LCP Substrate Research Articles

Electrical Equivalent Circuit Modeling of Various Electrically Small Antennas for Biomedical Applications

This work outlines the design and development activities of various electrically small antennas for bio-medical applications. It also covers the electrical modeling aspects of all these miniaturized antennas. Three antennas with different specifications have been discussed with diversified proposed applications. First example deals with a single frequency (9.45 GHz) on-chip antenna, whereas the second one covers an ultra-wideband frequency range (2.5 to 20.6 GHz) and finally the third antenna targets an application for 100 GHz band. The size of the first one is 2×2.1 mm2, while the second on-chip antenna occupies an area of about 4.6 ×11.5 mm2 over silicon substrate. The third antenna module is developed on LCP substrate, which can be accommodated within 12.5×27 mm2 area. Though the two on-chip antennas offer only lower gain of around -29 dBi and -3 dBi respectively implementing silicon as a base material, but it paves the way for monolithic integration within a chip. The third candidate exhibits a directive gain of 19-20 dBi with a radiation efficiency of 80% over 100 GHz band. The highlighted portion of this current research work is to propose empirical modeling of electrically small antennas. The proposed methods claim to be most simple in nature and without applying complicated mathematical jugglery easy circuit models are presented for these aforesaid antennas, going to the insight of device physics. A comparative study has been carried out with the proposed model and full-wave simulated results for each antenna, to validate the circuit models.

Holistic investigation of the electrospinning parameters for high percentage of β-phase in PVDF nanofibers

PVDF is a piezoelectric polymer that exists in five phases with the β-phase contributing the maximum to its piezoelectricity. Electrospinning is the most popular method used by researchers for developing PVDF nanofibers-based sensors. A holistic study pertaining to all the important electrospinning parameters is done in this paper to quantify their effects on the percentage of β-phase in the electrospun PVDF nanofibers. A new strategy to group the different electrospinning parameters based on their effect on various phases of the electrospinning process has been devised. Spin distance has been found to have the maximum effect with a variation of 6.6% on the percentage of β-phase in the PVDF nanofibers. The other parameters with a large effect on the percentage of β-phase are the electric field between needle and collector, the speed of the drum and the flow rate of the solution with variations of 6.3, 5.9 and 5.7% respectively. The group of parameters with the largest effect on the percentage of β-phase is the one directly affecting the stretching of the nanofibers (containing spin distance, drum speed and electric field) in the PVDF solution in the electrospinning process. A sensor has been developed with the use of the optimized parameters on a flexible LCP substrate. The voltage output of the sensor is studied for different electrospinning time (mat thicknesses) for a dynamic strain stimulus and is found to be maximum for sensor developed with 1 h of electrospinning. This is a systematic and comprehensive study that can be utilized for any electrospinning set-up for optimizing the properties of the nanofibers.

Photonic Curing of Copper Ink Films on Liquid Crystal Polymer Substrate

AbstractThe application of intense pulsed light (IPL) to printed copper nanoparticle (CuNP) films enables rapid curing on low temperature substrates in ambient conditions. In this work, we printed CuNP ink on liquid crystal polymer (LCP; Vectra A resin) and then cured the films using a high energy density light pulse. High-resolution SEM images of the cured films revealed that the CuNPs on LCP were fused together. Optimal curing parameters were a 5 ms pulse, 75% duty cycle, and an energy density range of 4.2–5.2 J⋅cm-2. Sheet resistance, Rs, values as low as ~0.1 Ω⋅sq-1were obtained. The LCP substrate took on a yellowed appearance after the application of five pulses and exhibited a surface free energy increase. A filter that blocked wavelengths <450 nm was placed over the printed copper film on LCP. As expected, the presence of the filter decreased the total energy density and produced a cured film with high Rs; however, when the energy density was increased in the presence of the filter, the Rs remained high (0.95 Ω⋅sq-1). This preliminary work indicates that additional studies are required not only to understand low thermal budget curing on LCP, but also to elucidate the properties of substrates that enable low Rs.

Graphene based strain sensor with LCP substrate

A flexible strain sensor constructed by an efficient, low-cost fabrication strategy is presented in this paper. It is assembled by adhering grid-like graphene on LCP substrate. Kinds of measurement setup have been designed to verify that the proposed flexible sensor device is suitable to be used in health monitoring system. From the experiment results, it can be proved that the sensor exhibits the following features: ultra-light, relatively good sensitivity, high reversibility, superior physical robustness, easy fabrication. With the great performance of this flexible strain sensor, it is considered to play an important role in body monitoring, structural health monitoring system, fatigue detection and healthcare systems in the near future.

Broadband SIW-to-Waveguide Transition in Multilayer LCP Substrates at W-Band

In this letter, we present a substrate-integrated waveguide (SIW) to air-filled rectangular waveguide (WG) transition in multilayer liquid crystal polymer substrates at W-band. The proposed transition is achieved by using a SIW-fed linearly flared antipodal slot line inserted into a WG. To minimize packaging leakage, no guided vias are utilized in the slot line region. Full-wave simulation reveals a low insertion loss of 0.8 dB for the proposed transition at W-band. To experimentally demonstrate this design, a WG-to-SIW-to-WG transition was fabricated and characterized. The measured insertion and reflection loss of the back-to-back transition is less than 1.8 and −11 dB, respectively, at W-band.

