Low-frequency Test Research Articles

Implementation of microcontroller board on a sustainable and degradable PLA/flax composite substrate: a case study

In this paper, we present a novel polylactic-acid/flax-composite substrate and the implementation of a demonstrator: a microcontroller board based on commercial design. The substrate is developed for printed circuit board (PCB) applications. The pre-preg is biodegradable, reinforced, and flame-retarded. The novel material was developed to counter the increasing amount of e-waste and to improve the sustainability of the microelectronics sector. The motivation was to present a working circuit in commercial complexity that can be implemented on a rigid substrate made of natural, bio-based materials with a structure very similar to the widely used Flame Retardant Class 4 (FR4) substrate at an early technological readiness level (2–3). The circuit design is based on the Arduino Nano open-source microcontroller board design so that the demonstration could be programmable and easy to fit into education, IoT applications, and embedded designs. During the work, the design was optimized at the level of layout. The copper-clad pre-preg was then prepared and processed with subtractive printed wiring technology and through hole plating. The traditional surface mounting methodology was applied for assembly. The resulting yield of PCB production was around 50%. Signal analysis was successful with analogue data acquisition (voltage) and low-frequency (4 kHz) tests, indistinguishable from sample FR4 boards. Eventually, the samples were subjected to highly accelerated stress test (HAST). HAST tests revealed limitations compared to traditional FR4 printed circuit materials. After six cycles, the weight loss was around 30% in the case of PLA/Flax, and as three-point bending tests showed, the possible ultimate strength (25 MPa at a flexural state) was reduced by 80%. Finally, the sustainability aspect was assessed, where we found that ∼95 vol% and ∼90 wt% of the traditional substrate can be substituted, significantly easing the load of waste on the environment.

A dynamic correction method for the optimal value settings of the solution purification process at multiple time scales

The solution purification process includes multiple continuous reactors. Setting the key technical indicators of each reactor through global optimization is the prerequisite for realizing the optimal operation of the entire process. Affected by fluctuations in inlet conditions, adjustments of operating parameters, and random disturbances, the operating status of the solution purification process will change accordingly, causing the optimal value settings based on global optimization to become no longer applicable. To ensure the applicability of the optimal value settings as the process changes and considering that the production data collected at different time scales contain different process information, this study proposes a dynamic correction method for the optimal value settings of the solution purification process at multiple time scales. First, considering the low-frequency testing data that can reflect the operation effect, the low-frequency correction is realized by combining mechanism knowledge and expert experience. Second, based on the characteristic that the high-frequency detection data can reflect the changing operating status in time, a supervised self-organizing map method is proposed to classify the changing trends in the operating status. Finally, an integrated, spatiotemporal, just-in-time learning method (with multiple changing trends in the operating status) is proposed to realize high-frequency correction. The experimental results show that the proposed method can dynamically correct the optimal value settings and reduce resource consumption while ensuring product quality.

Promiscuous involvement of metabotropic glutamate receptors in the storage of N-methyl-d-aspartate receptor-dependent short-term potentiation.

Short- and long-term forms of N-methyl-d-aspartate receptor (NMDAR)-dependent potentiation (most commonly termed short-term potentiation (STP) and long-term potentiation (LTP)) are co-induced in hippocampal slices by theta-burst stimulation, which mimics naturally occurring patterns of neuronal activity. While NMDAR-dependent LTP (NMDAR-LTP) is said to be the cellular correlate of long-term memory storage, NMDAR-dependent STP (NMDAR-STP) is thought to underlie the encoding of shorter-lasting memories. The mechanisms of NMDAR-LTP have been researched much more extensively than those of NMDAR-STP, which is characterized by its extreme stimulation dependence. Thus, in the absence of low-frequency test stimulation, which is used to test the magnitude of potentiation, NMDAR-STP does not decline until the stimulation is resumed. NMDAR-STP represents, therefore, an inverse variant of Hebbian synaptic plasticity, illustrating that inactive synapses can retain their strength unchanged until they become active again. The mechanisms, by which NMDAR-STP is stored in synapses without a decrement, are unknown and we report here that activation of metabotropic glutamate receptors may be critical in maintaining the potentiated state of synaptic transmission. This article is part of a discussion meeting issue 'Long-term potentiation: 50 years on'.

