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Bacteriophages represent the most extensive group of viruses within the human virome and have a significant impact on general health and well-being by regulating bacterial population dynamics. Staphylococcus aureus , found in the anterior nostrils, throat and skin, is an opportunistic pathobiont that can cause a wide range of diseases, from chronic inflammation to severe and acute infections. In this study, we developed a human cell-based homeostasis model between a clinically isolated strain of S. aureus 141 and active phages for this strain (PYOSa141) isolated from the commercial Pyophage cocktail (PYO). The cocktail is produced by Eliava BioPreparations Ltd. (Tbilisi, Georgia) and is used as an add-on therapy for bacterial infections, mainly in Georgia. The triptych interaction model was evaluated by time-dependent analysis of cell death and inflammatory response of the nasal and bronchial epithelial cells. Inflammatory mediators (IL-8, CCL5/RANTES, IL-6 and IL-1β) in the culture supernatants were measured by enzyme-linked immunosorbent assay and cell viability was determined by crystal violet staining. By measuring trans-epithelial electrical resistance, we assessed the epithelial integrity of nasal cells that had differentiated under air-liquid interface conditions. PYOSa141 was found to have a prophylactic effect on airway epithelial cells exposed to S. aureus 141 by effectively down-regulating bacterial-induced inflammation, cell death and epithelial barrier disruption in a time-dependent manner. Overall, the proposed model represents an advance in the way multi-component biological systems can be simulated in vitro.

Reduced graphene oxide (rGO) is a derivative of graphene, which has been widely used as the conductive pigment of many water-based inks and is recognized as one of the most promising graphene-based materials for large-scale and low-cost production processes. In this work, we evaluate a custom functionalised reduced graphene oxide ink (f–rGO) via inkjet-printing technology. Test line structures were designed and fabricated by the inkjet printing process using the f–rGO ink on a pretreated polyimide substrate. For the electrical characterisation of these devices, two-point (2P) and four-point (4P) probe measurements were implemented. The results showed a major effect of the number of printed passes on the resulting resistance for all ink concentrations in both 2P and 4P cases. Interesting results can be extracted by comparing the obtained multipass resistance values that results to similar effective concentration with less passes. These measurements can provide the ground to grasp the variation in resistance values due to the different ink concentrations, and printing passes and can provide a useful guide in achieving specific resistance values with adequate precision. Accompanying topography measurements have been conducted with white-light interferometry. Furthermore, thermal characterisation was carried out to evaluate the operation of the devices as temperature sensors and heaters. It has been found that ink concentration and printing passes directly influence the performance of both the temperature sensors and heaters.

Thermal sensors are mainly based on the selective heating of specific areas, which in most cases is a critical feature for both the operation and the performance of the thermal device. In this work, we evaluate the thermoelectrical response of two graphitic materials, namely (a) a commercial 2.4%wt graphene–ethyl cellulose dispersion in cycloxehanone and terpineol (G) and (b) a custom functionalized reduced graphene oxide (f-rGO) ink in the range of −40 to 100 °C. Both inks were printed on a flexible polyimide substrate and the Thermal Coefficients of Resistance (TCR) were extracted as TCRG = −1.05 × 10−3 °C−1 (R2 = 0.9938) and TCRf-rGO = −3.86 × 10−3 °C−1 (R2 = 0.9967). Afterward, the inkjet-printed devices were evaluated as microheaters, in order to exploit their advantage for cost-effective production with minimal material waste. f-rGO and G printed heaters reached a maximum temperature of 97.5 °C at 242 mW and 89.9 °C at 314 mW, respectively, applied by a constant current source and monitored by an infrared camera. Repeatability experiments were conducted, highlighting the high robustness in long-term use. The power–temperature behavior was extracted by self-heating experiments to demonstrate the ability of the devices to serve as heaters. Both static and dynamic evaluation were performed in order to study the device behaviors and extract the corresponding parameters. After all the experimental processes, the resistance of the samples was again evaluated and found to differ less than 13% from the initial value. In this work, fabrication via inkjet printing and demonstration of efficient and stable microheaters utilizing a custom ink (f-rGO) and a commercial graphene ink are presented. This approach is suitable for fabricating selectively heated geometries on non-planar substrate with high repeatability and endurance in heat cycles.

