The present disclosure relates to the field of so-called “supercapacitors” and such like, associated apparatus, methods and computer programs, and in particular concerns the integration of a supercapacitor within a flexible printed circuit (FPC) structure. Certain disclosed example aspects/embodiments relate to portable electronic devices, in particular, so-called hand-portable electronic devices which may be hand-held in use (although they may be placed in a cradle in use). Such hand-portable electronic devices include so-called Personal Digital Assistants (PDAs).
The portable electronic devices/apparatus according to one or more disclosed example aspects/embodiments may provide one or more audio/text/video communication functions (e.g. tele-communication, video-communication, and/or text transmission, Short Message Service (SMS)/Multimedia Message Service (MMS)/emailing functions, interactive/non-interactive viewing functions (e.g. web-browsing, navigation, TV/program viewing functions), music recording/playing functions (e.g. MP3 or other format and/or (FM/AM) radio broadcast recording/playing), downloading/sending of data functions, image capture function (e.g. using a (e.g. in-built) digital camera), and gaming functions.
Multimedia enhancement modules in portable electronic devices (such as camera flash modules, loudspeaker driver modules, and power amplifier modules for electromagnetic transmission) require short power bursts. Typically, electrolytic capacitors are used to power LED and xenon flash modules and conventional capacitors are used to power loudspeaker driver modules, but neither are able to satisfy the power demands needed for optimal performance.
The situation could be improved by the use of supercapacitors. In an LED flash module, for example, double the light output can be achieved using supercapacitors instead of electrolytic capacitors. The problem is not as straight forward as simply switching one type of capacitor for the other, however. In modern electronic devices, miniaturisation is an important factor, and state-of-the-art supercapacitors do not fulfil the size and performance requirements in currently available packaging. Power sources for modules requiring high power bursts have to be implemented close to the load circuit, which for flash and speaker applications means closer than 10-30 mm. Unfortunately, present supercapacitors can be bulky, can suffer from electrolyte swelling, and can have the wrong form factor for attachment to the circuit boards of portable electronic devices. In addition, the attachment of supercapacitors often requires several undesirable stages of processing.
The apparatus and associated methods disclosed herein may or may not address one or more of these issues.
The listing or discussion of a prior-published document or any background in this specification should not necessarily be taken as an acknowledgement that the document or background is part of the state of the art or is common general knowledge. One or more example aspects/embodiments of the present disclosure may or may not address one or more of the background issues.
An apparatus comprising first and second circuit boards, and an antenna for transmitting and/or receiving electromagnetic signals,
The apparatus may comprise an amplifier configured to drive the antenna. The amplifier may be electrically connected to the electrically conductive layer of the first circuit board.
The amplifier may be positioned to minimise the distance between the capacitive elements and the amplifier.
The apparatus may form part of an electronic device. The electrically conductive layer of the first circuit board may be electrically connected to at least one grounded part of the electronic device. The electronic device may comprise a motherboard. The first circuit board may comprise part of the motherboard.
The antenna may be one of the following: a monopole, dipole, loop, inverted-F, planar inverted-L, or planar inverted-F antenna. The planar inverted-F antenna may be one end of the first circuit board which has been bent around on itself to define a cavity.
One or both of the first and second circuit boards may be flexible printed circuit boards. One or both of the first and second circuit boards may be flexible regions of a rigid-flex circuit board.
The capacitive elements may be referred to as “electrodes”. Each capacitive element may comprise a high surface area material. Each capacitive element may comprise an electrically conductive region having a surface. The electrically conductive region may comprise one or more of the following materials: copper, aluminium, and carbon. The high surface area material may be disposed on the surface of each electrically conductive region. In each of the example embodiments described herein, the respective surfaces/high surface area materials of the electrically conductive regions may be configured to face one another.
The high surface area material may be electrically conductive. The high surface area material may comprise one or more of the following: nanoparticles, nanowires, nanotubes, nanohorns, nanofibers and nano-onions. In particular, the high surface area material may comprise one or more of the following: activated carbon, carbon nanowires, carbon nanotubes, carbon nanohorns, carbon nanofibres and carbon nano-onions. The carbon nanotubes may be multiple wall carbon nanotubes.
The electrically conductive regions may be configured to maximise adhesion of the high surface area material to the surfaces of the electrically conductive regions. The electrically conductive regions may be configured to minimise the electrical resistance of the capacitive elements. The thickness of the high surface area material may be configured to minimise the electrical resistance of the capacitive elements.
The electrically conductive layers of the first and second circuit boards may be coated on one or both sides with a layer of electrically insulating material. The electrically conductive layers may be electrically connected to the electrically conductive region by one or more of the following: a connector, a vertical interconnect access (VIA) connection, a pogo pin, a solder contact, a wire, and an electrically conductive adhesive (such as an anisotropic conductive adhesive, a pressure setting adhesive or a temperature setting adhesive). The electrically conductive layers may comprise copper.
The layers of electrically insulating material may comprise polyimide. The layers of electrically insulating material may be adhered to the electrically conductive layers by an adhesive. Each of the first and second circuit boards may comprise a layer of surface protection material between the electrically conductive region and the high surface area material. The layer of surface protection material may comprise an organic surface protection (OSP) material.
