Phillip Durdaut

Synchronisation using wireless trigger-broadcast for impedance spectroscopy of battery cells

In electric vehicles, batteries with many cells are used to supply the high voltages needed for the power train. The battery is controlled by a battery management system (BMS) which needs measurement data from each individual cell. Up to now, wired solutions with specialized measurement controllers for battery modules are in use. Some of these communicate over data bus structures. Our group proposes as an alternative solution the use of wireless communication in the near RF field area. The basics of this solutions have already been published [1]. In this article we present more advanced functionality for the wireless sensors approach. A functional module has been developed for impedance spectroscopy of each individual cell in the battery stack during automotive operation. Electrochemical impedance spectroscopy is a powerful method to determine the battery state beyond common and simple models. This technique needs precise and synchronized measurements of the common current and the voltages of the individual cells. A communication and control protocol has been implemented in hard- and software, including a trigger-broadcast operating mode. This solution has to fulfill the time precision requirements of the distributed measurements in the range of a few μs. Therefore, proprietary protocol solutions have been developed. Additional modules in the sensor system allow other functions such as cell balancing and an energy saving wake-up function for the sensor modules. These sensor modules are designed as tailored hardware for integration inside the individual battery cells.

Thermal-Mechanical Noise in Resonant Thin-Film Magnetoelectric Sensors

Thin-film magnetoelectric sensors, i.e., composites of magnetostrictive and piezoelectric materials, are able to measure very low magnetic flux densities in the picotesla range. In order to further improve the limit of detection it is of high importance to understand and quantify the relevant noise sources. In this paper, a common model for the deflection noise in vibrational structures is applied to the cantilever structure of resonant magnetoelectric sensors. By means of deflection and noise measurements the existence of thermal-mechanical noise even in sensor structures with a size in the centimeter range is proven. Based on these findings a noise equivalent circuit is suggested which allows not only the distinction between the impact of different sensor-intrinsic noise sources and also the involvement of the preamplifier noise. We found that the thermal-mechanical noise is the dominant noise source if direct signal detection is performed at the first bending resonance frequency of the sensor. However, this kind of noise is not the limiting influence when applying magnetic frequency-conversion techniques.

Generalized Magnetic Frequency Conversion for Thin-Film Laminate Magnetoelectric Sensors

Magnetic frequency conversion is a promising technique to enhance the limit of detection of magnetoelectric sensors detecting low-frequency magnetic signals. In comparison with the direct detection in the mechanical resonance of the sensor, this method shows a limit of detection increased, i.e., worsened, by approximately 2.5 decades. For the detection of bio-magnetic signal, frequencies ranging from 0.1 Hz up to approximately 100 Hz though the method yield a better limit of detection than direct detection. Still, it is worse than theoretically expected. The cause of the deterioration of the signal-to-noise ratio during magnetic frequency conversion is investigated. Besides the conversion loss, it is due to the arising magnetic noise during excitation of a magnetostrictive material with a pumping signal, which is also in the order of approximately 2.5 decades. The noise can be reduced by applying an additional dc-bias field, which simultaneously results in less output signal. Measurements are confirmed by a numerical model. An existing equivalent noise model for magnetoelectric sensors is extended accordingly.

Wide Band Low Noise Love Wave Magnetic Field Sensor System

We present a comprehensive study of a magnetic sensor system that benefits from a new technique to substantially increase the magnetoelastic coupling of surface acoustic waves (SAW). The device uses shear horizontal acoustic surface waves that are guided by a fused silica layer with an amorphous magnetostrictive FeCoSiB thin film on top. The velocity of these so-called Love waves follows the magnetoelastically-induced changes of the shear modulus according to the magnetic field present. The SAW sensor is operated in a delay line configuration at approximately 150 MHz and translates the magnetic field to a time delay and a related phase shift. The fundamentals of this sensor concept are motivated by magnetic and mechanical simulations. They are experimentally verified using customized low-noise readout electronics. With an extremely low magnetic noise level of ≈100 pT/

Modeling and Analysis of Noise Sources for Thin-Film Magnetoelectric Sensors Based on the Delta-E Effect

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Noise of a JFET Charge Amplifier for Piezoelectric Sensors

Hz, a bandwidth of 50 kHz and a dynamic range of 120 dB, this magnetic field sensor system shows outstanding characteristics. A range of additional measures to further increase the sensitivity are investigated with simulations.

Evaluation of magnetoelectric sensor systems for cardiological applications

Thin-film magnetoelectric sensors reach a sensitivity in the picotesla range around the resonance frequency of the mechanical structure. Using magnetic frequency conversion, a magnetic low-frequency signal can be transferred to the sensors resonance frequency. However, the required additional large carrier signal leaks to the sensors output with a large amplitude, requiring a wide dynamic range of the sensor electronics. In this paper, it is shown that the unbalance of the magnetostriction curve is responsible for this leakage and that a suppression approach is devised. After theoretical analysis of the nonlinear magnetostriction characteristic, a carrier suppression is achieved through balancing by an altered signal excitation. A suppression of the carrier signal of about three orders of magnitude is measured. Thus, the requirements regarding analog-to-digital conversion can be reduced.

Noise Limits in Thin-Film Magnetoelectric Sensors With Magnetic Frequency Conversion

We present a comprehensive noise model for an electromechanical resonator that is utilized as a magnetic field sensor. The cantilever-type sensor is coated with a magnetostrictive film that exhibits a change in elastic modulus E with a magnetic field and therefore detunes the resonator—the so-called delta-E effect. The noise model contains all relevant noise sources from the operational electronics, the wiring, and the sensor itself. Measurements show good agreement up to a certain excitation voltage, where an additional dominant noise source appears. It is identified as originating from the magnetic film. With the results of the model, the operational parameters of such sensors are discussed. The model predicts that the limit of detection at 10 Hz for the present sensors can be improved to 60 pT/(Hz)