D. Krizaj

Validation of an accelerometer for determination of muscle belly radial displacement

A commercial variable-capacitance micromachined accelerometer was validated for muscle belly radial displacement measurement. The displacement was calculated by the acceleration data being integrated twice and was compared with the results obtained simultaneously by an accurate mechanical displacement sensor based on an optical encoder. The aim of the investigation was to evaluate the accuracy and precision of an accelerometer for tensiomyography, which is a method for the detection of skeletal muscle contractile properties on the basis of muscle belly radial displacement. A hundred measurements at a bandwidth of 2300 Hz were performed. It was shown that the accuracy and precision in determination of the maximum displacement and the time of the maximum displacement from the calculated curve were satisfactory, in spite of the standard deviation of the twice-integrated acceleration growing approximately linearly with time. The results were accurate enough since the elapsed time from the beginning of the integration was small (less than 75 ms). The measured maximum displacement ranges were between 9.2 and 10.2 mm. The mean relative error was less than 1% (SD=0.02 mm) for the maximum displacement and about 1% (SD=0.6 ms) for the time to maximum displacement. The accuracy of the half-relaxation time determination was more uncertain because of the relatively high relative error of −2.4% (SD=3 ms). Results showed that a commercial micromachined accelerometer could be suitable for the measurement of muscle belly radial displacement and used for development of a future miniaturised and flexible system for the measurement of similar displacements.

Multivariate analysis of electrical impedance spectra for relaxed and contracted skeletal muscle.

Four-electrode impedance spectra of relaxed and contracted muscle biceps brachii were analyzed in an adult human subject over the frequency range from 300 Hz to 75 kHz. A feasibility of the principal component analysis of bioimpedance measurement for the evaluation of skeletal muscle contractile state was examined. The principal components score plots show a data grouping of the impedance spectra from the two muscle groups. The classification was performed using a soft independent modeling of class analogy (SIMCA) method. The data set comprised 32 samples (16 samples of contracted muscle and 16 samples of relaxed muscle). The leave-one-out test of the classification yields about 80% of correctly classified samples (11 samples for contracted and 15 samples for relaxed muscle).

Numerical computation of impedances of a human tooth for estimation of the root canal length

Alternative current (ac) current conduction through a human tooth has been investigated through numerical simulation. Numerical calculation of the impedance between the file (electrode) inserted in the root canal of the tooth and the outer electrode enables investigation of the impedance method used in dentistry for evaluation of the root canal length. Simulations confirm the improved sensitivity of the impedance method using the results of multiple frequency measurements.

Modelling and characterization of thin film planar capacitors: inherent errors and limits of applicability of partial capacitance methods

The analytical partial capacitance methods (PCM) widely accepted for calculation of properties of capacitors with planar electrodes, coplanar strip waveguides (CPS) and coplanar waveguides (CPW) are reviewed based on the challenges met during the development and tailoring of (Ba, Sr)TiO3 thin films fabricated on different types of substrates. An alternative view on the conformal mapping method is given, a correction for electrodes of finite thickness is introduced and the applicability of easy-to-use simplified analytical equations is reviewed and extended. Calculation results obtained with different models are compared against the results of FEM numerical simulation in the parameter range relevant for development of tuneable ferroelectric films. The models were found to be less accurate than previously reported. Accordingly, guidelines for extending the applicability domain and for minimizing the inherent errors of the analytical models are presented. The discussion is focused on the possible improvements of the measurement techniques.

