ABSTRACT:

Biomedical telecommunication permits the transfer of information from one body to off the body or from on the body to on the body. Patch antennas and its different variations as implantable medical devices are one of the highest, particularly in receiving attention for scientific interest in integrating these implanted devices and radio frequency enabled telemetry. The design of these implanted devices has been considerable attention in regards to the developments of various parameters like biocompatibility, miniaturization of size, patient safety, improved quality of communication with exterior and interior control equipment, insensitivity of tuning etc. Various mathematical method and optimization techniques are also intriguing. The objective of my paper is to provide an overview of these challenges and to discuss the ways in which these are dealt.

INTRODUCTION:

In recent years flexible and portable electronics have received increasing attention due to their wide variety of applications and applicability. They are particularly interested in bio-medical applications, in which they now are being widely deployed. Implants or implantable antennas are one area where wide applications are being done. According to a market analysis these flexible electronics have a market estimate of us dollar 200 billion in the international consumer market. Among the components of implants biomedical telemetry of play an important role, where antennas come into the picture, because antenna plays the crucial link between the implanted device inside the body and the receiver. However, this design is crucial because of the various physical, biological limitations inside the human body and the regulations of the radiation for implanted devices.

Human bodies are lossy and consists of different tissues of high values of permittivity and conductivity and these values again differ from one tissue to another tissue which requires different considerations, for each tissue. Different implantable antennas are designed for different tissues for different applications and sites of implantations. Some are designed to work beneath the skin, some in the muscles and few in the bones. Unlike muscles and skin which have high permittivity for bone cortical and bone marrow. This requires miniaturization further and frequently results in narrower bandwidth which causes mistuning in the actual human bodies. Low- frequency inductive links have long been the most prevalent method for the biomedical telemetry for implanted medical devices. Nevertheless, they suffer from low data rates (1-30kbps), restricted range of communication (<10cm) and increased sensitivity to inter-coil positioning. Thus the current in most implantable devices is towards radio frequency linked ones. Millions of people in the world currently depend on various implanted RF linked devices for biomedical applications, including temperature monitors, pacemakers and cardioverter defibrillators, functional electrical stimulators, blood glucose sensors and cochlear and retinal implants. As technology is evolving, new implantable devices are now being produced and their utilization is expected to increase rapidly from an already large home.

Until recently, no globally accepted frequency band has been dedicated to biotelemetry for implantable medical devices. This scenario change with the ITU-R recommendation SA.1346,which outlined the use of the 402-405MHz frequency band for medical implant communication systems(MICS).The spectrum of 3MHz allows for 10 channels(a bandwidth of 300KHz each) in order to support simultaneous operation of multiple implantable medical devices in the same area and to limit interference from the co-located meteorological aids service band(401-406 MHz).the MICS band is regulated by the FCC and the ERC(European Radio-communication Commission).The 433.1-434.8 MHz,868-868.6 MHz,902.8-928 MHz and 2400-2500 MHz, ISM bands are also suggested for implantable medical device biotelemetry in some countries. However, focus is on the MICS band, because of its advantages of being available worldwide and being feasible with low-power and low-cost circuits, reliably supporting high data transmissions, falling within a relatively low-noise portion of the spectrum, lending itself to small antenna designs and acceptably propagating through human tissue.

A key and critical component of RF linked implanted medical devices is the integrated implantable antenna, which enables bidirectional communication with the exterior monitoring control equipment. Patch designs are currently receiving considerable attention for implantable antennas, because they are highly flexible in design, shape and conformability, thus allowing for relatively easy miniaturization and integration into the shape of the implanted medical device. In a realistic scenario, implanted patch antennas will be mounted on the existing hardware of the implantable medical device, which also serves as a ground plane.

