Evidence of surface loss as ubiquitous limiting damping mechanism in SiN micro- and nanomechanical resonators

Silicon nitride (SiN) micro- and nanomechanical resonators have attracted a lot of attention in various research fields due to their exceptionally high quality factors ($Q$s). Despite their popularity, the origin of the limiting loss mechanisms in these structures has remained controversial. In this paper we propose an analytical model combining acoustic radiation loss with intrinsic loss. The model accurately predicts the resulting mode-dependent $Q$s of a low-stress silicon-rich and a high-stress stoichiometric SiN membrane. The large acoustic mismatch of the low-stress membrane to the substrate seems to minimize radiation loss and $Q$s of higher modes ($n \wedge m \geq 3$) are limited by intrinsic losses. The study of these intrinsic losses in low-stress membranes with varying lengths $L$ and thicknesses $h$ reveals an inverse linear dependence of the intrinsic loss with $h$ for thin resonators independent of $L$. This finding was confirmed by comparing the intrinsic dissipation of arbitrary (membranes, strings, and cantilevers) SiN resonators extracted from literature, suggesting surface loss as ubiquitous damping mechanism in thin SiN resonators with $Q_{surf} = \beta \cdot h$ and $\beta = 6\times10^{10} \pm4\times 10^{10}$~m$^{-1}$. Based on the intrinsic loss the maximal achievable $Q$s and $Q\cdot f$ products for SiN membranes and strings are outlined

Shape Memory Polymer Resonators as Highly Sensitive Uncooled Infrared Detectors

Uncooled InfraRed (IR) detectors have enabled the rapid growth of thermal imaging applications. These detectors are predominantly bolometers, where the heating of pixel from incoming IR radiation is read out as a resistance change. Another uncooled sensing method is to transduce the IR radiation into the frequency shift of a mechanical resonator. We present here a highly sensitive, simple to fabricate resonant IR sensor, based on thermo-responsive Shape Memory Polymers (SMPs). By exploiting the phase-change polymer as the transduction mechanism, our approach provides 2 orders of magnitude improvement of the temperature coefficient of frequency (TCF). The SMP has very good absorption in IR wavelengths, obviating the need for an absorber layer. A Noise Equivalent Temperature Difference (NETD) of 22 mK in vacuum and 112 mK in air are obtained using f/2 optics. Such high performance in air eliminates the need for vacuum packaging, paving a path towards flexible IR sensors

Frequency fluctuations in nanomechanical silicon nitride string resonators

High quality factor ($Q$) nanomechanical resonators have received a lot of attention for sensor applications with unprecedented sensitivity. Despite the large interest, few investigations into the frequency stability of high-$Q$ resonators have been reported. Such resonators are characterized by a linewidth significantly smaller than typically employed measurement bandwidths, which is the opposite regime to what is normally considered for sensors. Here, the frequency stability of high-$Q$ silicon nitride string resonators is investigated both in open-loop and closed-loop configurations. The stability is here characterized using the Allan deviation. For open-loop tracking, it is found that the Allan deviation gets separated into two regimes, one limited by the thermomechanical noise of the resonator and the other by the detection noise of the optical transduction system. The point of transition between the two regimes is the resonator response time, which can be shown to have a linear dependence on $Q$. Laser power fluctuations from the optical readout is found to present a fundamental limit to the frequency stability. Finally, for closed-loop measurements, the response time is shown to no longer be intrinsically limited but instead given by the bandwidth of the closed-loop tracking system. Computed Allan deviations based on theory are given as well and found to agree well with the measurements. These results are of importance for the understanding of fundamental limitations of high-$Q$ resonators and their application as high performance sensors.Comment: 8 pages, 6 figure

Factors determining the persistence of campesino corn farming: The case municipality of Libres, Puebla

The most important economic activity in the municipality of Libres Puebla, in terms of harvested area and production value, is the corn production. This activity is characterized by plots of less than two hectares, low application of modern inputs and rain-fed production. Even though these production systems faced adverse technical, political and market conditions in the last two decades, the production of white corn is sustained by small scale campesino farming systems, combining sustainable traditional practices including a multicrop systems, conservation and use of landrace corn seed,family labor, and use of income from non-agricultural activities to finance agriculture. In most cases, production economic costs are higher than economic benefits, but including social benefits, such as food security objectives and campesino preferences; total benefits overcome economic production costs

Pd-functionalized MEMS resonator for hydrogen gas sensing

This work presents the fabrication and characterization of a novel hydrogen-detecting micro-resonator based on the expansion of palladium (Pd) as it is exposed to hydrogen (H2) gas. The working principle of the device has been confirmed and it shows a stronger response at a given H2 partial pressure than what theory predicts using bulk Pd material parameters. This may be explained by properties that are specific for Pd thin films in the nanometre range. The results suggest that the presence of very dilute amounts of hydrogen gas could be detected and the dynamic range of the device could be greatly increased if the device is optimized further

Social impact and health prevention, case of a hamlet of green pampas, Ucayali región, Peru

La investigación muestra la evaluación del impacto social en la prevención de la salud que ha generado el proyecto de Instalación de agua potable y saneamiento en el caserío de Pampas Verdes en el distrito de Campo Verde, provincia de Coronel Portillo, Región Ucayali, Perú, ubicado en una zona rural de la amazonia del Perú, en la cual participaron los 126 pobladores. Se realizaron censos en la población casa por casa, encuestas y entrevistas para lograr medir el impacto social, observándose grandes expectativas en la población y satisfacción al tener baños en sus casas denominados Unidades Básicas de Saneamiento (UBS), evidenciándose que se está alcanzando el logro de los objetivos a corto y largo plazo, así se tiene, acceso permanente al agua potable con saneamiento y la población tiene mayor conciencia de la importancia del consumo de agua potable, higiene personal, lavado de manos y una reducción importante en las enfermedades diarreicas agudas y otras, el proyecto para lograr sus objetivos ha contado con un componente técnico y un componente social, el componente social a través del gestor social ha implementado talleres y capacitaciones con la población logrando tener un impacto social positivo.The research shows the evaluation of the social impact on health prevention generated by the project for the Installation of drinking water and sanitation in the Pampas Verdes village in the Campo Verde district, Coronel Portillo province, Ucayali Region, Peru, located in a rural area of ​​the Peruvian Amazon, in which the 126 inhabitants participated. House-by-house censuses, surveys and interviews were carried out in order to measure the social impact, observing great expectations in the population and satisfaction with having bathrooms in their houses called Basic Sanitation Units (UBS), evidencing that the achievement is being achieved. of the short and long-term objectives, as it is, permanent access to drinking water with sanitation and the population is more aware of the importance of drinking water consumption, personal hygiene, hand washing and a significant reduction in acute diarrheal diseases and others, the project to achieve its objectives has had a technical component and a social component, the social component through the social manager has implemented workshops and trainings with the population, achieving a positive social impac

A Resonant Graphene NEMS Vibrometer

Measuring vibrations is essential to ensuring building structural safety and machine stability. Predictive maintenance is a central internet of things (IoT) application within the new industrial revolution, where sustainability and performance increase over time are going to be paramount. To reduce the footprint and cost of vibration sensors while improving their performance, new sensor concepts are needed. Here, double-layer graphene membranes are utilized with a suspended silicon proof demonstrating their operation as resonant vibration sensors that show outstanding performance for a given footprint and proof mass. The unveiled sensing effect is based on resonant transduction and has important implications for experimental studies involving thin nano and micro mechanical resonators that are excited by an external shaker