Vaishnavi Ranganathan

Power Delivery and Leakage Field Control Using an Adaptive Phased Array Wireless Power System

Efficient wireless power transfer and precise control of power delivery and leakage field strength can be achieved using a phased array wireless power transfer system. This has particular importance for charging multiple devices simultaneously, or charging devices in environments where humans or foreign objects will be in close proximity. The phased array wireless power system consists of two or more phase-synchronized power amplifiers each driving a respective transmit coil. The system can maximize power delivery to an intended receiver in one location while simultaneously minimizing power delivery and leakage fields in other locations. These functions are possible by varying the amplitude and phase of each transmitter. This paper provides an analysis of a phased array wireless power transfer system using near-field magnetically coupled resonators, and derives parameters that can be used to automatically determine the optimal magnitude and phase of each transmitter to deliver power to one or more receivers. Experimental results verify the theoretical analysis and additional features of the full system are demonstrated.

Nanomechanical non-volatile memory for computing at extreme

A computing platform that works under extreme conditions (> 250 °C and at radiation > 1 Mrad) can be attractive in a number of important application areas, including automotive, space and avionics. Nanoelectromechanical systems (NEMS) switches have emerged as promising candidates for computing in harsh environment. Designing reliable memory specifically non-volatile memory is a major challenge for these computing systems. In this paper, we propose a novel non-volatile memory (NVM) design for reliable operation in extreme environment using NEMS structure. It exploits a common failure mode in these devices, namely stiction. Unlike traditional charge-based memories, it relies on the mechanical state of a NEMS switch as information carrier. We analyze device and circuit-level design issues to enable robust NVM array implementation with NEMS devices.

Dual band wireless power and bi-directional data link for implanted devices in 65 nm CMOS

Implantable neural recording and stimulation devices hold great promise in monitoring and treatment of neurological disorders, limb reanimation and, development of brain-computer interfaces among other applications. However, transcutaneous wires limit the lifetime of such devices and there is a need for self-contained fully implantable solutions. In this work, we propose a novel dual-frequency approach for simultaneous wireless power transfer and low-power communication for small form factor fully implantable neural devices. We deliver wireless power using efficient magnetically coupled resonators operating at 13.56MHz and communicate using ultra-low power backscatter communication at 915 MHz. We leverage the frequency separation to combine wireless power and communication resonators with minimal interference using a novel concentric design, which meets the stringent size restrictions. We implement the wireless power receiver and communication front end of the implanted device in 65 nm CMOS and demonstrate 25 mW power delivery and 6 Mbps communication link.

Implantable Ultrasonic Imaging Assembly for Automated Monitoring of Internal Organs

An implantable miniaturized imaging device can be attractive in many clinical applications. They include automated, periodic, high-resolution monitoring of susceptible organs for early detection of an anomalous growth. In this paper, we propose an implantable ultrasonic imager capable of online high-resolution imaging of a region inside the body. A feasibility analysis is presented, with respect to design of such a system and its application to online monitoring of tumor growth in deep internal organs. We use ultrasound (US) imaging technology, as it is safe, low-cost, can be easily miniaturized, and amenable for long-term, point-of-care (POC) monitoring. The design space of the proposed system has been explored including form factor, transducer specifications and power/energy requirements. We have analyzed the effectiveness of the system in timely detection of anomalous growth in a case study through software simulations using a widely-accepted ultrasonic platform (Field II). Finally, through experimental studies using medical grade phantoms and an ultrasound scanner, we have evaluated the system with respect to its major imaging characteristics. It is observed that interstitial imaging under area/power constraints would achieve significantly better imaging quality in terms of contrast sensitivity and spatial resolution than existing techniques in deep, internal body parts, while maintaining the automated monitoring advantages.

A wearable ultrasonic assembly for point-of-care autonomous diagnostics of malignant growth

Clinicians generally agree that the most effective way to treat a malignant tumor within body organs is to detect it early. Currently, detection is mostly based on clinical diagnostics triggered by specific symptoms, which is often too late allowing the malignancy to reach an advanced stage. Automated high-resolution monitoring of body parts at regular intervals can be highly effective for detection of an anomalous growth - either primary or recurrence - at an early stage. In this paper, we propose a wearable, point-of-care (POC) ultrasonic imaging assembly to perform unsupervised, periodic monitoring of body parts for early detection of cancerous growths. We use ultrasound technology, which is safe, low-cost, can be easily miniaturized, and amenable for long-term, convenient, online monitoring. The proposed system is capable of providing automated high-resolution images of susceptible volumes of interest in superficial cancer-prone organs (e.g. prostate, uterus, kidney, ovary and bladder) at periodic intervals. We explore the design space for such a system encompassing transducer design parameters, power and memory requirements. Next, we study the effectiveness of such a system using both ultrasonic software simulation (with Field II) as well as experimental evaluation (with medical ultrasound transducers and phantoms). We show that the proposed POC diagnostic system can reliably detect an anomaly at a much smaller size (mostly stage 1) than typically achieved through conventional symptomatic detection.

