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A series of hole-transporting materials (HTMs) based on [2,2]paracyclophane and triphenyl-amine (TPA) was synthesized. We studied the effect of the chemical structure of the HTM on the photovoltaic performance of perovskite solar cells by varying the number of TPA charge transporting components in the HTM. Tetra-TPA, in which four TPAs are incorporated into the [2,2]paracyclophane core, exhibited better hole transport properties than di-TPA and tri-TPA, which contain two and three TPAs, respectively. In particular, incorporation of the TPA group with a multi-armed structure effectively enhanced the conductivity of the HTM layer in the out-of-plane direction in the solar cell device. Due to the improved charge transport and appropriate molecular energy levels of tetra-TPA, the perovskite solar cell based on the tetra-TPA HTM achieved higher Jsc and FF values than the devices based on di-TPA and tri-TPA HTMs, with a high solar cell efficiency (17.9%).

We prepared a series of small molecules based on 7,7'-(4,4-bis(2-ethylhexyl)-4H-silolo[3,2-b:4,5-b']dithiophene-2,6-diyl)bis(4-(5'-hexyl-[2,2'-bithiophene]-5-yl)benzo[c][1,2,5]thiadiazole) with different fluorine substitution patterns (0F-4F). Depending on symmetricity and numbers of fluorine atoms incorporated in the benzo[c][1,2,5]thiadiazole unit, they show very different optical and morphological properties in a film. 2F and 4F, which featured symmetric and even-numbered fluorine substitution patterns, display improved molecular packing structures and higher crystalline properties in a film compared with 1F and 3F and thus, 2F achieved the highest OTFT mobility, which is followed by 4F. In the bulk heterojunction solar cell fabricated with PC71BM, 2F achieves the highest photovoltaic performance with an 8.14% efficiency and 0F shows the lowest efficiency of 1.28%. Moreover, the planar-type perovskite solar cell (PSC) prepared with 2F as a dopant-free hole transport material shows a high power conversion efficiency of 14.5% due to its high charge transporting properties, which were significantly improved compared with the corresponding PSC device obtained from 0F (8.5%). From the studies, it is demonstrated that low variation in the local dipole moment and the narrow distribution of 2F conformers make intermolecular interactions favorable, which may effectively drive crystal formations in the solid state and thus, higher charge transport properties compared with 1F and 3F.

A new miniaturized 4-port waveguide generating a transverse electromagnetic wave is proposed. The waveguide presents enhanced performance of higher field uniformity in extended test volume up to an increased test frequency limit compared to that of the conventional 2-port waveguide. The advantageous features of the proposed waveguide have been obtained through a new design scheme based on effective miniaturization maintaining good impedance matching. Consequently, we can provide a more accurate electromagnetic compatibility test method, covering larger devices operating in higher frequencies, which is a marked improvement upon the conventional approaches.

The specific absorption rates (SARs) in 7-year-old Korean, and 5- and 9-year-old European child head models were evaluated and compared with those of the specific anthropomorphic mannequin (SAM) phantom for mobile phone exposure at 835 and 1900 MHz. Compression of the pinnae was also considered for the 5- and 7-year-old child models during the evaluation. The cheek and tilt positions occurring when the earpiece of the phone is placed at the ear entrance canal (EEC) were analyzed against the same positions occurring when the earpiece is placed at the ear reference point (ERP). SAR variations were investigated for different skin and fat properties, as well as for different internal fat and muscle morphologies in the tissue area near the phone. A basic phone model with a monopole antenna was used for SAR calculation at each frequency. A phone model with a planar inverted F antenna was also used for verification, since the SAR results in the child models were higher than those in the SAM phantom at 1900 MHz. The spatial peak 10-g SAR values in all tissue including the pinnae and head-only were normalized to a forward power of 1 W at the feedpoint of the phone. Our results can be summarized as follows. First, a compressed pinna did not show significant changes in SAR values at 835 MHz; however, at 1900 MHz, there was an average 25% increase in spatial peak 10-g SARs for pinna-excluded tissue and a 29% increase for pinna-included tissue. Second, a phone earpiece placed at the EEC provided higher SARs in many cases compared to placement at the ERP. Third, the peak 10-g SAR was found to be very sensitive to the fat and muscle structure under the skin when touched by the mobile phone; a muscle-dominant internal head structure led to a higher peak 10-g SAR. Finally, the SAM phantom does not seem to provide a conservative estimation of child head exposure at 1900 MHz; 45% (pinna-excluded: IEEE Std C95.1) and 75% (pinna-included: ICNIRP guidelines) of the 40 total cases we reviewed showed higher SAR results than the SAM phantom.

