One of the main difficulties with modern electronic devices is how to provide enough energy for the electronics to run over a reasonable amount of time without making the battery too large or the device bulky. As EH replaces need of batteries in sensors and thus, using EH sensors could be best option to be integrated by IoT to facilate real-time applications, smart cities, M2M, environment monitoring and remote patient monitoring. This article will bring out some facts and factors on EH significance in IoT & wireless applications.
Energy-harvesting devices efficiently and effectively capture, accumulate, store, condition and manage conventional energy and supply it in a form that can be used to perform a helpful task. An Energy Harvesting Module is an electronic device that can perform all these functions to power a variety of sensor and control circuitry for intermittent duty applications. Advanced technical developments have increased the efficiency of devices in capturing trace amounts of energy from the environment and transforming them into electrical energy. Also advancements in microprocessor technology have increased power efficiency, effectively reducing power consumption requirements. In combination, these developments have sparked interest in the engineering community to develop more and more applications that utilize energy harvesting for power. Many real life applications are using energy harvesting system now a day. Wireless sensor network systems such as Zig-Bee systems often benefit from energy harvesting power sources. For example, when a wireless node is deployed at a remote site where a wall plug or a battery is either unreliable or unavailable, energy harvesting can augment or supply power. In another example, a remote control node running on energy harvesting can be implemented as a self-powered electronic system.
And in yet other situations, multiple energy sources can be used to enhance the overall efficiency and reliability of any system.
EH Ideal for IoT & Wireless Networks Power Hunger
The Internet of Things (IoT) consists of sensors and smart things/objects that are connected to the internet anytime and anywhere. Acting as a perception layer of IoT, wireless sensor networks (WSNs) play an important role by detecting events and collecting surrounding context and environment information. Since sensors are battery powered, replacing the batteries in each smart object/thing/sensor is very difficult to implement.
For the sustainability of network operations, energy harvesting and energy management technologies have recently gained much attention. Energy management is the most important technology for prolonging the network lifetime of WSNs. The design of efficient energy management involves several aspects, including physical, MAC and network elements as well as application aspects.
Energy harvesting is a novel and promising solution that sees each node equipped with a harvesting module. Recent research efforts in energy harvesting can be classified into two categories: energy scavenging and energy transferring. In energy scavenging technologies, the sensor can be recharged from the ambient environment, including electromagnetic waves, thermal energy and wind energy. In energy transferring technologies, the mobile node can play the role of charger which is able to wirelessly transfer energy to those sensors located within its recharging range.
Low-power wearable may soon bid to batteries and start drawing energy generated by body heat and movement, and ambient energy from the environment. Consumer electronics devices are getting smaller but conventional batteries are not, and it’s important to start implementing new energy harvesting techniques to keep devices powered for long periods of time. There will be billions of Internet-connected devices supplying real-time information in the coming year. Data-gathering instruments today are designed around the size of batteries, and self-powered devices could resolve some power and size issues.
The researchers said that energy harvesting technologies could be relevant in smoke detectors, alarm sensors, smart meters and even remote controls. There will be 26 billion Internet connected devices by 2020. Sensors will be used in wearable, industrial equipment, energy monitors, telematics systems, home appliances and other “intelligent” appliances. Wireless terminals equipped with sensors are included among the things and devices on the IoT. Wireless sensor terminals connected to a network will collect information about the environment surrounding the sensor terminal. A key requirement for IoT and
M2M is the ability to place wireless sensor terminals in all kinds of locations to collect data. But there is one big issue: the installation of power-distribution wires, or, in the case of battery use, the battery life or the time period for battery replacement. Nobody would find this a problem with 10 or 20 batteries, but when there are 10,000 or a million or a hundred million, there are concerns not only for battery costs but also the enormous scale of maintenance expenses. This is one reason the dissemination of wireless sensor terminals have become a concern. Energy harvesting may provide a solution. Energy harvesting technologies use power generating elements such as solar cells, piezoelectric elements, and thermoelectric elements to convert light, vibration, and heat energy into electricity, then use that electricity efficiently. These technologies can be produced now because semiconductors have achieved a balance between the improving performance of power generating elements and falling power consumption of active devices. This is the reason attention is being showered on this key technology that can solve the dissemination problem for wireless sensor terminals as part of the IoT.
