Rectenna Technology

BACKGROUND

From the very beginning we have known about the principle of Conservation of energy which states that "Energy can neither be created nor be destroyed". This means that the amount of energy present in the world is constant, so the question arises why we are about to face an energy crisis in the near future. This is simply because we are not able to convert all the available forms of energy into our desirable form of energy. This can be understood as analogous to that all the water resources can’t be utilized as drinking water. Similarly we have not been so successful in converting all the energy sources available to us into our most desirable form of energy i.e. electricity. 

With the rapid development of wireless system and demands of low power integrated electron technology IC circuits, various researchers have tended to study about this.

History of wireless power transmission can be traced back to tesla who first pursued it over a century ago. However it faced several challenges but recently, Energy Harvesting and Wireless Power Transmission Technology have been a subject of deep interest and research. Rectenna is also among such technologies.

INTRODUCTION

Fig: A printed meshed rectenna lighting an LED

Rectenna or simply Rectifying Antenna is a special type  of receiving antenna that is used for converting  electromagnetic energy into Direct (DC) current. It is  simply a combination between a receiving antenna and  rectifier circuit. A Simple rectenna element is a  combination of a dipole antenna along with an radio  frequency diode connected across the dipole elements. Here, the diode is responsible for rectification of AC  induced in the antenna by the microwaves to produce  DC power which powers a load connected across the  diode.

HISTORY

Tracing back to the history of rectennas we come across that this technology was first invented by U.S electrical engineer William C. Brown of the Raytheon Company who demonstrated it with a model Helicopter powered by microwaves transmitted from ground received by an attached rectenna. He faced challenge of how to efficiently receive and convert to DC power. Wireless power transmission was a new concept then as it had begun by Tesla. Tesla had managed to demonstrate this concept although

he had never found an applicable route into its commercialization. Although the Helicopter model given by Brown worked he was aware of his flaws in his system and continued to work on its other possibilities.

Fig (a): W.C. Brown holding the Rectenna helicopter platform Fig (b): In flight demonstration of the rectenna helicopter 

In 1963 ,Brown met with his colleague Roscoe George who had been working on a microwave point-contact semiconductor diode. Following discussions between them a device was conceived and it was named ”Rectenna” and the name rectenna was coined.

This was followed by publishing of first official report of Rectenna concept by R.L Bailey of the university of Florida in 1972. However with the growing years, several researchers have worked towards development of Rectenna technology.

USES

• In recent years research is being done to use rectennas as power source for small wireless microelectronic devices. The largest current use of rectennas is in RFID, Proximity cards and contactless smart cards.
• Another interesting application of this technology is powering data communications of implantable medical devices . For ex - Researchers are beginning to develop pills that can be swallowed by patients and stream health data back to a computer for diagnostics.

A lot of other applications of rectenna can be seen in recent days all over the world . Hope one day the whole world will be covered with safe and easily accessible forms of wireless technology like rectenna.

IMPLEMENTATION

• Researchers from MIT have designed the first fully flexible rectenna that could be used to power flexible and wearable electronics and medical devices.
• University of Colorado Bouder scientists have used a poltergeist-like feature of electrons to create devices that can gather surplus heat from the environment and convert it to power. This is a unique optical rectenna.

More than actual discoveries several theories had been proposed regarding this technology.

PROBLEMS

• A Major challenge in the design of rectenna is Impedance matching network. As rectifier is a non-linear device ,its input impedance is a function of frequency ,input power and load impedance. Hence, designing an impedance matching network is necessary which is hard to maintain.
• Most of the Rectenna discovered so far operate at low frequencies.
• Traditional rectennas use either silicon or gallium arsenide for rectifiers. Using these materials to cover vast areas such as the surface of a building is cost prohibitive.