28 novembre 2020

Projects for internal 200-hour traineeship



Title: Realization of all-digital test station for tuning forks excitation and signal recovering

Objectives: Signal Generation, Data Acquisition, LabVIEW programming

Description: This project aims to realize a test station based on the Digilent Analog Discovery 2, a multi-function instrument that allows the generation and recording of signals. The analogue output will be used to generate a sinusoidal excitation to a quartz tuning fork (QTF) at one of its flexural resonance modes. The generated QTF signal will be sampled via the analogue input. The acquired signals at the stated sampling rates will provides a way to measure QTF resonance parameters of interest that are otherwise not easily obtainable. The test station aims to be a portable alternative to a stack of benchtop equipment. The project requires the building of a custom application in LabVIEW.




Title: Digital dual-phase sensitive signal detection with a lock-in amplifier

Objectives: Phase-Sensitive detection, Data Acquisition, LabVIEW programming

Description: The electrical signal generated by an excited quartz tuning fork (QTF) requires a lock-in detection. The lock-in measurement extracts signals in a defined frequency band around the reference frequency, efficiently rejecting all other frequency components. In this project, the QTF will be excited by a sinusoidal voltage signal and its response signal will be sent to a FEMTO lock-in amplifier for a digital dual-phase demodulation. The lock-in signal will be sampled by Digilent Analog Discovery 2 board controlled by a custom application in LabVIEW to be realized. The software has also to analyze long-term data acquisitions by implementing an Allan deviation analysis to study the signal-to-noise ratio as a function of the acquisition time.




Title: Analysis of influence of gas pressure on tuning fork resonance properties

Objectives: Modeling, Data analysis

Description: While it is vibrating, a quartz tuning fork (QTF) mainly loses energy via the interaction with the surround viscous medium. This damping mechanism affects the resonance frequency as well as its quality factor. The project aims to perform a theoretical and experimental investigation of the dependence of resonance properties of a QTF as a function of the air pressure. The QTF will be enclosed in a vacuum seal housing. An air handling system composed by a vacuum pump, valves and a pressure controller (Edwards or Bronkhorst) will be realized in order to vary and fix the air pressure within the housing. The pressure dependence of both resonance frequency and quality factor will be modelled by using Eulero-Bernoulli theory and Hosaka’s model, respectively. The theoretical prediction will be compared with obtained experimental results.




Title: Measurement of spatial quality of a laser beam by using an infrared pyro-camera

Objectives: Data analysis, LabVIEW programming

Description: Many applications require laser beams with a Gaussian-like, high quality spatial mode. In this project, the output mode profile in the far field condition of a mid-infrared quantum cascade laser beam will be recorded by using a pyrocamera (Pyrocam III, Ophir Spiricon) with pixel sizes of 100 X 100 µm. A LabVIEW-based software will be developed to estimate the beam width in two orthogonal directions by calculating the second-order moment of the beam intensity distribution. By using the pyrocamera, the laser output-beam profile will be acquired at different distances from the laser source, in order to estimate the beam divergence in both directions. The spatial beam quality will be evaluated by estimating the M-squared factor.




Title: Second Harmonic Simulation in Wavelength Modulation Spectroscopy

Objectives: Modeling, MATLAB programming

Description: Wavelength Modulation Spectroscopy is performed by rapidly dithering the wavelength of a laser over an absorption feature of a gas species. The fast modulation results in a series of harmonics on the detected laser intensity, occurring at multiples of the fast modulation frequency. In a typical diode laser, the modulation is applied via injection current tuning, which induces wavelength modulation together with intensity modulation of the laser. In this project, a MATLAB code will be developed to simulate the second harmonic generation via a dithering of the wavelength of a laser emission while it is crossing a Voigt absorption profile provided by HITRAN database. The shape of the second harmonic signal will be discussed as a function of operating parameters, such as the modulation depth and residual amplitude modulation.




