Power harvesting and telemetry in CMOS for implanted devices

Implanted sensors offer many advantages to study and monitor the human body. Wires or batteries often compromise their usefulness. We describe a telemetry chip that by inductive coupling supplies power to and transmits digital data from an implantable sensor. The same two coils are used to transmit both power and data. The chip fabricated in 0.5-/spl mu/m CMOS technology supplies 1.7 mA at 3.3 V, over a distance up to 25 mm between coils. Experiments emulating the effect of human tissue by introducing water bearing colloids between the two coils revealed a negligible loss of transfer efficiency. With modified Miller encoding, the data link attained 3 10/sup -5/ bit error rate at 10 kbps transmission speed over 25 mm distance. Repeated tests using the same colloids between coils resulted in a slight decrease in the signal to noise ratio of the data stream with increasing thickness.     

Modeling and canceling tremor in human-machine interfaces

Zero-phase modeling and canceling of tremor can improve precision in human-machine control applications. Past methods of tremor suppression have been hindered by feedback delays due to phase lag and by the inability to track tremor frequency over time. The weighted-frequency Fourier linear combiner (WFLC) is an adaptive noise canceller that precisely models tremor with zero phase lag. This article briefly presents the WFLC algorithm and describes its application to computer input filtering, clinical tremor quantification, and active tremor canceling for microsurgery     

Adaptive Fourier estimation of time-varying evoked potentials

An estimation procedure for dealing with time-varying evoked potentials is presented here. The evoked response is modeled as a dynamic Fourier series and the Fourier coefficients are estimated adaptively by the least mean square algorithm. Approximate expressions have been developed for the estimation error and time constant of adaptation. A procedure for optimizing the estimator performance is also presented. The effectiveness of the estimator in dealing with simulated as well as actual evoked responses is demonstrated.     

Ground-Free ECG Recording with Two Electrodes

ECG recordings normally use three electrodes?two for the differential inputs of the ECG amplifier and the third for ground. We analyze those situations where the ground electrode can be eliminated. We propose a model for the source of electrical interference and determine various parameter values. Making use of experimentally obtained data for the model parameters we suggest optimal design for a two-electrode amplifier. The two-electrode design is useful for biotelemetry, portable Holter monitors, and portable arrhythmia monitors. Under certain circumstances it may be useful for grounded monitoring equipment. The two-electrode technique has the advantage that it improves patient safety by eliminating the ground electrode. Fewer electrodes make patient attachment easier and lower electrode costs.     

Spinal Cord Injury Detection and Monitoring Using Spectral Coherence

In this paper, spectral coherence (SC) is used to study the somatosensory evoked potential (SEP) signals in rodent model before and after spinal cord injury (SCI). The SC technique is complemented with the Basso, Beattie, and Bresnahan (BBB) behavior analysis method to help us assess the status of the motor recovery. SC can be used to follow the effects of SCI without any preinjury baseline information. In this study, adult female Fischer rats received contusion injury at T8 level with varying impact heights using the standard New York University impactor. The results show that the average SC between forelimb and hindlimb SEP signals before injury was relatively high ( ges0.7). Following injury, the SC between the forelimb and hindlimb SEP signals dropped to various levels (les0.7) corresponding to the severity of SCI. The SC analysis gave normalized quantifiable results for the evaluation of SCI and recovery thereafter using the forelimb signals as an effective control, without the need of any baseline data. This technique solves the problems associated with the commonly used time-domain analysis like the need of a trained neurophysiologist to interpret the data and the need for baseline data. We believe that both SC and BBB may provide a comprehensive and complementary picture of the health status of the spinal cord after injury. The presented method is applicable to SCIs not affecting the forelimb SEP signals.     

Impact of surface loading on catalytic activity of regular and low micropore SBA-15 in the Knoevenagel condensation

The mesopores of SBA-15 are well-suited for immobilizing catalytic aminosilanes for converting substrates for fine chemicals, but these materials have micropores that could impact the observed reaction rate of immobilized catalysts. Materials are synthesized with conventional methods that produce micropores (Regular Micropore SBA-15; REG) and compared to materials with limited to no micropore volume (NMP SBA-15). These materials are functionalized with aminosilanes for testing in the Knoevenagel condensation. For low amine loadings, NMP materials have a higher observed reaction rate compared to REG materials, achieving twice the conversion in the same time. As the surface density increases, the reaction rate for NMP materials decreases since organosilane functionalization consumes surface silanols that interact cooperatively with the amine. Regardless of surface density, the NMP materials have higher observed reaction rate than the REG materials. These results demonstrate the importance of reducing micropore volume to create highly active catalytic materials.     

Effect of tantalum substitutions on microstructures and dielectric properties of calcium copper titanate (CaCu3Ti4O12) ceramic

Tantalum (Ta⁵⁺) doped CaCu₃Ti_4−xTa_xO₁₂ (x = 0.05 and 0.10) ceramics were prepared by semi-wet route using solid Ta₂O₅ powder and metal nitrate solutions. Powder X-ray diffraction confirmed the major phase formation of cubic CaCu₃Ti₄O₁₂ ceramic in the doped samples sintered at 900 °C for 6 h. Microstructure has been studied using field-emission scanning electron microscopy. The grain size is in the range of 150 nm to 1 μm for both compositions. Dielectric constant of the samples increases with increasing tantalum concentrations.     

Multiway sequential hypothesis testing for tachyarrhythmiadiscrimination

A multiway sequential hypothesis testing (M-SHT) algorithm is proposed for simultaneous discrimination of cardiac tachyarrhythmias-supraventricular tachycardia (SVT) and ventricular tachycardia (VT)-from normal sinus rhythm (NSR). The M-SHT algorithm calculates a likelihood function from atrio-ventricular delay measurements, and compares this function with thresholds derived from specified error probabilities for the arrhythmias to be discriminated. Performance of this algorithm was evaluated on dual channel endocardial electrograms recorded in the cardiac electrophysiology laboratory. Two databases were developed, one for development of the algorithm and another for evaluation. The M-SHT algorithm accurately classified 26 out of 28 NSR (2 misclassified as SVT), 31 out of 31 cases of SVT, and 41 out of 43 VT (2 misclassified as NSR). The average length of time taken for classification of the three rhythms was: 3.6 s for NSR, 5.0 s for SVT, and 1.6 s for VT. Unique features of this algorithm are that acceptable error rates for each arrhythmia are independently specified and accuracy can be traded off for a faster detection time, and vice versa     

A Battery-Powered Digital Modem for Telephone Transmission of ECG Data

We present the design of a battery-powered digital modem for transmitting ECG signals. It operates from a 5-V battery supply, uses a coil or acoustic coupler for a telephone interface, and consumes only 30 mW during transmission. We show error rates comparable to regular stand-alone modems, well within the acceptable limit of 1 bit per 100 kbits transmitted at a transmission speed of 300 Bd.