7,709 research outputs found

    Beam scanning by liquid-crystal biasing in a modified SIW structure

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    A fixed-frequency beam-scanning 1D antenna based on Liquid Crystals (LCs) is designed for application in 2D scanning with lateral alignment. The 2D array environment imposes full decoupling of adjacent 1D antennas, which often conflicts with the LC requirement of DC biasing: the proposed design accommodates both. The LC medium is placed inside a Substrate Integrated Waveguide (SIW) modified to work as a Groove Gap Waveguide, with radiating slots etched on the upper broad wall, that radiates as a Leaky-Wave Antenna (LWA). This allows effective application of the DC bias voltage needed for tuning the LCs. At the same time, the RF field remains laterally confined, enabling the possibility to lay several antennas in parallel and achieve 2D beam scanning. The design is validated by simulation employing the actual properties of a commercial LC medium

    Novel 129Xe Magnetic Resonance Imaging and Spectroscopy Measurements of Pulmonary Gas-Exchange

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    Gas-exchange is the primary function of the lungs and involves removing carbon dioxide from the body and exchanging it within the alveoli for inhaled oxygen. Several different pulmonary, cardiac and cardiovascular abnormalities have negative effects on pulmonary gas-exchange. Unfortunately, clinical tests do not always pinpoint the problem; sensitive and specific measurements are needed to probe the individual components participating in gas-exchange for a better understanding of pathophysiology, disease progression and response to therapy. In vivo Xenon-129 gas-exchange magnetic resonance imaging (129Xe gas-exchange MRI) has the potential to overcome these challenges. When participants inhale hyperpolarized 129Xe gas, it has different MR spectral properties as a gas, as it diffuses through the alveolar membrane and as it binds to red-blood-cells. 129Xe MR spectroscopy and imaging provides a way to tease out the different anatomic components of gas-exchange simultaneously and provides spatial information about where abnormalities may occur. In this thesis, I developed and applied 129Xe MR spectroscopy and imaging to measure gas-exchange in the lungs alongside other clinical and imaging measurements. I measured 129Xe gas-exchange in asymptomatic congenital heart disease and in prospective, controlled studies of long-COVID. I also developed mathematical tools to model 129Xe MR signals during acquisition and reconstruction. The insights gained from my work underscore the potential for 129Xe gas-exchange MRI biomarkers towards a better understanding of cardiopulmonary disease. My work also provides a way to generate a deeper imaging and physiologic understanding of gas-exchange in vivo in healthy participants and patients with chronic lung and heart disease

    ABC: Adaptive, Biomimetic, Configurable Robots for Smart Farms - From Cereal Phenotyping to Soft Fruit Harvesting

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    Currently, numerous factors, such as demographics, migration patterns, and economics, are leading to the critical labour shortage in low-skilled and physically demanding parts of agriculture. Thus, robotics can be developed for the agricultural sector to address these shortages. This study aims to develop an adaptive, biomimetic, and configurable modular robotics architecture that can be applied to multiple tasks (e.g., phenotyping, cutting, and picking), various crop varieties (e.g., wheat, strawberry, and tomato) and growing conditions. These robotic solutions cover the entire perception–action–decision-making loop targeting the phenotyping of cereals and harvesting fruits in a natural environment. The primary contributions of this thesis are as follows. a) A high-throughput method for imaging field-grown wheat in three dimensions, along with an accompanying unsupervised measuring method for obtaining individual wheat spike data are presented. The unsupervised method analyses the 3D point cloud of each trial plot, containing hundreds of wheat spikes, and calculates the average size of the wheat spike and total spike volume per plot. Experimental results reveal that the proposed algorithm can effectively identify spikes from wheat crops and individual spikes. b) Unlike cereal, soft fruit is typically harvested by manual selection and picking. To enable robotic harvesting, the initial perception system uses conditional generative adversarial networks to identify ripe fruits using synthetic data. To determine whether the strawberry is surrounded by obstacles, a cluster complexity-based perception system is further developed to classify the harvesting complexity of ripe strawberries. c) Once the harvest-ready fruit is localised using point cloud data generated by a stereo camera, the platform’s action system can coordinate the arm to reach/cut the stem using the passive motion paradigm framework, as inspired by studies on neural control of movement in the brain. Results from field trials for strawberry detection, reaching/cutting the stem of the fruit with a mean error of less than 3 mm, and extension to analysing complex canopy structures/bimanual coordination (searching/picking) are presented. Although this thesis focuses on strawberry harvesting, ongoing research is heading toward adapting the architecture to other crops. The agricultural food industry remains a labour-intensive sector with a low margin, and cost- and time-efficiency business model. The concepts presented herein can serve as a reference for future agricultural robots that are adaptive, biomimetic, and configurable

