Wireless sensor WiFi radio frequency energy acquisition and conversion power supply system

Abstract

According to the wireless sensor WiFi radio frequency energy acquisition and conversion power supply system, through a WiFi radiation source, a receiving antenna, a radio frequency matching network, a radio frequency rectification module and a terminal load, a WiFi transmitting end transmits electromagnetic wave energy into a space, at the moment, the receiving antenna of a receiving end receives an electromagnetic wave signal and converts the electromagnetic wave signal into an electric signal, and the electric signal is transmitted to a wireless sensor. A radio frequency alternating current signal is transmitted to the radio frequency rectification circuit through the radio frequency matching network, then the alternating current signal is subjected to AC-DC conversion and boost by the radio frequency rectification module to convert the alternating current signal into a direct current signal, and finally the direct current signal is output to a terminal load, so that energy collection of 1000 meters is realized, and the sensitivity of the radio frequency circuit module reaches 30 dBm; wiFi energy supply does not increase the weight and the size of the sensor, so that the miniaturization of the sensor is facilitated, and the application is more convenient; the problems of frequent battery replacement and instability do not exist; the benefit of the acquisition and conversion system is not limited by the natural environment, and especially has obvious advantages in the scene that the battery is inconvenient to replace.

Description

Technical Field

[0001] The present application relates to a sensor WiFi energy collection and conversion system, and in particular to a wireless sensor WiFi radio frequency energy collection, conversion and power supply system, belonging to the technical field of sensor WiFi conversion and power supply. Background Art

[0002] With the development of information technology and sensor networks, wireless sensor network nodes of various functions and forms are everywhere in daily life. As an energy consumption unit that needs external power supply for continuous energy supply, wireless sensor network nodes currently rely on batteries for energy supply. However, there are many disadvantages of using batteries for power supply. First, the introduction of batteries will increase the weight and volume of the sensor itself, which is not conducive to the miniaturization of the sensor and causes inconvenience in application. Secondly, the battery power is limited, and there will be problems of frequent battery replacement and unstable disadvantages. Thirdly, in some special cases, battery replacement is dangerous and will cause harm to the system, people and even the environment, such as the sky, underground and places that are not easy to reach.

[0003] To solve the power supply problem of wireless sensors, people have turned their attention to solar energy, wind energy, radio frequency energy, pressure energy, vibration energy and even bioenergy collection, so that wireless sensors can be self-powered. However, the benefits of these energy collection and conversion systems are limited by the natural environment.

[0004] RF energy collection and conversion has its unique advantages compared to other energy collection and conversion methods. In the current environment, signal base stations, mobile phones, routers, radio stations, radio stations and some sources of RF signals are spread all over the environment and are becoming more and more dense, which also provides the most direct energy source for realizing RF energy collection.

[0005] Through the RF energy harvesting and conversion system, the RF energy collected from the environment is used for low-power sensor network nodes to achieve self-powering. Among them, the antenna, as the receiver of the RF energy harvesting and conversion system, will directly affect the efficiency of energy harvesting and the output voltage of the system. An antenna with excellent performance can increase the power of RF energy collected from the environment, while improving the efficiency of RF energy conversion, and concentrate the collected energy on power supply, solving the energy consumption problem of low-power and low-power electronic equipment, and eliminating the impact of battery replacement. Therefore, in the RF energy harvesting and conversion system, the design of the antenna is very important.

[0006] For RF rectifier circuits, conversion efficiency is a key indicator. However, at present, under the condition of 2.45GHz frequency, the conversion efficiency of RF rectifier circuits is 15%-50%. In recent years, RF energy harvesting technology has received extensive attention from major companies and R&D teams at home and abroad, and its technology has also been greatly developed and improved. However, in order to realize the miniaturization, convenience, broadband and practicality of RF energy harvesting, there are still many problems that need to be solved.

[0007] In summary, there are still several problems and defects in the wireless sensor power supply of the prior art. The difficulties and problems to be solved in this application are concentrated in the following aspects:

[0008] First, the energy supply of sensor nodes in the existing technology mainly relies on batteries, but the use of batteries for power supply has many disadvantages. First, the introduction of batteries will increase the weight and volume of the sensor itself, which is not conducive to the miniaturization of the sensor and causes inconvenience in application; second, the battery power is limited, there will be problems with frequent battery replacement and unstable disadvantages; third, in some special circumstances, replacing batteries is dangerous and will cause harm to the system, people and even the environment; in order to solve the power supply problem of wireless sensors, the existing technology turns to solar energy, wind energy, pressure energy, vibration energy and even bioenergy collection for power supply, but the benefits of these energy collection and conversion systems are limited by the natural environment, and the stability and reliability are seriously insufficient, and there are many problems in practical applications.

[0009] Second, the existing technology lacks a reasonable and reliable way to supply energy to sensors. WiFi, as the main way of wireless network connection, has many advantages, but the existing technology lacks an efficient method for WiFi RF energy collection, conversion and power supply, and lacks matching WiFi receiving antennas, RF matching networks, RF rectifier modules and terminal loads. When the WiFi transmitter emits electromagnetic wave energy into space, the receiving antenna at the receiving end receives the electromagnetic wave signal, but cannot convert it into an electrical signal. There is a lack of a reliable method for the RF matching network to transmit the RF AC signal to the RF rectifier circuit, the RF rectifier module to perform AC-DC conversion on the AC signal, and the boost to convert the AC signal into a DC signal, and finally output it to the terminal load. Therefore, WiFi cannot be used to power wireless sensors, and long-distance energy collection cannot be achieved, which loses the advantage of using WiFi for power supply.

[0010] Third, the prior art lacks a WiFi radio frequency energy collection and conversion system, lacks a targeted receiving antenna and rectifier circuit design, and cannot increase the output circuit voltage and power conversion efficiency, resulting in the inability to match the power supply requirements of wireless sensors, and the collected radio frequency signals cannot be transmitted to the load point to the maximum extent; the sensor antenna module lacks targeted designs such as antenna collection circular polarization, wireless radio frequency rectification circuit, and energy conversion array. The sensor antenna of the prior art has a high profile, high cost, and heavy weight, which is not conducive to energy collection. It lacks circular polarization design for antennas, lacks energy conversion array methods, and does not use power dividers and quarter-wave converters to match antenna array antenna feed network design, resulting in low power collection and power supply, poor anti-interference ability in complex environments, and cannot be promoted to practical applications. ;

[0011] Fourth, the prior art lacks wireless RF rectification circuit power supply, lacks reliable WiFi RF circuit modules, wireless RF rectification circuits, and RF matching circuit modules. The rectification and boosting circuit based on RF energy collection cannot use the fourth-order rectification and boosting circuit to convert the RF energy collected by the antenna. There is a lack of design simulation and optimization of antenna arrays, matching circuits, and rectification and boosting circuits using high-frequency structure simulation HFSS and ADS. There is a lack of optimization of RF diodes, RF rectification circuits, and wireless RF rectification circuit components. There is a lack of physical correction and optimization of antenna arrays, and the optimal load impedance value cannot be obtained, resulting in very low conversion efficiency of the RF rectification circuit, poor stability and power supply quality, and almost losing its practical application value. Summary of the invention

[0012] This application focuses on the key issues in the design of wireless RF energy harvesting and conversion systems, and achieves the goal of improving the stability of energy harvesting and the output voltage. The circular polarization repetition of the microstrip antenna and the energy conversion array repetition are developed and designed, and they are combined into a circularly polarized microstrip antenna array, thereby improving the energy harvesting capability of the receiving antenna. The antenna array is designed and matched with the antenna feed network using a power divider and a quarter-wave converter; the RF energy harvesting rectification and boosting circuit is developed and designed, and the RF energy harvested by the antenna is effectively converted using a fourth-order rectifier boosting circuit, so that the output power of the system can meet the power supply requirements of low-power wireless sensors; the designed and manufactured microstrip antenna and antenna array are measured in kind using a microwave darkroom, a network analyzer, an RF signal source, and a signal analyzer, and a RF energy harvesting platform is built to obtain the optimal load impedance value. The experimental results show that when the transmitting antenna angle changes using a circularly polarized microstrip antenna array, the output voltage of the RF energy harvesting and conversion system is stable, which fully meets the actual application scenario.

