High-sensitivity Measurements Research Articles

Modification of transformer coupled permeameter for frequency extension

A broadband and high-sensitivity permeability measurement system that covers 10 MHz–20 GHz was previously developed and named the transformer coupled permeameter (TC-Perm). This paper describes the modifications of the TC-Perm system to further extend the operation frequency range on both the high and low frequency sides. In the previous system, the high frequency limit was set by a large notch appearing at around 22 GHz, which was considered to be caused by the excitation of two unwanted modes. In the new system, the jig design was modified to have a back ground plane and vias to suppress these unwanted modes, which resulted in a clean transmission characteristic over the entire frequency range up to 44 GHz. The low frequency limit is determined by the noise figure (NF) of the vector network analyzer input, which was measured to be ∼35 dB in the previous system configuration. The new system employed a low noise amplifier and analog switches to improve the NF to be 2.7 dB below 100 MHz. As a result of these modifications, the operation frequency range of the new TC-Perm system was extended to cover 1 MHz–44 GHz, which is sufficient for characterizing magnetic materials used in noise suppression sheets targeting fifth-generation millimeter-wave (5G mmWave) wireless communication.

Ruling out acute myocardial infarction based on a single high-sensitivity troponin measurement in the emergency department: a clinical practice review

Ruling out acute myocardial infarction based on a single high-sensitivity troponin measurement in the emergency department: a clinical practice review

Fiber liquid-pressure sensor with high sensitivity and a wide measurement range using photopolymer.

This paper presents a novel fiber liquid-pressure sensor that uses photopolymer glue to generate Fabry-Perot (F-P) interference, resulting in high sensitivity and a wide measurement range. The sensor comprises a single-mode fiber and photopolymer glue; the latter adheres to the fiber's end face and is decomposed by a 405-nm laser to create an air channel with a diameter of 5.9 µm and a length of 50 µm. When the air channel is placed underwater, a 17.5-µm air cavity forms between the fiber core and the air-liquid boundary due to the pressure balance, creating an F-P interferometer. Based on experimental results, the sensor has an average pressure sensitivity of 5.68 nm/kPa over 0.49-2.94 kPa. The sensitivity can be maintained at this level across different pressure measurement ranges (up to about 500 kPa) by using a 980-nm laser's radiation pressure to reset the air-liquid boundary. Besides its high sensitivity and wide measurement range, the sensor's straightforward structure, durability, affordability, compactness, and simple construction make it an appealing choice for liquid pressure measurement applications in various fields.

Determination of xanthates as Cu(II) complexes by high-performance liquid chromatography - Inductively coupled plasma tandem mass spectrometry.

The present study provides a novel, selective analysis method for the determination of low xanthate concentrations. The rising concern over the environmental effects of xanthates demands the development of analysis methods which this study answers. Complex formation in aqueous solution between xanthates and an excess of Co(II), Ni(II), Pb(II), Cd(II), Cu(II), and Zn(II) ions was utilized to selectively determine xanthates by high-performance liquid chromatography-inductively coupled plasma tandem mass spectrometry for the first time. The complexes that were formed were extracted to ethyl acetate using liquid-liquid extraction and separated by high-performance liquid chromatography technique before the quantitative determination of metal ions and sulfur in the xanthate complexes. Good separation and high measurement sensitivity were achieved using Cu(II) as the complex metal ion. The analysis method was optimized for the determination of sodium isopropyl xanthate and sodium isobutyl xanthate with detection limits of 24.7 and 13.3μg/L, respectively. With a linear calibration range of 0.1-15mg/L and a total analysis time of 4-5min, the present method is a fast and sensitive option for selective xanthate determination.

