Our road and skyways have become overcrowded with vehicles, which has created the need to shift to another transportation solution: railways. This shift has played a major role in pushing the railway industry to improve infrastructure and maintenance processes. Consequently, about 25 to 35 percent of total train operating expenses are for track maintenance needs. What is needed are cost effective rail solutions.

The need for solutions that can optimize the work in the railway industry has gained much more importance. These solutions will help detect defects at an early stage of their development, allowing an operator to repair the damage before it becomes serious. When a vehicle is scheduled for maintenance or overhaul, knowledge of the damage and severity is beneficial, resulting in fewer operational problems, optimizing the fleet availability, and reducing the overall losses and interruption expenses.

Mechanical Sensors
One of the solutions implemented is mechanical sensors. These sensors were applied to measure track geometry parameters. The electromagnetic technique was one of the primary tools for inspecting rail internal defects in highspeed networks until 1953 when ultrasonic transducers were introduced to railway inspection. Since then, various inspection methods have been used for monitoring the health of railway infrastructure or as a preventive measure against rail failures.

Rail axle bearings and wheels are essential parts of the train; any defect might result in severe consequences. Premature failure of rail axle bearings causes a significant increase in train operating costs and can impact train safety. Healthy bearings produce a certain level of vibration and noise, but a bearing with a defect causes substantial vibration and noise levels. Similarly, wheel defects on railway wagons have been identified as an important source of damage to the railway infrastructure and rolling stock. They also cause noise and vibration emissions that are costly to mitigate.

Wheel defects of railway vehicles have a direct impact in causing an increase in attrition and damage to the railway infrastructure. Consequently, this adds additional costs to maintenance and repair, leading to a reduced lifetime and availability of rolling stock. Early detection of wheel defects on trains plays a major role in providing the train operators with timely information on necessary repairs that can prevent further deterioration of the wheels and further damages to the railway infrastructure.

There was an increased focus on the quality of the measurement technologies used to support decision-making within the railway domain with the help of the data-driven railway in the last few decades. Traditionally speaking, a combination of high precision inspection against set standards or, where inspection is impractical, periodic action was used to support safety-based decisions within the railway. While safety is still the main priority, maintenance decisions have gained increased attention. Condition monitoring systems are designed to identify the condition of an asset and inform decision-making processes. Consequently, this helps reduce the incidence of urgent and costly unplanned interventions leading to improvements in performance and safety.

Sensing Technologies
Different sensing technologies monitor axle box bearings and wheels, such as vibration/acceleration, microphone/sound measurement, acoustic emissions/ultrasound, and thermal. Vibration, sound measurement, and ultrasound technologies are used to detect early-stage defects. On the other hand, Thermal sensors are based on detecting the heat generated by severely defected bearings and wheels.

Demand for even more cost-effective and environmentally friendly provided solutions was arisen by railway operators. This led to many technologies integrated into the sensors themselves as a way of cutting extra expenses. New sensors in the market, for example, are based on the vibration energy harvesting technology within the piezoelectric PVDF material, which is environmentally friendly and low-cost. This technology is integrated with the sensor’s design utilizing Piezoelectric PVDF material to convert vibrations into electricity. This technology is based on the cantilever structure, and as the cantilever vibrates, it generates electricity stored in a supercapacitor. Afterward, the electricity from the capacitor is passed to the sensor.

In conclusion, the current market is placing specific demands on the railway industry, resulting in increased needs for cost-effective and safety-oriented solutions. Rail axle bearings and wheels sensors play a major role in detecting early defects that may cause severe consequences. Energy harvesting technology plays its part in saving money and the environment as well.

Energy harvesting, the collection of small amounts of ambient energy from the surrounding environment to power autonomous electronic devices or circuits, is a promising technique that can help produce renewable and clean energy and improve infrastructure sustainability. This technique is used to extract a sample of energy from physical phenomena and the maximum feasible amount of energy. This article introduces the different technologies used to convert the harvested energy from vibrations into electricity in the railway industry.