In this paper, we proposed the method of the interference evaluation between the microwave oven noise and the wireless LAN(Local Area Network) by using the GTEM cell. We used microwave oven noise in time to assess the interference unintentional noise effects on wireless LAN and realized by combining an AM(Amplitude Modulation) modulator and a FM(frequency Modulation) modulator. Also the GTEM cell can be used to guarantee the reliability by the evaluations of the frequency and time responses. As measurement results for the APD(Amplitude Probability Distribution) of the interfering noise we analyzed the effect of microwave oven noise to the throughput of wireless LAN.

The far-field pattern and gain obtained using the far-field measurement method can be highly accurate when the distance between the source antenna and the antenna under test (AUT) satisfies the Rayleigh far-field criterion. In this letter, we propose an improved Fresnel region measurement method that can be applied in a shortened distance between two antennas. The many Fresnel fields required are captured by changing angle phi of the scanning plane. This scanning involves rotating the roll positioners of the source antenna and the AUT in the same direction and by the same amount, and rotating the azimuth positioner in the horizontal plane. The radiation pattern and gain from the simulation and experimental measurements agreed closely with the reference far-field pattern and gain. The proposed antenna measurement method in Fresnel region by phi-variation scanning can be easily applied to most popular far-field measurement systems without any additional cost.

The small anechoic chambers built by many small-/medium-sized companies and universities present difficulties in testing electrically large antennas because the chamber size cannot satisfy the far-field criterion of large antennas. In this paper, a method for Fresnel-region measurement on a cylindrical surface with variation of the measurement height is proposed and verified by both calculations and experiments. We implement the proposed method using a direct far-field measurement system by adding a few supporting structures. The results show good accuracy.

In this letter, we designed and fabricated a broadband probe with a double-ridged waveguide for broadband near-field measurements. An exponentially tapered ridge in the rectangular waveguide and a novel waveguide transition were used for broadband impedance matching and suppression of higher order modes. The probe has broadband characteristics and its measured impedance bandwidth is approximately 123% (4.17:1) in the range 12.0-50 GHz for standing wave ratios (SWR)

For the commercial development of organic photovoltaics (OPVs), laboratory-scale OPV technology must be translated to large area modules. In particular, it is important to develop high-efficiency polymers that can form thick (>100 nm) bulk heterojunction (BHJ) films over large areas with optimal morphologies for charge generation and transport. Here, D1-A-D2-A random terpolymers composed of 2,2′-bithiophene with various proportions of 5,6-difluoro-4,7-bis(thiophen-2-yl)-2,1,3-benzothiadiazole and 5,6-difluoro-2,1,3-benzothiadiazole (FBT) are synthesized. It is found that incorporating small proportions of FBT into the polymer not only conserves the high crystallinity and favorable face-on orientation of the D-A copolymer FBT-Th4 but also improves the nanoscale phase separation of the BHJ film. Consequently, the random terpolymer PDT2fBT-BT10 exhibits a much improved solar cell efficiency of 10.31% when compared to that of the copolymer FBT-Th4 (8.62%). Moreover, due to this polymer's excellent processability and suppressed overaggregation, OPVs with 1 cm2 active area based on 351 nm thick PDT2fBT-BT10 BHJs exhibit high photovoltaic performance of 9.42%, whereas rapid efficiency decreases arise for FBT-Th4-based OPVs for film thicknesses above 300 nm. It is demonstrated that this random terpolymer can be used in large area and thick BHJ OPVs, and guidelines for developing polymers that are suitable for large-scale printing technologies are presented.

