Micromachined Magnetoelastic Sensors and Actuators for Biomedical Devices and Other Applications.

Magnetoelastic materials exhibit coupling between material strain and magnetization; this coupling provides the basis for a number of wireless transducers. This thesis extends past work on microfabricated magnetoelastic sensors in three ways. First, a new class of strain sensors based on the ΔE effect are presented. Two sensor types are described – single and differential. The single sensor has an active area of 7×2 mm2 and operates at a resonant frequency of 230.8 kHz with a sensitivity of 13×103 ppm/mstrain and a dynamic range of 0.05-1.05 mstrain. The differential sensor includes a strain-independent 2×0.5 mm2 reference resonator in addition to a 2.5×0.5 mm2 sensing element. The sensor resonance is at 266.4 kHz and reference resonance is at 492.75 kHz. The differential sensor has a dynamic range of 0-1.85 mstrain, a sensitivity of 12.5×103¬¬ ppm/mstrain, and is temperature compensated in the 23-60°C range. Second, fluidic actuation by resonant magnetoelastic devices is presented. This transduction is performed in the context of an implantable device, specifically the Ahmed glaucoma drainage device (AGDD). Aspherical 3D wireless magnetoelastic actuators with small form factors and low surface profiles are integrated with the AGDD; the fluid flow generated by the actuators is intended to limit cellular adhesion to the implant surface that ultimately leads to implant encapsulation and failure. The actuators measure 10.3×5.6 mm2 with resonant frequencies varying from 520 Hz to 4.7 kHz for the different actuator designs. Flow velocities up to 266 μm/s are recorded at a wireless activation range of 25-30 mm, with peak actuator vibration amplitudes of 1.5 μm. Finally, detection techniques for improving the measurement performance of wireless magnetoelastic systems are presented. The techniques focus on decoupling of the excitation magnetic signal from the sensor response to improve measurement sensitivity and noise immunity. Three domains – temporal, frequency, and spatial – are investigated for signal feedthrough. Quantitative results are presented for temporal and frequency domain decoupling. Temporal decoupling is used to measure strain sensors with resonant frequencies in the 125 kHz range, whereas frequency domain decoupling is implemented to measure 44 kHz magnetoelastic resonators.PhDElectrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/116647/1/venkatp_1.pd

WIRELESS IMPLANTABLE MAGNETOELASTIC SENSORS AND ACTUATORS FOR BIOMEDICAL APPLICATIONS

Magnetoelastic sensors represent a low-cost wireless and battery-less method for monitoring parameters in embedded or implanted applications; however, some limitations still exist preventing their commercial implementation. Presented in this work are a variety of studies that are aimed at improving the feasibility of magnetoelastic materials for sensing and actuating applications. Magnetoelastic resonant sensors of non-standard geometries were investigated to determine if geometry could play a role on the sensitivity of the sensor response to mass loading. It was shown that a significant increase in sensitivity could be achieved by using triangular sensors rather than standard rectangular strips. A method for monitoring multiple parameters on a single magnetoelastic resonant strip was also pursued. It was demonstrated that multiple parameters will have different effects depending on the location of the applied load due to the effect of sensor areas with zero vibration at different harmonics of the fundamental resonant frequency. Magneto-harmonic sensors and actuators were also explored in this work. Specifically, it was demonstrated that magnetoelastic sensors could be implemented as a means of detecting stresses on deep tissue wounds, which are critical for proper healing of certain wound sites after surgery. Both a suture and a suture anchor design were investigated for their efficacy at monitoring forces applied to tendon repair sites. Two detection devices were fabricated and built for this work which represent low-cost alternatives (both less than $200 each) to commercially available alternatives that minimally cost tens of thousands of dollars. This advancement reinforces the claim that magnetoelastic materials are a low-cost and portable sensing solution. The biodegradability and cytotoxicity of a promising magnetoelastic material for biomedical applications, specifically Galfenol (iron-gallium), was also investigated. Cytotoxicity tests demonstrated that concentrations much higher than would be likely to be encountered in vivo are necessary to cause significant cellular toxicity. Additionally, surface characterization of the degraded materials suggests that the degradation rate of Galfenol can be wirelessly controlled through application of externally applie

Improving the mechanistic study of neuromuscular diseases through the development of a fully wireless and implantable recording device

