Medical Implant Communication Service Band Research Articles

A monolithic 180 nm CMOS dosimeter for wireless In Vivo Dosimetry

The design, fabrication and testing of a novel monolithic system-on-chip dosimeter fabricated in a standard 180 nm CMOS technology is described. The device, implementing a radiation sensor and an RF transmitter, is proposed to address the need for real-time In Vivo Dosimetry (IVD) of radiation during Linac radiotherapy sessions. Owing to its small size, of approximately 1 mm3, such solution could be made in-body implantable and, as such, provide a much-enhanced high-resolution, real-time dose measurement to improve Quality Assurance (QA) in radiation therapy. The device transmits the related information on dose of radiation wirelessly to a remote receiver operating in the Medical Implant Communication Service (MICS) band. Comprehensive description of the various phases of this project, including the development of the radiation sensors and integrated RF transmitter to perform the readout, along with the final test results using a radiation beam, will be given.

Reduction of detuning effects using robust parameter design for implantable antennas

A new design framework for implantable antennas to reduce detuning effects due to various dielectric properties is presented. Conventionally, in order to overcome the detuning effects, it is highly demanded to have a broadband impedance matching to compensate the frequency shift. However, achieving a wider impedance bandwidth leads to larger antenna dimensions, and lack a mathematical treatment to optimise implantable antennas against the variation of tissue properties to date. A new methodology based on robust parameter design is proposed to cope with the detuning effects. Instead of designing the antenna in one single tissue environment, the proposed technique analyses the variation of dielectric properties in distinct tissue environments. The optimised performances show that robust impedance matching in the medical implant communication services band is achieved, although the dielectric constant varies from 35 to 55. Simulated and measured results are presented to demonstrate the validity of the proposed design methodology.

A 1.3 mW low-IF, current-reuse, and current-bleeding RF front-end for the MICS band with sensitivity of -97 dbm

A low-power, low-intermediate frequency (IF) radio frequency (RF) front-end, including low-noise amplifier (LNA) and mixer for the medical implant communications service (MICS) RF band, is presented. The frequencies of LNA and mixer range from 402 MHz to 405 MHz, while the IF of the mixer is 450 KHz. Current-reuse, back-gate coupling, current-bleeding, and feedback circuit design techniques are utilized in the LNA design to achieve 10 dB of gain and the required noise figure (NF) under the low power consumption of 0.94 mW. By contrast, the Gilbert-type mixer generates 20 dB of conversion gain by using current-reuse, back-gate coupling, and current-bleeding techniques. The front-end is operated using a 1.8 V power supply and is capable of achieving a -97 dBm sensitivity using quadrature phase shift keying modulation while consuming 1.3 mW. The proposed front-end is implemented in TSMC 0.18 μm CMOS process with a total area of 1.4 mm × 1.2 mm. The gain enhancement technique has been substantially optimized compared with previous works and measurement results indicate that the front-end obtains the highest figure of merit compared with previous works.

A 0.33 nJ/bit IEEE802.15.6/Proprietary MICS/ISM Wireless Transceiver With Scalable Data Rate for Medical Implantable Applications.

This paper presents an ultra-low power wireless transceiver specialized for but not limited to medical implantable applications. It operates at the 402-405-MHz medical implant communication service band, and also supports the 420-450-MHz industrial, scientific, and medical band. Being IEEE 802.15.6 standard compliant with additional proprietary modes, this highly configurable transceiver achieves date rates from 11kb/s to 4.5 Mb/s, which covers the requirements of conventional implantable applications. The phase-locked loop-based transmitter architecture is adopted to support various modulation schemes with limited power budget. The zero-IF receiver has programmable gain and bandwidth to accommodate different operation modes. Fabricated in 40-nm CMOS technology with 1-V supply, this transceiver only consumes 1.78 mW for transmission and 1.49 mW for reception. The ultra-low power consumption together with the 15.6-compliant performance in term of modulation accuracy, sensitivity, and interference robustness make this transceiver competent for various implantable applications.

Experimental Path Loss Models for In-Body Communications Within 2.36-2.5 GHz.

