To download the latest issue
Nov 8th, 2013
Vibrating microplates bring order to overcrowed radio spectrum
GSM, WiFi, Bluetooth, 4G, GPS: a smartphone already has to handle many wireless standards. And this number will only increase further. There are still no good filters to keep all those future standards separate. Researchers at the MESA+ Institute for Nanotechnology have taken an important step with a new type of filter, based on micromechanics. They have published their finding in Applied Physics Letters.
Filters that can be accurately tuned to the frequency band you want to receive as a user are becoming increasingly important. Otherwise, if a nearby signal is much stronger, it drowns out the signal you want to receive. The number of available frequencies is limited, so it is becoming ever busier. Intelligent use of the airwaves, by utilising every available piece, is becoming more important. The filters now presented by the researchers are based on micromechanical resonators and can be accurately tuned to the desired frequency.
The two rectangles in the center of this SEM (Scanning Electron Microscopy) image are the resonators, together forming a band-pass filter
Output signal of one resonator is subtracted from the other (purple and red, with at the peak their resonance frequencies) so that a narrow pass-band is formed, determined by the difference between both frequencies. Lower and higher frequencies are filtered out adequately.
The researchers also expect that these resonators can be integrated on the chip or directly ‘bonded’ to the chip: they are much smaller than inductors. It therefore becomes possible to apply fifty resonator pairs, which facilitates flexible use of frequencies. This is needed, for example, in ‘cognitive radio’, that uses each piece of free space as it becomes available and then jumps to another frequency when needed.
The research was conducted by the Transducers Science and Technology Group of the University of Twente MESA+ Institute for Nanotechnology in collaboration with the CTIT Institute Integrated Circuit Design group. There was also cooperation with the spinoff company SolMateS, which is specialised in making piezoelectric layers on chips. The project is financed by Dutch Technology Foundation STW.
More MEMS news