The conventional method of diagnosing disorders of the human gastro-intestinal (GI) tract is by sensors embedded in cannulae that are inserted through the anus, mouth, or nose. However, these cannulae cause significant patient discomfort and cannot be used in the small intestine. As a result, there is considerable ongoing work in developing wireless sensors that can be used in the small intestine. The radiation characteristics of sources in the GI tract cannot be readily calculated due to the complexity of the human body and its composite tissues, each with different electrical characteristics. In addition, the compact antennas used are electrically small, making them inefficient radiators. This paper presents radiation characteristics for sources in the GI tract that should allow for the optimum design of more efficient telemetry systems. The characteristics are determined using the finite-difference time-domain method with a realistic antenna model on an established fully segmented human body model. Radiation intensity outside the body was found to have a Gaussian-form relationship with frequency. Maximum radiation occurs between 450 and 900 MHz. The gut region was found generally to inhibit vertically polarized electric fields more than horizontally polarized fields.

Glasgow ePrints Service http://eprints.gla.ac.uk 60" of arc with a radius of 51 and a height 1OA with A= 1 m. A vertical dipole is placed at a distance of 101 from the centre of the cylinder. Fig. 1 shows the interpolated values for the amplitude and the phase of the current on the cylinder. The difference between these values and the exact ones are shown in Fig. 2. As shown in Fig. 2 the interpolation error is negligible. The maximum relative errors in this case are 2.0 x IOp4 for the amplitude and 4.0 x IO-' for the phase.Fig. 1 Interpolated amplitude and phase of current induced by dipole on a section of cylinder with 60" of arc a Amplitude b Phase 0 02 6 4 0 4 02 4 0 4 1 0 P z 2 0 -2 1 0 0 1 0 Fig. 2 Error of interpolated amplitude and phase functions for current induced by dipole on a section of cylinder with 60" of arc a Amplitude functions b Phase functions Conclusions:A new method to represent the induced current in an accurate and efficient way has been presented. The method is based on the interpolation of the amplitude and phase by means of Btzier surfaces. An example has been shown to prove the potential of the method to represent the current with a negligible error using a low amount of sample points. This method can be used to analyse large problems by rigorous methods, or to obtain higher-order reflections in an iterative way by using asymptotic techniques. Acknowledgment: This work has been supported in part by theReferences 1 CHEW, wc , JIN, J , MICHIELSSEN, E and SONG, J (Eds.): 'Fast and efficient algorithms in computational electromagnetics' (Artech House, 2001) 2 CATEDRA, M.F., PEREZ, J., SAEZ DEADANA, E, and GUTIERREZ, 0.: 'Efficient ray-tracing techniques for 3D analysis of propagation in mobile communications. Application to picocell and microcell scenarios',The performance of wireless devices, using electrically small antennae, in the human intestine is investigated using the finite difference time domain method in recommended biomedical device telemetry bands. The radiation field intensity was found to depend on position but more strongly on frequency, with a transmission peak at 650 MHz. Introduction:There is an increasing number of applications for wireless devices designed for use close to or inside the human body. The design of such devices poses many problems, not least of which is the effect of the environment on radio signals. In this Letter we consider the effect of the human body on the propagation of radio signals from a wireless ingested diagnostic device in the gastrointestinal tract (GIT), in the 150 MHz to 1.2 GHz range, encompassing several international medical telemetry bands (pan-European allocation [I] and the US Federal Communications Commission allocationsregulations S5.150, US209 and US350).

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The statistics of the fields within an enclosure illuminated by an external field via an aperture have been investigated using Monte-Carlo methods. The field statistics in the volume of the enclosure are shown to correspond to the Rayleigh statistics found in properly functioning reverberation chambers when a sufficiently large number of modes is excited. The variation of field behaviour near the conducting walls is investigated. The deviation of the field statistics from the Rayleigh distribution as the number of excited modes falls is also investigated.

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