Digital Phase Sensitive Detector Research Articles

A simple digital phase-sensitive detector using AVR microcontroller

We have described a simple and inexpensive digital phase-sensitive detector using a low-cost AVR microcontroller. To store a large number of data, we have added external memory (RAM) to the microcontroller. A message passing interface daemon-based software has been implemented to control the whole operation. Performance of the system has been tested using precise signals generated through a D/A converter controlled by an 8085 microprocessor. The phase resolution of the system has been reported to be better than 0.1°. This phase-sensitive detector would be very useful for low-budget laboratories that deal with low-frequency AC signal applications.

Survey of signal clamping for digital phase sensitive detector.

Electrical capacitance tomography (ECT) is a multiphase flow detection technology, which has the advantages of nonradioactive, noninvasive, and on-line visualization measurements. In ECT measurements, the digital phase sensitive demodulation (PSD) plays an important role in guaranteeing the accuracy of small capacitance measurements. Generally, the clamping circuit is implemented to protect the A/D converter. In the measuring circuit, a programmable gain amplifier is usually employed to expand the dynamic range of PSD. However, the measured signal may exceed the measurement range from time to time, which induces the signal clamping effect. In this case, the digital PSD will present large errors in the capacitance measurements. In consideration of the frequency spectrum characteristic of the clamped signal, two digital PSD methods have been proposed. The proposed methods have been implemented in a field programmable gate array based measurement system. The experimental results show that the proposed multisine PSD method could expand the dynamic range by a factor of 5, at a relatively low error, i.e., ≤2%.

A rapid and sensitive assay of intercellular coupling by voltage imaging of gap junction networks

BackgroundA variety of mechanisms that govern connexin channel gating and permeability regulate coupling in gap junction networks. Mutations in connexin genes have been linked to several pathologies, including cardiovascular anomalies, peripheral neuropathy, skin disorders, cataracts and deafness. Gap junction coupling and its patho–physiological alterations are commonly assayed by microinjection experiments with fluorescent tracers, which typically require several minutes to allow dye transfer to a limited number of cells. Comparable or longer time intervals are required by fluorescence recovery after photobleaching experiments. Paired electrophysiological recordings have excellent time resolution but provide extremely limited spatial information regarding network connectivity.ResultsHere, we developed a rapid and sensitive method to assay gap junction communication using a combination of single cell electrophysiology, large–scale optical recordings and a digital phase–sensitive detector to extract signals with a known frequency from Vf2.1.Cl, a novel fluorescent sensor of plasma membrane potential. Tests performed in HeLa cell cultures confirmed that suitably encoded Vf2.1.Cl signals remained confined within the network of cells visibly interconnected by fluorescently tagged gap junction channels. We used this method to visualize instantly intercellular connectivity over the whole field of view (hundreds of cells) in cochlear organotypic cultures from postnatal mice. A simple resistive network model reproduced accurately the spatial dependence of the electrical signals throughout the cellular network. Our data suggest that each pair of cochlear non−sensory cells of the lesser epithelial ridge is coupled by ~1500 gap junction channels, on average. Junctional conductance was reduced by 14% in cochlear cultures harboring the T5M mutation of connexin30, which induces a moderate hearing loss in connexin30T5M/T5M knock–in mice, and by 91% in cultures from connexin30−/− mice, which are profoundly deaf.ConclusionsOur methodology allows greater sensitivity (defined as the minimum magnitude of input signal required to produce a specified output signal having a specified signal−to−noise ratio) and better time resolution compared to classical tracer–based techniques. It permitted us to dynamically visualize intercellular connectivity down to the 10th order in non−sensory cell networks of the developing cochlea. We believe that our approach is of general interest and can be seamlessly extended to a variety of biological systems, as well as to other connexin−related disease conditions.

Design of Digital Micromachined Thermal Gas Gyroscope

Embedding microcontroller into sensor in order to make it smart has become one of development trends of sensor, especially for MEMS sensor. In this paper, the way of embedding microcontroller into sensor to design the digital micromachined thermal gas gyroscope (DMTGG) is discussed. The scheme of micromachined thermal gas gyroscope (MTGG) is introduced first, basing on it, the design of DMTGG is proposed. The design of digital drive module for MTGG, the design of signal detection of MTGG based on digital phase sensitive detector, and the design of embedded microcontroller system are introduced. The designed DMTGG has been tested by experiments. The measurement results of DMTGG show a system scale factor of 4.119mV/(o/s) ,a non-linearity of 0.38 %, a dissymmetry of 0.19%, a zero-bias stability of 1.05 o/s and a noise density of 0.95 o/s/Hz-1/2.

An absorption-type proton NMR magnetometer for measuring low magnetic fields

A highly sensitive absorption-type nuclear magnetic resonance (NMR) magnetometer capable of measuring low magnetic fields below 1 mT with a NMR sample volume of 3 cm3 is described. It will be used for calibration purposes in an accredited calibration laboratory. The magnetometer uses a direct digital synthesizer for generation of the radio frequency signal, a sampling detector for demodulation of the radio frequency signal and a digital signal processor with an analogue-to-digital converter and a digital-to-analogue converter for signal processing using a lock-in technique with a digital phase sensitive detector. Frequency traceability of the NMR magnetometer reference oscillator is established by means of the long-wave transmitter DCF77.

