High-efficiency Electromagnetic Interference Shielding Research Articles

Flexible poly (vinylidene fluoride) composite with magnetite-modified graphene: Electromagnetic shielding in X-band

Electromagnetic pollution, or electromagnetic interference (EMI), is a phenomenon that has arisen due to the fast spread of electronic gadgets. To overcome EMI problem, polymer-based composites have sparked considerable attention among researchers owing to their superior qualities. Hence, this work utilizes magnetite-modified graphene (MMG) filler with polyvinylidene fluoride (PVDF) polymer to form polymer composites in various proportions ranging from 2 to 10 wt% to study the EM properties in the X-band. It was observed that the sample composite having a MMG filler content of 10 wt% possesses a relatively higher electrical conductivity of 0.65 S/cm as compared to the other prepared composites in this research work. The same sample composite also attained a total shielding efficacy of 53.04 dB at a thickness of 3 mm. Moreover, it was observed that the filler has improved the material's thermal stability and microwave absorption capacity, making it a high-efficiency EMI shielding material appropriate for usage in the electronic and aviation industries.

Construction of rGO-MXene@FeNi/epoxy composites with regular honeycomb structures for high-efficiency electromagnetic interference shielding

With the rapid development of 5G communication technology and wearable electronic devices, the demand for low-reflection electromagnetic interference (EMI) shielding materials is becoming increasingly urgent. In this work, reduced graphene oxide-MXene (rGMH) @FeNi/epoxy EMI shielding composites with a regular honeycomb structure were successfully prepared by the combination of surface functionalization modification, sacrificial template, and freeze-drying. The effects of magnetic FeNi alloy particle loading mode and loading amount on the EMI shielding performance of composites were investigated. The results show that rGMH@FeNi/epoxy EMI shielding composites have the highest EMI shielding effectiveness (EMI SE) and the lowest reflection shielding effectiveness when magnetic FeNi alloy particles are loaded only on the graphene skeleton. In this composite, the EMI SE value of the composite is 61 dB when the rGMH@FeNi mass fraction is 5.4 wt% (f-FeNi mass fraction is 0.9 wt%), which is 4.7 times that of the blended rGO/MXene/FeNi/ epoxy resin composite (13 dB) with the same mass fraction. At the same time, the rGMH@FeNi/epoxy composite has excellent thermal stability (heat-resistance index of 190.3 °C) and mechanical properties (energy storage modulus of 8606.7 MPa). These polymer-based EMI shielding composites with excellent EMI shielding properties and low reflection effectiveness have great potential in the protection of high-power, portable and wearable electronic devices against electromagnetic pollution.

Electromagnetic porous lignocellulosic matrix composites: A green electromagnetic shielding material with high absorption efficient electromagnetic interference

Electromagnetic interference (EMI) shielding materials play a vital role in human society, especially in light of the rapid development of electronic communication equipment. Therefore, it is urgent to develop green, high-efficiency EMI shielding materials. Wood, as a renewable raw material, possesses significant structural advantages in studying EMI materials due to its unique 3D pore structure. Herein, we report magnetoelectric lignocellulosic matrix composites derived from the delignified wood for efficient EMI shielding. The composite was fabricated by in-situ polymerization of PEDOT conductive coating and magnetic Fe3O4 in delignified wood. The conductive 3D pore structure of Fe3O4/PEDOT@wood could effectively cause dielectric loss and multiple internal reflections. Combined with the magnetic loss of Fe3O4, the material exhibited excellent EMI shielding effectiveness (SE), which could be attributed to the synergistic effect of dielectric and magnetic losses. The Fe3O4/PEDOT@wood showed excellent conductivity (103 S/m), good magnetism (26.7 emu/g), the EMI SE up to 59.8 dB, and high SEA/SET ratios of∼84.2 % to 95.7 % at 2 mm in X -band. Moreover, the material exhibited a high compressive strength and tensile strength of 100.8 MPa and 18.1 MPa, respectively. Therefore, this work provided a reference for the preparation of high-efficiency EMI shielding materials.

