Brazilian researchers created ultrasensitive temperature sensor

Publicado em 11 dezembro 2017

Por Joao Moraes

By José Tadeu Arantes / Fapesp Agency 12/07/2017

A "thermometer" of minimum dimensions (in the form of thin film or micrometric or even nanometric particles); able to operate in real time and in very well defined regions (with spatial resolution varying from centimeter to micrometer); and capable of measuring temperatures with exceptional sensitivity in the wide range from 80 Kelvin (K) (193 ° C negative) to 750 Kelvin (476 ° C): this feature already exists.

It is a temperature sensor that practically does not change the temperature of the measured object. The device was created in the laboratory by researchers from the University of São Paulo (USP) and the State University of Campinas (Unicamp) and is in the process of patenting for commercial production.

The sensor was described in an article in the journal Scientific Reports of the Nature group. Those responsible for the novelty are Fernando Alvarez and Diego Scoca (Gleb Wataghin Institute of Physics of Unicamp) and Antonio Ricardo Zanatta (Institute of Physics of São Carlos of USP). The research is supported by FAPESP through the Thematic Project " Research and development of nanostructured materials for electronic applications and surface physics ", coordinated by Alvarez.

"The temperature sensor consists of a system composed of titanium dioxide (TiO2) doped with thallium ions (Tm3 +). By being able to measure a very broad spectrum of temperatures, it can be used both in the sensing of industrial processes, in which the temperature sometimes reaches very high levels, to biological processes, very sensitive to the lowest temperature variations. " Alvarez told. When excited by a laser pulse, the material emits light with a wavelength sensitive to the temperature of the medium in which it is. It is the very precise measurement of the wavelength that allows determining the temperature of the medium.

Material developed at USP and Unicamp, which records temperatures in the range of 80 to 750 Kelvin (from minus 193 ° C to 476 ° C), described in Scientific Reports, can be used in industrial and biological processes.

"The wavelength variation of the light emission is absolutely linear between 80 K and 750 K. And the equipment remains intact and stable throughout this temperature range," Zanatta said. "At this stage, we arranged the material in the form of thin film. With it, it is possible to cover, in theory, any surface: flat, curved, smooth or rough. The material can also be presented as micro or nanoparticles. "

This technological development does not yet exist, but in principle, it would be possible to encapsulate the laser emitter, the temperature sensor, the wavelength detector and a radio communications device within a small dragee.

Swallowed with a little water, the dragee could provide information about the temperature along the digestive tract, until it was eliminated from the organism at the opposite end: a futuristic scenario, but not so far from the science already available.

"A much simpler use, which can be made quickly, is to deposit the sensor material on a plastic substrate and apply it on the skin. Importantly, in addition to being abundant and easy to obtain, titanium dioxide is biocompatible, therefore, non-toxic. It is already used in many prostheses in the medical field, "said Alvarez.

Sensor applications range from the identification of hotspots in electronic equipment to the detection of viral or bacterial infections in specific regions of the body.

In the form of thin film, the material can extend from centimetres to square meters and be applied on the surfaces of components of land vehicles or aircraft or transformers of the electric network. In the form of micrometric or nanometric particles, it may be dispersed in a liquid medium, but remains solid.

The patent process of the sensor is running, with support from Inova Unicamp.

"Because the device is optical, it is possible to obtain information about the temperature of the object of interest without coming into direct physical contact with that object. Simply project a laser beam over the sensor and observe how it responds. By measuring the wavelength of the light emitted by the sensor by means of a detector, it is possible to determine, with great precision, the temperature of the object, "said Zanatta.

The wavelength range is approximately 2 picometers (2x10-12 m) per degree of temperature. By means of spectroscopy, this minimum wavelength variation can be recorded by the detector. However, the need for a detector, dedicated to making the record, constitutes, at the current stage, one of the limiting factors, both in terms of cost and a greater portability of the device.

"Today, the associated instrumentation is expensive, because a laser and a detector are needed. But we believe that as technology advances, it will be possible to make an integrated device, bringing together semiconductor laser, temperature sensor and detector. And from the laboratory scale to the industrial scale, we can cost a lot, "Zanatta said.

The article A suitable (wide-range + linear) temperature sensor based on Tm3 + ions (doi: 10.1038 / s41598-017-14535-1), by AR Zanatta, D. Scoca and F. Alvarez, can be read here (Click)