Use of the Optical Cantilever Microphone in Photoacoustic Spectroscopy

A novel cantilever pressure sensor was developed in the Department of Physics at the University of Turku in order to solve the sensitivity problems which are encountered when condenser microphones are used in photoacoustic spectroscopy. The cantilever pressure sensor, combined with a laser interferometer for the measurement of the cantilever movements, proved to be highly sensitive. The original aim of this work was to integrate the sensor in a photoacoustic gas detector working in a differential measurement scheme. The integration was made successfully into three prototypes. In addition, the cantilever was also integrated in the photoacoustic FTIR measurement schemes of gas-, liquid-, and solid-phase samples. A theoretical model for the signal generation in each measurement scheme was created and the optimal celldesign discussed. The sensitivity and selectivity of the differential method were evaluated when a blackbody radiator and a mechanical chopper were used with CO2, CH4, CO, and C2H4 gases. The detection limits were in the sub-ppm level for all four gases with only a 1.3 second integration time and the cross interference was well below one percent for all gas combinations other than those between hydrocarbons. Sensitivity with other infrared sources was compared using ethylene as an example gas. In the comparison of sensitivity with different infrared sources the electrically modulated blackbody radiator gave a 35 times higher and the CO2-laser a 100 times lower detection limit than the blackbody radiator with a mechanical chopper. As a conclusion, the differential system is well suited to rapid single gas measurements. Gas-phase photoacoustic FTIR spectroscopy gives the best performance, when several components have to be analyzed simultaneously from multicomponent samples. Multicomponent measurements were demonstrated with a sample that contained different concentrations of CO2, H2O, CO, and four different hydrocarbons. It required an approximately 10 times longer measurement time to achieve the same detection limit for a single gas as with the differential system. The properties of the photoacoustic FTIR spectroscopy were also compared to conventional transmission FTIR spectroscopy by simulations. Solid- and liquid-phase photoacoustic FTIR spectroscopy has several advantages compared to other techniques and therefore it also has a great variety of applications. A comparison of the signal-to-noise ratio between photoacoustic cells with a cantilever microphone and a condenser microphone was done with standard carbon black, polyethene, and sunflower oil samples. The cell with the cantilever microphone proved to have a 5-10 times higher signal-to-noise ratio than the reference detector, depending on the sample. Cantilever enhanced photoacoustics will be an effective tool for gas detection and analysis of solid- and liquid-phase samples. The preliminary prototypes gave good results in all three measurement schemes that were studied. According to simulations, there are possibilities for further enhancement of the sensitivity, as well as other properties, of each system.Siirretty Doriast

Labour consumption models applied to motor-manual pre-commercial thinning in Finland.

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Simulation of an experimental database of infrared spectra of complex gaseous mixtures for detecting specific substances. The case of drug precursors

This work is motivated by the need to develop suitable databases in absence of real experimental data, for instance when spectra measured with a newly developed instrumentation on real samples are not available yet. This notwithstanding, in fact, the realization of the physical project should be addressed by a starting database, also invaluable in order to test its effectiveness. In this article we face the issue of simulating gas mixtures spectra for the development of a new sensor for External Cavity-Quantum Cascade Laser Photoacoustic Spectroscopy (EC-QCLPAS) starting from literature FT-IR spectra of pure components: a dataset is realized suitable to realistically represent the ensemble of spectra of the gas mixtures of interest. The informative data deriving from the literature spectra were combined with the stochastic component extracted from a sample spectrum recorded with a prototype instrument, allowing us to build a matrix containing thousands of simulated spectra of gaseous mixtures, accounting for the presence of different components at different concentrations. Signal processing and experimental design techniques were used along the whole path leading to the dataset of simulated spectra. In particular, the goal of the construction of the database lies in the development of a final system to detect drug precursors in the vapour phase. The comparison of some EC-QCLPAS spectra with the corresponding simulated signals confirms the validity of the proposed approach

A feature selection strategy for the analysis of spectra from a photoacoustic sensing system

