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Measuring the static (DC) electric field has always been challenging, because the measurement system can interfere with the field it measures. Therefore, optical readouts such as a Michelson interferometer can be used in combination with a transducer that converts the quantity electric field strength into an out-of-plane vibration with an amplitude that is proportional to the field strength. For such a system, a stable working point needs to be maintained. Due to different effects including thermal fluctuations in the optical fibers the working point is constantly drifting. Therefore, a stabilization of the working point at a fixed value of the optical phase is absolutely necessary. This paper describes a feedback mechanism that measures and controls the working point at a fixed value. We compare three setups. The first one without stabilization substantiates the need for the stabilization. The second one using a piezoelectric buzzer as a proxy to test the stabilization. In the third one, we used the actual electric field transducer. This shows a new way of a backaction-free readout of electric field transducers.

Many phenomena of atmospheric electricity are still not well understood, as most of the processes involved can only be observed in real nature. For this purpose, reliable and stable measurements of the electric field strength are mandatory. While for high-frequency fields, there exists a large variety of equipment, in the quasi-static and especially static regime, such systems are scarce. The „standard“ device for the application is the electrostatic field mill which uses a rotating, electrically grounded shutter electrode to alternatingly expose and shield measurement electrodes to/from the electric field. While they achieve good-enough resolution, there are many inherent problems associated with the measurement principle, such as mechanical wear, massive field distortions, size and weight. As a consequence, they are typically installed at a fixed points and cannot be easily moved or mounted. Miniaturised field mills have minimised some of these issues, the shutter priniciple leads to very fragile structures.We present an alternative way of measuring low-frequency and static electric fields (E-field), which does not suffer from the hindering drawbacks of field mills. The underlying mechanism converts the E-field to a mechanical oscillation of a microelectromechanical system (MEMS). This is achieved by applying an AC voltage to a compliant mechanical structure. As a result of the AC voltage, alternating charges accumulate at the surface of the MEMS. When exposed to the E-field, this leads to a force deflecting the structure at a known frequency. For this kind of active mechanism, the power consumption is minimal, since the current flow is practically zero. Therefore, the system can be used in a floating way without grounded connections and therefore minimum field distortions. The mechanical motion can then be read out optically, also to avoid field distortions and backaction. If the system is driven at the mechanical resonance, the quality factor can be exploited to boost the sensitivity. In this case the bandwidth of the system ranges from 0 Hz to twice the resonance frequency.Several MEMS sensors with different resonance frequencies (ranging from ~100 Hz to ~1 kHz) have been fabricated and tested in the laboratory. The sensors have been mounted between two parallel field plates supplied with a DC voltage, which provides the static electric field. A tiny hole in one of the field plates allowed for optical readout of the sensor movement with a laser-Doppler vibrometer (Polytec MSA-400). The sensors have been tested for different field strengths (10 V/m – 30 kV/m) and different AC voltages (0.02 V – 20 V) confirming linearity in both quantities. In terms of field strength, a resolution as good as ~25 V/m was achieved for a sensor with a resonance frequency of 167 Hz. These promising results substantiate that this sensor is a potentially low-weight, low-cost alternative for classical field mills. The next steps will be to investigate long-term stability and environmental effects on the sensor (temperature, humidity) and, finally, installation and test in the open area during fair weather and thunderstorm activity.

Small-scale and distortion-free measurement of electric fields is crucial for applications such as surveying atmospheric electrostatic fields, lightning research and safeguarding areas close to high-voltage power lines. A variety of measurement systems exist, the most common of which are field mills, which work by picking up the differential voltage of the measurement electrodes while periodically shielding them with a grounded electrode. However, all current approaches are bulky, suffer from a strong temperature dependency or severely distort the electric field, and thus require a well-defined surrounding and complex calibration procedures. Here we show that microelectromechanical system (MEMS) devices can be used to measure electric field strength without significant field distortion. The purely passive MEMS devices exploit the effect of electrostatic induction, which is used to generate internal forces that are converted into an optically tracked mechanical displacement of a spring-suspended seismic mass. The devices exhibit resolutions on the order of 100 V m−1 Hz−1/2 with a measurement range of up to tens of kilovolts per metre in the quasi-static regime ≲300 Hz). We also show that it should be possible to achieve resolutions of around 1 V m−1 Hz−1/2 by fine-tuning the sensor embodiment. These MEMS devices are compact and could be mass produced easily for wide application. The detection of force-induced displacements within compact MEMS (microelectromechanical system) devices can be used to measure electric field strength without significant field distortion.