Impacts of Ce3+ doping on temperature sensing characteristics of LuAG: Yb3+/Ho3+ up-conversion fluorescent materials

A series of LuAG: 5 mol%Yb3+/0.5 mol%Ho3+/x mol%Ce3+ (x = 0, 0.2, 0.5, 1.0, 2.0) up-conversion (UC) fluorescent materials were prepared using CO2 laser heating zone melting method. The X-ray diffraction (XRD) patterns confirm that the prepared samples have a pure LuAG crystal phase. Under excitation of a 980 nm laser, the up-conversion luminescence (UCL) spectra of the prepared samples were obtained. Two UCL emission bands of Ho3+ ions were observed, including green emission band of the 5F4/5S2→5I8 transition, and red emission band of the 5F5→5I8 transition. Due to the cross-relaxation (CR) processes between Ce3+ ions and Ho3+ ions, the doping of Ce3+ ions can effectively improve the UCL efficiency of Ho3+ ions, and the emission intensity reaches maximum when doped with 1 mol% Ce3+. The temperature sensing characteristics of LuAG: Yb3+/Ho3+ and LuAG: Yb3+/Ho3+/Ce3+ from 303 K to 723 K were studied by fluorescence intensity ratio (FIR) method. By doping 1 mol% Ce3+ ions, the absolute sensitivity of the sample has been significantly improved, with the maximal absolute sensitivity of 0.0951 K−1 (303 K), and the maximal relative sensitivity of 0.0103 K−1 (343 K). The high sensitivity and wide measurement range make LuAG: Yb3+/Ho3+/Ce3+ UCL material ideal for temperature sensing.

Vernier effect-based optical fiber sensor for dynamic sensing using a coarsely resolved spectrometer.

Vernier effect-based optical fiber sensors have been demonstrated for high-sensitivity measurements of a diverse array of physical and chemical parameters. The interrogation of a Vernier sensor typically needs a broadband source and an optical spectrum analyzer to measure amplitudes over a broad wavelength window with dense sampling points, facilitating accurate extraction of the Vernier modulation envelope for sensitivity-improved sensing. However, the stringent requirement on the interrogation system limits the dynamic sensing capability of Vernier sensors. In this work, the possibility of employing a light source with a small wavelength bandwidth (35 nm) and a coarsely resolved spectrometer (∼166 pm) for the interrogation of an optical fiber Vernier sensor is demonstrated with the assistance of a machine learning-based analysis technique. Dynamic sensing of the exponential decay process of a cantilever beam has been successfully implemented with the low-cost and intelligent Vernier sensor. This work represents a first step towards a simpler, faster, and cheaper way to characterize the response of optical fiber sensors based on the Vernier effect.

Ultra-broadband direct dielectric spectroscopy of liquids using a calibrated Microwave-Fluidic vertical Two-Wire sensor with Bi-Material 3D printed chamber

A novel ultra-broadband dielectric spectroscopy technique for liquids is introduced. A two-wire transmission line sensor is employed in which the liquid-under-test comprises fully the propagation medium ensuring high sensitivity and direct permittivity measurement. A vertical wire arrangement is exploited fed by a double-sided parallel stripline with a microstrip interface and no bandwidth-limiting impedance transformation. A seal-integrated flex-rigid 3D-printed liquid container is developed for robust assembly. A raw measured propagation constant correction is proposed through setup calibration using only one reference liquid, which can be air. Sensor operation and design aspects are discussed in detail and an exemplary sensing setup is developed for experimental validation. A set of liquids is characterized within a three-decade bandwidth up to 42 GHz and fitted into a relaxation model along with a comparison against industry-standard broadband open-coax sensor captured data. The conducted study and error analysis certified the performance of the proposed setup.

Design and test of a FBG acceleration sensor basedon multi-stage flexible hinges.

High-precision and high-sensitivity vibration acceleration sensors have been a research hotspot in engineering technology, which play an important role in engineering structural health monitoring, earthquakes, tsunamis, and geological exploration. A novel, to the best of our knowledge, fiber Bragg grating (FBG) acceleration sensor incorporating a mass block and flexible hinge was proposed against the low sensitivity and poor transverse interference resistance of existing FBG acceleration sensors. The FBG accelerometer with the multi-stage flexible hinge was modeled and theoretically analyzed, the structural parameters of the sensor were optimized and actual sensors were developed, and a sensor performance test experiment was carried out in the end. The result suggested that the sensor's natural frequency was as high as 1400Hz, and its response was flat in the frequency range of 50-800Hz; its sensitivity was 18.4pm/g, linearity R 2 was 0.9983, and transverse interference immunity was below 3.2%. The research findings offered a new way of thinking about high-precision and high-sensitivity vibration measurement in engineering technology.

