ALBERT

Description: An improved glucose-sensitive membrane (GSM) was prepared by immobilizing glucose oxidases (GODs) onto silica mesocellular foams and trapping them in a polyacrylamide gel. This gel was then coated on a gold/glass sheet to realize surface plasmon resonance (SPR) sensors. A series of sensing experiments was conducted to obtain the optimized parameters with the improved GSM. The experimental results showed that the improved SPR glucose sensor has a sensitivity of 0.0135 degree/(mg/dL) and a linear range of 0–160 mg/dL. This linear range is twice that obtained with the GSM by immobilizing GODs on SiO 2 nanoparticles.

Description: Methane is one of the indicative gases in power transformer oil, and the detection of methane dissolved in oil with high accuracy is of great importance for dissolved gases analysis and fault diagnosis inside power transformers. Based on the Beer–Lambert spectral absorption law, dissolved methane detection with tunable diode laser absorption spectrum (TDLAS) is proposed in this paper for the advantages of high sensitivity and resolution. On the basis of wavelength modulation spectroscopy, a specialized TDLAS system was established. To meet the actual needs of field testing, the anti-vibration design of an integrated Herriott cell and a gas pressure (P)/temperature (T) setting are worked out. Photodetector, collimator, and Herriott cell are integrated into one component to reduce the effects of vibration. It is investigated that the temperature has little effect on the second harmonic amplitude in the range of 30 °C ~ 50 °C, and the vacuum pressure is reasonably set at about 1 kPa. Experimental results showed that the resolution of sensitivity could be reached as 6.8 mV/( $mu$ L/L), the maximum deviation was less than $pm 4~mu$ L/L, and the response time is less than 5 min. In the end, field application was also carried out, proving it is a prospective online sensing technique to serve oil-immersed power transformers better.

Description: This paper presents fixed point operation-based Field Programmable Gate Arrays (FPGA) implementation of Steinhart–Hart Equation (SHHE) for thermistor linearization. FPGA implementation issues of SHHE are presented and their solutions are proposed and experimentally validated in a LabVIEW TM environment. Experimental temperature calibration, performed using a M/S Fluke drywell calibrator, revealed a lowest nonlinearity of 0.11% for an industrial grade thermistor in the input temperature range from −20 °C to 120 °C. Therefore, the main contribution of this work is to demonstrate the lowest nonlinearity for a wider temperature range. This work is expected to be very useful to instrumentation engineers as it employs a time-tested technique, for thermistor linearization in FPGA, leading to the lowest nonlinearity for a larger input temperature range.

Description: This paper reports on a novel force/moment transducer small enough to replace the root of an artificial tooth. Its dimensions of 4.5 mm in diameter and 16.4 mm in height are identical to the former state-of-the-art design. However, the new design requires a significantly reduced assembly effort and imposes lower demands on the external read-out periphery. The latter improvement facilitates the simultaneous operation of a larger number of force/moment transducers. The novel design was optimized using the finite-element analysis, whose results are experimentally validated. The new design and the former state-of-the-art design are extensively tested with the same test procedure for ranges of ±3 N and ±30 Nmm. The measurement accuracies are measured to be 10, 23, and 64 mN for the forces $f_{x}$ , $f_{y}$ , and $f_{z}$ , respectively, and $161times 10^{-3},,text {Nmm}$ , $302times 10^{-3},,text {Nmm}$ , and $42times 10^{-3},,text {Nmm}$ for the moments $m_{x}$ , $m_{y}$ , and $m_{z}$ . Despite the simpler assembly effort and device handling, the accuracy is better or at least close to former designs. Especially, the more critical force measurements are significantly improved. Long-term stability tests show only little change in measurement performance of the two designs in time.

Description: This paper illustrates the extension of Rayleigh wave-based surface acoustic wave (SAW) viscosity and density sensor previously developed by the authors for integration with microfluidics and printed circuit board (PCB)-based electronics. The SAW device is first modeled with a microchannel and analyzed using finite-element method (FEM) software. Precise fabrication, alignment, and bonding of polydimethylsiloxane microchannels on diced $Y$ - $Z$ lithium niobate substrates are accomplished. A high-frequency PCB is built to obtain a better performance for SAW device testing. Low glycerin concentrations in deionized (DI) water are analyzed. The FEM simulation results and vector network analyzer measurements of the devices with the microchannel and PCB integration are presented. For low-frequency SAW sensor, a sensitivity of 171.9 Hz/(% glycerin) or 5.57 kHz/(kg/ $text{m}^{2}surd text{s}$ ) in frequency shifts, 0.09°/(% glycerin) or 2.92°/(kg/ $text{m}^{2}surd text{s}$ ) in phase difference, and minimum signal-to-noise ratio of 13.9 dB are achieved at peak frequency of 29.7 MHz. On the other hand, high-frequency (86.1 MHz) SAW sensor provides a sensitivity of 937.5 Hz/(% glycerin) or 37.15 kHz/(kg/ $text{m}^{mathbf {2}}surd text{s}$ ) in absolute frequency shifts, 0.37°/(% glycerin) or 14.7°/(kg/ $text{m}^{mathbf {2}}surd text{s}$ ) in phase difference, and minimum signal-to-noise ratio - f 20.5 dB.

