Hartmut Ewald - Academia.edu (original) (raw)

Papers by Hartmut Ewald

IEEE Sensors Journal, Mar 1, 2012

Proceedings of SPIE, May 15, 2011

A robust optical fibre based CO2 exhaust gas sensor operating in the mid infrared spectral range ... more A robust optical fibre based CO2 exhaust gas sensor operating in the mid infrared spectral range is described. It is capable of detecting on board carbon dioxide (CO2) emissions from both diesel and petrol engines. The optical fibre sensor is not cross sensitive to other gaseous species in the exhaust such as water vapour (H2O), carbon monoxide (CO), oxides of

BMC Emergency Medicine, Dec 1, 2017

ABSTRACT This paper deals with the optimization of a customary inductive proximity sensor. The fo... more ABSTRACT This paper deals with the optimization of a customary inductive proximity sensor. The focus in this paper lays on the significance of the side metal effect in magnetic sensors, which has remarkable influence on the accuracy of these sensors. It will be explained what the sensors field of application is and the difficulties to handle with. Furthermore, solutions for reducing the side metal effect are explained and evaluated.

A real time, high resolution LED based, spectroscopic gas concentration measurement system is pre... more A real time, high resolution LED based, spectroscopic gas concentration measurement system is presented. This kind of measuring techniques was enabled by the advances in the fabrication of ultraviolet LEDs (UV-LEDs). The system presented here has a relatively compact design and small application efforts. Different hardware setups have been evaluated to design a system for real time high resolution LED absorption spectroscopy. Applied are two concave mirrors, two photo detector diodes and a 405nm LED mounted in a small device. A standard low power microcontroller was applied as signal processor. The few, robust, reasonable priced components enables high volume applications for this sensor. Different optical simulations provide optimized system parameters for gas concentration measurements in the low ppm range. NO2 concentrations of 200 ppm have been measured with a resolution of ~1.5% counts (16-Bit-ADC). Therefore the ppb range becomes an available measurement range with higher ADC-Resolutions.

Proceedings of SPIE, Jan 14, 2007

With two orthogonal spatial filters all directions of two-dimensional motion can be measured. A m... more With two orthogonal spatial filters all directions of two-dimensional motion can be measured. A modification of the aperture function of the lattice allows an innovative measuring real time system for particle sizing and position monitoring. Every plane motion can be described with two velocity components. If two planar local filters are formed, then the directional characteristic can be changed, so that for all directions of object motion an evaluable output signal is generated. It is preferable to use orthogonal speed components because these produce minimal resultant error in the velocity vector. In our approach two-dimensional structured photo detector arrays are used as a spatial filter [1-3]. A modification of the aperture function of the lattice allows the realization of an innovative measuring system for particle sizing. The output signal is comprised of equidistant signal effacements, whose distances are dependent on the particle size [4-6]. What makes this method very interesting, particularly with regard to real time systems, is the possibility of pixel linking inside the sensor.

Proceedings of SPIE, Feb 8, 2007

Photo-plethysmography (PPG) is frequently used in research on microcirculation of blood. It is a ... more Photo-plethysmography (PPG) is frequently used in research on microcirculation of blood. It is a non-invasive procedure and takes minimal time to be carried out. Usually PPG time series are analyzed by conventional linear methods, mainly Fourier analysis. These methods may not be optimal for the investigation of nonlinear effects of the hearth circulation system like vasomotion, autoregulation, thermoregulation, breathing, heartbeat and vessels. The wavelet analysis of the PPG time series is a specific, sensitive nonlinear method for the in vivo identification of hearth circulation patterns and human health status. This nonlinear analysis of PPG signals provides additional information which cannot be detected using conventional approaches. The wavelet analysis has been used to study healthy subjects and to characterize the health status of patients with a functional cutaneous microangiopathy which was associated with diabetic neuropathy. The non-invasive in vivo method is based on the radiation of monochromatic light through an area of skin on the finger. A Photometrical Measurement Device (PMD) has been developed. The PMD is suitable for non-invasive continuous online monitoring of one or more biologic constituent values and blood circulation patterns.

Proceedings of SPIE, Oct 30, 2001

An optical fibre (3 sensor) multipoint U-Bend evanescent wave absorption sensor system is reporte... more An optical fibre (3 sensor) multipoint U-Bend evanescent wave absorption sensor system is reported which is capable of detecting contaminants in water and depositions by coating on its surface. The sensor is based on a continuous 1Km 62.5micrometers core diameter ...

Proceedings of SPIE, Feb 25, 2013

Based on the human circulatory system, an artificial blood circulatory system was developed to al... more Based on the human circulatory system, an artificial blood circulatory system was developed to allow the controlled variation of the following blood parameters: total hemoglobin concentration (ctHb), oxyhemoglobin (O2Hb) methemoglobin (MetHb) and carboxyhemoglobin (COHb). The optical properties of the blood were observed by online spectrometer measurements. The purpose of this was to observe and quantify the absorption, transmission and scattering properties of human whole blood in the wavelength range of 400 to 1700 nm. All the non-invasive measurements of the whole blood transmission-spectra were compared with sample results obtained by a Blood Gas Analyzer (BGA) to validate the results. For all measurements, donor erythrocyte concentrates were used. The concentration of hemoglobin was changed by adding fixed amounts of blood plasma to the erythrocyte concentrate. Oxygen saturation and COHb were adjusted by a continuous flow of N2, N2-CO and compressed air through a hollow fibre membrane oxygenator. Different methemoglobin concentrations were adjusted by using natrium nitrite. The blood temperature was kept constant at 37 °C via a tube heating mechanism, with a separate circulation of water passing through the membrane Oxygenator. The Temperature and pressure of the system were automatically controlled and monitored. The model was also used to test new non-invasive measurement systems, and for this reason special cuvettes were designed to imitate human tissue and generate plethysmographical signals. In the future, the blood circulatory system has the potential to be used for testing, validating and also to calibrate newly developed optical prototype devices. It can also be used to further investigate blood components of interest.

