Near-Infrared Temperature Measurement Technique for Water Surrounding an Induction-heated Small Magnetic Sphere

Summary

A technique utilizing wavelengths of 1150 and 1412 nm to measure the temperature of water surrounding an induction-heated small magnetic sphere is presented.

Abstract

A technique to measure the temperature of water and non-turbid aqueous media surrounding an induction-heated small magnetic sphere is presented. This technique utilizes wavelengths of 1150 and 1412 nm, at which the absorption coefficient of water is dependent on temperature. Water or a non-turbid aqueous gel containing a 2.0-mm- or 0.5-mm-diameter magnetic sphere is irradiated with 1150 nm or 1412 nm incident light, as selected using a narrow bandpass filter; additionally, two-dimensional absorbance images, which are the transverse projections of the absorption coefficient, are acquired via a near-infrared camera. When the three-dimensional distributions of temperature can be assumed to be spherically symmetric, they are estimated by applying inverse Abel transforms to the absorbance profiles. The temperatures were observed to consistently change according to time and the induction heating power.

Introduction

A technique to measure temperature near a small heat source within a medium is required in many scientific research fields and applications. For example, in the research on magnetic hyperthermia, which is a cancer therapy method using electromagnetic induction of magnetic particles, or small magnetic pieces, it is critical to accurately predict the temperature distributions generated by the magnetic particles^1,2. However, although microwave^3,4, ultrasound^5,6,7....

Protocol

1. Experimental Setup and Procedures

Prepare an optical rail to mount a sample and optics for NIR imaging as follows.

1. Sample preparation.
   Note: When using water or aqueous liquid, do Step 1.1.1. When using an aqueous gel with high viscosity, do Step 1.1.2.
   1. Steel sphere setting in water.
      1. Fix a 2.0-mm-diameter steel sphere to the end of a thin plastic string using a small amount of glue.
      2. Hang the steel sphere at the center of the rectangular glass cell with an optical path length of 10.0 mm, a width of 10 mm, and a height of 45 mm (Figure 3).....

Results

Images of ΔA_i(x, z) at λ = 1150 nm for a 2.0-mm-diameter steel sphere in water and at λ = 1412 nm for a 0.5-mm-diameter steel sphere in maltose syrup are presented in Figure 5a and Figure 6a, respectively. In both cases, the sphere was located 12 mm below the bottom of the coil along its central axis. Figure 5

Discussion

The technique presented in this paper is a novel one using the temperature dependence of NIR absorption of water and presents no significant difficulty in setting up the necessary equipment and implementation. The incident light can be easily produced by using a halogen lamp and an NBPF. However, lasers cannot be used, because coherent interference patterns would appear on the images. Common optical lenses and glass cells for visible-light use can be used, as they transmit an adequate amount of light at λ =.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Induction heating system	CEIA, Italy	SPW900/56	780 kHz, 5.6 kW (max).
Coil	SA-Japan	custom	Water-cooled copper tube; two-turn; outer dia. 28 mm.
Water chiller	Matsumoto Kikai, Japan	MP-401CT
Halogen lamp	Hayashi Watch-Works, Japan	LA-150UE-A
Narrow bandpass filter for λ = 1150 nm	Andover	115FS10-25	Full width at half-maximum (FWHM): 10 nm.
Narrow bandpass filter for λ = 1412 nm	Andover	semi-custom	Full width at half-maximum (FWHM): 10 nm.
Bandpass filter for λ = 850−1300 nm	Spectrogon	SP-1300
Bandpass filter for λ = 1100−2000 nm	Spectrogon	SP-2000
NIR camera	FLIR Systems	Alpha NIR	InGaAs
Image acquisition software	FLIR Systems	IRvista
Image processing software	NIH	ImageJ	ver. 1.51r
Image processing software	MathWorks	Matlab	ver. 2016a
Telecentric lens	Edmond Optics	55350-L	X1
Steel sphere (0.5 mm dia.)	Kobe Steel, Japan		Fe-1.5Cr-1.0C-0.4Mn (wt %)
Steel sphere (2.0 mm dia.)	Kobe Steel, Japan		Fe-1.5Cr-1.0C-0.4Mn (wt %)
Maltose syrup as aqueous gel	Sonton, Japan	Mizuame	Food product