New Sensor Technologies Mean New Opportunities

New sensor technologies are making it possible to measure variables that until recently were too difficult or expensive to sense. According to experts in the field, three areas may cause a transformation in the next few years: nanotechnology-based sensors, wireless sensors, and 3D vision sensors.

Nanotechnology-Based Sensors
Small sensors are not new; micro electromechanical system (MEMS) pressure sensors, accelerometers, and gyroscopes have been available from some years; the airbags in most cars are triggered by MEMS accelerometers. But now chemical sensors based on nanotechnology show considerable promise. An example is a line of nanotech-based sensors from Nanomix that, says president and CEO David Macdonald, form a universal detection platform capable of detecting a wide array of substances with great specificity and high sensitivity. The company’s Sensation technology sensing element, which draws on research done at UC Berkeley, consists of a random network of carbon nanotubes on a silicon substrate. The nanotubes are coated with a chemical recognition layer that causes the electrical resistance of the network to change when the substance to be sensed is present. It’s possible to build sensors for H2, CO2, CO, H2S, NH3, CH4, glucose, explosives, chemical warfare agents, and specific DNA fragments. By combining several different recognition chemicals it is possible to do a signature analysis and identify a particular group of molecules.

Other companies are also working on nano-scale chemical sensors. The Cyranose sensor, developed by Cyrano Sciences Inc. and based on technology from Caltech, contains an array of tiny sensors made of carbon-black particles coated with a nonconductive polymer that swells when exposed to a target substance. The swelling increases the sensors’ electrical resistance. Putting 32 sensor dots with different polymers onto a single MEMS substrate and using pattern-recognition software allows the Cyranose to detect a wide variety of substances.

Synkera Technologies makes nanostructured mixed metal oxide sensors using 5-50 nm conformal coatings inside arrays of high density aligned nanopores on an alumina substrate. Units are available for H2 (trace), H2 (LEL), NH3, NOX, VOC, flammable gas, NF3, moisture/humidity, H2S, and NO2.

Sandia National Laboratories has developed a handheld chemical detection unit that analyzes airborne samples to detect toxic substances and explosives, and to perform breath analysis on patients. The system uses a combination of micro-scale gas chromatography and liquid chromatography, nanoparticles that change their electrical conductivity as they are exposed to specific chemicals, and a MEMS-based mechanical resonator that changes frequency or amplitude as chemicals are absorbed by a polymer layer on its surface. Unfortunately, the technology is presently the subject of a legal imbroglio and it is unlikely that commercial products will appear until the legal issues are settled.

Wireless Sensors
The idea of a sensor that requires no wiring has considerable attraction — still more if it can run for a year or more on battery power. Over the past few years a number of wireless protocols have been developed that make it possible to create mesh networks, in which arrays of short-range wireless devices self-organize into a network that can pass data from unit to unit and thence to a factory network, and automatically reconfigure if one unit in the mesh stops working. Individual nodes in the mesh spend most of their time asleep, waking up anywhere from every few minutes to every few days to transmit a brief burst of data.

“Over the past six months or so the industry has really taken off,” says Rob Conant, vice president of business development at Dust Networks. “In the industrial market specifically it’s really going gangbusters.” Frost & Sullivan, in its market report “World Wireless Sensors and Transmitters Markets,” predicts that the worldwide market for wireless sensors will reach $1 billion by 2010. Conant reports that his company has inked deals with a number of major OEMs to include Dust’s new SmartMesh-XT equipment in their products; it has also brought out a new line of wireless devices. The 900-MHz M1030 as well as the 2.4 GHz M2030 and M2135 can act, says Conant, “like an Ethernet card for sensors.” A set of companion cards provide configuration, management, and gateway functions for a network of motes.

There is still some question about the protocol to be used for wireless sensors. Many use proprietary protocols, including Crossbow Technology’s MoteWorks, Dust Networks’ SmartMesh, Ember Corp.’s EmberNet, Millennial Net’s Meshscape 4.0 system, and Sensicast Systems’ Sensicast. U
The best-known standardized protocol is ZigBee, controlled by the ZigBee Alliance, which has more than 100 members, including most of the companies with proprietary systems. ZigBee equipment is used in building automation and home networking, with some industrial applications. ZigBee’s DSSS (direct sequence spread spectrum) transmission method tends to be less resistant to interference than frequency hopping spread spectrum (FHSS). “ZigBee is designed for the home market,” says Conant. “It does a god job in the home market where the IT manager is the owner of the house, the same person who is responsible for buying new equipment. In an industrial setting it’s entirely different.”

A number of industry groups are working to standardize industrial wireless communication. Perhaps in response to the Fieldbus wars, the groups have announced plans to coordinate their activities.
The ISA-SP100 committee states that it is working to establish “standards, recommended practices, technical reports, and related information that will define procedures for implementing wireless systems in the automation and control environment at the field level.” In May the committee announced the establishment of two working groups: SP100.14, for “industrial monitoring, logging and alerting applications,” and SP100.11, for “a wide range of applications optimized but not restricted to the unique performance needs of control applications ranging from closed loop regulatory control through open loop manual control.” Carving out a place with so many other standards in place might prove problematic, and part of the working groups’ mission, according to SP100.11 Working Group Chair Pat Kinney of Kinney Consulting LLC., will be to “address coexistence with other wireless devices anticipated in the industrial work space, such as 802.11x, 802.15x, 802.16x, cell phones, RFID, SP100.14, and Wireless-HART.”

The Sensation technology sensing element consists of a random network of carbon nanotubes on a silicon substrate. The nanotubes are coated with a chemical recognition layer that causes the electrical resistance of the network to change when the substance to be sensed is present.

The HART Communications Foundation (HCF) announced in December of 2005 that it was making progress on defining a wireless HART standard, and was on track to have a draft specification by the spring of 2006, but little has been announced since that time. The main function of wireless HART, according to HCF, is for “process and machinery monitoring applications for energy management, asset management, asset optimization, environmental monitoring, predictive maintenance, diagnostics, control, and SIS — safety.” Conant reports t