Contact Configuration Research Articles

Friction in Oil-Lubricated Rolling–Sliding Contacts with Technical and High-Performance Thermoplastics

Thermoplastics show great potential due to their lightweight design, low-noise operation, and cost-effective manufacturing. Oil lubrication allows for their usage in high-power-transmission applications, such as gears. The current design guidelines for thermoplastic gears lack reliable estimates for the coefficient of friction of oil-lubricated rolling–sliding contacts. This work characterizes the friction of elastohydrodynamic rolling–sliding contacts with technical and high-performance thermoplastics with oil lubrication. The influence of polyoxymethylene (POM), polyamide 46 (PA46), polyamide 12 (PA12), and polyetheretherketone (PEEK), as well as mineral oil (MIN), polyalphaolefin (PAO), and water-containing polyalkylene glycol (PAGW), was studied. Experiments were carried out on a ball-on-disk tribometer, considering different loads, speeds, temperatures, and surface roughness. The results show that, for fluid film lubrication, there is very low friction in the superlubricity regime, with a coefficient of friction lower than 0.01. Both sliding and rolling friction account for a significant portion of the total friction, depending on the contact configuration and operating conditions. In the mixed to boundary lubrication regime, the sliding friction depends on the thermoplastic and rises sharply, thus increasing the total friction.

Metallic material microstructure grain size measurements from backscattering signals in ultrasonic array data sets

Ultrasound backscattering signals from material microstructures can be used to evaluate the material microstructure grain size. This typically involves making pulse-echo immersion measurements at multiple locations using a focused ultrasonic transducer in order to obtain an accurate estimate of the root-mean-square amplitude of the back-scattered signal at a specified focal position. However, this restricts some practical applications of using such techniques in, for example, on-line measurements in high-value manufacturing and in-service inspections where multiple immersion measurements are not feasible to use. The main benefit of using ultrasonic phased arrays is that one array probe at one position can focus ultrasound beams at multiple points using different focal laws either physically or in data postprocessing. Potentially this means that accurate grain size measurements can be obtained from a single array measurement. In this paper, the classic backscattering method for conventional transducers is adapted to be used for full matrix capture datasets from an ultrasonic array. Three-dimensional ultrasonic models are developed in the proposed inverse process to measure material microstructure grain size. Experimental validations were performed on two metallic materials: copper (EN1652) and bright mild steel (BS970). A good agreement is shown between the experimentally measured grain sizes from array data and metallography measurements. Compared to the classic pulse-echo immersion back-scattering measurements, the proposed method enables accurate measurement of grain size in a direct contact configuration at fewer locations. This has potential to make on-line grain size measurements possible.

Enhancement of tunneling electroresistance in metal/two-dimensional ferroelectric tunnel junctions: route for polarization-modulated interface transport

In fabricating ferroelectric tunnel junction (FTJ) devices, it is essential to employ low-resistance metals as electrodes interfacing with two-dimensional (2D) ferroelectric materials. For FTJs with a top contact configuration, two interfaces for charge transport are present, namely the vertical interface between the metal electrode and the 2D ferroelectric material, and the lateral interface between the electrode and the central scattering region. These interfaces significantly influence the tunneling electroresistance (TER) of FTJs. However, there exists a notable deficiency in comprehension concerning the physics of charge transport at the interface. In this work, we explore the interface transport properties in FTJs featuring a top contact configuration between metal and the typicalα-In2Se3monolayer. By employing the non-equilibrium Green's function method, we observe a TER ratio of1.15×105% for the Pd top contact interfacing with anα-In2Se3monolayer. The significant TER effect is attributed to polarization-controlled interface transport, which is further elucidated through an analysis of the transport mechanisms influenced by the out-of-plane polarization ofα-In2Se3at the vertical interface and the in-plane polarization at the lateral interface. This investigation of the fundamental physical mechanisms of polarization-controlled interface transport demonstrates significant potential for enhancing non-volatile memory devices.

