Theses 2013

Awano, Nebiat Tekle

Design, Implementation and Calibration of Compact MIMO 5.8 GHz Radar/RFID Transceiver Frontend

Abstract: The project deals with design, implementation and calibration of 5.8 GHz (ISM band) RFID/radar transceiver frontend. The idea is based on theimplementation of the principle of FMCW (Frequency Modulated Continuous Wave) radar to estimate the Angle of Arrival (AOA) for 3D positioning. MIMO implementation is realized with one transmit and three receive channels.

Such systems are affected by noise; thus, emphasis is given to generate stable 5.8 GHz frequency synthesizer to reduce the phase noise. Accordingly, a board with PLL-VCO (Phase Locked Loop- Voltage Controlled Oscillator) combination circuit is implemented and tested.

Homodyne (direct conversion) transceiver architecture is used due to its low hardware complexity. One of its main disadvantages is the DC offset created by self-mixing of the local oscillator at the receiver. This and related problems call for Calibration circuit. Besides, since the transceiver implements quadrature modulation, some components such as mixers corrupt the signal by introducing carrier leakage, quadrature imbalance and phase skewing. These effects are mitigated with the help of the calibration circuit. Since calibration is done first or the transmitter and then for all of the three receive channels, the whole system will be calibrated.

Successful operation of transceiver circuit depends also on good componentselection, power planning and applying principles of high frequency design carefully. Discrete circuit implementation is followed due to its ease of manufacturing and testing compared to MIC or MMIC implementations. Design tools such as Matlab and Agilent ADS were used when needed. Circuit schematics and layout was designed with Cadsoft Eagle.

Awel, Salah

Optimization of a Calibration Strategy to Reduce the Retrace Error in Structured Illumination Macroscopy (SIMA)

In the main part of this work the systematic errors that existed in the first model-free calibrationimplementation by Yang is investigated. These systematic error sources are classifiedinto three main parts and optimized accordingly.

The first category of error sources are those errors which are introduced during measuring the retrace error over the full field and full angular dynamics. These include errors due to the photogrammetric accuracy, the instability of the calibration hardware and the intrinsic error in the SIMA measured height due to bat-wing effect at the boundary of the markers. The photogrammetric accuracy is estimated and the instability is optimized by careful design of the calibration marker plate and the calibration hardware. Furthermore, to improve the effect of bat-wing in the SIM measured height, vertical and horizontal sinusoidal fringe are projected in a single measurement and the height of the marker is evaluated from the mean contrast fromvertical and horizontal fringes. By doing so it has been managed to improve the bat-wing effectas well as reduce the magnitude of the retrace error in general.

The second categories of error sources are those errors which are introduced during approximating the underlying 5D calibration function (LUT). From simulation as well as measurements it is known that the retrace error has sharp dip in the angular domain at around zero degree. However, polynomial approximation usually fails to represent such sharp deeps. In order to solve this problem, different kind of freeform approximation algorithms like RBF and NURBS are investigated and implemented. This investigation has shown that NURBS and RBF can represent the freeform surface with accuracy in the order of the noise level.

The third error source that is optimized is the systematic error in the slope measured by PMD. This error source was not taken into account in the first implementation of the model-free calibration. However, it was one of the biggest error sources. For example, on a measured slope of ball bearing of diameter 10mm using PMD in +/-17°  angular dynamics there was systematic error up to 6°. Using a model-free calibration approach this systematic error is reduced by more than half on the calculated slope Sx and Sycompere to the previous modal-based approach. However, due to the discontinuity on the marker plate, there are still remaining systematic error of 2.5°  for example on the slope Sy. This could be further improved by using an appropriate calibration object such as a half-sphere.

After these optimization procedures it is managed to reduce the systematic error of SIMA by a factor of six compared to not corrected data . Compared with the first implementation by Yangthe systematic error has been reduced by nearly a factor of three on ball bearing of diameter 10mm measured by SIMA in +/-17°  angular dynamics. In addition to the systematic error, it is also managed to increase the angular dynamics of SIMA from +/-12°  in the first implementation to +/- 17° .

In the final part of this work the optimization of precision by integrating SIMA with μPMD is presented. This has been done by extracting the good features from SIMA and μPMD and integrating them together. By combining the global shape from SIM and the local detail in formation from μPMD we managed to optimized local precision down to few nanometers.

