Search

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.

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.

This paper reports a MEMS gradiometer consisting of two independent, laterally oscillating masses on a single chip with integrated optical readout featuring a responsitivity of 35V/T at resonant operation. 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 lateral 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 reveal information about the uniformity of an external applied magnetic field, hence, enables the measurement of gradient-, homogeneous- and offset gradient magnetic fields.

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.

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.

This paper reports on a novel, miniaturized magnetomechanical transducer/sensor made of borosilicate glass with wide dynamic range. The prototype is manufactured with laser micromachining and ablation techniques. Compared to state of the art, borosilicate glass substrate offers the highest thermal shock resistance and is best suited for MEMS magnetometers, for aerospace and space applications or magnetic monitoring systems for diagnostics and plasma stability control of nuclear fusion experiments, where thermal shock resistance is a critical requirement.

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 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%.

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.

A passive thermal micro-actuator with large area specific work and large displacement, fabricated of electroplated nickel on a silicon substrate is presented. The actuation relies on the thermal expansion of beams in a V-shaped geometry. Two V-shaped beam stacks are aligned opposite to each other and are coupled to a lever transmission. The actuator exhibits low energy losses due to the deformation of the structure and can efficiently convert the thermally induced elastic energy into mechanical work. An analytical model considers these thermally induced mechanical energies and the energy losses caused by the deformation of the material. The calculated deflections are compared with the measured ones and results of finite-element method simulations. The presented actuator operates completely passive, relies only on temperature changes of the surrounding environment, and exhibits a measured temperature-dependent linear deflection coefficient of $1.48~\mu \text{m}$ /K with a simulated blocking force of $57~\mu \text{N}$ /K. The structure occupies an area of $2135 \,\, \times \,\, 1831~\mu \text{m}^{2}$ and the area specific work is calculated to be $21.7~\mu \text{J}/\text{K}^{2}/\text{m}^{2}\vphantom {\sum ^{R^{R}}}$ , beating state of the art thermal actuators. As proof-of-concept, a passive micro-electro-mechanical systems temperature threshold sensor is fabricated, featuring the actuator and a bistable beam that switches between two stable positions when a specific threshold temperature is exceeded. [2014-0317]

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.

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).

A magnetostrictive actuator approach based on micromechanical structures is presented. Planar geometries are designed, comprising V-shaped beams and lever transmissions. Several V-shaped beams are stacked in parallel and two of such stacks are placed facing each other. Both are connected to a lever beam. When a magnetic field is applied, the magnetostriction of the active material leads to an elongation/shortening of the V-shaped beams. The lever transmission converts the magnetically induced elastic energy into a reliable in-plane displacement. The overall dimensions of the devices are in the range of 4 mm $\times 2$ mm $\times 0.4$ mm and hence, way smaller compared with state-of-the-art magnetostrictive actuators. For a magnetic flux density of 14 mT, a stroke displacement of 10.2 $\mu $ m was achieved. With a spring stiffness of 5.56 N/m obtained from simulations, a theoretical area specific work of 72 $\mu $ J/ $\mathrm{m}^{2}$ was accomplished.

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).

Accurate knowledge of the spatial magnetic field distribution is necessary when measuring field gradients. Therefore, a MEMS magnetic field gradiometer is reported, consisting of two identical, but independent laterally oscillating masses on a single chip. The sensor is actuated by Lorentz force and read out by modulation of the light flux passing through stationary and moving arrays of the chip. This optical readout decouples the transducer from the electronic components. Both phase and intensity are recorded which reveals information about the uniformity of the magnetic field. The magnetic flux density is measured simultaneously at two points in space and the field gradient is evaluated locally. The sensor was characterised at ambient pressure by performing frequency and magnitude response measurements with coil and various different permanent magnet arrangements, resulting in a responsivity of 35.67 V/T and detection limit of 3.07 &micro, T/ Hz (@ 83 Hz ENBW). The sensor is compact, offers a large dynamic measurement range and can be of low-cost by using conventional MEMS batch fabrication technology.

