With the rapid diversification of application scenarios, flexible piezoelectric sensors are often required to be attached to objects with irregular surfaces, which demands that such sensors possess not only high sensitivity but also excellent shape adaptability. Therefore, flexible piezoelectret metamaterials have emerged as ideal sensor materials. In this study, environmentally friendly polylactic acid (PLA) films were selected as the substrate material, and its electret properties were optimized through pre-treatment to enhance charge storage stability. Subsequently, based on the optimized PLA films subjected to corona polarization, piezoelectret metamaterials with a double-V structure were fabricated using 3D-printed molds combined with thermal bonding. The results indicate that the fabricated piezoelectret metamaterial exhibits significant transverse piezoelectric activity, with a piezoelectric d₃₁ coefficient reaching 340 pC/N, and maintains stable output even under different bending conditions, thus demonstrating excellent shape adaptability. Sensors based on this material can accurately detect both the quasi-static deformation induced by thin-plate bending and dynamic deformation generated by U-shaped bracket vibrations. Furthermore, the PLA metamaterial sensors also demonstrate strong applicability in respiratory health diagnostics for human lung function. This research provides a robust solution for fully implementation of piezoelectret metamaterial sensing applications on irregularly shaped objects.

Biodegradable piezoelectret force sensors have emerged as a pivotal platform for advancing sustainable soft bioelectronics, enabling wearable and implantable biomedical applications that align with the global demand for eco-friendly and bio-friendly healthcare solutions. In this work, we report a facile, scalable strategy for fabricating high-performance, stretchable polylactic acid (PLA)-based piezoelectret force sensors through integrated manufacturing processes, including hot pressing, corona polarization, thermal bonding, and biodegradable silicone encapsulation. A micro air‑cell design methodology combined with a robust elastic encapsulation strategy is developed to fabricate highly sensitive PLA‑based piezoelectret sensors. The fabricated prototype integrates slowly biodegradable Ecoflex encapsulation and non-bioresorbable aluminum (Al) electrodes for reliable electromechanical performance, and future replacement of Al with bioresorbable electrode materials will realize full transient bioelimination of the sensor. The proposed design endows the devices with superior mechanical robustness and stretchability, enabling their versatile applications as both pressure and tensile stress sensors. Benefiting from such structural advantages, the force sensor achieves a high pressure sensitivity (∼22 V/kPa), tensile stress sensitivity (∼7‍ V/MPa), excellent stability (∼40,000 cycles), and rapid dynamic response (45 ms response/recovery time). Additionally, the sensor exhibits an extensive measurable pressure range from 0.06 to 62 kPa and tensile stress range from 1.5 to 9 MPa, outperforming most reported eco-friendly piezoelectric sensors. Practical utility is validated across diverse biomedical scenarios, including underwater finger bending detection, high-fidelity monitoring of carotid artery pulse and wrist pulse signals, multi-sensor array-based dynamic motion tracking, and simultaneous acquisition of heart rate and respiratory signals. These results demonstrate the sensor’s promising potential for wearable biomechanical monitoring, laying a solid foundation for next-generation sustainable soft bioelectronics that meet the growing demands of safe, high-performance, and environmentally sustainable medical devices.

Flexible piezoelectret sensors have significant advantages in the application of electronic skin to capture dynamic mechanical signals, showing promise in robotic perception. In this study, polypropylene (PP) piezoelectret films with an arched air-filled channel structure were designed and systematically investigated by theoretical analysis, simulation calculation and experimental verification. The results demonstrate that the piezoelectric properties of such piezoelectrets can be predicted via a capacitance energy method, and the films exhibit significant anisotropy in their piezoelectric response and excellent shape adaptability. Specifically, for piezoelectret film samples constructed from two 38 μm-thick PP electret films, with an arch height (apex-to-base distance) of 200 μm and a cell width of 2 mm, the piezoelectric d33 coefficient attains its maximum value when the surface potentials of the two films are set to ±1176 V, respectively. The anisotropic piezoelectric response in the films was successfully leveraged for multi-dimensional force sensing. When the applied force (~82 mN) slides along different in-plane directions, the sample yields markedly distinct piezoelectric responses. The motion perpendicular to the arched air-channel axis generates a periodic charge signal (~40 pC), while the motion parallel to the arched air-channel axis almost don’t generate discernible signal, manifesting a pronounced anisotropy. Therefore, taking into account the distance between the channels, the device can identify direction and speed of force sliding on it.

