WO2022008631A1

WO2022008631A1 - Capacitive power transfer for space sensitive electronic devices

Info

Publication number: WO2022008631A1
Application number: PCT/EP2021/068931
Authority: WO
Inventors: Zhe Zhang; Yi DOU; Xu Chen
Original assignee: Danmarks Tekniske Universitet
Priority date: 2020-07-08
Filing date: 2021-07-08
Publication date: 2022-01-13

Abstract

The present disclosure relates to An electronic system with integrated capacitive power transfer, the electronic system comprising: an electronic device comprising a connecting part having a connecting surface; a charging device comprising a recess for docking the electronic device in a docking position, wherein a recess surface of the recess at least partly coincides with the connecting surface; and a capacitive power transfer system comprising two capacitor pairs configured for capacitive power transfer from the charging device to the electronic device in the docking position, each capacitor pair comprising: one power receiving capacitor plate integrated in or on the connecting surface of the electronic device; and one power transmitting capacitor plate integrated in or on the recess surface of the charging device, wherein the power receiving capacitor plate and the power transmitting capacitor plate of each capacitor pair are substantially aligned in the docking position.

Description

Capacitive power transfer for space sensitive electronic devices

The present disclosure relates to an electronic system with integrated capacitive power transfer, and further an electronic device configured for capacitive power transfer, and a charging device configured for capacitive power transfer.

Background of invention

For several types of electronic devices, especially portable electronic devices, there is a strong need for them to be fabricated as small and light as possible. This applies for example to wearable electronic devices such as headphones and hearing aids, wherein a small and light form factor ensures that they can be worn with ease for a prolonged amount of time while at the same time a small form factor ensures that the visual impact of the electronic devices can be increased and/or that the device can be made more aesthetically pleasing.

However, the desire for smaller electronic devices is not compatible with the desire for a high performance of the same. Instead, the performance of the electronic device is typically increased by the incorporation of bulkier components. The performance may be considered in terms of the computational power, but for wearable electronic devices, especially wearable medical devices, such as hearing aids, the performance in terms of the battery life may be even more important for an end-user, wherein a depleted battery may have significant consequences for the user. For other types of electronic devices an increased battery life relieves the user from frequent charging of the electronic device.

However, irrespective of the performance indicator, the general rule is that an increased performance of the electronic device comes at a cost of bulkier components. For example, for improving the battery life, a larger battery has to be incorporated into the electronic device, wherein the battery life scales approximately linear to the battery volume, due to the constant energy density.

Thereby, there is a trade-off between the small form factor and the performance of the electronics device, such as in terms of the battery life, resulting in that the electronic device may either have a small form factor or a long battery life. This trade-off is applicable to a large number of space-sensitive electronic devices, such as smartphones, tablets, smart watches, hearing aids and headphones to name a few.

Continuous development of the batteries and electronic components, such as the transducers and integrated circuits, act to improve the ratio between the performance of the electronic device and the form factor.

Several wearable electronic devices rely on wireless power transfer, between a charging device and an electronic device. This offers several important advantages, with respect to wired power transfer, such as convenience to the end-user as the wireless power transfer negates the requirement of connecting a charging cable.

At the same time, wireless power transfer requires the incorporation of wireless power receiving units in the electronic device. Thereby, extra space needs to be reserved for these components, which typically consist of a receiver coil and magnetic shielding layers. To include this in a space sensitive device, together with other required components of such a system, including a voltage regulator circuit to charge the battery with the required voltage and power, design trade-offs needs to be made, either the volume of electronic components needs to be reduced, such as the battery thereby affecting the battery life, or the overall volume of the electronic device needs to be increased, acting to form a bulkier electronic device.

Summary of invention

The present inventors have realized how capacitive power transfer can be used for charging electronic devices.

The present disclosure relates, according to a first embodiment, to an electronic system with integrated capacitive power transfer, the electronic system comprising:

• an electronic device comprising a connecting part having a connecting surface;

• a charging device comprising a recess for docking the electronic device in a docking position, wherein a recess surface of the recess at least partly coincides with the connecting surface; and

• a capacitive power transfer system comprising two capacitor pairs configured for capacitive power transfer from the charging device to the electronic device in the docking position, each capacitor pair comprising: o one power receiving capacitor plate integrated in or on the connecting surface of the electronic device; and o one power transmitting capacitor plate integrated in or on the recess surface of the charging device, wherein the power receiving capacitor plate and the power transmitting capacitor plate of each capacitor pair are substantially aligned in the docking position.

One advantage offered by the electronic system of the present disclosure, relying on capacitive power transfer for charging the electronic device, is the smaller volume as compared to a corresponding system relying on inductive power transfer.

This allows for the fabrication of electronic devices with a smaller form factor or to increase the size of other components of the electronic device, such as the battery, thereby extending the battery life.

Another advantage of the present disclosure is that the capacitor plates of each capacitor couple do not necessarily need to be planar, but instead the capacitor plates may have curved shapes or even be irregular shaped, acting to alleviate the design restrictions on the electronic system. Thereby, the electronic system may not necessarily be configured for conductive power transfer between two planar surfaces.

The capacitive plates may thereby have any shape, and the receiving capacitive plates may for example have a shape matching individual parts of the connecting surface of the connecting part of the electronic device. Similarly the transmitting capacitive plates may have a shape matching individual parts of the recess surface.

In fact, the power receiving capacitor plates may be integrated in or on the connecting surface of the electronic device while the power transmitting capacitor plates may be integrated in or on the recess surface of the charging device. Furthermore, the capacitor plates may form an integral part of the casing, i.e. a casing of the electronic product or a casing of the charging device.

The capacitive plates may further be covered, by either a part of the casing, or an insulating layer. An outer surface of the connecting part may thereby be a continuous layer. This may further be true for the charging device, wherein the recess surface may be a continuous layer. A continuous outer surface of the electronic device and/or the charging device may act to increase the durability and the hygiene. Firstly, by the use of a continuous outer layer the electronic device, or the charging device, may be water resistant. This may thereby act to ensure a durable electronic device and/or charging device, as it may be able to withstand liquids, such as water.

