Slide 1Tunable Terahertz Metamaterials by means of Piezoelectric MEMS Actuators
Antonios X. Lalas, Nikolaos V. Kantartzis, and Theodoros D. Tsiboukis
Telecommunications Division Department of Electrical and Computer Engineering,
Aristotle University of Thessaloniki, Thessaloniki GR-54124, GREECE
META 2014, 20-23 May, Singapore
Motivation and objective.
Piezoelectric MEMS microgripper.
Reconfigurable THz metamaterial.
Conclusions and future aspects.
Motivation and objective
Motivation:
Metamaterials, exhibit extraordinary electromagnetic properties not available in nature.
Real-life configurations are limited, mainly due to the lack of a wide spectral bandwidth, especially in the THz regime.
RF-MEMS provide efficient solutions, acting as tuning mechanisms in contemporary RF technology.
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Microelectromechanical systems (MEMS)
Structures exhibiting dimensions between 1μm and 1 mm, that combine electrical and mechanical components to realize complex and controllable functions.
They are considered as transducers, since they absorb energy in one form and convert it to an other form.
Two main categories are denoted, i.e. sensors and actuators.
Several coupled physical phenomena must be considered, when analyzing a MEMS device.
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A fragment of a piezoelectric material can be considered as a voltage-driven actuator.
Piezoelectric MEMS microgripper
Design parameters: L1 = 2 μm, L2 = 8 μm,
L3 = 6 μm, w1 = w2 = 1 μm, g = 2 μm
Implementation Materials: Metal parts: Gold
Piezoelectric Material: Lead Zirconate Titanate (PZT-5H)
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Principle of operation
Electrical: An electrostatic field is created by setting a potential difference between the edges of the piezoelectric material.
Piezoelectric: A strain due to the piezoelectric effect is generated resulting in piezoelectric expansion of the actuator.
Structural: A deflection occurs owing to the actuator’s expansion and thus the arms are deflected towards each other, resulting in gripping procedure.
Piezoelectric MEMS microgripper
Reverse procedure: When the bias voltage is decreased, or reversed, the contraction of the device releases an object.
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Total displacement distribution on the actuator (in μm) at the actuation voltage of 200 V
Piezoelectric MEMS microgripper
Tip displacement vs actuation voltage
Maximum displacement ~ 0.162 μm @ 220 V
Minimum displacement ~ -0.165 μm @ -220 V
Piezoelectric MEMS microgripper
Reconfigurable THz metamaterial
Characterization of metamaterials
Our design approach focuses mainly on tunable MNG and ENG marerials, but DNG configurations are, also, feasible.
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Similar performance to an equivalent LC network.
A robust homogenization method is utilized to retrieve the constitutive effective parameters of the proposed metamaterials.
To extract the S-parameters, a parallel-plate waveguide approach is adopted, which requires the use of PEC and PMC boundary conditions.
Conventional metamaterial unit cell
META 2014, 20-23 May, Singapore
• Piezoelectric actuators enable fine tuning.
• A bias network is also necessary for applying the actuation voltage.
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Reconfigurable THz metamaterial
Design parameters: h1 = 5 μm, h2 = 3 μm, α = 18 μm, Gold layer’s thickness = 0.4 μm,
PZT-5H layer’s thickness = 0.4 μm, Si3N4 substrate’s thickness = 2 μm
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Principle of operation
When a certain voltage is applied, the resulting piezoelectric expansion or contraction, deforms the structure and the gaps are shortened or enlarged, respectively.
A shortened or enlarged gap results in increased or decreased capacitance and therefore a frequency swift is revealed.
Variations in voltage levels introduce tunable gaps and as a consequence a programmable SRR.
Reconfigurable THz metamaterial
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As the actuation voltage increases from -200 V to 200 V, a shift at the resonant frequency
is achieved.
Reconfigurable THz metamaterial
Similar deductions are drawn from the shift of the real part of
the effective magnetic permeability.
Electric field snapshots
Reconfigurable THz metamaterial
Actuation Voltage (V)
Frequency Regions Start (THz) End (THz) BW (GHz)
-200 4.1807 4.1813 0.6 -100 4.1760 4.1770 1.0
0 4.1372 4.1389 1.7 100 4.1083 4.1104 2.1 200 4.0396 4.0424 2.8
The narrow bandwidth of 1.7 GHz, is artificially extended to 141.7 GHz, offering an improvement of 83 times magnification.
The maximum values occur in the vicinity of
the gap yielding an MNG performance.
Vact = -200 @ 4.181 THz Vact = 200 @ 4.041 THz
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Surface current distribution
200 V.
Reconfigurable THz metamaterial
The maximum value is obtained upon the surface of the SRR and especially the inner part of the resonator, denoting the presence of an MNG resonance.
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Rotated orientation of the complex medium
• The wave is rotated 90o in comparison to the initial orientation.
• The electric field is perpendicular to the piezoelectric actuators, while the magnetic field is perpendicular to the loops.
An ENG THz resonance of the complex medium is associated with this topology.
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As the actuation voltage increases from -200 V to 200 V, a shift at the resonant frequency
is observed.
Rotated orientation of the complex medium
A bandwidth enhancement of the real part of the effective electric
permittivity is also observed.
Electric field snapshots
Actuation Voltage (V)
Frequency Regions Start (THz) End (THz) BW (GHz)
-200 4.1842 4.2229 38.7 -100 4.1772 4.2263 49.1
0 4.1331 4.1899 56.8 100 4.1001 4.1598 59.7 200 4.0253 4.0832 57.9
The narrow bandwidth of 56.8 GHz, is artificially extended to 201 GHz, offering an improvement of 253.9%.
The maximum values are located at the half part of the resonator, thus displaying the
ENG behavior.
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The maximum value is observed only upon the half portion of the SRR. Thus, the unit cell acts as a metal
wire, sustaining an ENG resonance.
Rotated orientation of the complex medium
Surface current distribution
200 V.
Possible applications
The reconfigurable unit cells exhibit MNG behavior as well as ENG performance depending on the orientation of the device.
The design of several implementations, such as tunable THz filters and modulators is feasible.
Antenna configurations exploiting controllable ground planes or reconfigurable reflectors are also possible.
META 2014, 20-23 May, Singapore
An elaborated multiphysics investigation concerning the performance of the piezoelectric MEMS microgripper has been successfully conducted.
A novel design incorporating the MEMS microgripper into metamaterial unit cells has been proposed, achieving tunability and overcoming bandwidth restrictions.
The response of the complex medium with a different orientation is also examined.
Future investigation involves modeling of combined electrostatic and electrothermal RF-MEMS as tuning components.
A detailed study extended in more complex metamaterial unit cells.
Conclusions and future aspects