Thus the design of implantable patch antennas has attracted high scientific interest in fulfilling the requirements of bio-compatibility, miniaturization, patient safety and high-quality communication with exterior equipment. Numerical and experimental investigations are also highly intriguing. An overview of these challenges is hereafter presented and ways in which they have been dealt are briefly tried to discuss.

1 .DESIGN

1.1 Bio-compatibility

The very important criteria in implantable antennas are that it should biologically adhere well to the human body in order to preserve safety and prevent rejection of the implant. Further, we should that since human bodies are partly conductive, it would short the implanted antennas if it once comes in direct contact with the metallization.

These teams of researchers have proposed a flexible slot antenna operating in the ISM band. To make their design biocompatible for implantation, they embedded the antenna into PDMS (Poly Dimethyl Siloxane) [1].

They then tested it by immersing it in a human phantom liquid, imitating the dielectric and electrical properties of the human muscle tissue a study of the sensitivity of the antenna performance as a function of the dielectric parameters was performed. The design issues addressed by their model are:-

1. Evaluation of the characteristics of the antenna in terms of reflection coefficient in planar and bent state, E-field and gain.

2. Study of the sensitivity of the liquid mimicking the human muscle tissue, varying its nominal dielectric values.

3. Checking the SAR limitations, by means of SAR measurements.

Further measurements show that the s11 parameters in planar and bent state in the ISM band demonstrate a very large bandwidth in both states, fully covering the ISM band. The s11 shows at -23.8dB gain at theta=-46 and phi=90. Also the measured SAR values with an input power of 2Mw averaged in 1g and 10g tissue shows that the antenna respects the ICNIRP and FCC guidelines for general public exposure.

Fig1.1.1:SAR distribution for an input power of 2Mw [1]

Gain fig1. 1.2:2.45GHz [1]

Fig1.1.3:Top view of the flexible antenna without PDMS [1]

Fig1.1.4:Side view of antenna and cable embedded in PDMS [1]

Fig1.1.5; PDMS

Another widely used method is to simply prevent the direct contact with the metallization of the antenna with the human tissue, to ensure the biocompatibility of the human body with the antenna substrate. Here commonly used materials include Teflon (€r=2. 1, tanδ=. 001, ceramic alumina (€r=6. 1, tanδ=0. 006) [2,3,4].

Fig1.1.7: biocompatibility issues for implantable patch antennas: [2]

An insulating antenna with a thin layer of low loss biocompatible coating is also another reported approach as shown below in the figure:

Fig 1.1: a) silicone b) antenna encased in silicon

Other materials also include Zirconia (€r=29, tanδ=0), biomedical grade based Elastomer (€r=3. 3, tanδ=0), PEEK (€=3. 2, tanδ=0. 01)

2.

2.1: – miniaturization

As per the advances in the implanted biomedical device\’s technology the need for an ultra small design for implanted devices is very much required for traditional antennas of half wavelength (λ/2) and quarter wavelength (λ/4) are deemed unfit to be used as implanted biomedical devices.

2.1.1 Use of PIFA antenna:-

An implantable compact planar inverted antenna designed for wireless telemetry is being proposed operating in the Australian ISM band of 900 MHz and 915-928 MHz. This antenna has been tested in the body of a live rat. The dimensions are (12*12*12) mm cube [5]. The PIFA antenna is basically developed from the monopole antenna. Inverted L is realized by folding down the monopole in order to decrease the height of the antenna at the same time maintaining identical resonating length. When feed is applied to the inverted L, the antenna appears as inverted F. The thin top wire of inverted F is replaced by planar element to get the planar inverted F antenna. Also the addition of a shorting pin between the ground plane and patch planes increases the effective size of the antenna, thus further reducing the physical dimensions.

Fig:2.1.1:Pifa from monopole[8]

The predicted bandwidth was found to be 8.5% at 10dB return loss. The sensitivity of antenna impedance matching to variations in the rats body material in investigated. The antenna works well in the ISM band, even when body tissue parameters change within a significant range. The antenna model was designed using the CST software [5].

