Advances in Silicon Resonant Pressure Transducers

This paper presents a MEMS Resonant Pressure Transducers (RPT) that is produced using a flexible fabrication route to allow pressure ranges from 1bar to 700bar in fully oil isolated hermetic packages without compromising sensor performance. The fabrication method makes use of silicon fusion bonding (SFB) and deep reactive ion etching (DRIE) to build up a three-layer die, with the middle layer consisting of a strain sensitive resonator. The key aspects of the fabrication process and sensor design that make this possible are presented, along with data showing long-term stability of better than 100ppm drift per year.     

A novel SOI Pirani sensor with triple heat sinks

In this paper, we will present a novel MEMS Pirani sensor with triple heat sinks. The sensors are made on SOI (Silicon On Insulator) wafers leading to a very simple process and good mechanical structures as compared to alternative surface micromachining processes. Moreover, the proposed Pirani has three heat sinks. The area of heat loss through the ambient gas is greatly enlarged as compared to Pirani sensors with one or dual heat sinks without increasing the dimension of the sensor. Consequently, the dynamic pressure range of the Pirani sensor will be enlarged.     

On the simultaneous optimization of pressure and layout for gas permeation membrane systems

We present a methodology for the simultaneous optimization of pressure and network configurations for gas separation membrane permeators. The methodology targets and refines pressure clusters for efficient operation of membrane networks and follows a three-stage strategy. The first stage produces a pressure target curve (PTC) that allows the identification of Pareto optimal pressure cluster combinations. This is followed by a second stage, where the different optimal pressure ratios are used in an optimal search for process structures to identify the performance of the individual clusters. The third stage processes the information generated in the first two stages in a generalized process superstructure model. Throughout the methodology, a modified process synthesis model for membrane network optimization and design is employed which can be optimized robustly using the simulated annealing algorithm. Three illustrative examples are presented to demonstrate the proposed methodology for simultaneous pressure and layout optimization.     

Multiparameter Sensor Chip with Barium Strontium Titanate as Multipurpose Material

It is well known that biochemical and biotechnological processes are strongly dependent and affected by a variety of physico‐chemical parameters such as pH value, temperature, pressure and electrolyte conductivity. Therefore, these quantities have to be monitored or controlled in order to guarantee a stable process operation, optimization and high yield. In this work, a sensor chip for the multiparameter detection of three physico‐chemical parameters such as electrolyte conductivity, pH and temperature is realized using barium strontium titanate (BST) as multipurpose material. The chip integrates a capacitively coupled four‐electrode electrolyte‐conductivity sensor, a capacitive field‐effect pH sensor and a thin‐film Pt‐temperature sensor. Due to the multifunctional properties of BST, it is utilized as final outermost coating layer of the processed sensor chip and serves as passivation and protection layer as well as pH‐sensitive transducer material at the same time. The results of testing of the individual sensors of the developed multiparameter sensor chip are presented. In addition, a quasi‐simultaneous multiparameter characterization of the sensor chip in buffer solutions with different pH value and electrolyte conductivity is performed. To study the sensor behavior and the suitability of BST as multifunctional material under harsh environmental conditions, the sensor chip was exemplarily tested in a biogas digestate.     

Reforming Catalysts of the PR Family: Scientific Foundations and Technological Advancement

Results of investigations of the state of active sites in aluminoplatinum reforming catalysts (RCs) are summarized. Laws governing the formation and the role of platinum ionic species in the adsorption and catalytic conversion of hydrocarbons are presented. Strategies for the design of highly efficient catalysts, the development of catalyst manufacturing technologies, and operation in the production of motor fuels and aromatic hydrocarbons are formulated. Data are reported on the full-scale operation of catalyst PR-51/04 (PR-71), a new RC, and full-scale tests of the Biforming process, a new process for motor fuel production by coprocessing C₃-C₄ hydrocarbon gases and gasoline fractions.     

Novel pressure stable thermoelectric flow sensor in non-steady state operation mode for inline process analysis in micro reactors

In this contribution results of the non-steady state operation of a novel pressure stable thermoelectric flow sensor chip for the inline chemical process analysis in micro reactors are presented. The sensor chip consists of a heater in between two thermopiles on a novel perforated membrane, thus liquid flows on both sides. Compared to the conventional constant overtemperature/current operation the heater is now operated in non-steady state/pulsed mode and step responses of both thermopiles are evaluated. Based on our results the non-steady operation of the heater leads to a better discrimination between thermal conductivity and heat capacity of the liquid.     