We propose a flexible proximity sensor to detect sub-centimeter distance with an ultra-high displacement resolution. The proximity sensor is realized by integrating a semi-transparent organic photo detector with a transparent top electrode and a finger-type bottom electrode. By placing the semi-transparent finger-type photodetector on a light source, such as a light-emitting diode (LED), the photodetector can detect the light reflected from an object on top of the sensor. With the highly compact structure, the detecting range is from 1 mm to 30 mm. From 1 mm to 10 mm, the sensor is particularly sensitive and delivers a resolution of 1 mm. The air-stable photodetector can also be fabricated on a flexible substrate without encapsulation, enabling the integration with arbitrary light sources. After 1000 times bending, the flexible photodetector shows no obvious degradation.

We report on an analytical model for the air damping of laterally oscillating MEMS and MOEMS following up on our recent paper [1] . It can be used to more efficiently design micromechanical devices with tailor-made Q -factors for specific applications. The surface force responsible for the air damping was divided into contributions which were investigated separately. These include squeeze-film damping and the viscous forces responsible for shear wave emission and Couette type flow. Since the squeezing part is mostly underestimated in the current models, we applied more appropriate boundary conditions during the solution of Reynold's lubrication equation. The viscous contributions were investigated with respect to how holes – due to fabrication process or readout – in the moving plate affect the damping. We tested this model against FVM computations (OpenFOAM) and measurements of MOEMS test devices. It was in good agreement with both.

Reliable measurement of the low-frequency and static electric field strength are essential in a number of areas such as atmospheric electricity, high-voltage infrastructure and safety. Such measurements are hard to achieve, since inherent distortions or limited bandwidth render them impossible. This paper shows a distortion-free electric field strength sensor based on a completely passive micromechanical structure with significantly improved suspension for vibration suppression. With this suspension, the responsivity to electric fields was increased while the responsivity to vibrations was decreased by separating the according modes. This trend can be continued to achieve even more robust and more sensitive sensors. The exemplary structure presented in this contribution features a resolution limit of 370 V/m/Hz1/2 and a quotient of 0.39 between the vibrational and the measurement mode frequency.

Many upcoming experiments in antimatter research require low-energy antiproton beams. With a kinetic energy in the order of 100 keV, the standard magnetic components to control and focus the beams become less effective. Therefore, electrostatic components are being developed and installed in transfer lines and storage rings. However, there is no equipment available to precisely map and check the electric field generated by these elements. Instead, one has to trust in simulations and, therefore, depend on tight fabrication tolerances. Here we present, for the first time, a noninvasive way to experimentally probe the electrostatic field in a 3D volume with a microsensor. Using the example of an electrostatic quadrupole focusing component, we find excellent agreement between a simulated and real field. Furthermore, it is shown that the spatial resolution of the probe is limited by the electric field curvature which is almost zero for the quadrupole. With a sensor resolution of $61\text{ }\text{ }\mathrm{V}/\mathrm{m}/\sqrt{\mathrm{Hz}}$, the field deviation due to a noncompliance with the tolerances can be resolved. We anticipate that this compact and practical field strength probe will be relevant also for other scientific and technological disciplines such as atmospheric electricity or safeguarding near power infrastructure.

