The BBC World News team reviews the latest gadgets and major technology news. This week they reported on the history and future of the microchip, where reducing power consumption while increasing performance is driving the industry. This video shows how Texas Instruments’ MSP430 ultra-low power microcontroller is powered solely by AdaptivEnergy’s Joule-Thief™ Module for a remote wireless sensing solution.

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Energy harvesting has been steadily gaining interest in the technology sector, but without useful applications it will remain just an intellectual curiosity. The continuously decreasing power requirements of electronics, however, have increased the number of applications for which this technology can be used effectively. One such application is the wireless sensor system.

click here to read the full Sensors Magazine article

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The last time I really got my hands dirty playing with a piezoelectric transducer was for a small control system I designed back in college. That was a generic device that was more or less plug-and-go, so I can’t recall much about it. However, given the recent uptick in interest in energy-harvesting technology as a possible solution to powering remote and embedded devices, I figured it was time to take a closer look at piezoelectric (PE) transducers and their related electronics to see how far they’d come. So, I got hold of the Joule-Thief demonstration kit from AdaptivEnergy, performed an exam, and was blown away.

click here to read the full EE Times article

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HAMPTON, Virginia – December 3, 2008 – AdaptivEnergy has successfully doubled the power output of the Joule-Thief™ Energy Harvesting Power Generator.

The performance increase was the result of ongoing development of AdaptivEnergy’s unique stress biased RLP® technology to achieve significantly greater stress in the core piezoceramic material. For a given input the ability to increase the stress in the piezoceramic produces a far greater power output over competitive piezoelectric energy harvesting devices.

AdaptivEnergy’s continual improvement in ambient power conversion is successfully broadening the range and usefulness of vibration energy harvesting technology.

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Also called energy scavenging, energy harvesting uses piezoelectric, photovoltaic, thermoelectric and inductive devices to convert ambient energy (kinetic, light and thermal) into electrical energy. This energy can then be stored locally to power ‘perpetual’ devices, usually sensors or other monitoring and control devices with a wireless communications interface. It’s this storage that dispels another misconception: that harvested energy is too little to be of practical use. In almost all applications, it’s the timed use of accumulated energy that makes the devices practical.

The concept of energy harvesting is clearly not new; the most obvious instantiation is solar-powered cameras used on highways. (For a list of energy-harvesting companies involved in the area, go to www.energyharvesting.net.) However, what is new are the increasingly efficient conversion and power-management ICs, innovative power storage techniques and the availability of low-cost, low-power ICs that are combining to enable greater functionality per millijoule of generated energy.

This has opened up a whole range of truly tether-free applications from wireless sensor networks for structural monitoring of buildings and bridges to battlefield sensors, backpack power generators and communicators, devices embedded within airplane wings and other hard-to-access locations.

In the consumer space, medical applications that take advantage of thermal and kinetic energy are an exciting area of development, while solar-powered Bluetooth headsets and cell-phone chargers are already plentiful. Meanwhile, ‘green’ automotive designers are looking at perpetual devices to reduce the amount of expensive and weighty harnessing required.

For 2009, consumers can expect a flotilla of devices, particularly in the medical field, as companies such as Texas Instruments Inc. continue seeding the market with kits that combine its low-power MSP430 microcontroller with conversion technologies from the likes of AdaptivEnergy LLC and Perpetuum Ltd., as well as innovative battery technology from Cymbet Corp. Other IC companies also improving the state of the art here include National Semiconductor, International Rectifier and Linear Technology.

However, for designers, the space is rife with opportunities. More research is need for ultra-low-power conversion and power management circuits. Power storage techniques may include ultracapacitors and novel battery chemistries. As innovations are made in those fundamental areas, the system applications for energy-harvesting devices are set to rise exponentially over the coming months.

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Unlike competing piezo fan products, the RLP® Vibratory Fan mated with Energy Key™ technology provides for maximum air movement throughout its operating temperature and humidity range.

• Improves cooling effectiveness over natural convection
• Very quiet operation
• Reliable operation even in harsh industrial environments

The Joule-Thief™ has been designed to deliver electrical power at relatively high density (power per unit volume) compared to competing piezoelectric energy harvesting products. A simple schematic of the piezoelectric composite beam energy harvester is shown in Figure 1. In the figure, a0 is the input acceleration, fext is the excitation frequency of the base vibration and V is the resulting voltage from the PZT.

Figure 1: Schematic of a Piezoelectric Composite Beam Energy Harvester

The cantilever beam and proof mass is analogous to a simple single-degree-of-freedom oscillator subject to a base excitation as shown in Figure 2.

Figure 2: Single-Degree-of-Freedom Representation of the Energy harvesting Beam

AdaptivEnergy has developed a comprehensive analytical toolset that accurately models the behavior of a piezoelectric composite beam energy harvester as depicted in Figure 1.  This electromechanical lumped-element model is valid for a cantilever beam until its first mode of vibration and is modeled using Euler-Bernoulli beam theory.  This modeling technique employs circuit analogues using a two-port network transducer theory to effectively represent the complete energy harvesting beam in an equivalent circuit form.  This model captures the interaction between various energy domains that are present in the energy harvester, namely, mechanical and electrical.

