Ultra-Stretchable Kirigami Piezo-Metamaterials for Sensing Coupled Large Deformations

Abstract

Mechanical metamaterials are known for their prominent mechanical characteristics such as programmable deformation that are due to periodic microstructures. Recent research trends have shifted to utilizing mechanical metamaterials as structural substrates to integrate with functional materials for advanced functionalities beyond mechanical, such as active sensing. This study reports on the ultra-stretchable kirigami piezo-metamaterials (KPM) for sensing coupled large deformations caused by in- and out-of-plane displacements using the lead zirconate titanate (PZT) and barium titanate (BaTiO₃ ) composite films. The KPM are fabricated by uniformly compounding and polarizing piezoelectric particles (i.e., PZT and BaTiO₃ ) in silicon rubber and structured by cutting the piezoelectric rubbery films into ligaments. Characterizes the electrical properties of the KPM and investigates the bistable mechanical response under the coupled large deformations with the stretching ratio up to 200% strains. Finally, the PZT KPM sensors are integrated into wireless sensing systems for the detection of vehicle tire bulge, and the non-toxic BaTiO₃ KPM are applied for human posture monitoring. The reported kirigami piezo-metamaterials open an exciting venue for the control and manipulation of mechanically functional metamaterials for active sensing under complex deformation scenarios in many applications.

Keywords: active sensing; bistable mechanoelectrical response; coupled large deformations; kirigami piezo-metamaterials (KPM).

Figure 1

Design and fabrication of the KPM. a) Fabrication process and SEM image of the PZT and BaTiO₃ rubbery films. b) Mechanism of the PZT and BaTiO₃ rubbery films in the initial, poled, stretched, and released states. Schematic illustrations of the kirigami patterns and deformation characteristics of the c) C‐KPM and d) R‐KPM.

Figure 2

Experimental setup and deformation analysis of the KPM. a) The cyclic tensile testing machine is used to apply the cyclic pullout displacement and record the reaction force, and the electrometer is used to collect the electrical signals generated by the C‐KPM and R‐KPM. b) Different deformation states of the C‐KPM during displacements from 0 to 8 cm. c) Deformation analysis of the symmetric ligaments in the C‐KPM. d) Deformation of the R‐KPM at the same states and the same displacement as the C‐KPM. e) Deformation analysis of the chiral ligaments in the R‐KPM. f) Coupled large deformations of the C‐KPM with the predefined displacement angles of 0°, 30°, 45°, and 60°.

Figure 3

Electrical response of the KPM. Voltage variations of the a) C‐KPM and b) R‐KPM during cyclical 7 and 10 cm displacements at a constant loading frequency of 1 Hz. c) Voltage variations of the C‐KPM and R‐KPM at cyclical displacement of 5 cm at 1–5 Hz. Current variations of the d) C‐KPM and e) R‐KPM at 1 Hz, 7 cm, and 10 cm cyclical displacements. f) Current variations of the C‐KPM and R‐KPM at 1–5 Hz, 5 cm cyclical displacement. g) Peak voltage‐displacement and h) peak current‐displacement relations of the C‐KPM and R‐KPM with different thickness t and width d (θ = 0°). i) Fatigue testing results of voltage for the C‐KPM under the 2000‐cycle out‐of‐plane displacement.

Figure 4

Mechanoelectrical response of the KPM. a) Comparison of the C‐KPM deformation in the FE models and experiments. Force‐displacement relationships of the C‐KPM with b) the thickness of t = 1 mm and ligament width of d = 5 mm and c) at the displacement angle of θ = 30°. d) Comparison of the maximum forces at the displacement of 8 cm from experiments and FE simulations for the C‐KPM under different displacement angles. e) Mechanoelectrical response (i.e., voltage vs force) of the C‐KPM with different thicknesses t and ligament widths d. f) Comparison of the R‐KPM deformation in the FE models and experiments. g) Force‐displacement relationship of the R‐KPM with the thickness of t = 1 mm and ligament width of d = 5 mm. h) Mechanoelectrical response of the same R‐KPM. i) Peak voltages for the C‐KPM under different displacement angles. j) Comparisons of the peak voltage and maximum stretching ratio between the KPM and published piezoelectric films with plate‐like or kirigami structures.^{[ 34} , ⁴³ , ⁴⁴ , ⁴⁵ , ⁴⁶ , ^{47 ]}

Figure 5

PZT and BaTiO₃ KPM sensors in active sensing. Schematic application scenarios and working mechanisms of the a) PZT KPM sensors for vehicle tire bulge monitoring and b) BaTiO₃ KPM sensors in portable wearable devices. c) Schematic diagram of the signal collection and transmission circuit. d) Field‐testing images of the PZT KPM sensors used for tire bulge monitoring. e) Field‐testing results of the voltage curve during the tire bulging deformation. f) Wireless monitoring systems consisted of the sensing module of the KPM sensors, the processing module of Arduino MEGA 2560 and the communication module of ESP8266. g) Nontoxic BaTiO₃ KPM sensors illustrated in the healthcare applications of human elbow posture monitoring under different bending angles. h) Electrical response of the BaTiO₃ KPM sensors under different bending angles.