GB2628164A - A tuneable capacitor - Google Patents

Abstract

A tuneable capacitor comprises at least two parallel and coaxial conductive electrode bodies 101, 103. Each electrode body has a circular array of curved plates 105, 107 extending transversely from the electrode body towards the opposite electrode body, with the array of curved plates extending from one electrode body being radially spaced from the array of plates extending from the opposite electrode body. At least a portion of one of the electrode bodies may be rotatable about a central axis so that the mutual overlap between side surfaces of the curved plates of opposite electrode bodies is varied by the rotation of the portion of the electrode body relative to the opposite electrode body, thereby varying the capacitance with the rotation angle. The circular arrays may comprise several concentric rings of curved plates, with the concentric rings of one electrode body interleaved with the concentric rings of the opposite electrode body.

Description

A TUNEABLE CAPACITOR

FIELD OF THE INVENTION

The invention relates to a tuneable capacitor. In particular, it relates to a tuneable capacitor for continuous capacitance variation.

BACKGROUND TO THE INVENTION

A capacitor is a device that stores electrical energy in an electric field by accumulating electric charges on two proximate surfaces which are insulated from one another. Most capacitors consist of at least two electrical conductors or electrodes separated by a dielectric medium or insulator. When a voltage is applied across the electrodes, a static electric field develops that results in a positive charge collecting on one electrode and a negative charge collecting on the opposite electrode. The capacitance is the ratio of the electric charge on each electrode to the potential difference between them. A capacitor is an important component in radio frequency (RF) systems.

Supercapacitors, also known as Electrostatic Double Layer Capacitors (EDLCs), provide a higher capacitance than conventional capacitors and are suitable for electrical charge storage-related applications. In comparison to batteries and/or conventional capacitors, supercapacitors may have shorter charging and discharging cycles which ultimately results in faster-charging mechanisms of electronic devices. Supercapacitors also have a high power density and a high charge or energy storage density. Technological advancements in the manufacturing of supercapacitors and the materials they are made of has resulted in an increased usage of supercapacitors for short-term energy storage in communication systems, electronic devices, and portable electronic gadgetry.

Supercapacitors may be used for charging a smartphone, an Internet of Things (loT) device, an electric vehicle as battery back-ups, solar power banks and in other applications where a short-term power boost is required. Supercapacitors may also be used in resonant circuits, radio tuners, antenna impedance matching applications, frequency mixers, signal coupling and decoupling, electronic noise filtering, remote sensing, and prototyping an electronic circuit design.

In many applications, it is necessary or desirable to obtain a variable output from a capacitor. The capacitance of a capacitor may be varied by changing the overlap area between the electrodes, the spacing between the electrodes, or the quality factor (Q) of the capacitor. Capacitance variation can also be achieved by changing the dielectric medium between the electrodes. Material and/or substrate changes, microelectromechanical systems (M EMS) or micromachining techniques, electrostatic drive-based methods, and electronic or mechanical external mechanisms can be used to change the capacitance of a capacitor.

Russian patent application number SU641516A1 describes a variable vacuum capacitor comprising a housing with packages of movable and stationary cylindrical electrodes that are made stepped and are arranged coaxially. The capacitor has a mechanical mechanism for moving the electrodes in an axial direction to increase or decrease the mutual overlap between the packages of cylindrical electrodes to vary the capacitance.

Sarafian H. and Sarafian N. (J. Electromagnetic Analysis & Applications, 2009, 3: 138-144) describe a rotating parallel-plate capacitor in which one of the plates turns about the common vertical axis through the centers of the square plates to change the overlapping area of the plates thus the capacitance.

United States patent number US 9,424,994 82 relates to a tunable capacitor implemented as interdigitated arrays of finger elements arranged so that the spacing between finger arrays may be adjusted. The design has a number of advantages including high capacitance for a given circuit area, small area for a given desired capacitance, mechanical stability, high self resonance frequency, and high quality factor.

United States patent application number US 2005/0013087 Al describes a MEMS tunable capacitor with angular vertical comb-drive AVC actuators where high capacitances and a wide continuous tuning range is achieved in a compact space. The comb fingers rotate through a small vertical angle which allows a wider tuning range than in conventional lateral comb drive devices.

There remains a need for a tunable capacitor providing a high capacitance and having a continuous mechanism for varying capacitance that does not involve movement of the electrodes apart, which changes the outer dimensions of the capacitor and therefore requires more space in a circuit or device.

The preceding discussion of the background to the invention is intended only to facilitate an understanding of the present invention. It should be appreciated that the discussion is not an acknowledgment or admission that any of the material referred to was part of the common general knowledge in the art as at the priority date of the application.