Biomedical implantable sensors transmitting a variety of physiological signals have been proven very useful in the management of chronic diseases. Currently, the vast majority of these in-body wireless sensors communicate in frequencies below 1GHz. Although the radio propagation losses through biological tissues may be lower in such frequencies, e.g., the medical implant communication services band of 402 to 405MHz, the maximal channel bandwidths allowed therein constrain the implantable devices to low data rate transmissions. Novel and more sophisticated wireless in-body sensors and actuators may require higher data rate communication interfaces. Therefore, the radio spectrum above 1GHz for the use of wearable medical sensing applications should be considered for in-body applications too. Wider channel bandwidths and smaller antenna sizes may be obtained in frequency bands above 1GHz at the expense of larger propagation losses. Therefore, in this paper, we present a phantom-based radio propagation study for the frequency bands of 2360 to 2400MHz, which has been set aside for wearable body area network nodes, and the industrial, scientific, medical band of 2400 to 2483.5MHz. Three different channel scenarios were considered for the propagation measurements: in-body to in-body, in-body to on-body, and in-body to off-body. We provide for the first time path loss formulas for all these cases.

A NOVEL RECONFIGURABLE SPIRAL-SHAPED MONOPOLE ANTENNA FOR BIOMEDICAL APPLICATIONS

In this paper, a new reconfigurable antenna is introduced. This antenna is a printed spiral- shaped monopole antenna with a compact structure. By embedding microwave switches in the structure of the antenna, different resonance frequencies can be achieved in different states of the switches. The introduced antenna is capable to cover two standard frequency bands for biomedical applications, i.e., Medical Implant Communication Service (MICS) and Industrial, Scientific and Medicine (ISM) bands. MICS band covers 402 MHz to 406 MHz and ISM covers 2.4 GHz to 2.5 GHz frequency range. The proposed antenna has a compact size of 32 mm × 50. 3m m× 1. 8 mm, and it is fabricated on an FR4 substrate. The measurement results are in a good agreement with the simulations.

A Fast Settling Phase Modulator for Outphasing Transmitters in 65-nm CMOS

We present a phase modulator architecture with very fast settling time for use in high data-rate outphasing transmitters. The proposed design utilizes the phase-shifting capabilities of a resonant tank and the ability to separately control the circuit properties via its components. A prototype in 65-nm CMOS achieves 9 bits of effective resolution, with a fast settling time of less than five carrier cycles to within 1 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> . The circuit is also tested as a standalone transmitter showing an error vector magnitude of less than 5% for 8-PSK modulation at maximum data rate of 240 Mb/s, meeting the Federal Communications Commission requirements for operation at the medical implant communication services band.

A fully integrated wireless system for intracranial direct cortical stimulation, real-time electrocorticography data transmission, and smart cage for wireless battery recharge.

Wireless transmission of cortical signals is an essential step to improve the safety of epilepsy procedures requiring seizure focus localization and to provide chronic recording of brain activity for Brain Computer Interface (BCI) applications. Our group developed a fully implantable and externally rechargeable device, able to provide wireless electrocorticographic (ECoG) recording and cortical stimulation (CS). The first prototype of a wireless multi-channel very low power ECoG system was custom-designed to be implanted on non-human primates. The device, named ECOGIW-16E, is housed in a compact hermetically sealed Polyether ether ketone (PEEK) enclosure, allowing seamless battery recharge. ECOGIW-16E is recharged in a wireless fashion using a special cage designed to facilitate the recharge process in monkeys and developed in accordance with guidelines for accommodation of animals by Council of Europe (ETS123). The inductively recharging cage is made up of nylon and provides a thoroughly novel experimental setting on freely moving animals. The combination of wireless cable-free ECoG and external seamless battery recharge solves the problems and shortcomings caused by the presence of cables leaving the skull, providing a safer and easier way to monitor patients and to perform ECoG recording on primates. Data transmission exploits the newly available Medical Implant Communication Service band (MICS): 402–405 MHz. ECOGIW-16E was implanted over the left sensorimotor cortex of a macaca fascicularis to assess the feasibility of wireless ECoG monitoring and brain mapping through CS. With this device, we were able to record the everyday life ECoG signal from a monkey and to deliver focal brain stimulation with movement elicitation.

