Amplitude Detection Research Articles

Quadrature Block for UHF Reflection Coefficient Measurements Using a Directional Coupler and Injection Locking

The measurement of the radio frequency reflection coefficient is widely used in characterizing various materials nondestructively. Generally, the measurement is done using a one port vector network analyzer together with some sort of probe. Here, the design theory of a new, low-cost replacement for such a network analyzer is explained. The proposed Cartesian reflection coefficient measurement block is outlined as well as the results of computer simulations and measurements on a printed circuit board (PCB) setup. Unlike previous approaches, it explores the use of injection locking to enhance the performance of quadrature amplitude demodulation of both the forward and the reflected waves as sampled from the output path of an ultrahigh-frequency power amplifier by a bidirectional coupler. Computer simulations at 400 MHz resulted in an average error of 3.4% full scale on the reflection coefficient, including extreme impedance values as well as various parasitic effects of the circuit measurements on a simplified PCB setup, also at 400 MHz.

Low-level radio-frequency system upgrade for the IMP Heavy Ion Reach Facility in Lanzhou (HIRFL)

The upgrade of the Heavy Ion Research Facility in Lanzhou (HIRFL) began in 2000 to enhance the performance in nuclear physics, atomic physics, irradiative materials, and biology, cancer therapy using heavy ions and hadron physics. The upgraded program of HIRFL aimed to provide all ions from protons to uranium for higher beam intensity. As one of subprojects upgrade program in HIRFL, the low-level radio frequency (LLRF) system is also completely redesigned to better stabilize the beam acceleration parameters during the machine operation.The purpose of this article is to describe the design and implementation of the new fully digital LLRF system for six sets of radio frequency (RF) systems at the HIRFL. All components, including the quadrature demodulation, phase and amplitude detectors, phase shifter, and proportional integral (PI) loop filter, were designed in detail and realized in field programmable gate array (FPGA). A special synchronous RF source was designed to provide a phase reference for the different RF systems. A new tuning system was designed to ensure that the RF system remains in a good working state. An economical compensation method for the temperature drift in the pick-up cables was designed to improve the control accuracy of the system. The new LLRF systems have passed a 24 h high power test on the HIRFL cavities. The phase stabilization control accuracy was |Δϕ|≤0.2o, and the amplitude fluctuation was |ΔA|≤2∗10−3. Compared with the original analog system, the control precision and stability have been improved by an order of magnitude. The extraction beam energy of SFC was measured, and its stability is better than 4.3∗10−3, after this LLRF system is applied successfully.

A comparison of three ECG-derived respiration methods for sleep apnoea detection

This study compared three different methods of estimating ECG-derived respiration (EDR) from full overnight single lead ECG signals. The first EDR method was based on calculating an area enclosed by each QRS complex (EDR-A), the second method was an amplitude demodulation method (EDR-B), and the third method used a novel algorithm to provide fast calculation of principal component analysis (PCA) to estimate the EDR (EDR-P). The ‘Apnea-ECG’ MIT-BIH PhysioNet dataset was used to enable the comparisons. An assessment of the Pearson correlation of each EDR method with selected segments of chest respiratory effort was performed. Following this, a comparative assessment of the performance of each EDR method to automatically detect epochs of sleep apnoea was performed. Identical features were derived from the three EDR signals and processed with automated classifiers developed by the linear-discriminant analysis and the extreme-learning machine algorithms. The pooled average correlation for the EDR-A, EDR-B and EDR-P methods against the chest respiratory effort signal were 0.82, 0.79, 0.73. The classification accuracy for detecting one-minute epochs of sleep apnoea was 84%, 79% and 81% with the LDA classifier. We conclude that the EDR-A method provides best performance of the methods.

Algebraic Aspects of the Exact Signal Demodulation Problem

Abstract In this paper we introduce a general class of problems originating from gearbox vibration analysis. Based on a previous work where demodulation was formulated as a matrix approximation problem, we study the specific case applicable to amplitude and phase demodulation. This problem can be rewritten as a polynomial system. Based on algebraic methods such as linear algebra and homological algebra, we focus on the characterization of the problem and solve it in the noise-free case.

