In this paper, a tunable metamaterial consisting of periodic layers of steel, polyurea and piezoelectric ceramic transducer
(PZT) was presented. The PZT layer in this structure was connected to an inductor L. Transfer matrix method was used
to calculate the band structure of the sample. It was observed that an extremely narrow stop band was induced by the
PZT layer with inductor L. This narrow stop band was attributed to the resonance circuit constituted by the piezoelectric
layer, for the piezoelectric layer with electrodes could be seen as a capacitor. Further, homogenization was used to
calculate the effective elastic constants of the sample. Results showed that the effective parameters of this structure
behaved negative in the narrow stop band. The location of the narrow stop band was in the charge of inductor L, which
could be used to design acoustic filters or noise insulators by changing the parameters of structure.
A high-sensitivity pressure sensor based on wavelength detection technology of fiber Bragg grating (FBG) is proposed in this paper. The FBG pressure sensor can be used to measure downhole pressure of oil and gas wells. An eccentric-pushrod structure is used to improve the sensitivity of the sensor. The effect of adhesive on elastic hysteresis of the sensor is analyzed, and the adhesive with large shear modulus is used to reduce the hysteresis of the sensor. Numerical and experimental results show that this sensor possesses good linearity and repeatability, as well as little elastic hysteresis. The sensitivity of the sensor can reach 230.9 pm/MPa when the measured pressure is in the range of 0 to 20 MPa.
The chemically powered nanowire model consisting of a catalytic and a noncatalytic nanowire confined in a cubic box is investigated. The interactions between nanowire and solvent are simulated using hybrid molecular dynamics/ multiparticle collision dynamics. The motion of the nanowire is analyzed using rigid body dynamic. The effect of temperature and solvent concentration on the center-of-mass velocity of motor are provided. The center-of-mass velocity of the nanomotor along its axis increases with an increase of temperature and solvent concentration. The results are also compared with existed nanodimer model.
Microcantilever sensors have been widely used in designing force, strain and biochemical sensors. The fast-growing applications in nanoelectromechanical systems (NEMS) lead to strong demands to downsize the sensing elements to nanometer scale. In this paper, the detected environment on the performance of this photonic crystal sensor is investigated. The nanocavity, which can be used to localize the electromagnetic field in a low refractive index region, is a new sensing method to measure nano-scaled deformation. Through numerical simulation, we demonstrate that the range of the force sensor in each component force in X and Y directions are 0-1μN. In X direction, the minimum detectable applied forces are about 0.057μN and 0.070μN for the microcantilever operated in the water and air, respectively. And these in Y direction are 0.043μN and 0.053μN, respectively. Hence, it shows that a better resolution of applied force can be achieved in water than in air.
With advantages of ultra-compact size, high resolution, and easy integration, nano-scaled force sensors based on photonic crystal are widely used in microelectromechanical systems (MEMS) and nanoelectromechanical systems (NEMS). The performances of these nano-scaled force sensors are mainly determined by the shape nanocavity. The principle of the sensor is that the output wavelength of the force sensor using photonic crystal varies as a function of force and pressure. In this work, a novel three dimensional nano-scaled force sensor based on silicon photonic crystal, in which a nanocavity is embedded in an S-shaped elastic body, is provided and studied numerically. The advantage of this force sensor is that it can be used in the NEMS to measure the component force in the X direction, Y direction and Z direction, simultaneously. The relationship between the force and the output wavelength is determined using finite element method (FEM) and finite difference time-domain method (FDTD).
Considering the choice of sensors in optical fiber temperature sensing field, temperature
measurement experiments on fiber Bragg grating, optical fiber Brillouin scattering, Raman Scattering
Fiber Optic sensors which are based on three different theories were carried out, so temperature
measurement results are obtained, meanwhile, the temperature characteristics these three kinds of
sensors can get known by comparison between sensing principle and experimental data. This can
provide a reference for application of fiber optic temperature sensor in the temperature monitoring field.
Space infrared cameras have been widely used for weather prediction, earth resource detection, military reconnaissance
and astronomy observation. In order to design and produce an excellent space camera, the optical and mechanical
structures of the camera are deeply investigated. Firstly, according to the technical targets and interface requirements for
infrared sensor, optical modulation transfer function (MTF) must be up to 0.65 in the central field and more than 0.55 in
the marginal field at the cut-off frequency of the optical system. Secondly, in accordance with the requirement of optical
system, the structure of body tube is designed and a new type of material- graphite fiber reinforced aluminium matrix
composite (Gr/Al composite) is used for the first time. The weight of Gr/Al composite body tube is 31.8% lighter than
that of Titanium alloy. Thirdly, in terms of the theory of modal analysis, the resonance frequencies and modal sharps of
body tube are acquired. The first order resonance frequency is 292Hz. Finally, the test of random vibration is conducted.
