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Nature offers bionic inspirations for elegant applications of mechanical principles such as the concept of snap buckling, which occurs in several plants. Exploiting mechanical instabilities is the key to fast movement here. We use the snap-through and snap-back instability observed in natural rubber balloons to design an ultrafast purely mechanical elastomer actuator. Our design eliminates the need in potentially harmful stimulants, high voltages, and is safe in operation. We trigger the instability and thus the actuation by temperature changes, which bring about a liquid/gas phase transition in a suitable volatile fluid. This allows for large deformations up to 300% area expansion within response times of a few milliseconds. A few degree temperature change, readily provided by the warmth of a human hand, is sufficient to reliably trigger the actuation. Experiments are compared with the appropriate theory for a model actuator system; this provides design rules, sensitivity, and operational limitations, paving the way for applications ranging from object sorting to intimate human-machine interaction.

The study investigated farmer’s willingness to pay for getting quality fertilizers by employing probit and ordered probit models as the quality of fertilizers were often adulterated in Bangladesh. Primary data collected from 300 farm households were utilized. Results indicated that an average farmer’s willingness to pay was influenced significantly by the farm size group, annual income, off-farm income, product prices and financial constraints. All farmers except marginal farmers were more likely to be willing to pay more than market prices for urea and MoP. The findings suggested for adjusting the farm size group specific subsidy policies. More off-farm employment opportunities could be created in the farming regions to strengthen farmer’s financial capability.

Rural households in Bangladesh are now diversifying from full-time agriculture to part-time agriculture where they are engaging in different non-farm activities along with farming. This study intends to identify the determinants to diversify in each livelihood strategy individually and their effects on poverty. A total sample of 153 households from three districts of Bangladesh was selected through purposive sampling technique. Multinomial logistic regression and multidimensional poverty index were used for the likelihood of adopting one of the five probable activity portfolios and their poverty measurement, respectively. The results reveal that age and farming experience of the household head, and total land cultivated by a household play a significant negative role in diversifying into any activities in non-farm sector. Higher education boosts the possibility to participate in wage-employment based strategy. In addition to active male labor, better infrastructural facilities enhance the probability of engaging in wage and self-employment based non-farm activities. Moreover, access to non-farm activities especially self-employment and international migration are determined by credit receptiveness. Generally, shifting from full-time agriculture to partly non-farm sector is more welfare generating strategies (by reducing poverty) for rural households in Bangladesh. Therefore, policy should be directed to facilitate strategy-based rural non-farm activities and enhance balanced economic growth of the country.

Conventional refrigeration relies on hazardous agents, contributing to global warming. Soft, cheap, biodegradable solid-state elastocaloric cooling based on natural rubber offers an environmentally friendly alternative. However, no such practical cooler has been developed, as conventional soft elastocaloric designs are not fast enough to ensure adiabaticity. Here, we combine snap-through instability with strain-induced crystallization and achieve a sub-100 ms quasi-adiabatic cycling, which is 30 times faster than previous designs. Negligible heat exchange in expansion/contraction stages combined with the latent heat of phase transitions results in a giant elastocaloric crystallization effect. The rubber-based all-soft heat pump enables a specific cooling power of 20.9 W g–1, a heat flux of 256 mW cm–2, a coefficient of performance of 4.7 and a single-stage temperature span between hot and cold reservoirs of 7.9 K (full adiabatic temperature change of rubber membrane exceeding 23 K). The pump permits a compact all-soft voltage-actuated set-up, opening up the opportunity of a viable plug-in-ready cooling device. Solid-state caloric cooling is a promising alternative to vapour compression, yet only a few prototypes have been shown. Greibich et al. now report an elastocaloric cooling device based on natural rubber with a cooling power of over 20 W g–1 that exploits snap-through instability and strain-induced crystallization.

Embedded sensors are key to optimizing processes and products; they collect data that allow time, energy, and materials to be saved, thereby reducing costs. After production, they remain in place and are used to monitor the long-term structural health of buildings or aircraft. Fueled by climate change, sustainable construction materials such as wood and fiber composites are gaining importance. Current sensors are not optimized for use with these materials and often act as defects that cause catastrophic failures. Here, flexible, highly permeable, and imperceptible sensors (iSens) are introduced that integrate seamlessly into a component. Their porous substrates are readily infused with adhesives and withstand harsh conditions. In situ resistive temperature measurements and capacitive sensing allows monitoring of adhesives curing as used in wooden structures and fiber composites. The devices also act as heating elements to reduce the hardening time of the glue. Results are analyzed using numerical simulations and theoretical analysis. The suggested iSens technology is widely applicable and represents a step towards realizing the Internet of Things for construction materials.

