Henrik Staaf

Simulation of a Novel Bridge MEMS-PZT Energy Harvester for Tire Pressure System

Self-powering is becoming an important issue for autonomous sensor systems. By having an on-the-go power source the life span increases in comparison to a limited battery source. In this paper, simulation of an innovative design for a piezoelectric energy harvester for Tire Pressure Measurement System (TPMS) is presented. The MEMS-based thin-film PZT harvester structure is in the form of a bridge with a big central seismic mass and multiple electrodes. This design takes the advantage of the S-profile bending and a short beam length to concentrate the piezoelectric effect in a small segment along the beam and maximize the power output for a given displacement. From simulation in Comsol Multiphysics, the 9mm x 5mm bridge, seismic mass of 8.7mg and resonance frequency of 615Hz, generates 1 mu W by mechanical pulses excitation equivalent to driving at 60 km/h (roughly 180G).

Fabrication of High Temperature Thermoelectric Energy Harvesters for Wireless Sensors

Implementing energy harvesters and wireless sensors in jet engines could simplify development and decrease costs. A thermoelectric energy harvester could be placed in the cooling channels where the temperature is between 500–900°C. This paper covers the synthesis of suitable materials and the design and fabrication of a thermoelectric module. The material choices and other design variables were done from an analytic model by numerical analysis. The module was optimized for 600–800°C with the materials Ba8Ga16Ge30 and La-doped Yb14MnSb11, both having the highest measured zT value in this region. The design goal was to be able to maintain a temperature gradient of at least 200°C with high power output. The La-doped Yb14MnSb11 was synthesized and its structure confirmed by x-ray diffraction. Measurement of properties of this material was not possible due to insufficient size of the crystals. Ba8Ga16Ge30 was synthesized and resulted in an approximated zT value of 0.83 at 700°C. Calculations based on a module with 17 couples gave a power output of 1100mW/g or 600mW/cm2 with a temperature gradient of 200K.

Hierarchical cellulose- derived CNF/CNT composites for electrostatic energy storage

Today many applications require new effective approaches for energy delivery on demand. Supercapacitors are viewed as essential energy storage devices that can continuously provide quick energy. The performance of supercapacitors is mostly determined by electrode materials that can store energy via electrostatic charge accumulation. This study presents new sustainable cellulose-derived composite electrodes which consist of carbon nanofibrous (CNF) mats covered with vapor-grown carbon nanotubes (CNTs). The CNF/CNT electrodes have high electrical conductivity and surface area: the two most important features that are responsible for good electrochemical performance of supercapacitor electrodes. The results show that the composite electrodes have fairly high values of specific capacitance (101 F g(-1) at 5 mV s(-1)), energy and power density (10.28 W h kg(-1) and 1.99 kW kg(-1), respectively, at 1 A g(-1)) and can retain excellent performance over at least 2000 cycles (96.6% retention). These results indicate that sustainable cellulose-derived composites can be extensively used in the future as supercapacitor electrodes.

A Micromachined Coupled-Cantilever for Piezoelectric Energy Harvesters

This paper presents a demonstration of the feasibility of fabricating micro-cantilever harvesters with extended stress distribution and enhanced bandwidth by exploiting an M-shaped two-degrees-of-freedom design. The measured mechanical response of the fabricated device displays the predicted dual resonance peak behavior with the fundamental peak at the intended frequency. This design has the features of high energy conversion efficiency in a miniaturized environment where the available vibrational energy varies in frequency. It makes such a design suitable for future large volume production of integrated self powered sensors nodes for the Internet-of-Things.

Smart design piezoelectric energy harvester with self-Tuning

Piezoelectric energy harvesting on a gas turbine implies constraints like high temperature tolerance, size limitation and a particular range of vibrations to utilise. In order to be able to operate under these conditions a harvester needs to be space effective and efficient and to respond to the appropriate range of frequencies. We present the design, simulation and measurements for a clamped-clamped coupled piezoelectric harvester with a free-sliding weight, which adds self-Tuning for improved response within the range of vibrations from the gas turbine. We show a peak open circuit voltage of 11.7 V and a 3 dB bandwidth of 12 Hz.

Sustainable supercapacitor components from cellulose

Supercapacitors with superb electrochemical characteristics are very promising energy storage devices. At present, the production of various supercapacitor components is mostly dependent on unsustainable fossil resources. The preferential sustainable production of these components can be achieved with more extensive utilization of abundant renewable resources instead of fossils. In this study, cellulose-derived electrodes and separators were synthesized and electrochemically evaluated in a supercapacitor device. This device showed the following results: aerial capacitance of 64 μF cm-2, fast current-voltage response below 15s at current density of 2 A g-1 and capacitance retention of 97.9% after 2000 charge-discharge cycles.

Hierarchical cellulose-derived carbon nanocomposites for electrostatic energy storage

The problem of energy storage and its continuous delivery on demand needs new effective solutions. Supercapacitors are viewed as essential devices for solving this problem since they can quickly provide high power basically countless number of times. The performance of supercapacitors is mostly dependent on the properties of electrode materials used for electrostatic charge accumulation, i.e. energy storage. This study presents new sustainable cellulose-derived materials that can be used as electrodes for supercapacitors. Nanofibrous carbon nanofiber (CNF) mats were covered with vapor-grown carbon nanotubes (CNTs) in order to get composite CNF/CNT electrode material. The resulting composite material had significantly higher surface area and was much more conductive than pure CNF material. The performance of the CNF/CNT electrodes was evaluated by various analysis methods such as cyclic voltammetry, galvanostatic charge-discharge, electrochemical impedance spectroscopy and cyclic stability. The results showed that the cellulose-derived composite electrodes have fairly high values of specific capacitance and power density and can retain excellent performance over at least 2 000 cycles. Therefore it can be stated that sustainable cellulose-derived CNF/CNT composites are prospective materials for supercapacitor electrodes.