A laser and detector in one: a microscopic sensor has been developed at TU Wien, which can be used to identify different gases simultaneously.
As humans, we sniff out different scents and aromas using chemical receptors in our noses. In technological gas detection, however, there are a whole host of other methods available. One such method is to use infrared lasers, passing a laser beam through the gas to an adjacent separate detector, which measures the degree of light attenuation it causes. TU Wien’s tiny new sensor now brings together both sides within a single component, making it possible to use the same microscopic structure for both the emission and detection of infrared radiation.
Circular quantum cascade lasers
“The lasers that we produce are a far cry from ordinary laser pointers ,” explains Rolf Szedlak from the Institute of Solid State Electronics at TU Wien. “We make what are known as quantum cascade lasers. They are made up of a sophisticated layered system of different materials and emit light in the infrared range.”
When an electrical voltage is applied to this layered system, electrons pass through the laser. With the right selection of materials and layer thicknesses, the electrons always lose some of their energy when passing from one layer into the next. This energy is released in the form of light, creating an infrared laser beam.
“Our quantum cascade lasers are circular, with a diameter of less than half a millimetre,” reports Prof. Gottfried Strasser, head of the Center for Micro- and Nanostructures at TU Wien. “Their geometric properties help to ensure that the laser only emits light at a very specific wavelength.”
“This is perfect for chemical analysis of gases, as many gases absorb only very specific amounts of infrared light,” explains Prof. Bernhard Lendl from the Institute of Chemical Technologies and Analytics at TU Wien. Gases can thus be reliably detected using their own individual infrared ‘fingerprint’. Doing so requires a laser with the correct wavelength and a detector that measures the amount of infrared radiation swallowed up by the gas.
A laser that also detects
“Our microscopic structure has the major advantage of being a laser and detector in one,” professes Rolf Szedlak. Two concentric quantum cascade rings are fitted for this purpose, which can both (depending on the operating mode) emit and detect light, even doing so at two slightly different wavelengths. One ring emits the laser light which passes through the gas before being reflected back by a mirror. The second ring then receives the reflected light and measures its strength. The two rings then immediately switch their roles, allowing the next measurement to be carried out.
In testing this new form of sensor, the TU Wien research team faced a truly daunting challenge: they had to differentiate isobutene and isobutane – two molecules which, in addition to confusingly similar names, also possess very similar chemical properties. The microscopic sensors passed this test with flying colours, reliably identifying both of the gases.
“Combining laser and detector brings many advantages,” says Gottfried Strasser. “It allows for the production of extremely compact sensors, and conceivably, even an entire array – i.e. a cluster of microsensors – housed on a single chip and able to operate on several different wavelengths simultaneously.” The application possibilities are virtually endless, ranging from environmental technology to medicine.
Learn more: The quantum sniffer dog
A NIMS research team developed a new mass analysis technique that operates under a completely different principle from that of conventional mass analysis techniques.
- An ICYS-MANA researcher, Kota Shiba, International Center for Young Scientists (ICYS), National Institute for Materials Science (NIMS), and Genki Yoshikawa, a Group Leader of the Nanomechanical Sensors Group, International Center for Materials Nanoarchitectonics (MANA), NIMS, developed a new mass analysis technique that operates under a completely different principle from that of conventional techniques. The new technique can be performed even with a hand-held paper strip, applying gas flow to the strip at a constant flow rate, causing the strip to deform, and calculating the molecular weight of the applied gas based on the principle that the amount of deformation (deflection) varies according to molecular weight of the applied gas. The technique enables users to measure molecular weights of gaseous samples in the air in real time. The principle behind the technique appears to be very simple, but no one had reported it before. This discovery can be a breakthrough for the development of much smaller and inexpensive mass analysis devices than conventional ones.
- Mass analysis is a technique for analyzing molecular weights of samples, and this scientific method drew much public attention when Dr. Koichi Tanaka won a Nobel Prize in 2002. Conventionally, the molecular weight of a sample is measured by first ionizing the molecules through, for example, irradiation of electrons in a vacuum. Then, an electric or magnetic field is applied to these ions and their molecular weights are measured based on the principle that the ions travel in different directions according to their molecular weights. As also demonstrated by Dr. Tanaka’s research, this basic principle still remains valid in essence today since the time when the first mass analyzer was constructed in early 20th century. Although the molecular weights of samples can be accurately measured by conventional mass analyzers, it had been difficult to make these devices smaller due to the requirements of vacuum condition and ionization.
- The research team recently discovered a principle unused in conventional mass analysis, and developed a new kind of mass analysis technique based on the principle, which enables users to easily measure the molecular weights of gases in real time without a vacuum condition or ionization. The new principle indicates that when gaseous molecules flow toward a one-end-fixed elastic object, they cause the object to deflect, and the amount of deflection varies depending on the weight of the molecules. The team in fact experimentally confirmed that when gases were flowed toward a silicon micro-cantilever and a paper business card, the amount of deflection produced in these objects varied depending on the molecular weights of the applied gases. Figure illustrates that the molecular weights of gaseous samples were determined simply by flowing the gases toward the micro-cantilever and measuring its deflection. The team also successfully developed an analytical model of the relationship between the amount of deflection and the molecular weight of gases through the combination of basic principles in fluid dynamics, thermodynamics, and structural mechanics. In this manner, the team theoretically proved the validity of the proposed principle. Subsequently, the invented technique was named as “aero-thermo-dynamic mass analysis (AMA).”
- Based on these results, the research team intends to develop mobile mass analysis devices and apply them to various fields including health management, environmental monitoring, and disaster prevention. The team will also promote the use of AMA in the industrial sector through the integration with other techniques, such as gas chromatography, for process management etc.
Made of pure copper, the ultra-thin ‘shell’ conceals sensors from remote inspection while still allowing them to probe the exterior environment
A team of researchers from the National University of Singapore (NUS) has invented a novel camouflage technique that effectively hides thermal and electronic sensors without compromising performance. Led by Assistant Professor Qiu Cheng-Wei from the Department of Electrical & Computer Engineering at NUS Faculty of Engineering, the team created the world’s first multifunctional camouflage shell that renders sensors invisible in both thermal and electric environments.
Current technologies which make sensors ‘invisible’ usually also make them ineffective, while others only work in specific physical fields (i.e. either thermal or electrical). Over the past ten months, the NUS team has experimentally demonstrated that they could hide sensors in both thermal and electric fields without them being detected. The invisible sensors are also able to continue to probe on the environment while ‘under cover’.
Asst Prof Qiu explained, “We have designed a camouflage ‘shell’ that not only mimics surrounding thermal fields but also electric fields, both at the same time. The object under camouflage becomes truly invisible as its shape and position cannot be detected in terms of both thermal and electric images.”