Generalized Lyapunov Demodulator for Amplitude and Phase Estimation by the Internal Model Principle

Effective demodulation of amplitude and phase is a requirement in a wide array of applications. Recent efforts have increased the demodulation performance, in particular, the Lyapunov demodulator allows bandwidths up to the carrier frequency of the signal. However, being inherently restricted to a single order filtering of the input signal, signal components outside its passband are not sufficiently attenuated for all applications, such as in multifrequency atomic force microscopy. In this article, the structure of the Lyapunov demodulator is transformed to an equivalent form, taking advantage of the internal model representation of the sinusoid to be tracked. A generalization of this formulation allows the application of standard filtering techniques in order to shape the characteristics of the demodulator, while retaining the perfect tracking condition provided by the internal model. Guidelines for the filter design are provided in order to achieve the desired characteristics, such as filtering order, tracking bandwidth, and transient performance. The resulting generalized Lyapunov demodulator structure is highly flexible, allows for direct employment of any standard filter type, is computationally simple, and easy to implement requiring only a bandpass filter, a single integrator, and two nonlinear transformations. Numerical results demonstrate the effectiveness of the approach, and provide a comparison of the various filters considered.

A narrowband envelope spectra fusion method for fault diagnosis of rolling element bearings

Narrowband amplitude demodulation is an effective tool for extracting characteristic features in the fault diagnosis of rolling element bearings. The quality of demodulation largely depends on the frequency band selected for the demodulation. Numerous criteria have been constructed to determine the optimal frequency band. However, independent frequency interferences and in-band noises in narrowband signals can greatly affect the values of the criteria, which may lead to an inaccurate result in locating the optimal band, in demodulating fault features, and finally in the fault detection. Inspired by the nonlocal means (NL-means) denoising method that has been widely used in image processing, this paper proposes a narrowband envelope spectra fusion (NESF) method to enhance fault features and suppress in-band noises before criterion calculation. The method suppresses in-band noises by averaging envelope spectra at neighboring narrow bands. Meanwhile, some minor improvements are made to the conventional narrowband envelope spectrum calculation method to enhance the similarity of the narrowband envelope spectra containing fault features, and finally optimize the fusion process. Then, sparsity values of these denoised envelope spectra, which can lower the impact of independent frequency interferences, are utilized to determine the optimal band and select the optimal envelope spectrum. Frequency signatures of the extracted envelope spectrum can be utilized to indicate the status and fault types of rolling element bearings. A simulated bearing fault signal and three real bearing fault signals are used to validate the effectiveness of the proposed method through comparison studies with protrugram and sparsogram. The results show that the proposed method can effectively extract fault characteristics, even in a harsh environment.

Measurement of elastoresistivity at finite frequency by amplitude demodulation.

Elastoresistivity, the relation between resistivity and strain, can elucidate the subtle properties of the electronic structure of a material and is an increasingly important tool for the study of strongly correlated materials. To date, elastoresistivity measurements have predominantly been performed with quasi-static (DC) strain. In this work, we demonstrate a method using AC strain in elastoresistivity measurements. A sample experiencing AC strain has a time-dependent resistivity, which modulates the voltage produced by an AC current; this effect produces time-dependent variations in resistivity that are directly proportional to the elastoresistivity, and which can be measured more quickly, with less strain on the sample, and with less stringent requirements for temperature stability than the previous DC technique. Example measurements between 10 Hz and 3 kHz are performed on a material with a large, well-characterized and temperature dependent elastoresistivity: the representative iron-based superconductor Ba(Fe0.975Co0.025)2As2. These measurements yield a frequency independent elastoresistivity and reproduce results from previous DC elastoresistivity methods to within experimental accuracy. We emphasize that the dynamic (AC) elastoresistivity is a distinct material-specific property that has not previously been considered.

A novel phase-shift-based amplitude detector for a high-speed atomic force microscope.

In any atomic force microscope operated in amplitude modulation mode, aka "tapping mode" or "oscillating mode," the most crucial operation is the detection of the cantilever oscillation amplitude. Indeed, it is the change in the cantilever oscillation amplitude that drives the feedback loop, and thus, the accuracy and speed of amplitude detection are of utmost importance for improved atomic force microscopy operation. This becomes even more crucial for the operation of a high-speed atomic force microscope (HS-AFM), where feedback operation on a single or a low number of cantilever oscillation cycles between 500 kHz and 1000 kHz oscillation frequency is desired. So far, the amplitude detection was performed by Fourier analysis of each oscillation, resulting in a single output amplitude value at the end of each oscillation cycle, i.e., 360° phase delay. Here, we present a novel analog amplitude detection circuit with theoretic continuous amplitude detection at 90° phase delay. In factual operation, when exposed to an abrupt amplitude change, our novel amplitude detector circuit reacted with a phase delay of ∼138° compared with the phase delay of ∼682° achieved by the Fourier analysis method. Integrated to a HS-AFM, the novel amplitude detector should allow faster image acquisition with lower invasiveness due to the faster and more accurate detection of cantilever oscillation amplitude change.

