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We assess the impact of the fabrication-related variability of the thickness of the effective gap layers on the transmission (TX) and reception (RX) performance of a reverse-fabricated CMUT array by means of finite element analysis (FEA). The extreme values of the thickness of the passivation layers and of the cavity height, obtained by interferometry measurements during in-line wafer inspection, are applied to the simulated design of a reverse-fabricated CMUT array of circular cells. The analysis follows a 2-by-2 factorial approach to evaluate the variability of the TX and RX sensitivity amplitude, phase, and bandwidth caused by the fabrication tolerances, and compute the main effects and interactions of the effective gap layers.

This work reports on the investigation of the element beam pattern of a 2D CMUT spiral array by finite element analysis, aiming at assessing the effect of the transducer integration with the ASIC on the fluid-coupled transmission performance. The array element acoustic directivity is computed for the clamped substrate condition and compared with that obtained by coupling the transducer with a Benzocyclobutene (BCB) layer, used as an underfill between the CMUT and the ASIC. Different packaging solutions are considered and their effect on the element directivity is compared. The CMUT spiral array element is experimentally characterized in water-coupled transmission operation using a hydrophone to validate the finite element simulation.

The progress of technology and science has enabled new tools for the diagnosis and treatment of diseases based on electromagnetic (EM) fields. Radiofrequency (RF) EM fields also find application in aesthetic medicine treatments, e.g. for the removal of stretch marks and scars. The employment of EM fields in such treatments is regulated by national and supranational legislation, which limit the Specific Absorption Rate (SAR) below 0.4 W/kg and the temperature increase below 1°C. In this paper we propose the design and fabrication of a 3D printed carbon-based phantom, highly customizable, which mimics the thermal and electrical properties of the three layers of the skin and the abdominal muscle to measure the heating induced by electro-medical fields. The phantom was fabricated by means of Fused Deposition Modeling (FDM) 3D printing technique of nanocomposites. The used filaments are made of PLA filled with different concentrations of Graphene Nano-Platelets (GNPs) and Carbon Nanotubes (CNTs), designed to tune the thermal and electrical conductivity of the deposited layers according to the skin and muscle layers properties. Each layer has holes at different depths to allow inserting thermocouples for the measurement of the heating induced by electro-medical fields. The phantom has a cylindrical shape with a diameter of 120mm and a total thickness of 44.25 mm, for a total weight of 577.36 g, so it is compact and handy. This work paves the way to the development of reliable phantoms of human tissues by means of innovative materials for the thorough investigation of the EM fields effect on human bodies.

The interest in graphene-based electronics is due to graphene’s great carrier mobility, atomic thickness, resistance to radiation, and tolerance to extreme temperatures. These characteristics enable the development of extremely miniaturized high-performing electronic devices for next-generation radiofrequency (RF) communication systems. The main building block of graphene-based electronics is the graphene-field effect transistor (GFET). An important issue hindering the diffusion of GFET-based circuits on a commercial level is the repeatability of the fabrication process, which affects the uncertainty of both the device geometry and the graphene quality. Concerning the GFET geometrical parameters, it is well known that the channel length is the main factor that determines the high-frequency limitations of a field-effect transistor, and is therefore the parameter that should be better controlled during the fabrication. Nevertheless, other parameters are affected by a fabrication-related tolerance, to understand to which extent an increase of the accuracy of the GFET layout patterning process steps can improve the performance uniformity, their impact on the GFET performance variability should be considered and compared to that of the channel length. In this work, we assess the impact of the fabrication-related tolerances of GFET-base amplifier geometrical parameters on the RF performance, in terms of the amplifier transit frequency and maximum oscillation frequency, by using a design-of-experiments approach.

As CMUT technology moves towards the industrial phase, the robustness of the fabrication process becomes a key aspect to produce reliable and well-performing devices. CMUT arrays typically show a variability of the electromechanical and acoustic behavior among the transducer elements, which is mainly ascribed to tolerances of process-related parameters. This paper investigates the impact of process-related parameters variability on the performance of CMUT arrays, by proposing a local sensitivity analysis technique performed according to a Design of Experiments (DoE) approach based on Vertex Analysis. The sensitivity analysis is performed by simulating a Reverse-Fabricated CMUT using Finite Element Modeling (FEM), and computing the CMUT electromechanical parameters by varying the thicknesses of the front membrane layer, of the top and bottom passivation layers and of the sacrificial layer within a 10% tolerance range around the nominal set of values. The sensitivity analysis results are then compared to the variability observed in the data obtained characterizing a 256-element Reverse-Fabricated CMUT linear array for medical imaging.

In this paper, first experimental results obtained on a new resonant humidity sensor are presented. The resonant sensor is made of a piezoelectric material coated with a hygroscopic material, therefore able to adsorb the water molecules contained in the surrounding air. The adsorbed water increases the sensitive layer mass, thus varying the sensor resonance frequency. The sensor is included in an electronic oscillator that tunes its oscillating frequency with the sensor resonance frequency. The output voltage signal is sampled and processed by a microcontroller in order to measure the resonance frequency. By relating the device resonance frequency to the amount of water adsorbed by the polymeric layer, an accurate air humidity measurement can be obtained.