Development of a compact 406 nm diode laser-based cavity-enhanced spectrometer for high-sensitive detection of NO2 levels in exhaust gas

Nitrogen dioxide (NO2) is an important air pollutant due to its environmental impact and adverse effects on human health. It is released into the atmosphere primarily through anthropogenic activities. Here, we report on the development of a simple, compact, and cost-effective robust optical detection method exploiting cavity-enhanced absorption spectroscopy for high-sensitive and selective measurement of NO2 levels in real-time using a visible diode laser operating at 406 nm. A typical detection limit of ∼330 ppb for NO2 was achieved with an optimum acquisition time of ∼3.9 s, at optimal cavity pressure of 100 Torr. The sensor system demonstrates an effective optical path-length of 180 m in a high-finesse 50 cm long optical cavity in an interference-free spectral region and aerosol-free conditions. The spectrometer was optimized, calibrated, and demonstrated for the detection of NO2 levels in vehicular exhaust gases.

Ultra-high sensitivity temperature sensor based on PDMS-assisted-cascaded Mach–Zehnder Interferometer

In this paper, we propose and demonstrate an ultra-high sensitivity temperature sensor based on Polydimethylsiloxane (PDMS) assisted-cascaded Mach–Zehnder Interferometers (PAC-MZI). The sensor is first fabricated by periodically embedding four segments of hollow core fibers (HCF) in a single-mode fiber(SMF). Then, we drill holes into the sidewall of the HCF with a CO2 laser. Finally, the vacuum aspiration technique is used to introduce the PDMS into the HCF. In addition to serving as a beam splitter and combiner, the PDMS-filled HCF also guides multiple modes. The evolution of the transmission spectra during the fabrication process is thoroughly examined. The experimental temperature sensitivity of the sensor surpasses that of conventional interferometric temperature sensors by about 300 times to 9.53 nm/°C. Combining the advantages of easy packaging, compact structure, and high sensitivity, the proposed sensor has a wide range of potential applications in the field that require high-sensitivity temperature measurement.

金ナノフェーブ型SERS活性ナノ構造体とマイクロ流体デバイスの統合

Surface-enhanced Raman scattering (SERS) is expected to be applied to real-time measurements in bioanalysis and environmental analysis because of its high sensitivity, label-free measurements, and suitability for long-term measurements. We are focusing on gold nanofève (GNF)-SERS structure deposited on a boehmite substrate because it is capable to have high-sensitivity and high-resolution measurements in a wide area. GNF-SERS-active patterns with improved adhesion by magnetron sputtering process were fabricated to integrate a microfluidic system. To evaluate the performance of the system, 4, 4'-Bypiridine (4bpy) was used for SERS measurement in the microchannel. This study shows that our microfluidic systems with the GNF-SERS active patterned area have the adequate potential for application and development in environmental analysis.

Milli-Hertz Frequency Tuning Architecture Toward High Repeatable Micromachined Axi-Symmetry Gyroscopes

Axi-symmetry micro gyroscopes are increasingly popular for its ultra high measurement sensitivity. However, a side effect is the bias repeatability problem. In this paper, we propose and demonstrate an ultra-precise frequency tuning solution to achieve the state-of-the-art repeatability performance. The gyroscope dynamics are firstly analyzed and the major error source is confirmed as the frequency split. Then, an advanced frequency tracker and a precision tuning architecture are developed to improve the bias repeatability. The experimental results prove that the frequency tracker can identify the frequency splits at mHz level. Consequently, a state-of-the-art turn-on to turn-on bias repeatability of 3.6<inline-formula><tex-math notation="LaTeX">$^\circ$</tex-math></inline-formula>/hr is conducted that shows orders of magnitude better than conventional solutions.

Coupled-oscillator model to analyze the interaction between a quartz resonator and trapped ions

The novel application of a piezoelectric quartz resonator for the detection of trapped ions has developed in the observation of the quartz-ions interaction under non-equilibrium conditions, opening new perspectives for high-sensitive motional frequency measurements of radioactive particles. Energized quartz crystals have (long) constant-decay times in the order of milliseconds, permitting the coherent detection of charged particles within short times. In this publication we develop in detail a model governing the interaction between trapped $^{40}$Ca$^+$ ions and a quartz resonator connected to a low-noise amplifier. We apply this model to experimental data and extract relevant information like the coupling constant $g=2\pi \times 1.449(2)$~Hz and the ions' modified-cyclotron frequency in our 7-tesla Penning trap. The study on the latter is specially important for the use of this resonator in precision Penning-trap mass spectrometry. The improvement in sensitivity can be accomplished by increasing the coupling constant through the quality factor of the resonator. This can develop in the use of the hybrid quartz-ion system for other applications.

