Sol-gel zinc oxide humidity sensors integrated with a ring oscillator circuit on-a-chip.

The study develops an integrated humidity microsensor fabricated using the commercial 0.18 µm complementary metal oxide semiconductor (CMOS) process. The integrated humidity sensor consists of a humidity sensor and a ring oscillator circuit on-a-chip. The humidity sensor is composed of a sensitive film and branch interdigitated electrodes. The sensitive film is zinc oxide prepared by sol-gel method. After completion of the CMOS process, the sensor requires a post-process to remove the sacrificial oxide layer and to coat the zinc oxide film on the interdigitated electrodes. The capacitance of the sensor changes when the sensitive film adsorbs water vapor. The circuit is used to convert the capacitance of the humidity sensor into the oscillation frequency output. Experimental results show that the output frequency of the sensor changes from 84.3 to 73.4 MHz at 30 °C as the humidity increases 40 to 90%RH.

A robust reference signal generator for synchronized ventricular assist devices.

Ventricular assist devices (VADs) are blood pumps that offer an option to support the circulation of patients with severe heart failure. Since a failing heart has a remaining pump function, its interaction with the VAD influences the hemodynamics. Ideally, the heart's action is taken into account for actuating the device such that the device is synchronized to the natural cardiac cycle. To realize this in practice, a reliable real-time algorithm for the automatic synchronization of the VAD to the heart rate is required. This paper defines the tasks such an algorithm needs to fulfill: the automatic detection of irregular heart beats and the feedback control of the phase shift between the systolic phases of the heart and the assist device. We demonstrate a possible solution to these problems and analyze its performance in two steps. First, the algorithm is tested using the MIT-BIH arrhythmia database. Second, the algorithm is implemented in a controller for a pulsatile and a continuous-flow VAD. These devices are connected to a hybrid mock circulation where three test scenarios are evaluated. The proposed algorithm ensures a reliable synchronization of the VAD to the heart cycle, while being insensitive to irregularities in the heart rate.

Intra-cavity gain shaping of mode-locked Ti:sapphire laser oscillations.

The gain properties of an oscillator strongly affect its behavior. When the gain is homogeneous, different modes compete for gain resources in a 'winner takes all' manner, whereas with inhomogeneous gain, modes can coexist if they utilize different gain resources. We demonstrate precise control over the mode competition in a mode locked Ti:sapphire oscillator by manipulation and spectral shaping of the gain properties, thus steering the competition towards a desired, otherwise inaccessible, oscillation. Specifically, by adding a small amount of spectrally shaped inhomogeneous gain to the standard homogeneous gain oscillator, we selectively enhance a desired two-color oscillation, which is inherently unstable to mode competition and could not exist in a purely homogeneous gain oscillator. By tuning the parameters of the additional inhomogeneous gain we flexibly control the center wavelengths, relative intensities and widths of the two colors.

Extreme ultraviolet light source based on intracavity high harmonic generation in a mode locked Ti:sapphire oscillator with 9.4 MHz repetition rate.

We report on the realization of an intracavity high harmonic source with a cutoff above 30 eV. The EUV source is based on a high power, hard-aperture, Kerr-lens mode-locked Ti:sapphire oscillator with a repetition rate of 9.4 MHz. The laser is operated in the net negative dispersion regime resulting in intracavity pulses as short as 17 fs with 1 µJ pulse energy. In a second intracavity focus, intensity more than 10¹4 W/cm² has been achieved, which is sufficient for high harmonic generation in a Xenon gas jet.

Frequency stability of a femtosecond optical parametric oscillator frequency comb.

Carrier-envelope-offset (CEO) and pulse-repetition frequencies of a Ti:sapphire-pumped femtosecond optical parametric oscillator were locked to uncertainties of 0.09 Hz and 0.16 mHz respectively, with the CEO beat signal linewidth being stabilized to 15 Hz (instrument limited). In-loop phase-noise power spectral density measurements showed a contribution of our servo electronics to the comb-line frequency uncertainty of up to 110 Hz. Complementary time-series data implied an in-loop comb instability of 2 x 10(-11) (1-s gate time), matching the Rb-stabilized reference used and verifying that dual servo-control of the CEO and repetition frequencies was effective in stabilizing the comb to at least this precision.

Automodulations in an extended cavity, passively modelocked Ti:Sapphire oscillator--period doubling and chaos.

An extended cavity Ti:Sapphire oscillator exhibits stable operation for positively chirped pulses, while in the negative chirp regime multiple pulses are present in the cavity. At the border of these regimes automodulations, being an effect of the interplay between population inversion, laser medium polarization and the laser pulse field, appear. Two particular instabilities: period doubling and chaotic behavior of the pulse train envelope are observed. Complex temporal evolution of the pulse spectrum within the modulation period is investigated.

High-power Yb-doped fiber amplification synchronized with a few-cycle Ti:sapphire laser.

