Charging circuit and system for radio frequency energy collection
Through the synergistic design of multi-stage RF rectifiers, low-frequency charge pumps, and voltage drop converters, the problems of low sensitivity and low energy utilization in RF energy harvesting systems are solved, achieving high-efficiency energy conversion and stable driving capability, making it suitable for devices with low voltage requirements.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Filing Date
- 2025-03-26
- Publication Date
- 2026-03-17
AI Technical Summary
Existing radio frequency energy harvesting systems have low sensitivity, struggle to achieve target output voltage, have low energy utilization, and cannot drive high-power loads.
The system employs a collaborative design of multi-stage RF rectifiers, multi-stage low-frequency charge pumps, and voltage drop converters. The multi-stage RF rectifiers rectify the RF signal into initial DC current, the multi-stage low-frequency charge pumps boost the voltage level, and the voltage drop converters step down the voltage to output drive current. Combined with voltage monitoring and switching protection measures, the system ensures the stability and efficiency of energy conversion.
It significantly improves the energy utilization and driving capability of radio frequency energy harvesting systems, enabling effective driving of loads under low voltage conditions, especially for miniaturized and low-power devices, and features efficient energy conversion and overvoltage protection.
Smart Images
Figure CN224006535U_ABST
Abstract
Description
Technical Field
[0001] This utility model relates to the field of circuit technology, and in particular to a charging circuit and system for radio frequency energy harvesting. Background Technology
[0002] The existing methods for radio frequency (RF) energy harvesting have the following drawbacks: First, low sensitivity. Existing RF energy harvesting systems require increasing the number of rectifier stages to increase sensitivity, but this often results in the output voltage failing to reach the target value. Second, low energy efficiency. Existing RF energy harvesting systems store energy in a capacitor using a rectifier, which then charges the load, leading to low energy efficiency. Third, the output current of existing RF energy harvesting systems is insufficient for power-intensive loads. Utility Model Content
[0003] The purpose of this invention is to provide a charging circuit and system for radio frequency energy harvesting, so as to alleviate the technical problems in the prior art, such as the output voltage not reaching the target value, low energy utilization, and inability to drive loads with high power consumption, so as to drive loads with high power consumption and improve energy utilization.
[0004] In a first aspect, this utility model provides a charging circuit for radio frequency energy harvesting, comprising: a multi-stage radio frequency rectifier, a multi-stage low-frequency charge pump, and a voltage drop converter connected in sequence; the multi-stage radio frequency rectifier is connected to an external antenna; the antenna is used to acquire radio frequency signals and transmit the radio frequency signals to the multi-stage radio frequency rectifier; the multi-stage radio frequency rectifier is configured to rectify the radio frequency signals to obtain an initial DC current; the multi-stage low-frequency charge pump is used to extract energy from the initial DC current and output an intermediate DC current with a voltage value reaching a first preset value; the voltage drop converter is used to step down the intermediate DC current and output a drive current with a drive voltage value reaching a second preset value to drive a load; the second preset value is less than the first preset value.
[0005] In a preferred embodiment of the present invention, the circuit further includes a switch and a voltage monitor between the multi-stage low-frequency charge pump and the voltage drop converter; the switch, the voltage monitor, and the multi-stage low-frequency charge pump are connected in sequence; the voltage monitor is used to monitor whether the intermediate DC current is within a preset voltage range, and when the intermediate DC current exceeds the voltage range, the switch is controlled to open to activate protection measures.
[0006] In a preferred embodiment of the present invention, the circuit further includes a low-dropout linear regulator connected to the voltage drop converter; the low-dropout linear regulator is used to regulate the driving current and output regulated DC power.
[0007] In a preferred embodiment of this invention, the low-dropout linear regulator is connected to the load.
[0008] In a preferred embodiment of this invention, the load is a Bluetooth device.
[0009] In a preferred embodiment of this invention, one end of a first filter capacitor is connected between the multi-stage low-frequency charge pump and the voltage drop converter; the other end of the first filter capacitor is grounded; the first filter capacitor is used to filter the intermediate DC current.
