Lock-in Amplifier Technique Research Articles

Action of salicylate on membrane capacitance of outer hair cells from the guinea‐pig cochlea.

1. The effect of salicylate on membrane capacitance and intracellular pH has been measured in isolated outer hair cells (OHCs) during whole cell recording. Cell membrane capacitance was measured using a lock-in amplifier technique. 2. Salicylate applied in the bath reduced the fast charge movement, equivalent to a voltage-dependent membrane capacitance, present in OHCs. Simultaneous measurement of membrane capacitance and voltage-driven cell length changes showed that salicylate reduced both together. 3. A small effect of salicylate on outward currents at 0 mV was observed. Sodium salicylate (5 mM) reduced the currents by 19% and another weak acid, sodium butyrate (10 mM), reduced outward currents in OHCs by 15%. 4. The ratiometric dye 2,7-bis(2-carboxymethyl)-5,6-carboxyfluorescein (BCECF) was used to measure pHi changes in OHCs during weak acid exposure. Membrane capacitance and pHi were measured simultaneously in OHCs exposed first to 10 mM sodium butyrate and then to 5 mM sodium salicylate. Although both compounds produced a similar reduction in pHi, butyrate decreased the resting capacitance from a mean resting capacitance of 35 pF (at -30 mV) by 5.4 +/- 2.1 pF, whereas salicylate decreased it by 15.7 +/- 2.3 pF (n = 4). 5. Exposure of OHCs to 10 mM sodium benzoate, an amphiphilic anion, reduced resting membrane capacitance at -30 mV by 9.2 +/- 3.2 pF (n = 3). Outward currents, measured at 0 mV, were reduced by 0.25 +/- 0.05 nA during benzoate application, comparable with the effect of salicylate. 6. Capacitance was measured during slow bath application of salicylate. The resulting dose-capacitance curve had a Hill coefficient of 3.40 +/- 0.85 (n = 4) and a half-maximal dose of 3.95 +/- 0.34 mM. The dose-capacitance curve was not significantly voltage dependent. 7. Salicylate had no detectable effect on the resting capacitance of Deiters' cells, a non-sensory cell type of the organ of Corti. 8. It is concluded that many of the described effects of salicylate on hearing may arise from the partitioning of the salicylate molecule into the membrane of the OHC and consequent inhibition of OHC motility.

Highly sensitive measurement of surface charge distribution using the Pockels effect and an image lock-in amplifier

A visualization and a quantification technique for a latent electric charge image on a dielectric material has been developed by using the Pockels effect and a computer imaging technique. An optical phase modulation technique and a computer image lock-in amplifier technique were used to improve the signal-to-noise ratio. The measurement system has several improved performances; sensitivity of surface change of 1 nC cm-2, spatial resolution of 200 mu m and discrimination of charge polarity. The basic principle of advanced electro-optic surface charge measurement is described and the typical surface charge distribution of positive discharge streamer produced by a high impulse voltage (5 kVpeak) is demonstrated. Also, comparison is made between the modulation method and the non-modulation method.

Infrared radiometry using silver halide fibers and a cooled photonic detector

A fiber optic radiometer based on a cooled photonic detector was designed and constructed. The radiometer is capable of measuring in real time the temperature of tissue irradiated with a CO 2 laser. A silver halide IR fiber is used to deliver the CO 2 laser radiation to the target and also to deliver the thermal radiation emitted from the target back to the detector. Two methods of measurements were examined, both of which solve the problem of detector blinding by reflected CO 2 radiation. A theory of operation for this silver halide fiber optic radiometer, based on lock-in amplifier techniques, is presented. A short discussion of the radiometer design and construction is given. This work forms a basis for the subject of measuring, in real time, fast radiometric signals caused by CO 2 laser irradiation. Such a radiometer is very useful when dealing with pulsed photo thermal radiation with 10.6-μm CO 2 laser radiation. This technique is very useful in medicine and industry.

