Search Results (95)

This work introduces a new method for creating patterned SiO₂ electrets using stamp-assisted capacitive coupling (SACC), enabling surface functionalisation without direct electrode contact. SACC applies an alternating current through capacitive coupling between a conductive stamp and an insulating substrate in high-humidity conditions, forming a nano-electrochemical cell that drives localised reactions. Using thermally grown SiO₂ films, we achieve submicrometre patterning with minimal topographical impact but significant electronic alterations. Characterisation via Kelvin Probe Force Microscopy and Electric Force Microscopy confirms the formation of charged regions replicating the stamp pattern, with adjustable surface potential shifts up to −1.7 V and charge densities reaching 300 nC·cm⁻². The process can be scaled to areas of 1 cm² and is compatible with conventional laboratory equipment, offering a high-throughput alternative to scanning-probe lithography. SACC combines simplicity, accuracy, and scalability, opening new opportunities for patterned electret production and functional surface engineering. Full article

Polyethylene (PE) films are widely used as waterproofing materials on the surfaces of metal pipelines. Poor adhesion of PE films to a metal substrate reduces durability, leading to shorter service life and higher economic costs. The current research aims to study the modification of PE films in atmospheric pressure gliding arc plasma (GAP). The adhesion properties of the modified films were investigated using the contact angle method and adhesion work calculations. During the modification process, the GAP treatment duration and deflector nozzle angle of attack were optimized to 10 s and 135°, respectively. It was established that the adhesion work increased from 62.1 to 141.3 mJ/m² after 10 s GAP modification compared to untreated PE. GAP modifying of PE films for 30 s or more is impractical, as the increase in the adhesion work ceases after that. It was found that surface roughness R_max increased by up to 4.1 times after 10 s GAP modification compared with nontreated PE. The PE films acquired hydrophilic properties after plasma modification, due to changes in the polymer surface’s chemical structure. The results of IR spectroscopy studies indicated oxidation of the film surface, an increase in the concentration of surface polar groups (-COOH, OH, C=O), and the formation of double bonds (C=C), which led to improved adhesive properties. A study of the electret properties showed that the observed decline and subsequent stabilization of values occurred within the first 24 h. Mechanical tests indicated improved performance of the GAP-modified PE films compared to the non-treated ones in the PE–mastic–PE and PE–mastic–steel systems. Due to their enhanced contact properties, the modified PE films are of interest as a base material for creating waterproofing materials. Full article

Cardiovascular diseases remain one of the leading causes of mortality worldwide, highlighting the importance of effective monitoring and early diagnosis. While electrocardiography (ECG) is the standard technique for evaluating the heart’s electrical activity and detecting rhythm and conduction abnormalities, it alone is insufficient for identifying certain conditions, such as valvular disorders. Phonocardiography (PCG) allows the recording and analysis of heart sounds and improves the diagnostic accuracy when combined with ECG. In this study, ECG and PCG signals were simultaneously acquired from a resting adult subject using a compact system comprising an analog front-end (model AD8232, manufactured by Analog Devices, Wilmington, MA, USA) for ECG acquisition and a digital stethoscope built around a condenser electret microphone (model HM-9250, manufactured by HMYL, Anqing, China). Both the ECG electrodes and the microphone were positioned on the chest to ensure the spatial alignment of the signals. An adaptive segmentation algorithm was developed to segment PCG and ECG signals based on their morphological and temporal features. This algorithm identifies the onset and peaks of S1 and S2 heart sounds in the PCG and the Q, R, and S waves in the ECG, enabling the extraction of the systolic time intervals such as EMAT, PEP, LVET, and LVST parameters proven useful in the diagnosis and monitoring of cardiovascular diseases. Based on the segmented signals, the measured averages (EMAT = 74.35 ms, PEP = 89.00 ms, LVET = 244.39 ms, LVST = 258.60 ms) were consistent with the reference standards, demonstrating the reliability of the developed method. The proposed algorithm was validated on synchronized ECG and PCG signals from multiple subjects in an open-source dataset (BSSLAB Localized ECG Data). The systolic intervals extracted using the proposed method closely matched the literature values, confirming the robustness across different recording conditions; in detail, the mean Q–S1 interval was 40.45 ms (≈45 ms reference value, mean difference: −4.85 ms, LoA: −3.42 ms and −6.09 ms) and the R–S1 interval was 14.09 ms (≈15 ms reference value, mean difference: −1.2 ms, LoA: −0.55 ms and −1.85 ms). In conclusion, the results demonstrate the potential of the joint ECG and PCG analysis to improve the long-term monitoring of cardiovascular diseases. Full article

