Electromagnetic Protection Research Articles

Electric-magnetic dual-gradient structure design of thin MXene/Fe3O4 films for absorption-dominated electromagnetic interference shielding

The challenge of achieving high-performance electromagnetic interference (EMI) shielding films, which focuses on electromagnetic waves absorption while maintaining thin thickness, is a crucial endeavor in contemporary electronic device advancement. In this study, we have successfully engineered hybrid films based on MXene nanosheets and Fe3O4 nanoparticles, featuring intricate electric–magnetic dual-gradient structures. Through the collaborative influence of a unique dual-gradient structure equipped with transition and reflection layers, these hybrid films demonstrate favorable impedance matching, abundant loss mechanisms (Ohmic loss, interfacial polarization and magnetic loss), and an “absorb-reflect-reabsorb” process to achieve absorption-dominated EMI shielding capability. Compared with the single conductive gradient structure, the dual-gradient structure effectively enhances the absorption intensity per unit thickness, and thus reduces the thickness of the film. The optimized film demonstrates a remarkable EMI shielding effectiveness (SE) of 49.98 dB alongside an enhanced absorption coefficient (A) of 0.51 with a thickness of only 180 μm. The thin films with a dual-gradient structure hold promise for crafting absorption-dominated electromagnetic shielding materials, highlighting the potential for advanced electromagnetic protection solutions.

Exceptional electromagnetic interference shielding using single-walled carbon nanotube/conductive polymer composites films with ultrathin, lightweight properties

The fundamental integrity of electronic devices depends heavily on appropriate electromagnetic protection measures. In this work, thin films of single-walled carbon nanotubes (SWCNTs) and poly(3,4-ethylene dioxythiophene): poly(styrene sulfonate) composites are presented, and their electromagnetic interference shielding effectiveness (EMI SE) is assessed in the X-band frequency range. The films are prepared via a simple benchtop process involving a vacuum filtration followed by a dip-coating. Notably, the composite with the highest thickness, measuring 2.12 μm, achieved the highest EMI SE of 55.53 dB, whereas the thinnest, measuring 0.24 μm, exhibited the highest specific SE divided by thickness (SSE/t) of 2,230,000 dB·cm2·g−1. Additionally, the composites demonstrated excellent physical and chemical stability, maintaining their performance under various harsh conditions. The highest shielding performance of our composite films among reported carbon-based polymer materials is attributed to the complementary spatial arrangement of inherently conducting materials, namely, the SWCNT and the conducting polymer. Our contribution here lays the groundwork for creating lightweight, flexible composites with superior EMI shielding performance, targeting next-generation flexible electronics.

A flexible and strong mechanical MXene/CNC electromagnetic shielding film with powerful light-to-heat conversion properties

High-performance electromagnetic interference (EMI) films with high EMI shielding efficiency, low thickness, high mechanical strength, and flexibility have promising applications in electromagnetic (EM) protection of electronic products. Here, a versatile and sustainable wearable EM shielding MXene/cellulose nanocrystals (CNC) composite film was developed by a simple vacuum-assisted filtration method. One-dimensional (1D) ultrafine CNC act as interfacial linkage enhancers, forming a dense ‘mortar-brick’ structure between CNC and MXene nanosheets, which improves the mechanical properties while maintaining the EMI shielding capability of the films. The obtained films show the better tensile strength (83 MPa) than the pure MXene film (12 MPa). More importantly, the MXene/CNC film exhibits excellent EMI shielding, with an EMI SE of nearly 30 dB at a very low thickness of 7 μm, and 64.5 dB at a thickness of 61 μm. In addition, the films possess good mechanical stability, which can be rapidly heated up to 76 ⁰C and remain stable for a long time. This study provides a promising strategy for the design of multifunctional flexible EMI shielding materials.