Pneumatic handling of droplets on-demand on a microfluidic device for seamless processing of reaction and electrophoretic separation

Sequential operations of pre-separation reaction process by picoliter droplets and following electrophoretic separation process were realized in a single microfluidic device with pneumatic handling of liquid. The developed device consists of a fluidic chip made of PDMS, an electrode substrate, and a temperature control substrate on which thin film heater/sensor structures are fabricated. Liquid handling, including introduction of liquid samples, droplet generation, and merging of droplets, was implemented by pneumatic manipulation through microcapillary vent structures, allowing air to pass and stop liquid flow. Since the pneumatic manipulations are conducted in a fully automated manner by using a programmable air pressure control system, the user simply has to load liquid samples on each liquid port of the device. Droplets of 420 pL were generated with an accuracy of ± 2 pL by applying droplet generation pressure in the range of 40-100 kPa. As a demonstration, a binding reaction of a 15 mer ssDNA with a peptide nucleic acid oligomer used as an oligoprobe followed by denaturing electrophoresis to discriminate a single-base substitution was performed within 1.5 min. By exploiting the droplet-on-demand capability of the device, the influence of various factors, such as reaction time, mixing ratio and droplet configurations on the ssDNA-peptide nucleic acid binding reaction in the droplet-based process, was studied toward realization of a rapid detection method to discriminate rapid single-base substitution.     

Optical Chemical Sensors Based on Sol-Gel Materials: Recent Advances and Critical Issues

The use of the sol-gel process to produce materials for optical chemical sensors and biosensors is attracting considerable interest. This interest derives mainly from the design flexibility of the sol-gel process and the ease of fabrication. In most applications the sol-gel material is used to provide a microporous support matrix in which analyte-sensitive species are entrapped and into which smaller analyte molecules may diffuse. Sensors based on entrapped organic and inorganic dyes, enzymes and other biomolecules have been reported. A range of sensor configurations has been employed, including monoliths, thin films, as well as more elaborate structures. In this paper a selection is presented of recent significant developments in optical chemical sensors which employ solgel-derived materials. These developments include the tailoring of sol-gel materials to optimise sensor response, advanced waveguide structures and novel probe-tip sensors. Those issues which remain critical to the eventual deployment of sol-gel sensors are examined. In particular, the problems of leaching, microstructural stability, diffusion-limited response time, and susceptibility to interferents are discussed and some solutions proposed.     

Preparation and spectroscopic properties of multiluminophore luminescent oxygen and temperature sensor films

A new luminescent oxygen and temperature sensor has been developed that utilizes two luminescent dyes, 5,10,15,20-tetrakis(pentafluorophenyl)porphyrin platinum(II) (PtTFPP, the oxygen sensor) and tris(1,10-phenanthroline)ruthenium(II) dichloride (Ruphen, the temperature sensor). The two dyes are dispersed in an oxygen-permeable polymer binder consisting of a copolymer of 4-tert-butylstyrene (tBS) and 2,2,2-trifluoroethyl methacrylate (p-tBS-co-TFEM). To alleviate energy transfer and other quenching interactions between the two luminescent dyes in the p-tBS-co-TFEM binder, the Ruphen temperature sensor is encapsulated in polyacrylonitrile (PAN) polymer nanospheres that are prepared by coprecipitation of PAN and Ruphen from N,N-dimethylformamide solution. The temperature and air-pressure response of the emission from the sensor film is fully characterized by using emission spectroscopy. The emission from the two luminescent dyes is spectrally well-separated. The intensity of the Ruphen emission varies strongly with temperature (approximately 1.4% degrees C(-1)), whereas the intensity of the PtTFPP emission varies with temperature and air pressure. The two-dye luminescent coating is useful as a pressure-sensitive paint (PSP), where the emission from the Ruphen temperature sensor is used to correct for the temperature dependence of the pressure response of the PtTFPP sensor. To demonstrate the PSP application, a coupon coated with the sensor was imaged using a CCD camera, and the CCD images were analyzed by intensity ratio methods. Spectroscopic studies were also carried out on a sensor that contains three dyes in order to demonstrate the feasibility of including an intensity reference dye along with the temperature and pressure dyes into the sensor.     

Paper-based piezoresistive MEMS sensors

This paper describes the development of MEMS force sensors constructed using paper as the structural material. The working principle on which these paper-based sensors are based is the piezoresistive effect generated by conductive materials patterned on a paper substrate. The device is inexpensive (～$0.04 per device for materials), simple to fabricate, lightweight, and disposable. Paper can be readily folded into three-dimensional structures to increase the stiffness of the sensor while keeping it light in weight. The entire fabrication process can be completed within one hour without expensive cleanroom facilities using simple tools (e.g., a paper cutter and a painting knife). We demonstrated that the paper-based sensor can measure forces with moderate performance (i.e., resolution: 120 μN, measurement range: ±16 mN, and sensitivity: 0.84 mV mN(-1)). We applied this sensor to characterizing the mechanical properties of a soft material. Leveraging the same sensing concept, we also developed a paper-based balance with a measurement range of 15 g, and a resolution of 0.39 g.     

