Mid Sweden University

A novel dual-band circularly polarized MIMO wearable antenna is screen-printed on a cotton polyester fabric to operate at 2.45 and 5.8 GHz wireless body area network communications. The MIMO fabric antenna is realized with two circularly polarized wearable antennas arranged in orthogonal directions, which provides a less than -10 dB bandwidth of 400 MHz from 2.2 to 2.6 GHz and 800 MHz from 5.3 to 6.1 GHz, with impedance bandwidth of 17 and 14% for lower and higher bands, respectively. The antenna provides an axial ratio bandwidth (below 3 dB) of 3% from 2.4 to 2.47 GHz and 8% from 5.45 to 5.94 GHz. The proposed MIMO antenna is integrated with an artificial magnetic conductor, which helps to create isolation between the human body and antenna, which also minimizes the specific absorption rate (SAR). The antenna SAR performance is tested on the HUGO model, which gives 0.025, 0.035 W/Kg for 1g tissue at 2.45 and 5.8 GHz. Furthermore, the antenna provides good MIMO characteristics such as envelope correlation coefficient, diversity gain, and channel capacity. The antenna is suitable for flexible wearable applications due to fabric substrate, screen printing, low SAR, and lightweight. 

A wearable dual-band dual-polarized fabric antenna is screen printed on a cotton polyester substrate to operate at the industrial scientific and medical band at 2.45 GHz and wireless local area network at 5.2 GHz. A rectangular slot with a pair of L-shaped branches are used to excite dual bands. The rectangular slot is used to achieve lower band resonance at 2.45 GHz with linear polarization, and an L-shaped branch with a stub is used to obtain the circular polarization at 5.2 GHz. A 3 × 3 electromagnetic bandgap (EBG) structure is enabled behind the antenna to minimize the back radiation and specific absorption rate (SAR). The antenna provides a measured impedance bandwidth (BW) of 25% from 2.1 to 2.7 GHz (600 MHz), and 18% from 4.5 to 5.7 GHz (1.2 GHz), respectively. The antenna also has a 3-dB axial ratio BW of 15% from 4.6 to 5.35 GHz (750 MHz). The antenna exhibits a measured gain of 5.1 dB at 5.2 GHz and 6.4 dB at 2.45 GHz. The SAR is validated by using a CST (computer simulation technology) voxel human body model and found to be 0.0949 and 0.127 W/kg for 1 g tissue at 5.2 and 2.45 GHz, respectively. The dimension of the proposed EBG integrated antenna is (0.52 λ × 0.52 λ × 0.07 λ). The antenna and EBG structure are screen printed with silver conductive ink, which provides good conductivity, conformability, comfort, wearability, and being lightweight. 

I dagens samhälle blir det allt viktigare att fortbilda sig under hela sitt yrkesverksamma liv. För att möta efterfrågan på det livslånga lärandet har Mittuniversitetet utvecklat och genomfört ett antal kurser som riktar sig mot yrkesverksamma ingenjörer. Detta arbete presenterar våra erfarenheter av att ge dessa kurser, med en tyngdpunkt på studenternas upplevelser. Syftet med detta är att bygga upp en vetenskaplig bas för vad vi gör som är bra, men även vad som kan förbättras och förändras. Målsättningen är att göra dessa specialanpassade kurser riktade mot yrkesverksamma ingenjörer så givande och flexibla som möjligt. Våra initiala resultat visar bland annat att studenternas negativa upplevelser ofta var kopplade till antagningsförfarandet och det praktiska genomförandet av kurserna. Man hade svårigheter med att hitta hur man skulle registrera sig på kursen och att tidsramen för registrering kunde vara ett problem. Läroplattformen uppfattades som svår att överblicka och det förekom även viss otydlighet gällande var undervisningen skulle äga rum. Den positiva responsen i utvärderingarna gällde främst det faktiska kursinnehållet, då man ansåg att uppgifter och kursmaterial var givande. Vidare uppskattades kursupplägget, att man kunde kombinera studierna med arbete. Framledes kommer vi att fortsätta med dessa utvärderingar i takt med att kurserna ges, och därefter anpassa vårt mottagande och kommunikationen med studenterna. Även kursupplägget ses över kontinuerligt via den återkoppling vi mottar. 

