Ac Amplitude Research Articles

GEL POLYMER ELECTROLYTES ELABORATED BY UV-IRRADIATION FOR THE ECO-DESIGN OF LI-ION BATTERIES

This study examines the chemical, thermal, and dielectric properties of gel polymer electrolytes (GPEs) based on poly(ethylene glycol) diacrylate (PEGDA, average Mn=700 g/mol). GPEs were synthesized via a single-step UV-irradiation process, whereby PEGDA was mixed with varying concentrations of a commercial liquid electrolyte (1 M LiPF6 in EC/DEC 50/50 v/v) ranging from 0 to 60 wt%. The results of the infrared analysis indicated that the liquid electrolyte was successfully immobilized within the polymeric matrix. The thermally stable nature of the synthesized GPEs was confirmed across a wide temperature range (-40 to 90°C) through thermal analysis. Furthermore, dielectric measurements were conducted in a frequency range of 0.1 to 106 Hz, with a sinusoidal AC amplitude of 10 mV, from 20 to 100°C. The results demonstrated that the ionic conductivity of GPEs increased with the addition of liquid electrolyte. The GPEs prepared with 60 wt% liquid electrolyte exhibited a conductivity value of approximately 6.6x10-3 S/m at 30°C, which is consistent with the conductivity range reported in the literature.

Charge-Based Separation of Microparticles Using AC Insulator-Based Dielectrophoresis.

Surface charge is an important property of particles. It has been utilized to separate particles in microfluidic devices, where dielectrophoresis (DEP) is often the driving force. However, current DEP-based particle separations based on the charge differences work only for particles of similar sizes. They become less effective and may even fail for a mixture of particles differing in both charge and size. We demonstrate that our recently developed AC insulator-based dielectrophoresis (AC iDEP) technique can direct microparticles toward charge-dependent equilibrium positions in a ratchet microchannel. Such charge-based particle separation is controlled by the imposed AC voltage frequency and amplitude but is nearly unaffected by the size of either type of particle in the mixture except for the time required to achieve an effective separation. This AC iDEP technique may potentially be used to focus and separate submicron or even nanoparticles because of its virtually "infinite" channel length.

AC losses in macroscopic thin-walled superconducting cylinders

Measurements of the ac response represent a valuable method for probing the properties of superconductors. In the surface superconducting state (SSS), a current exceeding the surface critical current I c leads to breakdown of SSS and penetration of external magnetic field into the sample bulk. An interesting free-of-bulk system in SSS is offered by thin-walled cylinders. According to the full penetration of magnetic flux (FPMF) model, each time the instant value of an ac field is equal to a certain critical value, the ac susceptibility χ will exhibit jumps as a function of the ac field amplitude H ac because of the periodic destruction and restoration of SSS in the cylinder wall. Here we study the low-frequency (128–8192 Hz) ac response of thin-walled niobium cylinders under superimposed dc and ac magnetic fields applied parallel to the cylinder axis. In contrast to the FPMF model predictions, experiments reveal a smooth χ(H ac) dependence. To explain the experimental observations, we propose a phenomenological partial penetration magnetic flux (PPMF) model, which assumes that after restoration of the superconducting state, the magnetic fields inside and outside the cylinder are unequal and the magnitude of the penetrating flux is random for every penetration. This model fits very well the experimental data on the temperature dependence of the first harmonic χ 1 for any dc field and ac amplitude.

A simple numerical simulation model can elucidate the key factors for designing a miniaturized ion trap mass spectrometer

BackgroundMiniature ion trap mass spectrometer enables mass-to-charge ratio analysis of ions via quadrupole field in a low vacuum environment. It plays an important role in on-site detection due to its portability and specificity. In order to gain a deeper understanding of the analysis mechanism of miniature ion trap mass spectrometers, a quadrupole MS ion trajectory numerical simulation model (QITNS) is established in this paper for ions trajectory calculation under the action of quadrupole field, exciting field and neutral gas molecule collision. Compared with the existing methods, the model in this paper is simpler and more direct, which effectively explored the effects of dipole excitation and quadrupole excitation on ion manipulation under high background pressure. ResultsThe simulation results demonstrate that high RF amplitude, low auxiliary AC amplitude and quadrupole excitation can effectively improve the isolation resolution. Besides, it clarified the difference between the analysis mechanism of ion trap mass spectrometers under high background pressure (above 13.332 Pa) and absolute vacuum conditions. The relevant results are consistent with the conclusions of previous experiments and other theories, proving the applicability and accuracy of the proposed calculation model and solution method. SignificanceThis research bears the guiding significance for further understanding the mechanism of quadrupole mass spectrometry as well as designing and developing miniature mass spectrometers.