Experimental results indicate that optical and mechanical systems do not change after vibration test. Namely, the
research above suggests that space infrared camera has an important utility value in the space remote sensing field.
The superior mechanical and thermal properties of continuous graphite fiber reinforced aluminum matrix composite
(Cf/Al) make it attractive from a design standpoint for space-based system for which the lightweight, high stiffness
structure is one of the key technologies. This paper describes the development process of a Cf/Al lens barrel used in
space infrared optical system including fabrication technology, structure design and simulation analysis. The advantages
and disadvantages of Cf/Al lens barrel compared with invar and CFRP lens barrel, whose structure parameters are
identical to that of Cf/Al lens barrel, are discussed. Some performance figures and data are given. The results indicate
that the performance of Cf/Al lens barrel is significantly better than the invar, and close to CFRP. However lower
outgassing than CFRP under the vacuum condition make Cf/Al become a better choice for space infrared applications.
Fiber Bragg Grating sensors are widely used in the field of optical sensing system for the Structure Health Monitoring
(SHM) during the last 10 years. It can be used for monitoring the strain, temperature pressure and some other characters
of the structure. In this paper a new kind of surface sticking strain sensor with sensitivity enhanced has been studied and
developed. The structure of the sensors is presented and the Ansys software has been used to optimize the structure. A
novel theory about how to enhance the sensitivity or widen the scale of the strain sensors based on FBG is introduced
too. Based on the theory two types of sensor have been developed. One is the long-scale sensor that is able to monitor
the big strain such as crack, the other is the high-precision sensor that is able to monitor the micro strain as O.5,&mgr;&Vegr; , and
we conclude the sensitivity enhancing coefficient. As the sensitivity coefficient of bare fiber is 1 .2pm/&mgr;&Vegr; ,the theoretical
enhancing sensitivity coefficient of long-scale sensor is K=3.3811 and the theoretical enhancing sensitivity coefficient
of high-precision sensor is K=O.58. Then groups of experiments were carried out to validate the theory. The
experimental sensitivity coefficient of long-scale sensor is O.35pm/&Vegr; with the coefficient of enhancing sensitivity
is K=3.4286. The experimental sensitivity coefficient of high-precision sensor is 1.96pm/&mgr;&Vegr; with the coefficient of
enhancing sensitivity is K=0.61 . Comparing the experimental results with the theory results, it proves that the two types
of strain sensors can really reflect the strain status and the damage information of the structure, and it is stable and
reliable for the practical project.
Two theoretical models of single-photon acquisition probability based on the fundamental-mode Gaussian beam are established for free-space quantum key distribution and are compared in theory and simulation. The parameters that influence the single-photon acquisition probability are the transmitter's tracking-pointing error, the far-field divergence angle, the link distance between the transmitter and receiver and the receiver's antenna aperture. The single-photon acquisition probability is analyzed in the numerical simulation and its orders of magnitude are given for the ground-to-ground, satellite-to-ground and satellite-to-satellite links. The results of the theoretical analysis and the numerical simulation show that it is feasible to acquire single-photon for the satellite-to-ground and satellite-to-satellite quantum key distribution.
In the present work, a modified vertical Bridgman technique for GaAs crystal is developed. The VB configuration in prototype includes a quartz ampoule and a quartz crucible. The quartz ampoule was sealed in order to prevent volatilization of components. Because the decomposition pressure of GaAs ia about 1 atm. at its melting point, the quartz ampoule can keep its shape under 1300 degrees Celsius in air atmosphere during GaAs growth. Seeded 25 mm diameter crystals are grown at the rate of about 0.1 - 0.6 mm/hr under the temperature gradient about 10 degrees Celsius/cm at the solid-liquid interface, and electrical properties of as-grown GaAs crystal are discussed.
Cr:LiCaAlF6 crystal was grown by modified Bridgman method. The growing process was described in detail. The distribution of Cr along the crystal growth direction was measured and the results showed that the segregation coefficient of Cr is less than 1 under this condition.
KEYWORDS: Sensors, Digital signal processing, Control systems, Actuators, Diamond machining, Signal processing, Servomechanisms, Computing systems, Signal detection, Spindles
Precision machining can achieve high levels of accuracy through the use of a highly accurate spindle, straight feed
mechanisms, a rigid base and a single-point diamond tool. Research is underway aimed at achieving even higher levels
of accuracy by adding computers, non-contact sensors and piezoelectric actuators for in-process measurement and control
to the workpiece. Based upon such idea, a workpiece form accuracy in-process measurement and control system is proposed
in this paper. The principle and a few key techniques for the system are discussed and some preliminary experiments are
given in the paper.
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