Investigation of MXene@APP/FDS/AgNPs@EG system for preparing multifunctional thermoplastic polyurethane composites with flame retardancy and electromagnetic shielding performance

In order to comply with the requirement of flame retardancy and electromagnetic interference (EMI) shielding for encapsulant applied to electronic devices, multifunctional thermoplastic polyurethane (TPU) composites are prepared with the construction of an intumescent flame retardant (IFR) system comprising internal conductive network. In this work, ammonium polyphosphate wrapped with MXene (MXene@APP) is attained by microencapsulation, and expandible graphite decorated with Ag nanoparticles (AgNPs@EG) is prepared by the reducibility of silk sericin. The IFR system with conductivity is established by the introduction of MXene@APP, AgNPs@EG and furfural-derived Schiff base (FDS). The as-prepared TPU/MXene@APP/FDS/AgNPs@EG composites are able to attain significant elevation in flame retardancy, exhibiting V-0 rating and a LOI value of 33.1 %. Furthermore, TPU composites are integrated with warp-knitted metal mesh (WMM) to fabricate TPU@WMM coated fabric, displaying strengthened electromagnetic interference (EMI) shielding effectiveness (SE) of 37.53 dB within X band. This work provides a potential method for application in encapsulant with flame retardancy and electromagnetic protection.

Highly reliable and ultra-wideband metamaterial absorber based on graphene-assembled films for extremes

Metamaterial absorbers have demonstrated significant potential in mitigating electromagnetic pollution, yet there is a dearth of research on absorbers that function effectively in extreme environments. In this work, a highly reliable and ultra-wideband metamaterial absorber based on graphene-assembled films (GAFs) is proposed. The presented absorber consists of four-layer structures, including a high-resistance GAF pattern layer, a polyimide medium layer, an air layer, and a low-resistance GAF layer. The periodic ring structure made of high-resistance GAF by screen printing with a sheet resistance of 57 Ω/sq exhibits excellent characteristics of wideband absorption and broad incidence angle absorption. The GAF absorber demonstrates a measured absorption efficiency exceeding 90 %, covering 4.24–17.90 GHz, and has a relative bandwidth of 123.4 %, which exhibits good stability when electromagnetic waves are incident at 0–30°. More importantly, the GAF absorber maintains excellent performance in various extreme conditions, including acid, alkali, salt spray, high-humidity, high-temperature, and low-temperature environments. Therefore, the GAF absorber demonstrates consistent reliability and stability under extreme conditions, which is significant for electromagnetic protection under extremes.

Wearable, eco-mimetic, and bicontinuous Ag-doped poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate)/MnO2/carbon fabric for multifunctionality

Wearable and bicontinuous Ag-doped poly (3,4-ethylenedioxythiophene): poly (styrenesulfonate)/MnO2/carbon fabric was manufactured in a facile, eco-friendly, and scalable approach. The high temperature-resistant textile performed a maximum specific capacitance of 2.97 F cm−2, and delivered 113 % retention at 80 °C compared with that at room temperature. At a cooling-heating-cooling cycle, the capacitance could recover to its initial value after 10000 charge-discharge tests at 20 mA cm−2. Density function theory proves that Ag dopants and the S-containing functional group improve the adsorption ability with Na+. The maximum energy and power density achieved 19.36 mWh cm−3 and 530.50 mW cm−3 over a wide potential window of 2 V, respectively. Moreover, the fabric could be operated at low-temperature climates by multi-offset Joule heating performance and a deicing/dewatering ability. The antimicrobial capacity against typical bacteria and fungi renders robust safety to the wearable electronics. The fabric performed shielding effectiveness of 45.95 dB at 377 μm and reliable durability after 1000 times bending cycles. The reflection-dominant shielding mechanism was further revealed by COMSOL Multiphysics software. The all-in-one fabric complies with Internet of Things design and can endure extreme environments over a wide temperature range, implying great potential for energy storage, thermal management, bacteriostasis, and electromagnetic protection.

Multi-interfaced FeCoNi@C/carbon cloth composites for eliminating electromagnetic wave pollution

To tackle the increasing electromagnetic pollution, new and efficient electromagnetic wave absorption (EWA) and shielding (EWS) materials are urgently needed. Multi-component synergism and complex microstructure design are effective measures to improve the EWA and EWS properties. However, how to implement the above designs still faces huge challenges. Herein, multi-interface carbon-coated FeCoNi nanoneedles grown on carbon cloth (FeCoNi@C/CC) were synthesized by a combination of hydrothermal process and chemical vapor deposition (CVD) technology with the concept of “green synthesis”. Using acetylene as the carbon source and atmosphere, the FeCoNi ternary hydroxide can be transformed into a multiple magnetic component (Fe3O4, Ni, and Co metals) by simple annealing. Simultaneously, a uniform carbon layer is formed on the surface, resulting in a composite system with a variety of heterogeneous interfaces and loss mechanisms. Additionally, the dielectric and magnetic loss capacities can be effectively adjusted by changing the temperature of CVD. The optimized FeCoNi@C/CC as filler exhibits remarkable EWA performance with a minimum reflection loss of −69.3 ​dB at a thickness of 1.82 ​mm and a maximum effective absorption bandwidth of 6.80 ​GHz. Moreover, the composites as an integrated component also show a fascinating electromagnetic interference shielding efficiency of 42.2 ​dB. This work provides a guide for the structural design of high-performance electromagnetic protection materials with multi-heterogeneous interfaces.