Electret filter media are electrostatically charged during the manufacturing process to activate effective electrical separation mechanisms. In order to investigate the influence of humidity on these mechanisms, the electric field, and filtration efficiency, a Direct Numerical Simulation (DNS) study of the aerosol deposition within wetted fibrous nonwoven filter media used in masks was carried out. Initial experimental investigations determined key properties of the filter material, including porosity, fiber diameter, and surface charge density. Using Micro-Computed Tomography (µCT), preferred locations for droplet deposition within the filter were identified. Additional experiments quantified the amount of water absorbed by the filter medium and assessed its impact on the existing electric field. Numerical simulations examined various models with differing porosity and fiber diameter, incorporating different levels of water content to analyze the changes in the electric field, flow velocity, and resulting filtration efficiency. The results provide valuable insights into the significant effects of fiber change on filtration performance, demonstrating the electret filter’s ability to partially compensate for the negative impacts of water. Full article

Measurement of respiratory patterns during sleep plays a critical role in assessing sleep quality and diagnosing sleep disorders such as sleep apnea syndrome, which is associated with many adverse health outcomes, including cardiovascular disease, diabetes, and cognitive impairments. Traditional methods for measuring breathing often rely on expensive and complex sensors, such as polysomnography equipment, which can be cumbersome and costly and are typically confined to clinical settings. These factors limit the performance of respiratory monitoring in routine settings and prevent convenient and extensive screening. Recognizing the need for accessible and cost-effective solutions, we developed a portable sleep sensor that uses an electret condenser microphone (ECM), which is inexpensive and easy to obtain, to measure nasal airflows. Constant current circuits that bias the ECM and circuit constants suitable for measurement enable special uses of the ECM. Furthermore, data transmission through the XBee wireless communication module, which employs the ZigBee short-range wireless communication standard, enables highly portable measurements. This customized configuration allows the ECM to detect subtle changes in airflow associated with breathing patterns, enabling the monitoring of respiratory activity with minimal invasiveness and complexity. Furthermore, the wireless module not only reduces the size and weight of the device, but also facilitates continuous data collection during sleep without disturbing user comfort. This portable wireless sensor runs on batteries, providing approximately 50 h of uptime, a ±50 Pa pressure range, and 20 Hz real-time sampling. Our portable sleep sensor is a practical and efficient solution for respiratory monitoring outside of the traditional clinical setting. Full article

This study explores the vibrational behavior of Thermoformed Magneto-Piezoelectrets (TMPs), multifunctional materials consisting of thermoformed piezoelectrets with open tubular channels integrated with an additional magnetic layer. The inverse piezoelectric effect was characterized using laser vibrometry analysis, measuring the mechanical response of TMPs subjected to electrical excitation over a frequency range of 0–20 kHz. Vibrational analysis was conducted at 144 spatial points, enabling the construction of detailed three-dimensional (3D) maps of the vibration operational modes and the spatial distribution of the piezoelectric coefficient ($d_{33}$). The results demonstrated significant frequency-dependent behavior, with open channels exhibiting pronounced resonance peaks, whereas valleys displayed smoother and more uniform responses due to enhanced damping effects. The observed heterogeneity in vibrational behavior is attributed to structural variations, material composition, and anisotropic coupling between the piezoelectric and magnetic properties. The findings presented in this research provide a comprehensive understanding of the development and utilization of TMPs, offering parameters for enhancing their application and supporting new discoveries in studies related to the fabrication of novel thermoformed piezoelectric sensors. Full article

This work presents the results of a multi-technique comparative investigation aimed at assessing the mineralogical composition and radioactivity levels of two stone fragments from different areas of the archaeological site of Halaesa (Sicily, Italy). The analysis employed an integrated approach combining μ-energy-dispersive X-ray fluorescence (μ-EDXRF) spectroscopy, µ-Raman spectroscopy, X-Ray Diffraction (XRD), ion chromatography (IC), High-Purity Germanium (HPGe) gamma spectrometry, and E-PERM electret ion chamber methods. By examining the stone composition at both the elemental and molecular scales, with support from ion chromatography data, potential degradation patterns linked to post-depositional weathering and external decay agents were identified. Moreover, the specific activity of radionuclides (²²⁶Ra, ²³²Th, and ⁴⁰K) and the ²²²Rn exhalation rates were measured, enabling the estimation of a set of radiological indices that assess potential health hazards associated with prolonged exposure to these lithic materials. The findings highlight how a multidisciplinary approach can foster the assessment of stone deterioration mechanisms, supporting the design of optimized conservation strategies aimed at preserving the archaeological heritage of Halaesa and ensuring the safety of both the public and onsite personnel. Full article

