Benjamin S.-Y. Ung

Mechanically tunable terahertz metamaterials

Electromagnetic device design and flexible electronics fabrication are combined to demonstrate mechanically tunable metamaterials operating at terahertz frequencies. Each metamaterial comprises a planar array of resonators on a highly elastic polydimethylsiloxane substrate. The resonance of the metamaterials is controllable through substrate deformation. Applying a stretching force to the substrate changes the inter-cell capacitance and hence the resonance frequency of the resonators. In the experiment, greater than 8% of the tuning range is achieved with good repeatability over several stretching-relaxing cycles. This study promises applications in remote strain sensing and other controllable metamaterial-based devices.

Experimental demonstration of reflectarray antennas at terahertz frequencies.

Reflectarrays composed of resonant microstrip gold patches on a dielectric substrate are demonstrated for operation at te rahertz frequencies. Based on the relation between the patch size and the reflectio n phase, a progressive phase distribution is implemented on the patch rray to create a reflector able to deflect an incident beam towards a predefine a gle off the specular direction. In order to confirm the validity of th e design, a set of reflectarrays each with periodically distributed 360 ×360 patch elements are fabricated and measured. The experimental results obta ined through terahertz time-domain spectroscopy (THz-TDS) show that up to n early 80% of the incident amplitude is deflected into the desired directi on at an operation frequency close to 1 THz. The radiation patterns of the reflec tarray in TM and TE polarizations are also obtained at different frequen cies. This work presents an attractive concept for developing components a ble to efficiently manipulate terahertz radiation for emerging terahertz com munications. OCIS codes:(300.6495) Spectroscopy, terahertz; (110.5100) Phased-a rray imaging systems; (240.6645) Surface differential reflectance. References and links 1. D. G. Berry, R. G. Malech, and W. A. Kennedy, “The reflectarr ay antenna,” IEEE Trans. Antennas Propag. 11, 645–651 (1963). 2. J. Huang and J. Encinar, Reflectarray Antenna . Wiley-IEEE Press, 2008. 3. J. P. Montgomery, “A microstrip reflectarray antenna elem ent,” Antenna Applications Symposium, University of Illinois (1978). 4. D. M. Pozar and T. A. Metzler, “Analysis of a reflectarray an tenna using microstrip patches of variable size,” Electron. Lett.29,657–658 (1993). 5. D. C. Chang and M. C. Huang, “Multiple-polarization micro strip reflectarray antenna with high efficiency and low cross-polarization,” IEEE Trans. Antennas Propag. 43,829–834 (1995). 6. J. P. Gianvittorio and Y. Rahmat-Samii, “Reconfigurable p atch antennas for steerable reflectarray applications,” IEEE Trans. Antennas Propag. 54,1388–1392 (2006). 7. J. Ginn, B. Lail, J. Alda, and G. Boreman, “Planar infrared binary phase reflectarray,” Opt. Express 33, 779–781 (2008). 8. J. Ginn, B. Lail, and G. Boreman, “Sub-millimeter and infr ared reflectarray,” U. S. Patent 7,623,071 B2 (2009). 9. R. D. Javor, X. D. Wu, and K. Chang, “Design and performance of a microstrip reflectarray antenna,” IEEE Trans. Antennas Propag. 43,932–939 (1995). 10. J. Encinar, M. Arrebola, L. F. de la Fuente, and G. Toso, “A transmit-receive reflectarray antenna for direct broadcast satellite applications,” IEEE Trans. Antennas P ropag.59,3255–3264 (2011). 11. L. Moustafa, R. Gillard, F. Peris, R. Loison, H. Legay, an d E. Girard, “The phoenix cell: a new reflectarray cell with large bandwidth and rebirth capabilities,” IEEE Anten nas Wirel. Propag. Lett. 10,71–74 (2011). 12. J. A. Encinar, “Design of a dual frequency reflectarray us ing microstrip stacked patches of variable size,” Electron. Lett.32,1049–1050 (1996). 