Description: Distributed Temperature Sensing (DTS) is a technique that uses the interaction of laser pulses with silica to continuously sense temperature along the length of fiber-optic cables. The temporal and spatial resolution of DTS makes it an excellent technique for monitoring the performance of district-scale geothermal exchange borefields. A dynamic, double-ended calibration routine developed in response to site-specific challenges and constraints (i.e., more than 5 km, many splices, different fiber segments, and extended observation periods) is systematically presented and analyzed to provide novel insight on calibration considerations. Results show that different combinations of calibration baths may change calibration accuracy, and over determination in the calculation of calibration parameters provides greater accuracy. Fixing the $gamma $ calibration parameter does not appreciably change accuracy but does provide a buffer against error from variations in calibration bath temperatures. Differential attenuation varied by up to 25% between discrete fiber sections and should be calculated for each array section to prevent errors generated from applying just one attenuation coefficient value for the entire fiber array. Furthermore, dynamically calculated differential attenuation may vary systematically with time and space. In a double-ended configuration, the consideration of whether the forward, reverse, or some combination of all light data is used will affect the robustness of the calibration over time. Each of these results may assist in thoughtful consideration of calibration design at future DTS installations facing similar challenges.

Description: This paper is conducted to design, fabricate, and characterize a novel high-density large-scale ultrasonic transducer, which is based on a $64times 4$ array of 0.753 MHz piezoelectric micromachined ultrasonic transducer (pMUT) with $100~mu text{m}$ size and $120~mu text{m}$ pitch. The fill factor of the array is 69.4%, which is higher than the other arrays in reports. Sol-gel method with layer-by-layer annealing is used to fabricate isolated piezoelectric lead zirconate titanate elements into a piezoelectric layer. The membrane of the pMUT is released by backside deep silicon etching. The impedance-frequency spectrum of a $4times 5$ subarray of the transducers is characterized by HP 4294A impedance phase analyzer. As a result, the mean value resonant frequency is 0.753 MHz, in reasonable agreement with COMSOL Multiphysics simulation results. And the array shows good uniformity in resonant frequency. The equivalent circuit of the transducer is extracted from the spectrum and the admittance circle deduced from the circuit is in accordance with experimental data. The results show that the present array has a good application prospect on ultrasonic imaging.

Description: Curvature sensors based on polymer optical fibers (POFs) present some advantages over the conventional technologies for joint angle assessment such as compactness, electromagnetic field immunity, and multiplexing capabilities. However, the polymer is a viscoelastic material, which does not have a constant response with stress or strain. In order to understand and model this effect, this paper presents the dynamic characterization of a POF. The effects of temperature, frequency, and loads on the fiber are analyzed for obtaining the influence of these parameters on the polymer dynamic Young modulus and time constant. Results show that a temperature on the range between 24 °C and 45 °C does not lead to considerable variations on the sensor output. Moreover, it is possible to estimate the storage modulus and loss factor from the frequency and temperature. The polymer time constant is defined on creep recovery experiments. Since the viscoelastic parameters are evaluated in different conditions of temperature, frequency, and load, a model for the stress behavior of the fiber is proposed. Such model leads to a root mean squared error between the modeled and measured results over 15 times lower than the one obtained with the model for bending stress without account the POF viscoelastic behavior.

Description: Near-infrared spectroscopy (NIRS) is a widely-used noninvasive optical technique for measuring concentration of hemoglobin species in human tissues. Despite its potential, NIRS has seen limited clinical application largely due to a lack of in-vivo standard reference. Hence, cross-validation studies to validate novel NIRS instrumentation against established NIRS devices are needed. This in-vivo study compared a wearable continuous-wave (CW-NIRS) oximeter against a non-wearable frequency-domain (FD-NIRS) oximeter on optical properties and hemoglobin concentrations. To measure absolute coefficients and stoichiometric hemoglobin concentrations, the CW-NIRS oximeter exploits spectral properties of water. Both CW-NIRS and FD-NIRS provided physiologically-valid measurements in skeletal muscles during normoxia, hypoxia, and hyperemia. Although absorption-scattering crosstalk was evident, absorption coefficient $mu _{a}$ and reduced scattering coefficient $mu '_{s}$ at 690nm and deoxyhemoglobin concentration (HbR) were mostly within agreement limits, and the measurements differed principally by a systematic offset. Specifically, CW-NIRS estimated larger $mu '_{s}$ values (+2 cm −1 ) and smaller $mu _{a}$ (from −0.04 to −0.08 cm −1 ) at all wavelengths. The results suggest that lower-cost, wearable CW-NIRS oximeters are a potential alternative to FD-NIRS to measure optical properties and molar concentration of oxyhemoglobin and HbR in skeletal muscles in-vivo as long as the estimated water content is reasonably accurate.

Description: Simultaneous measurement of hydrogen concentration and temperature with high sensitivity and high precision was realized by integrating a photonic crystal fiber (PCF) modal interferometer and a high-birefringence fiber loop mirror (HBFLM). The PCF was coated with sol-gel Pd/WO 3 coating, whose refractive index and volume would be changed along with the variation of surrounding hydrogen concentration or temperature, and then the resonant dip of PCF modal interferometer would shift accordingly. Meanwhile, the resonant dip of the HBFLM has a high sensitivity to surrounding temperature. By integrating PCF modal interferometer and HBFLM together, the two independent resonant dips that can be simultaneously monitored at the output spectrum of the integrated interferometers would all shift with the change of external hydrogen concentration or temperature. Finally, combined with the dual-wavelength matrix method, the hydrogen concentration and temperature could be simultaneously measured. Experimental results showed that the resonant dip of the PCF modal interferometer moved in the short wavelength direction with the increase of hydrogen concentration, and the sensitivity of the hydrogen concentration was −1.12 nm/% within the concentration range from 0% to 1%. In the process of temperature change, the HBFLM realized a higher temperature sensitivity of −1.84 nm/°C. The sensor had high sensitivity, low cost, and simple structure.