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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.

Micro mechanical light flux modulators enable high resolution inertial displacement sensors that are virtually free from reaction forces. The presented MOEMS (Micro-Opto-Electro-Mechanical System) transducer modulates the light flux of an LED by the relative movement of two aperture gratings one etched into a seismic mass and the other fixed to the sensor package. The modulated flux is registered by a photo transistor and amplified using a transimpedance amplifier. Theoretical examinations suggested that apertures featuring a high aspect ratio are performing best. Applying these design rules, an increase in sensitivity by a factor 4.72 to 0.532 μA/nm at a frequency of 10 kHz and an improvement in displacement resolution from 10.7 pm/ √Hz to 2.26 pm/ √Hz was found when compared to prior prototypes featuring a comparable mechanical characteristic. The system was also found to follow a linear characteristic over the tested amplitude range.