The improvement in the systematic error is significant as discussed above. However, there is still some room for improvement. For instance, the slope measurement sensor is still one of the biggest error source and instability of the marker due to thermal expansion could cause a bigsystematic error. The bat-wing effect is managed to tackle only for marker position of Φ close to π/4 and 3π/4 . However, for marker plate position of ‑ close to π/4 and 3π/4 we still have bat-wing effects in our measurement. This remaining error could be up to 20μm at the edge of the FOV of a marker plate tilted by Θ = 18  for Φ close to π/4 and 3π/4 . This can be improved further by projecting additional fringes other than the vertical and horizontal fringes or using a sphere as a calibration object.

Alhamwi, Nawras

Plethysmographic Sensor Design for Real-time and Remote Body Hemodynamic Monitoring – A New Approach for Early Shock Detection

The recent studies show that in order to detect the early signs of developing a clinical shock, many hemodynamics parameters should be continuously monitored especially in the intensive care units and the operation rooms. These parameters are: the heartbeat rate, respiration rate, blood oxygen saturation, blood flow velocity and the blood pressure.

In this thesis, a noninvasive, cheap, compact and easy to use sensor for a real-time monitoring is designed, programmed and tested to monitor these body hemodynamics parameters and predict the chances of developing a clinical shock.

The sensor is based on the photoplethysmography principle where the diffuse reflectance signal from the area under interest of the body is detected. Briefly, the sensor consists of a photodiode which collects the diffused reflected light from the tissue that shinned by using two wavelengths, 660 nm and 940 nm, emitted by two LEDs. The LEDs are operating alternatively and driven by a TTL signal. The output current of the photodiode is amplified and converted into a voltage by using a trans-impedance amplifier.

For a purpose of reducing the generated noise by the electrical components, ideal filters are applied by coupling the output signal of the amplifier to a computer by using Data Translation DT9816 module. The acquired signals by the computer are post-processed by using a LabView®2012 code to present, calculate and estimate the desired body hemodynamics parameters.

The PPG waveform and the respiration rate are presented after filtering out the noise. Additionally, the heartbeat rate is calculated by using two different approaches, the FFT approach and by counting the pulses and calculating the intervals between them. The SpO2 value is also calculated by using two approaches of estimating the ratio of variations in the acquired signals from the two wavelengths. Besides that, the PTT is estimated and the pulse period is calculated in order to estimate the blood flow velocity and the blood pressure.


The heartbeat rate, SpO2 and the blood pressure results of the designed sensor were tested by comparing them with results of instruments, as reference, which are normally used in hospitals in order to verify the quantification and the reproducibility of the sensor results. This investigation has been done by applying the sensor and the reference instruments on 21 different healthy subjects. The output results of this investigation show that the sensor results of measuring the heartbeat rate and the SpO2 were very close to the results obtained from the reference instrument with a very low and close standard deviation values to what the reference instrument has. Additionally, the blood pressure values were also very close to the reference values with an advantage of monitoring the blood pressure in a real-time without disturbing the subjects and with an acceptable standard deviation values according to the AAMI.

The heartbeat rate, SpO2 level and the blood pressure parameters are used in order to predict the clinical shock. This has been done by calculating predicted values, out of the previous values, with a range of tolerance and compares it with the new measured value. When the heartbeat rate is rising and the SpO2 level and the blood pressure are falling, a chance of developing a clinical shock is expected.

The results of this work have shown promising results for noninvasive and real-time monitoring of the body hemodynamic parameters that are used in the detection of early signs of the clinical shock development. It was shown that the hardware unit and software algorithm were successfully designed. The PPG waveform can be presented by using this sensor and extract many of the body hemodynamic parameters such as respiration rate, heartbeat rate, blood oxygen saturation, blood flow velocity and blood pressure out of it.

Additionally, it was shown that the output results of the sensor were very close to the reference values. The maximum absolute difference (MAD) between the mean values of the sensor and the values from the reference instrument was 2.6 Beat/min while the maximum absolute difference of the standard deviation of the heartbeat rate values was 2.6029 Beat/min. Regarding the SpO2 measurements, the MAD of the mean values from the sensor and the reference was 3.711 % with a 2.3766 % for the standard deviation error. Finally, the MAD of the mean values was 4.1 mmHg with a 6.8505 mmHg for the standard deviation error.