Design of Implantable Rectangular Spiral Antenna for Wireless Biotelemetry in the MICS Band

For this study, we designed an implantable rectangular spiral antenna for medical biotelemetry in the Medical Implant Communications Service band (402 MHz to 405 MHz). The designed antenna has a U-shaped loop for impedance matching. The antenna impedance is easily adjusted by controlling the shape and length of the U-shaped loop. Significant design parameters were studied to understand their effects on the antenna performance. To verify the potential of the antenna for the desired applications, we fabricated a prototype and measured its performance in terms of the resonant characteristics and gain radiation patterns of the antenna. In the testing phase, the prototype antenna was embedded in human skin tissue-emulating gel, which was developed to simulate a real operation environment. The measured resonant characteristics show good agreement with the simulations, and the -10 dB frequency band is within the range of 398 MHz to 420 MHz. The antenna exhibits a maximum gain of -22.26 dBi and an antenna efficiency of 0.215%.

Design and in Vitro Test of a Differentially Fed Dual-Band Implantable Antenna Operating at MICS and ISM Bands

The design of a novel differentially fed dual-band implantable antenna operating at 402-405 MHz Medical Implant Communication Services (MICS) band and 2.4-2.5 GHz Industrial, Scientific, and Medical (ISM) band is introduced. The proposed implanted antennas are for both planar and flexible implantation scenarios. Biocompatible material parylene-C is adopted to cover the implanted antenna. The size of the proposed antennas including the encapsulation for planar and flexible case is 179.0 mm3 and 186.3 mm3 respectively. The Specific Absorption Rate (SAR) distribution and the radiation pattern at both frequencies induced by the implanted antenna are evaluated. The performance of the communication link between the implanted antenna and an external half-wavelength dipole at two resonant frequencies is also presented. In vitro test in minced pork is performed to test the reliability of the antenna in the real implantation cases.

Characterization of path loss and absorption for a wireless radio frequency link between an in-body endoscopy capsule and a receiver outside the body

Abstract Physical-layer characterization is important for design of in-to-out body communication for wireless body area networks (WBANs). This paper numerically investigates the path loss and absorption of an in-to-out body radio frequency (RF) wireless link between an endoscopy capsule and a receiver outside the body using a 3D electromagnetic solver. A spiral antenna in the endoscopy capsule is tuned to operate in the Medical Implant Communication Service (MICS) band at 402 MHz, accounting for the properties of the human body. The influence of misalignment, rotation of the capsule, and three different human models are investigated. Semi-empirical path loss models for various homogeneous tissues and 3D realistic human body models are provided for manufacturers to evaluate the performance of in-body to out-body WBAN systems. The specific absorption rate (SAR) in homogeneous and heterogeneous body models is characterized and compliance is investigated.

Effect of Kidney Malignant Tissues on Antenna Resonance

A logarithmic spiral microstrip antenna (LSMA) is designed, simulated and measured in rabbit's kidney. The antenna operates in the Medical Implant Communications Service (MICS) band at 403 MHz. It is fabricated on Rogers RT6010 (lossy) with relative dielectric constant of 10.2 and thickness 1.9 mm. There is a good agreement between the measured and simulated results for LSMA in rabbit's kidney. A study is made to observe the effect of malignant tissues on the performance of the antenna. Results are considered as brain stone for early detection diagnosis for cancer.

Miniaturized Dual-Band Antenna for Implantable Wireless Communications

A miniaturized dual-band antenna is presented for implantable wireless communications. By introducing an offset at the feedpoint, dual-band performance of a dipole antenna is realized, operating at both Medical Implant Communications Service (MICS) 402-405 MHz and Industrial, Scientific, and Medical (ISM) 2.40-2.48 GHz bands. Parylene-C of thickness 20 μm is taken as a biocompatible insulating layer, and a rather compact size of 67.8 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> (10.02 mm × 10.02 mm × 0.675 mm) is obtained. In order to achieve good impedance matching at the feedpoint, an inductive loop is loaded at one of the dipole arms. The measured |S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> | in skin-mimicking gel shows that a bandwidth of 47.5% and 31.6% can be achieved at the MICS and ISM bands, respectively.

