AC Amplification Research Articles

AC amplification gain in organic electrochemical transistors for impedance-based single cell sensors

Research on electrolyte-gated and organic electrochemical transistor (OECT) architectures is motivated by the prospect of a highly biocompatible interface capable of amplifying bioelectronic signals at the site of detection. Despite many demonstrations in these directions, a quantitative model for OECTs as impedance biosensors is still lacking. We overcome this issue by introducing a model experiment where we simulate the detection of a single cell by the impedance sensing of a dielectric microparticle. The highly reproducible experiment allows us to study the impact of transistor geometry and operation conditions on device sensitivity. With the data we rationalize a mathematical model that provides clear guidelines for the optimization of OECTs as single cell sensors, and we verify the quantitative predictions in an in-vitro experiment. In the optimized geometry, the OECT-based impedance sensor allows to record single cell adhesion and detachment transients, showing a maximum gain of 20.2±0.9 dB with respect to a single electrode-based impedance sensor.

Photodiode working in zero-mode: detecting light power change with DC rejection and AC amplification

We propose a new mode of operation when using a photodiode to extract a variable optical signal from a constant (ambient) background. The basic idea of this 'zero-mode' of operation is to force the photodiode to operate at either zero current or zero voltage. We present possible implementations of this novel approach and provide the corresponding equivalent circuits while also demonstrating experimentally its performance. The gain and bandwidth of the zero-mode photodetector are measured and simulated, and they show highly agreement. The gain compression effect because of the nonlinearity of the forward bias region is also explored. Comparing to the conventional photoconductive photodetector, the zero-mode photodetector is able to obtain higher AC gain and lower noise. With the same component used in the circuit, the measured input referred root mean square noise of zero-mode photodetector is 4.4mV whereas that of the photoconductive mode photodetector is 96.9mV respectively, showing the feasibility of the zero-mode of operation for measuring the small variable light signal under a high power constant background light.

A Table-Top Pilot Experiment for Narrow Mass Range Light Cold Dark Matter Particle Searches

This report presents the detection framework and a proposal for a pilot table-top experiment (supported by simulations and preliminary test results) for adoption into narrow mass range light Cold Dark Matter (CDM) searches, specifically for axions or Axion-Like Particles (ALPs) in a resonant cavity-based scheme. The novelty of this proposal lies in an attempt to concentrate searches corresponding to specific axion masses of interest (coinciding with recent proposals), using multiple cavities in a symmetric scheme, instead of using noisy and complicated tuning mechanisms, and in reduction of associated hardware by employing simpler underlying instrumentation instead of heterodyne mode of detection, by means of a low-noise ac amplification and dc phase-sensitive detection scheme, in order to make a viable and compact table-top experiment possible. These simplifications could possibly be valuable in substantially reducing detection hardware, experiment complexities (and associated noise) and long run-times, while maintaining low noise similar to conventional axion searches. The feasibility of proposed scheme and the experiment design are demonstrated with some calculations, simulations and preliminary tests with artificial axion signals injected into the cavities. The technique and ideas reported here have significant potential to be developed into a small-scale table-top, narrow-range, dark matter axion/ALP spectroscopy experiment, in addition to aiding in the on-going resonant cavity-based and broadband experiments.

Laser Doppler Blood Flow Imaging Using a CMOS Imaging Sensor with On-Chip Signal Processing

The first fully integrated 2D CMOS imaging sensor with on-chip signal processing for applications in laser Doppler blood flow (LDBF) imaging has been designed and tested. To obtain a space efficient design over 64 × 64 pixels means that standard processing electronics used off-chip cannot be implemented. Therefore the analog signal processing at each pixel is a tailored design for LDBF signals with balanced optimization for signal-to-noise ratio and silicon area. This custom made sensor offers key advantages over conventional sensors, viz. the analog signal processing at the pixel level carries out signal normalization; the AC amplification in combination with an anti-aliasing filter allows analog-to-digital conversion with a low number of bits; low resource implementation of the digital processor enables on-chip processing and the data bottleneck that exists between the detector and processing electronics has been overcome. The sensor demonstrates good agreement with simulation at each design stage. The measured optical performance of the sensor is demonstrated using modulated light signals and in vivo blood flow experiments. Images showing blood flow changes with arterial occlusion and an inflammatory response to a histamine skin-prick demonstrate that the sensor array is capable of detecting blood flow signals from tissue.

