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Magnetoelectric (ME) thin film composites consisting of sputtered piezoelectric (PE) and magnetostrictive (MS) layers enable for measurements of magnetic fields passively, i.e. an AC magnetic field directly generates an ME voltage by mechanical coupling of the MS deformation to the PE phase. In order to achieve high field sensitivities a magnetic bias field is necessary to operate at the maximum piezomagnetic coefficient of the MS phase, harnessing mechanical resonances further enhances this direct ME effect size. Despite being able to detect very small AC field amplitudes, exploiting mechanical resonances directly, implies a limitation to available signal bandwidth along with the inherent inability to detect DC or very low frequency magnetic fields. The presented work demonstrates converse ME modulation of thin film Si cantilever composites of mesoscopic dimensions (25 mm × 2.45 mm × 0.35 mm), employing piezoelectric AlN and magnetostrictive FeCoSiB films of 2 µm thickness each. A high frequency mechanical resonance at about 515 kHz leads to strong induced voltages in a surrounding pickup coil with matched self-resonance, leading to field sensitivities up to 64 kV/T. A DC limit of detection of 210 pT/Hz1/2 as well as about 70 pT/Hz1/2 at 10 Hz, without the need for a magnetic bias field, pave the way towards biomagnetic applications.

High sensitivity magnetoelectric (ME) thin film composite sensors, which enable the detection of picotesla magnetic fields, are improved in terms of magnetic noise performance by the elimination of magnetic domain (MD) activity. Using an antiparallel (AP) exchange biasing scheme, suppression of magnetic noise is obtained. Postsetting of AP biased ferromagnetic/antiferromagnetic multilayers is accomplished by magnetic field free annealing with in-situ MD control. Overcoming the shape and demagnetization effects, stable single MD configurations in the magnetic sensing layers of magnetic multilayers are formed. Magnetic noise contributions are undetectable. The achieved single domain field stability opens the path to ultralow noise ME sensor applications. The demonstrated AP biasing scheme is applicable to other magnetic layer-based field sensing devices.High sensitivity magnetoelectric (ME) thin film composite sensors, which enable the detection of picotesla magnetic fields, are improved in terms of magnetic noise performance by the elimination of magnetic domain (MD) activity. Using an antiparallel (AP) exchange biasing scheme, suppression of magnetic noise is obtained. Postsetting of AP biased ferromagnetic/antiferromagnetic multilayers is accomplished by magnetic field free annealing with in-situ MD control. Overcoming the shape and demagnetization effects, stable single MD configurations in the magnetic sensing layers of magnetic multilayers are formed. Magnetic noise contributions are undetectable. The achieved single domain field stability opens the path to ultralow noise ME sensor applications. The demonstrated AP biasing scheme is applicable to other magnetic layer-based field sensing devices.

For high spatial resolution, deep body region measurement of biomagnetic signals in the pico- and femtotesla regime, dense vector-field sensor arrays are required. Current state-of-the-art sensors, like SQUIDs, are too bulky and not applicable. In this paper for the first time MEMS sensors based on magnetoelectric (ME) composites with vacuum encapsulation using wafer-level packaging technology are presented. Silicon device and cap wafers with 150 mm diameter were fabricated using micromachining processes and bonded afterwards for hermetic sealing. The device wafer contains rectangular cantilever beams with a stack composed of SiO2/Pt/AlN/FeCoSiB, Au metal-bond frames and conduction lines. The lateral dimensions of the cantilever were 200 μm × 900 μm with an overall thickness of 7.8 μm. The cap wafer comprised the vacuum cavities, alignment marks and Au/Sn metal-bond frames. For avoiding degradation of the temperature sensitive amorphous magnetic material [(Fe90Co10)78Si12B10] a special developed low-temperature, hermetic sealed transient-liquid phase bonding process was used to package the sensor devices. Characterization of a sensor showed a giant ME coefficient of 2390 (V/m)/(A/m) and a corresponding sensitivity of 3800 V/T in resonance at 7.1 kHz. A minimum resolution of 30 pT and noise levels as low as 27 pT/Hz1/2 have been reached in resonant operation.

A mere glance at the contents of any of the conferences organised by ISEMA (International Society for Electromagnetic Aquametry) [1] shows that the measurement and control of water (its quantity and states) in materials is a very wide and active field. That water lends itself to study in this way is because of its very dominant dispersive dielectric properties and an unusually large dipole moment for such a small molecule (1.84 Debye units). At room temperature the dispersion is centred on ∼ 12.5GHz and the real part of the relative permittivity at its upper and lower frequency extremes is ∼ 4.3 and 80 respectively [2]. The complex dielectric properties characteristic of this dispersion are the properties that are measured and correlated with whatever aspect of the water content is of interest. Historically much of the work was carried out at one or two frequencies, mostly in X-band where the dielectric loss is at a maximum, but the advent of time domain reflectometry (TDR) [3] for broadband dielectric measurements in the microwave region eventually led to such measurements being made using open ended coaxial sensors [4], although a greater potential of such measurements was only realised later by the authors. The use of such sensors freed the experimenter from the difficult task of defining the sample shape by means of a sample cell; the measurements still required however that the sensor be in contact with the sample. As a true frequency domain UWB application, dielectric measurements of foodstuffs over a wide range of frequencies (100MHz to 20GHz) were made using network analysers and such coaxial sensors [5, 6]. Drawing on the experience in other chemometric applications such as NIR (near infra-red spectroscopy) [7], the dielectric spectra obtained were subjected to various multivariate analyses (PCR (principal component regression), PLSR (partial least squares regression), and ANNs (artificial neural networks both linear and non-linear)). Such analyses both compress the data into orthogonal factors and extract from those factors the best information to predict the composition of the foodstuffs. In such analysis the important variables are, not so much the dielectric properties at each sampled frequency, but rather the shape of the spectrum. In effect the data reduction provides suitable shape descriptors, which are in the case of foods, very dependent on the water content and its interaction with other

Basic structural investigations on rape-seed as an example of a natural granular material with spherical shape are presented. Moisture dependent structure coefficients such as bulk and kernel density were measured in an especially developed apparatus. It was found, that density independence of a microwave moisture measurement could be obtained by applying a properly defined pre-pressure to a layer of material, thus obtaining moisture independent porosity and density. Furthermore, a permittivity model for rape-seed is presented, which relates dielectric constant, moisture content and structure coefficients. The various binding states ofwater as well as moisture dependent swelling of the seeds are included. The permittivity model was substantiated by dielectric measurements in X-band.

