No / In the past fifty years it has been clearly identified that the presence of biological tissues effect the performance of the antenna and considerable effort has been made to improve the characteristics of the mobile phone antenna's but very less effort has been put in to evaluate the effects of the radio frequency and energy absorption by the biological organisms and their effect. In this work as part of a bigger work package we have evaluated the effects of the handset orientation on the values of SAR and radiation efficiency as well as the effect of the distance upon these values. The study has produced some very interesting results showing that the most common way of holding the mobile phone i.e. microphone close to the mouth produces the highest SAR values.

No description available.

Two algorithms for estimating the frequency and power of the carriers of 20 GHz and 30 GHz satellite signals are compared. Both algorithms operate on a prefiltered sequence generated by lowpass filtering followed by signal decimation for the purpose of sampling rate reduction. The lowpass filtering is accomplished via the overlap-add method of FIR filtering using the FFT. Carrier frequency prediction and tracking is accomplished with a Kalman predictor, for which the frequency drift process is modeled via polynomial extrapolation. The Kalman predictor operates on frequency measurements provided by one of two frequency estimators. One of the frequency estimation algorithms, a refinement of the DFT-automatic frequency control technique, uses the Chirp-Transform algorithm in its aim for the maximum likelihood estimate of frequency and power. The averaged periodogram is computed from the prefiltered sequence and is used to measure the frequency of the drifting frequency signal as well as its power. One of the disadvantages of this algorithm is the bias present in the estimation of power. The bias can be removed only with knowledge of the noise power. The algorithm has the advantage of being almost exclusively a convolution and therefore is accomplished with minimal computation via the FFT. An alternative parametric approach to frequency estimation is also investigated. In this approach the weighted least-squares modified Yule-Walker method of autoregressive model estimation is used on the prefiltered sequence to yield frequency estimates. Power estimation is accomplished next via modal decomposition of the estimated correlation sequence. The advantage of this approach is that for slowly varying frequency drift paths (24 hour cycle) the frequency estimates exhibit MSE approximately 3 dB less than the Chirp-Transform algorithm over a wide range of SNR. There are two disadvantages to the parametric algorithm. First the parametric algorithm estimates power with MSE approximately 2 dB greater than the nonparametric algorithm. Secondly the algorithm is more complicated than the nonparametric Chirp-Transform algorithm because it requires matrix inversions and the determination of the roots of a polynomial. For the digital beacon receiver problem investigated here both algorithms perform similarly in two important respects. First both algorithms can lock onto a carrier signal whose frequency is drifting at the rate of 5 Hertz per second in a noise environment corresponding to a 15 dB/Hz SNR. Secondly both algorithms can make unbiased frequency estimates of the carrier signal allowing the receiver to track the carrier at 7 dB/Hz SNR. Both algorithms attain the Cramer-Rao bound for estimation of constant frequency sinusoids. For a simulated satellite signal with maximum frequency drift of 5 Hertz per second the Kalman frequency predictor is able to reduce the problem to nearly that of the constant frequency case so that the resulting performance corresponds to the Cramer-Rao bound for estimation of constant frequency sinusoids. Where computational considerations are critical the nonparametric algorithm is preferred. In fact, unless the superior accuracy of the frequency prediction afforded by the parametric algorithm is paramount, the nonparametric algorithm is to be chosen. / Master of Science

International Telemetering Conference Proceedings / October 30-November 02, 1995 / Riviera Hotel, Las Vegas, Nevada / This paper will present and compare several definitions of telemetry radio frequency (RF) signal bandwidth. Measured spectra for different signals will be presented. The bandwidths of these signals will then be determined and measurement methods will be discussed. This discussion will include the effects of spectrum analyzer resolution bandwidth, video bandwidth and detector type. Finally, a proposed spectral mask will be discussed. This spectral mask can be used to calculate the required attenuation for a given frequency offset from the center frequency. The required attenuation is a function of the the bit rate or maximum frequency of interest and the transmitter power. This spectral mask is proposed to be part of the next edition of the Telemetry Standards, Inter-Range Instrumentation Group (IRIG) Standard 106.

Radio frequency inductive coupling is extensively employed for wireless powering of embedded devices such as low power passive near-field RFID systems and implanted sensors. The efficiency of low power inductive links is typically less than 1%and is characterised by very unfavourable coupling conditions, which can vary significantly due to coil position and geometry. Although, a considerable volume of knowledge is available on this topic, most of the existing research is focused on the circuital modeling of the transformer action between the external and implanted coils. The practical issues of coil misalignment and orientation and their implications on transmission characteristics of RF links have been overlooked by researchers. The aim of this work is to present a novel analytical model for near-field inductive power transfer incorporating misalignment of the RF coil system. In this thesis the influence of coil orientation, position and geometry on the link efficiency is studied by approaching the problem from an electromagnetic perspective. In implanted devices some degree of misalignment is inevitable between external and implanted coils due to anatomical requirements. First two types of realistic misalignments are studied; a lateral displacement of the coils and an angular misalignment described as a tilt of the receiver coil. A loosely coupled system approximation is adopted since, for the coil dimensions and orientations envisaged, the mutual inductance between the transmitter and receiver coils can be neglected. Following this, formulae are derived for the magnetic field at the implanted coil when it is laterally and angularly misaligned from the external coil and a new power transfer function presented. The magnetic field solution is carried out for a number of practical antenna coil geometries currently popular in RFID and biomedical domains, such as planar and printed square, and circular spirals as well as conventional air-cored and ferromagnetic solenoids. In the second phase of this thesis, the results from the electromagnetic modeling are embodied in a near-field loosely coupled equivalent circuit for the inductive link. This allows us to introduce a power transfer formula incorporating for the first time coil characteristics and misalignment factors. This novel power transfer function allows a comparison between different coil structures such as short solenoids, with air or ferromagnetic core, planar and printed spirals with respect to power delivered at the receiver and its relative position to the transmitter. In the final stage of this work, the experimental verification of the model shows close agreement with the theoretical predictions. Using this analysis a formal design procedure is suggested that can be applied on a larger scale compared to existing methods. The main advantage of this technique is that it can be applied to a wide range of implementations without the limitations imposed by numerical modeling and existing circuital methods. Consequently, the designer has the flexibility to identify the optimum coil geometry for maximum power transfer and misalignment tolerance that suit the specifications of the application considered. This thesis concludes by suggesting a new optimisation technique for maximum power transfer with respect to read range, coil orientation, geometry and operating frequency. Finally, the limitations of this model are reiterated and possible future development of this research is discussed.

published_or_final_version / abstract / Electrical and Electronic Engineering / Doctoral / Doctor of Philosophy

published_or_final_version / abstract / Electrical and Electronic Engineering / Doctoral / Doctor of Philosophy

published_or_final_version / Electrical and Electronic Engineering / Doctoral / Doctor of Philosophy

No description available.

No description available.