[0010] In a preferred embodiment of this invention, one end of a second filter capacitor is connected between the multi-stage RF rectifier and the multi-stage low-frequency charge pump; the other end of the second filter capacitor is grounded; the second filter capacitor is used to filter the initial DC current.
[0011] In a preferred embodiment of the present invention, the circuit further includes a matching network connected in parallel with the multi-stage RF rectifier; the matching network is used to perform impedance matching between the RF signal and the multi-stage RF rectifier.
[0012] In a preferred embodiment of this invention, the matching network is provided with an automatic tuning circuit.
[0013] Secondly, this utility model provides a system for radio frequency energy harvesting, including: the above-mentioned charging circuit for radio frequency energy harvesting, and a radio frequency receiving antenna coupled to the charging circuit.
[0014] The present invention has the following beneficial technical effects:
[0015] This utility model provides a charging circuit and system for radio frequency energy harvesting, comprising: a multi-stage radio frequency rectifier, a multi-stage low-frequency charge pump, and a voltage drop converter connected in sequence; the multi-stage radio frequency rectifier is connected to an external antenna; the antenna is used to acquire radio frequency signals and transmit the radio frequency signals to the multi-stage radio frequency rectifier; the multi-stage radio frequency rectifier is used to rectify the radio frequency signals to obtain an initial DC current; the multi-stage low-frequency charge pump is used to extract energy from the initial DC current and output an intermediate DC current with a voltage value reaching a first preset value; the voltage drop converter is used to step down the intermediate DC current and output a drive current with a drive voltage value reaching a second preset value, so as to drive a load through the drive current; the second preset value is less than the first preset value. This technology, through the synergistic effect of the multi-stage radio frequency rectifier, the multi-stage low-frequency charge pump, and the voltage drop converter, can efficiently convert radio frequency signals into stable drive current, significantly improving the ability to drive loads, especially performing well in low-voltage demand scenarios. Attached Figure Description
[0016] To more clearly illustrate the specific embodiments of this utility model or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this utility model. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.
[0017] Figure 1 A schematic diagram of a conventional radio frequency energy harvesting scheme provided in an embodiment of this utility model;
[0018] Figure 2 A schematic diagram of a charging circuit for radio frequency energy harvesting provided for an embodiment of this utility model;
[0019] Figure 3 A schematic diagram of another charging circuit for radio frequency energy harvesting provided in an embodiment of this utility model;
[0020] Figure 4 This is a schematic diagram of a system for radio frequency energy harvesting provided in an embodiment of the present invention.
[0021] Icons: 11-Antenna; 12-Existing system for radio frequency energy harvesting; 13-Battery management system; 14-Load; 21-Multi-stage radio frequency rectifier; 22-Multi-stage low-frequency charge pump; 23-Voltage drop converter; 24-Switch; 25-Voltage monitor; 26-Low dropout linear regulator; 27-First filter capacitor; 28-Second filter capacitor; 29-Matching network; 41-Charging circuit for radio frequency energy harvesting; 42-Radio frequency receiving antenna. Detailed Implementation
[0022] To make the objectives, technical solutions, and advantages of the embodiments of this utility model clearer, the technical solutions of the embodiments of this utility model will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this utility model, and not all embodiments. The components of the embodiments of this utility model described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.
[0023] Existing radio frequency energy harvesting methods have three major drawbacks: low sensitivity, low energy utilization, and low output current. Specifically, although increasing the number of rectifier stages can improve sensitivity, it leads to the output voltage failing to meet the standard. Energy is stored in capacitors, resulting in efficiency loss and making it difficult to drive loads with high power consumption.
[0024] Specifically, Figure 1 This is a schematic diagram of a traditional radio frequency energy harvesting scheme provided for an embodiment of the present utility model.
