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Wireless Power TransferProject report for ECE 400 Senior Design

April 25, 2011Version 1.0Project team

Adam Myers (project leader), BS Electrical Engineering 2011, University of TennesseeTooraj Homayooni, BS Electrical Engineering 2011, University of Tennessee

Ali Ghezawi, BS Electrical Engineering 2011, University of TennesseeProject mentor

Professor Syed K. Islam, EECS, University of Tennessee

Summary. This document describes the board-level design of a portion of a specialized type ofmedical chip. The full chip will have an external unit, which sends power to the internal unit andreceives data from it at the time of powering it, and an internal unit, which receives power fromthe external unit and broadcasts collected data toward the external unit. In the full design, part ofthe internal unit will also collect data for transmission. However, this partial design will omit thecollection of data, using a function generator to simulate collected data, and it will only deal withthe transmission of data and power in the above description. The omitted data-collecting circuitwill be represented by a resistor sized to use a comparable amount of power to that data-collecting circuit. The power transmission will need to be wireless, to overcome the skin-barrier,and to have sustainable efficiency regardless of the suboptimal electromagnetic properties ofskin and air. As a result, for the full design, a patient can have internal measures and tests ranwithout the unwanted drawing of blood or the inconvenient visitation of doctors.


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o . Glossarydata modulation A technique to prepare a message for efficient transport fromsource to destination that is reversible enough (i.e. also resistant to noise enough) for ademodulating circuit to recover the message.E class amplifier a power amplifier that employs a single transistor driven to act as aswitch, and an output filter selected to bring the drain voltage to zero at the instant the transistoris switched on (answers.com). The E class amplifier has a theoretical power efficiency of 100%.external unit the device that will transmit power through the use of inductive coupling tothe internal unit; this device will also receive, demodulate, and display a data signal sent fromthe internal unitinductive coupling the transfer of energy from one circuit (such as a conductive antenna andassociated circuitry) to another by means of mutual inductance between the two circuits. SomeRFID tags and readers exchange information using inductive coupling between their antennas(technovelgy.com)internal unit the device that will be implanted in someone's skin; this device willreceive power through inductive coupling and then transmit data back to the external unitthrough a separate inductive coupling.on-off keying A type of modulation for binary data whereby an amplitude beyond areasonable threshold of the carrier represents a one and an amplitude of zero represents azero. This modulation requires to knowledge that data is being sent (since no signal translatesinto a binary zero), and its aim is to conserve power. It struggles with high noise pathways fromsource to destination.resonant circuitry Any circuit that does its task the best at a specific frequency.


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1. How this Product Can Solve Someone's ProblemThe following story illustrates how Wireless Power Transfer can fulfill someone's need.Sam's trips to the doctor

Sam is an 82-year-old man who lives alone and has no children. Unfortunately, he isrequired by his ailing condition to have certain tests done at his doctor's office every other week.He has to ride to the doctor by bus since he cannot drive a vehicle and since he has no family orfriends to drive him. Once he arrives at the doctor's office, he has to wait to see the labtechnician, take the tests, wait for the results, and wait to discuss the results with his doctor.These trips are very long and tiresome days for Sam, and his age only permits so muchexhaustion. He knows there has to be a better way. (See figure 1.1 below)

Figure 1.1

One day, Sam hears about an idea on how to solve his problem of going to the doctorevery other week. He considered this solution when he heard of a way to do the tests at home.This possible solution requires him to draw blood and send it in the mail to his doctor. WhenSam hears of this escape from his currently tediously cyclical trips of exhaustion, it makes himvery happy and he instantly wants to try it. His happiness quickly fades, however, when hediscovers that it is painful for him to draw his own blood. He needs to have the will power toprick himself with a needle, and he cannot fear his own blood, which he does (see figure 1.2 onthe next page). Making things worse than before, his painfully acquired blood often is lost in themail, and as a consequence, he never receives the results for those tests. Considering themedical urgency for his test, also, the delay between mailing and receiving results often bordersdangerously unacceptable. This medical urgency cries for more reliability and less wait, andSam cries for that as well as comfort.


