ChIMES (Chemical Identification by Magneto-Elastic Sensing) is a passive chemical sensing technology that can detect a very broad range of substances. The technology consists of a sensing element and a separate electronic package; the two components can communicate wirelessly through a metallic or nonmetallic barrier. Configurations can be built for real-time or persistent readout, and, with relatively small modifications, the system can function as a radiation detector. The electronics package is being miniaturized and is energy-efficient enough to power with onboard batteries. Both the chemical and radiation sensor versions have been demonstrated experimentally, and both have been patented.
The sensing element is tiny - the current design is 12.7 mm in length and 3.8 mm in diameter - and consists of a magneto-elastic wire hard-coupled to a “target response material” (TRM); the device can be produced by hand or through conventional manufacturing techniques. The wires are formed from alloys containing one or more ferromagnetic elements; one or more glass-forming elements; and sometimes small amounts of other elements such as Cr, Mn, Al, Cu, and Nb for enhancement of mechanical, magnetic, or anticorrosive properties. The cost of a sensing element could be as small as a few dollars, making ChIMES much less expensive than techniques such as gas chromatography.
The principle of operation is simple: the TRM expands when it encounters a targeted material and imposes stress upon the wire, changing its magnetic permeability. Using an excitation-detection coil set, the changes in permeability are observed by switching the magnetic domains in the wire and measuring the modifications in the Faraday voltage as the stress is varied.
Conceptually, a ChIMES sensor can be built for any target for which a TRM can be found. TRMs can come from many classes of chemical and biochemical compounds, with many degrees of selectivity. TRMs with strong affinities for specific targets, like aptamers and antibodies, can be used individually, whereas TRMs with distributed selectivity, such as polymer composites, can be formed into arrays with an artificial neural network or other machine-learning tool used for interpretation. Possible applications include explosives or taggants; chemical and biological warfare agents, and precursors or byproducts of their manufacture; exhaled gas constituents for health diagnostics and drug detection; toxic industrial chemicals and materials; food freshness and safety; volatile organic compounds; and other airborne and waterborne pollutants.
The separation of the sensing element and the electronics system in ChIMES offers exceptional latitude in tailoring the sensor to suit a specific application. For example, there are many situations in which penetrations into an environment are unwanted or infeasible because of health, safety, or environmental concerns, such as following the decomposition of a dangerous material in a sealed container. Covert applications are possible, since a sensing element could be deployed in a suspect environment and then retrieved for later analysis. And, because the sensor bodies contain just two components (and epoxy), they are much simpler than alternatives like radio frequency identification (RFID) tags, which incorporate memory, radio chips, and antennas.