13. J. A. Encinar, “Design of two-layer printed reflectarray s using patches of variable size,” IEEE Trans. Antennas Propag.49,1403–1410 (2001). 14. J. A. Encinar, “Recent advances in reflectarray antennas ,” Antennas and Propagation (EuCAP), 2010 Proceedings of the Fourth European Conference on (2010). 15. W. Hu, R. Cahill, J. A. Encinar, R. Dickie, H. Gamble, V. Fu sco, and N. Grant, “Design and measurement of reconfigurable millimeter wave reflectarray cells with nema tic liquid crystal,” IEEE Trans. Antennas Propag. 56, 3112–3117 (2008). 16. S. Ghadarghadr, Z. Hao, and H. Mosallaei, “Plasmonic arr ay nanoantennas on layered substrates: modeling and radiation characteristics,” Opt. Express 17, 18556–18570 (2009) 17. A. Ahmadi, S. Ghadarghadr, and H. Mosallaei, “An optical reflectarray nanoantenna: The concept and design,” Opt. Express18, 123–133 (2010). 18. N. M. Froberg, B. B. Hu, X.-C. Zhang, and D. H. Auston, “Ter ahertz radiation from a photoconducting antenna array,” IEEE J. Quantum Electron. 28, 2291–2301 (1992). 19. M. N. Islam, and M. Koch, “Terahertz patch antenna arrays for indoor communications,” Int. Conference on Next-Generation Wireless Systems 2006 (Dhaka, Bangladesh ) (2006). 20. K. Maki, T. Shibuya, C. Otani, K. Suizu, K. and Kawase, “Te rahertz beam steering via tilted-phase differencefrequency mixing,” Appl. Phys. Express 2, 022301 (2009). 21. Y. Monnai, V. Viereck, H. Hillmer, K. Altmann, C. Jansen, M. Koch, and H. Shinoda, “Terahertz beam steering using structured MEMS surfaces for networked wireless sens ing,” Ninth International Conference on Networked Sensing Systems (INSS) (2012). 22. T. Kleine-Ostmann and T. Nagatsuma, “A review on teraher tz communications research,” J. Infrared Millim. Terahz. Waves32, 143–171 (2011). 23. S. Lucyszyn, “Evaluating surface impedance models for t erahertz frequencies at room temperature,” PIERS Online 3, 554–559 (2007). 24. I. E. Khodasevych, C. M. Shah, S. Sriram, M. Bhaskaran, W. Withayachumnankul, B. S. Y. Ung, H. Lin, W. S. T. Rowe, D. Abbott, and A. Mitchell, “Elastomeric silicone s ubstrates for terahertz fishnet metamaterials,” Appl. Phy. Lett.100, 061101 (2012). 25. S. D. Targonski, and D. M. Pozar, “Analysis and design of a microstrip reflectarray using patches of variable size,” Antennas and Propagation Society International Sym posium, 1994. AP-S. Digest, 1820–1823 (1994). 26. M.-A. Milon, R. Gillard, D. Cadoret, and H. Legay, “Analy sis of mutual coupling for the simulation of reflectarrays radiating cells,” Proc. EuCAP 2006 , Nice, France, 1–6 ( 2006). 27. M.-A. Milon, D. Cadoret, R. Gillard, and H. Legay,“Surro unded-element approach for the simulation of reflectarray radiating cells,” IET Microw. Antennas Propag., 1, 289–293 (2007).Reflectarrays composed of resonant microstrip gold patches on a dielectric substrate are demonstrated for operation at terahertz frequencies. Based on the relation between the patch size and the reflection phase, a progressive phase distribution is implemented on the patch array to create a reflector able to deflect an incident beam towards a predefined angle off the specular direction. In order to confirm the validity of the design, a set of reflectarrays each with periodically distributed 360 × 360 patch elements are fabricated and measured. The experimental results obtained through terahertz time-domain spectroscopy (THz-TDS) show that up to nearly 80% of the incident amplitude is deflected into the desired direction at an operation frequency close to 1 THz. The radiation patterns of the reflectarray in TM and TE polarizations are also obtained at different frequencies. This work presents an attractive concept for developing components able to efficiently manipulate terahertz radiation for emerging terahertz communications.