Pinning Energy and Evidence of Granularity in the AC Susceptibility of an YBa2Cu3O7-x Superconducting Film

The study of granularity in superconducting films by using AC susceptibility has a crucial role in the development of and improvement in the ReBCO-coated conductors, which are a constantly evolving reality in the modern power applications of superconductivity. Specifically, the study of the granularity is essential because the ReBCO superconducting wires and tapes are far from the regularity of a single crystal while they often present an inter- and intragranular contribution to the critical current density. On the other hand, the AC susceptibility is a key part of the characterization of a granular sample because this technique is very sensitive to the presence of granularity in the superconductors and, moreover, the study of its first harmonic allows for determining pivotal properties such as the pinning energy as well as the dissipation processes acting in the sample. The pinning energy values and the granularity of an YBCO thin film have been studied by means of AC susceptibility measurements as a function of the AC amplitude, temperature, and DC field. In particular, the first harmonic imaginary component of the AC susceptibility χ1″ related to the dissipation processes of the sample has been studied. First, starting from the Brandt approach, the critical current density Jc and the pinning energy U of the sample have been extracted at 77 K by using the χ1″ measurements as a function of the AC amplitude at different AC frequencies and DC fields. From these measurements, a first signal of granularity appears. In order to confirm it, the temperature dependence of the χ1″ at different DC fields has been studied and a contribution deriving from the inter- and intragranular part of the sample has emerged. By taking the temperature corresponding to the crossover between the two contributions at the different DC fields, the intergranular and intragranular response has been separated. Successively, the temperature has been fixed to 77 K, together with an AC frequency equal to 1597.9 Hz, and the χ1″ as a function of the DC field at different AC amplitudes has been analyzed showing a clear presence of granularity in all the curves. By drawing the contour plot of the χ1″ with the DC and AC values, it was possible to determine the best parameters to put at 77 K in order to exploit the material for applications.

Effect of Electrolyte on Sodium-Ion Storage Behavior into Non-Graphitizable Carbon Negative Electrode

