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Inkjet printing has proven to be a promising alternative method in the fabrication of printed electronics, besides screen printing and photolithography etching. In this work, we characterize the electrical performance of inkjet printed circuits on flexible PET and glossy photo paper. The electrical circuits were printed using a commercial Epson L310 piezoelectric printer, and the NB series silver ink and chemical-sintering PET substrate from Mitsubishi Paper Mills. This method allows rapid prototyping of electronic circuits (~ 30 min design, ~ 5 s fabrication) and quick iteration of prototypes. The system has a resolution of 250 µm electrodes and 300 µm electrical gaps, and on average, 1.5 ± 0.2 µm in thickness. The effect of printing on different substrates, geometry and overprinting on sheet resistance was also studied. It was found that double printing produced better electrodes with lower resistances. A stable conducting circuit has a sheet resistivity of

The increased demand for highly sensitive body sensors have created a range of smart wearables. Strain sensors have evolved from semi-rigid to highly, stretchable, and flexible devices that can conform to the human skin. In contrast to complex conventional fabrication methods, this paper proposes a simple and cost-effective technique that combines stencil printing with kirigami cutting to produce flexible, stretchable, linear, disposable sensors using temporary tattoo paper and conductive carbon paste. Here, two sensor designs (straight line and serpentine) were fabricated and analyzed. The number of carbon-ink coatings were also varied to study the effect of number of coating layers to the sensitivities of the sensor. A total of117 samples were fabricated and tested. When tested on skin, the maximum strain that could be measured was 20% for the straight-line patterned sensors and 35% for the Kirigami structured sensors. Both designs demonstrated good adhesion to skin, are stretchable, and flexible. The best performing designs with the most reliable data were straight-line type sensor with width 9 mm and three-layer carbon ink coatings, and Kirigami sensor with width 8 mm and two-layer coatings of carbon ink. Both sensors exhibited high linearity of 0.9956 and 0.9813, but low sensitivities of 0.25 and 0.28. These sensors have potential applications in the biomedical field.

In this paper, a series-fed milimeter-wave microstrip patch antenna array operating at 28 GHz is presented for wearable radio-frequency (RF) energy harvesting applications. The antenna array is made of 4×4 rectangular microstrip elements on a polyethylene terephthalate (PET) substrate to provide conformability when directly attached on human body parts. A 4-way Wilkinson power divider is connected to the array for RF power combining. The overall size of the antenna is 47×28×0.25 mm. The halfpower beamwidth (HPBW) of the antenna array can be increased up to 151.9 via structural deformation making it suitable for energy harvesting applications. The performance of the antenna array is investigated in terms of impedance matching, gain and radiation pattern. The average simulated specific absorption rate (SAR) of the antenna is 0.52 W/kg which is well below the safety limit of 1.6 W/kg averaged over 1 g of tissue for 100 mW of input power. ⁰

This paper presents a wideband distributed coplanar waveguide (CPW) phase shifter for S-band operation. A 3-bit distributed MEMS transmission line (DMTL) phase shifter is developed by periodically loading MEMS shunt switches on a CPW transmission line (TL). A total of 105 MEMS shunt switches are utilized in the design to provide phase shifts of 0°, 45°, 90°, 135°, 180°, 225°, 270° and 315° at 2.45 GHz. Two large metal-insulator-metal (MIM) capacitors are implemented on the CPW centre conductor as DC blocking capacitors to separate the DC actuation voltage between three bit segments during operation. The high resistivity silicon substrate (ρ=10 Ω·cm) and 2 μm thick aluminium centre conductor are employed to reduce the insertion loss due to the transmission line (TL). The simulated reflection coefficients are better than −10 dB across the operating band with an average insertion loss of −2.94 dB at 2.45 GHz. The CPW transmission line has been meandered using 60° mitered bends to optimise the size of the phase shifter to result in overall size of 30 mm × 10 mm. The simulated pull-in voltage of the doubly clamped beams implemented in the design is 17.18 V. The proposed DMTL phase shifter is suitable for use in smart antenna applications, radar systems and ultra-wideband (UWB) microwave medical applications.

This paper presents the design and simulation of a 5-bit RF MEMS digital variable capacitor with high capacitance ratio (Cr) of 43 using SU-8 material. The proposed design implements five capacitive shunt switches over a coplanar waveguide (CPW) line. A novel horizontal truss fixed-fixed beam design is proposed to achieve RF power handling up to 2.2W. The simulated pull in and lift off voltages are 24.3V and 16V respectively. The contact area of the capacitor between the beams and the CPW line are varied in a binary configuration to realise 32 capacitance steps ranging from 84.5fF to 3.68pF (Cr=43). In order to increase the capacitance ratio of the varactor, SU-8 polymer has been utilised to form the base structure of the capacitor due to its low dielectric constant (er=4) hence reducing the overall minimum capacitance (Cmin). Moreover, the inclusion of semi-elliptical slot at the ground of CPW and variable sizes of CPW line further reduce the parasitic capacitance. To improve the reliability of the proposed variable capacitor design, a new Aluminium (Al) stopper design is employed to prevent contact between the beams and pulldown electrodes. A 2µm thick Aluminium layer is implemented as a CPW. Aluminum is also used to implement a 2µm beam structure to improve the Q-factor. A 0.25µm of silicon nitride (Si3N4) is used as the dielectric layer. The overall size of the varactor is 740µm × 653µm.