A Low Power MICS Band Phase-Locked Loop for High Resolution Retinal Prosthesis

Ultra low power dissipation is essential in retinal prosthesis and many other biomedical implants. Extensive research has been undertaken in designing low power biomedical transceivers, however to date, most effort has been focused on low frequency inductive links. For higher frequency, more robust and more complex applications, such as Medical Implant Communication Service (MICS) band multichannel transceivers, power consumption remains high. This paper explores the design of micro-power data links at 400 MHz for a high resolution retinal prosthesis. By taking advantage of advanced small geometry CMOS technology and precise transistor-level modeling, we successfully utilized subthreshold FET operation, which has been historically limited to low frequency circuits due to the inadequate transistor operating speed in and near weak inversion; we have implemented a low power MICS transceiver. Particularly, a low power, MICS band multichannel phase-locked loop (PLL) that employs a subthreshold voltage controlled oscillator (VCO) and digital synchronous dividers has been implemented on a 65-nm CMOS. A design methodology is presented in detail with the demonstration of EKV model parameters extraction. This PLL provides 600- mVpp quadrature oscillations and exhibits a phase noise of -102 dBc/Hz at 200-kHz offset, while only consuming 430- μW from a 1-V supply. The VCO has a gain (KVCO) of 12 MHz/V and is designed to operate in the near-weak inversion region and consumes 220- μA DC current. The designed PLL has a core area of 0.54 mm(2). It satisfies all specifications of MICS band operation with the advantage of significant reduction in power which is crucial for high resolution retinal prosthesis.

Miniaturised slot antenna for biomedical applications

An implantable slot antenna with a miniaturised size of 139.7 mm3 (10 × 11 × 1.27 mm) for biomedical applications is proposed. Operating at the Medical Implant Communications Service (MICS) band, miniaturisation of the antenna is realised by etching a meandered slot on the top metal with one end open. A microstrip line is utilised as excitation with a shorting connected to the radiator. In addition, two U-shaped stubs are adopted to match the feeding impedance to 50 Ω. The antenna is simulated in a one-layer skin model as well as in the arm of a human model and measured in skin-mimicking tissue. Good agreements can be obtained and the measurement results show that a broad bandwidth of 28.3% (from 354 to 469 MHz) for |S11| less than − 10 dB can be achieved.

Monolithic 180 nm CMOS Dosimeter for In Vivo Medical Applications

The design and development of a monolithic system-on-chip silicon device for real time measurement of radiation dose is described. The device is fabricated in a standard 180 nm CMOS technology. The proposed application is in the medical field of In Vivo Dosimetry, where the dose of radiation, delivered to patients during radiotherapy sessions, is monitored in real time by an in-body implanted device of 1 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> approximate size and the related information is transmitted wirelessly to an external receiver operating in the Medical Implant Communication Service (MICS) band. Along with standard electrical characterization, evaluation of device performance is carried out under radiation beam in a clinical environment. The design and initial test results of the first phase of the project, covering the radiation sensors, will be discussed. A description of the next project steps will also be given.

의료용 무선 중계 시스템용 이중 대역 인체 부착형 안테나 설계

본 논문에서는 MICS(Medical Implant Communication Service, 402~405 MHz)와 ISM(The Industrial, Scientific and Medical, 2.40~2.485 GHz) 대역에서 동작하는 의료용 무선 중계 시스템을 위한 이중 대역 인체 부착형 안테나를 제안하고, 인체의 영향을 고려한 안테나 성능에 대한 분석을 하였다. 제안된 안테나는 ISM 대역에서 동작하는 윗면의 패치와 MICS 대역에서 동작하는 바닥면의 패치로 구성되어 있다. 안테나가 실제 인체에 착용되어 사용되는 상황을 고려하고, 인체가 안테나에 미치는 영향을 분석하기 위하여 모의 인체를 이용하여 시뮬레이션과 측정을 수행하였다. 제안된 안테나의 반사 손실은 MICS 대역과 ISM 대역에서의 요구 대역폭을 만족하였고, 측정된 최대 이득은 MICS 대역과 ISM 대역에서 각각 -12.47 dBi, 1.71 dBi이었다. 제안된 안테나의 방사 패턴은 MICS 대역에서 인체 내부 지향성, ISM 대역에서 인체 외부 지향성을 가지며, 반사 손실 특성은 인체의 영향에 매우 둔감하므로 의료용 무선 중계 시스템용 인체 부착형 안테나로 활용되기에 적절할 것으로 사료된다. In this paper, a dual-band on-body antenna operating at MICS and ISM band for a wireless medical repeater system is proposed and the antenna performance including the human body effect is investigated. The designed dual-band antenna is comprised of a top patch for ISM band and bottom patch for MICS band. Simulation and measurement was carried out in order to analyze the effects of human body on antenna performance considering real use. The proposed antenna has required impedance bandwidth enough to cover both MICS and ISM bands. The measured peak gains were -12.47 dBi and 1.71 dBi at the each center frequency of MICS and ISM bands, respectively. Furthermore, the antenna has the maximum radiation directed toward the inside of the human body in the MICS band and directed toward the outside in the ISM band. In addition, the return loss property of the antenna is insensitive to human body effects so that the proposed antenna is well suited for the on-body wireless medical repeater system.