The first and second circuit boards may be configured to allow the apparatus to be bent through an angle of less than or equal to 180°. The first and second circuit boards may be sufficiently flexible to render the apparatus suitable for use in flex-to-install applications. Formation of the chamber may be configured to increase the rigidity of the first and second circuit boards. For example, each of the first and second circuit boards may have a minimum bending radius of 0.5 mm before formation of the chamber, and a minimum bending radius of 0.2-0.5 cm after formation of the chamber.
The apparatus may be configured to store electrical charge at the interface between the capacitive elements and the electrolyte. The electrolyte may be located between the capacitive elements. The first and second circuit boards may be sealed together to contain the electrolyte within the chamber. The electrolyte may comprise first and second ionic species of opposite polarity. The first and second ionic species may be configured to move towards the capacitive element of the first and second circuit boards, respectively, when a potential difference is applied between the capacitive elements. The electrolyte may be an organic electrolyte. The organic electrolyte may be based on an aprotic solvent such as acetonitrile, or on a carbonate-based solvent such as propylene carbonate. The electrolyte may comprise tetraethylammonium tetrafluoroborate in acetonitrile. The electrolyte may be an aqueous electrolyte. The electrolyte may be chosen such that a potential difference of between 0V and 0.9V may be applied between the capacitive elements without the electrolyte breaking down. Advantageously, the electrolyte may be chosen such that a potential difference of between 0V and 2.7V may be applied between the capacitive elements without the electrolyte breaking down.
The apparatus may comprise a separator between the capacitive elements. The separator may be configured to prevent direct physical contact between the capacitive elements. The separator may comprise one or more pores. The pores in the separator may be configured to allow the first and second ionic species to pass through the separator towards the capacitive elements when the potential difference is applied, thereby facilitating charging of the apparatus. Likewise, the pores in the separator may be configured to allow the first and second ionic species to pass through the separator away from the capacitive elements when the apparatus is used to power an electrical component, thereby facilitating discharging of the apparatus. The separator may comprise one or more of the following: polypropylene, polyethylene, cellulose, and polytetrafluoroethylene. The separator may comprise one, two, three, or more than three layers. Each layer may comprise one or more of the above-mentioned materials.
The apparatus may comprise a power supply configured to apply a potential difference between the capacitive elements. The power supply may comprise first and second terminals of opposite polarity. The electrically conductive layers of the first and second circuit boards may be electrically connected to the first and second terminals of the power supply, respectively.
The apparatus may comprise an electrical connector between the electrically conductive layers of the first and second circuit board. The electrical connector may be configured to enable a flow of electrical charge from the capacitive elements to provide power to one or more electrical components when the apparatus discharges. The one or more electrical components may be physically and electrically connected to the electrically conductive layer of one or both of the first and second circuit boards. The electrical connector may comprise an electrically conductive adhesive. The electrically conductive adhesive may comprise one or more of the following: an anisotropic conductive adhesive, a conductive pressure setting adhesive and a conductive temperature setting adhesive. The electrically conductive adhesive may be further configured to seal the first and second sections together to contain the electrolyte within the chamber. The electrical connector may comprise a metallic interconnector. The metallic interconnector may be a vertical interconnect access (VIA) connector. The apparatus may comprise a switch configured to connect and disconnect the electrical connector/connection. Disconnection of the electrical connector may be configured to allow the apparatus to be charged. Connection of the electrical connector may be configured to allow the apparatus to be discharged. The switch may be located on the first or second circuit board, or within a charger circuit forming part of the circuit board assembly.
According to a further aspect, there is provided a module for a portable electronic device, the module comprising any apparatus described herein. The apparatus may form part of a multimedia enhancement module. The multimedia enhancement module may be a power amplifier module for electromagnetic transmission/reception. The power amplifier module may be a power amplifier module for RF transmission.
According to a further aspect, there is provided a portable electronic device comprising any apparatus described herein. The apparatus may be a portable electronic device, circuitry for a portable electronic device or a module for a portable electronic device. The apparatus may form part of a portable electronic device or part of a module for a portable electronic device. The portable electronic device may be a portable telecommunications device.
According to a further aspect, there is provided a method of assembling an apparatus, the method comprising:
According to a further aspect, there is provided a method of powering an amplifier configured to drive an antenna, the method comprising:
The steps of any method disclosed herein do not have to be performed in the exact order disclosed, unless explicitly stated.
According to a further aspect, there is provided a computer program for controlling the power supply of an amplifier configured to drive an antenna using an apparatus, the apparatus comprising first and second circuit boards, and an antenna for transmitting and/or receiving electromagnetic signals,
The apparatus may comprise a processor configured to process the code of the computer program. The processor may be a microprocessor, including an Application Specific Integrated Circuit (ASIC).
The present disclosure includes one or more corresponding aspects, example embodiments or features in isolation or in various combinations whether or not specifically stated (including claimed) in that combination or in isolation. Corresponding means for performing one or more of the discussed functions are also within the present disclosure.
