Gyroscopes and accelerometers are so last gen. Here’s an in-depth look at the new wave of sensors that are likely to be at the heart of upcoming consumer devices.
The popular yardstick (though one that has lost relevance in the last decade) for progress in technology appears to have comfortably settled to Moore’s Law. It’s somewhat strange that this continues to be the popularly perceived rate of progress in the world of electronics, robotics, and their applications. In fact, the obsession with processing power often shadows the equally exciting developments in algorithms, architecture, and the focus of this article - sensors.
Sensor technology had its humble origins in the tactile switch - yes, the very same button that you press to turn on the lights. The concept is a general one. A sensor must follow three very simple rules:
The logical progression of thought was - what if other inputs could be used to control similar outputs? The boom in aircraft technology called for a tremendous innovation in sensors in the 60s, with the fly-by-wire, hands-on control systems gradually being phased out in lieu of slicker digital interfaces. And the robotics boom (did you know that robots probably sort your mail?) put the cherry on top as we entered the 2000s. Even so, ask an average (tech-savvy!) kid on the street to name some sensor types and the answers you get will be limited to accelerometers, gyroscopes, and perhaps photodiodes (or ‘light detectors’, as goes teenage jargon).
What are we missing out on here? A whole lot, honestly. The 21st century has ushered in a new wave of sensor-based research that is set to completely change the way we think of technology and its capabilities. It’s easy to see the problems with conventional sensors. They’re bulky, heavy, fragile, need batteries, and are bad for the environment. Ignoring aesthetics, consider their functionality. Traditional sensors are limited to coarse measurements of sound, light, speed and location - they lose out on chemical information like smell, on collaborative sensing, on very small inputs, and on most kinds of subtle information. Even worse, they often need to be treated with great care, and are next to useless in extreme conditions - imagine what you’d need to fly a drone over Mount Everest.
The 21st century, being the amazing period of time that it is, has seen fit to begin addressing all of these issues.
Biological research has been the driving force behind a lot of modern sensor applications, and perhaps the best example is micro- and nano-sensor research. These are sensors with an extreme scaling down - literally of the order of micro or nanometres in length. To put things in perspective, the average cell is a few micrometers across. Even with current applications that are mainly tactile, micro--sensors and robots at such scales will give us the ability to treat diseases at the cellular level, to monitor wound healing to micro-control drug dosage. In the future, they could perhaps even replace cell organelles in unhealthy cells, and in the very very long term, repair the telomeres that cap our DNA (whose wear has been directly linked with aging). Nanosensors open up a whole new paradigm. Not only can they revolutionize medicine with an unprecedented ability to interact one-on-one with viruses, but they will also induce huge strides in materials science research.
This device, based on modified carbon nanotubes, can detect amines produced by decaying meat. (Source: Sophie Liu /MIT News)
The thought of little robots swimming around in our bloodstreams might induce panic in some, and practical questions in others. How are these devices going to be powered? What happens when they wear out or need maintenance? The answers lie respectively in self-powered and biodegradable sensing technologies.
Research in self-powered sensing is throwing up all kinds of innovative answers. Work is currently being done on sensors that can derive energy from a heat difference (such as that between a patient’s body and the surrounding air), from radiation, from chemical energy in compounds like stomach acids, and even from vibrations (such as the beating heart, or thermal currents in the oceans and skies). As always, research is never unidirectional, and the potential for self-powered sensing is being extended to almost any application where it would be hard to keep replacing batteries. Underground vibration monitoring for earthquake and fault detection, especially in high-risk areas around fracking oil fields, is important.
A self-powered sensor developed by MSU researchers (Source: MSU Today)
The concept of biodegradable sensing offers a simple conundrum - the more complex a part, the harder it is to ensure that it disintegrates harmlessly. The idea is to print circuitry on sheets of silicon so thin that they dissolve in water over a period of days to weeks. The circuitry is wrapped in silk to vary this time period - progress has already been made with the fabrication of diodes as well micro-cameras of this type. The possible applications of such sensors are endless.
Post-operative care for sensitive organs like the brain and the heart often involve the insertion of sensors into these organs, which not only must be removed at a later date, but can also cause complications, swellings, and infections. The advent of innocuous biodegradable sensors stands to completely change this. The potential to non-intrusively collect data on the functioning of natural ecosystems, especially sensitive ones like coral reefs and rivers, also stands to gain.
Vibration sensing research has advanced to the extent that it is now commonly used in both industry and consumer applications. The running of huge, hundreds of kiloWatt-hour motors can throw up unexpected problems of alignment that quickly spiral out of control, permanently damaging often expensive equipment. Vibration sensors, especially in their modern avatars that provide compact, comprehensive sensing of amplitude, frequency, and wave modes, allow such catastrophes to be avoided in the pumping, automotive, manufacturing and power generation industries. Vibration sensing also has obvious applications in motion sensing and security.
Snakes, commonly thought to have no sense of hearing because they lack an external ear, can actually sense vibrations very accurately via an organ in their mouths. This allows them to pinpoint with remarkable accuracy whenever anything is moving around them. Particle sensing equipment has been a focus of sensor research with fairly straightforward applications. Quality control in factories, air conditioning applications, effluent analysis for toxins and particulates, and radiation monitoring are now all processes that can be easily and efficiently automated.
