A Two-Stage Process for Laser Prototyping of Microwave Circuits in LTCC Technology

An improved technique for laser prototyping of microwave circuits in low-temperature cofired ceramic (LTCC) technology is presented. This builds on the method of laser machining of conductor layers in unfired LTCC tapes. The proposed process presents the hybrid approach of circuit fabrication by employing both unfired and post fired laser machining of LTCC substrate, hence giving more flexibility of realizing multilayer components. This allows the low-tolerance microwave structures like couplers and filters to be fabricated on the outer layers because shrinkage uncertainty is no longer a problem. Track widths and gaps of 30 μm are demonstrated with an edge definition of ±2 μm. A stripline coupler and a four-layer spiral inductor is successfully fabricated using this technique to demonstrate the process. The improved process can produce high-precision microwave and millimeter-wave components on the outer layers and provides rapid system-in-package prototyping for research and development

Microwave Microlitre Lab-on-Substrate Liquid Characterisation based on SIW Slot Antenna

A microwave microlitre binary liquid mixture concentration detection sensor with potential biological analysis is presented. The microwave lab-on-substrate sensor is fabricated using a substrate integrated waveguide (SIW) slot antenna. The microfluidic channel encapsulating liquid under investigation is located on top of the antenna slot at a quarter wavelength from the short-circuited end of the SIW. The radiated electric nearfield interaction with the liquid mixture exhibits different relationships between the complex permittivity of the liquid mixtures versus the resonant frequency and return loss, discriminating types and percentages of mixed liquid. The sensor was initially demonstrated with three types of samples: deionised water, methanol and air. A resonant frequency shift of 110MHz was measured to discriminate between air and deionised water while we obtained a 20MHz resonant frequency shift between air and methanol. Furthermore, the sensor was used to assess deionised water-methanol mixtures with methanol fractional volumes of 0 to 1 in 0.2 steps. The microwave-microfluidic sensor is contactless, uses readily available materials, cost effective and offers fast and accurate liquid characterisation

Compact broadband electronically controllable SIW phase shifter for 5G phased array antennas

This work presents a novel compact and broadband electronically controllable substrate integrated waveguide (SIW) phase shifter intended for beamsteering applications in antenna arrays for 5G wireless communication. The proposed phase shifter is designed to operate over a large bandwidth (26 GHz–32 GHz) with a simulated maximum insertion loss of less than 3 dB and a maximum phase difference of more than 100°+5° over the entire band. The phase shift is provided via metal posts which are switched between capacitive and inductive loading through beam-lead PIN diodes

A Microfluidic-Integrated SIW Lab-on-Substrate Sensor for Microliter Liquid Characterization

A novel microfluidic-integrated microwave sensor with potential application in microliter-volume biological/biomedical liquid sample characterization and quantification is presented in this paper. The sensor is designed based on the resonance method, providing the best sensing accuracy, and implemented by using a substrate-integrated-waveguide (SIW) structure combining with a rectangular slot antenna operating at 10 GHz. The device can perform accurate characterization of various liquid materials from very low to high loss, demonstrated by measurement of deionized (DI) water and methanol liquid mixtures. The measured relative permittivity, which is the real part of complex permittivity, ranges from 8.58 to 66.12, which is simply limited by the choice of test materials available in our laboratory, not any other technical considerations of the sensor. The fabricated sensor prototype requires a very small liquid volume of less than 7 µl, while still offering an overall accuracy of better than 3 %, as compared to the commercial and other published works. Key advantages of the proposed sensor are that it combines 1.) a very low-profile planar and miniaturized structure sensing microliter liquid volume; 2.) ease of design and fabrication, which makes it cost-effective to manufacture and 3.) noninvasive and contactless measurements. Moreover, since the microfluidic subsystem can potentially be detached from the SIW microwave sensor and, afterward, replaced by a new microfluidic component, the sensor can be reused with no life-cycle limitation and without degrading any figure of merit

Analysis and design of a differential sampled-line six-port reflectometer

The analysis and design of a differential six-port reflectometer (SPR) based on a sampled-line structure is presented in this paper. The practical differential SPR is realized in Coplanar Strip (CPS) transmission line form, using two baluns for interfacing with the RF source and device under test (DUT) and four baluns connected to the RF logarithmic detectors. The performance of the proposed differential SPR structure is evaluated with a common-mode rejection ratio analysis and impedance measurement. A prototype differential SPR was designed and fabricated at 1 GHz in order to verify the analysis. Measurement results for various load impedances are compared with the measured results obtained from a commercial automatic vector network analyzer. It is shown that the differential structure gives a significant advantage in rejecting common-mode interference signals

