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Objective: This paper presents a Proof-of-Concept (POC) design and implementation of a biosensing and communication system that can be used for biotelemetry in neural and Gastrointestinal (GI) applications. Methods: Our proposed system is based on backscattering from a semi-passive Radio-Frequency-Identification-Device (RFID) implemented using an Application Specific Integrated Circuit (ASIC) in which electronic switching between transistor gates in high and low states create an impedance difference, thereby effectively changing the ASIC's Radar Cross Section (RCS) and thus modulating its backscattered field. The ASIC is used in conjunction with a biosensor to measure and transmit vital signs from within the body. With this system, we conducted backscatter propagation experiments through different biological and phantom tissues (in ex-vivo and in-vitro) in the GI and neural environments. Results: Our results show that the backscattered waveforms can penetrate tissues of various compositions and thicknesses with power received at distances of up to 55 cm away from the RFID ASIC. Furthermore, results from single- and multi-bit biotelemetry measurements showed a high signal fidelity with low Bit-Error-Rate (BER) while being able to resolve varying tissue temperatures measured by the biosensor in our system. Conclusion: We realized a POC system in which on-chip transistor switching in an ASIC can be used to achieve backscatter communication and biosensing. This system is deployable in neural and GI applications. Significance: Our findings in this work will provide an important practical basis for the design and development of RFID ASIC for biosensing and biotelemetry in medical applications. [ABSTRACT FROM AUTHOR]

Objective: In this paper, we investigate the use of commercial off-the-shelf diagnostic ultrasound readers to achieve multiaccess wireless in vivo telemetry with millimeter-sized sonomicrometry crystal transducers. Methods: The sonomicrometry crystals generate ultrasonic pulses that supersede the echoes generated at the tissue interfaces in response to M-scan interrogation pulses. The traces of these synthetic pulses are captured on an M-scan image and the transmitted data are decoded using image deconvolution and deblurring algorithms. Results: Using a chicken phantom and 1.3 MHz sonomicrometry crystals of diameter 1 mm, we first demonstrate that a standard ultrasound reader can achieve biotelemetry data rates up to 1 Mb/s for implantation depths greater than 10 cm. For this experiment the maximum power dissipation at the crystals was measured to be 20 \mu \textW and bit-error-rate of the telemetry link was shown to be \text10^-2 . We also demonstrate the use of this method for multiaccess biotelemetry where several sonomicrometry crystals simultaneously transmit the data using different modulation and coding techniques. Using a live ovine model, we demonstrate a sonomicrometry crystal implanted in the sheep 's tricuspid valve can maintain a continuous, reliable telemetry link at data rates up tob 800 Kb/s in the presence of respiratory and cardiac motion artifacts. Conclusion: Compared to existing radio-frequency and ultrasound based biotelemetry devices, the reported data-rates are significantly higher considering the transducer's form-factor and its implantation depth. Significance: The proposed technique thus validates the feasibility of establishing reliable communication link with multiple in vivo implants using M-scan-based ultrasound imaging. [ABSTRACT FROM PUBLISHER]

This paper presents a multiband conformal antenna for implantable as well as ingestible devices. The proposed antenna has the following three bands: medical implanted communication service (MICS: 402–405 MHz), the midfield band (1.45–1.6 GHz), and the industrial, scientific, and medical band (ISM: 2.4–2.45 GHz) for telemetry or wireless monitoring, wireless power transfer (WPT), and power conservation, respectively. A T-shaped ground slot is used to tune the antenna, and this antenna is wrapped inside a printed 3-D capsule prototype to demonstrate its applicability in different biomedical devices. Initially, the performance of the proposed antenna was measured in an American Society for Testing and Materials phantom containing a porcine heart in the MICS band for an implantable case. Furthermore, to stretch the scope of the suggested antenna to ingestible devices, the antenna performance was simulated and measured using a minced pork muscle in the ISM band. A modified version of the midfield power transfer method was incorporated to replicate the idea of WPT within the implantable 3-D printed capsule. Moreover, a near-field plate (NFP) was employed to control the leakage of power from the WPT transmitter. From the simulation and measurements, we found that use of a ground slot in the implantable antenna can improve antenna performance and can also reduce the specific absorption rate. Furthermore, by including the NFP with the midfield WPT transmitter system, unidirectional wireless power can be obtained and WPT efficiency can be increased. [ABSTRACT FROM PUBLISHER]

Implantable devices are becoming prevalent in the field of biotelemetry. However, designing implantable antennas is challenging, since compact structure, large bandwidth, and relatively high gain are required at the same time in the lossy human tissue. In this paper, we analytically derive the electromagnetic (EM) fields of the electric and magnetic dipoles in the lossy human tissue and compare their radiation performance. Based on the analysis, a coupled small loop antenna is designed to obtain a large bandwidth of 74.1% when embedded in the muscle. The antenna is composed of an inner loop and an outer loop with printed capacitive structures, and it can also be rolled up into a capsule using flexible substrate. The overall dimension is $30\times 16\times 0.5$ mm3 and $\pi \times (5)^{2} \times 16$ mm3 for the planar and the capsule structure, respectively. Compared with other implantable antennas, a relatively high gain of −23.19 dBi has been achieved for the planar small loop, as the magnetic antenna suffers from less power dissipation in the human tissue. The specific absorption rate (SAR) of the antenna is 177 W/kg with an input power of 1 W, which enables a maximum transmitting power of 9.03 mW according to the IEEE standard. The high transmitting power ensures the reliable communication link. The antenna prototypes were fabricated and measured in the minced pork, which has similar EM properties as the human muscle. The simulated and measured results basically agree with each other. The proposed implantable antenna is competitive in its balanced performance of wide band, high gain, low profile, and low SAR. [ABSTRACT FROM AUTHOR]

