Rectifier design for radio frequency energy harvesting system

This thesis presents the development of rectifying circuits suitable for Radio Frequency (RF) energy harvesting application with dual-band capabilities. The main contribution of this thesis is the development of compact dual-band two-stage rectifier with high efficiency. Firstly, a voltage doubler rectifying circuit is designed to get a compact size. A source-pull simulation of matching circuit is used to find the optimal load impedance and enhance the conversion efficiency over the frequency range. The accuracy of the design has been justified by the simulation and measurement results. Secondly, a dual-band impedance matching network based on transmission line is developed. A short stub and general impedance transformer are designed to match different complex impedance at the two operating frequencies. Measurement results have fully demonstrated. Thirdly, a new rectifier circuit is proposed. It employs a dual-band multi resonant matching network and a high efficiency modified quadruplor rectifier for harvesting the ambient RF power at both 2.45 GHz Global System for Mobile Communications (GSM) and 5.8 GHz Wireless Local Area Network (WLAN). An attempt was made for matching network with a series of combination of a capacitor and inductor with a parallel LC tank. For rectifier circuit part, low power harvested from the RF is boosted up using two-stage of voltage multiplier and the input capacitor is rearranged to be in parallel connection to get smaller size and uniform pressure on diode. The prototypes are developed, and simulation results are obtained. The proposed rectifier is proven to exhibit greatly higher output voltage and efficiency compared to the conventional circuit. The rectifier is designed on the FR-4 board. Its capability of working within two frequency bands at 2.45 GHz and 5.8 GHz is verified by measurement. The proposed rectifier has met the requirement of high conversion efficiency (79.1% and 78.4% at the respective 2.45 GHz and 5.8 GHz), and able to boost up to the maximum voltage level of 14V at 20 dBm input power. Hence, the aims of this research have been achieved and are practically suitable for the use in wireless sensor networks and low power devices

Antenna Development in Brain-Implantable Biotelemetric Systems for Next-Generation of Human Healthcare

In the growing efforts of promoting patients’ life quality through health technology solutions, implantable wireless medical devices (IMDs) have been identified as one of the frontrunners. They are bringing compelling wireless solutions for medical diagnosis and treatment through bio-telemetric systems that deliver real-time transmission of in-body physiological data to an external monitoring/control unit. To set up this bidirectional wireless biomedical communication link for the long- term, the IMDs need small and efficient antennas. Designing antenna-enabled biomedical telemetry is a challenging aim, which must fulfill demanding issues and criteria including miniaturization, appropriate radiation performance, bandwidth enhancement, good impedance matching, and biocompatibility. Overcoming the size restriction mainly depends on the resonant frequency of the required applications. Defined frequency bands for biomedical telemetry systems contain the Medical Implant Communication Service (MICS) operating at the frequency band of 402– 405 MHz, Medical Device Radiocommunication Service (MedRadio) resonating at the frequency ranges of 401– 406 MHz, 413 – 419 MHz, 426 – 432 MHz, 438 – 444 MHz, and 451 – 457 MHz, Wireless Medical Telemetry Service (WMTS) operating at frequency specturms of 1395 to 1400 MHz and 1427 to 1432 MHz, and Industrial, Scientific, and Medical (ISM) bands of 433.1–434.8 MHz, 868–868.6 MHz, 902.8–928.0 MHz, and 2.4–2.48 GHz. On the other hand, a single band antenna may not fulfill all requirements of a bio-telemetry system in either MedRadio, WMTS, or ISM bands. As a result, analyzing dual/multi-band implantable antenna supporting wireless power, data transmission, and control signaling can meet the demand for multitasking biotelemetry systems. In addition, among different antenna structures, PIFA has been found a promising type in terms of size-performance balance in lossy human tissues. To overcome the above-mentioned challenges, this thesis, first, starts with a discussion of antenna radiation in a lossy medium, the requirements of implantable antenna development, and numerical modeling of the human head tissues. In the following discussion, we concentrate on approaching a new design for far-field small antennas integrated into brain-implantable biotelemetric systems that provide attractive features for versatile functions in modern medical applications. To this end, we introduce three different implantable antenna structures including a compact dual-band PIFA, a miniature triple-band PIFA and a small quad-band PIFA for brain care applications. The compelling performance of the proposed antennas is analyzed and discussed with simulation results and the triple-band PIFA is evaluated using simulation outcomes compared with the measurement results of the fabricated prototype. Finally, the first concept and platform of in-body and off-body units are proposed for wireless dopamine monitoring as a brain care application. In addition to the main focus of this thesis, in the second stage, we focus on introducing an equivalent circuit model to the electrical connector-line transition. We present a data fitting technique for two transmission lines characterization independent of the dielectric properties of the substrate materials at the ultra-high frequency band (UHF). This approach is a promising solution for the development of wearable and off-body antennas employing textile materials in biomedical telemetry systems. The approach method is assessed with measurement results of several fabricated transmission lines on different substrate materials

A switchless multiband impedance matching technique based on multiresonant circuits

In a number of applications, a matching network capable of providing specified impedances at different frequencies is necessary. In this brief, we present a novel technique for switchless multiband impedance matching networks based on multiresonant circuits. To illustrate this, simulation results of dual-band and triband networks are also presented. In addition, a dual-band impedance matching network has been implemented and evaluated. The dual-band impedance matching network presents two specified impedances, one at 433 MHz and the other at 915 MHz with 0.82 and 0.20 dB of insertion losses, respectively