This paper presents the design and simulation of a 4-bit digital MEMS varactor with high capacitance ratio. The proposed varactor design consists of four beams over a co-planar waveguide (CPW) line. A new truss beam design is proposed in order to reduce the spring constant of conventional solid beam structure which results in pull-in voltage of 24.3V making it suitable for low loss phase shifters and tunable filters. A linear capacitance step is realized by varying the contact area between the CPW line and the beam based on binary weighted bit design. The width and the length of each beam is fixed to 50 μm and 550 μm respectively to ensure similar pull-in voltage for all beams. To improve the reliability of the design in terms of dielectric charging, side pull-down electrode and a new stopper design is introduced. The existence of the stopper would prevent a direct contact between the beams and the pull-down electrode. A high capacitance ratio of 35.7 is achieved through the implementation of a deep trench of 26.35 μm on the silicon substrate which decreases the parasitic and fringing field capacitance. 16 different capacitance states ranging from 95 fF to 3.4 pF are realised. The overall size of the varactor is 740 μm × 603 μm. The CPW line and the beams are made from 2 μm thick aluminium, while 0.25 μm thick silicon nitride is used as the dielectric layer. The mechanical simulation of the design is carried out using Coventorware 2008, while the characterization of the RF performance is conducted using CST Microwave Studio.

Surface Acoustic Wave (SAW) resonators are essential components for modern communication systems. They can function as filters and frequency synthesizers. SAW resonators operate based on the principle of acoustic waves propagating along the surface of a solid piezoelectric material. The waves are generated by injecting electrical energy using interdigitated transducers (IDTs) into the piezoelectric material which transforms it into propagating mechanical waves. This project intends to study the key design parameters that affect the performance of SAW resonator such as optimum spacing between IDT and reflector, optimum spacing of IDTs and the numbers of reflector in order to get the highest mechanical displacement. Key requirements of a SAW resonator include having precise resonant frequency (f r ), low insertion losses, and high quality factors (Q). To meet these requirements, it is necessary to investigate the key design parameters; number of reflectors, number of IDTs, periodic distance of transducer fingers (λ), spacing between IDT and reflector. Finite element simulations to determine the optimum SAW resonator design was performed using COMSOL Multiphysics™.

Surface Acoustic Wave (SAW) resonators are essential components in communication devices and are used mainly as oscillators, frequency synthesizers and transceivers. Common piezoelectric substrates are quartz, Lithium Tantalate (LiTaO 3 ) and Lithium Niobate (LiNbO 3 ). In this paper we describe the design and fabrication of SAW resonators on LiNbO 3 . The design of the SAW resonators was simulated using COMSOL MultiphysicsTM. Two SAW resonators with resonance frequency of 218MHz with varying number of reflectors were fabricated and measured. Measurements conducted using an RF Probe station and network analyzer yielded losses of −48.3dB and −49.32dB for Resonator 1 and Resonator 2 respectively.

This paper presents the design, simulation and analysis of a 5-bit RF MEMS digital variable capacitor using thick SU-8 polymer to achieve both high capacitance ratio ( $$\varvec{C}_{\varvec{r}}$$ ) and Q-factor. The proposed varactor design consists of five capacitive shunt switches loaded over a co-planar waveguide (CPW) line. This results 32 capacitance steps ranging from 102.23 fF to 3.57 pF ( $$\varvec{C}_{\varvec{r}}$$ = 35). The high capacitance ratio of the varactor is achieved by implementing SU-8 polymer as the base structure of the capacitor due to its low dielectric constant ( $$\varvec{\varepsilon}_{\varvec{r}}$$ = 4) hence reducing the overall minimum capacitance ( $$\varvec{C}_{{\varvec{min}}}$$ ). The optimization of the SU-8 thickness has been carried out to get the optimum capacitance ratio and Q-factor. Moreover, the inclusion of semi-elliptical slot at the ground of CPW and variable sizes of CPW line further reduce the parasitic capacitance. To improve the reliability of the variable capacitor design, a new aluminium (Al) stopper design is used to prevent contact between the beams and the pull-down electrodes. Mechanical simulations and analysis have been carried out to investigate the effects of in-plane residual stress and stress gradient on the spring constant and the initial displacement of the proposed horizontal truss fixed–fixed beam structure. Compared to the conventional doubly clamped solid beam design, the proposed beam has less sensitivity to in-plane residual stress. This makes the pull in voltage to be less affected by the stress due to the fabrication. The simulated pull-in and lift-off voltages are 30 and 25 V respectively while the estimated switching time for the beam is 4.64 μs. The overall size of the varactor is 740 μm × 653 μm. The proposed RF MEMS varactor could be integrated in reconfigurable filters, phase shifters and matching networks targeting future multi-standard wireless communication systems.