Secondly, while for example electronic devices relying on wired power transfer comprise cavities for connecting to a charging cable. The electronic system of the present disclosure preferably comprises a continuous outer layer, of the electronic product and/or the charging device, preventing the accumulation of contaminants during use. Furthermore, as the continuous layer may make the electronic system of the present disclosure water resistant, said system may be easily cleaned.

It is further a preference of the present disclosure that the electronic system comprises a control unit configured to control the DC power source and/or the inverter such that the capacitive power transfer system:

• in a constant current mode, operates at a constant current mode frequency (fee), wherein a constant current is provided to the load; and

• in a constant voltage mode, operates at a constant voltage mode frequency (fev), wherein a constant voltage is provided to the load.

The constant current mode frequency (f_cc) and the constant voltage mode frequency (f_ev), which are controlled by the control unit, may be determined based on the characteristics and selected components of the circuit. Thereby, the proposed topology and control scheme may act to form a capacitive power transfer system, which has one constant current output operation point and one constant voltage output operation point that are both load independent.

The electronic device preferably comprises a rectifier configured to convert an AC voltage into a DC output, such as a diode rectifier, said DC output connectable to a load, such as a rechargeable battery. The electronic device may further comprise a voltage regulator, such as a low dropout regulator or a switched capacitor DC/DC converter. Both the rectifier and the voltage regulator may be void of inductors, and consequently, the entire receiving side may be void of inductors. Instead, the use of capacitors allows for a compact electronic device, with a C compensation topology. The electronic system may further comprise a control unit configured to control the DC power source and/or the inverter such that the voltage input to the voltage regulator is near a predetermined value, for allowing optimal performance of the voltage regulator.

The present disclosure further relates to a compact rechargeable electronic device comprising:

• a casing, comprising a connecting part for being received by a corresponding recess of a charging device in a docking position, the connecting part having a connecting surface;

• a rechargeable battery; and

• two power receiving capacitor plates integrated in or on the connecting surface, the two power receiving capacitor plates arranged to form a capacitive power transfer from two corresponding power transmitting capacitor plates of the charging device in the docking position.

The present disclosure further relates to a charging device comprising:

• a recess for receiving a rechargeable electronic device in a docking position, the recess having a shape corresponding to a connecting part of the rechargeable electronic device; and

• two power transmitting capacitor plates integrated in or on a recess surface of the recess, the two power transmitting capacitor plates arranged to form a capacitive power transfer to two corresponding power receiving capacitor plates of the rechargeable electronic device in the docking position.

Description of drawings

Fig. 1 shows schematic illustrations of cross sections of an electronic system comprising an electronic device and a charging device according to an embodiment of the present disclosure..

Fig. 2 shows schematic illustration of an electronic device and a charging device according to an embodiment of the present disclosure..

Fig. 3 shows a schematic illustration of the layers forming the capacitive plate pairs according to an embodiment of the present disclosure..

Fig. 4 shows a circuit of the electronic system according to an embodiment of the present disclosure.. Fig. 5 shows a circuit of the electronic system without inductors on the receiving side according to an embodiment of the present disclosure..

Fig. 6 shows a schematic illustration of an electronic device comprising a switched capacitor DC/DC converter according to an embodiment of the present disclosure..

Fig. 7 shows a schematic illustration of an electronic device and a charging device according to an embodiment of the present disclosure.

Fig. 8 shows an electronic device together with measurement results.

Detailed description of the invention

The present disclosure relates to, according to a first embodiment, to an electronic system with integrated capacitive power transfer, the electronic system comprising: an electronic device comprising a connecting part having a connecting surface; a charging device comprising a recess for docking the electronic device in a docking position, wherein a recess surface of the recess at least partly coincides with the connecting surface; and a capacitive power transfer system comprising two capacitor pairs configured for capacitive power transfer from the charging device to the electronic device in the docking position.

Furthermore, each capacitor pair preferably comprises: one power receiving capacitor plate integrated in or on the connecting surface of the electronic device; and one power transmitting capacitor plate integrated in or on the recess surface of the charging device. It is a further preference that the electronic system is configured such that the power receiving capacitor plate and the power transmitting capacitor plate of each capacitor pair are substantially aligned in the docking position.

Capacitors shape

In one embodiment of the present disclosure the power receiving capacitor plate and the power transmitting capacitor plate of each capacitor pair have substantially the same shape. Although it may be a possibility, it is not a requirement that the size of the power receiving capacitor plate and the power transmitting capacitor plate of each capacitor pair have the same size. Thereby, when the sizes of the plates within the same pair are different, the larger plate may comprise a part which is substantially the same as the shape of the smaller plate.

Thereby, the power receiving capacitor plate and the power transmitting capacitor plate of each capacitor pair preferably have the same shape or comprise parts with the same shape. It may further be a possibility that the power transmitting capacitor plate of each capacitor pair are arranged in close proximity in the docking position. Said plates may be in closer proximity if said plates have the same shape or comprise parts with the same shape. However, this may also be possible without the plates having the same shape or comprise parts with the same shape.

In a preferred embodiment of the present disclosure, the power receiving capacitor plates wrap around at least half the connecting surface, such as along a plane intersecting the recess surface, more preferably the power receiving capacitor plates wrap around the entire recess surface. Additionally or alternatively the power transmitting capacitor may be provided along at least half the connecting surface, more preferably the power transmitting capacitor plates may be provided along the entire connecting surface. Two power transmitting capacitor plates of a charging device may thereby form two substantially parallel tracks along a part of the recess surface, such as the entire recess surface. Similarly, the power receiving capacitor plates may be provided as to form two substantially parallel tracks that wrap around the electronic device. By arranging the power receiving capacitor plates so as to wrap around the connecting surface of the electronic device, while the power transmitting capacitor plates are arranged in a complementary manner on the recess surface. The electronic device may be positioned in the docking position without being sensitive to the relative angle between the recess surface and the connecting surface. The power transmitting capacitor plates may be provided along a recess surface having an irregular shape and/or the power receiving capacitor plates may be provided around a connecting surface with an irregular shape. Preferably, each capacitor plate is provided along a plane, wherein said plane is parallel between each capacitor plate pair.

