Jianxun Zhao

Numerical dosimetry for cells under millimetre-wave irradiation using Petri dish exposure set-ups

We carried out a numerical dosimetry study for in vitro experiments on millimetre-wave (MMW) biological effects on cells. The cell layers are cultured in 35 mm Petri dishes placed in the far-field region of a rectangular horn irradiator generating a 50.0 GHz continuous sinusoidal MMW. The finite-difference time-domain (FDTD) method and the second-order approximation of the absorbing boundary conditions (ABCs) are applied in calculating the specific absorption rate (SAR) in the cells. The 0.125 mm and 0.25 mm voxel models of the Petri dish are used. The permittivity and the conductivity of the cells and those of the culture medium are obtained with Debyes dispersion equation. We measured the power pattern of the irradiator using the plane wave expansion (PWE) method, and developed a program module to calculate the FDTD-compatible incident field from the irradiator, whose position and orientation are adjustable. The MMW multiple reflection between the Petri dish and the irradiator is evaluated before being neglected. For the single-dish, double-dish and quadruple-dish exposure set-ups, the SAR intensity and the SAR uniformity are analysed and compared. The meniscus effect on the SAR distribution over the cell layer is evaluated for the single-dish set-up. The influence of the Petri dish interaction on the SAR distribution is examined for the double-dish and quadruple-dish set-ups.

DOSIMETRY AND TEMPERATURE EVALUATIONS OF A 1800 MHz TEM CELL FOR IN VITRO EXPOSURE WITH STANDING WAVES

A 1800MHz transverse electromagnetic wave (TEM) cell is introduced for experiments investigating efiects on biological samples caused by the exposure from mobile communications. To characterize and quantify the exposure environment in the setup for standardized in vitro experiments, we evaluate the dosimetry and the exposure- induced temperature rise in cultured cells. The study is numerically based on the flnite-difierence time-domain (FDTD) formulation of the Maxwell equations and the flnite-difierence formulation of the bioheat transfer equation, with all algorithms and models strictly validated for accuracy. Two sample formations of cells are considered including the cell layer and the cell suspension cultured in the 35mm Petri dish. The TEM cell is designed to establish standing waves with the maximum E fleld and the maximum H fleld, respectively, at the position of the Petri dish. The Petri dish is oriented to E, iE, H, k, and ik directions of the incident fleld, respectively, to receive the exposure. The speciflc absorption rate (SAR) is calculated in cells for 10 exposure arrangements combined from the maximum flelds and Petri dish orientations. A comparison determines the best arrangement with the highest exposure e-ciency and the lowest exposure heterogeneity. The dosimetry and the exposure-induced temperature rise in cells are evaluated for the selected arrangement. To avoid thermal reactions caused by overheating, the maximum temperature rises in cells are recorded during the exposure. Based on the records, the temperature control is performed by setting limits to the exposure duration. We introduce a method to further reduce the exposure heterogeneity and evaluate the in∞uence of the Petri dish holder on the dosimetry and temperature rise. The study compares the TEM cell to the waveguide, as well as the standing wave exposure

In Vitro Dosimetry and Temperature Evaluations of a Typical Millimeter-Wave Aperture-Field Exposure Setup

Aperture-field exposure setups are applied in experiments detecting the effects of millimeter-wave (MMW) exposure on cells in vitro. In this paper, the studied exposure setup with standard components includes cells plated in a 35-mm Petri dish at the aperture of a horn irradiating 50.0-GHz MMW. Incorporating the subvoxel model and symmetry formulas, the finite-difference time-domain algorithm of the Maxwell equations and the finite-difference algorithm of the Pennes bioheat equation are used to calculate the specific absorption rate (SAR), absorption efficiency of the MMW power, and temperature rise in the cell culture. The numerical methods and models are supported by experimental measurement and theoretical analyses. The exposure of 31.2-mW MMW results in an averaged SAR of 44.9 W/kg in cells, quantitatively compatible with the International Commission on Non-Ionizing Radiation Protection limits to the incident power density. 46.9% of the MMW power is efficiently absorbed and accumulates a maximum temperature rise of 0.12°C in cells. The exposure intensity is selectable with acceptable homogeneity by proper cell sampling. The MMW multiple reflection of the aperture-field exposure is analyzed about its significant influences on the dosimetry and temperature results. Another comparison reveals the efficacious power matching of the Petri dish and its dosimetric contribution. The power threshold for time-unlimited exposures, time limits for high-power exposures, and adaptive air cooling are quantified to control the temperature variance within ±0.1°C. This paper presents the first detailed quantification and characterization of the dosimetry and temperature environments for the MMW aperture-field exposure setup in application to in vitro experiments for over 30 years.

