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Vladimir Pašagic, Tijana Parlic Risovic
THE INFLUENCE OF TEMPERATURE AND PRESSURE ON PERFORMNCE OF OPTICAL SURVEYING INSTRUMENTS

Althought the surveying instruments grow ever more complex, yet the telescope remains the basic part of modern-day surveying instruments. When considering the problem of measuring with a surveying instrument, that is with the telescope, it is necessary to consider the issue as a whole. In other words it is necessary, alongside the function of the telescope, to take into consideration the object to be measured, atmosphere as the medium transmitting light and physiological and psychological attributes of the sighter. In order to define a complex optical system that would facilitate prediction of measurement's accuracy with the telescope, in dependence on atmosphere conditions, namely different temperature and preassure, it is necessery to provide a description of the atmosphere and telescope as independet optical systems. This is accomplished throught modulation transfer function that provides a complete description of the properties of a considered optical system. Starting with the fact that surveyors prior to their departure to outdoor measurings have at their disposal only the information on air temperature and pressure, we have conducted suitable theoretical study of the problem. The results of this study provide means to evaluate the limitations of resolution of a considered optical system imposed by the atmospher based on the knowledge of available meteorological parameters.

Erik Novak, Joanna Schmit
WHITE-LIGHT OPTICAL PROFILER WITH INTEGRATED PRIMARY STANDARD

White light interferometry has become a common tool for measuring surfaces with large height ranges, slopes, and large roughness. The object is generally scanned through focus, varying the optical path difference between the light reflected from the object and from a secondary reference surface. The quality of the measurement is dependent on having a known and constant- velocity scan, as well as knowing the effective wavelength of the white light source at all times. In this paper we present a white light interferometer with an embedded second interferometer utilising a HeNe laser which provides an interferometric reference signal. This signal, based on the primary standard of the HeNe wavelength is used to monitor the scan and use the known scan positions in the height calculation algorithms. This yields improvements in the accuracy, and repeatability of topography measurements, allowing higher scan speeds without loss of data integrity.

Erik Novak, Der-Shen Wan, Paul Unruh, Michael Schurig
MEMS METROLOGY USING A STROBED INTERFEROMETRIC SYSTEM

Accurate measurements of MEMS surfaces, geometries and motions are crucial to achieving the desired performance of the devices. The wide variety of MEMS devices in development and production requires very flexible metrology for single-platform characterization. In addition to having greatly varying geometries, devices must also be characterized statically and under actuation. White-light interferometry, fortunately, is a technique flexible and accurate enough to meet MEMS metrology needs. This high-speed, non-contact measurement method allows both large lateral and vertical ranges with nanometer-level vertical resolution and positional accuracy. When standard illumination is complemented with strobed light, dynamic measurements of MEMS can also be carried out. This paper presents some of the hardware and software design considerations for producing a single metrology platform with the required flexibility for production MEMS metrology. Several static and dynamic MEMS measurements are presented to illustrate the design requirements.

Leonardo D’Acquisto, Roberto Montanini
ON THE BEHAVIOUR OF IN-FIBRE BRAGG GRATING SENSORS FOR STRAIN MEASUREMENT ON PLANE AND CURVED SURFACES

When compared with traditional electrical strain gauges used for strain monitoring, Fibre Bragg Grating (FBG) sensors have several distinguishing advantages that make them very attractive for many applications in different fields. Nevertheless, for practical applications, their metrological performance needs to be assessed under different operative conditions. In this paper attention has been focused on the response of FBGs when glued on a metallic surface that is not flat. Hollow-tube specimens with two different curvatures have been considered, together with a plane specimen used as reference. FBG signals were compared with those produced by electrical strain gauges. In addition, for the two hollow tube specimens, shadow moiré images of the specimen area between the FBG sensor and the strain gauge have been recorded in order to check the displacement field induced on the specimen. Preliminary results obtained show that the optical signal is markedly affected by the radius of curvature of the surface when the FBG sensor is bonded on a curved surface.

Consolatina Liguori, Alfredo Paolillo, Antonio Pietrosanto
A PARAMETRIC MODEL FOR THE UNCERTAINTY OF DIGITAL IMAGES

In this paper a parametric model of the uncertainty of digital images in industrial contest is presented and characterized. The functional dependency of the model parameters from the operating conditions and the image characteristics are theoretically established and experimentally verified.