Study on human brain protection from electromagnetic radiation of mobile phone by plasma

The propagation characteristics of electromagnetic waves (EMW) in plasma with the plural dielectric properties (real and imaginary parts of the relative dielectric constant) were investigated in the virtual human brain (VHB) model by the full-wave solution. Simulation results indicate that the value of the electric and magnetic field amplitude of EMW with the frequency of 5 GHz and the value of specific absorption ratio within VHB can be reduced by more than 60% and 80%, respectively. After the secondary absorption of the plasma layer, the reflected wave amplitude is attenuated by 33.066 dB. The amplitude attenuation of EMW from 2.45 to 6 GHz can be exceeded 10 dB. Compared to the traditional absorbing materials for the electromagnetic protection, the plasma layer, as an absorbing medium, possesses wide frequency characteristics. These results have important reference value for reducing the high-frequency electromagnetic radiation to VHB.

Strong SiC@Carbon nanowire aerogel metamaterials for efficient electromagnetic interference shielding

Lightweight, high-strength and efficient electromagnetic interference shielding materials are in urgent demand for aerospace vehicles such as lunar and Mars rovers. SiC nanowire aerogels exhibit low density, chemical stability, and adjustable dielectric properties, rendering them as ideal candidates for high-performance electromagnetic wave protecting materials. However, developing SiC nanowire aerogels with simultaneous strong mechanical properties and efficient electromagnetic interference shielding performance remains challenging. Herein, a class of strong SiC@carbon nanowire aerogel metamaterials with both mechanical robustness and efficient electromagnetic interference shielding are obtained through microstructure design and compositional optimization. The aerogels with designed meta-structures are fabricated by 3D printing followed with chemical vapor deposition of graphene-like carbon. The optimized compressive strength and Young's modulus of the aerogel metamaterial reach up to 1.581 MPa and 46.230 MPa, respectively, showing an increase of about 50–60 times. It also exhibits an electromagnetic interference shielding effectiveness of 38.39 dB and specific shielding effectiveness of 666.53 dBcm3g−1. These good properties are attributed to the synergistic effects of the hierarchical meta-structure and the SiC@carbon nanowires composite constituents, which provides a feasible pathway toward further design of high-performance electromagnetic interference protection materials.

Empirical and numerical analysis of damage tolerance in multifunctional hybrid sandwich fiber reinforced polymers composite structures for aerospace applications using compression after impact (CAI) testing

AbstractThis study presents a novel hybrid‐sandwich composite structure, customized for nose radomes applications, incorporating a foam core and distinct opposite face sheets composed of Kevlar and S‐Glass materials. Addressing in‐phase electromagnetic properties, UV protection and low velocity impact responses in our previously published work, this paper empirically and numerically investigates the damage tolerance response of the proposed structures through compression after impact (CAI) testing. The low velocity impacts (LVIs) on S‐Glass face sheets exhibited unique energy dispersion and absorption mechanisms, resulting in variations in indent damage depths and widths across all impact energy levels as compared with LVIs on Kevlar face sheets. After experimentally assessing the CAI behavior, a FE model is developed to predict CAI behavior, which closely aligned with experimental findings. This study, unprecedented in existing literature, proposes hybrid sandwich structures for nose radome aerospace applications, with superior specific impact and residual strength compared to various composite sandwich structures documented in the published literature expanding its utility beyond radomes.Highlights Innovative composites with superior low velocity impact response, tested for compression after impact performance. Designed for nose radomes found suitable for other impact prone applications. Experimental and numerical modeling showed comparable results. Major differences observed in damage mechanics, resistance, and tolerances.

