Sensors Mag

Micromachined Gas Sensor Has Opportunities to Enhance Fire Detection

December 1, 2005 By: Peter Adrian

This content is excerpted from Sensor Technology Alert and Newsletter, a sensor intelligence service published by the Technical Insights unit of Frost & Sullivan.


Various sensing technologies are often used in fire alarms and smoke detectors including heat detectors, photoelectric detectors (which detect smoke), and ionization detectors (which are activated by the airborne particles of combustion). Moreover, optical flame detectors detect infrared or ultraviolet radiation emitted from a flaming fire.

While very inexpensive smoke detectors are ubiquitously used for fire detection, there are opportunities to use gas sensors for enhanced safety. For example, a carbon monoxide (CO) detector can detect CO emitted at the early stage of a fire, so preventive action can be taken. There are also opportunities to use integrated multisensor systems (that could include, for example, carbon monoxide and carbon dioxide sensors and a smoke particle detector) to provide a more complete fire signature and ensure greater immunity to false alarms.

Manifesting the realistic opportunities for gas sensors in fire detection, Owlstone Nanotech Inc., a subsidiary of Advance Nanotech Inc., (OTC BB: AVNA.OB), has garnered a beta testing program with Kidde, which is part of UTC Fire & Security, a business unit of United Technologies Corp. (NYSE: UTX). Owlstone's sensor, serving as a nanofabricated chemical detection system, is being tested for suitability in the next generation of Kidde's safety detection, prevention and protection systems.

The micromachined gas sensor under development, along with its associated electronics and software, will be designed to provide in effect an analytical instrument on a chip, programmable for a range of analytes. The technology holds promise for providing cost-effective detection of volatile organic compounds related to precombustion fire events and indoor air-quality monitoring. Selective detection of these parameters can be difficult to perform inexpensively using existing chemical sensors.

"Our mission is to make the world a safer place," stated Max Allsworth, senior research physicist at Kidde. "Owlstone is developing miniaturized chemical detection sensors that quickly and accurately identify trace elements of toxins, contaminants and chemical agents, something that may play an integral part in making the world safer. We are very excited to investigate how the Owlstone sensor may help Kidde bring new functionality to its industry-leading set of fire detection products."

Owlstone Nanotech has used innovative microfabrication and nanofabrication techniques to create a chemical detection system, purportedly one hundred times smaller and a thousand times cheaper than existing technology. The company partners with key market participants to integrate its technology into commercial applications to allow the efficient and accurate detection of various chemical agents, including contaminants, chemical warfare agents, and potentially harmful gases. The technology could potentially help redefine chemical detection systems and help drive the creation of innovative products across diverse industries.

Owlstone Nanotech's initial commercial product, the Owlstone detector, is a dime-sized device that can be programmed to detect a wide range of chemical agents that may be present in extremely small quantities. The company's technology can offer benefits such as small size, low manufacturing costs, minimal power consumption, reduced false-positives, and a customizable platform.

In the conventional ion mobility spectrometry (IMS) technique, chemical compounds pass down a length of tubing where they are ionized by a strong electric field. The distinctive drift speed and 'kinetic signature' of each molecule allows the sensor to discriminate between compounds with different mobilities.

The IMS technique can have several limitations. In addition to requiring a relatively large physical assembly for the drift tube and ionizing source, the complex physical assembly is fragile and difficult to assemble. The need for a high-ionizing voltage also limits the possibilities for battery-powered mobile and handheld applications.

Owlstone has purportedly surmounted such limitations of IMS via field asymmetric ion mass spectrometry (FAIMS) technology for the next-generation sensing platform based on a set of patented technologies developed in Cambridge by Owlstone.

Fabricated on a microscopic scale using lithographic techniques, the Owlstone solid-state detector serves as a comprehensive analytical sensor built on two silicon chips plus a separate ionization source. One chip is used for the sensor element and the other for the associated electronics. Capable of being manufactured at very low unit cost in large volumes, the Owlstone detector can outperform conventional IMS-based sensors in critical areas of size and weight, reliability, sensitivity, response speed, power consumption, reduce false positives, versatility and cost of manufacture.