Corresponding computer programs for implementing one or more of the methods disclosed are also within the present disclosure and encompassed by one or more of the described example embodiments.
The above summary is intended to be merely exemplary and non-limiting.
A description is now given, by way of example only, with reference to the accompanying drawings, in which:—
In electrical circuits, batteries and capacitors are used to provide other components with electrical power. These power supplies operate in completely different ways, however. Batteries use electrochemical reactions to generate electricity. They comprise two electrical terminals (electrodes) separated by an electrolyte. At the negative electrode (the anode), an oxidation reaction takes place which produces electrons. These electrons then flow around an external circuit from the anode to the positive electrode (the cathode) causing a reduction reaction to take place at the cathode. The oxidation and reduction reactions may continue until the reactants are completely converted.
Importantly though, unless electrons are able to flow from the anode to the cathode via the external circuit, the electrochemical reactions cannot take place. This allows batteries to store electricity for long periods of time.
In contrast, capacitors store charge electrostatically, and are not capable of generating electricity. A conventional capacitor (
Electrolytic capacitors (
A third type of capacitor, known as a supercapacitor (
Unlike batteries, the applied potential is kept below the breakdown voltage of the electrolyte 109 to prevent electrochemical reactions from taking place at the surface of the plates 106. For this reason, a supercapacitor cannot generate electricity like an electrochemical cell. Also, without electrochemical reactions taking place, no electrons are generated. As a result, no significant current can flow between the electrolyte 109 and the plates 106. Instead, the ions 110, 111 in solution arrange themselves at the surfaces of the plates 106 to mirror the surface charge 112 and form an insulating “electric double layer”. In an electric double layer (i.e. a layer of surface charge 112 and a layer of ions 110, 111), the separation, d3, of the surface charges 112 and ions 110, 111 is on the order of nanometers. The combination of the electric double layer and the use of a high surface area material 108 on the surface of the plates 106 allow a huge number of charge carriers to be stored at the plate-electrolyte interface.
Activated carbon is not the most suitable material 108 for coating the plates 106 of the capacitor, however. The ions 110, 111 in solution are relatively large in comparison to the pores in the carbon, and this limits the energy storage considerably. Recent research in this area has focused on the use of carbon nanotubes and carbon nanohorns instead, both of which offer higher useable surface areas than activated carbon.
Supercapacitors have several advantages over batteries, and as a result, have been tipped to replace batteries in many applications. They function by supplying large bursts of current to power a device and then quickly recharging themselves. Their low internal resistance, or equivalent series resistance (ESR), permits them to deliver and absorb these large currents, whereas the higher internal resistance of a traditional chemical battery may cause the battery voltage to collapse. Also, whilst a battery generally demands a long recharging period, supercapacitors can recharge very quickly, usually within a matter of minutes. They also retain their ability to hold a charge much longer than batteries, even after multiple rechargings. When combined with a battery, a supercapacitor can remove the instantaneous energy demands that would normally be placed on the battery, thereby lengthening the battery lifetime.
Whereas batteries often require maintenance and can only function well within a small temperature range, supercapacitors are comparatively maintenance-free and perform well over a broad temperature range. Supercapacitors also have longer lives than batteries, and are built to last until at least the lifetime of the electronic devices they are used to power. Batteries, on the other hand, typically need to be replaced several times during the lifetime of a device.
Supercapacitors are not without their drawbacks, however. Despite being able to store a greater amount of energy than conventional and electrolytic capacitors, the energy stored by a supercapacitor per unit weight is considerably lower than that of an electrochemical battery. In addition, the working voltage of a supercapacitor is limited by the electrolyte breakdown voltage, which is not as issue with batteries.
As mentioned earlier, existing supercapacitors can be bulky, can suffer from electrolyte swelling and may not have the optimum form factor for attachment to the circuit boards of portable electronic devices. Furthermore, the attachment of existing supercapacitors to circuit boards often requires several stages of processing, thereby rendering them impractical. There will now be described an apparatus and associated methods that may or may not overcome one or more of these issues.
In
The apparatus consists of two FPC boards 201, each comprising a layer of electrically conductive material 202. In this embodiment, the layer of electrically conductive material 202 on each FPC board 201 is coated on either side by a layer of electrically insulating material 203. Subtraction of the insulating material 203 is used to define conductive traces in the electrically conductive material 202. The insulating material 203 is also used to protect the electrically conductive material 202 from the external environment.
Each FPC board 201 further comprises a capacitive element 204 with an electrically conductive region 205. The electrically conductive regions 205 are electrically connected to the layers of electrically conductive material 202, e.g. by vertical interconnect access (VIA) connections 206. The capacitive elements 204 also comprise a high surface area material 207 on top of the electrically conductive regions 205, the material 207 comprising a mixture of one or more of activated carbon (AC), multiple wall carbon nanotubes (MWNTs), carbon nanohorns (CNHs), carbon nanofibers (CNFs) and carbon nano-onions (CNOs). AC, MWNTs, CNHs, CNFs and CNOs are used because of their large electrical conductivity and high surface area. As mentioned earlier, the high surface area allows adsorption of large numbers of electrolyte ions onto the surface of the capacitive elements 204.
