The piezoelectric effect is understood as the linear electro-mechanical interaction between the mechanical and the electrical state in crystalline materials with no inversion symmetry. The piezoelectric effect is a reversible process in that materials exhibiting the direct piezoelectric effect (the internal generation of electrical charge resulting from an applied mechanical force) also exhibit the reverse piezoelectric effect (the internal generation of a mechanical strain resulting from an applied electrical field).
Fig.3.1 Piezoelectric principle
Fig.3.2. Working principle
The nature of the piezoelectric effect is closely related to the occurrence of electric dipole moments in solids. The latter may either be induced for ions on crystal lattice sites with asymmetric charge surroundings or may directly be carried by molecular groups. The dipole density or polarization (dimensionality [cm/m3]) may easily be calculated for crystals by summing up the dipole moments per volume of the crystallographic unit cell. As every dipole is a vector, the dipole density P is a vector field. Dipoles near each other tend to be aligned in regions called Weiss domains. The domains are usually randomly oriented, but can be aligned using the process of poling (not the same as magnetic poling), a process by which a strong electric field is applied across the material, usually at elevated temperatures.
One of the decisive importance for the piezoelectric effect is the change of polarization P when applying a mechanical stress. This might either be caused by a reconfiguration of the dipole-inducing surrounding or by re-orientation of molecular dipole moments under the influence of the external stress.
Fig.3.3. Mechanism of kinetic footfall
3.1.1 Mechanical Stress
Here the mechanical stress is considered as the weight of the footsteps per unit area. The weight of the footsteps due to gravity is converted into mechanical rotation. stress is a physical quantity that expresses the internal forces that neighboring particles of a continuous material exert on each other. For example, when a solid vertical bar is supporting a weight, each particle in the bar pulls on the particles immediately above and below it. When a liquid is under pressure, each particle gets pushed inwards byall the surrounding particles, and, in reaction, pushes them outwards. These macroscopic forces are actually the average of a very large number of intermolecular forces and collisions between the molecules in those particles. Stress inside a body may arise by various mechanisms, such as reaction to external forces applied to the bulk material (like gravity) or to its surface (like contact forces, external pressure, or friction). Any strain (deformation) of a solid material generates an internal elastic stress, analogous to the reaction force of a spring that tends to restore the material to its original undeformed state. In liquids and gases, only deformations that change the volume generate persistent elastic stress. However, if the deformation is gradually changing with time, even in fluids there will usually be some viscous stress, opposing that change. Elastic and viscous stresses are usually combined under the name mechanical stress.
4.1 Case study
Based on the journals Power Generation Footstep by Shiraz Afzal,etal, and Proposed Method of Foot Step Power Generation Using Piezo Electric Sensor by Mr. A. Adhithan,etal,the feasibility of adopting power generation from footsteps is discussed.
4.2 Study area
The feasibility test of kinetic footfall was conducted at Time Square in New York City. Times Square is a major commercial intersection and neighborhood in Midtown Manhattan, New York City, at the junction of Broadway and Seventh Avenue, and stretching from West 42nd to West 47th Streets. With latitude and longitude coordinates: 40.758896, -73.985130.
4.3 Calculations and feasibility
The idea is to place pavegen tiles throughout Time square on the sidewalks. Since Time square gets roughly 350,000 pedestrians every day, it would make sense to put these on the sidewalks to generate a little electricity,.On average a pedestrian in New York City will walk approximately one mile a day or around 20 blocks. If we assume that each person who goes through Time Square walks one mile, the number of total steps taken is equal to around 650 million steps per day. This is calculated by multiplying the number of pedestrians, 350,000, by 5280 feet per mile and dividing that by 2.5ft per step. Pavegen tells us that each of their blocks will produce 7 watts per impulse of a step, which is 0.68 seconds when measured. This produces 4.76 Joules per step of energy. Multiplying this by the number of steps total for one day and then for one year, the amount of energy produced for one year is 1,105GJ. This is equal to about 307,000 kWh per year of electricity produced. If we assume that electricity costs $0.15 per kWh, the total savings of installing the tiles is $46,042 per year. Unfortunately, each tile costs well over $100 at the moment, and to cover all of Time Square's sidewalks with these tiles, needing around 236,000 of them, it would cost upwards of $23 million dollars. The number of tiles needed was calculated by knowing the area of each tile from Pavegen's website, and calculating the total area of sidewalk within Time's Square. This was done by assuming that each sidewalk is roughly 12 feet in width and then using Google Maps to determine how much sidewalk is in Time Square. The square footage of sidewalk estimated to be in Times Square is roughly 686,500 ft square.