The energy conversion between various modules of the energy harvester is explained next.  The ambient mechanical energy is first converted to its electrical equivalent using the piezoelectric transduction mechanism discussed earlier.  This transfer results in an AC voltage generated by the RLP® that is then converted into a DC voltage using the energy harvesting circuit and later stored in the battery for subsequent use.  Figure 3 represents the power transfer diagram for the Joule-Thief™. The objective of the power converter is to match the impedance of the RLP® energy harvesting beam to the load to maximize the power transfer.

Figure 3: Energy Flow in a Vibration-Based Energy Harvester

AdaptivEnergy uses both internally developed and commercial Finite Element Analysis software tools to analyze the projected performance of varying energy harvesting beam configurations.  Design features such as dimensions, end mass and resonant frequencies are determined prior to developing any physical prototypes. A bimorph (two layers of piezoceramic) design would be considerably stiffer than a unimorph (single layer of piezoceramic) design.
As indicated in the above figure, the RLP® is comprised of a stainless steel shim to which is bonded a PZT ceramic using AdaptivEnergy’s proprietary polyamide adhesive layer with a capping layer at the top to further stress bias the ceramic layer. The unimorph design results in a deflected modeshape due to the stress bias, while the bimorph results in a straight beam due to its symmetry.

III. ENERGY COLLECTION AND STORAGE ELECTRONICS

The AdaptivEnergy EHD energy harvesting circuit is designed to function as an interface between the RLP® energy beam and any battery.  Alternate version of the circuit that uses a capacitor as the storage mechanism is also available. The circuit is fully equipped to address issues such as avoiding over-charging and discharging beyond the allowable limits and preventing leakage when the module is not in use. Figure 5 shows a functional block diagram of the energy harvesting circuit. The EHD circuit consists of two functional sub-circuits that are designed to protect the battery from the above mentioned failure modes.

Figure 5: Functional Block Diagram of the EHD Energy Harvesting Circuit

Shown below is a picture of the evolution of the RLP® beams developed at AdaptivEnergy to harvest energy from a range of vibration sources. The sizes of the beams vary from 1.5” to 3.5” and 5 gm to 20 gm in mass. The beams are tuned to different frequencies to fit well with specific applications.

Figure 6: Joule-ThiefTM RLP® beams

Plots showing the performance curves for various Joule-Thief™ beams developed at AdaptivEnergy are included below. The first plot shows the power density with respect to volume for all the beams operating at their resonance as a function of input acceleration levels. These plots indicate the rms power delivered into an optimal load for each beam. The actual real power that is reclaimed will depend on the efficiency of the energy collection electronics. Energy harvesting circuits when designed to the right beam have been measured to be 60-80 % efficient. However, knowing the input vibration spectra such as acceleration, frequency is critical to achieve this efficiency.

The next plot shows the performance curve for power density with respect to overall mass of the package for various beams excited at resonance as a function of input acceleration. These plots should indicate the performance specs that can be achieved with the current selection of beams. More redesigning can be carried out with the internal modeling tools developed for this purpose to achieve higher power outputs at alternate frequencies.

JOULE-THIEF™ ENERGY HARVESTING BEAM
In the recent past, energy harvesting from the environment, including human movement, has generated a lot of research interest and many available ambient energy sources such as thermal, optical, mechanical, fluidic, etc. have been investigated.  AdaptivEnergy’s Joule-Thief™ is designed to harvest mechanical vibration energy and is particularly useful in harvesting low level vibrations.  Some of the main applications include operating as the power source for remote structural and condition monitoring, human wearable electronics, wireless sensing and switching applications, supplementing battery storage devices, etc.

Vibration-based piezoelectric energy harvesting generally consists of a power generator module which converts the ambient mechanical vibration energy into an electrical equivalent energy.  This is achieved using the RLP® beam.  The operating principle of the energy harvester involves a piezoelectric beam attached to a vibrating mechanical structure that converts the mechanical vibration energy into induced electric charge.  The generated equivalent voltage is then converted to a usable DC voltage using the power processor module. The final power storage module includes an electronics architecture that efficiently stores the generated power in a battery or a capacitor for end use.

The Joule-Thief™ is a composite beam that consists of a cantilever shim with an attached piezoelectric layer and a proof mass at its end. The proof mass essentially converts the input base acceleration into an effective inertial force at the tip that deflects the beam, thereby inducing mechanical strain in the piezoelectric layer.  This strain produces a net polarization in the piezoceramic.  When electrodes are placed on the ceramic this net polarization produces a flow of electrons, or a current.  The current produced is then converted into usable power by the power processor. For this application of the energy harvester, a tapered beam shape was adopted.  AdaptivEnergy has gained significant knowledge with studies on various EH beam shapes and configurations to conclude that a tapered cantilever beam design is the best option, particularly for low frequency vibration sources.  Since the ambient environment has a definite amount of energy at known amplitudes and frequencies, the fundamental optimization of the mechanical device would be to generate maximum power from a given source.  Consequently, the need to maximize the strain in the piezoelectric layer is essential as the voltage generated in the piezoceramic is proportional to the strain induced.

Technology

>	Product Brief TherMysticks Polymer
>	Joule-Thief™ White Paper

Air Movement/Fan

>	Product Brief Vibratory Fan
>	Piezoelectric Fans Heat Transfer Enhancement

Pumping

>	RLP-125 Technology Platform Datasheet
>	LPD-125 Pump Product Brief
>	LPD-125 Pump White Paper

Click here to read the full EE Times article.