[0013] In order to achieve the above technical effects, the technical solutions adopted in this application are as follows:

[0014] The wireless sensor WiFi radio frequency energy collection, conversion and power supply system includes: a WiFi radiation source, a receiving antenna, a radio frequency matching network, a radio frequency rectification module and a terminal load. The WiFi transmitting end transmits electromagnetic wave energy into space. At this time, the receiving antenna of the receiving end receives the electromagnetic wave signal and converts it into an electrical signal. The radio frequency matching network then transmits the radio frequency AC signal to the radio frequency rectification circuit. Then the radio frequency rectification module performs AC-DC conversion on the AC signal, boosts the AC signal to convert it into a DC signal, and finally outputs it to the terminal load to achieve energy collection at a distance of 1,000 meters. The sensitivity of the radio frequency circuit module is -30dBm.

[0015] M1: WiFi radio frequency energy collection and conversion system, the core part is the receiving antenna and the rectifier circuit. Improving the receiving antenna and the rectifier circuit can increase the output circuit voltage and improve the power conversion efficiency, so that the collected high-frequency microwave signal, that is, the radio frequency signal, can be transmitted to the load point to the maximum extent;

[0016] M2: Sensor antenna module, including: antenna collection circular polarization, wireless RF rectification circuit, energy conversion array. The sensor antenna is the front end of the RF energy collection and conversion system. The design uses a low-profile, easy-to-conform, low-cost, and light-weight microstrip antenna for energy collection. The microstrip antenna is circularly polarized, and the energy conversion array method is adopted. The antenna array is matched with the antenna feed network design using a power divider and a quarter-wave converter to improve the collected power and anti-interference ability in complex environments.

[0017] M3: Wireless RF rectifier circuit power supply, including: WiFi RF circuit module, wireless RF rectifier circuit, RF matching circuit module, rectifier boost circuit based on RF energy harvesting, using fourth-order rectifier boost circuit to convert the RF energy collected by the antenna, using high-frequency structure simulation HFSS and ADS to design, simulate and optimize the antenna array, matching circuit and rectifier boost circuit, through the design of RF diodes, RF rectifier circuit design, wireless RF rectifier circuit component optimization, the design adopts 2X2 circularly polarized microstrip antenna array, using network analyzer, RF signal source, signal analyzer and microwave darkroom, the antenna array is physically corrected and optimized to obtain the best load impedance value.

[0018] Furthermore, RF impedance matching: the impedance of the receiving antenna and the RF rectifier module are connected to the RF impedance matching network, and the actual input impedance of the RF rectifier module is measured. The working state of the unit RF rectifier circuit is divided into two different states: on and off within one cycle. When the circuit is in the on state, the junction resistance of the rectifier diode is ignored. At this time, the series resistance of the rectifier tube generates the RF signal current in the circuit. When the circuit is in the off state, the current generated by the charging and discharging of the junction capacitance is the current of the rectifier diode. At this time, the input impedance of the RF rectifier module is closely related to the power of the input signal. The impedance of the RF rectifier module changes periodically, and the impedance is a function of the signal amplitude. The impedance of the RF rectifier module matches the antenna impedance to maximize the transmission power. At this time, the impedance of the RF rectifier module should be the periodic time average value, that is, the average value of the input signal change in one cycle. The input impedance of the RF rectifier module changes with different input powers.

[0019] Furthermore, the antenna collects circular polarization: using a microstrip patch antenna, the array antenna polarization is the polarization of the electromagnetic wave it receives or radiates. The polarization of the electromagnetic wave is the direction of the trajectory of the endpoint of the electric field component of the electromagnetic wave in the direction of maximum reception or radiation, that is, the characteristics of the endpoint of the electric field vector in the radiation field at a given point in space changing with time. The trajectory formed by the endpoint in time describes the polarization characteristics of the electromagnetic wave;

[0020] Suppose there is a uniform plane wave propagating along the z-axis, and its electric field vector expression is E = e x E m cos(ωt-kz+φ), ω is the angular velocity, k is the coefficient, φ is the phase, E m is the amplitude, e represents the charge, and at any time, the direction of the electric field vector E of the electromagnetic wave always remains in the x direction. The electric field components of the electromagnetic wave in the x-axis direction and the y-axis direction are respectively represented by E x and E y :

[0021] E x =E xm cos(ωt-kz+φ x ) Formula 1

[0022] E y =E ym cos(ωt-kz+φ y ) Formula 2

[0023] The electric field of the composite wave is E = e x E x +e y E y , at any time, E x Quantity and E yThere are differences in the components. The electric field intensity vector of the synthetic wave at a certain point in three-dimensional space changes position with time, forming the polarization of the electromagnetic wave. At the point z = 0, Equation 1 and Equation 2 are rewritten as:

[0024] E x =E xm cos(ωt+φ x ) Formula 3

[0025] E y =E ym cos(ωt+φ y ) Formula 4

[0026] When the x-component and y-component of the electric field have the same amplitude but differ in phase by π / 2, that is, E xm =E ym =E m ,φ y -φ x = ±π / 2, the synthetic wave achieves circular polarization;

[0027] When φ y -φ x =π / 2, then φ y =φ x +π / 2, from equation 3 and equation 4 we get:

[0028] E x =E m cos(ωt+φ x ) Formula 5

[0029]

[0030] Therefore, the electric field strength of the synthetic wave is

[0031] The angle between the electric field of the synthetic wave and the x-axis is:

[0032]

[0033] The field strength of the composite wave is a constant value and does not change with time, but it keeps changing in direction. Its endpoints are on a circle and rotate at an angular velocity ω, making it a circularly polarized wave.

[0034] When φ y -φ x =-π / 2, the magnitude of the composite wave electric field does not change with time, but its direction changes with time. The angle between the composite wave electric field and the x-axis is:

[0035]

[0036] Any two linearly polarized waves with the same frequency, the same direction of travel, a polarization angle of 90 degrees, the same amplitude and a phase difference of π / 2 are circularly polarized waves.

[0037] If the amplitude of linearly polarized waves with polarization directions perpendicular to each other is equal and the phase difference between them is ±π / 2, the synthetic wave is a circularly polarized wave. At the same time, when the radio frequency energy collection array antenna is used in the present application, a circularly polarized array antenna design is adopted in collecting 2.45GHz electromagnetic wave energy, so as to enhance the antenna's ability to receive electromagnetic waves with different polarization directions and improve the voltage and power at the output end.

[0038] Furthermore, the unit size of the corner-cut circularly polarized antenna is determined: the dielectric constant of the dielectric plate of the antenna designed in this application is 2.33, the loss factor is 0.0012, and the thickness is 1.6 mm considering the influence of the thickness of the dielectric plate on the bandwidth of the microstrip antenna;

[0039] When the operating frequency is 2.45 GHz, the thickness of the dielectric plate is 1.6 mm, and the dielectric constant of the dielectric plate is 2.33, the radiation patch length of this antenna unit is b = 39.3 mm, the cut corner side length of the antenna is d = 5.03 mm, and the distance between the feeding point of a single cut corner antenna and the edge of the patch is 12 mm.

[0040] The edge impedance of the antenna is matched to 50 ohms that matches the SMA connector. Based on the above antenna parameters, modeling and settings are performed in the high-frequency simulation software HFSS. After simulating the antenna model in HFSS, the side length and the size of the cut angle of the radiation patch are optimized. Finally, it is determined that when the length of the radiation patch is 39 mm and the length of the cut angle is 5.58 mm, the antenna unit exhibits good antenna performance at 2.45 GHz.

[0041] Furthermore, energy conversion is arrayed: by cutting the square radiating patch in the microstrip antenna, perturbations are introduced to achieve individual circular polarization of the antenna array unit, and then these individual circularly polarized array elements form an antenna array;

[0042] Antenna array design is divided into the following four steps:

[0043] Step 1: Refer to the global structure, gain, power frequency and polarization information of the antenna, select an array arrangement that meets the requirements and is easy to implement, determine the spacing between each antenna subunit, and the phase relationship between each unit;

[0044] Step 2: Design of unit antennas in the array. After determining the distribution form of the antenna array, determine the shape and size parameters of the unit antenna according to the specific requirements of impedance matching frequency, bandwidth and polarization of each unit in the antenna array.