Early and multiple Ac transpositions in rice suitable for efficient insertional mutagenesis.

A GFP excision assay was developed to monitor the excision of Ac introduced into rice by Agrobacterium-mediated transformation. The presence of a strong double enhancer element of the CaMV 35S promoter adjacent to the Ac promoter induced very early excision, directly after transformation into the plant cell, exemplified by the absence of Ac in the T-DNA loci. Excision fingerprint analysis and characterization of transposition events from related regenerants revealed an inverse correlation between the number of excision events and transposed Ac copies, with single early excisions after transformation generating Ac amplification. New transpositions were generated at a frequency of 15-50% in different lines, yielding genotypes bearing multiple insertions, many of which were inherited in the progeny. The sequence of DNA flanking Ac in three representative lines provided a database of insertion tagged sites suitable for the identification of mutants of sequenced genes that can be examined for phenotypes in a reverse genetics strategy to elucidate gene function. Remarkably, two-thirds of Ac tagged sites showing homology to sequences in public databases were in predicted genes. A clear preference of transposon insertions in genes that are either predicted by protein coding capacity or by similarity to ESTs suggests that the efficiency of recovering knockout mutants of genes could be about three times higher than random. Linked Ac transposition, suitable for targeted tagging, was documented by segregation analysis of a crippled Ac element and by recovery of a set of six insertions in a contiguous sequence of 70 kb from chromosome 6 of rice.

Development of Ac and Ds transposon tagging lines for gene isolation in diploid potato

For the development of an efficient transposon tagging strategy it is important to generate populations of plants containing unique independent transposon insertions that will mutate genes of interest. To develop such a transposon system in diploid potato the behavior of the autonomous maize transposable element Ac and the mobile Ds element was studied. A GBSS (Waxy) excision assay developed for Ac was used to monitor excision in somatic starch-forming tissue like tubers and pollen. Excision of Ac results in production of amylose starch that stains blue with iodine. The frequency and patterns of blue staining starch granules on tuber slices enabled the identification of transformants with different Ac activity. After excision the GBSS complementation was usually not complete, probably due to the segment of DNA flanking Ac that is left behind in the GBSS gene. Molecular and phenotypic analyses of 40 primary transformants classified into 4 phenotypic classes revealed reproducible patterns. A very high percentage (32.5%) of the primary transformants clearly showed early excision in the first transformed cell as displayed both by the analysis of the GBSS excision marker gene as well as DNA blot analyses. Genotypes useful for tagging strategies were used for crosses and the frequency of independent germinal transpositions was assessed. In crosses to Ds genotypes, excision of Ds was revealed that correlated to the activity of the Ac genotype. A line displaying Ac amplification to multiple copies conferred a high frequency of independent Ds transpositions. The genotypes described here are useful in somatic insertion mutagenesis aimed at the isolation of tagged mutations in diploid potato.

Amplification of temporally modulated signal beams by two-wave mixing in Bi_12SiO_20

A theoretical analysis of two-wave mixing in a BSO crystal is developed in the undepleted-pump approximation for a modulated signal beam. It is shown that, for a modulation of high enough frequency, significant ac amplification is possible at three distinct values of pump-beam detuning. A signal beam that is amplitude modulated by a square wave is analyzed by means of the theory, and experimental results are presented in confirmation of the analysis. Finally, it is shown that in the presence of absorption the optimum detunings for dc and ac amplification are different.

Rapid proliferation of the maize transposable element Activator in transgenic tomato.

We have found that the maize transposable element Activator (Ac) can rapidly proliferate when transformed into tomato plants. The fate of transposed Ac elements in self-pollinated progeny of independent transgenic tomato plants was examined by DNA gel blot hybridizations. When a single copy of Ac was introduced into a transformant, the number of copies usually remained low in subsequent generations. In one lineage, however, the number of Ac elements increased from one to more than 15 copies in only two generations. DNA gel blot analyses indicated that the amplified elements were not grossly rearranged. Amplified copies of Ac resided at unique sites in the genome, and segregation analysis indicated that these sites were not tightly linked at one genetic locus. Taken together, these observations indicate that the mechanism of Ac amplification is associated with transposition.

