Design of Miniature Antennas for Biomedical Applications Term Paper

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Miniature Antennas for Biomedical Applications

Most of the studies on microwave antennas for medical applications have concentrated on generating hyperthermia for medical treatments and monitoring several physiological parameters. The types of antenna implanted depend of the location. Besides the medical therapy and diagnosis the telecommunications are considered as significant functions for implantable medical devices those needs to transmit diagnosis information. The design of the antennas catering to MEMS and NANO technology therefore should be smaller enough with cost effective, low power consumption etc.

Research is going on since long in the field of development of wireless interfaces for environmental and biomedical sensor devices. CMOS and RF MEMS circuits, miniature antennas and sensor networking are now being explored. Complete process involving such elements is developed and is being experimented. Wireless interfaces are now being devised for neural probes, cochlear implants and for development of other biomedical devices like arterial stent monitors etc. Further different techniques are being explored for development of moderate range, moderate rate, and wireless communication to environmental sensors. Research activities are being continued for development of wireless circuits on the basis of RF MEMS and nanometer CMOS.

The experimentation of low-power CMOS radios for the Zigbee 2.4GHz sensor network standard is now considered to as a medium term objective. Introduction of RF MEMS assures radical developments in terms of power efficiency of RF circuits. RF MEMS enhances the high-Q of micromechanical devices. The functioning of RF MEMS devices is presently considered closer to that of off-chip quartz components. There are explorations of the circuit and process techniques that make possible the integration of RF MEMS and CMOS wireless circuits, along with signal processing and miniature antennas. Further activities are involved in the development of many projects for devising the many devices involving such techniques and for developing a low power wireless receiver for sensor applications. (Wireless Interfaces)

Discussion

The applications like home automation, industrial control and biomedical and environmental sensors necessitate low-power transceivers for short distance and low data rate wireless communications. Currently, the IEEE 802.15.4 standards body has prescribed a wireless communication standard that is beneficial for such applications. A project was undertaken by Wireless Interfaces Thrust for development of a transceiver design for low power wireless sensor networks. The objective of this project was to develop a low-power and cost effective receiver IC that is in compliance to such standards. Such a receiver has its application in the sphere of the environmental test-bed platform that is under development in the WIMS ERC. Such project had the motive of enquiring efficient power receivers and data telemetry circuits. This was significant for the applicability and dependability of both environmental sensors and implanted sensors. This involved implementation of two prototype transponders in 0.25µm TSMC CMOS.

The performance of entire transponder was monitored. The refinements in respect of designs were going on for a final generation of the transceiver that will incorporate on-chip data processing. The application of standard CMOS refers that the circuitry is well-matched with the broadest range of sensors and systems. This project was sponsored by the Engineering Research Centers Program of the National Science Foundation. Another project was undergoing for development of low power transmitter for Sensor Networks. The objective of this research was to devise a wireless transmitter for a low power sensor node compliant with IEEE 802.15.4- Zigbee Wireless standard. It concentrates on the low power, small area device for a remote sensor. Till now, the primary concentration of the wireless industry was on communication with high data throughput. This however, has ignored a wide range of applications like remote sensors that necessitated simple wireless connectivity with relaxed throughput and latency. (Wireless Interfaces)

Such transmitter architecture functions direct modulation with variation of a phase-locked loop -- PLL divide ratio. Any of the frequencies between the two or more divider ratios can be selected. With a view to ensure an effective application in neural prostheses with larger number of stimulating sites a wireless neural stimulating micro-system has been developed. Such micro-system can effectively utilized in applications like auditory, visual, spinal cord, and deep brain stimulation prostheses to restore peripheral and central nervous system. The objective is to develop a modular 1024-site wireless 3-D micro-stimulating array with 128 simultaneous stimulating channels, each capable of sourcing ±100A. The project applies full integration, new current driver circuits, low power circuitry, and novel modulation/demodulation techniques for the purpose of low power high rate data transfer.

It has also developed a miniature system for reviewing the movements and inertial forces associated in sports and sports equipments by measuring all acceleration and angular rotation components during their application.