Physikalische Medizin und allgemeine Rehabilitation ist Teil der an Universitaten gelehrten State-of-the-art- bzw. konventionellen Medizin. Therapien (aktive und passive Masnahmen), dargestellt am Beispiel der onkologischen Rehabilitation, sind individuell aus dem Gesamtkonzept zu „rezeptieren“. Das Grundkonzept der Osteopathie beruht auf den komplexen Zusammenhangen zwischen der Dysfunktion verschiedener Gewebe des Korpers und deren Auswirkung auf den Bewegungsapparat. Die manuelle Diagnostik ist eine unverzichtbare Methode bei der Diagnostik, Therapie und Rehabilitation der Storungen des Bewegungsapparats, die manuelle Therapie eine okonomische und effiziente Form der Muskel- und Gelenkbehandlung; wichtigste Indikation bei den Gelenkfunktionen ist die Beweglichkeitseinschrankung. Das Wissen uber die biologisch-physiologischen Wirkungen von regelmasiger korperlicher Aktivitat hat nicht nur dazu gefuhrt, dass Bewegung und Sport als praventive Mittel, sondern auch in Form von Trainingstherapien im gesamten Therapiekonzept der Rehabilitation als unersetzliches Instrumentarium eingesetzt werden.

We present a simple equivalent circuit model for the transfer function of an optomechanical MEMS transducer capable of distortion-free electric field strength measurements. This model allows not only to qualitatively understand the characteristics of the transducer but also takes into account parasitic effects and material properties. Such parasitic effects have been observed while evaluating the first results of electric field measurements performed with the sensor. The model helped to identify and diminish these parasitic effects.

We present a displacement-sensitive sensor comprising a microelectromechanical (MEMS) chip and organic optoelectronic components capable of measuring the heart and respiration rate on humans. The MEMS sensor relies on the inertial deflection of a small silicon oscillator. The readout of the deflection is optical and works via modulation of the light flux passing through the MEMS. Organic optoelectronics are used as light source and detector, since these offer a homogeneous light distribution and a more compact package in a future integration. Two types of MEMS, differing in their resonance frequency, were designed and characterised in combination with both organic and inorganic optoelectronics prior to measuring heart and respiration rate. Subsequently, by measurements on the neck, pulse and respiration rate were successfully measured.

This work presents the investigation on a MEMS based optomechanical transducer for displacements or vibration regarding its cross-sensitivities to multidirectional input excitations. The principle of the optomechanical transducer is based on the modulation of the light flux passing through one static and one movable micromechanical aperture. This kind of transducer is of increasing interest for MEMS sensors since it has inherent benefits and can compete with state-ofthe- art readout concepts regarding its resolution. We have experimentally proven that the sensitivities of the device is 3.3 × 107 V/m in x-direction, 8.23 × 106 V/m in y-direction, while it is negligible in z-direction.

We report on a new optical sensing principle for measuring the electric field strength based on MEMS technology. This method allows for distortion-free and point-like measurements with high stability regarding temperature. The main focus of this paper rests on an enhanced measurement set-up and the thereby obtained measurement results. These results reveal an improved resolution limit and point to the limitations of the current characterization approach. A resolution limit of 222 V/m was achieved while a further improvement of roughly one order of magnitude is feasible.

This paper reports on a MEMS gradiometer consisting of two independent laterally oscillating masses on a single chip with integrated optical readout. The symmetrical design of the two masses offers high accuracy and low cost by using conventional MEMS batch fabrication technology. The sensing principle is based on laterally displacement of the masses actuated by Lorentz forces which modulates a light flux passing through a stationary mask and the moving mask integrated in the masses. Phase and intensity detected by photodiodes reveals information about the uniformity of an external applied magnetic field, hence, enables the measurement of gradient-, homogeneous-and offset zradient maanetic fields. A quadrupol magnetic field created from four identical neodymium bar magnets had been characterised to demonstrate the sensor's working principle.

We report on an accurate analytical model for the squeeze-film damping in laterally oscillating MEMS and MOEMS, which has not been available up to now. The models currently used are not able to correctly predict the damping and underestimate the squeeze- film contribution by a quite large factor of ∼4. This discrepancy was overcome by choosing more appropriate boundary conditions for solving Reynold's lubrication equation which governs the behavior of thin fluid films. The model was tested against numerical FVM computations with the open source software package OpenFOAM as well as measurements of MOEMS test devices with varying width of the squeeze-film gap and is in good agreement with both. This can now be used to increase the efficiency in thedesign step not only of laterally moving microstructures.

