Ultra-High Sensitivity Anisotropic Piezoelectric Sensors for Structural Health Monitoring and Robotic Perception

Abstract

Monitoring minuscule mechanical signals, both in magnitude and direction, is imperative in many application scenarios, e.g., structural health monitoring and robotic sensing systems. However, the piezoelectric sensor struggles to satisfy the requirements for directional recognition due to the limited piezoelectric coefficient matrix, and achieving sensitivity for detecting micrometer-scale deformations is also challenging. Herein, we develop a vector sensor composed of lead zirconate titanate-electronic grade glass fiber composite filaments with oriented arrangement, capable of detecting minute anisotropic deformations. The as-prepared vector sensor can identify the deformation directions even when subjected to an unprecedented nominal strain of 0.06%, thereby enabling its utility in accurately discerning the 5 μm-height wrinkles in thin films and in monitoring human pulse waves. The ultra-high sensitivity is attributed to the formation of porous ferroelectret and the efficient load transfer efficiency of continuous lead zirconate titanate phase. Additionally, when integrated with machine learning techniques, the sensor's capability to recognize multi-signals enables it to differentiate between 10 types of fine textures with 100% accuracy. The structural design in piezoelectric devices enables a more comprehensive perception of mechanical stimuli, offering a novel perspective for enhancing recognition accuracy.

1. Introduction

Sensors that can detect subtle mechanical stimuli along with their direction are highly desired for structural health detection and robotic sensory systems [1–6]. As space exploration advances, thin-film structures like antennas, solar wings, and solar sails are becoming widespread on spacecraft, leveraging their benefits of expansive area, minimal weight, and effortless deployment [7–9]. During operation, the harsh space environment can result in the abnormal deformation of the thin-film structures, leading to performance degradation and even catastrophic accidents, posing threats to life safety [10, 11]. Based on that, a flexible sensor is required to achieve the detection of anisotropic subtle structural deformation in real-time [12, 13].

On the other hand, tactile recognition systems are vital for robots to interact with their environment [14, 15]. The ability to discern textures similar to humans is a crucial aspect of these systems, enabling robots to perform intricate tasks such as inspection sampling, resource detection, and emergency rescues [16–18]. Flexible sensors capable of simultaneously identifying the roughness of textures and the direction of patterns can provide more physical information for texture recognition, thereby improving recognition accuracy.

Among the various types of sensors available, flexible piezoelectric sensors are intriguing for their capacity to convert mechanical energy into electrical signals without requiring an external power source [19, 20]. These sensors are fabricated from materials like piezoelectric ceramics [21], polymers [22], and two-dimensional materials [23] using methods such as 3D printing [24, 25], electrospinning [26], spin-coating [27] and so on. When evaluating the performance of flexible piezoelectric sensors, sensitivity, durability, response time, and multifunctionality are critical considerations. Of these, sensitivity stands out as paramount, reflecting the sensor's ability to detect subtle mechanical stimuli [28–30]. To enhance this capability, techniques such as improving the material's piezoelectric coefficient and enhancing mechanical transmission efficiency have been developed [31–33]. Nevertheless, achieving microscale deformation detection with piezoelectric sensors still poses a significant challenge.