A 19.8-mW Eddy-Current Displacement Sensor Interface With Sub-Nanometer Resolution

This paper presents an eddy-current sensor (ECS) interface intended for sub-nanometer (sub-nm) displacement sensing in hi-tech applications. The interface employs a 126-MHz excitation frequency to mitigate the skin effect, and achieve high resolution and stability. An efficient on-chip sensor offset compensation scheme is introduced which removes sensor-offset proportional to the standoff distance. To assist in the ratiometric suppression of noise and drift of the excitation oscillator, the ECS interface consists of a highly linear amplitude demodulation scheme that employs passive capacitors for voltage-to-current (V2I) conversion. Using a printed circuit board-based pseudo-differential ECS, stability tests were performed which demonstrated a thermal drift of $\sqrt {\mathrm{ Hz}}$ which corresponds to a displacement resolution of 0.6 nm in a 2-kHz noise bandwidth. The ECS interface is fabricated in TSMC 0.18- $\mu \text{m}$ CMOS technology and dissipates only 19.8 mW from a 1.8-V supply.

Amplitude demodulation for electrical capacitance tomography based on singular value decomposition.

Amplitude demodulation is essential in image reconstruction for electrical capacitance tomography (ECT). In this paper, an amplitude demodulation method is proposed based on singular value decomposition (SVD), which can substitute the role of phase-sensitive demodulation in ECT. First, an M × N Hankel matrix is constructed based on a set of discrete samples. Then, SVD operation is performed on the matrix. Finally, the mathematical expression between the sinusoid amplitude and effective singular values is given; i.e., the first two singular values are used to estimate the amplitude information of the acquired signal. The proposed method has the following advantages: (1) since no reference signals are needed, the synchronization between the acquired and reference signals is not necessary; (2) this method can obtain the amplitude information of the acquired signal with a high signal-to-noise ratio (SNR), even in the case of non-integrity period sampling; and (3) SVD itself can also implement the filtering function; thus, no additional low-pass filters are required in the signal conditioning module. The demodulation accuracy and feasibility of the proposed method were verified by numerical simulations and experiments, indicating that it can provide amplitude demodulation with excellent SNR and robust performances.

Моделирование приёмной системы с амплитудной демодуляцией и временным разделением каналов в среде LabView.

Моделирование приёмной системы с амплитудной демодуляцией и временным разделением каналов в среде LabView.

Assessing blood vessel perfusion and vital signs through retinal imaging photoplethysmography.

One solution to the global challenge of increasing ocular disease is a cost-effective technique for rapid screening and assessment. Current ophthalmic imaging techniques, e.g. scanning and ocular blood flow systems, are expensive, complex to operate and utilize invasive contrast agents during assessment. The work presented here demonstrates a simple retinal imaging photoplethysmography (iPPG) system with the potential to provide screening, diagnosis, monitoring and assessment that is non-invasive, painless and radiationless. Time series of individual retinal blood vessel images, captured with an eye fundus camera, are processed using standard filtering, amplitude demodulation and principle component analysis (PCA) methods to determine the values of the heart rate (HR) and respiration rate (RR), which are in compliance with simultaneously obtained measurements using commercial pulse oximetry. It also seems possible that some information on the dynamic changes in oxygen saturation levels (SpO2) in a retinal blood vessel may also be obtained. As a consequence, the retinal iPPG modality system demonstrates a potential avenue for rapid ophthalmic screening, and even early diagnosis, against ocular disease without the need for fluorescent or contrast agents.

