Design and characterisation of wideband antennas for microwave imaging applications

Magnetic Resonance Imaging (MRI) and Computed Tomography (CT) are well known equipments used to generate images to aid in diagnostic procedure. However, the imaging equipments have some limitations whereby the equipments are very expensive and therefore, they are not always accessible in many medical centres. Besides, the equipments are bulky and less mobility. Moreover, existing CT cannot be used frequently on the human body because the scanner exposes patients to more radiations of ionised frequency. The limitations of the equipment create a need to design an alternative imaging method which is relatively low cost, small in size, has high mobility, and non-ionise frequency. This research is to design an antenna for microwave imaging, namely corrugated u-slot antenna at 1.17-5.13 GHz with the reference of S11 less than -10 dB. Two corrugated u-slot antennas; namely antenna 1 and antenna 2 are placed on a mirror side of skull phantom to examine their ability to detect an object inside the skull. VeroClear-RGD810 skull phantom containing water is used, and the obtained results are verified using ZCorp zp-150 skull phantom which has approximately similar permittivity. Both the antennas are tested to detect the object which is located at 40 mm and 80 mm from the respective examined antenna. An Inverse Fast Fourier Transform (IFFT) technique is used to analyse the time domain reflection pulse according to the dielectric properties difference, as the electromagnetic wave propagates through the skull. The results show that the antenna 1 is able to detect the object faster than the antenna 2 for both skulls, due to inconsistent thickness of the phantoms. Furthermore, the antennas are fabricated in adjacent to measure decomposition and superposition specific absorption rate (SAR) in Specific Anthropomorphic Mannequin (SAM) head phantom at 1800 MHz and 2600 MHz. The maximum allowable SAR in head is 2 W/kg at 10 g contiguous tissue which is referred to International Commission on Non-Ionizing Radiation Protection (ICNIRP) guideline. Based on the measured results, superposition SAR of the antenna can reach up to ±12% of the maximum decomposition SAR. This research forms a significant contribution to medical engineering field in designing a corrugated u-slot antenna that serves to detect an abnormality inside human head at 1.17-5.13 GHz. The designed antenna satisfies the SAR standard, which is required in microwave imaging applications

Design and characterisation of wideband antennas for microwave imaging applications

Magnetic Resonance Imaging (MRI) and Computed Tomography (CT) are well known equipments used to generate images to aid in diagnostic procedure. However, the imaging equipments have some limitations whereby the equipments are very expensive and therefore, they are not always accessible in many medical centres. Besides, the equipments are bulky and less mobility. Moreover, existing CT cannot be used frequently on the human body because the scanner exposes patients to more radiations of ionised frequency. The limitations of the equipment create a need to design an alternative imaging method which is relatively low cost, small in size, has high mobility, and non-ionise frequency. This research is to design an antenna for microwave imaging, namely corrugated u-slot antenna at 1.17-5.13 GHz with the reference of S11 less than -10 dB. Two corrugated u-slot antennas; namely antenna 1 and antenna 2 are placed on a mirror side of skull phantom to examine their ability to detect an object inside the skull. VeroClear-RGD810 skull phantom containing water is used, and the obtained results are verified using ZCorp zp-150 skull phantom which has approximately similar permittivity. Both the antennas are tested to detect the object which is located at 40 mm and 80 mm from the respective examined antenna. An Inverse Fast Fourier Transform (IFFT) technique is used to analyse the time domain reflection pulse according to the dielectric properties difference, as the electromagnetic wave propagates through the skull. The results show that the antenna 1 is able to detect the object faster than the antenna 2 for both skulls, due to inconsistent thickness of the phantoms. Furthermore, the antennas are fabricated in adjacent to measure decomposition and superposition specific absorption rate (SAR) in Specific Anthropomorphic Mannequin (SAM) head phantom at 1800 MHz and 2600 MHz. The maximum allowable SAR in head is 2 W/kg at 10 g contiguous tissue which is referred to International Commission on Non-Ionizing Radiation Protection (ICNIRP) guideline. Based on the measured results, superposition SAR of the antenna can reach up to ±12% of the maximum decomposition SAR. This research forms a significant contribution to medical engineering field in designing a corrugated u-slot antenna that serves to detect an abnormality inside human head at 1.17-5.13 GHz. The designed antenna satisfies the SAR standard, which is required in microwave imaging applications

Nasopharyngeal method for selective brain cooling and development of a time-resolved near-infrared technique to monitor brain temperature and oxidation status during hypothermia