While the electronic device is not limited to any specific type of electronic device, the advantage with capacitor plates having the above mentioned configuration may be exemplified by an electronic stylus, see Fig. 7A-C, that typically has a rod-like shape. The power receiving capacitor plates may be provided so as to wrap around the stylus, e.g. wherein each power receiving capacitor plate substantially forms a tube, or any other arc length of a tube. The power receiving capacitor plates are preferably parallel around the stylus.

It is further a preference that the system is configured such that each capacitor pair forms a capacitive coupling, in the docking position. This may for example be enabled by the power receiving capacitor plate and the power transmitting capacitor plate of each capacitor pair preferably have the same shape or comprise parts with the same shape. Alternatively or additionally, it may be enabled by the configuration of the recess and the connecting part, such as the recess surface and the connecting surface and/or the configuration of the power receiving capacitor plate and the power transmitting capacitor plate, for example their location or rotation on said surfaces.

In an embodiment of the present disclosure one or both capacitor pairs are non-planar. Instead, any, or multiple of the capacitor plates may have curved shapes or even be irregular shaped, acting to alleviate the design restrictions on the electronic system. Thereby, the electronic system may not necessarily be configured for conductive power transfer between two planar surfaces. For capacitor plates of one capacitor pair that are curved or irregular shaped it is a preference that the power receiving capacitor plate and the power transmitting capacitor plate of each capacitor pair have the same (i.e. complementary) shape or comprise parts with the same shape, such that they can be in close proximity and form a capacitive coupling in the docking position. In an embodiment of the present disclosure, the power transmitting and/or power receiving capacitor plates are provided on the outside of the casing of the charging device and/or electronic device respectively. The power transmitting and/or power receiving capacitor plates may advantageously be provided as a thin film/foil, preferably covered by a coating layer, such as an insulating layer. In alternative embodiment of the present disclosure, the power transmitting and/or power receiving capacitor plates are provided as part of the casing of the charging device and/or electronic device respectively, such as wherein the power transmitting and/or power receiving capacitor plates. form an integral part of the casing of the charging device and/or electronic device respectively. The casing may act to insulate the power transmitting and/or power receiving capacitor plates in this configuration, i.e. the casing may cover the power transmitting and/or power receiving capacitor plates.

In an embodiment of the present disclosure, the power transmitting and/or power receiving capacitor plates are fixed in position with respect to the casing. The power transmitting and/or power receiving capacitor plates may be fixed in position with respect to the entire casing or parts thereof, such as the part of the casing that forms the recess and/or connecting surface respectively. Power transmitting and/or power receiving capacitor plates that are fixed in position, may for example enable devices with thinner plates, such as part of a casing or as a fixed film coated on a casing of a device. For example, in an embodiment of the present disclosure, the power transmitting and/or power receiving capacitor plates is a film with a thickness below 1 mm, such as below 500 pm.

In an embodiment of the present disclosure, the power transmitting and/or power receiving capacitor plates comprise or consist of a flexible material, such as a flexible metal foil. By the use of flexible metal foils, the capacitor plates may have a shape that conforms with the shape of the device of which the capacitor plates form a part (e.g. a charging device or an electronic device). In a preferred embodiment, the capacitor plate comprises a flexible metal foil (i.e. a metal layer) covered at least partly by an oxide layer, for example wherein the metal layer is aluminium and the oxide layer is aluminium oxide. The capacitor plates (transmitting and or receiving) may for example comprise or consist of an oxidized metal. A metal capacitor plate comprising an oxide layer may have a thickness of less than 50 pm, such as less than 20 pm.

It is a preference that the power receiving capacitor plates each have a shape matching individual parts of the connecting surface of the connecting part of the electronic device. Similarly, it may be a preference that the power transmitting capacitor plates each have a shape matching individual parts of the recess surface of the recess of the charging device (i.e. a complementary shape). The matching shapes preferably act to ensure that the capacitor pairs each form a capacitive coupling in the docking position.

In a further embodiment of the present disclosure the power receiving capacitor plates form an integral part of a casing of said electronic device. In an embodiment of the present disclosure, the power receiving capacitor plates are provided on the outside of the casing of the electronic device, preferably covered by an insulating layer. Alternatively, the capacitive plates may further be covered, by either a part of the casing, or an insulating layer. An outer surface of the connecting part may thereby be a continuous layer. This may further be true for the charging device, wherein the recess surface may be a continuous layer.

A continuous outer surface of the electronic device and/or the charging device may act to increase the durability and the hygiene. Firstly, by the use of a continuous outer layer the electronic device, or the charging device, may be water resistant. This may thereby act to ensure a durable electronic device and/or charging device, as it may be able to withstand liquids, such as water.

Thereby, in an embodiment of the present disclosure, the outer surface of the connecting part is a continuous layer and/or the outer surface of the recess is a continuous layer. Alternatively, or additionally, the power transmitting capacitor plates may form an integral part of the casing of said recess surface of the charging device and/or the casing of the connecting surface of the electronic device. Preferably, the recess surface and/or the connecting surface is a continuous layer.

Capacitors material

In a further embodiment of the present disclosure, the power receiving capacitor plates and the power transmitting capacitor plates are in a conductive material, such as a metal. Thereby, it is a preference that the power receiving capacitor plates and the power transmitting capacitor plates are conductive.

In another embodiment of the present disclosure, the capacitor plates comprise an insulating layer. The insulating layer is preferably on the outside of the electronic device and/or the charging device, thereby, the insulating layer may be the outermost layer of one, or more, such as all, of the capacitor plates. Preferably the insulating layer is configured such that the capacitor plates of each capacitor pair does not short-circuit, for example in the docking position.