Study of fretting wear mechanisms of complete contacts

The Ti-6Al-4V fretting wear of complete contacts on a proving ring-like rig is investigated in this paper. Under this contact configuration, the Ti-6Al-4V alloy exhibited distinctive fretting wear behaviors. Especially in the continuous wear zones of the fretting specimen and pad, a paired continuous pit and peak were formed, respectively, and moved inward as the continuous wear zones expanded. To explain these fretting wear behaviors of the fretting configuration, a novel phenomenological fretting wear model is proposed in this paper. Additionally, due to the failure of the conventional FE method with a constant wear coefficient to simulate the fretting wear, a new local wear coefficient model, which is position-dependent and time-dependent fretting, is also proposed in this paper.

Observation of voltage dependent negative differential resistance (NDR) in SnS2-GO nanocomposites

This study investigates the structural, optical, and electrical properties of tin disulfide (SnS2) and SnS2-graphene oxide (GO) nanosheets synthesized via chemical bath deposition method (CBD). Structural characterization confirms the formation of hexagonal crystal phases with nanosheet morphology. It shows a well distribution of nanosheet average square sizes of 10 nm for SnS2 and 6 nm for SnS2-GO. Optical analysis shows blue shifts in absorption edges compared to bulk SnS2, attributed to quantum confinement effects. Photoluminescence emission peaks exhibit different energy levels in SnS2-GO originated to native defects. The composites show a sharp reduced of PL intensity due to enhanced charge carrier separation. Electrical measurements on SnS2-GO thin films demonstrate negative differential resistance (NDR) behavior in both planar and sandwich contact configurations, suggesting electron injection/extraction mechanisms. The NDR phenomenon exhibits a dependence on voltage scan rate, indicating the involvement of electronic and ionic elements in charge transport mechanisms. Overall, this study provides insights into the NDR properties of SnS2-GO nanocomposite, laying the groundwork for their potential applications in optoelectronics and nanoelectronics.

(Invited) Influence of the Semiconductor Thin Film Morphologies on Dntt Organic Electronic Devices Performances

Interest in organic semiconductors has grown enormously in the last few years, indeed their use in microelectronics is continuously rising up in a large range of fields, spanning from academic to industrial new applications [1]. They provide a large number of interesting properties that have pushed a gradual replacement of classical amorphous silicon-based devices with organic ones [2], as they promise to be the best candidates as drivers of the necessary green and digital transition and become the building blocks in a huge number of future applications.In most devices, particularly in OTFTs, the quality and properties of the interface between semiconductor and dielectric are of fundamental importance for the device electrical characteristics [3-4]. Dinaphtho [2,3-b:2′,3′-f] thieno [3,2-b] thiophene (DNTT)-based OTFTs are among the best-known devices as they provide good performances in terms of charge mobility, good stability as well as easy processing and they are particularly suitable to study deeper the role of insulator/semiconductor interface [5-6]. It has been widely reported that the best performances of the small molecule organic based transistors, in terms of charge mobility as well as stability, are obtained when the molecules align with their long axis almost perpendicular to the growth surface. The DNTT molecules deposited on SiO2, align to form a homogeneous film, which results to be highly crystalline and provides good transport properties. However, in DNTT-based OTFTs different insulator surfaces, above which the active layer is grown, can provide different properties in terms of morphology and surface energy so that the electrical performances of the resulted devices can span in a wide range [7].In this work, we have studied the growth of DNTT semiconductor thin films on two different dielectric materials relating the ordered DNTT thin film structure to the OTFTs' electrical characteristics. OTFTs have been fabricated with Bottom Gate Top Contact (BGTC) configuration using thermal SiO2 or a double layer of SiO2/CytopTM as gate dielectrics. Semiconductor thin films, with thicknesses ranging from 3 nm to 50 nm, were detailed analyzed with high resolution AFM and XRD measurements (Fig. 1a, b, c, d) for different growth conditions to understand the morphologies of the films starting by the very first ordered layers of DNTT semiconductors. Our measurements show that DNTT molecules on SiO2 and Cytop pack into ordered structures placing themselves with their long axis perpendicular to the plane of the substrate (edge-on). However, in the case of DNTT on SiO2, a portion of ordered molecules can lie horizontally on the substrate (face-on). This causes an increase of defective states for the majority carriers in the conductive channel of the transistor, with a consequent reduction of the field-effect mobility (Fig. 1a, b). Numerical simulations were performed to analyze the effects of different semiconductor film morphologies on the electrical characteristics of the OTFTs. We also show that the morphological semiconductor differences lead to better performances for organic phototransistors based on DNTT/Cytop interface [8].[1] C. Wang et al., Chemical reviews 2012, 112 (4), 2208-2267.[2] Y. Bonnassieux et al., Flexible and Printed Electronics 2021, 6 (2), 023001.[3] H. I. Un et al., Advanced Science 2019, 6 (20), 1900375.[4] H. Sirringhaus et al., Advanced materials 2014, 26 (9), 1319-1335.[5] H. Chang et al., Org. Electron., 2015, 22, 86-91.[6] Q. Wang et al., ACS applied materials & interfaces 2018, 10 (26), 22513-22519.[7] M. Geiger et al., Advanced Materials Interfaces 2020, 7 (10), 1902145.[8] S. Calvi, et al., Org. Electron., 2022, 102, 106452. Figure 1