[0045] Step 3: Global analysis of the array. After determining the parameters of the units in the array and the arrangement of the array, analyze the global antenna array to obtain the array performance. If the antenna array can meet the requirements under this condition, proceed to the next step for the final design; otherwise, it is necessary to return to the previous step to optimize the antenna units and arrangement.

[0046] Step 4: Feed network design.

[0047] Furthermore, the antenna array design is specifically designed as follows: the material is FR4 plate with a dielectric constant of 4.4, the feeding method is side feeding, and the initial values ​​of the size of each radiating patch are calculated as follows: the side length is 39.3mm, and the frequency of the resonance point of the array antenna is 2.61GHz. Using the parameter scan provided by HFSS, the length of the patch is optimized to be 29.1mm, the resonance point is 2.45GHz, the side length is 39mm, and the cut-off side length is 5.3mm;

[0048] Each unit is connected through microstrip line sections and quarter-wave converters. The impedance in each part of the microstrip line is different, and the corresponding width is different, which is 3.06mm for 50ohm, 1.61mm for 70.7ohm, and 0.70mm for 100ohm. As a quarter-wave converter, the corresponding line length is 17.1mm when the impedance is 70.7ohm.

[0049] The present application designs a circularly polarized microstrip patch antenna array, the operating frequency of the array antenna is 2.45 GHz, and each unit is connected in parallel through a microstrip line.

[0050] Furthermore, the WiFi radio frequency circuit module: the rectifier boost circuit works through a diode and a capacitor. When designing the rectifier boost circuit, different operating frequencies and the impedance matching of the circuit are considered. When the positive half-cycle of the radio frequency signal collected by the antenna is injected from the Pl port, the voltage of the diode d2 gradually increases. When the voltage is greater than its turn-on voltage, the diode d2 is turned on, the capacitor C2 starts to charge, and the charge is stored on the capacitor C2; when the negative half-cycle of the radio frequency signal collected by the antenna is injected from the P1 port, the diode d1 is turned on, the capacitor C1 starts to charge, and the charge is stored on the capacitor C2; the diode converts the full-wave signal into a half-wave signal, and the charging and discharging circuit composed of the large capacitor converts the radio frequency signal into a low-frequency signal.

[0051] Furthermore, the design of the RF diode: a zero-bias improved SBD diode is selected, with a minimum critical voltage of 150mV and a minimum junction capacitance of 0.18pF. The high-order harmonics generated in the RF rectification circuit are filtered by an RF filter at the RF input end and a DC filter at the DC output end to generate a more stable DC voltage signal;

[0052] The improved SBD diode has a forward voltage drop of only 150mV, a small package size, and a small parasitic resistance, where R is the parasitic resistance of the diode, C is the junction capacitance of the diode, and R j is the diode junction resistance, the diode parasitic resistance R s Smaller, the output voltage is proportional to R s Unrelated, the diode is equivalent to a single-pole single-throw switch. Under the condition of forward bias, the depletion layer of the improved SBD junction is a high resistance area. All applied voltage drops in the depletion layer weaken the electric field direction of the electric field strength, keep the electric field relative to the SBD junction barrier to reduce the number of charges; reduce the total charge depletion layer thinner, improve the SBD barrier height to reduce the voltage, at this time the drift current is less than the diffusion current, the forward bias makes a large number of electrons flow through the improved SBD junction, and generate a very large forward current in the external circuit; under the condition of applied voltage, the diode junction resistance drops rapidly until it is within a few ohms; at the same time, the electric field in the same direction, the total electric field increases, the amount of free charge increases, the depletion layer thickens, the barrier height increases, it is difficult for electrons to diffuse through the semiconductor to the metal, and the diffusion current is less than the drift current; calculate the parasitic resistance, first measure the current and voltage at each point, and draw the volt-ampere characteristic curve, then go to the position with higher current, calculate the slope point, and then convert the slope into resistance, the relationship is as follows:

[0053]

[0054] The electrical characteristics of the SBD barrier diode at room temperature are set as:

[0055]

[0056] The HSMS2852 from the HSMS-285x series diodes that meet the 2.45GHz requirements is used, and a rectifier and boost circuit is formed by the HSMS2852 and a capacitor.

[0057] Further, the RF rectifier circuit design: a single HSMS2852 is used to build the RF rectifier circuit, where the terminal load is 15KQ, the rectifier capacitor is 100pF, the bypass capacitor is 1nF, the input signal is 2.45GHz, and harmonic balance is used;

[0058] The output voltage is further increased by adopting a multi-stage parallel connection method, with an input energy frequency of 2.45GHz, an amplitude of 1V, and an input power of 3mW;

[0059] Four rectifier boost circuit units are connected in parallel to increase the voltage value at the output end.

[0060] Furthermore, the components of the wireless RF rectifier circuit are optimized: the optimization objects are the rectifier capacitor C0 and the bypass capacitor C1, the optimization target is the output efficiency, the optimization range of C0 is 1 to 1000pF, and the optimization range of C1 is 1 to 1000nF;

[0061] The final optimized results are: C0 is 372pF and C1 is 176nH.

[0062] Compared with the prior art, the innovations and advantages of this application are:

[0063] First, this application focuses on the key issues of the design of wireless RF energy harvesting and conversion system, and achieves the goal of improving the stability of energy harvesting and the output voltage. First, through the design of 2.45GHz WiFi signal acquisition, the circular polarization repetition of the microstrip antenna and the energy conversion array repetition are developed and designed, and they are combined into a circular polarization microstrip antenna array, thereby improving the energy harvesting ability of the receiving antenna, and the antenna array is designed and matched with the antenna feed network using a power divider and a quarter-wave converter; second, the RF energy harvesting rectification and boosting circuit is developed and designed, and the RF energy collected by the antenna is effectively converted using a fourth-order rectification and boosting circuit, so that the output power of the system can meet the power supply requirements of low-power wireless sensors; third, the designed and manufactured microstrip antenna and antenna array are measured in kind using a microwave darkroom, a network analyzer, an RF signal source, and a signal analyzer, and a RF energy harvesting platform is built, and the output load impedance is compared and tested, and the optimal load impedance value is obtained. The experimental results show that when the transmitting antenna angle changes using a circularly polarized microstrip antenna array, the output voltage of the RF energy harvesting and conversion system is stable, which fully meets the actual application scenario.

[0064] Second, this application proposes a wireless sensor WiFi RF energy collection, conversion and power supply system. Through a WiFi radiation source, a receiving antenna, an RF matching network, an RF rectifier module and a terminal load, the WiFi transmitter emits electromagnetic wave energy into space. At this time, the receiving antenna of the receiving end receives the electromagnetic wave signal and converts it into an electrical signal. The RF matching network then transmits the RF AC signal to the RF rectifier circuit. The RF rectifier module then performs AC-DC conversion on the AC signal, boosts the AC signal to convert it into a DC signal, and finally outputs it to the terminal load, achieving energy collection 1,000 meters away, and the sensitivity of the RF circuit module reaches 30dBm; WiFi power supply does not increase the weight and volume of the sensor itself, which is conducive to the miniaturization of the sensor and is more convenient to use; there is no problem of frequent battery replacement and instability; the benefits of the collection and conversion system are not limited by the natural environment, especially in scenarios where battery replacement is inconvenient.

[0065] Third, WiFi is currently spread throughout the environment and is becoming more and more dense. WiFi provides the most direct energy source for realizing the collection of RF energy. This application makes full use of this and proposes a WiFi RF energy collection and conversion system, the core part of which is the receiving antenna and the rectifier circuit. The receiving antenna and the rectifier circuit are improved to increase the output circuit voltage and improve the power conversion efficiency. The conversion efficiency is high and the output power is large, so that the collected high-frequency microwave signal, that is, the RF signal, is transmitted to the load point to the maximum extent; a sensor antenna module is proposed, which uses circular polarization of antenna collection, wireless RF rectification circuit, and energy conversion array to design and adopt a microstrip antenna with a low profile, easy conformal, low cost, and light weight for energy collection, circularly polarized microstrip antenna, and energy conversion array method. The antenna array is designed with a power divider and a quarter-wave converter to match the antenna feeding network design, thereby improving the collected power and the anti-interference ability in complex environments, and fully meeting the actual application requirements of wireless sensors for power supply voltage and stability.