When Capacitive Micromachined Ultrasonic Transducers (CMUTs) are coupled with water, they show high front-face acoustic reflectivity, due to the impedance mismatch between the transducer substrate material, typically based on silicon, and the propagation medium. During pulse-echo operation, surface reflectivity is responsible for multiple reflections of the received acoustic signals, which result in a set of unwanted echoes. In ultrasound imaging applications, this signal reverberation creates artifacts and reduces the image contrast. In this paper, a method to reduce front-face reflectivity is proposed, and a Reverberation Level (RL) index is introduced in order to quantify the unwanted reverberation of the signal returned to the transducer surface. The proposed method combines the increase of the bias voltage, the application of an optimized resistive load and the addition of a low-impedance acoustic backing to CMUTs realized by Reverse Fabrication Process (RFP). In this way, the mechanical energy conversion and transmission to the backing, as well as the electrical energy dissipation, are improved, thus reducing the energy reflection into the medium. The proposed method is analyzed by means of Finite Element simulations and is experimentally validated by characterizing single-element RFP-CMUTs, provided with different backing materials and electrical loads. In the analyzed prototypes, a RL reduction of 8.6 dB is obtained.

Liquids density measurements are highly required in both research and industrial applications, from process control in petrochemical industry to product monitoring in food processing. Commercial devices are often expensive or unwieldy; therefore, in a previous work, a cheap and handy resonant sensor, based on a piezoelectric bimorph, was introduced. The operating principle is based on the variation of the device electrical impedance, due to the liquid mass. By fixing the liquid volume, the frequency variation can therefore be related to the liquid density. The maximum sensitivity of the device was obtained when the resonance frequency was higher. In this paper, two piezoelectric bimorphs with smaller diameter, and therefore resonating at higher frequencies, were considered as active elements and analyzed by means of a FEM commercial code, in order to maximize the device sensitivity, varying the liquid height. Finally, the sensitivity was computed, by using the height with the best sensitivity, and varying the liquid density. Best results were obtained by using the smallest diameter bimorph. First experimental measurements confirmed simulation results.

Due to the widespread use of portable devices, there is a strong focus on possible methods of interaction between man and the device, in order to exchange information. Capacitive touchscreens are commonly used on the front of smartphones or tablets; nevertheless, for some applications it can be useful to have a pointing solution on the back of the device, so that fingers do not cover the visible area. The solution proposed in this paper is to turn the plastic back cover of the device into a position encoder, by gluing some piezoelectric small plates, electrically connected in parallel, on its inner surface. Moving the finger on the back cover causes a variation of the electrical impedance of the structure, thus the desired position can be revealed and reported on the front screen. In this work, the performances of a trackpad based on piezoelectric elements are investigated by Finite Elements Analysis, and an automatic method for the recognition of the finger position is proposed. Experimental tests were also conducted on a prototype, in order to confirm the capabilities of the proposed device.

Front-face acoustic reflectivity of ultrasonic imaging transducers, due to acoustic impedance mismatch with the propagation medium, may cause reverberation phenomena during wideband pulse-echo operation. Front-face reflectivity may be reduced by promoting the transmission of the echoes, received from the medium, to the transducer backing, and by maximizing the mechanical-to-electrical energy conversion and dissipation by tuning the electrical load impedance connected to the transducer. In Capacitive Micromachined Ultrasonic Transducers (CMUTs), the energy transfer from the medium to the backing is very low due to the large impedance mismatch between the medium and the transducer substrate, typically made of silicon. Reverse Fabrication Process (RFP) makes it possible providing CMUTs with custom substrate materials, thus eliminating the original silicon microfabrication support. In this paper, we propose two methods for the front-face reflectivity reduction in RFP-CMUTs: the first one is based on the use of low-impedance, highly attenuating backing materials, and the second one is based on the maximization of the mechanoelectrical energy conversion and dissipation. We analyze the methods by finite element simulations and experimentally validate the obtained results by fabricating and characterizing single-element RFP-CMUTs provided with different backing materials and electrical loads.

Density is a characteristic property of a substance related to its mass and its volume. On-line density sensors play an important role in several industrial applications, for example in the monitoring of liquid products. In this work a resonant sensor to measure the density of liquids is proposed. The sensor active element is a piezoelectric bimorph, extensively used in buzzers and telephone receivers. The border of the bimorph is clamped into a steel structure, designed to realize the open chamber into which the liquid is poured. By fixing the volume of the chamber, the volume of the liquid is also fixed; thus, the variation of the resonance and anti-resonance frequencies of the bimorph, due to the mass of the liquid sample, can be related to its density. In the paper, the dimensions of the chamber are optimized by means of a Finite Element Analysis performed by ANSYS ® in order to maximize the device sensitivity.

We report the performance of a graphene-enhanced THz grating fabricated by depositing a gold layer on the femtosecond micromachined SiO2 substrate. The morphology of the gold plated patterned substrate was studied by scanning electron microscopy (SEM) and atomic force microscopy (AFM), while the quality of the chemical vapor deposition (CVD) graphene was evaluated by Raman spectroscopy. The electromagnetic (EM) response of the metasurface comprising the graphene sheet and the gold plated substrate was studied by THz time domain spectroscopy in the 100 GHz–1 THz frequency range. We employed the finite elements method (FEM) to model the metasurface EM response by adjusting the ac conductivity of the gold layer covering the patterned SiO2 substrate to reproduce the measured transmission/reflection spectra. The results of the numerical simulation reveal the impact of the imperfectness of the gold layer on the performance of the THz metasurface. The experimental results are well described in terms of the Drude–Smith model of metal conductivity that takes into account the anisotropic scattering of the carriers in thin metal films.