Diverse set of income generating activities may have varying effect on household’s welfare situation. This study intends to assess the extent of different income diversification strategies on rural household welfare. A total sample of 153 households from three districts of Bangladesh was randomly selected. Considering simultaneous causality between different livelihood strategies and welfare indicators, the Two Stage Least Square (2SLS) methods with instrumental variable was applied to estimate impact of the strategies on household welfare. Household per capita expenditure was treated as the welfare indicator which includes both food and non-food expenditures. The findings show that involving in any type of non-farm activities jointly with farming has a significantly positive effect on the household’s welfare. Among different non-farm activities, participation in wage employment and migration along with agricultural activities ensured significantly higher per capita household expenditure. On the other hand, the impact of currently participation in only agricultural activities on household expenditure is insignificant. Besides, Farm size, higher education and infrastructural facilities also play an important role in improving household’s welfare. Therefore, policy should be directed to create opportunities to participate in non-farm activities through establishment of small and medium industries, especially agro-based industries in the rural areas. J. Bangladesh Agril. Univ. 17(1): 73–79, March 2019

The dataset explicates farmer׳s perceptions about fertilizer subsidy policy in Bangladesh and the factors that affect farm level fertilizer usage. Primary data were collected from 300 farm households from three regions of the country belonging to four farm size groups i.e., marginal, small, medium and large. Dataset reveals that a major part of sampled marginal farmers was unaware that government is providing huge subsidy on the fertilizer market. Most of the marginal farmers were dissatisfied claiming the uneven distribution of subsidy benefit whereas majority of large farmers were satisfied with current policy and market prices. At the same time, output prices relative to fertilizer price received by the farmers, off-farm income and extension services were significantly affecting fertilizer use intensity of different farm size groups while subsidy policy impact was not significant.

Soft materials that exhibit electromechanical coupling are an important element in the development of soft robotics, flexible and stretchable electronics, energy harvesters, sensor and actuators. Truly soft natural piezoelectrics essentially do not exist and typical dielectric elastomers, predicated on electrostriction and the Maxwell stress effect, exhibit only a one-way electromechanical coupling. Extensive research however has shown that soft electrets i.e. materials with embedded immobile charges and dipoles, can be artificially engineered to exhibit a rather large piezoelectric-like effect. Unfortunately, this piezoelectric effect—large as it may be—is primarily restricted to an electromechanical coupling in the longitudinal direction or what is referred colloquially as the d33 piezoelectric coefficient. In sharp contrast, the transverse piezoelectric property (the so-called d31 coefficient) is rather small. This distinction has profound implications since these soft electrets exhibit negligible electromechanical coupling under bending deformation. As a result, the typically engineered soft electrets are rendered substantively ill-suited for energy harvesting as well as actuation/sensing of flexure motion that plays a critical role in applications like soft robotics. In this work, we analyze nonlinear bending deformation of a soft electret structure and examine the precise conditions that may lead to a strong emergent piezoelectric response under bending. Furthermore, we show that non-uniformly distributed dipoles and charges in the soft electrets lead to an apparent electromechanical response that may be ambiguously and interchangeably interpreted as either transverse piezoelectricity or flexoelectricity. We suggest pragmatic routes to engineer a large transverse piezoelectric (d31) and flexoelectric coefficient in soft electrets. Finally, we show that in an appropriately designed soft electret, even a uniform external electric field can induce curvature in the structure thus enabling its application as a bending actuator.

Hydrogen-bonding (H-bonding) is a relatively strong, highly directional, and specific noncovalent interaction present in many organic molecules, and notably is responsible for supramolecular ordering in biological systems. The H-bonding interactions play a role in many organic electrically conducting materials - in particular in those related to biology, e.g. melanin and indigo. This article aims to highlight recent work on application of nature-inspired H-bonded organic molecules in organic electronic devices. Three topics are covered in this brief review: (1) electrical and ionic conduction in natural H-bonded systems, (2) semiconducting properties of H-bonded organic pigments, and (3) exploitation of H-bonding for supramolecular assembly of organic conductors. H-bonding interactions are ubiquitous in biology, thus making the study of H-bonded organic semiconductors highly pertinent where interfacing of electronics with biological systems is desired.