Slot-Coupled Directional Filters in Multilayer LCP Substrates at 95 GHz

In this paper, traveling-wave directional filters (DFs) in multilayer liquid crystal polymer substrates were proposed at 95 GHz, consisting of two terminating microstrip lines (MSLs) in the top circuit layer, a shared ground and coupling slots in the second layer, and MSL loop resonators in the bottom layer. By using asymmetric phase topology for the loop, the proposed DFs address higher directivity and Q-factor over the traditional symmetric traveling-wave DFs. The single-loop DF was demonstrated with a 3-dB passband width of 4.8% and an insertion loss of 4.6 dB at 94 GHz. To improve the directivity, particularly the insertion loss, two identical DFs were cascaded in series in the direction of the terminating lines. A bandwidth of 8% and a low insertion loss of 2.6 dB can be obtained with a phase delay of 360° between the two DFs. Limited by the practical application, the proposed DFs were fabricated and demonstrated in hybrid substrates, which slightly increases the insertion loss. The measured insertion loss of the single-loop and double-loop DFs is 5.2 and 3.1 dB at 95 GHz, respectively, showing good agreement with the simulated data.

Ultrawide band CBCPW to stripline vertical transition in multilayer LCP substrates

This article presents an improved design of conductor-backed coplanar waveguide (CBCPW)-to-stripline (SL) vertical transition in multilayer liquid crystal polymer substrates. The CBCPW and SL is designed on the top and second conductor layers, respectively, and electrically connected with each other through micro-vias. The reported transition is optimized using High Frequency Simulation Software, and the simulated results predict low loss over an ultrawide bandwidth. To validate our design, a CBCPW-to-SL-to-CBCPW transition was fabricated and characterized. The back-to-back transition shows an insertion loss of less than 2.5 dB and a return loss of less than −10 dB over a frequency band from DC to 78 GHz. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:1481–1484, 2015

Dual Band-Reject UWB Antenna With Sharp Rejection of Narrow and Closely-Spaced Bands

An ultrawideband (UWB) antenna that rejects extremely sharply the two narrow and closely-spaced U.S. WLAN 802.11a bands is presented. The antenna is designed on a single surface (it is uniplanar) and uses only linear sections for easy scaling and fine-tuning. Distributed-element and lumped-element equivalent circuit models of this dual band-reject UWB antenna are presented and used to support the explanation of the physical principles of operation of the dual band-rejection mechanism thoroughly. The circuits are evaluated by comparing with the response of the presented UWB antenna that has very high selectivity and achieves dual-frequency rejection of the WLAN 5.25 GHz and 5.775 GHz bands, while it receives signal from the intermediate band between 5.35-5.725 GHz. The rejection is achieved using double open-circuited stubs, which is uncommon and are chosen based on their narrowband performance. The antenna was fabricated on a single side of a thin, flexible, LCP substrate. The measured achieved rejection is the best reported for a dual-band reject antenna with so closely-spaced rejected bands. The measured group delay of the antenna validates its suitability for UWB links. Such antennas improve both UWB and WLAN communication links at practically zero cost.

Study of Electrohydrodynamic Micropumping Through Conduction Phenomenon

In the present paper, a single-stage axisymmetric conduction micropump in the vertical configuration has been proposed. This micropump consists of four components: high-voltage ring electrode, grounded disk-shaped electrode, insulator spacer, and inlet/outlet ports. The high-voltage electrode and grounded electrode of the device were patterned on the two separate commercial LCP substrates with 30 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\mu\hbox{m}$ </tex></formula> copper cladding using standard lithographic techniques. The final spacing between two electrodes and the overall size of the device were measured to be 286 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\mu\hbox{m}$</tex> </formula> and <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$50\ \hbox{mm} \times 70\ \hbox{mm} \times 5\ \hbox{mm}$</tex> </formula> , respectively. The static pressure generation of the micropump was measured at different applied voltage using three different dielectric liquids, 10-GBN Nynas and Shell Diala AX transformer oils, and N-hexane. The range of applied voltages was between 300 and 1500 VDC, and maximum pressure generation up to 100 Pa was achieved at 1500 VDC applied voltage. To further verify the experimental results, a numerical simulation was also performed. The pressure head generation was predicted numerically and compared with experimental results at different applied voltages.

