A Flexible Self-Powered Occlusal Force Sensor Array for Assisting Oral Occlusion Reconstruction

Flexible triboelectric sensor array based on 3D printed bead-on-string sacrificial layer for human-machine interactions

Flexible pressure sensor arrays have emerged as a key enabling technology in the era of the Internet of Things and artificial intelligence, offering real-time, distributed, and multidimensional sensing capabilities. The micro/nano-engineered sensor arrays, composed of numerous integrated sensing units, show tremendous potential in human-machine interactions. However, meeting the increasing demands for high-resolution, high-performance area sensing presents critical challenges, including the fabrication of high-density arrays, mitigation of signal crosstalk, and the integrated optimization of sensing performance. This paper briefly summarizes and reviews the existing research strategies of flexible sensor arrays, from high-density sensor array manufacturing technology, anti-crosstalk design of multi-pixel units, performance control methods for sensing units, to intelligent human-machine interaction applications. Finally, a future outlook is proposed in light of the current state to promote the wider application of sensing arrays in human-machine interactions.

As the digital devices have been developed, hand gesture recognition plays an important role in Human-Computer interface (HCI) for direct interaction without contact. Among them, the non-contact methods do not require attaching sensors to human's body and mostly use visual technologies such as Kinect or camera sensors. Various wearable devices have been developed using contact sensors such as inertial sensor, magnetic sensor, gyro sensor, electromyography (EMG), FSRs, and others to identify gestures. However, various drawbacks remain for these sensor in detecting gestures. In this paper, we propose a new method using strain gauges-based Flexible Epidermal Tactile Sensor Array to overcome the drawbacks of the existing sensors. It acquires electric signals generated according to the movements of the wrist based on strain gauge estimating the degree of deformation such as tension, compression, and twist. The proposed sensor array shows robustness, stability, and repeatability through various experiments for testing the sensor array. Furthermore, the proposed method is verified by confirming gesture recognition accuracy with multiple subjects and has a greater performance than the existing gesture recognition devices in accuracy tests.

An interactive surface using bending gestures as the input is proposed by integrating a flexible strain sensor array and a flexible display screen. To create such a flexible strain sensor array, formation of a reliable interconnection between the elastic sensitive regions and the rigid contact regions is vital to achieve required sensitivity and durability. In this work, a new design with an added interconnect layer on top of the interface regions is used to reduce the bending induced local stress. A stretchable conductive composite by blending carbon black (CB) with polydimethylsiloxane (PDMS) and Ecoflex (CB‐PDMS/Ecoflex) is developed for the interconnect layer. CB‐PDMS/Ecoflex is compatible with the blade coating for facile processing, and demonstrates a similar low Young's modulus as that of the sensitive region composed of silver nanowires and PDMS. Printing processes are developed to fabricate a 4 × 9 flexible strain sensor array based on the proposed design and the interconnect layer. It is shown that the sensor with CB‐PDMS/Ecoflex interconnect layer can sustain more than 3000 bending cycles. Finally, the sensor array is integrated with a flexible active‐matrix organic light‐emitting diode display to construct the bendable interactive surface, demonstrating the capability of controlling the ball movement via bending gestures.

Recent progress in high-resolution tactile sensor array: From sensor fabrication to advanced applications

Flexible planar electromagnetic sensor array fabricated with printing electronic technology

In this paper, we present a novel flexible sensor array manufacturing process that involves transfer printing methods using a chip mounter with a vacuum collet. We successfully transfer-printed continuously very fragile microelectromechanical systems (MEMS)-based 5-mm-long, 1-mm-wide, 5-µm-thick high-aspect-ratio ultra-thin PZT(1.9µm)/Si(3µm) strain sensors onto a polyimide based flexible printed-circuit (FPC) substrate with etched Cu wiring. Then, we connected the sensors to the Cu wiring by printing insulating and conductive pastes using a screen printer. The output voltage based on the deformation behavior of the test plate was generated from the flexible piezoelectric strain sensor array attached to the plate. Therefore, the developed piezoelectric sensor array is capable of easily performing the distribution measurement of the strain leading to damage such as cracks.

A large area and mechanically flexible active matrix image sensor array is made by integrating organic photo diode (OPDs) onto a high resolution organic thin-film transistor (OTFT) backplane on plastic substrate. The maximum process temperature is less than 100 °C. The sensor array has an imaging area of 130 mm × 130 mm and resolution of 1536 ×1536 (~300 ppi), which, to our best knowledge, is a state-of-the-art result among all reported all organic active matrix image sensor arrays.

Achieving a balance between high spatial resolution, minimal crosstalk, and long-term stability remains a critical challenge in the design of flexible tactile sensor arrays for robotic applications. While increasing array density enhances perception, it often compromises signal integrity due to mechanical coupling. To address these conflicting objectives, this paper proposes a multi-objective co-design strategy for a finger-interdigitated piezoresistive sensor based on carbon nanotubes and polyimide. Using the COMSOL Multiphysics simulation platform, the performance of three array density configurations—2 × 2, 3 × 3, and 4 × 4—under static pressure and creep conditions was systematically analyzed. A key theoretical finding is that the normalized piezoresistive sensitivity remains independent of array density, demonstrating the excellent scalability of the proposed architecture. Performance trade-offs, however, are significant: the low-density (2 × 2) array offers superior mechanical isolation but suffers from greater long-term drift, while the high-density (4 × 4) array provides the best creep resistance and wide-range stability at the cost of higher crosstalk. A comprehensive evaluation reveals that the 3 × 3 array achieves an optimal balance, with moderate crosstalk and excellent stability, making it the most suitable configuration for practical applications such as robotic fingers that require both sensing accuracy and reliability. This study provides a theoretical foundation and design guidelines for optimizing the trade-offs in high-density flexible skins.