The effects of some parameters, environmental model parameters and biocompatible layer permittivity on antenna return loss have been investigated. It is also found that the possible variations in rat tissue do not have a significant effect on antenna matching and bandwidth. Hence the designed antenna operates well if those parameters change for reasons.

2.1.2: -Use of high permittivity dielectrics

The use of high permittivity materials: high permittivity dielectrics are also selected for miniaturization of implanted antennas, e.g.: Rogers 3210, ceramic alumina, Teflon. Because they shorten the wavelength and result in lower resonance frequencies, thus assisting in antenna miniaturization. Even the use of such high superstrate materials is not good enough because the superstrate layer still insulates the antenna from the higher permittivity tissue [7].

Dielectric materials with high permittivity values and thin superstrate layers are thus solicited.

2.1.3: -Lengthening the current flow path

As another means for miniaturization is shown by the ref [8]. longer effective current flow paths excited about the radiation patch can also further reduce the resonance frequency. So non- conventional shapes like spiral and hook slotted are being used.

3: -Health hazards and safety to human bodies

According to [9] Issues related to patient safety limit the maximum allowable power incident on the implantable antenna. The Specific Absorption Rate (SAR) (the rate of energy deposited per unit mass of tissue) is generally accepted as the most appropriate dosimetric measure, and compliance with international guidelines is assessed. For example, the IEEE C95.1-1999 standard restricts the SAR averaged over any 1 g of tissue in the shape of a cube to less than 1.6 W/kg (SAR1g, max = 1.6 W/kg). ICNIRP basic restrictions limit the SAR averaged over 10 g of contiguous tissue to less than 2 W/kg.According to [10] for reducing the spatially averaged SAR in human tissue. Replacing the uniform-width spiral radiator of an implantable MICS PIFA with a non-uniform width radiator was found to decrease the electric field intensity and, in turn, the SAR 1g, max. The simulated near-electric-field distribution showed that the high electric field area of the PIFA employing the non-uniform width radiator (Figure 4a) was much smaller than that of the original PIFA. The value of SAR 1g, max was thus reduced from 310 W/kg to 210 W/kg, considering a net input power of 1 W.

4. FIELD GAIN

According to [11] Medical implant communication systems (MICS) are comprised of the implantable medical device and an exterior monitoring/control device, which is placed at some distance (typically, 2m) away from the body implantable antenna should thus provide a signal that is strong enough to be picked up by the exterior device, regardless of any power limitations. It is important to highlight that apart from patient safety, interference issues also limit the maximum allowable power incident on the implantable antenna. For example, a strict limit of -16 dB (25μW) has been set on the effective radiated power (ERP) of implantable medics. Given the SAR and effective radiated power limitations, the far-field gain of the implantable antenna indicates the desired receiver sensitivity for achieving reliable biotelemetry communication. In order to increase the range of biotelemetry communication, implantable antennas with enhanced gain are solicited. However, reduced-size antennas exhibit degraded electromagnetic performance: miniaturization degrades gain, while high gain antennas exhibit relatively increased size. The symmetry of the implanted tissue model affects symmetry of the antenna’s far-field radiation pattern, accordingly. Omnidirectional, monopole-like radiation is observed inside symmetrical tissue models, whereas asymmetrical radiation is recorded within anatomical tissue models that are irregular and inhomogeneous.

5. Power consumption

[12] If operated continuously, the implantable medical device’s transceiver will consume significant energy, and reduce the lifetime of the implantable medical device. There exist some methods for recharging the battery (e.g., via an inductive-loop approach. However, using the biotelemetry link only when necessary would be highly advantageous. For this purpose, a transceiver with dual-band operation may be used, such as the commercially available Zarlink ZL70101 transceiver. The system uses two frequency bands, one for “wake-up” and one for transmission. The transceiver stays in “sleep mode” with low power consumption (1μW) until a “wake-up” signal is sensed in the 2450 MHz ISM band. In the normal mode, the implantable medical device is fully powered, and exchanges data in the MICS band. Following the data transfer, the implantable medical device’s transceiver returns back to the “sleep mode.” The exterior device may be programmed to wake up the implanted device according to a physician defined schedule, or only when a patient event is detected.

