Miniaturized magnetic sensors for implantable magnetomyography

Magnetism‐based systems are widely utilized for sensing and imaging biological phenomena, for example, the activity of the brain and the heart. Magnetomyography (MMG) is the study of muscle function through the inquiry of the magnetic signal that a muscle generates when contracted. Within the last few decades, extensive effort has been invested to identify, characterize and quantify the magnetomyogram signals. However, it is still far from a miniaturized, sensitive, inexpensive and low‐power MMG sensor. Herein, the state‐of‐the‐art magnetic sensing technologies that have the potential to realize a low‐profile implantable MMG sensor are described. The technical challenges associated with the detection of the MMG signals, including the magnetic field of the Earth and movement artifacts are also discussed. Then, the development of efficient magnetic technologies, which enable sensing pico‐Tesla signals, is advocated to revitalize the MMG technique. To conclude, spintronic‐based magnetoresistive sensing can be an appropriate technology for miniaturized wearable and implantable MMG systems

Mutual injection locking of oscillator circuits through inductor coupling

This work presents an investigation of mutual injection locking of oscillator circuits through inductor coupling. A realistic analytical formulation provides insight into system behavior, with coexistent oscillation modes. The stability of these modes is determined through a perturbation analysis, extended to the calculation of the phase-noise spectral density. An analytical expression enables an understanding of the phase-noise reduction mechanism. The cases of two coupled oscillators at the fundamental frequency and two distinct oscillators at a 1/3 frequency ratio are considered. Possible applications include the oscillator phase-noise reduction and the implementation of sensors using the phase shift between the two oscillator elements.Work supported by the Spanish Ministry of Science and Innovation (ERDF/FEDER) TEC2017-88242-C3-1-R

Ultra-Low-Power Sensors and Receivers for IoT Applications

The combination of ultra-low power analog front-ends and CMOS-compatible transducers enable new applications, such as environmental monitors, household appliances, health trackers, etc. that are seamlessly integrated into our daily lives. Furthermore, wireless connectivity allows many of these sensors to operate both independently and collectively. These techniques collectively fulfil the recent surge of internet-of-things (IoT) applications that have the potential to fundamentally change daily life for millions of people.In this dissertation, the circuit and system design of wireless receivers and sensors is presented that explores the challenges of implementing long lifespan, high accuracy, and large coverage range IoT sensor networks. The first is a wake-up receiver (WuRX), which continuously monitors the RF environment to wake up a higher-power radio upon detection of a predetermined RF signature. This work both improves sensitivity and reduces power over prior art through a multi-faceted design featuring an impedance transformation network with large passive voltage gain, an active envelope detector with high input impedance to facilitate large passive voltage gain, a low-power precision comparator, and a low-leakage digital baseband correlator.Although pushing the prior WuRX performance boundary by orders of magnitude, the first work shows moderate sensitivity, inferior temperature robustness, and large area with external lumped components. Thus, the second work shows a miniaturized WuRX that is temperature-compensated, yet still consumes only nano-watt power and millimeter area while operating at 9 GHz. To further reduce the area, a global common-mode feedback is utilized across the envelope detector and baseband amplifier that eliminates the need for off-chip ac-coupling components. Multiple temperature-compensation techniques are proposed to maintain constant bandwidth of the signal path and constant clock frequency. Both WuRXs operate at 0.4 V supply, consume near-zero power and achieve ~-70 dBm sensitivity.Lastly, the first reported CMOS 2-in-1 relative humidity and temperature sensor is presented. A unified analog front-end interfaces on-chip transducers and converts the inputs into a frequency vis a high-linearity frequency-locked loop. An incomplete-settling switched-capacitor-based Wheatstone bridge is proposed to sense the inputs in a power-efficient fashion

Wearable, low-power CMOS ISFETs and compensation circuits for on-body sweat analysis

Complementary metal-oxide-semiconductor (CMOS) technology has been a key driver behind the trend of reduced power consumption and increased integration of electronics in consumer devices and sensors. In the late 1990s, the integration of ion-sensitive field-effect transistors (ISFETs) into unmodified CMOS helped to create advancements in lab-on-chip technology through highly parallelised and low-cost designs. Using CMOS techniques to reduce power and size in chemical sensing applications has already aided the realisation of portable, battery-powered analysis platforms, however the possibility of integrating these sensors into wearable devices has until recently remained unexplored. This thesis investigates the use of CMOS ISFETs as wearable electrochemical sensors, specifically for on-body sweat analysis. The investigation begins by evaluating the ISFET sensor for wearable applications, identifying the key advantages and challenges that arise in this pursuit. A key requirement for wearable devices is a low power consumption, to enable a suitable operational life and small form factor. From this perspective, ISFETs are investigated for low power operation, to determine the limitations when trying to push down the consumption of individual sensors. Batteryless ISFET operation is explored through the design and implementation of a 0.35 \si{\micro\metre} CMOS ISFET sensing array, operating in weak-inversion and consuming 6 \si{\micro\watt}. Using this application-specific integrated circuit (ASIC), the first ISFET array powered by body heat is demonstrated and the feasibility of using near-field communication (NFC) for wireless powering and data transfer is shown. The thesis also presents circuits and systems for combatting three key non-ideal effects experienced by CMOS ISFETs, namely temperature variation, threshold voltage offset and drift. An improvement in temperature sensitivity by a factor of three compared to an uncompensated design is shown through measured results, while adding less than 70 \si{\nano\watt} to the design. A method of automatically biasing the sensors is presented and an approach to using spatial separation of sensors in arrays in applications with flowing fluids is proposed for distinguishing between signal and sensor drift. A wearable device using the ISFET-based system is designed and tested with both artificial and natural sweat, identifying the remaining challenges that exist with both the sensors themselves and accompanying components such as microfluidics and reference electrode. A new ASIC is designed based on the discoveries of this work and aimed at detecting multiple analytes on a single chip. %Removed In the latter half of the thesis, Finally, the future directions of wearable electrochemical sensors is discussed with a look towards embedded machine learning to aid the interpretation of complex fluid with time-domain sensor arrays. The contributions of this thesis aim to form a foundation for the use of ISFETs in wearable devices to enable non-invasive physiological monitoring.Open Acces

