## 1 Introduction
Finally, the wireless communication can also be implemented in many various ways [2; 9; 10]; employing the short range (e.g., IEEE 802.15.4 or Bluetooth Low Energy (BLE)) or the long range (e.g., Low Power Wide Area Network (LPWAN) technologies), operating in the license-free Industrial, Scientific and Medical (ISM) or in licensed (e.g., Long Term Evolution (LTE) or the recently introduced cellular IoT technologies) frequency bands, etc. The short-range technologies typically outperform the other alternatives with respect to their consumption due to the lower transmit power, the short on-air time, and the more simple protocols. The downside of these systems is the need for more dense infrastructure. The long-range technologies, and particularly, LPWAN systems, typically feature much higher consumption and thus require a node to process and store much more energy for communication, which increases the complexity and cost of the node. There are several alternatives from where a node may attempt to obtain energy for its operation, including, e.g., the solar light, vibration, etc. Nonetheless, most of the potential energy sources are ambient and thus very opportunistic. In contrast to them is the wireless energy transmission, which implies purposeful delivery of the energy to a device in some form over a wireless channel. The comprehensive survey of wireless energy transmission techniques and technologies has been presented in Ref. [11] and references therein. The typical wireless power transfer (WPT) system consists of the three components--the base station emitting the signal carrying the energy, the transmission channel and the energy harvester. The latter typically represents a system receiving the signal (e.g., an antenna) and converting the high-frequency signal to the direct current (DC) (i.e., the rectifier). The survey presents various energy-harvesting circuit topologies and state-of-the-art Schottky diode based circuit designs. The obtained efficiencies range from 1.2 to 72.8 percent in 869-2450 MHz frequency range for input radio power levels of \(-25\) to over +60 dBm [11]. Even though the losses are still quite high, they may already enable particular real-life IoT applications. Therefore, in this study, we propose a methodology for designing a real-life IoT application based on radio frequency (RF) wireless power transfer. Then, we show how this methodology can be employed by developing a WPT-powered solution to sense the temperature and the angular velocity in the rotating industrial environment. These two constitute the main contributions of this paper. Importantly, in the process of our development, we discuss the key trade-offs arising when selecting and designing the critical components of the system: the sensor node, the RF energy harvester, the antennas, and the WPT transmitter. For each of these components, we present and detail our solutions and describe the results of their evaluations. Finally, we integrate all the developed elements and evaluate the complete system, proving that it is capable of meeting all the design goals and requirements. To the best of our knowledge, this is one of the first attempts to propose a methodology of engineering a WPT-based solution, and to develop the complete real-life IoT application based on the non-inductive WPT concept. The very initial results of this study have been reported in [12]. The rest of the paper is organized as follows. Section 2 presents and discusses the related works. In Section 3, we first introduce our proposed development methodology for the WPT-powered applications. Then, we detail our target scenario and show how our proposed methodology can be applied to develop the practical IoT application based on RF-based WPT power supply. The evaluation results for individual components of our solution and the system as a whole are reported also in Section 3. Section 4 concludes the paper, summarizes the results and points out the further challenges and the directions of future works.