Viorel Avramescu

Surface acoustic wave humidity sensor

Embodiments of the present disclosure include devices and methods for humidity and temperature sensing. For example, in one embodiment, a sensing device can include a first surface acoustic wave (SAW) component, wherein the first SAW component is a temperature component, a second SAW component, wherein the second SAW component is a humidity component, a third SAW component, wherein the third SAW component is a reference component, and a piezoelectric layer, wherein the first SAW component, the second SAW component, and the third SAW component are on a surface of the piezoelectric layer.

Surface Acoustic Wave devices and their sensing capabilities

Since mid 60s, Surface Acoustic Wave (SAW) devices have been using extensively in electronics for telecommunication. However, their potential use in the sensors field is only a matter of recent interest. This paper presents an overview of the sensing mechanisms that allow detection of temperature, strain (for pressure & torque), mass, conductivity (e.g. gas detection) and viscosity by means of SAW based devices. Design and technological challenges are presented, as well as solutions to overcome them in order to obtain reliable devices. The possibility of using such devices as passive wireless sensors is also discussed.

Lead-free galvanic oxygen sensors — A conceptual approach

Within this paper we present a thermodynamic methodology for the selection of non-toxic metals which could be used as lead-free consumable anodes in electrochemical galvanic oxygen sensors. Starting from thermodynamic nobility theory, metals like copper, bismuth or antimony are proposed to replace lead in future galvanic O2 sensors. The thermodynamic theory provides voltage windows which increase from copper (0.7 V), to bismuth (0.857 V) and antimony (1.076 V). The experimental voltage windows are smaller than the theoretical ones, but these experimental values increase in the same order from Cu, to Bi and Sb, as predicted by our methodology.

Low Power Resistive Oxygen Sensor Based on Sonochemical SrTi0.6Fe0.4O2.8 (STFO40)

The current paper reports on a sonochemical synthesis method for manufacturing nanostructured (typical grain size of 50 nm) SrTi0.6Fe0.4O2.8 (Sono-STFO40) powder. This powder is characterized using X ray-diffraction (XRD), Mössbauer spectroscopy and Scanning Electron Microscopy (SEM), and results are compared with commercially available SrTi0.4Fe0.6O2.8 (STFO60) powder. In order to manufacture resistive oxygen sensors, both Sono-STFO40 and STFO60 are deposited, by dip-pen nanolithography (DPN) method, on an SOI (Silicon-on-Insulator) micro-hotplate, employing a tungsten heater embedded within a dielectric membrane. Oxygen detection tests are performed in both dry (RH = 0%) and humid (RH = 60%) nitrogen atmosphere, varying oxygen concentrations between 1% and 16% (v/v), at a constant heater temperature of 650 °C. The oxygen sensor, based on the Sono-STFO40 sensing layer, shows good sensitivity, low power consumption (80 mW), and short response time (25 s). These performance are comparable to those exhibited by state-of-the-art O2 sensors based on STFO60, thus proving Sono-STFO40 to be a material suitable for oxygen detection in harsh environments.

Damping effects in MEMS resonators

Damping effects are very important in MEMS-based sensors and actuators. In this paper we use analytical models and finite element (FE) computations to quantify the energy losses due to viscous fluid damping, acoustic radiation and thermo-elastic damping. To treat the case where squeeze/slide film models can not be applied, we have implemented in a commercial FE package a new incompressible flow solver based on a gauge formulation. We are thus able to solve for full flows around complex 3D geometries in the frequency domain and predict viscous damping of resonant MEMS structures. The full methodology is exemplified on the response of a MEMS silicon resonator, including acoustic driving and piezoelectric sensing.

Experimental evidence of long life lead-free oxygen galvanic sensors

In this work we present an experimental study of the lifetime of O2 galvanic sensors in KOH aqueous solution, considering bismuth, copper and antimony as the candidates for lead anode replacement in present devices. An initial accelerated ageing test in 100% O2 suggested antimony for the next stage. Further experiments have shown an accelerated ageing factor of 18, which allowed the estimation of a lifetime of more than five years for an O2 galvanic sensor based on Sb anode of large surface area. A scaling law in lifetime as a function surface area (or anode current density) was found, which agreed with electrochemical passivation studies of Sb in alkaline solutions.

SOI membrane-based pressure sensor in stress sensitive differential amplifier configuration

This paper introduces a pressure sensing structure configured as a stress sensitive differential amplifier (SSDA), built on a Silicon-on-Insulator (SOI) membrane. Theoretical calculation show the significant increase in sensitivity which is expected from the pressure sensors in SSDA configuration compared to the traditional Wheatstone bridge circuit. Preliminary experimental measurements, performed on individual transistors placed on the membrane, exhibit state-the-art sensitivity values (1.45mV/mbar).

Oxygen sensor based on photo acoustic effect

This paper presents a potentially cheap oxygen sensor based on photo acoustic (PA) principle. Commercially available low cost devices are used for this implementation. The presentation is focused on aspects related to PA signal analysis, PA chamber influence on sensor response and environmental humidity impact on sensor sensitivity.

Novel materials for oxygen sensing technologies

The paper reviews the state-of-the-art in oxygen sensing, focusing on low power technologies suitable for portable applications. Employment of novel materials in electrochemical, optical, acoustic and resistive oxygen sensing structures, substantiated by extensive theoretical considerations and experimental data, is discussed. Merits and drawbacks of each technology are presented, together with possible means of optimization.

CMOS-compatible SOI micro-hotplate-based oxygen sensor

The paper reports upon the design and characterization of a resistive O2 sensor, which is fully CMOS-compatible and is based on an ultra-low-power Silicon on Insulator (SOI) micro-hotplate membrane. The microsensor employs SrTi0.4Fe0.6O2.8 (STFO60) as sensing layer. Thermo-Gravimetric Analysis (TGA) Energy-Dispersive X-ray Spectroscopy (EDX), X-ray Diffraction (XRD) and Scanning Electron Microscope (SEM) techniques have been used to assess the quality of both the sensing layer and STFO-SOI interface. At room temperature, the SOI sensor shows good sensitivity and fast response time (≤ 6 seconds) to O2 concentration ranging from 0% to 20% in a nitrogen atmosphere. This is the first experimental result showing the potential of this structure as O2 sensor.