3D numerical simulation of a lab-on-a-chip--increasing measurement sensitivity of interdigitated capacitors by passivation optimization

Interdigital electrode structures (IDES) play a major role in many technical and analytical applications. In particular, they are a key technology in modern lab-on-a-chip (LOC) devices. As high sensitivity is a key component of any (bio)analytical method, the presented work is aimed at designing a novel dielectric sensing system, which exhibits maximum sensor sensitivity using passivated dielectric microsensors. Although the implementation of high-ε(r) dielectric passivation materials such as tantalum oxide or titanium oxide showed increased sensor sensitivity by a factor of 5, simulations revealed that sensor sensitivity is ultimately determined by the dielectric properties of the analyte. Ideally, dielectric properties of the passivation material need to be adjusted to the dielectric properties of the material under investigation and any deviations (e.g. higher or lower dielectric constants) will result in significant loss of sensitivity. To address these shortcomings we have developed a novel dielectric sensing concept based on a dual-material passivation geometry. The novel design consists of electric flux barriers that are layered between the finger electrodes, as well as electric flux guides which are located above the electrode structures that direct the entire generated electric flux to the object under investigation. Our 3D numerical results clearly show that the novel design offers two main advantages: firstly, the measurement sensitivity is further increased by more than a factor of two in comparison to a homogeneous passivation material sensing strategy. Secondly, maximum sensitivity for a given set of finger geometries can be achieved using a single sensor design regardless of the frequency-dependent dielectric properties of the measured objects. Hence, the novel approach is capable of reducing design and manufacturing costs of lab-on-a-chip devices.     

High sensitivity in gas analysis with photoacoustic detection

Introduction of a new type of pressure sensor has been shown to improve orders of magnitude the sensitivity of a photoacoustic measurement system using a black body radiation source. A new pressure sensor was developed to overcome the limitations in the capacitive microphone technology and to obtain ultimate sensitivity in photoacoustic gas detection when using low modulation frequency below 500 Hz. The pressure sensor is a cantilever-type microphone with interferometric measurement of the sensor displacement. By using conventional filter-type photoacoustic setup with the cantilever microphone and a black body radiation source, we obtained a detection limit in the sub-ppb range for methane gas with 100 s measurement time.     

Discrete element simulation of the dynamics of adsorbents in a radial flow reactor used for gas prepurification

Radial flow reactors (RFR) are used in thermal swing adsorption (TSA) processes for gas prepurification. The aim of this work is to show the validity of the discrete element method (DEM) to simulate the effect of thermal expansion and contraction cycles occurring in such processes on the packed bed of RFR reactors. Both mono-layered and bi-layered packed beds of adsorbents are investigated. A DEM-based model of a full-scale size unit was developed, the parameters of which were calibrated by means of particle-scale experimental measurements and simple auxiliary DEM simulations. The DEM-based model used is isothermal and the thermal expansion and contraction phenomena are modelled through the displacement of the inner and outer walls of the computational domain. First, the accuracy of this model is assessed using analytical values of the static wall pressure (i.e. with no wall motion) as well as experimental measurements of the dynamic wall pressure (i.e. with wall motion) of a bi-layered bed. Next, simulation results for a few process cycles in the case of a bi-layered packed bed indicates that little mixing occurs at the interface between the two types of adsorbents. To our knowledge, this is the first time that simulation is used to investigate the behavior of the packed bed of a RFR in a TSA process. The results obtained with the proposed model show that the DEM is a valuable tool for the investigation of such slow dynamical processes, provided a careful calibration is done.     

A novel monolithic silicon sensor for measuring acceleration,pressure and temperature on a shock absorber

A fabricated micro-mechanical sensor to assess the condition of automotive shock absorbers is presented. The monolithic sensor, measures the oil temperature, acceleration and internal pressure of the shock absorber. A dual mass accelerometer with optimized beam geometry is used for acceleration readout. In addition, a 23.1 μm thickness square membrane and two buried resistors are used for pressure and temperature sensing respectively. The proposed miniaturized sensor can be effectively integrated with standard single- and dual-tube shock absorbers. The data acquired during normal vehicle operation can be continuously used to monitor the condition of the shock absorbers, allowing shock absorbers to be replaced before their degradation significantly reduce the comfort, performance and safety of the vehicle.     