The power-generating element must be selected after considering the type of energy to be collected from the surrounding environment, whether vibration, light, or heat. The most common elements used are solar, piezoelectric, or thermoelectric. It is also important that the power IC for use with the power-generating element efficiently collects the power from that element without loss, and that it supplies the stabilized power to a later stage IC. The generated power for each element changes according to the size and generating environment. When integrating it into a device, it is necessary to comprehensively investigate the following. It is also necessary to select a power IC that is matched to the power generating element. Regarding the selection of wireless communications for a wireless sensor network terminal, the selection must be matched to the purpose for the power generating element. Key aspects include the communication distance, the type of network to be built, the data transmission amount, the application, and the power consumption. When used in combination with energy harvesting, the key point is low power consumption, so wireless technologies in focus are EnOcean, ZigBee and Bluetooth LE. When using energy harvesting, there is a point to be considered—striking a balance between power generation and power consumption. This is because the device will not work if the power generation is smaller than the power to be consumed by the device. Although the generating characteristics of power generating elements are improving year by year, it is difficult to continuously deliver sufficient power to a device on an ongoing basis. A way to solve this is to collect the generated power in a capacitor and execute sensor operation at intervals, resulting in a method that balances the power generation with the power consumption. To do this, the designer needs to have an accurate understanding of the generating environment for the power generating element, the power generated, and the time required.
Smart RF Energy Harvesting
RF energy harvesting (RFH) is emerging as a potential method for the proactive energy replenishment of next generation wireless networks. Unlike other harvesting techniques that depend on the environment, RFH can be predictable or on demand, and as such it is better suited for supporting quality-of-service-based applications. However, RFH efficiency is scarce due to low RF-to-DC conversion efficiency and receiver sensitivity. In recent times, RF energy harvesting (RFH) has emerged as a promising technology for alleviating the node energy and network lifetime bottlenecks of wireless sensor networks (WSNs).
The RF radiation pattern is generally wide+angled; radio waves can simultaneously carry information and energy, and the radiation directivity can be electronically steerable. These features have been exploited in multihop energy transfer (MHET) as well as combining it with data transfer over the same RF signal (called simultaneous wireless information and power transfer, or SWIPT), without requiring critical alignment of the nodes. Besides, RFH has found applications in cognitive radio networks, wireless body area networks and systems.
Energy Harvesting MEMS
Piezoelectric micro-electromechanical systems (MEMS) have been proven to be an attractive technology for harvesting small magnitudes of energy from ambient vibrations. This technology promises to eliminate the need for replacing chemical batteries or complex wiring in microsensors/microsystems, moving us closer toward battery-less autonomous sensors systems and networks. The key attributes to make a good piezoelectric MEMS energy harvester include its compactness, output voltage, bandwidth, operating frequency, input vibration amplitude, lifetime, and cost. Among them, higher power density and wider bandwidth of resonance are the two biggest challenges currently facing the technology. Giant piezoelectric coefficient materials, epitaxially grown films, grain textured piezoelectric materials and thin films, and high performance lead-free piezoelectric materials are recent advancements made toward increasing the electromechanical energy conversion of piezoelectric harvesters. Nonlinear resonators are extremely promising to extract more electrical energy from the beam with much wider bandwidth.
For electric vehicles, the main focus on energy harvesting remains with enhanced methods to power up the prime traction drive and recharge the traction battery. The prime traction battery in an electric vehicle can hold half of overall the cost of the vehicle, so the ability to control more ambient energy sources enable the usage of the smaller batteries that can be recharged from various sources inside the vehicle. Electric cars are expected to have almost six types of energy harvesting MEMS systems to convert infrared, ultra violet, vibration, visible light, lateral, vertical, and forward movement into electricity. Using MEMS energy harvesting shock absorbers are trialed on buses. Proponents expect to move into car market around 5 years after buses adopt them. The global electric vehicle industry is developing rapidly to become a large market.
