GB2550115A

GB2550115A - An energy harvester

Info

Publication number: GB2550115A
Application number: GB1607786.9A
Authority: GB
Inventors: Edward Myers James; Savanth Anand; Weddell Alex
Original assignee: ARM Ltd; Advanced Risc Machines Ltd
Current assignee: ARM Ltd
Priority date: 2016-05-04
Filing date: 2016-05-04
Publication date: 2017-11-15
Anticipated expiration: 2036-05-04
Also published as: GB2550115B; WO2017191436A1; GB201607786D0

Abstract

An energy harvester comprises a transducer 102 generating an alternating current output Mp, Mn in response to ambient energy, and further generating control data Ca, Cb, wherein the control data relates to a characteristic of the alternating current output. A control unit 104 comprising control circuitry 106 is configured to receive the alternating current output and the control data; and wherein the control circuitry is configured to rectify the alternating current output to generate a direct current output in response to the control data. The control circuitry 114 generates switch control signals (analogue or digital) which drive the switches of the rectifier 112 to provide a DC output to operational circuitry 108 which may include a storage device 110 (e.g. battery, capacitor).The transducer 120a may be a piezoelectric device with an output power generating element 124 and an assist element 126 which outputs the control signals. There may be more than on assist element.. The transducer may alternatively be an electrostatic device or an electromagnetic device (figs 4b,4c,4d not shown).displacement may be caused by vibration etc. or thermal using a bimetal. Circuitry 108 may comprise a CPU, communications circuitry (e.g. WiFi, Bluetooth), sensing circuitry and/or a power management circuit.

Description

An energy harvester

The present invention relates to the field of electronic apparatuses, and particularly, but not exclusively to apparatuses having an energy harvester, which generates an alternating current output.

There is an increasing demand for electronic devices having a reduced power budget, especially as part of the increasing move towards the "Internet of Things" (loT) in which relatively small devices are connected together, for example for performing tasks such as monitoring temperature or other environmental conditions, controlling heating in a home for example.

While mobile applications have been designed with a relatively low power budget relative to laptops and desktop computers because their battery is expected to last at least a day on a single charge, the power budget for wireless sensor nodes, and other relatively small embedded devices in the loT is several orders of magnitude lower.

Many sensor applications do not have the option for wired charging of batteries, and also cannot be powered from wall sockets. This energy constraint is unlike many other applications where the design trade-off has primarily been between speed and power.

Therefore, there is an increasing demand for sensors which can harvest energy from their environment to reduce battery usage and prolong battery lifetime. The present techniques seek to provide a more energy efficient way for apparatuses to exploit energy from ambient sources.

In a first aspect there is provided an apparatus comprising: an energy harvester comprising: a transducer to generate an alternating current output in response to ambient energy, and to generate control data, wherein the control data comprises information relating to a characteristic of the alternating current output; a control unit comprising: control circuitry to receive the alternating current output and the control data; and wherein the control circuitry is configured to rectify the alternating current output to generate a direct current output in response to the control data.

In a further aspect there is provided an energy harvester comprising: a transducer to generate an alternating current output based on or in response to ambient energy; and to generate a control signal comprising information relating to a characteristic of the alternating current output.

In a further aspect there is provided a method for actively rectifying an alternating current at an apparatus comprising an energy harvester and a control unit, the method comprising: generating, at a transducer on the energy harvester, the alternating current in response to ambient energy; generating, at the transducer, control data comprising information relating to a characteristic of the alternating current; receiving, at control circuitry on the control unit, the alternating current and the control data; generating, at the control circuitry, a direct current output in response to the alternating current output and the control data.

