Browsing by Subject "Temperature measurement"
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Item Open Access Absolute temperature monitoring using RF radiometry in the MRI scanner(Institute of Electrical and Electronics Engineers, 2006) El-Sharkawy, A.-M. M.; Sotiriadis, P. P.; Bottomley, P. A.; Atalar, ErginTemperature detection using microwave radiometry has proven value for noninvasively measuring the absolute temperature of tissues inside the body. However, current clinical radiometers operate in the gigahertz range, which limits their depth of penetration. We have designed and built a noninvasive radiometer which operates at radio frequencies (64 MHz) with ∼100-kHz bandwidth, using an external RF loop coil as a thermal detector. The core of the radiometer is an accurate impedance measurement and automatic matching circuit of 0.05 Ω accuracy to compensate for any load variations. The radiometer permits temperature measurements with accuracy of ±0.1°K, over a tested physiological range of 28°C-40 °C in saline phantoms whose electric properties match those of tissue. Because 1.5 T magnetic resonance imaging (MRI) scanners also operate at 64 MHz, we demonstrate the feasibility of integrating our radiometer with an MRI scanner to monitor RF power deposition and temperature dosimetry, obtaining coarse, spatially resolved, absolute thermal maps in the physiological range. We conclude that RF radiometry offers promise as a direct, noninvasive method of monitoring tissue heating during MRI studies and thereby providing an independent means of verifying patient-safe operation. Other potential applications include titration of hyper- and hypo-therapies.Item Open Access Comments on "Ensuring Safety of Implanted Devices Under MRI Using Reversed Polarization"(Wiley, 2011-10-24) Eryaman, Y.; Hersek, S.; Atalar, ErginItem Open Access Effect of the superconductivity transition on the response of YBCO edge transition bolometers(2003) Bozbey, Ali; Fardmanesh, Mehdi; Askerzade, I. N.; Banzet, M.; Schubert, J.Dependence of the phase and magnitude of the response of Y-Ba-Cu-O edge transition bolometers on the superconducting transition is studied. The responses of both large and small area devices were investigated and several anomalies are observed. The response of small area LaAlO3 devices considerably differed from that expected based on the dR/dT curve. This discrepancy is observed to be strongly dependent on the superconducting transition. Both the phase and magnitude/(dR/dT) of the response of the devices showed abrupt changes for below the Tc-onset when measured versus temperature, while the phase variation also showed strong dependence on the modulation frequency. We present the analysis and propose mechanisms responsible for the modulation frequency dependence of the response characteristics versus temperature, within the superconductivity transition region of the devices.Item Open Access Electronic structure, insulator-metal transition and superconductivity in K-ET2X salts(1998) Ivanov V.A.; Ugolkova, E.A.; Zhuravlev, M.Ye.; Hakioǧlu, T.The electronic structure and superconductivity of layered organic materials based on the bis(ethylenedithio)tetrathiafulvalene molecule (BEDT-TTF, hereafter ET) with essential intra-ET correlations of electrons are analysed. Taking into account the Fermi surface topology, the superconducting electronic density of states (DOS) is calculated for a realistic model of K-ET2X salts. A d-symmetry of the superconducting order parameter is obtained and a relation is found between its nodes on the Fermi surface and the superconducting phase characteristics. The results are in agreement with the measured non-activated temperature dependences of the superconducting specific heat and NMR relaxation rate of central 13C atoms in ET. © 1998 John Wiley & Sons, Ltd.Item Open Access RF radiometery sensor sensitivity and detection profile(IEEE, 2008-11) El-Sharkawy, A.-M.M.; Sotiriadis, P. P.; Bottomley, P. A.; Atalar, ErginTemperature sensing using microwave radiometry has proven value for non-invasively measuring the absolute temperature of tissues inside the human body. However, current clinical radiometers operate in GHz or infrared frequency ranges; this limits their depth of penetration since the human body is not "transparent" at these frequencies. To address this problem, we have previously designed and built an advanced, near-field radiometer operating at VHF frequencies (64MHz) with a ∼100 KHz bandwidth. The radiometer has performed accurate temperature measurements to within ±0.1°C, over a tested physiological range of 28-40°C in saline phantoms whose electric properties match those of human tissue. In this work we analyze radiofrequency (RF) coil designs suitable for RF Radiometry. We investigate the coil profile sensitivity to look where temperature information is coming from and the depth of penetration associated with the receiver used. We also look into the virtues of using multi-turn coils versus single loop coils. We conclude that by using multi-turn coils the received noise signal is more sensitive to sample noise and temperature can be estimated more accurately especially with the use of smaller receivers. © 2008 IEEE.Item Open Access Sorption studies of Cs+ and Ba2+ cations on magnesite(Elsevier, 1998-05-11) Shahwan, T.; Süzer, Şefik; Erten, H. N.The adsorption behavior of Cs+ and Ba2+ cations on magnesite has been studied as a function of time, cation concentration and temperature, utilizing both the radiotracer method and X-ray photoelectron spectroscopy (XPS). Saturation was approached in about I day for both cations. The sorption data were found to follow Freundlich type isotherms. Sorption of both Cs+ and Ba2+ cations were found to be exothermic in nature with ΔH0 (kJ/mol) of -37, -13 and ΔS0 (kJ/mol·K) of -0.09, -0.009, respectively. Negative ΔG0 values were obtained for both cations, indicating the spontaneity of their sorption on magnesite. The magnitude of ΔG0 suggest that ion exchange is the dominating sorption mechanism. The adsorption behavior of Cs+ and Ba2+ cations on magnesite has been studied as a function of time, cation concentration and temperature, utilizing both the radiotracer method and X-ray photoelectron spectroscopy (XPS). Saturation was approached in about 1 day for both cations. The sorption data were found to follow Freundlich type isotherms. Sorption of both Cs+ and Ba2+ cations were found to be exothermic in nature with ΔH0 (kJ/mol) of -37, -13 and ΔS0 (kJ/mol·K) of -0.09, -0.009, respectively. Negative ΔG0 values were obtained for both cations, indicating the spontaneity of their sorption on magnesite. The magnitude of ΔG0 suggest that ion exchange is the dominating sorption mechanism.