Absorption dominated broadband terahertz electromagnetic shielding properties of ultrathin rGO paper

The demand for absorption-dominated terahertz (THz) electromagnetic shielding materials is critical in THz devices or components for electromagnetic compatibility and protection. However, it is challenging to find out an ultrathin, absorption-dominated shielding material with high absorptivity in a broad range. Herein, we demonstrate the hydrogen iodine (HI) acid reduced graphene oxide (rGO) ultrathin paper as a promising candidate for absorption-dominated electromagnetic interference (EMI) shielding. By optimizing the conductivity and layered structures, rGO paper with thickness of only 13 μm exhibited an absorption-dominated EMI shielding effectiveness (SE) of 21.09 dB in a broad band from 0.2 to 1.2 THz. Simple stacking of the rGO papers further improved the EMI SE up to 42.53 dB with a total thickness of 40 μm. rGO papers can also be integrated into structured substrates for applications in different scenarios. Covering a single rGO paper onto the wedge structure array, a broadband THz absorption over 99 % can be achieved. Similarly, combining rGO papers and arrays of zinc pyramids, and the average SE and the max THz absorption were enhanced to 54.83 dB and 99.986 %, respectively. We believe this absorption-dominated THz shielding rGO paper paves an efficient avenue towards high performance THz shielding/absorption devices for diverse applications.

Design of polyimide/carbon nanotube@Ag@polyimide/graphene composite aerogel for infrared stealth and electromagnetic interference protection

CHATGPT artificial intelligence is taking the world by storm, and countless electronic devices will generate massive amounts of electromagnetic interference (EMI). Hence, there is a pressing demand for materials exhibiting high thermal conductivity and superior EMI shielding effectiveness (SE). Thus, we construct a polyimide/carbon nanotube@Ag@polyimide/graphene (PCAPG) composite aerogel with porous, layered, and homogeneous structures in one, which provides a new idea for the multi-interface polarization interaction and special structure of anti-EMI materials. PCAPG has high thermal conductivity of ∼ 0.259 W (mK)-1 at 25 °C, excellent EMI SE of ∼ 90.28 dB and specific shielding effectiveness (SSE) of ∼ 940.42 dB cm3 g−1. The synergistic EMI attenuation mechanism of the PCAPG composite structure is analyzed using an aerogel unit. This composite aerogel provides a viable solution for infrared stealth, promoting heat dissipation from electronic components and reducing electromagnetic interference.

Roll-to-roll joule-heating to construct ferromagnetic carbon fiber felt for superior electromagnetic interference shielding

The effective safeguard from electromagnetic radiation damage via electromagnetic interference shielding (EMI) materials is crucial for diverse applications, especially in modern aerospace, medical, and human body protection endeavors. Despite great efforts have been made to surmount challenges encompassing scalability, sustainability and cost, the integrated and continuous production of large-area electromagnetic shielding materials remains unsolved for industrial-scale demands. Herein, we develop a cascaded methodology involving spray loading and Joule-heating for fabricating hybrid EMI fabric with superior efficiency, where ferromagnetic Fe3O4 nanoparticles are further successfully in situ deposition on ultralight carbon fiber felt (Fe3O4/FePc@CFF) in a roll-to-roll (R2R) manner. Fe3O4/FePc@CFF characterized by a surface density of only 64.76 g/m2, achieves specific shielding effectiveness per unit thickness (SSE/t) remarkable values of 9604 dB cm2 g−1 and 10947 dB cm2 g−1 within the X-band and Ku-band, respectively. Considering the high compatibility with assembly on flow line production, this research offers substantial development potential for further design and advancement of pivotal materials in the realm of electromagnetic protection.

Microporous Cobalt Ferrite with Bio-Carbon Loosely Decorated to Construct Multi-Functional Composite for Dye Adsorption, Anti-Bacteria and Electromagnetic Protection.

