Response of Insulated Electric Field Probes in Finite Heterogeneous Biological Bodies

Mousavinezhad, S. Hossein; Chen, K.-M.; Nyquist, D.P.

doi:10.1109/tmtt.1978.1129444

Cited by 5 publications

(2 citation statements)

References 12 publications

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“…muscle, and that for other tissue types the accuracy may differ. However, as indicated by the work of Smith 10 and Mousavinezhad et al 11 , the response of a well insulated E-field sensor (ratio insulation to probe thickness minimal 1.5) is independent of the dielectric characteristics of the surrounding tissue as long as the dielectric constant of the tissue is at least five times greater than that of the insulating material. Hence, for use of the Schottky diode sheet under clinical conditions it might be desirable to increase the probe insulation thickness to meet the above criteria and in order to have a sensor with a low dependency on tissue variations.…”

Section: Discussionmentioning

confidence: 99%

Accuracy of electrical field measurement using the flexible Schottky diode sheet at 433 MHz

Rhoon

Ameziane

Lee

et al. 2003

International Journal of Hyperthermia

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In this study, the accuracy of Schottky diode sensors mounted as a two-dimensional array on a flexible 125 micro m thick polyester foil has been studied. The diodes are placed at a distance of 2.5 x 2.5 cm, resulting in a measuring area of 20 x 20 cm. The diodes are placed across the gap between both arms (3 x 5 mm) of a dipole, total length 12 mm. High resistance (1 M Omega/m) carbon transmission lines printed on the sheet are used to connect each electrical (E) field sensor to the read-out electronics and a data-acquisition system. It is demonstrated that the flexible Schottky diode sheet can quantitatively measure E-field distributions at 433 MHz with an overall accuracy of approximately 6% (1 SD). The largest contribution to the inaccuracy is related to the phantom heterogeneity. The absolute sensitivity of this electrical field sensor is 0.71 V/m per V/m of the applied external electromagnetic field. The DC-voltage signal of the diodes shows a more or less square root relation to the RF-power applied to the applicator over a 15-fold range. An important feature of the system is that it provides the ability to perform on-line monitoring of the E-field, i.e. the SAR distribution of 433 MHz applicators. Further, it enables the introduction of fast and easy quality control protocols for superficial hyperthermia applicators.

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Section: Discussionmentioning

confidence: 99%

Accuracy of electrical field measurement using the flexible Schottky diode sheet at 433 MHz

Rhoon

Ameziane

Lee

et al. 2003

International Journal of Hyperthermia

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show abstract

“…To obtain a response that is independent of the dielectric characteristics of the surrounding medium, the probe must be insulated (Smith 1975, Mousavinezhad et al 1978. This independent response is achieved provided that the dielectric of the medium is at least five times greater than that of the insulation, ε medium 5ε insulator .…”

Section: Probe Calibrationmentioning

confidence: 99%

Design and calibration of electric field probes in the range 10 - 120 MHz

1997

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In view of potential thermal hazards, there is a need to determine the specific absorption rate (SAR) distributions associated with radiofrequency coils used in magnetic resonance imaging (MRI) (typically 10-120 MHz). Electric field (E-field) distributions in tissue-equivalent phantoms may be determined using a probe comprising a dipole antenna and a detector. The geometry of the dipole dictates the sensitivity of the device, thus two designs are discussed in this paper. Both probes are compact, have a spatial resolution of 2.5 cm3, operate at MR frequencies and have a response independent of the dielectric characteristics of the phantom material. Calibration of these probes requires a system capable of producing a known E-field both in air and in a tissue-like medium at frequencies between 10 and 120 MHz. Transverse electromagnetic wave (TEM) cells answering these specifications are described and the calibration procedure outlined. Accurately calibrated E-field probes can make field measurements in phantoms which can be used to verify predictions from numerical models. These numerical techniques may then be used to predict E-fields, and hence SAR, in patients.

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