# State-of-the-Art Techniques in RF Energy Harvesting Circuits

^{1}

^{2}

^{*}

## Abstract

**:**

## 1. Introduction

^{2}range. An example is an RFID chip that is powered by an RFID reader. The dedicated source enables embedded devices to recharge batteries. On the other hand, a circuit that harvests RF energy from an ambient source, can exploit this energy to charge various storage systems. This type of circuit is expected to produce power levels in the 2 nW/cm

^{2}range. Typical ambient sources include Wi-Fi, GSM/Cellular, FM/TV/DTV, Bluetooth, etc. This type of source is common for applications for which is very difficult or impossible to replace batteries [3]. RF energy scavenging circuits are known for more than 60 years, but only a few have been able to harvest energy from ambient RF sources [4].

## 2. Materials and Methods

## 3. Results

#### 3.1. Design Methology

- The procedure of choosing the right energy harvesting circuit topology.
- The selection process of a suitable diode.
- The design of an appropriate impedance matching network.
- The design, the optimization, and the simulation of the whole system [7].

#### 3.2. Design Specification

#### 3.2.1. Receiving Antenna

#### 3.2.2. Impedance Matching Network

_{Source}+ jX

_{Source}) has to be matched with the load impedance (R

_{Load}+ j0). This can be achieved with a matching network (−jX

_{Match}), which has equal and opposite reactance from the source. In this way, the opposite reactance gets canceled thereby matching the source and the load (assuming R

_{Source}= R

_{Load}). Theoretically, if the impedances of the source and the load are completely matched, we will have a transfer without losses, all the energy from the source will be transferred to the load. Therefore, it can be understood that the IMN makes a condition in which we have left only pure resistance value at the source and the load. This can be achieved if the load impedance changes into a complex conjugate of the source impedance.

#### 3.2.3. Diodes

_{j}is the junction capacitance, R

_{s}is the series resistance, R

_{j}is the junction resistance) are presented in Figure 7a. Figure 7b illustrates the I-V characteristic of a Schottky diode and Figure 7c depicts the symbol of Schottky diode [38].

_{s}, whereas the second one has a low barrier and high values of R

_{s}[7]. In [41] a dual-stage voltage doubler was manufactured for operation at a frequency of 3.5 GHz using HSMS-2820 diodes. In [42] the authors designed three rectifiers and connected them in series. Each rectifier is a single series diode rectifier. For this design, they used an SMS7630-079 diode. A voltage doubler was manufactured in [43] with an efficiency of 50.7% at 2.45 GHz and 20.1% at 5.85 GHz. The authors used the SMS-7630 diode [44].

_{s}or decrease of junction capacitance Cj [7].The authors in [45] designed a dual-band (1800 MHz, 2.1 GHz) rectenna in which the rectification was achieved with a single diode rectifier (by the use of an SMS7630 diode). The efficiency of this work is 33% for −7 dBm input power. The authors have used HSMS-285C diodes in [46] to manufacture and compare a 1-stage Dickson rectifier and a 3-stage Dickson rectifier. The circuits tune in 1 GHz and for −7 dBm input power. The first circuit achieved 70.5% efficiency while the second circuit achieved 77% efficiency. The authors in [47] designed a rectenna in which HSMS-286C diodes were used. The circuit resonates at 868 MHz. The maximum efficiency is 44.5% at −10 dBm. Table 4 lists the most common types of diodes that are used in various rectifiers’ designs.

#### 3.2.4. Rectifier

_{TH}. In the DTMOS (Dynamic Threshold MOSFET) architecture shown in Figure 11b the substrate (bulk) and the gate are connected to dynamically change the V

_{TH}of the transistor, using the following equation. In which V

_{TH}is the threshold voltage, V

_{T0}is the zero bias threshold voltage with V

_{SB}= 0, γ is called body-effect coefficient or body factor and φ

_{F}is the inversion layer voltage.

_{SB}voltage values [78,79]. The authors in [80] designed a N(1,2,3)-stage rectifier used the DTMOS technique. They achieved for 1-stage at 900 MHz efficiency 79.4% and sensitivity −32 dBm.

#### 3.2.5. Load

_{in}is the RF input power, P

_{out}refers to the output power with V

_{out}as the output voltage and RL as the output load. To achieve maximum efficiency of the device, the load resistance must be adjusted. However, high voltage requires high resistance, according to Ohm’s law. Therefore, trade-off becomes inevitable. From the above equation, we understand the importance of choosing the proper load value. The load can be capacitive, inductive, or purely ohmic. For this reason, all works involved in the design of such circuits are given a special study of what load will be used. As can be deduced from [43,54], the efficiency of the system decreases when the load increases. As a result of the previous analysis, we notice that it is very important that the load impedance be carefully selected for a specific energy harvesting circuit [81]. Figure 13 depicts the change of the PCE depending on the output loads for various power inputs [82].