The objective of this paper is to design a microstrip patch antenna for communication with medical implants in the 402-405-MHz Medical Implant Communications Services band. Microstrip antenna design parameters are evaluated using the finite-difference time-domain method, and are compared to measured results. The effects of shape, length, size, location of feed point and ground point, substrate and superstrate materials, and their thicknesses are evaluated. An extensive study of the performance of the antennas to changes in these parameters was under- taken. The results of this paper provide guidance in the design of implantable microstrip antennas. [ABSTRACT FROM AUTHOR]

Monitoring blood flow rate inside prosthetic vascular grafts enables an early detection of the graft degradation, followed by the timely intervention and prevention of the graft failure. This paper presents an inductively powered implantable blood flow sensor microsystem with bidirectional telemetry. The microsystem integrates silicon nanowire (SiNW) sensors with tunable piezoresistivity, an ultralow-power application-specific integrated circuit (ASIC), and two miniature coils that are coupled with a larger coil in an external monitoring unit to form a passive wireless link. Operating at 13.56-MHz carrier frequency, the implantable microsystem receives power and command from the external unit and backscatters digitized sensor readout through the coupling coils. The ASIC fabricated in 0.18-μm CMOS process occupies an active area of 1.5 × 1.78 mm^2 and consumes 21.6 μW only. The sensors based on the SiNW and diaphragm structure provide a gauge factor higher than 300 when a small negative tuning voltage (−0.5–0 V) is applied. The measured performance of the pressure sensor and ASIC has demonstrated 0.176 mmHg/√Hz sensing resolution. [ABSTRACT FROM PUBLISHER]

This paper presents the design of a wideband spiral antenna for ingestible capsule endoscope systems and a comparison between the experimental results in a human phantom and a pig under general anesthesia. As wireless capsule endoscope systems transmit real-time internal biological image data at a high resolution to external receivers and because they operate in the human body, a small wideband antenna is required. To incorporate these properties, a thick-arm spiral structure is applied to the designed antenna. To make practical and efficient use of antennas inside the human body, which is composed of a high dielectric and lossy material, the resonance characteristics and radiation patterns were evaluated through a measurement setup using a liquid human phantom. The total height of the designed antenna is 5 mm and the diameter is 10 mm. The fractional bandwidth of the fabricated antenna is about 21% with a voltage standing-wave ratio of less than 2, and it has an isotropic radiation pattern. These characteristics are suitable for wideband capsule endoscope systems. Moreover, the received power level was measured using the proposed antenna, a circular polarized receiver antenna, and a pig under general anesthesia. Finally, endoscopic capsule images in the stomach and large intestine were captured using an on–off keying transceiver system. [ABSTRACT FROM AUTHOR]

The paper introduces numerical and experimental investigations of biotelemetry radio channels and wave attenuation in human subjects with ingested wireless implants. The study covers commonly used frequencies in telemedicine applications: ultrahigh frequencies at 402 MHz, 868 MHz and the industrial, scientific and medical (ISM) band frequency at 2.4 GHz. Numerical electromagnetic analysis is applied to model in/on-body radio propagation channels and the resulted parameters demonstrated the importance of digital phantom accuracy in characterization of wave absorption and attenuation with regards to organ contents, specifically for the digestion system, Path gain variations of biotelemetry radio channels, in the close vicinity of the subject, with wireless implants were measured using a near field scanner. Simulation results were verified with measurement in good agreement. [ABSTRACT FROM AUTHOR]

In this paper, an analysis of radio channel characteristics for single- and multiple-antenna bodyworn systems for use in body-to-body communications is presented. The work was based on an extensive measurement campaign conducted at 2.45 GHz representative of an indoor sweep and search scenario for fire and rescue personnel. Using maximum-likelihood estimation in conjunction with the Akaike information criterion (AIC), five candidate probability distributions were investigated and from these the κ - μ distribution was found to best describe small-scale fading observed in the body-to-body channels. Additional channel parameters such as autocorrelation and the cross-correlation coefficient between fading signal envelopes were also analyzed. Low cross correlation and small differences in mean signal levels between potential dual-branch diversity receivers suggested that the prospect of successfully implementing diversity in this type application is extremely good. Moreover, using selection combination, maximal ratio, and equal gain combining, up to 8.69-dB diversity gain can be made available when four spatially separated antennas are used at the receiver. Additional improvements in the combined envelopes through lower level crossing rates and fade durations at low signal levels were also observed. [ABSTRACT FROM AUTHOR]

Implantable devices have been investigated with great interest as communication tools. These implantable devices are embedded into the human or pet body. The vital information (such as temperature, blood pressure, cardiac beat, etc.) can be transmitted from implantable devices to the external equipment by use of a wireless communication link. Therefore, the research on the antenna for implantable devices (implanted antennas) is very important. This paper proposes an implanted H-shaped cavity slot antenna for short-range wireless communications. This type of antenna, which is designed to operate at the industrial-scientific-medical band (2.45 GHz), is investigated by using finite-difference time-domain calculation. We analyzed the performances of the proposed antenna which is embedded into the human body between the shoulder and the elbow. However, since the proposed antenna is too small to fabricate, a scale model is adopted for antenna measurements. Some characteristics of the scale model of the antenna are also calculated and measured by using the 2/3 muscle-equivalent phantom. The results show that the proposed antenna has promise for use in an implant. [ABSTRACT FROM AUTHOR]

