Gert Holler

The floating water bridge

When high voltage is applied to distilled water filled in two glass beakers which are in contact, a stable water connection forms spontaneously, giving the impression of a floating water bridge. A detailed experimental analysis reveals static and dynamic structures as well as heat and mass transfer through this bridge.

Reconstruction of inhomogeneities in fluids by means of capacitance tomography

Electrical capacitance tomography (ECT) is a technique for reconstructing information about the spatial distribution of the contents of closed pipes by measuring variations in the dielectric properties of the material inside the pipe. In this paper, we propose a method that solves the non‐linear reconstruction problem directly leading to less iterations and higher accuracy than linear back projection algorithms currently in use in most ECT systems.

Dynamics of the floating water bridge

When high voltage is applied to distilled water filled into two beakers close to each other, a water connection forms spontaneously, giving the impression of a floating water bridge (Fuchs et al 2007 J. Phys. D: Appl. Phys. 40 6112–4). This phenomenon is of special interest, since it comprises a number of phenomena currently tackled in modern water science. The build-up mechanism, the chemical properties and the dynamics of this bridge as well as related additional phenomena are presented and discussed.

Analysis of hardware concepts for electrical capacitance tomography applications

This paper presents two front-end circuit concepts for electrical capacitance tomography sensors. Input stage circuit models are used to analyze the robustness against stray capacitances, indicating clear advantages of the displacement current based approach. Hence, a further examination of this concept is carried out

Adaptive regularization parameter adjustment for reconstruction problems

In reconstruction (i.e., determining the states of a model from measurements of model outputs), one is often forced to search for a regularized solution due to poor sensitivity of model outputs with respect to the model states. The amount of regularization is controlled by the regularization parameter, a scalar value multiplied with the so-called regularization term. The choice of the regularization parameter is crucial for the reconstruction process. In this paper, a new method to estimate the regularization parameter in an adaptive way is proposed. A condition-number based estimate of the regularization parameter for the first iteration step is required to choose the weighting factor for adapting the regularization parameter iteratively. By virtue of controlling the regularization term, a kind of edge preservation can be achieved. The validity of this method will be demonstrated for a capacitance tomography problem, which is solved applying a Gauss-Newton scheme.

Automatic Antenna Tuning Unit to Improve RFID System Performance

Systems for radio-frequency identification (RFID) realize a bidirectional wireless communication between a reader device and cheap passive tags (e.g., an RFID chip with an antenna printed on badges for access-control systems) in the near field of an antenna. This paper deals with the automatic and fast tuning of the resonant reader antennas in the widely used 13.56-MHz frequency band, resulting in a performance improvement and an increased read/write range. A novel RFID reader system is proposed with a tuning transformer for the automatic adjustment of the resonant circuit center frequency. This is achieved by shifting the magnetic operating point (i.e., the biasing direct-current (dc) magnetization) of a Ni-Zn ferrite transformer by means of an additional dc winding. The operation principle and the performance potential of this device are demonstrated by measurements on a prototypical RFID system.

Design and analysis of a capacitive moisture sensor for municipal solid waste

This paper presents a capacitive sensor conception to measure the moisture content (MC) in municipal solid waste that is primarily used for energy recovery by means of combustion. The sensor principle is based on a two-channel I/Q measurement of the complex impedance of the waste. The specific design of the sensor front-end allows for a robust MC determination in a non-contacting manner. In this paper, a detailed analysis of the sensor performance, including an estimation of the sensor cross-sensitivity on saline contamination and on metal components in the waste, is provided. Experiments are conducted under laboratory conditions and measurement results are presented.

Wireless Communication and Power Supply Strategy for Sensor Applications Within Closed Metal Walls

Passive or semiactive wireless sensors, i.e., sensors that require neither wires nor external power supply/batteries, are attractive for many measurement problems. Standard approaches based on Radio Frequency Identification technology usually have difficulties when a fairly conductive matter such as steel or a large amount of water is in the vicinity of the devices. This paper investigates methods for power and data transmission, even through the metal walls, e.g., of a tank or a pipe using super low frequency carrier signals. The feasibility is demonstrated by means of finite-element analysis and laboratory experiments and validated with a prototype setup for both a steel pipe and a tin container. Experimental results for capacitive fill-level measurement inside a metallic container are reported.

An Investigation on Wireless Communication and Power Supply Through Metal Tank Walls

Passive wireless sensors, i.e. sensors that do neither require wires nor external power supply/batteries, are attractive for many measurement problems. Standard approaches based on radio frequency identification technology usually have difficulties when fairly conductive matter such as steel or large amount of water is in the vicinity of the devices. This paper investigates methods for power and data transmission even through metal walls, e.g. of a tank or a pipe using super low frequency carrier signals. The feasibility is demonstrated by means of finite element analysis and laboratory experiments and validated with a prototype setup for both a steel pipe and a tin container.

Capacitance-Based Sensing of Material Moisture in Bulk Solids: Applications and Restrictions

This paper presents applications of capacitive techniques for moisture sensing of bulk solids. Based on experimental measurement data for three test materials, theoretical considerations on moisture models in bulk solids are undertaken and the reliability of these models is discussed. The sensitivity of the capacitive setup on the moisture distribution inside the particles is analyzed by means of a multilayer model and Finite Element Analysis methods. A planar sensor topology featuring spatial resolution is proposed and the cross-sensitivity on material compression as well as the influence of the inter-electrode distance are investigated. Strengths and weaknesses of capacitive moisture sensing are discussed.