Figure la illustrates a problem with a known electronic device having a known energy harvester;

Figure lb shows a piezoelectric transducer of the energy harvester of Figure la;

Figures 2a-d show known rectification circuits used in the electronic device of Figure la;

Figure 3 schematically shows a first example of an electronic device having an energy harvester according to the present techniques;

Figures 4a-d schematically show example transducers according to the present techniques;

Figure 5a schematically shows an example switch-control circuit according to the present techniques;

Figure 5b schematically shows an example rectification circuit according to the present techniques;

Figure 6a is a graph showing two AC outputs from an energy harvester according to the present techniques;

Figure 6b is a graph showing control data output from an energy harvester according to the present techniques;

Figure 6c schematically shows two inputs to the switch-control circuit of Figure 5a according to the present techniques;

Figure 6d schematically shows two outputs from the switch-control circuit of Figure 5a according to the present techniques; and

Figure 7 schematically shows one method of operation of the disclosed technique.

Figure la illustrates a known electronic device 1 having known energy harvester 2 and control unit 4. In Figure la the energy harvester 2 is configured to harvest energy from vibrations. In Figure lb, the energy harvester 2 is depicted as comprising a piezoelectric transducer 6, which converts vibrations into an alternating current (AC) output.

The control unit 4 comprises rectification circuitry 8, operational circuitry 10 (e.g. central processing unit (CPU), communications circuitry, sensing circuitry) and energy storage circuitry 12.

The rectification circuitry 8 receives positive part (Mp) and negative part (MN) of AC output, and rectifies the AC output to generate a DC current output. In operation, the DC current output may be used to power the operational circuitry 10, and/or may also be used to charge storage circuitry 12.

Figures 2a-2d show examples of conventional rectification circuits 8a-8d used to rectify outputs from known energy harvesters 1.

Figure 2a shows a voltage doubler circuit rectification circuit 8a having diodes 14 which switch state when following the alternating voltage (V|N) from the energy harvester (not shown), so as to provide a rectified output Vout- It will be appreciated that switching the state of the diodes 14 results in losses (e.g. diode drops/voltage drops/power losses) in the rectification circuit 8a.

Figure 2b shows a full-wave rectifier circuit 8b having diodes 14 arranged to provide a rectified output (Vout) in response to the alternating voltage (V|N) from the energy harvester. As above, it will be appreciated that switching the state of the diodes 14 results in losses in the rectification circuit 8b.

Figure 2c shows a synchronous rectifier circuit 8c, whereby a MOS transistor 16 is biased so as to minimise the voltage drop across the diode 14. Flowever, a comparator 18 is required to determine when the bias is applied for the MOS transistor 16. The comparator 18 is powered by a power source (not shown) independent of the energy harvester. Therefore, such circuits may not be suitable for low-powered sensor applications.

Figure 2d shows a self-driven synchronous rectification circuit 8d, whereby a transformer 20 is arranged to drive the synchronous rectification. It will be appreciated that the transformer 20 may be relatively bulky and may introduce losses into the rectification circuit 8d. Therefore, such self-driven rectification circuits as shown in Figure 2d are not suitable for electronic devices which require a small form factor and low-power operation.

Figure 3 schematically shows an apparatus or device 100 comprising an energy harvester 102 and a control unit 104 according to the present techniques.

The energy harvester 102 comprises a transducer (not shown in Figure 3) and is configured to harvest energy from an ambient source, and converts the ambient energy into an alternating current (AC) output, comprising positive part (MP) and negative part (Mm).

The energy harvester 102 is also configured to generate control data comprising one or more signals which are used by the control unit 104 to control the rectification of the AC output to direct current (DC), hereinafter "control signals".

In Figure 3, the energy harvester 102 is depicted as generating two control signals (CA & CB). The control signals may take any suitable form. For example, the control signals may comprise analog signals, digital signals, optical signals or a combination of analog and digital signals.

The control unit 104 comprises control circuitry 106, which may be provided in electrical communication with operational circuitry 108. The operational circuitry may also comprise storage circuitry 110.

The control circuitry 106 comprises rectification circuitry 112 having switch logic (not shown in Figure 3), and which is configured to rectify the AC output from the energy harvester 102 and generate a DC output.