Assessment of auditory perception abilities using temporal envelope and fine structure processing in children with self-limited epilepsy with centrotemporal spikes

ObjectivesChildren with self-limited epilepsy with centrotemporal spikes (SeLECTS) exhibit difficulty processing spoken messages without hearing loss. The temporal envelope and fine structure processing abilities are the fundamental aspects of the normal listening process. There is limited literature on the temporal envelope and fine structure processing in children with SeLECTS. We evaluated the temporal envelope and fine structure processing in children with SeLECTS. DesignThe study included 35 children with SeLECTS and 50 typically developing children (TDC). The temporal envelope processing was measured using the temporal modulation transfer function (TMTF) and temporal fine structure using the temporal fine structure low-frequency (TFS LF) test. The TMTF was measured for the modulation rates 4, 8, 16, 32, 64 and 128 Hz. The TFS LF was done for 250, 500 and 750 Hz. ResultsThe difference in modulation detection thresholds at 4 Hz was not found to be significant, whereas there was a significant difference in modulation detection thresholds observed for all the other modulation frequencies (p < 0.05) between the children with SeLECTS and TDC. The thresholds at 250, 500 and 750 Hz were higher (poorer) for children with SeLECTS than the TDC and was significant (p < 0.05). ConclusionsThe TMTF and TFS LF tests were of practical use in evaluating temporal envelope and fine structure processing abilities in children with SeLECTS. The results suggest that children with SeLECTS have a poor temporal envelope and fine structure processing compared to the TDC.

Demonstration of Interface Circuits for Adiabatic Quantum-Flux-Parametron Cell Library Using an Eight-Metal Layer Superconductor Process

In this paper, we designed and demonstrated interface circuits between AQFP (adiabatic quantum-flux-parametron) and RSFQ (rapid single-flux-quantum) circuits according to the established AQFP and RSFQ cell libraries using the MIT LL SFQ5ee process. The principles of these interfaces are based on ones that were previously designed and demonstrated using a four-metal-layer superconductor process. The AQFP-to-RSFQ interface is based on an RSFQ comparator, where an output current from an AQFP buffer is converted to an SFQ pulse output. The RSFQ-to-AQFP interface is based on an RSFQ D flip-flop, where the internal state of the D flip-flop is read out by an AQFP buffer. Thanks to the eight-metal-layer process, the interfaces can be designed with reduced circuit area compared to original designs with the four-metal-layer process. We designed, fabricated, and tested an AQFP-RSFQ hybrid multiplexer test circuit as an example of utilization of the interfaces, which results in correct operation with reasonably wide bias margins in low-frequency tests.

Rotating cantilever-based low-frequency double-fiber grating acceleration sensor.

Acceleration sensors play an important role in bridges, dams, seismic monitoring, geological exploration, and more. Aiming at the problem that it is still difficult to accurately measure low-frequency vibration signals with low-frequency acceleration sensors, a high-sensitivity, wide-low-band fiber Bragg grating (FBG) acceleration sensor incorporating a rotating cantilever and springs was proposed. A sensor mechanics model was built, and its key parameters were analyzed theoretically and optimized in size. ANSYS Workbench was used for simulation analysis, and the physical sensor was developed while a low-frequency test platform was established for performance tests. The experimental results suggested that the natural frequency of the sensor was 78Hz, the operating frequency band was 1-55Hz, the sensitivity was 1127.2 pm/g, the transverse interference immunity was less than 5.45%, and the dynamic range was 86.45 dB. With high sensitivity, wide low frequency band, and excellent temperature compensation characteristics, the designed sensor could provide a reference for the design of like FBG acceleration sensors.

Application of Stewart Platform in the Low-Frequency Vibration Characteristic Test of Space Truss Deployable Antenna on Satellite

The space truss deployable antenna has low natural frequency, multi-closed-loop, and multiredundant structure characteristics, which is a kind of flexible antenna. It is hard to obtain the vibration characteristics under low frequency by finite element analysis or conventional shaking table test. To verify the structure characteristics of the antenna in the folded state below 2 Hz, a low-frequency vibration system is established based on the 6-DOF Stewart platform. Rotation matrix analysis method was adopted to obtain the platform’s velocity and acceleration characteristics. Then, a low-frequency vibration test was carried out on the platform. The results show that the natural frequency of the antenna is 1.51 Hz and the maximum dynamic displacement is 140.6 mm, which provides a certain foundation for the further development of the space truss antenna.

Outcomes Associated With High- Versus Low-Frequency Laboratory Testing Among Hospitalized Children.