Physiological Measurement, Aug 1, 2001

Journal of Marine Systems, Dec 1, 2012

ABSTRACT Wind flats are typical coastal landscape elements of the tide-less Southern Baltic Sea. ... more ABSTRACT Wind flats are typical coastal landscape elements of the tide-less Southern Baltic Sea. These sediment areas exhibit an irregular and unpredictable pattern of emersion and flooding as a function of the prevailing wind direction and speed. Consequently, wind flats represent very specific and unique coastal habitats that, however, are ecologically poorly understood. The irregular and unpredictable water level fluctuations cause strong physico-chemical gradients which favour the development of laminated microbial mats. These micro-ecosystems accumulate organic material, enrich the sediment with nutrients and reduce erosion of sand particles. In the present study we developed a new autonomous measuring device for precise water level changes and recorded for the first time under in-situ conditions the irregular flooding events of the wind flat Bock (Zingst Peninsula, German Baltic Sea coast). The measured water level changes were compared and correlated with the closest gauging station and the prevailing wind conditions (direction, speed) to better understand the effects of hydrology and meteorology on duration and intensity of inundation. From the 12 measuring periods of over 2.5 years we noted that about half of the time the wind flat was fully exposed and dry, and the other half at least wet with <1 cm water levels. The strongest flooding of up to 20 and 50 cm water height was a relatively rare event, which, however, depended on wind speed and direction, i.e. wind speed above 8 m s(-1) from north to northeast direction. The undertaken measurements on exposure and inundation intervals of this unique sedimentary ecosystem describe well the wind-driven high dynamics and strong gradients in the environmental parameters, and explain well the abundant occurrence of microbial mats in wind flats.

Real time, high resolution measurements of gas concentrations are a task in many industrial appli... more Real time, high resolution measurements of gas concentrations are a task in many industrial applications like smoke detectors, medical and analytical devices. By usage of LED sources for optical absorption spectroscopy, such systems have a high potential to replace commonly used electrochemical sensors, even in low-cost applications. Depending on the gases, they can provide higher sensitivity, selectivity and dynamical response. Background of this paper is the optical gas concentration measurement by usage of LEDs, which are matching the specific absorption lines of different gases. The paper describes in detail a laboratory device, developed for high precision, multispectral (up to 8 wavelengths), referenced (20-bit, two-channel simultaneous sampling) measurement system with temperature stabilized LED sources. While the described system was developed for laboratory purposes with high precision and flexibility in mind, the key components (ADC/LED-Driver) are very low-cost and the system could also be driven by a simple microcontroller.

Conference proceedings, Dec 1, 2006

Today for clearing areas from landmines, beside dogs and searching needles, almost excluding meta... more Today for clearing areas from landmines, beside dogs and searching needles, almost excluding metal detectors are used. Available metal detectors, specialised for mine clearance, are highly sensitive also on small metal parts. Nevertheless, they give no further information about the buried object (depth, size, shape, material). Besides, the high false alarm rate of the hand-held detectors makes the mine clearance a protracted and cost-intensive process. Reasons for the high false alarm rate (up to 1000 false alarms per mine) are "uncooperative" soils, harmless metallic objects like shell splinters, but also the low metal content in newer anti-personnel mines. In this paper a method is described which provides more information about the buried object by using image processing and signature classification, which works also in the presence of "uncooperative" soil. In many cases, there are only one or two different mines in a minefield. So it is possible to use a database with mine signatures for an automatic object classification in order to decrease the false alarm rate

Proceedings of SPIE, Nov 14, 1996

The nondestructive eddy current methods are commonly used for automated defect inspection to dete... more The nondestructive eddy current methods are commonly used for automated defect inspection to detect cracks in materials which are used in cars, power and aircraft industries. The eddy current signal from a infinitely long crack can be classified with the help of the fuzzy logic and the neural network techniques. A rule based fuzzy logic classification guarantees better results than fuzzy-cluster- means algorithm, because the classification results can be increased in this case step by step. By using the neural network for the classification of the crack signals it is very important to have a good 'learning pattern.' The advantage of time-delay networks in this application is the fact that the network can 'learn' the eddy-current time signal; a signal preprocessing is not necessary.

Proceedings of SPIE, Jun 3, 2005

Conventional humanitarian mine detectors based on magnetic and magneto-inductive procedures are a... more Conventional humanitarian mine detectors based on magnetic and magneto-inductive procedures are able to detect very small metal pieces in the ground. These evaluation methods however result in a high rate of false alarm; the presence of metallic parts detected which are not to be assigned as mines. If you want to classify the metal piece in the ground (e.g. the shape) you have to measure the electro-magnetic field at different positions. Therefore the actual position must be known for each measuring point. By use of the optical spatial filtering method we are able to measure the velocity vector. With the sample time we get the required x-y-position. In our approach we use structured photo detectors as a filter grating and as a detector too. This technique for position determination possesses some interesting advantages such as the use of incoherent light and simplicity of the optical and mechanical set up. New two-dimensional CMOS sensor arrays with direct pixel access allow a fast read out of sub frames. A disadvantage is the slow signal to noise ratio and the price of industrial CMOS cameras that facilitate frame grabbing. The use of simple CCD web cameras limit the maximum measurable velocity, having a read out time of 60 Hz (max), but the price decrease extreme. Early tests using structured photo detectors and spatial filtering methods for position determination show very good results for velocities from 0 to 250 mm/s. A local resolution of 1 mm can be achieved. Tests have also been performed using an ordinary optical mouse as the position determination system.