Ashraf B. Islam

An Inductive Link-Based Wireless Power Transfer System for Biomedical Applications

A wireless power transfer system using an inductive link has been demonstrated for implantable sensor applications. The system is composed of two primary blocks: an inductive power transfer unit and a backward data communication unit. The inductive link performs two functions: coupling the required power from a wireless power supply system enabling battery-less, long-term implant operation and providing a backward data transmission path. The backward data communication unit transmits the data to an outside reader using FSK modulation scheme via the inductive link. To demonstrate the operation of the inductive link, a board-level design has been implemented with high link efficiency. Test results from a fabricated sensor system, composed of a hybrid implementation of custom-integrated circuits and board-level discrete components, are presented demonstrating power transmission of 125 mW with a 12.5% power link transmission efficiency. Simultaneous backward data communication involving a digital pulse rate of up to 10 kbps was also observed.

A Mediator Free Amperometric Bienzymatic Glucose Biosensor Using Vertically Aligned Carbon Nanofibers (VACNFs)

A biosensor is proposed for selective and sensitive detection of glucose. This electrochemical amperometric bienzymatic glucose biosensor is constructed by co-immobilization of horseradish peroxidase and glucose oxidase on vertically aligned carbon nanofibers (VACNFs). An enzyme wiring technique is used to plug the enzymes with the metal electrode using VACNFs, which facilitates an effective way to transfer electrons from the electrode to the electrochemical reaction centers. Direct electron transfer of horseradish peroxidase at the VACNF electrode is observed. Mediator or membrane free operation of this biosensor can potentially result in the application of these sensors in environmental monitoring, healthcare, as well as in varieties of scientific experiments. Experimental results indicate that the proposed biosensor can detect very low level of glucose (as low as 0.4 μM). Operational characteristics of the bienzymatic biosensor in terms of detection limit, sensitivity, and selectivity are also examined.

A potentiostat circuit for multiple implantable electrochemical sensors

This work proposes a potentiostat circuit for multiple implantable sensor applications. Implantable sensors play a vital role in continuous in situ monitoring of biological phenomena in a real-time health care monitoring system. In the proposed work a three-electrode based electrochemical sensing system has been employed. In this system a fixed potential difference between the working and the reference electrodes is maintained using a potentiostat to generate a current signal in the counter electrode which is proportional to the concentration of the analyte. This potential difference between the working and the reference electrodes can be changed to detect different analytes. The designed low power potentiostat consumes only 66 µW with 2.5 volt power supply which is highly suitable for low-power implantable sensor applications. All the circuits are designed and fabricated in a 0.35-micron standard CMOS process.

A vertically aligned carbon nanofiber (VACNF) based amperometric glucose sensor

Due of the clinical significance of measuring blood glucose levels of diabetic patients substantial research and development efforts have been devoted to the realization of reliable glucose sensors for in vitro or in vivo applications [1]. Wang et al introduced a mediator-free and membrane-free biosensor which provided a novel direction for biosensor development [2]. On the other hand the presence of defect sites in vertically aligned carbon nanofiber (VACNF) results in better mechanical stability, sensitivity and response compared to carbon nanotubes (CNT) for sensor applications [3–4]. Based on these scientific observations a mediator-free, bienzyme, glucose sensor incorporating VACNF is proposed in this paper.

A digitally controllable current readout circuit and modulator unit for remote monitoring and biotelemetry applications

Healthcare providers are depending on remote patient monitoring system more and more to treat a patient before the conditions become acute. Low-power electronics is an integral part of the remote patient monitoring system which is required for data acquisition, signal processing and data transmission. This work reports a low-power digitally controllable current readout circuit and a modulator unit designed for remote patient monitoring system. The current readout block converts current (0.2 µA to 5 µA) from biosensors to a data signal whose frequency is proportional to the sensor current. A switched capacitor based modulator is realized which modulates the data using a low-power digital modulation scheme. The current readout and the modulator units are digitally controllable to save power and to provide either ASK or FSK modulated output signal. The circuit is simulated using a 0.35-µm standard CMOS process and it occupies less than 0.053 mm2 of chip area. Power consumption of the circuit varies from 44 µW to 57 µW for 0.2 µA to 5 µA input current with 1.5 V supply, which is very attractive for biosensor applications.

