Search

EP-3646435-B1 - AN ENERGY HARVESTER TO CONVERT INCIDENT RADIO FREQUENCY ENERGY TO DIRECT CURRENT AS WELL AS A CORRESPONDING METHOD AND SENSOR COMPRISING THE ENERGY HARVESTER

EP3646435B1EP 3646435 B1EP3646435 B1EP 3646435B1EP-3646435-B1

Inventors

  • RODRIGUES MANSANO, ANDRÉ LUÍS
  • LINK, Omar Vince
  • VAN DER JAGT, Simon

Dates

Publication Date
20260506
Application Date
20180627

Claims (13)

  1. : An energy harvester to convert incident radio frequency, RF, energy associated with an RF signal to direct current energy, the energy harvester comprising: - a rectifier (5) comprising a pre-storage capacitor (4), wherein said rectifier (5) is arranged to rectify said incoming incident RF energy thereby storing said RF energy into said pre-storage capacitor (4); - an energy transfer unit (22) comprising a storage output capacitor (23), wherein a capacitance value of said storage output capacitor (23) is higher than a capacitance value of said pre-storage capacitor (4), and wherein said energy transfer unit (22) is arranged to transfer said energy in said pre-storage capacitor (4) into said storage output capacitor (23); - a control unit (2) arranged for controlling said energy transfer unit (22), wherein said control unit (2) is arranged to measure a voltage over said pre-storage capacitor (4), and wherein said control unit (2) is further arranged to: o activate said energy transfer unit (22) to start transferring said energy in said pre-storage capacitor (4) into said storage output capacitor (23) when said measured voltage is above a first voltage threshold, characterised in that said energy transfer unit (22) comprises: - a low-power oscillator (24), connected to said pre-storage capacitor (4), wherein said low-power oscillator (24) is arranged to provide for an oscillation output signal based on said energy stored in said pre-storage capacitor (4); - an Alternating Current, AC, to Direct Current, DC, converter (25) connected to said low-power oscillator (24) and to said storage output capacitor (23), wherein said AC-to-DC converter (25) is arranged for converting said oscillation output signal to a DC output signal, wherein said DC output signal is provided to said storage output capacitor (23), o wherein said control unit (2) is arranged to activate and deactivate said energy transfer unit (22) by activating and deactivating said low-power oscillator (24), - wherein said energy transfer unit (22) is deactivated whenever said voltage over said pre-storage capacitor (4) falls below a second voltage threshold, wherein said first voltage threshold is higher than said second voltage threshold and wherein: - said pre-storage capacitor (4) has a capacitance value of between 100 picofarad, pF, and 100 nanofarad, nF; - said storage output capacitor (23) has a capacitance value of between 1 microfarad, µF, and 100 millifarad, mF.
  2. : An energy harvester in accordance with claim 1, wherein said energy harvester comprises a power management unit (7), connected to said storage output capacitor (23), wherein said power management unit (7) is arranged to convert a voltage over said storage output capacitor (23) to an operating DC voltage.
  3. : An energy harvester in accordance with claim 2, wherein said control unit (2) is further arranged to measure a voltage over said storage output capacitor (23), and wherein said control unit (2) is further arranged to: - activate said power management unit (7) to start converting said voltage over said storage output capacitor (23) to said operating DC voltage when said measured voltage over said storage output capacitor (23) is above a predetermined threshold.
  4. : An energy harvester according to any of the previous claims, wherein said control unit (2) is further arranged to: - deactivate said energy transfer unit (22) to stop transferring said energy in said pre-storage capacitor (4) into said storage output capacitor (23) when said measured voltage is below a second voltage threshold; - wherein said first voltage threshold is higher than said second voltage threshold.
  5. : An energy harvester according to any of the previous claims, wherein said power management unit (7) comprises: - a switched-mode boost converter for boosting said voltage over said pre-storage capacitor thereby obtaining a boosted voltage over said storage output capacitor.
  6. : An energy harvester according to any of the previous claims, wherein said energy harvester (7) further comprises a battery for supplying energy to said control unit (2).
  7. : An energy harvester according to any of the previous claims, wherein said rectifier (5) comprises one or more diodes selected from a group comprising a Schottky diode, a PN junction diode and a tunnel diode.
  8. : An energy harvester according to any of the previous claims, wherein said control unit (2) comprises an operational amplifier, op-amp, comparator with hysteresis for providing said first voltage threshold and said second voltage threshold.
  9. : An energy harvester according to any of the previous claims, wherein said harvester further comprises: - a bypass switch for bypassing said energy transfer unit (22); - wherein said control unit (2) is further arranged for determining that said incoming incident energy is non-fluctuating based on said measured voltage over said pre-storage capacitor (4), and for activating said bypass switch based on said determination.
  10. : An energy harvester according to any of the previous claims, and claim 2, wherein a boost factor of said power management unit (7) is controllable, and wherein said controller is arranged to control said boost factor.
  11. : A sensor device comprising: - an energy harvester according to any of the previous claims; - an antenna (3) connected to said rectifier, wherein said antenna (3) is arranged for receiving said RF signal; - a sensor for performing a measurement.
  12. : A sensor device according to claim 11 and claim 2, wherein said sensor device further comprises: - a controller arranged for measuring said operating DC voltage, and for initiating said sensor to perform said measurement and for transmitting a performed measurement whenever a measured operating DC voltage exceeds a predetermined operating voltage.
  13. : A method of converting incident radio frequency, RF, energy associated with an RF signal to direct current energy using an energy harvester in according with any of the claims 1 - 10, said method comprising the steps of: - rectifying, by said rectifier (5), said incoming incident RF energy thereby storing said RF energy into said pre-storage capacitor; - transferring, by said energy transfer unit (22), said energy in said pre-storage capacitor (4) into said storage output capacitor (23); - controlling, by said control unit (2), said energy transfer unit (22), wherein said controlling comprises measuring a voltage over said pre-storage capacitor (4), and wherein said controlling further comprises: o activating said energy transfer unit (22) to start transferring said energy in said pre-storage capacitor (4) into said storage output capacitor (23) when said measured voltage is above a first voltage threshold; o deactivating said energy transfer unit (22) to stop transferring said energy in said pre-storage capacitor (4) into said storage output capacitor (23) when said measured voltage is below a second voltage threshold; - wherein said first voltage threshold is higher than said second voltage threshold. wherein said method further comprises - providing, by a low-power oscillator (24) of the energy transfer unit (22) and connected to said pre-storage capacitor (4), an oscillation output signal based on said energy stored in said pre-storage capacitor (4); - converting, by an Alternating Current, AC, to Direct Current, DC, converter (25) of the energy transfer unit (22) connected to said low-power oscillator (24) and to said storage output capacitor (23), said oscillation output signal to a DC output signal, and - providing said DC output signal to said storage output capacitor (23), wherein said control unit (2) is arranged to activate and deactivate said energy transfer unit (22) by activating and deactivating said low-power oscillator (24).