Introduction Sodium-ion batteries (SIBs) are expected to be an alternative power source to lithium-ion batteries (LIBs) because their abundant resources reduce the cost of SIBs. As the negative electrode of SIBs, non-graphitizable carbon recieves a lot of attention because it can store ions not only in the graphene interlayer but also in its internal pores.[1] By controlling the pores, it is possible to achieve larger reversible capacity of more than 400 mAh g−1.[2] While many researchers have studied non-graphitizable carbon from the viewpoint of thermodynamics, there are a few reports that pay attention to kinetic viewpoint. The kinetic viewpoint is a very important factor because it affects the rate performance of the battery.We have focused on the interfacial reactions of non-graphitizable carbon electrodes and found that the charge-transfer resistance and the activation energy of the charge-transfer reaction in SIBs were larger than those in LIBs.[3] This result and the Lewis acidity indicated that the desolvation process was not identified as the rate determining step in the charge-transfer reaction. One of the significant factors responsible for the increased resistance is the effect of the solid electrolyte interphase (SEI). Objective In this work, we used six types of electrolytes and formed SEI on the surface of non-graphitizable carbon. The interfacial reaction of non-graphitizable carbon with SEI derived from these electrolytes was investigated.In this paper, we report about the effects of SEI on the interfacial reaction between electrolyte and non-graphitizable carbon electrode. Experimental Non-graphitizable carbon heat-treated at 2273 K (HC-2000) was used as the negative electrode material. A three-electrode cell was used for electrochemical measurements. HC-2000 composite electrode, natural graphite composite electrode, and sodium metal were used as the working electrode, counter electrode, and reference electrode, respectively. The electrolytes were prepared using sodium bis(trifluoromethanesulfonyl) amide (NaTFSA), sodium bis(fluorosulfonyl) amide (NaFSA), and NaPF6 as sodium salts and ethylene carbonate (EC) + diethyl carbonate (DEC) (1:1 by volume) and fluoroethylene carbonate (FEC) as solvents.Cyclic voltammetry (CV) was performed to form SEI on HC-2000. The scan rate and range were 0.1 mV s−1 and 0–2.5 V, respectively. After CV, electrochemical impedance spectroscopy (EIS) was performed with an electrode potential of 0.2 V and an AC amplitude of 10 mV in the frequency range of 100 kHz–10 mHz. In addition, X-ray photoelectron spectroscopy (XPS) was used to analyze the electrode after CV measurements with respect to SEI. Results and discussion Figure 1 shows the Nyquist plots obtained from the EIS analyses. The semicircles in the low frequency region were attributed to the charge-transfer resistances. Among EC+DEC solvents, the system of NaFSA had the largest charge-transfer resistance. For NaTFSA and NaPF6, the charge-transfer resistances increased in the FEC solvent, while no significant differences in the charge-transfer resistance were observed for the NaFSA system in the EC+DEC and FEC solvents.The SEI components of the HC-2000 composite electrode in each electrolyte were determined by XPS analysis after CV measurements. In NaFSA/EC+DEC system, the amount of NaF was remarkably large, while the amount of NaF was relatively small in NaTFSA/EC+DEC and NaPF6/EC+DEC systems. On the other hand, in FEC solvents, the amount of NaF increased in NaTFSA and NaPF6 systems. The systems with higher NaF contents had the larger charge-transfer resistances. This result indicates that NaF was involved in the charge-transfer resistance.Finally, EIS analyses were performed at different temperatures. The activation energies were calculated using Arrhenius plots and the Arrhenius equation. The values of the activation energies were in the range of 60–70 kJ mol−1. There was a slight variation in the values, but they were within the error range and were not significantly different for all systems. These results showed that NaF affects the frequency factor rather than the activation energy. Conclusion The effects of SEI on the interfacial reaction between electrolyte and non-graphitizable carbon were investigated. The systems with the large charge-transfer resistance had a large amount of NaF. NaF did not affect the activation energy of charge-transfer resistance but did affect the frequency factor.

Oxidation of Alloy 690 in Simulated Pressurized Water Reactor Primary Coolant – Experiments and Modeling

During normal operation of the primary loop of a water cooled-water moderated energy reactor (WWER), the associated water chemistry evolves from an initially high-boron high-potassium (beginning-of-cycle, 1200 ppm B and 8 ppm K) to significantly lower concentrations (ca. 400 ppm B and 3.5 ppm K) at the end of the respective campaign. In addition to that, the concentration of Li produced by transmutation of B reaches ca. 0.7 – 0.9 ppm. To the best of our knowledge, the effect of such water chemistry changes on pressurized water reactor (PWR) internals such as Alloy 690 have not been studied yet. Such a study appears relevant also within the frames of a discussion for a possible transition from B-Li to B-K water chemistry in PWRs.In the present paper, the effect of evolution of primary water chemistry during operation on the corrosion rate and conduction mechanism of oxide films on Alloy 690 is studied by in-situ impedance spectroscopy at 280 °C / 8 MPa during 1-week exposures in an autoclave connected to a re-circulation loop. Impedance measurements were performed in three-electrode mode featuring a Pt sheet counter electrode and a Pd electrode negatively polarized with a current of -10 µA vs. another Pt to approximate the reversible hydrogen electrode (RHE). Spectra were recorded at the corrosion potential in a frequency range 10 kHz – 0.1 mHz using an ac amplitude of 50 mV (rms). At the end of exposure, the samples were polarized in the range of potentials -0.1 to 0.5 V vs. RHE to evaluate the stability of the passive oxide. Separate samples of Alloy 690 were simultaneously exposed in the autoclave and subsequently analyzed by Glow-Discharge Optical Emission Spectroscopy (GDOES) in order to estimate the thickness and the in-depth composition of the formed oxides.Impedance data were quantitatively interpreted using the Mixed-Conduction Model for Oxide Films (MCM) to estimate the rates of metal oxidation at the alloy/oxide interface, oxide dissolution and restructuring at the film/coolant interface and ion transport in the protective layer. The effect of water chemistry evolution on corrosion rate and conduction mechanism in the oxide on Alloy 690 in primary coolant is discussed on the basis of the obtained parameters.Acknowledgments: This study is funded by the European Union-NextGenerationEU, through the National Recovery and Resilience Plan of the Republic of Bulgaria, project № BG-RRP-2.004-0002 (BiOrgaMCT).