Over the last few decades, Bangladesh has experienced significant structural changes within the agricultural sector. This research estimates the current and forecasts the future changes of farm size and labor occupational mobility over time and across the region. A panel dataset, which is used in this study, was collected in the three different years (1988, 2000 and 2008) from 62 villages across 57 districts. Stationary Markov chain approach was used in this analysis to estimate structural change. The results of this study imply that the agricultural sector is dominated by small farms in past, present and also in the future. The forecasting predicts that the numbers of marginal, medium and large farms are going to decrease in future. Moreover, it indicates that the average farm size of small landholders will slightly increase as the numbers of marginal and large landowners reduces. The analyses of the transition probabilities of labor occupational change show that rural households are gradually shifting to non-farm activities and mostly part-time farming from other income generating activities over time. In general, the forecast also suggests narrowing of agricultural activities and expansion of part-time farming and non-farm activities in future.

In his Discorsi, Galileo aimed to correct centuries of Aristotelian “unreason” concerning the physics of falling objects by introducing a thought experiment that pointed out contradictions when combinations of one light and one heavy body are dropped. Inspired by Galileo's story, we sought to formulate research questions and design experiments for students to enable independent learning based on the history of science. The experiments involve commonly used or inexpensive equipment and free software, and show that Aristotle and Galileo did not disagree about falling objects, but were focusing on different kinds of motion. We assess data generated by high-speed video motion tracking of the fall of various combinations of simple handmade paper cones, following closely the discussion between Simplicio, Salviati and Sagredo in the Discorsi, and demonstrate that every statement in Galileo's reductio ad absurdum holds true and that his argument is in fact free of contradiction.

The study has been conducted to assess the micro level impact of fertilizer subsidy on farming efficiency given the heterogeneous farm structures and universal subsidy policy in Bangladesh. The research utilizes primary data, which were collected through personal interview of 300 farm households located in three districts from northern part of Bangladesh. Multistage purposive sampling was followed for selecting the sampling units based on concentration of rice farming. Data Envelopment Analysis (DEA) reveals that the farms are inefficient in combining inputs in a cost minimizing way, although they are technically more efficient. Results from Tobit models for different farm size groups prove that fertilizer subsidy has significant impact on improving farming efficiencies for marginal and small farms in study areas while leaving insignificant impact for medium and large farms. Further increases in fertilizer subsidy will bring significant productivity increases for these smallholder farmers. Therefore, policy interventions should favor these farms for acceleration of agricultural growth.

In this paper, we describe the design, fabrication and functional principle of microfluidic diodes – devices for directional liquid transport. They are passive (i.e., need no external energy input) and are capable of unidirectional water transport even vertically against gravity, i.e. they prevent backflow of liquid. In designing the devices with an area of several cm2, we used a capillary channel network that was bio-inspired by the skin of the Texas horned lizard (Phrynosoma cornutum). By means of a CO2 laser, we engraved the microfluidic structures into plates made of poly(methyl methacrylate) (PMMA), a low-cost technical polymer commonly used in disposable microfluidics. We then characterized the topography of the fabricated 3D structures by optical coherence tomography (OCT). Theoretical analysis of the OCT data enabled us to determine their working principle which differs from that presented previously in the literature. We accessed the fluid transport properties of the device by measuring distance, velocity, wetted area and flow asymmetry. Biomimetic abstraction led to a simplified structure which was validated experimentally. All tested devices allowed unidirectional liquid transport at velocities in the range of a few mm/s in the forward direction while preventing backflow of volumes of about 0.5 ml in the backward direction on an area of approximately 28 mm x 14 mm. The transport velocity of about 1 mm/s was found to be nearly constant for a distance of approximately 2 cm, beyond which it decreased. The application spectrum ranges from biomedical microfluidics, lab-on-a-chip and micro-analysis devices to filtration, lubrication, cooling of electronics and e-ink displays.

We present a device for passive unidirectional liquid transport. The capillary channels used are bioinspired by the shape of the spermathecae (receptaculum seminis) of rabbit fleas (Spilopsyllus cuniculi) and rat fleas (Xenopsylla cheopis). The spermatheca is an organ of female fleas that stores sperm until suitable conditions to lay eggs are found. We translated and multiplied the natural form and function of a spermatheca to create a continuous capillary system from which we designed our microfluidic device based directly on the model from nature. Applying the Young-Laplace equation, we derived a theoretical description of local liquid transport, which enables model-guided design. We arranged the bioinspired capillaries in parallel and engraved them in poly(methyl methacrylate) (PMMA) plates by CO2 laser ablation. The fabricated structures transport soapy water passively (i.e., without external energy input) in the forward direction at velocities of about 1 mm·s−1 while halting the liquid fronts completely in the backward direction. The bioinspired capillary channels are capable of unidirectional liquid transport against gravity. Distance and velocity measurements prove the feasibility of the concept. Unidirectional passive liquid transport might be advantageous in technical surfaces for liquid management, for instance, in biomedical microfluidics, lab-on-chip, lubrication, electronics cooling and in micro-analysis devices.

