Josef Schalk

Resonant accelerometer with self-test

A new resonant accelerometer is presented consisting of a doubly clamped beam coupled to a seismic mass. The beam is thermally excited by an implanted resistor and its vibration is sensed piezoresistively. An acceleration which deflects the seismic mass leads to characteristic strains inside the resonator, shifting its resonance frequency. We studied the oscillation characteristics of the resonant beam. The non-linearity at high excitation amplitudes is treated theoretically and experimentally. Further, it is shown that the electrical and thermal cross-talk can be eliminated. The resonant sensing principle ensures a quasi-digital output signal, high sensitivity and a mechanical integrity test. Advanced automotive safety systems and x-by wire applications require a high reliability of the employed sensors. The sensor presented here allows an on-going self-test without any constructive changes of the sensor element. The self-test concept, we developed also finds applications in other sensors with resonant structures.

Silicon angular rate sensor for automotive applications with piezoelectric drive and piezoresistive read-out

In this work a silicon angular rate sensor for automotive applications with a new architecture is presented. It is based on the vibrating tuning fork principle with excitation direction of the tines perpendicular to the wafer surface. This arrangement allows the design of tines with significant inertial masses which lead to substantial signal. The oscillation of the tines is excited by a piezoelectric drive using an AlN thin film layer. The angular rate to be measured causes a torsional oscillation of the stem. The torsional amplitude is proportional to the angular rate and is measured by a piezoresistive read-out structure. We use silicon bulk micromachining based on a new twofold SOI-technique.

Tuning fork silicon angular rate sensor with enhanced performance for automotive applications

This paper reports on a silicon angular rate sensor designed for automotive applications like overroll protection and electronic skidding protection. The sensor is based on a tuning fork principle with the tines being piezoelectrically excitated perpendicular to the wafer surface. Due to the Coriolis effect, an angular rate parallel to the axis of the stem generates a periodic torque, which results in a torsional oscillation of the stem. This torsional oscillation is detected with an implanted piezoresistor located in the middle of the stem. A slot in the center of the stem enhances the shear stress at the read-out piezoresistor position resulting in a higher sensitivity. The latest sensor design with a split electrode allows an electronic compensation of mechanical imbalance in order to reduce the sensor offset and offset drift. Additionally, this electrode configuration can generate a periodic torque to perform a permanent test of the sensor functioning and the sensitivity during operation.

Wireless Sensing of Physical Parameters Inside Hermetically Enclosed Conductive Envelopes

In the modern aeronautics and aerospace industry, there is a manifold amount of applications emerging for wireless sensors. While many new systems are making use of radio transmitters, EADS Innovation Works has developed a concept for transmitting energy and data to the inside of hermetically sealed envelopes used for hydraulic accumulators, fuel tanks, oxygen bottles, etc. For such kind of metal enclosures, the use of radio frequency is impossible as the electromagnetic waves are blocked by the surrounding material. Classical approaches like using wire-based feed-throughs threaten the reliability of the overall system and hence, they are less attractive especially when safety relevant components are targeted. The system described in this paper makes use of ultrasonic transmission techniques in order to power and communicate with a wireless sensor inside a metal enclosure. An innovative platform and communication concept allows to efficiently read data from basically any type of low power commercial sensors of the shelf. Major design drivers for the overall system are a high level of integration and high reliability.Copyright

Robust and Selftestable Silicon Tuning Fork Gyroscope with Enhanced Resolution

Advanced automobile electronic systems like overroll protection , electronic skidding protection and x-by-wire systems require at least one robust and reliable angular rate sensor. Therefore a silicon micromachined gyroscope based on a tuning fork structure was developed with all resonant frequencies being above 10kHz and the primary and secondary gyroscope oscillation frequency being close to 40kHz. Additionally no other resonant frequencies arc within a bandwidth of 10kHz around the gyroscope modes in order to be insensitive to random vibrations occurring in automotive applications and to withstand high shock impacts .

A New Generation of Micromachined Accelerometers For Airbag Applications

In this contribution an overview concerning the design, fabrication and performance of a new generation of micromachined silicon accelerometers will be given.

Wireless optical OFDM implementation for aircraft cabin communication links

The state of development of optical devices has led to increased interest in high data rate wireless optical communication schemes that today constitute a viable alternative to conventional wireless technologies for information exchange. In this work, a high data rate wireless optical link, based on OFDM modulation, conventional laser diodes and large area photodiodes, was implemented and investigated. A laboratory prototype was used to demonstrate a data rate of 19.6Mbit/s. A 64-subcarrier OFDM signal with different subcarrier modulation schemes (BPSK, QPSK) was examined. Target applications are video, high speed internet etc. within the confines of an intra-cabin wireless optical topology

Performance analysis of modulation schemes for wireless optical in-cabin aircraft networks

One of the major tasks in the future of aircraft inflight entertainment is to provide wireless connectivity throughout the cabin. In this work an optical OFDM modulation scheme for cellular network architecture is investigated in comparison to other conventional optical modulation techniques (PPM, OOK). An analysis of efficient cabin link layout with respect to seat rows per cell and available data rates, allowing high quality services for specific application (e.g. Video, data transfer), is presented for an implemented minimum of 10Mbit/s per cell. A wireless optical OFDM communication prototype has also been implemented in a laboratory experiment and compared to a conventional diffuse optical 2PPM, achieving 17.2Mbit/s data transmission, thus doubling the previously achieved performance, but being based on line of sight links in the laboratory only. Both implementations prove the usefulness of the investigated modulation schemes.

Aerospace applications of mass market MEMS products

Aerospace applications of MEMS products, originally developed for automotive mass markets, are discussed. Various sensor examples with a high dual use potential are presented: inertial sensing, flow and gas sensing, robust micro sensors including SiC- and GaN-based devices, as well as first approaches towards flexible and distributed microsystems. In Europe the automotive industry is one of the main MEMS market drivers, simply because of the sheer size of this market and Europes strong position in this industrial field. Main MEMS activities are development and integration of vehicle dynamics sensing systems, passenger safety and navigation systems, air and fuel intake systems, as well as sensor systems for exhaust gas after treatment and climate control. Benefits on the customer side are increased safety, passenger comfort and reduced fuel consumption. Benefits on the manufacturers side are increased sub-system integration, modularity and reduced production cost. In the future the aerospace industry is likely to benefit from the introduction of micro-systems for the same reasons as the automotive industry. Interests of the aerospace industry are increasing safety and reliability of airplane operation, health and state monitoring of fuselage and airplane subsystems as well as improving service and maintenance procedures. In comparison to automotive applications, the numbers of devices needed is likely to be much smaller, however, new challenges arise in so far as distributed sensing and actuating microsystems will be needed. The idea is to identify and to exploit synergies between automotive mass market MEMS applications and lower-volume aerospace ones. The effort necessary to meet aerospace requirements and the extent of necessary trade-offs in customizing automotive MEMS is addressed considering the above-mentioned examples.