Description

Technical field The present disclosure is generally related to harvesting of energy and, more specifically, to a concept of efficiently storing harvested energy associated with an RF signal. Background Nowadays, billions of radio frequencies, RF, transmitters are broadcasting RF energy in a continuous manner. For example, mobile telephones, base stations, radio broadcast stations, WiFi access points as well as handheld radios all transmit RF signals. The ability to harvest RF energy, from ambient or dedicated sources, enables wireless charging of, for example, sensor devices. Energy harvesting, also known as power harvesting or energy scavenging or ambient power, is the process by which energy is derived from external sources, for example Radio Frequency energy, solar power, thermal energy, wind energy, salinity gradients, and kinetic energy, also known as ambient energy, captured, and stored for small, wireless autonomous devices, like those used in wearable electronics and wireless sensor networks. Energy harvesters provide a very small amount of power for low-energy electronics. While the input fuel to some large-scale generation costs resources (oil, coal, etc.), the energy source for energy harvesters is present as ambient background. For example, temperature gradients exist from the operation of a combustion engine and in urban areas, there is a large amount of electromagnetic energy in the environment because of radio and television broadcasting. The present disclosure is explicitly directed to the harvesting of energy from RF energy associated with an RF signal. The concept of harvesting RF energy is already known. One of the challenges in this field is to improve the energy harvesting. That is, the RF energy received at an antenna should be converted and/or stored as efficiently as possible. Preferably, the RF energy should be converted and stored such that no battery is required any more. All the energy for operating the device, for example the sensor, is then obtained from the RF signals. Following the above, it is a drawback of the known energy harvesters that the received RF power is not converted and stored efficiently. Summary It would be advantageous to achieve an energy harvester that is able to efficiently convert and store Radio Frequency, RF, energy associated with an RF signal. It would also be desirable to achieve a corresponding method as well as a sensor device comprising such an energy harvester. The invention is set out by the appended claims. To better address one or more of these concerns, in a first aspect of the disclosure, an energy harvester is provided to convert incident radio frequency, RF, energy associated with an RF signal to direct current energy. The energy harvester comprising: a rectifier comprising a pre-storage capacitor, wherein said rectifier is arranged to rectify said incoming incident RF energy thereby storing said RF energy into said pre-storage capacitor;an energy transfer unit comprising a storage output capacitor, wherein a capacitance value of said storage output capacitor is higher than a capacitance value of said pre-storage capacitor, and wherein said energy transfer unit is arranged to transfer said energy in said pre-storage capacitor into said storage output capacitor;a control unit arranged for controlling said energy transfer unit, wherein said control unit is arranged to measure a voltage over said pre-storage capacitor, and wherein said control unit is further arranged to: o activate said energy transfer unit to start transferring said energy in said pre-storage capacitor into said storage output capacitor when said measured voltage is above a first voltage threshold. wherein said energy transfer unit is deactivated whenever said voltage over said pre-storage capacitor falls below a second voltage threshold, wherein said first voltage threshold is higher than said second voltage threshold and wherein: said pre-storage capacitor has a capacitance value of between 100 picofarad, pF, and 100 nanofarad, nF;said storage output capacitor has a capacitance value of between 1 microfarad, µF, and 100 millifarad, mF. The present disclosure is based on the concept that the RF energy associated with an RF signal is relatively low. This energy is rectified by the rectifier and stored in the pre-storage capacitor. The pre-storage capacitor will thus be energized via the RF energy associated with the RF signal. The inventors have found that the pre-storage capacitor does not form a stable voltage reference point. A stable voltage reference point is, however, preferred as an input signal for any Direct Current, DC, to DC converter. As such, it was one of the insights that a stable voltage reference point should be created, which stable voltage reference point can be used as an input for any DC to DC converter connected thereto. The above is realized using the energy transfer unit. The energy transfer unit is arranged to transfer the energy comprised by the pre