A design scheme for embedding a chipless radio frequency identification (RFID) tag in a quick response (QR) code is proposed and demonstrated. By searching for QR modules that can be metalized to form a loop resonator in the edge area and to load the loop in the central area, the chipless RFID tag with an optimized loaded-loop resonator can be designed in the QR code. A specific loop genetic operator is proposed for optimization searching. The optimized loaded-loop resonator has a sharp dominant resonant peak at frequency as low as possible and a harmonic resonant peak at frequency as high as possible, which provides large space for data encoding of chipless RFID. By removing or demetalizing the metalized loading modules, the resonant frequency can be tuned conveniently for frequency shift keying (FSK) coding. For demonstration, the chipless RFID tag embedded in the QR code is designed and tested. It is shown that the RFID tag allows at least nine distinct resonant frequencies for simple FSK coding, which indicates a coding capacity of 3.17 bits and a normalization coding density of approximately 501.78 bits/ $\lambda _{\mathrm {g}}^{2}$ /GHz for the chipless RFID tag embedded in the QR code. 

This paper presents a posture recognition system aimed at detecting sitting postures of a wheelchair user. The main goals of the proposed system are to identify and inform irregular and improper posture to prevent sitting-related health issues such as pressure ulcers, with the potential that it could also be used for individuals without mobility issues. In the proposed monitoring system, an array of 16 screen printed pressure sensor units was employed to obtain pressure data, which are sampled and processed in real-time using read-out electronics. The posture recognition was performed for four sitting positions: right-, left-, forward- and backward leaning based on k-nearest neighbors (k-NN), support vector machines (SVM), random forest (RF), decision tree (DT) and LightGBM machine learning algorithms. As a result, a posture classification accuracy of up to 99.03 percent can be achieved. Experimental studies illustrate that the system can provide real-time pressure distribution value in the form of a pressure map on a standard PC and also on a raspberry pi system equipped with a touchscreen monitor. The stored pressure distribution data can later be shared with healthcare professionals so that abnormalities in sitting patterns can be identified by employing a post-processing unit. The proposed system could be used for risk assessments related to pressure ulcers. It may be served as a benchmark by recording and identifying individuals’ sitting patterns and the possibility of being realized as a lightweight portable health monitoring device.

Optical fiber microducts are joined together by mechanical joints. These mechanical joints are bulky, require more space per joint, and are prone to air pressure leakage and water seepage during service. A battery powered electrofusion welding system with a resistive-type joint has been recently developed to replace mechanical joints. These resistive-type electrofusion joints require physical connectors for power input. Due to a different installation environment, the power input connectors of resistive optical fiber microduct joints may corrode over time. This corrosion of connectors will eventually cause water seepage or air pressure leakage in the long run. Moreover, due to connector corrosion, resistive-type optical fiber microduct joints cannot be re-heated in future if the need arises. In this study, an inductively coupled electrofusion-type joint was proposed and investigated. This inductive-type electrofusion joint is not prone to long-term corrosion risk, due to the absence of power connectors. Inductive-type electrofusion joints can be re-heated again for resealing or removal in the long run, as no metal part is exposed to the environment. The battery powered inductive welding system can be easily powered with a 38 volts 160 watt-hour battery. The inductive-type electrofusion joint was welded within one second, and passed a 300-newton pull strength test and a 10-bar air pressure leakage test. It was demonstrated that the power input requirement for inductive electrofusion joints is 64% higher than that of resistive electrofusion joints. However, these inductive joints are relatively easy to manufacture, inexpensive, have no air leakage, and no water seepage risk in highly corrosive environments. 