Sweat and microwave manageable textiles for efficient personal thermal comfort and electromagnetic radiation defend

Although electromagnetic interference (EMI) shielding fabrics integrated with absorption and reflection have recently shown attractive defense performance, effective sweat management is still scarce for simultaneously achieving sustainable personal comfort. Here, we demonstrate a hierarchically arrayed fabric for personal EMI shielding and thermal comfort management. By integrating EMI shielding interfaces and spatially distributed channels, the fabric exhibits high-efficiency EMI shielding ability and enhanced sweat transportation. We demonstrate the tuning electromagnetic response with maximum EMI shielding efficiency value of ∼118 dB and continuous one-way liquid sweat flow with a temperature of ∼3.5 °C lower than that of conventional EMI shielding fabrics. In addition, the fabric shows substantially stabilized EMI shielding performance for long-term use by transporting and repelling internal liquid sweat. The high performance of our fabric makes it a promising design paradigm for personal electromagnetic interference shielding and thermal management.

Sandwich-Structured Mxene/Waste Polyurethane Foam Composites For Highly Efficient Electromagnetic Interference, Infrared Shielding and Joule Heating.

Electromagnetic interference (EMI) shielding and infrared (IR) stealth materials have attracted increasing attention owing to the rapid development of modern communication and military surveillance technologies. However, to realize excellent EMI shielding and IR stealth performance simultaneously remains a great challenge. Herein, a facile strategy is demonstrated to prepare high-efficiency EMI shielding and IR stealth materials of sandwich-structured MXene-based thin foam composites (M-W-M) via filtration and hot-pressing. In this composite, the conductive Ti3C2Tx MXene/cellulose nanofiber (MXene/CNF) film serves as the outer layer, which reflects electromagnetic waves and reduces the IR emissivity. Meanwhile, the middle layer is composed of a porous waste polyurethane foam (WPUF), which not only improves thermal insulation capacity but also extends electromagnetic wave propagation paths. Owing to the unique sandwich structure of "film-foam-film", the M-W-M composite exhibits a high EMI shielding effectiveness of 83.37dB, and in the meantime extremely low emissivity (22.17%) in the wavelength range of 7-14µm and thermal conductivity (0.19W m-1 K-1), giving rise to impressive IR stealth performance at various surrounding temperatures. Remarkably, the M-W-M composite also shows excellent Joule heating properties, capable of maintaining the IR stealth function during Joule heating.

Cellulose Nanofiber/Carbon Nanotube@Polypyrrole-Silver Nanowires Composite Films with a Multilayer Double Conductive Structure for High-Efficiency Electromagnetic Interference Shielding and Infrared Stealth

Cellulose Nanofiber/Carbon Nanotube@Polypyrrole-Silver Nanowires Composite Films with a Multilayer Double Conductive Structure for High-Efficiency Electromagnetic Interference Shielding and Infrared Stealth

Durable and sustainable CoFe2O4@MXene-silver nanowires/cellulose nanofibers composite films with controllable electric–magnetic gradient towards high-efficiency electromagnetic interference shielding and Joule heating capacity

Exploring electromagnetic waves (EMW) absorption-dominated high-performance electromagnetic interference (EMI) shielding materials with robust mechanical properties and remarkable Joule heating capability is highly desired but remains a daunting challenge for the development of modern electronic equipment. Herein, durable and multifunctional cellulose nanofiber-based composite films with elaborate electric–magnetic dual gradient structure were successfully fabricated through highly controllable vacuum-assisted filtration technology. The electric–magnetic dual gradient network consists of CoFe2O4@MXene hybrids with electric–magnetic cooperative loss concentrated on the top region as impedance matching layer and silver nanowires (AgNWs) with high conductivity placed on the bottom as high-efficiency shielding layer. Benefiting from the construction of dual gradient network with rational arrangement of the impedance matching layer and conductive shielding layer, the synergy of electric–magnetic loss, polarization loss induced by the numerous heterointerfaces and “absorption-reflection-reabsorption” shielding mechanism, the resultant composite films simultaneously reveal ultraefficient EMI shielding effectiveness (SE) and low EMW reflectivity. The prepared composite films (0.1 mm in thickness) achieve an extraordinary EMI SE of 84.3 dB and a satisfactory reflection coefficient of 0.42, realizing EMW absorption-dominated shielding feature. Moreover, the mechanical properties and Joule heating capacity of the prepared composite films are outstanding, which mainly benefits from the construction of hierarchically layered structure. This work paves a novel route for designing and fabricating absorption-dominated high-performance EMI shielding composite films with durable mechanical performance and outstanding Joule heating capability, which are potentially suitable for new-generation advanced electronics.