The basic development of a contactless optionally density-independent and continuously operating on-line microwave moisture sensor for organic bulk materials is presented. Moisture determination by means of microwave power is volumetric, but for process control, quality preservation etc. the water content in weight percentage is recommended. Therefore, density and structure parameters, as well as dielectric properties, of different organic bulk materials with characteristic particle shape are measured and compared under different moisture content. Due to cellular tissues and organic compounds, structural behaviour depends very much on moisture and temperature. Results from compression experiments show the possibility of keeping the bulk structure constant within a wide range of water content. Consequently, microwave moisture measurement could be density-independent. A first calculation model shows the correlation between structure properties and the dielectric constant.

This paper presents a method for the non-contacting moisture prediction of small objects using m-sequences. The objects under test are placed in a free-space transmission path. Their UWB impulse responses are captured using an m-sequence method which provides high signal quality by means of ultra low jitter and noise. The size of the objects is in the range of the coherence length and smaller than the footprints of the antennas. The impulse responses depend on the moisture content (dielectric properties) and the geometry. Multivariate calibration is applied in order separate these influences and to develop a statistical model for the moisture content. For the prediction of moisture content an accuracy of 0.55% was achieved while it was varied in a range between 4.3% and 23.4%.

The method shows that by means of an hybrid-mode field an exact equivalent network for a class of waveguide T-junctions can be derived directly. Unlike mode matching, moment and other field related techniques, this model combines simplicity of form with accuracy and guarantees quick convergence suitable for computer optimization of complex multiple junctions.

A long and well known subfield of the ultra-wideband technology is the time-domain-reflectometry (TDR), which found its ways in a wide field of applications. This paper describes different aspects regarding the way from the first concept of a TDR prototype instrument towards a fully engineered device, suitable for food quality management in an industrial scale. The concept of the described TDR widely depends on the frequency range of the task to be solved, thus is one of the most important aspects in the chain of development. Furthermore industrial requirements with respect to handling of the device and the integration in existing systems have to be kept in mind.

We present a fully integrated microelectromechanical magnetic field sensor based on the ΔE effect. The vacuum encapsulated sensor extends our previous approach [B. Gojdka et al., Appl. Phys. Lett. 99, 223502 (2011); Nature 480, 155 (2011)] and now involves an intermediate piezoelectric AlN layer between a SiO2 cantilever and a magnetostrictive FeCoBSi top layer. The AlN layer serves two functions: It drives the resonator, and it is used for electrical read out. The limit of detection was strongly enhanced to 12 nT/ Hz at 10 Hz.

Self-biased magnetoelectric composites, which are realized with the exchange bias effect, hold an increased total anisotropy field compared to systems without exchange bias. Thus, small exchange bias fields are favorable because of a minor reduction of magnetic permeability and magneto-electric voltage coefficient. However, weakly biased magnetoelectric composites lose their self-biasing properties and possibly show an increase of discontinuities in magnetization reversal due to the formation of magnetic domains. By a thickness variation of the ferromagnetic layer, a maximum voltage coefficient αME ≈ 430 V/cm Oe was found for a magnetostrictive multilayer of 3 × (5 nm Ta/3 nm Cu/8 nm Mn-Ir/333 nm Fe-Co-Si-B). Yet, a stable single domain state indicating a well defined magnetization reversal by coherent magnetization rotation was achieved for layer thicknesses up to 100 nm Fe-Co-Si-B with αME ≈ 340 V/cm Oe. This slight reduction is overcompensated by the improved control of the magnetic domain pattern which is highly beneficial for magnetic field sensing applications and of special importance, when frequency conversion techniques are applied.

Magnetoelectric (ME) thin film composites on silicon cantilevers are fabricated using Pb(Zr0.52Ti0.45)O3 (PZT) films with interdigital transducer electrodes on the top side and FeCoSiB amorphous magnetostrictive thin films on the backside. These composites without any direct interface between the piezoelectric and magnetostrictive phase are superior to conventional plate capacitor-type thin film ME composites. A limit of detection of 2.6 pT/Hz1/2 at the mechanical resonance is determined which corresponds to an improvement of a factor of approximately 2.8 compared to the best plate type sensor using AlN as the piezoelectric phase and even a factor of approximately 4 for a PZT plate capacitor.

Nach der Beschreibung der dielektrischen Eigenschaften von gesundem Korpergewebe und von Tumorgewebe wird die Moglichkeit der Lokalerwarmung im Korper mit fokussierenden Antennengruppen diskutiert, ein automatisches temperaturgeregeltes Hyperthermiesystem zur Krebstherapie vorgestellt und sein Einsatz im Tierversuch beschrieben. Zur drahtlosen lokalen Temperaturmessung im Korper wurde ein Verfahren auf der Basis implantierter FMR-Sensoren (FMR = ferrimagnetische Resonanz) entwickelt. Schlieslich werden die grundlegenden Eigenschaften der Mikrowellen-Thermographie erlautert und die Ergebnisse klinischer Anwendungsstudien berichtet.