Mr. Tony Armstrong, Director Product Marketing – Power Products, Linear Technology Corporation
As per Mr. Armstrong, at the low end of the power spectrum are the nanopower conversion requirements of energy harvesting systems such as those commonly found in IoT equipment, which necessitate the use of power conversion ICs that deal in very low levels of power and current. These can be 10s of microwatts and nanoamps of current, respectively. State-of-the-art and off-the shelf EH technology for example in vibration energy harvesting and indoor or wearable photovoltaic cells, yield power levels in the order of milliwatts under typical operating conditions. While such power levels may appear restrictive, the operation of harvesting elements over a number of years can mean that the technologies are broadly comparable to long-life primary batteries, both in terms of energy provision and the cost per energy unit provided. Moreover, systems incorporating EH will typically be capable of recharging after depletion, something that systems powered by primary batteries cannot do. Nevertheless, most implementations will use an ambient energy source as the primary power source, but will supplement it with a primary battery that can be switched in if the ambient energy source goes away or is disrupted.
Of course, the energy provided by the energy harvesting source depends on how long the source is in operation. Therefore, the primary metric for comparison of scavenged sources is power density, not energy density. EH is generally subject to low, variable and unpredictable levels of available power so a hybrid structure that interfaces to the harvester and a secondary power source is often used. The secondary source could be a rechargeable battery or a storage capacitor (maybe even supercapacitors). The harvester, because of its unlimited energy supply and deficiency in power, is the energy source of the system. The secondary power reservoir, either a battery or a capacitor, yields higher output power but stores less energy, supplying power when required but otherwise regularly receiving charge from the harvester. Thus, in situations when there is no ambient energy from which to harvest power, the secondary power reservoir must be used to power the down-stream electronic systems or WSN. Talking about new trends in Energy Harvesting and IoT Technology he said, the proliferation of wireless sensors supporting the “Internet of Things” (IoT) has increased the demand for small, compact and efficient power converters tailored to untethered lower power devices. One of the more recent emerging market segments covered under the IoT which is particularly interesting from an energy harvesting perspective is the wearable electronics category. Linear has introduced a number of power conversion ICs which have the necessary features and performance characteristics to enable such low levels of harvested power to be used in IoT. The LTC3331 is a complete regulating EH solution that delivers up to 50mA of continuous output current to extend battery life when harvestable energy is available. It requires no supply current from the battery when providing regulated power to the load from harvested energy and only 950nA operating when powered from the battery under no-load conditions. The LTC3331 integrates a high voltage EH power supply, plus a synchronous buck-boost DC/DC converter powered from a rechargeable primary cell battery to create a single noninterruptible output for energy harvesting applications such as those in WSNs. The LTC3331’s EH power supply, consisting of a fullwave bridge rectifier accommodating AC or DC inputs and a high efficiency synchronous buck converter, harvests energy from piezoelectric (AC), solar (DC) or magnetic (AC) sources. A 10mA shunt allows simple charging of the battery with harvested energy while a low battery disconnect function protects the battery from deep discharge. The rechargeable battery powers a synchronous buckboost converter that operates from 1.8V to 5.5V at its input and is used when harvested energy is not available to regulate the output whether the input is above, below or equal to the output. The LTC3331 battery charger has a very important power management feature that cannot be overlooked when dealing with micro-power sources. The
LTC3331 incorporates logical control of the battery charger such that it will only charge the battery when the energy harvested supply has excess energy. Without this logical function the energy harvested source would get stuck at startup at some non-optimal operating point and not be able to power the intended application through its startup.