The control circuitry 106 further comprises switch-control circuit 114, which is configured to receive the control data from the energy harvester 102 and generate one or more switch-control signals (depicted as SC1-SC4 in Figure 3) in response thereto. Using the present techniques, the rectification circuitry 112 actively rectifies the AC output in response to the one or more switch-control signals.

The switch-control signals may take any suitable form. For example, the switch-control signals may comprise all analog signals, all digital signals or the switch-control signals may comprise a combination of analog and digital signals.

The operational circuitry 108 and storage circuitry 110 may be similar to that as described above with respect to the conventional electronic device 1. For example, the operational circuitry 108 may comprise any suitable components or logic such as, for example, a central processing unit (CPU), communications circuitry (e.g. Bluetooth, Bluetooth Low Energy (BLE), WiFi), sensing circuitry (e.g. vibration sensor, chemical sensor, temperature sensor) and/or power management circuitry (e.g. a maximum power point tracking (MPPT) circuit and/or a power management integrated circuit (PMIC)).

Furthermore, the storage circuitry 110 may comprise a capacitor, but may alternatively comprise a battery or other suitable storage component(s).

Figures 4a-d schematically show example transducers 120a-120d according to the present techniques.

Figure 4a schematically shows a piezoelectric transducer 120a, whereby a cantilever support 122 is clamped towards one end thereof and is arranged to vibrate (e.g. sinusoidally) in response to ambient energy (as indicated by arrow 127). The cantilever support 122 has first and second surfaces, whereby a primary piezoelectric element 124 and an assist piezoelectric element 126 are depicted as being co-fabricated on a first surface of the cantilever support 122, whereby co-fabrication is taken to mean fabricated at substantially the same time and/or using similar processing steps.

The primary piezoelectric element 124 is arranged so as to generate a primary AC output (comprising MP and MN) in response to the mechanical stress and strain applied thereto as a result of the vibrations of the cantilever support 122.

Furthermore, the assist piezoelectric element 126 is arranged to generate control data in the form of a control AC output (e.g. signals CAand CB) in response to the mechanical stress and strain applied thereto as a result of the vibrations of the cantilever support 122.

In the present illustrative example, the magnitude of the primary AC output is larger in comparison to the control AC output. Flowever, both the primary and control AC outputs are generated in response to the movement of the cantilever support 122.

Although the primary and assist piezoelectric elements 124, 126 may be arranged in any suitable configuration on the surface of the cantilever support 122, as the mechanical stress and strain experienced by such piezoelectric elements will be greatest towards the clamped end, arranging the primary piezoelectric element(s) generating the primary AC output (MP and MN) towards the clamped end, whilst arranging the assist piezoelectric elements generating the control signals (Ca and CB) towards the distal end will minimize energy loss due to loss of harvester area.

Further co-fabricated piezoelectric elements (not shown) may be provided on a second surface of the cantilever support 122 opposite to the first surface so as to generate additional or alternative AC outputs.

In the present illustrative example, the ambient energy which causes the motion of the cantilever may be mechanical energy resulting from vibrations from a motor in proximity to the transducer, acoustic energy (e.g. soundwaves), wind energy etc.

Alternatively, the ambient energy may be thermal energy whereby the cantilever support 122 may comprise a bimetal material which deforms due to heat and arranged to oscillate between a hot and a cold surface. When the distal end of the cantilever support 122 contacts the cold surface it loses heat and bends and makes contact with the hot surface and bends and makes contact with the cold surface, at which point the process repeats. In some examples, the thermal energy required to heat the hot surface may be obtained from electromagnetic radiation (e.g. sunlight).

Figure 4b schematically shows an electrostatic transducer 120b, whereby a plurality of primary electrodes 130 are arranged on opposing support plates 132,134 in a primary capacitive array 131 (hereinafter "primary array"), whilst a plurality of assist electrodes 136 are co-fabricated with the primary electrodes 130 on the support plates 132,134 in one or more assist capacitive arrays 138,140 (hereinafter "assist arrays"), whereby the support plates 132,134 are moveable with respect to one another in the direction as indicated by the arrow 129.

