# Piezoelectric Energy Harvesting Prediction and Efficient Management for Industrial Wireless Sensor
## 1 Introduction
### Motivation and Main Contribution  
As mentioned above, this work's main issue is the fluctuating character (due to the engines' operating regime that varies depending on its load) of the amount of energy harvestable from vibrations for supplying the IWSs. Thus, this work's first contribution will then be to design a harvestable energy predictor from an industrial process's vibrations. The above literature overview has also highlighted the need to focus not only on the harvestable energy rate but also on the efficient management of this energy. However, most studies are limited to the performance of the PT without defining the IWS stand-alone specifications. For example, in [27], a PT capable of harvesting power of 8.9 mW at 8.3 Hz is proposed; it would then be interesting to define an application (data size, transmission frequency, or transmission range) for this energy level. The architecture of the proposed system in our study is shown in Figure 1 below. The system includes the IWS, which must measure, process, and transmit the data to a collection point called Base Station (BS). A Predictor of the Harvestable Energy from Vibrations (PHEV) is used to predict the amount of energy available in each transmission cycle. Under the basis of the available power and the sensor's energy requirement, the Power Management Module (PMM) defines the maximum size of the data that can be transmitted to the BS. To quantify the sensor energy requirement, it is necessary to consider the hardware components of the IWS. The hardware is based on three main parts shown in Figure 1 (the sensor, the microprocessor, and the RF transceiver). The characteristics of some ultra-low consumption components currently marketed are shown in Table 1. From the electrical characteristics taken from the component datasheets, the most significant consumption is due to the data communication with power levels of up to 54 mWif we consider the case of the CC2430 transmitter from Texas Instruments [28]. These consumption levels will be even higher if the sensor's energy consumption during sleep mode is considered. The PT must supply the above power levels; Table 2 carries some PT currently marketed and the power density's performance. The most popular and increasingly used transducers are those of Made-Technology [37] because of their high-power density. From the characteristics in Table 2, it appears that the commercially available transducers are useful for a specific predefined frequency band. The power levels supplied are low compared to the energy requirements reported in Table 1. Some research has investigated this issue, and the proposed method is to leave the sensor in sleep mode as long as the stored energy is not sufficient for transmission. For example, in [38], it took 12 h of charging on a 0.33 pF capacitor before the sensor was able to transmit data. In [19], only 512 bits was transmissible every 7 min at less than one kilometer. This poor QoS is because most of the consumption models considered for stand-alone IWSs are based on short-range communication modules like the CC2520 from Texas Instruments. Thus, the solutions proposed so far come to the detriment of the QoS of the IWS, which justifies the need for a new design method, which is the goal of this paper. It is then proposed here to define the specifications of the IWS based on the possibility of predicting the amount of energy harvested during each measurement cycle. The main contributions are to design a predictor of harvestable energy of the surrounding vibrations and the implementation of protocols allowing the