This paper presents a magnetic field sensor with capacitive read-out, whose active element is a micromachined mechanical resonator. The MEMS magnetic field sensor exploits the Lorentz force to detect external magnetic flux density through the displacement of the resonant structure, which can be measured with optical and capacitive sensing techniques. The micromachined U-shaped cantilever features a length of 2 mm, a base width of 90 μm and a thickness of 20 μm, and is manufactured in SOI technology. The designed sensor has a measured resonant frequency of 4.359 kHz for the fundamental mode and a calculated mass of the flexible structure of 24.5 ng. A quality factor in the order of 104 at an ambient pressure of 0.3 Pa has been measured where a magnetic field resolution of 15 nT can be achieved. Although these arrangements are well suited to capacitively sense the vibrations caused by the Lorentz force on the current lead on the silicon part, care has to be taken to avoid undesired mutual interferences. A serious interference was observed in case of a DC bias voltage at the readout capacitance and a significant voltage drop caused by the current needed for the generation of the Lorentz force. This work investigates in detail this phenomenon as well as the complete physical transduction chain and improves the understanding of such microelectromechanical systems significantly. An analytical model of the electrostatic system is established including all relevant components and their interactions as well as the motion of the MEMS part. The importance of electrostatic back-action for a feasible detection limit for magnetic fields was recognized for the first time.

The thermal actuator presented in this paper consists of two symmetrically V-shaped beam stacks, where each stack consists of six beams in parallel. The stacks are coupled facing each other and slightly shifted along the mirror axis. Both stacks are connected to a lever beam and fixed at four anchor regions to the substrate. Due to the difference in the coefficient of thermal expansion of the material of the beams and the one of the substrate, the tip of the lever moves perpendicular to the mirror axis. The device is fabricated from galvanic deposited nickel on a silicon substrate. Finite element simulations were carried out to optimize the design with respect to the sensitivity and the maximum mechanical stress. The stress needs to be lower than the yield strength of the material. Otherwise, plastic deformations of the beams would lead to irreversible deflections of the beam tip. This limits the overall sensitivity of the design. First results of the device with 400 μm long bent beams show a linear behavior and a sensitivity of 0.5 μm/K and forces of 66 μN/K for a temperature range of ź30 °C up to +40 °C.

This paper presents a design guideline for matching a fully implantable middle ear microphone with the physiology of human hearing. The guideline defines the first natural frequency of a seismic sensor placed at the tip of the manubrium mallei with respect to the frequency-dependence hearing of the human ear as well as the deflection of the ossicular chain. A transducer designed in compliance with the guideline presented reduces the range of the output signal while preserving all information obtained by the ossicular chain. On top of a output signal compression, static deflections, which can mask the tiny motions of the ossicles, are reduced. For guideline verification, a microelectromechanical system (MEMS) based on silicon on insulator technology was produced and tested. This prototype is capable of resolving 0.4 pm/Hz with a custom made read-out circuit. For a bandwidth of 0.1 kHz, this deflection is comparable with the lower threshold of speech (≈ 40 phon).

For vibration and displacement sensors, robustness is one of the key requirements. Optical measurement concepts are among the most promising possibilities to achieve it. The presented microoptoelectromechanical system sensor modulates a light flux by means of two congruently placed aperture gratings: one etched into a seismic mass and the other fixed to the sensor package. Commercially available LED and photodetector components at the top and bottom of the sandwich structure generate and detect this modulated light flux and allow for a cost-effective implementation. The prototype used for experimental verification is actuated by inertial forces and exhibits a high sensitivity of 0.85 mV/nm for displacements of the seismic mass and a corresponding noise level of about 14 pm/√Hz. This sensitivity and noise level can be further improved, paving the way for small, lightweight, robust, and high-precision displacement sensors for a large variety of applications.

This work reports a novel construction of a micromachined MEMS magnetometer detecting static magnetic fields of CERN's reference dipole with a custom made capacitive read-out. The magnetic flux density is characterized via vibration modes of the MEMS structure which are sensed capacitively. The device consists of a single-crystal silicon clamped-free plate (cantilever) carrying a thin conductor. The cantilever and thin film metal electrodes are separated by a small gap, building a vibrating plate capacitor. Movements of the cantilever are read out conveniently by electronic circuits. A static magnetic field generates a force density acting on the conductor that alternates according to the frequency of the current. By knowing the electrical current, the deflection amplitude of the cantilever is a measure of the component of the magnetic flux density that points perpendicular to the current. The highest vibration amplitudes are expected, of course, in the vicinity of resonance frequencies of the micromachined structure. At ambient pressure the prototype sensor has a measured resonance frequency of 3.8 kHz for the fundamental mode and 20 kHz for the first antisymmetric mode. In experiments, the magnetic flux of the dipole has been characterized between 0.1 and 1 T, with a relative uncertainty of 3·10−4.