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Figure 1.2The next trip to the doctor makes Sam even more excited, because his doctor tells him

of a chip based on Wireless Power Transfer that can be implanted under his skin. With this chipimplant and an external device for powering and reading results, he will be able to test himselfeasily at home. Sam has the implant inserted with a simple outpatient procedure and goeshome to try the new idea installed chip. Now Sam can do his testing at home, and his resultsare emailed instantly to the doctor. Sam is relieved from the pain of needles and exhaustion oflong days. He can finally relax at home and still receive his urgent medical attention. Further, thespeed of testing helps Sam to have optimal medicine combinations determined from the test inalmost real-time.

I ) .I '_..., _~ ...... //L~~~It' .. Figure 1.3


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2. Why the Product Is Needed

People need medical testing, and this need for testing can often be frequent. These testscan be done in numerous ways, such as taking blood and extracting other bodily fluids. All ofthese tests require trips to the doctor or to a lab to have them done, and they can also be painfulif the test needs to puncture the body to extract fluids. Sometimes the testing is so frequent thata person may be confined to an assisted living home or hospital so the tests can be performed.Frequent trips to the doctor or supervised living create many problems for many people. Theylose freedom and joy in life, and they have to pay a premium for the assisted-living or for eachdoctor visitation. If there was a way for an individual to perform these tests on his or her ownfrom the comfort of his or her home, many of these issues could be resolved. This is why theproject, "Wireless Power Transfer," is needed. It is a board-level design that could later beimplemented at chip level, which delivers power and data in a wireless manner to meet thisneed.

The market for wireless power transfer extends beyond this medical niche, too. Peopleare quickly growing irritated or, at the least, are preferring no wires in their electronicexperience. As a result, the market has gained several recharging platforms for various portableelectronics. Though this specific need is not addressed in our design constraints and goals,transport from this medical application to that leisurely application is easy.3. Target Narket -- Who Needs the Product

People in need of medical testingDoctorsManufacturers of medical equipmentHospitalsWireless recharging of electronics

4. Description of Similar Products

visual neuroprosthesisThe visual neroprosthesis uses prosthesis to solve blindness. This visual-aide is similar

to this project, because a visual prosthesis system consists of an external (or implantable)imaging system that acquires and processes the video. Power and data transmit back to theimplant wirelessly by the external unit. The implant uses the received power and data to convertthe digital data to an analog output, which will be delivered to the nerve via micro electrodes.(Wikipedia)

strain monitoring in orthopedic implantsUsing an implantable sensor along with technology similar to this project (RFID), these

devices (that are not easily found on the market but are found in research often) monitor thestrain on orthopedic implants. The RFID is a radio-frequency technology for transmitting data,and our design uses radio frequencies too. Similar to our design, also, the orthopedic implantsuse active telemetry, meaning the chip only works while receiving power wirelessly.


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strain sensing in femoral nail platesThe strain sensing in femoral nail plates type of products (that are not on easily found on

the market, but are found in research often) uses the same strategy of active telemetry to powera data-collecting unit internal to the user and then to transmit that data to the external poweringunit.

neu ral micro-sti muIatorsThis is a technique that stimulates a small population of neurons by passing a smallelectrical current through a nearby microelectrode. This is done in a similar fashion as thisproject transmits power (Wikipedia 2). As before, this is a general label on an idea, often foundin research, but there are few recognizable names of these products on the market that wecould specifically cite and test.

Abeed Mohammad's Circuit (Masters Thesis)His circuit was designed under our mentor's supervision, so it has many of the same

design considerations and goals. Further, he arrived to a circuit similar to our design. He has aclass-E amplifier in the same fashion we do with a single inductive link that transmits power anddata. Differently, however, his primary side is a single circuit that includes filters that separatepower and data, so the data can be demodulated and viewed. Also, his circuit uses a tank circuiton the secondary side whereas ours uses a series capacitor in conjunction with our inductorfrom the inductive link. Similar to our design, he also modulates and transmits data. However,he uses FSK whereas we chose to use OOK. Also, repeated from above, he transmitted data onthe same inductive link, so he had to send the data back toward the power transmitting circuit.With our circuit, we simply modulate and send the data on its own inductive link.5.) Measurements of Similar Products

Below in figure 5.1 is a graph of a comparison between our design and similar products.We found this data in the thesis of our closest competitor, Mohammad Abeed's design (Abeed).The final product, for reference, operates best at .5 cm, though it was designed toaccommodate 1 cm to 5 m.