Piezoelectric functional films based on biomass materials are attractive due to their promising sustainable applications in wearable/implantable sensors, actuators, and energy harvesters, especially for biological systems. However, their widespread use is often hampered by the high stiffness and weak piezoelectricity of the involved biomaterials. In addition, the introduction of optical transparency is highly desirable, which can lead to the integration of tactile and visual intelligence in a piezoelectric sensor/actuator system. Herein, by leveraging space charge injection and a microstructural engineering strategy, biodegradable and transparent soft piezoelectret (BTSP) sensors from PLA films with artificially formed air cells were proposed. Artificial air cells drastically reduce the compressive modulus of elasticity of BTSP (∼0.02 MPa), resulting in a high longitudinal piezoelectric d33 coefficient (∼6000 pC/N), which is 2 to 3 orders of magnitude larger than that of conventional biodegradable piezoelectric material counterparts. Additionally, a large transverse piezoelectric coefficient (d31 ∼-10 pC/N) and exceptional electromechanical sensing stability determined by performing 70,000 mechanical loading cycles are simultaneously combined with the high resolution in terms of pressure and location. Thus, the presented BTSP has significant advantages over conventional biodegradable piezoelectric materials as they possess both high out-of-plane/in-plane piezoelectric coefficients and remarkable flexibility. This work paves the way for a simple but effective method to fabricate high-performance biodegradable piezoelectric materials and promotes their practical applications in the field of biological and medical microdevices.

Flexible wearable sensors are widely explored for human-machine interaction and health monitoring. Electronic textiles (E-textiles) offer a promising pathway toward comfortable wearable devices by integrating sensing fibers directly into fabric structures. Among them, compared with piezoresistive and capacitive fiber sensors, piezoelectric fiber sensors require no external power supply. Compared with triboelectric fiber sensors, which are highly sensitive to humidity and temperature, piezoelectric fiber sensors provide more stable and reliable electrical signals. However, conventional piezoelectric fiber sensors still face challenges in achieving long-term wearing comfort and reliability under harsh environments. Herein, we develop a breathable, washable, and wide-temperature-tolerant based on piezoelectric perfluoroalkoxy (PFA) fibers, which can be readily integrated into E-textiles. The textile is produced via a weft knitting process that integrates coaxially structured PFA fibers with wool yarns, combining stable piezoelectric performance with wearing comfort. The fibers exhibited a charge sensitivity of (2.6 ± 0.2) pC/N at 0.2 MPa. The resulting E-textile exhibits a charge sensitivity of up to (316.6 ± 45.9) pC/N and a voltage sensitivity of (744.9 ± 73.9) mV/N. The textile maintains stable operation over a wide temperature range from -78 °C to 150 °C. Its weft-knitted structure provides breathability, while the textile also offers washability, UV resistance, and mechanical durability exceeding 10,000 stretching or bending cycles. Furthermore, the textile can effectively monitor various human motions. A smart glove constructed from five-channel PFA fibers achieved recognition accuracies above 95% for five hand gestures, demonstrating the potential offer self-powered E-textile as a wearable sensor for human-machine interaction.

Piezoelectrets refer to a type of micro-porous structured polymer systems containing oriented macroscopic dipoles and showing a strong piezoelectricity. They are considered as a promising functional material for various transducer applications, and several cellular structures have been proposed to realize high performance piezoelectrets. In this study, we designed a compound-structure piezoelectret system by combining a foam and a layer structure, where polypropylene and fluorinated polymers together were used to store dipoles and form the compressible and reversible cellular structure. Experimental results showed that the compound system can obtain a strong mechanical stability, high resistance to temperature and humidity, and favorable electrical outputs. The high sensitivity and stable output characteristics make the compound piezoelectret system suitable for a wearable monitoring of human respiration, heartbeat, and walking, as demonstrated by the application assessments.