SUMMARY OF THE INVENTION

In accordance with the invention there is provided a tuneable capacitor comprising at least two parallel and coaxial conductive electrode bodies, each electrode body having a circular array of curved plates extending transversely therefrom and in the direction of an opposite electrode body with the circular array of curved plates from one electrode body being radially inwardly or outwardly spaced from the circular array of curved plates extending from the opposite electrode body, wherein at least a portion of one of the electrode bodies is configured to be rotatable about a central axis passing through the circular arrays of curved plates so that the overlap between side surfaces of the curved plates of opposite electrode bodies is varied by rotation of the portion of the electrode body relative to the other electrode body, thereby varying the capacitance of the tuneable capacitor in use.

The circular array may comprise or consist of several concentric rings of curved plates that are radially spaced on the electrode body so that the concentric rings of curved plates extending from one electrode body interdigitate the concentric rings of curved plates extending from the opposite electrode body. The at least one electrode body as a whole and all the concentric rings of curved plates extending from the at least one electrode body may be configured to be rotatable together about the central axis. Alternatively, each concentric ring of curved plates may be configured to be individually rotatable about the central axis. In such an embodiment, the electrode body may be modular and comprise individually rotatable parts.

The curved plates in the circular array may be equally circumferentially spaced and one or more of the curved plates in the circular array may have a different plate width to the other curved plates. Preferably, all the curved plates along the circumference of a single circular array or ring have a different plate width. The plate width of adjacent circumferentially spaced curved plates may increase stepwise along the circumference of the circular array or ring. Alternatively, the curved plates in the circular array or ring may have an equal plate width but are differently circumferentially spaced along the circumference of the circular array, i.e., have different circumferential spacings between them. The circumferential spacings between adjacent curved plates in a single circular array or ring may increase stepwise along the circumference of the circular array or ring. Each circular array or ring of curved plates may have the same or a different number of curved plates.

Free ends of the curved plates extending from the electrode body may include a projection or ridge configured to be at least partially received in a circular groove defined in the opposite electrode body without contacting the opposite electrode body to increase the overlapping surface area of the electrode bodies and thus the capacitance of the tuneable capacitor. The projection and the groove may define or include complementary fractal geometries or structures to further increase the surface area of the electrode bodies for increased capacitance formation.

The electrode bodies may be disc shaped. The circular arrays of curved plates may extend from a generally flat surface of the disc-shaped electrode body.

One or more dielectric disc may be supported between and coaxially with the electrode bodies, the dielectric disc defining apertures through which the curved plates from each electrode body extend and curved projections which extend laterally from side walls of the apertures and partially into radial spaces between the circular arrays of plates, wherein either one or more of the electrode bodies is configured to be rotatable about the central axis relative to the dielectric disc or the dielectric disc is configured to be rotatable relative to the electrode bodies by a selected range of degrees depending on the size and shape of the aperture to vary the capacitance of the tuneable capacitor in use. A plurality of dielectric discs may be supported between the electrode bodies. Each dielectric disc may have a different permittivity.

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings: Figure 1 is a three-dimensional view of a first embodiment of a tuneable capacitor in a disassembled condition; Figure 2 is a three-dimensional view of a rectangular curved plate with its plate width (pw), plate length (pi) and plate thickness (pt) illustrated; Figure 3 is a schematic diagram of a circular-disc parallel plate capacitor in which rotary movement is incorporated as a mechanism to vary capacitance; Figure 4 is a cross-sectional view of a portion of two circular arrays of curved plates on opposite electrode bodies; Figure 5 is a schematic diagram illustrating the fragmentation of an electrode body with cylindrical projections along a secant line to form discrete, curved plates; Figure 6 is a three-dimensional view of a disc shaped electrode body with concentric rings of curved plates extending therefrom; Figure 7 is a top view of the disc shaped electrode body of Figure 6; Figure 8 is a schematic diagram illustrating how rotation of the electrode body of Figure 6 may vary capacitance; Figure 9 is a three-dimensional view of a part of an electrode body with projections on the free ends of the curved plates and complementary grooves on the electrode body that are configured to receive the projections on the curved plates of an opposite electrode body; Figure 10 is a three-dimensional view of a second embodiment of a tuneable capacitor with dielectric discs supported between the electrode bodies; Figure 11 is a schematic diagram showing A) a dielectric medium between curved plates of two opposite electrode bodies; B) the movement of the dielectric medium relative to the plates and C) the movement of one of the curved plates relative to the other curved plate and the dielectric medium; Figure 12 is a top view of a first embodiment of a dielectric disc; Figure 13 is a cross-sectional view of a sector of the dielectric disc of Figure 12 supported between two electrode bodies; Figure 14 is a top view of a second embodiment of a dielectric disc; Figure 15 is a three-dimensional view of a series of dielectric discs to be assembled into a tuneable capacitor; Figure 16 is a three-dimensional view of a third embodiment of a tuneable capacitor with dielectric discs supported between the electrode bodies in a disassembled condition; Figure 17 is a schematic diagram of a tuneable capacitor in which the circles represent the circular arrays of curved plates extending from electrode bodies; and Figure 18 is a schematic diagram of an aperture of a dielectric disc with curved plates extending therethrough.

