Tag Archives: IoT Devices

High-Efficiency Solar Cells for IoT Devices

As per expert estimates, by 2025, the worldwide number of IoT, or the Internet of Things, could rise to 75 billion. However, most IoT devices have sensors that run on batteries. Replacing these batteries can be a problem, especially for long-term monitoring.

Researchers at the Massachusetts Institute of Technology have now produced photovoltaic-powered sensors. These sensors can transmit data potentially for several years, before needing a replacement. The researchers achieved this by mounting thin-film perovskite cells as energy harvesters on low-cost RFID or radio-frequency identification tags. Perovskite cells are notoriously inexpensive, highly flexible, and relatively easy to fabricate.

According to the researchers, the future will have billions of sensors all around. Rather than power the sensors with batteries, the photovoltaic-powered sensors could use ambient light. It would be possible to deploy them and then forget them for months at a time or even years.

In a pair of papers the researchers have published, they have described the process of using sensors to monitor indoor and outdoor temperatures continuously over many days. No batteries were necessary for the sensors to transmit a continuous stream of data over a distance greater than five times that traditional RFID tags could. The significance of a long data transmission range means the user can employ one reader for collecting data simultaneously from multiple sensors.

Depending on the presence of moisture and heat in the environment, the sensors can remain under a cover or exposed for months or years before they degrade enough requiring a replacement. This can be valuable for applications requiring long-term sensing indoors as well as outdoors.

For creating self-powered sensors, many other researchers have tried solar cells for IoT devices. However, in most cases, these were the traditional solar cells and not the perovskite type. Although traditional solar cells can be long-lasting, efficient, and powerful under certain conditions, they are rather not suitable for universal IoT sensors.

The reason is, traditional solar cells are expensive and bulky. Moreover, they are inflexible and non-transparent—suitable and useful for monitoring the temperature on windows and car windshields. Most designs of traditional solar cells allow them to effectively harvest energy from bright sunlight, but not from low levels of indoor light.

On the other hand, it is possible to print perovskite cells using easy roll-to-roll manufacturing techniques costing only a few cents each. They can be made into thin, flexible, and transparent sheets. Furthermore, they can be tuned to harvest energy from outdoor or indoors lighting.

Combining a low-cost RFID tag with a low-cost solar power source makes them battery-free stickers. The combination allows for monitoring billions of products all over the world. Adding three to five cents more, it is possible to add tiny antennas working at ultra-high frequencies to the stickers.

Using a communication technique known as backscatter, RFID tags can transmit data. They reflect the modulated wireless signals from the tag and send it back to their reader. The reader is a wireless device, very similar to a Wi-Fi router, and it pings the tag. In turn, the tag powers up and using backscattering, sends a unique signal with information about the product on which it is stuck.

Energy from Vibrations for IoT Devices

Producing energy from vibrations is nothing new, and the world is always hungry for more clean energy. Engineers now have a new material that can convert simple mechanical vibrations all around it, to electricity. The electricity is enough to power most sensors on the Internet of Things ranging from spacecraft to pacemakers.

Engineers at the University of Toronto and the University of Waterloo have produced the material after decades of work. Their research has generated a novel compact electricity-generating system that they claim is reliable, low-cost, and green.

According to the researchers, their achievement will have a significant impact on social and economic levels, as it will reduce the reliance on non-renewable energy sources. They claim the world needs these energy-harvesting materials critically at this moment in time.

Energy harvesting technology produces small amounts of energy from external effects such as heat, light, and vibrations. For instance, an energy-harvesting device worn on the body could generate energy from body movements, such as from the legs or arm movements while walking. Most such devices produce enough energy to power personal health monitoring systems.

Based on the piezoelectric effect, the new material that the researchers have developed generates an electric current when there is pressure on it. Mechanical vibrations are one example of the type of pressure on the appropriate substance.

The piezoelectric effect is known and in use since 1880, and people have been using many piezoelectric materials like Rochelle salts and quartz. The technology has been in use for producing sonars, ultrasonic imaging, and microwave devices.