The high surface area material 207 may be prepared by mixing different proportions of AC, MWNTs and CNHs together using polytetrafluoroethylene (PTFE) as a binder and acetone as a solvent, and homogenising the mixture by stirring. Following this, the resulting slurry is applied by rolling the mixture onto the surface of each electrically conductive region 205. The FPC boards 201 are then annealed at 50° C. for 20 minutes to drive off the solvent and consolidate the mixture. To maximise its surface area and electrical conductivity, the high surface material 207 is applied to the electrically conductive regions 205 as a thin film.
As shown in
The electrically conductive regions 205 may be formed from a variety of different materials, but advantageously are made from copper, aluminium or carbon. The choice of material affects the physical and electrical properties of the supercapacitor. Copper, and to a lesser extent aluminium, exhibit favourable electrical conductivity. This is advantageous because it allows charge carriers from the electrically conductive material 202 to flow through the electrically conductive region 205 to the high surface area material 207 with minimum resistance. On the other hand, carbon offers better adhesion to the high surface area material 207 than copper and aluminium, and is more cost effective. Carbon also provides a low resistance (ESR) path between the electrically conductive region 205 and the high surface area material 207. Using carbon, supercapacitors with an ESR of ˜3Ω can be produced. Furthermore, the resistance between the electrically conductive material 202 and the electrically conductive region 205 may be reduced by increasing the number or size of the electrical connections (VIAs) 206. The resistance may also be reduced by removing insulating material 203 adjacent the electrically conductive region 205 such that electrically conductive region 205 can be deposited directly onto the electrically conductive material 202. The electrically conductive regions 205 may also comprise a surface finish (coating) to protect the electrically conductive regions 205 or to modify their structural or material properties. Possible surface materials include nickel-gold, gold, silver, or an organic surface protection (OSP) material.
As mentioned in the background section, supercapacitors may be used to power multimedia enhancement modules in portable electronic devices. For modules that require high power bursts, such as LED flash modules, the supercapacitor needs to be implemented close to the load circuit. In the present case, the FPC structure 216 (within which the supercapacitor is integrated) forms the multimedia enhancement module, with the various components of the module physically (and electrically) connected to the FPC boards 201. In
An electrolyte is required between the capacitive elements 204 to enable the storage of electrical charge. To achieve this, the FPC boards 201 are configured to form a chamber within which the electrolyte can be contained. The chamber is illustrated in cross-section in
In another embodiment, a ring may be incorporated into the FPC structure to form a chamber. In this embodiment (not shown), the ring is positioned around the capacitive elements 303 and sandwiched between the FPC boards 304. In practise, this may involve placing a first FPC board face-up on a flat surface; placing the ring (which has a diameter of at least the largest in-plane dimension of the capacitive elements 303) around the capacitive element of this FPC board; sealingly attaching the ring to the FPC board; filling the ring with electrolyte 305; placing a second FPC board face-down on top of the first FPC board such that the capacitive element of the second FPC board is contained within the ring and facing the other capacitive element; and sealingly attaching the second FPC board to the ring. Ideally, the thickness of the ring should be substantially the same as the total thickness of the FPC structure. Nevertheless, due to the flexibility of the FPC boards 304, the ring thickness may deviate from the total thickness of the FPC structure and still allow formation of the chamber.
In another embodiment, the ring may comprise an aperture. In this embodiment, the electrolyte may be introduced to the chamber via the aperture and subsequently sealed to retain the electrolyte 305.
It should be noted, however, that the thickness, t1, of the chamber 301 is exaggerated in
To charge the apparatus, a potential difference is applied across the capacitive elements 402, 403 (
A variety of different configurations may be used to discharge the apparatus. In one configuration (shown in
As illustrated in
The plating process (possibly with additional lithography to form the pads) described above is time consuming, labour intensive and expensive. It is also technically difficult to implement. A more efficient process for forming the electrical connector will now be described with reference to
Anisotropic conductive adhesive (ACA), encompassing both anisotropic conductive film (ACF) and anisotropic conductive paste (ACP), is a lead-free and environmentally friendly interconnect system commonly used in liquid crystal display (LCD) manufacturing to make electrical and mechanical connections from the driver electronics to the glass substrates of the LCD. It has more recently been used to form the flex-to-board or flex-to-flex connections used in handheld electronic devices such as mobile phones, MP3 players, or in the assembly of CMOS camera modules. The material consists of an adhesive polymer containing electrically conductive particles.
ACA may be applied to the surfaces of the FPC boards to form an electrical connection. To achieve this, the electrically conductive layers 604 must first be exposed. This is performed by removing some of the insulating material 610 above and below the electrically conductive layers 604 of the bottom 603 and top 602 FPC boards, respectively (possibly by drilling). Once the electrically conductive layers 604 are exposed, ACA 611 is deposited on the top surface 607 of the bottom FPC board 603 in physical contact with the exposed material of the electrically conductive layers 604. This may be done using a lamination process for ACF, or either a dispense or printing process for ACP. The top FPC board 602 is then placed in position over the bottom FPC board 603 (i.e they are aligned with one another), and the two FPC boards 602, 603 are pressed together to mount the top FPC board 602 on the bottom FPC board 603. Mounting may be performed using no heat, or using just enough heat to cause the ACA 611 to become slightly tacky.