In operation, an electric field may be induced between the electrodes on the opposing support plates 132, 134, such that relative movement of the support plates 132, 134 effects a variation in a capacitance (C) of the respective arrays 131, 138, 140 (e.g. by changing the effective distance (D) thereof). Varying the capacitance, e.g. due to the support plates vibrating in response to ambient energy (e.g. mechanical energy), will result in an AC output.

For example, when (C) of the primary array 131 increases, the corresponding voltage (V) will decrease, whilst when (C) decreases (V) will increase. Therefore, it will be appreciated that the output of the primary array 131 will vary in response to the support plates moving relative to each other. The alternating output from the primary array 131 will be a primary AC output comprising Mp and MN, dependent on the specific movement.

Furthermore, varying values for (C) and (V) of the respective assist arrays 138, 140 will be indicative of, for example, the direction of movement of the support plates 122. Therefore, the outputs from the assist array 138, 140 may be taken to be control signals CAand Cb.

Figure 4c schematically shows a cross-section of an electromagnetic transducer 120c, whereby a magnet 144 is arranged to move in a channel 145 relative to a primary coil 146. The channel 145 may be formed within a support structure 143 around which the primary coil is wound. The support structure 143, may, for example, comprise a plastic former.

Two assist coils 147, 148 are co-fabricated with the primary coil 146 on the support structure 143. In Figure 4c, the movement of the magnet 144 within the channel 145 is depicted as being constrained by resilient means 150 (e.g. springs).

In operation, the magnet 144 oscillates in the channel 145, as indicated by arrow 149, in response to ambient energy, for example, mechanical energy (e.g. movement, acoustic energy) or electromagnetic energy (due to a magnet in proximity to the magnet 144 causing it to move), whereby the oscillations induce an electromagnetic force (EMF) in the primary coil 146, such that the primary AC output comprising MP and MN is output therefrom.

Similarly, the oscillations also induce an EMF in the assist coils 147, 148 at each end of the channel 145, whereby a first control signal Ca is output from first assist coil 147, whilst a second control signal CB is output from second assist coil 148.

It will be appreciated that it may be advantageous to minimise the output impedance of the primary coil 146 so as to maximise the efficiency thereof. Therefore, the thickness of the primary coil 146 may be increased so as to decrease the impedance thereof. The number of turns achievable for the primary coil 146 may be reduced as the thickness increases.

Preferably, the current of the control signals CA and CB will preferably be less than 5% of the primary AC output. More preferably, the current of the control signals CA and CB will be less than 1% of the primary AC output. Therefore, the impedance of the assist coils 147, 148 may be higher than that of the primary coil 146 and, therefore, the diameter of the assist coils 147,148 may be reduced in comparison to the diameter of the primary coil 146. The reduced diameter allows the assist coils 147, 148 to comprise an increased number of turns in comparison to the primary coil 146. Therefore, a higher output voltage may be achievable across the assist coils 147,148 in comparison to the primary coil 146.

Figure 4d, schematically shows a further electromagnetic transducer 120d, whereby a cantilever support 152 comprises a primary coil 154 co-fabricated with an assist coil 156 on a first surface thereof, adjacent to a magnet 155.

When the cantilever support 152 vibrates, an EMF will be induced in both coils 154 and 156, whereby the primary coil 154 is arranged to generate a primary AC output (e.g. comprising MP and Mn), whilst the secondary coil may be used to generate one or more control signals. Further coils (not shown) may be provided on a second surface of the cantilever support 152 opposite to the first surface so as to generate additional or alternative AC outputs.

Similar to the example described in Figure 4a, the cantilever 152 may vibrate in response to ambient energy including one or more of: mechanical energy, thermal energy and electromagnetic energy.

Whilst the transducer elements generating the primary AC output and control signals in Figures 4a-4d are depicted as being the same type (e.g. coils, electrodes, piezoelectric elements), there is no requirement for the transducer elements to be the same type.