DETAILED DESCRIPTION WITH REFERENCE TO THE DRAWINGS

A tuneable capacitor for use as a variable electric circuit component is provided. The tuneable capacitor comprises at least two parallel and coaxially arranged conductive electrode bodies. The electrode bodies are preferably generally disc shaped, i.e., flat and circular in which case the electrode bodies may also be described as top and bottom parallel discs. Each electrode body has a circular array of rectangular, curved plates extending transversely therefrom and in the direction of an opposite electrode body. The projected plates may be formed from the same conductive material as the rest of the electrode body. The plates may be integrally formed with the electrode body or attached thereto.

The circular arrays of plates of one electrode body are arranged to be radially inwardly or outwardly spaced from the circular array of curved plates extending from the opposite electrode body when the electrode bodies are adjacent and parallel to one another. The spacing between the plates of opposite electrode bodies is selected to ensure capacitance formation between them. Accordingly, the plates participate in capacitance formation together with the opposite flat surfaces of the disc-like electrode bodies. In effect, the curved plates provide a larger surface area for an increased overall capacitance.

At least a portion of one or both of the electrode bodies is configured to be rotatable about a central axis passing through the circular arrays of plates so that the overall or total mutual overlap between the sides of the discrete plates of opposite electrode bodies can be varied by rotation of the portion of the electrode body relative to the other electrode body, thereby varying the capacitance of the tuneable capacitor in use. It is preferred that one electrode body as a whole is configured to be rotatable about the central axis passing through the coaxial electrode bodies to vary the surface area overlap between the plates.

In one embodiment, the circular array of plates on each electrode body consists of a plurality of concentric rings of plates with the concentric rings being radially spaced from one another on the electrode body. The concentric rings on the one electrode body is radially offset from that of the opposite electrode body so that the concentric rings of curved plates extending from one electrode body interdigitate or interpose the concentric rings of curved plates extending from the opposite electrode body. The circular array of plates on an operatively upper electrode disc accordingly fits into the array on the operatively lower electrode disc, whilst allowing for rotary motion of the one disc and its plates relative to the other. Preferably, one or both of the electrode bodies and their associated plates are configured to be rotatable about the central axis. Rotation of the one electrode body relative to the other electrode body being useful for varying the mutual area overlap between the plates of the electrode bodies to change the capacitance of the capacitor. In another embodiment, the electrode bodies may further be configured to be moved or translated axially, i.e, closer together or apart, to further vary the capacitance of the tuneable capacitor.

The curved plates in the circular array may be equally circumferentially spaced with one or more of the curved plates in the circular array having a different plate width to the other curved plates. Preferably, all the curved plates along the circumference of a single circular array or ring have a different plate width. In one such embodiment, the plate width of adjacent circumferentially spaced curved plates increases stepwise along the circumference of the circular array or ring. In an alternative embodiment, the curved plates in the circular array or ring have an equal plate width but are differently circumferentially spaced along the circumference of the circular array, i.e., have different circumferential spacings between them. The circumferential spacings between adjacent curved plates in a single circular array or ring may increase stepwise along the circumference of the circular array or ring. Each circular array or ring of curved plates may have the same or a different number of curved plates.

A first exemplary embodiment of a tuneable capacitor (100) is shown in a disassembled condition in Figure 1. The tuneable capacitor (100) has a first electrode body (101) that is opposite to and parallel with a second electrode body (103). Generally rectangular or cuboid-shaped, curved plates (105, 107) or extrudes extend from the electrode bodies (101, 103). The electrode bodies (101, 103) are shown in a disassembled condition in which the electrode bodies (101, 103) have been moved axially apart in Figure 1. In an assembled condition of the tuneable capacitor, the plates (105) of the upper electrode body (101) are at least partially interposed between the plates (107) of the lower electrode body (103). The curved plates (105) extending generally perpendicularly from the first, operatively upper electrode body (101) are arranged in concentric circles with the plates (105) sized and shaped to fit into the radial spacings (109) between the complementary array of plates (107) on the second, operatively lower electrode body (103) and vice versa. The radial spacings (109) defined between the concentric circles on each of the electrode bodies are circular and allow for the continuous rotation of the one electrode body relative to the other. Either the upper electrode body (101) or the lower electrode body (103) may be configured to be rotatable by any suitable rotary mechanism associated with the electrode bodies, whereas the other electrode body may remain fixed to allow for relative rotation. Alternatively, both electrode bodies may be configured to be rotatable in opposite directions, i.e, one in a clockwise direction and the other in an anticlockwise direction.