Preferably, the insulating layer is in an insulating material, and may be less than 100 micrometers in thickness, preferably less than 10 micrometers, or even more preferably less than 1 micrometer. The insulating layer, and/or the capacitor plates, may be manufactured by a thin-film technology, such as physical vapor deposition (PVD), chemical vapor deposition, sputtering, and thermal evaporation. However, in an embodiment of the present disclosure, the insulating layer, and/or the capacitor plates, may have been manufactured by physical vapor deposition. Thereby, at least a part of the capacitor plates may be the result of a process comprising physical vapor deposition.

Physical vapor deposition is also sometimes called physical vapor transport (PVT), and comprises a number of vacuum deposition methods for producing thin films and coatings. Typically, PVD is characterized by a process in which the material goes from a condensed phase to a vapor phase and then back to a thin film condensed phase. Two common PVD processes are sputtering and evaporation.

Therefore, in an embodiment of the present disclosure, each capacitor plate is a film with a thickness below 100 micrometers, preferably below 10 micrometers, yet more preferable below 1 micrometer.

It should be noted that the coupling capacitance is given by

C _r = A A e- = e- (Eq. 1) d ( -2 d₂ +d₃ -) , wherein A is the capacitor plate area, e is the permittivity and d is the distance between two capacitor plates. Therefore, a shorter distance between the capacitor plates (d) will result in a higher capacitance. Therefore, by decreasing the thickness of the insulating layers and/or the distance between the insulating layers of a capacitor pair (decreasing the air gap), such as in the docking position, the coupling capacitance may be increased.

Capacitor properties In an embodiment of the present disclosure, the surface area of each capacitor plate is between 1 mm² and 2500 mm². As the coupling capacitance is proportional to the surface area, a larger surface area is typically preferred. At the same time, in an embodiment of the present disclosure, the footprint of each capacitor plate is between 1 mm² and 2500 mm². Thereby, the footprint may be equal to the surface area. This is in contrast to an inductor, wherein the surface area may be considered to be the area occupied by the coil. However, the same inductor would have a footprint which is larger than said surface area. For an electronic device, the important aspect may be the volume taken up by the power receiving component, such as an inductor or a capacitor. As further discussed elsewhere herein, the volume occupied by a capacitor, for reaching the same power transfer characteristics, between a charging device and an electronic device is smaller, thereby it would be preferred to have capacitive charging for space-sensitive electronic devices.

Electronic devices that are space-sensitive, may include, but are not limited to, smartphones, smart watches, hearing aids, wireless headphones and industrial sensors. Typically, the electronic device comprises a battery, such as a rechargeable battery.

In an embodiment of the present disclosure, the electronic device comprises a battery and wherein the electronic system is configured for charging said battery. Preferably, charging of said battery comprises capacitive power transfer, such as between transmitting capacitive plates and receiving capacitive plates, for providing a charge from the charging device and the electronic device, and subsequently the electronic system may be configured to provide said charge to the battery.

In another embodiment of the present disclosure the capacitive power transfer is wireless power transfer. Thereby, power may be wirelessly transmitted from the charging device to the electronic device. Preferably, the electronic system comprises a transverse design capacitive coupling.

In an embodiment of the present disclosure, the interface voltage between the capacitor plates of each capacitor pair is less than 30 V, preferably less than 15 V, yet more preferable around 5 V. Decreasing the interface voltage, while simultaneously keeping the transferred power constant, may be possible by increasing the coupling capacitance, the frequency, and/or the dielectric material between the plates.

Therefore, in an embodiment of the present disclosure, the coupling capacitance is at least 10 pF. In certain embodiments of the present disclosure, the coupling capacitance may however be at least 100 pF. The coupling capacitance is typically related to the area of the capacitor plates. For example, capacitor plates with surface areas of at least 100 mm² each may allow for a coupling capacitance of at least 100 pF.

In another embodiment of the present disclosure, the charging device further comprises: an inverter configured to convert a DC supply voltage into an AC voltage; a C or an LCL compensation topology arranged between the inverter and the transmitting capacitor plates. Said LCL compensation topology may be arranged between the inverter and the capacitive coupler. The value of the coupling capacitance depends on factors such as the plate area, distance between the plates and the dielectric material between the plates. Since the permittivity constant of air is small the value of the coupling capacitance is typically limited. The role of the C or LCL compensation topology may therefore be to provide resonance such that sufficiently high voltages to generate electric fields between the plates are generated. In one embodiment of the presently disclosed power transfer system, the C or LCL compensation topology is configured to resonate with the capacitive coupler. If the receiving side of the electronic system does not comprise any inductors, the receiving side of the electronic system may be made smaller. Therefore, it may be an advantage to only have a C compensation topology.

On the receiving side, the capacitive power transfer system may further comprise a rectifier configured to convert the wirelessly transferred AC voltage into a DC output. The DC output can be connected to a load, such as a rechargeable battery of the electronic device. The capacitive power transfer system may further comprise a control unit configured to control the DC power source and/or the inverter. Preferably, the control unit is configured to control the DC power source and/or the inverter such that the capacitive power transfer system: in a constant current mode, operates at a constant current mode frequency (f_cc), wherein a constant current is provided to the load; and in a constant voltage mode, operates at a constant voltage mode frequency (fcv), wherein a constant voltage is provided to the load. The inventors have realized that by controlling the switching frequency of the inverter at the constant current mode frequency (f_ee) and the constant voltage mode frequency (f_cv), wherein the frequencies are based on component parameter values of the LCL compensation topology, load independent output current and output voltage can be achieved.

Therefore in one embodiment of the presently disclosed power transfer system, the constant current in the constant current mode and the constant voltage in the constant voltage mode are load independent. The proposed capacitive power transfer system may operate without the need for LCL compensation and DC-DC conversion on the receiving side. Therefore, in one embodiment of the presently disclosed power transfer system, the system is configured to operate without a compensation topology and/or without a DC-DC receiver on a receiving side of the capacitive power transfer system.