Non-Invasive Millimeter-Wave Profiler for Surface Height Measurement of Photoresist Films

This work presents a low-cost non-invasive millimeter-wave surface-height measurement sensor of dielectric and polymer films on glass and quartz substrates. The surface-height profiler utilizes near-field resonance measurement technique operating at 96 GHz implemented by using a single complementary split-ring resonator (CSRR) integrated with a tailor-made WR10 rectangular waveguide. By placing a glass or quartz substrate uniformly coated with SU-8 photoresist on top of the CSRR, the thickness of the SU-8 polymer can be extracted based on the reflected and transmitted electromagnetic-wave energy interacting at the electrical boundary between the substrate and polymer film. Uniform single layers of SU-8 polymer with thicknesses from 3 to 13 μm, coated on top of glass substrate are measured and characterized. The extracted polymer-film thicknesses from the sensor in this work show an agreement of higher than 95% as compared to the commercial surface profiler instrument, while offering various advantages e.g. non-invasion, ease of measurement setup, low-cost and miniaturization

High Performance Compact Multilayer Circular Spiral Inductors in Advanced Photoimageable Technology

This paper presents the development and thorough analysis of a wide range of coplanar-waveguide circular spiral inductors with remarkably high performance and inductance density using advanced multilayer (ML) photoimageable thick-film (Pimage-TF) multichip module (MCM) technology. The performances of the embedded spiral inductors are thoroughly analyzed, modeled, and compared with the competitive MCM technologies and are superior to most of the published results. A new design and layout generation technique with a simplified closed form expression for circular spiral inductors is proposed. Moreover, the impact of MCM/system-on-package technologies on inductor key parameters has been explained in detail and compared with other technologies. The cost-effective Pimage-TF-based inductors demonstrate the highest level of self-resonance frequency, as well as inductance density (15 nH/$mathrm{mm}^{mathrm {mathbf {2}}}$ ) reported to date in conventional thick-film-based ML MCM technologies, including low temperature cofired ceramic

Wireless Power Transfer for Gas Pipe Inspection Robots

Wireless power transfer in metal pipes is a promising alternative to tethered exploration robots, with strong potential to enable longer operating times. Here we present experimental results, including rectification efficiency, for a prototype gas pipe inspection robot with wireless power receiver functionality

Low-Cost Microfabrication for MEMS Switches and Varactors

This paper presents a low-cost micro-fabrication technique for manufacturing RF MEMS switches and varactors without intensive cleanroom environments. The fabrication process entails only laser micro-structuring technique, noncleanroom micro-lithography, standard wet-bench and hot-film emboss of SU-8 and ADEX polymers. MEMS movable structures were fabricated out of 14-μm-thick Aluminum foils and suspended above coplanar-waveguide transmission lines, which were implemented on top Duroid substrates, via 5-μm-thick SU-8 dielectric anchors. Both MEMS structures and Duroid substrate were integrated using micro-patterned polymers, developed by using dry-film ADEX and SU-8 polymers, for a composite assembly. An average fabrication yield of higher than 60% was achieved, calculated from ten fabrication attempts. The RF measurement results show that the RF MEMS devices fabricated by using the novel micro-fabrication process have good figure-of-merits, at much lower overall fabrication costs, as compared to the devices fabricated by conventional cleanroom process, enabling it as a very good micro-fabrication process for cost-effective rapid prototyping of MEMS

Wireless Power Transfer System for Battery-Less Sensor Nodes

For the first time, the design and implementation of a fully-integrated wireless information and power transfer system, operating at 24 GHz and enabling battery-less sensor nodes, is presented in this paper. The system consists of an RF power source, a receiver antenna array, a rectifier, and a battery-less sensor node which communicates via backscatter modulation at 868 MHz. The rectifier circuits use commercially available Schottky diodes to convert the RF power to DC with a measured efficiency of up to 35%, an improvement of ten percentage points compared with previously reported results. The rectifiers and the receive antenna arrays were jointly designed and optimised, thereby reducing the overall circuit size. The battery-less sensor transmitted data to a base station realised as a GNU Radio flow running on a bladeRF Software Defined Radio module. The whole system was tested in free-space in laboratory conditions and was capable of providing sufficient energy to the sensor node in order to enable operation and wireless communication at a distance of 0.15 metres