In order to improve the results and reduce the standard deviation values, the motion artefacts should be reduced. The sensor should be fixed to the body in a way that reduces the motion artefacts but also without disturbing the subject. Many shapes of the sensor probe can be used, according to the studied area of the body, where the clip shape, which is normally used in the pulse oximeter, can be used to attach the sensor to one of the fingers or by using a rubber band for the arms and legs areas. More compact design of the current probe can be made to attach the sensor to the rest of the body areas since the effect of the motion artefacts is low in these areas. Additionally, the prediction of the clinical shock development can be improved by applying it in the Labview code in order to predict in online mode and optimize the used approach of defining prediction tolerance.

Balz, Nathalie

Development of a Miniaturized Laser Scanning Microscope

Conclusion: The developed laser scanning microscope shows that the principle of the resonant scanner is working. The advantage of such a scanner is clearly the high speed. But a crucial point is the received Lissajous curve, which demonstrates the bigest disadvante of such a system. The problem of the curve is that the scanning lines do not have a constant distribution. The 90:1 Lissajous figure shows that the lines in the center of the pattern have larger distances to each other than at the right and left sides and the distribution of lines is higher at the turning points of the scanner. The reason for this behaviour is the cosine-like velocity of the scanner, which results in a velocity of zero at the turning points of the scanner and a maximum velocity in the middle of one scan. The result is a different amount of data points at the turning points and in the middle of the pattern and a signal with different sized pulses in time. As discussed, a Ronchi grating would be a possibility to overcome the problem with the cosine velocity and to process the data. Another possibility is to develop a software program that is capable of compensating these different distributions of scanning lines, to obtain an undistorted image. Further, the obtained data from the PDS will generate th information of th eposition of the laser beam across the scan pattern and can then be overlaid with the obtained signal to recieve an undistorted image with position information. These problems will be some of the points for the further development of the setup.

Another point for optimizing this setup is that the equipment has to be changed to more expensive and higher quality devices. Therefor, an adequate funding is needed. If this current setup is working as expected with the new equipment, a further research topic will be to miniaturize the setup even more and to use the system as an endocsope for examining living animals.

Bayat, Shahin

Influence of a Laser Power Modulation on the Element Intermixture at Austenitic-ferritic Stainless Steel Welds

Summary: Tha aim of this research is an experimental study of the correlation between laser power modulation and corresponding weld seam properties. The main reasons to perform laser trials with power-modulated laser beam instead of continuous wave laser are to reduce the average energy consumption and to manipulate the element intermixture inside the weld seam. This manipulation is an increase in the element intermixture homogenity and an improvement in laser-metal thermal impact. The weld trials were carried out with two different spot sizes and three different modulations. Electon microprobe analysis, Vickers micro hardness measurment, sulfuric acid corrosion test and tensile analysis were performed to study weld seam properties.

By doubling the spot size from 300 μm to 600 μm, the weld seam element intermixture homogeneity decrese that was also proved by electron microprobe analysis. The reason is that by increasing the spot size, the average heat input decreases and leads to an element intermixing reduction. The transverse and top-view analysis of weld seams for each modulation shapte did not reveal any considerable effect on increasing intermixture homegeneity and all moduation shapes had similar impact on weld seam. The hardness profile across the weld seam mixing compunds reveald high Vickers values which indicate that the power-modulated laser welding can lead to an increase in overall weld seam hardness. In 600 μm spot size, laser power modulation exposed higher hardness values compared with non-modulated beam but this effect was not observed in 300 μm spot size. In both 300 and 600 μm spot sizes independent of power modulation, high pick values in similar ferritic butt-joints above expected base material detected. The tensile test over all similar butt-joint showed that the overall strength increases in welded regions since all specimens failed in base material. There was also a slight increase in tensile strength since all specimens failed in base materials. There was also a slight increase in tensile strength in 600 μm spot size copared to 300 μm spot size.

To sum up the idea, power-modulated laser beam welding can be employed instead of normal continuous wave beam welding by considering two aspects. First, the same or improved weld seam properties can be achieved by laser power modulation besides having less energy consumption. Second, element intermixture homogeneity and corrosion resistance can be increased in some modulation shapes compared with non-modulated beam which is demandes in energy laser beam weld process.