3D-Printed Carbon-Based Conformal Electromagnetic Interference Shielding Module for Integrated Electronics

Highlights3D printable functional inks incorporated with graphene and carbon nanotube nanoparticles were well-formulated by manipulating their rheological performanceThe frame with ultralight structure (0.076 g cm−3) and high-efficiency electromagnetic interference shielding (61.4 dB) was assembled3D-printed c-SE module was in situ integrated onto the electronics, affording multiple functions of electromagnetic compatibility and thermal dissipation.

Lightweight HfC nanowire-carbon fiber/graphene aerogel composites for high-efficiency electromagnetic interference shielding

Electromagnetic interference (EMI) and pollution triggered by electromagnetic waves are becoming a severe issue with the rapid development of various e-devices. Developing low-density and high-efficiency electromagnetic shielding materials is of great importance. Carbon aerogel materials have received worldwide attention due to their significant electromagnetic interference shielding properties and physicochemical stability. Herein, lightweight hafnium carbide nanowire (HfCnw)-carbon fiber (CF)/graphene aerogel (GA) composites with excellent electromagnetic shielding performance were fabricated by successively introducing CF via hydrothermal process, pyrolytic carbon (PyC) coating via chemical vapor infiltration (CVI), and HfCnw via catalytic chemical vapor deposition (CCVD) into GA. It was found that the electrical conductivity of the HfCnw-CF/GA composites with the HfCnw growth time of 4 h reached 94.0 S/cm, which was far higher than 1.1 S/cm of pristine GA and 2.7 S/cm of the CF/GA composites. The EMI shielding effectiveness (SE) of the HfCnw-CF/GA composites was as high as 66.4 dB in the X-band, which was 3 times that (25.4 dB) for GA and 1.5 times that (45.8 dB) for the CF/GA composites. The EMI shielding performance of the HfCnw-CF/GA composites was improved mainly due to the enhanced multiple reflection loss, conductance loss, and interfacial polarization loss. Moreover, the HfCnw-CF/GA composites had a specific SE (SSE) value of 364.1 dB cm3/g, which exhibits good application prospects in the EMI field to meet the needs for light weight and high SE.

Self-Assembly TiO2-Ti3C2Tx Ball-Plate Structure for Highly Efficient Electromagnetic Interference Shielding.

MXene is a promising candidate for the next generation of lightweight electromagnetic interference (EMI) materials owing to its low density, excellent conductivity, hydrophilic properties, and adjustable component structure. However, MXene lacks interlayer support and tends to agglomerate, leading to a shorter service life and limiting its development in thin-layer electromagnetic shielding material. In this study, we designed self-assembled TiO2-Ti3C2Tx materials with a ball-plate structure to mitigate agglomeration and obtain a thin-layer and multiple absorption porous materials for high-efficiency EMI shielding. The TiO2-Ti3C2Tx composite with a thickness of 50 μm achieved a shielding efficiency of 72 dB. It was demonstrated that the ball-plate structure generates additional interlayer cavities and internal interface, increasing the propagation path for an electromagnetic wave, which, in turn, raises the capacity of materials to absorb and dissipate the wave. These effects improve the overall EMI shielding performance of MXene and pave the way for the development of the next-generation EMI shielding system.

Mechanically strong, flexible, and flame-retardant Ti3C2Tx MXene-coated aramid paper with superior electromagnetic interference shielding and electrical heating performance

Undesirable electromagnetic interference (EMI) created by modern electronic devices has detrimental effects on the performance of high-precision electronic devices, information security, and human health. Therefore, lightweight, flexible, robust, and easy-to-fabricate EMI shielding materials with integrated functions are highly desirable to combat electromagnetic pollution. Herein, we report a scalable and facile strategy to prepare a flexible Ti3C2Tx MXene-coated aramid paper (MAP) with high-efficiency EMI shielding and excellent electrical heating performance. The intertwined network by aramid fibers endows the aramid paper (AP) with superior mechanical properties. After selectively single/dual coating with MXene onto AP, the MAP maintains a superior tensile strength of 73.6 MPa and enormous folding endurance of 4156 times. Owing to the exceptional electrical conductivity of MXene, the MAP with a relatively low MXene content (∼9.0 wt%) exhibits excellent overall performance with an EMI shielding effectiveness (SE) of 38 dB and SE/t of 422.2 dB mm−1. It’s noteworthy that the EMI SE of the MAP remains almost unchanged (37.4 dB) even after experiencing 5,000 repeated bending cycles. Additionally, the MAP shows satisfactory Joule electric-heating capability (a heating temperature rise of 130 °C at a low driving voltage of 5 V) and excellent flame-retardancy. This work provides a feasible strategy for large-scale production of flexible EMI shielding paper with multifunctional properties for future wearable facilities.