Using Hitachi™ chemical AC2051/AC2056 as the ACA, the temperature, pressure and time parameters required to successfully mount the top FPC board 602 on the bottom FPC board 603 are 80° C., 10 kgf/cm2 and 5 secs, respectively. Using 3M™ ACF 7313 as the ACA, the temperature, pressure and time parameters are 100° C., 1-15 kgf/cm2 and 1 sec, respectively.
Bonding is the final stage in the process required to complete the ACA assembly. During lamination and mounting, the temperature may range from ambient to 100° C. with the heat applied for 1 second or less. In order to bond the FPC boards 602, 603 together, however, a greater amount of thermal energy is required, firstly to cause the ACA 611 to flow (which allows the FPC boards 602, 603 to be positioned for maximum electrical contact), and secondly to cure the ACA 611 (which allows a lasting and reliable bond to be created). Depending on the specific ACA and FPC materials used, the required temperature and heating time may range from 130−220° C. and 5-20 secs, respectively. Bonding is performed by pressing a bonding tool head (not shown) onto the top FPC board 602. The tool head is maintained at the required temperature and is applied to the top FPC board 602 at the required pressure for the required period of time. The required pressure may range from 1-4 MPa (˜10-40 kgf/cm2) over the entire area under the tool head.
Using Hitachi™ chemical AC2051/AC2056 as the ACA, the temperature, pressure and time parameters required to successfully bond the top FPC board 602 to the bottom FPC board 603 are 170° C., 20 kgf/cm2 and 20 secs, respectively. Using 3M™ ACF 7313 as the ACA, the temperature, pressure and time parameters are 140° C., 15 kgf/cm2 and 8-12 secs, respectively.
When the ACA 611 is compressed, the electrically conductive particles contained within the adhesive polymer are forced into physical contact with one another, thereby creating an electrical path from the electrically conductive layer 604 of the top FPC board 602 to the electrically conductive layer 604 of the bottom FPC board 603. The electrical path is highly directional (hence anisotropic conductive adhesive). It allows current to flow in the z-axis, but prevents the flow of current in the x-y plane. This feature is important in the present apparatus, because it prevents (or minimises) electrical shorting of the electrolyte. As the ACA 611 cures, the electrically conductive particles are fixed in the compressed form, thereby maintaining good electrical conductivity in the z-axis.
Rather than having to apply heat to bond the FPC boards together, a conductive pressure setting adhesive (PSA) may be used instead. A PSA is an adhesive which forms a bond with an adherend under pressure alone. It is used in pressure setting tapes, labels, note pads, automobile trim, and a wide variety of other products. As the name suggests, the degree of bonding is influenced by the amount of pressure applied, but surface factors such as smoothness, surface energy, contaminants, etc can also affect adhesion. PSAs are usually designed to form and maintain a bond at room temperature. The degree of adhesion and shear holding ability often decrease at low temperatures and high temperatures, respectively. Nevertheless, special PSAs have been developed to function at temperatures above and below room temperature. It is therefore important to use a PSA formulation that is suitable for use at the typical operating temperatures of the electronic circuitry.
As described previously, the FPC boards need to be sealed together in order to form the chamber and prevent the electrolyte from escaping. An electrically conducting or non-conducting adhesive may be used for this purpose. In one embodiment, the ACA or conducting PSA used to provide the electrical connection between the FPC boards could also be used to seal the structure. In this configuration, the fabrication procedures of providing the electrical connection and sealing the structure are combined as a single procedure. In another embodiment, the procedure of providing the electrical connector may be performed separately from the procedure of sealing the structure. In this latter embodiment, either the same or different adhesives could be used for each procedure.
It will be appreciated that, in certain embodiments (as shown in
Integration of the supercapacitor within the FPC structure increases the possibility of distributed local capacitor placement. This feature enables power to be received from local sources without the resistive and inductive losses caused by electrical junctions (e.g. connectors, vias, pogo pins, solder contacts etc). Supercapacitor integration also reduces the number of manufacturing processes in the assembly phase.
As described previously, the multimedia enhancement module needs to be connected to the main board of the electronic device. With rigid and flexible circuit boards, this is usually achieved with a board-to-board (B2B) connector (215 in
The rigid regions 701, 702 of a rigid-flex circuit board may be used to form the main board and multimedia enhancement module, respectively, thereby obviating the need for a B2B connector. In addition, the supercapacitor may be integrated within a flexible region 703 of the rigid-flex circuit board, thus freeing up space on the rigid regions 701, 702 for other electrical components 704. Furthermore, given that rigid-flex circuit boards can be bent about the flexible region 703 (in some cases through an angle of up to 180°), they are well-suited to flex-to-install and/or dynamic flex applications.