Fretting fatigue life prediction of full-scale dovetail joints using the theory of critical distances with mesh control

The fretting fatigue life of full-scale dovetail joints in two contact configurations was estimated using the theory of critical distance with the area method (TCD-AM) and the mesh control method (TCD-MC). The TCD-MC method demonstrated prediction accuracy comparable to the traditional TCD-AM method, while improving computational efficiency by 85 %. By incorporating a calibration strategy with the TCD-MC method, the predicted fatigue life was within the scatter band of factor 3 when compared with the experimental data, indicating its reliability. The proposed parameter-fitting method for TCD-MC yielded results nearly identical to the conventional method, while reducing the workload by 75 %. The TCD-MC method is expected to provide a potentially novel and convenient approach for fretting fatigue life prediction in full-scale specimen.

Development and Investigation of a Grasping Analysis System with Two-Axis Force Sensors at Each of the 16 Points on the Object Surface for a Hardware-Based FinRay-Type Soft Gripper.

The FinRay soft gripper achieves passive enveloping grasping through its functional flexible structure, adapting to the contact configuration of the object to be grasped. However, variations in beam position and thickness lead to different behaviors, making it important to research the relationship between structure and force. Conventional research using FEM simulations has tested various virtual FinRay models but replicating phenomena such as buckling and slipping has been challenging. While hardware-based methods that involve installing sensors on the gripper and the object to analyze their states have been attempted, no studies have focused on the tangential contact force related to slipping. Therefore, we developed a 16-way object contact force measurement device incorporating two-axis force sensors into each of the 16 segmented objects and compared the normal and tangential components of the enveloping grasping force of the FinRay soft gripper under two types of contact friction conditions. In the first experiment, the proposed device was compared with a device containing a six-axis force sensor in one segmented object, confirming that the proposed device has no issues with measurement performance. In the second experiment, comparisons of the proposed device were made under various conditions: two contact friction states, three object contact positions, and two object motion states. The results demonstrated that the proposed device could decompose and analyze the grasping force into its normal and tangential components for each segmented object. Moreover, low friction conditions result in a wide contact area with lower tangential frictional force and a uniform normal pushing force, achieving effective enveloping grasping.