This work concerns the design, fabrication, and preliminary characterization of a novel sensor for determining the air intake of low and medium power internal combustion engines employed at various applications in the marine industry. The novelty of the presented sensor focuses on the fabrication process, which is based on additive manufacturing combined with PCB technology, and the design of the sensing elements housing geometry, which is derived through suitable CFD simulations and is based on standard airfoil geometry. The proposed process enables low-cost, fast fabrication, effective thermal isolation, and facile electrical interconnection to the corresponding circuitry of the sensor. For initial characterization purposes, the prototype device was integrated into a DIESEL engine testbed while a commercially available mass air flow sensor was employed as a reference; the proper functionality of the developed prototype has been validated. Key features of the proposed device are low-cost, fast on-site manufacturing of the device, robustness, and simplicity, suggesting numerous potential applications in marine engineering.

Cell-based biosensors appear to be an attractive tool for the rapid, simple, and cheap monitoring of chemotherapy effects at a very early stage. In this study, electrochemical measurements using a four-point probe method were evaluated for suspensions of four cancer cell lines of different tissue origins: SK–N–SH, HeLa, MCF-7 and MDA-MB-231, all for two different population densities: 50 K and 100 K cells/500 μL. The anticancer agent doxorubicin was applied for each cell type in order to investigate whether the proposed technique was able to determine specific differences in cell responses before and after drug treatment. The proposed methodology can offer valuable insight into the frequency-dependent bioelectrical responses of various cellular systems using a low frequency range and without necessitating lengthy cell culture treatment. The further development of this biosensor assembly with the integration of specially designed cell/electronic interfaces can lead to novel diagnostic biosensors and therapeutic bioelectronics.

The airway epithelium is the primary site where inhaled and resident microbiota interacts between themselves and the host, potentially playing an important role on allergic asthma development and pathophysiology. With the advent of culture independent molecular techniques and high throughput technologies, the complex composition and diversity of bacterial communities of the airways has been well-documented and the notion of the lungs' sterility definitively rejected. Recent studies indicate that the microbial composition of the asthmatic airways across the spectrum of disease severity, differ significantly compared with healthy individuals. In parallel, a growing body of evidence suggests that bacterial viruses (bacteriophages or simply phages), regulating bacterial populations, are present in almost every niche of the human body and can also interact directly with the eukaryotic cells. The triptych of airway epithelial cells, bacterial symbionts and resident phages should be considered as a functional and interdependent unit with direct implications on the respiratory and overall homeostasis. While the role of epithelial cells in asthma pathophysiology is well-established, the tripartite interactions between epithelial cells, bacteria and phages should be scrutinized, both to better understand asthma as a system disorder and to explore potential interventions.

The present work reports on the detailed electro-thermal evaluation of a highly water dispersible, functionalized reduced graphene oxide (f-rGO) using inkjet printing technology. Aiming in the development of printed electronic devices, a flexible polyimide substrate was used for the structures’ formation. A direct comparison between the f-rGO ink dispersion and a commercial graphene inkjet ink is also presented. Extensive droplet formation analysis was performed in order to evaluate the repeatable and reliable jetting from an inkjet printer under study. Electrical characterization was conducted and the electrical characteristics were assessed under different temperatures, showing that the water dispersion of the f-rGO is an excellent candidate for application in printed thermal sensors and microheaters. It was observed that the proposed f-rGO ink presents a tenfold increased temperature coefficient of resistance compared to the commercial graphene ink (G). A successful direct interconnection implementation of both materials with commercial Ag-nanoparticle ink lines was also demonstrated, thus allowing the efficient electrical interfacing of the printed structures. The investigated ink can be complementary utilized for developing fully printed devices with various characteristics, all on flexible substrates with cost-effective, few-step processes.

In this work we demonstrate the enhancement of Seebeck coefficient of poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) ink via CarbonQuantum-Dot (CQD)-based nanocomposite material (CQDnm). Key innovations are the nanocomposite preparation and composition, and retainment of the newly formulated ink’s printability onto a flexible substrate. A relationship between Seebeck coefficient’s increase and CQDnm/PEDOT:PSS ratio was experimentally extracted. Inkjet droplets and patterning onto polyimide were unaffected by the nanocomposite addition at different ratios. Devices with Seebeck coefficient values ranging from 18.51 μV/K to 28.08 μV/K were successfully developed, verifying that the proposed approach can lead to an increase of Seebeck by 51.7%.

The development and the corresponding evaluation of a multidirectional thermal flow sensor are presented in this work. The sensor was fabricated on a flexible substrate, allowing for new applications, since it provides the possibility of installation in nonplanar surfaces such as pipelines. Furthermore, the sensing elements are not in direct contact with the fluid, which increases the device reliability, extends its application range, and allows the noncontact monitoring of fluids. This was achieved by utilizing the substrate as a protective layer between the sensing elements and the fluid under measurement. The operation principle is based on the determination of the flow-induced temperature profile variations. A dedicated experimental setup was designed and used for the device evaluation. Both flow velocity value and direction were successfully extracted, while the results were consistent with the predicted theoretical values. A single-layer back propagation neural network that correlates the sensors’ readouts to the angle of rotation was implemented, which leads to a mean absolute direction estimation error in the order of 2.7 degrees independent to the training procedure datasets.