Determination of relative number density and decay rate for atomic sodium in an atmospheric premixed flame by asynchronous optical sampling

Asynchronous Optical Sampling (ASOPS) is a pump/probe method that utilizes a dual timebase scheme to determine number densities and decay rates. In the ASOPS technique, two lasers are mode-locked at slightly different frequencies, causing a relative phase walkout between the pump and probe lasers. This allows the dynamic measurement of subnanosecond excitation processes in a time scale on the order of milliseconds. The current ASOPS instrument consists of two dye lasers synchronously pumped by two frequency-doubled Nd:YAG lasers at a repetition rate of ∼82 MHz. The ASOPS signal is obtained by AC amplification of the probe beam voltage, which is measured by a single photodiode at a beat frequency of 10 kHz. In this paper we report the first use of ASOPS in a flame environment. The relative number density and decay time of atomic sodium are measured by aspirating a sodium chloride solution into an atmospheric premixed CH 4 /O 2 /N 2 flame. The pump and probe beams are each tuned to the D 2 transition (589.0 nm). Both ASOPS and laser-induced florescence are used to determine relative concentration profiles and saturation curves. Measurements obtained using these techniques are found to be in close agreement, demonstrating the viability of the ASOPS method as a combustion diagnostic and its potential for use in high-pressure, turbulent flames.

Mechanism of spontaneous rhythmic contraction in isolated rat large artery.

The mechanism of spontaneous contraction of vascular smooth muscles in the elastic artery was studied in a ring-shaped preparation isolated from the rat aorta. The observation of small changes in vascular tension with a high gain AC amplification of tension signal provided a reliable detection of spontaneous contractions. The spontaneous rhythmic contraction (RC) occurred consistently in the preparation taken from the thoracic aorta without external stimuli. The RC (frequency, 5-20 cycle/min; amplitude, 10-100 mg) was accompanied with small oscillatory changes in the membrane potential (2-5 mV, peak to peak). A reduction in temperature (below 30 degrees C) or superfusing the preparation with Ca-free solution inhibited the generation of RC. Ca-entry blockers (verapamil and nifedipine) also inhibited the RC. The cessation of RC by these procedures reduced the vascular tension by about 40% of control baseline tension. The application of adrenergic blockers had little effect on the pattern of RC and on the vascular tension. The results suggest that the RC is generated by a synchronization of electrical and mechanical activities in relatively small groups of smooth muscle cells, which depends upon the temperature and requires the Ca-entry into the cells. The process of initiation of spontaneous RC in the rat aorta was discussed.

A system for monitoring the radial pulse: application to pulse transit time measurement.

A transducer and circuit for continuous monitoring of the radial pulse are described. The wrist transducer is small, robust and easily constructed. The system responds mechanically to surface movement caused by the arterial pulse, and converts the motion photoelectrically to a signal suitable for AC amplification and input to a chart recorder. Output closely follows the shape of the intraarterial pressure pulse. A computer algorithm is described for beat-to-beat calculation of pulse transit time from an ECG R-wave reference.

Correlation between the presence of dislocations and vacancies in N-Type gallium arsenide : E. Fabre and C. Schiller. Solid State Commun.10 (1972), p. 81

Asynchronous Optical Sampling (ASOPS) is a pump/probe method that utilizes a dual timebase scheme to determine number densities and decay rates. In the ASOPS technique, two lasers are mode-locked at slightly different frequencies, causing a relative phase walkout between the pump and probe lasers. This allows the dynamic measurement of subnanosecond excitation processes in a time scale on the order of milliseconds. The current ASOPS instrument consists of two dye lasers synchronously pumped by two frequency-doubled Nd:YAG lasers at a repetition rate of ∼82 MHz. The ASOPS signal is obtained by AC amplification of the probe beam voltage, which is measured by a single photodiode at a beat frequency of 10 kHz.In this paper we report the first use of ASOPS in a flame environment. The relative number density and decay time of atomic sodium are measured by aspirating a sodium chloride solution into an atmospheric premixed CH4/O2/N2 flame. The pump and probe beams are each tuned to the D2 transition (589.0 nm). Both ASOPS and laser-induced florescence are used to determine relative concentration profiles and saturation curves. Measurements obtained using these techniques are found to be in close agreement, demonstrating the viability of the ASOPS method as a combustion diagnostic and its potential for use in high-pressure, turbulent flames.