Comprehensive accuracy analysis for large closed-loop deployable structures based on matrix structure analysis and linear-complementarity-based contact analysis of spatial joint clearances

The surface accuracy of the deployable structure is crucial in determining the electromagnetic performance of the large satellite antenna. This paper proposes a comprehensive accuracy analysis framework for deployable structures considering clearances of spatial joints, geometric deviations, elastic deformations, external loads, and preloads, all of which can affect surface accuracy during the assembly process. Surface accuracy is calculated by combining the global equilibrium analysis of the deployable structure with the local equilibrium analysis of clearance-affected joints. First, a global elastostatic equilibrium analysis of the deployable structure is performed based on a unified mathematical formulation that describes the elasticity of beams and joints. Then, the local equilibrium analysis for the clearance-affected joints is transformed into a quadratic optimization problem through a linear-complementarity-based method. This method avoids the necessity for a combinatorial search for several traditional discontinuous contact configurations. Considering both global and local equilibrium in iterative analysis, the surface accuracy of the antenna is calculated. This integration avoids prior artificial assumptions about contact configurations of the joints. Finally, the proposed method is validated by comparing it with simulations and experimental results.

Role of various influencing parameters on high temperature fretting behaviour of different tribopairs in liquid lead

The increasing interest in liquid metal cooled nuclear reactors provides technical and scientific challenges such as the understanding, prevention, and prediction of the degradation of materials in liquid lead. Critical components include the fuel rods, heat exchanger tubes, and pump impellers. These functional elements are exposed to mechanical loading (up to 40 MPa), high temperatures (450–550 °C), and fluid-induced vibrations (up to 25 Hz). Under such conditions, fretting wear occurs between e.g., the spacer wire and the outer surface of the fuel or heat exchanger tubes. This work is aimed to establish a laboratory-scale fretting wear test setup and develop test methodology to enable systematic material characterisation in liquid metal environments. The results obtained by using the described methodology indicate that adhesive wear is the dominant degradation mechanism, and 316L stainless steel shows a higher coefficient of friction but a lower wear volume/tribolayer volume compared to 100Cr6 bearing steel. These results are in agreement with those reported in open literature and demonstrates the suitability of the presented method for conducting fretting tests and analysis for various materials and contact configurations in liquid lead environment.

Impact of Rh, Ru, and Pd Leads and Contact Topologies on Performance of WSe2 FETs: A First Comparative Ab Initio Study.

2D field-effect transistors (FETs) fabricated with transition metal dichalcogenide (TMD) materials are a potential replacement for the silicon-based CMOS. However, the lack of advancement in p-type contact is also a key factor hindering TMD-based CMOS applications. The less investigated path towards improving electrical characteristics based on contact geometries with low contact resistance (RC) has also been established. Moreover, finding contact metals to reduce the RC is indeed one of the significant challenges in achieving the above goal. Our research provides the first comparative analysis of the three contact configurations for a WSe2 monolayer with different noble metals (Rh, Ru, and Pd) by employing ab initio density functional theory (DFT) and non-equilibrium Green's function (NEGF) methods. From the perspective of the contact topologies, the RC and minimum subthreshold slope (SSMIN) of all the conventional edge contacts are outperformed by the novel non-van der Waals (vdW) sandwich contacts. These non-vdW sandwich contacts reveal that their RC values are below 50 Ω∙μm, attributed to the narrow Schottky barrier widths (SBWs) and low Schottky barrier heights (SBHs). Not only are the RC values dramatically reduced by such novel contacts, but the SSMIN values are lower than 68 mV/dec. The new proposal offers the lowest RC and SSMIN, irrespective of the contact metals. Further considering the metal leads, the WSe2/Rh FETs based on the non-vdW sandwich contacts show a meager RC value of 33 Ω∙μm and an exceptional SSMIN of 63 mV/dec. The two calculated results present the smallest-ever values reported in our study, indicating that the non-vdW sandwich contacts with Rh leads can attain the best-case scenario. In contrast, the symmetric convex edge contacts with Pd leads cause the worst-case degradation, yielding an RC value of 213 Ω∙μm and an SSMIN value of 95 mV/dec. While all the WSe2/Ru FETs exhibit medium performances, the minimal shift in the transfer curves is interestingly advantageous to the circuit operation. Conclusively, the low-RC performances and the desirable SSMIN values are a combination of the contact geometries and metal leads. This innovation, achieved through noble metal leads in conjunction with the novel contact configurations, paves the way for a TMD-based CMOS with ultra-low RC and rapid switching speeds.