A supercapacitor balancer is also integrated allowing for increased output storage. In July of 2015, Linear is going to introduce the LTC3335 – a nanopower buck-boost DC/DC converter with an integrated coulomb counter aimed at wireless sensor networks and general purpose energy harvesting applications. It is a high efficiency, low quiescent current (680nA) converter. Its integrated coulomb counter monitors accumulated battery discharge in long life battery powered applications.
This counter stores the accumulated battery discharge in an internal register accessible via an I2C interface. The buck-boost converter can operate down to1.8V on its input and provides eight pin selectable output voltages with up to 50mA of output current.
Mr. Keita Sekine, Senior Product Marketing Engineer, Analog Business Unit, Cypress Inc.
The Energy harvesting base wireless sensor network will be widely adopt and contribute to improve of constructing, using, maintaining and managing these infrastructures, and reducing environmental pollution aiming to host of Olympic Games in India As per Mr. Sekine, aiming to IoT era, the wireless sensor market is expecting rapid growth with implementing trillion of wireless sensors in everywhere. But the battery of each sensor node has critical issue with it lifetime and replacing.
Regarding the iBeacon service which was announced by Apple also requires battery based Beacon units for its service. Since it hasn’t solved battery-life and its replacement issues, therefore the market hasn’t been exponentially expanded, yet. The wireless sensor market has same issues.
Cypress Energy Harvesting solution can solve these issues.
Recently, new breakthroughs are made which are 2-nd generation of Energy Harvesting and evolution of wireless sensor technology. The Bluetooth Low Energy (BLE) technology is it which is a kind of wireless communication standard with drastically reduced power consumption compares with traditional protocol. This new protocol is rapidly and broadly adopting in wearable devices.
And its advantages of low-power and connectivity with Smartphone/PC, the wireless market is also expecting to adopt this protocol. The new trend is combination of BLE and Energy Harvesting.
It also made breakthrough in harvester which is perovskite-solar-cell. This new solar cell can generate electricity with high efficiency and can manufacture with low cost. It’s still under research stage but is gathering high interest from Energy Harvesting Industry and solar-cell industry. The battery-less wireless sensor combined of perovskite-solar-cell and BLE is the key technology of upcoming wireless sensor market Cypress is providing 2 types of PMIC (Power Management IC) products as the core of Energy Harvesting. Regarding the Energy Harvesting, to manage time is also important in addition to manage traditional Power Management. Since the generation of electricity in Energy Harvesting system is unstable and small, the high efficient power management technology is crucial. Cypress Energy Harvesting PMICs are developed with focusing on the features of Energy management and high efficient electric power extraction. Our customer can extract electricity efficiently and manage it with leveraging of Energy Harvesting PMIC of MB39C811andMB39C831. India is 2nd largest country of population and has many rapidly developing cities. Therefore India has common problems of fast growing countries such as infrastructures (traffics, electricity, water-supply and gas,) and environment pollution. The advanced wireless sensor network to manage these infrastructures has ability to solve or improve these problems. Particularly, India has Power infrastructure problem, the wireless sensor network with Energy Harvesting is mandatory to precede these approach. The Energy harvesting base wireless sensor network will be widely adopt and contribute to improve of constructing, using, maintaining and managing these infrastructures, and reducing environmental pollution aiming to host of Olympic Games in India .