    Design and Implementation of Indoor Disinfection Robot System

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    After the outbreak of COVID-19 virus, disinfection has become one of the important means of epidemic prevention. Traditional manual disinfection can easily cause cross infection problems. Using robots to complete disinfection work can reduce people's social contact and block the spread of viruses. This thesis implements an engineering prototype of a indoor disinfection robot from the perspective of product development, with the amin of using robots to replace manual disinfection operations. The thesis uses disinfection module, control module and navigation module to compose the hardware of the robot. The disinfection module uses ultrasonic atomizers, UV-C ultraviolet disinfection lamps, and air purifiers to disinfect and disinfect the ground and air respectively. The control module is responsible for the movement and obstacle avoidance of the robot. The navigation module uses Raspberry Pi and LiDAR to achieve real-time robot positioning and two-dimensional plane mapping. In terms of robot software,we have done the following work: (1) Based on the ROS framework, we have implemented functions such as SLAM mapping, location positioning, and odometer data calibration.(2) Customize communication protocols to manage peripheral devices such as UV-C lights, ultrasonic atomizers, air purifiers, and motors on the control board. (3) Develop an Android mobile app that utilizes ROSBridge's lightweight communication architecture to achieve cross platform data exchange between mobile devices and navigation boards, as well as network connectivity and interaction between mobile phones and robots Finally, this thesis implements an engineering prototype of a household disinfection robot from the perspective of product development

    Information limits of imaging through highly diffusive materials using spatiotemporal measurements of diffuse photons

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    Conventional medical imaging instruments are bulky, expensive, and use harmful ionising radiation. Combining ultrafast single-photon detectors and pulsed laser sources at optical wavelengths has the potential to offer inexpensive, safe, and potentially wearable alternatives. However, photons at optical wavelengths are strongly scattered by biological tissue, which corrupts direct imaging information about regions of absorbing interactions below the tissue surface. The work in this thesis studies the potential of measuring indirect imaging information by resolving diffuse photon measurements in space and time. The practical limits of imaging through highly diffusive material, e.g., biological tissue, is explored and validated with experimental measurements. The ill-posed problem of using the information in diffuse photon measurements to reconstruct images at the limits of the highly diffusive regime is tackled using probabilistic machine learning, demonstrating the potential of migrating diffuse optical imaging techniques beyond the currently accepted limits and underlining the importance of uncertainty quantification in reconstructions. The thesis is concluded with a challenging biomedical optics experiment to transmit photons diametrically through an adult human head. This problem was tackled experimentally and numerically using an anatomically accurate Monte Carlo simulation which uncovered key practical considerations when detecting photons at the extreme limits of the highly diffusive regime. Although the experimental measurements were inconclusive, comparisons with the numerical results were promising. More in-depth numerical simulations indicated that light could be guided in regions of low scattering and absorption to reach deep areas inside the head, and photons can, in principle, be transmitted through the entire diameter of the head. The collective evidence presented in this thesis reveals the potential of diffuse optical imaging to extend beyond the currently accepted limits to non-invasively image deep regions of the human body and brain using optical wavelengths

    1-D broadside-radiating leaky-wave antenna based on a numerically synthesized impedance surface

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    A newly-developed deterministic numerical technique for the automated design of metasurface antennas is applied here for the first time to the design of a 1-D printed Leaky-Wave Antenna (LWA) for broadside radiation. The surface impedance synthesis process does not require any a priori knowledge on the impedance pattern, and starts from a mask constraint on the desired far-field and practical bounds on the unit cell impedance values. The designed reactance surface for broadside radiation exhibits a non conventional patterning; this highlights the merit of using an automated design process for a design well known to be challenging for analytical methods. The antenna is physically implemented with an array of metal strips with varying gap widths and simulation results show very good agreement with the predicted performance