Neuromuscular diseases manifest by a handful of known phenotypes affecting the peripheral nerves, skeletal muscle fibers, and neuromuscular junction. Common signs of these diseases include demyelination, myasthenia, atrophy, and aberrant muscle activity—all of which may be tracked over time using one or more electrophysiological markers. Mice, which are the predominant mammalian model for most human diseases, have been used to study congenital neuromuscular diseases for decades. However, our understanding of the mechanisms underlying these pathologies is still incomplete. This is in part due to the lack of instrumentation available to easily collect longitudinal, in vivo electrophysiological activity from mice. There remains a need for a fully wireless, batteryless, and implantable recording system that can be adapted for a variety of electrophysiological measurements and also enable long-term, continuous data collection in very small animals. To meet this need a miniature, chronically implantable device has been developed that is capable of wirelessly coupling energy from electromagnetic fields while implanted within a body. This device can both record and trigger bioelectric events and may be chronically implanted in rodents as small as mice. This grants investigators the ability to continuously observe electrophysiological changes corresponding to disease progression in a single, freely behaving, untethered animal. The fully wireless closed-loop system is an adaptable solution for a range of long-term mechanistic and diagnostic studies in rodent disease models. Its high level of functionality, adjustable parameters, accessible building blocks, reprogrammable firmware, and modular electrode interface offer flexibility that is distinctive among fully implantable recording or stimulating devices. The key significance of this work is that it has generated novel instrumentation in the form of a fully implantable bioelectric recording device having a much higher level of functionality than any other fully wireless system available for mouse work. This has incidentally led to contributions in the areas of wireless power transfer and neural interfaces for upper-limb prosthesis control. Herein the solution space for wireless power transfer is examined including a close inspection of far-field power transfer to implanted bioelectric sensors. Methods of design and characterization for the iterative development of the device are detailed. Furthermore, its performance and utility in remote bioelectric sensing applications is demonstrated with humans, rats, healthy mice, and mouse models for degenerative neuromuscular and motoneuron diseases

Wireless Power Transfer Techniques for Implantable Medical Devices:A Review

Wireless power transfer (WPT) systems have become increasingly suitable solutions for the electrical powering of advanced multifunctional micro-electronic devices such as those found in current biomedical implants. The design and implementation of high power transfer efficiency WPT systems are, however, challenging. The size of the WPT system, the separation distance between the outside environment and location of the implanted medical device inside the body, the operating frequency and tissue safety due to power dissipation are key parameters to consider in the design of WPT systems. This article provides a systematic review of the wide range of WPT systems that have been investigated over the last two decades to improve overall system performance. The various strategies implemented to transfer wireless power in implantable medical devices (IMDs) were reviewed, which includes capacitive coupling, inductive coupling, magnetic resonance coupling and, more recently, acoustic and optical powering methods. The strengths and limitations of all these techniques are benchmarked against each other and particular emphasis is placed on comparing the implanted receiver size, the WPT distance, power transfer efficiency and tissue safety presented by the resulting systems. Necessary improvements and trends of each WPT techniques are also indicated per specific IMD

Microelectromechanical Systems and Devices

The advances of microelectromechanical systems (MEMS) and devices have been instrumental in the demonstration of new devices and applications, and even in the creation of new fields of research and development: bioMEMS, actuators, microfluidic devices, RF and optical MEMS. Experience indicates a need for MEMS book covering these materials as well as the most important process steps in bulk micro-machining and modeling. We are very pleased to present this book that contains 18 chapters, written by the experts in the field of MEMS. These chapters are groups into four broad sections of BioMEMS Devices, MEMS characterization and micromachining, RF and Optical MEMS, and MEMS based Actuators. The book starts with the emerging field of bioMEMS, including MEMS coil for retinal prostheses, DNA extraction by micro/bio-fluidics devices and acoustic biosensors. MEMS characterization, micromachining, macromodels, RF and Optical MEMS switches are discussed in next sections. The book concludes with the emphasis on MEMS based actuators

Beyond Tissue replacement: The Emerging role of smart implants in healthcare

Smart implants are increasingly used to treat various diseases, track patient status, and restore tissue and organ function. These devices support internal organs, actively stimulate nerves, and monitor essential functions. With continuous monitoring or stimulation, patient observation quality and subsequent treatment can be improved. Additionally, using biodegradable and entirely excreted implant materials eliminates the need for surgical removal, providing a patient-friendly solution. In this review, we classify smart implants and discuss the latest prototypes, materials, and technologies employed in their creation. Our focus lies in exploring medical devices beyond replacing an organ or tissue and incorporating new functionality through sensors and electronic circuits. We also examine the advantages, opportunities, and challenges of creating implantable devices that preserve all critical functions. By presenting an in-depth overview of the current state-of-the-art smart implants, we shed light on persistent issues and limitations while discussing potential avenues for future advancements in materials used for these devices