However, until now, most traditional piezoelectric materials in use in commercial devices have had a low finite capability for generating electricity. Moreover, most of these materials use Lead, which is detrimental to the environment and to human health as well.

The researchers solved both the above problems in one go. They grew a single large crystal of a molecular metal. This was a halide compound known as edabco copper chloride. For this, they used the Jahn-Teller effect, which is a well-understood concept in Chemistry, and offers a spontaneous geometric distortion in the crystal field.

The researchers proceeded to fabricate nanogenerators with the highly piezoelectric material they had produced. The nanogenerators had a significant power density and could harvest small mechanical vibrations in many dynamic circumstances involving those from automobile vehicles and even human motion. The nanogenerators neither used Lead nor needed non-renewable energy sources.

Each nanogenerator is just a shade smaller than an inch square, or 2.5 x 2.5 cm, and the thickness of a business card. It is possible to use them in various situations. They have a significant potential for powering sensors in vast arrays of electronic devices, such as those used by IoT or the Internet of Things, of which the world uses billions, and requires substantially more.

According to the researchers, the new material could have far-reaching consequences. For instance, the vibrations from an aircraft would be enough to power its systems for monitoring its various sensors. On the other side, vibrations from a person’s heartbeat could power their pacemaker, which can run without a battery.

Boosting Battery Life in IoT Devices

Earlier, the assumption was unused energy from the environment, machines, people, and so on could be used to power valuable devices and this would be done for free. The assumption was based on the convergence of four key technologies to enable mass adoption of energy harvesting—efficient voltage converters, efficient harvesting devices, low-power sensors, and low-power microcontrollers. However, it was soon realized that although energy harvesting does operate for free, the system needs investment, which is not free. That has led to the thinking that perhaps energy harvesting may not be the right technology for powering smart energy applications.

Now, with the growth of IoT devices, more sophisticated sensors, more pervasive connectivity, and secure, low-power microcontrollers, there are more devices to be powered than ever before. With most devices being small and battery powered, design engineers are facing challenges such as energy efficiency and long battery life.

In reality, it is no longer worthwhile using sensors for measuring and analyzing the energy consumption of individual light bulbs, since the cost of such a system would be more compared to the energy cost to run the lamp. In addition, there are numerous low-energy-consuming light sources available.

Development of engineering systems now place more emphasis on maximizing performance and saving energy. This is because most IoT devices spend a significant part of their life sleeping or hibernating, where the part is neither operating nor completely shut down. In this state, the device is actually drawing quiescent current, and this places the maximum impact on battery life, as it contributes to the standby power consumption of the system.

The development of nanoPower technology has led to great advancements in maximizing performance and saving energy. Newer products, with advanced analog CMOS process technology, now operate in their quiescent state with nanoampere currents that are almost immeasurable. The trick in maximizing energy-saving benefits from these products is first by duty-cycling them, and secondly by decentralizing the power-consuming architecture.

Benefits of nanoPower technology also extend to their ability to turn off circuits within the system. For instance, the nanoPower architecture may allow powering critical components such as real-time clocks and battery monitoring, while cutting off power to major consumers such as the RF circuits and the microcontroller, which can either turn off or enter their lowest power-consumption mode.

System monitoring ICs play a huge role here with their small packages and nanoamp quiescent current levels. Comparators, op amps, current sense amplifiers, and more help ensure important issues such as the voltage levels on microcontrollers are at proper levels. For instance, a nanoPower window comparator monitors the battery voltage and provides an alert if the battery voltage goes beyond allowable levels. Apart from being a valuable safety function, this also helps to extend the battery life, as the microcontroller need not operate until it has received an alarm from the comparator.

Another power-saving scheme is OR-ing the battery supply with voltage from a wall wart or an additional battery, using OR-ing diodes. These are Schottky diodes in series with the battery supply for limiting the voltage drop. For instance, MAX402000 diodes can save tens to hundreds of milliWatts of battery power when used in a smart way.