Ivana Jokić

A Wireless System for Liquid Level Measurement

A wireless system for liquid level measurement is presented. It is developed in order to meet stringent power consumption requirements, but without sacrificing the accuracy of the built-in pressure sensor. The communication is realized using Bluetooth modules. An alternative solution based on radio units for 10.4 GHz is also discussed. The receiver is a personal computer with both the radio module and the appropriate software for reception and presentation of the acquired data. The developed wireless sensors have a very high performance/power consumption ratio.

Temperature measurement using silicon piezoresistive MEMS pressure sensors

In industrial processes, as well as in many other fields from vehicles to healthcare, temperature and pressure are the most common parameters to be measured and monitored. Silicon microelectromechanical (MEMS) piezoresistive pressure sensors are the first and the most successful MEMS sensors, widely used in the industry in various measurement configurations. The inherent temperature dependence of the output signal of such sensors adversely affects their pressure measurement performance. However, it can be utilized for temperature measurement, thus enabling new sensor applications. In this paper a method is presented for temperature measurement using MEMS piezoresistive pressure sensors.

Adsorption-induced fluctuations and noise in plasmonic metamaterial devices

The investigation represented here is focused on fundamental intrinsic fluctuations caused by the adsorption and desorption (a–d) of surrounding particles on the active surface in plasmonic metamaterial devices. The variance and relative fluctuations in adsorption–desorption dynamics are studied based on two different kinetic models (pseudo-first order kinetics and second order kinetics). The limits of the applicability of the pseudo-first order model are determined, thus ensuring the use of the vast mathematical heritage developed for linear systems in calculation of a–d noise, while at the same time speeding up and simplifying calculations. An approach is proposed to assess adsorption in a metamaterial sensor using an effective parameter dependent on the properties of the metamaterial unit cell.

Adsorption-desorption noise in nanowire FET biosensors

The adsorption-desorption (AD) noise in nanowire FET biosensors is analyzed, which manifests itself in the form of gate voltage fluctuations resulting from the fluctuations of the number of adsorbed particles. The derived theoretical model of the fluctuations takes into account the mass transfer effects. The numerical calculations show that when the mass transfer is slow, the low-frequency amplitude and the corner frequency of the Lorentzian AD noise spectrum obtained by derived expressions are significantly different compared to the same parameters predicted by the model that neglects mass transport effects. The presented analysis enables good estimation of these parameters from the measured noise spectrum, which is important because they are used as the source of information about the analyte concentration and the kinetics of biomolecular interactions.

Adsorption-desorption phase noise in RF MEMS/NEMS resonators

In this paper the analysis is presented of the dependence of adsorption-desorption phase noise in MEMS/NEMS resonators of their resonant frequency, operating pressure and temperature. Results of the analysis are useful for optimization of parameters and operating conditions of such components in order to fulfill the requirements of existing and future telecommunication systems.

RF MEMS and NEMS components and adsorption-desorption induced phase noise

Radio frequency micro- and nanoelectro-mechanical systems (RF MEMS and RF NEMS) and technologies have a great potential to overcome the constraints of conventional IC technologies in realization of fully integrated transceivers of next generation wireless communications systems. During the last two decades a considerable effort has been made to develop RF MEMS/NEMS resonators so that they could replace conventional bulky off-chip resonators in wireless transceivers. In MEMS, and especially in NEMS resonators, additional noise generating mechanisms exist that are characteristic for structures of small dimensions and mass, and high surface to volume ratio. One such mechanism is the adsorption-desorption (AD) process that generates the resonator frequency (phase) noise. In the first part of this paper a short overview of RF MEMS resonators is given, including comments on the necessary improvements and the direction of future research in this field (especially having in mind the need for NEMS resonators), with the intention to optimize RF MEMS and NEMS components according to requirements of both current and future systems. The main part of the paper presents a comprehensive theory of AD noise in MEMS/NEMS resonators. Apart from having a theoretical significance, the derived models of AD noise in multiple different cases of adsorption are also a useful tool for the design of optimal performance RF MEMS and NEMS resonators. The model of the MEMS/NEMS oscillator phase noise that takes into account the influence of AD noise is presented for the first time.

Influence of adsorption-desorption process on resonant frequency and noise of micro- and nanocantilevers

Scientists in the field of NEMS today are focused on the problem of achieving the lowest detectable mass of the atomic force microscope and molecular microscope probes. This paper deals with this problem starting from the theory of the adsorption-desorption noise and also the noise caused by temperature fluctuations and Johnsons noise. We found that the adsorption-desorption noise clearly exceeds the noise of the other sources at lower frequencies. According to the results we obtained for a typical microcantilever fabricated by NEMS processes, the order of magnitude of the noise equivalent mass (NEM) is NEM/spl sim/10/sup 4/ D (1 D=1.7/spl middot/10/sup -27/ kg).

A measurement setup enabling automatic characterization of silicon piezoresistive MEMS pressure sensors

In this paper a measurement setup is presented that enables automatic characterization of silicon piezoresistive MEMS pressure sensors. It is used for determination of the pressure and temperature dependences of sensor electrical parameters. Some of the equipment in the setup, and the software application that controls the process, are developed at the Center of Microelectronic Technologies (CMT). The main objective of the work is to make the sensor characterization experiment as efficient as possible, without sacrificing measurement performance. An example of obtained measurement results is given for 3 sensors fabricated at CMT. The work greatly facilitates small series production of pressure sensors and instruments, as well as research activities in the field of pressure sensors at CMT.

A method enabling simultaneous pressure and temperature measurement using a single piezoresistive MEMS pressure sensor

In this paper we present a high-performance, simple and low-cost method for simultaneous measurement of pressure and temperature using a single piezoresistive MEMS pressure sensor. The proposed measurement method utilizes the parasitic temperature sensitivity of the sensing element for both pressure measurement correction and temperature measurement. A parametric mathematical model of the sensor was established and its parameters were calculated using the obtained characterization data. Based on the model, a real-time sensor correction for both pressure and temperature measurements was implemented in a target measurement system. The proposed method was verified experimentally on a group of typical industrial-grade piezoresistive sensors. The obtained results indicate that the method enables the pressure measurement performance to exceed that of typical digital industrial pressure transmitters, achieving at the same time the temperature measurement performance comparable to industrial-grade platinum resistance temperature sensors. The presented work is directly applicable in industrial instrumentation, where it can add temperature measurement capability to the existing pressure measurement instruments, requiring little or no additional hardware, and without adverse effects on pressure measurement performance.

Highly sensitive graphene-based chemical and biological sensors with selectivity achievable through low-frequency noise measurement — Theoretical considerations

We have developed a theory of the low-frequency noise caused by interaction of the analyte with the active area of chemical and biological sensors. The main result is an analytical expression for the spectral density of the fluctuations of the number of particles adsorbed onto the sensing surface, taking into account the processes of mass transfer through the sensor reaction chamber, adsorption and desorption, and surface diffusion of adsorbed particles. The performed numerical calculations show good agreement with the experimental data from the literature, obtained for a graphene-based gas sensor. The derived theory contributes to the theoretical basis necessary for the development of a new method for the recognition and quantification of analytes, based on the measured noise spectrum.