Optical telemetry has long been an option for transcutaneous data transfer and has been used in various types of implanted systems. This telemetry modality and the efficiency of these optical links are becoming ever more important as higher bandwidth sources such as cortical recording arrays are being implemented in implanted systems. The design of the transmitterskin-receiver interface (the "optical interface") is paramount to the operation of a transcutaneous optical telemetry link. This interface functions to achieve sufficient receiver signal power for data communication. This paper describes a mathematical analysis and supporting data that quantitatively describes the relationship between the primary interface design parameters. These parameters include the thickness of the skin through which the light is transmitted, the size of the integration area of the optics, the degree of transmitter-receiver misalignment, the efficiency of the optics system, and the emitter power. The particular combination of these parameters chosen for the hardware device will determine the receiver signal power and, therefore, the data quality for the link. This paper demonstrates some of the tradeoffs involved in the selection of these design parameters and provides suggestions for link design. This analysis may also be useful for transcutaneous optical powering systems. [ABSTRACT FROM AUTHOR]

Antennas implanted in a human body are largely applicable to hyperthermia and biotelemetry. To make practical use of antennas inside a human body, resonance characteristics of the implanted antennas and their radiation signature outside the body must be evaluated through numerical analysis and measurement setup. Most importantly, the antenna must be designed with an in-depth consideration given to its surrounding environment. In this paper, the spherical dyadic Green's function (DGF) expansions and finite-difference time-domain (FDTD) code are applied to analyze the electromagnetic characteristics of dipole antennas and low-profile patch antennas implanted in the human head and body. All studies to characterize and design the implanted antennas are performed at the biomedical frequency band of 402-405 MHz. By comparing the results from two numerical methodologies, the accuracy of the spherical DGF application for a dipole antenna at the center of the head is evaluated. We also consider how much impact a shoulder has on the performance of the dipole inside the head using FDTD. For the ease of the design of implanted low-pro- file antennas, simplified planar geometries based on a real human body are proposed. Two types of low-profile antennas, i.e., a spiral microstrip antenna and a planar inverted-F antenna, with superstrate dielectric layers are initially designed for medical devices implanted in the chest of the human body using FDTD simulations. The radiation performances of the designed low-profile antennas are estimated in terms of radiation patterns, radiation efficiency, and specific absorption rate. Maximum available power calculated to characterize the performance of a communication link between the designed antennas and an exterior antenna show how sensitive receivers are required to build a reliable telemetry link. [ABSTRACT FROM AUTHOR]

In this paper, we investigate a novel approach of establishing a data telemetry link for a dual-unit retinal prosthesis at microwave frequencies (1.45 and 2.45 GRz) using a Pair, of microstrip patch antennas. Appropriately sized extraocular (25 × 25 mm) and intraocular (6 × 6 mm) antennas are designed to operate at both the frequencies using the finite-difference times domain method, and the coupling between them is exam, med computationally in the presence of a 0.25.mm resolution human-head model. Good agreement between numerical and experimental Coupling results is shown and it is observed that the eyeball acts as a dielectric lens for the implanted antenna, thus improving the coupling between the extraocular and intraocular antenna. Specific absorption rate (SAR) computations are also performs at both the frequencies, and the peak 1-g SAR value is calculated. Detailed analysis of the design issues of the antennas, results of the numerical and experimental coupling measurements and SAR calculations are presented. [ABSTRACT FROM AUTHOR]

Telemetry systems enable researchers to continuously monitor physiological signals in unrestrained, freely moving small rodents. Drawbacks of common systems are limited operation time, the need to house the animals separately, and the necessity of a stable communication link. Furthermore, the costs of the typically proprietary telemetry systems reduce the acceptance. The aim of this paper is to introduce a low-cost telemetry system based on common radio frequency identification technology optimized for battery-independent operational time, good reusability, and flexibility. The presented implant is equipped with sensors to measure electrocardiogram, arterial blood pressure, and body temperature. The biological signals are transmitted as digital data streams. The device is able of monitoring several freely moving animals housed in groups with a single reader station. The modular concept of the system significantly reduces the costs to monitor multiple physiological functions and refining procedures in preclinical research. [ABSTRACT FROM PUBLISHER]

The two major challenges associated with the conversion of a wireless system operating in air to an implantable version, antenna detuning and biocompatibility, are addressed in a coherent way. An RF identification (RFID)-based biomedical telemetry system designed for free-space operation was chosen as the starting reference. A new pin-compatible space-saving antenna with a ground plane was designed, fabricated, and tested to replace the original “free-space” antenna in the active RFID tag without making any other changes to the tag circuit, such that the tag would function well when it is placed under rat skin and fat. Biocompatibility and potential antenna detuning due to rat tissue variations were addressed in the design process, without significantly increasing the tag physical height, by applying a thin coating of biocompatible material directly over the antenna. The operation of the medical telemetry system was successfully demonstrated, with the tag placed under rat skin and fat, and its range of 60–72 cm was found to be sufficient to support medical research experiments conducted with rats in cages. Due to the biocompatible coating over the antenna, antenna matching is very insensitive to changes in tissue dielectric constants and thickness. The footprint of the new antenna is 33% less than that of the original antenna, its measured 10-dB return-loss bandwidth is 100 MHz or 11%, and overall efficiency is 0.82% at 920 MHz. [ABSTRACT FROM AUTHOR]

