INITIAL DESIGN & ASSUMPTI

ONS

MODELING &

OPTIMIZATION

FABRICATION &

TESTING

COMPARISON OF

SIMULATION TO

EXPERIMENT

Design of a Novel Microfabricated Antenna for Use in Lossy Media

Tom Sanders1, Maximilian Scardelletti2, Rocco Parro3, and Christian Zorman3

1Department of Physics, Case Western Reserve University2Electron and Optical Device Branch, NASA Glenn Research Center

3Department of Electrical Engineering and Computer Science, Case Western Reserve University

a.) b.)

c.) d.)

Figure 3. a.) and b.) show respectively the geometry of a 168mm-long square-spiral microstrip antenna and a 196mm-long square-spiral antenna; while c.) and d.) show respectively the scattering parameters (S11) for the 168mm-long and 196mm-long antennas. Both simulated and experimental data is shown for antennas in air, while simulated data is shown for antennas in saltwater. Discrepancies between simulated and experimental data are most likely due in large part to lack of a filled via connecting the microstrip and ground plane in the current test antennas.

ABSTRACT

Microelectromechanical systems (MEMS) technology has advanced to the point where wireless systems that incorporate microfabricated, thin film antennas are beginning to emerge; especially for applications were wired systems are not practical options.1-5 This project involves the design and optimization of a rugged, microfabricated antenna intended for use in harsh aqueous environments (i.e. saltwater solution) using a combination of numerical simulations and device testing. The antenna is fabricated using standard lithographic microfabrication techniques and uniquely packaged using thin film silicon carbide in order to protect it from the structural degradation that otherwise would result naturally in solution.

MATERIALS AND METHODS

As previously mentioned, this project involved the integration of numerical simulation and experimental characterization of microfabricated devices (see Fig. 1). Electromagnetic simulations were carried out using the High Frequency Structure Simulation (HFSS) software suite by Ansoft Corp. Simulation-based designs were fabricated using standard microfabrication techniques (see fabrications sequence below). Experimental data will be used to motivate the succeeding round of designs.

Device Fabrication Sequence:1) Polyimide substrate, 3 mil (0.0762mm) thick2) Photoresist application by spin-coating3) Resist patterning using optical photolithography4) Pattern development using wet chemical etch5) Sputter deposition of gold cladding layers6) Resist lift-off to produce patterned antenna7) Via formation and back-filling for grounding pin8) Silicon carbide deposition using PECVD

PRELIMINARY CONCLUSIONS

We have constructed several antennas which are currently undergoing experimental testing. Based upon our preliminary results, we can draw several conclusions:

• Fabrication of antennas on polyimide substrates can be accomplished using available microfabrication resources

• Microstrip antennas printed on polyimide perform in useful and predictable manner

• Current numerical models using HFSS provide an accurate means of predicting antenna performance in air

FUTURE WORK

Continued experimental testing will allow us to expand our understanding of current and future microstrip antennas of this type. Further tests and procedures will likely include:

• Adding grounding pins and silicon carbide cladding layers to the current test antennas in order to more fully explore their behavior

• Antenna testing within a saltwater bath in order to evaluate antenna performance and the accuracy of our numerical simulations

• Verifying antenna durability while submerged in saltwater bath

ACKNOWLEDGEMENTS

I would like to thank the staff of the NASA GRC’s Microfabrication Facility, in particular Nick Varaljay and Elizabeth McQuaid for their CAD and fabrication efforts.This project was funded in partby the NASA Glenn Research Center's Independent Research and Development (IR&D) Fund. 

REFERENCES

[1] Felix A. Miranda, Rainee N. Simmons, and David G. Hall. Radio and Wireless Conference, IEEE. 203- 206(2004)19.[2] P. Soontornpipit, C.M Furse, and Y. Chung Chung. IEEE Transactions on Microwave Theory and Techniques, Vol. 52, No. 8, Aug. 2004.[3] C.M. Lee, T.C. Yo, and C.H. Luo. “Compact broadband stacked implantable antenna for biotelemetry with medical devices.” WAMI Conference, Nov. 2006. [4] Jaehoon Kim and Yahya Rahmat-Samii. IEEE Transactions on Microwave Theory and Techniques, pg 1934- 1943, Volume: 52, Issue: 8, Part 2, Aug. 2004.[5] William G. Scanlon, J. Brian Burns, and Noel E. Evans. IEEE Transactions on Biomedical Engineering, pg 527-534 Volume: 47, Issue: 4, Apr 2000.

DEVICE DESCRIPTION

Microstrip antennas, sometimes known as printed antennas, are a type of simple microfabricated antenna. The microstrip antennas employed in this study use a thin, metallic conducting layer patterned into a thin strip atop a solid dielectric layer. The antenna is grounded through the substrate to a metallic grounding plane. An electrical signal sent into the microstrip generates high electric fields, with field lines terminating at the metallic grounding plane.

Device Design Summary:1) Microstrip-PIFA design in the form of a square spiral2) Gold conducting microstrip and grounding plane3) Flexible polymeric substrate (polyimide)4) Amorphous silicon carbide cladding layer5) Resonant peaks at ~500-600 MHz in air6) Resonance expected at ~300-400 MHz in saltwater

PRELIMINARY RESULTS

Figure 1. Design & Optimization Process.

Figure 2. Cross-sectional schematic of a microstrip, grounding plane and dielectric substrate. Field lines are a guide to the eye.