Capillary and Electrodynamic Forces-Driven Separation Detection of Metal Ions Using a Disposable Microfluidic Sensor with a Composite Electrode.

A disposable microfluidic channel sensor printed on a plastic platform was developed to analyze heavy metal ions (HMIs) as a model target species. Precise separation and detection of multiple targets were established by symmetrically applying a small AC potential on the carbon channel walls to induce an electrodynamic force. The separation device was constructed by covering it with a plastic lid to achieve capillary action in the channel. The sample flow rate was regulated by the hydrophilicity of the lid plastic and electrodynamic convection by the AC field, which was characterized by the contact angle measurement and the additional electrodynamic force. The flow variables and their relevance to the capillary phenomena were demonstrated, and the analytical parameters were optimized. The working electrode was modified with poly(diamino terthiophene) anchored with nanosized graphene oxide (pDATT/GO) to enhance the detection performance. The experimental variables for separating and detecting the target species were optimized according to the AC frequency and amplitude, sample flow rate, electrolytes, pH, temperature, and applied potential for detection. The linear dynamic ranges were between 0.1 and 200.0 ppb, with detection limits of 0.04 ± 0.023, 0.29 ± 0.05, 0.07 ± 0.011, and 0.14 ± 0.06 ppb for Cu2+ Cd2+, Hg2+, and Pb2+, respectively. Finally, the reliability of the proposed method was evaluated through analysis of HMIs in real water samples. The results were matched to those obtained through parallel analysis using ICP-MS at a 95% confidence level.

Multivariate Data Analysis of Multisine Impedimetric Fingerprints in Electroanalysis of Biochemical Compounds

While Electrochemical Impedance Spectroscopy (EIS) is found as one of the most versatile tools of electrochemical characterization, it suffers a major drawback when the process in question is non-stationary. On the other hand, Dynamic Electrochemical Impedance Spectroscopy (DEIS) offers an ultra-fast measurement time. DEIS utilizes an approach where all the elementary components are superimposed as one multi-component perturbation signal, offering impedance spectra collection in seconds. This particular advantage allows for the effective use of DEIS in the monitoring of the adsorption processes in multiple fields, such as (bio)sensing, corrosion science, energy storage, or AFM-coupled impedance mapping.This presentation aims at highlighting the DEIS monitoring utility carried out with changes of an independent variable, such as adsorbate concentration or even under linear polarization sweep. Rapid and accurate determination of adsorption isotherms for green organic corrosion inhibitors or Michaelis-Menten constant for enzyme-based glucose (bio)sensors with DEIS operating in galvanostatic mode and under iDC = 0 were already established. When it comes to impedimetric macromolecular electroanalysis, measuring charge transfer resistance upon analyte adsorption is the most common approach. However, the detection may also base on other factors, such as adsorbed layer capacitance or even disturbance in frequency dispersion of capacitance. Most recently, DEIS under polarization sweep mode allowed us to obtain the unique fingerprint of the electric parameter changes, specific to studied macromolecules (such as DNA strings, viral proteins, RNA polymerase, and enzymes). To effectively use our approach DEIS is combined with multivariate data analysis (principal component analysis with partial least square regression). Multivariate data analysis processes large amounts of generated impedimetric data and defines analyte-sensitive conditions (DC polarization, AC amplitude, frequency range, etc.), which can be done just by using the raw data by the singular-value decomposition method to support the sensing mechanisms. The proposed approach neglects some of the reproducibility issues induced by non-specific adsorption and fouling and reveals the measurement conditions that offer the highest variation of studied parameters upon specific analyte adsorption. The authors acknowledge the financial support of these studies by the National Science Centre (Republic of Poland) under project 2020/37/B/ST7/03262.

