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 generator by PVDF ?lm which was made of two bended piezoelectric generators associated consecutive Ref 27. Average Output voltage of 14 V AC of and a average current of 18 mA AC can be gotten by incorporating the structure into a shoe-insole. The piezoelectric transducer in shoe can be intended to create vitality for controlling pedometer. For instance Ishida 2013 built up a shoe insole pedometer that comprises of a piezoelectric power generator and a 2 V natural pedometer circuit Ref 28. PVDF ?lm was utilized as a piezoelectric power generator and it was cut into little pieces and rolled to increase the surface , since generated current of the power generator is proportional to its surface area . Most prominently, one of the PVDF rolls was utilized as a pulse generator to identify step count . In this study, additionally recommended that the recti?ers ought to be appropriated taken after each PVDF those are in parallel to enhance the ef?ciency of the power generator .
Comparing other energy types , cantilever bar is straightforward and perfect. They are compatible with MEMS producing forms, which is about by studied numerous scientists. At the point when the force contact on beams the beam can come back to its initial shape and the inertia will reasoned to the beam make vibration around the underlying area 34.
Johnson exhibited that unimorph cantilever shaft con?guration can create high power though there is lower excitation frequencies and load protections 35. Besides,Ng was designed an enhanced bimorph structures including series and parallel types.36– 37. Moro (2010) develop a piezo electrical material, PZT was mounted inside the shoe heel utilizing a convectional clamp clip without loss of solace in shoe outline 38,
They likewise built up a preparatory investigation and con?rmed that shoe-mounted scavenger has the ability of giving suf?cient electrical power levels under foot sole area increasing speeds while human walking . In any case, Mateu completed a comprehensive and fastidious examination for various piezoelectric bar structures made of PVDF and prove the characteristics of these structures 39. They demonstrated that triangular cantilever endures more strain than a cantilever with a rectangular shape and the most extreme de?ection is happen in triangular cantilever. Goldschmidtboeing also identi?ed that triangular-formed bars are more powerful than rectangular-molded 40.Shenck(1999) explain that along these lines, a triangular cantilever bars would be a superior decision for a shoe embed41 . Roundy presents that the trapezoidal formed cantilever was shown that it can generate more power than rectangular one .42– 43. Since the most extreme de?ection is restricted in a useful shoe embed. Mostly shoes which can generate power consists of rectangular-shaped beam type piezoelectric transducers .
Meier (2014) create power generator of PZT, shoe-mounted framework, which utilized piezoelectric transducers with cantilever structure 46. Camilloni . likewise presents a piezoelectric power collecter which has a piezoelectric beam with a proof mass joined to the corner of the beam 47. The above study introduced an electric-mechanical model of a piezoelectric transducer in a cantilever con?guration, and the model can be utilized for distinguishing the ideal position in which the piezoelectric cantilever beam is set on a shoe for the most extreme power generation while walking or running.
