Power Amplifiers for Electronic Bio-Implants

Healthcare systems face continual challenges in meeting their aims to provide quality care to their citizens within tight budgets. Ageing populations in the developed world are perhaps one of the greatest concerns in providing quality healthcare in the future. The median age of citizens in economically developed regions is set to approach 40 years by the year 2050, and reach as high as 55 years in Japan. This trend is likely to lead to strained economies caused by less revenue raised by smaller workforces. Another effect of ageing populations is the need of further care in order to remain healthy. This care varies from frequent check-ups to condition monitoring, compensation for organ malfunction and serious surgical operations. As a result of these trends, healthcare systems will face the task of servicing more people with more serious and expensive health services, all using less available funds. Effort is being focused on running cheaper and more effective healthcare systems and the development of technology to assist in this process is a natural research priority

Cost-Effective and Energy-Efficient Techniques for Underwater Acoustic Communication Modems

Finally, the modem developed has been tested experimentally in laboratory (aquatic environment) showing that can communicates at different data rates (100..1200 bps) compared to state-of-the-art research modems. The software used include LabVIEW, MATLAB, Simulink, and Multisim (to test the electronic circuit built) has been employed.Underwater wireless sensor networks (UWSNs) are widely used in many applications related to ecosystem monitoring, and many more fields. Due to the absorption of electromagnetic waves in water and line-of-sight communication of optical waves, acoustic waves are the most suitable medium of communication in underwater environments. Underwater acoustic modem (UAM) is responsible for the transmission and reception of acoustic signals in an aquatic channel. Commercial modems may communicate at longer distances with reliability, but they are expensive and less power efficient. Research modems are designed by using a digital-signal-processor (DSP is expensive) and field-programmable-gate-array (FPGA is high power consuming device). In addition to, the use of a microcontroller is also a common practice (which is less expensive) but provides limited computational power. Hence, there is a need for a cost-effective and energy-efficient UAM to be used in budget limited applications. In this thesis different objectives are proposed. First, to identify the limitations of state-of-the-art commercial and research UAMs through a comprehensive survey. The second contribution has been the design of a low-cost acoustic modem for short-range underwater communications by using a single board computer (Raspberry-Pi), and a microcontroller (Atmega328P). The modulator, demodulator and amplifiers are designed with discrete components to reduce the overall cost. The third contribution is to design a web based underwater acoustic communication testbed along with a simulation platform (with underwater channel and sound propagation models), for testing modems. The fourth contribution is to integrate in a single module two important modules present in UAMs: the PSK modulator and the power amplifier

Rail-to-Rail Operational in Low-Power Reconfigurable Analog Circuitry

Analog signal processing (ASP) can be used to decrease energy consumption by several orders of magnitude over completely digital applications. Low-power field programmable analog arrays (FPAA) have been previously used by analog designers to decrease energy consumption. Combining ASP with an FPAA, energy consumption of these systems can be further reduced. For ASP to be most functional, it must achieve rail-to-rail operation to maintain a high dynamic range. This work strives to further reduce power consumption in reconfigurable analog circuitry by presenting a novel data converter that utilizes ASP and rail-to-rail operation. Rail-to-Rail operation is achieved in the data converter with the use of an operational amplifier presented in this work. This efficient yet elementary data converter has been fabricated in a 0.5$\mu$m standard CMOS process. Additionally, this work looks deeper into the challenges of students working remotely, how MATLAB can be used to create circuit design tools, and how these developmental tools can be used by circuit design students

A fully on-chip LDO voltage regulator with 37 dB PSRR at 1 MHz for remotely powered biomedical implants

This article presents a fully on-chip low-power LDO voltage regulator dedicated to remotely powered wireless cortical implants. This regulator is stable over the full range of alternating load current and provides fast load regulation achieved by applying a time-domain design methodology. Moreover, a new compensation technique is proposed and implemented to improve PSRR beyond the performance levels which can be obtained using the standard cascode compensation technique. Measurement results show that the regulator has a load regulation of 0.175 V/A, a line regulation of 0.024%, and a PSRR of 37 dB at 1MHz power carrier frequency. The output of the regulator settles within 10-bit accuracy of the nominal voltage (1.8 V) within 1.6μs, at full load transition. The total ground current including the bandgap reference circuit is 28μA and the active chip area measures 290μm×360μm in a 0.18μm CMOS technolog

