Design and Implementation of Wireless Power Transfer based on Spider Web Coil for Biomedical Implants

DOI : 10.17577/IJERTCONV10IS09034

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Design and Implementation of Wireless Power Transfer based on Spider Web Coil for Biomedical Implants

C. Narayanan

Assistant Professor,

Department of Biomedical Engineering, Dhanalakshmi Srinivasan Engineering College (Autonomus), Perambalur, Tamilnadu, India

M. Barath

UG Scholar, Department of Biomedical Engineering, Dhanalakshmi Srinivasan Engineering College (Autonomus), Perambalur, Tamilnadu, India

R. Jagadeesh

UG Scholar,

Department of Biomedical Engineering, Dhanalakshmi Srinivasan Engineering College (Autonomus), Perambalur, Tamilnadu, India

  1. Karuppusamy

    UG Scholar, Department of Biomedical Engineering, Dhanalakshmi Srinivasan Engineering College (Autonomus), Perambalur, Tamilnadu, India

    D. Madhan

    UG Scholar, Department of Biomedical Engineering, Dhanalakshmi Srinivasan Engineering College (Autonomus), Perambalur, Tamilnadu, India

    Abstract:- A biomedical implant (BMI) is a device adopted, respectively. A power transfer of 12.42Wand transfer efficiency of 93.38% were achieved at 2 cm for when a 150- resistive load that allows patients to monitor their health condition at any time and obtain care from any location. However, the functionality of these devices is limited because of their restricted battery capacity, such that a BMI may not attain its full potential. Wireless power transfer technology based magnetic resonant coupling (WPT_MRC) is considered a promising solution to the problem of restricted battery capacity in BMIs. In this paper, spider web coil-MRC (SWC-MRC) was designed and practically implemented to overcome the restricted battery life in low-power BMIs. A series/parallel (S/P) topology for powering the BMI was proposed in the design of the SWC- MRC. Several experiments were conducted in the lab to investigate the performance of the SWC-MRC system in terms of DC output voltage, power transfer, and transfer efficiency at different resistive loads and distances. The experimental results of the SWCMRC test revealed that when the Vsource is 30 V, the DC output voltage of 5 V can be obtained at 1 cm. At such a distance (i.e., 1 cm), the SWC- MRC transfer efficiency is 91.86% and 97.91%, and the power transfer is 13.26 W and W when 50- and 100- resistive loads were and a Vsource of 35 V were considered. The achieved performance was adequate for charging some BMIs, such as a pacemaker.

    Keywords: Biomedical implant, MRC, power transfer, transfer efficiency, voltage, WPT.

    1. INTRODUCTION Biomedical implant (BMI) systems depend on the

      type of electronic device implanted to enhance the quality of life as well as to observe, diagnose, and substitute the function of an organ or bodily function without restricting the patients movement. Generally, a BMI is either biodegradable or powered by limited-

      storage internal batteries or super capacitors. Therefore, the patient should replace the implant battery before it is dry. The need for repeated replacement is impractical and requires a high cost to patients due to surgical intervention. Wireless power transfer (WPT) involves transferring electrical energy from the transmitter to the receiver ends without using wires. These WPTs can be divided into two categories based on the coupling region between the transmitter and receiver:

      (i) Nonradiative or nearfieldregion (ii)Radiative or far-fieldregion.

      Battery-powered electronics systems, such as wearable and mobile devices, wireless sensors, and medical devices are widely used during the everyday life. Implantable medical devices (IMDs) represent a category of electronic systems which have an increasing impact in the improvement of quality of life since they enable monitoring or replacing of sensory functions. The idea of using an IMD to assist patients originates since 1950swhen the appearance of transistors opened the possibility of implementing a fully implantable pacemakers . From that, various devices have been developed such as heart rate monitors, cochlear implants, retinal implants and brain- computer interfaces.


