“With the rapid application of the concept of intelligence to many “things” around us, from light bulbs, household appliances and cars, to medical sensors, industrial equipment, and even entire cities, the Internet of Things (IoT) is obviously being rapidly applied. According to Gartner’s analysis data, by 2020, the number of IoT nodes is expected to reach 20.4 billion, which is equivalent to many times the current number of people on the planet.
With the rapid application of the concept of intelligence to many “things” around us, from light bulbs, household appliances and cars, to medical sensors, industrial equipment, and even entire cities, the Internet of Things (IoT) is obviously being rapidly applied. According to Gartner’s analysis data, by 2020, the number of IoT nodes is expected to reach 20.4 billion, which is equivalent to many times the current number of people on the planet.
However, the development of the Internet of Things has not been smooth sailing. One of the challenges is to make these billions of IoT devices work 24 hours a day, 7 days a week, regardless of their specific location and application. Regular replacement of the battery will definitely increase the cost and human resource input. In addition, the environmental impact of the increased energy required by these devices also needs to be carefully considered.
An emerging solution that can meet these challenges is currently emerging. This new technology is energy harvesting. Using this technology, energy can be captured from the surrounding environment and converted into electrical energy. The source of energy may include a variety of possible ways (such as ambient light, vibration, heat or radio frequency, etc.). If this energy is not used, it will be wasted in vain. .
In the Internet of Things environment, the goal of energy harvesting is not to generate a large amount of electricity, but to use it wherever a little energy can be found. Taking ambient light as an example, the collected power is usually between 10µW/cm2 and 10mW/cm2 depending on whether the light source is outdoors or indoors. The energy generated by movement is about 4μw/cm2 to 100μw/cm2, also depending on the energy source (that is, whether the movement originates from a person or a machine). Similarly, the thermal energy that can be extracted from the human body is about 30μW/cm2, and the energy that can be extracted from RF is about 0.1μW/cm2.
Simply put, energy harvesting technology will enable companies to truly utilize the energy in the Internet of Things, while saving the investment and time originally spent on batteries. According to the data of market research company IDTechEx, by 2022, the global annual energy harvesting revenue will exceed 5 billion U.S. dollars. Considering the future growth trend of this technology, what impact does it have on the industry?
Building blocks of energy harvesting systems
Essentially, energy harvesting is divided into three steps: collection, conditioning, and storage. The sensor captures energy from energy sources (such as ambient light, heat, vibration, pressure, radio frequency, etc.) and outputs electrical energy. Next, the power management IC adjusts the input voltage to meet the load requirements, and then delivers the energy to the storage device (usually a super capacitor), which acts as a buffer between low power, intermittent main energy, high power, and continuous load .
Depending on the main energy source, the energy harvesting system uses different types of sensors. For example, photovoltaic energy harvesting systems can capture light energy from outdoors and indoors to supplement or even eliminate batteries in consumer and industrial applications. Similarly, piezoelectric sensors can generate voltage when there is mechanical stress due to pressure or movement. In cars, airplanes, automated equipment, and even human vibrations, these sensors can provide energy for many IoT devices. The PPA-1021 from Mide is a 0.74mm thick piezoelectric sensor that captures vibration energy to produce a 4.5MW DC output at 28.2V.
By using waste heat, pyroelectric sensors can generate power when there is a temperature difference between two different metals. This phenomenon is called the Seebeck effect. The Micropelt TE-CORE heat collection module is used to collect locally available waste heat and convert it into electricity.it is at
Manage collected power
In order to regulate the collected energy and maintain a stable power supply connected to the load, the energy harvesting device needs to include some form of power management integrated circuit (PMIC). Cypress’s energy harvesting power management IC S6AE101A is designed for ultra-low power deployments, requiring only 250nA and 1.2µW operating current and startup power, respectively. By using this chip, compact solar cells can provide enough power for IoT devices to operate under low illumination conditions of about 100lx. As shown in Figure 1, it uses built-in switch control to store the generated electrical energy in the output capacitor. If the power of the solar cell is not enough to meet the demand of the connected load, the power reserve of the battery can supplement the power. As a battery-free wireless sensor node solution, it has an over-voltage protection (OVP) mechanism. Its applications include wireless sensors for heating, ventilation and air conditioning, lighting and security systems, and Bluetooth smart sensors.