With the rapid development of emerging technologies such as artificial intelligence of things (AIoTs), a wide variety of sensors, including flexible and wearable sensors, are in high demand. Among them, advanced flexible functional fibers which can be integrated into textile seamlessly by traditional weaving processes, forming smart textile in a designed way and keeping flexibility, breathability, and washability, are promising. In this article, thermally stable coaxial piezoelectric fiber sensors based on perfluoroalkoxy alkane (PFA) piezoelectrets are designed, theoretically analyzed, optimized by simulation, and produced in an industrial production line. The results show that piezoelectric fiber sensors can be made by adopting a lotus root structure in the piezoelectret layer, and the sensitivity and resonant frequency of the PFA fiber sensors can be tuned by adjusting the geometric parameters such as the diameter of the core electrode, the thickness of PFA piezoelectret layer, and the curvature radius of support beams in PFA layer, as well as charge distribution. Therefore, for specific application scenarios, an optimized piezoelectric fiber sensor can be obtained. Combining theoretical derivation and simulation analysis, and considering actual conditions, a batch of optimized PFA fiber sensors with a length of 350 m is successfully produced in an industry production line. The fabricated PFA fiber sensors have a small diameter of 0.3 mm, a radial resonance frequency of 15 kHz, a hydrostatic sensitivity of 3.5 pC/N at 0.1 MPa, and a broad working temperature ranging from -78.5 degrees C to 150 degrees C, making them ideal for comfortable textile sensors to monitor vital signals and joint motion of humans over the long term, as well as for special clothing used in extreme environments.

High-precision deposition in material extrusion-based additive manufacturing (MEX-AM), especially in mid-air extrusion, is essential for creating microfluidic channels, integrated sensors, and tissue scaffolds with fine vascular features. However, despite advances in support-free slicing and multi-axis printing, no standardized method exists for fabricating enclosed air cavities with high shape fidelity, particularly in single-layer structures. Reliable deposition at sub-millimeter scales remains challenging, especially when printing low-stiffness polymers such as polypropylene (PP), due to delayed solidification and viscoelastic effects. This study introduces a flow-rate-dependent analytical model to predict extrusion behavior, interfacial bonding, and surface morphology in self-supporting single-layer PP structures. To validate the model, surface roughness, material distribution, and intralayer bonding were quantified using spectral analysis, cross-sectional thickness measurements, and Abbott-Firestone curve evaluation. Results show that reducing the flow rate (relative to 100% nominal flow through a 0.4 mm nozzle) to 40% improves surface roughness (Ra) to below 20 mu m on average across all surfaces, with the lowest Ra of 4.52 +/- 0.49 mu m observed at a 20% flow rate on the top surfaces enclosing the cavity. The intralayer bonding between adjacent extruded lines increases up to 70%, improving deposition uniformity. Nozzle-induced smoothing effects enhance surface quality at flow rates of 60% or lower, while higher flow rates result in increased surface waviness and geometric irregularities. These findings enable the fabrication of enclosed microfluidic channels and functional cavities with well-defined surfaces and reduced mechanical stiffness, suitable for applications involving sensing, controlled deformation, or flexible system integration.

Ferroelectret coaxial sensors (FCSs) combine a coaxial structure with high piezoelectricity, flexibility, lightweight, demonstrating great potential in biomedical applications. However, due to its complex structure and materials, theoretically predicting and analyzing the piezoelectric properties of FCS is challenging. This article initially proposes a theoretical model based on piezoelectric equations to determine the equivalent moduli of FCS's ground and shielding electrode and outer jacket, respectively, which are experimentally verified to be 40 and 35 MPa, respectively. Subsequently, a finite element (FEM) model considering the ferroelectret's anisotropic hyperelastic properties is developed and validated. The study further explores the impacts of material properties, structural dimensions, and prestress on FCS piezoelectric properties to guide the optimization of designed strategies. The results demonstrate that increasing the core electrode diameter can significantly improve FCS's piezoelectric performance. Selecting a ferroelectret film with a high d(31) effect not only enhances the piezoelectric response but also improves the linearity. In contrast, introducing a large amount of prestress during manufacturing will noticeably reduce the piezoelectric properties of FCS. Finally, the real-time tracking capability for key physiological parameters-including respiratory rate (1225 breaths/min) and heart rate (60100 b/m)-has been successfully measured through FCS-based smart textile, confirming their efficacy in vital signs monitoring.

Biodegradable piezo/ferroelectrets featuring void microstructure have emerged as highly promising candidates for next-generation sustainable bioelectronics.