      Wireless power transfer system is an emerging technology that is useful to recharge the battery wirelessly for various portable and biomedical implant devices, battery free sensors, passive RF identification, near-field communications, and many others in near field region. WPT is a fundamental enabling technology which eliminates wired power connections. It is a very broad research area that has recently become applicable to

      implantable medical devices. Biomedical implanted devices are becoming popular in health and medical applications in a wide range of areas, such as, cardiac pacemakers, retinal prosthesis, cochlear implants, defibrillator, smart orthopedic implants, artificial hearts etc. The most important advantage of wireless power transfer system is longer life span as compared to non- rechargeable batteries and capability to deliver power without costly invasive surgery. In addition invasive surgery involves serious health hazards which are totally eliminated by Wireless Power Transfer System. commercial implanted devices utilize high volume, non- rechargeable batteries. These batteries inevitably need to be replaced at the end of their life span by costly surgery. In addition, bulky size of the batteries due to high energy requirement becomes an obstacle in design of compact implantable device most common method of powering larger implants such as pacemakers and deep brain stimulation devices is via batteries. However, batteries are difficult to miniaturize and remain the size-limiting component of many implants. In addition, the lifetime of batteries limits the useful life of potential implants. Battery replacement for implantable devices often requires an additional surgery and can cause many complications.

      Wireless power transfer (WPT) to implantable devices has attracted significant attention in the last decade. It is a promising choice for delivering power to the implants which may avoid the surgery required to replace batteries. This power transfer takes place when a voltage is induced at a receiver due to electric and magnetic fields generated by an external transmitter. Traditionally, two major techniques of delivering power wirelessly into the implant exist. The first one is far-field transmission using antennas. An external antenna is placed away from the body to power and communicate with implants through an implantable antenna. This approach restricts the patients mobility and exposes the whole body to the radiated power. The second technique is the inductive coupling between two coils. These coils should be kept aligned well; otherwise, the strong electromagnetic coupling will be lost. Inductive coupling is not restricted to coils. Antennas can be used in power transmission based on this technique if it is placed in close proximity within the near-field region. These antennas are wearable on the body and used to wirelessly charge as well as communicate with implants. Loop antennas are widely used for this purpose in the literature because of the high magnetic field in the near- field region. A pair of square loop antennas was used to characterize the effect of the human head on the transmission of RF signal at the Med Radio band. Another pair of circular loop and triangle patch antennas was used to improve communications with implants. In, a near-field wireless power link was established between a brain implantable bowtie antenna and an off-body exterior loop antenna. A meta surface-based WPT link consists of transmitting patch, and receiving implantable loop antenna is roposed. A dual broadband loop antenna was developed for WPT and communications

      with implantable antennas. A pair of square loop antennas was used for WPT. A parasitic patch implantable antenna was utilized to improve the WPT with a transmitting array antenna. A multiband antenna with a T-shaped ground slot is proposed for WPT and Telemetry. A circular loop antenna and an implantable cubic loop antenna were used for powering brain- machine interfacing. In these applications, it is very difficult to know the location and orientation of the implants accurately. Consequently, the misalignment issue is expected to occur. Different Approaches for a Wireless Power Transfer System The lifespan of IMDs is limited to battery capabilities. Patient pain and the danger of infection are the major development concerns in implantable medical systems because using implanted batteries can cause diseases. Therefore, the WPT link is a safer option to power biomedical implants. Improving WPT techniques and efficiency will enable rechargeable batteries to be employed for IMDs rather than non-rechargeable batteries, which usually have a greater weight and volume and a shorter period of effectiveness compared to rechargeable batteries. Medical implants like implanted spinal cord stimulators can use a rechargeable battery to improve their capability and reduce overall costs Lately, there has been a great interest in the usage of WPT for medical applications. The development of implantable electronic devices in biological systems has made it easier to use this technology for powering various IMDs, such as biological sensors, pacemakers, and neuro stimulator, working in a range of power from a few microwatts to a few watts. The power ranges of common IMDs are illustrated. The WPT systems for the neuro stimulator and the pacemaker are discussed in detail. There are three major ways to accomplish a near-field WPT: capacitive coupling based on electric fields; inductive coupling based on magnetic fields; and magnetic resonant inductive coupling, which include a resonant circuit in transmitter and receiver coils. Far-field WPT is also known as microwave coupling. Hybrid wireless power transmission (HWPT) includes both far-field and near-field WPT. The biomedical implants are intended to be used for biological studies, therapy, and medical diagnostics. Novel biological materials also provide additional biocompatibility and efficiency, as well as reduced expenses. Implantable medical devices (IMDs) can be classified into two primary categories based on their methodologies for the transmission of power. Transfer mechanisms such as inductive coupling, optical charging, and ultrasound are included in the first category. The second category is split into two subsections: batteries, such as lithium; and natural harvesting, including bio fuel cell, thermoelectricity, piezoelectricity, electrostatic, and electromagnetic.