In the embodiment of Figure 1, the plates in one concentric circle, as demonstrated by the outer circle of plates on the lower electrode body (103), are each equally circumferentially spaced by a preselected distance (111). However, the plate width (see Figure 2) varies both in a circumferential direction and a radial direction in the array. The plate width increases stepwise in a radial direction away from the centre of the array. The plate width may also increase stepwise along the circumference of a single concentric ring in a clockwise or anticlockwise direction. The plate width of the plates (105) of the upper electrode body (101) and the plates (107) of the lower electrode body (103) follow a similar pattern to ensure that variation in capacitance is achieved by rotation from a position of the electrode bodies with a maximum area of overlap between side surfaces of the plates of opposite electrode bodies to a reduced area of overlap upon rotation of one electrode body relative to the other.

The dimensions of a rectangular, curved plate (105) are demonstrated in Figure 2. The plate length (pi) or height of all the plates on the electrode bodies may be preselected with longer lengths increasing the capacitance of the tuneable capacitor. In embodiments in which the electrode bodies are also moved axially apart to vary capacitance, a longer plate length will contribute to a larger range of variation. The plate thickness (pt) will determine the radial spacing (109) required in the circular array of plates on the opposite electrode, since the radial spacing has to be more than the plate thickness (pt) to ensure that the plates are able to rotate through the radial spaces without contacting each other. The lateral surface (113) at the free end (115) of the plate (107) also contributes to capacitance formation by being supported close to the lateral flat surface of the opposite electrode disc. The plate width (pw) is the circumferential distance that a plate spans in a circular array of plates. The curved major vertical side surfaces (117) of the plate (107) are opposite curved major vertical side surfaces of plates (105) of the opposite electrode body when the capacitor is assembled and the mutual area overlap of the major side surfaces of opposite electrode plates may be varied by rotating one electrode body relative to the other. The plate width of plates arranged in a circular array may vary to introduce further variability in capacitance when rotating an electrode body relative to a complementary electrode body with the same variation in plate width in its array.

The schematic diagram of Figure 3 demonstrates how rotation of circular parallel electrode bodies (201, 203) allows for continuous relative movement one or more of the electrode bodies that ultimately results in continuous variation in capacitance in a tuneable capacitor with a circular array of curved plates (not shown) extending from the parallel electrode bodies. At the same time, the overlapping area between the two circular parallel surfaces (225, 227) of the electrode bodies (201, 203) remains constant for capacitance formation between the parallel electrode bodies. The first, operatively upper electrode body (201) and second, operatively lower electrode body (203) are separated by a distance (206). This distance (206) may be selected to obtain a specific capacitance according to an operational requirement. In this embodiment, the second electrode body (203) is fixed, whereas the first electrode body (201) may be rotated about the central axis (208) to bring about variation in area overlap between vertically extending plates (not shown) on the electrode bodies and thus variation in capacitance.

Figure 4 is a cross-sectional view of adjacent plates (105, 107) of opposite electrode bodies. The plates (105, 107) of each electrode body are equally circumferentially spaced by preselected distance (123). The plates (105) on the one electrode body are radially inward to the plates (107) of the opposite electrode body. The arrow (121) demonstrates the mutual area overlap between the major side surfaces (117, 119) of the plates (105, 107). Clockwise or anticlockwise rotation of one array of plates (105) extending from one electrode body varies the area overlap between the sides (117, 119) of the elongate plates (105, 107) and thus varies the capacitance.

Figure 5 is a schematic diagram illustrating how the capacitance variability mechanism may be created via a secant line. The secant line (302) represents a cut made to fragment cylindrical projections (316) extending from the circular electrode body (301). The cylindrical projections on the circular, disc shaped electrode bodies of the tuneable capacitor may be cut at different points (304, 306, 308, 310, 312, 314) via the secant line (302). At each point (304, 306, 308, 310, 312, 314) the secant line (302) passes through the projections (316) on the electrode discs of the capacitor, lateral capacitances between the adjacent plates of the same discs and the number of individual capacitor units being formed between corresponding plates are increased. This results in increased capacitance formation. Only one secant line is shown in Figure 5, but it will be appreciated that for creating cut curved plates multiple secant lines at different angles are to be used.

