Design, simulation, fabrication and measurement of two different novel flexible bow-tie antennas, a conventional and a modified bow-tie antenna with reduced metallization, are reported in this paper. ...The antennas are mounted on a flexible substrate fabricated at the Flexible Display Center (FDC) of Arizona State University (ASU). The substrate is heat stabilized polyethylene naphthalate (PEN) which allows the antennas to be flexible. The antennas are fed by a microstrip-to-coplanar feed network balun. The reduction of the metallization is based on the observation that the majority of the current density is confined towards the edges of the regular bow-tie antenna. Hence, the centers of the triangular parts of the conventional bow-tie antenna are removed without compromising significantly its performance. The return losses and radiation patterns of the antennas are simulated with HFSS and the results are compared with measurements, for bow-tie elements mounted on flat and curved surfaces. The comparisons show that there is an excellent agreement between the simulations and measurements for both cases. Furthermore, the radiation performance of the modified bow-tie antenna is verified, by simulations and measurements, to be very close to the conventional bow-tie.
We present two improvements to the subspace-based phasor measurement unit (PMU) algorithms based on ESPRIT frequency estimation. The first is a dynamic, real-time thresholding method to determine the ...size of the signal subspace. This allows for accurate ESPRIT-based frequency estimates of the nominal system frequency and the frequencies of any out-of-band interference or harmonic frequencies. Since other frequencies are included in the least squares (LS) estimate, the interference from frequencies other than nominal can be excluded. This results in a near flat estimation error over changes in: 1) nominal system frequency; 2) harmonic distortion; and 3) out-of-band interference. We also reduce the computational burden of ESPRIT and demonstrate the proposed algorithm running in real time on resource-constrained platforms. The accuracy of this algorithm is evaluated using the IEEE standard for synchrophasor estimation, IEC/IEEE 60255-118-1, and compared with another state-of-the-art PMU algorithm.
This letter presents the fabrication details and measured performance of a prototype flexible extended-gate ion-sensitive field effect transistor (ISFET) biosensor, manufactured using a metal oxide ...indium-gallium-zinc oxide thin film transistor and an indium-tin oxide sensing layer on a 125- μm thick flexible plastic substrate. ISFET drain current was shown to respond correctly to the pH buffer concentration with repeatable pH sensitivity observed over multiple cycles. These results demonstrate the initial viability of directly extending flexible plastic substrate organic light emitting diode display technology to the production of low-cost, plastic ISFET biosensors.
Electrical capacitance tomography is employed for various process tomography applications, typically with circular imaging regions (e.g., to estimate fluid levels in plastic pipes). Typical ...state-of-the-art implementations focus on circular or cylindrical sensor arrays. In contrast, this research explores using a planar 2D array of electric-field sensors to image volumes composed of various dielectric materials. The array is designed to be used with very-low-frequency electric fields, which are desirable due to their ability to differentiate between various non-conducting objects. D-dot sensors (i.e., charge induction sensors) are used as the electric-field sensing element. In this research, imaging regions of interest are modeled as a composition of (25 cm) 3 voxels of dielectric material with randomized relative permittivities. Neural networks are utilized as the inversion algorithm to map measured E-field distortions to the voxels' relative permittivities. Three applications are explored in a simulated environment: 1) predicting relative permittivities of the entire (pseudo-3D) imaging region from one measurement of electric-field distortions (modeled in free space), 2) imaging regions arbitrarily large (in two dimensions) using the planar array as an imaging kernel, and 3) repeating application (1) in a model of a practical, real-world imaging scenario both with and without interfering material. Application (3) is performed with a real-world experimental setup using a room-sized "E-field Cage" meant to generate a uniform electric field. This work showcases a new electric-field imaging modality using a planar 2D D-dot sensor array paired with a DNN-based inversion algorithm.
This paper reviews amorphous silicon thin-film-transistor (TFT) degradation with electrical stress, examining the implications for various types of circuitry. Experimental measurements on ...active-matrix backplanes, integrated a-Si:H column drivers, and a-Si:H digital circuitry are performed. Circuit modeling that enables the prediction of complex-circuit degradation is described. The similarity of degradation in amorphous silicon to negative bias temperature instability in crystalline PMOS FETs is discussed as well as approaches in reducing the TFT degradation effects. Experimental electrical-stress-induced degradation results in controlled humidity environments are also presented.
We present a microelectromechanical systems (MEMS)-based electrostatic actuator on a flexible substrate, made of polyethylene naphthalate, which emits acoustic waves at ultrasonic frequencies. The ...actuator has a suspended diaphragm, made of parylene, of 2-6-mm diameter and a 6-μm gap between the diaphragm and substrate. The actuator is driven by hydrogenated amorphous silicon integrated circuits. The driving circuits consist of voltage-controlled oscillator and buffer chain, which can tune the output voltage from 3 to 32 V with 35-V supply. A single actuator emits ultrasonic waves at 25 kHz and pressure of 27-dB sound pressure level (SPL), and a 1 × 2 array emits up to 34.6-dB SPL at 1-cm distance.
Mixed-oxide thin-film transistors (TFTs) have been extensively researched due to their improved stability under electrical bias stress compared to amorphous-silicon TFTs. However, there are many ...challenges before they can reach the manufacturing stage. At the Flexible Display Center (FDC), Arizona State University, Tempe, we are developing a low temperature indium-zinc-oxide (IZO) TFT process suitable for flexible substrates such as polyethylene naphthalate (PEN). We report the effect of bias stress on the performance of these IZO TFTs and compare it with a-Si:H TFTs. We also report the design and fabrication of a 3.8-in QVGA electrophoretic display on PEN substrate using IZO TFT backplane.
This letter describes a method to identify the channel region of hydrogenated amorphous silicon thin film transistors (a-Si:H TFTs) in which threshold voltage(V th ) degradation occurs. The TFTs are ...subjected to gate bias stress under different operating conditions. Asymmetry in the measured TFT drain current in the forward direction (same source and drain during stress and measurement) and reverse direction (interchanging the source and drain terminals) shows localization of the gate-voltage dependent V th shift mechanism. Based on the observations, a charge-based expression for V th shift is derived.
It is shown that an array of D-dot sensors can be implemented to not only detect, but for the first time, image very low-frequency electric fields. D-dot sensors sense current proportional to the ...time derivative of the electric field. The signal of interest is extracted from each D-dot pixel using a lock-in amplifier through an automated multiplexer. We have successfully rendered very low-frequency electric field images from energized wires using the proposed electric field imager. As a proof-of-concept, the arrays were fabricated on both a printed circuit board and a flexible polyethylene naphthalate substrate, the latter of which incorporates a thin-film transistor process. Such a device will have commercial and industrial applications, such as imaging sources of electromagnetic interference as well as security applications for noninvasive monitoring.
In this letter, we demonstrate the feasibility of building thin-film transistor (TFT) complementary metal-oxide-semiconductor (CMOS) operational amplifiers (op-amps) at low temperature (180°C) for ...large-area sensor applications. The classic two-stage Miller-compensated CMOS design is built using a-Si:H and pentacene TFTs. In addition, we have studied the impact of electrical stress-induced aging of TFTs on op-amp performance using two different kinds of biasing circuits.