We demonstrated the synchronized high-power ytterbium-doped fiber amplification of the near-infrared spectral fraction of a few-cycle Ti:sapphire laser at 79.5-MHz repetition rate, which was experimentally realized with a two-stage ytterbium-doped fiber pre-amplifier and a two-stage double-clad fiber power amplifier in cascade. An overall power amplification up to 86.1 dB was achieved at 1030 nm with sufficient suppression of amplified spontaneous emission noises, achieving to the best of our knowledge the highest synchronized laser pulses of 262 W in average power. The amplified high-power pulses were demonstrated to maintain good temporal synchronization with the few-cycle signal pulses.

High power and efficient long wave IR ZnGeP2 parametric oscillator.

A high power, efficient, and tunable laser source in the 8-10 microm range, based on a ZnGeP(2) optical parametric oscillator (OPO) pumped by a hybrid 2.1 microm laser is demonstrated. The hybrid laser consists of a Q-switched Ho:YAG laser pumped by a 15 W CW thulium fiber laser. With 8.9 W of 2.1 microm pump power we obtained 0.95 W at 8 microm with an M(2)-value of 2.7 from an OPO with two walk-off compensating crystals.

Ultrafast double-pulse parametric amplification for precision Ramsey metrology.

We demonstrate phase stable, mJ-level parametric amplification of pulse pairs originating from a Ti:Sapphire frequency comb laser. The amplifier-induced phase shift between the pulses has been determined interferometrically with an accuracy of approximately 10 mrad. Typical phase shifts are on the order of 50-200 mrad, depending on the operating conditions. The measured phase-relation can be as stable as 20 mrad rms (1/300(th) of an optical cycle). This makes the system suitable for Ramsey spectroscopy at short wavelengths by employing harmonic upconversion of the double-pulses in nonlinear media.

Towards versatile coherent pulse synthesis using femtosecond laser and optical parametric oscillators.

Pulses from a tunable near-infrared femtosecond optical parametric oscillator and its Ti:sapphire pump laser were phase-locked by matching their carrier-envelope phase-slip frequencies to one quarter of their common pulse repetition frequency. Interferometric second-order cross-correlation and spectral interferometry traces demonstrated their mutual coherence for periods of at least 20 ms, compared with individual coherence times of 0.1 ms estimated from their phase-noise power spectra. This result is a prerequisite for versatile coherent pulse synthesis. Implications for the synthesis of arbitrary waveforms from multi-colour pulses are discussed.

Skin stimulation by the fluid powered self-excited oscillation and its effect on the human body.

A novel fluid power actuator called Flat Ring Tube (FRT) is introduced in this paper. The mechanism of FRT is so simple that it only needs a urethane flat tube and water pressure power source. No valves or switches are required. Applying constant water pressure results in periodic oscillation of the tube. The frequency is proportional to the flow rate of water and inversely proportional to the tube length. By contacting the tube with a passively supported shaft, it rotates due to the periodic tube oscillation. This principle can also generate the linear driving force, when FRT is mounted so as to kick the ground. Such kind of performance can be also expected to stimulate the blood flow rate, when FRT touches on the skin of the human body appropriately. The experimental results showed us the developed wearable massage device could effectively improve both the circulation of the blood flow and the density of oxygen in blood, which resulted in let the people feel more comfortable than conventional massage devices.

Ultrabroadband noncollinear optical parametric amplification with LBO crystal.

Ultrabroadband visible noncollinear optical parametric amplification (NOPA) was achieved in an LBO crystal, with a continuum seed pulse generated from a sapphire plate. The spectral bandwidth of the amplified visible pulse was about 200 nm, which can support sub-5 fs pulse amplification. An amplified output of 0.21 microJ with an average gain of about 210 was achieved. This provides, to the best of our knowledge, the first-time demonstration of such broadband amplification with a biaxial nonlinear optical crystal. Both the simulation and experimental results indicate that the LBO has a great potential as nonlinear medium in power amplifier for TW to PW noncollinear optical parametric chirped pulse amplification (NOPCPA) systems.

A narrow-band injection-seeded pulsed titanium:sapphire oscillator-amplifier system with on-line chirp analysis for high-resolution spectroscopy.

A narrow-band tunable injection-seeded pulsed titanium:sapphire laser system has been developed for application in high-resolution spectroscopic studies at the fundamental wavelengths in the near infrared as well as in the ultraviolet, deep ultraviolet, and extreme ultraviolet after upconversion. Special focus is on the quantitative assessment of the frequency characteristics of the oscillator-amplifier system on a pulse-to-pulse basis. Frequency offsets between continuous-wave seed light and the pulsed output are measured as well as linear chirps attributed mainly to mode pulling effects in the oscillator cavity. Operational conditions of the laser are found in which these offset and chirp effects are minimal. Absolute frequency calibration at the megahertz level of accuracy is demonstrated on various atomic and molecular resonance lines.

Oscillation and its inhibition in a neural oscillator model for tinnitus.

Tinnitus is a symptom of perceiving phantom sounds. As one of its treatment techniques, tinnitus retraining therapy (TRT) has been proposed. It consists of psychotherapy by counseling and physical therapy based on masking theory by external stimuli. Our interest is to explain medical effects of the physical therapy from the viewpoint of engineering. In this paper we proposed a neural oscillator model with plasticity as a model for the tinnitus generation in the auditory central nervous system and its treatment. We investigated not only oscillatory phenomena observed in the model but also inhibition of the oscillation by external stimulus.