Nowadays, humans rely increasingly on smart electronics to address grand challenges and to improve life conditions in the era of digitalization and big data. However, electronics often have a limited lifespan, and they may bring electronic waste problems after their service. To mitigate this problem, environmentally sustainable methods of electronic device production and disposal are highly recommended, where advanced functional materials should be redesigned with improved sensing performance over the entire operational life while also being naturally degradable at the end. Herein, a biodegradable and flexible bifunctional electroacoustic transducer was fabricated with the utilization of cellular polylactic acid (PLA) ferroelectret films, possessing a small acoustic impedance of similar to 0.02 MRayl which is quite close to that of air and a high figure of merit (FOM: d(33)g(33)) of similar to 11 GPa(-1). Such devices have a prominent signal-to-noise ratio (SNR) of similar to 23.5 dB @1 kHz and can work either as a microphone by direct piezoelectric effect or a loudspeaker by reverse piezoelectric effect in air medium. When used as a microphone, the flexible device exhibits a prominent receiving sensitivity up to 4.2 mV/Pa (similar to-47.5 dB/ref. 1 V/Pa) at 1 kHz. When served as a loudspeaker, it is capable of yielding high sound pressure levels (SPLs) ranging from 60 to 103 dB (ref. 20 mu Pa) in a broad frequency range of 1-80 kHz with an active area of 3.14 cm(2). Additionally, the electrical response curve of the device is very flat in a wide frequency range from 300 to 3000 Hz. With the high-performance acoustic-electric conversion capacity, the PLA ferroelectret-based flexible and filmlike electroacoustic transducer was used to realize accurate speech recognition and control, providing a strong impetus for its advanced and eco-friendly applications in the era of the internet of things (IoT) and artificial intelligence.

风暴岩是由风暴形成的事件性沉积序列.风暴的形成理论上要求水体温度26.5℃以上.由于宽度和水温的限制,使得湖泊上空不太可能形成热带气旋并出现风暴岩.四川盆地上三叠统须家河组为一套辫状河三角洲-湖泊相建造,近年来广泛报道有风暴沉积记录.广元紫兰坝剖面须五段古土壤层面的原位树木化石材料提供了风暴的新证据. 9例材料中6份原位树木的倒伏方向集中呈北西向,与下伏地层中古水流数据相反,推测广元地区三叠纪末期曾盛行东南风.新店子剖面和四川盆地须家河组内砂岩内普遍发育有呈撕裂状或具塑性变形的泥砾.泥砾无搬运痕迹,显“八”字型特征,被解释为风暴滞留沉积,表明须家河组沉积时期曾普遍受到风暴作用的影响.晚三叠世期间盛行“巨型季风”气候,“巨型季风”因其表面风最大风速低,并非四川盆地须家河组风暴沉积的原因.“巨型季风”气候体制下,须家河组风暴岩的驱动机制是特提斯洋上空热带气旋东移登陆四川盆地西缘的结果.环特提斯域风暴岩对比统计数据显示,三叠纪末期特提斯低纬度地区普遍出现大规模风暴潮,四川盆地须家河组顶部广泛出现的风暴岩很可能是三叠纪末期极热事件的沉积响应.

Eco-friendly sensors fabricated from biocompatible and biodegradable materials are promising candidates for wearable and implantable electronics due to their environmental sustainability and biosafety. This article reports a fully biodegradable electromechanical sensor (FBES) utilizing a sandwich structure with macro ripple structured polylactic acid (PLA) electret films acting as sensitive layers and molybdenum (Mo) sheets serving as electrodes for a wearable device application. The stability of the space charge stored within the PLA film has been enhanced by introducing an internal cellular structure and improving the polarization process. A macro ripple structure of the PLA layer with higher deformation is a great guarantee for boosting the pressure sensitivity. The results indicate that inserting cell microstructures and optimizing the polarization process significantly improve the charge storage stability of PLA films by nearly 55%. This enhancement is attributed to several factors, including the extended charge drift path of the charges in cellular films, a synergy effect of surface charges, and "macroscopic" dipole charges distributed in the cells. The fabricated sensor achieves a high sensitivity of 1000 pC/kPa, a wide pressure detection range of 0.03-62.4 kPa, and satisfactory stability. Such sensors are not only sensitive to body movements but also to subtle physiological signals, satisfying the diverse needs of wearable healthcare. Importantly, all the composition materials of the sensor can be completely degraded after their service, aligning with the environmentally friendly principles of green development.