A dielectric elastomer transducer is a deformable capacitor, and is under development as a sensor, actuator, or generator. Among various geometric configurations, laterally-constrained transducer, also known as pure-shear transducer, is easy to implement and effective to couple mechanical force and electrical voltage. This analytical study reveals that lateral pre-stretch enhances actuation, far exceeding previously reported actuation strokes. Laterally-constrained transducers exhibit complex electromechanical behavior. As voltage increases, an actuator may undergo electromechanical instability, or form wrinkles, or suffer electrical breakdown. We survey the behavior of actuators under all possible states of pre-stretches, and identify five modes of actuation. Our analysis predicts that laterally-constrained actuators can achieve actuation stroke of 1000% for an acrylic elastomer, and 230% for natural rubber. This analysis opens the door to design actuators of simple geometry capable of a very large range of electromechanical actuation.

Biodegradable and biocompatible elastic materials for soft robotics, tissue engineering or stretchable electronics with good mechanical properties, tunability, modifiability or healing properties drive technological advance, and yet they are not durable under ambient conditions and do not combine all the attributes in a single platform. We have developed a versatile gelatin-based biogel, which is highly resilient with outstanding elastic characteristics, yet degrades fully when disposed. It self-adheres, is rapidly healable and derived entirely from natural and food-safe constituents. We merge all the favourable attributes in one material that is easy to reproduce and scalable, and has a low-cost production under ambient conditions. This biogel is a step towards durable, life-like soft robotic and electronic systems that are sustainable and closely mimic their natural antetypes.

Smallholder farmers in Bangladesh face many difficulties. A trend towards fish farming has opened new opportunities in recent years. This research focuses on the concern, whether smallholders could improve their gross margins by improving the allocation of the available physical and non-physical resources. Combinations of the participatory, qualitative and quantitative methods were used for primary data collection. A linear programming based modelling approach shows that farmers can increase the farm gross margin by reallocating the land in the model solution. Essential requirements, e.g. determined by household consumption requirements, determine parts of the resource allocation. The remaining land is in tendency allocated to fish farming; where one specific fish farming alternative is dominant to others. In the scenario analysis, all farming groups keep the same proportion of land use pattern until a certain level of price change, beyond that crop farming is selected. Scenarios modifying the available fish feed show the significant sensitivity of this resource on the land allocation.

The volume of literature recognizing the importance of rural credit in developing countries has grown significantly in recent years. However, previous studies have mainly assumed that credit has a homogeneous impact on recipients. This paper contributes to the literature by further examining the impacts of credit on different groups of accessed households categorized by relative poverty, loan volumes, access to agricultural extension services and ethnicity in Vietnam. This paper uses data of 1338 households collected from the Vietnam Access Resources Household Survey in 2012. To increase the reliability of estimation measures, the distribution for the impact estimator is further constructed by applying the bootstrapping approach to the Propensity Score Matching. Results show that credit access affects recipient groups heterogeneously. Although there is strong evidence of positive impacts on non-farm income, credit has no effect on farm income, even for recipients with more annual visits to agricultural extension. While credit significantly increases total income, per capita income, and nonfarm income of the Kinh majority, it has little to no impact on those income components of ethnic minorities. Credit tends to have significantly positive impacts on household income of the better-off, the richest and those receiving larger credit volumes. Results imply that households with favorable economic conditions tend to benefit from accessing rural credit.

Engineered wood, a high-tech material of the 21st century demonstrates the revival of timber for the construction of green urban eco-buildings. However, the testing of wood-based materials is still based on destructive methods known for centuries. In-situ monitoring of curing, cross-linking, and aging is essential for the optimisation of glues, resins and coatings. For press moulding, impedance spectroscopy is the only practical way for in-line detection of the crosslinking. Flat sensors that can be integrated into glue joints are known, but the substrate material of these sensors weakens the glue joint as they do not interact with the commonly used wood glues. Sensors printed on porous paper and wood can solve this problem. We show that although almost every tested paper is printable but not all of them are suitable for the detection of cross-linking analysis, since paper additives can catalyse or inhibit the cross-linking of glues or resins. Printed impedance sensors on pH-neutral porous papers allow an unaltered in-situ analysis of the cross-linking in complex glue joints. The porous papers allow the glue or resin to penetrate the paper and bridge it. Integrated sensors can provide valuable information about the state (aging, moisture) of bonding throughout the life cycle of the engineered wood. With the help of paper-based sensors, wood can be equipped integratively, network-compatible and communicative. Damage in the glue joints can be detected on time. With this innovative sensor technology, wood is not only an ingenious material, but also an intelligent one.

