This study demonstrates integration of a zeolite material in a ceramic microcomponent intended for use in sampling and analysis of environmental carbon dioxide (CO2). The zeolite material was integrated in bulk form, allowing for adsorption of large quantities of CO2 compared to previous integration attempts as thin films. To obtain a porous bulk material, an injectable slurry was developed, where expandable polymeric microspheres were added as a sacrificial template. By varying water and sphere contents of the slurry, it was possible to tune the porosity of the zeolite material between 55% and 72%. This in turn affected the flow resistance of the microcomponents, where an increase in the porosity of the filling from 62% to 72% reduced the flow resistance from 84 to 28 kPa min cm-3. In addition, the spheres facilitated complete fillings free from cracks. The zeolite material was seen to retain its ability to adsorb CO2 after processing, but it was not possible to quantify the level of retention compared to unprocessed zeolite.

This paper introduces and evaluates a novel, highly scalable fabrication technique for folding flexible printed circuit board (PCB) features into polydimethylsiloxane (PDMS). The technique is then used to create fast and effective skin-heaters in a prototype gas collector for transcutaneous blood gas monitoring (TBM), a well-established technique to non-invasively measure the amount of CO 2 and O 2 in a patient’s blood. Previous studies have shown that TBM can be made safer by heating the patient’s skin with short pulses rather than continuously. Hence, the effects of incorporating a resistive heater with folded heating elements into a PDMS gas collector was investigated and compared to a heater with surface mounted heating elements. The results show that the fabrication technique provides consistent, controllable folding angles using only the surface and viscous forces of the flexible PCB and PDMS. With the investigated design- and material parameters a maximum folding angle of 30° was achieved, resulting in a 2000% increase in initial surface heating compared to an un-folded reference. For the intended application, this corresponds to reducing the time needed to heat the skin of a patient to less than half. The presented fabrication technique is, however, not limited to the application investigated in this paper, but rather offers the possibility to quickly and automatically fold complex structures and circuits into the bulk of the PDMS without introducing any time overhead as the number of features and folds grow.

This Letter presents a method for gas sensing based on differential microplasma emission spectroscopy. The method used two strip line split-ring resonator microplasma sources that were powered differentially by modulated power supplies. It was shown to reduce 1/f noise and improve the signal-to-noise ratio and exhibited good accuracy and linearity for sensing CO2 concentration over close to two orders of magnitude. The focus of the study was improved response time and stability, and the results show a 0.2 s response time dominated by advection through the integrated fluidics, and a more than six times stability improvement compared to previous studies. The latter was likely due to several parallel effects, including reduced heat loss in the microplasma sources, and the differential embodiment of the system that balanced temperature and pressure-dependent drift. In a preliminary evaluation, the system displayed a sensitivity of 19 μV/% CO2, a linearity of 0.999, an accuracy of 580 ppm, a response time of 0.2 s, and a maximum averaging time of 620 s, along with ample opportunities for further optimization. Overall, the proposed sensing method shows promise for many kinds of gas sensing applications, particularly for stable and precise measurements in environments where drift is a concern.

Objective: Current methods for transcutaneous blood gas monitoring (TBM) – a common health monitoring method in neonatal care - comes with a suite of challenges like limited attachment opportunities, and risks of infections from burning and tearing of the skin, which limits its use. This study presents a novel system and method for rate-based transcutaneous CO 2 measurements with a soft, unheated skin-interface that can address many of these problems. Additionally, a theoretical model for the gas transport from the blood to the system's sensor is derived. Methods: By simulating CO 2 advection and diffusion through the cutaneous microvasculature and epidermis to the system's skin interface, the effect of a wide range of physiological properties on the measurement has been modeled. Following these simulations, a theoretical model for the relationship between the measured CO 2 concentration and that in the blood was derived and compared to empirical data. Results: Applying the model on measured blood gas levels, even when the theory was based solely on the simulations, produced blood CO 2 concentrations within ∼35% of empirical measurements from a state-of-the-art device. Further calibration of the framework, also using the empirical data, yielded an output with a Pearson correlation of 0.84 between the two methods. Conclusion: Compared to the state-of-the-art device the proposed system measured the partial CO 2 pressure in the blood with an average deviation of 0.04 kPa and 1.97σ of ±1.1 kPa. However, the model indicated that this performance could be hampered by different skin properties. Significance: Given its soft and gentle skin interface and lack of heating, the proposed system could significantly decrease health risks like, burns, tears, and pain, currently associated with TBM on premature neonates.

