Chin Lung Yang

Location Estimation in Ad Hoc Networks with Directional Antennas

With the development of location aware sensor applications, location determination has become an increasingly important middleware technology. Numerous current technologies for location determination of sensor nodes use the received signal strength from sensor nodes using omnidirectional antennas. However, an increasing number of sensor systems are now deploying directional antennas due to their advantages like energy conservation and better bandwidth utilization. In this paper, we present techniques for location determination in a sensor network with directional antennas under different kinds of deployment of the nodes. We show how the location estimation problem can be solved by measuring the received signal strength from just one or two anchors in a 2D plane with directional antennas. We implement our technique using Berkeley MICA2 sensor motes and show that it is up to three times more accurate than triangulation using omnidirectional antennas. We also perform Matlab simulations that show the accuracy of location determination with increasing node density

Energy-efficient on-demand reprogramming of large-scale sensor networks

As sensor networks operate over long periods of deployment in difficult to reach places, their requirements may change or new code may need to be uploaded to them. The current state-of-the-art protocols (Deluge and MNP) for network reprogramming perform the code dissemination in a multihop manner using a three-way handshake where metadata is exchanged prior to code exchange to suppress redundant transmissions. The code image is also pipelined through the network at the granularity of pages. In this article we propose a protocol called Freshet for optimizing the energy for code upload and speeding up the dissemination if multiple sources of code are available. The energy optimization is achieved by equipping each node with limited nonlocal topology information which it uses to determine the time when it can go to sleep since code is not being distributed in its vicinity. The protocol to handle multiple sources provides a loose coupling of nodes to a source and disseminates code in waves each originating at a source with a mechanism to handle collisions when the waves meet. The protocols performance with respect to reliability, delay, and energy consumed is demonstrated through analysis, simulation, and implementation on the Berkeley mote platform.

Implantable Wireless Telemetry Boards for In Vivo Transocular Transmission

We report live animal studies that verify and quantify successful transocular transmission of data from a miniature low-power implant. To minimize damage, implantation within layers of the eye requires an ultrasmall device on a scale of just a few millimeters on each side and less than 500 mum in thickness. A high-frequency transmitter integrated circuit (IC) was designed, fabricated, and bonded onto a board containing an antenna, matching network components, and interconnects. The transmitter must achieve sufficient efficiency to draw minimal power from the limited onboard storage array while outputting a sufficiently large signal to overcome tissue-induced attenuation. Two different versions of the system were developed, one using a low-temperature co-fired ceramic material for the substrate and the other using silicon. Animal studies performed using live rabbits followed by empirical measurements verified the feasibility of a wireless telemetry scheme for a low-power miniature ocular implant.

Thickness and Permittivity Measurement in Multi-Layered Dielectric Structures Using Complementary Split-Ring Resonators

This paper presents a non-invasive microwave method based on a square-shaped complementary split-ring resonator (CSRR) to measure the thickness and permittivity of multilayer dielectric structures. The CSRR sensor is etched on the ground plane of a microstrip line. The change of resonance frequency depends on the thickness and permittivity of the multilayer dielectric sample below the ground plane. For resolution analysis, the resonance frequency shifts caused by a variation of permittivity (Δε = 0.01) and thickness (Δd=0.01 mm) in the detection layer were compared across various design dimensions. Sensor size optimization improved the resolution in permittivity and thickness measurement by 66% and 37%, respectively. Subsequently, the permittivity and thickness resolution was improved by 28% and 16%, respectively, by optimizing the separation of the etched CSRRs. The analysis results show that a CSRR sensor can be designed with excellent resolution in core layer permittivity changes and thickness resolution in multilayered dielectric structures.

Wireless Powering and the Study of RF Propagation Through Ocular Tissue for Development of Implantable Sensors

This paper evaluates RF powering techniques, and corresponding propagation through tissue, to supply wireless-energy for miniature implantable devices used to monitor physical-conditions in real-time. To improve efficiencies an impulsive powering technique is used with short duty-cycle high instantaneous-power-bursts, which biases the rectifier in its nonlinear regime while maintaining low average input-powers. The RF rectifier consists of a modified two-stage voltage multiplier which produces the necessary turn-on voltage for standard low-power CMOS systems while supplying the required current levels. The rectifier, fabricated on the TI 130 nm CMOS process, measures 215 μm × 265 μm, and is integrated with an antenna to quantify wireless performance of the power transfer. In-vivo studies performed on New Zealand white rabbits demonstrate the ability of implanted CMOS RF rectifiers to produce 1 V across a 27 kΩ load at a distance of 5 cm with a transmit-power of just over 1.5 W. Using a pulsed-powering technique, the circuit generates just under 0.9 V output with an average transmit-power of 300 mW. The effects of implantation on the propagation of RF powering waves are quantified and demonstrated to be surmountable, allowing for the ability to supply a low-power wireless sensor through a miniature rectifier IC.