Pal Greguss , Edith Greguss
FOLDED OPTICAL SYSTEM FOR SIMULTANEOUS ATTITUDE MEASUREMENT AND GROUND IMAGING - A PROPOSAL

Panoramic Annular Lens based Attitude Measurement sensor combined with Ground Imager (PALAMGI) for satellites. There is a need of miniaturized platform elements of spacecrafts, especially for nano and micro satellites programs. A single unit is proposed instead of two separate ones using the newly developed Humanoid PAL vision system.

Marta Valledor, Juan Carlos Campo, Miguel A. Perez, Juan C. Alvarez, Juan C. Viera
A NEW METHOD FOR PHOSPHORESCENCE MEASUREMENTS IN THE PRESENCE OF SCATTERED LIGHT

Phosphorescent sensors are usually based on measurement of light intensity or lifetime of sensor emitted light. This goal may be accomplished by measuring the phase-shift between the excitation and the emitted light. Scattered signals must be removed to perform the measurement; however, some of the scattered light due to fluorescence is impossible to remove when measuring phosphorescence decay times. In this paper, a new method to measure lifetime in the presence of fluorescence light emitted by the phosphorescence sensor is presented. This method is based on the measurement of the phase-shift at two different frequencies. Theoretical aspects, the optimal frequencies and experimental results are discussed.

Wolfgang Holzapfel, Nejat Mahdavi, Martin Suske
INERTIAL GRADE LASER ACCELEROMETER-PRACTICABILITY AND BASIC EXPERIMENTS

A novel laser accelerometer is introduced, its physical principle and main characteristics are explained, and preliminary experimental results are presented. The accelerometer utilizes two Nd:YAG laser crystals and a common proof mass which operate in push-pull mode. The main advantages of the described laser accelerometer are wide measuring range which covers 9 decades up to 100 m/s², very high linearity over measuring range and excellent dynamics (20 kHz bandwidth). In comparison to servo accelerometers, these results represent a high-performance sensor. The measurement uncertainty and precision analysis have been carried out according to GUM guidelines. The analysis shows that the relative uncertainty in sensitivity of the laser accelerometer amounts to 10-6.

Andrea Cataldo, Bahram Nabet, Adriano Cola, Amerigo Trotta
HMSM PHOTODETECTORS FOR HIGH-SPEED APPLICATIONS

In this paper we describe the characterization of a family of optical devices based on heterojunction and heterodimensional structures and we investigate their static and dynamic properties. Such devices are good candidates, due to their high performance, for utilization as the sensing element for the realization of sensors in the fields of telecommunications, remote sensing, LIDAR and medical imaging. First, we present a Heterostructure Metal-Semiconductor-Metal (HMSM) photodetectors that employ a uniformly doped GaAs/AlGaAs heterojunction for the dual purpose of barrier height enhancement and creating an internal electric field that aids in the transport and collection of the photogenerated electrons. In this first family of devices, two doping levels are compared showing the direct effect of the aiding field due to modulation doping. Subsequently, we analyse a novel Resonant-Cavity-Enhanced (RCE) HMSM photodetector in which a Distributed Bragg Reflector (DBR) is employed in order to reduce the thickness of the absorption layer thus achieving good responsivity and high speed as well as wavelength selectivity. Current-voltage, photocurrent spectra and highspeed time response measurements point out the better performance of this last family of detectors, as they can operate in tens of Giga-Hertz range with low dark current and high responsivity. Particularly, the I-V curves show a very low dark current (around 10 picoamps at operative biases) and the photocurrent spectrum shows a clear peak at 850 nm wavelength. Combination of very low dark current wavelength selectivity, and compatibility with high electron mobility transistors makes these devices especially suitable for the above-mentioned applications.

Christof Bosbach, Tilo Pfeifer, Frank Depiereux
ABSOLUTE DISTANCE MEASUREMENT WITH MINIATURIZED

White light interferometry or coherence radar is a well known and established measurement technique for years. But especially the field of production technology and medical technology need measurement systems with continuously increasing performance. This paper demonstrates, how the use of special optical components for higher measurement frequencies and the miniaturizing of the sensor tip can enlarge the application fields for this system. First, the fundamental aspects of white light interferometry are presented and lead to the new concept of a distance measurement system. It is shown how the inset of a special stepped mirror in the detection interferometer increases the measurement frequency and how the sensor is miniaturized using a Fabry-Perot interferometer.

Page 935 of 939 Results 9341 - 9350 of 9382