A 3rd-order Butterworth active-RC complex band-pass filter was presented for Zig Bee(IEEE802.15.4) transceiver applications. The filter adopted cascaded complex pole stages to realize the 3 MHz bandwidth with a centre frequency of 2 MHz which was required by the Zig Bee transceiver applications. An automatic frequency tuning scheme was also designed to accommodate the performance deterioration due to the process, voltage and temperature(PVT) variations. The whole filter is implemented in a 0.18 μm standard process and occupies an area of 1.3 mm×0.6 mm. The current dissipation is 1.2 m A from a 1.8 V single power supply. Measurement results show that the image rejection ratio(IRR) of the filter is 24.1 d B with a pass-band ripple less than 0.3 d B. The adjacent channel rejection is 29.8 d B@7 MHz and alternate channel rejection 47.5 d B@12 MHz, respectively.
Image enhancement technology plays a very important role to improve image quality in image processing. By enhancing some information and restraining other information selectively, it can improve image visual effect. The objective of this work is to implement the image enhancement to gray scale images using different techniques. After the fundamental methods of image enhancement processing are demonstrated, image enhancement algorithms based on space and frequency domains are systematically investigated and compared. The advantage and defect of the above-mentioned algorithms are analyzed. The algorithms of wavelet based image enhancement are also deduced and generalized. Wavelet transform modulus maxima(WTMM) is a method for detecting the fractal dimension of a signal, it is well used for image enhancement. The image techniques are compared by using the mean(μ),standard deviation(?), mean square error(MSE) and PSNR(peak signal to noise ratio). A group of experimental results demonstrate that the image enhancement algorithm based on wavelet transform is effective for image de-noising and enhancement. Wavelet transform modulus maxima method is one of the best methods for image enhancement.
Lanthanide-based upconversion core-shell NaGdF4 nanocrystals with strong upconversion luminescence and biocompatibility were synthesized by the solvothermal method.The multicolor upconversion emission of these NaGdF4 nanoparticles could be easily obtained by controlling the core-shell compositions.These multicolor core-shell NaGdF4 upconversion nanocrystals could be employed as fluorescent probes for imaging the mouse hair,by which the porous and scalelike structure of the mouse hair were presented clearly.Meanwhile,it was directly shown by fluorescent signals that the mouse hair could resist the corrosion of the strong acid even when the concentration of hydrochloric acid was increased to 36.5%,but could not avoid the carbonization at high temperature of 400 oC.This procedure based on upconversion fluorescent nanoprobes opens a novel route for investigating the basic physical structure and chemical properties of biological tissue and organism.
采用简易的热熔剂法,成功地制备了Yb3+和Er3+共掺杂的Na Lu F4纳米晶。由于其很强的上转化发光及经过表面修饰后很好的生物相容性,Na Lu F4纳米晶被应用作为上转化荧光探针,对西红柿表皮细胞进行荧光成像,结果表明,上转化纳米探针能很好地吸附在西红柿细胞的细胞壁,对细胞的形貌进行清晰的成像,为动植物细胞的研究提供了新的成像途径。
考虑到超宽带通信系统对现有其它无线通信系统运行的影响,设计一种具有WiMAX陷波特性的超宽带天线。该天线尺寸大小为0.8 mm ×30 mm ×34 mm,采用圆弧状T形贴片作为辐射单元,并通过在该辐射贴片上开L形槽来实现陷波特性。仿真实验结果表明:天线的带宽为2.9~10.8 GHz,同时具有3.2~3.8 GHz的陷波,平均增益约为4.0 dBi,并具有稳定的准全向性辐射特性。该天线能够满足多种超宽带通信系统的应用要求。
Lanthanide doped NaYF4 microcrystals were synthesized via a facile hydrothermal method. Multicolor upconversion luminescence was observed in NaYF4 microcrystals doped with yb^3＋/Er^3＋, yb^3＋/Tm^3＋, and yb^3＋/Er^3＋/Zm^3＋ under the excitation of 980 nm infrared light. Importantly, the excitation power density dependence of upconversion emission intensity indicated clearly the energy transfer from Tm^3＋ to Er^3＋ ions under the excitation of low power density （5× 10^2× 10^2 W/cm^2）. Meanwhile, the inverse energy transfer from Er^3＋ to Tm^3＋ ions under the excitation of relatively higher power density （4.1 × 10^4.9× 10^4 W/cm^2） was also revealed. This was a direct evidence for reversible energy transfer between Er^3＋ and Tm^3＋ ions. Under the excitation of high power density （4.1 ×10^4-4.9× 10^4 W/cm^2）, dark sensitizers were also motivated so that the bottleneck effect of high concentration Yb^3＋ ion doping was broken. This was the main reason for realizing high upconversion efficiency of the samples with heavy doping of Yb^3＋ ion.
Metal organic chemical vapor deposition(MOCVD) is a key equipment in the manufacturing of semiconductor optoelectronic devices and microwave devices in industry. Heating system is a vital part of MOCVD. Specific heating device and thermal control technology are needed for each new reactor design. By using resistance-wire heating MOCVD reaction chamber model, thermal analysis and structure optimization of the reactor were developed from the vertical position and the distance between coils of the resistance-wire heater. It is indicated that, within a certain range, the average temperature of the graphite susceptor varies linearly with the vertical distance of heater to susceptor, and with the changed distances between the coils; furthermore, single resistance-wire heater should be placed loosely in the internal and tightly in the external. The modulate accuracy of the temperature field approximately equals the change of the average temperature corresponding to the change of the coil position.
Lanthanide doped bifunctional materials are potentially important for developing multifunctional devices. Here, NaLuF4:Yb3+/Tm3+/Gd3+/Sm3+ optical-magnetic bifunctional microcrystals were successfully synthesized by hydrothermal method, which could emit ~480 nm blue light from the1G4→3H6 electronic transition and ~800 nm infrared light from the3H4→3H6electronic transition of Tm3+ ion, under the excitation of 980 nm infrared light. By doping Sm3+ ion into NaLuF4:Yb3+/Tm3+/Gd3+, the infrared emission peak centered at 800 nm would shift obviously to longer wavelength. This indicated that Sm3+ ion could efficiently tune the energy level gaps of Tm3+ ions in NaLuF4 host which was demonstrated based on the crystal field theory. In addition, these NaLuF4:Yb3+/Tm3+/Gd3+/Sm3+ microcrystals presented unique ferromagnetic property instead of usually reported paramagnetic prop-erty. Importantly, the ferromagnetic property decreased with increasing the concentration of Gd3+ ion. This was in good agreement with Swift’s theoretical investigation that the coexistence of light rare earth (Gd3+) and heavy rare earth (Yb3+/Tm3+) would lead to the anti-ferromagnetic coupling in the sub-lattices.