This contribution describes a novel magnetic field transducer based on a MOEMS (micro-opto-electo-mechanical-system) readout. The silicon structure is deflected in a static magnetic field due to the Lorentz force This deflection is measured with the mechano-optical transducer [1] . The transduction method is based on the modulation of a perpendicularly introduced light flux. The modulation is achieved by one movable optical grating on a suspended structure and a second grating that is fixed to the foundation of the system. The proof-of-concept device was characterized at ambient pressure exhibiting a sensitivity of 200 mV/T. The noise equivalent magnetic resolution limit is 1.5 μT/√Hz which results mainly from the opto-electrical evaluation circuit. By introducing advanced opto-electronics and using improved MEMS devices it is feasible to reduce this value down to 1 nT/√Hz which is equivalent to the fundamental mechanical Brownian noise limit.

Depending on the geometry, microstructures oscillating laterally in air are mainly damped by Couette-type flow or shear waves emitted into the surrounding. Models for these types of damping imply a flat, closed, laterally moving plate. Due to fabrication or readout, such MEMS/MOEMS often feature holes in the plate. Therefore, the requirement of a perfect surface is certainly not fulfilled. We present measurements that show how these holes influence the damping of laterally oscillating MOEMS. In two series of test structures, both the size and the number of the holes are varied investigating the respective differences in the damping.

This contribution describes an opto-mechanical transducer with a non-linear transfer behaviour and its impact on the quantification of static and dynamic displacements in a vibrating measurement mode. The device's output signal is proportional to a lightflux that is modulated by two overlapping gratings. One of the gratings is deposited on a fixed glass cover while the other one is etched into a moveable seismic mass of a Si MEMS chip. The non-linear transfer characteristic is achieved by paring a triangular grating with a rectangular one. The mass is actuated by a mechanical shaker unit and the resulting 1 st and 2 nd harmonic of the output signal are recorded with Lock-In amplifiers. These harmonics contain information about the static displacement and the vibration amplitude of the mass. The presented method allows for a precise measerement of the static displacement with an error of ±0.017% compared to DC measurements exhibiting an error of ±0.066%.

In the past years, researches demonstrated the great potential of novel MOEMS vibration sensors regarding their displacement resolution and sensitivity. The authors show that it is possible to further enhance the dynamic range of these sensors. This is achieved by utilizing feedback mechanisms such as electrostatic actuation without any crosstalk to the optical readout. Furthermore, this allows for canceling out unwanted ringing. The discussed proof of concept prototypes incorporate two electrostatic comb-drive actuators. They enable the seismic mass to reset along the main oscillation axes over a path of several microns and up to the resonance frequency of 400 Hz. It was proven that there is no unwanted crosstalk between the actuation and the position readout. The MOEMS readout features a sensitivity of approximately 200 mV/μm with a noise equivalent displacement of 35 pm/√Hz.

We present a first proof of principle of applying organic semiconductors as key components in micro-mechanical vibration sensors. The mechanical part of the MOEMS sensor readout is etched into the device layer of an SOI chip and consists of a laterally deflecting inertial mass that features a two-dimensional grid of rectangular holes. An identical grid is evaporated onto a glass chip bonded onto the silicon chip in such way that any deflection of the seismic mass will modulate the light flux passing through the device. The light flux is provided in this case by an OLED and detected by an OPD. It is shown with a proof of concept device that for such sensors organic optoelectronics can replace inorganic ones, which is the starting point for developing a variety of MOEMS sensors based on printed optoelectronic devices.