Furthermore, whilst the transducer elements generating the primary AC output and control signals are depicted as being co-fabricated with each other, there is no requirement for the transducer elements to be co-fabricated with each other.

As above, the control circuitry comprises switch-control circuitry, which is configured to receive the control signals from the energy harvester and generate one or more switch-control signals in response thereto, so as to control the rectification process.

Figure 5a schematically shows an example switch-control circuit 160, depicted as an SR latch, including inverters 162a & 162b, NAND gates 164a & 164b and NOR gates 166a & 166b, whereby the switch-control circuit 160 is configured to generate outputs Q and Qn in response to digital input signals C,1 & 02.

Taking the electromagnetic transducer 120c of Figure 4c as an illustrative example, control signals C,1 & C,2 are digitised versions of control signals CA and CB. The control signals may be transformed into digital signals using any suitable techniques e.g. via a comparator, Schmitt trigger, inverter or an analog-to-digital controller (ADC), which may be provided as part of the energy harvester or the control circuitry.

In the present illustrative example, when an EMFis induced in first assist coil 147 control signal Cil is provided as an input whereby the output Q is high and Qn is low.

Similarly, when an EMF is induced in second assist coil 148, control signal C,2 is provided as an input whereby the output Qn is high and Q is low.

The respective outputs Q and Qn will continue to transition between high and low, dependant on the control signals CAand CB.

The outputs Q and Qn can then be used as switch-control signals for the rectification circuitry which receives the Mp and Mn from the primary coil.

Control signals from other types of transducers, such as those illustratively shown in Figures 4a, b & d may be used as inputs to the switch-control circuit so as to generate switch-control signals for the rectification circuitry.

It will also be appreciated that the switch-control circuit is not limited to receiving two inputs or generating two outputs, and any number of inputs/outputs may be provided.

It will also be appreciated that the switch-control circuit is not limited to comprising a latch circuit as depicted in Figure 5a, but may comprise any suitable configuration/logic/components, and, for example, may comprise machine learning neural network circuitry.

Figure 5b schematically shows an example rectification circuit 180, comprising inputs 182a&b for receiving MP and MN from the energy harvester (not shown in Figure 5b), switch logic in the form of switch devices 184a&b and 186a&b and output terminals 188a&b. In the present example the output terminals 188a&b are provided in electrical communication with the operational circuitry 108.

In the present illustrative example, the switch devices 184a&b and 186a&b are depicted as transistors (depicted as MOS transistors in Figure 5b), whereby the gates of the transistors are actively controlled based on, or in response to, the switch-control signals from switch-control circuit (as described in Figure 5a).

The rectification circuit 180 comprises a first current path for Mn through the switch devices 186a&b and the operational circuitry 108 when Qn is high, whilst the rectification circuit 180 comprises a second current path for Mp through the switch devices 184a&b and the operational circuitry 108 when Q. is high. Using such functionality, the rectification circuitry generates a DC output through the operational circuitry 108 based on, or in response to, the switch-control signals.

It will be appreciated that the rectification circuit is not limited to the configuration depicted in Figure 5b, and any suitable rectification circuit may be provided.

It will also be appreciated that the switch-logic depicted in Figure 5b is not limited to comprising transistors, and may take the form of any suitable combination of hardware and or software components.

As depicted above, the control signals comprise information generated, based on, or in response to, ambient energy (e.g. phase information, amplitude information, frequency information, harmonics information), and from which characteristics of the electronic device 1 (e.g. an operational state or condition) may be derived such that the rectification circuitry may 180 be actively controlled or configured accordingly.

It will be appreciated that such information relates to the characteristics of the electronic device, and may be dependent on, for example the position, direction, rate of vibration of the transducer and which, in turn, may be used to control the state of the switching devices in the rectification circuit so as to minimise the losses which would otherwise occur (e.g. diode drops). By reducing losses in the control circuit, the lowest voltage at which power can be extracted from the energy harvester may be decreased.

It will be appreciated that such information is not limited to being generated based on, or in response to, ambient energy. For example, the control signals may comprise integrated time information which may be used by the control circuitry to counter ageing or "wear and tear".