[0066] Fourth, this application proposes a wireless RF rectifier circuit power supply, through the WiFi RF circuit module, wireless RF rectifier circuit, RF matching circuit module, based on the RF energy collection rectifier boost circuit, using the fourth-order rectifier boost circuit to convert the RF energy collected by the antenna, using high-frequency structure simulation HFSS and ADS to design and simulate the antenna array and matching circuit and rectifier boost circuit, through the design of RF diodes, RF rectifier circuit design, wireless RF rectifier circuit component optimization, the design uses a 2X2 circularly polarized microstrip antenna array, using a network analyzer, RF signal source, signal analyzer and microwave darkroom, the antenna array is physically corrected and optimized to obtain the best load impedance value. The results show that the circularly polarized antenna array improves the output power of RF energy collection and the collection capability under different polarization signal sources, realizes the effective collection of WiFi signal energy, can provide high-quality and stable power for wireless sensors, and greatly improves the power conversion efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0067] Figure 1 This is the framework diagram of the WiFi radio frequency energy harvesting and conversion system.

[0068] Figure 2 It is a schematic diagram of the structural model of a single circularly polarized corner-cut antenna.

[0069] Figure 3 This is the parameter diagram of the S11 corner-cut circularly polarized antenna at 2.45GHz.

[0070] Figure 4 It is the EH plane radiation pattern of the 2.45GHz cut-angle circularly polarized antenna.

[0071] Figure 5This is a 3D directional diagram of a 2.45GHz corner-cut circularly polarized antenna.

[0072] Figure 6 It is a specific design flow chart of antenna array design.

[0073] Figure 7 This is the structural diagram of the 2.45GHz circularly polarized antenna array.

[0074] Figure 8 This is the structure diagram of the WiFi radio frequency energy harvesting and conversion system.

[0075] Fig. 9 It is the schematic diagram of a single rectifier boost circuit unit.

[0076] Fig.10 It is the circuit diagram of a single rectifier boost unit.

[0077] Fig.11 It is a comparison chart of different rectifier circuit units in the test experiment.

[0078] Fig.12 It is a specific circuit diagram of four-unit parallel rectification and boosting.

[0079] Fig.13 This is the circuit structure and its setting diagram optimized by ADS.

[0080] Fig.14 It is a measured model diagram of a low-power RF energy harvesting and conversion system. DETAILED DESCRIPTION

[0081] The following is a further description of the technical solution of the wireless sensor WiFi radio frequency energy collection, conversion and power supply system provided by the present application in conjunction with the accompanying drawings, so that those skilled in the art can better understand the present application and implement it.

[0082] The deployment of wireless sensors is becoming more and more popular, but there is an urgent problem to be solved, that is, how to efficiently and conveniently power these scattered wireless sensors. In order to solve this problem, the current focus is on energy harvesting technologies including solar energy, wind energy, thermal energy, vibration energy and radio frequency energy. The collection of radio frequency energy is not limited by time and natural conditions. Based on this, this application has achieved some breakthroughs in the conversion and power supply of wireless sensor WiFi radio frequency energy collection, including the following aspects.

[0083] First, the RF energy harvesting and conversion system consists of four parts: receiving antenna, matching network, rectifier circuit and output. The core parts are the receiving antenna and rectifier circuit. Improving the receiving antenna and rectifier circuit can increase the output circuit voltage and improve the power conversion efficiency.

[0084] Secondly, the sensor antenna module includes: antenna collection circular polarization, wireless RF rectification circuit, and energy conversion array. The sensor antenna is the front end of the RF energy collection and conversion system. It uses a low-profile, easy-to-conform, low-cost, and light-weight microstrip antenna for energy collection. The microstrip antenna is arrayed and circularly polarized to improve the collected power and anti-interference ability in complex environments.

[0085] Secondly, wireless RF rectification circuit power supply, including: WiFi RF circuit module, wireless RF rectification circuit, RF matching circuit module, use high-frequency structure simulation HFSS and advanced design system ADS to design and simulate the antenna array, matching circuit and rectification boost circuit, through the design of RF diodes, RF rectification circuit design, wireless RF rectification circuit component optimization, design 2X2 circularly polarized microstrip antenna array, use network analyzer, RF signal source, signal analyzer and microwave darkroom to modify and optimize the antenna array;

[0086] Finally, a wireless RF energy harvesting platform was built, and simulation tests and comparative experiments were conducted on WiFi signals operating near 2.45GHz. The results show that the circularly polarized antenna array improves the output power of RF energy harvesting and the harvesting capability under different polarization signal sources, realizes the effective harvesting of WiFi signal energy, and can provide high-quality and stable power for wireless sensors.

[0087] 1. WiFi RF Energy Harvesting and Conversion System

[0088] The RF energy collection and conversion system includes a WiFi radiation source, a receiving antenna, a RF matching network, a RF rectifier module and a terminal load. The overall structural block diagram is as follows: Figure 1 As shown, the RF energy collection and conversion system consists of an antenna, an RF matching network, an RF rectifier module, and a terminal load. The overall process is as follows. The WiFi transmitter emits electromagnetic wave energy into space. At this time, the receiving antenna at the receiving end receives the electromagnetic wave signal and converts it into an electrical signal. The RF matching network then transmits the RF AC signal to the RF rectifier circuit. The RF rectifier module then performs an AC-DC conversion on the AC signal, outputs it as a stable DC voltage through a DC boost circuit, and finally outputs it to the terminal load to achieve energy collection at a distance of 1,000 meters. The sensitivity of the RF circuit module needs to reach -30dBm.

[0089] (I) RF impedance matching

[0090] In the RF energy collection and conversion system, the collected high-frequency microwave signal, namely the RF signal, is transmitted to the load point to the maximum extent possible, reducing signal reflections along the way and improving energy utilization efficiency.

[0091] The impedance of the receiving antenna of the present application is greatly different from the input impedance of the RF rectifier module, and an RF impedance matching network must be connected to maximize the conversion efficiency. The actual input impedance of the RF rectifier module is measured. The working state of the unit RF rectifier circuit is divided into two different states: on and off within one cycle. When the circuit is in the on state, the junction resistance of the rectifier diode is very small and can be ignored. At this time, the series resistance of the rectifier tube generates the RF signal current in the circuit. When the circuit is in the off state, the current generated by the charging and discharging of the junction capacitance is the current of the rectifier diode. At this time, the input impedance of the RF rectifier module is closely related to the power of the input signal. The impedance of the RF rectifier module changes periodically, and the impedance is a function of the signal amplitude. The impedance of the RF rectifier module matches the antenna impedance to maximize the transmission power. At this time, the impedance of the RF rectifier module should be the periodic time average, that is, the average value of the input signal change in one cycle. The input impedance of the RF rectifier module changes with different input powers.

[0092] (II) RF energy harvesting and conversion system architecture

[0093] This application is to match the receiving antenna to the rectifier circuit, use harmonic balance to match the output efficiency, and repeatedly optimize the matching circuit to obtain the optimal solution at 2.45GHz, ultimately further improving the conversion efficiency of the RF energy harvesting and conversion system.

[0094] The radio frequency energy collected in this application is relatively small. In order to achieve an output voltage of more than 3V, a multi-stage voltage doubling circuit is used to increase the output voltage.

[0095] In summary, the antenna module and the RF module are components of the energy collection and conversion system. The receiving antenna in the antenna module collects the electromagnetic wave energy in the free space, and then inputs it into the RF rectifier module through the RF matching circuit. The RF filter, rectifier circuit and low-frequency filter of the RF rectifier module output it as a DC voltage, and then it is output as a stable DC voltage through the DC boost circuit.

[0096] 2. Sensor Antenna Module

[0097] (I) Antenna collection circular polarization

[0098] Using microstrip patch antennas, the polarization of the array antenna is the polarization of the electromagnetic waves it receives or radiates. The polarization of the electromagnetic wave is the direction of the trajectory of the endpoints of the electric field component of the electromagnetic wave in the direction of maximum reception or radiation, that is, the characteristics of the endpoints of the electric field vector in the radiation field at a given point in space changing with time. The trajectory formed by the endpoints in time describes the polarization characteristics of the electromagnetic wave.