In the known systems, a DC-DC converter is typically used to regulate the output. In the present system such DC-DC converters can be eliminated. The control unit may be configured to control the AC voltage from the inverter by phase-shift control and/or by controlling the DC supply voltage from the DC power source. In one embodiment the DC power source comprises a DC-DC converter. The DC supply voltage can be controlled by controlling the DC-DC converter. The control unit may also control a phase-shifting of the inverter to change the output of the inverter. By using the presently disclosed constant current mode or constant voltage mode, the current or voltage can be kept stable.

No inductors

As mentioned elsewhere herein, replacing inductors with capacitors saves spaces. For example, the conductive power transfer saves a significant amount of space with respect to similar electronic devices relying on inductive power transfer. Additionally, to further decrease the size of space-sensitive devices, such as the electronic device, and/or allow for increasing other components of the same, other inductors, such as all inductors on the receiving side of the electronic system. This further acts to free up space, in order to decrease the size of the electronic device and/or to use said space for other electronic components.

Therefore, in an embodiment of the present disclosure, the receiving side of the electronic system may comprise a rectifier, such as a diode rectifier. Preferably, the receiving side of the electronic system further comprises a voltage regulator, such as a low dropout regulator or a switched capacitor DC/DC converter. A low-dropout or LDO regulator is a DC linear voltage regulator that can regulate the output voltage even when the supply voltage is very close to the output voltage. Typical advantages of a low dropout voltage regulator over other DC to DC regulators comprise the absence of switching noise, as no switching takes place, smaller device size, as neither large inductors nor transformers are needed, and greater design simplicity, typically consisting of a reference, an amplifier, and a pass element. Low-dropout regulators typically use an open collector or an open drain topology, wherein the transistor may be easily driven into saturation with the voltages available to the regulator. This allows the voltage drop from the unregulated voltage to the regulated voltage to be as low as the saturation voltage across the transistor.

As the LDO regulator typically requires its supply voltage to be close to the output voltage, it is a further preference that the receiving side of the electronic system comprise a control unit configured to control the DC power source and/or the inverter such that the voltage input to the voltage regulator is near a predetermined value. Alternatively, or additionally, the voltage regulator may be a switched capacitor DC/DC converter. A switched capacitor DC/DC converter is known to the person skilled in the art, and further disclosed in “Design of DC-DC Converters for Rechargeable Hearing Aids”, Larsen, 2018. This is a DC/DC converter that only requires semiconductors and capacitors, i.e. said converter does not rely on inductors.

The present disclosure further relates to a compact rechargeable electronic device comprising a casing, comprising a connecting part for being received by a corresponding recess of a charging device in a docking position, the connecting part having a connecting surface; a rechargeable battery; and two power receiving capacitor plates integrated in or on the connecting surface, the two power receiving capacitor plates arranged to form a capacitive power transfer from two corresponding power transmitting capacitor plates of the charging device in the docking position.

The present disclosure yet further relates to a charging device comprising: a recess for receiving a rechargeable electronic device in a docking position, the recess having a shape corresponding to a connecting part of the rechargeable electronic device; and two power transmitting capacitor plates integrated in or on a recess surface of the recess, the two power transmitting capacitor plates arranged to form a capacitive power transfer to two corresponding power receiving

Detailed description of drawings

The invention will in the following be described in greater detail with reference to the accompanying drawings. The drawings are exemplary and are intended to illustrate some of the features of the presently disclosed electronic system with integrated capacitive power transfer, and further an electronic device configured for capacitive power transfer, and a charging device configured for capacitive power transfer, and are not to be construed as limiting to the presently disclosed invention.

Fig. 1 A and 1 B show schematic illustrations of perpendicular cross sections of an electronic system. The electronic system (1) comprises an electronic device (2) and a charging device (3), both comprising two capacitor plates (4). The electronic system is simplified, and not all electronic components are shown, instead the electronic circuit of the charging device can be simplified as an AC power (5), that following capacitive power transfer to the electronic device, is supplied to a load (6), potentially in the form of a rechargeable battery. The electronic system is here shown in the docking position, wherein the electronic device may receive power from the charging device, by capacitive power transfer.

The two main components of the electronic system, the electronic device (2) and the charging device (3), are selectively attachable and detachable, and shown in Fig. 2A and 2B, respectively, in their separated mode. The electronic device comprises a connecting part (7), having a connecting surface (8), and the charging device comprises a recess (9) for docking the electronic device in a docking position, said recess comprises a recess surface (10). The electronic device further comprises an electronic device case (11) and the charging station comprises a charging device case (12). As seen in the figures, the capacitive plates may form part of the case, and may thereby be provided in arbitrary shapes, such as irregular shapes or curved surfaces. The recess surface and/or the connecting surface may be a continuous surface, covering the capacitor plates.

The system is configured such that each capacitor pair forms a capacitive coupling, in the docking position, Fig 3. The capacitor pair may comprise five layers, wherein each side of the capacitor pair comprise a capacitor plate (4), preferably covered by an insulating layer (13) in an insulating material. The insulating layers may be distanced from each other, such that an air gap is formed in between the two. As the coupling capacitance is typically inversely proportional to the distance between the two capacitor plates, there is a strong desire to minimize the same. This may include fabrication of the insulating layer and/or the capacitor plates by thin-film technology, such as physical vapor deposition. Furthermore, the air gap may be minimized by ensuring a match between the connecting part and the recess, specifically the connecting surface and the recess surface. Wires (15) may be used to electrically connect the capacitive plates with the other components of the electronic system.

A simplified schematic illustration of the electronic circuit of the electronic system is given in Fig 4. The electronic system comprises a DC power source (5) providing an input DC supply voltage and an inverter (17) configured to convert the DC supply voltage into an AC voltage. The inverter may be implemented as any type of suitable inverter, such as a full-bridge inverter, for example comprising four power switches (25), a half-bridge inverter, or a Class-E inverter. The electronic system further comprises a capacitive coupler (19) configured to transfer the AC voltage wirelessly. In the example, the capacitive coupler (19) is implemented as two pairs of coupled plates (C_pi and C_P2). The electronic system further comprises an LCL compensation topology (18) arranged between the inverter (17) and the capacitive coupler (19). On the receiving side, there is a secondary compensation circuit (20) and a rectifier (21), configured to convert the wirelessly transferred AC voltage into a DC output. In the example, the rectifier is a full-bridge diode rectifier comprising four diodes (25). Alternatively, the rectifier (21) may be implemented as any other suitable passive or active rectifier. The DC output is connected to a load (5), which has an output capacitor

(22) arranged in parallel. The electronic system further comprises a control unit (23) configured to control the DC power source (16) and/or the inverter (17) to operate the capacitive power transfer system in a constant current mode and in a constant voltage mode.