Taking the electromagnetic transducer 120c of Figure 4c as an illustrative example. Figure 6a is a graph showing an AC output from the primary coil comprising MP 202 & Mn 204.

Figure 6b is a graph showing control data in the form of control signals Ca 206 and Cb 208, which are output from the assist coils, and Figure 6c schematically shows digitised versions C,1 208 and C,2 210 of the control signals 206, 208, which are used as inputs to the switch-control circuity of Figure 5a. In the present example the AC output control signals 206,208 are transformed into a digital signal using any suitable techniques

Figure 6d schematically shows two switch-control signals Q 214 and Qn 216, which are output from the schematic switch-control circuity of Figure 5a.

In the present illustrative example, control signal Ca is high when there is a zero crossing 218 on Mp rising, whilst when control signal CB is high there is a zero crossing 220 on Mn rising.

The period between control signals may be indicative of the position, direction and rate of travel of the magnet of Figure 4c, such that the orientation, velocity, acceleration of the electronic device may be derived. For example, when the magnet travels slower in a first direction in the channel in comparison to a second direction (e.g. due to gravity) such that any resulting variations in the period of the control signals pulses may be indicative of the orientation of the device.

Alternatively, the period between control signals Ca and CB may be shorter than the period between control signals CB and Ca, and this may, for example, be indicative of a duty cycle problem with the transducer, which may be compensated for as appropriate by one or more of: the energy harvester, the switch-control circuit, rectification circuitry and the operational circuitry.

Alternatively, taking the piezoelectric transducer of Figure 4a as an example, the cantilever vibrating outside of its resonant frequency may be identifiable from the control signals, which in turn may be taken to be indicative of a problem with the functionality of the energy harvester. The cantilever may then be controlled as appropriate such that the cantilever oscillates at the resonant frequency.

Whilst the primary AC output and control signals are depicted as separate outputs in Figures 6a-6d, the primary AC output and control signal(s) may, in alternative examples, be modulated/ embedded on the same output. The control circuitry may be configured to undertake demodulation to extract the primary AC output and the control signals. It will be appreciated that modulating the primary AC output and control signals into as few outputs as possible means the number of terminals on the control circuitry may be minimised, as fewer pads (1C outputs) are required to receive the signals, and therefore the size of the control circuitry may be reduced.

Method begins at Start step 300, whereby at step 302 an energy harvester of an electronic device generates an AC output in response to ambient energy, such as vibrations. The energy harvester also generates control data, whereby, for example, the control data comprises control signals which are also generated in response to the ambient energy. In alternative examples, the control data may be generated independently of the ambient energy (e.g. integrated time information).

At step 304, a control circuit of the electronic device receives the AC output and the control data, whereby at step 306 the control circuit, for example, using a switch-control circuit, generates switch-control signals based on, or in response to the control data.

At step 308, the control circuit rectifies, using rectification circuitry, the AC output in response to the switch-control signals and at step 310 provides the DC output to operational circuitry on the electronic device. The method finishes at End step 312.

Whilst conventional rectification circuits are reactive to the AC output from the energy harvester, the present techniques mean that the rectification circuitry will be reactive to the control signals, which, as in the illustrative example above, provide for controlled rectification using switching devices. Furthermore, as diodes are not required to rectify the AC output, there will be no diode losses. Whilst the switching devices may replace diodes for rectification, it will be appreciated that diodes may be provided in the control circuitry as required for a specific application.

The present techniques are applicable to electronic devices in various applications and solutions.

For example, a wireless sensor according to the present techniques may be located in or on an industrial motor having bearings. As described above, an energy harvester may provide AC power and control data to a control unit of the wireless sensor in response to vibrations from the motor. When vibrations exceed a certain threshold, this may be indicative of wear on the motor, and possible imminent failure.

