Despite the advancements in flexible sensors over the past decade, accurately measuring complex deformation caused by forces or strains from multiple axes remains a challenge due to the limitations in detecting multi-axial stimuli independently.
One of the main obstacles to achieving independent perception of biaxial stimuli is the Poisson's effect in sensing materials. To address this issue, researchers have turned to
However, creating ZPR elastomer membranes is difficult due to the incompressible property and nearly 0.5 Poisson's ratio of elastomers. In a recent study led by Prof. Hao Wu of Huazhong University of Science and Technology, it was proposed that a combination of traditional positive Poisson's ratio (PPR) structures and negative Poisson's ratio (NPR) structures could achieve a ZPR structure.
The team discovered that the Poisson's ratio of a hybrid structure was the sum of the individual structures. By varying the feature size and width of the hybrid structure, the Poisson's ratio could be adjusted between positive and negative values.
Through finite element analysis, the researchers identified the optimal parameters for creating ZPR membranes. The PDMS membrane with a hybrid structure demonstrated a Poisson's ratio of 0.07, compared to 0.43 for a PDMS membrane without the hybrid structure.
The ZPR flexible sensors based on these membranes were able to accurately detect uniaxial stimuli and independently detect biaxial stimuli. When stretched along one axis, the sensors showed a linear increase in electrical resistance, while the resistance along the perpendicular axis remained relatively unchanged.
This allowed the sensors to independently detect biaxial stimuli, making them suitable for use in complex deformation scenarios such as robotic manipulation and locomotion. They can accurately measure contact forces, normal bending of fingers, and unexpected collisions with obstacles.
In addition, the ZPR flexible sensors can also detect the distance and direction of movement in soft robots. With their exotic sensing capabilities, these sensors have potential applications in healthcare, human-machine interfaces, and robotic tactile sensing. The study was published in the National Science Review journal.