skip to main content
US FlagAn official website of the United States government
dot gov icon
Official websites use .gov
A .gov website belongs to an official government organization in the United States.
https lock icon
Secure .gov websites use HTTPS
A lock ( lock ) or https:// means you've safely connected to the .gov website. Share sensitive information only on official, secure websites.

Explore Research Products in the PAR
It may take a few hours for recently added research products to appear in PAR search results.


  • NSF Public Access
  • Search Results
  • Barium Ferrite/Carbon Nanotube Nanocomposites for Millimeter‐Wave Electromagnetic Shielding Enhanced by Ferromagnetic Resonance Absorption
Title: Barium Ferrite/Carbon Nanotube Nanocomposites for Millimeter‐Wave Electromagnetic Shielding Enhanced by Ferromagnetic Resonance Absorption
In this work, a composite of barium ferrite (BaM) and multiwalled carbon nanotubes (CNTs) in a polymer matrix of polydimethylsiloxane (PDMS) are reported for the purpose of suppressing electromagnetic interference (EMI). Shielding is accomplished primarily through absorption, which arises from a combination of the ferromagnetic resonance (FMR) from the BaM and conductive losses from the CNTs. The composite is fabricated by mixing commercially available BaM nanoparticles and CNTs into PDMS, screen printing the mixture into molds, then curing at 80 °C in a DC magnetic field. Characterization involves placing the composite in the cross‐section of a rectangular waveguide, then using a vector network analyzer (VNA) to measure scattering (S) parameters from 33–50 GHz. Using the measured S parameters, power reflected and absorbed can be calculated and used to characterize the composite's shielding effectiveness (SE), and the complex permittivity and permeability can be determined. The resulting 2.4 mm thick composite shows a peak absorption of 26.9 dB at the FMR frequency of 47.4 GHz. When normalized for thickness, the composite, on average, absorbs 11.3 dB mm−1and operates at a higher frequency than other shielding composites found in the literature.  more » « less
Award ID(s):
1939009
PAR ID:
10570116
Author(s) / Creator(s):
; ; ;
Publisher / Repository:
John Wiley & Sons, Inc.
Date Published:
Journal Name:
Advanced Engineering Materials
Volume:
26
Issue:
9
ISSN:
1438-1656
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. ; ; ; ; ; ; ; ; (, Advanced Materials Technologies)
    Abstract Simulation and experimental studies are carried out on single‐layer and double‐layer embedded metal meshes (SLEMM and DLEMM) to assess their performance as transparent electromagnetic interference (EMI) shielding. The structures consist of silver meshes embedded in polyethylene terephthalate (PET). As a transparent electrode, SLEMMs exhibit a transparency of 82.7% and a sheet resistance of 0.61 Ωsq−1as well as 91.0% and 1.49 Ωsq−1. This performance corresponds to figures of merit of 3101 and 2620, respectively. The SLEMMs achieve 48.0 dB EMI shielding efficiency (SE) in the frequency range of 8–18 GHz (X‐ and Ku‐bands) with 91% visible transmission and 56.2 dB EMI SE with 82.7% visible transmission. Samples exhibit stable performance after 1000 bending cycles with a radius of curvature of 4 mm and 60 tape test cycles. DLEMMs consist of fabricating SLEMM on opposite sides of the substrate where the distance can be varied using a spacer. Simulations are performed to investigate how varying spacer distance between two layers of metal meshes influences the EMI SE. DLEMMs are fabricated and achieved an EMI SE of 77.7 dB with 81.7% visible transmission. SLEMMs and DLEMMs may have a wide variety of applications in aerospace, medical, and military applications. 
    more » « less
  2. ; ; (, Journal of Physics: Photonics)
    Abstract We present a metal–semiconductor (M–S) based electro-optic modulator designed for functional plasmonic circuits, utilizing the active control of surface plasmon polaritons (SPPs) at M–S junction interfaces. Through self-consistent multiphysics simulations, including electromagnetic, thermal, and current–voltage (IV) characteristics, we estimate bias- and doping concentration-dependent SPP modulation and switching times. This study focuses on germanium-based Schottky contacts and can be extended to other semiconducting materials. We performed parametric analysis using the developed thermo-electro-optic model to identify device parameters and dimensions for enhanced optical confinement and faster operation. The studied device exhibits signal modulation exceeding −28 dB, responsivity greater than −1800 dB V−1, and switching rates of 8 GHz, suggesting potential data rates above 16 Gbit s−1. Additionally, frequency response analysis using the numerical model confirms the device’s electrical tunability and predicts a 3 dB bandwidth of up to 4 GHz. These findings highlight the significant potential of Schottky junctions as active components in the development of plasmonic-based integrated circuits. 
