layer. An electronic device according to any preceding claim, wherein the electrode of the third layer is provided within the third layer. An electronic device according to any preceding claim, wherein the electrodes comprise a stretchable material. An electronic device according to claim 11, wherein the stretchable material is a silver ink. An electronic device according to any preceding claim, wherein the first and second ridged surfaces each comprise ridges defined by protrusions and recesses. An electronic device according to claim 13, wherein the protrusions of the first ridged surface are capable of receiving the recesses of the second ridged surface in the compressed state. An electronic device according to claim 13 or 14, wherein the protrusions and recesses are sinusoidal, triangular or square peaks and troughs in a given plane. An electronic device as claimed in any one of the preceding claims, wherein the electronic device is, or forms part of, a force sensor. A method: providing first and second layers each comprising a first triboelectric material, wherein the first and second layers comprise first and second ridged surfaces respectively, providing a third layer that is elastically deformable and comprises a second triboelectric material, wherein the first triboelectric material has an opposite charge type to the second triboelectric material; providing an electrode on or within each layer; sandwiching the third layer between and in physical contact with the first and second ridged surfaces, such that in a compressed state the first and second ridged surfaces cooperatively deform the third layer, and such that in a released state the first and second ridged surfaces provide a separation between the first ridged surface and the third layer and between the second ridged surface and thethird layer.

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