Fikret Hacizade

A new inverted pendulum to determine anelastic behavior of metals: Design and characterization

An inverted pendulum with a copper-beryllium (Cu-Be) flexure element was designed and its performance was determined by detecting the respective angular changes of the pendulum using a CCD (charge-coupled device) camera within an oscillation period range of 2-30s. An arrangement was made by clamping the flexure element and pendulum rod to avoid subjecting them to compression stress due to the weight of the overall pendulum mass on the flexure. This form of inverted pendulum employs a flexure specially clamped to the pendulum rod to provide tension deformation under the weight of the mass and could be used for dynamic testing of highly sensitive flexure elements. The quality factors of the pendulum were determined with respect to flexure elements by measuring free oscillations decaying exponentially. The results showed that the inverted pendulum with a different connection between the flexure element, and pendulum rod can be used to measure the anelasticity of materials and to test elements under bending d...

Low-cost pulsed solid state illumination for microPIV measurements

Particle Image Velocimetry (PIV) is a non-invasive, full-field optical measurement technique that has become a dominant tool for velocity measurement of fluids and gases at both macro (traditional PIV) and micro (microPIV) scales. In PIV experiments, the fluid under the investigation is seeded with tracer particles, which are shining under an excitation by a properly tuned light source. The idea behind the method is to precisely register the position of corresponding particles in two shifted instances of time and then using these records calculating particle displacements, i.e. flow velocity. In most PIV experimental setups, illumination is performed using dual cavity pulse lasers, whose outputs reach several hundreds mJ at short pulse lengths (tens of nano-seconds). Unfortunately, such laser systems are very expensive and bulky. In this work, we investigate a possibility to replace the laser illumination with a high power LED illumination, aiming towards the development of the cost effective and portable microPIV systems. We have developed an electronic circuit, which drives LEDs with a high current over short time duration. The driver circuit is triggered by an internal electronics of the CCD camera, and is able to produce single or double current pulses per camera trigger. Besides, the circuit also allows i) flexible adjustment of the pulse duration (from 1 μs up to tens of msec), ii) the time delay within pulse pairs, which is crucial for double-frame mode, and iii) time delay between the trigger signal and current pulses. We present experimental results of flow velocity measurements obtained using the microPIV system and the developed illumination setup. We have investigated the flow of water, which was seeded with the spherical-polystyrene-fluorescent particles, inside rectangular microchannels. For illumination, a LumiLED LED with a peak wavelength at 470 nm was used at the double-illumination mode, where current pulses of up to 10 A at duration of 5 μs were achieved.

The influence of CCD pixel binning option to its modulation transfer function

In recent years CCD manufacturers have been supplying their devices with multi-purpose abilities to manipulate the CCDs readout pattern, where one of these versatile options is a flexible pixel binning option. The pixel binning is a process of combining multiple pixel charges in horizontal, vertical or in both directions simultaneously, into a single charge. The binning process positively influences to the signal-to-noise ratio, sensitivity and frame rate at the cost of decreasing spatial resolution, which, in its turn, negatively influences to the spatial frequency response of the imaging system (i.e. to the output image quality). The modulation transfer function (MTF) is an essential measure for characterizing the spatial-frequency response of the array imaging system. In this work we have performed a theoretical and experimental investigation of the MTF of CCD array in the context of the pixel binning option. We have derived a generalized equation of the geometrical MTF for the v x h binning mode, where v and h denote the numbers of binned pixels in vertical and horizontal directions, respectively. The MTF measurements were performed using a method, based on the generation of laser speckle and utilizing the high resolution (1360×1024) monochrome CCD array. The MTF of normal mode, 2×1-horizontal, 1×2 - vertical, and 2x2 quadratic binning modes were measured by employing single-slit aperture method. CCD binning is widely used in spectroscopy, astronomy, in many image processing applications, such as autofocus, object tracking, etc. The results of this work can be useful for designing optical systems, involving CCD pixel binning option.