[0099] Suppose there is a uniform plane wave propagating along the z-axis, and its electric field vector expression is E = e x Em com(ωt-kz+φ), ω is the angular velocity, k is the coefficient, φ is the phase, E m is the amplitude, e represents the charge, and at any time, the direction of the electric field vector E of the electromagnetic wave always remains in the x direction. The electric field components of the electromagnetic wave in the x-axis direction and the y-axis direction are respectively represented by E x and E y :

[0100] E x =E xm cos(ωt-kz+φ x ) Formula 1

[0101] E y =E ym cos(ωt-kz+φ y ) Formula 2

[0102] The electric field of the composite wave is E = e x E x +e y E y , at any time, E x Quantity and E y There are differences in the components. The electric field intensity vector (regardless of magnitude or direction) of the composite wave at a certain point in three-dimensional space changes position with time, forming the polarization of the electromagnetic wave. At the point z = 0, Equation 1 and Equation 2 are rewritten as:

[0103] E x =E xm cos(ωt+φ x ) Formula 3

[0104] E y =E ym cos(ωt+φ y ) Formula 4

[0105] When the x-component and y-component of the electric field have the same amplitude but differ in phase by π / 2, that is, E xm =E ym =E m ,φ y -φ x =±π / 2, the synthetic wave achieves circular polarization.

[0106] When φ y -φ x =π / 2, then φ y =φx + π / 2, from equation 3 and equation 4 we get:

[0107] E x =E m cos(ωt+φ x) Formula 5

[0108]

[0109] Therefore, the electric field strength of the synthetic wave is

[0110] The angle between the electric field of the synthetic wave and the x-axis is:

[0111]

[0112] The field strength of the composite wave is a constant and does not change with time, but it keeps changing in direction. Its endpoints are on a circle and rotate at an angular velocity ω, making it a circularly polarized wave.

[0113] When φ y -φ x =-π / 2, the magnitude of the composite wave electric field does not change with time, but its direction changes with time. The angle between the composite wave electric field and the x-axis is:

[0114]

[0115] Any two linearly polarized waves with the same frequency, the same direction of travel, a polarization angle of 90 degrees, the same amplitude but different phases (difference of π / 2) are circularly polarized waves.

[0116] If the amplitude of linearly polarized waves with polarization directions perpendicular to each other is the same and the phase difference between them is ±π / 2, the synthetic wave is a circularly polarized wave. At the same time, when the radio frequency energy collection array antenna is used in the present application, a circularly polarized array antenna design is adopted in collecting 2.45GHz electromagnetic wave energy to enhance the antenna's ability to receive electromagnetic waves with different polarization directions, so as to increase the voltage and power at the output end.

[0117] The principle of circular polarization achieved by cutting the corners of a square patch is shown in the figure. The unit size of the cut-corner circularly polarized antenna is determined: the dielectric constant of the dielectric plate of the antenna designed in this application is 2.33, and the loss factor is 0.0012. Considering the impact of the thickness of the dielectric plate on the bandwidth of the microstrip antenna, the thickness is 1.6mm.

[0118] When the operating frequency is 2.45 GHz, the thickness of the dielectric plate is 1.6 mm, and the dielectric constant of the dielectric plate is 2.33, the radiation patch length of this antenna unit is b = 39.3 mm, the cut corner side length of the antenna is d = 5.03 mm, and the distance between the feeding point of a single cut corner antenna and the edge of the patch is 12 mm.

[0119] The edge impedance of the antenna is matched to 50 ohms which matches the SMA connector. Based on the above antenna parameters, the model is modeled and set in the high-frequency simulation software HFSS. The structure diagram is as follows: Figure 2After simulating the antenna model in HFSS, the side length and the size of the cut angle of the radiation patch were optimized. Finally, it was determined that when the length of the radiation patch was 39mm and the side length of the cut angle was 5.58mm, the antenna unit showed good antenna performance at 2.45GHz. The simulation results are shown in Figure 3 shown.

[0120] Where △S is the sum of the areas of the two cut corners, S is the total area of ​​the entire patch, d is the length of the side of the triangle cut corner, and a is the length of the side of the square patch.

[0121] from Figure 3 It is concluded that the return loss of the antenna at 2.45 GHz is -17.8 dB, and the bandwidth of -10 dB is 80 MHz, which meets the requirement that the return loss of the antenna at 2.45 GHz is less than -10 dB.

[0122] At the frequency of interest, 2.45 GHz, the normalized impedance of the antenna is 1.004+0.2604i, indicating that the antenna is well matched with the 50 ohm feed line.

[0123] At 2.45GHz, the standing wave ratio is 1.30, indicating that the electromagnetic waves are effectively transmitted after being received by the antenna, and the electromagnetic wave energy can smoothly reach the output end and be absorbed by the subsequent circuit.

[0124] Depend on Figure 4 and Figure 5 It is found that the antenna has a gain of 4.057dB when its maximum radiation direction is 0 degrees.

[0125] The total gain of the antenna is approximately equal to the gain of the right-hand circular polarization wave, indicating that the polarization mode of the antenna unit is right-hand circular polarization.

[0126] (II) Energy conversion array

[0127] The present application introduces perturbations by cutting corners of square radiation patches in microstrip antennas, thereby achieving individual circular polarization of antenna array units, and then the antenna array is composed of these individual array elements with circular polarization characteristics.

[0128] Antenna array design is divided into the following four steps:

[0129] Step 1: According to the actual application needs, refer to the global structure, gain, power frequency and polarization information of the antenna, select an array arrangement that meets the requirements and is easy to implement, determine the spacing between each antenna subunit, and the phase relationship between each unit;

[0130] Step 2: Design of unit antennas in the array. After determining the distribution form of the antenna array, determine the shape and size parameters of the unit antenna according to the specific requirements of impedance matching frequency, bandwidth and polarization of each unit in the antenna array.

[0131] Step 3: Global analysis of the array. After determining the parameters of the units in the array and the arrangement of the array, analyze the global antenna array to obtain the array performance. If the antenna array can meet the requirements under this condition, proceed to the next step for the final design; otherwise, it is necessary to return to the previous step to optimize the antenna units and arrangement.

[0132] Step 4: Feed network design.

[0133] According to the above four steps, the specific design flow chart of antenna array design is as follows: Figure 6 shown.

[0134] The material used is FR4 plate with a dielectric constant of 4.4, and the side feeding method is selected. The initial values ​​of the size of each radiating patch are calculated as follows: the side length is 39.3mm. At this time, the frequency of the resonance point of the array antenna is 2.61GHz. Using the parameter scan provided by HFSS, the length of the patch is optimized to be 29.1mm, the resonance point is 2.45GHz, the side length is 39mm, and the cut-angle side length is 5.3mm.

[0135] Each unit is connected through microstrip line sections and quarter-wave converters. The impedance in each part of the microstrip line is different, and the corresponding width is different, which is 3.06mm for 50ohm, 1.61mm for 70.7ohm, and 0.70mm for 100ohm. As a quarter-wave converter, the corresponding line length is 17.1mm when the impedance is 70.7ohm.

[0136] This application designs a circularly polarized microstrip patch antenna array. The operating frequency of the array antenna is 2.45GHz. Each unit is connected in parallel through a microstrip line. Its simulation structure and physical diagram are as follows Figure 7 shown.

[0137] (III) Actual measurement verification of receiving antenna

[0138] According to the design and simulation optimization results, the array antenna and the single circular polarization antenna unit are drawn in the drawing software DXP, and the PCB is made. The circular polarization angle-cut antenna array is tested using the laboratory network analyzer and microwave darkroom.

[0139] The measurement platform in the microwave darkroom consists of a horn antenna and a test turntable. The horn antenna is used as a transmitting or receiving end and has a 1-port. The antenna under test connected to the test turntable has a 2-port. The distance between the horn antenna and the antenna under test is 2.2 meters. The darkroom is surrounded by absorbing materials, creating a pure electromagnetic environment without electromagnetic interference. The network analyzer and the antenna test platform controller are connected to the two ports outside the darkroom and inside the darkroom, which are responsible for controlling the test platform and recording test data.

[0140] It can be concluded from the test data that at 2.45 GHz, the return loss of the circularly polarized antenna array is -12.76 dB, which is below -10 dB. The actual performance of the antenna array meets the requirements for antenna operation.

[0141] The measured data show that the antenna array meets the return loss requirement of less than -10dB, which proves the rationality of the design. It can be seen that the performance of the antenna array meets the basic requirements of energy harvesting.