    Valorisation of rice straw by obtaining active compounds and cellulosic materials for the development of biodegradable food packaging systems

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    Tesis por compendio[ES] En esta tesis se obtuvieron fracciones celulósicas y extractos activos de paja de arroz mediante diferentes técnicas de extracción y purificación, utilizando agua como disolvente. Estas fracciones se incorporaron en películas de almidón y PLA, y en bicapas de almidón-PLA, para obtener materiales de envasado activos para extender la vida útil de diferentes alimentos. Los extractos obtenidos por combinación de ultrasonidos y calentamiento a reflujo (USHT) y con agua subcrítica (SWE) (a 160 °C (SWE-160) y 180 °C (SWE-180)) presentaron un alto contenido fenólico (37, 51 y 83 mg GAE.g-1 de extracto seco, respectivamente) y actividad antioxidante (6,3, 2,0 y 1,2 mg de extracto seco.mg-1 DPPH, respectivamente). Los extractos SWE fueron activos contra L. innocua y E. coli. Se aislaron fibras de celulosa (FC) del residuo insoluble de las diferentes extracciones. A pesar de las ligeras diferencias en el grado de purificación, los nuevos métodos dieron lugar a FCs con rendimientos más elevados que el método alcalino (35-39 % frente al 29 %), con cristalinidad (60-69 %), comportamiento térmico y relación de aspecto (20-60) similares. Se incorporaron fibras USHT al 1, 3 y 5 % (p/p) en películas termoprocesadas de almidón de maíz, y de almidón de maíz modificado térmicamente. La incorporación al 3 % dio lugar a películas con mejores propiedades funcionales. Los extractos activos (al 4, 6 y 8 % en peso) en la matriz de almidón, con o sin CF (3 %), dieron lugar a películas más extensibles y menos resistentes, con mayor capacidad de barrera al oxígeno. Las bolsas monodosis de aceite de girasol con estas películas activas y reforzadas redujeron eficazmente la oxidación. Las películas activas de PLA termoprocesado, con diferentes proporciones (2, 4 y 6 % p/p) del extracto USHT, presentaron color y propiedades mecánicas ligeramente peores, pero con mayor barrera al oxígeno. La cinética de liberación de los antioxidantes incorporados en simulantes alimentarios de diferente polaridad (A: productos acuosos; y D1: sistemas de aceite en agua), mostró que las películas con un 6% de extracto, tuvieron una capacidad antioxidante similar en simulantes con distinta polaridad. Se obtuvieron bicapas biodegradables laminando PLA, con y sin extracto USHT (6 %), y almidón termoplástico, con o sin FC USHT (3 %). Las bicapas mostraron mejor capacidad de barrera global que las monocapas. Sin embargo, la migración de compuestos entre capas dio lugar a películas menos rígidas y resistentes de lo esperado de la contribución del film de PLA. Las bicapas activas y reforzadas alargaron la vida útil de carne de cerdo refrigerada. Las películas de PLA con un 6 % (p/p) de los diferentes extractos (USHT, SWE-160 y SWE-180) presentaron menor resistencia mecánica y capacidad de barrera al vapor de agua, pero una mayor capacidad de barrera al oxígeno y a la luz UV. Además, estas películas, especialmente con el extracto SWE-180, alargaron la vida útil de la carne de cerdo refrigerada. Las FCs obtenidas con los diferentes métodos de purificación también se utilizaron para producir aerogeles de celulosa. Las diferencias composicionales afectaron a la microestructura de los aerogeles. La capacidad de absorción y de retención de agua de los aerogeles estuvo dentro de los rangos descritos para este tipo de materiales. Por tanto, fue posible obtener fracciones valorizadas de la paja de arroz, extractos activos y fibras celulósicas, útiles en el desarrollo de materiales biodegradables activos a base de almidón y PLA. Son necesarios más estudios para validar la seguridad alimentaria de los materiales, así como para el desarrollo de otras aplicaciones en el campo de la industria alimentaria o farmacéutica.