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Such a tiny wireless system involves commercial MEMS inertial sensors for measuring inertial data about al three axes. Sensor data is recorded amplified, multiplexed, and transmitted out to an external receiver applying FM telemetry. It involves application of two 2-D accelerometers -- ADXL210E made by Analog Device having a sensing range of +/-10g and three 1-D gyroscopes -- KX210 manufactured by Kionix having a range of ~700°/sec to quantify the fast rotation of a golf club in 0.1sec. An analog multiplexer accords sensor signals through low-pass filters with 50Hz bandwidth to deter from the interactions between the sensors and multiplexer. (Wireless Interfaces)

There is the process of transmission of multiplexed signals by wireless means to an FM receiver and the received data is fed to a laptop and assessed by MATLAB. The developed system is calibrated and several experiments applying the system have been implemented. The measured performance of the system is then measured with the same parameters applying a commercial optical device. The result predicts the system to be much dependable. A project is undergoing for development and demonstrating of a relatively wide band miniaturized slot antenna that can entail a high-impedance match to the bank of micro mechanical filters chalked out for the front end of the wireless interface. The antenna is so designed as to be in line with the Zigbee standard and also adaptable to the high impedance or standard load.

Moreover, it remains to be comparatively, high efficiency and small size, embracing an area no larger than 1cm2 at 2.4GHz. The designing of such an antenna involves three essential phases. Firstly, a technique for designing high-efficiency miniaturized slot antenna capable of conserving as much power as possible is devised. As the second phase it involves the design of the bandwidth and efficiency of such an antenna when it is placed above a ground plane. In the third phase in input impedance of the antenna is enhanced so that it can be matched to a micro-machined disk-resonator filter. The first phase is attained through design and fabrication of a number of inductively and capacitive loaded slot and printed wire antenna. (Wireless Interfaces)

MEMS the acronym of micro-electromechanical-systems technology has been infused into varied fields including RF, optoelectronics, and biomedical applications, MEMS research and development has been evolving for decades through out the globe. The pharmaceutical industry is applying the MEMS devices increasingly for experimentation of new drugs. The blood screening sensors that are applied for complete lab tests at bedside are considered another potential medical application. The biomedical applications of MEMS technology include networks of channels, pumps, valves and mixers for analytical devices. MEMS can also be applied as molds for plastic microfuidic parts. The MEMS devices are thought of for designing miniature surgical tools fluid dispensing heads and drug delivery and implantable sensors. The MEMS also miniaturize the RF components. (Lilliputian Machines Set To Revolutionize RF, Optoelectronics, and Biomedical Applications: MEMS in Biomedical Applications)

The wireless industry is confronted with a number of tough design challenges. A3G smart phone, PDA or base station could necessitate as many as five radios for TDMA, CDMA, 3G, Bluetooth and GSM. Such supplementary features generate and enhancement in component count. However, at the same time the industry must satisfy consumer demand form factors, low costs and reduced power utilization. The MEMS-based RF switches utilizes the proprietary membrane process to generate a low loss, low-power device. The RF switch contains a movable metallic membrane. With application of an electrostatic force the membrane is pulled down to complete the circuit.

Microfluidics a MEMS technology facilitates the fabrication of networks of channels, chambers and valves to regulate the flow of liquid in amounts as small as one picoliter. Such systems have less moving parts and necessitate little assembly. They are benefited by the physical phenomena like electro-osmosis, dielectro phoresis and suface interaction effects. Micralyne makes the microfluidic Tool Kit, a user configurable instrument which is being applied in the corporate and academic research laboratories for desired bio-analytical applications in protein, DNA and cellular analysis. Data Knife, a set of surgical tools has been introduced by the Verimetra that involves sensing and measuring devices. The Data Knife incorporates sensing and data gathering capabilities on the edges of several surgical tools. (Lilliputian Machines Set To Revolutionize RF, Optoelectronics, and Biomedical Applications: MEMS in Biomedical Applications)

Such instruments are capable of differentiating tissues like cartilage, bone,….....

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