This study aims to develop a smart shoe which can generate sufficient electrical power and monitor accurate step count distance and velocity more than pedometer through the online server
In this chapter, we will be focusing on the secondary data used for the study based on books, journal articles, magazines, newspaper, etc. This will be focusing on Piezo electric power generators ,weaknesses of solar power energy generators for the wearable devices and IOT based technology .
Piezo electric power generators
Piezoelectric material will generate electric energy when it is pressed. For example, two piezoelectric ?lms which were connected in parallel directly put inside a shoe to generate electric energy from foot step Ref 9.
Rocha, Goncalves and Silva (2010) Ref 4 realized a prototype based on an electrostatic generator located in the bottom of the shoe. The energy was gathered by the deformation of dielectric elastomer loaded. Researchers in Portugal have created a prototype using two PVDF piezoelectric sheets placed in zones subject to greater change of pressure .it is observed that energy has increased By coupling piezoelectric elements in this study .
Few prototype of smart shoes were developed by MIT media laboratory in Cambridge using different technologies. One of prototype consisted of glued 8 sheets of PVDF piezoelectric material with dominant polarization on the ?exible plastic sheet . The system recovers energy depend on the flexibility of the sole, generating a mean power of 1.1mW. The second prototype has been developed by the pressure exerted by the heel and using a layer of PZT (piezoelectric ceramic material) mounted on a sheet of spring steel. It could be generating a mean power of 1.8 mW. The last prototype adapts with a standard rotatable electromagnetic generator through a back plate located on the side of the shoe and it is activated by the pressing on the foot , It could be generating a mean power of 0.23 W.Ref 5-7 .According to the MIT studies ,It is observed that more electric power can be generated by second prototype which is capable to generate 1.8mW .The last prototype mentioned above is totally fail because less power generates and physical structure of the device is relatively large and it makes user uncomfortable, Actually it cannot be considered as a wearable smart device .
The smart energy harvesting systems incorporating piezostack ,piezoelectric PVDF, buzzer with the aim of showing sevaral different possible solutions to recover the energy needed to provide GPS module. As the ?rst solution, a PVDF piezoelectric sheet has been positioned at the place parallel to the heel of the soleRef 8. The shoe should have capability to subject considerable higher stresses .Thus, piezoelectric materials those are characterized by brittle behavior have been considered unsuitable for smart shoes and the choice has fallen on the PVDF material as its ?exibility.
In the second solution there are two energy generating systems four buzzers on the rear of the sole and the ?lm of PVDF piezoelectric material placed on the front of the sole .Ref 8 Though this model is most
expensive and complex , this is the most ef?cient during the device operation even in lower weight user situations. The dual power system ensures the continue power generating even in case of failure of one power generating system or ensures the adaptation to any style of walking .
In the third solution, an Energy Harvesting system is based on ?-PVDF piezo electrical material which is capable of generating electric current not only walking, but in compression and when it is bent. In order to exploit this feature the piezoelectric sheet material must be kept folded Ref 8 .In this method maximum bent angle is limited and therefore more piezoelectric sheets should be merged to produce enough voltage to consume .
Also in the another solution, Dual Energy Harvesting method have been used. 12 piezo stack positioned in the heel area and a folded sheets of piezoelectric material is positioned in the forefoot area . The piezo stacks in the heel are positioned inside using a 3D printer, which has as its main purpose to provide a rigid base to piezo stacks otherwise it would sink into the rubber plate of the sole reducing large sector of their deformation and thus the power generated.Ref 8.in this method is relatively good because of dual energy harvesting but it is more costly using 3D printer.
Flat plate type
The piezoelectric foil which can be shaped into an elongated hexagon type to conform to the bending distribution of a standard sole of shoe, as depicted by Paradiso and Shenck Ref 5
Frontoni(2013) developed a new device which can be built in a shoe, and the device was assembled ceramic piezo materials and polymer accomplished by injecting molding to implement both outdoor GPS tracker and indoor radio frequency identi?cation (RFID) Ref 11. Gatto(2014) presented four different solutions of smart shoes based on PVDF sheet to supply a GPS device Ref 29. Hwang (2015) designed a piezoelectric floor tile based on PZT piezo material , which are indirect energy transmission using and a tip mass and springs, 55 mW electricity power can be generated through comparison of impedance Ref 12. The sole was divided into 8 elements that were connected in parallel, and each element can provide a 2 V open-circuit voltage can be generated when 70kg of weight human wear a shoe Ref 14. Almusallam made a screen printed piezoelectric shoe including energy generator using an ?exible PZT-polymer material Ref 13. Razian(2003) created tri-hub transducer with 10 * 10 *2.7 mm made of PZT to estimation in-shoe force Ref 15. Moreover Geng (2010) built up a more smaller than normal tri-pivotal piezoelectric transducer made of PZT, which was just 10*10*1 mm Ref 16. Nevill likewise built up a piezoelectric transducer made of copolymer (PVDF-TrFE) to quantify in-shoe press and accomplished an objective of 10% vulnerability Ref 17.
Since this type piezoelectric transducer can create bigger strain than ?at plate compose, it can enhance the ef?ciency of piezoelectric power generation 18. MIT Lab in California teammates investigated an unpretentious 31 mode piezoelectric vitality scavenging based on PZT I sheets in shoes, which is known as a “dimorph”, comprising of two consecutive, single-sided unimorph Ref 5. The gadget is to tackle foot strike energy by ?attening bended. Hu propose a ridged PVDF bimorph control collector Ref 20. Also, they demonstrated that the versatility of a gatherer can be enhanced significantly by planning the reaping structure with customizable resounding recurrence., Zhao ( 2014) proposed a sandwich structure that is a multilayer PVDF ?lm sandwiched between two wavy surfaces, which is promptly perfect with a shoe Ref 19. The structure can enhance the generating performances since it empowers the PVDF ?lm to produce a substantial longitudinal stretch and diminish the reaper thickness. Additionally, the structure can be coordinated into a shoe whose inward space is restricted. Fourie built up a horseshoe-formed structure, which is situated on the foot rear area of shoes Ref 21. PVDF ?lms were embedded in the notches vertically. Amid a foot rear area strike, for the ?exibility of the PVDF ?lm, the ?lm fortified on the plastic ?lm substrate twisted, and the substrate comes back to its previous shape after deformation the piezoelectric charges can be collected.
Kim(2004) built up a piezoelectric transducer in view of PZT which worked in ?ex-tensional (F-T) mode Ref 22. Also Li (2011) built up a piezoelectric transducer which worked in ?ex-compressive (F-C) mode Ref 23. The transducer in F-C mode, which exchanges a transversely connected power F into an ampli?ed longitudinal power N to keep piezoelectric clay piece from being broken ,it can withstand a bigger force and enhance output voltage contrasted with F-T mode.
Palosaari produced a piezoelectric power generator using Cymbal design type which was made of PZT Ref 24. Palosaari demonstrated that the generated power can fulfill the requests of some observing hardware or convenient gadgets., Daniels (2012) create a new piezoelectric power generator gadget that is known as the piezoelectric ?ex transducer (PFT).It can withstand relatively higher powers than cymbal transducer Ref 25, The gadget made of PZT can create a normal most extreme energy of 2.5 mW when retro?tted into a shoe. Yangbuilt up a shell shape power generator, comprising of a PVDF ?lm connected to a bended substrate to overcome the dif?culty that the plan of a piezoelectric transducer required high moving rate to gather energy from human movement Ref 26. The structure can create high voltage and power although the user weight is low or the motional is low. Jung composed a capable bended piezoelectric