Most of man’s senses were at a time con-strained by distance. He could see, hear, feel, taste or smell only what was near him. However, sensors came and changed all that. These little electronic nodes can act as eyes, ears, skin, nose or taste buds. They can be placed near or far, and even in environments that man cannot stand—biting cold, scorching heat, dangerous cliffs, toxic chemical vats and so on. And they do their owner’s bid—measuring pressure (pressure sensors), temperature (heat sensors), vibration (vibration sensors), speed (motion sensors), brightness (light sensors), etc. What is more, they dutifully send this information to a computer or some other device that collates, interprets and acts on the information sent by several sensors.
Sensors have not only made measurement and monitoring easier but also increased our control over processes, especially critical ones. This has made them imperative in this age and time when quality control and compliance with other regulations are very important. With sensors, the meteorology department can collect detailed information about weather conditions anywhere in the world, estate owners can watch the movement across their fences, process firms can monitor every minute detail of the environment and the assembly line that is required to ensure perfect execution, logistics firms can track their fleet and forest officers can monitor the movement of rare animals. In these and so many other ways, they let us watch the required details keenly and act immediately.
Endless uses, thanks to wireless
From the examples discussed, it is evident that there is no end to the types of sensors or the range of applications each might be put to. The scope has increased immensely, thanks to the wireless generation of sensors. An application is no longer constrained by cumbersome wires, and it is possible to install a sensor practically anywhere.
Vivek Tyagi, country manager-sales, Freescale Semiconductor India explains, “Wireless has gained popularity over its wired counterpart primarily due to its vast applications and lowered cost of setup. Globally, wireless sensors are popularly used for military, medical and environmental applications since these are the most critical areas that need to be addressed. Apart from these, automotive, aerospace, manufacturing and consumer electronics sectors are also heavily dependent on these sensors.”
A sensor hardly operates individually, although each single node is typically an autonomous instrument. Sensor nodes always act cooperatively with other sensors, as a network, with each node communicating with the others and/or with a central computer that acts as the ‘leader.’
Depending on the setup, the sensor nodes might use short-range wireless technologies such as radio frequency identification (RFID) or Bluetooth to communicate with neighbouring sensors, or long-range communication technologies like Wi-Fi to communicate directly with a central computing device. In most cases, however, sensor nodes communicate in ‘hops’—the message hops from one node to the other before reaching the leader.
Another critical part of the wireless sensor network is the standards and specifications that serve as a guideline to set up the network. “There are various standards and specifications for a variety of sensor applications. For example, Freescale’s ZigBee is a proprietary mesh-networking specification used for embedded sensing, medical data collection, consumer devices (television remote controls) and home automation, while WirelessHART is an extension of the highway address-able remote transducer protocol and specifically designed for industrial applications like process monitoring and control,” says Tyagi.
In addition to the radio transceiver or other wireless communication system, a sensor node contains a small microcontroller and a power source. Some of today’s wireless sensors go a step further and charge themselves using power gleaned from the wireless signals or from ambient sources such as the sun or wind, thereby not requiring a separate power source. This not only increases the scope of applications but also makes the use of sensors practically maintenance-free.
In short, wireless sensors and related technologies—sensor nodes, communication and networking technologies, and software applications that make use of the information collected by the sensors—have all developed significantly in the past few years, extending the potential and practical uses of sensors beyond the mundane.
The following snip-pets provide a sample of the kind of developments happening in the wireless sensors space—technological developments, innovative uses and ingenious adaptations!
Quick and easy, green sensor network
At the American Geophysical Union meet held in San Francisco in December last year, a company called Crossbow Solutions demonstrated its award-winning eKo system—a simple, starter-level sensor network kit for gathering environmental data.
The kit consists of sensors, which, in turn, are connected to nodes that read the sensor data and wirelessly transmit it to the base radio. The nodes can send their own information as well as re-transmit data sent from other nodes. The data sent from all nodes is received at the base radio and forwarded to a gateway. The gateway then stores and forwards data from the sensor network, making it accessible via a simple Web-based graphical user interface. While the starter kit has only the basic sensors, environmentalists can expand this array by adding other sensors to precisely measure the parameters they want—be it soil moisture, leaf wetness or the weather.
What makes the eKo system worth a dekko is that the nodes are all solar-powered—making it a green technology. The data can also be viewed anywhere, anytime over the Internet, making it easy for even non-techie environmentalists to use. The alarm settings and alerts can be customised, as can be the assortment of sensors used. This makes the system suitable for hobbyists as well as critical environment-monitoring purposes.