Figure 5.1 Similar Design Operating Distances


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Figure 5.2 Similar Design Operating FrequenciesWe found a great list of similar product's data from the same source (Abeed),

shown in figure 5.2. This chart compares the operating frequencies for the power transfer. Mostare well below our operation, too low to be in the ISM frequency range unlike our design. Thestrain-monitoring system, on the other hand, is far too high since its electromagnetic radiationheats the skin up too much for continual usage by a patient.


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6.) Constraints on the Design

Number one constraint is time (final deadline April 27th)

Must use Class-E switching amplifier on power transmitter side This design is constrained to board level. Must operate in the 13 MHz range for power transmission Needs around 5V on the output of the voltage regulator (internal unit) Has to transmit power and data through wireless media such as skin and air. Cost (trying to keep budget below $100)

7.) Initial Prototypes of the Project

Figure 7.1 Initial PrototypeThe initial prototype, seen in figure 7.1, had a single working inductive link, the two larger

coils in the picture, formed by hand-winding wire a certain number of times based oncalculations to reach a certain inductance. On the power-sending side, a capacitor was put inseries with the winding, and on the power-receiving side, a tank circuit was made with a parallelcapacitor. The output of the power-receiving side was hooked up to a few light-emitting diodesto signify power transmission had occurred. The two other coils seen in the picture were modelsof the final inductive link for data transmission, and we also modeled the actual modulation,sending, demodulation, and viewing of data using paper with binary ones and zeros written onit. A human pulled each strip out slowly, signifying the transmission of data.


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Figure 7.2 Dead-bug testingFigure 7.2 shows the secondary prototype of the project, which used nearly the final-

selected values for each component, found through calculation and simulation in SPICE. Thecomponents were inserted into vector board, with their leads resembling an upside-down bugwithout life, and they were twisted around each other. The circuit on the left was the internalcircuit, and the one on the right was the external circuit. Not pictured, there were also two hand-wound, square inductors for the power transmission. This prototype completely omitted the datasection.

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Figure 7.3 SPICE Simulation of Power Transfer Circuit

This SPICE simulation acted together with the dead-bug testing as our final prototypethat we arrived to after much iteration between dead-bug testing and SPICE simulation. Wewould iterate through making a working SPICE simulation, a build of that simulation on a vectorboard using dead-bug testing, and then a modified SPICE simulation based on our problematicresults. We would then repeat the process until the dead-bug design worked flawlessly. Thereason behind the need for iteration was that the non-idealities of each component interact inunforeseeable ways regardless of perfect theoretical calculation or simulation. The SPICEsimulation can be seen in figure 7.3. On the left side, there was the class E amplifier linking anamplified version of the 5V sinusoid supplied at the gate to the low-linking, air-connectedtransformer. On the sides of the transformer were the series capacitors chosen specifically forits resonant effect, acting dually as a band-pass filter and increaser of efficiency at the tunedfrequency. The four diodes to the right of the tuned transformer rectified the pseudo-sinusoidfully, and the rest of the inductors and capacitors further to the right acted as a low pass filter,smoothing out the AC signal into a DC signal with small ripples. The LT1521-5 then flattened thetiny ripples out since it is a voltage regulator. The 200 ohm resistor represented the data-collecting and data-sending circuitry.


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despite the board-level nature of our design not reaping in the space advantage. On the otherhand, a BJT switched faster than a MOSFET. However, the power and data frequencies of13.56 MHz and 20 MHz were not high enough to let the BJT's superior switching even show.Thus, the two primary advantages of the MOSFET overtook the single moot advantage of theBJT, and we chose the MOSFET.

Throughout the design of everything, we had to choose between absolutely optimalperformance (with perhaps an increase in circuital complexity disproportionate to the increase inperformance) and having a simpler design that saved space. As the end-goal was to simulate achip-level design internal to a human, we decided often to take the circuit with fewercomponents (yet perhaps more complex) to minimize space.

When we arrived to the data portion of the circuit, we needed to decide betweenamplitude shift keying (ASK) and frequency shift keying (FSK). FSK had a greater resistanceagainst interference compared to ASK with the cost of more circuit components and complexity.Given our need to remain small due to our considerations on space usage, we chose ASK. Thisdecision gained fortification since the separate inductive links minimized interference, makingFSK's main advantage moot.