Affinity of Phospholipids Vesicles with Pyrolytic Carbon Shoulder Implant

Shoulder hemiarthroplasty is a minimally invasive procedure that requires less surgical time and better preserves healthy cartilage compared to total arthroplasties. However, patient outcomes are not always conclusive, and this is because metal humeral heads induce cartilage erosion and the release of local tissue metal toxicity. The recently developed InSpyre (Tornier-Wright) consists of a graphite substrate coated with pyrolytic carbon (PyC). Due to its specific surface characteristics and previous medical applications (heart valves and joint implants), PyC could suppress metal toxicity and limit tissue wear due to its Young's modulus close to that of bone (30 MPa vs. 50MPa respectively). In a previous study, we found that phospholipids adsorbed 3 times more onto PyC after friction against living cartilage compared to cobalt alloy. As PLs are known to be involved in lubrication, this suggests a reduction in friction against the tissue by the affinity of PyC to PLs. However, it is not known how PLs affect the electrochemical resistance of PyC and whether friction is necessary to promote PLs adsorption. This study aims to determine whether the physicochemical structure of PLs affects the reactivity of PyC by comparing its electrochemical properties in cell culture medium without, with PLs vesicles, and with disrupted PLs vesicles. A custom electrochemical setup based on a Petri dish with pyrolytic carbon disks was used. The electrolyte is a synthetic synovial fluid based on DMEM/F12 (cell culture medium, CCM) with or without hyaluronic acid (HA)-phospholipid vesicles (PLs). These vesicles represent synthetic surface-active phospholipids, conferring the lubricating capacity of synovial fluid. Characterization of the biomaterial/electrolyte interface and the adsorption process was performed by EIS measurements performed after 10 and 60min of exposure. Measurements were performed from 1mHz up to 105 Hz, at 9 cycles/dec with an ac amplitude of ± 10mV. Tests were performed in an incubator (95% humidity, 5% CO2, 37°C). Analogous electrochemical tests with a surfactant (Triton X-100) were performed to simulate disrupted phospholipid vesicles, to reproduce the physicochemical modification of synovial fluid of joint disease. Statistical differences between solutions were performed using a nonparametric Kruskal-Wallis test (SPSS Inc, Chicago, IL). The significance level was set at P<0.05. The OCP of PyC in DMEM with and without PLS is decreasing reaching an average potential of 51 and 83 mV/AgAgCl, respectively (Fig 1A, B). This negative evolution of the OCP of PyC indicates the formation of a non-protective layer on the biomaterial surface. The lower OCP in the presence of PLs vesicles suggests a surface modification due to PLs adsorption. By adding the surfactant to the solution, the OCP started at a lower potential value (14 mV/AgAgCl) and increased during a 1h exposure (Fig 1 C). The addition of PLs produced a change on the electrochemical reactions (taking place on the biomaterial/body fluid interface, cathodic and anodic reaction) at the OCP. The EIS plots show a typical passive state shape characterized by high impedance values with non-ideal capacitive behavior. The EIS results were fitted with a Randles circuit including a phase angle element (CPE) to replace the capacitor for the non-ideal behavior of the capacitive elements due to different physical phenomena. It was found that the addition of PLs strongly increases the resistance of PyC after a one-hour polarization (Fig 1D). The presence of PLs vesicles resulted in a greater increase in charge transfer resistance compared with DMEM under identical conditions. These changes in charge transfer resistance and capacity are attributed to the formation of a phospholipid layer on the PyC surface. Addition of surfactant (Triton X100) resulted in similar capacitance and charge transfer resistance to DMEM after 1 h of exposure, suggesting that the disrupted vesicles do not adsorb or protect PyC (Fig 1D,E). Surface analysis and observations are required to confirm these preliminary results. This study reveals that the physicochemical structure of synthetic synovial fluid impacts the chemical resistance of PyC, conferring better protection with the addition of PLs vesicles. Joint disease was simulated by disrupting PLs vesicles with the introduction of a surfactant. It reveals the loss of protective behavior, emphasizing that concentration is not the main factor in the chemical resistance of biomaterials. The affinity of PLs with the current main metallic orthopedic implants, Cobalt and Titanium alloys, is an ongoing project to define how phospholipid vesicles impact their corrosion resistance. Figure 1