Nonlinear parity readout with a microwave photodetector

Robust high-fidelity parity measurment is an important operation in many applications of quantum computing. In this work we show how in a circuit-QED architecture, one can measure parity in a single shot at very high contrast by taking advantage of the nonlinear behavior of a strongly driven microwave cavity coupled to one or multiple qubits. We work in a nonlinear dispersive regime treated in an exact dispersive transformation. We show that appropriate tuning of experimental parameters leads to very high contrast in the cavity and therefore to a high efficiency parity readout with a microwave photon counter or another amplitude detector. These tuning conditions are based on nonlinearity and are hence more robust than previously described linear tuning schemes. In the first part of the paper we show in detail how to achieve this for two qubit parity measurements and extend this to $N$ qubits in the second part of the paper. We also study the QNDness of the protocol.

Multi-scale signed envelope inversion

Envelope inversion based on modulation signal mode was proposed to reconstruct large-scale structures of underground media. In order to solve the shortcomings of conventional envelope inversion, multi-scale envelope inversion was proposed using new envelope Fréchet derivative and multi-scale inversion strategy to invert strong contrast models. In multi-scale envelope inversion, amplitude demodulation was used to extract the low frequency information from envelope data. However, only to use amplitude demodulation method will cause the loss of wavefield polarity information, thus increasing the possibility of inversion to obtain multiple solutions. In this paper we proposed a new demodulation method which can contain both the amplitude and polarity information of the envelope data. Then we introduced this demodulation method into multi-scale envelope inversion, and proposed a new misfit functional: multi-scale signed envelope inversion. In the numerical tests, we applied the new inversion method to the salt layer model and SEG/EAGE 2-D Salt model using low-cut source (frequency components below 4 Hz were truncated). The results of numerical test demonstrated the effectiveness of this method.

P07-Automatic pallidal neurons recognition based on the detection of the number of clusters from microrecordings in dystonia

Intraoperative microelectrode records (MER) are considered as the standard electrophysiological method for the precise positioning of the deep brain stimulation (DBS) electrode into the Globus pallidus interna (GPi). The final GPi position is chosen based on the firing patterns of individual neurons. Finding the number of neurons is usually done manually during the spike sorting. We propose methodology for neurons recognition based on the unsupervised learning. Thirty MERs (24 kHz 10s) of the basal ganglia from 10 patients (43.3(±14), 5F) with dystonia were recorded during DBS implantation. MERs were filtered in the 300–3000 Hz band and the amplitude detector (3× std of the background noise) was used to detect spikes. The WaveClus features were computed and its 2 PCA components were extracted for every spike. The optimal number of clusters evaluated by an expert rater, K-means + gap criterion (alg. 1) and the GMM + BIC (alg. 2) were analyzed. The total Intraclass correlation showed a significant inter-rater agreement for all 3 rater procedures (ICC = 0.62, p It can contribute to better description of type of the GPi neurons involved in (non)motor functions. Supported by the GACR No. 16-13323S and AZV No. 16-28119a.

Lyapunov Estimator for High-Speed Demodulation in Dynamic Mode Atomic Force Microscopy

In dynamic mode atomic force microscopy (AFM), the imaging bandwidth is governed by the slowest component in the open-loop chain consisting of the vertical actuator, cantilever, and demodulator. While the common demodulation method is to use a lock-in amplifier (LIA), its performance is ultimately bounded by the bandwidth of the postmixing low-pass filters. This brief proposes an amplitude and phase estimation method based on a strictly positive real Lyapunov design approach. The estimator is designed to be of low complexity while allowing for high bandwidth. In addition, suitable gains for high performance are suggested such that no tuning is necessary. The Lyapunov estimator is experimentally implemented for amplitude demodulation and shown to surpass the LIA in terms of tracking bandwidth and noise performance. High-speed AFM images are presented to corroborate the results.

Lyapunov estimation for high-speed demodulation in multifrequency atomic force microscopy.

An important issue in the emerging field of multifrequency atomic force microscopy (MF-AFM) is the accurate and fast demodulation of the cantilever-tip deflection signal. As this signal consists of multiple frequency components and noise processes, a lock-in amplifier is typically employed for its narrowband response. However, this demodulator suffers inherent bandwidth limitations as high-frequency mixing products must be filtered out and several must be operated in parallel. Many MF-AFM methods require amplitude and phase demodulation at multiple frequencies of interest, enabling both z-axis feedback and phase contrast imaging to be achieved. This article proposes a model-based multifrequency Lyapunov filter implemented on a field-programmable gate array (FPGA) for high-speed MF-AFM demodulation. System descriptions and simulations are verified by experimental results demonstrating high tracking bandwidths, strong off-mode rejection and minor sensitivity to cross-coupling effects. Additionally, a five-frequency system operating at 3.5 MHz is implemented for higher harmonic amplitude and phase imaging up to 1 MHz.

