In this contribution, the method of Code-division Multiplexing (CDM) is investigated for its dynamic measurement capabilities. In earlier publications, this technique has already been shown to be capable of measuring thousands of Draw Tower Grating® (DTGs®) in a single fiber, where many FBGs with identical wavelengths are used. The basics of CDM are explained. In addition, the ability to do dynamic measurements is investigated theoretically and experimentally and the results are presented. Good correspondence between theory and experiment could be found. Possible system improvements are proposed to find a suitable compromise between detection accuracy and system speed for massive optical sensor networks.

Awareness of catheter tip interaction forces is a crucial aspect during cardiac ablation procedures. The most important contact forces are the ones that originate between the catheter tip and the beating cardiac tissue. Clinical studies have shown that effective ablation occurs when contact forces are in the proximity of 0.2 N. Lower contact forces lead to ineffective ablation, while higher contact forces may result in complications such as cardiac perforation. Accurate and high resolution force sensing is therefore indispensable in such critical situations. Accordingly, this work presents the development of a unique and novel catheter tip force sensor utilizing a multi-core fiber with inscribed fiber Bragg gratings. A customizable helical compression spring is designed to serve as the flexural component relaying external forces to the multi-core fiber. The limited number of components, simple construction, and compact nature of the sensor makes it an appealing solution towards clinical translation. An elaborated approach is proposed for the design and dimensioning of the necessary sensor components. The approach also presents a unique method to decouple longitudinal and lateral force measurements. A force sensor prototype and a dedicated calibration setup are developed to experimentally validate the theoretical performance. Results show that the proposed force sensor exhibits 7.4 mN longitudinal resolution, 0.8 mN lateral resolution, 0.72 mN mean longitudinal error, 0.96 mN mean lateral error, a high repeatability, and excellent decoupling between longitudinal and lateral forces.

Structural health monitoring and other smart structures gain an increased attention which can be satisfied by the quasi-distributed optical sensing approach. Serial fiber optic sensors, such as fiber-Bragg gratings (FBGs) provide among others small size, immunity to electro-magnetic interference, an accurate sensing accuracy and a high multiplexing capability to increase the amount of sensing points in an optical sensor network. Different multiplexing approaches demonstrated a limited number of FBGs, such as time-division multiplex, optical frequency domain refractometry or frequency shifted interferometry. This work introduces a code-division multiplex (CDM) - wavelength-division multiplex (WDM) interrogator for massive serial FBG sensor networks. The interrogation of 4000 serial sensors in a network with a length of 113m, 200 identical WDM sections over a length of 200m and a network with 1000 sensors and a length of 1.6km show a massive multiplexing capability of up to 16000 sensors and possible network lengths of several kilometers. Strain measurements with FBGs in rear sections prove the sensing applicability of the CDM-WDM scheme.

Utilizing a Coherent-Correlation-OTDR, 2000 draw tower gratings in 100 meter fiber with a spatial resolution of 50 mm were successfully interrogated. Spooling of the fiber results in variations of the FBG reflection spectra.

The soluble cytoplasmic ATPase motor protein SecA powers protein transport across the Escherichia coli inner membrane via the SecYEG translocon. Although dimeric in solution, SecA associates monomerically with SecYEG during secretion according to several crystallographic and cryo-EM structural studies. The steps SecA follows from its dimeric cytoplasmic state to its active SecYEG monomeric state are largely unknown. We have previously shown that dimeric SecA in solution dissociates into monomers upon electrostatic binding to negatively charged lipid vesicles formed from E. coli lipids. Here we address the question of the disposition of SecA on the membrane prior to binding to membrane embedded SecYEG. We mutated to cysteine, one at a time, 25 surface-exposed residues of a Cys-free SecA. To each of these we covalently linked the polarity-sensitive fluorophore NBD whose intensity and fluorescence wavelength-shift change upon vesicle binding report on the the local membrane polarity. We established from these measurements the disposition of SecA bound to the membrane in the absence of SecYEG. Our results confirmed that SecA is anchored in the membrane interface primarily by the positive charges of the N terminus domain. But we found that a region of the nucleotide binding domain II is also important for binding. Both domains are rich in positively charged residues, consistent with electrostatic interactions playing the major role in membrane binding. Selective replacement of positively charged residues in these domains with alanine resulted in weaker binding to the membrane, which allowed us to quantitate the relative importance of the domains in stabilizing SecA on membranes. Fluorescence quenchers inside the vesicles had little effect on NBD fluorescence, indicating that SecA does not penetrate significantly across the membrane. Overall, the topology of SecA on the membrane is consistent with the conformation of SecA observed in crystallographic and cryo-EM structures of SecA-SecYEG complexes, suggesting that SecA can switch between the membrane-associated and the translocon-associated states without significant changes in conformation.

