Bioinspired Hierarchical Structure for an Ultrawide‐Range Multifunctional Flexible Sensor Using Porous Expandable Polyethylene/Loofah‐Like Polyurethane Sponge Material

Abstract

Capacitive sensors show promising applications for human–computer interface due to their potential capabilities of both pressure and proximity sensing. However, the sensitivity loss at large strain and the complicated process of fabrication technology limit related applications. Herein, inspired by gradient and hierarchical structures in biological systems and using porous materials with different stiffness, a capacitive flexible sensor with both proximity and pressure sensing abilities is proposed. Such hierarchical structures effectively reduce the attenuation of sensitivity as the pressure increases, realizing an ultrawide detection range with high sensitivity. A theoretical mathematical model is developed and the corresponding capacitive sensor is fabricated by using the high‐performance porous impregnated dust‐free paper as the electrode and expandable polyethylene (EPE)/loofah‐like polyurethane sponge (LPS) as double‐layer porous dielectric. This sensor has an ultrawide detection range up to 3000 kPa with a significantly low sensitivity loss of 0.0195% kPa−1 and the noncontact sensing mode reaches a sensing range up to 28 cm (0.122 cm−1). Notably, a strategy is provided to design the high sensitivity sensor over an ultrawide detection range from approaching to pressuring, and eventually its promising application is presented as human–computer interaction.

High-Sensitive Wearable Capacitive Pressure Sensor with Hemispherical Porous Electrode

“…When the pressure is greater than 100 kPa, although the continued compression also increases the contact, the increased contact is small compared with the previous contact surface, so the resistance change is small. The electrodes maintain a stable resistance resulting in good response time and durability of the sensor …”

“…The electrodes maintain a stable resistance resulting in good response time and durability of the sensor. 26 Furthermore, we investigated the effect of different CNT concentrations on sensor performance. Figure 3d shows that when the CNT concentration is less than 10 mg/mL, the increase in concentration can effectively improve the sensitivity of the sensor.…”

“…Flexible capacitive pressure sensors require significant deformation when subjected to external pressure in order to produce significant capacitance changes and improve the response to pressure signals . Among various elastomeric polymer materials, polydimethylsiloxane (PDMS) has been extensively investigated in the dielectric layer or electrode design due to its flexibility and chemical stability. − One option to improve the performance of capacitive pressure sensors is to design the dielectric layer as a porous structure, relying on the change in dielectric constant and thickness of the porous material. − The porous structure can have more compression space and deformation, giving the sensor a higher sensitivity and continuous detection capability over a wide pressure range. However, the change in dielectric constant and thickness of the porous material is still very limited, which makes the capacitance variation of the pressure sensor not easy to improve .…”

Sensitive, Robust, Wide-Range, and High-Consistency Capacitive Tactile Sensors with Ordered Porous Dielectric Microstructures

“…During unloading, the elastic restoring force of the elastomer portion allows for the reopening of the closed pores, thus restoring the porous structure to its initial state. This will lead to a perfect recovery of the sensor response, effectively mitigating the viscoelastic behavior of the dielectric material. − Therefore, the porous microstructured dielectric layer can lead to higher reduction in both the equivalent compression modulus and viscoelastic resistance compared with surface microstructured dielectric ones. As a result, the compressibility and dynamics of the sensor are maximized, which ultimately contributes to a higher sensitivity, faster response and relaxation times in a broad pressure range.…”

Flexible Capacitive Sensors Based on Liquid Crystal Elastomer

“…Flexible capacitive sensors offer numerous advantages, such as their simple structure, low working current, and minimal energy consumption. , These sensors hold significant potential for a wide range of applications, including human–mechanical interaction , and medical equipment. ,, Commonly employed flexible dielectric materials include PDMS, polyethylene terephthalate (PET), polyimide (PI), polyethylene (PE), and polyurethane (PU) . However, their relative dielectric constants typically remained below 4.0.…”