A practical optical rotary joint and optical links were prepared for an antenna measurement. The rotational variation loss of the optical rotary joint depends on the mechanical misalignments. To achieve 0.2 dB or less rotational variation loss, we proposed a new structure that has a noncontact interface using two size-mismatched fibers without a lens. The optical links are made of a distributed-feedback laser diode, a PIN-photodetector, and single-mode fiber jumper cords. The proposed rotary joint has very low rotational variation loss. The optical links are sufficiently stable to be applied to the antenna measurement. We verified that the rotary joint and optical links can be adopted in RF antenna test applications.

A whole-body voxel model of a 7-year-old male volunteer was developed from 384 axial magnetic resonance images (MRIs). The MRIs were acquired with intervals of 3 mm for the entire body in a body coil. In order to reduce the MRI acquisition time for the child, the repetition and echo times under T1 weighted image were chosen to be 566 ms and 8 ms, respectively. The MRIs were classified according to 30 types of tissues with known electrical parameters. The developed voxel model was adjusted to the physical average of 7-year-old Korean boys. The body weight of the adjusted model, calculated with the mass tissue densities, is within a 6% difference from the 50th percentile weight.

In this letter, we propose a new method to predict the field at the finite distance from a source antenna. The Fresnel fields measured using a far-field measurement system are transformed into the Fresnel or finite-distance far field, after multiplying with a weighting factor. To check the validity of this method, we compared the results with a simulated aperture antenna with uniform current distribution, as well as with an actual horn antenna. The transformed patterns agreed closely with the exact field patterns. The proposed method is very useful for predicting the electromagnetic field located out of chamber range in a far-field measurement system.

A wideband coupled transmission line (CTL) cell to measure the operating range of an UHF RFID (ORUR) is presented. Also, an ORUR test system is proposed to increase the isolation to more than 55 dB. It is shown that the ORUR measured by this proposed cell agrees well with the measured data using a fully anechoic chamber.

Differential site attenuation (DSA) to verify the performance of electromagnetic compatibility (EMC) facilities, open area test site and semi-anechoic chamber, without using a calibrated free space antenna factor (AFFS) is proposed. In the evaluation of EMC facilities, the AFFS is one of the main uncertainty contributions. The measured results are reported and compared with the current site attenuations. It is shown that the proposed DSA has good discrimination capability in verifying the performance of EMC facilities.

This study presents a broadband double-ridged horn antenna for millimeter-wave applications. The proposed broadband antenna has a bandwidth of 12.1–63.2 GHz and peak radiation gain of 12.1–19.8 dBi. The performance of this antenna is verified by the measured results and is in good agreement with the simulated results. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 2165–2167, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21884

This paper designes an optimized straight CTL cell whose uniform area is 20 mm × 20 mm and generates the dominant E-field and H-field to calibrate small EM field probes by using a wideband balun and a wideband power divider. The fabricated optimized straight CTL cell can operate on the broadband frequency range up to 2800 MHz except 2170 MHz. The fabricated two baluns, low frequency band balun and high frequency band balun, that consisted of a divider and two 3-dB quadrature coupler within 0.27 dB of the amplitude difference and 180 ±2.6° of the phase difference from 800 to 3000 MHz. And, the fabricated two power divider use the 3-section Wilkinson power divider type. The field uniformity of the uniform area in the fabricated optimized straight CTL cell is within +1 dB. The measured dominant E & H-field and resonant frequencies of the designed CTL cell agree well with the simulated results.