A rigid-flex integrated supercapacitor is shown in
A number of different methods may be used to assemble a rigid-flex integrated supercapacitor, four of which will now be described with respect to
In each of the example embodiments described below, the first and second sections of the flexible region are sealed together to define a chamber, within which the capacitive elements, the electrolyte, and the separator are contained. This is necessary to prevent the electrolyte from escaping. The electrolyte may be a solid or gel electrolyte, in which case the electrolyte may be added before the first and second sections are sealed at all, or may be a liquid electrolyte, in which case a small hole may be left unsealed for injection of the electrolyte before the structure is sealed completely. As described previously, the separator is configured to prevent direct electrical contact between the capacitive elements.
One method of assembly is shown in
A second method of assembly is shown in
In another embodiment (shown in
A final embodiment is shown in
Rather than using a rigid material to stiffen the rigid regions of the circuit board, the number and/or thickness of the electrically conductive and electrically insulating layers may be increased in these regions to provide greater rigidity. Furthermore, the structure may also incorporate one or more of the following: a cover layer, an electromagnetic shield layer, a thermal protection layer, and an organic surface protection layer, which may also increase the rigidity of the structure. Any of the above-mentioned layers may be incorporated within the rigid or flexible regions of the circuit board.
The structure may also comprise an electrical connector (as described with respect to
One advantage of the embodiment shown in
In each of the example embodiments described above, the presence of the supercapacitor (chamber) within the flexible region may increase the rigidity of the flexible region. In some situations this may be beneficial. For example, in flexible circuit boards, stiffeners are sometimes added to minimise shock and vibration of the circuit board during assembly and/or operation of the device. These vibrations can damage the electrically conductive traces and is therefore an important consideration.
As previously mentioned, the working voltage of a supercapacitor is limited by the breakdown voltage of the electrolyte. There are two types of electrolyte typically used in supercapacitors—aqueous electrolytes and organic electrolytes. The maximum voltage for supercapacitor cells that use aqueous electrolytes is the breakdown voltage of water, ˜1.1V, so these supercapacitors typically have a maximum voltage of 0.9V per cell. Organic electrolyte supercapacitors are rated in the range of 2.3V-2.7V per cell, depending on the electrolyte used and the maximum rated operating temperature. In order to increase the working voltage of a supercapacitor, several supercapacitor cells may be connected in series.
In
Furthermore, the electrical components may be electrically connected (e.g. surface mounted) to either or both of the circuit boards 1002, 1003.
In
To test the behaviour of the supercapacitors, cyclic voltammetry experiments were performed using a 5 cm2-area supercapacitor with a 1M solution of tetraethylammonium tetrafluoroborate in acetonitrile as the electrolyte. Cyclic voltammetry is a type of potentiodynamic electrochemical measurement which involves increasing the electrode potential linearly with time whilst measuring the current. This ramping is known as the experiment scan rate (V/s). In this case, a scan rate of 50 mV/s was used. Once the voltage reaches a set potential, the potential ramp is inverted. This inversion is usually performed a number of times during a single experiment. The current is then plotted against the applied voltage to give the cyclic voltammogram trace.
This experiment produced a rectangular trace (not shown) indicating good capacitor behaviour. Furthermore, during the experiment the applied voltage was increased to 2.7V without degradation of the supercapacitor performance.
Following this, the effect of varying the number of separator layers in the supercapacitor was studied. Again, these experiments were performed using 5 cm2-area supercapacitors with a 1M solution of tetraethylammonium tetrafluoroborate in acetonitrile as the electrolyte. It was found that an increase in the number of separator layers from 1 to 2 caused an increase in capacitance and a decrease in ESR. The same trend was observed when the number of separator layers was increased from 2 to 3. This may be attributed to a greater number of pores available to accommodate the ionic species in the electrolyte, which may allow more ions to interact with the high surface material. When the number of separator layers was increased beyond 3, however, there was no further change in capacitance.
Charge-discharge (V) curves (not shown) cycled at ±1 mA (+1 mA for charging the cell and −1 mA for discharging the cell, each cycle lasting 20 secs) revealed capacitances of between 250-649mF with ESRs of between 5.35-1.8Ω. The capacitance was deduced from the slope of the discharging curve where C=I/(dV/dt), C is the capacitance of the cell in farads, I is the discharge current in amperes, and dV/dt is the slope in volts per second. The direct current ESR was calculated using ESR=dV/dI, where dV is the voltage drop at the beginning of the discharge in volts, and dI is the current change in amperes.
The effect of varying the high surface material in the supercapacitor was also studied. Three formulations of high surface material were tested: 97% activated carbon and 3% PTFE (binder), (ii) 87% activate carbon, 10% carbon nanotubes and 3% PTFE, and (iii) 77% activated carbon, 20% carbon nanotubes and 3% PTFE. Again, these experiments were performed using 5 cm2-area supercapacitors with a 1M solution of tetraethylammonium tetrafluoroborate in acetonitrile as the electrolyte.
Cyclic voltammetry experiments produced rectangular traces (not shown) for each sample, indicating good capacitor behaviour. Furthermore, charge-discharge (V) curves (not shown) cycled at ±1 mA revealed respective capacitances of 476, 500 and 649mF with respective ESRs of 2.3, 1.8 and 1.8Ω. The increase in capacitance and decrease in ESR with nanotube content may be attributed to the high surface area and high electrical conductivity of the carbon nanotubes.