Study and design of an interface for remote audio processing

This project focused on the study and design of an interface for remote audio processing, with the objective of acquiring by filtering, biasing, and amplifying an analog signal before digitizing it by means of two MCP3208 ADCs to achieve a 24-bit resolution signal. The resulting digital signal was then transmitted to a Raspberry Pi using SPI protocol, where it was processed by a Flask server that could be accessed from both local and remote networks. The design of the PCB was a critical component of the project, as it had to accommodate various components and ensure accurate signal acquisition and transmission. The PCB design was created using KiCad software, which allowed for the precise placement and routing of all components. A major challenge in the design of the interface was to ensure that the analog signal was not distorted during acquisition and amplification. This was achieved through careful selection of amplifier components and using high-pass and low-pass filters to remove any unwanted noise. Once the analog signal was acquired and digitized, the resulting digital signal was transmitted to the Raspberry Pi using SPI protocol. The Raspberry Pi acted as the host for a Flask server, which could be accessed from local and remote networks using a web browser. The Flask server allowed for the processing of the digital signal and provided a user interface for controlling the gain and filtering parameters of the analog signal. This enabled the user to adjust the signal parameters to suit their specific requirements, making the interface highly flexible and adaptable to a variety of audio processing applications. The final interface was capable of remote audio processing, making it highly useful in scenarios where the audio signal needed to be acquired and processed in a location separate from the user. For example, it could be used in a recording studio, where the audio signal from the microphone could be remotely processed using the interface. The gain and filtering parameters could be adjusted in real-time, allowing the sound engineer to fine-tune the audio signal to produce the desired recording. In conclusion, the project demonstrated the feasibility and potential benefits of using a remote audio processing system for various applications. The design of the PCB, selection of components, and use of the Flask server enabled the creation of an interface that was highly flexible, accurate, and adaptable to a variety of audio processing requirements. Overall, the project represents a significant step forward in the field of remote audio processing, with the potential to benefit many different applications in the future

A Novel Power-Efficient Wireless Multi-channel Recording System for the Telemonitoring of Electroencephalography (EEG)

This research introduces the development of a novel EEG recording system that is modular, batteryless, and wireless (untethered) with the supporting theoretical foundation in wireless communications and related design elements and circuitry. Its modular construct overcomes the EEG scaling problem and makes it easier for reconfiguring the hardware design in terms of the number and placement of electrodes and type of standard EEG system contemplated for use. In this development, portability, lightweight, and applicability to other clinical applications that rely on EEG data are sought. Due to printer tolerance, the 3D printed cap consists of 61 electrode placements. This recording capacity can however extend from 21 (as in the international 10-20 systems) up to 61 EEG channels at sample rates ranging from 250 to 1000 Hz and the transfer of the raw EEG signal using a standard allocated frequency as a data carrier. The main objectives of this dissertation are to (1) eliminate the need for heavy mounted batteries, (2) overcome the requirement for bulky power systems, and (3) avoid the use of data cables to untether the EEG system from the subject for a more practical and less restrictive setting. Unpredictability and temporal variations of the EEG input make developing a battery-free and cable-free EEG reading device challenging. Professional high-quality and high-resolution analog front ends are required to capture non-stationary EEG signals at microvolt levels. The primary components of the proposed setup are the wireless power transmission unit, which consists of a power amplifier, highly efficient resonant-inductive link, rectification, regulation, and power management units, as well as the analog front end, which consists of an analog to digital converter, pre-amplification unit, filtering unit, host microprocessor, and the wireless communication unit. These must all be compatible with the rest of the system and must use the least amount of power possible while minimizing the presence of noise and the attenuation of the recorded signal A highly efficient resonant-inductive coupling link is developed to decrease power transmission dissipation. Magnetized materials were utilized to steer electromagnetic flux and decrease route and medium loss while transmitting the required energy with low dissipation. Signal pre-amplification is handled by the front-end active electrodes. Standard bio-amplifier design approaches are combined to accomplish this purpose, and a thorough investigation of the optimum ADC, microcontroller, and transceiver units has been carried out. We can minimize overall system weight and power consumption by employing battery-less and cable-free EEG readout system designs, consequently giving patients more comfort and freedom of movement. Similarly, the solutions are designed to match the performance of medical-grade equipment. The captured electrical impulses using the proposed setup can be stored for various uses, including classification, prediction, 3D source localization, and for monitoring and diagnosing different brain disorders. All the proposed designs and supporting mathematical derivations were validated through empirical and software-simulated experiments. Many of the proposed designs, including the 3D head cap, the wireless power transmission unit, and the pre-amplification unit, are already fabricated, and the schematic circuits and simulation results were based on Spice, Altium, and high-frequency structure simulator (HFSS) software. The fully integrated head cap to be fabricated would require embedding the active electrodes into the 3D headset and applying current technological advances to miniaturize some of the design elements developed in this dissertation