[0025] Depend on Figure 1 As seen, radio frequency signals are acquired through antenna 11, and then converted into DC power by the existing radio frequency energy harvesting system 12. Next, the DC power is managed by the battery management system 13 to supply power to the load 14.
[0026] The existing RF energy harvesting system 12, which typically uses a multi-stage RF rectifier, cannot achieve the target 3.3V output voltage. This is because there is a trade-off between the input signal amplitude and the number of stages at low input power; increasing the number of stages in the RF rectifier reduces the input signal amplitude, creating a vicious cycle that prevents the achievement of a high output voltage, i.e., a 3.3V output voltage. Furthermore, the existing RF energy harvesting system 12 typically stores energy in a capacitor, which then directly powers the load 14. For example, charging the capacitor to 1.2V to drive the load 14, stopping the load 14 when the voltage drops to 1V, and then continuing to charge the capacitor results in an energy utilization rate of only 30.5%.
[0027] The specific calculation formula is as follows:
[0028]
[0029] Where η is the energy efficiency ratio, C is the capacitance value, and V is the capacitance value. 1.2 V1 indicates that the output voltage is 1.2V, and V2 indicates that the output voltage is 1V.
[0030] Based on this, this utility model provides a charging circuit and system for radio frequency energy harvesting. This technology can efficiently convert radio frequency signals into stable drive current, significantly improving the ability to drive loads, especially performing well in low-voltage demand scenarios. For ease of understanding, a charging circuit for radio frequency energy harvesting is first introduced.
[0031] Example 1
[0032] In this embodiment, Figure 2 This is a schematic diagram of a charging circuit for radio frequency energy harvesting provided in an embodiment of the present invention.
[0033] Depend on Figure 2 As seen, the circuit includes: a multi-stage radio frequency rectifier 21, a multi-stage low-frequency charge pump 22, and a voltage drop converter 23 connected in sequence; the multi-stage radio frequency rectifier 21 is connected to an external antenna 11; the antenna 11 is used to acquire radio frequency signals and transmit the radio frequency signals to the multi-stage radio frequency rectifier 21; the multi-stage radio frequency rectifier 21 is configured to rectify the radio frequency signals to obtain an initial DC current; the multi-stage low-frequency charge pump 22 is used to extract the energy of the initial DC current and output an intermediate DC current with a voltage value reaching a first preset value; the voltage drop converter 23 is used to step down the intermediate DC current and output a drive current with a drive voltage value reaching a second preset value to drive the load through the drive current; the second preset value is less than the first preset value.
[0034] In this embodiment, the initial DC voltage is 500mV, the intermediate DC voltage of the first preset value is 3.3V, and the driving current voltage of the second preset value is 1.2V.
[0035] In practical applications, the multi-stage RF rectifier 21 is a three-stage RF rectifier, and the multi-stage low-frequency charge pump 22 is a six-stage low-frequency charge pump.
[0036] In this embodiment, the radio frequency (RF) signal is converted into initial DC power stage by stage 21 of multi-stage RF rectifiers. Although each stage of rectifier may result in some energy loss, sufficient energy can be accumulated through the multi-stage design. Subsequently, a multi-stage low-frequency charge pump 22 performs voltage multiplication on the initial DC power output from the multi-stage RF rectifiers 21, gradually boosting it to the target value of 3.3V. This structure combines the high sensitivity of the multi-stage RF rectifiers 21 with the efficient voltage boosting capability of the multi-stage low-frequency charge pump 22, thereby enabling the charging circuit for RF energy harvesting to operate normally under low input power conditions (e.g., -28dBm).
[0037] Furthermore, by using a multi-stage low-frequency charge pump 22, an output voltage exceeding 3.3V can be generated, meaning that when the output voltage reaches 3.3V, it can power the aforementioned load 14.