Physics Based Temperature Dependent EIS Simulation on 18650 NMC/Graphite Cell

Electrochemical Impedance Spectroscopy (EIS) is a non-destructive method that provides crucial insights regarding the battery processes. EIS is mainly done by applying a small amplitude AC with a 10 mHz to 1 MHz frequency range. One can determine the electrolyte's ohmic resistance, the Solid Electrolyte Interface (SEI) capacitance, electron transfer rate and the diffusion mechanisms at separate frequency regions from each other.One disadvantage of EIS is the ambiguity of the analyses of the data. The equivalent circuit models used are not unique, and the correspondence between the various elements in the equivalent circuits to electrochemical phenomena are suspect. A new approach on EIS analysis is sought after in order to improve the interpretation. For example, distribution of relaxation times (DRT) was proposed by Zhang et al. in 2015 .Using physics-based models in order to model EIS has been published by Murbach and Schwartz in 2018. In their work, they created a physics-based simulation which uses a pseudo two-dimensional battery model. Their main aim was to present a new approach to EIS data analysis by using a physics-based model rather than equivalent circuit models. They created a data set with 38.800 separate spectra and match the experimental data by using least squares matching approach with the previously computed data. Though this work improved the understanding, multiple calculated data sets matched the experiments with similar errors.Ultimately, in order to achieve an EIS analysis method that is directly related to the fundamental parameters regarding the electrochemistry, degeneracies have to be removed via temperature dependence and the non-linearities as extra dependent variables. This way, the ambiguities and the suspicious parameter assigning can be fixed.We will be reporting on T-dependent linear and nonlinear simulations on 18650 NMC/Graphite battery. All the simulations were done on Python by using a physics-based model PyBaMM (Sulzer, Valentin, et al. "Python battery mathematical modelling (PyBaMM)." Journal of Open Research Software 9.1 (2021).). Impedance data was obtained via simulating voltage as a function of current within 100 µHz to 10 kHz frequency range. Temperature range was set to -25°C to 65°C with 10°C increments. The linear and non-linear impedance is analyzed as a function of temperature. Our results will be compared with experimental temperature dependent linear/nonlinear spectra in order to obtain proper fundamental parameters

Modelling and analysis of LCC‐HVDC converter station for harmonic coupling of AC/DC power grid during geomagnetic storm

AbstractIn this paper, the problem of harmonic coupling between the converter transformer and the converter under the action of geomagnetically induced current (GIC) is proposed to be investigated. Firstly, a model of a 12‐pulse line commutated converter high voltage direct current (LCC‐HVDC) converter station based on harmonic state space (HSS) theory is established. Secondly, the harmonic components of the interaction between the AC‐side harmonic current and the DC‐side harmonic voltage are qualitatively analyzed by using the harmonic modulation theory. Through the simulation model and harmonic state space (HSS) calculation model, the harmonic coupling characteristics of power grid are analyzed. Finally, the harmonic current and voltage amplitude of AC / DC power grid under different GIC are calculated, and the characteristics and rules of AC / DC harmonic propagation are revealed. Among them, the amplitude of the 2nd harmonic current on the AC side and the 3rd harmonic current on the DC side increases linearly with the GIC. In addition, the 3rd and 9th harmonics on the AC side are also greatly affected by the magnetic bias of the converter.

Bias Current Modulation of DC and RF Properties of AlmGa1‐m∼GaN Heterojunction IMPATT at Sub‐Millimeter Wave Frequency

AbstractLarge signal RF properties of double drift region (DDR) Impact Avalanche Transit Time (IMPATT) device based on AlmGa1‐m∼GaN heterojunction (HT) are investigated and their variation with bias currents has been presented here. These RF properties and their modulation will significantly validate the acceptability of the particular HT in the sub‐millimeter wave frequency domain. Avalanche noise plays the prime ground for making the IMPATT diode basically noisy and tunneling decays the performance of the device, as we move towards the higher frequency range like the sub‐millimeter frequency. These setbacks can be done with if the homojunction (HM) is replaced by heterojunction. This authenticates the choice of heterojunction over homojunction. Here, the author takes 500 GHz as the frequency of concern in the sub‐millimeter wave range. Here, two complementary heterojunctions of AlmGa1‐m∼GaN is taken with m = 0.4 or the mole fraction of Al in the alloy being 40% and their RF results are compared with two homojunctions of GaN and AlGaN for double drift region (DDR) IMPATT diode. Outcomes indicate that HT diodes surpass the high‐frequency performance of HM diodes if compared on the basis of dc to RF conversion efficiency and output power due to the influence of large amplitude ac signal. It is also observed that with increasing bias voltage dependent current, which is varied from 20 × 108to 40 × 108Am−2, the efficiency of conversion together with the power output increases. These results will be very important for further research in this domain.

