Rui-Feng Xue

Differentially Fed Dual-Band Implantable Antenna for Biomedical Applications

A novel differentially fed dual-band implantable antenna is proposed for the first time for a fully implantable neuro-microsystem. The antenna operates at two center frequencies of 433.9 MHz and 542.4 MHz, which are close to the 402-405 MHz medical implant communication services (MICS) band, to support sub-GHz wideband communication for high-data rate implantable neural recording application. The size of the antenna is 480.06 mm3 (27 mm × 14 mm × 1.27 mm). The simulated and measured bandwidths are 7.3% and 7.9% at the first resonant frequency, 5.4% and 6.4% at the second resonant frequency. The specific absorption rate (SAR) distribution induced by the implantable antenna inside a tissue-mimicking solution is evaluated. The performance of the communication link between the implanted antenna and external half-wavelength dual-band dipole is also examined.

Implantable Polyimide Cable for Multichannel High-Data-Rate Neural Recording Microsystems

To avoid or minimize postimplantation injury as a result of brain micromotion relative to the skull, a flexible multichannel polyimide (PI) cable was designed and microfabricated for data and power transmission between an intracranial IC recording from a neural probe array and an extracranial IC exchanging power and data wirelessly with an external unit. Surface characteristics, electrical properties, and cytocompatibility of the PI ribbon cable were investigated in this study. Scanning electron microscopic examination and atomic force microscopy analyses showed that the surface of the PI ribbon cable became significantly rougher due to the reactive oxygen ion etching process to open bonding pads. The enhanced surface roughness was also responsible for the increase in wettability and water absorption rate. However, water permeability measurement revealed that the micromachining fabrication process did not meaningfully affect the acceptable water vapor transmission rate of PI. Moreover, electrical properties, such as insertion loss, isolation between channels and data transmission capacity, were assessed for each channel of the PI ribbon cable on the basis of scattering parameter (S-parameter) measurement. Finally, 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide assay and live/dead intracellular staining tests were carried out to evaluate cell behaviors on the PI ribbon cable, indicating that the PI ribbon cable did not have acute cytotoxicity and appeared to be as cytocompatible as blank PI foils.

A wirelessly powered and interrogated blood flow monitoring microsystem fully integrated with a prosthetic vascular graft for early failure detection

This paper presents an implantable blood flow monitoring microsystem embedded in a prosthetic graft for early graft failure detection. The microsystem consists of two MEMS pressure sensors, an inductively powered wireless sensor interface ASIC, two miniature coupling coils, and a flexible cable connecting them. The implantable microsystem is powered and configured by an external monitoring device using 13.56-MHz carrier frequency. The blood flow rate information is sensed in the form of an oscillation frequency and transmitted to the external monitoring device through backscattering. The ASIC fabricated in 0.18-μm CMOS process occupies a total area of 0.5 × 3.3 mm2 including pads and consumes a total power of 12.6 μW. With the high-efficiency design of coupling coils, rectifier and LDO, the wireless power link achieves an overall power efficiency of 2% through 5-cm-thick tissue. With the ultra low power consumption and high-efficiency power transfer, the ASIC can be powered by transmitting only 630-μW RF carrier from the external device. The measured performance of the blood flow monitoring microsystem demonstrates a 0.17-psi pressure resolution.

A wireless power management and data telemetry circuit module for high compliance voltage electrical stimulation applications

A wireless power management and data telemetry circuit module for high compliance voltage electrical stimulation applications is presented in this paper. The system consists of rectifier, LDOs, DC-DC step-up charge pump and power monitoring circuit for closed loop wireless power management. The system also consists of a clock and data recovery (CDR) circuit and load shift keying (LSK) modulator for bidirectional data telemetry. The system operates at 13.56MHz. The wireless power management block receives AC power through an implantable coil and outputs three DC levels: 1V, 1.8V and 10V. The CDR circuit recovers clock and data from the 13.56MHz RF carrier through the same coil. The power efficiency of the wireless power management system is measured as 42% with 100μA current load connected on each supply output. The forward and backward data rate of the data telemetry achieves 61.5 kbps and 33.3 kbps, respectively. The system is implemented in 0.18μm CMOS process with 24V HV LDMOS option, occupying a core area of 1.8 mm × 1.8 mm.

A 20V-compliance implantable neural stimulator IC with closed-loop power control, active charge balancing, and electrode impedance check

An inductively powered implantable neural stimulator IC is presented in this paper. It features closed-loop power control, active charge balancing, and electrode impedance check functions. The stimulator IC is powered through 13.56MHz inductive link and supports 33.3kbps bi-directional telemetry with ASK for forward command transmission and LSK for backward data transmission, achieving 20V high compliance voltage, maximum 1.24mA stimulation current, and the resting potential of 50mV. The IC has an active area of 2mm×2mm implemented in 0.18-μm CMOS process with 24V LDMOS option.

An Integrated Wireless Power Management and Data Telemetry IC for High-Compliance-Voltage Electrical Stimulation Applications

This paper describes a 13.56-MHz wireless power recovery system with bidirectional data link for high-compliance-voltage neural/muscle stimulator. The power recovery circuit includes a 2-stage rectifier, 2 LDOs and a high voltage charge pump to provide 3 DC outputs: 1.8 V, 3.3 V and 20 V for the stimulator. A 2-stage time division based rectifier is proposed to provide 3 DC outputs simultaneously. It improves the power efficiency without introducing any impact on the forward data recovery. The 20 V output is generated by a modified low ripple charge pump that reduces the ripple voltage by 40%. The power management system shows 49% peak power efficiency. The data link includes a clock and data recovery (CDR) circuit and a load shift keying (LSK) modulator for bidirectional data telemetry. The forward and backward data rates of the data telemetry are 61.5 kbps and 33.3 kbps, respectively. In addition, a power monitor circuit for closed-loop power control is implemented. The whole system has been fabricated in a 24 V HV LDMOS option 1.8 μm CMOS process, occupying a core area of around 3.5 mm 2.

An efficient wireless power link for neural implant

An efficient resonant tuned wireless power transfer (WPT) link using inductive coupling has been proposed for the neural implant application in this work. The power link is optimized for an operating frequency of 10 MHz using coil, load and frequency optimization. The lossy tissue model was used to mimic the power loss in tissue and the simulated (HFSS) peak SAR values were within the allowed limit for 20 mW power received at implant. The power transfer efficiency for implant coil sizes of 250 mm2 for a power transmit range of 10 mm was simulated using HFSS to be around 82%.

High-efficiency transcutaneous wireless energy transfer for biomedical applications

Transcutaneous wireless power transfer to implantable devices with high efficiency is the research focus due to the unfavorable coupling conditions in biomedical applications. This paper analyzes the overall efficiency from the system point of view and two key factors are elaborated. First, the choice of the optimal power carrier frequency is considered by decomposing of inductive coupling and transcutaneous effects, which is seldom highlighted before. Second, resonant coupling as a promising energy transfer method for biomedical implants is compared with conventional inductive coupling. Some encouraging conclusions are drawn and further ongoing research is also included.