6. Modeling of human tissues

[13] In numerical simulations, implantable antennas are analyzed inside inhomogeneous lossy media that simulate biological tissues. Biological tissues have their own permittivity (€r), conductivity (σ), and mass-density values. Canonical tissue models are often used to speed up simulations, and to ease the design of implantable antennas. These may be a single layer, thus accounting for a generic tissue- implantable antenna. They may also be multilayer, thus providing a simplified model of a specific implantation site inside the human body

As far as antenna design is concerned, it is important to highlight that multilayer canonical models have proven to provide an acceptable model for the human body. Highly similar return-loss characteristics have been found in implantable patch antennas inside a three-layer planar geometry and a realistic model of the human chest, as well as inside a three-layer spherical and an anatomical model of the human head.

7. Fabrication of the models

As per [14] Due to the unavailability of biocompatible materials in some laboratories, other dielectrics with similar electrical properties may be selected for prototype fabrication. For instance, Rogers 3210 (€r =10. 2, tanδ=0. 003) is often used. Prototype fabrication of implantable antennas meets all classical difficulties of miniature antennas. For example, additional glue layers used to affix all components together strongly affect antenna performance, by shifting the antenna’s resonance frequency and degrading its matching characteristics. Furthermore, the coaxial cable feed used to connect the antenna with the network analyzer may give rise to radiating currents on the outer part of the cable, which, in turn, deteriorate measurements. The effects of different feeding techniques for implantable patch antennas were analyzed. Patch antenna prototypes immersed inside phantoms, with the ground plane being in direct contact with the tissue-emulating material, were found to be insignificant influenced by the coaxial feeding cable.

8.Use of High frequency

9. Testing inside body phantoms

As per [15] Testing inside phantoms is relatively easy and practical to implement. The fabricated prototype is immersed inside a tissue phantom (i.e., a container filled with a liquid or gel material that mimics the electrical properties of biological tissue), and measured. For validation purposes, the same scenario as that of the numerical simulations has to be considered. Canonically-shaped phantoms have so far been used for testing of implantable patch antennas. In this case, the main challenge lies in the formulation and characterization of tissue-emulating materials. To prevent the formation of air bubbles and/or gaps, the mixture must be carefully heated and stirred, and slowly poured inside the contain of the phantom. Since it is not possible to produce a valid approximation to human tissue for a broad frequency spectrum using a single formula, separate recipes are given for different frequency bands.

10. Testing inside animal tissues

As per [16] implantable antenna inside tissue samples from donor animals, or by surgically implanting the antenna inside live model animals (in-vivo testing). In the first case, electrical properties of the test tissue can be measured using a dielectric probe kit and a network analyzer.The use of animal tissue samples provides an easy adapted pork were found to be Tested inside animal tissue can be performed either by embedding the approach to mimicking the frequency dependency characteristics of the electrical properties of tissues. This can prove highly advantageous when carrying out measurements for multi-band implantable antennas. In the literature, an implantable patch antenna with dual resonances at 380 and 440 MHz was tested inside test tissue obtained by grinding the front leg of a pig. The electrical properties of the between those of human skin and muscle in the MICS band. A dual-band skin-implantable patch antenna operating in the MICS and 2450 MHz ISM bands was also tested in real animal skin. Skin samples with dimensions of 50 mm × 50 mm × 5 mm were extracted from the dorsal area of three donor rats to cover the designed antenna, and measurements were performed within 30 minutes of euthanasia. Finally, a triple-band implantable patch antenna was tested inside a minced front leg of a pig. The electrical properties of the minced pork were measured, and found to correspond to those of human skin and muscle between 100 MHz and 3 GHz. In-vivo investigations are also vital in order to investigate the effects of live tissue on the performance of implantable patch antennas, while providing valuable feedback for antenna design and analysis. Testing inside living animals is highly challenging. An in-vivo testing protocol needs to be developed before the experimental investigations. This needs to deal with the choice and number of animals, pre-surgical preparation, anesthesia, surgical procedure, measurements (e.g., repeatability requirements, determination of potential sources of noise) and post-surgical treatment. In-vivo studies reported in the literature are very limited. The return loss frequency response of a skin-implantable antenna was measured using rats as model animals. In this study, the antenna was implanted by means of a surgical operation inside the dorsal midline of three rats (for validation purposes), and euthanasia was applied after the measurements (approximately 13-15 minutes after the surgery).