In Owlstone's patented FAIMS technology, gas is ionized and passed through the sensing chip. By programming the device with suitable drive signals, individual gases can be detected quickly in very small quantities. The FAIMS approach sorts compounds according to how their charged forms move through a gas when subjected to electric fields. Each substance has its own characteristic smell, or fingerprint. The Owlstone detector acts as a filter; and compounds of interest are filtered and detected, while interfering substances are screened out.

The research on the company's FAIMS technology began at the University of Cambridge (England) in 2001 by three engineering researchers: Andrew Koehl, David Ruiz-Alonso and Billy Boyle. They subsequently spun out the company in early 2004.

Owlstone's detector is fabricated on a microscopic scale, using lithographic techniques where the sensor components are etched on a silicon micro-electromechanical systems substrate. This mode of fabrication can offer a number of advantages over other chemical sensor technologies, such as size, cost and ease of mass production, as well as the sensor's ability to be programmed for a particular application.

The detector's drive signals and signal processing can be 'fine tuned' to recognize the unique signature of virtually any gas--or range of gases--whether airborne or dissolved in water or other fluids. The detector generates a continuous 'spectrum' of information about any chemical agents in its presence. The unique molecular signatures of several chemical compounds can be identified simultaneously, rendering the sensor highly versatile in a wide range of defense/security, medical and industrial applications.

Owlstone chemical sensing technology can address any application that depends on the rapid, cost-effective detection of organic and inorganic chemical agents--whether airborne or in solution. Owlstone is working across the following market segments: defense and security (for example, explosives detection); medical (where there are opportunities in such areas as a breath analyzer to identify volatile compounds produced by disease, such as, for example, acetone, which can be used to monitor diabetes); industrial; environmental; and consumer (for example, a household fire detector for detecting precombustion products formed before the flames begin). They are in discussion with a number of targeted partner companies across such application segments.

Owlstone notes that existing technologies cannot meet the challenges of chemical and explosive detection in such application areas as transport networks, government buildings, public spaces, and financial institutions, with respect to technological capability and cost.

Billy Boyle, director, Owlstone Nanotech, told Sensor Technology that the fabrication process and materials used in Owlstone's gas sensor are similar to those utilized in standard microchip design, allowing for readily ramping-up production to the high volumes required for consumer markets.

Boyle explained that Owlstone's detector technology was designed in response to requirements outlined by US government organizations, such as the Department of Defense and the National Institute of Justice. Such requirements included the desire for a miniature, low-cost detection system as opposed to just a sensor.

Boyle noted that Owlstone has successfully designed and integrated all the components in the detection system, including such subsystems as those for electronics and fluidic handling. Owlstone's design and fabrication approach allows for integrating subsystems to create a miniature, low-cost detection system. The high degree of integration in Owlstone's miniature gas sensor detection system can allow for greatly reducing the cost of manufacturing, Boyle underscored.

"Looking forward to novel applications that demand cost in the region of dollars (advanced smoke detection, indoor air-quality monitors in every office) with a high-performance detection capability," Boyle noted, "I cannot see how it is possible for other FAIMS products to hit the volume price points that we can achieve, and to provide the solutions that we can provide. This is evident when examining the complexity of existing products that require high-voltage electronics, high-power pumps, which impacts unit cost, and, ultimately, limits the ability to use in new applications and deploy in new and novel ways."

Initially, Owlstone is developing a two-chip 'system-in-package' solution to minimize development risk and cost. Once they gain market traction, they would move to a 'system-on-chip' (in which the sensor and electronics would be on a single chip) "in order to supply very large volumes and drive down cost, allowing us to further penetrate consumer markets," Boyle explained.

Boyle indicated that a key issue impacting the development of Owlstone's micro gas detection system is the degree to which particular segments become fully viable and significant markets for their technology. "With the combination of low cost, small size and ease of customization, we are aiming to use our detector in 'game changing' scenarios," he stated. "While we see areas, such as medical diagnostics, advanced smoke detection, and so forth as being exciting high-value opportunities, there is also uncertainty associated with the probability that those markets will be there."

'Proto-product' test and development platforms are now available from Owlstone. Products for commercial use will be available in the third quarter of 2006.

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