Study on Optical Fiber CO Gas Sensor Based on Difference Absorption

By analysing the near infrared spectral absorption of CO molecule and considering factors such as compatibility with the transmission characteristics of silica optical fiber and the price, a kind of all- fiber remote sensor utilizing Fiber Bragg Grating(FBG) filters and 1.567μm high power light-emitting diode (LED) was developed for real time absorption measurement. And a novel faint signal detective method by using a digital phase sensitive detector (DPSD) is designed. FBG has a low insert loss and can be produced easily compared with dielectric interference filters. Theory and experiment proved that the system has simple construct and high sensibility.

Optimization of phase sensitive detectors using fast Fourier transform

The rapid development of data acquisition and processing products provides an opportunity for the use of the fast Fourier transform (FFT) in a digital phase sensitive detector (PSD), where the measurement quality is largely dependent on the signal sampling. The error analysis on this scheme is related to the general error analysis of FFT, but there exist some essential differences between the two. The authors study the optimization of, and present several rules for, the signal sampling in a PSD, using FFT. The results are useful in reducing the influence of stationary and periodic interferences.

An instrument for alternating current voltammetry featuring a digital phase‐sensitive detector: Application to flow‐injection analysis using ac amperometry

AbstractAn instrument, which incorporates a lock‐in amplifier based on a digital phase sensitive detector, has been designed and constructed for ac electrochemical measurements of solutions containing low concentrations of analyte. The performance of the lock‐in amplifier was characterized experimentally. Phase angle resolution is better than 0.01°, and signal capture ratios up to about 80,000 can be attained. An up/down counter replaces the multiplier of the typical analog phase‐sensitive detector. Provision was made to sum the net count over a preselected number of cycles of the reference signal to improve the sensitivity and signal‐to‐noise ratio of the phase‐sensitive detector. The lock‐in amplifier output can be read on a recorder via a digital‐to‐analog converter or sent to a computer. Overall instrument performance is demonstrated using ac amperometry at a carbon paste electrode and flow injection techniques to determine o‐dianisidine. Peak currents corresponding to a solution concentration of 6 nM in the detector were successfully measured.

Digital phase-sensitive detector using a Z80A single-board computer

A digital phase-sensitive detector was designed and built to circumvent the relatively slow, ∼1-ms response time of commercial lock-in amplifiers. A Z80A single-board computer with a suitably programmed EPROM and analog-to-digital and digital-to-analog converters is used. The response time, ∼40 μs, is primarily limited by the throughput of the analog-to-digital converter.

A hardwired digital phase-sensitive detector applied to spectroscopy

A versatile phase-sensitive detector based on digital techniques has been designed and tested for spectroscopic studies. It can collect the signal given by DC or pulsed-output detectors and can provide an analogue and a digital (microcomputer-compatible) output. Its construction is easy and inexpensive.

An efficient digital phase-sensitive detector for use in electron-spin-resonance spectroscopy

A digital phase-sensitive detector for a modified Bruker electron-spin-resonance (ESR) spectrometer, equipped with an Aspect 2000 minicomputer is described. Magnetic field modulation is derived from a clock in the computer, which makes it possible to perform the data acquisition fully synchronously with the modulation. The resulting high phase accuracy makes it possible to compress the data to a single modulation period before the Fourier transformation. Both the in-phase and the phase-quadrature signals (of the first or second harmonic) are recorded simultaneously. The system is so efficient that the data processing including the Fourier transformation is approximately 1000 times faster than a previously reported digital phase-sensitive detector system for ESR [T. Watanabe et al., Appl. Spectrosc. 34, 456 (1980)].

An on-line digital phase sensitive detector in the range 2 mHz-2 kHz

A digital phase sensitive detector (PSD) has been designed and built which may be used in conjunction with a SQUID-based AC susceptibility measurement system. The system operates in a useful frequency range from 2 mHz-2 kHz and measures both in-phase and the quadrature component. The digital PSD, which is based on a small minicomputer, corrects for DC drift and flux quantum jumps of the SQUID and operates in 'real time'. An analysis of its design and several properties and measuring results are presented.

Microcomputer based phase sensitive detector

A fully digital phase sensitive detector which utilises a microprocessor card is presented. This unit can replace a sophisticated lock-in amplifier in most applications. The instrument stores the signal in a 1024 channel memory, thus permitting further numerical processing of the data. The programs for data processing can be implemented by the use to suit each particular experimental situation. The noise bandwidth of the instrument has been theoretically evaluated, and compared with that of a conventional phase detector, a degradation of the S/N ratio of 1.6 was obtained. The prototype has been used for the detection of the signal in a wide line NMR spectrometer substantially confirming the theoretical results. The instrument operates from 1 Hz to 32.25 kHz.

Pulsed optically detected resonance in semiconductors

A pulsed optically detected magnetic resonance spectrometer has been used to investigate time dependent recombination processes in ZnS and CdS. The detection of magnetic resonance by optical methods requires the observation of changes in the luminescence induced by microwaves at the resonant magnetic field. The pulsed system involves a two channel sample and hold unit with a digital phase-sensitive detector used with a pulsed nitrogen laser and either a magnetron or a kylstron plus travelling wave amplifier. The luminescence can be sampled with gatewidths variable down to 35 ns. The microwaves are pulsed at half the sampling rate so that the detector output is proportional to the microwave induced changes in the luminescence. In ZnS, separate donor and acceptor resonance are observed from distant pairs, whereas, for the shorter lived pairs, a new resonance corresponding to close-pair, excitonic, decay is detected. These time resolved resonance spectra and measurements of spin lattice relaxation times in CdS are reported.