Cancer cell lines are important tools for anticancer drug research and assessment. Impedance measurements can provide valuable information about cell viability in real time. This work presents the proof-of-concept development of a bioelectrical, impedance-based analysis technique applied to four adherent mammalian cancer cells lines immobilized in a three-dimensional (3D) calcium alginate hydrogel matrix, thus mimicking in vivo tissue conditions. Cells were treated with cytostatic agent5-fluoruracil (5-FU). The cell lines used in this study were SK-N-SH, HEK293, HeLa, and MCF-7. For each cell culture, three cell population densities were chosen (50,000, 100,000, and 200,000 cells/100 &mu, L). The aim of this study was the extraction of mean impedance values at various frequencies for the assessment of the different behavior of various cancer cells when 5-FU was applied. For comparison purposes, impedance measurements were implemented on untreated immobilized cell lines. The results demonstrated not only the dependence of each cell line impedance value on the frequency, but also the relation of the impedance level to the cell population density for every individual cell line. By establishing a cell line-specific bioelectrical behavior, it is possible to obtain a unique fingerprint for each cancer cell line reaction to a selected anticancer agent.

Printing technologies have been attracting increasing interest in the manufacture of electronic devices and sensors. They offer a unique set of advantages such as additive material deposition and low to no material waste, digitally-controlled design and printing, elimination of multiple steps for device manufacturing, wide material compatibility and large scale production to name but a few. Some of the most popular and interesting sensors are relative humidity, temperature and strain sensors. In that regard, this review analyzes the utilization and involvement of printing technologies for full or partial sensor manufacturing; production methods, material selection, sensing mechanisms and performance comparison are presented for each category, while grouping of sensor sub-categories is performed in all applicable cases. A key aim of this review is to provide a reference for sensor designers regarding all the aforementioned parameters, by highlighting strengths and weaknesses for different approaches in printed humidity, temperature and strain sensor manufacturing with printing technologies.

This work concerns the evaluation of a novel sensor for determining the air intake of a typical low power engine. The sensor is based on PCB technology enabling effective thermal isolation and direct communication to the macroworld. The device was integrated into a DIESEL engine testbed for characterization purposes while a commercially available mass air flow sensor was employed as a reference; the proper functionality of the developed prototype has been validated. Key features of the proposed device are robustness, simplicity and low-cost suggesting numerous potential applications in the automotive area.

A standalone, portable system for characterization and electrical measurements of thermal sensors was developed and evaluated. The system is able to provide an adjustable power to the heating element, under any of the common modes of operation (e.g. CR, CV, CC), and simultaneously measure the resulting output. Four independent constant current excitation sources and measurement channels are also available for the connection of respective sensing elements; therefore various principles of operation (e.g. hotwire, calorimetric) can also be supported. The output data can either be displayed on a built-in LCD graphic display, stored on integrated, non-volatile memory or directly transmitted to a PC via the USB interface. The custom implementation provides a low-cost, high precision alternative to commercial general purpose measurement systems and can also be utilized for electrical characterization of various experimental devices as well as other laboratory applications.

This work presents the evaluation of a multiparametric sensing device on paper fabricated by inkjet printing, for applications such as smart packaging-labeling and disposable biosensors where biocompatibility and low cost are key factors. The device is able to measure simultaneously relative humidity, temperature and compressive and tensile bending. Commercial silver nanoparticle ink and PEDOT:PSS were printed onto inkjet photo glossy paper using a drop-on-demand inkjet printer forming an interdigitated electrode array and a meander shaped micro-ribbon. Humidity measurements revealed that sensor response, which is effectively expressed by the relationship between paper substrate resistance and relative humidity was similar for both materials utilized as electrodes. Temperature coefficients of resistance (TCR) were extracted for Ag-nanoparticle and PEDOT:PSS - based temperature sensors respectively in the range of 25–45 °C. The bending tests indicated that both materials exhibited similar trend in tensile bending, with resistance increasing in a linear manner up to a maximum tensile length of 900 μm. Ag-nanoparticle ink outperformed PEDOT:PSS ink in terms of repeatability, sensitivity and hysteresis. In compressive bending measurements Ag-nanoparticle and PEDOT:PSS gauge factors exhibited similar gauge factor of opposite sign.