This work evaluates the accuracy of a code-division multiplex (CDM) - wavelength-division multiplex (WDM) inter-rogation system for massive serial fiber optical sensing using fiber-Bragg gratings. The standard deviation of wavelength detection dependent on a signal-to-noise-ratio, referred to as static deviations, is measured to be less than 3 pm. Two consecutive correlation steps are subtracted. Dynamic influences occur due to a wavelength shift between the correlation steps. They are investigated using a gradient from a linear regression. Dynamic self interference ranges from 0 pm/pm (picometer deviation per picometer wavelength shift) for the maximum peak to -3.47 pm/pm at 20 % of the maximum peak height. Dynamic multi-user interference, caused by spectral overlapping sensors, starts at -0.5 pm/pm down to -7.27 pm/pm, which makes this system well competitive to other multiplexing techniques.

This contribution demonstrates a massive hybrid code-division multiplexing (CDM)-wavelength-division multiplexing (WDM) scheme that interrogates 2×2000 serial fiber-Bragg gratings (FBGs). The overlapping FBG spectra lead to maximum deviation errors of only 8 pm at a reflectance of 1 %.

This article presents a new interrogation technique for serial fiber optical sensor networks. A hybrid code-division multiplexing (CDM)-wavelength-division multiplexing (WDM) scheme allows interrogating 2000 serial fiber-Bragg grating (FBG) sensors in a network with a length of 50 m. Furthermore, an interrogation of 477 sensors over a length of 150 m is shown. The work focuses on influences given by the above-mentioned sensor networks, such as reflectance, multiple reflections, and overlapping FBG spectra, as well as on specifications of used equipment. Since CDM relies on orthogonal codes, an autocorrelation function of a code is presented that suits for the interrogation of the previous mentioned sensor networks. A simulation of the interrogation scheme allowed for the study of the overall sensor network performance and the impact of its different components. The promising results were reproduced in a testbed. Furthermore, strain calibration measurements showed a high level of accuracy. The proposed hybrid CDM-WDM interrogation scheme can deal with sensor network lengths from a few meters to the range of a few kilometers with massive numbers of freely distributable sensors in the fiber. It is a promising approach in the field of FBG based optical sensing.

This contribution shows the interrogation of 4000 serial fiber-Bragg gratings (FBGs) by means of a hybrid code-division multiplex (CDM) - wavelength-division multiplex (WDM) scheme. A strain measurement shows no influence of a strained WDM-section to another non-strained WDM-section. Polarization effects are diminished by the implementation of a semiconductor optical amplifier.

We have used a single-span MalE/RodZ chimeric protein to determine the stability of single-span transmembrane segments (H-segments). The constructs consist of a fusion of preMalE, an engineered H-segment, and the RodZ periplasmic domain. If the H-segment has a low hydrophobicity (e.g. A17) ∼ 90% of the protein is secreted into the periplasm; if the H-segment is moderately greasy (e.g. A13L4 or A27) it is 50% secreted and 50% membrane inserted; if the H-segment has a high hydrophobicity (e.g. L16 or L24) the whole protein is membrane-incorporated. Using the preMalE/RodZ chimera with a moderately greasy H-segment (A27, A17, L9, and L7) in which the center position is successively replaced by all the natural amino acids, we determined an in vivo hydrophobicity scale (ΔGapp). Moderately hydrophobic H-segments are targeted to the membrane by SecA via the first-occurring signal sequence and inserted, but subsequently cleaved by GlpG. ΔGapp values were obtained by comparing the ratio of full-length (secreted) protein to GlpG-cleaved protein (membrane incorporated) for each amino acid. The topologies were confirmed by proteinase K digestion of spheroplast preparations using a GlpG− strain. Interestingly, we observed a significant change in membrane incorporation efficiency based on the E. coli growth temperature (24°, 30°, or 37°C). We hypothesize that this phenomenon is caused by changes in membrane thickness resulting from changes in inner-membrane lipid composition.