Within the subset of ASK, we could choose what amplitude in the carrier would representa digital one and what amplitude in the carrier would represent a digital zero. With the limitedamount of power available in the internal circuit for modulation, we chose the more power-efficient version of ASK called on-off keying (OOK). In this implementation, digital zero isrepresented by a carrier amplitude of zero, and a binary one is represented by an amplitude inthe carrier beyond a certain threshold. Thus, when data of digital zero was to be sent, no powerwas used. This cut down on the total amount of power used in the internal circuit. Further, OOKsometimes suffers from not knowing when data is being transmitted. Without that knowledge,the destination easily could assume the message was all zeros. Our application, however, hadno such ambiguity since data always transmits when the circuit was powered, and the circuitwas always powered when the receiver was nearby.One of the less crucial design decisions was to choose between a series or parallelcapacitor in the resonant circuit for the four locations presented by the two inductive links. Wechose series capacitors for all four areas. The series capacitor needed maximal voltage swingfrom the E-class amplifier, but it also needed minimal current. A parallel combination wouldreverse that trend.

The entire design process can be seen pictorially in figure 9.1.


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Figure 10.1 Final Component ValuesThe design used a class-e amplifier, which theoretically has one hundred percent

efficiency while it amplifies power. Alongside this efficient amplifier, the primary and secondarycoils used resonant tuning with the addition of capacitors in series with the coils to result in evengreater power transfer efficiency. Combining all of the above, the project is highly optimizedtoward unbeatably efficient power transmission.

Ashraf gave us inductive values and dimensions to use for the two transformers, so ourwork dealt with optimizing power-transfer efficiency around those constraints.

We started with the design of the secondary side, because its impedance as seenthrough L 1 effects the calculations of the Class-E amplifier. Immediately, we knew the circuit,from right to left, would be the load, a voltage regulator, a low-pass filter, a full-wave rectifier,and then the resonant transformer. So we chose the LT1521-5 to regulate the rippling voltagefrom the lowpass filter. According to the component's documentation, it needed a minimum of a2.2 IJFcapacitor on the output and a 1.0 IJFcapacitor on the input. Thus, we chose capacitorsthat were slightly more to ensure success.

We then optimized the lowpass filter by choosing a cutoff frequency of 1Mhz. That way,we minimized the size of the components, yet we ensured enough filtration to reduce the 13.56Mhz signal to almost a DC signal at the input of the voltage regulator. Further, we chose aButterworth filter due to its maximal flatness in the passband. Next, we iterated through, usingMATLAB development tools, from the lowest order upward until the realization of the filter gaverealistic component values. The 6th order Butterworth gave realistically small component values,so we settled on that order and used the outputted component values from MATLAB rounded tothe nearest available capacitor or inductor value.

Next, we optimized the rectification circuitry for the hefty frequency it would need toaccommodate. Thus, we chose the schottky for its superior switching ability. We arranged themin the standard bridge rectification pattern.After this theoretical optimization, we inputted this half of the circuit in SPICE, shown infigure 10.2, with a test 13.56 Mhz signal generator hooked up in place of the transformer. Wethen verified the output was a 5V signal. We then built the circuitry on a vector board, usingdead-bug design, and confirmed the results. As this half the circuit was largely independent ofthe remainder circuits, we no longer needed to optimize or change it. We had finished the easierpart of the project.I~::~::~::~~~~~~~~~

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We then calculated the optimal series capacitors for the resonant circuitry, using (10.1):1c2 = 2 2 =55.5p4;r J L (10.1 )

where c is the series capacitor,J is the frequency of the resonant circuitry, and L is the inductanceof the side of the transformer with c. We tested this resonant circuit with the AC- DC attachedboth in SPICE and on the vector boards with good results. We then moved on to designing theclass-E amplifier where some previous results (for the resonant circuitry) would change, andwhere we needed to do much iteration in trial to workout the optimal performance.

We used the ideal equations for the class- E amplifier to calculate the starting capacitorand inductive values, L2 and CI from figure 10.1, showing in (10.2) and (10.3):

c1= 2 [;r2 J = 7.18pF;r jR -+1

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1 (10.2)

c ~c 5.447[1+ 1.153 J / \ Q = 2;rjL22 1 QL Q L-1.153 L R (10.3)

With R being the estimated load resistance (300 ohms),Jbeing the frequency, and the inductorsand capacitors being from figure 10.1.

We then tested the build in SPICE with little success. Itbecame obvious we had usedsome simplifying assumption along the way, a non-ideality that SPICE simulates, so we neededto tweak the parameters intelligently in an iterative process to effect an optimized and workingamplifier.