In addition to a reliable wireless mesh communication backbone, the system features the environmental sensor bus (ESB) for plug-and-play sensor capability.
Web 2.0 intelligence expanded
Libelium is a company that offers a range of wireless sensor network solutions for requirements ranging from agriculture and cattle farming to health-care, marketing, industrial processes, logistics and smart metering. The base products comprising their solutions include the Waspmote, a low-power sensor device capable of withstanding adverse environmental conditions, and Meshlium, a multi-tech router that enables connections to ZigBee, Wi-Fi, GPRS and Bluetooth networks in addition to GPS geo-location.
Recently, the company released notes on how to send the data collected by its sensor network to Twitter and WordPress. Basically, it enables the environment to ‘talk’ through a Web presence, updating information about itself in real time.
The Waspmote sensor platform collects the information, while the Meshlium router acts as a bridge between the 802.15.4/ZigBee network and the Internet. This open source solution would make it possible to create a blog or micro-blog for a city, forest or a river that updates itself with information collected by the installed sensors—be it about the temperature of a city, the speed or volume of water flowing through a river, the humidity prevalent in a tropical forest or the movement of exotic animals in the forest.
Some months ago, Libelium also released notes on how to program the Meshlium to automatically send SMS and e-mail alerts based on the sensor data.
Your mobile phone too could be a sensor
Andy Rubin, engineering director, Google, wrote an article on the future of mobiles, based on ideas collated from many experts, and posted it on his blog last year. Therein, he mentions that your mobile phone, if used as a sensor, could reveal tonnes of global patterns and real-time information, very easily.
“Your phone knows a lot about the world around you,” he writes. “If you take that intelligence and combine it in the cloud with that of every other phone, we have an incredible snapshot of what is going on in the world right now. Weather updates can be based on not hundreds of sensors, but hundreds of millions. Traffic reports can be based not on helicopters and road sensors, but on the density, speed and direction of the phones (and people) stuck in the traffic jams.”
Looks like somebody has decided to try this out too! The National Science Foundation, USA, has awarded a $1.5-million grant to CitiSense, a cell-phone-based sensor network system, to develop and deploy hundreds of small environmental sensors that can be carried by the public in San Diego. These sensors will use cellphones to relay data. In addition to environmental sensors, the people can volunteer to wear biological monitors to collect health-related statistics. The information will then be analysed using computing systems and relayed back to the people.
In November 2009, telecom service provider NTT DOCOMO Inc. announced the trial operation of a network of environmental sensors that measure pollen, carbon dioxide (CO2), ultraviolet (UV) sunlight and other atmospheric conditions that can affect human health and daily life. This information will then be provided to companies, healthcare institutions, municipalities, etc, for use in various commercial and educational applications, such as weather forecasting and other information services. The network of sensors appears to be the largest and densest of its kind in Japan.
Gaming console sensor put to different usage
Wiimote is the key control device for Nintendo’s Wii console. It is known for its motion sensing and gesture recognition capabilities. It uses an accelerometer and optical sensor technology to allow users to interact with the on-screen items through gestures or by pointing their fingers.
This device has fired the imagination of many a hacker. Last year, a developer called Johhny Chung Lee turned it into a finger-tracking device and a touch-screen whiteboard. You can do it too, thanks to his do-it-your-self instructions available at ‘http://johnnylee.net/projects/wii/’.
Inspired by this, physicist Rolf Hut of the Delft University of Technology has built a Wiimote wind sensor. In a Wired Science report, Hut comments, “It was just a bendy pole with an empty bottle on top with an LED light on the bottle.” It was built in a single day, and a little soldering is all it took.
If the report is to be believed, there is nothing you cannot sense with a Wiimote and an LED light. Of course, it might not be the best way of sensing a parameter, but you can definitely find a way out with it. For example, you can put a Wiimote atop a collapsing building and find out how fast it fell.
In another success story, Willem Luxemburg, a hydrologist at the same university as Hut, demonstrated a water-level sensor made from a Wiimote and a plastic boat. This sensor solves a problem that has intrigued hydrologists for long—measuring evaporation on a body of water. An acceptable, expensive but inaccurate technique followed till date is to place vessels full of water near or atop the water body and put pressure sensors in them. The sensors record the drop in pressure as the water evaporates. You can measure it more easily with a $40 Wiimote adapted for the purpose.