In some examples, the energy harvester may function as a coarse sensor, whereby once a frequency threshold is reached, the harvester may send a further signal to the control unit so as to activate an additional high-power fine sensor on the operational circuitry in communication therewith to perform fine sensing. Therefore, such a high-power fine sensor may be in a sleep mode until the threshold is reached.

Similarly, wireless sensors may be located in bridges to sense stress and strain vibrations, and warn when, for example, the frequency or amplitude of such vibrations reaches a certain threshold.

In alternative examples, apparatuses according to the present techniques may function as a thermal sensor or light sensor.

In alternative examples, apparatuses according to the present techniques may be incorporated in clothing, e.g. to warm-up shoes or gloves or power/charge a further electronic device in response to a wearer's movement.

In alternative examples, apparatuses according to the present techniques may be incorporated beneath roadways and charge storage circuitry in response to vibrations resulting from vehicles travelling on the roadway.

It will be appreciated that any suitable manufacturing techniques may be used to fabricate the components of the electronic device (e.g. energy harvester/control unit).

The energy harvester and/or the control circuit may be fabricated on a substrate (e.g. a silicon die), whereby any suitable fabrication techniques may be used.

For example, any suitable selective deposition techniques may be used to create features as appropriate, e.g. growing materials or by blanket deposition or targeted deposition of material(s) on the surface of a substrate such as by physical vapour deposition (PVD), spin coating, atomic layer deposition (ALD), sputtering, chemical vapour deposition (CVD) or Plasma enhanced CVD (PECVD) to deposit the required material. Additionally, or alternatively, any suitable selective removal techniques may be used (e.g. wet chemical etching, ion etching).

It will be appreciated that the energy harvester and control circuit may be provided as part of the same substrate or on different substrates. Furthermore, the control circuit and operational circuitry may be provided as part of the same or different substrates.

It will also be clear to one of skill in the art that all or part of a logical method according to the preferred embodiments of the present techniques may suitably be embodied in a logic apparatus comprising logic elements to perform the steps of the above-described methods, and that such logic elements may comprise components such as logic gates in, for example a programmable logic array or application-specific integrated circuit. Such a logic arrangement may further be embodied in enabling elements for temporarily or permanently establishing logic structures in such an array or circuit using, for example, a virtual hardware descriptor language, which may be stored and transmitted using fixed or transmittable carrier media.

Although illustrative embodiments of the disclosure have been described in detail herein with reference to the accompanying drawings, it is to be understood that the disclosure is not limited to those precise embodiments, and that various changes and modifications can be effected therein by one skilled in the art without departing from the scope and spirit of the disclosure as defined by the appended claims.

It will be appreciated that the present techniques provide an electronic device comprising: an energy harvester configured to generate an alternating current output in response to ambient energy, and further configured to generate control data.

In examples, the information relating to a characteristic of the alternating current output comprises one or more of: phase information, pulse width information, amplitude information, harmonics information and frequency information.

In examples, the control data may be generated in response to the ambient energy, wherein the ambient energy comprises mechanical energy.

In some embodiments the transducer comprises a first piezoelectric element arranged to generate the alternating current output and a second piezoelectric element arranged to generate a first control signal of the control data and wherein the second piezoelectric element may be further arranged to generate a second control signal of the control data. In examples, the first and second piezoelectric elements are co-fabricated with each other.

In embodiments, the transducer may comprise two or more coils such that an electromagnetic force is induced in the two or more coils in response to relative movement with a magnet, wherein a first coil is arranged to generate the alternating current output and a second coil is arranged to generate a first control signal of the control data. A third coil may be arranged to generate a second control signal of the control data. In examples, the first, second and/or third coils may be co-fabricated with each other.

In some embodiments the transducer may comprise a first electrostatic array arranged to generate the alternating current output and a second electrostatic array arranged to generate a first control signal of the control data. The transducer may further comprise a third electrostatic array arranged to generate a second control signal of the control data. In examples, the first, second and/or third arrays may be co-fabricated with each other.

