John Tudor

Optimization of an Electromagnetic Energy Harvesting Device

This paper presents the modeling and optimization of an electromagnetic-based generator for generating power from ambient vibrations. Basic equations describing such generators are presented and the conditions for maximum power generation are described. Two-centimeter scale prototype generators, which consist of magnets suspended on a beam vibrating relative to a coil, have been built and tested. The measured power and modeled results are compared. It is shown that the experimental results confirm the optimization theory

Vibration based electromagnetic micropower generator on silicon

This paper discusses the theory, design and simulation of electromagnetic micropower generators with electroplated micromagnets. The power generators are fabricated using standard microelectromechanical system processing techniques. Electromagnetic two-dimensional finite element anlysis simulations are used to determine voltage and power that can be generated from different designs. This paper reports a maximum voltage and power of 55 mV and 70 W for the first design, incorporating microfabricated two-layer Cu coils on a Si paddle vibrating between two sets of oppositely polarized electroplated Co50Pt50 face centered tetragonal phase hard magnets. A peak voltage and power of 950 mV and 85 W are obtained for the second design, which includes electroplated Ni45Fe55 as a soft magnetic layer underneath the hard magnets. The volume of the device is about 30 mm3.

Inkjet-Printed Microstrip Patch Antennas Realized on Textile for Wearable Applications

This letter introduces a new technique of inkjet printing antennas on textiles. A screen-printed interface layer was used to reduce the surface roughness of the polyester/cotton material that facilitated the printing of a continuous conducting surface. Conducting ink was used to create three inkjet-printed microstrip patch antennas. An efficiency of 53% was achieved for a fully flexible antenna with two layers of ink. Measurements of the antennas bent around a polystyrene cylinder indicated that a second layer of ink improved the robustness to bending.

Waterproof and durable screen printed silver conductive tracks on textiles

Conductive textiles are fabrics that include conductive yarns woven into or conductive tracks printed on to the textiles. Conductive textiles have attracted significant attention, since they are fundamental for the integration of electronic functions to achieve wearable devices. Screen printing is a well-established and cost-effective fabrication method; it enables a versatile layout of conductive tracks. The limitation of the current screen-printed conductive textiles is low durability to weathering, abrasion and washing. This paper presents a process for producing a waterproof and durable conductive textile using only screen printing. A three functional layer design was used to fabricate the durable conductive tracks. Firstly, an interface layer was printed to provide a smooth surface for subsequent printing, under-side protection and electrical insulation. Next, a silver layer provided the conductive track and finally an encapsulation layer was printed on top to provide upper-side protection and electrical insulation. The printed silver tracks achieved maximum conductivity using a single print. The conductivity of the silver tracks returned to its original value when they were dried after soaking in water continuously for 24 hours.

Vibration energy harvesting using the Halbach array

This paper studies the feasibility of vibration energy harvesting using a Halbach array. A Halbach array is a specific arrangement of permanent magnets that concentrates the magnetic field on one side of the array while cancelling the field to almost zero on the other side. This arrangement can improve electromagnetic coupling in a limited space. The Halbach array offers an advantage over conventional layouts of magnets in terms of its concentrated magnetic field and low-profile structure, which helps improve the output power of electromagnetic energy harvesters while minimizing their size. Another benefit of the Halbach array is that due to the existence of an almost-zero magnetic field zone, electronic components can be placed close to the energy harvester without any chance of interference, which can potentially reduce the overall size of a self-powered device. The first reported example of a low-profile, planar electromagnetic vibration energy harvester utilizing a Halbach array was built and tested. Results were compared to ones for energy harvesters with conventional magnet layouts. By comparison, it is concluded that although energy harvesters with a Halbach array can have higher magnetic field density, a higher output power requires careful design in order to achieve the maximum magnetic flux gradient.