In vitro study of the electromagnetic interaction between wireless phones and an implantable neural stimulator.

Several clinical and laboratory studies have demonstrated electromagnetic interaction between implantable medical devices like pacemakers and cell phones being operated in close proximity. Those devices are largely now immune to phone interaction or procedures have been established to limit their interaction. The use of cell phones near people with implanted neural stimulators has not been studied. This research was initiated to investigate electromagnetic interaction between current cell phone technology and specific models of Cyberonics neural stimulators. Out of 1080 test runs conducted for this study, no interactions were observed, and it was concluded that the phone technologies examined in this study did not adversely affect the Cyberonics NeuroStar (Model 102) NeuroCybernetic Prosthesis (NCP) System. This article provides details on the experimental procedure that was used, which can also be used to test other neural stimulators and test technologies, and the results obtained.

RF nonlinear interactions in living cells--II: detection methods for spectral signatures.

The presence of harmonic products due to possible nonlinear interaction of amplitude modulated RF signals in living cells is best detected by using a cavity with high quality factor. Harmonic products generated by elementary oscillators can be trapped and accumulated in a cavity, permitting detection sensitivity much greater than in an open environment, where they would be radiated in all directions. The experimental method described herein is a systematic approach to detection of the non-Planck RF energy (if any) emitted by an exposed sample of living cells. Balzano and Sheppard [Balzano and Sheppard (2003): Bioelectromagnetics 24:473-482] classified the non-Planck RF emissions from living cells as coming from (1). nonlinear interactions and (2). inelastic interactions. Nonlinear harmonic products would appear in the band at twice the frequency of an amplitude modulated RF carrier. Inelastic interaction products resulting from the interaction between the incident RF energy and normally occurring mechanical vibrations are found in the band immediately adjacent to the carrier. Detection of the latter signals is difficult because of this close spectral proximity, for example, 1 part in 10(7) for 100 Hz modulation of a GHz carrier. Modern audio spectrum analyzers have excellent selectivity, providing 60 dB rejections only 2 kHz away from the carrier. By judicious selection of the amplitude modulation (AM) frequency, frequency of the RF carrier, and size of the biological sample, it is possible to achieve very high sensitivity (about -90 dBm) with commercially available instrumentation. The presence (or absence) of harmonics in the band adjacent to the amplitude modulated RF carrier would establish (or negate) the existence of coherent interactions between mechanical vibrations in the cell ensemble and the incident RF signal.

Multirhythmicity generated by slow variable diffusion in a ring of relaxation oscillators and noise-induced abnormal interspike variability.

The deterministic and noise-dependent dynamics of a ring of three Ohmically coupled electronic relaxation oscillators are considered by means of numerical simulations. Each isolated oscillator is described by a set of two ordinary differential equations with very different characteristic times. The emergence of the limit cycle via the Hopf bifurcation results from the N-shaped current-versus-voltage characteristic of the nonlinear resistor. The phase diagram is calculated for a ring of three such oscillators in the presence of small detuning. Special attention is focused on two parameter areas, one near a transition to the homogeneous and the other near the inhomogeneous stable steady state. Along with other nontrivial limit cycles, essentially asymmetrical limit cycles termed dynamic traps may arise in these two areas. A dynamic trap is a regime in which one or two oscillators do not perform full-amplitude oscillations and, correspondingly, do not generate spikes. The interspike interval (ISI) distribution in the presence of noise is calculated as a function of the coupling strength in both areas of the parameter plane. The distributions are extremely polymodal near the homogeneous steady state even if the in-phase limit cycle is dominating. The origins of this abnormal enhancement of ISI variability are discussed in detail. A similar analysis shows that nontrivial periodic attractors are observable in the vicinity of the inhomogeneous stable steady states only if the level of noise is relatively low. In this case, the dominance of the in-phase limit cycle basin results in an almost unimodal distribution of interspike intervals.

[Fourier analysis of pupil oscillations for measuring central activation in psychosomatic patients]. / Fourieranalyse der Pupillenoszillationen zur Messung der zentralen Aktiviertheit bei psychosomatischen Patienten.

The aim of the study was to answer the question if there are any differences in the central activation of different groups of psychosomatic patients and patients with eating disorders, which was measured by means of Fourier analysis of pupillary oscillations. A total of 132 patients (110 f, 22 m) with a mean age of 29.69 years (standard deviation: 9.9) participated in the study. In anorectic and bulimic patients high central activation was observed. Different groups of psychosomatic patients showed significant differences in their central nervous activation. In the group of subjects with the ICD-10 diagnosis F 41.3 (mixed anxiety disorders) the highest amplitudes was observed not only in the particular frequency bands but also in the total spectrum (power), which reflects high central activation. Reduced activation was found in subjects with somatoform autonomic function disorder of the upper and lower gastrointestinal tract (F 45.3). The measurement of central activation in psychosomatic disorders could have consequences for therapeutic interventions.