Conventional polarizers usually include complicated corrugations and lossy insertions such as an iris, septa and dielectric slab, causing performance degradation and fabrication difficulties. At high frequencies, such fabrication difficulties and lossy components are limiting factors to achieving low costs and high performance. In this paper, a novel waveguide-type polarizer with an oval shaped cross-section that is inclined at a ± 45° angle for right-handed and left-handed circular polarization is presented. Due to the oval cross-section, the polarizer can be easily fabricated by mechanical processing with considerable performance. The proposed polarizer structure is fabricated using a pyramidal horn with a square aperture. From measured results, it is confirmed that the horn antenna has a gain of 9.4 dBi at 30.5 GHz with 20 dB cross-polarization level. The return loss is below -15 dB from 28 GHz to 34 GHz, and the axial ratio bandwidth is about 18% at a 3-dB level. This horn antenna will be applied to a feeder design with electrical beam scanning for a reflector-based mobile satellite antenna terminal.

A novel broadband microwave absorber based on a lossy Electromagnetic Bandgap (EBG) structure is presented, and the absorption performance is examined. The proposed absorber includes a lossy EBG surface with the specific sheet resistance, which replaces the conventional resistive sheet of Salisbury screen. The measured result for the absorber showing a broadband reflectivity response with about 76% fractional bandwidth below −10 dB is presented, and a new structure with more enhanced absorption characteristic and other computational results to confirm the functioning of the absorber are presented. The measured and simulated results for the proposed absorber are in good agreement.

To build a stable power distribution network (PDN) in high-speed digital systems, the simultaneous switching noise (SSN) should be sufficiently suppressed. In view of the results of recent research, the uni-planar compact electromagnetic bandgap (UC-EBG) structure is regarded as a promising solution to cope with the SSN problems until the GHz frequency ranges. However, if UC-EBG is adopted for the power/ground plane in the multilayer PCB/package structures, problems of signal integrity may result from the high speed signals passing over the EBG patterns because of the discontinuities of the etched reference plane. In this paper, the partial placement of EBG unit cells only near the sources of noise and/or the noise sensitive components is proposed as a means of both suppressing the noise propagation and minimizing the effects of a discontinuous reference plane. The SSN suppression performance of the proposed structure is validated and investigated both numerically and experimentally.

The design method and analysis of novel broadband electromagnetic (EM) wave absorbers is presented in this paper. The proposed absorber is a planar structure based on lossy Electromagnetic Bandgap (EBG) surface with the specific sheet resistance, which replaces conventional resistive layer of Salisbury screen. The absorber performance can be easily controlled by simply modifying the EBG surface. The analysis for the reflectivity response due to the phase variation of the reflection and transmission recognizes electrical characteristics of the proposed absorber. A broadband reflectivity response with about 96% fractional bandwidth below -10 dB is presented. The computational results are presented to verify the functioning of the proposed absorber.

The author describes an optimized straight CTL cell whose uniform area is 2cm times 2cm and field uniformity is plusmn1 dB to calibrate small EM field probes in air. We could obtain the cell with the broadband frequency range up to 2.1 GHz. The field uniformity and frequency range of the cell are compared with those of square type CTL cell and symmetric TEM cell with same test zone in this paper. It is shown that the optimized CTL cell can provide the standard EM fields with broadband frequency range. The measured electric fields and resonant frequencies of the designed CTL cell agree well with the simulated results by moment methods (MM) and variational method (VM) respectively

A new single waveguide cell for EMC testing, the uniform area of which is 0.216×0.296m, is presented. It is possible to change easily the polarisation of standard EM fields, such as the TTEM cell. The field uniformity of the proposed waveguide cell is compared to that of the TTEM cell. It is shown that it provides the standard EM fields with high field uniformity in dual polarisations simultaneously.

Results are presented of a designed straight coupled transmission line (CTL) cell with a 3×3 cm test zone for calibrating small electromagnetic (EM) field probes up to about 900 MHz in air. The field uniformity and frequency bandwidth of the straight CTL cell are compared to those of a symmetric transverse electromagnetic (TEM) cell with the same afore mentioned test zone. It can provide the standard EM fields with high field uniformity and broadband frequency range simultaneously.