Li (2010) built up a PZT cantilever piezoelectric power generator with a bended L-formed verification mass, which accomplished a fundamental frequency that was 20%– 31% lower than that of the piece molded mass collector and a power density , which was 68% higher than that of the regular cantilever piezoelectric power generator 48
Rguiti(2014) built up a piezoelectric generator, which was made of six at the end 49, as appeared in Fig. 9(a). They described and investigated its piezoelectric reaction and demonstrated that it can work at low and numerous thunderous frequencies. They understood that the recurrence data transfer capacity was broadened up to 200% contrasted with the one acquired from a solitary cantilever bar.The most extreme power output came to around 2.5 microWatt at the load resistance of 275 kiloOhm . When all cantilevers were in parallel and the power was expanded by 39% when contrasted with the energy of a single bar.,
Additional piezoelectric materials for transdusers
This part reviews about piezoelectric material for energy generations transdusers in addition to PZT and PVDF. , Klimiec (2011) developed mini power harvester based on PVDF polypropylene (PP) piezoelectric material to generate energy while walking 51. About 5.3 mW of electric power was produced by single layer PP ?lm and about 3.3 mW of electric power was prodused by poly vinylidene ?uoride ?lm. The collected voltage from polypropylene (PP) is about 12V and about 3.5V for PVDF ?lm. In the present most scientists attention studies about AlN ?lm and ZnO nanoparticles as new piezo electric materials., Elfrink (2009) presented the data sheets of AlN ?lm based piezoelectric energy generating 52. The AlN ?lms which has a thickness about 400nm were deposited by reactive sputtering from an Al target. 60 mW output electrical powers can be generated by an unpacked AlN device at an acceleration of 2g with a resonance frequency of 570 Hz. AlN could be considered as a good piezoelectric material because of easiness of processing and high power generation compared to PZT. Prashanthi(2013) fabricated a nanocomposite adding ZnO nanoparticles (NPs) and a photosensitive SU-8 polymer matrix for energy generator 53.The highly piezoelectric properties of ZnO and the photo-patternability of the SU-8 polymer can be combined by including ZnO nanoparticles into a photosensitive SU-8 polymer matrix. ZnO nanoparticles exhibits the both piezoelectric and semiconducting properties as well as the formation of a Schottky effect at the electrode contact, Due to excellent performances of these nanoparticle piezoelectric transducers, the wide range of study area will be covered by the researches in the future.
*** Energy Harvesting (EH) technologies could be an answer to many power supply related issues especially in IoT & wireless projects. EH technology is not only green and clean but reduces lots of hassle & price considerations. We hope to see our future in-sight smart cities and industrial set-ups to be equipped with EH sensors and power modules.
IoT & wearable technology
Wireless sensors and smart devices can be controlled by the internet anytime and anywhere with the IoT concept.Wireless sensor networks (WSNs) mostly seen in detecting events and identifying surrounding information. Since sensors which are in wearable devices are powered by portable battery , recharging the batteries of smart devices by home electricity is very hard to achieve.For the most of smart online operations, energy generating studies have been much attention through the researchers. The researchers said that energy generating technologies could be applied in, alarm sensors, smart meters, smoke detectors and remote controls. There will be 25 billions of Internet connected devices by 2020 according to calculations of statistics specialists . Wireless sensors which are included in IoT devices are connected to a network will gather information about the environment from the sensor terminals. A key requirement for IoT andM2M concept is the ability to locate place wireless sensors in any kind of locations to obtain the necessary signals .In spite of above there is another big issue is the battery use and life or the installation of power distribution by the wire network or the time period for the replacement of battery . It is worst that fixing this a problem with 10 -20 batteries or huge battery with large capacity . there are lots of people those are concerns about not only initial costs for battery but also the large scale of maintenance costs .Those facts reasoned for spread the studies about the portable energy generation with the smart wearable devices. solar cells, piezoelectric elements, and thermoelectric elements are used as power generating elements to convert vibration, light and heat into electric power, then use that electric power efficiently. IoT based technologies and wireless networks would be produced now because semiconductors have achieved a point between the improving power generating element and reduction power consumption of active electronic devices.
The power generating type must be chosen considering the type of energy to be gathered from the environment, whether light, vibration or heat. Mostly solar, piezoelectric, or thermoelectric are used. power IC for use with the power generating element efficiently should gather the electric power from that element without energy loss. The generated power for each energy harvesting devices changes according to the size and the surrounding environment. It is necessary to consider the following. Selecting a power IC which is suitable for the power generating element. Regarding the selection of wireless communication type between wireless sensor network and computer , the selection can be attached for the power generating element. The communication distance, the type of network, the data transmission speed and the power consumption should be analyzed.
ZigBee ,EnOcean and Bluetooth technologies are low power consumption wireless technologies in the present. There is a point to be considered in energy harvesting, identify power generation and power consumption of the device. This is why of the device will not work if the energy generating is smaller than the consumed power of the device. Although the energy harvesting property of power generating devices are developing day by day, it is less possibility supply continuous power to a device .To overcome this problem generating energy is collected in a capacitor and execute sensor operation at intervals, resulting in a manner which balances the energy harvesting and