    more » « less
  3. ; ; (, Physics in Medicine & Biology)
    Abstract Cortical bone is characterized by a dense solid matrix permeated by fluid-filled pores. Ultrasound scattering has potential for the non-invasive evaluation of changes in bone porosity. However, there is an incomplete understanding of the impact of ultrasonic absorption in the solid matrix on ultrasound scattering. In this study, maps were derived from scanning acoustic microscopy images of human femur cross-sections. Finite-difference time domain ultrasound scatter simulations were conducted on these maps. Pore density, diameter distribution of the pores, and nominal absorption values in the solid and fluid matrices were controlled. Ultrasound pulses with a central frequency of 8.2 MHz were propagated, both in through-transmission and backscattering configurations. From these data, the scattering, bone matrix absorption, and attenuation extinction lengths were calculated. The results demonstrated that as absorption in the solid matrix was varied, the scattering, absorption, and attenuation extinction lengths were significantly impacted. It was shown that for lower values of absorption in the solid matrix (less than 2 dB mm−1), attenuation due to scattering dominates, whereas at higher values of absorption (more than 2 dB mm−1), attenuation due to absorption dominates. This will impact how ultrasound attenuation and scattering parameters can be used to extract quantitative information on bone microstructure. 
    more » « less
  4. ; ; ; ; ; ; ; ; (, Sensors)
    The magnetoelectric effect (ME) is an important strain mediated-phenomenon in a ferromagnetic-piezoelectric composite for a variety of sensors and signal processing devices. A bias magnetic field, in general, is essential to realize a strong ME coupling in most composites. Magnetic phases with (i) high magnetostriction for strong piezomagnetic coupling and (ii) large anisotropy field that acts as a built-in bias field are preferred so that miniature, ME composite-based devices can operate without the need for an external magnetic field. We are able to realize such a magnetic phase with a composite of (i) barium hexaferrite (BaM) with high magnetocrystalline anisotropy field and (ii) nickel ferrite (NFO) with high magnetostriction. The BNx composites, with (100 − x) wt.% of BaM and x wt.% NFO, for x = 0–100, were prepared. X-ray diffraction analysis shows that the composites did not contain any impurity phases. Scanning electron microscopy images revealed that, with an increase in NFO content, hexagonal BaM grains become prominent, leading to a large anisotropy field. The room temperature saturation magnetization showed a general increase with increasing BaM content in the composites. NFO rich composites with x ≥ 60 were found to have a large magnetostriction value of around −23 ppm, comparable to pure NFO. The anisotropy field HA of the composites, determined from magnetization and ferromagnetic resonance (FMR) measurements, increased with increasing NFO content and reached a maximum of 7.77 kOe for x = 75. The BNx composite was cut into rectangular platelets and bonded with PZT to form the bilayers. ME voltage coefficient (MEVC) measurements at low frequencies and at mechanical resonance showed strong coupling at zero bias for samples with x ≥ 33. This large in-plane HA acted as a built-in field for strong ME effects under zero external bias in the bilayers. The highest zero-bias MEVC of ~22 mV/cm Oe was obtained for BN75-PZT bilayers wherein BN75 also has the highest HA. The Bilayer of BN95-PZT showed a maximum MEVC ~992 mV/cm Oe at electromechanical resonance at 59 kHz. The use of hexaferrite–spinel ferrite composite to achieve strong zero-bias ME coupling in bilayers with PZT is significant for applications related to energy harvesting, sensors, and high frequency devices. 
    more » « less
  5. ; ; ; ; ; ; ; ; ; ; et al (, Advanced Materials)
    Abstract Polymer composite films containing fillers comprising quasi‐1D van der Waals materials, specifically transition metal trichalcogenides with 1D structural motifs that enable their exfoliation into bundles of atomic threads, are reported. These nanostructures are characterized by extremely large aspect ratios of up to≈106. The polymer composites with low loadings of quasi‐1D TaSe3fillers (<3 vol%) reveal excellent electromagnetic interference shielding in the X‐band GHz and extremely high frequency sub‐THz frequency ranges, while remaining DC electrically insulating. The unique electromagnetic shielding characteristics of these films are attributed to effective coupling of the electromagnetic waves to the high‐aspect‐ratio electrically conductive TaSe3atomic‐thread bundles even when the filler concentration is below the electrical percolation threshold. These novel films are promising for high‐frequency communication technologies, which require electromagnetic shielding films that are flexible, lightweight, corrosion resistant, inexpensive, and electrically insulating. 
    more » « less
  • Citation Formats
  • MLA
  • APA
  • Chicago
  • BibTeX
  • Save / Share this Record
  • Send to Email