No abstract

Magnetoresistive spin valve sensors based on the giant-(GMR) and tunnelling-(TMR) magnetoresisitve effect with a flux-closed vortex state free layer design are compared by means of sensitivity and low frequency noise. The vortex state free layer enables high saturation fields with negligible hysteresis, making it attractive for applications with a high dynamic range. The measured GMR devices comprise lower pink noise and better linearity in resistance but are less sensitive to external magnetic fields than TMR sensors. The results show a comparable detectivity at low frequencies and a better performance of the TMR minimum detectable field at frequencies in the white noise limit.

No abstract

No abstract

In this paper we present an occupant detection system based on a capacitive sensing technique. The capacitive detector is designed to distinguish between an empty and occupied vehicle seat. Additionally, the coupling between the seated passenger and the car-body can be investigated. This occupant detection system provides valuable additional information for airbag controlling system. By launching airbags well matched and controlled, the injuring risk of a passenger can be minimized in case of a car crash. In comparison to standard pressure sensors capacitive sensors are contactless and have no wearing parts [1], this leads to economic benefits. The detector operates in a frequency range between 50 kHz and 5 MHz with 5 mV RMS sine signals, by using a precision impedance analyzer. In our laboratory setup, the car seat measuring assembly is shielded by a copper chassis cage which can be connected either to the low or high-potential of the impedance analyzer or can be kept floating. This feature enables us to analyze the effect of the variable passenger to ground coupling. Each of the 16 sensor electrodes, located at the backrest and seating surface area, can be switched to low potential, high potential or can be left unconnected during a measurement. In order to determine the posture of the passenger body, we record coupling capacitances between single electrode pairs. Furthermore impedance characteristics over a wide frequency range can be analyzed based on appropriate impedance models in order to receive more information about the occupancy status of the car seat.

Automotive magnetic field sensing applications require a robust sensing concept. One way to meet the corresponding sensor requirements, such as a negligible hysteresis and a large linear working range, is to employ the vortex state. Consequently, the nucleation field Hn of the vortex state becomes a highly important sensor parameter. In this study, we examine different factors that affect Hn. Tunneling magnetoresistance spin-valve sensors with disk-shaped CoFeB free layers, which energetically favor the nucleation of the vortex state, are electrically characterized and compared with micromagnetic simulations. Phase transitions into intermediate magnetic states, such as various buckling states, the S-state, or the double vortex state, are extracted from hysteresis loops. The resulting phase diagrams show that the formation of the S-state only occurs below a thickness of approximately 25 nm, whereas the double vortex state nucleates frequently only above approximately 35 nm. Both the S- and double vortex states lower the nucleation field of the single vortex state compared to higher order buckling states. Understanding both the origin and the influence of the intermediate phases opens the way to designing a robust and reliable vortex sensor concept.

No abstract

We implement an efficient energy-minimization algorithm for finite-difference micromagnetics that proofs especially useful for the computation of hysteresis loops. Compared to results obtained by time integration of the Landau-Lifshitz-Gilbert equation, a speedup of up to two orders of magnitude is gained. The method is implemented in a finite-difference code running on CPUs as well as GPUs. This setup enables us to compute accurate hysteresis loops of large systems with a reasonable computational effort. As a benchmark we solve the µMag Standard Problem #1 with a high spatial resolution and compare the results to the solution of the Landau-Lifshitz-Gilbert equation in terms of accuracy and computing time.