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Optically Based T-Sensor Could Be Used in Manufacturing, Biomedicine

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SÃO PAULO, Jan. 24, 2018 — A temperature-sensor (T-sensor) has been developed that is capable of precisely measuring temperatures in a wide band — between 80 Kelvin (−190 °C) and 750 Kelvin (476 °C). The ultrasensitive sensor, created in the laboratory by researchers at the University of São Paulo (USP) and the University of Campinas (UNICAMP) in São Paulo,  is optically based and produces minimal (if any) disturbance on the regions it probes.

Ultra-sensitive optical temperature sensor, University of Sao Paulo and University of Campinas.
Material measures temperatures in the range of 80-750 kelvin (-193 °C to 476 °C) and could be used in manufacturing and biological processes. Courtesy of the research team from University of São Paulo (USP) and the University of Campinas (UNICAMP).

When excited by a laser pulse, the sensor, which consists of a system made of titanium dioxide (TiO2) doped with thulium ions (Tm3+), emits light at wavelengths that vary depending on the temperature of the environment. A precise measurement of the wavelength is taken to determine the temperature.

“Because the device is optical, information on the temperature of the object of interest can be obtained without direct physical contact between them. It suffices to 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, the temperature of the object can be determined with great precision,” said USP researcher Antonio Ricardo Zanatta.

The wavelength varies approximately 2 picometers (2 x 10−12 m) per degree of temperature. The research team used spectroscopy to detect this tiny wavelength variation.

“Variation in the wavelength of the emitted light is absolutely linear between 80 and 750 Kelvin, and the device remains integral and stable throughout this temperature range,” Zanatta said.

Where applicable, researchers compared the spectroscopic data of the Tm3+ ions with those of the well-established pressure- and T-sensor ruby. Experimental results indicated that the Tm3+-related wavelength shift was linear and required almost no spectra deconvolution-analysis. Also, the Tm3+ ions exhibited a smaller blue-shift, though over a considerable dynamic range (83 to 750 Kelvin).

Researchers believe that the experimental results suggest the suitability of the TiO2: Tm3+ system as an optically based T-sensor that could be used over a wide linear dynamic range.

The sensor could be used for a range of applications, from the identification of hotspots in electronic equipment to the detection of infection in specific regions of an organism.

“Because it’s capable of measuring a very broad spectrum of temperatures, it can be used in manufacturing — where temperatures sometimes reach very high levels — as well as biological processes, which are highly sensitive to the slightest temperature variations,” said Fernando Alvarez, a researcher from UNICAMP.

“At this stage, we’ve arranged the material in the form of a thin film. Theoretically, this can be used as a coating for any surface, be it flat or curved, smooth or rough,” said Zanatta, noting that the material could also be presented as microparticles or nanoparticles.

As a thin film, the material could be made as small as a few square-centimeters or as large as several square-meters, for use as a surface coating on components in land vehicles, aircraft or power grid transformers. As micrometric or nanometric particles, the material could be dispersed in a liquid medium while remaining solid.

In principle, it would be possible to encapsulate the laser emitter, temperature sensor and wavelength detector with a radio communicator inside a small pill. When swallowed, the pill would transmit temperature data while moving along the digestive tract until its ejection from the organism.

“A very simple application, which could rapidly be made feasible, would entail coating a plastic substrate with the sensor and fixing it to a patient’s skin. It’s important to note that titanium dioxide is abundant, easy to obtain and biocompatible, i.e., non-toxic. It’s already used in many medical prosthetic devices,” Alvarez said.

In its present state, the T-sensor requires a dedicated detector — a limiting factor in terms of both the cost and portability of the device.

“The associated instrumentation is costly today, given the need for a laser and a detector,” Zanatta said. “We believe, however, that as technology advances, it will be possible to fabricate an integrated device with a semiconductor laser, temperature sensor and detector. And the cost can be considerably reduced when we go from laboratory to industrial scale.”

A patent application form for commercial production has been filed with support from UNICAMP’s incubator, the Inova UNICAMP.

The research was published in Scientific Reports (doi:10.1038/s41598-017-14535-1).
Jan 2018
fluorescence spectroscopy
The spectroscopic study of radiation emitted by the process of fluorescence.
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