Previous pediatric studies have revealed substantial variation in laboratory testing for specific conditions, but clinical outcomes associated with high- versus low-frequency testing are unclear. We hypothesized that hospitals with high- versus low-testing frequency would have worse clinical outcomes. We conducted a multicenter retrospective cohort study of patients 0 to 18 years old with low-acuity hospitalizations in the years 2018-2019 for 1 of 10 common All Patient Refined Diagnosis Related Groups. We identified hospitals with high-, moderate-, and low-frequency testing for 3 common groups of laboratory tests: complete blood cell count, basic chemistry studies, and inflammatory markers. Outcomes included length of stay, 7- and 30-day emergency department revisit and readmission rates, and hospital costs, comparing hospitals with high- versus low-frequency testing. We identified 132 391 study encounters across 44 hospitals. Laboratory testing frequency varied by hospital and condition. We identified hospitals with high- (13), moderate- (20), and low-frequency (11) laboratory testing. When we compared hospitals with high- versus low-frequency testing, there were no differences in adjusted hospital costs (rate ratio 0.89; 95% confidence interval 0.71-1.12), length of stay (rate ratio 0.98; 95% confidence interval 0.91-1.06), 7-day (odds ratio 0.99; 95% confidence interval 0.81-1.21) or 30-day (odds ratio 1.01; 95% confidence interval 0.82-1.25) emergency department revisit rates, or 7-day (odds ratio 0.84; 95% confidence interval 0.65-1.25) or 30-day (odds ratio 0.91; 95% confidence interval 0.76-1.09) readmission rates. In a multicenter study of children hospitalized for common low-acuity conditions, laboratory testing frequency varied widely across hospitals, without substantial differences in outcomes. Our results suggest opportunities to reduce laboratory overuse across conditions and children's hospitals.

Mechanical impact test methods for hard coatings of cutting tools: a review

Impact tests of different frequencies can be applied to simulate the cyclic fatigue load of the tool under different working conditions as well as different impact frequencies. The main objective of the present article is to review different impact test methods for hard tool coatings. In this regard, impact tests are divided into three categories, including high-frequency, medium-frequency, and low-frequency tests. In terms of the impact scale, impact tests can be divided into micro-scale and nano-scale tests. The impact tests at micro-scales and nano-scales aim to characterize the coating substrate and the coating itself, respectively. It is found that the interface properties between the coating and the substrate have a remarkable impact on the fatigue resistance of the tool coating. Finally, the design and future development of the impact test are discussed.

Exchange biased delta-E effect enables the detection of low frequency pT magnetic fields with simultaneous localization

Delta-E effect sensors are based on magnetoelectric resonators that detune in a magnetic field due to the delta-E effect of the magnetostrictive material. In recent years, such sensors have shown the potential to detect small amplitude and low-frequency magnetic fields. Yet, they all require external magnetic bias fields for optimal operation, which is highly detrimental to their application. Here, we solve this problem by combining the delta-E effect with exchange biased multilayers and operate the resonator in a low-loss torsion mode. It is comprehensively analyzed experimentally and theoretically using various kinds of models. Due to the exchange bias, no external magnetic bias fields are required, but still low detection limits down to {{text{350 pT}} mathord{left/ {vphantom {{text{350 pT}} {sqrt {{text{Hz}}} }}} right. kern-nulldelimiterspace} {sqrt {{text{Hz}}} }} at 25 Hz are achieved. The potential of this concept is demonstrated with a new operating scheme that permits simultaneous measurement and localization, which is especially desirable for typical biomedical inverse solution problems. The sensor is localized with a minimum spatial resolution of 1 cm while measuring a low-frequency magnetic test signal that can be well reconstructed. Overall, we demonstrate that this class of magnetic field sensors is a significant step towards first biomedical applications and compact large number sensor arrays.

Comparison of low-frequency non-sinusoidal measurement for transformer no-load characteristics based on different interpolation methods

As the calculation of transformer no-load characteristics measured by low-frequency test method is not perfect, different interpolation methods are explored to fit and convert the transformer's volt-ampere characteristics under power frequency (50 Hz) excitation to find the best interpolation fitting conversion method. The no-load test of transformer is carried out by using 10 Hz, 15 Hz, 20 Hz low-frequency square wave and triangular wave excitation. Then the measured excitation voltage, excitation current and no-load loss are converted to those of 50 Hz sine wave excitation. The converted volt-ampere characteristic curve is calculated by the proposed algorithm, and compared with the measured results under the 50 Hz sine wave excitation. Experiments show that under the condition that the magnetic flux amplitudes are equal at each frequency of non-sinusoidal and sine waves, whether it is square wave or triangular wave excitation, the volt-ampere characteristic curve converted to the 50 Hz sine wave excitation by the proposed method can better approximate the curve of the measured 50 Hz sine wave excitation. The average values of the relative errors of the converted excitation current of the three frequencies are within 4%, and those of the converted excitation voltage of the square wave are within 1.1%, and those of the converted excitation voltage of the triangular wave are within 0.47%. Compared with the generalized Steinmetz equation method and the multi-frequency method, the proposed method has a better conversion effect and can almost replace the no-load test results of the 50 Hz sine wave, which has practical value in engineering.

