Inhomogeneous Human Head Research Articles

Microwave power penetration enhancement inside an inhomogeneous human head

The penetration of microwave power inside a human head model is improved by employing a dielectric loaded rectangular waveguide as the transmission source. A multi-layer reflection model is investigated to evaluate the combined material characteristics of different lossy human head tissues at 2.45 GHz. A waveguide loaded with a calculated permittivity of 3.62 is shown to maximise the microwave power penetration at the desired frequency. A Quartz (SiO2) loaded rectangular waveguide fed by a microstrip antenna is designed to validate the power penetration improvement inside an inhomogeneous human head phantom. A measured 1.33 dB power penetration increment is observed for the dielectric loaded waveguide over a standard rectangular waveguide at 50 mm inside the head, with an 81.9% reduction in the size of the transmission source.

Compact coplanar waveguide fed wideband directional antenna for medical diagnosis

This paper presents a compact coplanar waveguide fed antenna for medical diagnosis of the human head. Early diagnosis of the sophisticated organs inside the human body is possible through microwave medical imaging, which has recently achieved its popularity due to its numerous advantages. The crucial functional element for microwave medical imaging is the antenna. The antenna presented in this paper is conceived and evaluated in contact with an inhomogeneous human head tissue medium, increasing the signal penetration by removing the antenna–air–tissue transition loss. A combination of a meandered line and circular slot are utilized to achieve wideband performance at a subwavelength size. A rectangular cavity is introduced at the back of the antenna to attain directional radiation towards the inhomogeneous human head phantom. The antenna achieves increased bandwidth covering the lower microwave frequency region for medical diagnosis of a human head while minimizing ill-directed radiated fields which interfere with imaging computations. The salient characteristics of compact size, high near-field directionality, lower microwave operating frequency range and low impact on the skin surface make the proposed antenna a suitable candidate for microwave imaging of the human head.

Compact 3-D Antenna for Medical Diagnosis of the Human Head

A compact 3-D antenna for microwave medical diagnosis is presented. The antenna is matched with an inhomogeneous human head allowing higher signal penetration so as to obtain more meaningful data reflected from inside the brain. Utilizing a folded inverted F-like structure and a slot-loaded ground plane, the antenna is a compact $0.23\,\,\lambda \times 0.23 \,\,\lambda \times 0.04 \,\,\lambda $ in size with respect to the lowest operating frequency. The antenna is backed with a rectangular cavity to minimize sidelobe and backlobe radiation. The cavity and folded antenna configuration achieve a highly directional radiation pattern toward the head with a front-to-back ratio of more than 17 dB. A curved inhomogeneous human head phantom is fabricated to validate the antenna performance for medical diagnosis applications. An operational frequency band from 1 to 1.7 GHz is achieved with the antenna attached to the surface of the phantom. Less than 0.0147 W/kg SAR is achieved throughout the operating frequency range, which is lower than the state of the art for comparable antennas. The salient characteristics of the proposed antenna make it a suitable candidate for microwave diagnosis of the human head.

Temperature Increase in Human Heads Due to Different Models of Cellular Phones

The temperature increase in a realistic human head model exposed to five different cellular phone models is investigated by a bioheat equation and the finite-difference time-domain (FDTD) method at 900 and 1800 MHz, respectively. These five cellular phone models are greatly differ from each other in structure. The realistic human head model is used to investigate the temperature increase in the head affected by varying factors including; electric properties of human head tissues, hand absorption power effect, cellular phone models, homogeneous and inhomogeneous head models, cellular phone material, and the distance between the cellular phone and the head. Computed results show that the temperature increase in the head reaches the steady-state value for exposure time of about 20 minutes. For worst-case, the maximum temperature increase in the head is found to be 0.19° C at 900 MHz and 0.055° C at 1800 MHz for the inhomogeneous human head with six tissues exposed to a metallic handset held by a hand, with antenna output power of 0.6 W and 0.125 W, respectively. The maximum temperature increase in the head is far less than the threshold temperature increase of 4.5° C which can cause neuron damage.

SAR affected by shapes and electrical properties of the human head exposed to a cellular phone

AbstractThe local maximum specific absorption rate (SAR) induced in spherical, cubical, coarse, and realistic human‐head models exposed to a cellular phone is investigated using the finite‐difference time‐domain (FDTD) method at 900 and 1800 MHz, respectively. These four human‐head models each have greatly different shapes but almost the same volume. Obtained local maximum SARs induced in these four human‐head models for homogeneous cases are found to have an average differences of about 15% and 12% at 900 and 1800 MHz, respectively. A comparison of SARs induced in the realistic human‐head model for homogeneous and inhomogeneous cases is also made. It is found that the local maximum SAR induced in the homogeneous human‐head model is larger than that induced in the inhomogeneous human head model. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 42: 1–4, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20189