In the frame of the EU project CUSTOM, a new sensor system for the detection of drug precursors in gaseous samples is being developed, which also includes an External Cavity-Quantum Cascade Laser Photo Acoustic Sensor (ECQCLPAS). In order to define the characteristics of the laser source, the optimal wavenumbers within the most effective 200 cm -1 range in the mid-infrared region must be identified, in order to lead to optimal detection of the drug precursor molecules in presence of interfering species and of variable composition of the surrounding atmosphere. To this aim, based on simulations made with FT-IR spectra taken from literature, a complex multivariate analysis strategy has been developed to select the optimal wavenumbers. Firstly, the synergistic use of Experimental Design and of Signal Processing techniques led to a dataset of 5000 simulated spectra of mixtures of 33 different gases (including the 4 target molecules). After a preselection, devoted to disregard noisy regions due to small interfering molecules, the simulated mixtures were then used to select the optimal wavenumber range, by maximizing the classification efficiency, as estimated by Partial Least Squares - Discriminant Analysis. A moving window 200 cm -1 wide was used for this purpose. Finally, the optimal wavenumber values were identified within the selected range, using a feature selection approach based on Genetic Algorithms and on resampling. The work made will be relatively easily turned to the spectra actually recorded with the newly developed EC-QCLPAS instrument. Furthermore, the proposed approach allows progressive adaptation of the spectral dataset to real situations, even accounting for specific, different environments

Optical power detector with broad spectral coverage, high detectivity, and large dynamic range

Optical power measurements are needed in practically all technologies based on light. Here, we report a general-purpose optical power detector based on the photoacoustic effect. Optical power incident on the detector's black absorber produces an acoustic signal, which is further converted into an electrical signal using a silicon-cantilever pressure transducer. We demonstrate an exceptionally large spectral coverage from ultraviolet to far infrared, with the possibility for further extension to the terahertz region. The linear dynamic range of the detector reaches 80 dB, ranging from a noise-equivalent power of 6 nW/root Hz to 600mW (independent of signal averaging time). Published by Optica Publishing Group under the terms of the Creative Commons Attribution 4.0 License.Peer reviewe

Valaistuksen uusiminen : Tampereen ammattikorkeakoulu C-rakennus

Tämän opinnäytetyön tarkoitus oli tarkastella Tampereen ammattikorkeakoulun C-rakennuksen opetustilojen valaistusta ja miettiä niihin energiatehokkaammat ratkaisut, tilojen käyttöolosuhteet ja standardit huomioiden. Automatisoidut ohjaukset tuovat energiasäästöjä, sekä käyttömukavuutta, mutta valaisimien täytyy sopia tähän tarkoitukseen ja keskukseen tarvitaan myös uusia komponentteja valaistusta ohjaamaan. Työn tavoitteena oli saada aikaan valaisin- ja komponenttivalinnat ja laskea niiden hankintakustannukset, takaisinmaksuajat sekä potentiaalinen energiansäästö. Opinnäytetyö tehtiin Tampereen ammattikorkeakoululle. Opinnäytetyön tilaajan edustajina toimi kiinteistöpäällikkö Petri Ojala ja kiinteistöhuollon sähkömestari Jarmo Lehtonen. Tilaajan edustajat määrittelivät vaatimukset tilojen valaistukselle. Työssä käsiteltiin läpi valaistuksen energiatehokkuuteen vaikuttavia asioita, valaistuksen suunnitteluun liittyviä valosuureita ja valaistusstandardin SFS 12464-1:2011 määrittämiä vaatimuksia. Työssä myös mallinnettiin rakennus käyttämällä Dialux Evo -ohjelmaa, jolla laskettiin tilojen valaistusominaisuudet. Työn tuloksena saatiin selvitettyä alustavat kustannus- ja hyötyarviot, sekä takaisinmaksuajat. Nämä tiedot välitetään kiinteistön ylläpidosta vastuussa oleville tahoille, jotka laskelmien perusteella tekevät päätöksen kohteen tarkemmasta suunnittelusta ja toteuttamisesta.The purpose of this thesis was to inspect lighting in the C-wing at the premises of Tampere University of Applied Sciences and to choose more energy efficient solutions while observing standards and operating circumstances. Automated controls bring energy savings and ease of use, but luminaires have to be suitable for this purpose and new components are needed in the switchboard to control the lighting. The main goals of this thesis were to make luminaire and component choices, and calculate costs, payback times and potential energy savings. In this thesis, discussion is provided on things that have an effect on energy efficiency, the features of different light quantities in view of lighting design, and the requirements set by standards. A 3D model of the building was also made to measure lighting in the premises. As a result of thesis, rudimentary calculations of expenses, benefits and payback times were made. This information will be given to people responsible of maintaining the property, who will then use it when they decide on the details of the planning and realization stages

Valkohäntäkauris runsastuu - tutkittu tieto tarpeen

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Kuusen istutusalojen varhaisperkaustarpeen estimointi

TutkimusselosteSeloste artikkelista: Uotila, K., Rantala, J. & Saksa, T. 2012. Estimating the need for early cleaning in Norway spruce plantations in Finland. Silva Fennica 46(5): 683–693