This paper presents encouraging results of a novel optoelectronic conversion method for relative displacement. An optical modulator responding to acceleration and gravitation is used for characterization. The Si microelectromechanical system (MEMS) component comprise a spring suspended, in-plane oscillating mass carrying an array of optical apertures. Light flux modulation is achieved with a second array of complementary apertures that is fixed to the Si frame. The investigated device comprises a sandwich structure of an SMD LED, the MEMS aperture gratings, and a phototransistor. Relative displacements of the gratings generate a modulation of the LED light flux that is detected by the phototransistor. Depending on the aperture design, the relative displacement may extend over several tens of microns maintaining a sub-nm resolution. Thus, no closed-loop position control system is required, resulting in minimum complexity and energy consumption of the MEMS component. This setup simplifies the manufacturing process as much as possible, which is one of the significant advantages of the sensor principle. Furthermore, the presented prototype exhibits a promising high sensitivity of 60 nA/nm for displacement, featuring a noise level of about 8 pm/√Hz.

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.

Miniaturized force sensors are indispensable components in various applications such as atomic force microscopes. In most cases the sensor is sensitive only to a single component at the force vector. For a complete characterisation of the actual load state all three components are required and this in combination with the three torque components (six-axis force/torque sensor). We report on a sensor to measure two components of the force vector and three components of the torques simultaneously using a resonant vibrating cross-shaped bar. The sensor is manufactured on an SOI wafer with standard Si-technology. The sensing structures are excited by Lorentz forces and detuned by the mechanical stress due to the applied force and torque. Currently, the shifts of the resonant frequencies are measured with a scanning laser vibrometer. To be able to compensate the influence of temperature additional Pt-termistors on the surface of the structure measure the actual temperature. Furthermore, the sensing structure is suspended to the sensor frame with compliant structures to reduce the temperature interferences. To investigate the effect of these substructures three different types are compared. With the multiaxial MEMS force sensor we achieved a sensitivity of almost 10 pN Hz−1.

This work describes the temperature dependence of two sensors for magnetic field gradients sensors and demonstrates a structure to compensate the drift of the resonance frequency over a wide temperature range. The temperature effect of the sensing element is based on internal stresses induced by the thermal expansion of the material wherefore FEM is used to determine the change of the eigenvalues of the sensing structure. The experimental setup utilizes a Helmholtz coil system to generate the magnetic field and to excite the MEMS-structure with Lorentz forces. The MEMS structure is placed on a plate heated with resistors and cooled by a Peltier element to control the plate temperature. In the second part, we describe how one can exploit the temperature sensitivity for temperature measurements and show the opportunity to include the temperature effect to increase the sensitivity of single-crystal silicon made flux density gradient sensors.

This paper describes major contributions to a MEMS magnetic field gradient sensor. An H-shaped structure supported by four arms with two circuit paths on the surface is designed for measuring two components of the magnetic flux density and one component of the gradient. The structure is produced from silicon wafers by a dry etching process. The gold leads on the surface carry the alternating current which interacts with the magnetic field component perpendicular to the direction of the current. If the excitation frequency is near to a mechanical resonance, vibrations with an amplitude within the range of 1–103 nm are expected. Both theoretical (simulations and analytic calculations) and experimental analysis have been carried out to optimize the structures for different strength of the magnetic gradient. In the same way the impact of the coupling structure on the resonance frequency and of different operating modes to simultaneously measure two components of the flux density were tested. For measuring the local gradient of the flux density the structure was operated at the first symmetrical and the first anti-symmetrical mode. Depending on the design, flux densities of approximately 2.5 µT and gradients starting from 1 µT mm−1 can be measured.

We report a novel exact closed-form solution of the Euler-Bernoulli beam equation expressible in terms of Meijer G-functions. This solution allows for analytically studying the natural frequencies and mode shapes of a very general class of beams characterized by both a polynomially varying flexural beam bending stiffness EI(x) and beam cross section A(x), but a constant EI(x)=A(x)-ratio. Its application is exemplarily demonstrated on cantilevers characterized by a uniform thickness and a spatially narrowing width of either linear form (i. e., trapezoid cantilevers) or describable by a power function of higher order. The analytically deduced results are validated by computer numerical simulations and compared to test measurements carried out on micromachined thin-film cantilevers.