Mr. Vidyasagar, Head of Automation – Product Engineering, Services (PES), Embitel Technologies
Energy harvesting MEMS technology has the true potential of being one of the significant driving factors for widespread adoption of IoT. EH based wireless sensors/switches with robust energy conversion ratios that are good enough to replace batteries, has been a design challenge for companies. However, this journey has been exciting and to the credit of all the market players, both the EH and IoT ecosystem have been innovating at break-neck speed. This includes the EH sensor designs, IoT infrastructure (gateway, cloud and other hardware) and IoT applications (software, UI and analytics). The IoT ecosystem participants, have been innovating to develop solutions and frameworks for industry applications like Smart Cities, Predictive Healthcare, Smart Home Automation, Factory Automation/Industry 4.0, Omni-channel Retail, and Connected Cars. In this context, the value-add that EH technology offers has potential to reduce total cost of ownership for businesses migrating to IoT framework. Battery-less equipments powered by off-grid renewable energy and reduced maintenance costs not only translate into significant dollar savings for stakeholders, but also helps to transform more and more devices into an IoT node. As far as EH market maturity is concerned, the largest addressable market lies in the range of one watt to 10 kW, which is suitable for IoT applications. However, innovators are working on EH designs that will power Vehicles and Building structures as well! At Embitel Technologies, teams have been innovating in this space with great success. Embitel is a part of EnOcean Alliance, a consortium of companies, who are at the forefront of innovations in energy efficient technology solutions for building automation (residential, commercial and industrial buildings). Embitel Technologies has been relentlessly working towards one of the significant goals of the EnOcean Alliance, which is to ‘establish energy harvesting wireless technology as the wireless standard for sustainable buildings’. In this context, Embitel is pleased to share that Embitel Technologies has designed and developed an IoT solution for Home Automation based on “EnOcean’s energy harvesting sensors and gateway hardware”. This solution is also a demonstration of Edge to Edge Communication in IoT. For this Embitel designed a Sensor network comprising of various wireless devices operating under EnOcean standards. Energy harvesting based sensors communicates with a Gateway, which consolidates and forwards data to a backend Cloud Framework. Inter Protocol communication has been facilitated using custom built Gateway. Mobile and Web Applications consume this data and facilitate bi-directional communications. Controlling and Monitoring of all devices in the network is made possible via cloud and there notifications built into the system. MQTT based communication is used in this setup. Additionally Data Analytics and Machine Learning concepts have been implemented.
Jean Pierre Mars, VP Applications Engineering, CAP-XX (Australia) Pty Ltd
Energy harvesters are increasingly being used to power autonomous products and wirelessly networked devices. Ambient energy sources include solar, wind, fluid, kinetic, radio and heat. While these energy harvesters have abundant energy, they are only capable of providing very low power. They are not able to support loads with occasional high power bursts, even though the load’s average power is less than the power that can be delivered by the energy harvester. An energy harvester, coupled with a supercapacitor, is an ideal energy source enabling a low power energy harvester to support low average power loads with high peaks. The supercapacitor acts as a power buffer. The energy harvester charges the supercapacitor at very low power, typically a few mW as low as 1mW, and the supercapacitor can periodically or sporadically enable a higher power application such as collection and transmission of data. The only constraint is that the average power supplied by the supercapacitor < the power supplied by the energy harvester, or, duty cycle x application power < energy harvester average power. The key attributes of supercapacitors coupled with energy harvesters are very low leakage current, typically < 1 micro amp, and the ability to be charged with a very simple circuit that only requires over voltage protection, unlike a battery charging circuit that requires constant current and constant voltage control. Many of these applications run at low voltages, in the range of 2.7V down to 1.8V. In this case, use a single cell supercapacitor which is smaller, lower cost and does not require any cell balancing. If your circuit must run at higher voltages, up to 5V, you will need a dual cell CAP-XX supercapacitor which has 2 matched cells in series. In this case CAP-XX can recommend a simple balancing circuit that does not add any extra leakage current. A discharged supercapacitor looks like a short circuit and will draw high inrush current. Fortunately most energy harvesting sources can supply short circuit current and will charge a supercapacitor from 0V. If a regulator or DC:DC converter is used to charge the supercapacitor from the energy harvesting source, then it must behave gracefully into a short circuit. Also, the current it draws for its own operation should be << energy harvesting current for efficiency. CAP-XX has the supercapacitors and power design capabilities to enable this solution.
Conclusion
Energy Harvesting (EH) technologies could be an answer to many power supply related issues especially in IoT & wireless projects. EH technology is not only green and clean but reduces lots of hassle & price considerations. We hope to see our future in-sight smart cities and industrial set-ups to be equipped with EH sensors and power modules.