[0142] 3. Wireless RF Rectification Circuit Power Supply

[0143] (1) WiFi RF circuit module

[0144] After the antenna array collects electromagnetic waves, the signal energy needs to be processed by subsequent matching and rectification and boost circuits so that the power and voltage collected by the system are large enough to power the load. Figure 8 shown.

[0145] The rectifier boost circuit works through diodes and capacitors. When designing the rectifier boost circuit, different operating frequencies and circuit impedance matching issues should be considered. The basic structural principle diagram is as follows Fig. 9 shown.

[0146] When the positive half cycle of the RF signal collected by the antenna is injected from the Pl port, the voltage of the diode d2 gradually increases. When the voltage is greater than its turn-on voltage, the diode d2 is turned on, the capacitor C2 starts to charge, and the charge is stored on the capacitor C2; when the negative half cycle of the RF signal collected by the antenna is injected from the P1 port, the diode d1 is turned on, the capacitor C1 starts to charge, and the charge is stored on the capacitor C2; the diode converts the full-wave signal into a half-wave signal, and the charging and discharging circuit composed of the large capacitor converts the RF signal into a low-frequency signal.

[0147] (II) Wireless RF Rectification Circuit

[0148] 1. Design of RF diode

[0149] In the RF rectification circuit, the performance of the RF rectification diode is a key factor affecting the rectification efficiency. The diode selected in this application must work under the large signal state. Since the attenuation of electromagnetic waves is very severe in the general environment and the energy received by the antenna is relatively weak, it is even more important to ensure that the diode works under the large signal state. At the same time, the nonlinear characteristics of the RF diode should be analyzed and simulated, and the influence of different diodes and different circuit parameter values ​​on the rectification efficiency should be analyzed.

[0150] In the RF to DC diode conversion circuit, the indicator for selecting the diode is the critical voltage. When the input signal power is large, the critical value of the diode is small and will not cause a big change to the input signal. However, when the input signal power is small, the performance of the RF rectifier circuit is more closely related to the critical voltage.

[0151] This application chooses to use a zero-bias improved SBD diode with a minimum critical voltage of 150mV and a minimum junction capacitance of 0.18pF. The high-order harmonics generated in the RF rectifier circuit are filtered by an RF filter at the RF input end and a DC filter at the DC output end to generate a more stable DC voltage signal. The center frequency of the receiving antenna is 2.45GHz, and the operating bandwidth of the RF diode is 0 to 6GHz, which meets the operating frequency requirements of the receiving antenna.

[0152] The forward voltage drop of the improved SBD diode is only 150mV, the package size is very small, and the parasitic resistance is small. The improved SBD diode effective circuit, where R is the parasitic resistance of the diode, C is the junction capacitance of the diode, and R j is the diode junction resistance, the diode parasitic resistance R s Smaller, the output voltage is proportional to R s Unrelated, the diode is equivalent to a single-pole single-throw switch. Under the condition of forward bias, the depletion layer of the improved SBD junction is a high resistance area. All applied voltage drops in the depletion layer weaken the electric field direction of the electric field strength, keep the electric field relative to the SBD junction barrier to reduce the number of charges; reduce the total charge depletion layer thinner, improve the SBD barrier height to reduce the voltage, at this time the drift current is less than the diffusion current, the forward bias makes a large number of electrons flow through the improved SBD junction, and generate a very large forward current in the external circuit; under the condition of applied voltage, the diode junction resistance drops rapidly until it is within a few ohms; at the same time, the electric field in the same direction, the total electric field increases, the amount of free charge increases, the depletion layer thickens, the barrier height increases, it is difficult for electrons to diffuse through the semiconductor to the metal, and the diffusion current is less than the drift current; calculate the parasitic resistance, first measure the current and voltage at each point, and draw the volt-ampere characteristic curve, then go to the position with higher current, calculate the slope point, and then convert the slope into resistance, the relationship is as follows:

[0153]

[0154] The electrical characteristics of the SBD barrier diode at room temperature are set as:

[0155]

[0156] In order to achieve lower response voltage and fast response, this application adopts HSMS2852 in the HSMS-285x series diodes that meet the requirements of 2.45GHz. This diode has the characteristics of low cost and high capacity. The rectifier boost circuit is composed of HSMS2852 and capacitors.

[0157] 2. RF rectifier circuit design

[0158] In the RF energy harvesting system, the efficiency of the RF rectifier circuit determines the energy collection efficiency of the entire system. For the RF energy harvesting system of this application, it is critical to select a suitable rectifier circuit. In addition, since the feed source of this application is an antenna, its receiving power capacity is limited, so the input voltage and input power values ​​are small, so it is necessary to select an appropriate RF rectifier circuit so that its output voltage meets the requirements and the output efficiency is maximized as much as possible.

[0159] A single HSMS2852 is used to build an RF rectifier circuit and analyze it. The terminal load is 15KQ, the rectifier capacitor is 100pF, the bypass capacitor is 1nF, the input signal is 2.45GHz, and harmonic balance is used for simulation. The simulation circuit diagram is as follows Fig.10 shown.

[0160] Comparison of results of a single rectifier boost circuit: the frequency of the input voltage is 2.45GHz, and the amplitude is 1.08V. The corresponding output voltage frequency is DC, and the amplitude is 1.62V. The frequency of the input power is 2.45GHz, and the amplitude is 3.1mW. The corresponding output power frequency is DC, and the amplitude is 1.75mW. The power conversion efficiency is 56.1%.

[0161] The input voltage fed by the antenna is relatively small, about 1V, and the boost range of a single rectifier boost unit is limited and cannot meet the voltage requirements, so a multi-stage parallel connection is used to further increase the output voltage. However, the diode itself has certain losses. Using too many diodes will cause a large amount of output power loss in the diodes, so a balance is achieved between output voltage and output power, and simulation optimization is performed. Multiple rectifier boost circuits are simulated to compare their output voltages and output efficiencies. The input energy frequency is 2.45GHz, the amplitude is 1V, and the feed power is 3mW. The comparison results are shown in the figure below. Fig.11 shown.

[0162] Depend on Fig.11It can be seen that when the number of rectifier circuit units increases, the output voltage also increases, but when the number is greater than 4, the voltage increase is not obvious. At the same time, the output efficiency also decreases as the number of circuit units increases. Therefore, this application adopts a method of connecting four rectifier boost circuit units in parallel to increase the voltage value at the output end. Its structural principle is as follows Fig.12 shown.

[0163] Then the circuit schematic diagram that has been simulated and optimized is used for layout drawing and design, and the actual circuit PCB layout of the four-unit RF rectifier boost circuit is obtained.

[0164] 3. Optimization of wireless RF rectifier circuit components

[0165] The operating frequency of this application is 2.45GHz. Unlike the general low-frequency rectifier circuit, the value of each component has a great impact on the rectification efficiency. Therefore, the components used are simulated and optimized to maximize the conversion efficiency of the RF rectifier network.

[0166] The optimization objects are the rectifier capacitor C0 and the bypass capacitor C1, the optimization target is the output efficiency, the optimization range of C0 is 1 to 1000pF, the optimization range of C1 is 1 to 1000nF, the optimized circuit structure and its settings are as follows Fig.13 shown.

[0167] The final optimized result is that C0 is 372pF, C1 is 176nH, and the corresponding output power result has a conversion efficiency of 62.3%.

[0168] (III) RF matching circuit module

[0169] Since the impedance of the receiving antenna is quite different from the impedance of the RF rectifier module, it is necessary to design an RF impedance matching circuit to match the impedance of the antenna module and the RF rectifier module. In addition, the input impedance of the RF rectifier module is also different under different input powers. When the input power of the RF rectifier module is small, the conversion efficiency is also low. Therefore, the design of the RF matching circuit is particularly important.

[0170] Match the rectifier boost circuit with the antenna at the RF energy receiving end, use ADS to simulate the circuit, and use S-parameter scanning and Smith circle diagram tools.

[0171] After simulation calculation, the parameters of the matching circuit are obtained using the capacitor-inductor matching method.

[0172] When a 1.8nH inductor is connected in parallel in the circuit and a 0.5pF capacitor is connected in series, matching is achieved.

[0173] As can be seen from the figure, at this time, the performance of the matching circuit meets the requirements within the working range, and the RF signal is introduced into the rectifier boost circuit. The matching and rectifier boost circuits are integrated into the same PCB board for drawing.