[0038] This utility model provides a charging circuit for radio frequency energy harvesting, comprising: a multi-stage radio frequency rectifier, a multi-stage low-frequency charge pump, and a voltage drop converter connected in sequence; the multi-stage radio frequency rectifier is connected to an external antenna; the antenna is used to acquire radio frequency signals and transmit the radio frequency signals to the multi-stage radio frequency rectifier; the multi-stage radio frequency rectifier is used to rectify the radio frequency signals to obtain an initial DC current; the multi-stage low-frequency charge pump is used to extract energy from the initial DC current and output an intermediate DC current with a voltage value reaching a first preset value; the voltage drop converter is used to step down the intermediate DC current and output a drive current with a drive voltage value reaching a second preset value to drive a load; the second preset value is less than the first preset value. The core of this technology lies in achieving efficient conversion of radio frequency signals through the coordinated work of the multi-stage radio frequency rectifier, the multi-stage low-frequency charge pump, and the voltage drop converter. Specifically, the multi-stage radio frequency rectifier is responsible for gradually rectifying the received radio frequency signal into a DC voltage, while the multi-stage low-frequency charge pump further enhances and stabilizes this voltage level, ensuring the stability of the output current. Meanwhile, the voltage drop converter plays a crucial role in this process, effectively reducing voltage losses caused by energy conversion, thus ensuring a stable and efficient final output drive current. This synergistic mechanism not only improves the overall system's energy efficiency but also significantly enhances its ability to drive loads. Particularly in low-voltage demand scenarios, such as portable electronic devices or IoT sensors, this technology performs exceptionally well, providing sufficient drive capability under lower voltage conditions to meet the needs of various miniaturized, low-power devices. Therefore, this technology offers a new solution for the field of radio frequency energy harvesting and conversion, with broad application prospects.
[0039] Example 2
[0040] In one of the implementations, Figure 3 This is a schematic diagram of another charging circuit for radio frequency energy harvesting provided in an embodiment of the present invention.
[0041] Depend on Figure 3 As seen above, the circuit also includes a switch 24 and a voltage monitor 25 that connect the multi-stage low-frequency charge pump 22 and the voltage drop converter 23. The switch 24, the voltage monitor 25, and the multi-stage low-frequency charge pump 22 are connected in sequence. The voltage monitor 25 is used to monitor whether the intermediate DC current is within a preset voltage range. When the intermediate DC current exceeds the voltage range, the switch 24 is controlled to open to activate protection measures.
[0042] In practical applications, the addition of the aforementioned voltage drop converter 23 enhances the output current capability, enabling power supply to a load 14 with higher power consumption. However, due to the relatively high power consumption of the voltage drop converter 23, a short operating time will cause the monitoring voltage of the voltage monitor 25 to drop rapidly. When the monitoring voltage of the voltage monitor 25 falls below 1.5V, switch 24 is turned off to shut down the voltage drop converter 23, stopping power supply to the load 14. Since switch 24 is turned off, the monitoring voltage potential of the voltage monitor 25 can continue to rise until it reaches 3.3V, at which point it can resume power supply to the load 14 for a new cycle. The energy utilization rate is calculated using the following formula:
[0043]
[0044] Among them, V 3.3 The output voltage value is 3.3V. 1.5 This indicates that the output voltage is 1.5V.
[0045] As can be seen from the comparison, the charging circuit for radio frequency energy harvesting provided by this utility model has a higher energy conversion rate than the existing charging circuits for radio frequency energy harvesting.
[0046] Based on this, by using the voltage drop converter 23, high power loads can be effectively driven, and due to its high-efficiency energy conversion capability, energy loss can be minimized and sufficient power output can be ensured.
[0047] In some examples, the circuit above also includes a low-dropout linear regulator 26 connected to the voltage drop converter 23; the low-dropout linear regulator 26 is used to regulate the driving current and output regulated DC power.