Autocorrelation analysis of spectral dependency of surface roughness speckle patterns

When a surface is illuminated with a highly coherent light such as a laser beam, the speckle pattern of bright and dark regions is observed. It depends on the surface parameters and carries important information about the roughness of the surface. Various methods and techniques are employed for the determination of surface roughness parameters from speckle pattern properties. In this paper, an experimental approach for surface roughness evaluation based on the autocorrelation analysis of the spectral properties of speckle patterns caused by milled metal surfaces is reported. The speckles at three 633, 604 and 543 nm wavelengths of He-Ne laser were analyzed. It was found that autocorrelation analysis is very sensitive to small variations in speckle sizes, caused by spectral properties of speckle patterns such as increasing the wavelength lead to increased speckle sizes. The results are in good agreement with the results obtained from the mechanical stylus profilometer for the milled metal surfaces with roughness values Ra; 0.36µm (low roughness) and 1.98µm (high roughness). The technique reported here has a great potential for precise and non-contact optical measurements of rough surfaces.

Passive millimeter-wave band data acquisition setup and associated image processing techniques

Surveillance systems that are effective and functional even during harsh weather conditions are essential for many applications. The main advantage of utilizing electromagnetic waves beyond the visual spectrum in millimeter and sub-millimeter wave band for imaging purposes is their robust and almost lossless propagation through mediums that are not accessible by conventional optical systems, such as smoke, snow, fog and sand storms. Unfortunately, sensing equipment that operates in that band is complex and further requires bulky mechanical setups for image acquisition. In this work, we present our setup for passive millimeter-wave data acquisition and its associated modules. The main focus of the current work is the image processing and data visualization techniques that are further applied to the acquired data to obtain human comprehensible images.

Hyperspectral image processing and display techniques in the context of forensic document investigation

Nowadays, deployment of forensic document investigation systems that employ hyperspectral image processing is being widespread. The reason such systems are being preferred is mainly due to their non-destructive nature of document investigation, fast processing time, and the ability to reveal erased and covered writings, and details. On the other hand, analyzing hyperspectrum, obtained after a document scan, is a nontrivial task, which requires special training. Even trained document investigators may spend a plenty of effort to reveal covert evidence. In this work, we discuss hyperspectral image processing and display techniques we have developed to ease the job of forensic document investigators. Besides, our techniques will help to the investigators performing more constructive guesses during their investigation process. Additionally, this work aims to provide general knowledge about the hyperspectral image processing based document investigation to the interesting reader.

Seamless image stitching algorithm using radiometric lens calibration for high resolution optical microscopy

Image mosaicing method is an image-based rendering and visualization method which is a common procedure in the generation of panoramic (composite) images and applications, such as creating virtual reality, super resolution, object insertion and object removal, etc. Specifically, the image stitching approach becomes common in super resolution digital imaging microscopy, where it is required to achieve both high magnification and a large field of view. This work presents the algorithm for the stitching of different overlapped high resolution views of the whole scene obtained from high magnification optical microscopes into a large radiometric balanced image through maximization of a cross-correlation function. To seamlessly blend and reduce the possibility of intensity and color mismatching of multiple source images in mosaicing, a radiometric calibration of the microscope optical system is employed. The algorithm was tested with grayscale and color images, and showed convincing and robust results in image stitching and blending.

3D sub-terahertz anaglyphic radiometric imaging system

Experimental results of preliminary work on creation of 3D radiometric images of objects passively scanned at sub-terahertz frequency range (97 to 107 GHz) using anaglyphic projection are discussed.

Reflection, transmission and color measurement system for the online quality control of float glass coating process

Over the past century there has been a dramatic increase in the demand for float glass in many fields of industry. Usually, 10 to 30% of produced float glass is coated with various coatings for different purposes. As a consequence quality control of the coatings is one of the most current issues during the process of float glass manufacturing. In this work we describe a system designed for the online control of reflectivity, transmittance and color coordinates of the coatings during the glass production process. The working principle of the system is based on the measurement of the spectral characteristics of reflectivity and transmittance of coatings within the 400-700 nm spectrophotometer spectral range during the online coating process. The measurement unit consists of two microspectrometers (one for the measurements of the spectral characteristics of the reference source, and the other for the measurements of the reflectance spectrum), illumination head (consisting of one white 1W LED and collimating lenses), stabilized power supply, microprocessor and 18 bits precision ADC. The use of the reference channel allows us to stabilize the intensity of the incident light up to 10-4 level. The repeatability of the measurement of reflectivity coefficient in laboratory conditions was in range of ± 0.001. However, in the measurements in the factory environment, due to the vibration of the glass ribbon on the conveyer, the measurement reproducibility was about ± 0.005.