Complementary split-ring resonators for measuring dielectric constants and loss tangents

A noninvasive planar complementary split-ring resonator (CSRR) for measuring the dielectric constants and loss tangents of material is presented in this letter. Measurements were developed to extract the complex permittivity of the material under test (MUT) using the equivalent RLC resonator circuit model. This technique enables a single-step measurement of the MUT without the need for machining or reshaping. The method requires calculating only two parameters, the resonant frequency (fr) and the magnitude (dB) response, thus achieving a substantial reduction in cost and computation time. A CSRR sensor operating in the 1.8 to 2.8 GHz band is fabricated and tested for verification. The measurement errors in the dielectric constant were less than 7.6%. An efficient technique of CSRR measuring complex permittivity is experimentally verified.

Location tracking with directional antennas in wireless sensor networks

I n t h i s p a p e r , w e i n v estigate the use of multiple directional antennas on sensor motes for location determination and mobile node monitoring. One key aspect that distinguishes wireless sensor networks is inexpensive transmitters and receivers that still maintain acceptable connectivity. Therefore, complex RF solutions are often not applicable. We propose and demonstrate a location estimation algorithm on a single sensor node equipped with inexpensive directional antennas by measuring the received signal strength of the transmission peers. This algorithm is further applied to the dynamic tracking of a wandering mote. The location tracking error can be reduced from 30% to 16% by using moving average schemes and merging estimates from different sets of antennas. The mean error of tracking estimates can be obtained to provide the certainty of location tracking. Therefore, only a single mote with angular diverse multiple antennas is needed to determine the location of a mote without triangulation.

Noncontact Measurement of Complex Permittivity and Thickness by Using Planar Resonators

This paper presents a novel noncontact measurement technique that entails using a single-compound triple complementary split-ring resonator (SC-TCSRR) to determine the complex permittivity and thickness of a material under test (MUT). The proposed technique overcomes the problem engendered by the existence of air gaps between the sensor ground plane and the MUT. In the proposed approach, a derived governing equation of the resonance frequencies is used to estimate the thickness and complex permittivity of the MUT by calculating the resonant frequency (f r) and magnitude response in a single-step noncontact measurement process. This study theoretically analyzed and experimentally verified a simple and low-cost SC-TCSRR measurement method for assessing materials in a noncontact method. For a 0.2-mm air gap, the experiments yielded average measurement errors of 4.32% and 5.05% for the thickness and permittivity, respectively. The proposed SC-TCSRR technique provides excellent solutions for reducing the effect of air-gap conditions on permittivity, thickness, and loss tangent in noncontact measurements.

Novel wireless impulsive power transmission to enhance the conversion efficiency for low input power

This paper applies UWB technologies in a special aspect for the transmission of energy rather than messages to achieve a novel wireless impulsive powering approach and enhance the power conversion efficiency (PCE) for low average input power. The whole impulsive wireless power transmitting and receiving systems are implemented to validate the feasibility of the wireless power transmission (WPT) using impulsive waves and the improvement of the conversion efficiency of the rectifier circuitry. Experimental results prove that this technique is quite suitable for low input power transmission which is good for biomedical applications. In order to deliver the UWB power efficiently, a horn antenna with high directivity, large gain, and broad bandwidth acts as the transmit antenna. The impulsive power generated by the impulse generator is amplified by the UWB power amplifier and then delivered through the horn antenna. And the received impulsive power is converted by the voltage-doubler rectifier composed of Schottky diodes into a direct current (dc) power to supply the chips or rechargeable batteries. In this paper, the UWB impulsive wireless transmission systems have been proved to achieve 50% power conversion efficiency (PCE) even when the input power of the rectifier is lower than 0 dBm. Due to the fact that low transmission power has relatively little impacts and causes relatively slight injury to human bodies, it is one of the essential key technologies in biomedical implant chips and devices.

Novel Compact Eye-Shaped UWB Antennas

This letter proposes a novel shrinking technology of ultrawideband (UWB) antennas among the conventional various ultrawideband antenna structures. An eye-shaped UWB antenna was designed to extend the lower frequency band under a limited antenna size. The operating band (1.2 ~ 4.5 GHz) can reach a fractional bandwidth of as high as 142%. The overall dimension, including the ground area, can be shrunk to 0.027λ02. The group delay is nearly constant to ensure minimal distortion and dispersion. From the measurement, the antenna radiation pattern is close to omnidirectional and is suitable for general applications.