J.D. Aguilera, P. de la Presa, P. Marín, M.C. Horrillo, D. Matatagui
he XIII European Magnetic Sensors and Actuators Conference (EMSA 2022)
Del 5 al 8 de julio de 2022, Madrid, España.
We built an innovative sensor based on the interaction between nanostructures and gases using spin waves to detect the induced magnetic changes (Fig. 1). The device is sensitive to low gas concentration of acetone, ammonia, carbon monoxide and benzene. The presence of these substances in human breath is related to different metabolic mechanisms, so they could be used to diagnose complex diseases like cancer [1]. When traces of these gases diluted in air pass through magnetic nanoparticles, which are contained in a 2 mm diameter teflon tube, the magnetic properties of the nanostructures are modified. This variation is detected by means of spin waves: due to the known dependence of their propagation on the external field [2], their frequency will shift as the nanoparticles’ properties change. These excitations propagate along the surface of a 2 μm thick epitaxial film made of YIG (Yttrium Iron Garnet), a ferrimagnetic insulator with a quite narrow magnetic resonance line. The frequency of the spin waves is detected by means of an oscillator circuit connected to a frequency counter.
The device was exposed to the target gas for one minute, then purged with pure air for nine minutes. The active material consists in 30 nm diameter magnetite (Fe3O4) nanoparticles. The sensitivity of the equipment is under 50 ppm of the reducing gases acetone, ammonia, carbon monoxide and benzene. An important feature is the selectivity of nanoparticles: different gases show high differenced affinities (adsorption and desorption rates), particularly in benzene case (Fig. 2). This fact implies that a sensor array with many different nanostructures could be built to analyze complex gas mixes. Besides, the magnetic nanoparticles are reusable few minutes after each measurement, although in few cases the purge time should be longer to bring the nanoparticles back to their initial state. The results show the possibility of developing new inexpensive, reusable, contactless magnetic sensors employing spin waves as mechanism of transduction. Considering the low concentrations of the target gases, the outcome of this novel experiment is rather promising.
References:
[1] W. Miekisch, J. Schubert, and G. F. E. Noeldge-Schomburg, Diagnostic potential of breath analysis— focus on volatile organic compounds, Clin.Chim. Acta 347 (2004), 25–39.
[2] J. R. Fragoso and D. Matatagui, Bicapas de guías magnónicas para el procesamiento de señales, Universidad Nacional Autónoma de Mexico, 2016.