V0405 Dra: A New Deep and Low Mass Ratio Contact Binary with Extremely Fast Decrease in the Orbital Period

V0405 Dra is a W UMa-type binary star. Based on the TESS data, we have conducted an orbital period study and performed a light curve analysis for the system. The orbital period study reveals that the O − C curve for V0405 Dra exhibits secular decrease at an extremely high rate of dP/dt = −2.71 × 10−6 day year−1, along with periodic variations characterized by an amplitude of A 3 = 0.0032 day and a period of P 3 = 1.413 years. The orbital periodic change is possibly due to the light-travel time effect resulting from an additional third body in the system, for which we estimate a minimum mass of M 3 = 0.77M ⊙. By employing the 2013 version of the Wilson-Devinney (W-D) method to synthesize a light curve, we derived photometric solutions indicating that V0405 Dra is a new deep (f = 68.7%) and low-mass ratio (q = 0.175) contact binary. The fast decrease in its orbital period is likely caused by mass transfer from the more massive primary star to the less massive secondary star, or due to angular momentum loss. With further mass transfer and loss of angular momentum, the binary will gradually evolve into a tighter contact configuration, eventually leading to a merger into a single star, following the evolutionary paths suggested for such deep and low mass ratio contact binaries.

Modal Derivatives for Efficient Vibration Prediction of Geometrically Nonlinear Structures with Friction Contact

This paper evaluates the performance of the Rubin reduction methods, enhanced with static modal derivatives, for vibration analysis of geometrically nonlinear structures with friction contact. Static modal derivatives are computed numerically based on Rubin reduction, which includes free interface normal modes and residual flexibility attachment modes, by introducing a finite displacement around these modes. Then, the most relevant static modal derivatives are selected using an improved strategy that incorporates weighting factors derived from both a nonlinear static analysis and a geometrically linear transient run. This enhanced Rubin method is also compared with the previously used enhanced Craig–Bampton method, which is based on fixed normal modes, constraint modes, and their static derivatives. The effectiveness of these methods is demonstrated through vibration analysis of a geometrically nonlinear beam in different contact configurations. Both methods proved their robustness, achieving accurate results with a relatively small number of modes in the reduced space, thus ensuring low online computation times. Furthermore, the analyses show the significant impact of using a geometrically nonlinear model on the accurate prediction of a contact state.

Nonlinear dynamics and onset of steady precession of a ring on a vertical rod.

We report on the unexpected precessional motion that occurs when a small, rigid ring is rotated on a vertical smooth rod. Using high-speed imaging, two distinct regimes of motion are observed experimentally. (i) Oscillatory motion when the ring has a single contact with the rod (transient motion). (ii) Steady state (terminal velocity) when the ring has two instantaneously stationary contacts with the rod. These two regimes and the transition between them are analyzed through qualitative, analytical, and numerical means. One key feature of the steady-state motion is energy dissipation through rolling resistance and air drag. Our model predicts that steady-state motion occurs only when certain geometric conditions (the ratio of the radii of a ring and a rod, and the tilt angle) are fulfilled. As the steady-state regime is often found to be the preferred final state, the dynamic stability of the single contact configuration is investigated through bifurcation, phase-space, and linear stability analyses. Our numerical simulation accounts for the stick-slip transition at the contact point, and is in good agreement with experimental data across all experiments. Our findings have potential applications in various engineering fields, such as studying the vibrational detachment of threaded fasteners and developing gravity-driven centrifuges.