As mentioned in the background section, multimedia enhancement modules in portable electronic devices often require fast power transients. This is particularly true of power amplifier modules for RF transmission, which may require over 3 W of power during transmission peaks. This power is typically supplied from a battery, with the current travelling from the battery, through conductive tracks on the transmission line substrate, to the power amplifier which drives the antenna. The further the battery is from the power amplifier, the greater the power dissipated in the transmission line impedance. To minimize this loss, the power source should therefore be placed as closely as possible to the power amplifier. Current state-of-the-art devices employ discrete (aluminium-plastic bag) supercapacitors between the battery and the power amplifier. Supercapacitors can charge and discharge quickly, and when combined with a battery, can remove the instantaneous energy demands that would normally be placed on the battery. Despite these advantages, however, the location of discrete supercapacitors on the circuit board is limited by their size and shape.
An antenna is a transducer which transmits and/or receives electromagnetic waves, and comprises an arrangement of one or more electrical conductors (usually called “elements”). During transmission, an alternating current is created in the elements by applying a voltage at the antenna terminals, causing the elements to radiate an electromagnetic field. During reception, an electromagnetic field from another source induces an alternating current in the elements and a corresponding voltage at the antenna terminals.
Several critical parameters affect an antenna's performance and can be adjusted during the design process. These include resonant frequency, impedance, antenna gain, radiation pattern, polarization, efficiency, and bandwidth. Transmission antennas may also have a maximum power rating, whilst receiving antennas differ in their noise reduction properties.
There are at least two main types of antenna currently in use in mobile phones—internal monopole antennas, and planar inverted-F (PIFA) antennas. Unlike the wire antennas of older mobile phones, for example retractable or non-retractable external helices, monopoles or whip antennas, internal monopole and PIFA antennas are internal to the device. The internal monopole and PIFA antennas may be fabricated as planar antennas, which may be advantageous in portable electronic devices because they can be fabricated directly onto circuit boards, have a low cost, a low profile and are simple to manufacture. Alternatively, these internal antennas may be fabricated using other materials, for example, wire formed on plastic frames or moulded into plastic housings. Internal antennas can be substantially planar or they may be disposed in three dimensions over the length of the antenna element. Furthermore, internal antennas may be curved in three dimensions.
As an example,
As shown in
The PIFA antenna is based on the structure of a microstrip (or patch) antenna. A standard microstrip antenna produces linearly polarized electromagnetic fields, and is shown in plan view and side view in
Antenna designers often look to improve performance. One method used in microstrip antennas is to introduce a shorting pin 1205 between the antenna 1201 and the ground plane 1204 in at least one location. By taking a quarter-wavelength antenna 1201 (i.e. same as microstrip antenna 1201 of
The PIFA antenna (
By using the FPC or rigid-flex integrated supercapacitor described herein, it is possible to place the antenna and power amplifier in close proximity to the power source. In this way, power loss in the transmission line can be minimized.
The monopole 1401 or PIFA antenna 1402 may simply be an extension of the electrically conductive layer 1404, or a separate conductive element which has been connected to the electrically conductive layer 1404. Rather than attaching a shorting pin 1408 between the PIFA antenna 1402 and the electrically conductive layer 1404 of the first circuit board 1405, however, the first circuit board 1405 may be bent around onto itself to define the air cavity 1407 (
Whilst monopole 1401 and PIFA 1402 antennas have been described above, a person skilled in the art of antennas will appreciate that other types of antenna, such as planar inverted-L, loop, dipole, and inverted-F antennas, may also be integrated within the supercapacitor structure described herein.
For greater control of the resonance peak, the ground plane of an antenna may be electrically connected to other grounded parts of the device (which may be a mobile phone, PDA, or laptop etc). In this respect, the first circuit board 1405 may be connected to, or form part of, the device motherboard. When a rigid-flex circuit board is used, one rigid region of the circuit board may constitute the motherboard, with the other rigid region constituting the RF module. In this configuration, the flexible region connecting the two rigid regions (within which the supercapacitor structure is formed) could provide the electrical contact. In another embodiment, the RF module may be formed on the flexible region, thereby allowing the second rigid region to be used as another device module. When two FPC boards are used, connectors may be used to provide the electrical connection between the first circuit board 1405 and the device motherboard. On the other hand, if the first circuit board 1405 forms part of the device motherboard, the ground connection continuity is increased. This has the advantage of reducing unwanted resonances and emission associated with electrical discontinuities.
The antenna-integrated supercapacitor 1602 forms part of an RF module for the device 1601. The supercapacitor itself is used to store electrical charge for powering the various components of the RF module (e.g. power amplifier and smoothing capacitor).