This study presents an unique process to integrate the temperature sensing/heating elements, multi-layer through-hole vias (THVs), and electrical routings on parylene substrate to implement a multi-functional flexible temperature sensor array. Moreover, the polymer-staking processes with 3D electrical routings enable the further integration of various devices. In application, this study also demonstrates the implementation and integration of flexible temperature sensor array by: (1) temperature distribution and contour measurement using 4×4 temperature sensor array, (2) temperature monitoring and control using the integration of Pt-sensor and Pt-heater, (3) heterogeneous integration of temperature sensor array with LED-chip for LED temperature monitoring, and (4) 3D integration of temperature sensor array with LED and micro-lens and micro chamber.

The rapid increase in the aging population prompts the development of wearable devices and sophisticated robots. With their ability to collect complex information about their surroundings via e-skins, robots could perform more dynamic and variable tasks such as rescue missions or caring for the elderly. In this paper, we present a new concept of utilizing a very simple, highly flexible and stretchable capacitor sensor array, that can be attached on the surface of a retractable robot hand to realize three functions: determining the location, shape, and pressure of an object. This adaptive sensing system is accomplished using capacitors connected by aligned carbon nanotube (CNT) films constructed on an elastomer dielectric material, which can reduce the requirement on the accuracy of the machine vision system. This study has a very broad application in the manufacture of intelligent software robots.

With the rapid emergence of flexible electronics, flexible pressure sensors are of importance in various fields. In this study, a dopamine-modified melamine sponge (MS) was used to prepare a honeycomb structure of carbon black (CB)/MXene-silicone rubber (SR)@MS flexible pressure sensor (CMSM) through layer-by-layer self-assembly technology. Using SR as a binder to construct the honeycomb structure not only improves the mechanical properties of the sensor but also provides more attachment sites for CB/MXene, enhancing the stability of the conductive network. The honeycomb structure CMSM flexible pressure sensor exhibits high sensitivity (7.44 kPa-1), a wide detection range (0-240 kPa), short response/recovery times (150 ms/180 ms), and exhibits excellent stability. In addition, a flexible smart insole has been developed based on a 6-unit CMSM sensor array, achieving plantar pressure detection. By combination of the ResNet-50 neural network algorithm with plantar pressure data under different postures, the recognition of 16 types of human motion postures has been achieved, with an accuracy rate of 90.63%. This study proposes a flexible sponge pressure sensor with excellent mechanical performance and sensing capabilities, providing new ideas and references for the design of flexible wearable sensor devices.

Sorts of Li-ion batteries (LIB) have been becoming important energy supply and storage devices. As a long-standing obstacle, safety issues are limiting the large-scale adoption of high-energy–density batteries. Strategies covering materials, cell, and package processing have been paid much attention to. Here, we report a flexible sensor array with fast and reversible temperature switching that can be incorporated inside batteries to prevent thermal runaway. This flexible sensor array consists of PTCR ceramic sensors combined with printed PI sheets for electrodes and circuits. Compared to room temperature, the resistance of the sensors soars nonlinearly by more than three orders of magnitude at around 67 °C with a 1 °C/s rate. This temperature aligns with the decomposition temperature of SEI. Subsequently, the resistance returns to normal at room temperature, demonstrating a negative thermal hysteresis effect. This characteristic proves advantageous for the battery, as it enables a lower-temperature restart after an initial warming phase. The batteries with an embedded sensor array could resume their normal function without performance compromise or detrimental thermal runaway.

This paper presents the first multiparametric flexible sensor arrays system for in situ immediate diagnosis of glossitis, which may furnish clues for certain systemic diseases. The system includes a multiparametric flexible sensor array and accompanying signal processing circuitry. The flexible sensor arrays are obtained by facile micro-fabrication and chemical modifications. The sensors are affixed to the tongue mucosa for simultaneous monitoring the signals of sodium, potassium, pH, and temperature variations, which are transmitted to a smart terminal via the circuitry. In vitro tests have demonstrated excellent response linearity, sensitivity, selectivity, and reproducibility of this sensor arrays system. The signal processing circuitry provides reliable support for integrated testing of multiparametric sensors. Simulating the tongue state with agar, the system significantly detected changes in marker levels from the exudate on the agar surface. The multiparametric flexible sensor arrays system is expected to tackle the “black box” issues in several clinical diagnostics in the future.

Detecting volatile organic compounds (VOCs) in human breath is critical for the early diagnosis of diseases. Good selectivity of VOC sensors is crucial for the accurate analysis of VOC biomarkers in human breath, which consists of more than 200 types of VOCs. In this paper, a flexible virtual sensor array (FVSA) was proposed based on a sensing layer of MXene and laser-induced graphene interdigital electrodes (LIG-IDEs) for detecting VOCs in exhaled human breath. The fabrication of LIG-IDEs avoids the costly and complicated procedures required for the preparation of traditional IDEs. The FVSA's responses of multiple parameters help build a unique fingerprint for each VOC, without a need for changing the temperature of the sensing element, which is commonly used in the VSA of semiconductor VOC sensors. Based on machine learning algorithms, we have achieved highly precise recognition of different VOCs and mixtures and accurate prediction (accuracy of 89.1%) of the objective VOC's concentration in variable backgrounds using this proposed FVSA. Moreover, a blind analysis validates the capacity of the FVSA to identify alcohol content in human breath with an accuracy of 88.9% using breath samples from volunteers before and after alcohol consumption. These results show that the proposed FVSA is promising for the detection of VOC biomarkers in human exhaled breath and early diagnosis of diseases.