Canine studies for trans-scalp evaluation of a scalp-implantable antenna at 2450 MHz were also presented. Canine models were selected to ensure a large head size. An intracranial pressure monitoring device with an integrated PIFA was fixed to the skull. The monitor was tested while the dog was still under anesthesia. After the measurements, the animal was allowed to emerge from anesthesia and taken to the recovery area

CONCLUSION

In this paper, I have presented an overview of the challenges faced and solutions suggested regarding the design, numerical simulations and experimental investigations of implantable patch antennas for biomedical designed for this purpose that “wake up” the implantable medical device only when there is a need for information telemetry. The design of implantable antennas mainly emphasizes miniaturization issues and biocompatibility. However, electrically small antennas present poor radiation performance and relatively narrow bandwidths. Even though gain enhancement is considered crucial, compromises in the system performance are generally inevitable. Conserving energy to extend the lifetime of the implantable medical device is also significant. Multi-band antennas are being exchanged. Patch antennas are based on the Finite-Element and Finite-Difference Time-Domain Methods. Several methodologies have been proposed for the implantable antenna design, all of which need to take into account the computational tools that are most commonly used for the numerical simulations of the implantable host body. Simplified tissue models have proven to be able to substitute for complex anatomical tissue models, thus speeding up simulations. Although a homogenous model is sufficient for basic antenna design, a more realistic model is needed to refine the final antenna design and provide accurate results. Using efficient and accurate simulation tools an tissue model is a key issue for both design and performance analysis. Regarding experimental investigations, implantable antennas exhibit tight fabrication tolerances, attributed to their miniature size. Testing inside tissue-emulating phantoms mainly need to deal with the formulation and characterization of the tissue-mimicking liquid or gel. To benefit from frequency-dependent tissue electrical properties, testing in animal tissue samples can additionally be performed. However, the highest challenge lies in measurements within living animals, for which careful consideration is required for developing the optimal testing protocol. Implantable medical devices are a growing technology with a high potential for improving patients’ life and the quality of healthcare. RF technology for implantable medical devices promises many benefits for both patients and caregivers. Even though emphasis has been given to implantable patch antennas, it is worth noting that the shape of the implantable medical device and the intended implantation site will actually dictate the type of the antenna. Patch antennas are appropriate for being integrated onto most flat implantable devices.

REFERENCES

1. Design of an implantable slot dipole conformal flexible antenna for biomedical applications, IEEE transactions on antennas, Vol. 59, no. 10, October 2011

2. T. Karacolak, A. Z. Hood, and E. Topsakal, “Design of a Dual-Band Implantable Antenna and Development of Skin Mimicking Gels for Continuous Glucose Monitoring,” IEEE Transactions on Microwave Theory and Techniques, 56, 4, April 2008, pp. 1001-1008

3. R. Warty, M. R Tofighi, U. Kawoos, and A. Rosen, “Characterization of Implantable Antennas for Intracranial Pressure Monitoring: Reflection By and Transmission Through a Scalp Phantom,” IEEE Transactions on Microwave Theory and Techniques, 56, 10, October 2008, pp. 2366-2376.

