2016 International Conference on Advanced Materials Science and Technology (AMST 2016)
ISBN: 978-1-60595-397-7
Novel Electrostatically Tunable Frequency Selective Surface with
PZT/FeGaB Films
Xi-xi FENG*, Jiang JIA, Yuan-yuan ZHANG and Hou-jun SUN
Beijing Key Laboratory of Millimeter Wave and Terahertz Techniques, Beijing Institute of
Technology, No.5 Zhongguancun South Street, Beijing, China
*Corresponding author
Keywords: Frequency selective
Magnetoelectric (ME) couplings.
surface
(FSS),
Tunable
devices,
PZT/FeGaB
films,
Abstract. Strong magnetoelectric (ME) coupling can be realized in multiferroic heterostructures,
which have led to a variety of devices. Here, a novel electrostatically tunable frequency selective
surface (FSS) with PZT/FeGaB films is reported, which shows a high resonant frequency tunability.
A high X to Ku band resonant frequency tunability of ∆f = 2.75 GHz or ∆f/f= 24% was demonstrated
in the FSS with PZT/FeGaB films, which was 10 times of the similar FSS structure with only FeGaB
film. This electrostatically tunable FSS with strong ME coupling will provide great opportunities for
more energy efficient, less noisy, compact and light-weight microwave devices with frequency
tunabilities.
Introduction
Frequency selective surface (FSS) is a periodic etching gap or paste metal patch unit on a
conductive metal surface, forming periodic "electric stator structure", which has the character of
electromagnetic wave reflection or transmission of according to its frequency [1]. Because of good
filtering properties, FSS is widely used in the various frequencies like microwave, millimeter wave,
infrared, and even light waves, receiving great attention in both military and civilian [2]. To obtain a
tunable property of the resonant frequency, FSSs with ferrite materials whose properties can be
controlled through the use of a DC magnetic bias field are investigated a lot in recent years [3-7].
Compare to conventional tunable magnetic microwave devices tuned by magnetic field,
electrostatically tunable multiferroic microwave devices are much more energy efficient, less noisy,
compact and light-weight[8].In recent decades, magnetoelectric effect in multiferroic materials has
attracted extensive attention owing to the upcoming demands for new-generation multi-functional
magnetoelectronic devices. This gives people a strong push to explore the multiferroic materials with
a effective coupling between electric and magnetic orderings, especially at room
temperature[9]-[11].According to A. E. Clark .etc[12], the FeGaB films constitute great candidates
for tunable ME microwave devices with combined narrow FMR linewidth, largeλs and the large
saturation magnetization.
In this paper, a novel electrostatically tunable frequency selective surface with PZT/FeGaB films is
designed and simulated. An X to Ku band resonant frequency tunability of ∆f = 2.75 GHz or ∆f/f =
24% was demonstrated in the simulation. Compared with the resonant frequency tunability of ∆f =
0.25 GHz or ∆f/f = 2.5% realized of the FSS with same sized FeGaB film only, the strong ME
coupling in PZT/FeGaB microwave multiferroic heterostructures and its high frequency tunability
was demonstrated well.
Design Methods
In this work, a ring-shaped FSS on Rogers 5870 substrate is used, with PZT/FeGaB films placed
above it. For ordinary ring-shaped FSS, the resonant frequency f can be calculated as:
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2πR=nλg
(1)
f=c/λg.
(2)
where R is the radius of the ring, n is the mode number, λg is the wave length and c is light velocity.
As is schematically shown in Fig. 1, the 4 mm×4 mm Rogers 5780 substrate with a thickness of 200
µm is used. A 200 nm ferromagnetic FeGaB film is assigned above it, and on the bottom is a 200 µm
ferroelectric PZT film. The ring-shaped copper is assigned between Rogers 5870 substrate and FeGaB
flim, inside radius R of which is 2.618 mm and the width w is 0.312 mm, whose resonant frequency is
calculated to be around 11GHz.
Figure 1. Top view and cross-section structure of the electrostatically tunable FFS with PZT/FeGaB films.
Because of the restricted condition of simulation software, the electric field applied on the PZT
film is not realized directly. As a replacement, we adjust the relative permeability of PZT in HFSS
simulation manually to simulate the induced effect of an extra electrostatic field. For real situations,
when piezoelectric or ferroelectric materials are assembled with magnetostrictive materials, the
magnetic moment of the material will change through the application of an external electric field. This
is a kind of product property by magnetostriction and piezoelectricity, which can be regarded as the
transfer of the mechanical energy. The induced mechanical stress can finally lead to a change in the
materials’ relative permittivity [13].
Simulation and Discussion
The proposed FSS were with PZT/FeGaB films simulated with Ansoft High Frequency Structure
Simulator (HFSS) 15.0, and sweep frequencies are investigated at 5-15GHz. The properties of PZT
and FeGaB are as shown in Table 1 and a bias magnetic field is applied along the the planar of ferrite.
Table 1. Material properties of PZT and FeGaB.
Material name
PZT
FeGaB
Relative permittivity
15
1
Material properties
Relative permeability
1
500
Saturation magnetization
0Guass
1500Guass
Figure 2. Transmission of the FFS with PZT/FeGaB films. The dc bias magnetic field is 50 Oe.
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Figure 2 shows the transmission coefficients of the FSS versus frequency when adjusting the
relative permittivity of PZT, which is equivalent to adjusting the voltage applied across the pzt. There
the magnetic bias field H0 is 50Oe. It can be observed that the resonant frequency f increases from
11.30 GHz to 13.98 GHz as the relative permittivity ε decreases from 20 to 8. The frequency
tunability can be observed as ∆f =2.68 GHz or ∆f/f =23%.
As the magnetic bias field H0 adjusted to 0 Oe, the transmission coefficients of our FSS with
PZT/FeGaB films changes slightly than before, which is shown in figure 3. The resonant frequency f
increases from 11.24 GHz to 13.99 GHz as the relative permittivity ε decreases from 20 to 8. The
frequency tunability can be observed as ∆f =2.75 GHz or ∆f/f = 24%. The 50Oe decrease of dc bias
magnetic field brings a little increasement for ∆f and ∆f/f.
Figure 3. Transmission of the FFS with PZT/FeGaB films. Thedc bias magnetic field is 0 Oe.
For comparison, the transmission coefficients of another FSS without PZT film is given as figure 4.
Scaling is did to ensure the unbaised resonant frequency remains around 11GHz.It can be seen that as
the magnetic bias field H0 increases from 0 Oe to 200 Oe, the resonance frequence changes from
10.35 GHz to 10.57 GHz. The frequency tunability without ME coupling can be observed as ∆f = 0.23
GHz or ∆f/f = 2.2% (around 10 percent of that of our FFS with PZT/FeGaB films).
Figure 4. Transmission of a ferromagnetic tunable FFS without PZT films.
Summary
In conclusion, a novel electrostatically tunable FSS with PZT/FeGaB films is designed and simulated.
With the strong ME coupling realized in our multiferroic heterostructures, a high X-band resonace
frequency tunability of ∆f = 2.75 GHz or ∆f/f = 24% was demonstrated. At the same time, a samilar
FSS structure with only FeGaB film is simulated for comparison and the new resonace frequency
tunability appears to be weaken by 90%. This novel electrostatically tunable FFS model provides
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great opportunities for tunable ME microwave devices which are much more energy efficient, less
noisy, compact and light-weight.
Acknowledgement
The authors would like to thank Beijing Institute of Technology for the technical support to carry out
the research.
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