A Microstrip Transmission Line Biosensor to Measure the Interaction between Microliter Aqueous Solutions and 1.0-17.0 GHz Radio Frequencies.

Radio frequency (RF) biosensors are an expanding field of interest because of the ability to design noninvasive, label-free, low-production-cost sensing devices. Previous works identified the need for smaller experimental devices, requiring nanoliter to milliliter sampling volumes and increased capability of repeatable and sensitive measurement capability. The following work aims to verify a millimeter-sized, microstrip transmission line biosensor design with a microliter well operating on a broadband radio frequency range of 1.0-17.0 GHz. Three successive experiments were performed to provide evidence for (1) repeatability of measurements after loading/unloading the well, (2) sensitivity of measurement sets, and (3) methodology verification. Materials under test (MUTs) loaded into the well included deionized water, Tris-EDTA buffer, and lambda DNA. S-parameters were measured to determine interaction levels between the radio frequencies and MUTs during the broadband sweep. MUTs increasing in concentration were repeatably detected and demonstrated high measurement sensitivity, with the highest error value observed being 0.36%. Comparing Tris-EDTA buffer versus lambda DNA suspended in Tris-EDTA buffer suggests that introducing lambda DNA into the Tris-EDTA buffer repeatably alters S-parameters. The innovative aspect of this biosensor is that it can measure interactions of electromagnetic energy and MUTs in microliter quantities with high repeatability and sensitivity.

Improving the Accuracy, Robustness, and Dynamic Range of Digital Bead Assays.

We report methods that improve the quantification of digital bead assays (DBA)─such as the digital enzyme-linked immunosorbent assay (ELISA)─that have found widespread use for high sensitivity measurement of proteins in clinical research and diagnostics. In digital ELISA, proteins are captured on beads, labeled with enzymes, individual beads are interrogated for activity from one or more enzymes, and the average number of enzymes per bead (AEB) is determined based on Poisson statistics. The widespread use of digital ELISA has revealed limitations to the original approaches to quantification that can lead to inaccurate AEB. Here, we have addressed the inaccuracy in AEB due to deviations from Poisson distribution in a digital ELISA for Aβ-40 by changing the AEB calculation from a fixed threshold between digital counting and average normalized intensity to a smooth, continuous combination of digital counting and intensity. We addressed issues with determining the average product fluorescence intensity from single enzymes on beads by allowing outlier, high intensity arrays to be removed from average intensities, and by permitting the use of a wider range of arrays. These approaches improved the accuracy of a digital ELISA for tau protein that was affected by aggregated detection antibodies. We increased the dynamic range of a digital ELISA for IL-17A from AEB ∼25 to ∼130 by combining long and short exposure images at the product emission wavelength to create virtual images. The methods reported will significantly improve the accuracy and robustness of DBA based on imaging─such as single molecule arrays (Simoa)─and flow detection.

Theoretical analysis of a multi-grating-based cross-dispersed spatial heterodyne spectrometer.

This paper presents a multi-grating-based cross-dispersed spatial heterodyne spectrometer (MGCDSHS). The principle of generation of two-dimensional interferograms for two cases, where the light beam is diffracted by one sub-grating or two sub-gratings, is given and equations for the interferogram parameters in these two cases are derived. An instrument design with numerical simulations is presented that demonstrates the spectrometer's ability to simultaneously record separate interferograms corresponding to different spectral features with high resolution over a broad spectral range. The design solves the mutual interference problem caused by overlapping of the interferograms, and also provides the high spectral resolution and broad spectral measurement range that cannot be achieved using conventional SHSs. Additionally, by introducing cylindrical lens groups, the MGCDSHS solves the throughput loss and light intensity reduction problems caused by direct use of multi-gratings. The MGCDSHS is compact, highly stable, and high-throughput. These advantages make the MGCDSHS suitable for high-sensitivity, high-resolution, and broadband spectral measurements.