The Impact of Acute Loud Noise on the Behavior of Laboratory Birds.

Husbandry procedures and facility settings, such as low-frequency fire alarms, can produce noises in a laboratory environment that cause stress to animals used in research. However, most of the data demonstrating harmful effects that have, consequently, led to adaptations to management, have largely come from laboratory rodents with little known of the impacts on avian behavior and physiology. Here we examined whether exposure to a routine laboratory noise, a low-frequency fire alarm test, induced behavioral changes in laboratory zebra finches (Taeniopygia guttata). Twenty-four breeding pairs of zebra finches were randomly selected and exposed to the low-frequency fire alarm (sounding for 10–20 s) or no noise (control) on separate test days. All birds were filmed before and after the alarm sounded and on a control day (without the alarm). The zebra finches decreased their general activity and increased stationary and social behaviors after exposure to the alarm. Brief exposure to a low-frequency alarm disrupted the birds' behavior for at least 15 min. The induction of this behavioral stress response suggests that low-frequency sound alarms in laboratory facilities have the potential to compromise the welfare of laboratory birds.

СОВРЕМЕННЫЕ ТЕНДЕНЦИИ РАЗВИТИЯ АКУСТИЧЕСКИХ МЕТОДОВ НЕРАЗРУШАЮЩЕГО КОНТРОЛЯ В АВИАЦИОННОЙ ОТРАСЛИ (обзор)

The document includes the below main trends in development of acoustic non-destructive testing methods in aviation industry: automation and enhancement of the sensitivity the testing, development of Procedures for acoustic non-destructive testing methods for products in case of repair and use of products, probabilistic assessment of the outcomes of the ultrasonic non-destructive testing, mathematic simulation of the ultrasonic non-destructive testing, development of the ultrasonic non-destructive testing by applying state-of-the-art technologies, development of the low-frequency acoustic testing methods, development of a Procedure on training of specialists who conduct NDT. The experience of NRC «Kurchatov institute» – VIAM is pointed out to show an example on the implementation of main trends on ultrasonic testing development.

Demonstration of a Single-Flux-Quantum Microprocessor Operating With Josephson-CMOS Hybrid Memory

We have been developing Josephson-CMOS hybrid memory to realize large-scale single-flux-quantum (SFQ) digital systems. In this article, we present the first demonstration of a Josephson-cryo complementary-metal-oxide-semicoductor (CMOS) memory hybrid system composed of an SFQ microprocessor and cryo-CMOS memory. We designed a single-instruction SFQ microprocessor whose data memory is implemented using Josephson-CMOS hybrid memory with a 16 × 4-b accessible address space. The Josephson and CMOS circuits were fabricated using the AIST Nb standard process and the Rohm 180-nm process, respectively. Low-frequency tests confirmed the correct operation of the single instruction SUBNEG (subtract and branch if negative), which verifies the read and write operations of data between the SFQ microprocessor and the hybrid memory. We also demonstrate the operation of an integer sorting program, which is composed of 16 SUBNEG instructions.

Measurement of Complex Permeability of Thick Film Materials in the 0.1 GHz~0.6GHz Band

The existing low-frequency magnetic parameter test is mainly based on impedance analysis,Its sample needs to be prepared into a ring,the hard materials are difficult to process into rings for testing. Small piece of material cannot be tested using impedance analysis because it is too small to be cut into a ring for testing. In this paper, the principle of impedance analysis and the basic theory of strip line be used, an empirical formula for the complex permeability of the magnetic bulk thick film material in the 0.1Ghz~0.6GHz frequency band is obtained through design and test by design simulation and physical fixture, it makes the testing of the complex permeability of thick film materials easier due to it avoid damage and ring cutting before testing.

Graphene@poly(dopamine)-Ag core–shell nanoplatelets as fillers to enhance the dielectric performance of polymer composites