[CA] En aquesta tesi doctoral es van obtenir fraccions cel·lulòsiques i extractes actius de palla d' arròs mitjançant l'aplicació de diferents tècniques d'extracció i purificació, utilitzant aigua com a dissolvent. Aquestes fraccions es van incorporar a pel·lícules de midó i PLA, i bicapes de midó-PLA, per obtenir materials d'envasament actius útils per allargar la vida útil de diferents aliments. Els extractes combinant ultrasons i escalfament a reflux (USHT) i amb aigua subcrítica (SWE) (a 160 °C (SWE-160) i 180 °C (SWE-180)) van mostrar un alt contingut fenòlic (37, 51 i 83 mg GAE.g-1 d'extracte sec, respectivament) i activitat antioxidant (6,3, 2,0 i 1,2 mg d'extracte sec.mg-1 DPPH, respectivament). Els extractes SWE van mostrar activitat antibacteriana contra L. innocua i E. coli. Es van aïllar fibres de cel·lulosa (FC) de les fraccions insolubles de l'extracció. Malgrat les lleugeres diferències en el grau de purificació, els nous mètodes van donar lloc a FCs amb rendiments més elevats que el mètode alcalí (35-39 % enfront del 29 %), amb cristal·linitat (60-69 %), comportament tèrmic i relació d'aspecte (20-60) similars. Es van incorporar fibres USHT a l'1, 3 i 5 % (p/p) en pel·lícules de midó de dacsa, i de midó de dacsa modificat per tractament tèrmic. La incorporació al 3 % va donar lloc a pel·lícules amb les millors propietats funcionals. Els extractes actius (al 4, 6 i 8 % en pes) a la matriu de midó, amb o sense CF (3 %), proporcionaren pel·lícules més extensibles i menys resistents, però amb més capacitat de barrera a l'oxigen. Les bosses monodosi de l'oli de gira-sol amb aquestes pel·lícules actives i reforçades van reduir eficaçment l'oxidació. Les pel·lícules actives de PLA amb diferents proporcions (2, 4 i 6 % p/p) de l'extracte USHT, presentaren color i propietats mecániques lleugerament pitjors, però amb major capacitat de barrera a l'oxigen. La cinètica d'alliberament dels antioxidants incorporats, en simulants alimentaris de diferent polaritat (A: productes aquosos; i D1: sistemes d'oli en aigua), va mostrar que les pel·lícules amb un 6% d'extracte, tenien una capacitat antioxidant similar en simulants amb diferent polaritat. Es van obtenir bicapes biodegradables laminant PLA, amb i sense extracte USHT (6 %), i midó termoplàstic, amb o sense FC USHT (3 %). Les bicapes van mostrar millor capacitat de barrera global que les monocapes. No obstant això, la migració de compostos entre capes va donar lloc a pel·lícules menys rígides i resistents respecte a l'esperat de la contribució de la pel·lícula de PLA. Les bicapes actives i reforçades van allargar la vida útil de carn de porc refrigerada. Les pel·lícules de PLA amb un 6 % (p/p) dels diferents extractes (USHT, SWE-160 i SWE-180) van presentar menor resistència mecànica i capacitat de barrera al vapor d'aigua, però una major capacitat de barrera a l'oxigen i a la llum UV. A més, aquestes pel·lícules, especialment amb l'extracte SWE-180, van allargar la vida útil de la carn de porc refrigerada. Les FCs obtingudes amb els diferents mètodes de purificació també es van utilitzar per produir aerogels de cel·lulosa. Les diferències composicionals van afectar la microestructura dels aerogels. La capacitat d' absorció i de retenció d'aigua dels aerogels va estar dins dels rangs descrits per a aquest tipus de materials. Per tant, va ser possible obtenir fraccions valoritzades de la palla d' arròs, extractes actius i fibres cel·lulòsiques, útils en el desenvolupament de materials biodegradables actius a base de midó i PLA. Són necessaris més estudis per validar la seguretat alimentària dels materials, així com per al desenvolupament d' altres aplicacions en el camp de la indústria alimentària o farmacèutica.