Researchers develop compact antenna for communication in difficult locations

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slac compact antenna radios
A new compact antenna for very low frequency (VLF) transmissions, developed and tested at SLAC, consists of a 4-inch-long piezoelectric crystal (clear rod at center) that generates VLF radiation. Credit: Dawn Harmer/SLAC National Accelerator Laboratory

Department of Energy at SLAC National Accelerator Laboratory has developed a pocket-sized antenna of a new kind which is capable of enabling mobile communication in circumstances where normal radios are unable to function such as underground locations, underwater bodies or long distances through the air.

This device emits radiation of very low frequency (VLF) which has a wavelength ranging from tens to thousands of miles. These radiations travel very large distances far greater than the horizon and it can also penetrate through the environments which would have normally blocked the radio waves of shorter wavelengths. The most powerful VLF technology which is currently in use needs huge emitters while this mini-sized antenna is just about four inches tall. Because of its small size and compactness, it can be used for several tasks that have the requirements of very high mobility. Two very appropriate examples are in rescue and defense operations.

Mark Kemp from SLAC who is also the principal investigator of this project reported that the antenna is many times more efficient and is also capable of transmitting data faster than other devices of comparable size. The performance of this device helps in broadening the reach of present technological possibilities and it also increases the feasibility of the VLF applications which can send text messages in difficult situations.

These results were published by the team in Nature Communications.

In modern communications, information is transmitted through the air by radio waves for various purposes such as radio broadcasts, navigation systems and several other applications. But there are many limitations to the radio waves with shorter wavelengths. The transmitted signal gets very weak over large distances, they are unable to propagate through water and are also blocked in the presence of several layers of rock.

On the other hand, the longer wavelength signals can travel huge distances ranging through hundreds of feet. It can also propagate through water bodies and several miles beyond the horizon. But there are some challenges to this technology. One of them being the size of the antenna. For maximum efficient propagation, the antenna’s size must be comparable to the wavelength which it emits. To satisfy this condition, antennas have to stretch for large distances which is not feasible. On the other hand, if the VLF transmitters are small in size, it means that they weigh hundreds of pounds and are thus much less efficient.

The design of the new antenna has taken place with all these factors under consideration. The main working is based on piezoelectric effect, which is a process that converts mechanical stress to electric charge. A rod-shaped crystal of material such as lithium niobate is used as the antenna and when voltage is applied to it, it vibrated, and the mechanical stress triggered electric current wherein the electromagnetic energy is transmitted as the radiation.

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