Green emission ZnO quantum dots were synthesized by an ultrasonic sol-gel method. The ZnO quantum dots were synthesized in various ultrasonic temperature and time. Photoluminescence properties of these ZnO quantum dots were measured. Time-resolved photoluminescence decay spectra were also taken to discover the change of defects amount during the reaction. Both ultrasonic temperature and time could affect the type and amount of defects in ZnO quantum dots. Total defects of ZnO quantum dots decreased with the increasing of ultrasonic temperature and time. The dangling bonds defects disappeared faster than the optical defects. Types of optical defects first changed from oxygen interstitial defects to oxygen vacancy and zinc interstitial defects. Then transformed back to oxygen interstitial defects again. The sizes of ZnO quantum dots would be controlled by both ultrasonic temperature and time as well. That is, with the increasing of ultrasonic temperature and time, the sizes of ZnO quantum dots first decreased then increased. Moreover, concentrated raw materials solution brought larger sizes and more optical defects of ZnO quantum dots.

An ultra-wideband microstrip bandpass filter which operates from 3.1 GHz to 10.6 GHz, with high selectivity and sharp notched band is presented and experimentally verified. The filter is composed of a square loop shaped defected ground structure, metal faces, and microstrip lines. By adding two short stubs connected by a short circuit point on the microstrip lines, the filter achieves an attractive capacity in out-of-band rejection. By placing open stubs in microstrips, the filter realizes a notched band in passband. To illustrate the possibilities of the new approach, an ultra-wideband microstrip bandpass filter is designed and fabricated. Measured results agree well with the predicted counterparts. 1. INTRODUCTION Ultra-wideband (UWB) technology has been receiving tremendously increasing attention in high performance communication systems because it successfully overcomes the drawbacks of many classical communication technologies with its high speed, high immunity of noise, and low transmitting power [1]. Corresponding to this trend, various UWB filters with compact size, light weight, and adequate electrical characteristic performances have been extensively studied and explored [2]. One of the design techniques for obtaining high performance microwave filters is using defected ground structure (DGS) [3] resonators which are typically etched as various shaped breaks in the ground plane. DGSs act as parallel L-C resonators which resonate at certain frequencies depending on their dimensions and shapes for harmonic suppression [4-6]. UWB filters using DGS are always smaller than general UWB filters using multi-mode resonators in size and easy to manufacture. Moreover, rejection band is typically wider, and multi-pole characteristic can be set with combining several multimode resonators that have different sizes or shapes for harmonic suppression [7-10]. In this paper, a new UWB bandpass filter is proposed and implemented based on DGS. The proposed square ring shaped DGS is positioned symmetrically between the ports on the ground plane of initial filter. Hence, the filter itself is composed of dual metal faces and dual microstrip lines with short stubs to enhance out-of-band rejection and open stubs to create a notched band in passband. In the design process, the performance of BPF with the proposed DGS is investigated intensively to obtain the optimum design of overall structure. A UWB BPF with compact size and high performance is then presented, and predicted results are experimentally verified by testing the fabricated filter.

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Green emission ZnO quantum dots were synthesized by an ultrasonic microreactor. Ultrasonic radiation brought bubbles through ultrasonic cavitation. These bubbles built microreactor inside the microreactor. The photoluminescence properties of ZnO quantum dots synthesized with different flow rate, ultrasonic power and temperature were discussed. Flow rate, ultrasonic power and temperature would influence the type and quantity of defects in ZnO quantum dots. The sizes of ZnO quantum dots would be controlled by those conditions as well. Flow rate affected the reaction time. With the increasing of flow rate, the sizes of ZnO quantum dots decreased and the quantum yields first increased then decreased. Ultrasonic power changed the ultrasonic cavitation intensity, which affected the reaction energy and the separation of the solution. With the increasing of ultrasonic power, sizes of ZnO quantum dots first decreased then increased, while the quantum yields kept increasing. The effect of ultrasonic temperature on the photoluminescence properties of ZnO quantum dots was influenced by the flow rate. Different flow rate related to opposite changing trend. Moreover, the quantum yields of ZnO QDs synthesized by ultrasonic microreactor could reach 64.7%, which is higher than those synthesized only under ultrasonic radiation or only by microreactor.