      The different blocks shown in the block diagram were implemented separately and then integrated together. Below are descriptions of each block and specifications for each.



To overcome the limitation of battery capacity in BMIs, the materials and methods introduced in this work involve the design and implementation of the SWC- MRC system to solve the problem of charging BMI batteries wirelessly. The proposed SWC-MRC design involves using an S/P coil topology based on spider-web coils to analyze different performance metrics, including DC output voltage, transferred power, and transfer efficiency. The adopted SWC- MRC design can be experimentally implemented and tested at different resistive loads. The transfer distance between transmitter and receiver coil is 1-10 cm in every 1-cm step. The transmitter coil was fixed during measurement while the receiver location was varied. Different power supply values were adopted in the experiment, ranging between 5-60 V in a 5-V step for each case to explore which voltage provides the best performance. A comparison was made between each supply and at each distance. The previously mentioned materials and methods can be used assuming the following:

  1. The spider web-coil form was designed with an inner diameter of 10.5 cm and an outer diameter of 24 cm. The form is fabricated on clear polyvinyl chloride

  2. A copper coil with the dimension of 20 American wire gauge (AWG) in diameter was manually wrapped above the spider coil form. Four turns were wrapped on the transmitter spider-web form. The receiver was wrapped in three turns.

  3. All required devices and tools were prepared for both the transmitter and receiver side

  4. Simple mathematical models were used to calculate the delivered power measured in watts (W), and a percentage of transferred efficiency was introduced to analyse the performance metrics of the SWC-MRC.

  5. The SWC-MRC design was presented to provide adequate voltage to charge a BMI. The SWC-MRC contains the transmitter and receiver parts. Each part involves a specific device and tools to meet the required aims of the work.

  6. As the overall design component was prepared, three experiments were configured and conducted to evaluate the performance of SWC-MRC according to the load. The system design and parameters were explained in detail.

  7. An analysis of each experiment was introduced, and the results were described. The proposed SWC-MRC system consists of a transmitter and receiver parts. The transmitter contains two power supplies: a high- efficiency zero voltage switching (ZVS)differential- mode class-D power amplifier based on development board EPC9065, and a spider-web transmitter coil to convert an electrical field to a magnetic field with a compensated capacitor (CTx). The receiving part includes a spider Web receiver coil to convert the magnetic field to an electrical signal, CRx, a bridge rectifier (based on Schottky-diodes) characterized by its small size and low cost, capacitance filter (C), and resistive load (RL). The key to the design of the system is the spider web coils of the transmitter and receiver, as

shown The direct current (DC) generated by the power supply is converted to a sinusoidal alternating- current (AC) wave with an oscillator frequency of 6.78 MHz using ZVS from GaN-based power management technology as shown in Fig. 2a and 2b. This frequency was selected because at high frequency, especially in the Industrial, Scientific, and Medical (ISM) band (2.2 and

6.78 MHz), the output power could be small, and the BMI does not require an extra electronic circuit. In addition, this frequency (i.e., 6.78 MHz) reduces the eddy current effect in the receiver circuit, hence the WPT efficiency can be improved. Furthermore, decreasing the eddy currents will reduce the temperature of the receiving circuit implanted in the human body will decrease, which prevent side effectson the tissues and cells of the body. The ZVS is connected directly to the transmitter circuit. The current flows through the transmitter (Tx) coil, resulting in an electromagnetic field passing through the receiver (Rx) coil. Therefore, the Rx coil produces an induced current to perform the wireless-energy transmission from the Tx coil to the Rx one. The transferred energy from the Tx to the Rx coils suffers some loss.

Therefore, the current in the Rx coil is smaller than that of the Tx coil. The Tx side involves a bridge rectifier to convert AC to DC, which is usable power. The Tx and Rx coils should resonate at the same frequency to obtain an efficient power transfer. This technique is characterized by its high-transfer efficiency that is unaffected by the environment.

Movable coil

Fixed coil

The resonance frequency of the transmitter coil and receiver coil is wTx and wRx, respectively, and is equal to w, which is 6.78 MHz. The system works in the S/P configuration. The proposed system was tested with an air gap ranging from 1-10 cm separating the transmitter coil and receiver coil. Several induced voltages ranging from 5- 60 V were used to test the system. The LRx and CRx indicate the receiver-coil inductance and receiver- compensation capacitor, respectively. The outer diameter of the transmitter coil (dTx ) is 12.2 cm, and the outer diameter of the receiver (dRx) is 11.5 cm. The induced and rejected voltage is described by mutual inductance M and Lthe operation frequency wo. The value of M is determined by inducing an electromotive force in threceiver coil by current through it.



