Impedance Transformers

Non

Implantable Transducers for Neurokinesiological Research and Neural Prostheses

The objective of this thesis was to develop a family of advanced electrical and mechanical interfaces to record activity of nerves and muscles during natural movements. These interfaces have applications in basic research and may eventually be refined for used in restoring voluntary control of movement in paralyzed persons. I) A muscle length gauge was designed that is based on piezoelectric crystals attached at the ends of a fluid filled extensible tubing. The in-vivo performance of these gauges was equal to previous length gauge designs. In addition, the ultrasound based design provided for the first time a direct muscle length calibration method. 2) An innovative nerve cuff closing technique was devised that does not reqmre suture closures. The new design uses interdigitated tubes to lock the opening and fix the lumen of a nerve cuff. The cuffs were tested in long-term mammalian implants and their performance matched or surpassed previous closure designs. The nerve cuff was further redesigned to include a more compliant cuff wall and wire electrodes. 3) Floating microelectrodes previously used for central nervous system recordings were adapted for chronic use in the peripheral nervous system. These electrodes proved disappointing in terms of signal quality and longevity. The reasons for failure are thought to be of both electrical and mechanical origin. 4) An innovative silicon micromachined peripheral single unit electrode was designed and tested. In the in-vivo tests, a limited number of recording sites successfully established short-term neural interfaces. However, the quality of the electrode performance, in terms of signal amplitude and ability to discriminate single unit potentials, was insufficient. 5) Using a finite difference model, a numerical simulation of static and dynamic electrical interactions between peripheral axons and microelectrode interfaces was derived. The model consisted of resistive and capacitive elements arranged in a 3-dimensional conductive universe (two spatial dimensions and time). Models of intrafascicular fine wire or silicon based electrodes were used to record simulated propagating action potentials. It was confirmed that electrode movement affected the recorded signal amplitude and that a dielectric layer on a silicon electrode accentuated the recorded potential field. A conducting back plane facing away from axon sources did not have a significant effect on the electrode recording properties. In conclusion, several novel implantable transducers were developed for use in neurokinesiological research. A numerical simulation of the axonal potentials recorded by intrafascicular electrodes helped interpret various shortcomings found in the in-vivo electrode performance. Although not attempted in the present thesis some of the developed technologies may have potential of transferring to clinical neural prostheses applications

Ambulatory biopotential measurement

Biopotential signals measure the electrical activity of different parts of the body. Conventional bedside monitors only provide information about the body under restricted conditions. Observation and documentation of biopotential signal during daily activities and the relation to patient symptoms may be important factors for clinical decision-making. Ambulatory monitoring helps to monitor the biopotential signal of a patient in the natural environment. The effective ambulatory system can help a physician to diagnose the patient\u27s abnormality. In this project, a low cost and flexible ambulatory biopotential system, compared to the commercially available systems, was designed and tested. Concurrently a software program was developed for data acquisition and analysis with a Personal Data Assistant (PDA). The data was analyzed in real time using the Lab VIEW PDA. Pilot data was collected using the developed hardware during different normal activities to confirm the accuracy and reliability of the developed hardware and data was collected simultaneously from both a standard ECU machine and the developed system. It was shown that during some activities the system performed as designed, however under extreme conditions where there was more motion artifact, the number of missing R waves increased. The quality of raw ECU from the developed system was as good as the standard ECU during low motion artifact. It has been demonstrated that this newly developed biopotential system is less expensive, flexible, accurate, and more reliable than the commercially available systems and could be used in different clinical and research studies

The Status of Stochastic Cooling

Presented at a symposium to celebrate the 30th anniversary of electron cooling, this report is intended to give the status of the companion technique, stochastic cooling, some 28 years after its invention. An overview of past developments reveals the close relationship between the two cooling ideas. Then the report concentrates on the principal ingredients of stochastic cooling in order to discuss the limits encountered and some recent ideas for pushing back these limits

Stable broadband tunnel-diode amplifiers in rectangular waveguides

Imperial Users onl

Measurements, Models, Systems and Design

531 s.