In this work we present the development of a low-cost humidity and temperature sensing platform on paper by inkjet printing, using a commercial AgNPs conductive ink. The humidity sensing module was capable of measuring relative humidity in the range of 0⁻90%rH, exhibiting linear response with minimal memory effect when returning to 0%rH baseline signal while the temperature sensor performed linearly as well in the range of 25⁻75°C. Process repeatability has been verified by electrical and optical characterization. Mechanical bending results highlight the platform’s capability to serve as an easy to install, flexible multi-parametric sensing platform.

The evaluation of glucose metabolic activity in immune cells is becoming an increasingly standard task in immunological research. In this study, we described a sensitive, inexpensive, and non-radioactive assay for the direct and rapid measurement of the metabolic activity of CD4+ T cells in culture. A portable, custom-built Cell Culture Metabolite Biosensor device was designed to measure the levels of acidification (a proxy for glycolysis) in cell-free CD4+ T cell culture media. In this assay, ex vivo activated CD4+ T cells were incubated in culture medium and mini electrodes were placed inside the cell free culture filtrates in 96-well plates. Using this technique, the inhibitors of glycolysis were shown to suppress acidification of the cell culture media, a response similar to that observed using a gold standard lactate assay kit. Our findings show that this innovative biosensor technology has potential for applications in metabolic research, where acquisition of sufficient cellular material for ex vivo analyses presents a substantial challenge.

2,4,6-trichloroanisole (TCA), the cork taint molecule, has been the target of several analytical approaches over the few past years. In spite of the development of highly efficient and sensitive tools for its detection, ranging from advanced chromatography to biosensor-based techniques, a practical breakthrough for routine cork screening purposes has not yet been realized, in part due to the requirement of a lengthy extraction of TCA in organic solvents, mostly 12% ethanol and the high detectability required. In the present report, we present a modification of a previously reported biosensor system based on the measurement of the electric response of cultured fibroblast cells membrane-engineered with the pAb78 TCA-specific antibody. Samples were prepared by macerating cork tissue and mixing it directly with the cellular biorecognition elements, without any intervening extraction process. By using this novel approach, we were able to detect TCA in just five minutes at extremely low concentrations (down to 0.2 ppt). The novel biosensor offers a number of practical benefits, including a very considerable reduction in the total assay time by one day, and a full portability, enabling its direct employment for on-site, high throughput screening of cork in the field and production facilities, without requiring any type of supporting infrastructure.

A thermal gas flow sensor was developed and evaluated. The presented implementation requires only low-cost manufacturing techniques and readily available components, while maintaining a high level of detection range and sensitivity. Heater and sensing elements were integrated on a flexible substrate and the device was formed by bending the substrate so that the active elements were placed on the external surface of the formed channel, therefore zero flow interference is achieved and a wide variety of fluids can be measured without compromising the sensor integrity. Evaluation was made using air flow rates in the range of 0-65SLPM utilizing electrical measurements and IR imaging techniques simultaneously.

In this work, the assessment of the interactions of a bioactive substance applied to immobilized cells in either a two-dimensional (2D) or three-dimensional (3D) arrangement mimicking in vivo tissue conditions is presented. In particular, dopamine (DA) was selected as a stimulant for the implementation of an impedance analysis with a specific type of neural cells (murine neuroblastoma). The aim of this study was the extraction of calibration curves at various frequencies with different known dopamine concentrations for the description of the behavior of dopamine applied to 2D and 3D cell cultures. The results present the evaluation of the mean impedance value for each immobilization technique in each frequency. The differential responses showed the importance of the impedance when frequency is applied in both 2D and 3D immobilization cases. More specifically, in 2D immobilization matrix impedance shows higher values in comparison with the 3D cell culture. Additionally, in the 3D case, the impedance decreases with increasing concentration, while in the 2D case, an opposite behavior was observed.

The aim of this study was the development of a rapid novel biosensor system based on the Bioelectric Recognition Assay (BERA) for the detection of aflatoxin M1 (AFM1). Membrane-engineering was achieved by electroinsertion of AFM1-homologous antibodies into the membrane of the cells. The sensor measured the electric response of cultured membrane-engineered fibroblast cells suspended in an alginate gel matrix due to the change of their membrane potential after the interaction of the analyte molecules with the antibodies. The BERA-based sensor was able to detect AFM1 rapidly (3min) at very low concentrations (5 pg/ml = 5 ppt), thus demonstrating a higher sensitivity than most currently available biosensor-based methods. In addition, the assay was quite selective against other aflatoxins, such as aflatoxin B1 and ochratoxin A. Furthermore, the assay system allowed for high throughput AFM1 analysis (160 individual tests/h), due to its multiple cell–electrode interface array. Although further research is required for the optimization of the assay, the elimination of possible matrix effects and its validation by assaying actual food samples, this novel biosensor offers new perspectives for ultra-rapid, ultra-sensitive and low-cost monitoring of mycotoxins in food commodities.