Non-contact near-field cavity perturbation method for quantitative dielectric measurement and metallic defect inspection

Low dielectric constant (low-k) materials are essential in electronic industry aiming at new generation high-speed communications. Dielectric constant of these materials are measured by standard procedures and instruments with conventional contact configuration. Non-contact and in-situ techniques for low-k dielectric measurement are highly demanded in practice and worth of investigation. We hereby proposed a near-field microwave probe (NFMP) to accurately measure dielectric constant of low-k samples in a non-contact manner with a quantitative electromagnetic (EM) cavity perturbation theory. An NFMP set was designed, optimized by finite-element method (FEM) and fabricated with handy materials in the lab. Frequency response of the NFMP was tested experimentally and further used for subsequent frequency displacement analysis. Various low-k samples were tested by the non-contact NFMP set and dielectric constant were extracted based on the field perturbation theory. The relative error was obtained less than 0.5 % for low-k materials. The NFMP was then fixed on a micrometer stage and worked in a line-scan mode to inspect conductive defects in a low-k substrate. Both surface and subsurface defects were inspected by analyzing displaced central frequencies. The NFMP system is promising to facilitate quantitative and non-contact dielectric property measurement in electronics.

Freshwater and minerals recovery from synthetic produced water by membrane distillation/membrane crystallization processes

The purpose of this work is to study the influence of oil and surfactant present in produced water on the membrane distillation and membrane crystallization performance. The latter is evaluated in terms of permeate flux, quality of permeate and sodium chloride crystallization kinetics. Polypropylene and Hyflon AD40H/PVDF composite membranes with 0.2 μm\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\mathrm{\\mu m}$$\\end{document} pore size were used in the investigation. The tests were carried out in direct contact configuration using two synthetic feed solutions: the first one without oil and surfactant, and the second one with oil and surfactant. The achieved results showed a permeate flux reduction of 20 and 40% for PP and AD40H, respectively, in membrane distillation and of 35% in membrane crystallization. These results may be attributed to the interaction between the salts and surfactant, which led to the deterioration of the membrane performance. Despite this, high salt rejection factors greater than 99.9% and total carbon rejections ranging between 80 and 90% indicated the good potential of membrane distillation technology for the treatment of produced water. Moreover, good quality crystals and high total water recovery factor (97%) were achieved using the membrane crystallization process. Nevertheless, the presence of oil and surfactant in the feed caused an increase in the induction time compared to the system without oil and surfactant. In addition, in the performed experiments, simple physical cleaning with distillate water was sufficient to recover the initial trans-membrane flux of the membranes.

Testing of an organic metal halide perovskite for fast neutron detection

In this work, we synthesized and characterized the Methylhydrazinium Lead Trichloride MHyPbCl3(CH3NH2NH2PbCl3) perovskite as a fast neutron detector. The high hydrogen density of MHyPbCl3 enables efficient energy conversion from a fast neutron into a recoiled proton through the 1H(n,n)1H elastic scattering interaction, thereby, allowing for direct charge detection. Through IV characterization and X-Ray excitation, the crystal demonstrated a high resistivity at 4.43E11Ωcm and a good mobility-lifetime product (μτ) of 9.1E-3 cm2V, respectively, under C60/BCP/Cu and Au contact configuration to form an ohmic-ohmic detector. The crystal showed a good sensitivity to X-rays using an x-ray tube. The feasibility of the direct neutron conversion detector is demonstrated using the fast neutron beam at a Research Reactor. Waveforms from a charge-sensitive pre-amplifier showed distinct radiation-induced pulses from the MHyPbCl3 detector in response to the reactor neutron beam. Using a thermal neutron filter and gamma shielding in the beam, we showed that the pulses produced were more likely from neutron interactions, despite the Pb containing MHyPbCl3 is also sensitive to gamma-rays. With those fast neutron pulses, a post-pulse processing code was used to conduct pulse height analysis (PHA) and reconstruct an energy spectrum.