Wireless power, when coupled with miniaturized implantable electronics, has the potential to provide a solution to several challenges facing neuroscientists during basic and preclinical studies with freely behaving animals. The EnerCage system is one such solution as it allows for uninterrupted electrophysiology experiments over extended periods of time and vast experimental arenas, while eliminating the need for bulky battery payloads or tethering. It has a scalable array of overlapping planar spiral coils (PSCs) and three-axis magnetic sensors for focused wireless power transmission to devices on freely moving subjects. In this paper, we present the first fully functional EnerCage system, in which the number of PSC drivers and magnetic sensors was reduced to one-third of the number used in our previous design via multicoil coupling. The power transfer efficiency (PTE) has been improved to 5.6% at a 120 mm coupling distance and a 48.5 mm lateral misalignment (worst case) between the transmitter (Tx) array and receiver (Rx) coils. The new EnerCage system is equipped with an Ethernet backbone, further supporting its modular/scalable architecture, which, in turn, allows experimental arenas with arbitrary shapes and dimensions. A set of experiments on a freely behaving rat were conducted by continuously delivering 20 mW to the electronics in the animal headstage for more than one hour in a powered 3538 cm^2 experimental area. [ABSTRACT FROM PUBLISHER]

This paper presents a novel fully implantable wireless sensor system intended for long-term monitoring of hypertension patients, designed for implantation into the femoral artery with computed tomography angiography. It consists of a pressure sensor and a telemetric unit, which is wirelessly connected to an extracorporeal readout station for energy supply and data recording. The system measures intraarterial pressure at a sampling rate of 30 Hz and an accuracy of ±1.0 mmHg over a range of 30–300 mmHg, while consuming up to 300 μW. A special peel-away sheath introducer set was developed to support the implantation procedure. The system delivered stable measurements in initial animal trials in sheep, with results being in good agreement with reference sensor systems. [ABSTRACT FROM PUBLISHER]

The development of a long-term wireless implantable biosensor based on fluorescence intensity measurement poses a number of technical challenges, ranging from biocompatibility to sensor stability over time. One of these challenges is the design of a power efficient and miniaturized electronics, enabling the biosensor to move from bench testing to long term validation, up to its final application in human beings. In this spirit, we present a wireless programmable electronic platform for implantable chronic monitoring of fluorescent-based autonomous biosensors. This system is able to achieve extremely low power operation with bidirectional telemetry, based on the IEEE802.15.4-2003 protocol, thus enabling over three-year battery lifetime and wireless networking of multiple sensors. During the performance of single fluorescent-based sensor measurements, the circuit drives a laser diode, for sensor excitation, and acquires the amplified signals from four different photodetectors. In vitro functionality was preliminarily tested for both glucose and calcium monitoring, simply by changing the analyte-binding protein of the biosensor. Electronics performance was assessed in terms of timing, power consumption, tissue exposure to electromagnetic fields, and in vivo wireless connectivity. The final goal of the presented platform is to be integrated in a complete system for blood glucose level monitoring that may be implanted for at least one year under the skin of diabetic patients. Results reported in this paper may be applied to a wide variety of biosensors based on fluorescence intensity measurement. [ABSTRACT FROM AUTHOR]

Bioimplantable sensors using radio-frequency telemetry links that enable the continuous monitoring and recording of physiological data are receiving a great deal of attention. The objective of this paper is to study the feasibility of an implantable sensor for tissue characterization. This has been done by querying an LC sensor surrounded by dispersive tissues by an external antenna. The resonant frequency of the sensor is monitored by measuring the input impedance of the antenna, and correlated to the desired quantities. Using an equivalent circuit model of the sensor that accounts for the properties of the encapsulating tissue, analytical expressions have been developed for the extraction of the tissue permittivity and conductivity. Finally, experimental validation has been performed with a telemetry link that consists of a loop antenna and a fabricated LC sensor immersed in single and multiple dispersive phantom materials. [ABSTRACT FROM AUTHOR]

In this paper, a novel multinode wireless monitoring platform, based on ZigBee communication standard, is presented and tested in vivo. The transmission power levels needed to establish a reliable connection from the different gastrointestinal districts are reported and compared with safety levels from international guidelines. These findings can be useful to evaluate the effectiveness of a commercial and standardized approach to implantable and miniaturized monitoring of physiological parameters. [ABSTRACT FROM AUTHOR]

In this study, we present a small-size dual medical implant communications service (MICS) (402-405 MHz) and industrial, scientific, and medical (ISM) (2.4-2.48 GHz) band implantable antenna for continuous glucose-monitoring applications. The antenna is optimized for dual-band operation by combining an in-house finite-element boundary integral electromagnetic simulation code and particle swarm optimization algorithm. In order to test the designed antenna in vitro, gels mimicking the electrical properties of human skin are also developed. The optimized antenna is fabricated and measured in the gel. The simulated and measured bandwidths are found to be 20.4% MICS, 4.2% ISM, and 35.3% MICS, and 7.1% ISM, respectively. Although we have emphasized continuous glucose monitoring throughout this paper, the antenna and skin mimicking gels presented here can be used for many other wireless telemetry applications. [ABSTRACT FROM AUTHOR]