This work concerns the development of a novel actuator based on water electrolysis for pumping use in microfluidic systems. The electrolysis is performed inside a confined reservoir integrated on a PCB substrate which is connected to a microchannel. During the electrolysis process, the generated gases within the enclosed structure lead to a significant pressure increase which can be employed in order to move a liquid inside the microchannel. In order to demonstrate the device's principle of operation, water is driven through a meander microchannel structure which is connected at the output of an appropriate micro-tank; the effectiveness of employing electrolysis as an actuating principle has been investigated by monitoring the resulting pressure increase for a device with a larger reservoir. Furthermore, the operation of such a device as a micro-pump was successfully demonstrated by extracting the resulting flow-rate experimentally; the obtained results from the first prototype are clearly promising.

A flexible gas flow sensor was developed and characterized. The sensor was fabricated on a flexible PCB substrate and is able to quantify flow rate based on the thermal transfer principle. Direct electrical communication to the macroworld is achieved, while the effective thermal isolation enhances sensor performance. Characterization in the range of 1-10 SLPM is presented.

A thermal accelerometer was developed and evaluated. The presented device was fabricated directly on an organic substrate, which ensures a high level of thermal isolation, while also facilitating direct electrical communication to the macroworld. The role of the seismic mass was utilized by a fluid (water), which was confined in a tank adjusted on the sensor surface. Acceleration quantification is achieved by the monitoring of the cooling effect on the heating element. A sensor signal of 32 mV for an acceleration of 1 g was obtained.

Recent advances in flow control have the potential for significant impact on the engineering design. Fluidic flow control is a method for altering flows over aerodynamic surfaces which does not rely upon altering the physical shape of the surface (typically through moving control surfaces such as flaps). The steady air flow along a basic geometry of a backward facing step is used to study the alterations of the resulting recirculation area ether spontaneously or by applying pulsating fluid injection below the edge of the step as control actuator. The PIV method is used to monitor the velocity field and determine the reattachment point. Applying flow sensors based on hot wire anemometry on the bottom wall boundary it is possible to estimate parameters such as the recirculation length or even the region of intense turbulent activity as compared and verified by the PIV. Preliminary measurements by thermal sensors reveals fingerprints of the reattachment zone applying time-frequency analysis.

A micro system utilizing a novel sensing principle is presented in this paper. The determination of position is performed by exploiting the heat transfer between a heating source and a sensing device. The device itself consists of an array of temperature sensing elements, fabricated entirely on a plastic substrate. A specific fabrication technology was implemented which allows direct integration with read-out electronics and communication to the macro-world without the use of wire bonding. The fabricated sensing elements are temperature sensitive Pt thermistors. The device is able to detect both the position and the motion of a heating source by monitoring the induced resistance variation on the thermistor array. The heating source which performs a one-dimensional motion in a parallel plane to the temperature sensing array can be any element that can provide a highly localized temperature field. The system operation was characterized under both steady-state and dynamic conditions. In steady state mode the sensor exhibits a resolution of +/[email protected], while in dynamic conditions the device can detect signal frequencies up to 10Hz.

A novel, simple approach for analytical modelling of thermal flow sensors has been implemented. It is based on unification of results obtained using the already developed two-zone analytical model and theory of laminar fluid flow over uniformly heated plate. This model can be used in order to extract the main parameters for various geometrical configurations of thermal flow sensors. Presented analytical model was further verified by experimental results. Flow tests were performed using multipurpose MEMS flow sensors consisting of two thermopiles, with 30 p(+)Si/Al thermocouples each, and a "U" shaped p(+)Si heater. Thermally isolating membrane was formed of sputtered SiO(2) and residual n-Si layer. Experimental evaluation was performed under various flow conditions and applied heating power values. The results showed excellent agreement with theoretical predictions.

This work presents the characterization of a thermal vacuum sensor, directly integrated on a printed circuit board (PCB) substrate. The sensor consists of a thin platinum strip, in direct electrical contact with the patterned Cu tracks of the FOB.; The platinum resistor that resides on a thick SU-8 layer on the PCB, acts as both heating and temperature sensing element. Both PCB substrate and SU-8 have low thermal conductivity values, therefore ensuring a high degree of thermal isolation. Under electrical current flow through the Pt heater, an elevated temperature field is developed in its vicinity due to Joule heating. The overall heat exchange rate is a function of the surrounding gas pressure in certain pressure regimes due to the contribution of different heat transfer mechanisms. The determination of heat transfer allows for the 0 extraction of the corresponding vacuum value. The sensor operation was tested in a pressure range from 10 3 to 10∼5 mbar for three different operation modes, namely that of constant current (CI), constant temperature (CT) and constant power (CP).