Light Weight, Flexible and Ultrathin PTFE@Ag and Ni@PVDF Composite Film for High-Efficient Electromagnetic Interference Shielding.

Dopamine was used to modify polytetrafluoroethylene (PTFE) in order to obtain functional polydopamine (PDA) surface-modified PTFE microporous film (PTFE@PDA). Ag was deposited on the surface of PTFE@PDA using electroless plating in order to obtain Ag-wrapped PTFE@PDA film (PTFE@Ag). A liquid-phase chemical reduction method was employed to prepare nickel nanochains. A Ni@PVDF cast film was obtained by mechanically blended nickel nanochains and polyimide (PVDF). The above two films were hot pressed to give a flexible, ultra-thin, and highly effective electromagnetic shielding composite film with a "3+2" layered structure. IR, XRD, and TEM results showed the PTFE@PDA film surface was coated by a tight plating layer of Ag particles with a particle size of 100~200 nm. PTFE@Ag+Ni@PVDF composite film exhibited excellent electromagnetic shielding effectiveness, with the conductivity of 7507.5 S/cm and the shielding effectiveness of 69.03 dB in the X-band range. After a 2000-cycle bending, this value still remained at 51.90 dB. Furthermore, the composite film presented excellent tensile strength of 62.1 MPa. It has great potential for applications in flexible and wearable intelligent devices.

Tough and durable silver-plated graphene oxide/polyurethane composite foam for efficient electromagnetic shielding

With the rapid development of modern information technology, electromagnetic wave has become a new type of pollution source, so there is an urgent need for an efficient electromagnetic interference (EMI) shielding material to control electromagnetic pollution. Among them, EMI shielding materials in many fields are required to be lightweight, efficient and durable. In this study, silver-plated graphene oxide (GO@Ag) is added as a conductive filler to the polyurethane (PU) matrix, and a composite EMI shielding material with excellent conductive network structure is obtained through co-foaming. Conductive network structure provides high EMI shielding effectiveness (EMI SE) and good mechanical properties for composite shielding materials. When the content of GO@Ag is 15%, the EMI SE reaches 29.4 dB, and the specific EMI SE (SSE) reaches 237.9 dB×cm3 ×g−1. Reflection is the main shielding mechanism of composite shielding materials. Good conductivity makes the shielding materials and air impedance mismatched. When electromagnetic waves contact the shielding materials, the reflection effect will occur. Furthermore, this work provides a new research direction for EMI shielding in the fields of aerospace, precision electronics and lightweight equipment.

Robust multifunctional composite films with alternating multilayered architecture for highly efficient electromagnetic interference shielding, Joule heating and infrared stealth

Developing ultrathin electromagnetic interference (EMI) shielding materials with high-efficiency EMI shielding effectiveness (SE), anisotropic thermal conductivity and robust mechanical performance is urgently required but challenging to satisfy the integration and miniaturization of modern flexible electronics. Herein, an alternating multilayered film containing alternating CoFe2O4@MXene/cellulose nanofibers (CNF) layers and silver nanowires (AgNWs)/CNF layers was successfully fabricated via a facile alternating vacuum-assisted filtration strategy. Profiting from the rational arrangement of CoFe2O4@MXene/CNF layers and AgNWs/CNF layers, electric/magnetic coupling effect and unique “absorption-reflection-reabsorption” shielding behavior among the alternating multilayered films, the resultant composite film with alternating six-layered architecture realizes an ultra-high EMI SE of 87.8 dB with low electromagnetic waves reflection effectiveness of 5.6 dB at a thickness of only 0.1 mm. The film remains reliable EMI shielding performance (over 97% EMI SE retention) after undergoing persistently physical damage and prolonged chemical attack. Meanwhile, owing to the construction of overlapping AgNWs network, the obtained film acquires outstanding in-plane thermal conductivity (6.875 W/(m·K)) and controllable Joule heating performance (steady temperature over 90 °C at applied voltage of 3.0 V within 20 s). The inferior through-plane thermal conductivity (0.689 W/(m·K)) caused by the design of multilayered structure guarantees the remarkable infrared stealth performance. Additionally, the good interfacial interaction endows the prepared film with robust mechanical properties (tensile strength of 183.2 MPa and fracture strain of 5.4%). This work not only offers a creative avenue for designing and preparing multifunctional EMI shielding composite films with excellent mechanical properties, but also broadens the applications of EMI shielding composite films in military fields, artificial intelligence and wearable electronics.