Chahine, Charlotte

Characterization and Optimization of a Lithography Stepper

Summary: Over the last decade the importance of the litography has pushed the study of the physical and chemical mechanismn of the litography process. Nevertheless, litographic modelin played a dramatic role in gving a comprehension of the experimental outcomes rapidyl and straightforwrdly. Therefore, in order to characterize and optimize the application of a new Ultratech „Sapphire 100E“ wafer stepper at Fraunhofer IISB, we combined litographic simulation and exposure experiments.

To achieve our aim several aspects were tackled on the simulation and experiment level. This work showed the elements of an optical lithography tool to get a better understanding of each element task and utility in the i-line wafer stepper. Furthermore, the chapter introduced the DNQ-based positive photoresit QZ ECI3007, and explained the optical lithography process steps: wafer preparation, spin coting, soft-bake, exposure, post exposure and development.

the aerial image in optical projection litography was familiarized and simulated aerial images of the mask pattern with different features size of the dark and bright mask field were predented. The images showed that the stepper can print with good resolution, though the optical proximity effects, down to 0.6 μm.

The process windows of the features for different sizes of lines and spaces were plotted and the focus and threshold latitudes were extracted. The Focus latitudes are relatively huge even for the smaller features of 0.6 μm. The process linearity curve was presented as well and it showed that the stepper can print resolvable features szie only down to 0.8  μm.

Next, the litographic modeling was introduced for the bulk image, exposrue, post-exposure bake, development model and the full resist model simulation. Additionally the genetic calibration algorithm was announced along with the optimization problem setting.

The choice of experimental exposure dose and development time in practices was diccussed. Furthermore the influence of PEB on the resit profile was shown for the three cases: no PEB applied, PEB applied at a temperature of 90°C for 60sec, and PEB applied at a temperature of 110°C for 60sec. The profiles showed that the PEB at very higher temperature is able to suppress standing waves effects and results in vertical sidewalls.

The experimental sets of feature CDs data were introduced with different conditions:

  • Exposure dose of 115 mJ/cm2, no PEB applied.
  • Dose matrix from 60 mJ/cm220 mJ/cm2. PEB applied.
  • Focus matrix from -7.0 μm to 7.0  μm, PEB applied.

The differences that appeard between the data sets were discussed.

The last part of this work showed the two calibrated models one for the case of no PEB application and another for a PEB application. The simulated resist models results were compared with the experimental data and the aerial image extracted data. The first model showed fitting data with the experimental data. As for the second model it exhibits a slight difference due to SEM measurements erros.

The aerial image comparison data with the resist model simulated data shows typical agreement at best dose and focus; yet a difference start appearing when looking at CDs away from these best conditions.

The process windows based on rsist model as well and we have registered a drop in the values of the focus latitudes.

The lithographic modeling provided the opportunity to investiage and optimize the Ultratech „Sapphire 100E“ wafer stepper under a variety of lithographic conditions with accurate results.

Jamshidipour, Hamed

Optical Sensor for Estimating Focal Distance and Cut Width During Laser Cutting

Summary: In this thesis, a new fiber-based optical sensor for sensing distance during laser cutting is introduced. This sensor works based upon different angles of the reflected pilot laser beam in order to gauge the workpiece displacement. During this investigation, the aim was to assess the optimal sensor resolution and measurement range.

In the setup there is a sensor box which receives the reflected beam from the workpiece in different ways. It consists of a shielded case, two photodiodes and a tapered fiber. This fiber is cut and polished at 42° angle and adjusted in front of two photodiodes inside the box. The total internal reflection law defines the intensity of the light that each photodiode captures. Any displacement of the workpiece changes the reflected beam’s focal point and angle and consequently, changes photodiodes’s output voltages. The fraction of these two voltages defines the measurement function of the sensor. In this study, two different methods for a capturing reflected beam have been examined in order to compare to each other. Additionally this difference gives us opportunity to sensing the gap as well as the distance.

