the near future,Yang Canhui's team from the Department of Mechanics and Aerospace Engineering and Ge Qi's team from the Department of Mechanical and Energy Engineering at Southern University of Science and Technology collaborated in Nature Communications》Published under the title“Polyelectrolyte elastomer-based ionotronic sensors with multi-mode sensing capabilities via multi-material 3D printing”The paper reported that throughIntegrated design and manufacturing of multimodal sensing ion capacitive sensors based on polyelectrolyte elastomers using multi material digital photopolymerization 3D printing technology.

In the past decade, ion electron hybrid devices (i.e. devices based on the synergistic effect of ions and electrons) have attracted increasing attention due to their inherent advantages such as flexibility, stretchability, optical transparency, and biocompatibility. However, the existing off-duty sensors have poor device stability and single sensing function due to their simple device structure and easy component leakage, which greatly limits their practical applications. Therefore, designing and manufacturing high-performance and multi-mode sensing sensors with stable performance has important engineering application value. This study solves the problems of poor stability and single functionality of traditional ionization sensors, providing a new solution for the design, intelligent manufacturing, and application of stretchable ionization sensors.

Figure 1.Skin inspired multi-mode sensing ionization sensor (a) Schematic diagram of multiple force sensors within human skin (b) Human skin can sense a single mechanical signal such as tension, compression, compression+shear, compression+torsion (c) Based on multi material digital photopolymerization 3D printing technology, an ionization sensor with multi-mode sensing capability is prepared.

As shown in Figure 1, inspired by the multimodal sensing ability of human skin to external forces such as tension, compression, torsion, and their combinations, researchers have used multi material digital light processing (DLP) 3D printing technology to prepare an ionization sensor with multimodal sensing capability. The sensor adopts polyelectrolyte elastomer (PEE), which contains fixed anions or cations and movable counterions in its polymer network, and has the characteristic of anti ion leakage. During the printing process, a strong interface adhesion is formed between the PEE material and the dielectric elastomer (DE) material on the sensor through covalent and topological interconnections.

Figure 2.The design, preparation, optical, mechanical, electrical properties, as well as thermal and solvent stability of polyelectrolyte elastomers.

Researchers first synthesized a monomer called 1-butyl-3-methylimidazole-134-3-sulfopropyl acrylate (BS) as one of the components of polyelectrolyte materials, and copolymerized it with another hydrophobic monomer called MEA. Then, by optimizing the ratio of BS and MEA, the mechanical and electrical properties of the polyelectrolyte material are balanced, thereby optimizing the performance of the sensor, as shown in Figure 2.

Figure 3.Off electric sensingThe tool's ability to hitPrinting and Performance (a) Curve of PEE Storage Modulus and Loss Modulus with Light Curing Time (b) Relationship between Curing Time and Energy Density with Layer Thickness (c) Display of Printed PEE Array (d) 180 ° Peel Curve of 3D Printed and Manually Assembled PEE/DE Double Layer Structure (e) Schematic Diagram of PEE/DE Double Layer Structure Body Fracture in 3D Printed (f) Schematic Diagram of Interface Fracture of Manually Assembled PEE/DE Double Layer Structure (g) Curve of Δ C/C0 with Time for PEE and LiTFSI Doped Ion based Capacitive Sensors (h) No Ion Leakage for PEE based Capacitive Sensors (i) Capacitive Sensor based on LiTFSI Doped Ion based Elastomers Schematic diagram of sensor ion leakage.

As shown in Figure 3, the researchers conducted optical rheological tests to verify the printability of the developed PEE material. Then, the interface adhesion strength of the PEE/DE bilayer structure, which was 3D printed and manually assembled, was measured through a 180 ° peel test. The results indicate that the double-layer structure of 3D printing has a strong and tough interface due to the covalent bonds and topological entanglement formed between PEE and DE. The peeling process resulted in the fracture of the PEE material, with an adhesive energy of 339.3 J/m²In contrast, the manually assembled PEE/DE bilayer structure has a weak interface and interface fracture occurs during the peeling process, with an adhesive energy of only 4.1 J/m²In durability testing, capacitive sensors based on PEE can maintain stable signals for a long time due to no ion leakage, while sensors based on traditional LiTFSI doped ion elastomers continue to drift due to ion leakage until a short circuit occurs.