Preparation of a second station for the measurement of solar oscillations of low degree

An observing station to detect low-degree global solar oscillations is already operational at Jet Propulsion Laboratory (Pasadena, CA-USA). In collaboration with Reparto Raggi Cosmici, I.F.S.I.-C.N.R., a second station for continuative measurements of such oscillations has recently been installed and successfully tested in Rome. The high transmission and stability of the magneto-optical filter (MOF) coupled with the lock-in amplifier technique allow analogic and real time detection of oscillation modes with a noise level of only a few cm/s. We show observing runs and estimates of the signal-to-noise ratio in time and frequency domains. Routine observations will establish whether the MOF sensitivity and stability is suitable to detect stellar oscillations.

Spatially resolved lifetimes in polycrystalline silicon

Spatially resolved carrier lifetimes have been obtained for polycrystalline silicon samples using a modified scanning laser microscope. Photoconductivity as a function of illumination modulation frequency was measured at a set of positions across a grain boundary. Improved response models for light focussed both at a grain boundary and in the bulk have been introduced and applied to the measured frequency responses. The spatially resolved lifetimes were obtained from these frequency response spectra. Since frequency response measurements employ lock-in amplification techniques, they allow for lower illumination levels, smaller illuminated areas, and lower applied biases than can be used for photoconductivity decay measurements of lifetimes. The variation of grain boundary lifetime with illumination intensity has also been investigated.

An experimental technique for measurements of capillary waves

An experimental method has been developed for the measurements of wave profiles at liquid interfaces. An oscillating string was used to generate interface waves, which gave rise to oscillations of a laser beam reflected from the interface. These oscillations were detected using a lock-in amplifier technique, which allowed us to measure the derivative of the surface wave profile at any given phase in the wave period. We discuss in detail experiments on the water-air interface. From the observed form of the capillary waves, we deduce the surface tension and the viscosity. The dispersion relation of capillary waves has been observed, and we found a spatial damping coefficient and wave number consistent with results obtained by dynamic light scattering and mechanical methods. Our technique is to a large extent insensitive to mechanical and optical noise and determines the capillary waveform reliably and reproducibly.

Spectral response measurements on polarisation splitting ratio of fused-taper single-mode fibre couplers

Using a Ge PIN photodiode cooled to 77 K (?196°C) with liquid nitrogen and the lock-in amplification technique, an automatic polarisation spectral response measurement system with a measuring dynamic range of about 36 dB has been developed. It has been confirmed experimentally that the spectral response of polarisation beam-splitting ratios of fused-taper fibre couplers depend on the incident polarisation angle

Electrogenerated Chemiluminescence Detector for Flow Injection Analysis

A new kind of detector system based on electrogenerated chemiluminescence (ECL) was devised for flow injection analysis. The flow through type of electrolytic cell was modified to observe the ECL. The quartz optical window was set in front of the working electrode (Pt plate). The observed luminescence intensity was amplified by using a lock-in amplification technique. The preliminary examination of the whole system was performed using luminol with a strong ECL. The injection of a sample solution in a carrier solution of sodium carbonate caused a peak-shaped luminescence at the electrode. Next the determination was performed for non-luminescent compounds after the pre-labeling with luminol. It was found that oligo peptides or bovine serum albumin can be determined by ECL method. Though, the sensitivity and the reproducibility of ECL method are almost comparable to existing methods, it has the advantage that two kinds of quantities, the luminescence intensity and the electrolytic current, can be obtained at the same time.

The magnetophonon effect: A tool for characterizing Hg1−xCdxTe

We have investigated magnetophonon (MP) resonance oscillations in Hg1−xCdxTe at various temperatures for samples with x≂0.22 and x≂0.31 using magnetic field modulation and lock-in amplifier techniques. Analysis of the MP resonant field positions with a three band model allowed the determination of the fundamental energy gap Eg, the band-edge effective mass, and the effective g factor over a temperature range of 40 to 190 K. The x values were found by fitting the observed MP resonant magnetic field positions to calculated positions using the Hansen, Schmidt, and Casselman empirical relationship for Eg(x,T).