Reduction of Exposure Inhomogeneity for Millimeter-Wave Experiments on Cells In Vitro

An in vitro experiment of millimeter-wave effects requires a minimum exposure inhomogeneity for cells to receive the same exposure intensity. Two methods are studied to minimize the inhomogeneity for far-field exposures. The propagation and polarization directions of incident waves are optimized to reduce the standard deviation (SD) of the specific absorption rate (SAR) in cells cultivated in a 35-mm Petri dish. The SAR distributions are characterized and the SAR variance is interpreted. Choke rings are introduced and optimized to support the Petri dish and decrease the SAR SD by canceling the scattered waves. The numerical study is based on the finite-difference time-domain algorithm. A six-degree-of-freedom algorithm is developed to generate incident waves with various properties in the problem space enclosing the model made of 0.125-mm voxels. The exposure scenarios include the plane-wave exposure and antenna exposures with different half-power widths, incident waves of various propagation and polarization directions, and frequencies of 42.3, 53.6, 61.2, and 60.5 GHz. The exposure with the upward wave is confirmed for the lowest SAR SD, which is reduced to well below 10% by using choke rings. The choke ring approach is comparatively validated in the simulation of an experimental setup.

Meniscus Effect on the In Vitro Dosimetry of the T25 Flask Under 2.45 and 5.25 GHz Exposures

A practical technique is proposed to precisely model the meniscus of the cell culture in the standard T25 flask used in bioelectromagnetic experiments on RF exposure effects. In standard exposure scenarios, the numerical calculation with the meniscus model effectively improves the accuracy of the in vitro dosimetry, as compared to results from the conventional model with a flat liquid surface. The numerical study uses the finite-difference time-domain (FDTD) method incorporated with a conformal algorithm, which is examined for accuracy against the theoretical analysis.

Application of the planar-scanning technique to the near-field dosimetry of millimeter-wave radiators

The planar-scanning technique was applied to the experimental measurement of the electric field and power flux density (PFD) in the exposure area close to the millimeter-wave (MMW) radiator. In the near-field region, the field and PFD were calculated from the plane-wave spectrum of the field sampled on a scan plane far from the radiator. The measurement resolution was improved by reducing the spatial interval between the field samples to a fraction of half the wavelength and implementing multiple iterations of the fast Fourier transform. With the reference to the results from the numerical calculation, an experimental evaluation of the planar-scanning measurement was made for a 50 GHz radiator. Placing the probe 1 to 3 wavelengths from the aperture of the radiator, the direct measurement gave the near-field data with significant differences from the numerical results. The planar-scanning measurement placed the probe 9 wavelengths away from the aperture and effectively reduced the maximum and averaged differences in the near-field data by 70.6% and 65.5%, respectively. Applied to the dosimetry of an open-ended waveguide and a choke ring antenna for 60 GHz exposure, the technique proved useful to the measurement of the PFD in the near-field exposure area of MMW radiators.

Dosimetry and Temperature Evaluation of TEM Chamber for Cell Exposure at 1800 MHz

Using the finite-difference time-domain (FDTD) method, we make a dosimetry study on the specific absorption rate (SAR) in cells exposed to 1800 MHz standing waves produced by the transverse electromagnetic (TEM) chamber. Two types of cultured cells are used, namely, the cell layer and the cell suspension. Based on the calculated SAR distribution, the exposure is characterized by the SAR intensity and homogeneity. We consider different exposure arrangements as the combination of the maximum fields of the standing wave and the polarizations of the Petri dish. The maximum E field and maximum H field are used in turn in the exposure volume, where the Petri dish is polarized in the E, H, k and k directions, respectively. The best exposure arrangements are determined by measuring the intensity and homogeneity of the SAR distribution in cells. For a tight control of the thermal environment, the temperature rise in the cell culture induced by the exposure is calculated by using the finite-difference formulation of the bio-heat conduction equation. The linear relation between the maximum temperature rise and the absorbed power is determined to quantify the exposure power for the temperature control.

SAR and Temperature Evaluations of a 900 Mhz TEM Chamber for Cell Exposure

A dosimetry study is made for experiments on cultured cells exposed to 900 MHz microwave in the transverse electromagnetic (TEM) chamber. The exposure is characterized by the intensity and homogeneity of the specific absorption rate (SAR), as well as the exposure-induced temperature rise. The SAR distribution is calculated by using the finite-difference time-domain (FDTD) algorithm of the Maxwell equations. The finite-difference formulation of the bioheat conduction equation is used to calculate the temperature rise of the in vitro environment. Evaluations of the SAR and temperature are performed systematically for scenarios including two formations of cultured cells, two maximum fields, and four polarizations of the Petri dish holding the cell culture. The exposure is optimized by selecting scenarios with the highest SAR intensity, the best SAR homogeneity, and the effective temperature control.