In this paper, we present a radiotelemetry sensor, designed as a lab-in-a-pill, which incorporates a two-channel micro-fabricated sensor platform for real-time measurements of temperature and pH. These two parameters have potential application for use in remote biological sensing (for example they may be used as markers that reflect the physiological environment or as indicators for disease, within the gastrointestinal tract). We have investigated the effects of biofouling on these sensors, by exploring their response time and sensitivity in a model in vitro gastrointestinal system. The artificial gastric and intestinal solutions used represent a model both for fasting, as well as for the ingestion of food and subsequent digestion to gastrointestinal chyme. The results showed a decrease in pH sensitivity after exposure of the sensors for 3 h. The response time also increased from an initial measurement time of 10 s in pure GI juice, to Ca. 25 s following the ingestion of food and 80 s in simulated chyme. These in vitro results indicate that changes in viscosity in our model gastrointestinal system had a pronounced effect on the unmodified sensor. [ABSTRACT FROM AUTHOR]

This paper presents a four-channel telemetric microsystem featuring on-chip alternating current amplification, direct current baseline stabilization, clock generation, time-division multiplexing, and wireless frequency-modulation transmission of microvolt- and millivolt-range input biopotentials in the very high frequency band of 94-98 MHz over a distance of ∼ 0.5 m. It consists of a 4.84-mm² integrated circuit, fabricated using a 1.5-µm double-poly double-metal n-well standard complementary metal-oxide semiconductor process, interfaced with only three off-chip components on a custom-designed printed-circuit board that measures 1.7 × 1.2 × 0.16 cm³, and weighs 1.1 g including two miniature 1.5-V batteries. We characterize the microsystem performance, operating in a truly wireless fashion in single-channel and multichannel operation modes, via extensive benchtop and in vitro tests in saline utilizing two different micromachined neural recording microelectrodes, while dissipating ∼ 2.2 mW from a 3-V power supply. Moreover, we demonstrate successful wireless in vivo recording of spontaneous neural activity at 96.2 MHz from the auditory cortex of an awake marmoset monkey at several transmission distances ranging from 10 to 50 cm with signal-to-noise ratios in the range of 8.4-9.5 dB. [ABSTRACT FROM AUTHOR]

This paper presents a low-phase-noise, hybrid LC-tank, analog frequency modulator for wireless biotelemetry employing on-chip NMOS varactors in the inversion region as the frequency tuning element. We demonstrate that a correct estimate for the destination signal-to-noise ratio, which quantifies the quality of the wirelessly received signal in a frequency-modulated biotelemetry system, is only achieved after taking into account the large-signal oscillation effect on the tank varactor. A prototype chip is fabricated using AM! 1.5-pm double-poly double-metal n-well CMOS process, and exhibits a measured gain factor of 1.21 MHz/V in the mid-range of the tuning voltage and a phase noise of -88.6 dBc/Hz at 10-kHz offset from the 95.1-MHz carrier while dissipating 1.48 mW from a 3 V power supply leading to a figure of merit (FOM) of -166.5 dBc/Hz. The VCO is successfully interfaced with a penetrating silicon microelectrode with 700 μm² iridium recording sites for wireless in vitro recording of a 50 Hz simulated normal sinus rhythm signal from saline over a distance of 0.25 m. Given a typical gain of ∼ 40 dB for fully integrated front-end bioamplifiers, a wireless recording microsystem employing this VCO would be capable of detecting Input biopotentials down to the submilivolt range. [ABSTRACT FROM AUTHOR]

A miniature implantable and dynamically configurable potentiostat and galvanostat for two- and three-electrode biosensors with a telemetry electronic package was developed to provide remote monitoring of implantable amperometric and voltametric biosensors such as for glucose. Included are circuitry for sensor biasing, a transimpedance amplifier to produce the sensor proportional output signal, and a transceiver (transmitter and receiver) which can both receive setup parameter values and transmit the biosensor concentration data to a corresponding remote transceiver and computer for monitoring. Remotely cone figurable features included in the in vivo implanted unit include: sensor excitation changes; filter frequency cutoff values, amplifier gain; and transmission intervals utilizing 303.825-MHz UHF RF telemetry for end-to-end remote data monitoring. The developed mP/Gstat printed circuit board measure about 51 × 22 × 1 mm thick, and is suitable for bench top or encapsulated use. Instrumentation developed in this paper will allow other researchers to develop implantable units. Evaluation in two- and three-electrode mPstat and two electrode mGstat modes with simulated biosensors showed overall average theoretical to actual recorded value differences of only 0.5859% reading (RDG) with a standard deviation (SD) of 0.5376% indicating excellent design performance. System testing in two-electrode mPstat mode with actual glucose sensors shows excellent stability and correlation to standard biosensor calibrations with an average difference of only 7.33% full scale (FS) with 3.65% SD, which is minimal considering two totally independent calibration instrument configurations. [ABSTRACT FROM AUTHOR]

Biotelemetric systems, especially those that employ implanted devices, work with inductive links, where usually large circular external coils are separated by relatively large distances (dimensions of centimeters) from the small/Millimeter- or submillimeter-size) implanted coils. This paper shows that order these conditions, a simplified method for calculation of the mutual (M) between the coils, avoiding elliptic integrals, can be obtained. A procedure for coil design, with maximum M between them, is also described. [ABSTRACT FROM AUTHOR]