MATLAB (matrix laboratory) is a numerical computing environment and fourth-generation programming language. Developed by Math Works, MATLAB allows matrix manipulations, plotting of functions and data, implementation of algorithms, creation of user interfaces, and interfacing with programs written in other languages, including C,C++,Java, and Fortran. Although MATLAB is intended primarily for numerical computing, an optional toolbox uses the MuPAD symbolic engine, allowing access to symbolic computing capabilities. An additional package, Simulink, adds graphical multi- domain simulation and Model-Based Design for dynamic and embedded systems. In 2004, MATLAB had around one million users across industry and academia. MATLAB users come from various backgrounds of engineering, science, and economics. MATLAB is widely used in academic and research institutions as well as industrial enterprises. MATLAB was first adopted by researchers and practitioners in control engineering, Little's specialty, but quickly spread to many other domains. It is now also used in education, in particular the teaching of linear algebra and numerical analysis, and is popular amongst scientists involved in image processing. The MATLAB application is built around the MATLAB language. The simplest way to execute MATLAB code is to type it in the Command Window, which is one of the elements of the MATLAB Desktop. When code is entered in the Command Window, MATLAB can be used as an interactive mathematical shell. Sequences of commands can be saved in a text file, typically using the MATLAB Editor, as a script or encapsulated into a function, extending the commands available.

Figure: Circuit Diagram

A micro controller is an embedded chip consisting of a powerful CPU tightly coupled with fixed amount of memory (RAM, ROM or EPROM), various devices such as serial port, parallel port, timer/counter, interrupt controller, ADC, DAC, everything integrated on to a single silicon chip. It does not mean that any micro controller should have all the above said features on chip. Depending on the area of application for which it is designed, the on chip may not include some of the sections.

Experimental setup of the proposed system.


In this section, we introduce findings from implementing our proposed SWC-MRC system converting AC to DC and analyzing the DC output voltage, delivered output power, and power-transfer efficiency as a function of applied voltage supply Vsource within a specifc range of transfer distance. We gradually increased the transfer distance between the transmitter and receiver coils from 1-10 cm by 1-cm steps to determine the maximum DC output voltage, delivered output power, transfer efficiency, and transfer distance that can be reached by this SWC- MRC system. In the proposed SWC-MRC system, DC output voltages were measured using a multimeter. The Vsource was varied from 5-60 V stepwise by 5 V. The DC output voltage was measured for each value of Vsource for three cases of resistive load. Moreover, measurements were obtained for different transfer distances between the transmitter and receiver coils. This transfer distance ranged from 1-10 cm stepwise by 1 cm. The change in Vsource, in volts, is plotted on the x-axis; the obtained DC output voltage, in volts.

Source Voltage Vs Outputvoltage

Output Waveform III.CONCLUSION

In this project, a novel technique of SWC-MRC is proposed. Sensors and BMI are crucial in monitoring, diagnosis and therapeutic application in recent medical and healthcare developments. Power supply and energy consumption are some of the challenges facing the use of these devices and sensors. Wireless power transfer is one of the solutions for overcoming battery capacity and charging problems. Wireless power transfer, specially MRC, plays an essential part in wirelessly charging implantable biomedical systems such as pacemakers and cochlear prostheses. A design and implementation of SWC-MRC with an S/P configuration to a wirelessly charged BMI system for various input supply and different transfer distances between the transmitter and receiver coils for three cases of loads 50 ohm, 100 ohm, and 150 ohm have been investigated. A spider coil with a 20-AWG coil diameter was designed for both transmitter

and receiver coils. The SWC-MRC implementation has been examined in an air medium without evaluating the human body nor electromagnetic field safety. We observed that the increase in the resistive load value resulted in improved delivery of power and efficiency at a larger transfer distance at the same input voltage. Also, the system efficiency decreases as the air gap between transmitter and receiver increases for the same input voltage. Moreover, the S/P configuration for asymmetrical coil succeeds in achieving adequate 5-V DC output for supplying voltage to the load or biomedical implant across a 2-cm air gap between transmitter and receivercoil.


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