## 4. Discussion

## 5. Conclusions

## Author Contributions

## Funding

## Institutional Review Board Statement

## Informed Consent Statement

## Data Availability Statement

## Conflicts of Interest

## References

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**Figure 4.**Different types of impedance matching networks with distributed elements: (

**a**) L-network, (

**b**) Reversed L-network, (

**c**) T-network, (

**d**) π-network [1].

**Figure 5.**Different types of impedance matching networks with lumped elements: (

**a**) T-Network (

**b**) L-Network (

**c**) π-Network.

**Figure 6.**L-network in combination with the microstrip line network is equivalent to the T- Impedance Matching Network (IMN).

**Figure 7.**The characteristics of a diode (

**a**) electronic equivalent circuit (

**b**) I-V characteristic of Schottky diode (

**c**) symbol of Schottky diode.

**Figure 8.**Types of rectifier configurations (

**a**) half-wave rectifier (

**b**) full-wave rectifier (

**c**) bridge rectifier [1].

Reference | Design/Type | Frequency Bands |
---|---|---|

[8,9] | Bowtie Antenna | 845 MHz, 3.5 GHz EGSM-1800 |

(1800 MHz), UMTS (2100 MHz) | ||

[10] | Log-Periodic Dipole Antenna | 650 MHz–2500 MHz |

[11] | Dipole Antenna | 902 MHz–928 MHz |

[12] | Monopole Antenna | 600 MHz–1500 MHz |

[13,14] | Loop Antenna | GSM1800 DTV, Cellular radio waves |

[15,16,17] | Yagi-Uda Antenna | GSM-1800 and UMTS-2100 2.45 GHz GSM-900, GSM-1800 |

[18] | Planar Inverted-F Antenna | GSM-900, GSM-1800 |

[19] | DRA | 1.67 GHz–6.7 GHz |

[20] | Differential Microstrip Antenna | 890–960 MHz |

[21,22,23] | Microstrip Patch Antenna | GSM- 900, GSM-1800, UMTS-2100 (NB-IoT), EGSM-900 GSM-1800, UMTS |

Reference | Matching-Network | Type of Elements |
---|---|---|

[29] | L-Type | Lumped |

[30] | T-type | Lumped |

[31] | L-Type | Distributed |

[32] | Multiband | Distributed |

[33] | L + μStrip Line Network | Distributed |

[34] | Combination of different types of Matching Networks | Distributed |

[35] | 2 Reverse L | Distributed |

Diode | Minimum Breakdown Voltage V_{BR} (V) | Maximum Forward Voltage V _{F} (mV) | Maximum Forward Volage V _{F} (V) @ I_{F} (mA) | Maximum Reverse Leakage I_{R} (nA) @ V _{R} (V) | Maximum Capacitance C _{T} (pF) | Typical Dynamic Resistance R_{D} (Ω) |
---|---|---|---|---|---|---|

HSMS282x | 15 | 340 | 0.5–10 | 100–1 | 1.0 | 12 |

SMS7630-079 | 2 | 60–120 | 50 | - | 0.3 | 5000 |

HSMS-285C | 3.8 | 150–250 | 1 | 0.175–2 | 0.3 | - |

HSMS 286C | 3 | 250–350 | 0.35–1 | - | 0.3 | - |

Reference | Diode | Circuit |
---|---|---|

[41] | HSMS2820 | Dual-Stage Voltage Doubler |

[42] | SMS7630-079 | 3 Rectifiers in Series |

[43] | SMS7630 | Voltage Doubler |

[45] | SMS7630 | Single Diode Rectifier |

[46] | HSMS-285C | 1-Stage Dickson Rectifier |

[47] | HSMS 286C | Rectifier |

Reference | Rectifier’s Topology | Diodes | Efficiency (Max) | Input Power | Frequency |
---|---|---|---|---|---|

[29] | CMOS Reconfigurable System | - | 25% | −14.8 dBm | 915 MHz |

[35] | Dual Band Voltage | SMS-7630 | 30.40% | −20 dBm | 925 MHz |

[43] | Dual Band Voltage Doubler | SMS-7630 | 57.10% | −10 dBm to −30 dBm | 2.45 GHz, 5.8 GHz |

[49] | Single Diode Rectifier | HSMS-2860 | 1.3% | −20 dBm | 2.45 GHz |

[50] | Voltage Multiplier | HSMS-2850 | 81.65% | 0 dBm | 868 MHz |

[51] | Greinacher Rectifier with Rat-Race coupler | SMS-7630 | 5% | −20 dBm to −10 dBm | 2.45 GHz |

[52] | Greinacher Rectifier with Rat-Race coupler | HSMS-285C | 71% | 4.7 dBm | 1850 MHz |

