Polymer-Based Micromachining for Scalable and Cost-Effective Fabrication of Gap Waveguide Devices Beyond 100 GHz

The terahertz (THz) frequency bands have gained attention over the past few years due to the growing number of applications in fields like communication, healthcare, imaging, and spectroscopy. Above 100 GHz transmission line losses become dominating, and waveguides are typically used for transmission. As the operating frequency approaches higher frequencies, the dimensions of the waveguide-based components continue to decrease. This makes the traditional machine-based (computer numerical control, CNC) fabrication method increasingly challenging in terms of time, cost, and volume production. Micromachining has the potential of addressing the manufacturing issues of THz waveguide components. However, the current microfabrication techniques either suffer from technological immaturity, are time-consuming, or lack sufficient cost-efficiency. A straightforward, fast, and low-cost fabrication method that can offer batch fabrication of waveguide components operating at THz frequency range is needed to address the requirements.A gap waveguide is a planar waveguide technology which does not suffer from the dielectric loss of planar waveguides, and which does not require any electrical connections between the metal walls. It therefore offers competitive loss performance together with providing several benefits in terms of assembly and integration of active components. This thesis demonstrates the realization of gap waveguide components operating above 100 GHz, in a low-cost and time-efficient way employing the development of new polymer-based fabrication methods.A template-based injection molding process has been designed to realize a high gain antenna operating at D band (110 - 170 GHz). The injection molding of OSTEMER is an uncomplicated and fast device fabrication method. In the proposed method, the time-consuming and complicated parts need to be fabricated only once and can later be reused.A dry film photoresist-based method is also presented for the fabrication of waveguide components operating above 100 GHz. Dry film photoresist offers rapid fabrication of waveguide components without using complex and advanced machinery. For the integration of active circuits and passive waveguides section a straightforward solution has been demonstrated. By utilizing dry film photoresist, a periodic metal pin array has been fabricated and incorporated in a waveguide to microstrip transition that can be an effective and low-cost way of integrating MMIC of arbitrary size to waveguide blocks

Polymer-Based Low-Cost Micromachining of Gap Waveguide Components

The millimeter-wave (mmWave) and sub-millimeter-wave (sub-mmWave) frequency bands have gained significant attention over the past few years due to the growth of commercial wireless applications. As the operating frequency approaches these higher frequencies, the dimensions of the waveguide-based components continue to decrease. The decreasing feature size of those waveguide components makes the traditional machine-based (computer numerical control, CNC) fabrication method increasingly challenging in terms of time and cost, especially above 100 GHz. Additionally, this method is a serial process and cost will not scale with volume production. Micromachining has the potential of addressing the manufacturing issues of mmWave components. However, the existing microfabrication techniques either suffer from technological immaturity, are time-consuming, or lack sufficient cost-efficiency. A straightforward, fast, and low-cost fabrication method that can offer batch fabrication of waveguide components operating at mmWave and sub-mmWave frequency range is desirable to address the needs for hardware on the growing market of mmWave and sub-mmWave wireless systems.Conventional metal waveguides have very strict fabrication requirements in terms of mechanical assembly and integration of RF electronics. In comparison, gap waveguide technology not only offers competitive loss performance but also provides several benefits in terms of assembly and integration of active components. A gap waveguide is a planar waveguide technology which does not suffer from the dielectric loss in planar waveguides and which does not require any electrical connections between the metal walls, in contrast to hollow waveguides. This thesis aims to realize gap waveguide components operating at mmWave and sub-mmWave frequency range, in a low-cost and time-efficient way by developing new polymer-based fabrication methods.A template-based injection molding process has been designed to realize a high gain antenna operating at D band (110 -170 GHz). We can confirm that injection molding of OSTEMER is a straightforward and fast device fabrication method. In the proposed method, the time-consuming and complicated parts need to be fabricated only once and can later be reused.A dry film photoresist-based method is also presented in this thesis to fabricate waveguide components operating between 220 - 320 GHz. Dry film photoresist offers rapid fabrication of waveguide components without using sophisticated tools. The measurement results presented in the thesis indicate that this dry film-based method is a promising method for fabricating waveguide components operating in mmWave and sub- mmWave frequency ranges

Micromachined Wideband Ridge Gap Waveguide Power Divider at 220-325 GHz

A micromachined ridge gap waveguide power divider operating at 220-325 GHz is presented. The device is fabricated by SUEX dry film photoresist. Dry film photoresist can be used to obtain geometrical features with high accuracy using a robust fabrication process. The designed power divider has simple geometrical features and a wide band performance. The measured transmission coefficients are equal to -3.5 \ub1 0.4 dB at 220-325 GHz and the measured input reflection coefficient is below -12 dB at 220-325 GHz. The measurement results are in good agreement with simulations, demonstrating that the proposed fabrication method is suitable for the fabrication of waveguide components operating at the millimeter and sub-millimeter wave range. The presented low-loss ridge gap waveguide power divider may enable cost-effective and rapid fabrication of passive devices such as high gain antennas operating up to THz frequencies