Mild hypothermia at 32-35oC (HT) has been shown to be neuroprotective for neurological emergencies following severe head trauma, cardiac arrest and neonatal asphyxia. However, HT has not been widely deployed in clinical settings because: firstly, cooling the whole body below 33-34°C can induce severe complications; therefore, applying HT selectively to the brain could minimize adverse effects by maintaining core body temperature at normal level. Secondly, development of an effective and easy to implement selective brain cooling (SBC) technique, which can quickly induce brain hypothermia while avoiding complications from whole body cooling, remains a challenge. In this thesis, we studied the feasibility and efficiency of selective brain cooling (SBC) through nasopharyngeal cooling. To control the cooling and rewarming rate and because core body temperature is different from brain temperature, we also developed a non-invasive technique based on time-resolved near infrared spectroscopy (TR-NIRS) to measure local brain temperature. In normal brain, cerebral blood flow (CBF) and energy metabolism as reflected by the cerebral metabolic rate of oxygen (CMRO2) is tightly coupled leading to an oxygen extraction efficiency (OEF) of around ~33%. A decoupling of the two as in ischemia signifies oxidative stress and would lead to an increase in OEF beyond the normal value of ~33%. The final goal of this thesis is to evaluate TR-NIRS methods for measurements of CBF and CMRO2 to monitor for oxidative metabolism in the brain with and without HT treatment. Chapter 2 presents investigations on the feasibility and efficiency of the nasopharyngeal SBC by blowing room temperature or humidified cooled air into the nostrils. Effective brain cooling at a median cooling rate of 5.6 ± 1.1°C/hour compared to whole body cooling rate of 3.2 ± 0.7 was demonstrated with the nasopharyngeal cooling method. Chapter 3 describes TR-NIRS experiments performed to measure brain temperature non-invasively based on the temperature-dependence of the water absorption peaks at ~740 and 840nm. The TR-NIRS method was able to measure brain temperature with a mean difference of 0.5 ± 1.6°C (R2 = 0.66) between the TR-NIRS and thermometer measurements. Chapter 4 describes the TR-NIR technique developed to measure CBF and CMRO2 in a normoxia animal model under different anesthetics at different brain temperatures achieved by whole-body cooling. Both CBF and CMRO2 decreased with decreasing brain temperature but the ratio CMRO2:CBF (OEF) remained unchanged around the normal value of ~33%. These results demonstrate that TR-NIR can be used to monitor the oxidative status of the brain in neurological emergencies and its response to HT treatment. In summary, this thesis has established a convenient method for selective brain cooling without decreasing whole body temperature to levels when adverse effects could be triggered. TR-NIRS methods are also developed for monitoring local brain temperature to guide SBC treatment and for monitoring the oxidation status of the brain as treatment progresses

Experimental Characterisation of Body-Centric Radio Channels Using Wireless Sensors

PhDWireless sensors and their applications have become increasingly attractive for industry, building automation and energy control, paving the way for new applications of sensor networks which go well beyond traditional sensor applications. In recent years, there has been a rapid growth in the number of wireless devices operating in close proximity to the human body. Wearable sensor nodes are growing popular not only in our normal living lifestyle, but also within healthcare and military applications, where different radio units operating in/on/off body communicate pervasively. Expectations go beyond the research visions, towards deployment in real-world applications that would empower business processes and future business cases. Although theoretical and simulation models give initial results of the antenna behaviour and the radio channel performance of wireless body area network (WBAN) devices, empirical data from different set of measurements still form an essential part of the radio propagation models. Usually, measurements are performed in laboratory facilities which are equipped with bulky and expensive RF instrumentation within calibrated and controllable environments; thus, the acquired data has the highest possible reliability. However, there are still measurement uncertainties due to cables and connections and significant variations when designs are deployed and measured in real scenarios, such as hospitals wards, commercial buildings or even the battle field. Consequently, more flexible and less expensive measurement tools are required. In this sense, wireless sensor nodes offer not only easiness to deploy or flexibility, but also adaptability to different environments. In this thesis, custom-built wireless sensor nodes are used to characterise different on-body radio channels operating in the IEEE 802.15.4 communication standard at the 2.45 GHz ISM band. Measurement results are also compared with those from the conventional technique using a Vector Network Analyser. The wireless sensor nodes not only diminished the effect of semi-rigid or flexible coaxial cables (scattering or radiation) used with the Vector Network Analyser (VNA), but also provided a more realistic response of the radio link channel. The performance of the wireless sensors is presented over each of the 16 different channels present at the 2.45 GHz band. Additionally, custom-built wireless sensors are used to characterise and model the performance of different on-body radio links in dynamic environments, such as jogging, rowing, and cycling. The use of wireless sensors proves to be less obstructive and more flexible than traditional measurements using coaxial cables, VNA or signal generators. The statistical analysis of different WBAN channels highlighted important radio propagation features which can be used as sport classifiers models and motion detection. Moreover, specific on-body radio propagation channels are further explored, with the aim to recognize physiological features such as motion pattern, breathing activity and heartbeat. The time domain sample data is transformed to the frequency domain using a non-parametric FFT defined by the Welch’s periodogram. The Appendix-Section D explores other digital signal processing techniques which include spectrograms (STFT) and wavelet transforms (WT). Although a simple analysis is presented, strong DSP techniques proved to be good for signal de-noising and multi-resolution analysis. Finally, preliminary results are presented for indoor tracking using the RSS recorded by multiple wireless sensor nodes deployed in an indoor scenario. In contrast to outdoor environments, indoor scenarios are subject to a high level of multipath signals which are dependent on the indoor clutter. The presented algorithm is based on path loss analysis combined with spatial knowledge of each wireless sensor