THE FIRST MULTICOLOUR PHOTOMETRY OF THE V840 LYR CONTACT BINARY STAR

Light curves for the total-eclipsing binary system V840 Lyr in the V, Rc, and Ic bands are presented; these display the O'Connell effect. Analysis was performed with the Phoebe031a software revealing that V840 Lyr is a W-type contact binary with a degree of contact factor of f = 15.1 ± 5.6%, a mass ratio of q = 0.4509 ± 0.0705, an inclination of i = 86.7°, and a temperature difference of ΔT = 45 K. An asymmetry in the light curves was modeled assuming a cool spot located on the secondary star. The period changes of the system are examined by combining our recently found times of light minima together with those in the literature. Absolute parameters were obtained as M1 = 0.74M⊙, M2 = 0.34M⊙, R1 = 0.74RM⊙, and R2 = 0.51RM⊙ from our photometric solutions, using some empirical relations. The long-term period increase and the contact configuration indicate that V840 Lyr will evolve into a fill-out overcontact binary.

Experimental Characterisation of BGBC OTFT for Indoor CO<sub>2</sub> Gas Sensing

Global warming is a concern nowadays due to excessive release of harmful gasses to the environment, leading to greenhouse effect phenomena worldwide. Based on the data provided by global pollution agencies, the release of greenhouse gasses to the atmosphere is the main cause of pollution and the increase in atmospheric temperature due to warming. Greenhouse gasses (GHGs) contents released to the environment is worrying, with carbon dioxide (CO2) is reported at the highest concentration compared to other gasses. There are many studies conducted to develop and evaluate the performance of harmful gas sensors incorporating inorganic and organic semiconductive materials. Organic semiconductors (OSCs) are environmentally friendly materials, relatively cheaper technology, and comprised of a wide range of materials with good carrier mobility. Therefore, in this work, Organic Thin Film Transistor (OTFT) is developed for gas sensor application. As global warming is becoming more serious, this solution is instead a sustainable solution to the environment, as organic molecules which are held together via Van der Waals bond are easily processed via low-temperature deposition and solution processing as compared to more complicated processes involved in conventional inorganic counterpart. In addition, the developed sensor is generally robust due to the ability to withstand high humidity conditions and can be fabricated on flexible substrates. In this work, suitable materials are identified in basic OTFT construction, which are the electrodes, dielectric and substrate. The scope is mainly focusing on the development of bottom gate OTFT construction, incorporating p-type active material which are Trisisopropylsilylethynyl Pentacene (TIPS Pentacene), Aluminium (Al) as drain and source electrodes, PEDOT: PSS as gate electrode and Polyvinyl alcohol (PVA) as gate dielectric. The materials in bottom gate bottom contact (BGBC) configuration, fabricated via screen printing technique is experimentally tested towards CO2 detection. CO2 is initially detected at 1618 ppm with contact resistance of 15 kΩ, and at 10 ml/minute flow rate, the developed configuration is demonstrated able to achieve sensitivity of 2.069 Ω/ppm. In conclusion, the studied BGBC OTFT has demonstrated suitability and applicability in CO2 gas sensing for sustainable environmental condition monitoring, that could lead to safer environment for the living things on earth. With the proposed dimensions, in the future it is possible to proceed with this work to be fabricated by using more advanced techniques such as photolithography and many others.

The generalized spring-loaded inverted pendulum model for analysis of various planar reduced-order models and for optimal robot leg design

This paper proposes a generalized spring-loaded inverted pendulum (G-SLIP) model to explore various popular reduced-order dynamic models’ characteristics and suggest a better robot leg design under specified performance indices. The G-SLIP model’s composition can be varied by changing the model’s parameters, such as ground contacting type and spring property. It can be transformed into four widely used models: the spring-loaded inverted pendulum (SLIP) model, the two-segment leg model, the SLIP with rolling foot model, and the rolling SLIP model. The effects of rolling contact and spring configuration on the dynamic behavior and fixed-point distribution of the G-SLIP model were analyzed, and the basins of attraction of the four described models were studied. By varying the parameters of the G-SLIP model, the dynamic behavior of the model can be optimized. Optimized for general locomotion running at various speeds, the model provided leg design guidelines. The leg was empirically fabricated and installed on the hexapod for experimental evaluation. The results indicated that the robot with a designed leg runs faster and is more power-efficient.