In the first method, the reflected beam from the workpiece is focused on a screen. A fiber is adjusted behind the screen to transmit the captured light to the sensor box. The results of experiments in this method indicate that there is a strong correlation between the optical signals and the workpiece displacement. In the first step of this method, a mirror is used to simulate a fully reflective workpiece. Our study shows that although in 4mm workpiece movement range, the photodiodes have considerable voltages, the effective range of high resolution measurement is in a range of 2mm. We observed a 25μm resolution for 100% direct reflection workpiece and zero cancellation of electronic noise or lateral laser profile fluctuations via the mean value calculation. By increasing the number of data sampling from one to 1000, the resolution is observed to be 10μm. Moreover, increasing the distance between the screen and the fiber from 0.5mm to 1.5mm improves the measurement range, although simultaneously decreases the resolution. Selecting a suitable measurement function and finding a tradeoff between the resolution and the measurement range depends upon the application of the sensor. In the second step of this method, a piece of steel sheet is used to simulate a partial diffuser workpiece. For this workpiece, we observed 205μm resolution while there is zero cancellation of electronic noise or lateral laser profile fluctuations via mean value calculation. Like previous step, increasing the number of sampling, improved the resolution to 120μm.

It was observed, for different workpiece by increasing the number of data sampling from one to 1000, the resolution of the sensor goes up as well. Increasing the number of the samples for mean value calculation, cancels the electronic noise and lateral laser profile fluctuation effect, partially. In addition, using 400μm fiber exhibits better sensing specification in comparison to the 105μm fiber. One of the possible reasons might be catching less light due to the smaller NA and diameter. To compensate this low intensity, the gain is increased and consequently the noise effects steps up. The high power laser source might improve the measurement function.

In the second method, the screen was removed and the fiber was placed at the focal point of the backward reflected beam. This experiment did not fulfill our expectations and has thrown up many questions in need of further investigation. The measurement function in this method has low gradient and measurement range. It is recommended that further research be undertaken in this area.

The second method can be improved by recalculating and changing the angle of the fiber inside the sensor box. Moreover, we suggest using 1mm fiber with higher quality and NA. Locating precisely a blocker in front of the fiber to completely eliminate middle part of the reflected beam might be another improvement for this sensor. Finally, some important limitations need to be considered: First, fiber bending can change the angle of the light significantly. Second, dirt on the fiber end can dramatically decrease the efficiency of the sensor. We suggest that all of these limitations and suggestions be studied in the future.

To sum up, fiber-based optical sensor with diffusion screen can be employed for distance sensing in material processing and especially in laser cutting. The statistical relation between the optical signals and the workpiece indicates that, by further optimization, higher sensor resolution can be achieved. In some applications such as scanner based remote laser welding, the angle of incidence changes during the process. In order to implement this new method, we should make sure the measurement function is independent of the angle of incidence; otherwise the angular changing should be measured and be considered in the calculation.

Kamal, Saikat

Non-Linear Impairment Compensation Using Correlated Backward Propagation

Abstract: The main distinction of a fiber optical link is that it modulates the light as a form of energy and use the optical fiber as a medium of propagation from source to destination. We can utilize light as a best source for communication if we can use the higher order modulation formats to increase the spectral efficiency and allow it to propagate over long distance fiber with minimal degradation. So in the Optical Fiber Communication chapter we have investigated the behaviour of light under certain condition as it passes through the optical fiber. Moreover in the past decades various algorithms for compensating optical fiber impairment have been playing a vital role in digital signal processing technologies causing a profound change in telecommunication revolution as bit rate gets higher from 112 Gbits/s to 224 Gbits/s. To compensate the deterministic nonlinear impairments we have also investigated the performance of Digital Backward Propagation (BP) and Correlated Backward Propagation (CBP) by digitally back propagating the received signal through a virtual fiber. The main objective of our study is to conclude the influence of various parameter which will provide a clear guideline for implementation of both algorithms in future real time digital signal processing. In our study we have used dual polarization 4 QAM transmitter signal through standard mode fiber (SSMF) of length 300 to 1200 km. We have used 5, 10 and 20 spans of 60 km standard signal mode fiber (SSMF) respectively with nonlinearity and dispersion. The attenuation of each span was compensated by an Erbium Doped Fiber Amplifier (EDFA). We have studied that the CBP performance is enhanced drastically compared to conventional BP if the parameters are optimized. Modeling and result has been sustained by the numerical simulation in Optisystem and Matlab.