Система автоматической регулировки амплитуды колебаний для однокольцевого RC-автогенератора

Harmonic RC oscillators have long been known and are widely used in various fields of radio engineering. They have become widely used in medical equipment, various sensors, measuring equipment, etc. Their main advantages in operating within short to long wave frequency bands are compact dimensions, simplicity and low cost of manufacturing, possibility of widely retuning the frequency, etc. In our previous articles, we examined several versions of such circuits, including single-loop RC oscillators, which are the simplest ones. It was shown that the major disadvantage of such self-oscillators in generating close-to-sinewave signals is the need to operate them with a very small self-excitation margin. An attempt to increase the self-excitation margin inevitably leads to a growth of higher harmonic components, distortion of the output signal, and failure of oscillations. As a result, additional techniques must be used to secure stable steady-state operation. One of such techniques is automatic amplitude control (AAC). With the AAC circuit switched in operation, the generator output signal amplitude is controlled, due to which a larger self-excitation margin is obtained at the initial time instant, and the required amplitude value is maintained during steady-state operation. The article presents a version of such system taking as an example a single-loop self-oscillator with the Wien bridge in the feedback circuit. As is known, the list of important issues to be taken care of in designing AAC systems includes, among other things, an analysis of their stability and the selection of time constants for the system functional units. There are many methods for analyzing the stability of an AAC system, and all of them involve the need to set up differential equations of the system. A version of addressing this objective is presented to produce the system of differential equations describing the operation of a self-oscillator fitted with the AAC system. The obtained system of equations was applied for selecting — using the Routh–Hurwitz stability criterion — the time constant for the low-pass filter (LPF) of the AAC system amplitude detector (AD). It has been shown that the selection of the time constant for the AD LPF is constrained, on the one hand, by the requirements for the amplitude detector operation mode, and on the other hand, by the need to ensure fast response of the AAC system to variations of the generator voltage amplitude. The time histories of the system response to variations of the generator voltage amplitude and the system phase-plane portrait have been obtained.

Joint Amplitude and Frequency Demodulation Analysis Based on Variational Mode Decomposition for Multifault Diagnosis of a Multistage Reducer

Multistage reducer vibration signals have complicated spectral structures owing to the amplitude and frequency modulations of gear damage‐induced vibrations and the multiplicative amplitude modulation effect caused by time‐varying vibration transfer paths (in the case of local gear damage) when the multistage reducer contains both planetary and spur gears. Moreover, the difference between the vibration energies of these gears increases the difficulty of fault feature extraction when multiple failures occur in the reducer. As the meshing frequency of each gear group often varies significantly, variational mode decomposition can be performed to decompose the vibration signal according to frequency, enabling separation of the vibration signals of the spur and planetary gears. The common fault features of these gears can be extracted from the spectrum of the amplitude demodulation envelope. To verify the effectiveness of this method, we first analyzed a simulation signal, and then utilized the experimental signals from a laboratory multistage reducer for verification. In the multistage reducer simulation, we considered the amplitude and frequency modulation of the gear damage and transfer paths. In the experimental verification, we processed local faults (broken teeth) and uniform faults (uniform wear) on the sun gear and the spur gear of the planetary gear separately.

Performance evaluation of IR-UWB detectors and fusion techniques for UWB transceiver platforms

In this paper, we analyse the performance of a multi-pulse impulse radio based ultra-wideband (IR-UWB) detector in an AWGN setting and provide different fusion strategies for fusing these detector outputs. To enable the transceiver to be used for multiple applications, the designers have different types of detectors such as energy detectors, amplitude detectors, etc., built in to a single transceiver architecture. In this paper, we derive the detection performance equation for commonly used detectors in terms of false alarm rate, shape of the pulse, and number of UWB pulses used in the detection and apply these in the fusion algorithms. We show that the performance can be improved by approximately 4 dB in terms of signal to noise ratio (SNR) for high probability of detection of a UWB signal (95%), by fusing decisions from multiple detector types compared to a standalone energy detector, in a practical scenario.