Near-field baseband communication system for use in biomedical implants

This thesis introduces the reader to the near-field baseband pulse radio communication for biomedical implants. It details the design and implementation of the complete communication system with a particular emphasis on the antenna structure and waveform coding that is compatible with this particular technology. The wireless communication system has great employability in small pill-sized biomedical diagnostic devices offering the advantages of low power consumption and easy integration with SoC and lab-in-a-pill technologies. The greatest challenge was the choice of antenna that had to be made to effectively transmit the pulses. A systematic approach has been carried out in arriving at the most suitable antenna for efficient emanation of pulses and the fields around it are analysed electromagnetically using a commercially available software. A magnetic antenna can be used to transmit the information from inside a human body to the outside world. The performance of the above antenna was evaluated in a salt solution of different concentrations which is similar to a highly conductive lossy medium like a human body. Near-field baseband pulse transmission is a waveform transmission scheme wherein the pulse shape is crucial for decoding information at the receiver. This demands a new approach to the antenna design, both at the transmitter and the receiver. The antenna had to be analysed in the time-domain to know its effects on the pulse and an expression for the antenna bandwidth has been proposed in this thesis. The receiving antenna should be able to detect very short pulses and while doing so has to also maintain the pulse shape with minimal distortion. Different loading congurations were explored to determine the most feasible one for receiving very short pulses. Return-to-zero (RZ), Non-return-zero (NRZ) and Manchester coded pulse waveforms were tested for their compatibility and performance with the near-field baseband pulse radio communication. It was concluded that Manchester coded waveform are perfectly suited for this particular near-field communication technology. Pulse interval modulation was also investigated and the findings suggested that it was easier to implement and had a high throughput rate too. A simple receiver algorithm has been suggested and practically tested on a digital signal processor. There is further scope for research to develop complex signal processing algorithms at the receiver

A long-range and long-life telemetry data-acquisition system for heart rate and multiple body temperatures from free-ranging animals

The system includes an implantable transmitter, external receiver-retransmitter collar, and a microprocessor-controlled demodulator. The size of the implant is suitable for animals with body weights of a few kilograms or more; further size reduction of the implant is possible. The ECG is sensed by electrodes designed for internal telemetry and to reduce movement artifacts. The R-wave characteristics are then specifically selected to trigger a short radio frequency pulse. Temperatures are sensed at desired locations by thermistors and then, based on a heartbeat counter, transmitted intermittently via pulse interval modulation. This modulation scheme includes first and last calibration intervals for a reference by ratios with the temperature intervals to achieve good accuracy even over long periods. Pulse duration and pulse sequencing are used to discriminate between heart rate and temperature pulses as well as RF interference

Performance Improvement in Passive Backscatter Based RFID System with Low DCR Modulations

This paper presents application of the low Duty Cycle Ratio (DCR) modulations: isochronous Digital Pulse Position Modulation (DPPM) and anisochronous Digital Pulse Interval Modulation (DPIM) in backscatter based passive RFID communication system. The proposed modulations are compared to commonly used Amplitude Shift Keying (ASK) modulation. Low DCR modulations are customized for data transmission through inductively coupled link between reader and the tag operating at frequency of 13.56 MHz. The RFID system is mathematically formulated and the performances of the tag are evaluated for each modulation. Observed parameters are modulation depth of backscattered signal, voltage-current characteristics of tag rectifier circuit and ripple of rectifier output voltage. The application of proposed low DCR modulation techniques improves the performance of the RFID system by up to 250%

