The control of a send-receive path of any electronic employment in the certain range of radio frequencies is a rather difficult process. For example, mobile phones already have to be able to accept signals in the ranges of a system cellular communication work, GPS, Wi-Fi, 4G, and millimetric range 5G will be added to this list in the near future. And the devices of the so-called Internet of things will need coverage of a bigger number of frequency ranges. But the work in each of ranges demands antennas of various length and forms which are often great to be placed in the portable electronic device.
The simple exclusive antennas, used practically in all modern devices, consist of the only conducting element. They provide maximum efficiency when their length is equal to a half of wavelength of the radio signal radiated or accepted by them. But for the devices working in several ranges of frequencies, such a restriction becomes a serious problem.
“A traditional solution is the use of a bank of the switched filters together with the recustomized antenna or the multiband antenna” – tells Jacob Adams, an engineer from North Carolina State University, – “The above-mentioned solutions are rather bulky, their realization requires a lot of space. And one of the miniaturization directions is the use of the only element having ample opportunities to change-over”. This element is an antenna made of liquid metal, capable to be adjusted for work in the necessary range due to change of its length within a special capillary.
Similar antennas are not a novelty, but the realization of a similar technology did not make great success because for the management of length of a liquid metal column, tiny pneumatic pumps were used. And, you see, it’s not easy to integrate such a design into the structure of the consumer electronic device, say, of the mobile phone.
Researchers left the need to use pneumatic pumps by means of electrostatic forces which force liquid metal to move within a capillary in which the operating electrodes are introduced. The liquid metal, an alloy of gallium, can stretch or be reduced depending on polarity of the voltage metal attached to a column. In this case, electrochemical processes are used, positive tension causes formation of an oxide layer on a metal surface, lowering the forces of a superficial tension that allows metal to flow easily, without encountering resistance. The enclosed negative tension deletes a layer of oxides, forces of a superficial tension increase that leads to the reduction of metal column length.
The prototype of the adjusted liquid metallic antenna created by the researchers, reminds the mercury thermometer a lot. But, unlike the thermometer where the height of a column depends on the surrounding temperature, in this case voltage is used, where changing can be regulated with the high precision height of a liquid metal column in a capillary.
Such liquid antennas working in the centimetric range will have rather big sizes and they, most probably, will be separate components of radio-electronic devices. But the liquid antennas working in the millimetric range can be integrated directly on the crystals of specialized chips.
Besides the use in portable consumer electronics, similar technologies can bring huge benefit and in more serious areas, for example, in satellite communications, in radar systems and in military equipment where the antenna groups covering ranges from several megahertz to tens gigahertzes are used. “But all the same, the only adjusted element, in most cases, will never be able to block the necessary range” – tells Jacob Adams, – “However, the use of such elements will allow to significantly reduce the sizes of antenna fields, vessels antenna systems, planes and other equipment that needs coverage of a wide range of radio waves”.