In this paper, we present research, development, calibration and characterization of a novel concept of a digitally compensated, low-noise magnetometer based on anisotropic magnetoresistance sensors that is suitable for space applications. The main idea of the design was to reduce the number of precise analog components while using the digital signal processing power available in a modern microcontroller. Our most recent effort targeted lowering power consumption, enhancement of radiation hardness and overall improvement of the parameters. The principle of operation is presented in detail, along with a detailed description of the instrumentation used to characterize the real instrument, including its noise, linearity, and temperature stability in the range of -20 to +70 °C. The results of total ionizing dose (TID) testing at a gamma-ray irradiation facility are discussed at the complete magnetometer and part levels. This is an extended version of a paper presented at I2MTC 2020 that contains the results of a second radiation test done with a slightly modified design. The instrument worked well throughout the entire irradiation session (TID of 1.05 kGy over 72 hours), and the stability of main parameters was very good (50 pT/Gy offset and 1 ppm/Gy sensitivity stability).

A new construction of magnetometer with commercially available AMR (anisotropic magnetoresistive) sensors intended for vehicle detection experiments is presented. Initial experiments with simple AMR gradiometer indicated viability of the approach in a real- world setup. For further experiments and acquisition of representative data, a new design of precise multi-channel magnetometer was developed. The design supports two models of commercial AMR sensors: the proven and reliable, but obsolete Honeywell HMC1021-series sensors and newly available Sensitec AFF755B sensors. In the comparison the two types are similar in most achieved parameters, except offset stability in flipped operation regime. Unfortunately, the new AFF755B sensors seem to have perhaps inferior coupling of the flipping (set/reset) coil to the ferromagnetic core that causes insufficient saturation of the AMR material. The issue is being solved by Sensitec, current deliverables of the AFF755B have "product sample" status (September 2015).

A compact magnetometer/gradiometer with combined homogeneous and gradient outputs facilitates precise measurement of both _H and _G values with good spatial and temporal coherence. By evaluating combination of both signals, it is possible to estimate distance to a dipole source with relatively small error and largely independent from precise knowledge of source strength, orientation and lateral displacement. The performance is limited primarily by ambient noise. With an AC-driven source, tool navigation or distance sensing is also possible.

In magnetopneumography (MPG), we scan weak remanent magnetic fields (in the range of nT) of ferromagnetic dust deposited in the lungs of affected workers. This is carried out in an unshielded lab. Variations of the background field during the scanning period bias the inversion process, i.e., the estimation of the magnetic sources from the measured field. We present an innovative mathematical technique of finding a field equation uniquely describing the magnetic moments in the nodes of the measurement space. Simultaneously, it enables the tracking of the values of the disturbing gradient created by external distant sources during the time of scanning. Our method preserves the first-order gradients obtained in multiple layers (scan heights above the object) instead of losing data with the higher order gradients which are not effective here. Six coaxially aligned fluxgates were used for scanning the field maps. The obtained five first-order gradients for each node give us the parameters of the respective ldquoequivalentrdquo magnetic sources. Furthermore, we obtain a parameter describing the error originating mainly from the background field. The main limits of the presented method are: 1) the alignment of the probes; 2) their number being limited by a minimum distance; and 3) nonhomogeneity of the external field.

We present a compact (10-cm head size, 3-cm base) axial magnetic gradiometer with a method of its astatization (i.e. suppression of false response to homogeneous field). For astatization, we use two integrated orthogonal sensors and a second-order polynomial correction; after astatization the gradiometer error is suppressed more than 1000×. The gradiometer has been successfully used in a real-world metal-detection task which was allowed by the low gradiometer astatization error of ± 50 nT/m and its noise of 1 nT/(m√Hz) @ 1 Hz.

In inversion of magnetic data the key task is the acquisition of sufficient number of measurements and suppression of field variations in them. In Magnetopneumography (MPG) we scan very weak magnetic fields of ferromagnetic dust deposited in the lungs of affected workers. Variations of the background field during scanning may bias the inversion such that the determination of the sources is not possible. Just one Is' order gradient for each node is not suitable for this kind of scanning, thus more probes were added. These can provide more information for the inversion at one node and should enable partial instant suppression of the far field variations. Subtraction of the gradients can be used or better during the processing one can use fitting of the measured gradients to equations derived from the models to determine the variations as offsets. The main problem is the exact alignment of the sensors and homogeneity of the far field in the sensor's area.