A 380-μW Electrochemical Impedance Measurement System for Protein Sensing

Diagnostic testing plays an important role in modern medicine, helping physicians make informed decisions regarding disease diagnosis and treatment. Proteins’ biomarkers are utilized to detect disease onset, progression, efficacy of medicines, and patient susceptibility to get a specific kind of disease. Electrochemical impedance spectroscopy (EIS) is likely to underpin the progressive drive toward sensitive, miniaturized, and portable biomarker detection practices. The EIS is a highly sensitive detection method adopted to find the electrical response of chemical samples by applying low amplitude ac voltages/currents with tunable frequency. Conventional EIS systems use mixers and lock-in amplifiers to find both the real and imaginary components of the complex impedance. In this article, we present a partially integrated EIS measurement system to find the impedance of a biological sample. It includes a programmable sine-wave synthesizer (SWS) block with a frequency range of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$500 \mu $ </tex-math></inline-formula> Hz to 100 kHz. The implementation is based on switched-capacitor filters that adjust the cutoff frequency by changing the clock. The sample impedance is measured through mostly digital magnitude and phase-detection blocks. The proposed EIS system is realized using a 0.18- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> technology with a 0.35-mm2 active area and 380- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{W}$ </tex-math></inline-formula> power consumption. The proposed magnitude detection archives a differential nonlinearity (DNL) performance of −0.34/+0.3 LSB and an integral nonlinearity (INL) of −0.75/+2 LSB. The system is used to measure the impedance of biological samples containing tumor necrosis factor alpha (TNF- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\alpha$ </tex-math></inline-formula> ) protein at variable concentrations.

A 0.00426 mm2 77.6-dB Dynamic Range VCO-Based CTDSM for Multi-Channel Neural Recording

Driven by needs in neuroscientific research, future neural interface technologies demand integrated circuits that can record a large number of channels of neural signals in parallel while maintaining a miniaturized physical form factor. Using conventional methods, it is challenging to reduce circuit area while maintaining the high dynamic range, low noise, and low power consumption required in the neural application. This paper proposes to address this challenge using a VCO-based continuous-time delta-sigma modulator (CTDSM) circuit, which can record and digitize neural signals directly without the need for front-end instrumentation amplifiers and anti-aliasing filters, which are limited by the abovementioned circuit-area performance tradeoff. Thanks to the multi-level quantization and intrinsic mismatch-shaping capabilities of the VCO-based approach, the proposed first-order CTDSM can achieve comparable electrical performance to a higher-order CTDSM while offering further area and power reductions. We prototyped the circuit in a 22-channel test chip and demonstrate, based on the chip measurement results, that the proposed modulator occupies an area of 0.00426 mm2 while achieving input-referred noise levels of 6.26 and 3.54 µVrms in the action potential (AP) and local field potential (LFP) bands, respectively. With a 77.6 dB wide-dynamic range, the noise and total harmonic distortion meet the requirements of a neural interface with up to 149 mVpp input AC amplitude or up to ±68 mV DC offsets. We also validated the feasibility of the circuit for multi-channel recording applications by examining the impact of cross-channel VCO oscillation interferences on the circuit noise performance. The experimental results demonstrate the proposed architecture is an excellent candidate to implement future multi-channel neural-recording interfaces.

An Air-Coupled Electrostatic Ultrasound Transducer Using a MEMS Microphone Architecture

We demonstrate the transmission of ultrasound in air using a device that resembles a MEMS microphone in its construction. The device has a 1 mm diameter diaphragm and uses a perforated backplate for electrostatic actuation. The device is driven with large amplitude AC signals, with peak values that exceed the pull-in voltage of the diaphragm. In doing so, relatively large diaphragm displacements are achieved, as the diaphragm oscillations traverse the complete diaphragm-backplate gap. Large amplitude diaphragm vibration is advantageous for high SPL applications in air, as sound pressure is directly proportional to diaphragm displacement for a given operating frequency. Transient diaphragm displacement waveforms are measured in response to tone-burst waveforms ranging in frequency from 4 kHz to 97 kHz. Resultant acoustic pressure waveforms in air are made using a broadband microphone. [2022-0082]