Elastomeric silicone substrates for terahertz fishnet metamaterials

In this work, we characterize the electromagnetic properties of polydimethylsiloxane(PDMS) and use this as a free-standing substrate for the realization of flexible fishnet metamaterials at terahertz frequencies. Across the 0.2–2.5 THz band, the refractive index and absorption coefficient of PDMS are estimated as 1.55 and 0–22 cm−1, respectively. Electromagnetic modeling, multi-layer flexible electronics microfabrication, and terahertz time-domain spectroscopy are used in the design, fabrication, and characterization of the metamaterials, respectively. The properties of PDMS add a degree of freedom to terahertz metamaterials, with the potential for tuning by elastic deformation or integrated microfluidics.

Flexible terahertz metamaterials for dual-axis strain sensing

Utilizing an elastic polymer, we design and experimentally demonstrate a four-fold symmetric flexible metamaterial operating at terahertz frequencies. The fabricated metamaterials exhibit good stretchability and recoverability. Two independent resonances can be observed when the structure is probed with linearly polarized terahertz waves in two orthogonal axes. Applying a stretching force along a main axis causes an observable frequency shift in the corresponding resonance, with minimal effect on the other. This study suggests a possible application of flexible metamaterials for dual-axis strain sensing.

Low-cost ultra-thin broadband terahertz beam-splitter

A low-cost terahertz beam-splitter is fabricated using ultra-thin LDPE plastic sheeting coated with a conducting silver layer. The beam splitting ratio is determined as a function of the thickness of the silver layer--thus any required splitting ratio can be printed on demand with a suitable rapid prototyping technology. The low-cost aspect is a consequence of the fact that ultra-thin LDPE sheeting is readily obtainable, known more commonly as domestic plastic wrap or cling wrap. The proposed beam-splitter has numerous advantages over float zone silicon wafers commonly used within the terahertz frequency range. These advantages include low-cost, ease of handling, ultra-thin thickness, and any required beam splitting ratio can be readily fabricated. Furthermore, as the beam-splitter is ultra-thin, it presents low loss and does not suffer from Fabry-Pérot effects. Measurements performed on manufactured prototypes with different splitting ratios demonstrate a good agreement with our theoretical model in both P and S polarizations, exhibiting nearly frequency-independent splitting ratios in the terahertz frequency range.

Dual-Mode Terahertz Time-Domain Spectroscopy System

Terahertz time-domain spectroscopy (THz-TDS) systems traditionally operate in a single mode, either in reflection or transmission. In cases where the sample has nonunity permeability, measurements in both reflection and transmission geometries are required. The process of shifting and swapping the samples during an experiment increases the measurement uncertainty. This paper therefore presents a system where both reflection and transmission measurements can be performed simultaneously to reduce both experimental error and acquisition time. The measurement results are validated against findings in literature.

Measurement of linearity in THz-TDS

This article presents an approach to the measurement of the amplitude linearity in terahertz time-domain spectroscopy (THz-TDS) systems. The approach exploits a single wafer of high-purity float-zone silicon to produce multiple Fabry-Pérot reflections, which are stepwise attenuated and delayed. Comparison between the theoretical and experimental results can indicate a deviation in linearity.

A preliminary study of hydrogenation of oils using terahertz time domain spectroscopy

This paper presents a preliminary investigation to determine the extent at which terahertz time domain spectroscopy is able to detect the hydrogenation of unsaturated fats and oils within a simulated home cooking environment.

Comparative investigation of detection of melamine in food powders

Recently, there have been numerous food scares particularly with the production of milk powders for infants. This has been caused by the addition of excess melamine to increase the tested protein count of a powder. In this paper we investigate the potential of THz-TDS for use in food quality control and compare this technique to other established techniques.