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Safety is a crucial issue in hydrogen energy applications due to the unique properties of hydrogen. Accordingly, a suitable hydrogen sensor for leakage detection must have at least high sensitivity and selectivity, rapid response/recovery, low power consumption and stable functionality, which requires further improvements on the available hydrogen sensors. In recent years, the mature development of nanomaterials engineering technologies, which facilitate the synthesis and modification of various materials, has opened up many possibilities for improving hydrogen sensing performance. Current research of hydrogen detection sensors based on both conservational and innovative materials are introduced in this review. This work mainly focuses on three material categories, i.e., transition metals, metal oxide semiconductors, and graphene and its derivatives. Different hydrogen sensing mechanisms, such as resistive, capacitive, optical and surface acoustic wave-based sensors, are also presented, and their sensing performances and influence based on different nanostructures and material combinations are compared and discussed, respectively. This review is concluded with a brief outlook and future development trends.

From electronic devices to large-area electronics, from individual cells to skin substitutes, printing techniques are providing compelling applications in wide-ranging fields. Research has thus fueled the vision of a hybrid, printing platform to fabricate sensors/electronics and living engineered tissues simultaneously. Following this interest, we have fabricated interdigitated-electrode sensors (IDEs) by inkjet printing to monitor epithelial cell cultures. We have fabricated IDEs using flexible substrates with silver nanoparticles as a conductive element and SU-8 as the passivation layer. Our sensors are cytocompatible, have a topography that simulates microgrooves of 300 µm width and ~4 µm depth, and can be reused for cellular studies without detrimental in the electrical performance. To test the inkjet-printed sensors and demonstrate their potential use for monitoring laboratory-growth skin tissues, we have developed a real-time system and monitored label-free proliferation, migration, and detachment of keratinocytes by impedance spectroscopy. We have found that variations in the impedance correlate linearly to cell densities initially seeded and that the main component influencing the total impedance is the isolated effect of the cell membranes. Results obtained show that impedance can track cellular migration over the surface of the sensors, exhibiting a linear relationship with the standard method of image processing. Our results provide a useful approach for non-destructive in-situ monitoring of processes related to both in vitro epidermal models and wound healing with low-cost ink-jetted sensors. This type of flexible sensor as well as the impedance method are promising for the envisioned hybrid technology of 3D-bioprinted smart skin substitutes with built-in electronics.

A novel capacitive sensor for measuring the water-level and monitoring the water quality has been developed in this work by using an enhanced screen printing technology. A commonly used environment-friendly conductive polymer poly(3,4-ethylenedioxythiophene):poly (styrenesulfonate) (PEDOT:PSS) for conductive sensors has a limited conductivity due to its high sheet resistance. A physical treatment performed during the printing process has reduced the sheet resistance of printed PEDOT:PSS on polyethylenterephthalat (PET) substrate from 264.39 Ω/sq to 23.44 Ω/sq. The adhesion bonding force between printed PEDOT:PSS and the substrate PET is increased by using chemical treatment and tested using a newly designed adhesive peeling force test. Using the economical conductive ink PEDOT:PSS with this new physical treatment, our capacitive sensors are cost-efficient and have a sensitivity of up to 1.25 pF/mm.

In this paper we present and discuss two innovative liquid-free SOI sensors for pressure measurements in harsh environments. The sensors are capable of measuring pressures at high temperatures. In both concepts media separation is realized using a steel membrane. The two concepts represent two different strategies for packaging of devices for use in harsh environments and at high temperatures. The first one is a “one-sensor-one-packaging_technology” concept. The second one uses a standard flip-chip bonding technique. The first sensor is a “floating-concept”, capable of measuring pressures at temperatures up to 400 °C (constant load) with an accuracy of 0.25% Full Scale Output (FSO). A push rod (mounted onto the steel membrane) transfers the applied pressure directly to the center-boss membrane of the SOI-chip, which is placed on a ceramic carrier. The chip membrane is realized by Deep Reactive Ion Etching (DRIE or Bosch Process). A novel propertied chip housing employing a sliding sensor chip that is fixed during packaging by mechanical preloading via the push rod is used, thereby avoiding chip movement, and ensuring optimal push rod load transmission. The second sensor can be used up to 350 °C. The SOI chips consists of a beam with an integrated centre-boss with was realized using KOH structuring and DRIE. The SOI chip is not “floating” but bonded by using flip-chip technology. The fabricated SOI sensor chip has a bridge resistance of 3250 Ω. The realized sensor chip has a sensitivity of 18 mV/µm measured using a bridge current of 1 mA.

In this paper we present a printed, fast, high-sensitive and cheap wireless incontinence sensor [...]

In this paper, we present our work developing a family of silicon-on-insulator (SOI)–based high-g micro-electro-mechanical systems (MEMS) piezoresistive sensors for measurement of accelerations up to 60,000 g. This paper presents the design, simulation, and manufacturing stages. The high-acceleration sensor is realized with one double-clamped beam carrying one transversal and one longitudinal piezoresistor on each end of the beam. The four piezoresistors are connected to a Wheatstone bridge. The piezoresistors are defined to 4400 Ω, which results in a width-to-depth geometry of the pn-junction of 14 μm × 1.8 μm. A finite element method (FEM) simulation model is used to determine the beam length, which complies with the resonance frequency and sensitivity. The geometry of the realized high-g sensor element is 3 × 2 × 1 mm3. To demonstrate the performance of the sensor, a shock wave bar is used to test the sensor, and a Polytec vibrometer is used as an acceleration reference. The sensor wave form tracks the laser signal very well up to 60,000 g. The sensor can be utilized in aerospace applications or in the control and detection of impact levels.

In this paper, we present and discuss our new WSi–WSiN–Pt metallization scheme for SiC-based microsystems for applications in harsh environments. Stoichiometric material WSi was selected as contact material for SiC. The diffusion barrier material WSiN was deposited from the same target as the contact material in order to limit the number of different chemical elements in the scheme. Our scheme was kept as simple as possible regarding the number of layers and chemical elements. Our scheme shows very good long-term stability and suitability for SiC-based microsystems. The experimental evaluation concept used here includes a combination of physical, electrical, and mechanical analysis techniques. This combined advance is necessary since modern physical analysis techniques still offer only limited sensitivity for detecting minimal changes in the metallization scheme.

Our recent development of a wireless humidity sensor system embedded in incontinence products enables new sensor applications to diagnose and supervise geriatric diseases (i.e., age-related diabetes mellitus type II). The measurement of glucose in urine, so-called glucosuria, is an early indicator for an incipient diabetes mellitus disease, whose symptoms are often age-related but misjudged. In this paper, an incontinence glucose sensor is printed with biocompatible ink and Prussian blue as an electron mediator on foil and functionalized with immobilized glucose oxidase. Inkjet printing of multiple layers of Nafion prevents large interference substances from diffusing into the measuring electrode and allows precise adjustment of the linear working range, which is significantly different from blood glucose measurement. Performance tests show the potential to detect minimum glucose values and store the sensor over a prolonged period at room temperature. The printed glucose sensor can be embedded into the absorber material of incontinence products, where capillary forces transport the urine analyte to the detection area. An attached readout module with an integrated potentiostat measures the glucose concentration in urine, which is transmitted wirelessly with incontinence events and stored in a cloud service for further analysis by medical staff and care workers.

Micro-Electro-Mechanical Systems (MEMS) devices are widely used for motion, pressure, light, and ultrasound sensing applications [...]