Thus, we held steady L2 as we iterated through, optimizing CI, and then we did theconverse. We repeated this until the increase in performance was naught. We also did the samething for capacitors C2 and C3. We then built the design on a vector board, backpropogating anyimportant differences as non-ideal resistances, inductances, and capacitances inside the modelsfor certain capacitors, inductors, and resistances in the SPICE until SPICE matched up with whatwe observed in real life. Then, we arrived to square one again, tweaking the SPICE model. Wewill now go through one of these iterations to showcase the technique, but we will not continuethe optimization up to the point of success. Itwould take too much meaningless writing and toomany meaningless figures.


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.. .... .. .... ..... ...Figure 10.3 Starting Values for Gradient DescentRunning the simulation a few times, the output at the secondary side was maximum if C3

increased to 65 pF (with all other parameters held constant). We then found similar values of C2being 63 pF, C] being 26 pF, and L2 being 16 uH. We then iterated through about three moretimes with the final values for so far being 22 pF, 70 pF, 60 pF, and 14 uH for C], C2, C3, and L2respectively. This result can be seen in figure lOA.

Figure lO A Values after a Four PassesWe then built this circuit, using the nearest values we could find as those simulated (and

changing the simulation to those values we were forced to use). Then, we measured fordifferences in voltages and currents that indicated where parasitic resistances were needed in theSPICE models. As an example, The node below L2 had a lower DC voltage than in thesimulation, so we added parasitic resistance in series with L2 until the voltages matched up,shown in figure 10.5. There was also a bit more DC current being drawn, so we added someparallel resistance.

Once we matched what we were seeing in real life as closely as we could withsimulation, we ran through the iteration process again until progress stopped. We then arrived onour final values.


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Figure 10.5 Tweaking Parasitic Resistances11. Components and production of the final product

We used a PCB (printed circuit board) for the final project, which we designed usingEZPC and sent off for fabrication, so the assembly of the final product was simple andsystematic. We put the ICs, such as voltage regulators, and discrete components, such asdiodes, capacitors, and inductors, into the slots of the PCB and soldered them in place.

Figure 11.1 PCB for ProjectFigure 11.1 has the PCB as we got it from the factory. The individual boards (the four

seen at the bottom of the figure) and the trial antennas (seen at the top of the figure as squaresof wires) were designed on one board to lower cost. We then used various saws and blades toseparate the boards from each other, shown in figure 11.2 on the next page.


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Figure 11.2 Separated PCB for ProjectThen, shown in figure 11.3, we soldered the final component values (which will be

discussed later in this section) on to the appropriate connections we designed on the PCB. Asall analog circuits have much variability from component to component or from connection to

connection, we also put several excess connections just in case we needed them to change thevalues. With these vast number of extra slots, we could make a wide range of decimal-precision

quantities through parallel and series combinations of inductors, capacitors, and resistors.

Figure 11.3 PCB with Final Component Values InstalledWe then placed the fitted PCB into circuit boxes we bought and planned where to insert

banana connections into the box for connection into the circuits, which needed drilling ofpermanent holes. We needed these for any outputs and inputs. This can be seen in figure 11.4.

Figure 11.4 PCB Placed in Boxes


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Figure 11.5 Final ProductFinally, we drilled holes and put the banana jacks into place, seen in figure 11.5. Then,

we soldered wires from the banana jacks to each of the inputs or outputs on the PCB. The finalproduct, concealed in its case, can be seen in figure 11.6. The LED on the top actived for anyone in the data, thus blinking as the circuit receives modulated data.

Figure 11.6 Final ProductTo see the final values of each component, go back to prototype 3 from figures 7.4 and

7.3. All of the inductors, capacitors, and resistors are the same. Further, the MOSFET was thesame. We used all of the same values as from that prototypical simulation. There were only twodifferences from the prototype compared to the final product. First, the AND gate, a4, was ideal


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in simulation. Differently, we used the TC4011 BP. Second, instead of the LT1521-5 voltageregular, we used the LM317.12. Measurements of the Final Product

Distance 5cm 4cm 3cm 2cm 1cm

Input voltage(p-p) 15V 15V 15V 15V 15V

Primary sidevolta e( - )

