Infrared sensors with application in infrastructures security

Project’s objectives

The main objective of this project is to develop non-dispersive optical sensors, having high sensitivity, to operate within the infrared spectral range. These sensors can be used for hazardous gas detection in industrial buildings to increase the security level of this type of infrastructures.

The main advantage of the proposed sensors is their high selectivity with respect to the types of gases detected (calibration on absorption spectral range specific to gas of interest – e.g. methane, carbon monoxide / carbon dioxide), which will reduce the risk of false negative or false positives signals.

The innovative side of the proposed project is based on achieving a high selectivity for the sensor by overlaying very precisely the spectral characteristic of the infrared source and the detector response that has the gas absorption bands in the Mid-IR range (3 μm – 8 μm). The novelty of this project consists in the application of a new concept in photonics, namely the metasurface, for controlling and adjusting the spectral characteristic (reflection, transmission, absorption, emission) of a micro / nanostructured surface.

Partners

IMT

National Institute for Research and Development in Microtechnologies (coordinator) (IMT)

www.imt.ro
INFLPR

National Institute for Laser, Plasma and Radiation Physics (INFLPR),

www.inflpr.ro

IMT is responsible for design of plasmonic metasurfaces, developing gas sensors and of related manufacturing technologies. INFLPR carries out the optical and mechanical tests and characterizations, including calibration of the sensor.

Results

During the Phase I the following activities were carried out:

  • the specifications of each component of the gas detection system were obtained together with the corresponding schemes.
  • two types of Fresnel lenses were designed to collimate radiation from the source and to focus the beam on the commercial gas detector.
  • different types of absorbing metasurface have been also studied to obtain the selective radiation sources and, at the same time, various geometries configured on three types of substrates, obtaining maximum absorption for several gases of interest.
  • moreover, at this stage, a technological flow necessary for the manufacturing of the desired structures was proposed;
  • the first technological tests were carried out, thus obtaining resistors based on meanders and metasurfaces made of circular resonators. The techniques used for this purpose were photolithography, lift-off method, sputtering or atomic layer deposition.
  • based on manufactured test structures, the experimental setups were developed to characterize the components of the gas sensor.

 

The project preliminary results obtained at this stage were presented at international conferences/workshops by our team younger researchers, Roxana Tomescu (project responsible, IMT), Laura Mihai (project responsible, INFLPR) and Bodgan Călin (INFLPR).

 

In addition, three new research assistant positions were occupied within the project: 2 positions – IMT-Bucharest and 1 job position – CETAL-INFLPR. The new researchers have the opportunity to use new generation equipment for simulation, design, manufacturing and characterization of developed system within the project, at the new research infrastructures CENASIC/IMT and CETAL-PhIL/INFLPR.

An example of metasurface with gold cylindrical resonators on Al2O3 substrate:

a) the sketch of the structure

b) the structure layout used in simulations

  1. c) the electromagnetic field distribution inside of metasurface.

Detection of proposed system: at the level of the thermal emission source, an electric current is applied which determines the heating of the resistance by Joule effect. The specifically tailored  metasurface, placed directly over the classical thermal source, will absorb all the radiation spectrum emitted and will filter and transmit to the detector wavelengths specific to the absorption lengths of the different gases that are found in industrial infrastructures; Fresnel lenses are used to collimate the radiation, and a commercial detector will be used for the radiation detection emitted by the selective source.

Three components of the proposed system were technologically fabricated and characterized during 2019: the large-spectrum radiation source, the metasurface specifically configured and the Fresnel lenses. In order to optimize the geometries and technological processes used, the following objectives were achieved:

  1. Design and simulation of a classical thermal source (resistor): using two different simulation approaches: i) using the Ansys Icepack software and applying a power of 0.2 or 4W; ii) using the COMSOL Multiphysics software and applying a voltage of 10V. Thus, the used materials, geometry (2 or 3 meander configurations with narrow or wide pads) and its area (1cm2) were established;
  2. The geometry of the absorbent metasurfaces configured specifically for absorption at certain wavelengths has been established;
  3. Fresnel lenses have been designed to operate at specific wavelengths, taking into account the results of metasurface absorption measurements (3.3 µm, 4.25 µm, 5.25 µm).
  4. Specific technological flows were established, followed by the fabrication and morphological characterization of the three components necessary for the development of the proposed gas detection system;
  5. The absorption of the metasurface as well as the emission of the radiation sources were measured.

Figure 1 Scheme of the gas detection system

Figure 2 Components of the thermal radiation source: a) Platinum resistance consists of 2 meanders (layout) and images of the obtained technologically resistor consists of 3 meanders; b) Proposed metasurfaces used as perfect absorber (layout and SEM image)