Doctor of Philosophy, Case Western Reserve University, 2022, EECS - Electrical Engineering

The development of flexible hybrid electronics (FHE) is enabling a new generation of highly functional implantable devices for a diverse set of applications including neural interfacing, drug delivery, pain management and cardiac monitoring. These devices leverage the mechanical flexibility and small form factor associated with FHE to produce devices that can conform to the irregular topographies associated with deployment. Next generation devices will require flexible materials for sensing elements as well as highly protective, mechanically compliant materials for device packaging. This dissertation explores the use of polydimethysiloxane (PDMS) for strain sensing and non-hermetic packaging. The first component of this dissertation involves the development of a flexible pulsation sensor (FPS) for real-time monitoring of blood pressure in vascular grafts using a piezoresistive PDMS composite for the strain sensing element. The composite is comprised of carbon-black and polydimethylsiloxane (CB-PDMS). It was determined that a carbon black concentration of 14 wt. % produced composite films with a gauge factor and Young's modulus suitable for the application. A fully integrated, wireless flexible pulsation sensor (FPS) was successfully developed and benchtop experiments showed that the CB-PDMS based FPS can precisely monitor pressure waveform in a vascular graft. The second component of this dissertation involves the development of an all-polymer, non-hermetic packaging technology for flexible implantable systems based on sequential stacks of PDMS and Parylene-C thin-film bilayers. The bilayer structure leverages the favorable attributes of the two materials while simultaneously compensating for their weaknesses. The multi-stack, bilayer architecture yields a non-hermetic package that is both highly protective of moisture intrusion and mechanically flexible. The stacked, bilayer structure capitalizes on the fact that failure-inducing defects in a single layer are l (open full item for complete abstract)

Committee: Christian Zorman (Committee Chair); Ming-Chun Huang (Committee Member); Gary Wnek (Committee Member); Kath Bogie (Committee Member) Subjects: Biomedical Engineering; Electrical Engineering

Doctor of Philosophy, Case Western Reserve University, 2014, EECS - Electrical Engineering

This work describes the design and testing of a wireless implantable bladder pressure sensor suitable for chronic implantation in humans. The sensor was designed to fulfill the unmet need for a chronic bladder pressure sensing device in urological fields such as urodynamics for diagnosis and neuromodulation for bladder control. Neuromodulation would particularly benefit from a wireless bladder pressure sensor providing real-time pressure feedback to an implanted stimulator, resulting in greater bladder capacity while using less power. The pressure sensing system consists of an implantable microsystem, an external RF receiver, and a wireless battery charger. The implant is small enough to be cystoscopically implanted within the bladder wall, where it is securely held and shielded from the urine stream, protecting both the device and the patient. The implantable microsystem consists of a custom application-specific integrated circuit (ASIC), pressure transducer, rechargeable battery, and wireless telemetry and recharging antennas. Because the battery capacity is extremely limited, the ASIC was designed using an ultra-low-power methodology in which power is dynamically allocated to instrumentation and telemetry circuits by a power management unit. A low-power regulator and clock oscillator set the minimum current draw at 7.5 µA and instrumentation circuitry is operated at low duty cycles to transmit 100-Hz pressure samples while consuming 74 µA. An adaptive transmission activity detector determines the minimum telemetry rate to limit broadcast of unimportant samples. Measured results indicated that the power management circuits produced an average system current of 16 µA while reducing the number of transmitted samples by more than 95% with typical bladder pressure signals. The wireless telemetry range of the system was measured to be 35 cm with a bit-error-rate of 10-3, and the battery was wirelessly recharged at distances up to 20 cm. A novel biocompatible (open full item for complete abstract)

Committee: Steven Garverick (Advisor); Swarup Bhunia (Committee Co-Chair); Margot Damaser (Committee Member); Pedram Mohseni (Committee Member); Christian Zorman (Committee Member) Subjects: Biomedical Engineering; Electrical Engineering

Doctor of Philosophy, Case Western Reserve University, 2012, EECS - Computer Engineering

Implantable systems are used in various contexts for interfacing with the body and for providing real-time monitoring and control capability. In particular, implantable neural interfaces can be used to radically improve our understanding of the nervous system and to provide precise treatments for a variety of neurological problems. However, these systems require significant computing power to perform real-time in-situ analysis of neural signals to recognize behaviorally meaningful patterns which are used to trigger appropriate corrective actions. Due to the tight area and power constraints of neural implants, it is important to develop novel algorithm-architecture-circuit co-design approaches for efficient implementation of neural signal analysis. First, we develop an algorithmic framework which is suitable for ultralow-power hardware implementation while simultaneously satisfying emerging design requirements like reliability and security. The algorithm is based on building a dynamic hierarchical multi-level vocabulary of neural patterns in the wavelet domain. The vocabulary-based analysis allows recognition of neural patterns at multiple levels (spike, burst, and pattern of bursts across multiple channels) and transmission of recorded data with large compression, thus, saving power and communication bandwidth of the integrated telemetry device. Hardware implementation of the proposed algorithm aims at reducing system power through choice of appropriate architecture and circuit-level design techniques. We show that a super-threshold design operating at a much higher frequency can achieve comparable energy dissipation as a sub-threshold low-frequency design through application of extensive power gating. It also provides significantly higher robustness of operation and yield under large process variations. We propose an architecture-level preferential design approach for further energy reduction at the cost of graceful degradation in output signal quality under voltag (open full item for complete abstract)

Committee: Swarup Bhunia PhD (Committee Chair); Christos Papachristou PhD (Committee Member); Steve Garverick PhD (Committee Member); Hillel Chiel PhD (Committee Member) Subjects: Biomedical Engineering; Computer Engineering

Doctor of Philosophy, Case Western Reserve University, 2009, EECS - Electrical Engineering

Genetic engineering of mice DNA sequences with real-time physiological monitoring has become the most critical research tool for identifying genetic variation susceptibility to diseases. Genetically engineered mice have been widely used as research vehicles with their physiological data being highly important for advanced biological research. Animal-based research results are expected to make a significant impact in treating similar human diseases. Due to the small size of a laboratory mouse, a miniature, light-weight, wireless, batteryless, and implantable multi-channel bio-sensing microsystem is developed to capture real-time accurate biological signals from an untethered animal in its natural habitat, thus eliminating stress and post-implant trauma-induced information distortion. A reliable radio frequency (RF) powering technique based on inductive coupling allows the batteryless microsystem to be achieved with a small form factor. The RF powering technique widely employed in biomedical applications typically relies on a set of external coil and an implantable coil with a relatively fixed position to inductively couple an external RF energy to an implanted microsystem. However, the proposed microsystem is implanted in a freely roaming mouse; hence resulting in a drastically changing magnetic coupling as the mouse moves and tilts its position with respect to the external stationary coil. Therefore, an optimized remote RF powering system with an adaptive control capability is designed and implemented. The prototype sensing microsystem can detect two vital signals, electrocardiogram (EKG) and core body temperature, and wirelessly transmit the information to a nearby receiver by employing a low power CMOS integrated circuits design with a minimal number of off-chip components for a high-level system integration. The overall implant unit exhibits a dimension of 9 mm x 7 mm x 3 mm and a weight of 400 mg including a pair of stainless steel EKG electrodes. A low power 2 (open full item for complete abstract)

Committee: Darrin Young (Advisor); Wen Ko (Committee Member); Francis Merat (Committee Member); Chung-Chiun Liu (Committee Member) Subjects: Electrical Engineering