4. P. Soontornpipit, C. M. Furse, and Y. C. Chang, “Design of Implantable Microstrip Antenna for Communication with Medical Implants,” IEEE Transactions on Microwave Theory and Techniques, 52, 8, August 2004, pp. 1944-1951.

5. P. Soontornpipit, C. M. Furse, and Y. C. Chang, “Design of Implantable Microstrip Antenna for Communication with Medical Implants,” IEEE Transactions on Microwave Theory and Techniques, 52, 8, August 2004, pp. 1944-1951.

6.A. K. Skrivervik and F. Merli, “Design Strategies for Implantable Antennas,” Proceedings of the Antennas and Propagation Conference, Loughborough, UK, November 2011.

J. Abadia, F. Merli, J. F. Zurcher, J. R. Mosig and A. K. Skrivervik, “3D Spiral Small Antenna Design and Realization for Biomedical Telemetry in the MICS Band,” radio-engineering, 18, 4, December 2009, pp. 359-367

7. A miniaturized implanted PIFA antenna for indoor wireless telemetry, 978-1-4673-0335-4, IEEE

8.A. Kiourti, M. Christopoulou and K. S. Nikita, “Performance of a Novel Miniature Antenna Implanted in the Human Head for Wireless Biotelemetry,” IEEE International Symposium on Antennas and Propagation, Spokane, Washington, July 2011.

9. Considerations and Link Budget Analysis,” IEEE Transactions on Antennas A. Kiourti and K. S. Nikita, “Miniature Scalp-Implantable Antennas for Telemetry in the MICS and ISM Bands: Design, Safety and Propagation (to appear

10. A. Kiourti and K. S. Nikita, “Meandered Versus Spiral Novel Miniature PIFAs Implanted in the Human Head: Tuning and Performance,” Proceedings of the 2nd ICST International Conference on Wireless Mobile Communication and Healthcare (MobiHealth 2012), Kos Island, Greece, October 2011.

11.P. Soontornpipit, C. M. Furse, and Y. C. Chang, “Miniaturized Biocompatible Microstrip Antenna Using Genetic Algorithm,” IEEE Transactions on Antennas and Propagation, AP-53, 6, June 2005, pp. 1939-1945.

12.W. C. Liu, S. H. Chen, and C. M. Wu, “Implantable Broadband Circular Stacked PIFA Antenna for Biotelemetry Communication,” Journal of Electromagnetic Waves and Applications, 22, 13, 2008, pp. 1791-1800

13. IEEE Standard for Safety Levels with Respect to Human Exposure to Radiofrequency Electromagnetic Fields, 3 kHz to 300GHz, IEEE Standard C95.1, 1999.

14.IEEE Standard for Safety Levels with Respect to Human Exposure to Radiofrequency Electromagnetic Fields, 3 kHz to 300 GHz, IEEE Standard C95.1, 2005.

15.J. Kim and Y. Rahmat-Samii, “SAR Reduction of Implanted Planar Inverted F Antennas with Nonuniform Width Radiator,” IEEE International Symposium on Antennas and Propagation, Albuquerque, New Mexico, July 2006

16.“International Telecommunications Union Radio-communications (ITU-R), Radio Regulations, SA.1346,” ITU, Geneva, Switzerland; available online: http://itu.int/home.

17.“International Telecommunications Union Radio-communications (ITU-R), Radio Regulations, SA.1346,”, ITU, Geneva, Switzerland; available online: http://itu.int/home.

