Current Issue : April - June Volume : 2014 Issue Number : 2 Articles : 7 Articles
A parallel-strip phase inverter with a pair of simple impedance matching networks is designed.The phase inverter introduces the\r\nalmost frequency independent 180�° phase shift and was employed in the wideband parallel-strip balun.Thebalun was designed and\r\nmeasured with themaximummagnitude imbalance of 0.5 dB and the maximumphase imbalance of 6.0�°.The proposed balun is used\r\nas input network for the wideband balanced frequency doubler.The proposed frequency doubler achieves significant conversion\r\ngain from 0.1GHz to 1.7GHz. The frequency doubler achieves 7.4 dB conversion gain and 23 dB fundamental signal suppression at\r\n1GHz....
This paper presents a class of wideband 180�° hybrid (rat race) couplers implemented by parallel-strip line. By replacing the 270�°\narm of a conventional 180�° hybrid coupler by a 90�° arm with phase inverter, the bandwidth of the coupler is greatly enhanced\nand the total circuit size is reduced by almost half. Simple design formulas relating the characteristic impedance of the arms and\npower division ration are derived. To demonstrate the concept, four couplers with different power division ratios of 1, 2, 4, and 8\nwere designed, fabricated, and tested. ??-parameters of the coupler are simulated and measured with good agreement. All working\nprototypes operate more than 112% impedance bandwidth with more than 25 dB port-to-port isolation and less than 5�° absolute\nphase imbalance. The proposed 180�° hybrid couplers can be employed as a wideband in-phase/differential power divider/combiner,\nwhich are essential for many RF and microwave subsystem designs....
We design a time domain microwave system dedicated to medical imaging.Themeasurement accuracy of the system, that is, signalto-\r\nnoise ratio, due to voltage noise and timing noise, is evaluated. Particularly, the effect of coupling media on the measurement\r\naccuracy is investigated both numerically and experimentally. The results suggest that the use of suitable coupling media betters\r\nthemeasurement accuracy in the frequency range of interest. A signal-to-noise ratio higher than 30 dB is achievable in the range of\r\n500MHz to 3GHz when the effective sampling rate is 50Gsa/s. It is also indicated that the effect of the timing jitter on the strongest\r\nreceived signal is comparable to that of the voltage noise....
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Germination is a key process in plants� phenological cycles. Accelerating this process could lead to improvment of the seedling\r\ngrowth as well as the cultivation efficiency. To achieve this, the effect of microwave frequency on the germination of rice seeds was\r\nexamined.The physiological feedbacks of the MR 219 rice variety in terms of seed germination rate (GR), germination percentage\r\n(GP), and mean germination time (MGT) were analyzed by exposing its seeds to 2450MHz of microwave frequency for one, four,\r\nseven, and ten hours. It was revealed that exposing the seeds to the microwave frequency for 10 hours resulted in the highest GP.This\r\ntreatment led to 100% of germination after three days with amean germination time of 2.1 days. Although the other exposure times\r\nof microwave frequency caused the moderate effects on germination with a GPa3 ranged from93% to 98%, they failed to reduce the\r\nMGTa3.The results showed that ten-hour exposure times of microwave frequency for six days significantly facilitated and improved\r\nthe germination indices (primary shoot and root length). Therefore, the technique is expected to benefit the improvement of rice\r\nseed germination considering its simplicity and efficacy in increasing the germination percentage and rate as well as the primary\r\nshoot and root length without causing any environmental toxicity....
This work reports on synthesis of zinc oxide/reduced graphene oxide (ZnO/rGO) nanocomposites in the presence of diethylenetriamine\r\n(DETA) via a facile microwave method. The X-ray diffraction (XRD) patterns of the nanocomposites correspond to the\r\nZnOhexagonal phase wurtzite structure.The high-resolution transmission electron microscopy (HRTEM) images revealed that the\r\nZnO nanorods, with an average length : diameter ratio of 10, were successfully deposited on the rGO sheets. Under the irradiation\r\nof sunlight, the nanocomposites showed enhanced adsorption-photocatalysis by more than twofold and photocurrent response\r\nby sixfold compared to the ZnO. The excellent photoactivity performance of the nanocomposites is contributed by smaller ZnO\r\nnanorod and the presence of rGO that acts as a photosensitizer by transferring electrons to the conduction band of ZnO within the\r\nnanocomposite during sunlight illumination....
The microwave assisted synthesis nowadays attracts a great deal of attention. Monoclinic phase VO2 (M) was prepared from\r\nNH4VO3 and H2C2O4 Ã?· 2H2O by a rapid microwave assisted technique. The synthesis parameters, microwave irradiation time,\r\nmicrowave power, and calcinations temperature were systematically varied and their influences on the structure and morphology\r\nwere evaluated. The microwave power level has been carried out in range 180ââ?¬â??600W. TEM analysis demonstrated nanosized\r\nsamples. The structural and morphological properties were measured using XRD, TEM, and thermal analyses. The variations of\r\nvanadium phase led to thermochromic properties...
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