Strain-Insensitive Hierarchically Structured Stretchable Microstrip Antennas for Robust Wireless Communication

Abstract

As the key component of wireless data transmission and powering, stretchable antennas play an indispensable role in flexible/stretchable electronics. However, they often suffer from frequency detuning upon mechanical deformations; thus, their applications are limited to wireless sensing with wireless transmission capabilities remaining elusive. Here, a hierarchically structured stretchable microstrip antenna with meshed patterns arranged in an arched shape showcases tunable resonance frequency upon deformations with improved overall stretchability. The almost unchanged resonance frequency during deformations enables robust on-body wireless communication and RF energy harvesting, whereas the rapid changing resonance frequency with deformations allows for wireless sensing. The proposed stretchable microstrip antenna was demonstrated to communicate wirelessly with a transmitter (input power of − 3 dBm) efficiently (i.e., the receiving power higher than − 100 dBm over a distance of 100 m) on human bodies even upon 25% stretching. The flexibility in structural engineering combined with the coupled mechanical–electromagnetic simulations, provides a versatile engineering toolkit to design stretchable microstrip antennas and other potential wireless devices for stretchable electronics.

Standalone stretchable RF systems based on asymmetric 3D microstrip antennas with on-body wireless communication and energy harvesting

“…The measured S11 curves of all three 3D microstrip antennas first shift to the high frequency (blueshift) in the first stage before the applied strain reaches the prestrain, which is then followed by a shift to the low frequency (redshift). The blueshift in the 1 st stage results from the increased effective dielectric constant from the reduced air gap between the arched patch and substrate (Figure S5), whereas the redshift in the 2 nd stage can be explained by the increased length of the patch as in previous studies [29,32]. In contrast, their 2D counterpart shows a decreased resonant frequency as the tensile strain is increased.…”

“…Another important consideration for stretchable antennas to be used on the body is the effect from the lossy human tissues [24,25], which drastically degrade the radiation performance to result in low on-body radiation efficiency. Compared with the bow-tie or dipole antennas [26][27][28] that do not have a ground plane, the antennas with a ground plane such as microstrip patch antennas [29][30][31] are less affected by the lossy tissues, manifested by a negligibly small change of S11 curves and radiation patterns. They also correspond to a low specific absorption rate (SAR), which is important for wearable RF applications.…”

Stretchable 3D Wideband Dipole Antennas from Mechanical Assembly for On-Body Communication

“…At a distance of 1 m, the onbody degradation in the optimized "3D_full" antenna is only 3 dB, which is much smaller than that of 16 dB in the 2D counterpart (Figure S16). This degradation is even comparable to that of 3 dB from the stretchable microstrip patch antenna that is known for good on-body performance 19 , showcasing the excellent on-body performance of the "3D_full" dipole antenna. The measured radiation pattern of the "3D_full" dipole antenna also shows a higher front-to-back ratio of 3.2 dB (more radiation along +z direction) than that of 1.1 dB from its 2D counterpart likely contributed by the air gap from the 3D structure (Figure S17).…”

“…12 Attempts to address this issue include the exploration of a wideband design in stretchable dipole antennas 18 or strain-insensitive stretchable microstrip antennas with a hierarchical structure. 19 The former couples two resonances from two pairs of radiation arms for a large operational band even under deformations, whereas the latter uses the mechanical assembly to generate the three-dimensional (3D) hierarchical structure. The wide bandwidth of the antenna also allows it to combine the RF energy over its wideband into a usable DC power (with the aid of a rectifier) at a much higher effective conversion efficiency, which is particularly important to harvest the ambient RF energy at typical radio signal levels.…”

Controlled Bi-Axial Buckling and Postbuckling of Thin Films Suspended on a Stretchable Substrate with Square Prism Relief Structures

“…Stretchable electronics holds great promise for various emerging applications, including flexible displays [Chen and Liu, 2013;Kwon et al, 2017;, solar cells [Hou et al, 2019;He et al, 2021;Wang et al, 2021], conformable sensors [Zheng and Cheng, 2019;, implantable transient electronics [Hwang et al, 2012;Hong et al, 2019;Song et al, 2019;Jiang et al, 2020;Lu et al, 2021], eye cameras [Song et al, 2013], stretchable antennas [Zhu and Cheng, 2018;Zhu et al, 2019;Xu et al, 2021;Zhu et al, 2021a;Zhu et al, 2021b] and medical monitoring devices [Chen et al, 2019;Park et al, 2020;Rwei et al, 2020]. One recent emphasis of stretchable electronics focuses on the design and manufacturing of novel structures at different levels for achieving high stretchability in the resulting electronic devices, including unfastened fractal serpentine interconnects [Huang et al, 2019;Liu et al, 2019;Feng et al, 2020;Nie et al, 2020],…”