Vibration and displacement sensors need to be compact for many applications in automation or consumer electronics, and microelectromechanical structures are a convenient way to implement such sensors. For these MEMS devices, optical readout methods have proven to be superior to capacitive or piezoresistive strategies in terms of sensitivity as well as noise and interference immunity, however the integration of light sources and detectors is not easily possible. This paper presents an approach to use organic optoelectronic devices for the readout. OLED and OPD (organic photo detector) are structured on the glass substrate and cover encapsulating the MEMS devices, allowing for a tightly integrated sensor based on vertical light flux modulation by a horizontally moving proof mass. The paper describes the principle sensor structure as well as the fabrication of suitable organic devices. First test results show that the approach is feasible.

A completely passively operating micro-mechanical switch is presented. The switch composes of a thermal actuator and a curved bistable beam. The actuator comprises V-shaped beams and a lever transmission. It is designed to operate passive only relying on the thermal expansion of the active material (electroplated Ni) and the temperature changes of the surrounding environment, where the temperature ranges from 40°C up to +50°C. The actuator exhibits a temperature dependent deflection sensitivity of 0.9 μm/K and sufficient force to push the bistable beam into is secondary position. Both subsystems are connected via a latching mechanism. A temperature difference of at least 35 K is required for activation of the switch. A self tailored measurement setup is used to quantify the temperature dependent deflections by means of an optical principle. The measured results are in good agreement with results of numerical simulations and analytical models.

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 thermal actuator based on two symmetrical V-shaped beam stacks (also called chevron-type) is presented. Each beam stack consists of 6 beams in parallel. The stacks are coupled facing each other and are slightly shifted along the mirror axis. Both stacks are connected to a lever beam. Due to the thermal expansion of the material, the tip of the lever moves up and downwards perpendicular to the mirror axis. The device is built up of galvanic deposited nickel. Finite element simulations were carried out for design considerations prior to the manufacturing of the device. The simulations were used to optimize the design regarding to the sensitivity and the maximum mechanical stress to be expected. The stress level needs to be lower than the yield strength of the material, to prevent plastic deformation and, therefore, irreversible tip defections. This also limits the overall sensitivity of the design. First results of the device with 400 µm long bent beams show a linear behavior and a sensitivity of 0.5 μm/K and expectable forces of 66 μN/K in a temperature range of -30°C up to +40°C.

A Lorentz-force actuated cantilever used as a magnetometer detecting alternating magnetic fields (AMF) is described. The device consists of a U-shaped single-crystal silicon cantilever manufactured in SOI technology. This micromachined cantilever features a length of 2mm, a base width of 90μm, and a thickness of 20μm, whereat the two 2mm cantilevers are hold together by a 1.5mm long bar at the free moving ends. The cantilever is placed in a vacuum chamber surrounded by a pair of coils configured as Helmholtz coil which generates the alternating magnetic field. The test structures are harmonically excited by the Lorentz force acting on the gold lead at the top surface of the cantilever carrying an alternating current. In the presence of a sinusoidal magnetic flux density, the resulting Lorentz force contains two alternating terms including the sum and difference of current and field frequencies. Therefore, the resonating cantilever is used as mixer in a heterodyne detector for alternating magnetic fields with variable frequency. Resonant excitation only occurs if one of these frequencies is close to a mechanical resonance that satisfies the selection rule imposed by the field configuration. In the experiments, emphasis is laid on the investigation of the first symmetric and first antisymmetric vibration mode, where the amplitude of the vibration is proportional to the exciting vector component of the magnetic field. For this work the harmonic deflection of the cantilever was measured with a capacitive readout system and additionally, with a laser-Doppler vibrometer. By changing the drive current, the operating range of the magnetometer can be varied from a few μT up to 1mT, whereas the sensitivity remains constant with an uncertainty of less than one percent, valid for both vibration modes. This operation principle of the prototype allows a further miniaturization leading to a spatial resolution of the magnetic field detection determined by the size of the cantilever.

Light flux modulators based on micro-opto-electro-mechanical systems (MOEMS) enable high resolution displacement based inertial sensors. The three major noise sources for such devices are the Brownian noise originating from the surrounding air, the noise emerging from the optoelectronic detector and the noise contributed by the amplifier circuit. To unveil the resolution limiting mechanisms, we investigated the performance of a transimpedance amplifier in relation to opto-electrical receivers. To verify this approach, a SPICE simulation model including all noise sources was set up and compared with measurements. The experimental data suggest that the noise of the utilized transimpedance amplifier can be optimized for a given dynamic resistance and noise current of a given photoreceiver.