Metamaterial MRI-based sensor for the post-operative monitoring of colorectal anastomosis

Anastomotic leakage (AL) is the leading cause of morbidity and mortality after bowel anastomosis, a surgical procedure used to restore luminal continuity after bowel tumour resection. Even after years of research, its occurrence has not decreased, and new methods of monitoring the wound and predicting anastomotic failure are therefore urgently required. Here we propose the use of an internal coil to increase the signal-to-noise ratio (SNR) during Magnetic Resonance Imaging (MRI ) and/or Spectroscopy (MRS). Both methods may be used to identify ischemia and oedema, considered to be clinical indications of AL. The annular nature of the anastomotic surgical wound suggests the use of a coil with an annular field-of view, mounted on a Biodegradable Anastomosis Ring (BAR), a surgical device commonly used as a temporary mechanical support that is fragmented and excreted from the body after wound healing. The proposed solution is a Magneto-Inductive (MI) ring resonator, based on a set of magnetically coupled L-C resonators. Its advantages are that its separate elements fit comfortably inside the BAR, are not mechanically connected, and consequently may be fragmented and excreted with the BAR itself. A coupled pair of 8-element MI ring resonators is proposed, operating on an anti-symmetric spatial mode to avoid coupling to the B1 field during the excitation phase of MRI. However, the electrical response of an early prototype shows that insufficient rejection of uniform fields is achieved using the most obvious arrangement. Therefore, a search of the effect of design parameters on the spectra of resonant modes supported by the electrical system is carried out to identify an arrangement offering improved decoupling. A suitable design is developed, based on physical overlap between adjacent elements in the same ring, which alters the sign and magnitude of a key magnetic coupling coefficient. MRI fields-of-view are theoretically estimated for several different arrangements for signal extraction, including devices that are mutually coupled to an external read coil and directly coupled devices. Difficulties with combining mutual coupling and B1 field rejection are identified, and wired connections are proposed as a solution. It is found that a device with a single such connection gives a sensitivity pattern with partial symmetry, whereas a quadrature tap restores full symmetry. In vitro 1H MRI is then carried out at 1.5 T and 3.0 T using agar gel immersion phantoms, both for mutually coupled systems and for directly coupled systems. As expected, mutual coupling is found to be an unsuitable readout method for a device operating on its anti-symmetric mode, but does allow analysis of the effectiveness of B1 field decoupling. Directly coupled devices operate essentially as expected, providing up to 15-fold local enhancement in SNR, compared to the system body coil.Open Acces

Navigation/traffic control satellite mission study. Volume 2 - Candidate navigation/ traffic control satellite systems identification, analysis and evaluation Final report

Satellite network for air traffic control and navigation in northern Atlantic Ocea

Intravascular Detection of Microvessel Infiltration in Atherosclerotic Plaques: An Intraluminal Extension of Acoustic Angiography

Cardiovascular disease is the leading cause of death worldwide, surpassing both stroke and cancer related mortality with 17.5 million deaths in 2014 alone. Atherosclerosis is the build-up of fatty deposits within arteries and is responsible for the majority of cardiovascular related deaths. Over the past decade, research in atherosclerosis has identified that a key limitation in the appropriate management of the disease is detecting and identifying dangerous fatty plaque build-ups before they dislodge and cause major cardiovascular events, such as embolisms, stroke, or myocardial infarctions. It has been noted that plaques vulnerable to rupture have several key features that may be used to distinguish them from asymptomatic plaques. One key identifier of a dangerous plaque is the presence of blood flow within the plaque itself since this is an indicator of growth and instability of the plaque. Recently, a superharmonic imaging method known as “acoustic angiography” has been shown to resolve microvasculature with unprecedented quality and could be a possible method of detecting blood vessel infiltration within these plaques. This dissertation describes the material and methods used to move the application of “acoustic angiography” to a reduced form factor typical of intravascular catheters and to demonstrate its ability to detect microvasculature. The implementation of this approach is described in terms of the contrast agents used to generate superharmonic signals, the dual-frequency transducers to image them, and the hardware needed to operate them in order to establish how these design choices can impact the quality of the images produced. Furthermore, this dissertation demonstrates how image processing methods such as adaptive windowing or automated sound speed correction can further enhance image quality of vascular targets. The results of these chapters show how acoustic angiography may be optimized using engineering considerations both in signal acquisition and post processing. Overall, these studies demonstrate that acoustic angiography can be performed using a catheter-deployable dual-frequency transducer to detect microvasculature through superharmonic imaging methods.Doctor of Philosoph