A glimpse of the future of IoT sensors

source: EDN article

Patrick Mannion -September 28, 2016
It’s not an exaggeration to say that sensors are the backbone of the Internet of Things (IoT), but it might be more accurate to say they’re the central nervous system and cold hard cash is the lifeblood. That’s why it’s important for designers, team leaders, and executives alike to take a look at the upcoming MEMS & Sensors Executive Congress 2016 in Scottsdale, AZ, this coming November 9-11.

The event is unique in that it mashes biz heads with the money, with technologists and designers who need to follow the money, and if you’re able to stop by you’ll be treated to high-level but grounded perspectives from AT&T, Local Motors, Bosch, and NXP. These are supported by deep dives into, for example, breakthroughs in gyroscope accuracy using bulk acoustic wave (BAW) resonators, perpetual sensing that leverages ambient energy, and an interesting treatise on the evolution of the human-computer network.

The mixture of biz and tech plays into the theme of invention, co-creation, and collaboration, explained Karen Lightman, executive director of the MEMS and Sensors Industry Group. “Attendees of this year’s MEMS & Sensors Executive Congress will hear how both titans of industry and nimble innovators approach technological innovation holistically – leveraging internal and external ecosystems to introduce meaningful products to market.” The event spans mobile and wireless, automotive, medical devices, energy, and as mentioned above, the intersection of human-computer networks.

Wireless and automotive are particularly interesting. With the evolution toward 5G networks, the Federal Communications Commission (FCC) recently (July) allocated mm wave spectrum above 24 GHz, paving the way for high-speed (10 Gbits/s) low-latency (<1-ms) sensor networks for time-sensitive, data-driven applications. More recently, the Department of Transportation (DoT) issued its policy on the safe testing and deployment of autonomous vehicles, which is a good, albeit controversial, start down the path toward some form of mutual understanding between government and innovators on the topic.

With a trillion sensors on the cusp of being deployed across cities, industry, vehicles, agriculture, and infrastructure, low latency and agreed-upon rules for low-latency communication and autonomy are critical. So too are the innovations in sensors that will take advantage of these new networks and policies.

Accurate gyroscopes and perpetual sensors

Take gyroscopes, for example. MEMS gyroscopes were supposed to be the answer to navigation and dead-reckoning applications, but they have historically been prone to excessive drift due to error sources such as shock and vibration. This puts extra accuracy requirements upon GPS/GNSS, accelerometers, and local wireless networks to maintain accuracy when, for example, a car goes into a tunnel.

To improve gyroscopic accuracy, Qualtré, Inc. licensed patents on BAW technology from the Georgia Institute of Technology and used them to develop three-axis and later single-axis gyroscopes that they will show can beat the accuracy of traditional MEMS “tuning-fork” gyroscopes (TFGs.)

While highly successful, the fundamental problem with TFGs, which are basically a type of flexural-mode resonator, is that they depend upon two proof masses that move as freely as possible (Figure 1). This makes them susceptible to vibration, shock, and stiction. Stiction is “static friction” whereby microstructures adhere to each other due to static electricity. TFGs also require vacuum packaging.

Figure 1 Tuning-fork gyroscopes (TFGs) depend upon two proof masses that move as freely as possible, making TFGs susceptible to vibration, shock, and stiction. They also require vacuum packaging. (Image courtesy of Qualtré, Inc.)
BAW resonators, on the other hand, depend upon the principle of a standing longitudinal wave traversing a medium (Figure 2). Qualtré’s implementation comprises a stationary silicon disk resonator with vibration amplitudes of less than 20 nm that is surrounded by electrodes separated from the disk by a small capacitive gap (typically 200 nm.) The inherent stiffness of the bulk approach provides higher resistance to shock and stiction, as well as higher resonant frequencies and a high Q factor without the need for vacuum packaging.

Figure 2 Qualtré, Inc’s BAW resonator-based gyroscope relies upon the stability of a bulk structure expanding and contracting along the direction of a standing longitudinal bulk-acoustic wave, instead of relatively free-floating masses. (Image courtesy of Qualtré, Inc.)
Farrokh Ayazi, chief technology officer at Qualtré, will be on hand at the congress to provide more details on the technology, the latest results, and the implications of the technology, particularly in the context of autonomous driving.

For perpetual sensing, the biggest obstacle is battery life. While there has been enormous interest in using ambient energy to recharge capacitors or batteries, from solar to vibration, pressure, thermal differentials, and various other sources, the lifespan of rechargeable batteries has been the gating factor. Other factors include temperature tolerance, form factor, safety, and charge retention, the latter of which is compounded by the unpredictability of the energy source.

A startup called Ilika applied its materials patents to develop a solid-state battery called Stereax that it will be showing off at the congress. Along with 40% higher energy density and a temperature tolerance above 100˚C, the battery uses a low-temperature process that allows it to be deposited on the back of a CMOS chip.

Figure 3 Designed specifically for the IoT, the Stereax solid-state battery is being offered as a solution to the problem of “perpetual sensing” by storing ambient energy better than any other storage technology on the market. So says Graeme Purdy, who will be presenting Ilika’s technology at the MEMS & Sensors Congress. (Image courtesy of Ilika.)

Assuming for a second that Ilika’s claims are accurate, and congress attendees will get the chance to pepper the company’s CEO, Graeme Purdy, at the event, then the Stereax battery may in fact be a really good solution to the question of how exactly do we power a trillion sensors in the field? Some of these sensors may be required long after the original systems that aggregate their data have long been upgraded – or even replaced. No one wants to have to go around replacing batteries every ten years.

That’s only one of the many questions being addressed and possibly answered at the MEMS & Sensors. Others include:

• What is the future of sensors and MEMS in the IoT? (AT&T)
• How are sensor technology, micro manufacturing, and open innovation making the first 3D-printed autonomous car a reality? (Local Motors)
• What is the role of sensors in human-computer synthesized networks? (MEMSIC)

In the latter, MEMSIC Chairman, President & CEO Yang Zhao will explain how computer networks will echo all the functions and capabilities of human biological networks. Artificial intelligence, wearable computing, and cloud computing are just part of it: sensors link the two networks and Zhao will dig into how and what this means. Should be interesting!

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