Jan Vcelak

Compact Digital Compass with PCB Fluxgate Sensors

The new compact digital compass with PCB fluxgate sensors and accelerometers will be introduced in this contribution. Competitive low-cost, low-accuracy compasses are dedicated for measurement in horizontal plane only. The main advantage of developed compass is that it is able to determine azimuth in every position. The compass module consists of a tri axial fluxgate magnetometer and tri axial MEMS accelerometer which is used as a tilt sensor. The excitation and evaluation electronics is build directly in the compass module. Compass module is driven by two microprocessors and is equipped with digital output. The dimensions and power consumption of the compass were decreased by using miniature PCB (Printed Circuit Board) fluxgate sensors, instead of traditional large ring core fluxgates. Improved calibration techniques have been used to decrease azimuth error of the compass. The using of accurate magnetic sensors leads to the possibility of using tri axial magnetometers for calculation of total Held intensity and use it as a vector magnetometer. The resulting device is small high accurate compass with digital output that is able to be used in underwater or underground exploration or measurement.

Iterative EM Based IMD Synchronization for Fast Time-Variant Channel with Subspace Order Recursive LS Iterator

We solve the problem of iterative expectation-maximization (EM) based information measure directed (IMD) synchronization in fast time-variant environment. We identified correspondence between the EM iterator and the weighted least squares (LS) problem. An order recursive form of the LS iterator reduces the implementation complexity. The channel coefficients are allowed to change arbitrarily up to the granularity of the symbol period. The coefficients are modeled using parametric subspace providing a wide range of configuration for the channel dynamics while reducing the dimensionality of the problem substantially

Long-range magnetic tracking

Two magnetic trackers are described in this paper. The first one is fully magnetic and has 1 meter range. This device can measure distance with 1 mm resolution and 1 cm total accuracy. The second system is a hybrid tracker using active magnetic ranger, three optical gyros and three micromachined inclinometers. It has 15 m range and for distances below 5 m the position accuracy is 50cm. The heading error is below 0.1 deg.

Bomb Detection in Magnetic Soils: AC versus DC Methods

We compare the performance of eddy-current metal detectors for finding small bombs and other items of unexploded ordnance (UXO) with the potencial of DC gradiometers of scalar and resonant type. Extensive database of results was collected during laboratory measurements and field trials performed by JRC. There are two main obstacles for bomb detection: false alarms caused by metal clutter and effect of magnetic soil and rocks. A number of soil samples were collected at mine fields and UXO affected areas. Magnetic properties of these soils were examined both in time and frequency domain. The results were compared with the detection depths measured both in soil and in air for various targets. In general, the most difficult soils show frequency dependent susceptibility, which creates signal similar to metal object. We show how to compensate such soils.

Fiber Bragg gratings embedded inside glued laminated timbers: an overview and evaluation

In this paper, the fiber Bragg gratings are investigated in the context of sensing of deformation inside a sample of a glued laminated timber. For this purpose, a fiber with acrylate recoated Bragg grating is placed and glued between the timber laminates. Since there are still some open questions leading now, one of the goals is to specify, if the sensor that is embedded inside the timber can operate as the sensor that is not. Therefore, the strain of the not embedded sensor is numerically investigated in the first step as the change in the grating period. In order to calculate the Bragg wavelength associated to the grating period, the light propagation through the fiber has been modeled by rigorous and versatile eigen mode expansion method. Based on the simulation result, the authors are able to determine the sample strain under the mechanical load by measuring the reflected Bragg wavelength. Moreover, the measured strain is compared with the strain analytically obtained from the known force applied on the sample. The both strains are in good agreement.

Long-Range Magnetic Tracking System

This paper presents a new long-range full 3-D magnetic tracking system for horizontal directional drilling, and describes its performance. The system is able to determine the full 3-D mutual position of the receiver with respect to the transmitter. The system presented here belongs to the category of hybrid trackers using an active magnetic ranger, an optical gyro, and three micromachined inclinometers. The gyro is used for dead-reckoning navigation over long distances (up to 2 km), and the magnetic tracking system, consisting of a coil magnetic transmitter and a magnetometer receiver, is used when two drill heads are approaching each other beneath the surface at the assumed meeting point. The functionality of the system was verified for the maximum range of 17 m with 1,2-m rms accuracy, and with 0,34-m rms accuracy for the range below 10 m.

Subspace recursive weighted LS solution of iterative synchronisation in time-variant channel

Expectation-Maximisation (EM) based iterative synchroniser is a particular form of the Information Measure Directed (IMD) synchroniser using a posteriori soft information from the iterative decoding network. We solve the problem of EM-based IMD synchronisation in the general fast time-variant channel. The channel coefficients are allowed to change arbitrarily up to the granularity of the symbol period. We have identified the correspondence between the EM iterator and the weighted least squares (LS) problem. This allows to utilise a wide range of solutions developed for the LS problem. Particularly interesting is the subspace order recursive form of the LS iterator which reduces the implementation complexity. The parameter subspace in the estimator is modelled using a wide range of configuration. This allows consideration for the channel dynamics while reducing the dimensionality of the problem substantially when the model is properly matched to the real channel behaviour including an adaptive subspace dimension setting. The procedure is demonstrated on example systems with the estimation of phase and jointly amplitude and phase on serially concatenated coding scheme. We use realistic Jakes Doppler dynamics as an example for the true channel and variety of subspace models for the EM estimator. Copyright

Optical Fiber Sensor for Timber Structure Monitoring

The paper deals with the experimental analysis focused on the determination of strain in wooden building structures using optical fibers with FBG sensors. Firstly, optical fibers were used to measure displacements of layers and surface strain of the lower surface of the ceiling panels made from mechanically jointed cross laminated timber (CLT). The measured displacement values of the optical fibers were compared with the results obtained from the inductive displacement sensors. Secondly, optical fibers were used for long-term monitoring of the roof structure of the sports hall. The fibers were mounted on chords of timber trusses and their correct function was verified by a load test.

Study of Stress-Induced Anisotropy in METGLAS 2714

METGLAS 2714AZ material has been stress annealed without any applied magnetic field to obtain suitable magnetic properties for use as low-noise fluxgate sensor core. During the development of magnetic cores, we observed an unusual change of the anisotropy direction on Co-based amorphous alloy of METGLAS 2714 AZ. The anisotropy direction moves from its original direction along the ribbon axis to the transverse direction as expected but for short annealing times the process is not monotonous. This occurs when annealing is performed above the Curie temperature. We explain it as a mixture of different anisotropies, which are built and released during the annealing process, since the 2714AZ ribbon has manufacturer-induced anisotropy in ribbon axis. The effect of ribbon cooling on the ribbon properties is also shown as annealing in the radiation furnace was done in different ways.

AMR proximity sensor with inherent demodulation

Our novel position sensor is based on the combination of the eddy-current and permeability effects. The primary field is excited by a coil, but instead of induction coil, the sensing part uses anisotropic magnetoresistor (AMR), which also measures dc magnetic field. As the AMR is being flipped at the excitation frequency, the sensor is self-demodulated and the output is dc. The AMR sensitivity does not depend on frequency; therefore, this sensor can be used at ultralow frequencies, where coils fail as sensors. We show the response of our sensor to ferromagnetic and nonferromagnetic metals and possibilities to distinguish between them. We also show that our sensor can measure position through the conducting sheath.