A new type of core–shell graphene@poly(dopamine)-Ag nanoplatelets was developed to improve the dielectric properties of thermoplastic polyurethane (TPU) nanocomposites. Dopamine was oxidatively polymerized to form a polydopamine (PDA) layer on the surface of graphene nanosheets (Gns), and then Ag nanoparticles were chemically reduced by silver nitrate and uniformly embedded on the surface of PDA. This obtained Gns@PDA-Ag core–shell nanoplatelets were filled into TPU to prepare a flexible dielectric material. The microstructure and dielectric performances were tested. Results indicated that the Gns@PDA-Ag core–shell nanoplatelets were evenly dispersed in TPU matrix. Moreover, the addition of Gns@PDA-Ag core–shell nanoplatelets could effectively improve the dielectric constant of the composite. Under low-frequency test conditions, the dielectric constant of the TPU/Gns@PDA-Ag (4 wt%) nanocomposite was 117.81, which was about 14 times higher than that of pure TPU. Theoretical analysis shows that the PDA shell not only promoted the uniform dispersion of Gns in TPU matrix, but also enhanced the interface bonding between the nanoplatelets and the TPU matrix. Moreover, introducing ultra-small Ag nanoparticles had effectively decreased the dielectric loss and conductivity of TPU/Gns@PDA-Ag composites due to its coulomb blockade and quantum trapped carrier structure effects, which resulted in the improvement of energy storage characteristics of composite.

A New Approach to Background Noise Cancellation in Time Domain for Low-Frequency Emission Testing

This article proposes a new approach to background noise (BN) cancellation for low-frequency electromagnetic compatibility (EMC) emission testing between 30 Hz and 10 kHz. The method proposed in this article is based on the streaming and recording of oscilloscope data in a continuous period without interruption and without losing phase information. In the proposed method, the continuous and consecutive stream of the oscilloscope data contains two adjacent data segments inside. The first data segment consists of the equipment under test (EUT) and BN information together, whereas the second segment contains only the BN because the EUT is switched off in the middle of the continuous data stream. After gathering all the oscilloscope data, the BN that exists in the first segment is precisely estimated by means of the BN information, which exits in the second segment. This estimation is easily attainable as the phase difference is accurately known between any two points in the first and second segments. Afterward, the simple subtraction of the estimated BN data from the actual combined EUT and BN data yields the EUT time-domain data. The proposed method assumes that the spectral content of the BN is stable during the entire streaming process, which may typically last for a range of 10–20 s. Ultimately, the effective performance of the method for the extraction of the EUT signal from the BN is theoretically and experimentally demonstrated with an average deviation of less than 0.6 dB for the low-frequency emission EMC testing.

Investigation of undesired ripple voltage across power source side and solutions in military low-frequency immunity tests

The MIL-STD-461 CS101 test is one of the essential low-frequency conducted immunity tests for military and aerospace equipment, however it includes some challenges in application. The major challenge is the necessity for the measurement of injected CS101 ripples under the power frequency of the EUT. The measurement of CS101 ripples on the power frequency is almost impossible without taking some extra precautions. In addition to the hard necessity of measuring the CS101 ripple voltage induced across the EUT power input, the other challenge of measuring the ripple voltage that drops across the power source side under the AC power frequency of the EUT is now required by MIL-STD-461G, which aggravates the severe CS101 test conditions of AC devices. In this paper, we propose a FFT-based time domain solution and a method to instantly check the ripple voltage that drops across the power source side, in other words across the 10 μF test capacitor, during the test under the AC EUT power frequency and to verify that it is low enough and not affecting the reliability of the test. The method proposed in this paper significantly overcomes the CS101 test challenges and makes CS101 test results more accurate. In this paper, we also extensively focused on effective solutions to reduce the ripple voltage induced across the power source side along with measurement uncertainty analysis.

A method for measuring the dynamic parameters by extracting the incident

The complex Young’s modulus of viscoelastic materials can be determined by monitoring the propagation of a traveling burst in a thin bar, which is called wave-speed method. While the test samples are always too short to make the incident wave for lower-frequency signals be detected, which lead to low-frequency test is difficult using this method. To solve this problem, a method of extracting the incident wave is presented in this paper. A pulse wave is generated by the exciter and is used to force the longitudinal vibration of a viscoelastic thin bar. The velocities of the two ends of the thin bar are measured by two laser Doppler vibrometers. The incident waves at both of the two ends of the sample can be easily extracted, and the dynamic parameters of the sample can be obtained by the ratio of the vibration velocities of them. This method expands the experimental frequency range of the wave-speed method and the measured results agree well with that of commercial viscoelastic instrument.

Choosing Expert Evaluations of Diagnostic Tests of Electric Insulation for High-Voltage Electric Machines

This article provides the results of studying the influence of test voltage frequency on the dynamic parameters (dielectric losses and characteristics of partial discharges) of micaceous insulation of stator winding for high-voltage (HV) electric machines. The tests have been conducted using mockup samples of stator insulation with an artificial defect in the front area. It has been established that the low-frequency (0.1 Hz) test voltage increases the dielectric loss tangent and, at the same time, reduces the peak apparent charge of external partial discharges compared to the tests at power frequencies. The established ratios must be taken into account when choosing expert diagnostic evaluations during high-voltage electric-machine tests.