Digital Phase-sensitive Detection Research Articles

Development of a scanning electron microscopy with polarization analysis system for magnetic imaging with ns time resolution and phase-sensitive detection.

Scanning electron microscopy with polarization analysis is a powerful lab-based magnetic imaging technique offering simultaneous imaging of multiple magnetization components and a very high spatial resolution. However, one drawback of the technique is the long required acquisition time resulting from the low inherent efficiency of spin detection, which has limited the applicability of the technique to certain quasi-static measurement schemes and materials with high magnetic contrast. Here we demonstrate the ability to improve the signal-to-noise ratio for particular classes of measurements involving periodic excitation of the magnetic structure via the implementation of a digital phase-sensitive detection scheme facilitated by the integration of a time-to-digital converter to the system. The modified setup provides dynamic imaging capabilities using selected time windows and finally full time-resolved imaging with a demonstrated time resolution of better than 2 ns.

Design of a temperature measurement and feedback control system based on an improved magnetic nanoparticle thermometer

Magnetic fluid hyperthermia, as a novel cancer treatment, requires precise temperature control at 315 K–319 K (42 °C–46 °C). However, the traditional temperature measurement method cannot obtain the real-time temperature in vivo, resulting in a lack of temperature feedback during the heating process. In this study, the feasibility of temperature measurement and feedback control using magnetic nanoparticles is proposed and demonstrated. This technique could be applied in hyperthermia. Specifically, the triangular-wave temperature measurement method is improved by reconstructing the original magnetization response of magnetic nanoparticles based on a digital phase-sensitive detection algorithm. The standard deviation of the temperature in the magnetic nanoparticle thermometer is about 0.1256 K. In experiments, the temperature fluctuation of the temperature measurement and feedback control system using magnetic nanoparticles is less than 0.5 K at the expected temperature of 315 K. This shows the feasibility of the temperature measurement method for temperature control. The method provides a new solution for temperature measurement and feedback control in hyperthermia.

Near-infrared spectroscopy using digital phase-sensitive detection

ABSTRACTScanning near-infrared (NIR) spectrometers commonly employ analog lock-in amplifiers for demodulation that require complex circuitry and are sensitive to electromagnetic interference. Here, a new sampling system based on digital phase-sensitive detection is reported that used a quadrature sampling algorithm to establish the sampling frequency as an integral multiple of four times the optical signal frequency. A complex programmable logic device was used to control the analog-to-digital converter. A digital signal processor was used to receive data, complete the quadrature calculations, and transfer the results to a computer. Consequently, the circuitry was simplified with reduced electromagnetic interference. Spectra were obtained using instrumentation based on analog and digital sensitive detection that showed the latter provided more accurate results. The optimum signal-to-noise ratio of 66.34 dB was higher than the value obtained by the analog system.

Dual-Comb Architecture for Fast Spectroscopic Measurements and Spectral Characterization

Optical frequency combs (OFCs) generated through the modulation of continuous-wave lasers offer higher power per component, simple comb spacing control, and lower complexity and cost than traditional OFCs. By these reasons, they are an interesting optical source for spectrometers. In this letter, a dual-comb architecture based on two OFCs generated from the same laser using optical phase modulators is presented. The system features a new placement for the spectroscopic sample that increases the versatility, robustness, and stability of the instrument without requiring any reconfiguration for carrying out different types of measurement. Besides this, a self-referenced detection setup based on digital phase sensitive multitone detection improves the SNR of the previous approaches offering more flexibility in its configuration and high data output rate. The proposed architecture is validated by measuring a ro-vibrational absorption feature of HCN at 1544.51 nm and characterizing the spectral response of a fiber-coupled Fabry–Perot filter.

