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Boost inertial MEMS apps with BAW gyroscope sensors

10 Jul 2014  | Mohammad Zaman, Sreeni Rao

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Perhaps the most distinct performance advantage of the BAW gyroscope enabled by the HARPSs fabrication process is its immunity to random vibration and shock as detailed in figure 5, where it is compared with existing tuning fork-based gyroscopes currently popular in the consumer market.

Figure 5: A comparison of gyroscope output offset shift measured during random vibration and shock test, showing the advantage of BAW technology over existing tuning-fork architectures.

The future: Lower power, more integration and innovation
Consumers are demanding products that are portable and accessible at all times. These untethered products can only be battery powered, forcing designers to constantly prioritise performance demands with battery life and size/weight. Devices that consume less power always offer an advantage in this engineering trade-off. The high frequency sensor design of the BAW gyroscope with its high Q mechanical gain and smaller drive-mode displacements (sub20nm) yield the lowest power per axis. This lower power consumption means longer battery life and greater consumer acceptance for any type of wearable or handheld battery-powered device.

For industrial and automotive applications where performance and robustness matter more, the BAW gyroscope offers the best possible combination of vibration immunity, low noise and linearity. In automotive, critical-safety applications such as anti-rollover are becoming mainstream, while new applications such as the use of gyroscopic control for radar positioning in ADAS systems are being increasingly adopted. In industrial manufacturing, for instance, gyroscopes are increasingly forming a critical part of the adaptive position control systems in robots. These applications demand performance and robustness, a combination that BAW is positioned to offer.

More dynamic applications of BAW MEMS technology can benefit when rotation is combined with other forms of inertial sensing. Personal or unmanned vehicular guidance systems call upon inertial measurement units (IMUs), which are a combination of accelerometers, gyroscopes, pressure sensors and magnetometers. The HARPSS processing technology, often referred to as the "CMOS" of MEMS, enables the integration of high-performance tri-axial micro-gyroscopes with tri-axial micro-accelerometers, and even tri-axial magnetometers on a common substrate to allow very favourable performance/size/cost ratios for devices such as an IMU. The high-Q operation of the BAW gyroscope can be maintained in near atmosphere conditions, and thereby does not limit the performance of devices such as pressure sensors and accelerometers built on the same platform.

Beyond navigation, IMUs provide 6 to 9 degrees of freedom sensing capabilities, bringing ultra-fine resolution to applications such as medical imaging equipment, surgical instrumentation, and advanced prosthetics. IMUs are also proving themselves useful in applications where the requirement for precision might not be as obvious and, as of recently, solutions were not available or practical. Among the more demonstrative examples are smart golf clubs, tennis racquets, and baseball bats that track and record every movement of an athletes' swing so that the user's technique can be refined. Accelerometers measure the acceleration, vibration, and swing plane while gyros measure pronation, or the twist of the user's hands, during the swing. Each sport usually comes with its own app, which records up to 1,000 data points per second from the sensors and shows the user precisely how hard, how fast, and from what angle they have hit the ball. There are even 3D models that lay out a swing completely, so it can analyse the user's mistakes. Each sport has an app that's completely tailored to its needs and recorded data collected during play or practice can be sent via Bluetooth to a smartphone or PC for analysis.

The BAW he BAW gyroscope, in its existing form-factor, is unique in its ability to achieve low-noise performance and wide dynamic range with excellent linearity while displaying superior immunity to the effects of temperature and mechanical shock/vibration and requiring low-power. This and other innovative designs using the HARPSS fabrication process are providing a platform for higher integration, smaller size, lower cost, and less system complexity. BAW gyroscopes will help design engineers innovate and differentiate their product designs by enabling new products that may not have been possible earlier.

About the authors
Mohammad Zaman and Sreeni Rao are with Qualtre Inc.

To download the PDF version of this article, click here.

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