Figure 1: Solar power harvesting power management system based on Cypress S6AE101A PMIC. (Source: Cypress)
Linear Technology’s LTC3588-2 is another energy-harvesting PMIC designed for direct connection with piezoelectric, solar or magnetic sensors. It can correct the voltage waveform and store the collected energy on an external capacitor. LTC3588-2 discharges excess power through an internal shunt regulator, and at the same time regulates the output voltage through an efficient nano-power synchronous buck regulator. It has four selectable output voltages, 3.45V, 4.1V, 4.5V and 5.0V, which can provide up to 100mA of continuous output current. In order to provide overvoltage protection, the chip includes an input protection shunt set to 20V, and its potential applications include tire pressure sensors and mobile asset tracking.
In order to charge and protect micro-power storage devices, MAX17710 PMIC provided by Maxim Integrated has a boost regulator circuit. The chip is packaged in a 12-pin UTDFN package, which is specifically optimized for poorly regulated power supplies that are common in energy harvesting scenarios. The applicable voltage level can be as low as 0.75V. The power output value of MAX17710 PMIC is between 1µW and 100mW. It also includes an internal voltage regulator for overcharge protection. The output voltage provided to the target application is regulated by a low-dropout (LDO) linear regulator with 3.3V , 2.3V or 1.8V optional output voltage. The output regulator can work in selectable low-power or ultra-low-power modes to minimize the power consumption of energy storage devices.
Figure 2: An energy harvesting system for charging micro-power storage devices implemented by Maxim MAX17710. (Source: Maxim Integrated)
Provide continuous stable power
Supercapacitors have high energy storage capacity and can provide stable power for continuous loads that depend on energy harvesting equipment. Murata’s DMH series of supercapacitors have high capacitance, which can provide energy buffering and peak power assistance for this type of equipment. These supercapacitors have a capacitance of 35mF, a rated voltage of 4.5V and a static resistance (ESR) of 300mΩ. The package size is 20mm x 20mm x 0.4mm and is suitable for applications with limited space and battery life. These supercapacitors have only the thickness of thin paper and can be installed under button batteries, inside smart cards, or behind device screens. Their key applications include wearable technology, retail systems, e-readers, and low-thickness I/O smart devices.
Development of new products
eZ430-RF2500-SHE is a solar energy harvesting development tool from Texas Instruments, which can help design engineers create and test a permanently powered wireless sensor network. The tool uses an ultra-low power MCU, including a high-efficiency solar panel, which can provide enough power to power wireless sensor applications without requiring any additional batteries even under indoor lighting conditions.
To Go Kit provided by Wurth Electronics is also a complete development tool, which can provide energy harvesting, energy management and storage functions through a package. The kit includes a solar panel (32mm x 50mm) and a thermos-generator (40mm x 40mm) as two energy harvesting sources, and is equipped with an EFM32 Giant Gecko MCU with a 48MHz ARM Cortex™ M3 core .
As energy harvesting technology is showing bright prospects for green energy in almost all fields, researchers are working hard to explore new possible applications. In this context, scientists at the University of Michigan have almost reached the core of this technology and developed a device that obtains energy from the human heartbeat to provide energy for pacemakers or implantable defibrillators. Progress can eliminate the risks and troubles associated with critical medical equipment requiring periodic battery replacement. Similarly, researchers are also working to obtain energy from human body heat, motion, and vibration to meet the power requirements of implantable IoT devices. There are many energy sources around us, but most of them cannot be effectively used as electrical energy at present. Energy harvesting technology bridges this gap, so it will play an important role in all our future efforts.
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