C. Y. Lee

Electromagnetic interference shielding efficiency of polyaniline mixtures and multilayer films

Abstract Electromagnetic interference shielding efficiency (SE) of the mixtures of polyaniline (PAN) and conducting powders such as silver (Ag), graphite, and carbon black is measured in the frequency range from 10 MHz to 1 GHz by using ASTM D4935-89 technique. The measured SEs of the mixtures are from 20 dB to 50 dB, which agree with theoretical values obtained from a good-conductor approximation. The SEs of the system increase with increasing DC conductivity. For the mixture of emeraldine base form of PAN and Ag powder doped with hydrochloric acid, the SE iElectromagnetic interference shielding efficiency (SE) of the mixtures of polyaniline (PAN) and conducting powders such as silver (Ag), graphite, and carbon black is measured in the frequency range from 10 MHz to 1 GHz by using ASTM D4935-89 technique. The measured SEs of the mixtures are from 20 dB to 50 dB, which agree with theoretical values obtained from a good-conductor approximation. The SEs of the system increase with increasing DC conductivity. For the mixture of emeraldine base form of PAN and Ag powder doped with hydrochloric acid, the SE iElectromagnetic interference shielding efficiency (SE) of the mixtures of polyaniline (PAN) and conducting powders such as silver (Ag), graphite, and carbon black is measured in the frequency range from 10 MHz to 1 GHz by using ASTM D4935-89 technique. The measured SEs of the mixtures are from 20 dB to 50 dB, which agree with theoretical values obtained from a good-conductor approximation. The SEs of the system increase with increasing DC conductivity. For the mixture of emeraldine base form of PAN and Ag powder doped with hydrochloric acid, the SE iElectromagnetic interference shielding efficiency (SE) of the mixtures of polyaniline (PAN) and conducting powders such as silver (Ag), graphite, and carbon black is measured in the frequency range from 10 MHz to 1 GHz by using ASTM D4935-89 technique. The measured SEs of the mixtures are from 20 dB to 50 dB, which agree with theoretical values obtained from a good-conductor approximation. The SEs of the system increase with increasing DC conductivity. For the mixture of emeraldine base form of PAN and Ag powder doped with hydrochloric acid, the SE is46 dB with70 μm thickness. Chemical doping in PAN mixture samples induces the increase of the SE. The model accounting for the increase of the SE in the mixture system is discussed. The effects of multilayer of PAN on the SE are presented.6 dB with70 μm thickness. Chemical doping in PAN mixture samples induces the increase of the SE. The model accounting for the increase of the SE in the mixture system is discussed. The effects of multilayer of PAN on the SE are presented.6 dB with70 μm thickness. Chemical doping in PAN mixture samples induces the increase of the SE. The model accounting for the increase of the SE in the mixture system is discussed. The effects of multilayer of PAN on the SE are presented.6 dB with70 μm thickness. Chemical doping in PAN mixture samples induces the increase of the SE. The model accounting for the increase of the SE in the mixture system is discussed. The effects of multilayer of PAN on the SE are presented.

Method and apparatus to measure electromagnetic interference shielding efficiency and its shielding characteristics in broadband frequency ranges

We have designed and manufactured a flanged coaxial line as a sample holder for measuring the electromagnetic interference (EMI) shielding efficiency (SE) of planar materials in broadband frequency ranges up to 18 GHz. Connecting the samples holder to a vector network analyzer (50u2009MHz⩽M⩽13.5u2009GHz), we measured the S (scattering)-parameters and the EMI SE of copper (Cu) as a highly conducting material and emeraldine salt form of polyaniline (PAN–ES) as an intermediately conducting one. The measured EMI SEs of the materials from 50 MHz to 13.5 GHz were compared with those obtained from the conventional ASTM D4935-99 method and theoretical simulation using dc conductivity. We observed that the EMI SEs measured by using both experimental techniques agree with each other in the common frequency range (50u2009MHz∼1.5u2009GHz). The EMI shielding characteristics of samples such as the contribution of absorption and reflection to total EMI SE were analyzed through the measured S parameters.

Electromagnetic interference shielding characteristics of fabric complexes coated with conductive polypyrrole and thermally evaporated Ag

Through the chemical coating of polypyrrole (PPy) doped with naphthalene sulfonic acid (NSA) on electrically insulating poly (ethylene terephthalate) (PET) woven fabric, PPy–NSA/PET complexes were synthesized. By using the electrochemical coating of PPy doped anthraquinone-2-sulfonic acid (AQSA) on PPy–NSA/PET complexes, PPy–AQSA/PPy–NSA/PET complexes were synthesized. The silver (Ag) was thermally vacuum evaporated on the surface of PPy–AQSA/PPy–NSA/PET complexes (Ag|PPy–AQSA/PPy–NSA/PET). Electromagnetic interference (EMI) shielding efficiency (SE) and dc conductivity (σdc) of fabric complexes were measured for EMI shielding characteristics and theoretical simulation. The measurement of EMI SE in the frequency range from 50 MHz to 1.5 GHz was performed by using ASTM D4935-99 method. The EMI shielding characteristics such as transmittance, reflectance and absorbance were obtained from the S (scattering)-parameter analysis. We control the contribution of the absorbance or the reflectance to total EMI SE through the coating of conductive PPy and the evaporation Ag.

