## 1 Introduction  
The Internet of Things (IoT) has emerged as a cornerstone of the Industry 4.0 revolution, transforming industrial operations through real-time monitoring, control, and optimization [1]. In the context of Industry 4.0, IoT enables the creation of smart factories where interconnected devices and systems communicate seamlessly, allowing for real-time monitoring and control of manufacturing processes. These IoT-enabled environments support the implementation of cyber-physical systems, where industrial machinery and IoT technologies converge to create highly adaptive and efficient production lines. By leveraging IoT sensors and actuators throughout the industrial ecosystem, industrial environments achieve unprecedented levels of automation, optimize resource allocation, and implement predictive maintenance strategies, ultimately leading to increased productivity and reduced operational costs [2, 3, 4]. As industrial IoT networks scale up, the number of connected devices and their associated tasks increases. However, the energy available to these devices is limited due to their constrained battery capacities and the often remote or hard-to-reach deployment locations, making frequent battery replacement impractical [5]. This limitation, combined with the drive towards zero-energy and self-powered IoT devices, underscores the need for innovative energy management and harvesting techniques [6; 7]. Since data processing and transmission dominate energy consumption, minimizing overheads and extending battery life through efficient load balancing is essential for the longevity of industrial networks. Therefore, energy efficiency remains a dominant factor when establishing IoT networks within Industry 4.0 [4; 8; 9]. Among the promising solutions, ambient backscatter communication systems (ABSCs) and simultaneous wireless information and power transfer (SWIPT) have gained significant attention. The ABCS allows ultra-low-power communication by reflecting existing RF signals, eliminating the need for active RF components [10]. This technique is highly energy-efficient, though it faces limitations in communication range and data rate, with performance depending on the availability of ambient RF signals. The ABCS operates by altering the impedance of the antenna in a backscatter device, modulating the phase and amplitude of the reflected signal, which can then be decoded by a receiver tuned to the ambient signal. While ABCS is ideal for energy-constrained IoT devices due to its minimal power consumption, challenges related to limited range, data rate, and dependency on RF signal strength remain [11]. Conversely, SWIPT enables simultaneous data and power transmission, optimizing spectrum usage and facilitating zero-energy device development in IoT networks [12]. SWIPT, leveraging electromagnetic waves for dual purposes, allows simultaneous information and power transfer, beneficial in areas where direct power sources are impractical. The two main SWIPT protocols--time switching (TS-SWIPT) and power splitting (PS-SWIPT)--alternate between energy harvesting (EH) and information decoding (ID) periods, or split the received signal power for ID and EH in an optimized ratio [13]. In addition to ABCS and SWIPT, other energy harvesting mechanisms such as solar-, thermal-, and vibration-based methods have been explored to address the energy needs of IoT devices in industrial applications. Solar energy harvesting is well suited for environments with ample sunlight, converting solar radiation into usable electrical energy for IoT nodes [14]. Thermal energy harvesting, which captures waste heat generated in industrial settings, presents a valuable option for energy recovery in temperature-variant environments [15]. Additionally, vibration energy harvesting leverages ambient mechanical vibrations from machinery and equipment, converting them into power suitable for low-energy IoT devices [16]. Each of these mechanisms has unique advantages and challenges, depending on environmental conditions and application requirements.