[54] | Double Diode Rectifier | SMS7630-040LF | 21% | −15 dBm | 97.5 MHz |

[55] | Voltage Quadrupler | HSMS-2862 | 75.108% | 20 dBm | 2.4 GHz, 5.8 GHz |

[56] | Latour Structure (Doubler) | - | 38% | −10 dBm | 850 MHz |

[57] | Voltage Doubler | SMS7630–005LF | 75% | 15 dBm | 0.1 GHz to 2.5 GHz |

[58] | Voltage Doubler | SMS7630-005LF | 68% | −10 dBm | 2.45 GHz |

[59] | Half-Wave Voltage Doubler | HSMS-2852 | 57% | <200 μW/cm^{2} | 1.7 GHz |

[60] | Cockcroft-Walton Voltage Doubler | HSMS-2852 | - | −22.5 dBm | 900 MHz |

[61] | Karthaus-Fisher Voltage Multiplier | HSMS-2862 | 70% | 23 dBm | 2.45 GHz |

[62] | 7-Stage Villard Voltage Doubler | HSMS-2850 | - | 0 dBm | 945 MHz |

[63] | Dickson Multiplier | HSMS-2852 | 55% | 0 dBm | 575 MHz, 900 MHz, 2.45 GHz |

[64] | Differential Doubler | SMS-7630 | 53% | 2 dBm | 1800 MHz |

[65] | 3-Stage Voltage Multiplier | HSMS-285C | 80% | 8 dBm | 915 MHz |

[66] | Balanced RF Rectifier | HSMS-2860 | 74.90% | Different input power levels | 2.34 GHz |

[67] | Greinacher Voltage Doubler | HSMS-2852 | 78.70% | −10 dBm | 900 MHz |

[68] | Voltage Doubler with Multistage Wilkinson | HSMS-286B | 78.06% | 20 dBm | 1.8 GHz |

[69] | Dual Band Rectifier | HSMS-2850 | 30% | −5 dBm | 900 MHz |

[70] | Single Diode Rectifier | HSMS-2850 | 28% | −15 dBm | 2.4 GHz, 2.5 GHz |

[71] | Single Stage Voltage Multiplier | HSMS-2850 | 50.2% | 14 dBm | 900 MHz |

[72] | Rectifier with RF Combiner | HSMS-2850 | 40% | −30 to −10 dBm | GSM1800, UMTS2100, Wi-Fi |

[73] | Single Stage Full-Wave Rectifier | SMS7630-079 | 60% | - | 800 MHz |

[74] | CMOS Rectifier | - | 86% | −18.2 dBm | 900 MHz |

[75] | CMOS Reconfigurable System | - | 99.8% (MPPT) | −22 to 4 dBm | 915 MHz |

[76] | Reconfigurable System | SMS7630-005LF | 45% | −15 to 20 dBm | 900 MHz |

[77] | CMOS Reconfigurable System | - | 92.2% | - | 6.78 MHz |

[37] | CMOS Villard multiplier | - | - | 0 dBm | 400 MHz, 2.4 GHz |

[80] | DTMOS N-stage rectifier | - | 79.4% | −32 dBm | 900 MHz |

Rectifier’s Topology | References |
---|---|

Dual Band Rectifier | [35,43,69] |

Single Diode Rectifier | [49,70] |

Voltage Multiplier | [50,71,73] |

Greinacher Rectifier with Rat-Race coupler | [51,52] |

Voltage Doupler | [54,56,57,58,59,60,62,64,67,68] |

Voltage Quadrupler | [55] |

Voltage Multiplier | [61,63,65] |

Balanced RF Rectifier | [66] |

Rectifier with RF Combiner | [72] |

Reconfigurable System | [29,75,76,77] |

CMOS Rectifier | [37,74,80] |

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## Share and Cite

**MDPI and ACS Style**

Bougas, I.D.; Papadopoulou, M.S.; Boursianis, A.D.; Kokkinidis, K.; Goudos, S.K.
State-of-the-Art Techniques in RF Energy Harvesting Circuits. *Telecom* **2021**, *2*, 369-389.
https://doi.org/10.3390/telecom2040022

**AMA Style**

Bougas ID, Papadopoulou MS, Boursianis AD, Kokkinidis K, Goudos SK.
State-of-the-Art Techniques in RF Energy Harvesting Circuits. *Telecom*. 2021; 2(4):369-389.
https://doi.org/10.3390/telecom2040022

**Chicago/Turabian Style**

Bougas, Ioannis D., Maria S. Papadopoulou, Achilles D. Boursianis, Konstantinos Kokkinidis, and Sotirios K. Goudos.
2021. "State-of-the-Art Techniques in RF Energy Harvesting Circuits" *Telecom* 2, no. 4: 369-389.
https://doi.org/10.3390/telecom2040022