The Department of Energy's SLAC National Accelerator Laboratory has just developed a new kind of pocket-sized antenna that will allow mobile communication where conventional radios don't work including beneath the water, through the ground, and over the very long distances through the air.
With wavelengths of tens to hundreds of miles, the device emits very low frequency (VLF) radiation. For these waves, they travel long distances beyond the horizon, and they have the potential of penetrating environments capable of blocking radio waves with shorter wavelengths. Against the most potent VF technology of today that requires large emitters, this antenna is four inches tall, and people can use it for tasks that demand high mobility such as defense and rescue missions.
The principal investigator of the project, Mark Kemp from SLAC said that their device is also hundreds of times most efficient and capable of transmitting data faster than previous machines of comparable size. He claimed that the performance of the devices pushes the limits of what's technologically possible and puts portable VLF applications, like sending short text messages in challenging situations within reach. The team from SLAC made their results available in Nature Communications.
The group had the challenge of size since in modern telecommunications, radio waves transport information through the air for radio broadcasts, radar and navigation systems and other applications. But radios with shorter-wavelengths waves have their limits. Their limits are the signal they transmit becomes weak over very long distances, cannot travel through water, and is quickly blocked by layers of rock.
Compared to that, the VLF's longer wavelength radiation gives it the capability to travel hundreds of feet through ground and water and thousands of miles beyond the horizon through the air.
For the VLF radiation to generate, the device exploits the piezoelectric effect that converts mechanical stress to a build-up of electrical charge.
For their antenna, the research utilized a rod-shaped crystal of a piezoelectric material and lithium niobate. As they applied an oscillating electric voltage to the rod, it vibrated and as an alternative, shrinking and expanding. This mechanical stress triggered an oscillating electric current whose electromagnetic energy then got emitted as VLF radiation.
The electric current stems from electric charges moving up and down the rod. As a convention for the antennas, these motions are close to the same size as the wavelength of the radiation they produce, and more compact designs require tuning units more substantial than the antenna itself.
They also discovered a smart way of tweaking the wavelength of the emitted radiation. As they switched the wavelength repeatedly during operation, it allowed them to transmit with a large bandwidth. This intelligent move is the key for them to achieve data transfer rates of more than 100 bits per second which is sufficient to send a simple text.