Powering soft embodiments of robots, machines and electronics is a key issue that impacts emerging human friendly forms of technologies. Batteries as energy source enable their untethered operation at high power density but must be rendered elastic to fully comply with (soft) robots and human beings. Current intrinsically stretchable batteries typically show decreased performance when deformed due to design limitations, mainly imposed by the separator material. High quality stretchable separators such as gel electrolytes represent a key component of soft batteries that affects power, internal resistance, and capacity independently of battery chemistry. Here, polymerized high internal phase emulsions (polyHIPEs) are introduced as highly ionically conductive separators in stretchable (rechargeable) batteries. Highly porous (>80%) separators result in electrolyte to polyHIPE conductivity ratios of below 2, while maintaining stretchability of 50% strain. The high stretchability, tunable porosity, and fast ion transport enable stretchable batteries with internal resistance below 3 and 16.8 mAh cm2 capacity that power onskin processing and communication electronics. The battery/separator architecture is universally applicable to boost battery performance and represents a step towards autonomous operation of conformable electronic skins for healthcare, robotics, and consumers. (VLID)4919304 Version of record

Soft materials that exhibit electromechanical coupling are an important element in the development of soft robotics, flexible and stretchable electronics, energy harvesters, sensor and actuators. Truly soft natural piezoelectrics essentially do not exist and typical dielectric elastomers, predicated on electrostriction and the Maxwell stress effect, exhibit only a one-way electromechanical coupling. Extensive research however has shown that soft electrets i.e. materials with embedded immobile charges and dipoles, can be artificially engineered to exhibit a rather large piezoelectric-like effect. Unfortunately, this piezoelectric effect-large as it may be-is primarily restricted to an electromechanical coupling in the longitudinal direction or what is referred colloquially as the d33 piezoelectric coefficient. In sharp contrast, the transverse piezoelectric property (the so-called d31 coefficient) is rather small. This distinction has profound implications since these soft electrets exhibit negligible electromechanical coupling under bending deformation. As a result, the typically engineered soft electrets are rendered substantively ill-suited for energy harvesting as well as actuation/sensing of flexure motion that plays a critical role in applications like soft robotics. In this work, we analyze nonlinear bending deformation of a soft electret structure and examine the precise conditions that may lead to a strong emergent piezoelectric response under bending. Furthermore, we show that non-uniformly distributed dipoles and charges in the soft electrets lead to an apparent electromechanical response that may be ambiguously and interchangeably interpreted as either transverse piezoelectricity or flexoelectricity. We suggest pragmatic routes to engineer a large transverse piezoelectric (d31) and flexoelectric coefficient in soft electrets. Finally, we show that in an appropriately designed soft electret, even a uniform external electric field can induce curvature in the structure thus enabling its application as a bending actuator.

Rainwater harvesting (RWH) has been practiced and promoted to address the temporal and spatial variability of rainfall, thereby enhancing agriculture production in rainfed systems. The practices could also address the problem of land degradation. However, there is limited practice of approaching RWH from the perspective of managing both the water and land resources. Research on water productivity and impact for poverty reduction mainly focused on irrigated agriculture while it is potential to provide the water needed to produce food for rapidly growing population is the subject of intense debate these days. An important option is to upgrade rainfed agriculture through better land and water management that improves soil moisture conservation and rainwater harvesting that provides supplementary irrigation. In the meantime, studies on impact of agricultural water management focused more on unidimensional poverty while poverty is multidimensional. This study investigates the impact of integrated RWH practices (IRWHPs) on multidimensional poverty in Ethiopia. Results show that the use of IRWHPs has a significant negative impact on the probability that a household is multidimensionally poor. This study suggests that policies that enhance the promotion of IRWHPs would be central for the sustainable intensification of smallholder agriculture that simultaneously alleviate poverty and enhance resource sustainability.