Work material related to the published article.

This study investigates the prospects of using emissions from the discharge of a stripline split-ring resonator microplasma source to measure the 13 C/ 12 C isotope ratio in CO 2 . The plasma source was used in a measurement scheme called microplasma emission spectroscopy, in which the visible emission spectrum of the CO 2 discharge was investigated using a Charge-Coupled Device (CCD) spectrometer. The study revealed that the major isotope dependencies of the spectrum originated from the Ångström system ( B 1 Σ + → A 1 Π) of CO molecules that had been converted from CO 2 in the discharge. Although at least four of the bands of the Ångström system showed clear isotopic dependences, the (0–3) band at 561 nm was concluded to show the most prospects for spectrometric applications because of a combination of wide isotopic shift and low background. A theoretical model of this band was constructed and used in a partial least squares fitting algorithm, to quantify the abundance of 12 C and 13 C in the sample. This signal processing method was shown to be robust and linear over the whole dynamic range of 13 C/ 12 C ratios (1%–100%) but required a ten-fold improvement in precision and accuracy at naturally occurring 13 C levels (1.07%–1.12%) to be useful in most scientific applications. However, several promising ways of achieving such an improvement have been presented, and the results demonstrate the potential of creating a simple, cost-effective, and highly miniaturized system for isotope ratio measurements, which could offer great advantages to scientists in many different fields, from environmental science to planetary exploration.

This study is an extensive comparison of the predictive performance of a bagging neural network (BANN), partial least squares (PLS) regressor, and a kernel-based, nonlinear PLS (KPLS) regressor, given experimentally obtained CO2-N2-Ar plasma emission spectra. The spectra, 3,62,31 in total, were obtained from controlled gas mixtures with varying CO2 concentrations fed to a stripline split-ring resonator microplasma source and recorded with an UV-NIR, 2 nm resolution spectrometer. The regression methods' dependence on (i) number of observations used in training, (ii) preprocessing steps, and (iii) feature selection (in this case wavelength ranges) was evaluated by training and testing 60–66 models per method, each with a unique combination of the aforementioned configuration options, and each trained 4 times with random train-test splits. To compare the models a custom metric that compounds R2, Pearson correlation, and a weighted root mean squared relative error was used. The results show that the BANN models outperform both PLS and KPLS, reaching a peak score of 0.873, with the others getting 0.561 and 0.581, respectively, using the (− ∞ , 1] metric. The top performing BANN model was trained without any feature selection or preprocessing, these steps were, however, required for both the best PLS and KPLS models. In a wider perspective, the results show that BANNs are not only suitable as in-place replacements for PLS-based methods, but increase regression model prediction accuracy on low resolution spectra to such an extent that they offer modelling of previously unattainable, nonlinear information contained in emission spectra datasets.

Premature neonates are too small for repeated blood sampling, but still require precise monitoring of blood gas levels. The standard method therefore involves transcutaneous blood gas monitoring (TBM), i.e. analyzing gas that permeates the skin. The method involves skin heating and requires frequent relocation of a rigid sensor that is adhesively mounted to the skin, which makes the monitoring intermittent and can cause tissue damage. To mitigate this, this paper introduces a TBM concept that replaces the sensor with a small, non-adhesive, flexible, polydimethylsiloxane patch, routing the gases through skin-facing microchannels laid out in various configurations, to an external optical emission spectroscopy system (OES). As the OES depends on a constant flow of gas, we have investigated the effects external loads, both vertical and with a transverse component, have on the aerodynamic resistance of the patches. The experiments show that patches with 200 μm wide channels can withstand uniformly distributed forces up to 25 N with a change in aerodynamic resistance of about 0.01 mbar per sccm per newton. In subsequent measurements, the proof of concept (POC) TBM system showed a strong and fast blood gas signal that was unaffected by all likely loads in the intended application. Moreover, the rise time of the signal is shown to be inversely proportional to the aerodynamic resistance, and the signal strength to be proportional to the skin area exposed to the microchannels. With these results, the POC TBM system is a viable first step towards truly continuous blood gas monitoring of prematurely born children.