Transmission Line Resistance Compression Networks and Applications to Wireless Power Transfer

Microwave-to-dc rectification is valuable in many applications, including RF energy recovery, dc-dc conversion, and wireless power transfer. In such applications, it is desired for the microwave rectifier system to provide a constant RF input impedance. Consequently, variation in rectifier input impedance over varying incident power levels can hurt system performance. To address this challenge, we introduce multiway transmission line resistance compression networks (TLRCNs) for maintaining near-constant input impedance in RF-to-dc rectifier systems. A development of TLRCNs is presented, along with their application to RF-to-dc conversion and wireless power transfer. We derive analytical expressions for the behavior of TLRCNs, and describe two design methodologies applicable to both single and multistage implementations. A 2.45-GHz four-way TLRCN network is implemented and applied to create a 4-W resistance compressed rectifier system that has narrow-range resistive input characteristics over a 10-dB power range. It is demonstrated to improve the impedance match to mostly resistive but variable input impedance class-E rectifiers over a 10-dB power range. The resulting TLRCN plus rectifier system has >50% RF-to-dc conversion efficiency over a >10-dB input power range at 2.45 GHz (peak efficiency 70%), and standing wave ratio <;1.1 over a 7.7-dB range, despite a nonnegligible reactive component in the rectifier loads

A Class-E Inductive Powering Link with Backward Data Communications for Implantable Sensor Systems

The design and implementation of a wireless power and data transfer system based on inductive coupling, having the potential to be used in numerous implantable bio-medical sensors and systems, is presented. The system consists of an external (primary) unit and an internal (secondary) unit. The external unit incorporates a high-efficiency switch-mode Class-E amplifier operating at ~200 kHz for driving the primary coil. The secondary unit consists of a parallel resonant coil followed by the power recovery circuitry. Means for backward data communication from the internal to the external unit over the same pair of coils has been realized using a simple FSK-based modulation scheme incorporated into the internal unit. FSK demodulation and associated filtering are integrated with the base inductive powering system. Prototype system test results indicate the inductive link efficiency can exceed 80% under optimum operating conditions with the overall power transfer efficiency of approximately 30%. The communication system is capable of transmitting up to 10kbps of data with the FSK carrier frequency (i.e., middle-frequency) being only 120kHz. The complete system functions reliably over an inter-coil distances exceeding 2.5cm with a 5V dc supply

Radio frequency energy harvesting for autonomous systems

A thesis submitted to the University of Bedfordshire in partial fulfilment of the requirements for the degree of Doctor of PhilosophyRadio Frequency Energy Harvesting (RFEH) is a technology which enables wireless power delivery to multiple devices from a single energy source. The main components of this technology are the antenna and the rectifying circuitry that converts the RF signal into DC power. The devices which are using Radio Frequency (RF) power may be integrated into Wireless Sensor Networks (WSN), Radio Frequency Identification (RFID), biomedical implants, Internet of Things (IoT), Unmanned Aerial Vehicles (UAVs), smart meters, telemetry systems and may even be used to charge mobile phones. Aside from autonomous systems such as WSNs and RFID, the multi-billion portable electronics market – from GSM phones to MP3 players – would be an attractive application for RF energy harvesting if the power requirements are met. To investigate the potential for ambient RFEH, several RF site surveys were conducted around London. Using the results from these surveys, various harvesters were designed and tested for different frequency bands from the RF sources with the highest power density within the Medium Wave (MW), ultra- and super-high (UHF and SHF) frequency spectrum. Prototypes were fabricated and tested for each of the bands and proved that a large urban area around Brookmans park radio centre is suitable location for harvesting ambient RF energy. Although the RFEH offers very good efficiency performance, if a single antenna is considered, the maximum power delivered is generally not enough to power all the elements of an autonomous system. In this thesis we present techniques for optimising the power efficiency of the RFEH device under demanding conditions such as ultra-low power densities, arbitrary polarisation and diverse load impedances. Subsequently, an energy harvesting ferrite rod rectenna is designed to power up a wireless sensor and its transmitter, generating dedicated Medium Wave (MW) signals in an indoor environment. Harvested power management, application scenarios and practical results are also presented