Conductivity and EMI shielding efficiency of polypyrrole and metal compounds coated on (non) woven fabrics

We synthesized polypyrrole (PPy) and metal (AgPd) compounds coated on woven polyethylene teraphthalate (PET) and nonwoven polyester (PE) fabrics. PPy coated on PET or PE fabrics was chemically polymerized by using naphthalene sulfonic acid (NSA) as a dopant and electrochemically synthesized by using anthraquinon-2-sulfonic acid (AQSA) as a dopant. Temperature dependences of de conductivity [σ dc (T)] of PPy-NSA/fabric and PPy-AQSA/fabric complexes are compared. The electromagnetic interference (EMI) shielding efficiency (SE) of PPy/fabric complexes is in the range of 20 ∼ 80 dB depending on the thickness and conductivity.

AC electrical properties of conjugated polymers and theoretical high-frequency behavior of multilayer films

Abstract AC electrical properties of various conjugated polymers such as emeraldine base form of polyaniline, polyacetylene derivatives, and poly(1,4-phenylenevinylene) and its derivative are studied. Dielectric constant and conductivity are measured in the frequency range from 10xa0Hz to 2xa0MHz and in the temperature range from 78 to 300xa0K. Frequency dependence of ac dielectric constant follows Debye or Cole–Cole dielectric relaxation equation, and temperature dependence of relaxation time τ follows Arrhenius equation τ=τ 0 exp (E a /k B T) . Frequency dependence of ac conductivity shows a constant behavior in low-frequency regime (≤10xa0kHz) and a power-law behavior ( σ ∼ ω s ) in high-frequency regime (≥100xa0kHz). For the applications of multilayer films of conducting polymers such as electromagnetic interference (EMI) shielding or optical filter, we theoretically calculate the reflectance, absorbance, and EMI shielding efficiency in high-frequency range (≥1xa0GHz) based on plane wave theory.

Electrical characteristics of light-emitting diode based on poly(p-phenylenevinylene) derivatives: CzEH-PPV and OxdEH-PPV

Abstract In the light-emitting devices (LEDs) based on the π-conjugated polymers, the relationship between the quantum efficiency and the balance of hole ( μ h ) and electron ( μ e ) mobility has been investigated. In order to measure the μ h and μ e of the LEDs based on π-conjugated polymers, we fabricated the hole transport device (HTD) and the electron transport device (ETD) by using various metal electrodes with different work functions. For the materials of light emitting layer, we synthesized poly[2-( N -carbazolyl)-5-(2-ethylhexyloxy)-1,4-phenylene vinylene] (CzEH-PPV) and poly[2-{4-[5-(4- tert -butylphenyl)-1,3,4-oxadiazolyl]-phenyl}-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (OxdEH-PPV) with electron-rich groups. The poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylene vinylene] (MEH-PPV), which is well known material for the polymer-based LED, was synthesized for the reference. We measured the current density vs. applied field ( J – E ) characteristics of the HTD and ETD with various thickness at different temperatures. The results of the J – E curves were analyzed by using the space charge limited conduction (SCLC) model. Based upon the SCLC model, μ h and μ e of MEH-PPV sample was measured to be ∼10 −6 xa0cm 2 /Vxa0s and ∼10 −8 xa0cm 2 /Vxa0s, respectively. For CzEH-PPV and OxdEH-PPV samples with electron-rich groups, μ h was similar to μ e with 10 −10 –10 −11 xa0cm 2 /Vxa0s. The μ h and μ e of CzEH-PPV and OxdEH-PPV samples was lower than that of MEH-PPV sample, but more balanced. The quantum efficiency of the LED by using CzEH-PPV or OxdEH-PPV materials was ∼10 times higher than that prepared from MEH-PPV. The balance of the μ h and μ e plays an important role for the quantum efficiency. We analyze the balance of the μ h and μ e and the relatively low mobilities of CzEH-PPV and OxdEH-PPV samples in terms of the heavier effective mass due to the asymmetric dipole distribution in the side chains. The results of photocurrent of the systems qualitatively agreed with the result of the electrical measurements. From AC impedance measurement of the LEDs, we observed that the relaxation time of MEH-PPV was shorter than that of OxdEH-PPV sample because of the higher mobility of MEH-PPV sample.