# Design of an Energy Harvester Based on a Rubber Bearing Floating Slab Track
## 1 Introduction  
In recent years, urban rail transit has been widely accepted as a large-capacity and low-carbon transportation mode. With the increasing mileage of rail transit operation, its operational safety has been paid more and more attention [1]. To ensure the safety of rail transit during the operation period, it is necessary to carry out health monitoring on its engineering structure. Traditional monitoring sensor networks are mainly connected to a mains power supply or battery, which has some problems such as high maintenance cost and environmental pollution. Since a large amount of mechanical energy will be generated by train operation in urban rail transit system [2], it is of great significance to design a kind of energy harvester to capture electric energy from the track structure. At present, many scholars have designed energy harvesters for rail transit infrastructure in order to capture energy from different structures and positions, mainly including rails, fasteners, and sleepers. For the rail, [PERSON] et al. [3] designed a broadband cantilever energy harvester, which installed a broadband piezoelectric array on one side of the rail to capture the track vibration mechanical energy during train operation at various frequencies. Due to the train vibration frequency deviating from its working frequency band in real environment, it did not achieve the expected effect. [PERSON] et al. [4] developed a portable and efficient electromagnetic energy harvesting system with supercapacitors, which wasinstalled at the bottom of rails to convert the energy of track vibration into electric energy and provide stable power output for external loads. For the fastener, [PERSON] et al. [5] designed a piezoelectric energy harvester installed under the fastener backing plate to capture the energy generated by train vibration, and the power obtained was sufficient to power the wireless sensor. For the sleeper, [PERSON] et al. [6] designed an energy harvester for the upper part of the sleeper based on the electromagnetic energy collection technology. It featured a gear structure that converted the irregular pulse bidirectional linear vibration of the track into adjustable unidirectional rotational motion to improve the output power and reliability. [PERSON] et al. [7] also designed an enabling structure for the upper part of sleeper, using a spring pretensioning and resetting device for quick installation without anchoring it into the railroad foundation. In addition to the design of energy harvesters starting from common track infrastructure components, scholars have carried out corresponding energy capture research on floating slab track. [PERSON] et al. [8] proposed a small but high bearing capacity piezoelectric energy harvester for steel spring floating slab track, which was mainly installed between track slab and steel spring supporting structure to improve the energy harvesting efficiency. At present, the design of energy harvesters for a floating slab track cannot cover all types, so it still needs further study. The piezoelectric energy harvesting structure utilizes the positive piezoelectric effect of piezoelectric materials to convert mechanical energy into electrical energy [9], thus achieving energy recovery and reuse. The materials involved in piezoelectric energy harvesting mainly include piezoelectric ceramics (PZT), polyvinylidene fluoride (PVDF), and piezoelectric fibers. Piezoelectric materials, especially PZT, are generally not directly exposed to the working environment in the process of energy conversion due to their own brittleness, weak bearing capacity, small displacement, and other characteristic limitations, but packaging structures are added outside them to form piezoelectric energy harvesters [10]. At present, there are many studies on piezoelectric energy harvesters.