Estimates for Best Placement of Voters in a Triplicated Logic Network

The digital analog converter with ac amplification (DACAC) described by the author [1] can be used in the design of a wide purpose function generator.

A Transistorized Digital Analog Converter with Ac Amplification

A new type of analog-to-digital converter is described. This converter presents one analog input and several outputs with two possible states. Each time, only one output is activated. The converter is built up with the following elements: controlled oscillator, saturated tuned amplifiers, detectors, and inverters. The converter principle is: a voltage input E <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> feeds a controlled oscillator whose output volttages are E <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> sin wt and -E sin wt, with E constant. These voltages feed the two sides of a voltage divider made up of resistors of convenient values. As the two voltages mentioned above are in phase opposition, one point of the divider, for each E <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> , presents zero potential. The detection of this zero potential point furnishes an activated output, for each input E <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> . A practical realization of the converter, all transistorized, is presented by the author.

Oximetry

Oximetry is the estimation of per cent oxygen saturation of blood by photometric means. Incident light may be reflected from a vascular bed or cuvette and the reflected light measured, or the transmitted light may be measured to yield the required data. Theoretically, transillumination lends itself to absolute measurement with a two-color system, whereas reflection oximetry requires three colors. The instrumentation described employs two colors along with an alternating light source to allow ac amplification. An analogue computer provides a continuous ratio of the corresponding two currents recorded by an ink-writing milliameter. The over-all response to a step change has a period of less than 0.5 seconds and is considered rapid enough for clinical dye curve studies. There is reason to believe that the deficient long-term stability of the photocells limits function as an absolute oximeter.

A CURRENT STABLIZER FOR β-RAY SPECTROMETER

The current stablizer, reported in this paper, is part of a β-ray spectrometer. Principally, it can also be used in other apparatus requiring stablized current. The stablizer can supply a maximum current of 100 A with a degree of stablity of 0.02% in ten minutes.We adopt the principle of negative feed back sevo-control in designing the stablizer. Firstly, the error signal of the DC current passing through a standard resistance is amplified. In order to avoid the drift effect of the usual DC amplifier, we use a bridge type balanced modulator to convert DC signal into AC signal. After AC amplification, the signal is demodulated by a phase sensitive demodulator. The amplification required is about 2×l04. Concerning the amplifier, the following problems are considered in detail: to keep the output of the modulator in zero potential while there is no input signal, the effect of the carrier component of the modulator, and the distortion of the modulated signal after amplification. After power amplification, the amplified signal is used to control the field supply of the DC generator. As there are capacitance and inductance in the system, the transmission of the signal in the system has time delay. In closed system, there is the possibility of instability of the nature of low frequency oscillation, and it is necessary to insert proper network in the system to suppress the oscillation. Finally, the detailed arrangements of the different components of the stablizer, its characteristics, and result of its operation are described.

Method for Determining the Ratio of Planck's Constant to the Charge of the Electron Employing AC Amplification

Filtered pulsating light from a mercury vapor lamp operated on ac is directed upon a commercial high-vacuum phototube, and the photocurrent, which is thereby pulsating dc, is passed by an ac amplifier whose output is fed to a dc milliammeter through a copper oxide rectifier. Using different light filters a retarding potential of increasing magnitude is applied to the phototube until the milliammeter readings reach respective minimum values which are plotted as ordinate against optical frequency as abscissa. The slope of the resulting line is taken as h/e.

Spectral and pressure observations of explosion phenomena.

A Perkin-Elmer Model 83 Monochromator covering a spectral range from the ultraviolet to 5.5μ is used for determining the light intensity as a function of time of an explosion in a bomb. [ Bullock Hornbeck Silverman , J. Chem. Phys.18, 1114 ( 1950)]. The radiation entering the spectrometer is chopped to allow ac amplification of the detector output with provision to allow transmission as well as emission measurements. A frequency modulated pressure gauge is used to determine the pressure change in the bomb. Time resolution of the order of magnitude of 10−3 sec may be obtained for both spectral and pressure observations. Results for typical carbon monoxide-oxygen explosions are shown. These preliminary results seem to indicate that there is equilibrium for approximately 0.02 sec after the flame front reaches the vessel wall.