An instrumentation amplifier as a front-end for a four-electrode bioimpedance measurement

The performance of a monolithic instrumentation amplifier used as an interface for a four-electrode bioimpedance measurement is examined with a commercially available impedance meter based on an auto-balancing bridge. The errors due to particularities in the input stage of the impedance meter, when used without a front-end, were several orders of magnitude higher than the measured quantity. The analysis was performed on an electrical circuit model of the skin and electrodes over a frequency range of 20 Hz to 1 MHz. The achieved accuracy with balanced electrode impedances for the frequencies up to 100 kHz can be below 0.2% for impedance magnitude and 0.1 degrees for impedance phase, which is within the specified basic accuracy range of the LCR-meter used for the measurements. At frequencies above 100 kHz the errors are increasing and are higher than the LCR-meters basic accuracy. This study indicates that use of an instrumentation amplifier as a front-end with the particular LCR-meter can significantly improve the measurement accuracy of the four-electrode bioimpedance measurement at low frequencies.

Side-illuminated 100 μm pitch X-ray detector for digital radiology

A side-illuminated silicon X-ray strip detector for digital radiology with 100 μm pitch was designed, fabricated and characterized. In order to reduce noise and improve resolution of the detector, design and processing was optimized for low leakage currents, high dynamic resistance of biasing resistors, reduced strip pitch and wafer thickness. Operation of the field oxide field effect transistor (FOXFET) structure was analyzed by a 2D numerical device simulator and compared to experimental results. Measured results reveal that the detector is suitable for application in X-ray detection systems.

Spiral junction termination

A new junction termination structure composed of a decreasing width spiral diffused resistor connecting anode and cathode region is presented. Leakage current through the spiral resistor results in optimized voltage distribution between the spiral turns which effectively reduces high electric field at the anode junction curvature. By circuit mode device modeling approach, the influence of several design parameters of importance on the breakdown properties were investigated. A major concern was shown to be the possibility of a premature reach-through between the spiral turns, resulting in increased leakage current and soft breakdown characteristics. A design with nonuniform spiral width and optimized spacing between the spiral turns is proposed, enabling almost ideal breakdown voltages with reduced spiral leakage current and eliminated reach-through between the spiral turns. Low susceptibility to oxide charges is confirmed by irradiation test, showing improvement of breakdown properties after irradiation. Further improvement in operation is obtained by a floating spiral structure due to spiral resistance limiting the increase of the multiplication induced current through the spiral. In comparison with common termination structures the spiral junction termination offers simple design and processing, close to ideal breakdown voltages and high reliability of operation.

Diffused spiral junction termination structure: modeling and realization

An innovative junction termination structure for efficient improvement of planar pn junction breakdown properties is studied. It is composed of a high-resistivity layer, connected to the anode junction and winding around it in a spiral fashion. Leakage current through the diffused resistor results in the spread of potential along the spiral resistor and reduction of high electric field at the junction curvature region. An optimized design with decaying spiral width and increasing spacing between the spiral turns leads to close to ideal breakdown voltages as confirmed by device modeling as well as experimental results.

Evaluation of muscle dynamic response measured before and after treatment of spastic muscle with a BTX-A − A case study

Contraction properties of spastic muscle has been evaluated using tensiomyographic method before and after treatment of spastic muscles with BTX-A. Significant differences are observed in TMG responses of a spastic muscle of cerebral origin before and after treatment with BTX-A. Typically, a TMG parameter Dm increases while time related TMG parameters Tr and Ts decrease after treatment of a muscle with a BTX-A. A parameter Tr/Dm has been found the most sensitive to changes of the muscle’s contractile properties. It is expected that the method can be used for determining muscle selection and therefore more effective use of expensive medicine and to evaluate the efficiency of the treatment.

Electrical impedance of relaxed and contracted skeletal muscle

A feasibility of bioimpedance measurement for the evaluation of skeletal muscle contractile state was examined. The 4-electrode impedance spectra of relaxed, moderately contracted and geometrically changed muscle biceps brachii were compared in a human subject over the frequency range from 300 Hz to 75 kHz. The frequency response was parameterized and a simple neural network was used to determine contractile state of a muscle. The parameters that could indicate skeletal muscle contractile state were found to be a frequency of the phase angle minimum and the rate of phase angle change with the frequency. The impedance spectra data set was further examined by a principal component analysis. The score plots show a data grouping of geometrically changed, relaxed and contracted muscle.