In this paper we present results of the evaluation of a thermal gas flow sensor device implemented on a printed circuit board (PCB) substrate by a combination of PCB and MEMs technologies. The device consists of 3 parallel Pt strip resistors in direct electrical contact to patterned copper tracks of the PCB. For planarization purposes, the Pt strips reside on a thick polymer layer (SU8). The central resistor plays the role of a heater and the two other resistors, situated symmetrically on both sides of the heater, are temperature dependent sensing elements. The three main advantages of this specific sensor are: the low thermal conductivity of the substrate materials (FR4 and SU8, with thermal conductivity ∼0.2 W(m·K)) which permits high sensitivity at low power, its robustness compared to suspended membrane sensors and its simple fabrication process. The sensor can operate in both hot wire and calorimetric modes. The sensor was mounted inside a 1.5m long tube with 25 mm2 cross sectional area and was evaluated in nitrogen flow up to 100 SLPM, which corresponds to Reynolds numbers up to 25.000. The sensor signal in both the calorimetric and the hot-wire modes is a monotonous function of the flow rate. A very high sensitivity is obtained in the calorimetric mode at very low flow rates (

The behaviour of a thermal flow sensor attached to the wall of a square tube is examined, exposed to gas flow for Reynolds numbers in the range 0–4.1 × 10 4 . Consisting of a polysilicon heater and a pair of thermopiles, the sensor’s three output signals (heater power, its electric resistance and the thermopile signal) are analyzed as a function of Re . Employing three different modes of operation (constant power (CP), constant voltage (CV) and constant temperature (CT)), it was found that the sensor sensitivity maximizes in CT mode. Heater power and its resistance vary with Re a where a changes significantly for Re > 2000. The thermopile signal, which corresponds to the streamwise temperature gradient across the heater, in contrast to the other two signals, is more sensitive in detecting flow disturbances. Its fluctuations increase with a high rate close to Re = 1800, a value which is smaller than the corresponding increase of the other two signals. The probability density function (pdf) of its fluctuations is negatively skewed consistently for the range 1500 Re Re > 11,000 it turns to a symmetric one. The pdf of the other two signals do not show any systematic trends with Re . The most striking difference of the thermopile signal behaviour compared to the other two is its multivalued relationship with Re in the range 2000 Re

A Si thermal accelerometer without solid proof mass, based on porous silicon (PS) technology has been developed and characterized. The device is compatible with silicon technology and it consists of a polysilicon heater and two thermopiles, situated symmetrically on each side of a heater. A thick PS layer provides thermal isolation from the Si substrate. The operation principle is based on the movement induced thermal convection variations between the heater and the hot thermopile contacts, which are caused by the movement of the hot fluid medium on top of the heater with respect to the sensor die. A detailed simulation by the FEA package Ansys was carried out in order to find the optimum geometrical parameters and the theoretical device behavior. The porous silicon thermal accelerometer (PSTA) was tested in a specially designed vibration system for various frequencies and accelerations. Different packaging configurations were also evaluated for both air and oil surrounding environments. The dependence of the PSTA response on applied power was studied for each surrounding environment. In each case, the response was compared with a commercial reference accelerometer and the corresponding sensitivities were extracted.

This work concerns the fabrication, modeling and characterization of a novel microfluidic flow sensor based on a microchannel capped with a porous silicon membrane, on top of which the sensor active elements are integrated. The microchannel is formed through a two-step anodization process. In the first step a mesoporous silicon layer is formed on a lithographically defined area, while in the second step a channel is formed underneath the porous layer by electropolishing. The channel is buried into bulk silicon and capped with a free-standing porous silicon layer, which is co-planar with the Si substrate. The overall developed process for the formation of the device will be described and simulation and device characterization results will be presented.

In the present work a thermal accelerometer without solid proof mass, based on a silicon sensor was studied. Its principle of operation is based on the acceleration induced thermal exchange variations due to convection between a heater and two series of thermocouples. A specially designed housing was fabricated, which allows the device to be covered with various liquids. The effect of the different liquid viscosities on the sensor characteristics was examined. The dependence of the accelerometer signal on both frequency and acceleration was determined for various configurations. It was found that depending on the packaging configuration the 3 db cut-off signal can be adjusted from some Hertz to several hundreds of Hertz. The sensitivity of the device as well as the accuracy of the waveform shapes can also be adjusted by regulating specific packaging parameters. A specially designed electronic interface was implemented for monitoring and controlling the input and output signals of the accelerometer. Different modes of operation were considered in order to improve the long term stability of the device.