Mechanical signal capture without physical contact has emerged as a highly promising research field and attracted tremendous attention due to its prosperous applications in household medical care, lifestyle monitoring and remote operation, offering users high level of safety, convenience and comfort. Moreover, noncontact sensing is ideal to maximize the immersive user experience in the human-machine interaction (HMI), eliminating interference to human activities and mechanical fatigue to the sensor, simultaneously. Herein, we report a self-powered flexible sensor integrated with irradiation cross-linked polypropylene (IXPP) piezoelectret film for noncontact sensing, featuring multi-functions to detect mechanical signals transmitted through solid, liquid and gaseous media and would facilitate their versatile practical applications. The folded-structure configuration of the sensor facilitates the improvement of the noncontact sensing sensitivity. For solid media, such as the rectangular wooden stick used in this study, the sensor can detect mechanical stimulus exerted at a distance of 100 cm. A system detection sensitivity up to 57 pC/kPa with a low detection limit of 0.6 kPa is achieved at a noncontact distance of 10 cm. Even when partly or completely immersed in water, the sensor effectively traces movement signals of human bodies underwater, demonstrating great advantages for non-inductive aquatic fitness training monitoring. Furthermore, due to the low acoustic impedance of piezoelectret film, speech recognition through gaseous medium is also achieved. We further introduce application demonstrations of the developed film sensors to monitor exercise postures and physiological signals without direct contact between human body and the sensor, displaying great potential to be incorporated into future smart electronics. This study commendably expands the application scope of piezoelectret materials, which will have profound implications for exploring novel intelligent human-machine interactions.

This study intends to compare the vocabulary learning strategies between high-achievers and low-achievers in junior high schools, and thus to explore effective vocabulary learning strategies to provide suggestions for English vocabulary teaching and learning practice. It is found out that high-achievers apply English vocabulary learning strategies more frequently than low-achieving students do. More specifically, in terms of meta-cognitive strategies, low-achievers use more pre-planning strategies, while high-achievers apply more selective attention strategies. For cognitive strategies, both high-achievers and low-achievers tend to use repetition strategies. Achievers are better at categorizing what they have learnt than low-achievers. For affective strategies, low-achievers apply reference books strategies most frequently and neither type of students uses authentic material strategies very often. Students’ beliefs, habits and attitudes towards vocabulary learning affect the application of strategies to some extent. High-achievers are better at utilizing the environment and even creating opportunities for English communication than underachievers. In addition, high-achievers have stronger learning motivation and they are also better at setting and achieving goals than low-achievers.

A theoretical model has been developed to express the longitudinal and transverse piezoelectric effects in ferro/piezoelectrets. This model is an extension of the classic model based on layer-dielectric structures that focuses on the longitudinal piezoelectric effect. The improved model reveals that the relation between the longitudinal piezoelectric d33 coefficient and the transverse piezoelectric d31 coefficient is associated with Poisson's ratio μ13 (or μ31) and Young's moduli Y1 and Y3. The polarity of the two coefficients is opposite for materials with a positive Poisson's ratio as normally observed in conventional piezoelectric materials, and the same for materials with a negative Poisson's ratio, i.e., auxetic materials. The experimental results available in the literature and obtained from ferroelectret metamaterials with a honeycomb cross-sectional structure and two-dimensional (2D) symmetric structure, called 2D ferroelectret metamaterials, designed and prepared in this study reasonably agree with theoretical predictions. This study not only extends the scope of the metamaterials by inducing the concept of ferroelectret metamaterials but also provides a strategy for designing ferroelectrets with designable properties.

Air-coupled ultrasonic transducers are widely used in non-destructive testing, acoustical sonar systems, and biomedical imaging. These applications require transducers that operate effectively across a broad acoustic frequency spectrum, offer adaptable geometric designs, and increasingly incorporate eco-friendly materials. In this work, we present a monolithic, 3D-printed air-coupled ultrasonic transducer based on ferroelectrets (FEs) and fabricated from biocompatible polylactic acid (PLA). We evaluated the transducer’s acoustical performance by measuring the surface velocity of its active area using laser Doppler vibrometry and assessed its robustness during continuous operation over a 19-day period. Additionally, we measured the sound pressure level (SPL) and wideband characteristics in an anechoic chamber across excitation frequencies from 1kHz to 100kHz. At a resonance frequency of 33kHz, our transducer achieved an SPL of 94.3dB and surface velocities up to 37mm/s. The measured bandwidth of 65.2kHz at the -6dB threshold corresponds to a fractional bandwidth of 189%. The observed exponential decay of the surface velocity, stabilizing at 15% of its initial amplitude, aligns with the isothermal surface potential decay typically observed in FE films made from PLA. These results demonstrate the effectiveness of the transducer, which features an adaptable backplate for tuning acoustic properties. The low-cost transducer, manufactured from biocompatible PLA, is particularly suited for imaging and biomedical applications furthering green electronics.