Dry film photoresist-based microfabrication: a new method to fabricate millimeter-wave waveguide components

This paper presents a novel fabrication method based on dry film photoresists to realize waveguides and waveguide-based passive components operating at the millimeter-wave frequency (30–300 GHz). We demonstrate that the proposed fabrication method has a high potential as an alternative to other microfabrication technologies, such as silicon-based and SU8-based micromachining for realizing millimeter-wave waveguide components. Along with the nearly identical transfer of geometrical structures, the dry film photoresist offers other advantages such as fewer processing steps, lower production cost, and shorter prototyping time over the conventional micromachining technologies. To demonstrate the feasibility of the fabrication process, we use SUEX dry film to fabricate a ridge gap waveguide resonator. The resonator is designed to exhibit two resonances at 234.6 and 284 GHz. The measured attenuation at 234 GHz is 0.032 dB/mm and at 283 GHz is 0.033 dB/mm for the fabricated prototype. A comparative study among different existing technologies indicates that the reported method can give a better unloaded Q-value than other conventional processes. The measured unloaded Q-values are in good agreement with the simulated unloaded Q-values. The signal attenuation indicates that SUEX dry film photoresists can be used to fabricate passive devices operating at millimeter-wave frequencies. Moreover, this new fabrication method can offer fast and low-cost prototyping

Multilayer Dry Film Photoresist Fabrication of a Robust >100 GHz Gap Waveguide Slot Array Antenna

This article presents the first use of a multilayer dry film photoresist to fabricate a slot array antenna by micromachining. The proposed fabrication process demonstrates a straightforward and fast method of realizing antenna structures and delicate features with very high accuracy above 100 GHz. The slot array antenna design is based on gap waveguide technology. The designed antenna consists of two layers: a slot layer and a feed layer with a transition to measuring waveguide. The antenna contains structures that require a multiple level dry film fabrication process with thicknesses ranging from 80 μm to 400 μm with \ub1 10 μm tolerance. The fabricated antenna shows good accuracy. To make the fabricated antenna layers conductive, the fabricated polymer antenna was coated with Ti and Au. The input reflection coefficient was measured to be below – 11 dB over a 10% bandwidth from 136-148 GHz, and the antenna gain was measured to be 11.4 dBi at 142 GHz, both of which are in fair agreement with simulations. A thermal cycling test has been conducted on the fabricated antenna and the results show insignificant degradation at least up to 300 cycles in the temperature range –50 \ub0C to 135 \ub0C which is the typical temperature gradient range for many practical outdoor wireless applications

Realizing a 140\ua0GHz Gap Waveguide–Based Array Antenna by Low-Cost Injection Molding and Micromachining

This paper presents a novel micromachining process to fabricate a 140\ua0GHz planar antenna based on gap waveguide technology to be used in the next-generation backhauling links. The 140\ua0GHz planar array antenna consists of three layers, all of which have been fabricated using polymer-based microfabrication and injection molding. The 140\ua0GHz antenna has the potential to be used as an element in a bigger 3D array in a line-of-sight (LOS) multiple input multiple output (MIMO) configuration to boost the network capacity. In this work, we focus on the fabrication of a single antenna array element based on gap waveguide technology. Depending on the complexity of each antenna layer’s design, three different micromachining techniques, SU8 fabrication, polydimethylsiloxane (PDMS) molding, and injection molding of the polymer (OSTEMER), together with gold (Au) coating, have been utilized to fabricate a single 140\ua0GHz planar array antenna. The input reflection coefficient was measured to be below − 11\ua0dB over a 14% bandwidth from 132 to 152\ua0GHz, and the antenna gain was measured to be 31 dBi at 140\ua0GHz, both of which are in good agreement with the simulations

Effect of early tranexamic acid administration on mortality, hysterectomy, and other morbidities in women with post-partum haemorrhage (WOMAN): an international, randomised, double-blind, placebo-controlled trial