In this work, an integrated thermal gas flow sensor was fabricated and evaluated using a new thermal isolation technique based on a porous silicon membrane over an air cavity in silicon. The fabrication process of a thermal gas flow sensor employing this type of micro-hotplate is described together with the theoretical estimation of the thermal distribution around the heater of the sensor. Experimental results of the thermal isolation achieved are shown. A flow evaluation of the sensor is presented and discussed. All the results obtained are compared with the corresponding ones for an identical sensor using a micro-hotplate made of porous silicon membrane but without the air cavity underneath. The improvement achieved by the air cavity is evaluated.

The study of the housing of a gas flow meter for use in medical equipment for respiratory control will be presented in this paper. The sensor is of the thermal type with dimensions 1.4 mm ×0.9 mm. The housing is developed so as to assure conditions of laminar flow in a flow range from −200 to +200 standard liters per minute (SLPM). An analytical approach is first used to determine the main housing configuration. The type and the position of a bypass tube, which is fixed to the main flow tube, are studied in detail. Extensive simulations of the flow in different housing configurations and different conditions at the inlet and outlet of the housing were performed, using the finite element analysis (FEA) software package ANSYS. The optimum housing was finally fabricated and evaluated in oxygen flow. Excellent agreement of experimental results with simulation was obtained.

This work presents a new method for the fabrication of buried microchannels, covered with porous silicon (PS). The specific method is a two-step electrochemical process, which combines PS formation and electropolishing. In a first step a PS layer with a specific depth is created at a predefined area and in the following step a cavity underneath is formed, by electropolishing of silicon. The shape of the microchannel is semi-cylindrical due to isotropic formation. The method allows accurate control of the dimensions of both PS and the cavity. The formation conditions of the PS layer and the cavity were optimized so as to obtain smooth microchannel walls. In order to obtain stable structures the area underneath the PS masking layer was transformed into n-type by implantation, taking advantage of the selectivity of PS formation between n- and p-type silicon. With this technique, a monocrystalline support for the PS layer is formed on top of the cavity. Various microchannel diameters with different thickness of capping PS layer were obtained. The process is CMOS compatible and it uses only one lithographic step and leaves the surface of the wafer unaffected for further processing. A microfluidic thermal flow sensor was fabricated using this technology, the experimental evaluation of which is in progress.

In this paper, the results of full characterization of a micromachined-silicon thermal gas flow sensor will be presented. The sensor is composed of two series of thermocouples on the right and left side of a polysilicon resistor, used as heater. The resistor and the hot contacts of the thermocouples lie on a thick porous silicon layer, which assures local thermal isolation, while the thermopile cold contacts lie on bulk silicon. Gas flow is parallel to the surface of the sensor and perpendicular to the resistor, which is heated at constant temperature. The power of the heater is stabilized by an external circuit, which provides a feedback current to compensate changes in the resistance of the heater under flow. Characterization of the sensor both under static conditions and under flow of different gases will be presented. The sensor shows high sensitivity [of the order of 175 /spl times/ 10/sup -3/ mV/(m/s)/sup 1/2/ per thermocouple] and very rapid response, below 1 ms, which makes it appropriate for use both under laminar and under turbulent flows.

Electrochemical Impedance Spectroscopy (EIS) has become a technique that is frequently used for biological assays. Impedance is defined as a complex – valued generalization of resistance and varies depending on its use per application field. In health sciences, bioimpedance is widely used as non-invasive and low cost alternative in many medical areas that provides valuable information about health status. This work focuses on assessing the effects of a bioactive substance applied to immobilized cells. Dopamine was used as a stimulant in order to implement impedance analysis with a specific type of cells. Dopamine constitutes one of the most important catecholamine neurotransmitters in both the mammalian central and peripheral nervous systems. The main purpose is to extract calibration curves at different frequencies with known dopamine concentrations in order to describe the behavior of cells applied to dopamine using an impedance measurement device. For comparison purposes, non-immobilized cells were tested for the same dopamine concentrations.

The present study demonstrates an inkjet – printed interdigitated electrode array on paper substrate and its evaluation as humidity sensor. Inkjet droplet formation analysis has been performed in order to achieve repeatable results regarding generated droplets, based on the driving pulses applied on the inkjet piezoelectric element. Droplet formation has been monitored using stroboscopic effect. Three different paper substrates, namely high glossy inkjet photo paper, glossy inkjet photo and matte inkjet photo paper have been evaluated to investigate compatibility with the ink. Relative humidity measurements have been carried out in a controlled environment. Material degradation, long term response and memory effect are some of the aspects which were studied within the frame of the present work. The proposed sensor provides the opportunity for novel biomedical applications given the flexible substrate nature and the low – cost, single – step fabrication approach.