RF Sensors for Monitoring the Electrical Properties of Electrolyte Solutions

A radio frequency electrical sensor for the qualitative analysis and monitoring of the electrical properties of electrolyte solutions is designed, simulated and experimentally tested in this research. This work is based on the use of planar inductors for the detection of a change in the concentration of ionic species in a liquid sample. At first a literature review on the physical chemistry of electrolyte solutions is provided. This will include topics on the conductivity and relaxation properties of electrolytes. This will be followed by a look at dielectric spectroscopy sensors, electrochemical sensors and inductive sensing devices. The principles of electrodynamics and constitutive equations are discussed. Based on these, the principles of operation of the RF electrical sensors are analysed. Two methods of theoretical analysis of such structures are investigated. These methods are; analytical solution and finite element computation method. The former offers greater insight into the system’s parameters whilst the latter offers more information regarding the whole system. Given the qualitative nature of the sensors under investigation and finite element approach was selected and used in latter chapters to obtain grater insight into the behaviour of the system. Planar inductor coils are designed on an FR4 substrate and packaged using PDMS to be used as sensors in the monitoring of electrical properties of electrolytes. Experimental results on these sensors are provided and discussed. The effects of solvent, acidity of the solutions, and environmental factors on the behaviour of the sensors shall be discussed. This is followed by finite element simulations of the sensor and the effect of various parameters on the overall behaviour of the sensing device. A transformer apparatus is also constructed and experimental data are provided for it. An electrolyte is placed on one of the coils of the transformer and scattering parameters are looked upon for data analysis. The results obtained using the FE method, is then used to obtain further information about the principle of operation of the device

Low power CMOS IC, biosensor and wireless power transfer techniques for wireless sensor network application

The emerging field of wireless sensor network (WSN) is receiving great attention due to the interest in healthcare. Traditional battery-powered devices suffer from large size, weight and secondary replacement surgery after the battery life-time which is often not desired, especially for an implantable application. Thus an energy harvesting method needs to be investigated. In addition to energy harvesting, the sensor network needs to be low power to extend the wireless power transfer distance and meet the regulation on RF power exposed to human tissue (specific absorption ratio). Also, miniature sensor integration is another challenge since most of the commercial sensors have rigid form or have a bulky size. The objective of this thesis is to provide solutions to the aforementioned challenges

Nonlinear analysis of oscillator mutual injection locking through inductor coupling

This work presents an in-depth investigation of the nonlinear behavior of two mutually injection-locked oscillators through inductor coupling. An analytical formulation, solved through an innovative procedure, facilitates the understanding of the qualitative transformations in the system solutions when increasing the coupling factor. The analysis demonstrates that, in a manner similar to the unilaterally injection-locked oscillators, families of disconnected/connected curves are obtained when increasing this factor, although the patterns, associated with distinct operation modes, are more complex. Then, an accurate numerical method to predict the behavior of coupled transistor-based oscillators is presented, based on nonlinear admittance models of the individual oscillators. Mathematical conditions are derived to solve the coupled system through a two-level contour-intersection technique. In this way, all the solutions coexisting for a given set of element and parameter values are calculated simultaneously, in an exhaustive manner. The cases of two coupled oscillators at the fundamental frequency and at 1:3 frequency ratio are considered. Possible applications include the oscillator phase-noise reduction and the implementation of sensors using the phase shift between the two oscillator elements.This work was supported in part by the Spanish Ministry of Economy and Competitiveness and the European Regional Development Fund (ERDF/FEDER) under research project TEC2017-88242-C3-1-R

Precision at Scale: System Design from Tiny Biosensors to Giant Arrays

In order to change the world, technological advancements must be made affordable and available for the general public to use. In other words, we must be able to scale our inventions effectively. Silicon integrated circuits are crucial components in scaling electronic systems because they are mass producible and offer a phenomenal cost-to-complexity ratio. This thesis summarizes the author’s work on highly scalable sensor and array systems. It presents three high precision systems, that demonstrate how the use of highly functional radio-frequency integrated circuits enables the realization of previously unfeasible architectures

Probing multivalent particle–surface interactions using a quartz crystal resonator

The rise in market-approved cellular therapies demands for advancements in process analytical technology (PAT) capable of fulfilling the requirements of this new industry. Unlike conventional biopharmaceuticals, cell-based therapies (CBT) are complex “live” products, with a high degree of inherent biological variability. This exacerbates the need for in-process monitoring and control of critical product attributes, in order to guarantee safety, efficacious and continuous supply of this CBT. There are therefore mutual industrial and regulatory motivations for high throughput, non-invasive and non-destructive sensors, amenable to integration in an enclosed automated cell culture system. While a plethora of analytical methods is available for direct characterization of cellular parameters, only a few satisfy the requirements for online quality monitoring of industrial-scale bioprocesses. [Continues.