The control circuitry may comprise: switch-control circuitry, arranged to receive the control data and generate a switch-control signal based on or in response to the control data; and rectification circuitry, wherein the rectification circuity comprises switch logic configured to actively rectify the alternating current output to generate a direct current output in response to the switch-control signal, wherein the control data comprises one or more analog signals and wherein the switch-control signal comprises one or more digital signal.

The rectification circuitry may comprise one or more transistors, wherein the one or more transistors may be actively controlled in response to the switch-control signal.

In examples, the switch-control circuitry and rectification circuity are fabricated on the same die.

In some examples, the control data may modulate the alternating current output.

Claims

1. An apparatus comprising: an energy harvester comprising: a transducer to generate an alternating current output in response to ambient energy, and to generate control data, wherein the control data comprises information relating to a characteristic of the alternating current output; a control unit comprising: control circuitry to receive the alternating current output and the control data; and wherein the control circuitry is configured to rectify the alternating current output to generate a direct current output in response to the control data.

2. The apparatus according to Claim 1, wherein the information relating to a characteristic of the alternating current output comprises one or more of: phase information, pulse width information, amplitude information, harmonics information and frequency information.

3. The apparatus according to any of claims 1 or 2, wherein the ambient energy comprises mechanical energy.

4. The apparatus according to any preceding claim, wherein the transducer comprises a first piezoelectric element arranged to generate the alternating current output and a second piezoelectric element arranged to generate a first and second control signal of the control data.

5. The apparatus according to claim 4, wherein the control data is generated from multiple assist elements.

6. The apparatus according to any of claims 1 to 3, wherein the transducer comprises two or more coils such that an electromagnetic force is induced in the two or more coils in response to relative movement with a magnet.

7. The apparatus according to claim 6, wherein a first coil is arranged to generate the alternating current output and a second coil is arranged to generate a first control signal of the control data.

8. The apparatus according to claim 7, wherein a third coil is arranged to generate a second control signal of the control data.

9. The apparatus according to any of claims 1 to 3, wherein the transducer comprises a first electrostatic array arranged to generate the alternating current output and a second electrostatic array arranged to generate a first control signal of the control data.

10. The apparatus according to claim 9, wherein a third electrostatic array is arranged to generate a second control signal of the control data.

11. The apparatus according to any preceding claim, wherein the control circuitry comprises: switch-control circuitry, arranged to receive the control data and generate one or more switch-controls signal based on or in response to the control data.

12. The apparatus according to claim 12, wherein the control circuitry comprises: rectification circuitry, wherein the rectification circuity comprises switch logic to actively rectify the alternating current output to generate a direct current output in response to the one or more switch-control signals.

13. The apparatus according to claim any of claims 11 or 12, wherein the one or more switch-control signals each comprise a digital signal.

14. The apparatus according to any of claims 11 to 13, wherein the switch logic comprises one or more transistors, wherein the one or more transistors are actively controlled in response to the switch-control signal to rectify the alternating current output.

15. The apparatus according to any of claims 11 to 14, wherein the switch-control circuitry and rectification circuity are fabricated on the same die.

16. The apparatus according to any preceding claim, wherein the control data modulates the alternating current output.

17. The apparatus according to any preceding claim, wherein the control data is generated in response to the ambient energy.

18. An energy harvester comprising: a transducer to generate an alternating current output based on or in response to ambient energy; and to generate a control signal comprising information relating to a characteristic of the alternating current output.

19. A method for actively rectifying an alternating current at an apparatus comprising an energy harvester and a control unit, the method comprising: generating, at a transducer on the energy harvester, the alternating current in response to ambient energy; generating, at the transducer, control data comprising information relating to a characteristic of the alternating current; receiving, at control circuitry on the control unit, the alternating current and the control data; generating, at the control circuitry, a direct current output in response to the alternating current output and the control data.

20. An apparatus substantially as hereinbefore described with reference to Figures 3 to 7.

21. An energy harvester substantially as hereinbefore described with reference to Figures 3 to 7.

22. A method substantially as hereinbefore described with reference to Figures 3 to 7.