Flow rate determination in microfluidic devices is important in numerous fields. In this paper, a novel technology which allows the formation of polymer microchannels on top of a specific PCB-based thermal flow senor is presented. The microchannel walls are defined by SU-8 on top of an array of Pt sensing elements. The sealing of the microchannel is performed by the thermal bonding of a PMMA plate (Plexiglas^(R)) on the upper surface of SU-8 layer which is covered with a thin PMMA layer. The width and depth of the microchannel can be fully controlled over an extended range. Excellent thermal isolation of the sensing elements is achieved due to the low thermal conductivity of the materials that comprise the structure. The conducted water flow rate measurements revealed high sensitivity and extended measurement range of the fabricated sensor.

A novel C-MOS compatible silicon gas flow sensor using porous silicon for thermal isolation has been designed and fabricated. The small sensor size combined with the very good thermal isolation by porous silicon assure fast response, with a time constant of the order of 1.5 ms. The principle of operation is based on heat transfer from a polysilicon resistor to the fluid and the detection of the flow-induced temperature difference by Al/polysilicon thermopiles, integrated at both sides of the heater. The sensor has been evaluated in nitrogen flows from 0 to 0.4 m/s. The sensitivity per heating power is 6.0 mV/(m/s)W and the responsivity is 0.65 V/W. The noise equivalent power and the minimum detectable velocity are 1.5×10 −8 W/Hz 1/2 and 4.1×10 −3 m/s, respectively. The chip size is 1.1 mm×1.5 mm.

A non-destructive method for evaluation of the thickness of films over bulk substrates is presented. This method is based on evaluation of the parameters of the decay part of the x-ray signal ratio. For a selected energy range of each film thickness it is demonstrated that the decay part follows an exponential law. The physical parameters involved in this law are the energy exponent and a constant that depends mainly upon the film thickness. The values found for the energy exponent are in the range 2.0–3.0. This is confirmed in a variety of cases (Al/Si, Ti/Si, Cu/Si, Pt/Si, Cu/Ni, Ti/Au and Pt/Au) for film thicknesses larger than a critical value. The experimental results are compared to those obtained by two theoretical methods and a Monte-Carlo approach. The first method is based on solution of the Boltzmann transport equation for the electron beam, an approach developed by one of the authors for e-beam lithography. The second is based on a previously developed semi-empirical formula for the x-ray depth distribution function. The energy dependence of the signal ratio is also discussed using this approach. © 1998 John Wiley & Sons, Ltd.

Large polycrystalline silicon membranes in the form of bridges suspended over deep monocrystalline silicon cavities have been fabricated by using porous silicon as a sacrificial layer. Stresses within the free-standing membranes as well as within supported polycrystalline membranes (pads) are measured through micro-Raman spectroscopy and a different model is used in each case in order to calculate the stresses from the observed Raman shifts. A detailed study of stress distribution along the membranes and pads has been performed, as a function of thickness and annealing treatment. The stress profiles reveal variations in stress along the membranes and pads.

Stress measurements were performed in a free standing monocrystalline cantilever and a polycrystalline silicon membrane suspended over a deep cavity, using micro-Raman spectroscopy. These micromechanical structures were fabricated using porous silicon as a sacrificial layer. The results show that the stress varies across the membrane and the cantilever, the level of stress in the latter being lower than in the membrane.

Porous-silicon technology is successfully used for frontside bulk silicon micromachining in a process which is fully C-MOS compatible. Porous silicon is used as a sacrificial layer and it is removed by C-MOS-compatible chemicals, leaving a very smooth bottom surface and sidewalls. Deep trenches, bridges with suspended membranes and cantilevers are formed, which open new possibilities in monolithic integration of sensors with electronics. Cavities as deep as ∼ 120 μm and suspended polysilicon membranes with a flat surface as large as 230 μm × 550 μm have been fabricated by this process. Also other micromechanical structures such as very flat polysilicon cantilevers of dimensions 150 μm × 2 μm × 2 μm are easily obtained after optimization of the process in order to minimize the strain within the polysilicon films.

A bulk silicon micromachining technique using porous silicon as a sacrificial layer is developed. The proposed process is fully C-MOS compatible and it was successfully used to fabricate deep cavities into silicon with very smooth bottom surfaces and sidewalls. Suspended flat polysilicon membranes were also produced of a surface as large as 230 × 550 μm2, as well as polysilicon cantilevers. This process opens important possibilities in silicon integrated sensor fabrication.