Currently, facing electromagnetic protection requirement under complex aqueous environments, the bacterial reproduction and organic dye corrosion may affect the composition and micro-structures of absorbers to weaken their electromagnetic properties. To address such problems, herein, a series of CoFe2O4@BCNPs (cobalt ferrite @ bio-carbon nanoparticles) composites are synthesized via co-hydrothermal and calcining process. The coupling of magnetic cobalt ferrite and dielectric bio-carbon derived from Apium can endow the composite multiple absorption mechanisms and matched impedance for effective microwave absorption, attaining a bandwidth of 8.12 GHz at 2.36 mm and an intensity of -49.85 dB at 3.0 mm. Due to the ROS (reactive oxygen species) stimulation ability and heavy metal ions of cobalt ferrite, the composite realizes an excellent antibacterial efficiency of 99% against Gram negative bacteria of Escherichia coli. Moreover, the loose porous layer of surface stacked bio-carbon can promote the adsorption of methylene blue for subsequent eliminating, a high removal rate of 90.37% for organic dye can be also achieved. This paper offers a new insight for rational design of composite's component and micro-structure to construct multi-functional microwave absorber for satisfying the electromagnetic protection demand in complicated environments.

Computational analysis of electromagnetic field exposure in passengers near high- current contact wire environments.

The electromagnetic environment of a railway station is composed of electrical, magnetic, and electromagnetic fields, which are generated by various sources such as traction current, voltage, pantograph-catenary arc, locomotive braking, wheel-rail rolling arc, and communication systems. However, there is public growing concern among the public about the potential negative human health effects of this electromagnetic environment. To analyze the distribution of electromagnetic fields in human tissues, electromagnetic simulation software is used to create a model that includes six track contact wires and four waiting passengers on three platforms. This model is used to analyze the magnetic field environment created by high currents in the contact wires of a multi-track high-speed railway station. By varying the loads on different contact wires, the distribution of electric field and magnetic flux density within human tissues of waiting passengers on different platforms is studied using this model. When the track is unoccupied, the calculation results show that the maximum values of the electric field and magnetic flux density of the passenger's human body tissue at the blind way on the platform and 1m of the blind way are 17.6mVm-1 and 52.7 μT, respectively. These values increase by 9.28mVm-1 and 16.4 μT compared to when the track is occupied. When more contact wires are loaded with currents, the electric field mode and magnetic flux density mode of human tissues increase at the same position on the platform. Specifically, when the contact wires of six tracks are loaded with current at the same time, the maximum values of the electric field mode and magnetic flux density mode of the waiting passengers' human tissues at the blind way on different platforms are 29.6mVm-1 and 88.1 μT, respectively. These maximum values are lower than the public electromagnetic exposure limits that are designated by the International Commission on Non-Ionizing Radiation Protection guidelines. The research results demonstrate that the magnetic field environment generated by the current in the contact wires of a railway station with six tracks does not pose a health risk to human tissues of passengers waiting at the blind way and 1m of the blind way on the platform. These findings can provide valuable data reference for the formulation of relevant standards for the design of electrified rail transit, as well as the suppression of electromagnetic interference and protection of human bioelectromagnetism.

Dynamically Controllable Terahertz Electromagnetic Interference Shielding by Small Polaron Responses in Dirac Semimetal PdTe2 Thin Films

AbstractTerahertz (THz) electromagnetic interference (EMI) shielding materials is crucial for ensuring THz electromagnetic protection and information confidentiality technology. Here, it is demonstrated that high electrical conductivity and strong absorption of THz electromagnetic radiation by type‐II Dirac semimetal PdTe2 film make it a promising material for EMI shielding. Compared to MXene film, a commonly used metallic 2D material, the PdTe2 film demonstrates a remarkable 40.36% increase in average EMI shielding efficiency per unit thickness within a broadband THz frequency range. Furthermore, it is demonstrated that a photoinduced long life‐time THz transparency in Dirac semimetal PdTe2 films is attributed to the formation of small polarons due to the strong electron‐phonon coupling. A 15 nm‐thick PdTe2 film exhibits a photoinduced change of EMI SE of 1.1 dB, a value exceeding three times that measured on MXene film with a similar pump fluence. This work provides insights into the fundamental photocarrier properties in type‐II Dirac semimetals that are essential for designing advanced THz optoelectronic devices.

