Abstract
In this paper, we proposed a stretchable radio frequency (RF) sensor to detect strain direction and level. The stretchable sensor is composed of two complementary split ring resonators (CSRR) with microfluidic channels. In order to achieve stretchability, liquid metal (eutectic gallium-indium, EGaIn) and Ecoflex substrate are used. Microfluidic channels are built by Ecoflex elastomer and microfluidic channel frames. A three-dimensional (3D) printer is used for fabrication of microfluidic channel frames. Two CSRR resonators are designed to resonate 2.03 GHz and 3.68 GHz. When the proposed sensor is stretched from 0 to 8 mm along the +x direction, the resonant frequency is shifted from 3.68 GHz to 3.13 GHz. When the proposed sensor is stretched from 0 to 8 mm along the −x direction, the resonant frequency is shifted from 2.03 GHz to 1.78 GHz. Therefore, we can detect stretched length and direction from independent variation of two resonant frequencies.
Highlights
In order to realize stretchable features, depositing thin-film metals on elastomers [1,2,3,4,5,6,7], filling microfluidic channels with conducting materials [8,9] and Deep Reactive Ion Etching (DRIE) of silicon [10] are typically used
A radio frequency (RF) complementary split ring resonator (CSRR) stretchable sensor sensor is proposed in order to detect strain level
The proposed sensor consists of the Ecoflex layers with microfluidic channel
Summary
In order to realize stretchable features, depositing thin-film metals on elastomers [1,2,3,4,5,6,7], filling microfluidic channels with conducting materials [8,9] and Deep Reactive Ion Etching (DRIE) of silicon [10] are typically used. A common way to fabricate microfluidic channels is sealing a substrate (e.g., glass or PDMS (polydimethylsiloxane)) [11,12,13,14]. This is realized by special methods such as thermal evaporation, electro- deposition, e-beam evaporation, sputtering, patterning the metal (lithography), spin coating and ultraviolet exposure. Because CSRR is usually etched on the ground plane of a substrate, it does not require additional area. It has the benefit of size reduction. In case of flexible and stretchable applications, the filling of microfluidic channels with conductive material, liquid metal (eutectic gallium-indium, EGaIn, Ga 75.5% and In 24.5%) has been widely used because it is non-toxic and easy to inject into a microfluidic channel [22,23,24]
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