Radio frequency harvesting | RF energy harvesting system

Energy harvesting systems are designed to capture and convert ambient energy from the environment into usable electrical power. The primary function of energy harvesting systems is to generate electricity from various sources to power electronic devices or recharge batteries.

Following are the typical energy harvesting schemes available today.
•  Solar energy •  Mechanical energy •  Thermal energy •  Radio Frequency energy •  Electromagnetic energy •  Biochemical energy •  Radioactive energy etc.

RF (Radio Frequency) energy harvesting systems are designed to capture and convert radio frequency signals from the environment into electrical power. RF energy harvesting is particularly useful in situations where ambient radiofrequency signals are available, such as in urban environments, near communication towers, or in proximity to electronic devices emitting radio frequency radiation such as wifi routers. These systems can be employed to power low-power electronic devices or recharge batteries, eliminating or reducing the need for conventional power sources. This technology uses intermediate stages of power conditioning, storage batteries or storage capacitors to conserve harvested energy from environment.

Radio Frequency waves used in RF harvesting system is part of electromagnetic spectrum. Maximum power available in RF energy harvesting technique is about 0.7 µWatt for 2.4GHz and about 1 µWatt for 900 MHz frequency theoretically. This can be achieved with free space distance of about 40meters.

RF energy harvesting system

Key features and considerations for radio frequency harvesting systems are as follows.
• These systems are designed to operate within specific frequency ranges.
• The efficiency depends on factors such as the antenna design, matching network, and rectifier efficiency.
Applications: RF energy harvesting has various applications, including wireless sensor networks (WSNs), IoT devices, and low-power electronics. It is particularly useful in scenarios where traditional power sources are impractical or where long-term, maintenance-free operation is desired.

The figure-1 depicts block diagram of RF energy harvesting system. It consists of following modules. It converts RF energy to DC energy hence it is also referred as RF to DC converter. Figure also mentions discrete circuit components used in these modules.
• Antenna • Matching Network • Rectifier and Voltage multipliers (one or more) • Energy storage elements and Load

RF energy harvesting system

Antenna: This device picks up RF radiations from various sources available in the free space. The picked up RF energy later is guided to the rest of the modules using transmission line or guided structures. Antenna converts electromagnetic energy picked up into elecrical signals. Refer types of antenna.

Matching Network : It is used to couple maximum RF energy into the circuit. The circuit is made of capacitor and inductor components.

Rectifier Circuit: The captured RF signals are then fed into a rectifier circuit. The rectifier is responsible for converting the alternating current (AC) signal induced in the antenna into direct current (DC), which can be used to power electronic devices or charge a storage device like a battery or a capacitor.

Voltage multiplier: Figure mentions voltage multiplier or rectifier made of diodes and capacitors. Higher are these stages higher is the voltage at the load and lesser is the current. But higher number of stages result into increase in charging delay before it goes for energy storage. Refer halfwave and full wave rectifier circuits.

Energy storage: In many RF energy harvesting systems, there is a storage component such as a battery or a capacitor. The energy harvested from RF signals can be stored in these devices for later use, allowing for continuous operation even when the RF signal source is not present or is intermittent.

Voltage Regulator : In some cases, a voltage regulator may be included to stabilize the output voltage. This ensures that the harvested energy is provided at a consistent and usable voltage level for the connected electronics. This module is optional and may not always required.

Load or Electronic Device: The harvested and rectified energy is then supplied to the load or electronic device, powering it directly or charging a connected energy storage device.

Advantages of Radio Frequency energy harvesting

Following are the benefits or advantages of RF energy harvesting:
1. Ubiquitous Power Source: This harvesting technique leverages ambient radio frequency signals, providing a continuous and ubiquitous power source for electronic devices.
2. WSNs : Enables the creation of self-sustaining wireless sensor networks (WSNs) by eliminating the need for frequent battery replacements.
3. Reduced Environmental Impact: Promotes sustainability by harnessing existing RF signals, reducing the reliance on disposable batteries and minimizing environmental impact.
4. Extended Device Lifespan: Enhances the lifespan of low-power devices by continuously harvesting energy from the surrounding RF environment.
5. Cost Savings: Reduces maintenance costs and enhances cost-effectiveness by eliminating the need for frequent battery replacements in remote or inaccessible locations.

Conclusion : RF energy harvesting systems contribute to the development of self-sustaining and energy-efficient devices, reducing the reliance on conventional power sources and enabling the deployment of wireless sensor networks in diverse environments.

Other energy harvesting techniques

Refer Energy Harvesting Methods which describes types and basics of energy harvesting techniques and energy harvesting materials. The energy harvesting techniques include thermoelectric energy harvesting, photovoltaic energy harvesting, piezoelectric energy harvesting, pyroelectric energy harvesting, rf or wireless or electromagnetic energy harvesting, wind energy harvesting, vibration energy harvesting etc.

RF and Wireless Terminologies