As detailed elsewhere herein, replacing inductors with capacitors saves space of electronic devices, therefore it may be a preference to rectify and regulate the voltage in the electronic system, on the electronic device side, without the use of inductors. This may be realized, as shown in Fig. 5, wherein the electronic system comprises a DC power source (5) providing an input DC supply voltage and an inverter (17) configured to convert the DC supply voltage into an AC voltage. The inverter may be implemented as any type of suitable inverter, such as a full-bridge inverter, for example comprising four power switches (25), a half-bridge inverter, or a Class-E inverter. The electronic system further comprises a capacitive coupler (19) configured to transfer the AC voltage wirelessly. In the example, the capacitive coupler (19) is implemented as two pairs of coupled plates (C_pi and C_P2). The electronic system further comprises an LCL compensation topology (18) arranged between the inverter (17) and the capacitive coupler (19). On the receiving side, the electronic system comprises a rectifier (20), here shown as a diode rectifier. Furthermore, a voltage regulator (24) is used to regulate the output voltage. To minimize the volume occupied by the electronic components of the receiving side of the electronic system, the voltage regulator preferably does not comprise any inductors. Preferably the voltage regulator is a switched capacitor DC-DC converter or a low-dropout regulator.

As the LDO regulator typically requires its supply voltage to be close to the output voltage, it is a further preference that the electronic system comprises a control unit

(23) configured to control the DC power source (16) and/or the inverter (17) such that the voltage input to the voltage regulator (24) is near a predetermined value. For this purpose, the control unit may further be configured to measure voltages (25), and further, to wirelessly communicate (26) with the DC power source (16) and/or the inverter (17). A switched capacitor DC/DC converter is known to the person skilled in the art, and further disclosed in “Design of DC-DC Converters for Rechargeable Hearing Aids”, Larsen, 2018. This is a DC/DC converter that only requires semiconductors and capacitors, i.e. said converter does not rely on inductors.

An electronic device (2) may be configured as shown in Fig. 6. The electronic device is here shown comprising a part of an electronic system (1) and configured for being wirelessly charged by capacitive power transfer (32). The receiving side of the electronic system may comprise a voltage regulator (24), such as a switched DC/DC converter, which is electrically connected to a battery management system (27), and a battery (28). The battery management unit may thereby control how the electronic device is powered. It may either be powered by the battery, or by the capacitive power transfer, or a combination of the two. Additionally, when the receiving side of the electronic system receives power by capacitive power transfer, the battery is preferably charged, such that the electronic device can be independently powered by the battery. The voltage regulator may supply other parts of the electronic device with power. For a hearing aid, the voltage regulator may thereby supply power to an analog-to-digital converter (ADC, 29), digital signal processing (DSP, 30), and digital-to-analog converter (DAC, 31).

The capacitor plates may be provided in many different configurations. In a preferred embodiment of the present disclosure, the power receiving capacitor plates are arranged to wrap around at least a part of the connecting surface, such as the entire connecting surface, and/or at least a part of the electronic device, such as the entire electronic device. Additionally or alternatively, the power transmitting capacitor plates may be arranged along at least a part of the recess surface, such as the entire recess surface. The recess surface is typically provided as an indentation of an exterior surface of the charging station. Here, it may be advantageous if the power transmitting capacitor plates are arranged to line the recess surface across said indentation. A similar arrangement is shown in Fig. 7 of a charging system (75). Here, a schematic illustration according to a specific embodiment is shown comprising a rod-shaped electronic device connected to a charging device. Fig. 7 A shows a top-down view of the electronic device (71) and charging device (72). The electronic device is located in an indentation of the exterior surface of the charging device, wherein said indentation forms a recess surface comprising power transmitting capacitor plates. The power receiving capacitor plates (73) of the electronic device wraps around said electronic device, and thus the connection between the power receiving capacitor plates and the power transmitting capacitor plates are not sensitive to rotation (around the axial length) of the electronic device when the electronic device has docked with the charging device, i.e. when the electronic device is received by the charging station within the indentation forming the recess surface, such as wherein the capacitor plate pairs are (electrically) connected. In this example, the connecting surface is provided around the entire axial length of the electronic device. When a part of the connecting surface is received by the recess surface, such that the capacitor plates engage, power may be provided from the charging device to the electronic device. It is a preference that the electronic system comprises alignment means (74), for aligning the capacitive plate pairs, typically along the axial length of the electronic device. The alignment means may be provided on the electronic device as a protrusion or indentation, and arranged to engage a corresponding protrusion or indentation on the charging device such that the capacitive plate pairs are aligned. The electronic device may for example comprise a protrusion, such as a flange, while the charging station comprises an indentation corresponding to said protrusion. Fig. 7B shows a schematic illustration of a cross section along line B of Fig. 7A. It can be seen that the recess surface of the charging station comprises power transmitting capacitor plates (76) arranged to engage with the power receiving capacitor plates (73) that wraps around the electronic device. Fig. 7C shows a schematic illustration of a cross section of the electronic device along line C in Fig. 7 A. It can be seen how the power receiving capacitor plate (73) wraps around the electronic device (71). Similarly, the power transmitting capacitor plate (76) is arranged across the recess surface. The capacitor plates are such that the rotation (along the axial length) of the electronic device, does not interfere with the coupling between the capacitor plates. The shown example may be provided in many different arrangements, for example the recess surface and/or the connecting surface may comprise an outer continuous layer (e.g. wherein the capacitor plates are arranged). Further, the capacitor plates do not necessarily extend along the entire recess/connecting surface. The shape of the electronic device does not have to be rod shaped, but could be any electronic device having a symmetry axis along the connecting surface. In an embodiment, the alignment means comprise only features positioned on the charging device. For example, in such an arrangement, the alignment means may comprise one or two stoppers positioned at one or both ends of the electronic device, when in docking positioned. Such an alignment means ensures that the capacitor plate pairs remain aligned by ensuring that the electronic device is prevented from sliding along the recess surface (in one or both directions). Typically, the recess surface extends along the axial length of the electronic device, in such a configuration the at least one stopper may be provided as part of the recess surface, such that the stopper is to, upon contact with the electronic device, prevent movement of the electronic device towards the stopper, such as sliding along the recess surface. The exemplified electronic device may be other types of electronic devices, for example hearing aids or headphones. It should be noted that while the electronic device, is exemplified as rod-shaped, the electronic device may be provided in any shape. For example, the electronic device may be arranged such that a cross-section perpendicular one or all of the capacitive plates have a regular or irregular shape. The shape may be polygonal, rounded, or a mix thereof. Preferably the transmitting capacitor plates are complementary shaped, such that the power receiving and power transmitting capacitor plates are spaced apart at a constant length over the entire lengths of said plates, when the electronic device is in docking position. Said lengths may be the thickness of the insulating layer (or layers if both the charging device and electronic device comprises an insulating layer).