Multiharmonic electron paramagnetic resonance for extended samples with both narrow and broad lines

Multiharmonic electron paramagnetic resonance spectroscopy was demonstrated for two samples with both narrow and broad lines: (i) α,γ-Bisdiphenylene-β-phenylallyl (BDPA) with ΔBpp of 0.85G plus ultramarine blue with ΔBpp of 17G, and (ii) a nitroxide radical immobilized in sucrose octaacetate. Modulation amplitudes up to 17G at 41kHz were generated with a rapid scan coil driver and Litz wire coils that provide uniform magnetic field sweeps over samples with heights of 5mm. Data were acquired with a 2-D experiment in the Xepr software through the transient signal path of a Bruker E500T and digitized in quadrature with a Bruker SpecJet II. Signals at the modulation frequency and its harmonics were calculated by digital phase-sensitive detection. The number of harmonics with signal intensity greater than noise increases as the ratio of the modulation amplitude to the narrowest peak increases. Spectra reconstructed by the multiharmonic method from data obtained with modulation amplitudes up to five times the peak-to-peak linewidths of the narrowest features have linewidths that are broadened by up to only about 10% relative to linewidths in spectra obtained at low modulation amplitudes. The signal-to-noise improves with increasing modulation amplitude up to the point where the modulation amplitude is slightly larger than the linewidth of the narrowest features. If this high a modulation amplitude had been used in conventional methodology the linewidth of the narrowest features would have been severely broadened. The multiharmonic reconstruction methodology means that the selection of the modulation amplitude that can be used without spectral distortion is no longer tightly tied to the linewidth of the narrowest line.

Wide-Bandwidth Biological Impedance Spectroscopy System Based on the Digital Lock-In Technique

ABSTRACT The spectra of biological impedance can reveal physiological conditions and biological events of biological samples. This paper presents the development of a novel biological impedance spectroscopy system using an improved digital lock-in technique. The hardware of the system mainly consists of a current source, a voltage detector, a clock generator, and a field-programmable gate array (FPGA) device. Digital phase-sensitive detection algorithms including direct digital synthesis, digital multipliers, and digital filters were implemented in the FPGA. Test results show that the proposed spectroscopy has good performance from low frequency to 5 MHz with 1% accuracy. It will be suitable for high-accuracy biological impedance spectra analysis in either in vitro or in vivo conditions.

Bioelectrical Impedance Measurement Way Based on an Improved DPSD Algorithm

In Bioelectrical impedance measurement, the impedance accuracy is a very important parameter. With the analysis of general Digital Phase Sensitive Detection (DPSD) algorithm and its error, this paper presents an improved DPSD algorithm. In this method, it firstly decomposes the orthogonal signals which have passed through the networks, and then sums (minus) the relevant signals to get the parameters amplitude and phase. By this way, it can avoid errors caused by filtering operation in general DPSD algorithm. At last, the paper gives a simulation which can be hardware-based achieved. The result proves the effectiveness and feasibility of this improved method.

Detecting Ferrite Nanobeads for Sentinel Lymph Node Mapping with a Highly Sensitive Hall Differential Magnetic Field Sensor

We fabricated a novel type of Hall differential magnetic field sensor for anti-cancer sentinel lymph node (SLN) mapping using ferrofluid as a marker. A pair of Hall devices are mounted on both end surfaces of a ferrite core (10 mm ϕ ×32 mm) of an electromagnetic coil which generates an AC exciting magnetic field at 2.5 kHz. The signals are retrieved by a digital phase sensitive detection circuit. Mapping a ferrofluid (ResovistR) sample of l00μg in Fe atomic amount (comparable to that accumulated in human SLNs) was attained when the sample was placed within 6 mm distance from the sensor head. The detectable distance is limited primarily due to the magnetic induction effect of the metal XYZ stage which held the sample.

Application of Digital Phase Sensitive Detection for Electromagnetic Propagation Logging while Drilling

Intense electromagnetic interference while drilling prevents traditional analog phase sensitive detection (APSD) from correctly acquiring electromagnetic wave signal of logging while drilling (LWD). A digital phase sensitive detection (DPSD) utilizes high-performance floating-point DSP and FPGA to separately process real part and imaginary part of the acquired logging signal, changes traditional calculating method, improves processing speed and calculating precision. The programmable technique used can fully utilize logging information, simplify control logic, improve precision of timing control and measuring precision. Discussed are the principle, characteristics, implement of circuit and analysis of experimental data. Testing result shows that the DPSD may utilize logging information effectively and optimize the LWD system.