According to the Wired Science report, “The Wiimote could overcome evaporation-measurement problems. It has a tri-axial accelerometer and a high-resolution, high-speed infrared (IR) camera which can sense movement with better than 1-millimetre accuracy. Luxemburg’s team tested it in a floating evaporation pan, using a float with an LED. With a Wiimote aimed at the float, and some hacking and programming of the Wiimote’s output, they were able to get highly accurate, real-time data on water level wirelessly sent to a laptop. The IR camera can track up to four LED lights at once, so scientists can use several floats to calculate the water’s plane. To be as accurate with pressure sensors, you would need more and costlier units.”
Sensors that consume less power
Apart from the several advantages, wireless networks have one significant disadvantage too over their wired incumbents—these consume more power, increasing the total cost of ownership of the sensor network in the long run.
A patent-pending media access protocol developed by researchers at the University of California at Berkeley might be the solution to this problem. This protocol is suitable for networks where the sensor nodes are power-con-strained but the network’s main access point has an unlimited power supply. It attempts to lower power consumption by minimising the power wasted due to radio operation inefficiencies at each node, and thereby increases battery lifetime.
In addition, this protocol offers excellent real-time delay guarantees, congestion control and data transmission fairness. When tested on a wire-less sensor network for traffic control, it demonstrated 1000 times lower power consumption than traditional contention network protocols. You can read more about this innovation at ‘http://techtransfer.universityofcali-fornia.edu/NCD/17287.html’
Applications in medical electronics
“One of the areas which are increasingly benefitting from wireless sensor technologies is medical electronics. According to a report by Electronics Industry Market Research and Knowledge Network, enabling wireless sensor solutions can reduce hospitalisation costs by promoting portable medical equipment. “This can collectively reduce costs for annual healthcare by $25 billion by 2012,” cites Tyagi of Freescale.
Freescale’s offerings in this space include the reference design for an automated home blood pressure monitor. This is an example of how the sensing, data communication and processing capabilities of Freescale’s Flexis QE128 product family can interact to create a handheld medical solution. This low-cost personal BP monitor is available at affordable price-points.
The company also offers piezoresistive pressure sensors that are suitable for medical instrumentation applications like portable digital blood pressure meters that can provide key diagnostics for healthcare patients.
Another concept put forth by the company is that of a personal electrocardiogram (ECG) monitor. Tyagi explains, “The high cost of a personal ECG monitor can be reduced through the use of new technologies which incorporate a microcontroller and digital signal processing into one device. A low-cost, single-chip solution by Freescale can help overcome this obstacle.”
Smart meters to help reduce electricity bills
Rising electricity bills can shock just about anybody. Companies want to reduce their energy costs, just as consumers seek more efficient means to man-age their own energy consumption. Smart meters could come to the rescue. These are essentially intelligent meters that can sense a home or organisation’s power consumption in more detail than a normal meter. This information can either be used by a consumer to better understand and manage his usage or relayed back to the service provider for billing purposes.
“ZigBee-enabled meters can communicate and control ZigBee-enabled devices in the home, such as the heating, cooling and air-conditioning systems, to enable utility company programs such as load control, demand response and time-of-use pricing. These programs not only reduce the peak load on the utility grid but also help the home owners make smart decisions about their energy usage,” says Tyagi. Though it might be a while before we see this in India, it is very useful for international service providers who have variable rates for power usage based on the time of the day. Consumption during night or other ‘happy hours’ will be charged less than usual timings; plus consumption by certain devices might be charged more than the others.
The planet’s central nervous system
Sensor technology is so hot today that almost every IT and electronics major has some or the other related project. HP Labs, for instance, announced a very ambitious project late last year. Their dream is to build a ‘central nervous system for the earth’ (CeNSE) that could well be a veritable backbone for the Internet of Things that has been spoken about for so long.
Their goal is to ‘make the earth speak for itself’ using a network of tiny, cheap, robust and very accurate sensors that will give the computers, devices and other tech toys around us the power to sense what is going on in the environment.
Peter Hartwell, senior researcher and team lead for this project, envisions sensing nodes about the size of a pushpin stuck to bridges and buildings to warn of structural strains or weather conditions; scattered along roadsides to monitor traffic, weather and road conditions; embedded in everyday electronics to track hospital equipment, sniff out pesticides and pathogens in food; and so on. Together, the network would make life easier and safer for mankind, while also collecting valuable information that will create awareness for a better tomorrow.
The first goal towards achieving this mega dream is to develop dirt cheap sensors.
