Testing of Flexible Metamaterial RF Filters Implemented through Micromachining LCP Substrates. Jonathan Richard Robert Dean Michael Hamilton

Transcription

1 Testing of Flexible Metamaterial RF Filters Implemented through Micromachining LCP Substrates Jonathan Richard Robert Dean Michael Hamilton

2 Metamaterials Definition Metamaterials exhibit interesting properties not readily observed in nature These properties emerge due to specific interactions with electromagnetic fields or due to external electrical control.

3 Introduction to Metamaterials Double Negative materials a.k.a. Left handed Has negative index of refraction Use of specially built structures Special structures use normal materials such as Rogers board, LCP, and Polyimides.

4 Combining Technologies Smaller feature size More complex structures Additional materials with useful properties Rigid or flexible substrates Enhanced Devices Integrated electronics Metamaterials MEMS

5 Common Uses Mirrors and lenses Transmission Lines Filters Invisibility cloaks

6 Cloak Structure Physical Layout E field view with and without structure Note: Only works at small frequency range and for one type of EM wave (i.e. TE01)

7 Common Filter Structures Split Ring Resonators (SRR) Complementary Split Ring Resonators (CSRR) Bandwidth is narrow Must be electrically small for lumped element assumptions Lumped element parameters derived from empirical data

8 CSRR Structure Lumped Element Representation Cg = Gap Capacitance Lc and Cc represent the resonator as a tank circuit L and C relate to the line per unit length Physical Layout Orange = ground plane White = etch off ground plane Blue = metal on surface

9 CSRR Gap Capacitance Effect No Gap Band Stop Gap Band Pass

10 Metamaterial Simulations ADS Momentum uses method of moments CSRR arrays constructed in ADS layout Frequency sweep and calculate S parameters 10 Element Array Single Element

11 Simulation Results (10 Element Array) Expected bandpass filter response

12 LCP Fabrication Overview Place mask on Liquid Crystal Polymer (LCP) with photolithography process Copper etching techniques LCP etching techniques

13 Photolithography Process Inspect and clean substrate with HCl bath Add HMDS to promote adhesion Spin on photoresist UV expose PR Develop PR

14 Copper Etching Before etching, cover opposite side with tape or photoresist since LCP comes double clad with copper Wet etching is isotropic which is accounted for with photolithography mask Slower wet etching causes less variance across the substrate Therefore an LCP with thin Cu cladding is desirable

15 Copper Etching Continued Over etched CSRR etched transmission gap

16 LCP Etching After copper has been fully removed where desired, E beam Al onto substrate Add mask using photolithography process Etch thin film Al mask with highly select etchant (PR developer) Use O 2 RIE to remove LCP followed by chemical Al mask removal Realizes holes and vias in metamaterials structures

17 Testing Procedure Setup Since the T lines were impedance matched to 50Ω, sma connectors could be easily connected Provide extra T line on masks to help with soldering and providing more surface area between LCP and Cu End Launch Connectors simplified testing and provided accurate results

18 Testing Procedure Short/open/load procedure Keep hands away from LCP and connectors during data capture to avoid stray capacitance Elevate LCP into the air to avoid affecting fringing capacitance for air calibration Test of flat PCB section Use PVC pipe of various radii to perform flexibility tests

19 T Line Calibration Air calibration PVC calibration

20 Multiple filters were flexed over 6 different sized pvc pipes Tested with respect to T line orientation both up and down Larger radii approached being flat Flexibility Testing Number PVC Diameter 1/2" 3/4" 1" 1 1/4" 1 1/2" 2" Radius of Curvature in inches

21 Testing Results Expected bandpass response observed Slightly lower frequency than simulation Flexing up or down had little effect on frequency response ½ PVC pipe flex testing: S21 (db) /2" pvc pipe S21 S21 - Cal down S21 - Cal up S21 - down 1 a S21 - down 1 b S21 - up 1 a S21 - up 1 b Frequency (GHz)

22 Applications Quality passive high order filters on flexible substrates Wearable electronics Flexible electronics RF cloaking Conformal to airfoils or vehicle bodies Reduction of radar cross section EMI/EMC improvement

23 Conclusions RF metamaterials possess interesting and useful properties Combining with MEMS technology enhances the usefulness of metamaterials LCP is a flexible substrate material with excellent RF properties RF metamaterials on flexible LCP substrates yield RF filters that can be conformably attached to nonplanar surfaces

24 Thanks