This study uses the Propensity Score Matching to examine the income impact of different credit sources on accessed households in the Northern Mountains of Vietnam. Results show that overall rural credit serves an important role in improving household income with respect to total income, per capita income and nonfarm income. However, different credit affects recipients heterogeneously. Whereas a significant increase in household income can be achieved through accessing commercial and informal loans, there is no significant increase of all income components associated recipients of preferential credit. These results imply that a successful credit scheme needs to consider variations in transaction costs, disbursement scheme, loan characteristics and typical socio-economic conditions of credit recipients.

Large-bandwidth, low-operation-voltage, and uniform organic amplifiers are fabricated on ultrathin foils. By the integration of short-channel OTFTs and AlOx capacitors, organic amplifiers with a bandwidth of 25 kHz are realized, demonstrating the highest gain-bandwidth product (GBWP) reported to date. Owing to material and process advancements, closed-loop architectures operate at frequencies of several kilohertz with an area smaller than 30 mm(2) .

Some influential variables that are import to farmers in Northern Bangladesh regarding land use decisions for farmlands, where such options are possible, were explored in this study. A multi-stage sampling procedure was followed to select the study area and the sampling unit. We selected four sub-districts in Mymensingh district, a suitable area in Bangladesh for freshwater fish farming: Mucktagachha, Trishal, Phulpur, and Bhaluka. The PROMETHEE (Preference Ranking Organization Method for Enrichment Evaluations) method was used to remove the problem of simultaneously selecting all criteria for land use decision-making, hence revealing the effects of some important variables on decisions on land use made by farmers. PROMETHEE model gave equal preference to rice over fish farming after all criteria were considered simultaneously. Although fish farming total return was about 6 times higher than rice farming, farmers were more interested in rice farming because of three major influential criteria: it requires less labor, operates at lower costs, and has zero conversion cost associated with rice farming.

The anodization behaviour of Hf/Al stacked thin films, sequentially deposited from vapour phase without breaking vacuum, was investigated using scanning droplet cell microscopy. Surface microstructure and crystallographic analysis revealed the formation of highly textured and compact hexagonal Hf films for thicknesses above 7.5 nm. Cyclic voltammetry suggested the formation of discrete anodic layers starting with pure HfO 2 on the surface, a mixture of HfO 2 and Al 2 O 3 as an intermediate layer and pure Al 2 O 3 in depth of the films. Coulometric investigations revealed oxide formation factors of 2.2 nm V −1 for HfO 2 while for pure Al 2 O 3 a maximum of 1.4 nm V −1 was measured. Electrochemical impedance spectroscopy performed for various Hf thicknesses and different final anodization potentials revealed almost ideal dielectrics formed from mixed HfO 2 /Al 2 O 3 , permittivities up to 26 being measured for the anodized Hf/Al films. Surface analytical investigations and depth profiling as well as high resolution transmission electron microscopy confirmed the discrete anodic layer growth and the mixing of both anodic oxides. The significant thickness values found for the mixed oxide layer must redefine the general expectations for the use of anodized superimposed layers in various applications.

Low density energy sources, like wind and solar energy, are widely available and they are increasingly used for electricity conversion worldwide. Ambient energy sources with even lower energy densities are universally available and could equally be converted into electricity with large scale special purpose converter systems. This work discusses a simple concept for an electret-based electrostatic converter suitable for large scale conversion of ambient low density energy sources. The converter is a capacitive charge pump capable of working at low frequencies ( ≤ 1 Hz ) with a very low mechanical input energy and a high conversion efficiency. With a charged electret-like elastomer membrane the converter can operate without an initial bias voltage supply. First tests with a simple proof-of-concept demonstrator resulted in a mechanical input energy of 332 μJ (9.1 μJ/cm 2 ) and a converted electrical output energy of 206 μJ (5.7 μJ/cm 2 ) per conversion cycle. This gives a total conversion efficiency of 63%.

Polymeric semiconductors have been prepared whose molecular properties make them stretchable and healable — a milestone in the development of sophisticated organic electronic surfaces that mimic human skin. See Letter p.411 There is great interest and potential in the development of skin-inspired flexible and wearable electronic devices. Such devices require materials that twist, fold and bend with no loss in electronic—or material—properties. Zhenan Bao and colleagues report a conjugated polymer that also incorporates non-covalent interactions between adjacent chains, enabling the material to accommodate up to 100% strain whilst maintaining high charge-carrier mobility. In this proof-of-principle study the authors use the polymers to fabricate flexible and stretchable organic transistors that combine robustness with good electronic properties.