Reduction of supply voltage and power consumption of an injection-locked oscillator for biomedical telemetry

A major design challenge for short-range wireless communication is a low-power transmitter with high efficiency. Unlike conventional transmitters used for cellular communication, injection-locked oscillator based transmitter shows greater promises with reduced power consumption and high transmitter efficiency. This paper presents a low-voltage low-power injection-locked oscillator (ILO) employing self-cascode structure and body-terminal coupling. The proposed oscillator has been fabricated using 0.18-µm RF CMOS process. Measurement results indicate that the proposed oscillator can operate with a supply voltage as low as 1 V and consumes only 2 mW of power, which makes the design highly suitable for low-power transmitter applications.

A highly selective mediator less glucose detector employing vertically aligned carbon nanofiber (VACNF)

This work reports a vertically aligned carbon nanofiber (VACNF) based glucose detector which shows excellent selectivity without employing any mediator or artificial membrane. Forests of VACNF are fabricated on silicon (Si) substrate using plasma enhanced chemical vapor deposition (PECVD) process and a metal layer is fabricated over silicon to serve as the electrode. VACNFs demonstrate superior conductive and structural properties compared to other carbon nano-materials and serve as an excellent location for charge transfer in electrochemical reaction process. Measurement results show that this glucose sensor can detect very low level of glucose with a high degree of linearity with respect to glucose concentration. Glucose detection is often interfered by several electro-active compounds and mediators/membranes are used to improve the performance of the detectors. Test results demonstrate that the proposed glucose sensor works well in presence of the interferer materials.

Ultra-Low-Power Sensor Signal Monitoring and Impulse Radio Architecture for Biomedical Applications

Remote diagnostics of patient’s vital information and initiation of necessary actions have resulted in the development of wireless body area network (WBAN). For almost zero maintenance of each sensor node within a WBAN, each node must work with a power consumption less than 100μW which can be achieved employing impulse radio architecture. In this work a low-power transmitter has been presented. The unit manifests a Data Generator Block, an Impulse Generator Block and a Buffer. The Data Generator Block converts any electrochemical sensor current in the range of 0.2μA to 2μA to digital data. The circuit can operate with a supply voltage of 1V and consume a power in the range of 0.427µW to 3.5µW. The Impulse Generator Block utilizes a RC network to generate impulses of approximately 110ns duration. Finally a Buffer circuit is used to drive a standard 50Ω load which could be an external antenna. The peak current consumption of the impulses is 2.81mA with peak output voltage of 140.2mV that makes it extremely suitable for short range wireless communication. The entire system has been designed and simulated using 0.35-μm standard CMOS process. The average power consumption of the system is only 68.30μW.

Wireless Power Transfer, Recovery, and Data Telemetry for Biomedical Applications

With the advancement of biomedical instrumentation technologies, sensor based remote healthcare monitoring system is gaining more attention day by day. These sensors can be classified as wearable and implantable. Implantable sensors include associated circuits for signal processing and data transmission and are placed inside the human body to acquire the information on the vital physiological phenomena. Powering the circuit is always a crucial design issue. Batteries cannot be used in implantable sensors which can come in contact with blood resulting in serious health risks. An alternate approach is to supply power wirelessly for tether-less and battery-less operation of the circuits. Inductive power transfer is the most common method of wireless power transfer to the implantable sensors. For good inductive coupling, the inductors should have high inductance and high quality factor. But the physical dimensions of the implanted inductors cannot be large due to a number of biomedical constraints. Therefore, there is a need for small sized and high quality factor inductors with high values of inductance for implantable sensor applications. On-chip inductors present a potential solution for further miniaturization of the implantable system. Implantable micro-systems require wireless transmission of the sensor data for real-time monitoring and diagnosis. Data telemetry can be achieved using two different schemes: forward telemetry which involves data transmission from power transmitter to power receiver and backward telemetry involving data transmission from power receiver to power transmitter. This chapter also briefly summarizes design of power recovery unit for wireless power recovery and energy conversion in biomedical implants. The basic design blocks of the wireless power recovery unit include matching network, rectifier and DC-DC converter. The charge pump A.B. Islam (*) • D. Costinett • S.K. Islam Department of Electrical Engineering and Computer Science, The University of Tennessee, Knoxville, TN, USA e-mail: ashraf.b.islam@gmail.com; daniel.costinett@utk.edu; sislam@utk.edu # Springer Science+Business Media LLC 2017 M. Sawan (ed.), Handbook of Biochips, https://doi.org/10.1007/978-1-4614-6623-9_15-1 1 based rectifier scheme can be successfully implemented to compensate for the low peak-to-peak voltage caused by coil misalignments and lower coupling in a practical system.