The damping of an oscillator is, next to the effective mass and the stiffness, one of the key parameters that determine its frequency response as well as its noise. Since there are numerous different applications for oscillating microstructures, there are also numerous requirements for the shape of the respective resonance peak. While fabricating the right mass and stiffness to obtain a desired resonance frequency is, in general, a basic task, designing a micro-oscillator featuring an intended damping is not trivial. We present a way of utilizing the surrounding air to adjust the passive damping of a laterally oscillating micromechanical system. This is shown to hold in a relatively wide range by comparing analytical models and finite volume method simulations with measurements of a number of micro-electro-mechanical test structures with optical readout.

High performance applications such as the detection of seismic activity or structural health monitoring require sensors with low resonance frequencies. For micro-electro-mechanical-system (MEMS) accelero-meters and vibration sensors it is crucial to lower the resonance frequency in order to increase its sensitivity or bandwidth. In contrast to commercial devices which exhibit resonance frequencies of more than 500 Hz, we present extremely sensitive, optically read-out devices with resonances down to 45 Hz. This low resonance frequency was mainly achieved by fabricating the complete seismic mass from one single crystal silicon block. Compared to previously reported work the resonance frequency could be lowered from over 940 Hz down to 45 Hz while the resolution was massively increased from 7.6 μg/sqrt(Hz) to 1.17 μg/sqrt(Hz) (@4 Hz).

The majority of MEMS vibration sensors requires relatively high resonance frequencies of several kilohertz to avoid mechanical contact of moving parts such as electrode plates. In contrast to that, our hybrid micro-opto-electro- mechanical system (MOEMS) enables sensor applications at low frequencies. This work describes a distinct MOEMS featuring extremely low resonance frequencies of below 200 Hz. It is operated ambient air without closed loop feed- back, extensive electronics and cooling. Due to the soft suspension of the micro-mechanical sub-system the funda- mental limit, the Brownian noise floor, is reached. The resulting noise equivalent displacement for frequencies above the resonance is 1.9 pm/ √Hz, which is equivalent to 0.29 μg/ √Hz below the resonance. We describe the design space for sensors with further enhanced sensitivity and resonance frequencies far below 100 Hz.

We report on design rules for the passive air damping of laterally oscillating MOEMS [1]. They allow for a tailor made charac- teristic of the transfer function of a microsensor for a given field of application. Measurements in air at atmospheric pressure as well as in vacuum at a pressure of 10−4 to 10−1 mbar were accompanied by finite volume method computational fluid mechanics simulations using the open source software OpenFOAM®. These were combined with analytic models to identify and quantify the important parameters of the air damping of a micromachined vibration sensor with optical read-out. Our results prove that the desired damping can be achieved with high precision. This important fact can now be used to design a wide range of MOEMS with a well-defined quality factor Q, e.g. for resonant sensing (high Q, low frequency range) or vibration sensing (low Q, high frequency range).

Methods for measuring low-frequency and static electric field strength are of great use in many areas ranging from meteorology to high-voltage infrastructure or safety. Nevertheless, all state-of-the-art methods have grave intrinsic drawbacks such as severe inherent field distortions or overpronounced temperature behavior. Recently, a method has been developed which allows for distortion-free and temperature-stable measurement. In this work, a micromechanical sensor based on this method is presented which features suspensions that suppress cross-sensitivities to vibrations. Two such types of suspensions were evaluated and compared in terms of their mechanical modes and susceptibility to electric fields and vibrations. It is shown that these suspensions indeed suppress the cross-sensitivities. The sensors exhibit field strength resolutions down to 737 V / m / Hz with a theoretical limit as low as 59.3 V / m / Hz.