An embodiment of an electrode body (401) is shown in Figures 6 to 8. Curved, rectangular plates (405) extend from the flat surface (407) of the disc shaped part of the electrode body (401). The discrete plates (405) are arranged in concentric rings (409) which are radially spaced from one another to receive a corresponding concentric ring array of curved plates on the other electrode body. The number of curved plates (405) and their spacing on the electrode body (401) may be optimised according to the dimensions of the capacitor and the variation in capacitance that is required for a particular application. The circumferential spacing (411) between two adjacent plates (405) in the same circle arrangement of one electrode body may be changed, which will affect the overlapping area between plates of opposite electrode bodies. The radial spacing (413) between two radially adjacent plates on the same electrode body is selected to be more than the plate thickness of the plates on the opposite electrode body.

The surface area of a single plate is: A = pt(pl + 1)[(4n -1)0 + 2] where pt is the plate thickness; pl is the plate length (or height of the plate); n is the total number of concentric rings of plates; and & is the width angle (415) of the plate.

The total surface area of all the plates on one electrode body may be calculated as follows: ed A= I 1z pt (pl +1)[(4x -1)0 + 2] 0 =t9, x =1 where z is the number of segments (plates) created in one circular path of a concentric ring, Ip E {et 92, and x c (1,2,3,... n}.

Rotation of the electrode body (401) about a central axis passing through the concentric rings (409) varies the area overlap between plates of opposite electrode bodies. The rotation may happen continuously or stepwise in any preselected angular increments, such as in increments of 90° by a rotation from 0° to 90°, 90° to 180°, 180° to 270° and 270° to 360° as demonstrated in Figure 8. Each 90° rotation of the electrode body relative to a stationary, complementary electrode body results in a quadrant change of the one electrode body relative to the other. In the embodiment of the electrode body (401) shown, each quadrant has a different number of plates and the plates are of a different size, notably different plate widths along the circumference of the circular array. With each quadrant change of the one electrode body relative to its fixed, complementary electrode body, the capacitance changes to a different value due to the varied area overlap between side surfaces of the plates of opposite electrode bodies.

In another embodiment of a tuneable capacitor, the electrode body (501) as shown in Figure 9, includes complementary projections and grooves for increasing the interacting surface area of the electrodes of the capacitor. The curved plates (505) in different concentric rings are each separated by a uniform and fixed radial spacing (513). The circumferential spacing (511) between adjacent curved plates in a single concentric ring is the same but decreases towards the center of the electrode body. It will be appreciated that any circumferential spacing between plates may be selected. For example, the circumferential spacing (511) may be changed in each quadrant depending on the size and width of the curved plates. The plate length (515) determines the effective surface area of the plates.

The embodiment partly shown in Figure 9 includes projections (517) or ridges extending from the free ends (519) of the curved plates (505) of the electrode body (501). The projections (517) are configured to be at least partially received in a complementary shaped and sized circular groove or channel defined in the opposite electrode body. The projection (517) extends partially into the groove (52) of the other electrode body without contacting it. The projection (517) and a groove (521) defined in the flat surface (523) of the disc shaped part (525) of the electrode body for the projection of an opposite electrode body increase the total overlapping area of the parallel electrode bodies and thus the capacitance of the tuneable capacitor. The projection and the groove may define or include complementary fractal geometries or structures to further increase the surface area of the electrode bodies for increased capacitance formation. The overlapping area of the respective electrode bodies directly relate to the capacitance of the capacitor.

Therefore, an increase in overlapping area by incorporating complementary fractal structures on opposite electrode bodies will increase the capacitance. The complementary projection (517) and groove (521) formations on the electrode bodies represents only a first-order fractal geometry which may be optimized to the nth order as may be required. The fractal geometry may exist along one axis or more.

Another mechanism of tuning the capacitance of the tuneable capacitor involves the incorporation of a dielectric medium or insulator between the electrode bodies and the control of the interacting surface area between the plates of opposite electrode bodies and the dielectric medium between the electrodes. The dielectric medium between plates may be altered by the inclusion of one or more dielectric disc in the tuneable capacitor. The dielectric discs are supported between and coaxial with the electrode bodies. The dielectric discs have apertures defined therein through which the curved plates from each electrode body extend. The dielectric discs further have curved projections which extend laterally from side walls of the apertures and partially into the radial spaces between the circular arrays of plates extending from opposite electrode bodies. The dielectric disc may be configured to be rotatable relative to the electrode bodies or one or both of the electrode bodies are configured to be rotatable relative to the dielectric disc to vary the capacitance of the tuneable capacitor by partially or wholly changing the dielectric material between the plates. The relative rotation of either the dielectric disc or one or both of the electrode bodies is limited to a selected range of degrees as determined by the size and shape of the aperture in the dielectric discs.

