U-Sung Choi

Electrical conductivity and CO gas sensitivity of ZnO-TiO/sub 2/ composites

Using complex impedance measurement, a voltage-current source and measurement unit, the AC and DC characteristics of ZnO-TiO/sub 2/ composites are investigated. The electrical conductivity increase with increasing TiO/sub 2/ content was explained by the connectivity of ZnO and TiO/sub 2/ grains. Compared with pure and ball-milled ZnO, the electrical conductivity of TiO/sub 2/ added ZnO in the impedance spectrum is four orders of magnitude smaller. The calculated relative dielectric constants for the 3, 5, and 7 mol% TiO/sub 2/ added ZnO are 7, 13, and 120, respectively. Compared with the relative dielectric constant of ZnO, the semicircle of 3 mol% TiO/sub 2/ added ZnO seems to be the ZnO grain. The sizes of the semicircle decrease with increasing TiO/sub 2/ content. These results are consistent with the trends of DC conductivity.

Theoretical study of the structures and nonlinear optical properties of hydrogen-bonded nitroaniline systems

Abstract The structures, first-, second-, and third-order polarizabilities for the linear hydrogen-bonded p-nitroaniline systems 1a – 5a and related systems 2b – 5b are calculated by the use of ab initio and PM3 semiempirical methods. The difference of ab intio and PM3 calculated OH hydrogen bond distances between NO 2 and NH 2 groups for 2a , 3a , 2b , and 3b are 0.31, 0.31, 0.18, and 0.27, respectively. The PM3-predicted frequency dependent asymptotic values of γ for the frequencies of 0.0eV, 0.25eV, and 0.5eV are 5.3e5, 5.7e5, and 7.4e5 10 −36 esu in the linear types, respectively. The linear hydrogen bonded p-nitroaniline systems exhibit power law dependences with the exponents 1.5852, 1.5946, and 1.6272, repectively.

Design and Fabrication of Dielectric Duplexer and Bandpass Filters for K-PCS and W-CDMA Dualband

¹ Department of Electrical. Information and Communication Engineering, Wonkwang University, Iksan 570-749, Korea² Department of Electronics, Kwangwoon University, Seoul 139-701, Korea³ Department of Chemistry, Chonbuk University, Jeounju 561-756, Korea⁴RD Revised November 5, 2012; Accepted November 7, 2012)Abstract: The K-PCS and W-CDMA dual band dielectric duplexer and bandpass filters have been designed and fabricated. The dual band duplexer consists of the separate monoblock K-PCS and W-CDMA duplexers using common antenna port. The coupling capacitance and I/O impedance matching have been designed to minimize the cross interference between the bands. Isolations of crosspoint between Tx and Rx in K-PCS and W-CDMA dualband were about 47 dB and 100 dB, respectively. On the other hand, isolations of Tx and Rx in K-PCS and W-CDMA were about 66 dB and 65 dB, respectively. The difference between 47 dB and 100 dB originated from the different center frequencies in Tx and Rx of K-PCS and W-CDMA bands. The coupling capacitance of the bandwidth, I/O capacitance of I/O matching and impedance matching, and various capacitances were important role to fabricate the dielectric duplexer and bandpass filters.Keywords: K-PCS, W-CDMA, Isolation, Capacitance

A Study on the Development of Gap filler Isolator by using the YIG Ferrite

In this paper, developed isolator for gap filler is analyzed and designed using the simulation tool. Using the designed parameters, isolator is fabricated and tested in gap filler band. Temperature characteristics of isolator depend on magnet, YIG ferrite, and conductor etc. These require temperature stability and possible method of compensation for the temperature dependent effects. The temperature stabilization tries to use Ni-alloy. Developed isolator that compare with room temperature and high temperature characteristics has change fewer than 20 MHz. Implemented isolator shows more than 20 dB isolation characteristic at center frequency(2,650 MHz) and has 0.2 dB insertion loss in overall 100 MHz operating bandwidth. Return losses of input and output port are measured below -20 dB.

Electrical characteristics of SnO/sub 2/ added ZnO

Using the 2-probe methods, the conductivities, dielectric loss factors, capacitances, and impedances were investigated to study the electrical properties for pure, ball-milled, 1, 2, 3, 5, 7 mol% SnO/sub 2/ added ZnO. We estimated the frequency dependent ac-conductivities, dielectric loss factors, and capacitances for infinitely long frequencies. The asymptotic ac-conductivities for 3, 5, and 7 mol% SnO/sub 2/ added ZnO are -5.16, -5.94, and -6.05, respectively. The calculated relative dielectric constant of 3, 5, and 7 mol% SnO/sub 2/ added ZnO are 55, 20, and 14 at the semicircle peak on the impedance spectrum, respectively. Therefore, the decrease of electrical conductivity of specimens was explained by the increase of grain resistance due to the increase of the number of ZnO grains.

A.C. and D.C. characteristics of ZnO-Al/sub 2/O/sub 3/ composites

Alternating current and direct current of pure, ball-milled, or Al/sub 2/O/sub 3/ added ZnO are investigated by means of complex impedance measurement and a voltage-current source measurement unit. The electrical conductivity of ZnO-Al/sub 2/O/sub 3/ composite increases when the content of Al/sub 2/O/sub 3/ is within 1 at.% and decreases when it is more than that. The increase and decrease of electrical conductivity seem to be due to the donor effect of Al/sub 2/O/sub 3/ and the increase of the number of ZnO grains, respectively. The impedance spectrum seems to be semicircular. The sizes of semicircle increase with increasing Al/sub 2/O/sub 3/ content. The calculated dielectric constants (at 50/spl deg/C) were about 70-140 at the peak of the semicircle.

The Frequency Dependent Nonlinear Optical Properties of Thiophene-, Furan-, Pyrrole-Nitro Polyene Systems

Abstract By using the semiempirical time-dependent Hartree-Fock PM3 calculations we have studied the frequency-dependent second-and third-order polarizabilities of thiophene-, furan-, pyrrole-nitro polyene systems. The PM3 predicted limiting average second-order polarizabilities increase in the order: pyrrole-> furan-> thiophene-nitro polyene systems. The average and longitudinal third-order polarizabilties have the following order: pyrrole->thiophene->furan-nitro polyene systems. In these trends, we sugest that pyrrole group is the best donor group among the three polyene systems.