Biomedical subjects

P J Dimbylow

Publications and source records attributed to P J Dimbylow.

5 recordsLinked to original sources

PubMed1991

Finite-difference time-domain calculations of SAR in a realistic heterogeneous model of the head for plane-wave exposure from 600 MHz to 3 GHz.

This paper presents finite-difference time-domain (FDTD) calculations of the specific energy absorption rate (SAR) in a fine-scaled, heterogeneous, realistic model of the head for frequencies ranging from 600 MHz to 3 GHz. The phantom has been derived from an atlas of cross-sectional anatomy. The cell size is 3.2 mm which results in a 120,000 cell head model comprising brain, bone/fat, muscle, skin, blood, air and eye humour, lens and sclera. Irradiation from the front and side for plane-wave exposure of an adult and an infant are considered.

Adult↗

PubMed1991

Finite-difference time-domain calculations of absorbed power in the ankle for 10-100 MHz plane wave exposure.

This paper presents finite-difference time-domain (FDTD) calculations of the short-circuit current and the specific energy absorption rate (SAR) in the ankle. Plane wave exposures from 10 to 100 MHz for an adult, a 10-year old and 5-year old are considered. The calculations are performed in two parts. Firstly, the coupling between a homogeneous whole body phantom and the applied field is calculated. The region around a lower leg is then expanded, the leg being described by a realistic fine-scale, heterogeneous model. Tangential electric field components from the first part are used as boundary conditions on the reduced domain of the second part. Electric field values based on a maximum SAR of 20 W . kg-1 are presented.

Adult↗

PubMed1988

The calculation of induced currents and absorbed power in a realistic, heterogeneous model of the lower leg for applied electric fields from 60 Hz to 30 MHz.

The ankle consists mainly of bone and tendon with little muscle. Currents will tend to preferentially flow through the high-conductivity muscle and this can result in very high local values of the specific energy-absorption rate (SAR). This paper presents a finite-difference method to calculate SAR in a realistic, heterogeneous model of the leg below the knee. The structure of the leg is defined by cross-sectional slices from an anatomical atlas which are converted into a 3D model of over 14,000 cells. Four types of tissue are included in the model--muscle, cortical bone, trabecular bone and connective tissue. Displacement as well as ionic currents are considered in a complex potential representation. The current to be injected into the limb model is obtained from the computed coupling of an applied vertical electric field with a 1.8 m tall, homogeneous phantom. Values of the maximum current density and SAR in the ankle from 60 Hz to 30 MHz are presented. Field limits based on a maximum SAR of 20 W kg-1 averaged over 1 g of tissue are given. Sensitivity analyses with regard to the range of tissue electric properties and the ankle cross-sectional area are performed.

Ankle↗

PubMed1987

Finite difference calculations of current densities in a homogeneous model of a man exposed to extremely low frequency electric fields.

This paper presents three-dimensional finite difference calculations of induced current densities in a grounded, homogeneous, realistically human-shaped phantom. Comparison is made with published experimental values of current density at 60 Hz, measured in conducting saline manikins with their arms down by the side. The congruence between calculation and experiment gives confidence in the applicability of the numerical method and phantom shape to other configurations. The effect of raising both arms above the head is to reduce the current densities in the head and neck by approximately 50% and to increase those from the thorax downwards by 20-30%. A sensitivity analysis was performed on the shape and dimensions of the phantom, from a 45-kg, 1.5-m-tall person to a 140-kg, 1.9-m-tall person. When the phantom is grounded through both feet the current densities range from 50 to 90 microAm-2 in the head (all values for a 60-Hz, 1-kVm-1, vertical applied field), 70 to 140 microAm-2 in the thorax, 150 to 440 microAm-2 at the crotch, and 500 to 2,230 microAm-2 in the ankle. When grounded through only one foot the current densities at the crotch range from 400 to 1,000 microAm-2 and from 1,000 to 4,400 microAm-2 in the ankle of the grounded leg. Scale transformations of the short-circuit current with phantom height, weight, and surface area are confirmed.

Animals↗

PubMed1985

Radon diffusion modelling.

A mathematical model has been developed that examines the ingress of radon into houses, through a vertical crack in an otherwise impervious concrete floor. Initially, the model considered the diffusive flow of radon from its soil source and this simulation has highlighted the dependency of the flux of radon into the house on the magnitude of various parameters, such as the diffusion coefficient of radon in soil. A preliminary investigation of the modelling of pressure-driven flow into a building is presented, and the potential of this type of analysis is discussed.

Diffusion↗