Browsing by Subject "Computer-Aided Design"

Now showing 1 - 6 of 6
  • Thumbnail Image
    ItemOpen Access
    Circuit topology and control principle for a first magnetic stimulator with fully controllable waveform.
    (Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Annual International Conference, 2012-01) Goetz, SM; Pfaeffl, M; Huber, J; Singer, M; Marquardt, R; Weyh, T
    Magnetic stimulation pulse sources are very inflexible high-power devices. The incorporated circuit topology is usually limited to a single pulse type. However, experimental and theoretical work shows that more freedom in choosing or even designing waveforms could notably enhance existing methods. Beyond that, it even allows entering new fields of application. We propose a technology that can solve the problem. Even in very high frequency ranges, the circuitry is very flexible and is able generate almost every waveform with unrivaled accuracy. This technology can dynamically change between different pulse shapes without any reconfiguration, recharging or other changes; thus the waveform can be modified also during a high-frequency repetitive pulse train. In addition to the option of online design and generation of still unknown waveforms, it amalgamates all existing device types with their specific pulse shapes, which have been leading an independent existence in the past years. These advantages were achieved by giving up the common basis of all magnetic stimulation devices so far, i.e., the high-voltage oscillator. Distributed electronics handle the high power dividing the high voltage and the required switching rate into small portions.
  • Thumbnail Image
    ItemOpen Access
    Design and in vivo evaluation of more efficient and selective deep brain stimulation electrodes.
    (Journal of neural engineering, 2015-08) Howell, Bryan; Huynh, Brian; Grill, Warren M

    Objective

    Deep brain stimulation (DBS) is an effective treatment for movement disorders and a promising therapy for treating epilepsy and psychiatric disorders. Despite its clinical success, the efficiency and selectivity of DBS can be improved. Our objective was to design electrode geometries that increased the efficiency and selectivity of DBS.

    Approach

    We coupled computational models of electrodes in brain tissue with cable models of axons of passage (AOPs), terminating axons (TAs), and local neurons (LNs); we used engineering optimization to design electrodes for stimulating these neural elements; and the model predictions were tested in vivo.

    Main results

    Compared with the standard electrode used in the Medtronic Model 3387 and 3389 arrays, model-optimized electrodes consumed 45-84% less power. Similar gains in selectivity were evident with the optimized electrodes: 50% of parallel AOPs could be activated while reducing activation of perpendicular AOPs from 44 to 48% with the standard electrode to 0-14% with bipolar designs; 50% of perpendicular AOPs could be activated while reducing activation of parallel AOPs from 53 to 55% with the standard electrode to 1-5% with an array of cathodes; and, 50% of TAs could be activated while reducing activation of AOPs from 43 to 100% with the standard electrode to 2-15% with a distal anode. In vivo, both the geometry and polarity of the electrode had a profound impact on the efficiency and selectivity of stimulation.

    Significance

    Model-based design is a powerful tool that can be used to improve the efficiency and selectivity of DBS electrodes.
  • Thumbnail Image
    ItemOpen Access
    High-fidelity, broadband stimulated-Brillouin-scattering-based slow light using fast noise modulation.
    (Opt Express, 2011-01-17) Zhu, Yunhui; Lee, Myungjun; Neifeld, Mark A; Gauthier, Daniel J
    We demonstrate a 5-GHz-broadband tunable slow-light device based on stimulated Brillouin scattering in a standard highly-nonlinear optical fiber pumped by a noise-current-modulated laser beam. The noisemodulation waveform uses an optimized pseudo-random distribution of the laser drive voltage to obtain an optimal flat-topped gain profile, which minimizes the pulse distortion and maximizes pulse delay for a given pump power. In comparison with a previous slow-modulation method, eye-diagram and signal-to-noise ratio (SNR) analysis show that this broadband slow-light technique significantly increases the fidelity of a delayed data sequence, while maintaining the delay performance. A fractional delay of 0.81 with a SNR of 5.2 is achieved at the pump power of 350 mW using a 2-km-long highly nonlinear fiber with the fast noise-modulation method, demonstrating a 50% increase in eye-opening and a 36% increase in SNR in the comparison.
  • Thumbnail Image
    ItemOpen Access
    Instrument independent diffuse reflectance spectroscopy.
    (J Biomed Opt, 2011-01) Yu, Bing; Fu, Henry L; Ramanujam, Nirmala
    Diffuse reflectance spectroscopy with a fiber optic probe is a powerful tool for quantitative tissue characterization and disease diagnosis. Significant systematic errors can arise in the measured reflectance spectra and thus in the derived tissue physiological and morphological parameters due to real-time instrument fluctuations. We demonstrate a novel fiber optic probe with real-time, self-calibration capability that can be used for UV-visible diffuse reflectance spectroscopy in biological tissue in clinical settings. The probe is tested in a number of synthetic liquid phantoms over a wide range of tissue optical properties for significant variations in source intensity fluctuations caused by instrument warm up and day-to-day drift. While the accuracy for extraction of absorber concentrations is comparable to that achieved with the traditional calibration (with a reflectance standard), the accuracy for extraction of reduced scattering coefficients is significantly improved with the self-calibration probe compared to traditional calibration. This technology could be used to achieve instrument-independent diffuse reflectance spectroscopy in vivo and obviate the need for instrument warm up and post∕premeasurement calibration, thus saving up to an hour of precious clinical time.
  • Thumbnail Image
    ItemOpen Access
    Parallel on-axis holographic phase microscopy of biological cells and unicellular microorganism dynamics.
    (Appl Opt, 2010-05-20) Ehlers, MD; Newpher, Thomas Mark; Shaked, NT; Wax, A
    We apply a wide-field quantitative phase microscopy technique based on parallel two-step phase-shifting on-axis interferometry to visualize live biological cells and microorganism dynamics. The parallel on-axis holographic approach is more efficient with camera spatial bandwidth consumption compared to previous off-axis approaches and thus can capture finer sample spatial details, given a limited spatial bandwidth of a specific digital camera. Additionally, due to the parallel acquisition mechanism, the approach is suitable for visualizing rapid dynamic processes, permitting an interferometric acquisition rate equal to the camera frame rate. The method is demonstrated experimentally through phase microscopy of neurons and unicellular microorganisms.
  • Thumbnail Image
    ItemOpen Access
    Slow light with a swept-frequency source.
    (Opt Express, 2010-12-20) Zhang, Rui; Zhu, Yunhui; Wang, Jing; Gauthier, Daniel J
    ct: We introduce a new concept for stimulated-Brillouin-scattering-based slow light in optical fibers that is applicable for broadly-tunable frequency-swept sources. It allows slow light to be achieved, in principle, over the entire transparency window of the optical fiber. We demonstrate a slow light delay of 10 ns at 1.55 μm using a 10-m-long photonic crystal fiber with a source sweep rate of 400 MHz/μs and a pump power of 200 mW. We also show that there exists a maximal delay obtainable by this method, which is set by the SBS threshold, independent of sweep rate. For our fiber with optimum length, this maximum delay is ~38 ns, obtained for a pump power of 760 mW.