An embodiment of a tuneable capacitor (600) with dielectric discs (631) supported between the electrode bodies (601, 603) is shown in Figure 10. A plurality of dielectric discs may be supported between the electrode bodies. In the embodiment of Figure 10, two dielectric discs (631) are supported between the electrodes. The dielectric discs (631) have apertures (633) defined therein through which the curved plates (605, 607) from each electrode body (601, 603) extend. The apertures (633) generally have a lateral dimension or width greater than the plate width to enable rotation of either the dielectric discs (631) relative to the electrode bodies (601, 603) or one or both electrode bodies (601, 603) relative to the dielectric discs (631) through a preselected range of degrees. A supporting structure or frame may be used to support the dielectric discs in a spaced apart configuration between the electrode bodies. The supporting structure of frame may include any suitable rotary mechanism or means for individually or simultaneously rotating the dielectric discs relative to the electrode bodies. Each dielectric disc may have a different permittivity. The different permittivity of the dielectric discs allow for further capacitance variation depending on which dielectric disc is moved relative to the electrode bodies.

Figure 11 demonstrates the mechanism whereby capacitance is varied in the embodiment of Figure 10. Capacitance forms between the overlapping area of the plates (705, 707) of opposite electrode bodies with a dielectric medium between the plates (705, 707). The dielectric medium may be in the form of a solid disc (731) with a different permittivity to surrounding air. The dielectric disc (731) between the opposite plates (705, 707) may be moved or rotated in a direction away from the overlapping plates of the electrodes as shown in Figure 11 B to vary the capacitance of the tunable capacitor. Alternatively, either one of the electrodes may be moved as shown in Figure 11C. Therefore, the capacitance can be varied by either changing the permittivity of the dielectric medium between the plates by moving a solid dielectric disc in the radial space between curved plates of opposite electrode bodies or by changing the size of the interacting or overlapping surface area of the plates.

A first embodiment of a flat dielectric disc (831) is shown in Figure 12 and includes solid sectors (833) and aperture sectors (835, 837). The apertures (835, 837) defined in the dielectric disc (831) are configured to receive radially spaced curved plates extending from both electrode bodies of the tuneable capacitor. The apertures (835, 837) are also configured, i.e., have a selected size and shape, to permit a degree of rotational movement of the curved plates while they extend through the apertures (835, 837). Curved dielectric projections (839) integrally formed with or attached to the solid sectors (833) of the dielectric disc (831) extend laterally into the apertures (835, 837). The embodiment shown in Figure 12 has four apertures (835, 837) and the projections (839) are arranged differently in adjacent apertures, i.e., the first aperture (835) and the second aperture (837).

As shown in Figure 13, each aperture (835) is configured to receive four radially spaced and interposed curved plates (843, 845, 847, 849), i.e., two curved plates (843, 847) extending from the first, operatively upper electrode body and two curved plates (845, 849) extending from the second, operatively lower electrode body. Referring back to Figure 12, the dielectric projections (839) are radially spaced along the radial side walls (841) of the apertures (835, 837) to at least partially extend between two plates of opposite electrode bodies when the dielectric disc (831) is assembled to the tuneable capacitor. When the dielectric disc (831) is rotated through a select range of degrees relative to the electrode bodies or vice versa, the dielectric projection (839) rotates and moves between the plates (843, 845 and 847, 849) of opposite electrode bodies to vary the capacitance of the tuneable capacitor.

A second embodiment of a flat dielectric disc (931) is shown in Figure 14 and includes solid sectors (933) and aperture sectors (935). In this embodiment, the dielectric projections (939) are arranged in the same configuration in each of the wedge-shaped apertures (935). The dielectric disc (931) can be used to tune the capacitance by rotation of the disc (931) relative to the electrode bodies of the capacitor or the electrode bodies relative to the disc (931) in the same manner described in relation to the first embodiment with reference to Figure 12.

A plurality of dielectric discs may be supported between the electrode bodies in a stacked configuration. In Figures 15 and 16, five dielectric discs (1031) are shown in a vertically stacked condition. When the dielectric discs (1031) are assembled between the parallel electrode bodies (1001, 1003) of the tuneable capacitor (1000), the curved plates (1005, 1007) of the electrode bodies (1001, 1003) pass through the apertures (1035) in the dielectric discs (1031) and one or both of the electrode bodies (1001, 1003) may be rotated by a specific range of degrees until the plates (1005, 1007) abut against the sides of the apertures (1035). Accordingly, the range of rotation of the electrode bodies is limited by the size of the aperture (1035) of a single dielectric disc (1031). Alternatively, one or more of the dielectric discs between the electrode bodies may be rotated within the range of rotation permitted by the apertures. Each dielectric disc may have the same or a different configuration in terms of the projections extending laterally from the apertures and between the plates of the electrode bodies when fitted between the electrode bodies.