Through-Casing Resistivity Logging Signal Acquisition and Processing Techniques

Weak signal detection is the key technique in developing through-casing resistivity logging tool. In this paper, ultra-low-noise preamplifier, oversampling method, sampling integration and sampling average method, digital phase-sensitive detection technique are applied in detecting logging signals and 30nV is achieved. The indoor calibration test and field experiment of through-casing resistivity logging model machine with those weak signal detection techniques were carried out. The result showed that the measurement range of formation resistivity is 0~200 Ω.m.

Reconstruction of the first-derivative EPR spectrum from multiple harmonics of the field-modulated continuous wave signal

Selection of the amplitude of magnetic field modulation for continuous wave electron paramagnetic resonance (EPR) often is a trade-off between sensitivity and resolution. Increasing the modulation amplitude improves the signal-to-noise ratio, S/ N, at the expense of broadening the signal. Combining information from multiple harmonics of the field-modulated signal is proposed as a method to obtain the first derivative spectrum with minimal broadening and improved signal-to-noise. The harmonics are obtained by digital phase-sensitive detection of the signal at the modulation frequency and its integer multiples. Reconstruction of the first-derivative EPR line is done in the Fourier conjugate domain where each harmonic can be represented as the product of the Fourier transform of the 1st derivative signal with an analytical function. The analytical function for each harmonic can be viewed as a filter. The Fourier transform of the 1st derivative spectrum can be calculated from all available harmonics by solving an optimization problem with the goal of maximizing the S/ N. Inverse Fourier transformation of the result produces the 1st derivative EPR line in the magnetic field domain. The use of modulation amplitude greater than linewidth improves the S/ N, but does not broaden the reconstructed spectrum. The method works for an arbitrary EPR line shape, but is limited to the case when magnetization instantaneously follows the modulation field, which is known as the adiabatic approximation.

The MAST motional Stark effect diagnostic

A motional Stark effect (MSE) diagnostic is now installed and operating routinely on the MAST spherical tokamak, with 35 radial channels, spatial resolution of ∼2.5 cm, and time resolution of ∼1 ms at angular noise levels of ∼0.5°. Conventional (albeit very narrow) interference filters isolate π or σ polarized emission. Avalanche photodiode detectors with digital phase-sensitive detection measure the harmonics of a pair of photoelastic modulators operating at 20 and 23 kHz, and thus the polarization state. The π component is observed to be significantly stronger than σ, in reasonably good agreement with atomic physics calculations, and as a result, almost all channels are now operated on π. Trials with a wide filter that admits the entire Stark pattern (relying on the net polarization of the emission) have demonstrated performance almost as good as the conventional channels. MSE-constrained equilibrium reconstructions can readily be produced between pulses.

Advantages of digital phase-sensitive detection for upgrading an obsolete CW EPR spectrometer

The replacement of the commonly used analog phase-sensitive detection (PSD) by digital PSD for demodulation of electron paramagnetic resonance (EPR) signals is suggested for upgrading of an out-of-date EPR spectrometer. Connection of the microwave bridge output to a fast analog-digital converter (ADC) eliminates some of the spectrometer’s components: the electronics responsible for analog PSD, ADC for sampling of demodulated signals, and a computer, as well as the usage of some of the spectrometer’s settings. The spectrometer is reduced to a magnet, microwave bridge, and personal computer containing an ADC board. EPR signals digitized for a set of magnetic field positions form a two-dimensional array which is stored in a personal computer. Demodulation and filtering are done numerically to produce a conventional EPR spectrum. In comparison with analog PSD, this numerical approach does not eliminate the out-of-phase component of the signal and the signals at the higher harmonics of the modulation frequency. The details of modernizing the Bruker ER200E SRC EPR spectrometer are discussed to demonstrate these and other advantages of digital demodulation.