The present paper describes a system and method for indirect emission spectroscopy of CO2 in the visible spectrum. This is achieved by using a microplasma spectrometer that first converts CO2 into CO and then measures emissions from the CO Ångström system (B1Σ + → A1Π) at 560 nm. The experiments were performed on gaseous samples of CO2, mixed in both N2 and air, to concentrations between 0.01% and 100%. In addition to the microplasma spectrometer, the process was monitored by mass spectrometry with a residual gas analyzer. The CO2 to CO conversion efficiency was found to be very high, reaching a maximum of 41% at close to 100% selectivity. Furthermore, the CO Ångström system was shown to facilitate excellent spectroscopic measurement of CO2 concentrations below 10%, with a linearity of R2 > 0.99 and an expected limit of detection in the parts-per-thousands range. The most promising aspect of the results was that the analysis was performed on extremely small total sample amounts where the gas flow through the systems was in the 0.1 µmole/s range. Hence, the present system has the prospect of filling a void in current sensor technology, where inexpensive and easy-to-use optical systems, such as nondispersive infrared sensors, cannot handle small sample amounts, while mass spectrometers, which can handle such samples, still are expensive, complex, and bulky.

The spectral emissions from a microplasma have been used to predict the CO 2 concentration in gas samples covering a concentration range of 0%–100%. Different models based on partial least squares have been evaluated, comparing two different spectral pre-processing filters –multiplicative scatter correction (MSC) and standard normal variate correction (SNV) – and three different wavelength ranges. The models were compared with respect to accuracy, precision, stability and linearity. CO 2 samples were mixed with either air or nitrogen. The choice of mixing gas influenced the predicted concentration and basing the models on data from only one mixing gas resulted in higher prediction power. Using air as mixing gas and SNV filtering resulted in a root mean square error of prediction (RMSEP) of 0.03 for an independent test dataset. This RMSEP was of the same range as the experimental error. On the other hand, the models with the best long term stability, reaching the lowest Allan variance, were based on observations with both mixing gases. Models based on MSC filtering generally had slightly higher RMSEP than those based on SNV filtering. Generally, the CO 2 concentration could be accurately predicted in the concentration range of 5%–90%. For higher and lower concentrations, the models underestimated the CO 2 concentration and were less accurate and precise. Basing the models on fewer wavelengths resulted in reduced linearity. The models were also evaluated by applying them for transcutaneous blood gas monitoring, where they helped to reveal new physiological information.

The research and development of small satellites has continued to expand over the last decades. However, the propulsion systems with adequate performance have persisted to be a great challenge. In this paper, the effects of three different heaters on the specific impulse and overall thrust efficiency of a cold gas microthruster are presented. They consisted of a conventional, printed resistive thick-film element, a freely suspended wire, and a stripline split-ring resonator microplasma source, and were integrated in a single device made from the high-temperature co-fired ceramics. The devices were evaluated in two setups, where the first measured thrust and the other measured shock cell geometry. In addition, the resistive elements were evaluated as gas temperature sensors. The microplasma source was found to provide the greatest improvement in both specific impulse and thrust efficiency, increasing the former from an un-heated level of 44–56 s when heating with a power of 1.1 W. This corresponded to a thrust efficiency of 55%, which could be compared with the results from the wire and printed heaters which were 51s and 18%, and 45s and 14%, respectively. The combined results also showed that imaging the shock cells of a plasma heated thruster was a simple and effective way to determine its performance, when compared to the traditional thrust balance method. [2018-0178]

The distinction between “Coriolis force” and “Coriolis effect” is primarily not a matter of semantics, but physics, since the latter also involves centrifugal and gravitational forces. In this connection some minor clarifications to the original article are made.

To target a wide range of high-temperature applications [1-4], the Angstrom Space Technology Centre has added High-Temperature Co-fired Ceramics, HTTC, technology to its repertoire. Usually, this ...

Recently Murnick et al. commented on our article "Intracavity OptoGalvanic Spectroscopy is not suitable for ambient level radiocarbon detection", stating that the methodology and conclusions we derived were incorrect. We completely disagree with the comments submitted by Murnick et al. and a detailed response to their comments is included here.