In addition, each of the five dielectric discs (1031) may have a different permittivity by being formed from different dielectric materials. The total permittivity of the dielectric discs will be the sum of the permittivity values of each. For example, the first dielectric disc may have a permittivity value of Et whilst the rest of the discs have permittivity values of E2 up to the nth permittivity value En for the nth disc assembled to the capacitor.

Er = + E2 + * + En where ET is total equivalent permittivity. ;The intermediate dielectric discs in the tuneable capacitor assist in variable capacitance formation by having different permittivity and by being individually rotatable. Accordingly, the number of combinations making capacitances is: k = 2dz (n -1) where k is the resulting combinations, d is the number of curved plates in a single circumferential ring of plates on the electrode body and z is the number of intermediate dielectric discs. ;The total capacitance for k combinations of curved plates is: ed n 0.222 51134 [(1.2 1 ((4)C -1)0 ± 2)) + 1.26 (9 + 1.66 (I3j) C = I zEk (13 =a1 x =1 + 4.12D HD 10.728 where 0 E (Si, 62, 93,,"en} and x E {1,2,3,... n}, pl is the plate length, c is dielectric constant, S is the spacing between interposed or interdigitated curved plates of the first and second electrode bodies, D is distance between the free end of a curved plate from the one electrode body to the opposite flat surface of the other electrode body and vice versa. ;The plate width angle for a certain capacitance is: 0.83D (C(S/D)134)pt ck /)0.222 p1 0d 1.26 (P -1.66 -4.12D -2 Where d {1,2,3,... pl is the plate length, pt is the plate thickness, E is dielectric constant, S is the spacing between interposed or interdigitated curved plates of the first and second electrode bodies, D is distance between the free end of a curved plate from the one electrode body to the opposite flat surface of the other electrode body and vice versa. ;Figure 17 is a schematic in which the concentric circles (1102, 1106) of a tuneable capacitor represents the circular arrangement or array of discrete curved plates on the one electrode body and the concentric circles (1104, 1108) represents the circular arrangement or array of discrete curved plates on the other electrode body. In the embodiment schematically illustrated in Figure 17, each concentric ring of curved plates is configured to be individually rotatable about the central axis passing through the circular arrays of plates. In such an embodiment, the electrode bodies that the circular arrays of plates extend from are modular and comprise individually rotatable parts or portions. Provided that the plate width in a circular array increases in a radial direction from the centre, the circular array closest to the centre, represented by the smallest diameter circle (1102) in Figure 17, will provide the smallest variation in capacitance when tuning the tuneable capacitor by rotating this circular array relative to all the other circular arrays of plates. Conversely, the largest circular array, represented by the largest circle (1108) in Figure 17, consisting of plates with longer plate widths compared to the smaller circular arrays will offer the largest variation in capacitance when it is rotated relative to the other circular arrays of plates. In this manner, the smallest circular array may be configured to offer the smallest variation in capacitance when rotated relative to the others which may be configured to be in the order of picofarad. The circular arrays farther from the centre may be configured to provide a capacitance variation that is in the order of nano, micro, and millifarad, respectively. ;Similarly, in the embodiment of the tuneable capacitor that includes dielectric discs, the plate width of the plates (1202, 1204, 1206, 1208) from both the electrode bodies increase along the radius from the centre of the disc-shaped electrode bodies as illustrated in Figure 18. At greater radii from the centre, the interacting or overlapping surface area between plates of opposite electrode bodies increase which results in the formation of a higher capacitance and potential capacitance variation and vice versa. It is foreseen that the dielectric discs can also be made to be modular to enable some curved projections to rotate between the radial spaces between overlapping plates and other projections to remain stationary to achieve further finetuning of the output capacitance. ;The tuneable capacitors described herein are easy to manufacture and low-cost electric circuit components. The tuneable capacitors provide a large and configurable tuning range and are therefore highly sensitive. The tuneable capacitors may be used in various application, including but not limited to, resonant circuits, radio tuners, antenna impedance matching applications, frequency mixers, signal coupling and decoupling, electronic noise filtering, remote sensing, and prototyping an electronic circuit design. Advantageously, the variation in capacitance using a rotary mechanism applied to circular arrays of discrete conductive plates extending transversely from circular electrode bodies enables maximum area consumption for capacitance variation. The rotary mechanism further provides continuous capacitance variation. Moreover, the dimensions of the tuneable capacitor do not change during operation, making it suitable for incorporation into small or compact devices or circuits. ;The tuneable capacitors described herein may be tuneable supercapacitors in which the electrodes are immersed in a liquid electrolyte that includes a select concentration of ions. The electrodes are optionally separated by a membrane separator. Any suitable liquid electrolyte may be used with the aim to increase the charge storage of the supercapacitor. The electrodes may be porous. The electrodes may be made from activated carbon. The dielectric discs may be made of any suitable solid dielectric material, such as ceramic, mica, or glass for example. ;The foregoing description has been presented for the purpose of illustration; it is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Persons skilled in the relevant art can appreciate that many modifications and variations are possible in light of the above disclosure. For example, the number of curved plates, their placement, size and the angle of the curved plates relative to the electrode body may be changed for a particular application. ;The plates may include a fine structure, preferably a fractal geometry, to increase the surface area available for capacitance formation. The electrode bodies need not necessarily be disc shaped and may have any cross-sectional shape, provided that the electrode bodies can support the curved plates in a circular array. Further, any number of electrode bodies may be stacked in series or in parallel combinations to increase the total capacitance and the tuning range of the tuneable capacitor. The resulting series or parallel combinations may be controlled by varying the connections of the conducting electrode bodies. ;The language used in the specification has been principally selected for readability and instructional purposes, and it may not have been selected to delineate or circumscribe the inventive subject matter. It is therefore intended that the scope of the invention be limited not by this detailed description, but rather by any claims that issue on an application based hereon. Accordingly, the disclosure of the embodiments of the invention is intended to be illustrative, but not limiting, of the scope of the invention, which is set forth in the following claims. ;Finally, throughout the specification and accompanying claims, unless the context requires otherwise, the word 'comprise' or variations such as 'comprises' or 'comprising' will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers. *