Lightweight carbon fiber hybrid film for high-efficiency electromagnetic interference shielding and electro/photo-thermal conversion applications

Enormous electromagnetic pollutions emerge with the rapid development of electronic technique, high-performance electromagnetic interference (EMI) shielding composites are greatly desired to protect human and precision instruments from electromagnetic interference. Here we fabricated a lightweight, porous carbon fiber felt/Ag/polydimethylsiloxane (CFF/Ag/PDMS) composite film via electroless plating and dip-coating method. The obtained homogenously distributed Ag nanoparticles on the surface of carbon fibers and the porous structure of CFF endow the film with excellent electrical conductivity and superior EMI shielding effectiveness (EMI SE). The maximum electrical conductivity and EMI SE value of the composite film with a thickness of 0.21 mm reach 540.9 S/cm and 105 dB at 8.2–12.4 GHz (X-band), respectively. Benefitting from the encapsulation of PDMS, the composite film exhibits outstanding corrosion resistance and oxidation resistance. Particularly, the composite film also exhibits excellent electro/photo-thermal conversion effect with outstanding heating controllability, cyclic stability, which shows great potential in 5 G communication technology and thermal management.

High-efficiency electromagnetic interference shielding and thermal management of high-graphene nanoplate-loaded composites enabled by polymer-infiltrated technique

Polymer composites embedded with high filler loads (≥50 wt%) are urgently needed to address the electromagnetic interference (EMI) shielding and thermal barrier problems for the high-power integrated electronic devices. However, designing polymer composites with high filler loads remains a challenge due to difficulties in processability and poor flexibility. Herein, high graphene nanoplates-loaded polyurethane (GNP/PU) composites were enabled by a tractable and scalable polymer-infiltrated technique, in which GNPs were in compact contact face to face and arranged along the in-plane direction. The formation of such structure provided good channels for the transmission of electrons and phonons in the GNP/PU composites. Impressively, the GNP/PU composites showed strong EMI shielding and thermal conductivity, with a superior EMI shielding effectiveness of 67.6 dB (0.4 mm thickness), and extremely high thermal conductivity of 41.60 W/(m·K). Moreover, the GNP/PU composites were proven to have excellent mechanical flexibility, EMI shielding stability, and thermal management capability. With good comprehensive performance and high processability, the GNP/PU composites hold great promise for EMI shielding and thermal management applications in the field of highly integrated electronics.

3D printing of ultralight MWCNT@OCNF porous scaffolds for high-efficiency electromagnetic interference shielding

Towards the difficulties of traditional processing technology in loading high-concentration functional fillers to realize the target electromagnetic interference shielding (EMI SE) performance, and constructing the arbitrary-designated architectures for serving advanced electronics, this work innovatively formulated a functional multi-walled carbon nanotubes@cellulose nanofibers (MWCNT@OCNF) ink for direct ink writing (DIW) 3D printing, which not only possessed high freedom on the proportion of functional particles, but also imparted to the ideal rheological performance for 3D printing. Based on the pre-programmed printing trajectories, a series of porous scaffolds featuring exceptional functionalities were architected. Particularly for the electromagnetic waves (EMWs) shielding behaviors, the optimized one with “full-mismatched” architecture posed the ultralight structure (0.11 g/cm3) and superior SE performance (43.5 dB) in the X-band frequency region. More encouragingly, the 3D-printed scaffold with hierarchical pores possessed the ideal electromagnetic compatibility on EMWs signal, where the radiation intensity generated by EMWs signal fluctuated in a step pattern in 0 and 1500 μT/cm2 as loading and unloading scaffolds. Overall, this study paved a novel path for the formulation of functional inks to print lightweight, multi-structure, and high-efficiency EMI SE scaffolds for the next-generation shielding elements.