Prolonged sitting can easily result in pressure injury (PI) for certain people who have had strokes or spinal cord injuries. There are not many methods available for tracking contact surface pressure and shear force to evaluate the PI risk. Here, we propose a smart cushion that uses two-dimensional force sensors (2D-FSs) to measure the pressure and shear force in the buttocks. A machine learning algorithm is then used to compute the shear stresses in the gluteal muscles, which helps to determine the PI risk. The 2D-FS consists of a ferroelectret coaxial sensor (FCS) unit placed atop a ferroelectret film sensor (FFS) unit, allowing it to detect both vertical and horizontal forces simultaneously. To characterize and calibrate, two experimental approaches are applied: one involves simultaneously applying two perpendicular forces, and one involves applying a single force. To separate the two forces, the 2D-FS is decoupled using a deep neural network technique. Multiple FCSs are embedded to form a smart cushion, and a genetic algorithm-optimized backpropagation neural network is proposed and trained to predict the shear strain in the buttocks to prevent PI. By tracking the danger of PI, the smart cushion based on 2D-FSs may be further connected with home-based intelligent care platforms to increase patient equality for spinal cord injury patients and lower the expense of nursing or rehabilitation care.

Piezoelectret metamaterials are a kind of piezoelectrets with distinctive properties such as negative Poisson's ratio and positive piezoelectric d(31) coefficient. These materials hold significant promise for applications in sensing and mechanical energy harvesting. In this article, flexible piezoelectret metamaterials with a simple double-V cell structure are designed, and their properties are theoretically analyzed, simulated, and experimentally tested. The results indicate that the effective piezoelectric d(33) and d(31) coefficients can be tuned over a wide range by adjusting the geometric parameters of the cell. The experimental results are consistent with the theoretical prediction and simulation calculation. Differing from the piezoelectric d(33) coefficient, which always has positive polarity, the sign of the piezoelectric d(31) coefficient depends on Poisson's ratio of the material. In particular, d(31) coefficients are negative for the materials with positive Poisson's ratio, while they have a positive sign when Poisson's ratio is negative. For a piezoelectret metamaterial sample prepared in this study, a large effective piezoelectric d(31) coefficient up to 1200 pC/N is achieved experimentally. The significant piezoelectric effects in the piezoelectret metamaterials as well as their excellent mechanical adaptivity to irregular surface structures, such as the curved surfaces of humanoid robots and aircraft wings, introduce a novel solution for diverse applications. (c) 2024 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution-NonCommercial 4.0International (CC BY-NC) license

The study focuses on the synthesis of thermoelectrets by combining epoxy oligomer, epoxy-urethane modifier (PEF-3A), and polyaminoamide curing agent (L-20) and the influence of the modifier and curing agent on electret properties and mechanical strength. The process involves polymer synthesis through curing the initial oligomer and modifier, as well as polarization in a constant electric field to create the electret state of the polymer dielectrics. The variation of the content (2.5-10.0 wt.%) of the modifier in the composition results in changes in the electret and mechanical characteristics, including surface potential, effective surface charge density, electrostatic field strength, and Shore D hardness. These changes are attributed to the interplay between reduced mobility of polar groups due to strong physical intermolecular interaction in the structure of the network of the 3-D polymer and an increased number of functional groups participating in polarization processes. Increasing the content of modifier PEF-3A in the composition of the basic oligomer DER-331 leads to a decrease in the frequency of the spatial mesh of the resulting 3-D structure due to the incorporation of an epoxy-urethane oligomer with a large molecular weight. The study of DER-331 and L-20 composite by the method of thermally stimulated depolarization (TSD) reveals the process of polymer devitrification and the occurrence of post-curing reactions. The dielectric spectroscopy method proves the dipole macromolecular group orientation of epoxy polymer material, typical for the electret state of polymer dielectrics. According to the calculation data of dielectric relaxation process activation energy, it is concluded that the electret state in the polymeric matrix formed during curing and fixed by the chemical bonds of a 3-D network is a free state of epoxyamine macromolecules. Dipole groups, mostly oriented in one direction, are "frozen" in the cured net structure, acting as thermoelectret charge carriers. An increase in the modifier content does not significantly impact hardness, while polarization results in a marked difference between the Shore D hardness of unpolarized and polarized samples. This difference can be attributed to the orientation of polar groups during the synthesis, which leads to the emergence of a denser mesh of physical bonds. Therefore, by changing the formulation of the epoxy composition, it is possible to regulate its electret and strength properties.