[0174] 4. Testing of RF Energy Harvesting and Conversion System

[0175] (I) Construction of experimental platform

[0176] This application builds a low-power RF energy harvesting and conversion system for measurement in an experimental environment. The system measurement model is as follows Fig.14 shown.

[0177] In order to develop the performance of circularly polarized microstrip antenna arrays in RF energy harvesting, an experimental platform was built using the actual antenna and RF circuit modules produced by this application and sent to the factory. The equipment and instruments used in the experiment include the MY46107385 network analyzer from Agilent Technologies, the SMBV100A RF signal source from Rohde & Schwarz, the EXA series signal analyzer N9010A from Agilent Technologies, and a multimeter.

[0178] Among them, the RF signal source is used to generate a 2.45GHz WiFi signal, and the frequency range of its transmitted signal is 9kHz-6GHz, which meets the experimental requirements; the transmitting antenna is used to transmit a radio frequency signal of a specific frequency; the transmitting antenna uses a 2.45GHz omnidirectional antenna, which is the same as the general WiFi signal source used in the actual environment. The receiving antenna is the antenna of our application, which receives the RF signal; the signal analyzer is used to test the power of the antenna receiving signal, and its operating frequency range is 9kHz-13.6GHz. In addition, the network analyzer used in the antenna performance test phase is used to test the port characteristics of the antenna and the rectifier circuit, and its operating range is 9kHz-4.5GHz.

[0179] (II) Analysis of test results

[0180] WiFi signals are widely distributed both indoors and in public places. This experiment used signals near 2.45 GHz and tested them using a circularly polarized antenna array.

[0181] During the experiment, the simulated WiFi signal transmission power is 33dBm, that is, 2000mW, the distance between the receiving antenna and the signal source is 20cm, the terminal load resistance is 5k2, and the angle between the transmitting antenna and the receiving antenna changes.

[0182] The above experiments show that the RF energy collection and conversion system of the present application has a small change in the energy collected when the direction of the transmitting antenna changes, and the output voltage is around 3V, which can provide uninterrupted energy supply for low-power wireless sensor networks. And the efficiency of the energy collection and conversion system will not change significantly due to changes in the location of the WiFi signal.

[0183] Experiments were also conducted for different load resistances. During the experiment, the simulated WiFi signal transmission power was 33dBm, i.e. 2000mW, the distance between the receiving antenna and the signal source was 20cm, the angle between the transmitting polarization and the receiving antenna was 0 degrees, and the terminal load resistance took different values.

[0184] The above experiments show that the RF energy collection and conversion system of the present application has the highest output power when the load resistance is 5kQ, and can supply energy to some low-power sensor elements. When the load resistance changes, the input impedance of the rectifier circuit and the load resistance will change, which will have a certain impact on the effect of the matching circuit, so the output power will change. Since the output power of WiFi is low, and the transmitted signal will produce a large loss due to the propagation distance during the space transmission process, this RF energy collection and conversion system can currently only be applied to low-power sensor network nodes. If an energy storage module is added to the output end, this micro-energy RF energy collection and conversion system can be applied to more environments.

Claims

1. Wireless sensor WiFi radio frequency energy collection, conversion and power supply system, characterized in that: include: WiFi radiation source, receiving antenna, RF matching network, RF rectification module and terminal load. The WiFi transmitting end transmits electromagnetic wave energy into space. At this time, the receiving antenna of the receiving end receives the electromagnetic wave signal and converts it into an electrical signal. The RF matching network then transmits the RF AC signal to the RF rectification circuit. Then the RF rectification module performs AC-DC conversion on the AC signal, boosts the AC signal to convert it into a DC signal, and finally outputs it to the terminal load, realizing energy collection at a distance of 1000 meters. The sensitivity of the RF circuit module is -30dBm. M1: WiFi radio frequency energy collection and conversion system, the core part is the receiving antenna and the rectifier circuit. Improving the receiving antenna and the rectifier circuit can increase the output circuit voltage and improve the power conversion efficiency, so that the collected high-frequency microwave signal, that is, the radio frequency signal, can be transmitted to the load point to the maximum extent; M2: Sensor antenna module, including: antenna collection circular polarization, wireless RF rectification circuit, energy conversion array. The sensor antenna is the front end of the RF energy collection and conversion system. The design uses a low-profile, easy-to-conform, low-cost, and light-weight microstrip antenna for energy collection. The microstrip antenna is circularly polarized, and the energy conversion array method is adopted. The antenna array is matched with the antenna feed network design using a power divider and a quarter-wave converter to improve the collected power and anti-interference ability in complex environments. M3: Wireless RF rectifier circuit power supply, including: WiFi RF circuit module, wireless RF rectifier circuit, RF matching circuit module, rectifier boost circuit based on RF energy harvesting, using fourth-order rectifier boost circuit to convert the RF energy collected by the antenna, using high-frequency structure simulation HFSS and ADS to design, simulate and optimize the antenna array, matching circuit and rectifier boost circuit, through the design of RF diodes, RF rectifier circuit design, wireless RF rectifier circuit component optimization, the design adopts 2X2 circularly polarized microstrip antenna array, using network analyzer, RF signal source, signal analyzer and microwave darkroom, the antenna array is physically corrected and optimized to obtain the best load impedance value.

2. According to claim 1, the wireless sensor WiFi radio frequency energy collection, conversion and power supply system is characterized in that: RF impedance matching: The impedance of the receiving antenna and the RF rectifier module are connected to the RF impedance matching network to measure the actual input impedance of the RF rectifier module. The working state of the unit RF rectifier circuit is divided into two different states: on and off within one cycle. When the circuit is in the on state, the junction resistance of the rectifier diode is ignored. At this time, the series resistance of the rectifier tube generates the RF signal current in the circuit. When the circuit is in the off state, the current generated by the charging and discharging of the junction capacitance is the current of the rectifier diode. At this time, the input impedance of the RF rectifier module is closely related to the power of the input signal. The impedance of the RF rectifier module changes periodically, and the impedance is a function of the signal amplitude. The impedance of the RF rectifier module matches the antenna impedance to maximize the transmission power. At this time, the impedance of the RF rectifier module should be the periodic time average, that is, the average value of the input signal change in one cycle. The input impedance of the RF rectifier module changes with different input powers.

3. According to claim 1, the wireless sensor WiFi radio frequency energy collection, conversion and power supply system is characterized in that: Antenna collection circular polarization: using microstrip patch antenna, the array antenna polarization is the polarization of the electromagnetic wave it receives or radiates. The polarization of the electromagnetic wave is the direction of the trajectory of the endpoint of the electric field component of the electromagnetic wave in the direction of maximum reception or radiation, that is, the characteristics of the endpoint of the electric field vector in the radiation field at a given point in space changing with time. The trajectory formed by the endpoint in time describes the polarization characteristics of the electromagnetic wave; Suppose there is a uniform plane wave propagating along the z-axis, and its electric field vector expression is E = e x E m cos(ωt-kz+φ), ω is the angular velocity, k is the coefficient, φ is the phase, E m is the amplitude, e represents the charge, and at any time, the direction of the electric field vector E of the electromagnetic wave always remains in the x direction. The electric field components of the electromagnetic wave in the x-axis direction and the y-axis direction are respectively represented by E x and E y : E x =E xm cos(ωt-kz+φ x ) formula1 E y =E ym cos(ωt-kz+φ y ) formula 2 The electric field of the composite wave is E = e x E x +e y E y , at any time, E x Quantity and E y There are differences in the components. The electric field intensity vector of the synthetic wave at a certain point in three-dimensional space changes position with time, forming the polarization of the electromagnetic wave. At the point z = 0, Equation 1 and Equation 2 are rewritten as: E x =E xm cos(ωt+φ x ) formula 3 E y =E ym cos(ωt+φ y ) formula 4 When the x-component and y-component of the electric field have the same amplitude but differ in phase by π / 2, that is, E xm =E ym =E m ,φ y -φ x = ±π / 2, the synthetic wave achieves circular polarization; When φ y -φ x =π / 2, then φ y =φ x +π / 2, from equation 3 and equation 4 we get: E x =E m cos(ωt+φ x ) formula 5 Therefore, the electric field strength of the synthetic wave is The angle between the electric field of the synthetic wave and the x-axis is: The field strength of the composite wave is a constant value and does not change with time, but it keeps changing in direction. Its endpoints are on a circle and rotate at an angular velocity ω, making it a circularly polarized wave. When φ y -φ x =-π / 2, the magnitude of the composite wave electric field does not change with time, but its direction changes with time. The angle between the composite wave electric field and the x-axis is: Any two linearly polarized waves with the same frequency, the same direction of travel, a polarization angle of 90 degrees, the same amplitude and a phase difference of π / 2 are circularly polarized waves. If the amplitude of linearly polarized waves with polarization directions perpendicular to each other is equal and the phase difference between them is ±π / 2, the synthetic wave is a circularly polarized wave. At the same time, when the radio frequency energy collection array antenna is used in the present application, a circularly polarized array antenna design is adopted in collecting 2.45GHz electromagnetic wave energy, so as to enhance the antenna's ability to receive electromagnetic waves with different polarization directions and improve the voltage and power at the output end.