The effect of annealing conditions on the power loss of amorphous ribbons

The power loss of amorphous ribbon toroids of Fe <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">81</inf> B <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">13.5</inf> Si <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3.5</inf> C <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> and Co <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">58</inf> Fe <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</inf> Ni <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</inf> Si <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</inf> B <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">16</inf> has been measured under sinusoidal flux conditions, using the lock-in amplifier technique, with flux densities up to 95% of saturation over a frequency from 20 Hz to 20 kHz. The toroids have been annealed at temperatures from 325°C to 425°C, under field and non-field conditions and in atmospheres of air, nitrogen and hydrogen. The effect of annealing conditions (temperature, field, atmosphere) on power loss over a wide range of flux density and frequency will be shown and optimum conditions discussed. It has been found that for iron-based ribbons the optimum annealing temperature depends upon the magnetizing frequency of the toroids, but field annealing in nitrogen gives the lowest power loss. It is found for the cobalt-based ribbon that the difference in loss between as-cast and annealed toroids is very small in contrast to the results for the iron-based ribbons. These experimental variations in power loss with annealing conditions and frequency will be explained by considering the observed domain structures and the metallurgical and magnetic properties of the amorphous ribbons.

A sensitive apparatus for the reproducible measurement of fluorescence polarisation

Continuous measurements of fluorescence polarisation are made using a chopped light source and detected via a continuously rotating polariser. Lock-in amplification techniques are used to recover the information from the photomultiplier output, thus ensuring good stability and high signal-to-noise ratio.

Total current spectroscopy

In total current spectroscopy (TCS) a beam of low energy (0–15 eV) electrons is directed upon a solid sample and secondary electron emission investigated by monitoring the current to the target, rather than by direct energy analysis of emitted electrons. A TCS signal is the derivative of the direct current with respect to the incident energy E 1 displayed as a function of that energy, and obtained experimentally in ultra high vacuum conditions using simple modulation and lock in amplification techniques. A typical experimental arrangement is described and factors influencing a typical spectrum outlined. A simple background theory is discussed and it is shown how TCS is a powerful tool for studying not only the surface and near surface regions, but also bulk physics. In particular the technique has already found application in studies of work function, chemi- and physisorption, epitaxy, interband transitions, densities of states, excitons, impurity atom excitation, plasmons, radiation damage and the measurement of thicknesses of very thin surface layers.

Deep-level-transient spectroscopy: System effects and data analysis

Studies of typical DLTS systems using either the dual-channel boxcar averager or the lock-in amplifier techniques are presented. The effects of nonzero gate width for the boxcar averager, phase angle adjustment for the lock-in amplifier, and response time of a typical commercial capacitance meter are investigated. Errors introduced in the measurements by these effects are calculated for typical cases. Measurements of the gold donor level in silicon are presented, along with calculated corrections. We find the corrections to be minimal in the boxcar-averager method, but significant in the lock-in amplifier approach.

Nuclear and electronic stopping powers of low energy ions with Z ⩽ 10 in silicon

Specific energy losses of H, He, B, C, N and Ne ions have been measured in silicon in the energy range from 2 keV to 60 keV, by using ion implanted, thin window silicon detectors. Chopped ion currents and lock-in amplification techniques were applied to avoid the problems of low signal-to-noise ratios. Both electronic and nuclear stopping powers have been measured. Comparison with LSS-theory is made.

Characterization of surfaces by low-energy helium scattering

An experimental apparatus is described which permits excellent sensitivity and energy resolution in atomic and molecular beam surface scattering experiments. It is suggested that the Boxcar Integrator, a low cost, commercial instrument, is ideally suited to these experiments and, for helium scattering, yields more information than the conventional lock-in amplifier technique. Preliminary data on low-energy helium scattering from unoriented W(100) facets, produced by annealing a tungsten ribbon, shows sharp diffraction effects due to a surface structure grating at least 70 Å in characteristic size. Applications to inelastic scattering studies are briefly discussed.

A method for determining photoconductive response times

It is shown how the photoconductive response time tau 0 can be readily determined from the phase shift between the exciting radiation and the photocurrent using a lock-in amplifier technique.

Microphonic potentials from skin predict inner ear defects in cats.

APPLICATION of a lock-in amplifier technique to cats with a wide range of cochlear defects1,2 has proved to be a reliable objective method for the detection of cochlear abnormality. It may be broadly applicable in evaluation of hearing in newborn infants or other subjects whose responses are hard to interpret.