This research aims to create a high-efficiency, low-resistance biodegradable air-filter structure containing beeswax as a result of the simultaneous production of fibers by solution-blowing and melt-blowing. The melt-blowing method is effective for producing micrometer fibers on an industrial scale. In turn, the solution-blowing method allows for the production of fibers with a nanometric diameter from solutions containing temperature-sensitive additives such as beeswax. Combining these two methods is a promising perspective for producing high-performance, functional air-filter materials. Beeswax is a natural material capable of accumulating an electrical charge. When an external electric field is applied, the presence of beeswax in the filter structure facilitates charge retention on the fiber surface. This results in a fully biodegradable filter material with high efficiency and low resistance. Full article

This paper presents a case study of the natural radioactivity level and radon exhalation in limestone and sandstone rocks from the archaeological park of Tindari, located in Sicily, southern Italy. These rocks were representative of natural stones utilised as building materials in the studied area. The activity concentrations of ²²⁶Ra, ²³²Th, and ⁴⁰K were assessed using high purity germanium (HPGe) gamma-ray spectrometry. Subsequently, the absorbed gamma dose rate (D), annual effective dose equivalent (AEDE), activity concentration index (ACI), and alpha index (I_α) were quantified to evaluate potential radiological health risks associated with radiation exposure from the analysed rocks. Finally, E-PERM electret ion chamber measurements were conducted to accurately quantify the radon exhalation rate from the investigated samples. The results obtained in this case study provide a foundation for further research into the background radioactivity levels in natural stones employed as building materials. Full article

Dielectric elastomer generators (DEGs) are electrostatic transducers capable of harvesting electrical energy from oscillating mechanical parts and storing it in a battery or supercapacitor. The energy conversion element typically consists of a flexible capacitor with a variable capacitance that depends on the applied stress cycle and requires an external voltage source (bias voltage). In designing an energy harvesting device from human gait, we propose integrating two components: a dielectric elastomer fabricated using a nanocomposite polyurethane (TPU-CaCu₃Ti₄O₁₂) and an electret serving as a bias voltage source. In this work, we report on the electret fabrication and long-term charge retention properties using corona charging. The manufactured electrets are tested in coupling with the dielectric elastomer and allowed us to harvest an energy amount of 62 µJ/cycle (3.1 µJ/cm²) on a resistive load of 450 MΩ during motion cycles at a frequency of 0.5 Hz. Given the materials used, this approach is well suited to harvesting energy from human gait and holds promise for powering wearable devices. Full article

Polyelectrolyte multilayers (PEMs) deposited on non-porous and porous blend substrates were studied. Films, prepared from two biodegradable polymers poly (D-lactic acid) (PDLA) and poly(ε-caprolactone) (PCL) and their blends were used as substrates in the present paper. All films were initially charged in a corona discharge (positive or negative corona). After charging, the initial surface potential of the samples V₀ was measured and the normalized surface potential was calculated. The dependencies on time of the normalized surface potential for electrets, possessing either positive or negative charges, were studied. It was found that the steady-state values of the normalized surface potential for the porous substrates were higher than those of the non-porous ones, independently of material type and corona polarity. It was also shown that the values of the normalized surface potential for the PCL electrets were the highest and decreased when the content of PDLA increased. Scanning electron microscopy (SEM) was utilized for the determination of the substrates’ surface morphology. With the largest pore size, PCL substrates allowed for a greater capture of charges on their surface and facilitated the retention of said charges for prolonged periods of time. Differential scanning calorimetry (DSC) measurements were performed to determine the degree of crystallinity, which was very high for PCL substrates, when compared to the other investigated substrates. The wettability of the investigated substrates was measured using the static water contact angle method. The obtained results demonstrated that the created blends were more hydrophilic than the pure films. The two chosen polyelectrolytes were layered onto the surface of the substrates with the use of the layer-by-layer (LbL) technique and benzydamine hydrochloride was loaded in the multilayers as a model drug. Its loading efficiency and release profile were carried out spectrophotometrically. It was determined that for non-porous substrates, independently of the corona polarity, the best fitting model was Korsmeyer-Peppas, while for the porous substrates the best fitting model was Weibull. Full article