Perioperative Considerations of a Patient with Implementable Pacemaker

A properly functioning cardiac conduction system is integral to a patient\u27s physiologic well-being, as it contributes to an efficient cardiac output. There are a growing number of indications for pacemaker therapy, including atrioventricular blocks, fascicular blocks, sinus node dysfunction, prevention and treatment of tachyarrhythmias, syncope, heart failure, and dilated cardiomyopathy (Gregoratos et al., 2005). Technology in these devices has evolved from simple single-chamber, fixed-rate pacemakers to more complex multichamber, rate-responsive units that have pacing, cardioversion, and defibrillation capabilities (Gregoratos et al., 2005). Indications for cardiac pacing are set to expand even further as technology continues to advance (Salukhe, Dob & Sutton, 2004). It is estimated that more than 325,000 pacemakers are implanted in the United States each year (Mattingly, 2005). The majority of the 1 million paced individuals in the United States are over the age of 65, currently the most rapidly growing segment of the population (Dawes, Mahabir, Hillier, Cassidy, Haas & Gillis, 2006). The aging population, improvements in implantable devices, and new indications for implantable cardiac devices will lead to an escalating number of patients in the new millennium with these devices (Miller, 2005). This will inevitably result in nurse anesthetists encountering more patients with cardiac devices in practice (Salukhe et al., 2004). Since the invention of pacemakers, technology has made them more resistant to electromagnetic interference (EMI); however, in the surgical setting several problems still occur. Although the complications are fairly low, they are serious and often life threatening when they do occur (Madigan, Choudlrri, Chen, Spotnitz, Oz & Edwards, 1999). Adverse outcomes associated with an implantable cardiac device include damage to the device, failure of the device to pace or shock, bums to the cardiac tissue, inappropriate reprogramming, asynchronous pacing, or inappropriate antitachy cardia pacing (Zaidan et al., 2005). Several adverse clinical outcomes that can be seen include tachyarrhythmia, bradyarrhythmia, hypotension, myocardial infarction, or actual damage to the myocardial tissue (Zaidan et al., 2005). Electrocautery can be a significant source of EMI in the operative setting, if proper precautions are not taken to decrease the incidence (Dawes et al., 2006)

Millimeter-Scale and Energy-Efficient RF Wireless System

This dissertation focuses on energy-efficient RF wireless system with millimeter-scale dimension, expanding the potential use cases of millimeter-scale computing devices. It is challenging to develop RF wireless system in such constrained space. First, millimeter-sized antennae are electrically-small, resulting in low antenna efficiency. Second, their energy source is very limited due to the small battery and/or energy harvester. Third, it is required to eliminate most or all off-chip devices to further reduce system dimension. In this dissertation, these challenges are explored and analyzed, and new methods are proposed to solve them. Three prototype RF systems were implemented for demonstration and verification. The first prototype is a 10 cubic-mm inductive-coupled radio system that can be implanted through a syringe, aimed at healthcare applications with constrained space. The second prototype is a 3x3x3 mm far-field 915MHz radio system with 20-meter NLOS range in indoor environment. The third prototype is a low-power BLE transmitter using 3.5x3.5 mm planar loop antenna, enabling millimeter-scale sensors to connect with ubiquitous IoT BLE-compliant devices. The work presented in this dissertation improves use cases of millimeter-scale computers by presenting new methods for improving energy efficiency of wireless radio system with extremely small dimensions. The impact is significant in the age of IoT when everything will be connected in daily life.PHDElectrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/147686/1/yaoshi_1.pd

A Versatile Hermetically Sealed Microelectronic Implant for Peripheral Nerve Stimulation Applications

This article presents a versatile neurostimulation platform featuring a fully implantable multi-channel neural stimulator for chronic experimental studies with freely moving large animal models involving peripheral nerves. The implant is hermetically sealed in a ceramic enclosure and encapsulated in medical grade silicone rubber, and then underwent active tests at accelerated aging conditions at 100°C for 15 consecutive days. The stimulator microelectronics are implemented in a 0.6-μm CMOS technology, with a crosstalk reduction scheme to minimize cross-channel interference, and high-speed power and data telemetry for battery-less operation. A wearable transmitter equipped with a Bluetooth Low Energy radio link, and a custom graphical user interface provide real-time, remotely controlled stimulation. Three parallel stimulators provide independent stimulation on three channels, where each stimulator supports six stimulating sites and two return sites through multiplexing, hence the implant can facilitate stimulation at up to 36 different electrode pairs. The design of the electronics, method of hermetic packaging and electrical performance as well as in vitro testing with electrodes in saline are presented

A Fully Implantable Opto-Electro Closed-Loop Neural Interface for Motor Neuron Disease Studies

This paper presents a fully implantable closed-loop device for use in freely moving rodents to investigate new treatments for motor neuron disease. The 0.18 µm CMOS integrated circuit comprises 4 stimulators, each featuring 16 channels for optical and electrical stimulation using arbitrary current waveforms at frequencies from 1.5 Hz to 50 kHz, and a bandwidth programmable front-end for neural recording. The implant uses a Qi wireless inductive link which can deliver >100 mW power at a maximum distance of 2 cm for a freely moving rodent. A backup rechargeable battery can support 10 mA continuous stimulation currents for 2.5 hours in the absence of an inductive power link. The implant is controlled by a graphic user interface with broad programmable parameters via a Bluetooth low energy bidirectional data telemetry link. The encapsulated implant is 40 mm × 20 mm × 10 mm. Measured results are presented showing the electrical performance of the electronics and the packaging method