Nkiwane, Emmanuel

Experimental Comparison of Different Pulse Shaping Techniques for Advanced Modulation Formats using a Recirculation Loop in Fiber Optic Communications

Abstract: Internet traffic is growing exponentially. This can be attributed to the high bandwidth services that are now available. Video streaming, video on demand, on-line gaming, on-line banking, social networking and cloud computing have contributed tremendously to the increase in data traffic. Consequently, there needs to be a matched increase in the transmission data rates.

There are several ways in which this could be accomplished. One way would be to use advanced modulation formats. The major advantage of this technique is that more data can be transmitted using the same bandwidth when compared to traditional modulation formats such as on-off keying. Another way of increasing capacity would be to use different pulse shaping techniques with advanced modulation formats for efficient use of the available bandwidth.

The main purpose of this thesis is to primarily compare the performance of different pulse shaping techniques when applied to a QPSK signal. Non-Return to Zero (NRZ), Nyquist, Raised Cosine and Root Raised Cosine are the pulse shapes that are to be investigated. Furthermore, the performance of QAM signals is also to be briefly investigated. For these investigations a recirculating loop was established in-order to transmit the different signals over varying transmission distances. EVM, SNR and BER are some of the measurement metrics that were used for performance evaluation.

Ramalingam, Arachana

Photonic Lantern Based Spatial Mode Multiplexer and Mode Equalizer

Abstract: The ever increasing demand for high capacity has led to the simultaneous implementation of dense wavelenght division multiplexing (DVDM), polarization multiplexing and higher order modulation formats. Nevertheless, studies show that the single mode fiber (SMF) capacity is fast approaching the theoretical capacity limit imposed by the Shannon’s information theory and nonlinear fiber effects. This calls for an alternative dimension to be explored to increase the capacity of SMF, which is space. Space division Multiplexing (SDM) happens to be the solution.

Mode multiplexing (MDM) ystems perform SDM. Usually MDM De/MUX approaches are based on beam optics, which uses mode splitters, combiners and mode converters. Due to lack of scalability and splitting and combining losses of the system De/MUX, alternative approaches, namely waveguide couplers, fiber butt coupling structures and fused fiber power dvidier are being used.

This thesis deals with the use of Phtonic lantern (PL), which is a type of fused fiber power divider as a mode converter. The purpose of this study is to optimize the waveguide separation function in order to minimize the cross coupling between the modes and estimating the length of the lantern for minimum crosstalk using coupled mode theory. Also the PL performance is computed in terms of the overall crosstalk between input MMF modes and output SMF modes using transfer matrix model. As a final step, optical MIMO equalizer filter with directional couplers design is discussed.

Reuter, Judith

Holographic Interferometry for Determination of Binary Diffusion Coefficients of Gas Mixtures of Helium with Krypton and Ammonia

Summary and outlook: This study presents experimental binary diffusion coefficient data measured with a Loschmidt cell combined with holographic interferometry for gas analysis. This measuring technique is supposed to be the most reliable absolute method for the determination of the concentration dependence of the binary diffusion coefficient of gases [3]. The Loschmidt cell is designed for a temperature range from 283.15 K to 353.15 K and a pressure range from vacuum to 10 bar. lt is equipped with two holographic interferometers, one for each half-ell. Starting the diffusion experiment with pure gases the upper half-cell provides data for the mole fraction range of the heavier compound 0 ::::: x1 ::::: 0.5 and the lower half-cell for 0.5 :::; x1 :::; 1. This way the concentration dependence can be determined over the complete mole fraction range in only one experimental run. Altogether our setup can investigate the concentration, temperature and pressure dependence of the binary diffusion coefficient in a timesaving way.

Measurements were conducted with the gas pairs krypton-helium and ammonia-helium. The system krypton-helium was investigated to validate the measuring range of our experimental setup. A noble gas pair was chosen because it shows weak real gas behaviour and the diffusion was supposed to be approximated by Fick’s second law. There is also a variety of theoretical and experimental data for this system available in literature for comparison. Ammonia-helium was chosen as a system with a molecular compound due to its stronger real gas behaviour. The influence on the data evaluation approximated by ideal diffusion should be tested. This gas pair has also a technical relevance; it is used for the design of diffusion absorption refrigerators where especially the concentration and pressure dependence are of interest.