The SecA motor ATPase of Escherichia coli translocates signal sequence-bearing periplasmic and outer membrane proteins through the SecYEG translocase located in the inner membrane [1]. Biochemical and biophysical studies of SecA are invariably conducted at room temperature in phosphate-buffered saline (PBS) solutions. Song and Kim [2] showed that SecA in PBS is 50% destabilized at 37 C. This is puzzling, because 37 C corresponds to the optimal E. coli growth temperature, suggesting either that partial destabilization of SecA is important for normal in vivo function or that studies in PBS are misleading. A fundamental question is thus the nature of the in vivo osmolyte composition of the cytoplasm. The primary cytoplasmic salt of E. coli is potassium glutamate (KGlu), which has been shown to be a strong structure stabilizer for some proteins when present at high concentration (> 0.3 M) [3]. Using a combination of several spectroscopic measurements, we find that KGlu strongly stabilizes SecA in vitro based upon significant upward shifts in the thermal transitions of SecA. Furthermore, the ATPase activity of the protein is greatly enhanced in the presence of KGlu. In PBS, SecA ATPase activity decreases when going from 20 to 37 C whereas a two-fold increase is observed over the same temperature range when KGlu is present. Finally, we find that the binding of SecA to large unilamellar lipid vesicles is stronger at 37 C in KGlu than at 20 C in PBS. Research supported by NIH grant GM-74637. [1] Driessen AJM and Nouwen N (2008) Annu. Rev. Biochem. 77:643-666. [2] Sengupta R et al. (2016) Biochemistry 55:2251-2259. [3] Song M and Kim H (1997) J. Biochem. 122:1010-1018.

Much is known about the structure, function, and stability of the SecA motor ATPase that powers the secretion of periplasmic proteins across the inner membrane of Escherichia coli. Most studies of SecA are carried out in buffered sodium or potassium chloride salt solutions. However, the principal intracellular salt of E. coli is potassium glutamate (KGlu), which is known to stabilize folded proteins and protein-nucleic acid complexes. Here we report that KGlu stabilizes SecA, including its dimeric state, and increases its ATPase activity, suggesting that SecA is likely fully folded, stable, and active in vivo at 37°C. Furthermore, KGlu also stabilizes a precursor form of the secreted maltose-binding protein.

In this paper, we report on an offshore field validation of a FBG based optical fiber sensor for simultaneous monitoring of hydrostatic pressure and temperature. The sensor consists of a femtosecond laser induced grating written in a Butterfly microstructured fiber. The sensor has an extremely low cross-sensitivity between temperature and pressure which makes it ideal for monitoring large transients in pressure or temperature, like is the case in wireline intervention. Pressure and temperature readings from the FBG based optical fiber sensor are compared with the readings from a battery powered electrical quartz gauge during an offshore wireline intervention job in an oil well. Good agreement was found between both measurements.

The influence of hydrogen gas on Fiber Bragg Grating (FBG)-based optical fiber sensors has been validated experimentally. More in particular, the focus was on FBGs written in the so-called Butterfly Micro Structured Fiber that targets simultaneous pressure and temperature monitoring with a minimum in cross-sensitivity to be used in, for example, downhole applications for the oil and gas market. The hydrogen-induced pressure and temperature errors from this type of sensor have been quantified as a function of the partial hydrogen pressure. The induced errors can be related to the diffusion of the hydrogen into the microstructure and to refractive index changes due to the presence of the hydrogen in the micro holes and penetration of it into the fiberglass. Furthermore, we have also shown that the hydrogen-induced errors scale with the partial hydrogen pressure.