Design and Optimization of Multi-Stage TMR Sensors for Power Equipment AC/DC Leakage Current Detection

Tunnel magnetoresistance (TMR) can measure weak magnetic fields and has significant advantages for use in alternating current/direct current (AC/DC ) leakage current sensors for power equipment; however, TMR current sensors are easily perturbed by external magnetic fields, and their measurement accuracy and measurement stability are limited in complex engineering application environments. To enhance the TMR sensor measurement performance, this paper proposes a new multi-stage TMR weak AC/DC sensor structure with high measurement sensitivity and anti-magnetic interference capability. The front-end magnetic measurement characteristics and interference immunity of the multi-stage TMR sensor are found to be closely related to the multi-stage ring size design via finite element simulation. The optimal size of the multipole magnetic ring is determined using an improved non-dominated ranking genetic algorithm (ACGWO-BP-NSGA-II) to derive the optimal sensor structure. Experimental results demonstrate that the newly designed multi-stage TMR current sensor has a measurement range of 60 mA, a fitting nonlinearity error of less than 1%, a measurement bandwidth of 0–80 kHz, a minimum AC measurement value of 85 μA and a minimum DC measurement value of 50 μA, as well as a strong external electromagnetic interference. The TMR sensor can effectively enhance measurement precision and stability in the presence of intense external electromagnetic interference.

Three-axis magnetic field measurement based on dual-pump polarization with high sensitivity and orthogonality

An optically pumped magnetometer (OPM) for three-axis magnetic field measurement is demonstrated based on dual-pump polarization in a time-sharing regime. By detecting light absorption, each pump beam can achieve high-sensitive transverse measurement under modulation magnetic fields around a near-zero field. After the combination and orthogonalization of two pumps according to the scale factors along the reference axis, a three-axis orthogonal measurement system is obtained. Compared with existing methods, this configuration reduces misalignment errors introduced by the nonorthogonality of the sensitive directions and avoid coupling errors introduced by cross-axis DC magnetic fields. The coupling among the three axes is below 0.39%. On this basis, this OPM performs equivalent performances of each axis measurement with high accuracy and realizes a high sensitivity of 10 fT/Hz1/2. This SERF OPM can be employed in wide variety of applications including biological magnetic detection and sensitive tests of fundamental physics.

Convex Microarrays-Based Liquid Metal Soft Piezoresistive Stress Sensor With High Sensitivity and Large Measurement Range

Liquid metal (LM) soft piezoresistive sensors-that is, devices that change resistance in response to mechanical forces have low hysteresis and high stability, which exhibit great promise for human health monitoring. Applying stress reduces the cross-sectional area of the LM conductive path in the sensor, increasing the resistance and enabling the measurement of stress. However, increasing the sensitivity of the sensor results in a reduced measurement range and an increase in the cost. To solve this problem, this paper presents a convex microarrays (CMs)-based LM soft piezoresistive stress sensor with high sensitivity and large measurement range. The CMs are located inside the microchannel, which improves the sensitivity of the sensor without reducing the measurement range. The CMs also enable the sensor to monitor bending. The mechanism of the CMs is verified by theoretical analysis, finite element simulation and experiments. The relationship between the height of the CMs and the sensitivity is investigated. The sensor can be used in the field of human health monitoring.

High-Sensitivity and Wide-Range Resistance Measurement Based on Self-Balancing Wheatstone Bridge and Gated Recurrent Neural Network

A Wheatstone bridge and the following amplifier are widely used for measuring resistance. But for the measurement of small resistance change, the gain of the amplifier must be very high, which can reduce measurement range and introduce obvious baseline drift into the measured signal inevitably. In this study, a self-balancing Wheatstone bridge is designed based on a digitally controlled potentiometer (DCP). During the initial balance of the Wheatstone bridge, the DCP is adjusted until the output of the bridge is close to zero volts. When the bridge works for the measurement of dynamic resistance, the DCP is readjusted to compensate the remarkable change in the resistance, and the output of the amplifier is thus limited in the input voltage range of the ADC. At the same time, the signal sampled by the ADC is processed by the least-squares fitting to extend the measurement range. In addition, an attention-based gated recurrent unit (AGRU) is proposed to remove the drift in the signal. The effectiveness, stability, and accuracy of the proposed method have been demonstrated through multiple force measurement experiments on the instrument of a robot assisted minimally invasive surgery (RMIS) system.