The system krypton-helium was investigated at 293.15, 313.15, 333.15 and 353.15 K and the pressures 1, 2, 5 and 10 bar. At 293.15 K we achieved increasing D12Pmix data with increasing mole fraction of krypton which accords with predictions from the kinetic theory of dilute gases. However, the upper half cell as weil as both half-cells at higher temperatures shows systematic deviations from the kinetic theory. Previous investigations suggested a correlation between the systematic deviation in the upper half-cell and the diffusive velocity. In this study the deviations in the upper half-cell increased with increasing temperature, i.e. with increasing velocity. However, a correlation for the lower half-cell could not be found. For the temperature dependence we produced increasing values of the binary diffusion coefficient with increasing temperature. Our data are in very good agreement with literature data and theoretical data based on the kinetic theory of dilute gases. Data for the pressure dependence of the binary diffusion coefficient is very rare. A comparison of our data with the only available literature data shows that both studies achieved slightly decreasing D12 ·pmix values with increasing pressure. We achieved uncertainties lower than 0.75% depending on the temperature and pressure.

For the system ammonia-helium sorption effects were discovered. According to the Kerl group [3, 32, 33] lubricants are the main reason for sorption. That is why the diffusion cell is constructed in a way that lubricants were necessary. However, we found sorption at the sealings and cell walls by investigating the pressure change inside the Loschmidt cell during diffusion of ammonia and helium. For compensation of this effect we tried saturating the cell with ammonia prior to the experiment. The saturation time had a strong influence on the concentration dependence of the diffusion coefficient data. As very long saturation times resulted in gas overflow between the two half-cells a compromise of two hours for saturation was applied. The sorption effect was not yet the uncertainties are smaller than 0. 75%. With our apparatus the determination of the concentration dependence of binary diffusion coefficients is still difficult, but we achieve very good results for the temperature and pressure dependence.

For future studies the data evaluation has to be extended to consider sorption effects as weil as further transport effects such as gravitational forces or convection. To learn more about these effects further measurements should be conducted for example on the noble gas system krypton-xenon. This gas pair is characterized by a very small binary diffusion coefficient and is therefore suitable for the characterization of the bending behaviour. Disagreements to the literature data should be less distinct if the correlation between the bending behaviour and the diffusive velocity holds.

Furthermore, systems with two molecular components should be investigated. The system carbon dioxide-nitrous oxide (C02-N20) is characterized by equal molar masses and approximately equal second pressure virial coefficients, i.e. the particle number in the two half-cells filled with pure gases are identical. This prevents convection due to difference in molar masses or particle numbers at the beginning of the diffusion measurement and allows the examination of the intluence of acceleration and delay of the particles in the upper and lower half-cell. The same weight force acts on the particles of the upper and lower half-cell, but the particles of the upper half-cell are accelerated whereas the particles from the lower half-cell get delayed. taken into account in the data evaluation.

Binary diffusion coefficients of the gas pair ammonia-helium were determined at 293.15, 313.15, 333.15 and 353.15 K and the pressures 1, 2, 5 and 8 bar. Due to the sorption effects it was not possible to reliably determine the concentration dependence. We found increasing as weil as decreasing values for D12 „Pmix in both half-cells. A correlation of the bending behaviour with the diffusive velocity was not observed for this system. However, our absolute values of D12 ·pmix agree very well with the literature data and theoretical values based on the kinetic theory of gases at zero density. For this system, too, our data for the temperature dependence are in good accordance with theoretical and experimental literature data. The pressure dependence of the diffusion coefficient for the system ammonia-helium was examined experimentally for the first time. Our data was compared to theoretical values calculated by the kinetic gas theory at zero density [17]. We obtained a stronger decrease for D12 ·pmix values with increasing pressure in comparison to the system krypton-helium. For the system ammonia-helium

Sadeghzadeh, Amirhossein

Head Tracking During Magneto-Encephalography (MEG) Data Recording via ‚Flying Triangulation‘

Summary of the results: In this wor, a prototype sensor based on the Flying Triangulation measurement principle and also compatible to MEG environment is developed and implemented in hardware. This sensor consist of two projection beam path and an observing pathes for 3 D data collection, mounted in 200 mm x 180 mm x 150 mm housing. To prevent any interposition between the MEG measurement and Flying Triangulation sensor acquisition, the housing is contructed with PVC. The triangulation angle for this sensor is Φ=6° and 3D data acquisition is 30 fps. For the light source two fiber-coupled laser diodes with 7 m multi-mide fiber length and output power 400 mW in wavelength λ=635 nm is used. For making the projection pattern, 25 lines DOE is implemented. For collimating the fiber output, f = 40 mm focal length collimator, which is not so perfect for our work, is used. This collimator can not focus the fiber output sharply, so we can not acquire thin lines and it increases our measurement uncertainty. The working distance of the sensor is dA = 1000 mm and measurement volume is 200 mm x 150 mm x 180 mm. By connecting the sensor to the ‚Flytr-Reg‘ software, we can calibrate and acquire the data which object motion is completely detectable.

