Buckled MEMS Beams for Energy Harvesting from Low Frequency Vibrations.

Vibration energy harvesters based on the resonance of the beam structure work effectively only when the operating frequency window of the beam resonance matches with the available vibration source. None of the resonating MEMS structures can operate with low frequency, low amplitude, and unpredictable ambient vibrations since the resonant frequency goes up very high as the structure gets smaller. Bistable buckled beam energy harvester is therefore developed for lowering the operating frequency window below 100Hz for the first time at the MEMS scale. This design does not rely on the resonance of the MEMS structure but operates with the large snapping motion of the beam at very low frequencies when input energy overcomes an energy threshold. A fully functional piezoelectric MEMS energy harvester is designed, monolithically fabricated, and tested. An electromechanical lumped parameter model is developed to analyze the nonlinear dynamics and to guide the design of the nonlinear oscillator based energy harvester. Multilayer beam structure with residual stress induced buckling is achieved through the progressive residual stress control of the deposition processes along the fabrication steps. Surface profile of the released device shows bistable buckling of 200µm which matches well with the amount of buckling designed. Dynamic testing demonstrates the energy harvester operates with 50% bandwidth under 70Hz at 0.5g input, operating conditions that have not been demonstrated by MEMS vibration energy harvesters before.

Energy Harvesting Combat Boot for Satellite Positioning.

Most portable electronic devices are power-limited by battery capacity, and recharging these batteries often interrupts the user's experience with the device. The product presented in this paper provides an alternative to powering portables by converting regular human walking motion to electricity. The device harvests electric power using air bulbs, distributed in the sole of a shoe to drive a series of micro-turbines connected to small DC motors. The number and position of air bulbs is optimized to harvest the maximum airflow from each foot-strike. The system is designed to continuously drive the micro-turbines by utilizing both outflow and inflow from the air bulbs. A prototype combat boot was fitted on the right foot of a 75 kg test subject, and produced an average continuous power on the order of 10 s of mW over a 22 Ω load during walking at 3.0 mph. This combat boot provides enough electric power to a passive GPS tracker that periodically relays geographical coordinates to a smartphone via satellite without battery replacement.

Extremely Elastic Wearable Carbon Nanotube Fiber Strain Sensor for Monitoring of Human Motion.

The increasing demand for wearable electronic devices has made the development of highly elastic strain sensors that can monitor various physical parameters an essential factor for realizing next generation electronics. Here, we report an ultrahigh stretchable and wearable device fabricated from dry-spun carbon nanotube (CNT) fibers. Stretching the highly oriented CNT fibers grown on a flexible substrate (Ecoflex) induces a constant decrease in the conductive pathways and contact areas between nanotubes depending on the stretching distance; this enables CNT fibers to behave as highly sensitive strain sensors. Owing to its unique structure and mechanism, this device can be stretched by over 900% while retaining high sensitivity, responsiveness, and durability. Furthermore, the device with biaxially oriented CNT fiber arrays shows independent cross-sensitivity, which facilitates simultaneous measurement of strains along multiple axes. We demonstrated potential applications of the proposed device, such as strain gauge, single and multiaxial detecting motion sensors. These devices can be incorporated into various motion detecting systems where their applications are limited to their strain.

[Closed suction drainage or non-drainage for total knee arthroplasty: a meta-analysis].

OBJECTIVES: To investigate the different effects of closed suction drainage and non-drainage for total knee arthroplasty(TKA) and to provide reference information for the choice of clinical treatment. METHODS: Randomized controlled trials (RCTs) of closed suction drainage versus non-drainage for TKA were collected from the Cochrane Library, PubMed, EMBase, Springer, CBM, CNKI, VIP and WANFANG database. Methodological quality of the RCTs was independently assessed using the Consolidated Standards of Reporting Trials (CONSORT) checklist. Data analysis was performed by RevMan Version 5.1.6 based on the methods recommended by the Cochrane Collaboration. RESULTS: Twenty-one RCTs without bias were finally enrolled, and 1920 enrolled knees were identified into drainage group (979 knees) and non-drainage group (941 knees). A lower incidence of soft tissue ecchymosis was demonstrated in the closed suction drainage group (OR = 0.30, 95%CI: 0.24 - 0.49); however, compared with the non-drainage group, more loss of blood (MD = 320.03, 95%CI: 235.31 - 404.76) and more need of homologous blood transfusion (OR = 1.83, 95%CI: 1.26 - 3.29) were found in the closed suction drainage group. In addition, there were no significant differences of postoperative infection (OR = 0.53, 95%CI: 0.22 - 1.32), deep venous thrombosis (OR = 1.00, 95%CI: 0.46 - 2.18), and the joint range of motion (MD = -0.04, 95%CI: -1.11 - 1.02) between the two groups. CONCLUSION: Based on the current evidence, no obvious advantage is demonstrated for closed suction drainage, in comparison with non-drainage for TKA.