Energy Harvesting Systems
To explain more about the main principle behind the energy harvesting systems, the energy can be gathered from different sources that are available in the industrial or the environmental surroundings such as natural or artificial light, elevated levels of noise, temperature gradients, mechanical vibration, pipes with air or water fluid. The energy is harvested in the peak time of energy availability. Then, it is being saved and stored in a storage device to be used later, meeting the demand and supply for the daily operation of an electronic system at specified periods. Therefore, the main goal of energy harvesting is to store the power to be used later in needed times.
The process of converting the vibrations into electricity demands three elements to be included in the energy harvesting system. First, a harvester is a part responsible for gathering energy from the surrounding environment. Second, a low power management system is responsible for converting the voltage level of the harvested energy to those of standelectronicsonic and power the electronic system. The last element is the storage system to save and store the excess of harvested energy. This process leads to many environmental and economic benefits, including the elimination of the dependency upon batteries, boosting and enhancing the functionality of the device, increasing the lifetime of the device, elimination of supply wires, facilitating the process of installation, lowering the level of environmental waste, and presenting cheaper options at lower costs.

Harvesting Types
There are currently three efficient types of harvesting which are currently commercialized in the market.

Electromagnetic Induction
The first one and the oldest technology is electromagnetic induction, discovered by Michael Faraday and James Clerk Maxwell more than two hundred years ago. However, electromagnetism has only been used to generate electricity since the early 1930s. According to Helios Vocca and Luca Gammaitoni, the base of the electromagnetic harvester is the electromagnetic induction phenomena, which are defined as “the production of a voltage across a conductor when it is exposed to a varying magnetic field.”

“The inductive technique is usually realized by coupling a permanent magnet and a solenoid in motion relative to each other. These systems show complementary behavior in terms of frequency bandwidth and optimal load in relation to piezoelectric techniques. They are recommended for low frequencies (2–20Hz), small impedance, and medium-size,” was stated in the 2015 book “Micro Energy Harvesting” from Briand, Yeatman, and Roundy.

The magnets and coils used in this technology bring their own advantages, including being reliable, maintenance-free, cost-effective, and configurable. On the other hand, they have many disadvantages, including quite a high price, very complicated manufacturing, and fragility during the chaotic vibrations. Regardless of their disadvantages, those harvesters are the most efficient ones in the market, generating the maximum power output from the vibrations.

Piezoelectric Ceramic
The second technology is piezoelectric ceramic. In the last few decades, piezoelectric materials have played a vital role as a mechanism of energy harvesting as the demand for high-power-density and long-lifespan power sources has become higher. The piezoelectric materials have a crystalline structure that facilitates transforming mechanical strain energy into electrical charge. This structure also plays an important role in converting an applied electrical potential into mechanical strain. The ability of such a structure to transform these types of energies helps in providing the wireless sensor nodes with their needs for electrical energy. This is possible by detecting and extracting the mechanical energy from a specified environment, then converting it into electrical energy.

There are many advantages when choosing piezoelectric technology in the process of converting mechanical energy into electrical energy. Advantages include high energy conversion efficiency, its ability to be made on a greatly reduced scale, and simple implementation. However, piezoelectric ceramic technology is probably the most complicated way of generating power from vibrations. First, it is made of very toxic materials. Second, it is fragile and can be easily damaged irreversibly, which is also not good for the railway industries since there are many tough vibrations. Third, it is costly. In addition to that, piezoceramics do not differ a lot from the market within its efficiency level. Therefore, it is likely the least desired way of extracting the energy from vibrations.

Piezoelectric Polymer Technology
The third way to do it is to use the piezoelectric polymer technology or a material called PVDF. A fragile film assembled on the cantilever structure with the tip mass on end moving up and down while installed on the vibrating equipment. This is the newest method of generating electricity from vibrations. And just as electromagnetic induction, it has its own advantages and disadvantages, including lower power output and lifetime limitations. However, offering it all at reasonably lower prices, much greater durability of acceleration shocks, and assembly using only environmentally friendly materials.

Modern Interest
In the last few decades, the interest in the electromagnetic and piezoelectric conversion mechanisms became of higher importance for their modernized provided solutions. These solutions include the higher capability of electromechanical coupling, their sustainability strategies, their simplified designs, and their ability to break through the old ways of dependency upon batteries. However, piezoelectric polymer technology has proved its superiority over piezoelectric ceramic and electromagnetic technologies from environmental and economic perspectives.

Viezo participated at PowerUp!2020, one of the biggest competitions for start-ups and energy industry entrepreneurs from Central – Eastern Europe.

After being recognised as one of the most innovative start-ups in our home country, we have represented Lithuania in European Finals.

We are more than glad to share with the community that Viezo vision has shared second place and the team has received a 10000 prize.

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