[EN] This Doctoral thesis focused on obtaining cellulosic fractions and bioactive extracts from rice straw (RS) by applying different extraction and purification techniques, using water as a green solvent. These fractions were incorporated into starch and poly (lactic acid) (PLA)-based films, as well as into starch-PLA bilayers, to obtain active packaging materials useful for extending the shelf life of different food matrices. The extracts obtained by applying a combined ultrasound-reflux heating method (USHT) and subcritical water extraction (SWE) (at 160 °C (SWE-160) and 180 °C (SWE-180)) exhibited high phenolic content (37, 51, 83 mg GAE.g-1 dry extract, respectively) and antioxidant activity (6.3, 2.0, and 1.2 mg dry extract.mg-1 DPPH, respectively). The SWE extracts showed antibacterial activity against L. innocua and E. coli. Cellulose fibres (CF) were isolated from the extraction insoluble fractions and compared with those obtained from the traditional alkaline method. Despite slight differences in the degree of purification, the new methods gave rise to CFs with higher yields than the alkaline method (35-39% vs. 29%), with similar crystallinity (60-69%), thermal behaviour, and aspect ratios. USHT fibres were incorporated into corn starch (1, 3, and 5% wt.), and corn starch-modified by heat treatment, obtained by thermoprocessing. The incorporation of CF at 3% gave rise to films with the best functional properties. When active extracts were incorporated at different ratios (4, 6, and 8% wt.) into the starch matrix, with or without CF (3%), the films were more stretchable and less resistant, but with higher oxygen barrier capacity. Likewise, mono-dose bags of these active and reinforced films effectively reduced the oxidation of packed sunflower oil. Active, plasticised PLA films were produced, incorporating USHT extract (2, 4, and 6% wt.) by thermoprocessing, which exhibited colour and slightly worsened tensile behaviour, but with higher oxygen barrier capacity. The release kinetics of the incorporated antioxidant compounds in food simulants of different polarity (A: aqueous products; and D1: oil-in-water systems) showed that films containing 6% of extract delivered similar antioxidant capacity regardless of the food simulant polarity. Biodegradable bilayers were obtained by laminating plasticised PLA, with and without USHT extract (6%), and thermoplastic starch, with or without USHT CFs (3%). The bilayers exhibited improved overall barrier capacity with respect to the monolayers. However, the interlayer compound migration led to less stiff and resistant films with respect to that expected from the PLA film contribution. The active and reinforced bilayers were able to extend the shelf life of the packed pork meat during cold storage. PLA films with 6% wt. of the different extracts (USHT, SWE-160, and SWE-180) were produced, which exhibited lower mechanical resistance and water vapour barrier capacity, but improved oxygen barrier capacity and intense UV light-blocking effect. Furthermore, the active PLA films, especially with SWE-180 extract, extended the shelf life of cold storage pork meat. The CFs obtained with the different purification methods were also used to produce cellulose aerogels. The differences in the chemical composition of the CFs affected the aerogels' microstructure. The water absorption and retention capacity of the aerogels were within the previously reported ranges for this type of material. Thus, it was possible to obtain valorised fractions of rice straw, active extracts and cellulosic fibres, useful in developing active biodegradable materials based on starch and PLA. Further studies are needed to validate the food safety of the materials, as well as for developing other applications in the food or pharmaceutical industry.The authors thank the Agencia Estatal de Investigación (Spain) for the financial support through projects PID2019-105207RB-I00/AEI/10.13039/501100011033 and Generalitat Valenciana [grant number GrisoliaP/2019/115].Vieira De Freitas, PA. (2022). Valorisation of rice straw by obtaining active compounds and cellulosic materials for the development of biodegradable food packaging systems [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/191380Compendi