Hartwell is working on the first such sensor—an accelerometer that can detect motion and vibration. The device is sensitive enough to detect a heartbeat, and contributes a sense of ‘touch and feel’ to CeNSE. As per details revealed by the company, “The source of that sensitivity is a 5mm2, three-layer silicon chip. A portion of the centre wafer is suspended between the two outer wafers by flexible silicon beams. When the chip moves, the suspended centre lags behind due to its inertia. A measurement of that relative motion is used to calculate the speed, direction and distance the chip has moved. This exquisitely sensitive accelerometer can detect a 10-femtometre change in the position of its centre chip. As a result, it can measure changes to acceleration in the micro-gravity range. That’s about 1000 times more sensitive than accelerometers used in a Wii, an iPhone or an automobile’s airbag system.”
Another interesting development is use of nanomaterials to boost a standard chemical and biological detection technology (Raman spectroscopy) to 100 million times its usual sensitivity rates. As sensitivity rises, sensor size can shrink. That could lead to detectors small enough to clip onto a mobile telephone. “With a wave over produce, the sensor might warn consumers of salmonella on spinach leaves or pesticides present in ‘organic’ produce,” Hartwell says in the press report. It adds the senses of taste and smell to CeNSE.
The team is simultaneously working on adding various other sensors ranging from light and pressure to temperature and humidity.
iphone turned sensor
It seems to be the season for mobile-sensor convergence, and it is not just hobbyists experimenting with such clip-onto-mobile sensors. Jing Li, a physical scientist at NASA’s Ames Research Center, has developed a technology to add low-cost, low-power, high-speed nanosensor-based chemical sensing capabilities to cellphones.
The stamp-sized device can be plugged into an iPhone’s 30-pin dock connector to collect, process and transmit sensor data. It is capable of detecting and identifying low concentrations of airborne ammonia, chlorine gas and methane. According to the NASA report, the device senses chemicals in the air using a ‘sample jet’ and a multiple-channel silicon-based sensing chip which consists of 16 nanosensors, and sends measured data to another phone or a computer via a telephone or Wi-Fi network.
Sensor network for aircraft monitoring
A team at Scotland’s Institute for System Level Integration (iSLI) has started designing a wireless sensor system that could well become a standard feature of the next generation of commercial aircrafts. The project has been launched with a budget of 3.3 million pounds, with contributions from various aerospace industry leaders.
The first prototype wireless sensor network, WiTNESS, will gather complex and accurate data from different parts of the aircraft, which will be used to help identify technical faults, optimise performance and monitor the overall health of the aircraft.
Wireless is a key capability to reduce the costs associated with wired sensor cables. According to Dr Begbie, director, iSLI, “Putting in cables adds to aircraft cost and, crucially, weight and it’s not the easiest thing to get in and maintain. If you take Rolls-Royce as an example, when it is developing a new engine it can have upwards of 3000 sensors attached when it is on the testbed. Routing all the wires to the sensors and bringing them all back to a collection point is a big job, and when you have 3000 cables running over a vibrating engine, you get a lot of difficulty with drop-outs. So Rolls-Royce wants us to look at how the wireless technology can help.”
Subsequently, the system can be improved to take on tasks like predictive maintenance and, ultimately, real-time data for safety-critical components. It may also be of great use in the carbon fibre components being developed to replace aluminium aircraft parts, where sensors can be used to help monitor how the components are coping with high pressures and heavy loads and allow manufacturers to get better information about super-structural capacity and the life expectancy of each component.
Wearables to fight flab
According to a recent New York Times report, scientists are developing wear-able wireless sensors to monitor over-weight and obese people as they go about their daily lives.
Made of sophisticated sensing instruments, the devices will track how many minutes the wearers work out, how much food they consume, whether they went for the routine walk at the park or sneaked into a fast-food joint, and so on. The goal is to make the users aware of where, when and how they added more calories to the existing pile—or, on a more positive note, how they managed to lose some of it!
Coming up next…
As far as the field of wireless sensors goes, we have seen only the tip of the iceberg.
The next generation might live a life completely controlled by sensors—sensors that detect how much they eat, how many calories they burn, by how many micrometres their waistline expands or shrinks in a day, how well their faculties and organs are functioning, how many minutes they work, how well their car is working, when and how many lights are turned on in their home, what volume of pollutants they add to the air, how much electricity they consume in an hour, how long they use each device and what not.
Some day, the bubble will burst as security and privacy issues loom large, but just as the World Wide Web emerged stronger and better after the dotcom bust, sensors too will emerge victorious and perhaps really make the whole Earth an Internet of Things.
The author is a freelance writer based in Bengaluru. She writes on a variety of topics, her favourites being technology, cuisine, and life