A compact ultra‐wideband bandpass filter with ultra‐fine conductor trace based on liquid crystal polymer substrates

PurposeLiquid Crystal Polymer (LCP) materials are considered to be promising substrates for wireless applications because of their excellent properties. The purpose of this paper is to describe now a novel and compact microstrip ultra‐wideband bandpass filter (UWB BPF) with ultra‐fine conductor traces working over 22 to 29 GHz is fabricated on LCP substrates.Design/methodology/approachUsing standard processing technology, such as photolithography, plasma pretreatment, sputter deposition and wet etching, a microstrip UWB BPF is fabricated on LCP substrates. In order to obtain better adhesion between LCP substrate and copper, the oxygen plasma pretreatment of the LCP substrate surface and a thin titanium adhesion layer are introduced before a copper layer is sputter‐deposited onto the substrate.FindingsThe measured and the simulated results agree well. The measured insertion loss is about 8 dB in the passband of the bandpass filter, which is a little high compared to the simulated result (∼5 dB). The out of band performance at both the high frequency and low frequency is very good, almost higher than 35 dB.Originality/valueThis paper presents the realization of (UWB BPF) working over 22 to 29 GHz based on an LCP substrate, which demonstrates the feasibility of the application of the LCP substrate in RF wireless systems and also gives some useful information for later research.

Evaluation of adhesion pull-off performance of nanoparticle-based inkjet-printed silver structure on various substrates

In this paper, we evaluated two different silver inks that differ about their particle size and used components in ink onto several commonly used substrates in the printed electronics, i.e., PEN, PI, PET, and LCP. Several sintering temperatures and durations were studied to select the right sintering profile for each ink-substrate combination for certain types of electronics application. The results showed that Ag C silver ink has the highest adhesion performance on PET and LCP substrates at 150°C for 60 min compared to the other sintering profile of the same ink which has been used in production of low-cost electronics. On the other hand, Ag H silver ink showed the highest adhesion performance on Kapton PI compared to the sintering profile of the same ink to produce high-frequency electronic applications, miniaturisation of microelectronic packages, and decreasing the width of the microelectronic circuits. In addition, to control the spreading mechanism of the ink droplets, the surface treatment applied before printing process and its effect on adhesion performance after printing and sintering process was investigated on selected ink-substrate combination. Tests results were presented and it showed that the electronic coating was weakening the adhesion performance of that selected ink-substrate combination.

High-Q Embedded Passives on Large Panel Multilayer Liquid Crystalline Polymer-Based Substrate

This paper presents high-Q embedded passives on a multilayer liquid crystalline polymer (M-LCP)-based substrate for a low-profile, compact, mixed-signal system integration with high performance. A low loss and a low water absorption are advantages of LCP. It is also lower-cost material than other high-frequency materials such as low-temperature cofired ceramic (LTCC) due to its compatibility to printed wiring board (PWB) process. Low loss characteristics of LCP provide high-Q passives such as inductors, capacitors, and matching networks. Seventy-six inductors and sixteen capacitors were characterized from three different 9 in times 12 in multilayer LCP panels. Two different locations from each board were chosen to preliminarily validate the large panel process of the M-LCP substrate. The highest quality factor (Q) of 164 was achieved with 2.55 nH at 5.05 GHz. The inductors range from 1.45 to 23.11 nH and Qs range from 43 to 164. Inductors in various embedded layers were characterized for realization of 3-D integration in multilayer LCP substrate for multiband applications. To remove the parasitics from pads and interconnections, a two-step de-embedding technique was applied. The model-to-hardware correlations are presented in this paper. Twelve 3-D capacitors were also designed and characterized, which provide more than double the capacitance of standard capacitors. Low-loss filters and baluns at 5 GHz were simulated and measured using the designed high-Q passives. The designed high-Q embedded passives on M-LCP-based substrates provide a systematic 3-D integration method for achieving low-profile, high-performance, and compact modules.

Statistical analysis and diagnosis methodology for RF circuits in LCP substrates

This paper presents the application of a fast and accurate layout-level statistical analysis methodology for the diagnosis of RF circuit layouts with embedded passives in liquid crystalline polymer substrates. The approach is based on layout-segmentation, lumped-element modeling, sensitivity analysis, and extraction of probability density function using convolution methods. The statistical analyses were utilized as a diagnosis tool to estimate distributed design parameter variations and yield of RF circuit layouts for a given measured performance. The results of statistical analysis and diagnosis were compared with measurement results of fabricated filters. Statistical methods were also applied for design space exploration to improve system performance, as well as estimation of yield and diagnosis of faults during batch fabrication.

Layout-level synthesis of RF inductors and filters in LCP substrates for Wi-Fi applications

A fast and accurate layout-level synthesis and optimization technique for embedded passive RF components and circuits such as inductors and bandpass filters have been presented. The filters are composed of embedded inductors and capacitors in a multilayer liquid crystalline polymer substrate. The proposed approach is based on a combination of segmented lumped-circuit modeling, nonlinear mapping using polynomial functions, artificial neural network-based methods, and circuit-level optimization. Synthesis and optimization results of inductors for spiral/loop designs based on microstrip and stripline configuration are within 5% of data obtained from electromagnetic (EM) simulations. For RF circuits, the methodology has been verified through synthesis of 2.4- and 5.5-GHz bandpass filters with and without transmission zeros. Scalability has been shown over a range of 2-3 and 4-6 GHz, respectively, with bandwidth variation of 0.5%-3% of center frequency. The synthesized models are within 3%-5% of EM simulation data.