Claims (12)

1. CLAIMS: 1. A tuneable capacitor comprising at least two parallel and coaxial conductive electrode bodies, each electrode body having a circular array of curved plates extending transversely therefrom and in the direction of an opposite electrode body with the circular array of curved plates from one electrode body being radially inwardly or outwardly spaced from the circular array of curved plates extending from the opposite electrode body, wherein at least a portion of one of the electrode bodies is configured to be rotatable about a central axis passing through the circular arrays of curved plates so that the overlap between side surfaces of the curved plates of opposite electrode bodies is varied by rotation of the portion of the electrode body relative to the other electrode body.
2. 2. The tuneable capacitor as claimed in claim 1, wherein the circular array comprises several concentric rings of curved plates that are radially spaced on the electrode body so that the concentric rings of curved plates extending from one electrode body interdigitate the concentric rings of curved plates extending from the opposite electrode body.
3. 3. The tuneable capacitor as claimed in claim 2, wherein the one electrode body and all the concentric rings of curved plates on the one electrode body are configured to be rotatable about the central axis.
4. The tuneable capacitor as claimed in claim 2, wherein each concentric ring of curved plates is configured to be individually rotatable about the central axis.
5. 5. The tuneable capacitor as claimed in any one of claims 1 to 4, wherein the curved plates in the circular array are equally circumferentially spaced and one or more of the curved plates in the circular array have a different plate width to the other curved plates.
6. 6. The tuneable capacitor as claimed in claim 5, wherein the plate width of adjacent circumferentially spaced curved plates increases stepwise along the circumference of the circular array.
7. 7. The tuneable capacitor as claimed in any one of claims 1 to 4, wherein the curved plates in the circular array have an equal plate width but are differently circumferentially spaced.
8. 8.
9. 9.
10. 10.
11. 11.
12. 12.The tuneable capacitor as claimed in any one of claims 1 to 7, wherein free ends of the curved plates extending from the electrode body include a projection configured to be at least partially received in a circular groove defined in the opposite electrode body.The tuneable capacitor as claimed in claim 8, wherein the projection and the groove define complementary fractal geometries.The tuneable capacitor as claimed in any one of claims 1 to 9, wherein the electrode bodies are disc shaped.The tuneable capacitor as claimed in any one of claims 1 to 10, wherein one or more dielectric discs is supported between and coaxially with the electrode bodies, the dielectric disc defining apertures through which the curved plates from each electrode body extend and curved projections which extend laterally from side walls of the apertures and partially into radial spaces between the circular arrays of plates, and wherein one or more of the electrode bodies is configured to be rotatable about the central axis relative to the dielectric disc or the dielectric disc is configured to be rotatable relative to the electrode bodies by a selected range of degrees to vary the capacitance of the tuneable capacitor in use.The tuneable capacitor as claimed in claim 11, wherein a plurality of dielectric discs is supported between the electrode bodies and each dielectric disc has a different permittivity.