Figure 4Tension, compression, shear, and torsion ionization sensors (a) Schematic diagram of tension sensor principle (b) Capacitive tensile strain curve (c) Schematic diagram of compression sensor principle (d) Capacitive pressure curve of pressure sensor with/without microstructure (e) ShearbiographysensorPrinciple diagram (f) A physical image of a shear sensor (g) Capacitance shear strain curve of shear sensors with different sensitivities (h) Fatigue test curve of shear sensors (i) Principle diagram of a torsion sensor (j) A torsion sensordevicereal(k) Capacitance torsion angle curves of torsion sensors with different sensitivities (l) Fatigue test curves of torsion sensors.

3D printing technology provides high flexibility for the structural design of devices. As shown in Figure 4, researchers designed and integrated four different types of piezoelectric sensors for stretching, compression, shearing, and twisting, all of which have good performance and stability. Specifically, through the structural design of the device, significant optimization of sensor sensitivity can be achieved. For example, by introducing microstructures into the dielectric elastomer layer of the compressed sensor, sensitivity can be increased by two orders of magnitude, and sensor sensitivity can be adjusted as needed. For example, by designing the contour line of the front end of the shear sensor or the number of fan-shaped areas of the torsion sensor, different corresponding shear sensors and torsion sensors can be achieved.

Figure 5.Combination type ionization sensor (a) Schematic diagram of tension compression combination sensor (b) Physical device diagram (c) Equivalent circuit diagram of tension compression combination sensor (d) Device signal under single sensing mode (e) Capacitance coil number change curve under compressive excitation (f) Capacitance coil number change curve under tensile excitation (g) Signal spectrum under tension compression combination deformation (h) Compression shear combination sensor displayIntention (i)Device physical diagram (j) Equivalent circuit diagram of compression shear combination sensor (k) Device signal in single sensing mode (l) Schematic diagram of compression torsion combination sensor (m) Device physical diagram (n) Equivalent circuit diagram of compression torsion combination sensor (o) Device signal in single sensing mode.

As shown in Figure 5, researchers further designed and integrated three types of combined piezoelectric sensors: tension compression, compression shear, and compression torsion. One of the challenges of the combined sensor is the mutual signal crosstalk between different sensing channels. For example, when the device is stretched, the Poisson effect of the material will lead to the reduction of the geometric size of the device in the vertical direction, which is equivalent to the compression deformation, resulting in the signal change of the compression channel caused by the tensile excitation. By combining finite element simulation analysis and rational device structure design, researchers have effectively avoided signal crosstalk between different channels.

Figure 6. Remote wireless control of unmanned aerial vehicles using a combined ionization sensor (a) Schematic diagram of the unmanned aerial vehicle control system (b) Schematic diagram of the working mode of the shear sensing module in the combined ionization sensor (c) Working principle of the shear sensing module (d) Testing of the five channel capacitance signals of the sensor (e) Instruction compilation logic (f) Real time capacitance signal of the combined ionization sensor (g) Unmanned aerial vehicle flight at different timesstatus

Finally, the researchers demonstrated a wearable remote control unit consisting of four shear sensors and one compression sensor, and connected it to a remote control system for remote wireless control of drone flight, as shown in Figure 6. The four shear sensors in this wearable remote control unit are responsible for sensing finger movements in the hand and controlling the direction of the drone. The compression sensor is used to sense the pressure on the fingers and control the rolling of the drone. The design of this wearable remote control unit can achieve human-computer interaction and provide more flexible control methods.