The conventional method of diagnosing disorders of the human gastro-intestinal (GI) tract is by sensors embedded in cannulae that are inserted through the anus, mouth, or nose. However, these cannulae cause significant patient discomfort and cannot be used in the small intestine. As a result, there is considerable ongoing work in developing wireless sensors that can be used in the small intestine. The radiation characteristics of sources in the GI tract cannot be readily calculated due to the complexity of the human body and its composite tissues, each with different electrical characteristics. In addition, the compact antennas used are electrically small, making them inefficient radiators. This paper presents radiation characteristics for sources in the GI tract that should allow for the optimum design of more efficient telemetry systems. The characteristics are determined using the finite-difference time-domain method with a realistic antenna model on an established fully segmented human body model. Radiation intensity outside the body was found to have a Gaussian-form relationship with frequency. Maximum radiation occurs between 450 and 900 MHz. The gut region was found generally to inhibit vertically polarized electric fields more than horizontally polarized fields. [ABSTRACT FROM AUTHOR]

We present a biocompatible high-contrast low-loss antenna (HCLA) designed for efficient into-body radiation for applications as diverse as medical telemetry, sensing, and imaging. The HCLA is wearable with a compact size of 2.62 cm3 and operates across the 1–5 GHz bandwidth. The quasi-bowtie antenna is loaded with a high-contrast (i.e., alternating layers of high- and low-permittivity materials) and low-loss dielectric to improve directivity and gain into the biological tissues. Measurement results at 2.4 GHz are in good agreement with simulations and show 5.72 dB improvement in transmission loss over the most efficient into-body radiator reported in the past. At the high end of the frequency bandwidth, the simulation results for two antennas placed across each other with tissue in between show ~12.5 dB improvement in transmission loss. The HCLA is fabricated with stable, low-loss materials that allow for repeatability and consistency in the fabrication process, thus addressing the limitations of the current state-of-the-art. It is also made from biocompatible materials that enable it to be placed directly on the skin for real-world implementation. In this article, we discuss the operation principle and design of the HCLA, its transmission performance, radiation patterns, and specific absorption rate (SAR). [ABSTRACT FROM AUTHOR]

In this study, an ultraminiaturized implantable antenna is developed for biotelemetry applications. It has triple-band characteristics in the industrial, scientific, and medical (ISM) bands of 902–928 MHz for data telemetry and 2400–2483.5 MHz for power-saving applications and midfield band (1824–1980 MHz) for wireless power transfer simultaneously. The size of the proposed antenna is 0.068 $\lambda _{g}\,\,\times0.048\,\,\lambda _{g}\,\,\times0.0036\,\,\lambda _{g}$ and it is the smallest size of any triple-band implantable antenna ever devised without using shortening vias. Such a compact size is achieved by meandering the shape of the radiating patch and adding open-ended ground slots. Unlike most miniaturized implantable antennas reported in the available literature, no shortening pin is used and this makes the fabrication of the antenna very easy. The bandwidths measured in minced pork muscles are 14% and 24% in the lower and upper ISM bands, respectively, and 12% in the midfield band. The maximum values of the realized gain of the proposed antenna obtained in the heterogeneous skin phantom at 915, 1900, and 2450 MHz are −27.2, −22.2, and −19.9 dBi, respectively. In addition, specific absorption rates (SARs) in the heterogeneous skin and muscle tissues at the three resonance frequencies are calculated and show compliance with the IEEE standards for ensuring human safety. Finally, the range of the biotelemetry link is evaluated by calculating the wireless communication link budget at data rates of 7 kb/s, 100 kb/s, and 10 Mb/s at resonance frequencies. [ABSTRACT FROM AUTHOR]

This article presents a deeply implanted stent antenna system for endovascular aneurysm repair (EVAR) to treat abdominal aortic aneurysm (AAA). The stent antenna is composed of multiple helical wires connected to form meshed rings incorporating a single feed wire, thereby precluding the random distribution of currents on the stent-struts. In addition to EVAR application, the key features of the proposed stent system are its better antenna characteristics, including an omnidirectional radiation pattern, high gain, and perfect impedance matching. The proposed stent antenna exhibits wide-band characteristics covering the frequency range from 850 to 950 MHz, including industrial, scientific, and medical bands (i.e., ISM 868 and 915 MHz). Moreover, the stent offers peak gain values of −20.75 and −19.04 dBi at the 868 and 915 MHz bands, respectively. Simulations were performed using the finite-element method and finite-difference time domain to evaluate the properties of the EVAR stent system. For validation, measurements were conducted with a 3-D printed AAA placed in a saline-filled American Society for Testing and Materials phantom and in minced pork. Good agreement between simulation and measured results was observed, thereby serving a first validation of the EVAR stent antenna attributes. A link budget analysis was performed to analyze the biotelemetry capabilities. [ABSTRACT FROM AUTHOR]

A wireless biotelemetry system operates in vivo, which requires low power consumption for long-lasting operation, high output power for long transferable distance, and high throughput for incorporating many recording electrodes and transmitting raw brain signals. An implantable 2.4-GHz on–off keying (OOK) transmitter with high throughput and high energy efficiency for wireless biotelemetry systems has been designed in a 0.18-\mum CMOS process. To balance power consumption and output power, a complementary voltage-controlled oscillator for the proposed transmitter is employed. Power consumption of the transmitter is reduced by switching the oscillator on and off to generate an OOK modulated signal. The transient delay for the transmitter is derived and applied to implement a high throughput transmitter. Rat skin-mimic emulating the implant environment such as electrical properties of the skin is used to measure the proposed transmitter in vitro. To transmit 136 Mb/s of OOK data, the transmitter consumes 3 mW of dc power and generates an output power of -14 dBm. The transmitter achieves energy efficiency of 22 pJ/bit with an associated bit error rate of \1.7 \times \10^- 3 without using an error correction scheme. [ABSTRACT FROM AUTHOR]