Persistently and reliably harvesting wind energy to power intelligent online monitoring devices for transmission lines promotes the intelligent and sustainable development of the Internet of Things. Current small-scale wind-energy-harvesting devices, relying on a single energy conversion principle, face challenges such as low efficiency and poor performance at low wind speeds. This paper presents a coaxial rotating non-contact coupling transducer structure, and its optimization methods have been studied, which are based on electret electrostatic induction and magnetically actuated piezoelectric conversion. By analyzing the principles of alternating positive–negative unipolar electret components and constructing a finite element model, improved output capacity is demonstrated. The electric signals from electret components are more suitable for inferring the shaft and wind speeds compared to piezoelectric components. The piezoelectric components utilize frequency up-conversion theory to enhance output while addressing the low power density of the electrostatic components. Experimental results indicate that the proposed structure operates reliably at rotational speeds of 100–700 rpm, achieving a maximum output power of 6.742 mW. The output power of the electret electrostatic component’s electrodes nearly doubled, with the signal positively correlated to rotation speed. The optimized structure of the magnetically actuated piezoelectric component achieved a power increase of 11.51% at four excitations and 250 rpm. This study provides a new design approach for more durable and efficient small-scale wind-energy-harvesting devices, as well as for achieving integrated measurement and supply. Full article

Most FFP (Filtering Face Piece) masks are made from nonwoven filter media that are electrostatically charged, resulting in the additional electrostatic capture mechanism of particles. The protective effect of these masks is therefore mainly dependent on the electric field surrounding the charged fibers. Upon prolonged wear, the mask becomes saturated with exhaled air, resulting in humidification on the wearer’s side. However, speaking, coughing, or sneezing also generate droplets, which can deposit on the mask from the person wearing it, as well as from other people. In order to investigate this influence on the filtration efficiency and the existing electric field, an experimental study was carried out. To imitate human breathing, a test setup was constructed using a Sheffield Head with different types of masks. This was followed by the cyclical humidification and drying of the masks through simulated breathing. By observing these phases in detail using sample sections, it was possible to continuously record the water content in the samples, the relative humidity, and the pressure drop (breathing resistance). The results demonstrate that moisture has an impact on the filtration efficiency of the electret FFP masks when worn under real-life conditions and that the initial condition can be restored with sufficient drying time. Full article

This study explores the fabrication of electret nonwoven structures for high-efficiency air filtration, utilizing the blow spinning technique. In response to the growing need for effective filtration systems, we aimed to develop biodegradable materials capable of capturing fine particulate matter (PM2.5) without compromising environmental sustainability. Polylactic acid (PLA) was used as the primary polymer, with the addition of SiO₂ and MoS₂ to enhance the fibers’ charge retention and filtration performance. The fibers were charged electrostatically to improve particle capture efficiency. The experimental results showed that fibers containing 5% MoS₂ exhibited the highest filtration efficiency, surpassing those with SiO₂, despite MoS₂ being a semiconductor and SiO₂ a dielectric. Furthermore, the addition of MoS₂ improved the filtration efficiency across a range of particle sizes (0.2–1 µm) while maintaining a manageable pressure drop. These findings suggest that incorporating MoS₂ in electret nonwoven structures can significantly improve filtration performance, making it a promising material for advanced air filtration applications. This study contributes to the development of eco-friendly filtration materials with high performance, essential in reducing exposure to airborne pollutants. Full article

This paper presents a comprehensive review of cardiorespiratory auscultation sensing devices (i.e., stethoscopes), which is useful for understanding the theoretical aspects and practical design notes. In this paper, we first introduce the acoustic properties of the heart and lungs, as well as a brief history of stethoscope evolution. Then, we discuss the basic concept of electret condenser microphones (ECMs) and a stethoscope based on them. Then, we discuss the microelectromechanical systems (MEMSs) technology, particularly focusing on piezoelectric transducer sensors. This paper comprehensively reviews sensing technologies for cardiorespiratory auscultation, emphasizing MEMS-based wearable designs in the past decade. To our knowledge, this is the first paper to summarize ECM and MEMS applications for heart and lung sound analysis. Full article