Interdigital Capacitor-Based Passive LC Resonant Sensor for Improved Moisture Sensing

Herein, a passive low-profile moisture sensor design based on radio frequency identification (RFID) technology is proposed. The sensor consists of an LC resonant loop, and the sensing mechanism is based on the fringing electric field generated by the capacitor in the circuit. A standard planar inductor and a two-layer interdigital capacitor (IDC) with a significantly higher fringing capacitance compared to that of a conventional parallel plate capacitor (PPC) are used, resulting in improved frequency offset and sensitivity of the sensor. Furthermore, a sensor tag was designed to operate at an 8.2 MHz electronic article surveillance (EAS) frequency range and the corresponding simulation results were experimentally verified. The IDC- and PPC-based capacitor designs were comprehensively compared. The proposed IDC sensor exhibits enhanced sensitivity of 10% in terms of frequency offset that is maintained over time, increased detection distance of 5%, and more than 20% increase in the quality factor compared to sensors based on PPC. The sensor’s performance as a urine detector was experimentally qualified. Additionally, it was shown experimentally that the proposed sensor shows a faster response to moisture. Both simulation and experimental data are presented and elucidated herein.

Study of two-layered circular patch using moment method and genetic algorithms

<table width="356" border="1" cellspacing="0" cellpadding="0"><tbody><tr><td valign="top" width="387"><table width="593" border="1" cellspacing="0" cellpadding="0"><tbody><tr><td valign="top" width="387"><p>In this paper, new expressions for the effective radius and fringing capacitance have been derived to predict accurately the resonant frequency of the two-layered circular microstrip patch antenna. These expressions are obtained based on genetic algorithm and the data base is generated using moment method (MOM). The proposed model is very simple, fast, and valid for an entire range of permittivities and thicknesses of two-layered substrate. The present model has been validated by comparing our numerical results obtained for the resonant frequencies with measurements. Finaly, the effect of the two-layered substrate on the resonant charateristics of the circular microstrip patch antenna has been presented.</p></td></tr></tbody></table></td></tr></tbody></table>

Application of 3D printed polymer composite as capacitive sensor

Purpose The purpose of this study is to demonstrate the usage of three-dimensionally (3D) printed polylactic acid (PLA)-carbon black (CB) conductive polymer composite in the measurement of the void fraction and liquid level. Design/methodology/approach PLA-CB conductive polymer composite is 3D printed through fused deposition modelling (FDM) technique and used as a capacitive sensor for void fraction measurement and liquid level sensing. The sensitivity of 3D printed ring and concave type capacitive sensors are compared for void fraction measurement. The effect of electrode length, thickness and pipe dimension on the capacitance achievable for the particular void fraction is studied. Concept of fringing capacitance is used for the sensing of liquid level. Findings Compared to the concave design comprising four electrodes, the ring-type capacitive sensor produced better results in void fraction measurement. Increase in pipe diameter and electrode length results in the enhancement of capacitance arising from specific void fraction. For a 100 mm diameter pipe, the capacitance of the 150 mm-long concave electrode (0.4 mm thick) increased from 9.98 to 67.77 pF as the void fraction decreased from 100% to 0%. Development of the fringing capacitance in 3D printed PLA-CB composite helps in the measurement of liquid level. Both parallel finger topology and interdigital electrode configuration are able to sense the liquid level. Originality/value Ability of the 3D printed conductive PLA-CB composite to act as a capacitive sensor is experimentally analysed. Performance of different electrode configuration is tested for both void fraction measurement and liquid level sensing. Results of experimentation prove that FDM printed PLA-CB composite is suitable for the void fraction and liquid level measurement.

Threshold Voltage Modeling of Double Gate-All-Around Metal-Oxide-Semiconductor Field-Effect-Transistors (DGAA MOSFETs) Including the Fringing Field Effects

In this paper, an analytical threshold voltage model of double gate-all-around metal-oxide-semiconductorfield-effect-transistors (DGAA MOSFETs) including the fringing field effects is developed. The total fringing capacitance arising due to induced fringing fields in the device is divided into inner, outer and bottom fringing capacitance. A simple expression for each fringe capacitance is developed individually. The 3-D Poisson's equation has been solved in the channel region using the parabolic potential approximation method to develop the surface potential expressions. The effects of fringing capacitances of inner and outer gates which causes charge induction in the source/drain regions have been incorporated within the developed surface potential expressions. The change in potential due to these induced charges of source/drain region along the channel is formulated and added with the developed surface potential expression at both surfaces. The obtained modified surface potential equations have been utilized to derive the expression of the threshold voltage of the device. The performance of the proposed model has been compared with the previously developed model of DGAA MOSFET structure without High-k dielectrics. The effects of variation of device parameters on the threshold voltage have been also analyzed. The accuracy of the proposed model has been verified by numerical simulation results obtained by a device simulator VTCAD from Cogenda Int.