Miniaturized optogalvanic spectroscopy (OGS) shows excellent prospects for becoming a highly sensitive method for gas analysis in micro total analysis systems. Here, a status report on the current development of microwave-induced microplasma sources for OGS is presented, together with the first comparison of the sensitivity of the method to conventional single-pass absorption spectroscopy. The studied microplasma sources are stripline split-ring resonators, with typical ring radii between 3.5 and 6 mm and operation frequencies around 2.6 GHz. A linear response (R-2 = 0.9999), and a stability of more than 100 s are demonstrated when using the microplasma source as an optogalvanic detector. Additionally, saturation effects at laser powers higher than 100 mW are observed, and the temporal response of the plasma to periodic laser perturbation with repletion rates between 20 Hz and 200 Hz are studied. Finally, the potential of integrating additional functionality with the detector is discussed, with the particular focus on a pressure sensor and a miniaturized combustor to allow for studies of solid samples.

The temperature dependent ion conductivity of yttria stabilized zirconia (YSZ) can be used to create a miniaturized flow sensor using a calorimetric measurement scheme. Such a sensor is compatible with harsh environments, and can sustain temperatures of up to 1000°C, although thermal crosstalk will limit its performance as the temperature rises. This paper investigates if the integration of thermal isolation in the form of sealed cavities can mitigate the detrimental effect of the thermal crosstalk, particularly by studying the conditioning time of the sensor to temperature changes. To this end, high temperature co-fired ceramic (HTCC) sensors were fabricated from tapes of 8mol-% YSZ that were screen printed with platinum paste. Definition of channels and structures were made by milling the green tapes, and sacrificial inserts were placed in all cavities to give mechanical support during lamination and sintering. Cavities with widths of 240μm, 400μm and 560μm were investigated, and sensors without cavities were also made to serve as references. Additionally, two different positions of the sensor element with respect to the edge of the cavity (560 or 800μm) were investigated. The results showed that it was possible to improve the conditioning time of the sensor by up to five times by the use of isolating cavities, and that this improvement is translated into a reduction in rate-dependent hysteresis for measurements with long elapse times. The latter effect is most pronounced for the sensors with the largest cavities.

Gas sensors are characterized by their sensitivity and selectivity. This is preferably combined with versatility, where the selectivity can be altered, without complex modifications and whiteout losing sensitivity. If aimed at lab-on-a-chip applications, the sensor also must be able to analyze small samples. Today, sensors combining selectivity and versatility for chip-level gas analysis are scarce; however, this paper investigates how miniaturized optogalvanic spectroscopy can fill this gap. By studying the spatial distribution of the optogalvanic signal inside a microplasma, it is shown that the signal is generated in the minuscule gas volume of the sheath surrounding the plasma probe that collects it. Nevertheless, a strong and stable spectroscopic signal can be extracted from the sheath, and the sample concentrations can be calculated using straightforward plasma theory. The minimum detectable absorption and the noise equivalent absorption sensitivity of the system are estimated to be less than 1.4 x 10(-9) Hz(-0.5) and 2.8 x 10(-9) cm(-1) Hz(-0.5), respectively, without cavity enhancement. Combined with inherited versatility from absorption spectroscopy and the capability of handling sub-nanogram samples, this makes optogalvanic spectrometry an excellent candidate for future lab-on-a-chip gas analyzers.

Monitoring and control of the principal properties of a discharge or plasma is vital in many applications, and sensors for measuring them must be integrated close to the plasma source in order to deliver reliable results. This is particularly important, and challenging, in miniaturized systems, where different compatibility issues set the closest level of integration. In this paper, a sensor for simultaneous measurement of the pressure and flow through a stripline split-ring resonator microplasma source is presented. The sensor utilized the fully integrated electrodes positioned upstream and downstream of the microplasma source to study these parameters and was found to deliver uniform and unambiguous results in the pressure and flow range of 1–6 Torr and 1–15 sccm, respectively. Furthermore, hysteresis and drift in the measurements were found to be mitigated by introducing a resistor in parallel with the plasma, in order to facilitate the discharging of the electrodes. Together, the results show that the sensor is fully compatible with the miniaturized microfluidic systems in general and a system for optogalvanic spectroscopy in particular.

This is a short summary of the authors' recent R&D on valves, combustors, plasma sources, and pressure and temperature sensors, realized in high-temperature co-fired ceramics, and an account for the first attempt to monolithically integrate them to form a lab on a chip for sample administration, preparation and analysis, as a stage in optogalvanic spectroscopy.