New Type of Filter May Help Bring Order to Crowded Radio Spectrum

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Scientists from the Netherlands have developed a new type of filter based on micromechanical resonators they say is ideal for maintaining order amidst the expected future growth of frequency standards.


According to researchers at the MESA+ Institute for Nanotechnology at the University of Twente, the new solution consists of two mechanical resonators that vibrate at an adjustable frequency thanks to the piezoelectric material zirconate titanate (PZT), which is applied to metal.

Vibrating-Microplates_SEM_347x320_2014aAccording to the study’s abstract, “each resonator consists of a 500 nm pulsed-laser deposited lead PZT thin-film on top of a 3 μm silicon (PZT-on-Si).  The resonators are actuated in-phase, and their outputs are subtracted. Utilizing this technique, the feed-through signals are eliminated while the outputs of the resonators are added up constructively, due to the phase difference between the two output signals. The band-pass filter is presented using 50 Ω termination with a bandwidth of approximately 3.9 MHz and 43 dB stopband rejection.”

“Normally, the piezoelectric material 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,” the researchers explained.

“This technique provides further opportunities for MEMs filter design in addition to existing methods [such as] mechanical and/or electrical coupling,” the researchers add in their paper’s abstract. “It also resolves the design issue associated with high feed-through when exploiting piezoelectric materials with high-dielectric constant like PZT.”

Graph_Narrow-pass-band_437x320_2014aWhile the filter presented in the research operates at approximately 400 MHz and is thus too low for mobile applications, higher frequencies needed for smartphones are feasible, according the researchers. In addition, because the resonators are small in size, they can be integrated on the chip or directly bonded to it in large numbers, allowing for flexible use of frequencies.

The research was conducted by the University of Twente team in collaboration with CTIT Institute’s Integrated Circuit Design group and SolMateS, which specializes in making piezoelectric layers on chips. Their research is published in the journal Applied Physics Letters.

Article: ITEM Media / Aliza Becker
Editor: M. Danmole’
Image: CSIR / UT

Bob Cole