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Self-Powered Sensory Transducers: A Way Toward Green Internet of Things

Rajeev Ranjan

School of Computer Science and Applications, REVA University, Bangalore, Karnataka, India

Abstract

A sensory transducer is a device that can convert environmental energy or event into a signal/energy that can be stored for further processing. For these conversions, small and low-cost devices are preferred by many engineers. Most of the devices used in such ubiquitous applications work in a hostile environment, where changing or replacing the power module is almost impossible. To overcome these problems, energy scavenging may be the solution. Researchers focus more on such devices because they regenerate power from the environment and can be used for a more extended period with less maintenance monitoring systems with the Internet of Things (IoT).

This work summarizes an overview of the low-cost, self-powered sensory transducers used in different areas of applications. The research aims at the different ways to generate/recharge the power sources and their uses on different applications. It also focuses on recent challenges and the future scope of the device. Moreover, the work enlightens on the interrelation of self-powered devices to the evolution of Green IoT.

Keywords: Self-powered transducers, sensors, WSAN, Internet of Things, green computing, energy harvesting, wireless sensor networks

1.1 Introduction

On May 19, 2021, Cyclone Tauktae struck the coast of India with a speed of 80 kmph. Likewise, two cyclones hit Indian states in the era of COVID-19 pandemic. However, the early detection of such kinds of natural calamities, for example, could reduce damage and life causalities. This early detection and monitoring of events are possible with advanced devices like sensors and actuators. A sensor works on the principle of transduction, which can convert environmental parameters in a readable signal form [1, 2]. The actuator performs necessary actions to the environment based on the sensed data [3].

The invention of sensors and actuators makes human life more manageable. The goal of the invention is to monitor objects and events in the area where human intervention is almost impossible [4]. In the present era, sensors can be used in almost every part of life. These sensors and actuators form Wireless Sensors and Actuator Networks (WSANs) to communicate wirelessly in a single-hop or multi-hop manner [5], and hence, they experience all the challenges faced by any wireless device. Furthermore, the device needs to work in a hostile environment with constrained resources [6-8] (Figure 1.1).

The sensory transducers require power to operate. A typical sensor required 50 microwatts (mW) to 150 mW of power in an active state [19]. As a result of the hostile working environment and complex applications, changing the power module is a bit tedious. Therefore, to overcome the problem, there are two ways: (i) to minimize the energy demand by the sensor devices and network, (ii) self-powered devices by generating energy from the environment. In the early days of sensor research, scientists proposed many techniques to optimize energy consumption. However, it lowers the Quality-of-Service (QoS) and affects the environment. Therefore, scientists have shown the path for the second option. Self-powered devices will help the system run for a more extended period with high QoS [9].

Figure 1.1 Constraints and challenges in WSAN.

Sensor is the primary element of a typical IoT application because it creates data in the form of signals [10-12]. The data created by sensor networks are saved, processed, and analyzed to gain information. The term IoT, coined by Kevin Ashton in 1999 [13], is associated with a heterogeneous set of such sensors, communicating devices, and networks working together with the Internet to achieve the goal(s).

IoT plays a significant role in information and communication technology (ICT) to automate and monitor remote events. Various hardware devices and software modules are working together in the ICT sector to achieve a goal in almost all human life fields. The hardware module includes electronic chips, antenna, processing units, and I/O devices. These devices need to work with different communication protocols, scheduling algorithms, and data processing in a few cases. In this process, most 2% of total greenhouse emissions are caused by ICT and related areas [14]. To minimize these emissions, self-powered sensors and actuators are one of the technologies leading to Green IoT [15]. Green IoT portraits the concept of reduced energy consumption of IoT devices and WSNs to make the environment safe.

In this work, the need and development of self-powered devices have been studied. The significant contribution of the work focuses on the following:

• The necessity of self-powered systems in IoT
• Finding a connection of the devices with green computation
• Parameter requirement and scope for development of such devices in different applications
• Future scope and challenges of the devices in the current scenario

1.2 Need of the Work

Self-powered systems play an important role in IoT applications because of high energy demand. However, developing and work with these systems is challenging in nature. A few reasons are:

• The sensors or actuators used in IoT are smaller in size and cost. These networks are always resource-constrained networks.
• These devices have to work in a hostile environment with different sets of hardware and software.
• The IoT applications use different transmission media, for example, RF, infrared, etc., for communication.
• The survivability and maintenance of the sensor mote working for ICT sectors are very challenging. However, applicability and users are enormous in numbers.

Moreover, generating power from the environment also requires advanced techniques and processes, which require more resources. Therefore, extensive research is the need of the hour, which concentrates on the process, techniques, requirements, applicability, challenges, and future scope of the work. It is also required exploring its ways toward green ICT Technology.

1.3 Energy Scavenging Schemes in WSAN

Energy scavenging from the environment is required to fill the gap between energy demand and supply in WSAN. As nonrechargeable primary batteries cannot increase the network lifetime and thus lower the QoS, researchers have proposed techniques for power generation. As a result of this, self-powered systems and devices become possible [16]. In this section, a few of such techniques and methods have been discussed.

1.3.1 Photovoltaic or Solar Cell

Sun is a significant source of energy in our universe. The average solar power radiation arrives at the earth's atmosphere annually is approximately 1361 W/m2 [17]. This gives a huge potential for the power-hungry device to work with a longer lifetime. The use of PV cell in WSN gives more advantages over another energy-generating mechanism.

Solar is a continuous and huge source of energy. It provides highest power density among other energy scavenging techniques [19]. Table 1.1 highlights the energy generated by PV cell.

Table 1.1 Energy harvesting by PV cell.

It can be used for power constrained, low cost, small size devices, as well as for heavy machines in an industry.

A typical solar cell consists of a semiconductor of NP junction [18] (Figure 1.2). When the light energy emits the semiconductor's surface, it converts the light energy into electrical energy. This ability of the conversion is called energy conversion efficiency. The energy conversion efficiency is calculated as the ratio of energy output from the solar cell to input energy from the sun. The typical conversion efficiency of a solar cell is approximately 10% to 15%. Some researchers have proposed a maximum power point tracker (MPPT) algorithm based photovoltaic power supply for WSN [20-23]. It is a prevalent technique used in PV cells to maximize power extraction. It has been proven that the algorithm improves the utilization by 85-90% with little effect from environmental disturbance and noise. Much earlier research focuses on solar power-based energy harvesting.

In the one hand, many researchers have focused on a solar-powered cell in many applications; on the other hand, there are certain limitations, which restrict the use of PV cell. The PV cell can be used only for terrestrial applications; however, many underwater and underground applications exist where PV cell usage is restricted. As the sensor and actuator network is a highly densely deployed and low-cost network, equipping each sensor with a solar panel will be a tedious task, increasing the deployment cost. The charging rate of a PV cell depends on the size of the solar surface and the application area. There is always a need to periodically clean the solar cell surface to ensure the required efficiency of the cell. As per the knowledge, the energy generation prediction is very general...