Example 1 A system for capacitive power transfer for a portable device A prototype of an electronic system with integrated capacitive power transfer was fabricated. The design specification are provided in Table I, below. As can be seen the device was set to operate at a frequency of 13.56 MHz, and with a desired output voltage of 2.8 V and current of 87 mA. TABLE I: Design specifications for a CPT system for a portable device

A system for capacitive power transfer for a portable device was assembled, according to the circuit diagram provided in Fig. 8A. As can be seen the setup resembles the one provided in Fig. 5. The electronic system comprises a transmitting side (81), e.g. a charging device, comprising an input voltage source (83), an inverter (84), an LCL compensation (85) and transmitting capacitor plates forming a capacitive coupling (86) with the receiving capacitor plates of the receiving side (82), e.g. a portable electronic device. The receiving side further comprises a rectifier (87) and a DC load (88). The properties of the components of the system are provided in Table II.

TABLE II: Detailed parameters of the 13.56 MHz CPT prototype

*lnductance and capacitance were measured by impedance analyzer Agilent 4294A.

A figure showing a part of the system is provided in Fig 8B.

The output current was characterized, as shown in Fig. 8C-D. Fig 8C shows the measured output current for the electronic device (from the full-load to the light-load condition). Fig. 8D shows the measured AC current of the electronic device in 13.56 MHz operation frequency.

Conclusion

The system for capacitive power transfer for a portable device was fully working.

Items

1. An electronic system with integrated capacitive power transfer, the electronic system comprising:

• a capacitive power transfer system comprising two capacitor pairs configured for capacitive power transfer from the charging device to the electronic device in the docking position, each capacitor pair comprising: o one power receiving capacitor plate integrated in or on the connecting surface of the electronic device; and o one power transmitting capacitor plate integrated in or on the recess surface of the charging device, wherein the power receiving capacitor plate and the power transmitting capacitor plate of each capacitor pair are substantially aligned in the docking position. 2. The electronic system according to item 1, wherein the power receiving capacitor plate and the power transmitting capacitor plate of each capacitor pair have substantially the same shape i.e. complementary shapes.

3. The electronic system according to any one of the preceding items, wherein the power receiving capacitor plate and the power transmitting capacitor plate of each capacitor pair are arranged in close proximity in the docking position.

4. The electronic system according to any one of the preceding items, wherein the system is configured such that each capacitor pair forms a capacitive coupling, in the docking position.

5. The electronic system according to any one of the preceding items, wherein one or both capacitor pairs are non-planar. 6. The electronic system according to any one of the preceding items, wherein the power receiving capacitor plates and power transmitting capacitor plates have curved geometries. 7. The electronic system according to any one of the preceding items, wherein the power receiving capacitor plates each have a shape matching individual parts of the connecting surface of the connecting part of the electronic device.

8. The electronic system according to any one of the preceding items, wherein the power receiving capacitor plates form an integral part of a casing of said electronic device.

9. The electronic system according to any one of the preceding items, wherein an outer surface of the connecting part is a continuous layer.

10. The electronic system according to any one of the preceding items, wherein the power transmitting capacitor plates form an integral part of the casing of said recess surface of the charging device.

11. The electronic system according to any one of the preceding items, wherein the recess surface is a continuous layer.

12. The electronic system according to any one of the preceding items, wherein the power receiving capacitor plates and the power transmitting capacitor plates are made of a conductive material, such as a metal.

13. The electronic system according to any one of the preceding items, wherein the capacitor plates comprises an insulating layer, formed on the outside of the devices, for avoiding short circuit.

14. The electronic system according to any one of the preceding items, wherein the power receiving capacitor plates and/or the power transmitting capacitor plates comprises a metal layer covered by an oxide layer. 15. The electronic system according to any one of the preceding items, wherein the capacitor plates and/or the insulating layers are formed by physical vapor deposition.

16. The electronic system according to any one of the preceding items, wherein each capacitor plate is a film, such as a metal film, with a thickness below 1 mm, such as below 500 pm, more preferably below 100 pm, yet more preferably below 50 pm.

17. The electronic system according to any one of the preceding items, wherein a surface area of each capacitor plate is between 1 mm² and 2500 mm².

18. The electronic system according to any one of the preceding items, wherein a footprint of each capacitor plate is between 1 mm² and 2500 mm², such as substantially equal to the surface area.

19. The electronic system according to any one of the preceding items, wherein said electronic device is a smart phone, stylus, smart watch, hearing aid, wireless headphones or industrial sensor.