The fields induced in the human head by the wireless telemetry used for Second Sight Medical Product, Inc.'s epiretinal prosthesis system are characterized for compliance testing with international safety standards using a three-dimensional (3-D) finite-difference time-domain (FDTD) code in D-H formulation. The specific system under consideration utilizes an inductive link with a primary coil mounted on the subject's eyeglasses and a secondary coil that is strapped on the eye, over the sclera. The specific absorption rate (SAR) and the current density have been obtained computationally for different relative positions of the primary and secondary coils to account for the relative misalignment of the two due to the movement of the eye with the implant. For a peak normalized current of 0.62 A in the primary coil at 10 MHz, the highest peak 1-g SAR was found to be 0.45 WIKg, and the maximum root mean square (rms) current density averaged over a 1-cm2 area was found to be 16.05 A/rn2, both of which are within the limits imposed by IEEE and ICNIRP safety standards. Simulations between 2 and 20 MHz indicated that the induced electric field values scale well with frequency, thus providing guidelines for the determination of the final frequency and input power requirements of operation for the telemetry system to meet safety standards. [ABSTRACT FROM AUTHOR]

Presents information on a study which fabricated a biopotential recording system to be used as backpacks for male giant sphinx moths to function as biohybrid robots. Circuit description and construction; Measurement results; Conclusion.

This article proposes an efficient and complete wireless power transfer (WPT) system (WPTS) for multipurpose biomedical implants. The WPTS is composed of a self-diplexing implantable antenna, efficient rectifier, and WPT transmitter (WPT Tx). The proposed system is capable of simultaneously transmitting recorded data and recharging the batteries of the devices (so as to elongate the implant life). The WPT Tx occupies dimensions of $50 \times 50 \times 1.6$ mm3 and is optimized to effectively transfer power at 1470 MHz to a 55-mm deep implantable device. An efficient and compact ($3.4 \times 6.7$ mm2) rectifier is used at 1470 MHz to convert the harvested RF power into a useful direct current (dc) power. The proposed rectifier circuit exhibits a high conversion efficiency of 50% even at an input power of −14 dBm and maximum efficiency of 76.1% at 2 dBm. The proposed self-diplexing implantable antenna occupies small dimensions (9.4 mm3) and operates at 915 and 1470 MHz by exciting ports 1 and 2, respectively. The biotelemetry operation is performed using a 915 MHz band (port 1), and the rectifier circuit is connected to port 2 (1470 MHz) to perform wireless powering. The simulated results are validated by examining the individual elements (WPT Tx, rectifier, and self-diplexing antenna) and overall WPTS in a saline solution and minced pork. The results prove that the proposed scheme is suitable for biotelemetry and wireless powering of biomedical implants. [ABSTRACT FROM AUTHOR]

Progress in implantable and ingestible wireless biotelemetry requires versatile and efficient antennas to communicate reliably from a body. We propose an ultraminiature 434 MHz antenna immune to impedance detuning caused by varying electromagnetic properties of the surrounding biological environment. It is designed for a standard input impedance of 50 $\Omega $ . The antenna is synthesized and miniaturized using a hybrid analytical–numerical approach, and then optimized to conform to the inner surface of a 17 mm long biocompatible encapsulation (7 mm diameter). The substrate is 50 \mu \text{m} thick. The capsule antenna is analyzed both in simplified and anatomically realistic heterogeneous phantoms. It remains matched at common implantation sites and through the whole gastrointestinal tract. Enhanced robustness allows using the antenna for a wide range of in-body applications. Computed reflection coefficients and radiation performance both show good agreement with measurements. The far field is characterized with the direct illumination technique using an analog fiber optic link. The realized gain (measured max. value −19.6 dBi) exceeds the counterparts by about 3 dBi. The proposed antenna contributes to the further development of a new generation of miniature in-body devices that involve complex and dense integration of sensors, logic, and power source. [ABSTRACT FROM AUTHOR]

Objective: We present a review of wireless medical devices that are placed inside the human body to realize many and different sensing and/or stimulating functionalities. Methods: A critical literature review analysis is conducted focusing on three types of in-body medical devices, i.e., 1) devices that are implanted inside the human body (implantables), 2) devices that are ingested like regular pills (ingestibles), and 3) devices that are injected into the human body via needles (injectables). Design considerations, current status, and future directions related to the aforementioned in-body devices are discussed. Results: A number of design challenges are associated with in-body devices, including selection of operation frequency, antenna design, powering, and biocompatibility. Nevertheless, in-body devices are opening up new opportunities for medical prevention, prognosis, and treatment that quickly outweigh any design challenges and/or concerns on their invasive nature. Conclusion: In-body devices are already in use for several medical applications, ranging from pacemakers and capsule endoscopes to injectable microstimulators. As technology continues to evolve, in-body devices are promising several new and hitherto unexplored opportunities in the healthcare. Significance: Unobtrusive in-body devices are envisioned to collect a multitude of physiological data from the early years of each individual. This big-data approach aims to enable a shift from symptom-based medicine to a proactive healthcare model. [ABSTRACT FROM AUTHOR]