Saeed, Ahmad

Multiband Gap Organic Solar Cells

Interlayer are essential part of tandem solar cells. To investigate interlayers various combinations of HTL and ETL materials were used. Metal electrode penetration in the thin filsm leads to the shunts an destroys the morphoslogy of the film. Initially AG electrode was tried as the top electrode while fabrication diodes (interlayer devices) but due to metal penetration into the thin films, short devices were frequently observed. As a remedy Al metal electrode was use which resulted in better resulty with the AZO based films as they are not nano particlse as in case of ZnO and have a smoother surface providing low chances of metal penetration. In case of ZnO, where the solution evaporates after thin film is laid, and nano particles are left behind, thus offering very rough surface, posses more chances of metal penetration into the ZnO film. As a result less success was achieved with the ZnO based diodes.

While AgNw have proved again and again that their presence in the interlayer provides very robust films and also protect the neighbouring layer from interpenetration of charge carriers. AgNw has also shown a significant property of establishing Ohmic contacts in the interlayer. On the other hand, OLED based normal structured devices give very good idea about the robustness of interlayers as no EL emission because of cross flow of charge carriers was observed. Where as to answer the question related to E-Field charge spouting, low temperature measurements can be performed in the future to anser the ambiguity about the processes in the inverted OLED based structures. Anothe possibility of future work can be carrying out capacitance – voltage (C-V) measurement in the similar fashion as J-V curves are measure for tandem solar cell by creating reference top and bottom subcells.

Soleimani Aligodarzi, Mehrbod

Varadhachari, Janani

Analysis of Multimode – Fiber Mode Multiplexer with Spatial Sampler

Abstract: Mode Division Multiplexing (MDM) has been used commonly in almost all optical networks for a while in order to overcome capacity limitations in communication networks. MDM in multimode graded index fiber has been evidently effective in matters of non-linearity and capacity. In this work, multiplexing of modes from single mode fibers into a multimode fiber for local area and other access networks is carried out. The performance of such MDM system with single mode fibers butt coupled to multimode fiber shall be analyized by increasing the number of spatial modes transmitted and the number of single mode fibers in the system. The optimized structure with minimal modal loss and crosstalk will be identified for an efficient transmission of signals. For the purpose of optimization, aperture masks are used. These masks avoid any spatial overlap between the modes and thus increase the efficiency of the MDM system. Finally an all pass MIMO filter shall be designed and implemented in the system to retrieve back the original signals.

Weigand, Marina

Phase Retrieval from Bright-Field Microscope Images

Abstract: Bright-field microscopy is a very essential tool in medicine and biology. Thereby cells in bright-field microscope images often lack contracts. The reason for that is that they nearly do not change the amplitude but introduce a phase shift. With standard microscopy techniques like phase contrast microscopy this phase shifts can be made visible. However, they only produce qualitative phase images where the phase information is coupled non-linearly and cannot be retrieved quantitatively. With numerical methods the pahse can be obtained quantiatively out of several in-focus and defocused images. An iterative approach to retieve the phase information out of bright-field images of cells is implemented for the first time. in addition, a non-iterative approach and aproaches to improve it are investigated. Till now no quantitative investigations have been performed. In this work a first method is presented to quantitatively evaluate the different algorithms with real bright field microscope images of cells with the help of Mutual Information and phase contrast images. It is possible to calculate phase images without any additional hardware than a standard bright field microscope. This makes these numerical methods very interesting for different applications, since already existing systems can easily be upgraded. For the evaluation nine data stacks were recorded for adherent and suspended L929 cells. The evaluation shows that for adherent cells in some areas the non-iterative approach provides the best result while for suspended cells and cells in areas disturbed by the noise of the non-iterative approach the iterative approach performs better. The presented approaches to improve the non-iterative method were successful.