Vibrating micro plates bring order to overcrowded radio spectrum

Oct 31, 2013
The two square rectangles in the center of this SEM picture are the two resonators.

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 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 now presented by the researchers are based on micromechanical and can be accurately tuned to the desired frequency.

One of the reasons for choosing a mechanical solution is that the conventional filter consists of an inductor and a capacitor, an 'LC circuit'. Especially a good quality inductor is hard to achieve on a chip. The result would be: separate LC circuits for each frequency band, mounted outside the chip, which would take up too much space. New solutions are already being sought all over the world. The current standard is the electromechanical filter called Surface Acoustic Wave filter, but this, too, requires too much space if you need several of them.

Vibration

The solution presented by the researchers consists of two mechanical resonators. They vibrate at an adjustable frequency thanks to the piezoelectric material PZT. This material is applied to metal. Normally, the vibrates perpendicular to the metal and the thickness of the layer determines the frequency. However,the frequency can be varied by making it vibrate in the same direction as the metal. Two resonators are used, which are not connected mechanically or electrically. By means of the intelligent handling of the input and output signals of the two resonators, adverse 'parasitic' effects are negated. This is done by subtracting the output signals, while the input signals are 'in phase'. The result is a selective filter - fourth order - that passes a limited part of the band and weakens the frequencies above and below. It can be accurately tuned with the vibrating frequencies of the two resonators. The filter presented by the researchers in Applied Physics Letters, operates at about 400 Megahertz. That is still too low for mobile applications, but new versions already reach higher frequencies, and Gigahertz frequencies needed for smartphones are feasible, according to the researchers.

The output signals of both resonators (red and purple). When one is subtracted from the other, a pass band remains. The difference in resonance frequencies defines the width of the pass band.

The researchers also expect that these resonators can be integrated on the chip or directly 'bonded' to the : 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 when needed.

Explore further: A new generation of storage—ring

More information: Yagubizade, H. et al. A 4th-order band-pass filter using differential readout of two in-phase actuated contour-mode resonators, Applied Physics Letters, 2013.

Related Stories

Making frequency-hopping radios practical

May 15, 2013

The way in which radio spectrum is currently allocated to different wireless technologies can lead to gross inefficiencies. In some regions, for instance, the frequencies used by cellphones can be desperately ...

Spirals of light may lead to better electronics

Sep 26, 2013

(Phys.org) —A group of researchers at the California Institute of Technology (Caltech) has created the optical equivalent of a tuning fork—a device that can help steady the electrical currents needed ...

'Nanoresonators' might improve cell phone performance

Aug 30, 2012

(Phys.org)—Researchers have learned how to mass produce tiny mechanical devices that could help cell phone users avoid the nuisance of dropped calls and slow downloads. The devices are designed to ease ...

Sensors for the real world

Nov 05, 2012

Over the last decade there has been an increased interest in developing resonators for gravitmetric sensing; however, the sensors' response to variations in temperature has prevented them from being used outside the laboratory. ...

Recommended for you

A new generation of storage—ring

22 hours ago

A bright synchrotron source that emits over a wide part of the electromagnetic spectrum from the infrared to hard X-rays is currently being built in Lund, Sweden. The MAX IV facility presents a range of technical ...

Universe may face a darker future

Oct 31, 2014

New research offers a novel insight into the nature of dark matter and dark energy and what the future of our Universe might be.

High-intensity sound waves may aid regenerative medicine

Oct 30, 2014

Researchers at the University of Washington have developed a way to use sound to create cellular scaffolding for tissue engineering, a unique approach that could help overcome one of regenerative medicine's ...

Formula could shed light on global climate change

Oct 30, 2014

Wright State University researchers have discovered a formula that accurately predicts the rate at which soil develops from the surface to the underlying rock, a breakthrough that could answer questions about ...

User comments : 1

Adjust slider to filter visible comments by rank

Display comments: newest first

beleg
not rated yet Oct 31, 2013
Why is the difference in frequencies being used and subtracted?
Use the differences in phase shift at the same frequencies and subtract instead.
The circuit implantation of this is realized without micro-mechanics at micron scaling.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.