RF signal based Energy Harvesting for Wireless Sensor Networks

Muhammad Tahir, Usman Asif and Ibraheem Bin Mehmood
Aim of Project

Wireless sensor networks (WSNs) guarantee a continuous and automated monitoring of a given field without any human presence. This distinguishing feature is attained through deploying a collection of battery-powered and wirelessly-connected miniature devices over the area of interest. The main task of such devices is to take measurements of the surrounding environment, to a base station to perform a centralized decision mechanism. Nowadays, wireless sensor networks are extensively being deployed in a wide range of real-world applications, such as home automation, detection of natural disasters, biological attacks and military tracking. Since WSN nodes are usually stand-alone and battery powered, extending the network lifetime is very critical.

In today’s wirelessly connected world, ambient Radio Frequency (RF) energy can be found almost everywhere. Technically, this free-flowing energy can be captured, converted and stored for use in other applications. This project aims to provide a continuous power source to low-powered devices, like WSN, by continuously harvesting the available ambient RF power so that their operation is not halted. It will also enable the battery-less operation of such devices, making them lesser in weight and more compact.

Summary

Radio Frequencies are spread all around the environment. The proposed solution is to harvest ambient RF energy and charge the battery or power up the WSN nodes. The basic schematics of the project is shown below:

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Main Idea of the Proposed Solution

The main idea is to use a wide band antenna to harvest the RF energy from ambient RF sources, like GSM, 3G, 4G and Wi-Fi signals etc. This RF energy is then converted to DC power so that it can be used for charging purposes. For that purpose, a custom-made rectifier to convert the RF energy to DC power is used. This DC power is then processed using a boost converter to step up the voltage level and make it easier to charge the battery.

During the development of the idea, we had to pay special attention to the following aspects:

  • Energy extracted was found to be very small and thus an antenna array is used to enhance energy levels.
  • The efficiency of the RF-DC conversion mechanism was found to be the most critical requirement.

A block diagram showing the complete system schematics is given below

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Main Idea of the Proposed Solution

Advantage of the Proposed solution
  • The proposed solution is primarily based on the concept of RF energy harvesting using a wideband antenna. We are aiming to obtain approximately 100uW from this source, which to the best of our knowledge, has not been successfully achieved in the existing literature.
  • We are working to reduce the size of the antenna as much as possible after achieving the desired power level, so our system can be easily employed in WSNs and other hand-held low power applications devices.

Market application and exploitation

Although the power available from ambient RF energy is very low (typically measured in microwatts), it has proven to be sufficient for a number of applications, such as:

  • RFID tags
  • Wireless sensor networks for remote monitoring
  • NFC functionality in contactless smart cards