Peter Glynne-Jones

A micro electromagnetic generator for vibration energy harvesting

Vibration energy harvesting is receiving a considerable amount of interest as a means for powering wireless sensor nodes. This paper presents a small (component volume 0.1 cm3, practical volume 0.15 cm3) electromagnetic generator utilizing discrete components and optimized for a low ambient vibration level based upon real application data. The generator uses four magnets arranged on an etched cantilever with a wound coil located within the moving magnetic field. Magnet size and coil properties were optimized, with the final device producing 46 µW in a resistive load of 4 k? from just 0.59 m s-2 acceleration levels at its resonant frequency of 52 Hz. A voltage of 428 mVrms was obtained from the generator with a 2300 turn coil which has proved sufficient for subsequent rectification and voltage step-up circuitry. The generator delivers 30% of the power supplied from the environment to useful electrical power in the load. This generator compares very favourably with other demonstrated examples in the literature, both in terms of normalized power density and efficiency.

Design and fabrication of a new vibration-based electromechanical power generator

A device is described for generating electrical power from mechanical energy in a vibrating environment. The design utilises an electromagnetic transducer and its operating principle is based on the relative movement of a magnet pole with respect to a coil. The approach is suitable for embedded remote microsystems structures with no physical links to the outside world. Simulation, modelling and test results following fabrication of a first prototype have demonstrated that generation of practical amounts of power within a reasonable space is possible. Power generation of more than 1 mW within a volume of 240 mm3 at a vibration frequency of 320 Hz has been obtained.

Self-powered autonomous wireless sensor node using vibration energy harvesting

This paper reports the development and implementation of an energy aware autonomous wireless condition monitoring sensor system (ACMS) powered by ambient vibrations. An electromagnetic (EM) generator has been designed to harvest sufficient energy to power a radio-frequency (RF) linked accelerometer-based sensor system. The ACMS is energy aware and will adjust the measurement/transmit duty cycle according to the available energy; this is typically every 3 s at 0.6 m s?2 rms acceleration and can be as low as 0.2 m s?2 rms with a duty cycle around 12 min. The EM generator has a volume of only 150 mm3 producing an average power of 58 ?W at 0.6m s?2 rms acceleration at a frequency of 52 Hz. In addition, a voltage multiplier circuit is shown to increase the electrical damping compared to a purely resistive load; this allows for an average power of 120 ?W to be generated at 1.7 m s?2 rms acceleration. The ACMS has been successfully demonstrated on an industrial air compressor and an office air conditioning unit, continuously monitoring vibration levels and thereby simulating a typical condition monitoring application

A novel thick-film piezoelectric micro-generator

The use of alternative electrical energy sources to batteries is of particular significance to remote sensor systems. A vibration-powered micro-generator, based on a screen printed piezoelectric material, is proposed for this purpose. Theoretical and experimental results show that 2 µW can be generated for a vibration frequency of only 80 Hz. The device is not optimized and significant improvements are envisaged in the future.

Self‐powered systems: a review of energy sources

A range of self-power technologies is reviewed. Self-powered systems are defined as those that operate by harnessing ambient energy present within the environment of the system. As MEMS and smart-material technologies mature, embedded and remote systems become more attractive. Self-power offers a potential for solving the difficult problem of supplying energy to these devices.

Array-controlled ultrasonic manipulation of particles in planar acoustic resonator

Ultrasonic particle manipulation tools have many promising applications in life sciences, expanding on the capabilities of current manipulation technologies. In this paper, the ultrasonic manipulation of particles and cells along a microfluidic channel with a piezoelectric array is demonstrated. An array integrated into a planar multilayer resonator structure drives particles toward the pressure nodal plane along the centerline of the channel, then toward the acoustic velocity maximum centered above the subset of elements that are active. Switching the active elements along the array moves trapped particles along the microfluidic channel. A 12-element 1-D array coupled to a rectangular capillary has been modeled and fabricated for experimental testing. The device has a 300-μm-thick channel for a half-wavelength resonance near 2.5 MHz, with 500 μm element pitch. Simulation and experiment confirm the expected trapping of particles at the center of the channel and above the set of active elements. Experiments demonstrated the feasibility of controlling the position of particles along the length of the channel by switching the active array elements.

Manipulation of microparticles using phase- controllable ultrasonic standing waves

A method of manipulating microparticles in a liquid using ultrasound is proposed and demonstrated. An ultrasonic standing wave with nodal planes whose positions are controllable by varying the relative phase of two applied sinusoidal signals is generated using a pair of acoustically matched piezoelectric transducers. The resulting acoustic radiation force is used to trap micron scale particles at a series of arbitrary positions (determined by the relative phase) and then move them in a controlled manner. This method is demonstrated experimentally and 5 μm polystyrene particles are trapped and moved in one dimension through 140 μm.

The Modelling of a Piezoelectric Vibration Powered Generator for Microsystems

As MEMS and Smart Material technologies advance, embedded and remote applications are becoming more widespread. Powering these systems can be a significant engineering problem, as traditional solutions such as batteries are not always appropriate. A method is described for modelling the power than can be produced from piezoelectric inertial generators. The method uses a combination of FEA and a complex stiffness model of a resistively shunted piezoelectric element. The model is verified with experimental results. Although the prototype produces only 3µW, the model reveals that orders of magnitude increase in power output are possible.

An investigation into the effect of modified firing profiles on the piezoelectric properties of thick-film PZT layers on silicon

Screen-printed lead zirconate titanate (PZT) layers offer possibilities both for sensing and for actuation applications. The reaction between PZT and silicon during the high temperature sintering phase is a problem when combining PZT layers with silicon microelectromechanical systems. In this study we investigate a range of longer, lower temperature firing profiles for thick-film PZT, to reduce this reaction. Methods of measuring the d 33 piezoelectric coefficient of thick-film PZT layers are reviewed and the test rig used to compare samples is described. Temperatures below 800 °C are found to be insufficient to produce sintering. At other low temperatures, longer firing times are found to be necessary in order to produce consistent results. A temperature of 800 °C for 8 h was found to produce a reduction in the level of reaction, without a serious reduction of the piezoelectric activity.

Deformation of red blood cells using acoustic radiation forces

Acoustic radiation forces have been used to manipulate cells and bacteria in a number of recent microfluidic applications. The net force on a cell has been subject to careful investigation over a number of decades. We demonstrate that the radiation forces also act to deformcells. An ultrasonic standing wave field is created in a 0.1 mm glass capillary at a frequency of 7.9 MHz. Using osmotically swollen red-blood cells, we show observable deformations up to an aspect ratio of 1.35, comparable to deformations created by optical tweezing. In contrast to optical technologies, ultrasonic devices are potentially capable of deforming thousands of cells simultaneously. We create a finite element model that includes both the acoustic environment of the cell, and a model of the cell membrane subject to forces resulting from the non-linear aspects of the acoustic field. The model is found to give reasonable agreement with the experimental results, and shows that the deformation is the result of variation in an acoustic force that is directed outwards at all points on the cell membrane. We foresee applications in diagnostic devices, and in the possibility of mechanically stimulating cells to promote differentiation and physiological effects.