A smart wearable textile array system (SWTAS) with direction of arrival (DoA) estimation and beamforming is proposed and developed for biomedical telemetry applications. This conformal system enables effective and continuous patient monitoring when combined with one or more health sensors, as information about the subject's health condition is received adaptively to guarantee link reliability. This operation is facilitated by a receiver front-end and a digital baseband beamforming network, which enables scalability and flexibility. The proposed SWTAS also features flexible antenna arrays made using textiles, which are arbitrarily located on a cylindrically shaped body phantom to ensure wide spatial DoA estimation capability. Besides being designed to suit on-body placement, the system performance is also characterized for on-body usage using a commercial body-emulating liquid, and placed at a realistic distance from the body, considering user clothing. Investigation indicated a good performance in the system's \pm\80^\circ forward plane with a DoA accuracy of 3^\circ. Finally, a practical evaluation is presented using two transmitters placed at distinct locations and distances. The system successfully estimated both DoAs and received the telemetry signals using beamforming. [ABSTRACT FROM PUBLISHER]

We study the design and radiation performance of novel miniature antennas for integration in head-implanted medical devices operating in the MICS (402.0–405.0 MHz) and ISM (433.1–434.8, 868.0–868.6 and 902.8–928.0 MHz) bands. A parametric model of a skin-implantable antenna is proposed, and a prototype is fabricated and tested. To speed-up antenna design, a two-step methodology is suggested. This involves approximate antenna design inside a simplified geometry and further Quasi-Newton optimization inside a canonical model of the intended implantation site. Antennas are further analyzed inside an anatomical human head model. Results indicate strong dependence of the exhibited radiation performance (radiation pattern, gain, specific absorption rate and quality of communication with exterior equipment) on design parameters and operation frequency. The study provides valuable insight into the design of implantable antennas, addressing the suitability of canonical against anatomical tissue models for design purposes, and assessing patient safety and link budget at various frequencies. Finite Element and Finite Difference Time Domain numerical solvers are used at different stages of the antenna design and analysis procedures to suit specific needs. The proposed design methodology can be applied to optimize antennas for several implantation scenarios and biotelemetry applications. [ABSTRACT FROM PUBLISHER]

Flexible polymers have gained much attention in the development of low cost, magnetic resonance compatible, and nonfragile implantable medical devices. However, efficacy of the conventional polymer encapsulations containing hybrid interfaces is limited due to their relatively high moisture absorption and unstable interfacial adhesion in aqueous environments. As an alternative, we report on a monolithic encapsulation platform for neuroprosthetic devices using liquid crystal polymers (LCPs), which have a very low degree of moisture absorption (<0.04%) and a fusion bondable interface. This platform offers monolithic encapsulation by fusion bonding of the hemispherical LCP package lids and LCP-based microelectrode arrays. The package lids were fabricated by thermoforming of the LCP films to provide the desired shape and size for encasing the electronic components and wireless telemetry coils. Fusion-bonded LCP encapsulations were evaluated using electrical leakage current measurements during in vitro soak tests. The measurements were done in both 37 °C and 75 °C phosphate-buffered saline (PBS) solution and showed that LCP encapsulation was superior and more reliable in PBS than polyimide and parylene-C encapsulations. In addition, LCP-based monolithic encapsulation provided reliable electrical insulation for more than 300 days in both 37 °C and 75 °C PBS solution. [ABSTRACT FROM PUBLISHER]

An ultra-low-power 401–406-MHz Medical Device Radiocommunications Service receiver RF front-end for biomedical telemetry applications is implemented using 0.18-\mum CMOS technology. A single-ended complementary current-reuse low-noise amplifier (CCRLNA) is proposed that achieves a power gain of 20 dB, noise figure (NF) of 2.8 dB, IIP3 of -8.1 dBm, and second-order intercept point of +34 dBm while consuming only 150 \muW at 1-V supply voltage. The total receiver RF front-end, including the proposed CCRLNA, in-phase/quadrature folded mixers, and local oscillator buffers, achieves a conversion gain of 28.7 dB, NF of 5.5 dB, and third-order intercept point of -25 dBm while consuming less than 500 \muW from a 1-V supply voltage and occupying 0.7 mm^2 of core die area. [ABSTRACT FROM PUBLISHER]

A novel antenna design that effectively covers three bands (the medical implant communications service (MICS) band at 402 MHz, and the industrial, scientific, and medical (ISM) band at 433 MHz and 2.45 GHz) using a \pi-shaped radiator with a stacked and spiral structure is described. The antenna has compact size of 254 mm 3 (10 mm by 10 mm by 2.54 mm). The proposed design is effective for triple-band biotelemetry with data telemetry (402 MHz), wireless powering transmission (433 MHz), and wake-up controller (2.45 GHz). An experimental prototype of the compact stacked rectenna was fabricated on a Roger 3210 substrate. This antenna was used in a rectenna (rectifying antenna) for 433 MHz wireless powering transmission, and provided a conversion efficiency of 86% when 11 dBm microwave power was received at 433 MHz with a 5 k\Omega load. The optimal antenna was fabricated and tested in a minced front leg of pork. The simulated and measured bandwidths were 86 MHz and 113 MHz in the MICS band, and 60 MHz and 70 MHz in the ISM band, respectively. [ABSTRACT FROM PUBLISHER]