20. The electronic system according to any one of the preceding items, wherein the electronic device comprises a rechargeable battery and wherein said system is configured for providing a charge to said rechargeable battery by capacitive power transfer.

21. The electronic system according to any one of the preceding items, wherein the capacitive power transfer is a wireless power transfer.

22. The electronic system according to any one of the preceding items, wherein an interface voltage between the capacitor plates of each capacitor pair is less than 30 V, such as less than 15 V, such as around 5 V.

23. The electronic system according to any one of the preceding items, wherein the coupling capacitance is at least 10 pF, such as at least 100 pF. 24. The electronic system according to any one of the preceding items, wherein the charging device further comprises:

• an inverter configured to convert a DC supply voltage into an AC voltage;

• a C or LCL compensation topology arranged between the inverter and the transmitting capacitor plates.

25. The electronic system according to any one of the preceding items, further comprising a control unit configured to control a DC power source and/or the inverter such that the capacitive power transfer system:

26. The electronic system according to any one of the preceding items, wherein the constant current in the constant current mode and the constant voltage in the constant voltage mode are load independent.

27. The electronic system according to any one of the preceding items, wherein the electronic device further comprises:

• a rectifier configured to convert an AC voltage into a DC output, said DC output connectable to a load, such as a rechargeable battery of the electronic device.

28. The electronic system according to item 26, wherein the receiving side of the electronic system has a C compensation topology.

29. The electronic system according to any of items 26-27, wherein the electronic system, on the receiving side, comprises a voltage regulator.

30. The electronic system according to item 28, wherein the voltage regulator is a low dropout regulator or a switched capacitor DC/DC converter. The electronic system according to any of items 28-29, wherein the electronic system comprises a control unit configured to control the DC power source and/or the inverter such that the voltage input to the voltage regulator is near a predetermined value. A compact rechargeable electronic device comprising:

• a casing, comprising a connecting part for being received by a corresponding recess of a charging device in a docking position, the connecting part having a connecting surface; · a rechargeable battery; and

• two power receiving capacitor plates integrated in or on the connecting surface, the two power receiving capacitor plates arranged to form a capacitive power transfer from two corresponding power transmitting capacitor plates of the charging device in the docking position. A charging device comprising:

• a recess for receiving a rechargeable electronic device in a docking position, the recess having a shape corresponding to a connecting part of the rechargeable electronic device; and · two power transmitting capacitor plates integrated in or on a recess surface of the recess, the two power transmitting capacitor plates arranged to form a capacitive power transfer to two corresponding power receiving capacitor plates of the rechargeable electronic device in the docking position.

Claims

• a capacitive power transfer system comprising two capacitor pairs comprising a metal film covered by an insulating layer, and wherein the capacitor pairs are configured for capacitive power transfer from the charging device to the electronic device in the docking position, each capacitor pair comprising: o one power receiving capacitor plate integrated in or on the connecting surface of the electronic device; and o one power transmitting capacitor plate integrated in or on the recess surface of the charging device, wherein the power receiving capacitor plate and the power transmitting capacitor plate of each capacitor pair are substantially aligned in the docking position.

2. The electronic system according to claim 1 , wherein the power receiving capacitor plates and the power transmitting capacitor plates have curved geometries and/or irregular shaped geometries and wherein the outer layer of the recess surface and the connecting surface are continuous layers.

3. The electronic system according to any one of the preceding claims, wherein the insulating layer is an metal oxide layer wherein the metal is the same material as the metal film, preferably aluminium.

4. The electronic system according to any one of the preceding claims, wherein the capacitor plate, such as the metal film and the insulating layer, has a thickness below 1 mm, such as below 500 pm, more preferably below 100 pm, yet more preferably below 50 pm

5. The electronic system according to any one of the preceding claims, wherein the power receiving capacitor plates and/or the connecting surface extends around a part of the electronic device such that the power receiving capacitor plates and/or the connecting surface form tubular shapes.

6. The electronic system according to claim 5, wherein the electronic system comprises alignment means, configured for aligning the capacitor plate pair by preventing sliding of the electronic device along the recess surface in at least one direction.

7. The electronic system according to any one of the preceding claims, wherein the power receiving capacitor plates form an integral part of a casing of said electronic device and/or wherein the power transmitting capacitor plates form an integral part of the casing of said recess surface of the charging device.

8. The electronic system according to any one of the preceding claims, wherein an interface voltage between the capacitor plates of each capacitor pair is less than 30 V, and wherein the coupling capacitance is at least 10 pF.

9. The electronic system according to any one of the preceding claims, wherein the charging device further comprises:

• an inverter configured to convert a DC supply voltage into an AC voltage;

• a C or an LCL compensation topology arranged between the inverter and the transmitting capacitor plates.

10. The electronic system according to claim 9, further comprising a control unit configured to control the DC supply voltage and/or the inverter such that the capacitive power transfer system:

11. The electronic system according to any one of the preceding claims, wherein the constant current in the constant current mode and/or the constant voltage in the constant voltage mode are load independent.

12. The electronic system according to any one of the preceding claims, wherein the electronic device further comprises:

13. The electronic system according to claim 12, wherein the receiving side of the electronic system has a C compensation topology; and/or wherein the electronic system, on the receiving side, comprises a voltage regulator and wherein the voltage regulator is a low dropout regulator or a switched capacitor DC/DC converter; and/or wherein the electronic system comprises a control unit configured to control the DC power source and/or the inverter such that the voltage input to the voltage regulator is near a predetermined value.

14. A compact rechargeable electronic device comprising:

• a rechargeable battery; and

• two power receiving capacitor plates, comprising a metal film covered by an insulating layer, integrated in or on the connecting surface, the two power receiving capacitor plates arranged to form a capacitive power transfer from two corresponding power transmitting capacitor plates of the charging device in the docking position.

15. A charging device comprising:

• two power transmitting capacitor plates, comprising a metal film covered by an insulating layer, integrated in or on a recess surface of the recess, the two power transmitting capacitor plates arranged to form a capacitive power transfer to two corresponding power receiving capacitor plates of the rechargeable electronic device in the docking position.