The processor 1603 is configured for general operation of the device 1601 by providing signalling to, and receiving signalling from, the other device components to manage their operation. In particular, the processor 1603 is configured to provide signalling to control the charging and discharging of the supercapacitor 1602. Typically, the supercapacitor 1602 will discharge whenever the antenna/power amplifier requires a short current burst. For example, a short burst of current will be required whenever the user of the device 1601 wishes to transmit information (e.g. text message, telephone call etc) from his/her device 1601 to a remote device. In this scenario, the processor 1603 provides signalling to instruct the supercapacitor 1602 to discharge and provide the antenna/power amplifier with the required current. After the supercapacitor 1602 has discharged, the processor 1603 instructs the supercapacitor 1602 to recharge using a connected battery (or other power supply). The use of a supercapacitor 1602 therefore removes the instantaneous energy demands that would normally be placed on the battery. The processor 1603 may provide signalling to operate a switch, operation of the switch configured to break and make the electrical connection between the capacitive elements to cause charging and discharging of the supercapacitor 1602, respectively.
The storage medium 1604 is configured to store computer code required to operate the apparatus, as described with reference to
The computer program may control the power supply of an amplifier configured to drive an antenna using an apparatus, the apparatus comprising first and second circuit boards, and an antenna for transmitting and/or receiving electromagnetic signals, the first and second circuit boards each comprising an electrically conductive layer, and a capacitive element configured to be charged and discharged, the apparatus configured such that a chamber is defined between the first and second circuit boards with the capacitive elements contained therein and facing one another, the chamber containing an electrolyte, wherein the electrically conductive layer of the first circuit board is configured to serve as a reference ground for the antenna, and wherein discharge of the capacitive elements is configured to provide a flow of current to an amplifier configured to drive the antenna, the computer program comprising code configured to control discharge of the capacitive elements to provide a flow of current to the amplifier configured to drive the antenna.
The key stages of the method used to assemble an antenna integrated with a supercapacitor are illustrated schematically in
It will be appreciated to the skilled reader that any mentioned apparatus/device/server and/or other features of particular mentioned apparatus/device/server may be provided by apparatus arranged such that they become configured to carry out the desired operations only when enabled, e.g. switched on, or the like. In such cases, they may not necessarily have the appropriate software loaded into the active memory in the non-enabled (e.g. switched off state) and only load the appropriate software in the enabled (e.g. on state). The apparatus may comprise hardware circuitry and/or firmware. The apparatus may comprise software loaded onto memory. Such software/computer programs may be recorded on the same memory/processor/functional units and/or on one or more memories/processors/functional units.
In some example embodiments, a particular mentioned apparatus/device/server may be pre-programmed with the appropriate software to carry out desired operations, and wherein the appropriate software can be enabled for use by a user downloading a “key”, for example, to unlock/enable the software and its associated functionality. Advantages associated with such example embodiments can include a reduced requirement to download data when further functionality is required for a device, and this can be useful in examples where a device is perceived to have sufficient capacity to store such pre-programmed software for functionality that may not be enabled by a user.
It will be appreciated that the any mentioned apparatus/circuitry/elements/processor may have other functions in addition to the mentioned functions, and that these functions may be performed by the same apparatus/circuitry/elements/processor. One or more disclosed aspects may encompass the electronic distribution of associated computer programs and computer programs (which may be source/transport encoded) recorded on an appropriate carrier (e.g. memory, signal).
It will be appreciated that any “computer” described herein can comprise a collection of one or more individual processors/processing elements that may or may not be located on the same circuit board, or the same region/position of a circuit board or even the same device. In some example embodiments one or more of any mentioned processors may be distributed over a plurality of devices. The same or different processor/processing elements may perform one or more functions described herein.
With reference to any discussion of any mentioned computer and/or processor and memory (e.g. including ROM, CD-ROM etc), these may comprise a computer processor, Application Specific Integrated Circuit (ASIC), field-programmable gate array (FPGA), and/or other hardware components that have been programmed in such a way to carry out the inventive function.
The applicant hereby discloses in isolation each individual feature described herein and any combination of two or more such features, to the extent that such features or combinations are capable of being carried out based on the present specification as a whole, in the light of the common general knowledge of a person skilled in the art, irrespective of whether such features or combinations of features solve any problems disclosed herein, and without limitation to the scope of the claims. The applicant indicates that the disclosed example aspects/embodiments may consist of any such individual feature or combination of features. In view of the foregoing description it will be evident to a person skilled in the art that various modifications may be made within the scope of the disclosure.
While there have been shown and described and pointed out fundamental novel features as applied to different example embodiments thereof, it will be understood that various omissions and substitutions and changes in the form and details of the devices and methods described may be made by those skilled in the art without departing from the spirit of the invention. For example, it is expressly intended that all combinations of those elements and/or method steps which perform substantially the same function in substantially the same way to achieve the same results are within the scope of the invention. Moreover, it should be recognized that structures and/or elements and/or method steps shown and/or described in connection with any disclosed form or embodiment may be incorporated in any other disclosed or described or suggested form or embodiment as a general matter of design choice. Furthermore, in the claims means-plus-function clauses are intended to cover the structures described herein as performing the recited function and not only structural equivalents, but also equivalent structures. Thus although a nail and a screw may not be structural equivalents in that a nail employs a cylindrical surface to secure wooden parts together, whereas a screw employs a helical surface, in the environment of fastening wooden parts, a nail and a screw may be equivalent structures.
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/IB2010/001867 | 7/28/2010 | WO | 00 | 5/6/2015 |