4. According to claim 3, the wireless sensor WiFi radio frequency energy collection, conversion and power supply system is characterized in that: Determine the unit size of the corner-cut circularly polarized antenna: The dielectric constant of the dielectric plate of the antenna designed in this application is 2.33, and the loss factor is 0.0012. Considering the influence of the thickness of the dielectric plate on the bandwidth of the microstrip antenna, the thickness is 1.6 mm; When the operating frequency is 2.45 GHz, the thickness of the dielectric plate is 1.6 mm, and the dielectric constant of the dielectric plate is 2.33, the radiation patch length of this antenna unit is b = 39.3 mm, the cut-corner side length of the antenna is d = 5.03 mm, and the distance between the feeding point of a single cut-corner antenna and the edge of the patch is 12 mm; The edge impedance of the antenna is matched to 50 ohms that matches the SMA connector. Based on the above antenna parameters, modeling and settings are performed in the high-frequency simulation software HFSS. After simulating the antenna model in HFSS, the side length and the size of the cut angle of the radiation patch are optimized. Finally, it is determined that when the length of the radiation patch is 39 mm and the length of the cut angle is 5.58 mm, the antenna unit exhibits good antenna performance at 2.45 GHz.

5. According to claim 1, the wireless sensor WiFi radio frequency energy collection, conversion and power supply system is characterized in that: Energy conversion array: By cutting the corners of the square radiating patch in the microstrip antenna, perturbations are introduced to achieve individual circular polarization of the antenna array unit, and then these individual circularly polarized elements form an antenna array; Antenna array design is divided into the following four steps: Step 1: Refer to the global structure, gain, power frequency and polarization information of the antenna, select an array arrangement that meets the requirements and is easy to implement, determine the spacing between each antenna subunit, and the phase relationship between each unit; Step 2: Design of unit antennas in the array. After determining the distribution form of the antenna array, determine the shape and size parameters of the unit antenna according to the specific requirements of impedance matching frequency, bandwidth and polarization of each unit in the antenna array. Step 3: Global analysis of the array. After determining the parameters of the units in the array and the arrangement of the array, analyze the global antenna array to obtain the array performance. If the antenna array can meet the requirements under this condition, proceed to the next step for the final design. Otherwise, it is necessary to return to the previous step to optimize the antenna units and arrangement; Step 4: Feed network design.

6. According to claim 5, the wireless sensor WiFi radio frequency energy collection, conversion and power supply system is characterized in that: Antenna array design: The material is FR4 plate with a dielectric constant of 4.4, and the feeding method is side feeding. The initial values ​​of the size of each radiating patch are calculated as follows: the side length is 39.3mm. At this time, the frequency of the resonance point of the array antenna is 2.61GHz. Using the parameter scan provided by HFSS, the length of the patch is optimized to be 29.1mm, the resonance point is 2.45GHz, the side length is 39mm, and the cut-angle side length is 5.3mm. Each unit is connected through each section of the microstrip line and a quarter-wave converter. The impedance of each section of the microstrip line is different, and the corresponding width is different, which is 3.06mm for 50ohm, 1.61mm for 70.7ohm, and 0.70mm for 100ohm. As a quarter-wave converter, the corresponding line length is 17.1mm when the impedance is 70.7ohm. The present application designs a circularly polarized microstrip patch antenna array, the operating frequency of the array antenna is 2.45 GHz, and each unit is connected in parallel through a microstrip line.

7. According to claim 1, the wireless sensor WiFi radio frequency energy collection, conversion and power supply system is characterized in that: WiFi RF circuit module: The rectifier boost circuit works through diodes and capacitors. When designing the rectifier boost circuit, different operating frequencies and circuit impedance matching issues are considered. When the antenna collects the positive half-cycle of the RF signal and injects it from the Pl port, the voltage of the diode d2 gradually increases. When the voltage is greater than its turn-on voltage, the diode d2 is turned on, and the capacitor C2 starts to charge, and the charge is stored on the capacitor C2; when the negative half-cycle of the RF signal collected by the antenna is injected from the P1 port, the diode d1 is turned on, and the capacitor C1 starts to charge, and the charge is stored on the capacitor C2; the diode converts the full-wave signal into a half-wave signal, and the charging and discharging circuit composed of the large capacitor converts the RF signal into a low-frequency signal.

8. According to claim 1, the wireless sensor WiFi radio frequency energy collection, conversion and power supply system is characterized in that: Design of RF diode: choose to use zero-bias improved SBD diode, with the minimum critical voltage of 150mV and the minimum junction capacitance of 0.18pF. The high-order harmonics generated in the RF rectification circuit are filtered by the RF filter at the RF input end and the DC filter at the DC output end to generate a more stable DC voltage signal; The improved SBD diode has a forward voltage drop of only 150mV, a small package size, and a small parasitic resistance, where R is the parasitic resistance of the diode, C is the junction capacitance of the diode, and R j is the diode junction resistance, the diode parasitic resistance R s Smaller, the output voltage is proportional to R s Unrelated, the diode is equivalent to a single-pole single-throw switch. Under the condition of forward bias, the depletion layer of the improved SBD junction is a high resistance area. All applied voltage drops in the depletion layer weaken the electric field direction of the electric field strength, keep the electric field relative to the SBD junction barrier to reduce the number of charges; reduce the total charge, the depletion layer becomes thinner, the improved SBD barrier height is reduced, and the voltage is reduced. At this time, the drift current is less than the diffusion current. The forward bias causes a large number of electrons to flow through the improved SBD junction, generating a very large forward current in the external circuit; under the condition of applied voltage, the diode junction resistance drops rapidly to within a few ohms; at the same time, the electric field in the same direction, the total electric field increases, the amount of free charge increases, the depletion layer becomes thicker, the barrier height increases, and it is difficult for electrons in the semiconductor to diffuse to the metal, and the diffusion current is less than the drift current; To calculate the parasitic resistance, first measure the current and voltage at each point and draw the volt-ampere characteristic curve. Then go to the position with higher current, calculate the slope point, and then convert the slope into resistance. The relationship is as follows: The electrical characteristics of the SBD barrier diode at room temperature are set as: The HSMS2852 from the HSMS-285x series diodes that meet the 2.45GHz requirements is used, and a rectifier and boost circuit is formed by the HSMS2852 and a capacitor.

9. The wireless sensor WiFi radio frequency energy collection, conversion and power supply system according to claim 1 is characterized in that: RF rectifier circuit design: A single HSMS2852 is used to build an RF rectifier circuit, where the terminal load is 15KQ, the rectifier capacitor is 100pF, the bypass capacitor is 1nF, the input signal is 2.45GHz, and harmonic balance is used; The output voltage is further increased by adopting a multi-stage parallel connection method, with an input energy frequency of 2.45GHz, an amplitude of 1V, and an input power of 3mW; Four rectifier boost circuit units are connected in parallel to increase the voltage value at the output end.

10. The wireless sensor WiFi radio frequency energy collection, conversion and power supply system according to claim 1, characterized in that: Optimization of wireless RF rectifier circuit components: The optimization objects are the rectifier capacitor C0 and the bypass capacitor C1, the optimization target is the output efficiency, the optimization range of C0 is 1 to 1000pF, and the optimization range of C1 is 1 to 1000nF; The final optimized results are: C0 is 372pF and C1 is 176nH.

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