    Antimicrobial Peptides Aka Host Defense Peptides – From Basic Research to Therapy

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    This Special Issue reprint will address the most current and innovative developments in the field of HDP research across a range of topics, such as structure and function analysis, modes of action, anti-microbial effects, cell and animal model systems, the discovery of novel host-defense peptides, and drug development

    Duct acoustics for air-coupled ultrasonic phased arrays

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    Air-coupled ultrasound is used in many applications such as range inding, tactile feedback, flow metering or non-destructive testing. The transducers directivity is a crucial acoustic property for all these applications. For instance, a narrow beam width allows for higher angular resolutions, whereas a wider beam width allows for emitting the sound wave in a bigger area for obstacle detection. However, the transducers dimensions influence its directivity and its resonance frequency. In order to decouple the acoustic aperture from transducer, acoustic waveguides are investigated in this work. This way, grating lobe free phased arrays can be built for unambiguous beamforming. In this thesis, the wave propagation inside these waveguides, including coupling mechanisms from the transducer till the free-field, are investigated. First, the state of the art of duct acoustics applications in the audible range and the ultrasound range are presented. Afterwards, different duct acoustics models are derived and compared. Each model is validated for 40 kHz, a duct length of 80 mm and an aperture between 10 mm and 3.4 mm. The challenge of the simulations is to take higher modes into account while reducing the calculation times. Therefore, analytical and numerical models were investigated. As a result, the boundary element method is the most efficient approach for the given geometry wavelength ratio using the commercial software COMSOL Multiphysics. With this method, free-field calculations on a single Xeon E5-2660 v3 CPU and 256 GB RAM without the need of a cluster are possible. The model is validated with calibrated measurements in an anechoic chamber. Therefore, an automated measurement system is established where a calibrated measurement microphone moves relative to the transducer, thus characterizing the sound field in front of the transducer. This setup can measure a hemisphere with a radius of up to 6 m and has a dynamic range of 111 dB. After the validation of the numerical model, waveguide geometry optimizations were conducted. The analyzed properties were: the influence of a perpendicular output and input surface on the wave propagation inside the waveguide; the size of the output aperture; length variations of the waveguide including temperature dependence; the position of tapering and types of losses due to the waveguide. As a result, the perpendicular input is crucial for fundamental mode propagation, otherwise higher modes occur, because the input diameter is bigger compared to the wavelength. The size of the output surface can be increased for line arrays with an SPL gain of +10 dB. However, the limit of the aperture size is 3.7 × λ, otherwise higher modes occur at the output which lead to defocusing of the main lobe. The length of the waveguide can increase the SPL. However, the industrial temperature demands of −25◦C to 75◦C have the same influence on the SPL as the length optimization (±4.8 dB), and, thus, are not investigated in more detail. The positioning of the tapering has just a minor influence of ±0.4 dB. The losses of the waveguide are −10 dB with diffraction loss as the dominant part. The losses inside the waveguide (reflection and thermoviscous losses) could not be validated with measurements due to the narrow bandwidth of the transducers, since the incident and reflected wave superposed. The derived results of the geometry optimization were used to build four line arrays. First, a waveguide with equal length ducts was built as a reference. Second, a Bézier waveguide with plane input surfaces for the transducers was designed. Third, the output aperture was changed from round outputs to rectangular shapes to increase the SPL and sensitivity. Last, a shortened version of the Bézier waveguide was built which has a reduced length of 65%. All four waveguides were simulated using the boundary element method and validated with the measurement etup. As a result, in both simulation and measurement the shorten waveguide has an increased SPL of +5 dB compared to the reference waveguide with equal length ducts. Thus, it is possible to build compact waveguides for air-coupled phased arrays. Next, the influence of different duct lengths in an acoustic waveguide is analyzed in more detail. Using ducts of different length offers more design freedom for the entire waveguide for compact design, easier assembly and reduced assembly time. However, different lengths must be compensated with additional time delays. Therefore, two waveguides were compared. First, an equal length waveguide was used. Second, a waveguide with Bézier-shaped ducts was used. The time delays, due to varying duct lengths, were measured and simulated with analytic and numerical methods. Afterwards, the directivity patterns of both waveguides were compared. As a result, the time compensation has no significant impact on the beam profile regarding side lobe level and half power beam width. In addition, SPL deviation of the waveguides are within the manufacturing tolerances of the transducers. The last aspect investigated in this thesis is the water resistance of the waveguide. Since it is designed for air-coupled ultrasound, it can be clogged due to dirt, dust or liquid. Two commonly known solutions for this issue is the use of hydrophobic fabrics or thin films. Therefore, both solutions were compared. First, these two approaches showed no significant impact on the beamforming capabilities of the phased array. In addition, the IP class of the fabric reached IPX7 and the thin film achieved even IPX8. Furthermore, the fabric has a minor insertion loss of just −1.8 dB. In contrast, the film reduces the SPL by −7.5 dB. This loss can be further reduced with special effort to +0.4 dB by changing the waveguide geometry and tuning the system to the correct resonance frequency. However, this shows that the film has a high temperature dependence compared to the fabric. In conclusion, acoustic waveguides enhance the acoustic properties of ultrasonic sensors. The directivity can be decoupled from the transducer and customized for a certain application
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