Screen printing of a capacitive cantilever-based motion sensor on fabric using a novel sacrificial layer process for smart fabric applications

Free-standing cantilevers have been fabricated by screen printing sacrificial and structural layers onto a standard polyester cotton fabric. By printing additional conductive layers, a complete capacitive motion sensor on fabric using only screen printing has been fabricated. This type of free-standing structure cannot currently be fabricated using conventional fabric manufacturing processes. In addition, compared to conventional smart fabric fabrication processes (e.g. weaving and knitting), screen printing offers the advantages of geometric design flexibility and the ability to simultaneously print multiple devices of the same or different designs. Furthermore, a range of active inks exists from the printed electronics industry which can potentially be applied to create many types of smart fabric. Four cantilevers with different lengths have been printed on fabric using a five-layer structure with a sacrificial material underneath the cantilever. The sacrificial layer is subsequently removed at 160 °C for 30 min to achieve a freestanding cantilever above the fabric. Two silver electrodes, one on top of the cantilever and the other on top of the fabric, are used to capacitively detect the movement of the cantilever. In this way, an entirely printed motion sensor is produced on a standard fabric. The motion sensor was initially tested on an electromechanical shaker rig at a low frequency range to examine the linearity and the sensitivity of each design. Then, these sensors were individually attached to a moving human forearm to evaluate more representative results. A commercial accelerometer (Microstrain G-link) was mounted alongside for comparison. The printed sensors have a similar motion response to the commercial accelerometer, demonstrating the potential of a printed smart fabric motion sensor for use in intelligent clothing applications.

A novel miniature wind generator for wireless sensing applications

This paper describes a novel miniature wind generator for wireless sensing applications. The generator consists of an aerofoil that is attached to a cantilever spring. The airflow over the aerofoil causes the cantilever to bend, the degree of bending being a function of the lift force from the aerofoil and the spring constant. As the cantilever deflects, the flow of air is reduced by a bluff body and the lift force therefore decreases causing the cantilever to spring back. The aerofoil is hence exposed to the full airflow again and the cycle is repeated. When the frequency of the movement matches the resonant frequency of the structure, the aerofoil has the maximum displacement. A permanent magnet is fixed on the aerofoil and a coil is attached to the base of the generator. The movement of the aerofoil causes the magnetic flux cutting the coil to change, which generates electrical power. The device has dimensions of 12 cm × 8 cm × 6.5 cm. Experiments have shown that the generator can operate at wind speeds as low as 2.5 m·s−1 with a corresponding electrical output power of 470 µW. This is sufficient for periodic sensing and wireless transmission. When the wind speed is 5 m·s−1, the output power is 1.6 mW.

Optimization of the electrodeposition process of high-performance bismuth antimony telluride compounds for thermoelectric applications

High-quality films of bismuth antimony telluride were synthesized by electrodeposition from nitric acid electroplating baths. The influence of a surfactant, sodium ligninsulfonate, on the structure, morphology, stoichiometry, and homogeneity of the deposited films has been investigated. It was found that addition of this particular surfactant significantly improved the microstructural properties as well as homogeneity of the films with a significant improvement in the thermoelectric properties over those deposited in the absence of surfactant. A detailed microprobe analysis of the deposited films yielded a stoichiometric composition of Bi(0.35)Sb(1.33)Te(3) for the films electrodeposited in the absence of surfactant and a stoichiometry of Bi(0.32)Sb(1.33)Te(3) for films deposited in the presence of surfactant.

Harvesting energy from vehicle wheels

This paper describes a new method to generate power from a rotating vehicle wheel using a ThunderTM piezoelectric generator [1]. The approach uses centripetal force to generate an impact on the piezoelectric transducer. The device was designed to be mounted on a vehicle rim. A generator with a volume of 2 cm3 produced 4 mW of electrical power at 800 rpm using a test wheel with 0.12 m diameter. Analytical results showed that the same amount of power can be produced by mounting the generator on a vehicle wheel with a diameter of 13 inches and a linear speed of 28.4 miles/h.

A Smart Textile Based Facial EMG and EOG Computer Interface

This paper investigates a wearable approach to facial electromyography and electrooculography. The aim is to reduce discomfort and setup time in electromyographic research, rehabilitation, and computer control. A screen and stencil printed passive electrode network is fabricated on a textile headband. When this headband is worn, an array of stencil printed electrodes makes contact with the skin. The electrodes are connected to external electronics by screen printed flexible conductive tracks. The printed electrode headband is used in a facial electromyographic control system to evaluate performance. The system can be used to control a mouse cursor or simulate keyboard functions. It was found that 50 Hz noise levels in the printed textile electrodes were similar to commercial disposable electroencephalography electrodes. The effect of a wearable approach on pressure variations and motion artefact is examined. The way in which this influences the design and performance of the control system is discussed.