Type II single-span membrane proteins, such as CadC or RodZ, lacking a signal sequence and having a far downstream hydrophobic segment, require the SecA secretion motor for insertion into the inner membrane of Escherichia coll. Using two chimeric single-span proteins containing a designed hydrophobic segment H, we have determined the requirements for SecA-mediated secretion, the molecular distinction between TM domains and signal peptides, and the propensity for hydrophobic H-segments to remain embedded within the bilayer after targeting. By means of engineered H-segments and a strategically placed SPase I cleavage site, we determined how targeting and stability of the chimeric proteins are affected by the length and hydrophobicity of the H-segment. Very hydrophobic segments (e.g., 16 Leu) are stably incorporated into the inner membrane, resulting in a C-terminal anchored membrane protein, while a 24L construct was not targeted to the membrane by SecA and remained in the cytoplasm. However, a construct carrying preMalE at the N-terminus led to SecA targeting to SecYEG via the native signal sequence and stable insertion of the downstream 24L H-segment. We show that the RseP intramembrane protease degrades weakly stable H-segments and is a useful tool for investigating the borderline between stable and unstable TM segments. Using RseP(-) cells, we find that moderately hydrophobic sequences (e.g., 5Leu + 11A1a) are targeted to SecYEG by SecA and inserted, but subsequently drop out of the membrane into the cytoplasm. Therefore, the free energy of transfer from translocon to bilayer is different from the transfer free energy from membrane to water. (C) 2019 Elsevier Ltd. All rights reserved.

The applicability of fiber Bragg gratings written in highly birefringent Butterfly micro-structured optical fibers (MS-FBG) for simultaneous High Pressure/High Temperature monitoring without a significant pressure/temperature cross sensitivity have recently been shown. This makes these MS-FBG sensors extremely interesting for downhole monitoring in the Oil & Gas industry. However, an important effect to be taken into account for these applications is the presence of hydrogen, as hydrogen is known to diffuse into the fiber structure and therefore might affect the wavelength responses of the sensor element. In this paper, the effect of hydrogen gas on the MS-FBG sensor readings by monitoring the wavelength changes of the MS-FBG sensor in a hydrogen rich environment have been investigated. In this experiments, two MS-FBG sensors were placed in a hydrogen test chamber: one with its fiber end sealed for pressure sensing and the other with its fiber end kept open for referencing purposes. It could be demonstrated that both sensors show a similar wavelength shift after some time and that due to the hydrogen diffusion, the pressure in the air-holes of the sealed MS-FBG sensor equalizes the hydrogen pressure in the chamber. Furthermore, it could be demonstrated that the refractive index seen by the waveguide of the fiber is also affected. Based on all these observations, the influence of the hydrogen on the temperature and pressure measurement performance of the MS-FBG sensor is estimated, and a mitigation scheme that partially compensates for this influence is discussed.

Dense arrays of Draw Tower Gratings (DTG®s) have been produced in 7 core multicore fiber. They are measured with a standard spectrometer based readout system using Wavelength Division Multiplexing. We demonstrate that these sensor arrays can be used for curvature and shape sensing in continuum robotics and the accuracy for the measurement of both parameters will be presented.

In this paper, a packaged FBG based optical fiber sensor written by femtosecond laser pulses in highly birefringent micro-structured optical fiber (MS-FBG sensor) is presented and validated for simultaneous pressure and temperature monitoring. The MS-FBG sensor is capable of separating the temperature information from pressure information without the need for an additional transduction mechanism and this with a negligible pressure-temperature cross-sensitivity. However, in order to use the sensor for downhole applications, a ruggedized sensor housing is required that not only offers mechanical protection to the fiber, but also provides pressure transfer from the well fluid to the sensing element without inducing an additional pressure-temperature cross-sensitivity. In this article, the design of the sensor housing is reported as well as the lab-scale validation up to a temperature and pressure of 150 °C and 700 bar, respectively.

identifier (CID) number is assigned to each article at the time of publication.Utilization of CIDs allows articles to

In this paper, we demonstrate that femtosecond laser pulse written fiber Bragg gratings (FBGs) fabricated in specialty highly birefringent micro-structured optical fiber (MSF) can be used for high pressure and high temperature monitoring in downhole applications. The design of the micro-structure allows encoding the pressure information into the spectral separation between the two Bragg peaks reflected by the obtained MS-FBG. We obtained a differential pressure sensitivity of 3.30 pm/bar over a pressure range from atmospheric up to 1400 bar and at temperatures between 40°C and 290°C. Owing to the negligible differential pressure-temperature cross-sensitivity of 6.06E-3 bar/°C, the proposed MSFBG sensor is an ideal candidate for pressure monitoring in the presence of high temperature transients.