We present a novel design of a resonant magnetic field sensor with capacitive read-out permitting wafer level production. The device consists of a single-crystal silicon cantilever manufactured from the device layer of an SOI wafer. Cantilevers represent a very simple structure with respect to manufacturing and function. On the top of the structure, a gold lead carries AC currents that generate alternating Lorentz forces in an external magnetic field. The free end oscillation of the actuated cantilever depends on the eigenfrequencies of the structure. Particularly, the specific design of a U-shaped structure provides a larger force-to-stiffness-ratio than standard cantilevers. The electrodes for detecting cantilever deflections are separately fabricated on a Pyrex glass-wafer. They form the counterpart to the lead on the freely vibrating planar structure. Both wafers are mounted on top of each other. A custom SU-8 bonding process on wafer level creates a gap which defines the equilibrium distance between sensing electrodes and the vibrating structure. Additionally to the capacitive read-out, the cantilever oscillation was simultaneously measured with laser Doppler vibrometry through proper windows in the SOI handle wafer. Advantages and disadvantages of the asynchronous capacitive measurement configuration are discussed quantitatively and presented by a comprehensive experimental characterization of the device under test.

The motion of the seismic mass that is induced by thermal noise limits the resolution of typical micromachined vibration sensors. Its value can be adjusted by the size of the proof mass which is also a quantity for the inertial actuation input. Owing to a novel transduction concept, micro-opto-electro-mechanical vibration sensors featuring approximately twice as much mass per chip area are feasible, while decreasing the technological efforts during fabrication. The essence of the devised sensor principle is the modulation of the intensity of a light flux propagating perpendicularly through a pair of micromachined apertures. One aperture is fixed to the encapsulation and the second one is deffected by inertial forces. Earlier attempts have employed opto-electrical transmitters and receivers operating at a wavelength where silicon is intransparent. Thus, openings in the silicon mass were necessary. The presented evaluation technique utilizes the transparency of silicon in the infrared region at wavelengths well above 1.1 μm. In contrast to the previously used optoelectronic components, an InGaAs LED and an InGaAs pin-diode were integrated. This all enables of thin-film metal apertures deposited on top of the silicon seismic mass instead of etched silicon windows. Beside the increase in mass, this approach offers larger scope for design and implies a reduced damping coefficient yielding an improved quality factor. A structure for the proof of concept was fabricated and characterized together with a sensor based on the preceding principle. The results are in good agreement with the predicted behavior and the parameters tested by FEM analysis considering the fabrication related underetching as well.

A miniaturised, piezoelectrically driven shaker system is presented which is suitable for MEMS characterisation in vacuum. It offers a broad frequency and amplitude range. The fully vacuum compatible shaker is constructed out of one single peace of aluminium with a piezo-stack-actuator working in-plane against four beam springs. It can easily be fabricated at low costs using a hand operated milling machine. The systems characteristics are easily tuned to different applications as the first resonance frequency is given by the stiffness of the beam springs and the mass of the moving shaker table. The utilised piezoelectric stack determines the maximum reachable amplitude for a given spring stiffness. Finite Element simulations have been carried out to design a at transfer characteristic of the shaker up to 10 kHz and amplitudes in the range from sub nanometres up to 1μm. The simulations were evaluated by laser vibrometer measurements of the shaker which also show a good linearity between electrical excitation signal and output deection amplitude. To account for other resonance frequencies introduced by a preexisting MEMS mounting device, the resulting vibration amplitude on the MEMS structure can be normalised by adjusting the electrical excitation amplitude with the help of a Polytec laser vibrometer.

Recently, dynamical mean field theory calculations have shown that kinks emerge in the real part of the self energy of strongly correlated metals close to the Fermi level. This gives rise to a similar behavior in the quasi-particle dispersion relation as well as in the electronic specific heat. Since f-electron systems are even more strongly correlated than the -hitherto studied- d-electron systems we apply the dynamical mean field approach with the numerical renormalization group method as impurity solver to study whether there are kinks in the periodic Anderson model., 6 pages, 7 figures

A new slab system was developed which allows large spans and easily accessible installations with large cross sections. The main concept aims at arranging the installations inside the load carrying structure. Thus a girder type structure with a plate on the bottom was used. The overall height of the slab system is lower while the static height becomes higher. Other advantages are the lower self weight and the large space available for installations. By covering the system with removable plates the installations are easily accessible during the entire life time of the structure. The girders are made of prefabricated elements, which contain large openings to allow for a flexible arrangement of the installations and a low self weight. Experiments on slab strips over two spans were performed.