Automatic design of planar directional coupler can be implemented by multi-objective optimization searching for the optimal planar fragment-type structure (FTS). The 2-bit FTS description scheme may include necessary fine structures in fragments to enhance the FTS design. By coding the coupler design space on PCB in 2-bit FTS, defining the FTS design matrix, and searching for the optimal structure, directional coupler can be designed without any structure presetting or artificial intervention. The scheme is demonstrated by designing 10-dB wideband directional coupler with 2-bit FTS scheme. The designed directional couplers are fabricated and tested to show maximum directivity of 58 dB with 36% operation bandwidth. 

A novel Monte Carlo‐based indoor radio‐frequency identification (RFID) positioning scheme is proposed for dual‐antenna RFID systems with the cooperation of dual‐antenna joint rec-tification. By deploying reference passive RFID tags on the ground to establish an RFID tag‐based map, indoor self‐positioning of a moving platform carrying an RFID reader with two forward‐look-ing antennas can be simply implemented by looking up the positions of responded RFID tags at each time step of movement, and estimating the platform position by using the proposed Monte Carlo‐based algorithm. To improve the positioning accuracy of Monte Carlo‐based positioning, each antenna channel, with its own footprint on the ground, may rectify its position estimation by using the tag position information interrogated by the other antenna channel. The algorithm for dual-antenna rectification is proposed. The performance of the proposed Monte Carlo‐based self‐posi-tioning scheme is demonstrated by both simulation and experiment tests. Some factors in a practical indoor‐positioning system, such as the reference tag distribution pattern, reader antenna footprint size, and footprint overlap, are discussed. Some guide rules for deploying the RFID indoor‐posi-tioning system are also reported. 

The development of wearable health devices is an emerging technology, and pressure sensors have been widely used in several of these applications. Plenty of research within pressure sensors is focused on tactile sensing and artificial skin. In this paper, a highly flexible and stretchable pressure sensor is presented. The sensor comprises stretchable thermoplastic polyurethane (TPU) film as substrate and stretchable conductive inks as electrodes and sensing material. Screen printing is used to fabricate electrodes and pressure sensing components on TPU sheets. Electrical and mechanical properties of the fabricated sensors indicate good mechanical and electrical stability while retaining pressure sensing properties and marginal deterioration even after 100 elongation cycles. The findings show that the presented stretchable pressure sensor has a great potential for usage on surfaces where bending and stretching will occur while retaining nearly all of its electrical and mechanical capabilities. The proposed sensor may be employed as a wearable device to detect human movements.

At present, optical fiber microducts are coupled together by mechanical types of joints. Mechanical joints are thick, require a large space, and reduce the installation distance in multi-microduct installation. They may leak or explode in the blown fiber installation process. Mechanical joints are subjected to time dependent deterioration under long service times beneath the earth's surface. It may start with a small leakage, followed by damage due to water freezing inside the optical fiber microduct. Optical fiber microducts are made up of high-density polyethylene, which is considered most suitable for thermoelectric welding. For thermoelectric welding of two optical fiber microducts, the welding time should be one second, and should not cause any damage to the inner structure of the microducts that are being coupled. To fulfill these requirements, an LTspice simulation model for the welding system was developed and validated. The developed LTspice model has two parts. The first part models the power input to joule heating wire and the second part models the heat propagation inside the different layers of the optical fiber microduct and surrounding joint by using electro-thermal analogy. In order to validate the simulation results, a battery powered prototype welding system was developed and tested. The prototype welding system consists of a custom-built electrofusion joint and a controller board. A 40 volt 4 ampere-hour Li-Ion battery was used to power the complete system. The power drawn from the battery was controlled by charging and discharging of a capacitor bank, which makes sure that the battery is not overloaded. After successful welding, a pull strength test and an air pressure leakage test were performed to ensure that the welded joints met the requirements set by the mechanical joints. The results show that this new kind of joint and welding system can effectively replace mechanical joints in future optical fiber duct installations.