[0048] Here, the primary function of the low-dropout linear regulator 26 is to precisely regulate and stabilize the drive current supplied by the preceding circuitry (e.g., the dropout converter 23), thereby outputting a constant and minimally fluctuating regulated DC voltage. Specifically, the low-dropout linear regulator 26 can adjust the input voltage to a fixed value and maintain its stability, ensuring the output voltage remains within a set range even as the input voltage or load current changes. The low-dropout linear regulator 26 typically has low output noise, making it ideal for powering circuits with high power quality requirements, ensuring these sensitive circuits are not affected by power supply noise. When the load current 14 changes rapidly, the low-dropout linear regulator 26 can react quickly, adjusting the output to adapt to the new load conditions while maintaining a stable output voltage. Compared to conventional linear regulators, the low-dropout linear regulator 26 can operate normally with a smaller input and output voltage difference. This means it can utilize the input voltage more efficiently, reduce energy loss, and improve the overall efficiency of the charging circuitry used for RF energy harvesting.
[0049] Furthermore, the aforementioned low-dropout linear regulator 26 is connected to the load 14. Here, the output voltage of the aforementioned low-dropout linear regulator 26 is 0.9V or 0.3V.
[0050] Among them, the aforementioned load 14 is a Bluetooth device.
[0051] In some of these examples, one end of a first filter capacitor 27 is connected between the multi-stage low-frequency charge pump 22 and the voltage drop converter 23; the other end of the first filter capacitor 27 is grounded; the first filter capacitor 27 is used to filter the intermediate DC current.
[0052] Furthermore, one end of a second filter capacitor 28 is connected between the multi-stage RF rectifier 21 and the multi-stage low-frequency charge pump 22; the other end of the second filter capacitor 28 is grounded; the second filter capacitor 28 is used to filter the initial DC current.
[0053] In other examples, the circuit also includes a matching network 29 connected in parallel with the multi-stage RF rectifier 21; the matching network 29 is used to impedance match the RF signal with the multi-stage RF rectifier.
[0054] The matching network 29 mentioned above is equipped with an automatic tuning circuit.
[0055] This utility model embodiment provides a charging circuit for radio frequency energy harvesting, comprising: a multi-stage radio frequency rectifier, a multi-stage low-frequency charge pump, and a voltage drop converter connected in sequence; the multi-stage radio frequency rectifier is connected to an external antenna; the antenna is used to acquire radio frequency signals and transmit the radio frequency signals to the multi-stage radio frequency rectifier; the multi-stage radio frequency rectifier is used to rectify the radio frequency signals to obtain an initial DC current; the multi-stage low-frequency charge pump is used to extract energy from the initial DC current and output an intermediate state DC current with a voltage value reaching a first preset value; the voltage drop converter is used to convert the intermediate state DC current into an intermediate state DC current. The intermediate-state DC current is stepped down to output a drive current with a drive voltage value reaching a second preset value, which drives the load. The second preset value is less than the first preset value. The circuit also includes a switch connecting the multi-stage low-frequency charge pump and the voltage drop converter, as well as a voltage monitor. The switch, voltage monitor, and multi-stage low-frequency charge pump are sequentially connected. The voltage monitor monitors whether the intermediate-state DC current is within a preset voltage range. If the intermediate-state DC current exceeds the voltage range, the switch is opened to activate protection measures. This charging circuit, through the synergistic effect of the multi-stage RF rectifier, multi-stage low-frequency charge pump, and voltage drop converter, efficiently converts the RF signal into a stable drive current. While ensuring load drive under low-voltage conditions, it utilizes the voltage monitor and switch for overvoltage protection, improving the circuit's stability and reliability.
[0056] Example 3
[0057] Based on the above embodiments, Figure 4 This is a schematic diagram of a system for radio frequency energy harvesting provided in an embodiment of the present invention.
[0058] Depend on Figure 4 As seen, the system includes: the charging circuit 41 for radio frequency energy harvesting described above, and a radio frequency receiving antenna 42 coupled to the charging circuit 41 for radio frequency energy harvesting described above.
[0059] The system for radio frequency energy harvesting provided in this embodiment of the present invention has the same technical features as the charging circuit for radio frequency energy harvesting provided in the above embodiments, and therefore can solve the same technical problems and achieve the same technical effects. Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the specific working process of the above system can be referred to the operating process of the charging circuit in the foregoing embodiments, and will not be repeated here.