314 V

1.40 rnA

300V

1.48 rnA

250V

1.38 rnA

212

1.30 rnA

183 V

0.95 rnArimary SideCurrentPrimary side

Power439.60mW 444mW 345mW 275.60mW 173.85 mW

Secondary sidevolta e( - )

50V

0.15 rnA

53 V

0.445 rnA

60V

0.98 rnA

65V

1.52rnA

66V

1.78 rnAecondary SideCurrent

Secondary sidePower

Output DCVolta eEfficiency

7.50mW

5.13 V

23.585 mW

5.13 V

58.80mW

5.13 V

98.80mW

5.13 V

117.48mW

5.13 V

1.71 % 5.312 % 17.04 % 53.07 % 67.57 %Table 12.1Measurements through Air


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Distance 5cm 4cm 3cm 2cm 1cm

Input voltage(p-p)

15 V 15 V 15 V 15 V 15 V

Primary sidevolta e( - )

314 V

1.48 rnA

270V

1.45 rnA

225 V

1.38 rnA

187

1.25 rnA

159V

1.02 rnArimary SideCurrent

Primary sidePower

464.72mW 391.50 mW 310.50 mW 233.75 mW 162.18 mW

Secondary sidevolta e( - )

48V

0.16 rnA

50V

0.51 rnA

53 V

0.95 rnA

56V

1.68 rnA

58V

1.70 rnAecondary SideCurrent

Secondary sidePower

7.68mW 25.50mW 50.35 mW 94.08mW 98.60mW

Output DCVolta e

Efficiency

5.13 V 5.13 V 5.13 V

Table 12.11Measurements through Meat

5.13 V 5.13 V

1.65 % 6.51 % 16.21 % 40.25 % 60.80 %

Tables 12.1and 12.11show the measurements of the final product. We exceeded theefficiencies of Mohammad's design, a great success. Further, about 5V was realized at theoutput of the voltage regulator for each test regardless of tissue.


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Figure 12.1 Efficiencies at Varying DistancesFigure 12.1 shows the same information as the past two tables in terms of efficiencies,

the main goal, except in a more compact and observable form

Figure 12.2 DC Voltage OutputFigure 12.2 shows the DC output from the voltage regulator. It was not perfectly steady,

but its ripple was only a few mV. Better yet, the average of the wave came in at 5.095V.Combining the previous figure with this one, power must have efficiently transferred to the loadresistor.


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Figure 12.3 Sent Data in Green and Received Data in YellowFigure 12.3 shows the output from the demodulating unit in yellow, located in the

external unit. It also shows the input to the modulating unit in green, located in the internal unit.Despite the small corruption of the original message by small distortions and ripples, themessage is fully recoverable with the proper threshold voltage set to represent a binary one.13. How to Operate the Product

Figure 13.1 External Unit Hook UpShown in figure 13.1, the black and yellow wires represent ground for the two voltage

sources used to power the external unit. These ground wires go into the only black banana jackon the external unit. The live banana jack next to the ground banana jack takes a 5V DC signal,grounded relative to the ground banana jack. The remaining banana jack, pictured above,


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accepts the 5V AC signal that the external unit amplifies, using the DC voltage, and sends offtoward the internal unit.

Figure 13.2 Internal Unit Hook UpFigure 13.2 shows the hook up details for the internal unit. The black banana jack

accepts the ground for each of the simulating data generators. The top red banana jack acceptsthe message square wave, amplitude put at 5V with a frequency below 5,000 Hz, and thebottom red banana jack accepts the carrier square wave with a frequency of 20 MHz and anamplitude of 5V.

Once all voltage sources are hooked up correctly and calibrated correctly, bring the coilsnear to each other with air or flesh between them. The coils' cross-sectional areas should alsobe aligned well, or the flux will travel elsewhere, resulting in no linking of the air-coretransformers.

As the coils gain proximity, the yellow power LED will brighten and remain bright, and thedata red data LED will blink every time a one passes to it in the data.14. Results from Testing the Project with External Users

Dr. Islam, and expert in electronics and wireless power transfer, grew impressed andsaid the project met all expectations. Ashraf, his lowly lab worker, concurred. The product lacksmarketable appeal since, in its final form, it is more of a prototype than a final project due to itbeing board-level instead of chip-level. Had we more time, a year or so, we could bring theboard-level design to chip-level design and make it final. Then, the masses could correctly judgethe project's worth by viewing its application. Until then, specialized opinions from our mentorand other qualified academics and engineering professionals must suffice. We also observedthe student body of ECE400 as we gave the practice presentation for our product. Peopleseemed genuinely disinterested for most of the presentation, and they laughed for other parts ofthe presentation.


