The discussion on expiration dates (best before and use by) has been going on for many years now, mainly because of their impact on food waste. Expiration dates are hard to estimate, and moreover dependent on the circumstances in which the products are transported and preserved. Real time supervision of the quality of a food package’s content is still a somewhat far-fetched dream, but realizing this would allow a substantial reduction in food waste and therefore lead to not only an economical but also an important ecological breakthrough.
This dream is slowly starting to become real, with a new millimetric scale system that is developed within the TERAFOOD project (https://terafood.iemn.fr/). The system uses light at TeraHertz(THz) frequencies to monitor the chemical content of the headspace of a food package in real time. The advantageous properties of THz frequencies are that they can go through almost all types of packaging materials, but also strongly interact with most volatile organic compounds (VOCs) that form during food spoilage. This THz food sensor uses a so-called photoacoustic technique converting a THz signal into an easier detectable acoustical signal (sound)1.
What’s unique in this TERAFOOD project, is the scale in which the sensor can be produced. Using a Silicium-based chipscale technologynot only allows for a compact technology but also for parallelizedchipscale mass manufacturing which enables a reduction of costs. However, a disadvantage of this Silicium-based chip is that it can be defined as a glass particle, which is not allowed in food packaging. Although a promising technology, it will not be ready for implementation just yet.
How does the sensor work?
The TERAFOOD sensor is based on a triply resonant mechanism (patent pending) to achieve an enhancement of the measured signals. An important first step towards such an integrated sensor is the realization of a Si-waveguide to control the propagation of the light on the chip at frequencies that cover the absorption lines of typical spoilage gases (ammonia, hydrogen sulfide, ethanol).
The dimensions chosen for this waveguide confine and guide the light at frequencies between 500 GHz and 3 THz, a frequency range containing many spectral linesof these VOCs. In order to guide this light efficiently inside the silicon layer, a “suspended” beam of just a few hundredths of mm2 has been realized using advanced clean room techniques by engineers of Vmicro, a start-up company and partner in the TERAFOOD consortium.