Waste flame-retardant polyurethane foam/ground tire rubber/carbon nanotubes composites with hierarchical segregated structures for high efficiency electromagnetic interference shielding

Recently, flexible conductive polymer composites (CPCs) have attracted increasing interests for their promise in electromagnetic interference (EMI) shielding. Inspired by the “steel reinforced concrete” structure, we proposed in this study a novel method to prepare a CPC with high EMI shielding performance from waste flame-retardant polyurethane foam (WFPUF) and ground tire rubber (GTR). In this CPC, WFPUF coated with carbon nanotubes (CNT) and cellulose nanofibers (CNF) served as a strong and conductive skeleton like the “steel” in “steel reinforced concrete”. Meanwhile, the GTR and CNT composite with a segregated structure occupied the pore space of WFPUF/CNT/CNF (WCC) to form the WCC/GTR/CNT composite, similar to the “concrete” in “steel reinforced concrete”. Owing to such a hierarchical structure, the resultant WCC/GTR/CNT demonstrated some coveted properties, including the enhanced mechanical properties, high electrical conductivity (84.0 S·m−1), excellent EMI shielding performance (53.8 dB), and long-term durability. Remarkably, the composite also showed great flame retardancy due to the presence of WFPUF. This work provided a promising strategy for the preparation of eco-friendly, low cost, flexible and efficient CPCs from polymer wastes, which showed high potential in EMI shielding.

Graphitized and flexible porous textile updated from waste cotton for wearable electromagnetic interference shielding

Developing easy-tailorable and high-efficient electromagnetic interference (EMI) shielding textile from waste textile is highly desirable to meet the demand for wearable electronics and economic sustainability for modern society. However, simultaneously featuring with good electrical conductivity and wearability of the derived waste textiles remains a daunting challenge, especially in the absence of conducting additives. Herein, we report the fabrication of a tailorable textile with high flexibility and conductivity to address this challenge via a straightforward graphitization strategy based on a mild reduction procedure. Aided by finite element analysis (FEA) and computer simulation technology (CST) for performance screening in advance, the mechanically-favorable but EMI shielding-unfavorable pores intrinsically produced in interwoven textile call for a low square resistance of the whole textile. The textile with desirable features is fabricated by the Ni-species catalyzed graphitization of cotton cellulose with large-scale production potential. Moreover, the low square resistance of the textile remains stable after immersion in extremely corrosive chemicals or 10000-times bending tests. The textile with a small thickness of 1.4 mm achieves an EMI shielding effectiveness (SE) of 107 dB in 12–18 GHz, 3 fold exceeding the demand for commercial applications (>30 dB). Practical demonstrations show that personal information in a mobile phone or ID card can be prevented from being read by pockets tailored from textiles. This work shows great potential for massive production of high-efficiency EMI shielding textiles for livelihood or military towards the next-generation wearable electronic technology.

Broadband transparent and flexible silver mesh for efficient electromagnetic interference shielding and high-quality free-space optical communication

A broadband transparent and flexible silver (Ag) mesh is presented experimentally for the first time for both efficient electromagnetic interference (EMI) shielding in the X band and high-quality free-space optical (FSO) communication. High transmission is achieved in a broad wavelength range of 0.4-2.0 µm. The transmittance of the Ag mesh relative to the substrate is around 92% and the sheet resistance is as low as 7.12 Ω/sq. The Ag mesh/polyethylene (PE) achieves a high average EMI shielding effectiveness (SE) of 28.8 dB in the X band with an overall transmittance of 80.9% at 550 nm. High-quality FSO communication with small power penalty is attributed to the high optical transmittance and the low haze at 1550 nm, superior to those of the Ag NW networks. With a polydimethylsiloxane (PDMS) coating, the average EMI SE is still up to 26.2 dB and the overall transmittance is increased to 84.5% at 550 nm due to antireflection. The FSO communication does not change much due to the nearly unchanged optical property at 1550 nm. Both the EMI shielding performance and the FSO communication function maintain after 2-hour chemical corrosions as well as after 1000 bending cycles and twisting. Our PDMS/Ag mesh/PE sandwiched film can be self-cleaned, suitable for outdoor applications.