Direct current driving impedance matching method for rectenna using medical implant communication service band for wireless battery charging

This study proposes a direct-current (DC) driving impedance matching method for rectennas for the wireless charging of implantable lithium-ion (Li-ion) rechargeable batteries using the medical implant communication service band. Unlike the traditional method, which uses only the DC resistive load or battery potential, the proposed method adopts the output DC current of the dual-diode rectifiers to establish a simple equivalent model for wireless battery charging. Using this model, the optimised impedance matching network of the rectenna is derived to maximise efficiency within the charging range of a Li-ion battery. For 10 dBm input radio-frequency (RF) power, the highest RF-to-DC conversion efficiency of the traditional matching method is 22.3%. For the proposed method, the RF-to-DC conversion efficiency is > 75% in the potential range of 3.7 to 4.2 V, which is the range used for over 90% of the charging duration. The best battery charging efficiency was 76.2% at a transmission distance of 50 cm.

Sub-mW $LC$ Dual-Input Injection-Locked Oscillator for Autonomous WBSNs

This paper presents a sub-mW, current-reused first-harmonic <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LC</i> injection-locked oscillator (ILO) using in-phase dual-input injection technique. It can be used as a power oscillator in the injection-locked transmitter of wireless biomedical sensor nodes (WBSNs) integrated into a wireless body area network. A prototype chip, implemented in a standard 0.13-μm CMOS process occupying 200 × 380 μm, operates in the medical implantable communications service (MICS) band for medical implants. Measurement results show that the proposed ILO features a wide locking range of 800 MHz (150-950 MHz) at an input power of 0 dBm. More importantly, it has a high input sensitivity of -30 dBm to lock the 3-MHz bandwidth of the MICS band, while consuming only 660 μW at 1-V supply. This ultralow power consumption enables autonomous WBSNs.

HERMETIC IMPLANTABLE ANTENNA INSIDE VITREOUS HUMOR SIMULATING FLUID

Retinal prosthesis system is currently being developed in various places around the world. This system involved data transfer between an implanted antenna inside an eyeball and an external camera that is located just in front of the eyeball. While there are plenty of publications about the stimulating electrodes or the processing unit of the system itself, very limited amount has been published regarding the wireless communication link between the two antennas despite the fact that the electromagnetic wave will propagate through a complex medium in the form of Vitreous Humor. This paper will discuss about the constraints associated with implanting an antenna into an eyeball. An antenna design and simulation was performed with the aid of High Frequency Structure Simulator (HFSS) and its Finite Element Method (FEM) mathematical solver in the operating frequency of 402{ 405MHz. The antenna, which was a 4 layer microstrip antenna, was positioned at the centre of a spherical model fllled with homogeneous Vitreous Humor material. Antenna performances that include return loss, bandwidth, gain, radiation pattern, and SAR value are analysed and compared against those of other implantable antennas operating in Medical Implant Communication Service (MICS) band. Free space and simulating ∞uid measurements were also conducted on the fabricated antenna to validate the simulation results. It was concluded that the fabricated antenna was able to produce the similar performance to the simulation results and hence at the same level as the other antennas operating in material with lower dielectric constants and conductivities.