A tactile sensor measures information arising from physical interaction with its environment.
While it doesn’t look like we’re going to have anything to compete with dogs for their olfactory abilities in the near future, it certainly behooves humans to try their luck. And so we see chemical reactant sensors, designed as electronic noses that react with specific compounds in the air to detect biohazards, gas leaks, rust and even alcohol on the breath!
Moisture sensing technology, though rooted in the mid-1900s, has come a long way - it no longer has to be replaced as often, offers a long life, low maintenance, and excellent accuracy. For certain kinds of post-operative care, it’s extremely important to keep a patient well-hydrated in a humid environment (a moist wound heals faster). Moisture sensing helps out here. Also, with integration with other sensors, smart refrigerators can decide your shopping list for you and modify the controls according to what’s inside.
A Soil moisture sensor (Source: Christine und Hagen Graf )
Speaking of integration, it’s only natural to question the efficacy of the lone sensor, working in isolation. So many kinds of useful insights can be gathered from aggregations of data of different kinds, and swarm sensors and Ubiquitous Sensor Networks (USNs) target an exploration of such potential.
Swarm sensors are now becoming the norm in large-scale surveillance. The idea behind swarms is to have a bunch of sensors working in communication and cooperation with each other so as to gather maximally useful information in the most efficient way. Simply put, instead of having robots work independently on the task at hand, which might lead to redundancies or wastage of resources, we train them to work constructively, eliminating waste. Swarms are today being used to survey agricultural land, forests, traffic routes, and even by space agencies in their strategies for extraterrestrial exploration.
By embedding spinach leaves with carbon nanotubes, MIT engineers have transformed spinach plants into sensors that can detect explosives and wirelessly relay that information to a handheld device similar to a smartphone. (Source: Christine Daniloff/MIT )
USNs incorporate the integration of multiple kinds of sensors into one large information processing pipeline - this could include camera data, motions sensors, vibration data, sound and so on. USNs have tremendous applications in security and surveillance - with efficient integration, they approach the efficiency of a human guard, while limiting the cost, and widening the area under surveillance. Like many technologies developed for defense, this has also leaked out to the entertainment industry - virtual reality is having a ball with the scope that USNs offer. VR now has the potential to react not just to your hand movement - but to your body temperature and facial expression that distinguish a frantic wave for help from a friendly one!
Diagram of an intact Self-healing ring
We come full circle with a return to the scope that biological inspiration offers sensing technology. Self-healing sensors are under rapid development. These are sensors that can actually sense and repair themselves post certain kinds of damage. The erstwhile comic book fantasy of an exoskeleton is thus under active development - this might well define the warfare of the 21st century. Self-repairing membranes for biological and chemical process plants, protective clothing for sports and adventures, as well as materials science for protective sheets, tarpaulins and roofs might eventually benefit from strides in this area.
Galvanic skin response sensors might appear to be straight out of science fiction. This remarkable technology senses various features of the skin, ranging from temperature to moisture, and has managed to effectively correlate these observations with emotion and mood. Besides the obvious applications to virtual reality (a mood or reaction-dependant plot twist in a movie or video game!), this creates the potential to monitor and study mental health and patient recovery in unprecedented detail. Similarly, it allows for the potential to tailor air-conditioning to individual preferences.
A remote sensing protective glove that can integrate galvanic skin response, self-healing, self-powered and other kinds of sensors. (Photo for representative purposes)
Electroencephalograms and electrooculograms (EEGs and EOGs) are a fascinating subset of sensing technology that tracks the electric fields produced by fluctuations in brain and eye activity respectively. These have been linked to certain determinate processes that can be used to control all manner of processes. Tests have revealed that EEG data can be accurately used to learn and replicate hand gestures from human test subjects. Anywhere where human skill is required remotely - consider the example of underwater welding, which would be greatly simplified if a human could be sitting in a control room, directing a robot – will be revolutionized by this technology. EOGs offer a unique advantage - they track eye movements and can be used in virtual reality, for attention measurement and psychological research and a host of other decisions. Consider data of where a driver’s eyes flit while driving being used for the efficient design of vehicular control systems.
A body monitoring chip (Source: Oregon State University)
With the advent of multidisciplinary research, the possibilities for sensor research are truly endless. Add to this the interfacing, processing and learning capabilities that are being rapidly advanced, and you have a recipe for a future that will be as unrecognizable as it is unpredictable. Indeed, with the Internet of Things, that allows all your devices to interface with each other, with self-driving cars, with virtual reality - the world around us is already starting to look somewhat surreal. If we can expect a layman from the 1980s to be startled by the technology we take for granted today, it’s only logical that humanity must be in for some big surprises in the 21st century.
For a technophile - there has never been a better time to be alive.
This article was first published in January 2017 issue of Digit magazine. To read Digit's articles first, subscribe here or download the Digit e-magazine app for Android and iOS. You could also buy Digit's previous issues here.
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