Novel membrane-based sensor for online membrane integrity monitoring

A novel membrane-based sensor device for upstream membrane integrity monitoring has been developed and evaluated in this study. The sensor is based on relative trans-membrane pressures created by two membranes in series inside the sensor device that detects deposition from the sample stream onto the first of the sensor membranes. The sensor pressure signals can distinguish between intact or damaged membranes in the upstream membrane filtration process. Studies were conducted to evaluate both stabilities and sensitivities of the relative trans-membrane pressure monitoring technique. Sensitivity, based on the response times of the membrane sensor for particle detection, was determined for a range of operating conditions, membrane sandwich configurations, and particle concentrations in both simulated membrane failures and for actual pin-hole defects on a submerged MF membrane. The results showed that both sensitivities and stability strongly depended on membrane sandwich configurations (membrane characteristics) in the sensor, and mode of operation (pressurized or vacuum). The membrane sensor detected bentonite particles with a concentration of 0.3 mg/L (turbidity ∼0.3 NTU) in approximately 35 min in the vacuum mode. The sensor is reliable, sensitive and low cost. It has potential applications in decentralized systems or in multichannel monitoring of local conditions in a large plant. Possible applications of the membrane sensor for fouling monitoring are also discussed.     

Rapid prototyping of multilayer thiolene microfluidic chips by photopolymerization and transfer lamination

A new fabrication process is described allowing rapid prototyping of multilayer microfluidic chips using commercial thiolene optical adhesives. Thiolene monomer liquid is photopolymerized across transparency masks to obtain partially cured patterns supported on thin polyethylene sheets. The patterns are easily laminated and transferred to a substrate due to the elastomeric nature and adhesiveness of partially cured thiolene. The process characteristics are evaluated by realizing several test structures and fluidic chips. As an example of application, the operation of a microfluidic bead array sensor for pH measurements is then described in some detail.     

Integrated ionic liquid-based electrofluidic circuits for pressure sensing within polydimethylsiloxane microfluidic systems

This paper reports a novel pressure sensor with an electrical readout based on electrofluidic circuits constructed by ionic liquid (IL)-filled microfluidic channels. The developed pressure sensor can be seamlessly fabricated into polydimethylsiloxane (PDMS) microfluidic systems using the well-developed multilayer soft lithography (MSL) technique without additional assembly or sophisticated cleanroom microfabrication processes. Therefore, the device can be easily scaled up and is fully disposable. The pressure sensing is achieved by measuring the pressure-induced electrical resistance variation of the constructed electrofluidic resistor. In addition, an electrofluidic Wheatstone bridge circuit is designed for accurate and stable resistance measurements. The pressure sensor is characterized using pressurized nitrogen gas and various liquids which flow into the microfluidic channels. The experimental results demonstrate the great long-term stability (more than a week), temperature stability (up to 100 °C), and linear characteristics of the developed pressure sensing scheme. Consequently, the integrated microfluidic pressure sensor developed in this paper is promising for better monitoring and for characterizing the flow conditions and liquid properties inside the PDMS microfluidic systems in an easier manner for various lab on a chip applications.     

Optical molecular sensing with semiconductor quantum dots (QDs)

Semiconductor quantum dots (QDs) exhibit unique optical and photophysical properties. These features are implemented to develop optical molecular sensor systems. The review addresses the methods to functionalize the QDs with chemical capping layers that enable the use of the resulting hybrid structures for sensing, and discusses the photophysical mechanisms being applied in the different sensor systems. Different methods to design the chemically-modified QDs hybrid structures for sensing low-molecular-weight substrates, metal ions, anions and gases are presented. These include the functionalization of the QDs with ligands that bind ions, the modification of the QDs with substrate-specific ligands or receptor units, and the chemical modification of the QDs upon sensing. Specific emphasis is directed to describe the cooperative catalytic functions of the QDs in the sensing processes, and to address the function of sensing with logic-gate operations.     

Novel electrochemical sensor system for monitoring metabolic activity during the growth and cultivation of prokaryotic and eukaryotic cells

A novel amperometric sensor system is presented which directly reflects the metabolic activity of prokaryotic and eukaryotic cells during cultivation. The principle of an externally mounted sensor is current measurement using a three-electrode system. Only living cells are detected since the current signal is based on a redox mediator. Added to a culture sample in its oxidized form, the mediator is reduced by cellular metabolism and subsequently re-oxidized at the anode. The spontaneous immobilisation of the cells in the reaction vessel of the sensor by swelling dextrane polymers (Sephadex) prior to measurement is the key to a fast, consistent signal. Even metabolically less active mammalian cells produce a reliable signal within a few minutes; this may open up future applications of the electrochemical sensor in closed loop process control not only for bacterial and fungal bioprocesses, but also in cell culture technology.