Broadband Noise Power Research Articles

Recording characteristics of electrical impedance-electromyography needle electrodes

Objective: Needle EMG remains the standard clinical test for neuromuscular disease (NMD) assessment, but it only characterizes myofiber membrane depolarization. On the other hand, electrical impedance provides non-electrically active structural and compositional data of tissues. Here, we designed a prototype of needle electrode integrating electrical impedance and EMG measurement capabilities, the so-called I-EMG needle electrode. Approach: We use finite element method models to study the impedance recording characteristics of I-EMG needle electrodes. The simulated electrical and mechanical design specifications are then manufactured to create a prototype of an I-EMG needle electrode. We pilot these new needle electrodes by conducting in vivo impedance measurements with muscle at rest on healthy wild-type (wt, n = 5) and muscular dystrophy (mdx, n = 5) mice. Comparisons between wt and mdx mice are performed using Mann–Whitney test, two-tailed, p < 0.05. The electrical characterization of the EMG electrode in the developed I-EMG needles was performed in vitro on saline solution and through EMG detection in wt animal at rest and during voluntary contractions. Results: Muscle impedance demonstrate good repeatability (p < 0.05 and p < 0.005 for resistance and reactance at 50 kHz, respectively) and agreement between different I-EMG needles. Impedance data allows us to discriminate between mdx and wt muscle (p < 0.05 and p < 0.005 for resistance and reactance at 10 kHz, respectively). EMG broadband noise power and peak amplitude using the I-EMG needle were similar to that of a commercial monopolar EMG needle. EMG recordings using the I-EMG needle measured electrical activity similar to a standard monopolar needle with muscle at rest and during voluntary contraction. Significance: Needle I-EMG technology may offer the opportunity to enhance the diagnostic capability and quantification of NMD beyond that possible with either impedance or EMG techniques separately. Ultimately, needle I-EMG could serve as a new bedside tool to assess NMD without increasing the complexity or duration of the EMG test.

Design and calibration of the 34 GHz Yale microwave cavity experiment

Several proposed models of the cold dark matter in the universe include light neutral bosons with sub-eV masses. In many cases their detection hinges on their infrequent interactions with Standard Model photons at sub-eV energies. We describe the design and performance of an experiment to search for aberrations from the broadband noise power associated with a 5K copper resonant cavity in the vicinity of 34GHz (0.1meV). The cavity, microwave receiver, and data reduction are described. Several configurations of the experiment are discussed in terms of their impact on the sensitivity of the search for axion-like particles and hidden sector photons.

Thin-film recording media on flexible substrates for tape applications

Co-based alloys were investigated as candidates for sputtered thin-film magnetic tape media. Magnetic media on polymeric substrates having acceptable magnetic properties were obtained by applying NiAl/CrMn underlayers prior to CoCrPt deposition with a nonmagnetic CoCrTa intermediate layer. Typical sputtered tape media deposited on traditional polymeric substrates at room temperature revealed sideband modulation noise and large intergranular exchange coupling. A substantial improvement in surface roughness by utilizing smooth polymeric substrates eliminated this modulation noise and accounted for the signal dependent broad-band noise power. This suggests that transition noise is a dominant component of medium noise in sputtered tape media. Additionally, substrate bias is shown to be effective in producing grain decoupling that is necessary for good signal-to-noise ratio.

The flux-dependent amplitude of broadband noise variability in X-ray binaries and active galaxies

Standard shot-noise models, which seek to explain the broadband noise variability that characterizes the X-ray light curves of X-ray binaries and active galaxies, predict that the power spectrum of the X-ray light curve is stationary (i.e. constant amplitude and shape) on short time-scales. We show that the broadband noise power spectra of the black hole candidate Cyg X-1 and the accreting millisecond pulsar SAX J1808.4–3658 are intrinsically non-stationary, in that rms variability scales linearly with flux. Flux-selected power spectra confirm that this effect is due to changes in power-spectral amplitude and not shape. The light curves of three Seyfert galaxies are also consistent with a linear relationship between rms variability and flux, suggesting that it is an intrinsic feature of the broadband noise variability in compact accreting systems over more than six decades of central object mass. The rms variability responds to flux variations on all measured time-scales, raising fundamental difficulties for shot-noise models which seek to explain this result by invoking variations in the shot parameters. We suggest that models should be explored where the longest time-scale variations are fundamental and precede the variations on shorter time-scales. Possible models which can explain the linear rms-flux relation include the fractal break-up of large coronal flares, or the propagation of fluctuations in mass accretion rate through the accretion disc. The linear relationship between rms variability and flux in Cyg X-1 and SAX J1808.4–3658 is offset on the flux axis, suggesting the presence of a second, constant-flux component to the light curve which contributes ∼25 per cent of the total flux. The spectrum of this constant component is similar to the total spectrum, suggesting that it may correspond to quiet, non-varying regions in the X-ray emitting corona.

Broadband current noise and ac induced current steps by a moving charge density wave domain

The influence of shot noise due to depinning fluctuations in a moving charge density wave (CDW) domain on ac induced steps in the current voltage curve (CVC) is investigated theoretically. The transport model used is that of an overdamped particle in a sinusoidal pinning potential. In spite of overdamping the proposed current noise produces a threshold hysteresis in the CVC. It also tends to suppress higher order current steps. The total broadband noise power under pure dc excitation and the effects of harmonic mixing due to two strong ac signals at frequencies ω and 2ω are also evaluated.

Investigation of the propagation stability of a doubly spread underwater acoustic channel

Investigation of acoustic propagation in an underwater channel is presented. Propagation between fixed transmitting and receiving sites is studied using a 420-Hz CW tone and a binary pulse sequence with 19 ms of time-delay resolution. The channel is shown to be underspread (BL < 1) so that unambiguous instantaneous measurements of the channel's approximate impulse response are obtained. The experiment is designed, in cooperation with the channel, to allow simultaneous and independent frequency spread, time spread, and broad-band noise power measurements. Some results and a preliminary model of the channel are presented.

Avalanche noise in GaAs m.e.s.f.e.t.s

Instabilities in the d.c. characteristics of GaAs m.e.s.f.e.t.s for drain to source voltages greater than 4 V. believed to be due to reloading of traps in the interface between active layer and bulk material, or gunn-domain formation, seem to have their origin in avalanche breakdown of the back diode under the drain contact. Microplasma switching, vertical to the active layer, strongly modulates the drain current producing large broadband noise power.

Power Spectrum of Hard-Limited Gaussian Processes

The power spectral density at the output of an ideal hard limiter (one-bit quantizer) is examined when the input is driven by a narrowband gaussian signal plus an additive gaussian noise that consists of a broadband background component plus narrowband interference. Assuming that the input signal-to-noise power ratio is small by virtue of the large bandwidth of the observed broadband noise, calculations are made of the average output signal power, the average output noise power in the signal band, and the average power of the strongest intermodulation product. The results support the intuitive conclusion that spectrum analyzer performance is degraded by the presence of the limiter and that this degradation is more pronounced when a strong narrowband interfering signal is present. They also indicate that the degradation can be minimized by making the bandwidth observed by the limiter sufficiently wide that the broadband noise power dominates both the signal and interference powers. In particular, for a typical example, the signal-to-noise power ratio measured in the signal band is degraded by less than about 1.3 dB by the presence of the limiter and the ratio of output signal power to power of the strongest intermodulation product is greater than about 14.5 dB as long as the broadband noise power exceeds the interfering-signal power.