Mechanical properties and electromagnetic wave absorption characteristics of solid waste low-carbon cementitious materials

A low-carbon multi-functional cement substitute material has been developed to reduce electromagnetic pollution in building spaces and protect human health. The solid waste electromagnetic absorption cementitious material (SWEACM) is produced by combining steel slag (SS), blast furnace slag (BFS), and phosphogypsum (PG). In this study, the properties of SWEACM were analyzed, including flow, electromagnetic wave absorption, strength, and environmental properties. Additionally, the hydration and electromagnetic wave absorption mechanisms were examined. The results indicate that SS, BFS, and PG content significantly affect the strength and electromagnetic wave absorption properties of SWEACM. S-6 exhibits the best overall performance (SS: BFS: PG = 3:6:1), with the highest strength (28 days compressive strength = 33.5 MPa) and fluidity (19.1 cm). Furthermore, it has excellent electromagnetic absorption performance (RLmin = −45.4 dB), with an adequate absorption bandwidth of up to 10 GHz in the 2–18 GHz range. The excellent electromagnetic wave absorption capability of SWEACM is mainly due to the resonance, polarization relaxation loss, and conduction loss of the magnetic and conductive components in the material. The results show that SWEACM can be used as a multi-functional construction engineering material for electromagnetic protection, combining high levels of high electromagnetic wave absorption, strength performance, and environmental benefits.

Proximity Effects of Electromagnetic Field Radiation from Cellular Wireless System on Living Things and Their Mitigation Techniques

Research on electromagnetic field radiation exposure from cellular wireless systems is expected to become more important, allowing researchers to provide solutions for the effects of this radiation on human living beings. During the research, experiment animals were unprotected to RF radiations for 8 hours every day for 30 days. The exposure duration involved the placement of test animals in Plexiglass boxes. An RF transmitter was placed on the cage's roof from within. The transmitter emitted EMF radiations that were noted in rats. An elevated plus maze and open field test was utilized to determine behavioral parameters. On the 8th, 15th and 30th day of exposure, behavioral tests were administered. According to our findings, EMF radiation toxicity is closely linked with the exposure to this form of radiation. An increase in the toxicity level was observed as exposure time passed. Furthermore, this research demonstrated that EMF radiation exposure resulted in neuronal injury. The RF transmitter was subjected to tests with shielding materials, including woven and non-woven fabrics, which serve as technical textiles for electromagnetic radiation protection.

Biomimetic Leaf-Vein Aerogel for Electromagnetic Wave Absorption and Thermal Superinsulation.

Electromagnetic protection in extreme environments requires materials with excellent thermal insulation capability and mechanical property to withstand severe temperature fluctuations and complex external stresses. Achieving strong electromagnetic wave absorption (EMA) while sustaining these exceptional properties remains a significant challenge. Herein, a facile approach is demonstrated to fabricate a biomimetic leaf-vein MXene/CNTs/PI (MCP) aerogel with parallel venations through bidirectional freeze-casting method. Due to its multi-arch lamellar structure and parallel venations within the aerogel layers, the ultralight MCP aerogel (16.9 mg·cm-3) achieves a minimum reflection loss (RLmin) of -75.8dB and a maximum effective absorption bandwidth (EABmax) of 7.14GHz with an absorber content of only 2.4wt%, which also exhibits superelasticity and structural stability over a wide temperature range from -196 to 400°C. Moreover, this unique structure facilitates rapid heat dissipation within the layers, while significantly impeding heat transfer between adjacent layers, achieving an ultralow thermal conductivity of 15.3 mW·m-1·K-1 for thermal superinsulation. The combination of excellent EMA performance, robust structural stability, and thermal superinsulation provides a potential design scheme under extreme conditions, especially in aerospace applications.

Electromagnetic wave absorption characteristics of silicon carbide modified concrete applied to protective engineering

Electromagnetic protection measures can effectively prevent electromagnetic waves from harming equipment, facilities, information security and human health. To enhance the electromagnetic wave-absorbing capacity of standard concrete, silicon carbide (SiC) was selected as an absorbing agent to produce wave-absorbing concrete. The influences of SiC content on the electromagnetic reflection loss, electromagnetic parameters, and mechanical properties of concrete were systematically investigated. After 28 days of curing, the concrete sample modified with 10 wt% SiC displays the compressive strength and splitting tensile strength of 36.12 MPa and 3.10 MPa, respectively. And the optimum electromagnetic absorption performance reaches −16.25 dB at 3.37 GHz and the electrical conductivity is 1.55×10−4 S/m. The SiC modified concrete demonstrates the dielectric loss type absorption characteristics. This research provides a practical solution for electromagnetic wave protection, which is expected to be used in both military and civilian applications.