In Time Square during the New Years Eve Celebration. The number of people that come to Time Square for the celebration is approximately one million. Plus, the area in which they are all moving around is much smaller than all of Times Square. Assuming that the area in which the one million people are is equal to a right triangle with lengths of 1500ft and 250ft, roughly half the area of 2 city blocks, and that each person again walks an estimated one mile total, the number of total steps taken for that night is 2.1 billion. The dimensions for the area of the celebration was gotten by using Google Maps and estimating the area as accurately as possible. With that many steps, the amount of power generated is equal to 14.8 million kW. Lets also assume that the celebration goes on from 7pm to 1am, or six hours, and therefore the number of kWh generated is equal to 2792 kWh.
4.3.1 Market Analysis
Energy harvesting (EH) has become a major area of focus in Europe and North America; Asian organizations too are investing in the various EH technologies. By 2020, the global energy harvesting market is expected to reach $4.4bn.
Majority of the sustainable energy technologies calls for a constant monitoring of, the surrounding environment of installation location. Further, the suitable type and specifications of the devices has to be decided based on the survey reports. Parameters such as size of the devices and place of installation also mandate the tedious, time and effort-consuming post-installation monitoring and maintenance tasks.
In contrast to other technologies for which locations are decided based on surveys conducted over a prolonged period, energy harvesting floors eliminate any pre-installation analyzing or monitoring to identify the ideal location. The sole criterion to be fulfilled for the installation is that the place should have human movement. Every city around the world has a huge, growing population, and public places like airports, railway stations and commercial complexes receive huge amount of footfalls throughout the day, thus making them suitable for energy harvesting floors
Energy harvesting tiles started off as prototypes in the beginning of the last decade; significant developments have given them a capability to produce up to 20 watts per hit and about 10 kilowatt-hours in a week. With the support from environmentalists, these tiles have become a runaway success around the world.
4.3.2 IP Perspective
The footfall energy harvesting floor technology came into existence in the mid of 20th century. However, it has received increased attention in the last few years, which is evident from a considerable increase in the number of patent filings in the piezoelectric sector. The traditional lead zirconatetitanate PZT ceramic is being replaced with organic alternatives such as polyvinylidenedifluoride. In addition to creating piezoelectric systems with enhanced efficiency and temperature performance, companies also lay emphasis on the flexibility of the materials.
Companies such as Toyota Boshoku Corp, Pavegen, Seratech, Hong Kong Applied Science and Technology Research Institute Co Ltd are prominent players in energy harvesting floors. Below is a comparative split of patents/publications owned by the players:
Fig.4.1. Assignee analysis
Fig.4.2 Product analysis
UK-based Pavegen has installed tiles in more than 100 locations, including Harrods and Heathrow Airport. In 2015 the startup raised £2 million from over 1,500 investors on equity crowdfunding platform Crowdcube.
4.3 Future Aspects
In future aspects we can use this principal in the speed breakers at high ways where are rushes of the vehicles too much thus increase input torque and ultimate output of generator. If this project is implemented at very busy stairs palace then we produce efficient useful electrical for large purpose.
- To store the electricity in battery.
- It can be use at any time when it necessary.
- Easy construction.
- Less number of parts required.
- Electricity can used for many purposes
- In street light.
- In LED light for specific purposes.
- In air circulation system for room by the small fans.
- For used in security alarm
- This can be implemented on railway station to generate elec-tric power.
- In bus station.
- In car parking system.
- In Airports.
- In Lift system.
- In car lifting system.
- Electric escalators