THEORETICAL ANALYSIS OF REAL-TIME AIR-GAP COUPLED SAW CONVOLVERS

In this paper,a new theory is developed for the analysis of real-time air-gap coupled SAWconvolvers.There are two important features about the theory proposed here.Firstly,we rigorouslyconsider the role of the surface states of semiconductors in acoustoelectric nonlinear interactions.Secondly,by means of a new equivalent circuit for such a convolver,we derive various new analyticalexpressions which describe the linear coupling coefficient for air-gap,nonlinear coupling coefficientfor acoustoelectric nonlinear interactions,and convolution output(or figure of merit);these expres-sions exhibit obvious dependence on bias.The frequency response of the surface states is also ana-lyzed. The theory presented here is a general formula applicable to dealing with the situation when thesemiconductor surface is accumulated,at flat-band,depleted,or inverted. The presented theory can essentially explain experimental results of SAW acoustoelectric non-linear interactions which were carried out by the author and others.     

TEMPERATURE DEPENDENCE OF FREQUENCY MEASUREMENT WITH SAW CZT PROCESSOR

Usually,frequency measurement with SAW chirp Z transform processor is something temperature depen-dent because of performance changes of SAW chirp delay lines used in processor with temperature.Hence,afull knowledge of the temperature dependence is necessary for practical processor design and compensation.So far,as we know,no adequate quantitative analysis has been given.In this paper a theoretical model is setup for the analysis of temperature dependence of ferequency measurement with a SAW CZT processorbased on time scale principle.A closed form expression is given to formulate the deviation of the measuredfrequency from the actual input when the temperature changes.The deviation is not only related with SAWtime delay temperature coefficient of the substrate used in SAW device and the parameters of SAW chirp de-lay lines,but also with the input frequency.A good agreement between our experiment and theory is shownand a reasonable explanation is given to the discrepancy between Claude Lardat‘s theory a     

Measurement of the Floor Tilt in Experimental Determination of the Gravitational Constant

A prototype of a device with an impact structure for measuring the floor tilt has been built in our laboratory. The mechanical construction and the capacitive transducer of the device are introduced. Experimental results indicate that the floor tilt is about 16#tad in our cavity laboratory, and the uncertainty AG/G caused by such tilt is less than 0.54 parts per million (ppm), so the floor tilt can be reasonably neglected in the experimental determination of the gravitational constant G with the total uncertainty of about l0ppm.     

ACOUSTIC DELAY LINE BASED ON PLATE MODES

A new kind of realizable ultrasonic delay line is proposed for long time delay application,which is basedon high efficient conversion between Rayleigh wave and plate modes by shallow groove gratings on substratesurface.The experimental devices fabricated on YZ-LiNb0_3 have exhibited the ability to delay a narrow-band singal for the delay time a couple of times longer than its Rayleigh wave counterpart.Because they aremade with the same planar lithographic technology as that used in SAW device,the new configuration retainsadvantages of reliability and reproducibility.Approximate analysis for the new device is provided forunderstanding its operation.     

Stop band characteristics of a TESLA cavity coaxial-type HOM coupler

A TTF-type coaxial higher order modes (HOM) coupler has been used in a TESLA 9 cell cavity. It is impossible to measure the stop band characteristics of the HOM coupler with the cavity. A measurement device for the coaxial transmission line type for the HOM coupler has been designed at Peking University. Experimentally it was shown that the average voltage standing wave ratio of the coaxial transmission line is smaller than 1.08. The experimental results of the stop band characteristics of the TTF-type HOM coupler have been fitted for the simulation. This paper describes the design of the measurement device and discusses the experimental and simulation results of stop band characteristics of the HOM coupler.     

Different operation states of soliton pulses in an erbium-doped fibre ring laser

We report on the experimental observation of soliton pulses in an erbium doped fibre ring laser. The passive mode-locking is achieved using the nonlinear polarization rotation technique. By adjusting the pump power and the intracavity polarization controllers, a normal soliton, a stable 8th harmonic mode-locked pulse and a noise-like pulse have been observed in our laser. The experimental results revealed that the noise-like pulse is not suitable for the optical telecommunication, and in order to obtain the stable harmonic mode-locked soliton, a strong unstable CW laser field is necessary to mediate global soliton interaction. The formation mechanism of the harmonic mode-locked pulse has also been analysed.     

Thermal diffusivity of light-emitting diode packaging material determined by photoacoustic piezoelectric technique

Thermal property is one of the most important properties of light-emitting diode (LED).Thermal property of LED packaging material determines the heat dissipations of the phosphor and the chip surface,accordingly having an influence on the light-emitting efficiency and the life-span of the device.In this paper,photoacoustic piezoelectric (PAPE) technique has been employed to investigate the thermal properties of polyvinyl alcohol (PVA) and silicon dioxide,which are the new and the traditional packaging materials in white LED,respectively.Firstly,the theory of PAPE technique has been developed for two-layer model in order to investigate soft materials;secondly,the experimental system has been set up and adjusted by measuring the reference sample;thirdly,the thermal diffusivities of PVA and silicon dioxide are measured and analysed.The experimental results show that PVA has a higher thermal diffusivity than silicon dioxide and is a better packaging material in the sense of thermal diffusivity for white LED.     

Design and FPGA Implementation of a new hyperchaotic system

In this paper, a new four-dimensional autonomous hyperchaotic system is designed for generating complex chaotic signals. In the design, its parameters are selected according to the requirements for chaos and hyperchaos. The hyperchaotic nature is verified theoretically by using the bifurcation analysis and demonstrated experimentally by the implementation of an analogue electronic circuit. Moreover, the Field Programmable Gate Array （FPGA） technology is applied to implementing a continuous system in a digital form by using a chip of Altera Cyclone II EP2C35F484C8. The digital sequence generated from the FPGA device is observed in our experimental setup.     

Siliconization for Wall Conditioning and Its Effect on Plasma Performance in HL-2A Tokamak

1 Experiments HL-2A tokamak is characterized by a large closed divertor chamber. Before the experimental campaign 2005 the surface of the shielding plates for the MP1 and MP2 has been covered with 2-D carbon fibre composite （about 30% of the first wall）, which can protect the first wall, and effectively shield the splash of heavy metal impurity. The vacuum vessel can be baked up to 120 ℃for degassing and a glow discharge device is installed in the vessel for cleaning the inner surface. Hydrogen glow discharge cleaning （GDC） is applied to remove impurities from the wall, and helium glow discharge cleaning for removing residual hydrogen.     

基于机械共振的声谱分析技术

A model for the accurate measurement of low frequency sound spectrum is put forward and a simplified experimental device is built. Based on the principle of mechanical resonance, the natural frequency ...