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Researchers create ultrasensitive temperature sensor

Material was described in the journal Scientific Reports and can be used in industrial and biological processes

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A “thermometer” of minimal dimensions (in the form of a thin film or micrometric or even nanometric particles); able to operate in real time and in very well-defined regions (with spatial resolution ranging from centimeters to micrometers); and capable of measuring temperatures with exceptional sensitivity, in the wide range of 80 Kelvin (K) (minus 193 ºC) to 750 Kelvin (476 ºC): this resource 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 being patented for commercial production.

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

Photo: Scarpa
Professor Fernando Alvarez, coordinator of the thematic project

“The temperature sensor consists of a system composed of titanium dioxide (TiO2) doped with thulium ions (Tm3+). Because it is capable of measuring a very broad spectrum of temperatures, it can be used both in sensing industrial processes, in which the temperature sometimes reaches very high levels, and even biological processes, which are very sensitive to the smallest temperature variations”, Alvarez told FAPESP Agency.

When excited by a laser pulse, the material emits light with a wavelength sensitive to the temperature of the medium in which it is found. It is the very precise measurement of wavelength that allows the temperature of the medium to be determined.

“The variation in the wavelength of light emission is absolutely linear between 80 K and 750 K. And the equipment remains intact and stable throughout this range of temperatures,” said Zanatta. “At this stage, we have the material in the form of a 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 communicator inside a small pill.

Photo: Reproduction
Antonio Ricardo Zanatta, from the São Carlos Institute of Physics at USP | Photo: Disclosure

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

“A much simpler use, which can be quickly implemented, is to deposit the sensor material on a plastic substrate and apply it to the skin. It is important to highlight that, in addition to being abundant and easy to obtain, titanium oxide is biocompatible and therefore non-toxic. It is currently used in many prosthetics in the medical field,” said Alvarez.

The sensor's applications range from identifying hotspots in electronic equipment until the detection of viral or bacterial infections in specific regions of the body.

In the form of a thin film, the material can extend from centimeters to square meters and be applied to the surfaces of components of land vehicles or aircraft or power grid transformers. In the form of micrometric or nanometric particles, it can be dispersed in a liquid medium, whilst remaining solid.

Photo: Scarpa
Diego Scoca, from the Unicamp Physics Institute

The sensor patent process is underway, 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 onto the sensor and observe how it responds. By measuring the wavelength of the light emitted by the sensor using a detector, it is possible to determine, with great precision, the temperature of the object,” said Zanatta.

The wavelength variation is approximately 2 picometers (2x10-12 m) per degree of temperature. Through spectroscopy, this minimum wavelength variation can be recorded by the detector. However, the need for a detector, dedicated to recording, constitutes, at the current stage, one of the limiting factors, both in terms of cost and 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 a semiconductor laser, temperature sensor and detector. And, moving from the laboratory scale to the industrial scale, we will be able to make costs much cheaper,” said Zanatta.

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 at: and www.nature.com/articles/s41598-017-14535-1.epdf .

 

JU-online cover image
The sensor: very precise wavelength measurement allows you to determine temperature | Photo: Antonio Scarpinetti

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