18.Medical Implantable RF Transceiver ZL70101 Data Sheet Zarlink Semiconductor, Ottawa, ON, Canada, October 2006

19.H. S. Savci, A. Sula, Z. Wang, N. S. Dogan, E. Arrivals, “MICS Transceivers: Regulatory Standards and Applications,” Proceedings of the IEEE International Southeast Conference, April 2005

20.J. Kim and Y. Rahmat-Samii, “Implanted Antennas Inside a Human Body: Simulations, Designs, and Characterizations,” IEEE Transactions on Microwave Theory and Techniques, 52, 8, August 2004, pp. 1934-1943

21.W. C. Liu, S. H. Chen, and C. M. Wu, “Implantable Broadband Circular Stacked PIFA Antenna for Biotelemetry Communication,” Journal of Electromagnetic Waves and Applications, 22, 13, 2008, pp. 1791-1800

22.A. Kiourti, M. Christopoulou, and K. S. Nikita, “Performance of a Novel Miniature Antenna Implanted in the Human Head for Wireless Biotelemetry,” IEEE International Symposium on Antennas and Propagation, Spokane, Washington, July 2011

25. W. C. Liu, S. H. Chen, and C. M. Wu, “Implantable Broadband Circular Stacked PIFA Antenna for Biotelemetry Communication,” Journal of Electromagnetic Waves and Applications, 22, 13, 2008, pp. 1791-1800

26.T. Karacolak, A. Z. Hood, and E. Topsakal, “Design of a Dual-Band Implantable Antenna and Development of Skin Mimicking Gels for Continuous Glucose Monitoring,” IEEE Transactions on Microwave Theory and Techniques, 56, 4, April 2008, pp. 1001-1008

27.Considerations and Link Budget Analysis,” IEEE Transactions on Antennas A. Kiourti and K. S. Nikita, “Miniature Scalp-Implantable Antennas for Telemetry in the MICS and ISM Bands: Design, Safety and Propagation (to appear

28.J. Abadia, F. Merli, J. F. Zurcher, J. R. Mosig, and A. K. Skrivervik, “3D Spiral Small Antenna Design and Realization for Biomedical Telemetry in the MICS Band,” radio-engineering, 18, 4, December 2009, pp. 359-367

29. P. Soontornpipit, C. M. Furse, and Y. C. Chung, “Design of Implantable Microstrip Antenna for Communication with Medical Implants,” IEEE Transactions on Microwave Theory and Techniques, 52, 8, August 2004, pp. 1944-1951.

30.T. Karacolak, A. Z. Hood, and E. Topsakal, “Design of a Dual-Band Implantable Antenna and Development of Skin Mimicking Gels for Continuous Glucose Monitoring,” IEEE Transactions on Microwave Theory and Techniques, 56, 4, April 2008, pp. 1001 T. Karacolak, A. Z. Hood, and E. Topsakal, “Design of a Dual-Band Implantable Antenna and Development of Skin Mimicking Gels for Continuous Glucose Monitoring,” IEEE Transactions on Microwave Theory and Techniques, 56, 4, April 2008, pp. -1008.

31.R. Warty, M. R Tofighi, U. Kawoos, and A. Rosen, “Characterization of Implantable Antennas for Intracranial Pressure Monitoring: Reflection By and Transmission Through a Scalp Phantom,” IEEE Transactions on Microwave Theory and Techniques, 56, 10, October 2008, pp. 2366-2376. T. Karacolak, R. Cooper, J. Butler, S. Fisher, and E. Topsakal, “In Vivo Verification of Implantable Antennas Using Rats as Model Animals,” IEEE Antennas and

32. T. Karacolak, R. Cooper, J. Butler, S. Fisher, and E. Topsakal, “In Vivo Verification of Implantable Antennas Using Rats as Model Animals,” IEEE Antennas and Wireless Propagation Letters, 9, 2010, pp. 334-337.

33.U. Kawoos, M. R. Tofighi, R. Warty, F. A Kralick, and A. Rosen, “In-Vitro and In-Vivo Trans-Scalp Evaluation of an Intracranial Pressure Implant at 2.4 GHz,” IEEE Transactions on Microwave Theory and Techniques, 56, 10, October 2008, pp. 2356-2365

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