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15. Health and Safety Risks Associated with the ProductThe device emits electromagnetic radiation, but it has been designed to have minimized

effect in humans through the proper choice of frequencies relative to the skin medium. Still,needless operation and proximity to humans is unwarranted. Therefore, operation of the productshould happen only when testing it or using it.Some of the inductors have led in them, a metal known for its poisonous properties, sotheir consumption and contact with human skin should be kept minimal. Thus, refrain fromopening and touching the internal components. Without tampering with the internals, contactwith this harmful metal will be nonexistent.

Capacitors can store lethal quantities of voltage and charge, so as recommended prior,do not open and touch the internal components to avoid shock or hurt.

Parts of the insides have jagged edges, further reinforcing the decree to avoid contactwith the internal components.

Avoid shorting any voltage sources that power the circuit. This includes the data-simulating square-wave generators, the DC-voltage source for the class-E amplifier, and the ACvoltage source given to the class-E gate that delivers the power to the internal circuit.

As with all circuits, the ground must not be near any live voltages. Doing so may result ina massive and dangerous serge of electricity.16. Environmental Hazards Associated with the Product

If the DC-voltage is provided by a battery, proper disposal of the discharged battery isneeded to stop harm of the environment. Further, the led-infused inductors need specialdisposal since led can contaminate nature and harm humanity. As an example, it cancontaminate an entire water source with enough led. In general, hire a professional todisassemble and to dispose of the electronics properly from our project.The solder used in the circuit is also full of led, so that is added harm to the environmentif the electronics from the project are not disposed of correctly.17. Legal Issues Associated with the Product

If enough voltage is supplied to the antennas, interference in the improper frequencybands is possible. However, the inductors and capacitors have been chosen in a band-passfashion to minimize the possibility of radiating the incorrect frequency. Legal action by the FCCis possible if the incorrect frequency is radiated, though. On a positive note, however, all otherbodily or environmental harm should not be legally troublesome because of the disclosure ofproper health safeguards and disposal procedures provided earlier. These precautionary andinstructive warnings prevent legal action from being effective against us even if our productharms the environment or a person. Also, the precautions described are extremely rare, so itwould also be extremely rare if the product was to hurt the environment or someone.


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18. How the product could be improvedThe product could always be made much more complex for tiny gains in performance.

Specifically, more advanced data modulation (and thus data modulating circuit) could increasepower efficiency and data versatility in terms of what kind of data it can send, how much it cansend, and how resistant the data is to noise. The class-e amplifier is a basic breed of a widevariety of tuned amplifier circuitry. More resonant circuits, amplifier stages, and much morecircuit complexity could be added there to make a far stronger amplification of the signal withbetter power-transfer efficiency. However, the added complexity would arguably be unwarrantedand inarguably be impossible to implement by us so soon. Making the leap to chip-level wouldalso greatly improve the design by amplifying its utility. These possibilities come with severedrawbacks, though. They would be a nightmare to tweak and build, since many more non-idealities would need to be considered, and they would take up much more space than thesimpler circuits. Space was one of our long-term goals in this design to accommodate the jumpto chip-level from board-level.

The product does need a low-noise, high gain amplifier on the data receiver end of theexternal circuit. Without it, the coils need to be brought closer together than we wanted.However, we can still transmit and view data fairly well despite the lack of a small signalamplifier.


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References cited(Adeeb). Adeeb, Mohammad. A C/ass-E Inductive Powering Link with Backward DataCommunications for Implantable Sensor Systems. Thesis, University of Tennesse, Knoxville.

(technovelgy.com). "Inductive Coupling." Technovelgy. 25 April 2011.(answers.com). "Class E Amplifier." Answers. 25 April 2011.(Wikipedia). "Neuroprosthetics ." Wikipedia.14 April 2011. Wikimedia Foundation, Inc.. 25 April2011. (Wikipedia 2). "Microstimulation." Wikipedia.1 0 February 2010. Wikimedia Foundation, Inc.. 25April 2011. http://en.wikipedia.org/wikilMicrostimulation
http://en.wikipedia.org/wikilMicrostimulationhttp://en.wikipedia.org/wikilMicrostimulation

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