Abstract-Injection Molding of Free-Standing, Three-Dimensional, All-Metal Terahertz Metamaterials

Full Paper

Injection Molding of Free-Standing, Three-Dimensional, All-Metal Terahertz Metamaterialshttp://onlinelibrary.wiley.com/doi/10.1002/adom.201400094/abstract

1. Jinqi Wang¹, 
2. Shuchang Liu¹, 
3. Sivaraman Guruswamy² and
4. Ajay Nahata^1,*

Article first published online: 17 APR 2014

DOI: 10.1002/adom.201400094

© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Issue

Advanced Optical Materials

Early View (Online Version of Record published before inclusion in an issue)

Fabrication of free-standing two- and three-dimensional terahertz meta­materials is demonstrated via injection molding of gallium, a metal that melts at temperatures just slightly above room temperature. Molds are created by inscribing the desired microchannel geometries in one or two polydimethylsiloxane (PDMS) films using conventional soft lithography techniques and then reversibly bonding the two films together using van der Waals forces. After heating gallium above its melting point (∼30 °C), the liquid metal is injected into the mold. Surprisingly, the metal does not solidify even after cooling the filled mold at −16 °C for 24 h. However, when the liquid metal comes into contact with solid gallium at room temperature, the entire metal device solidifies within the mold immediately. The PDMS films can then be peeled away, yielding a free-standing solid gallium structure. A 2D split ring resonator-based metamaterial is fabricated and three different approaches for creating 3D metamaterials are demonstrated: a multilayer stack, a manually folded structure that maintains its shape after folding, and a directly injection molded 3D structure. The transmission properties of these devices are measured using terahertz time-domain spectroscopy and are shown to not suffer from limitations imposed by substrates.

Abstract-Reconfigurable terahertz metamaterial device with pressure memory

Jinqi Wang, Shuchang Liu, Sivaraman Guruswamy, and Ajay Nahata  »View Author Affiliations

Optics Express, Vol. 22, Issue 4, pp. 4065-4074 (2014)
http://dx.doi.org/10.1364/OE.22.004065

We demonstrate a liquid metal-based reconfigurable terahertz (THz) metamaterial device that is not only pressure driven, but also exhibits pressure memory. The discrete THz response is obtained by injecting eutectic gallium indium (EGaIn) into a microfluidic structure that is fabricated in polydimethylsiloxane (PDMS) using conventional soft lithography techniques. The shape of the injected EGaIn is mechanically stabilized by the formation of a thin oxide surface layer that allows the fluid to maintain its configuration within the microchannels despite its high intrinsic surface energy. Although the viscosity of EGaIn is twice that of water, the formation of the surface oxide layer prevents flow into a microchannel unless a critical pressure is exceeded. Using a structure in which the lateral channel dimensions vary, we progressively increase the applied pressure beyond the relevant critical pressure for each section of the device, enabling switching from one geometry to another (split ring resonator to closed ring resonator to an irregular closed ring resonator). As the geometry changes, the transmission spectrum of the device changes dramatically. When the external applied pressure is removed between device geometry changes, the liquid metal morphology remains unchanged, which can be regarded as a form of pressure memory. Once the device is fully filled with liquid metal, it can be erased through the use of mechanical pressure and exposure to acid vapors.

© 2014 Optical Society of America