Localization of receivers using phased-array wireless power transfer systems

Wireless battery charging has been incorporated into an increasing number of commercial electronics with power requirements ranging from a few milliwatts to several hundred watts. With this growing number of deployed devices, there is a necessity to quickly locate and charge them individually. Conventional localization techniques either require intelligence and extra hardware or are limited to merely detecting the presence of an object and not its position. In the proposed localization technique, we use two wireless power transmitters (TX) operating at the the same frequency. The phase difference between the two TXs can be controlled. The forward/reflected signals are measured from each TX and are used to accurately localize the receiver in a two dimensional space. This system does not require additional hardware on the TX or RX side. The entire detection process can be confined to the transmitter firmware. We also formulate a simple localization parameter using the reflected signals to prove the concept of localization.

Analysis of practical scaling limits in nanoelectromechanical switches

The trend of miniaturization, along with modern microfabrication facilities, has led to the development of nanoelectromechanical systems (NEMS) switches for use in low power and harsh environment applications. Dimensional scaling is attractive to improve integration density and operating voltage of NEMS devices. However, its effect on switch performance, leakage and dynamic power as well as practical limits on dimensional scaling are not well studied. Existing work in this area models the scaling trend and device performance based on parameters like voltage and dimensions. Although, most of them do not consider the effects of some nanoscale phenomena (surface forces, tunneling current) and leakage currents at G and D (off-state leakage), which can greatly affect circuit performance. This paper reports modeling and analysis of scaling effects and practical limits of scaling in cantilever-structured NEMS switches considering effects at nanoscale dimensions. It also analyzes the effects from a circuit level perspective, which corresponds to the end application of these NEMS structures. The goal of this paper is to establish a working range of dimensions and parameters which could result in reliable operating NEMS devices that can be incorporated into circuits.

Toward ultralow-power computing at exteme with silicon carbide (SiC) nanoelectromechanical logic

Growing number of important application areas, including automotive and industrial applications as well as space, avionics, combustion engine, intelligent propulsion systems, and geo-thermal exploration require electronics that can work reliable at extreme conditions - in particular at a temperature > 250°C and at high radiation (1-30 Mrad), where conventional electronics fail to work reliably. Traditionally, existing wideband-gap semiconductors, e.g., silicon carbide (SiC) transistor-based electronics have been considered most viable for high temperature and high radiation applications. However, the large-size, high threshold voltage, low switching speed and high leakage current make logic design with these devices unattractive. Additionally, the leakage current markedly increases at high temperature (in the range of 10 μA for a 2-input NAND gate), which induces self-heating effect and makes power delivery at high temperature very challenging. To address these issues, in this paper we present a computing platform for low-power reliable operation at extreme environment using SiC electromechanical switches. We show that a device-circuit-architecture co-design approach can provide reliable long-term operation with virtually zero leakage power.

Implantable ultrasonic dual functional assembly for detection and treatment of anomalous growth

High Intensity Focused Ultrasound (HIFU) is emerging as an accurate, noninvasive method for ablation of certain primary and metastatic tumors. Typically, ablation is performed with an external therapeutic transducer. However, external HIFU treatment suffers from limitations of low therapeutic efficiency for ablation of tumors, deep in internal organs such as liver, kidney and brain. Interstitial HIFU through an internal transducer, implanted locally near the organ of interest, could alleviate some of these limitations. Furthermore, it can be attractive for point-of-care (POC) treatment. In this paper, we propose the design of a dual-functional implantable assembly for image-guided HIFU treatment of anomalous growth. It is realized by effective integration of a central HIFU array with two ultrasonic imaging arrays for high-resolution online monitoring and efficient treatment. We explore the design space for the implant and identify the major design parameters including the power requirement. Using a widely used simulation platform, we show that the proposed implant, besides providing a potential POC solution, achieves a better therapeutic performance for certain tumor positions in internal organs, than the extracorporeal HIFU treatment.

RF Bandaid: A Fully-Analog and Passive Wireless Interface for Wearable Sensors

This paper presents a passive wireless RF sensor platform (RFSP), with only analog components, that harvests energy from an RF source and reflects data as a direct subcarrier modulation, thus making it battery free. A fully-analog architecture results in an ultra-low power device (under 200 μW) with a low component count, reducing the physical footprint. We envision such a platform to enable medical sensing systems that fit on a small bandaid like flexible structure, require no-battery, or charging and are able to provide continuous physiological monitoring. To realize this vision, we have developed and optimized a novel RF architecture that 1) directly maps sensor output to frequency modulation and transmits it to a remote receiver processing unit (RPU). This direct frequency mapping allows all further digitization and computation to be moved to the RPU -- reducing power and size requirements on the RFSP; 2) harvests energy from the carrier signal transmitted by a simple continuous wave transmitter, thereby requiring no batteries or supercap; and 3) uses backscatter to communicate with the RPU enabling ultra-low power requirements. The total power consumption of our prototype device leveraging this architecture was measured to be between 35 μW and 160 μW. We demonstrate that the RFSP can harvest sufficient power, sense, and communicate continuously without necessity for energy storage at a distance of 4 m from a transmitter emitting a 915 MHz continuous wave at 26 dBm (0.39 W). Prior backscatter systems typically have power budgets of 1 mW and require energy storage (battery or supercap), RFSPs sub 200 μW power consumption provides a significant improvement and longer range for a given TX power. To demonstrate applicability to real-world health sensing and the flexibility to adapt to different sensors, this paper presents results from breathing, heart rate, temperature, and sound sensing applications.