Background Post-partum haemorrhage is the leading cause of maternal death worldwide. Early administration of tranexamic acid reduces deaths due to bleeding in trauma patients. We aimed to assess the effects of early administration of tranexamic acid on death, hysterectomy, and other relevant outcomes in women with post-partum haemorrhage. Methods In this randomised, double-blind, placebo-controlled trial, we recruited women aged 16 years and older with a clinical diagnosis of post-partum haemorrhage after a vaginal birth or caesarean section from 193 hospitals in 21 countries. We randomly assigned women to receive either 1 g intravenous tranexamic acid or matching placebo in addition to usual care. If bleeding continued after 30 min, or stopped and restarted within 24 h of the first dose, a second dose of 1 g of tranexamic acid or placebo could be given. Patients were assigned by selection of a numbered treatment pack from a box containing eight numbered packs that were identical apart from the pack number. Participants, care givers, and those assessing outcomes were masked to allocation. We originally planned to enrol 15 000 women with a composite primary endpoint of death from all-causes or hysterectomy within 42 days of giving birth. However, during the trial it became apparent that the decision to conduct a hysterectomy was often made at the same time as randomisation. Although tranexamic acid could influence the risk of death in these cases, it could not affect the risk of hysterectomy. We therefore increased the sample size from 15 000 to 20 000 women in order to estimate the effect of tranexamic acid on the risk of death from post-partum haemorrhage. All analyses were done on an intention-to-treat basis. This trial is registered with ISRCTN76912190 (Dec 8, 2008); ClinicalTrials.gov, number NCT00872469; and PACTR201007000192283. Findings Between March, 2010, and April, 2016, 20 060 women were enrolled and randomly assigned to receive tranexamic acid (n=10 051) or placebo (n=10 009), of whom 10 036 and 9985, respectively, were included in the analysis. Death due to bleeding was significantly reduced in women given tranexamic acid (155 [1·5%] of 10 036 patients vs 191 [1·9%] of 9985 in the placebo group, risk ratio [RR] 0·81, 95% CI 0·65–1·00; p=0·045), especially in women given treatment within 3 h of giving birth (89 [1·2%] in the tranexamic acid group vs 127 [1·7%] in the placebo group, RR 0·69, 95% CI 0·52–0·91; p=0·008). All other causes of death did not differ significantly by group. Hysterectomy was not reduced with tranexamic acid (358 [3·6%] patients in the tranexamic acid group vs 351 [3·5%] in the placebo group, RR 1·02, 95% CI 0·88–1·07; p=0·84). The composite primary endpoint of death from all causes or hysterectomy was not reduced with tranexamic acid (534 [5·3%] deaths or hysterectomies in the tranexamic acid group vs 546 [5·5%] in the placebo group, RR 0·97, 95% CI 0·87-1·09; p=0·65). Adverse events (including thromboembolic events) did not differ significantly in the tranexamic acid versus placebo group. Interpretation Tranexamic acid reduces death due to bleeding in women with post-partum haemorrhage with no adverse effects. When used as a treatment for postpartum haemorrhage, tranexamic acid should be given as soon as possible after bleeding onset. Funding London School of Hygiene & Tropical Medicine, Pfizer, UK Department of Health, Wellcome Trust, and Bill & Melinda Gates Foundation

Pick and place assembly technique for fabrication of groove gapwaveguide resonator

Gap waveguide are an innovative technology for millimeter-wave RF applications. There are some factors to be considered while using this technology at millimeter wave frequencies or above, particularly for low cost RF applications. Surface mount technology and pick and place machine technique can demonstrate a way to solve this problem. In this paper a groove resonator is presented which is manufactured by using pick and place technique. Brass pins of diameter 1.6mm and height 2.3mm was mounted on a 5mm thick copper plate. Lead free solder paste was used for solder joint

Micromachined Ridge Gap Waveguide Transmission Line and Transition at 220-310 GHz

This paper presents a vertical wideband transition between a standard WR-3.4 rectangular waveguide (RW) and ridge gap waveguide (RGW) operating at 220-310 GHz. To achieve a wideband impedance matching a capacitive stub is used instead of multiple steps in the ridge section to reduce the manufacturing complexity. The designed back-to-back transition is fabricated with SUEX dry film photoresist. The attractive features of the designed transition are simplicity and high tolerances to manufacturing errors, without compromising the wideband performance. The measurement results of the fabricated prototype show good agreement with simulations over the frequency band of interest and the measured average insertion loss is 0.075 dB/mm and the measured input reflection coefficient is below -12 dB for the back-to-back structure. Measurement results indicate that SUEX dry film photoresist is a suitable material to fabricate waveguide components operating at and above the millimeter-wave range

140 GHz Planar Gap Waveguide Array Antenna for Line of Sight (LOS) MIMO Backhaul Links

This paper presents a 140 GHz planar antenna array based on gap waveguide technology to be used in next generation backhauling links. Each antenna element in the bigger 3D-array is considered to have about 30dBi gain and each antenna element consists of several metal layers such as the cavity backed radiation layer and a corporate feed network layer. Micromachining based MEMS fabrication technology has been considered for realizing such high gain antenna element for the LOS MIMO array. The simulated performance of the single element antenna has more than 30 dBi gain and S11 lower than -10 dB over 132-150 GHz band corresponding to 14% relative bandwidth. Also we analyze the optimum array element separation in a 2D configuration for line of sight (LOS) MIMO system so as to support several independent channels between TX and RX links at 140 GHz