Vibration Characteristics of a Continuously Rotating Superconducting Magnetic Bearing and Potential Influence to TES and SQUID

We measured the vibration of a prototype superconducting magnetic bearing (SMB) operating at liquid nitrogen temperature. This prototype system was designed as a breadboard model for LiteBIRD low-frequency telescope (LFT) polarization modulator unit. We set an upper limit of the vibration amplitude at $36~\mathrm{\mu m}$ at the rotational synchronous frequency. During the rotation, the amplitude of the magnetic field produced varies. From this setup, we compute the static and AC amplitude of the magnetic fields produced by the SMB magnet at the location of the LFT focal plane as $0.24~\mathrm{G}$ and $3\times10^{-5}$$~\mathrm{G}$, respectively. From the AC amplitude, we compute TES critical temperature variation of $7\times10^{-8}$$~\mathrm{K}$ and fractional change of the SQUID flux is $\delta \Phi/\Phi_0|_{ac}=3.1\times10^{-5}$. The mechanical vibration can be also estimated to be $3.6\times 10^{-2}$$~\mathrm{N}$ at the rotation mechanism location.

Four-wavelength quadrature phase demodulation technique for extrinsic Fabry-Perot interferometric sensors.

In this Letter, we report a four-wavelength quadrature phase demodulation technique for extrinsic Fabry-Perot interferometric (EFPI) sensors and dynamic signals. Four interferometric signals are obtained from four different laser wavelengths. A wavelength interval of four wavelengths is chosen according to the free spectrum range (FSR) of EFPI sensors to generate two groups of anti-phase signals and two groups of orthogonal signals. The linear fitting (LF) method is applied to two groups of anti-phase signals to eliminate the dc component and ac amplitude to obtain two normalized orthogonal signals. The differential cross multiplication (DCM) method is then used to demodulate the phase signal from these two normalized orthogonal signals. The proposed LF and DCM (LF-DCM) based four-wavelength quadrature phase demodulation overcomes the drawback of the traditional ellipse fitting (EF) and DCM (EF-DCM) based dual-wavelength demodulation method that it is not suitable for weak signal demodulation since the ellipse degenerates into a straight line, which makes the EF algorithm invalid. Moreover, it also avoids the assumption that the dc component and ac amplitude of interferometric signals are identical, which is widely used in three-wavelength demodulation. An EFPI acoustic sensor is tested to prove the four-wavelength quadrature phase demodulation and experimental results show that the proposed phase demodulation method shows advantages of large dynamic range and wide frequency band. Linearity is as high as 0.9999 and a high signal-to-noise ratio (SNR) is observed from 1 Hz to 100 kHz.

The AC amplitude and channel characterization of high-resolution digitizers

High-resolution (24-bit) ADC based sampling devices e.g. NI PXI 5922 and NI PXI 4461 are usually used for precise electric power measurement purpose so it is required to characterize them in a proper way. According to that, several measurement techniques are proposed to characterize ac amplitude and channel characteristics at the maximum frequency of up to 100 kHz. An automated test and calibration system based on a planar multijunction thermal voltage converter and a modular electronic instrumentation platform has been developed. Furthermore, two ADCs, i.e. NI PXI 5922 and NI PXI 4461 have been compared with reference standard (Swerlein algorithm) to investigate their precision in RMS amplitude measurement of ac signals. In addition, this paper presents the PXI digitizers’ channel characterization in both sinusoidal and non-sinusoidal regime as the main contribution which results in comprehensive insight into digitizers’ performances and their mutual comparison. Accordingly, relevant uncertainty analysis is presented as well.

Modeling dipolar excitation for quadrupole mass filter.

The results of modeling AC and DC dipole excitation of ion oscillations in a quadrupole mass filter are presented. The simulation is done by numerical integration of the ion motion equations, ions' initial coordinates and velocities are distributed normally. For AC dipole excitation the instability bands on the (a, q) stability diagram follow along the isolines and , creating regular dips on the transmission contour. We show that AC excitation at frequency Ω/2 makes it possible to control the resolution of the mass filter by either changing the AC amplitude or phase. Instability bands can be used for mass selective excitation in a linear ion trap. Options for the joint use of DC and AC dipole excitation to form the mass peak shape are considered.