[0060] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.
[0061] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.
[0062] In the description of this utility model, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product of this utility model is in use. They are only for the convenience of describing this utility model and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this utility model. In addition, the terms "first," "second," and "third," etc., are only used to distinguish descriptions and should not be construed as indicating or implying relative importance.
[0063] Furthermore, terms such as "horizontal," "vertical," and "sag" do not imply that components must be absolutely horizontal or suspended, but rather that they can be slightly tilted. For example, "horizontal" simply means that its direction is more horizontal relative to "vertical," and does not mean that the structure must be completely horizontal, but can be slightly tilted.
[0064] In the description of this utility model, it should also be noted that, unless otherwise explicitly specified and limited, the terms "set," "install," "connect," and "link" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this utility model based on the specific circumstances.
[0065] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this utility model, and are not intended to limit it. Although the utility model has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this utility model.
Claims
1. A charging circuit for radio frequency energy harvesting, characterized by, The circuit comprises: a plurality of radio frequency rectifiers, a plurality of low-frequency charge pumps and a voltage drop converter connected in sequence; the plurality of radio frequency rectifiers are connected with an antenna of an external device; the antenna is used to acquire a radio frequency signal and transmit the radio frequency signal to the plurality of radio frequency rectifiers; the plurality of radio frequency rectifiers are configured to rectify the radio frequency signal to obtain an initial direct current; the plurality of low-frequency charge pumps are used to extract energy of the initial direct current and output an intermediate state direct current with a voltage value reaching a first preset value; the voltage drop converter is used to perform voltage drop processing on the intermediate state direct current and output a driving current with a driving voltage value reaching a second preset value, so as to drive a load by the driving current; the second preset value is less than the first preset value.
2. The charging circuit for radio frequency energy harvesting according to claim 1, wherein, The circuit further comprises a switch arranged between the plurality of low-frequency charge pumps and the voltage drop converter and a voltage monitor; the switch is connected with the voltage monitor and the plurality of low-frequency charge pumps in sequence; the voltage monitor is used to monitor whether the intermediate state direct current is in a preset voltage range; when the intermediate state direct current exceeds the voltage range, the switch is controlled to be turned off to start a protection measure.
3. The charging circuit for radio frequency energy harvesting according to claim 2, wherein, The circuit further comprises a low-dropout linear voltage regulator connected with the voltage drop converter; the low-dropout linear voltage regulator is used to stabilize the driving current and output a stabilized direct current.
4. The charging circuit for radio frequency energy harvesting according to claim 3, wherein, The low-dropout linear voltage regulator is connected with the load.
5. The charging circuit for radio frequency energy harvesting according to claim 4, wherein, The load is a Bluetooth device.
6. The charging circuit for radio frequency energy harvesting of claim 1, wherein, One end of a first filter capacitor is connected between the plurality of low-frequency charge pumps and the voltage drop converter; the other end of the first filter capacitor is grounded; the first filter capacitor is used to perform filter processing on the intermediate state direct current.
7. The charging circuit for radio frequency energy harvesting according to claim 1, wherein, One end of a second filter capacitor is connected between the plurality of radio frequency rectifiers and the plurality of low-frequency charge pumps; the other end of the second filter capacitor is grounded; the second filter capacitor is used to perform filter processing on the initial direct current.
8. The charging circuit for radio frequency energy harvesting of claim 1, wherein, The circuit further comprises a matching network connected in parallel with the plurality of radio frequency rectifiers; the matching network is used to perform impedance matching between the radio frequency signal and the plurality of radio frequency rectifiers.
9. The charging circuit for radio frequency energy harvesting according to claim 8, wherein, An automatic tuning circuit is arranged in the matching network.
10. A system for radio frequency energy harvesting, characterized by, The charging circuit for radio frequency energy collection in any one of claims 1 to 9, further comprising a radio frequency receiving antenna coupled with the charging circuit.