In situ Spectroscopy of Catalytic Solid–Liquid Interfaces and Chiral Surfaces

This contribution gives an overview of our recent effort to probe catalytic solid–liquid interfaces in situ and to investigate recognition processes at chiral surfaces. Attenuated total reflection infrared spectroscopy in a dedicated low volume flow-through cell is used to investigate the working catalytic interface. The latter technique is combined with modulation spectroscopy, which relies on the perturbation of the system under investigation by a periodically varying external parameter. A digital phase-sensitive detection results in high quality spectra. The method furthermore yields kinetic information and helps disentangle complex spectra. The described tool is therefore ideally suited for the investigation of complex systems. Applications in the fields of heterogeneous catalysis and recognition at chiral solid–liquid interfaces are presented. Our aim is a better molecular level understanding of these processes and, based on this knowledge, a rational design of better catalyst materials.

An Optical Fibre Sensor for Non-sinusoidal Current

Measurement of current and voltage in high voltage systems employing optical fibre sensors is becoming increasingly popular as the problem of insulation is practically eliminated. Vibrations, physical and acoustic, perturb the polarisation-preserving sensing fibre and cause added noise much in excess of the signal. The present paper discusses a method for reconstructing such a signal. The method, namely, signal-averaging digital phase sensitive detection (DPSD) recovers the signal of any arbitrary wave shape buried in noise. The only requirements are that the signal should be periodic and a local reference should be made available, conditions easily met in HV systems. The efficacy of the scheme is demonstrated by experimental results on a fibre optic current sensor with non-sinusoidal current.

A radiofrequency ESR spectrometer/imager

A Radiofrequency ESR spectrometer/imager is described. Modified from a Surrey Medical Imaging Systems NMR spectroscopy/imaging console, it uses a PC with associated waveform controller cards to perform CW ESR. Digital phase-sensitive detection is provided by a vector processor. The “target-field”-designed magnet and gradients are driven by audio amplifiers. The dual-channel broad-band RF bridge has a reflection homodyne configuration. Birdcage coils have been built that resonate near 200 MHz. Spectra and images of lossy samples of up to 4 cm diameter have been acquired.

An electrostatic audio generator : E. B. Kurtz and M. J. Larson ( Electrical Engineering, Vol. 54, No. 9)

Multiharmonic electron paramagnetic resonance spectroscopy was demonstrated for two samples with both narrow and broad lines: (i) α,γ-Bisdiphenylene-β-phenylallyl (BDPA) with ΔBpp of 0.85 G plus ultramarine blue with ΔBpp of 17 G, and (ii) a nitroxide radical immobilized in sucrose octaacetate. Modulation amplitudes up to 17 G at 41 kHz were generated with a rapid scan coil driver and Litz wire coils that provide uniform magnetic field sweeps over samples with heights of 5 mm. Data were acquired with a 2-D experiment in the Xepr software through the transient signal path of a Bruker E500T and digitized in quadrature with a Bruker SpecJet II. Signals at the modulation frequency and its harmonics were calculated by digital phase-sensitive detection. The number of harmonics with signal intensity greater than noise increases as the ratio of the modulation amplitude to the narrowest peak increases. Spectra reconstructed by the multiharmonic method from data obtained with modulation amplitudes up to five times the peak-to-peak linewidths of the narrowest features have linewidths that are broadened by up to only about 10% relative to linewidths in spectra obtained at low modulation amplitudes. The signal-to-noise improves with increasing modulation amplitude up to the point where the modulation amplitude is slightly larger than the linewidth of the narrowest features. If this high a modulation amplitude had been used in conventional methodology the linewidth of the narrowest features would have been severely broadened. The multiharmonic reconstruction methodology means that the selection of the modulation amplitude that can be used without spectral distortion is no longer tightly tied to the linewidth of the narrowest line.