Title: Butterworth–Van Dyke model of a quartz tuning fork vibrating at overtone modes

Objectives: Modeling, MATLAB programming

Description: When the quartz tuning fork (QTF) vibrates at the fundamental mode, the harmonic oscillator is an excellent model for the response of the tuning fork. Thus, a QTF can be modeled as a series resistance-inductor-capacitor circuit (RLC  Butterworth–Van  Dyke model) using an electrical analogy of a mechanical damped oscillator, in which the resistance represents the losses, the inductor represents the mass of the resonator, and the capacitor represents the stiffness of the equivalent spring. In this project, the first part aims to build a MATLAB code for simulate the RCL model for a QTF, including stray capacitance effect and the modeling of a standard operational amplifier for current-to-voltage conversion. The model aims to provide the spectral response of the QTF when it is electrically excited by a sinusoidal waveform. Then, the model will be extended to overtone resonances.




Title: Analysis of performance of low-noise current drivers for diode lasers

Objectives: Data analysis, LabVIEW programming

Description: Laser diode drivers with integrated temperature controller delivers current that can be modulated internally or externally.  Current fluctuations affect both the optical power and the wavelength emission. As a result, the bandwidth emission is broadened. Thus, low noise current drivers are largely required for narrow linewidth as well as long-term stability in power emission. This project aims to compare a standard current driver (ILX Lightwave LDX-3232) and a low-noise current driver (Wavelength Electronics LDTC2/2E), when used to polarize a diode laser or a quantum cascade laser under the same experimental conditions. A LabVIEW code will be developed to acquire and record the emitted optical power as a function of time. The data will be processed to retrieve the noise power spectral density.




Title: Real-time gas concentration measurement by analyzing the second harmonic signal in wavelength modulation spectroscopy

Objectives: Data acquisition and analysis, LabVIEW programming

Description: In wavelength modulation spectroscopy, the laser current is sinusoidally dithered while it scans across the gas absorption profile. Because of the non-linearity of the absorption cross section, harmonics of the absorption signal are generated. At a result, the second harmonic of the spectral scan of a Lorentzian-like absorption profile (2f-spectral scan) resembles the second derivative of the Lorentzian function. When a 2f- spectral scan is completely acquired, its peak value gives information about the gas concentration. This project aims to develop a LabVIEW application to recognize in real-time the 2f-spectral scan and extract the peak value. The application will also convert the peak values in gas concentration unit and plot them as a function of time.




Title: Finite Element Modeling of flexural modes of a quartz tuning fork by using COMSOL MultiPhysics

Objectives: FEM Modelling

Description: A quartz tuning fork (QTF) consists of two prongs connected at one end. The resonance frequencies of in-plane flexural mode are determined by the elastic properties (Young modulus) of the constituent material, quartz, and their shape and sizes. As a first approximation, each prong can be described as a single harmonic oscillator, neglecting the coupling with the other one. The project aims to simulate the QTF vibrations and their eigenfrequencies with 3-dimensional Finite Element Modeling (FEM) using COMSOL MultiPhysics software package and the Solid Mechanics module. The simulation will provide also eigenfrequencies, the vibration profile, i.e. the maximum amplitude vibration, and the strain field distribution. The influence of the prong sizes on these parameters will be investigated and discussed.



Title: Analysis of spectral response of a quartz tuning fork with a single-pulse excitation

Objectives: Signal Generation, Data Acquisition, LabVIEW programming

Description: The prongs of a quartz tuning fork (QTF) can be put in vibration via an external excitation that can be mechanical or electrical. During the excitation, energy can be provided to the QTF using a sinus, a pulse or a broadband white noise signal. When the excitation source is turned off, the QTF instantly oscillates at their natural frequencies, and slowly disperses the stored energy with a typical exponential decay whose time decay is related to the quality factor. This project aims to measure the QTF time-response by applying a short voltage pulse and to record the QTF ring-down signal. By processing the signal in frequency domain, the QTF resonance frequencies of flexural modes will be measured and compared with Euler-Bernoulli prediction.



Title: Realization of an all-digital Virtual Bench for signal generation and processing

Objectives: Signal Generation, LabVIEW programming

Description: When it comes to laboratory instrumentation, digital over older analog-based units represents the logical choice for experimental research field. Computer-based data acquisition system as well as digital signal generation have several advantages: low cost, compactness and high adaptability. The project aims to develop an all-digital Virtual Bench by using the high-speed Multifunction I/O Device PCIe-6363 designed by National Instruments. The virtual instrument has to combine a mixed-signal oscilloscope, an arbitrary waveform generator, a digital multimeter, and data acquisition board for analog signals. The ultimate performance in terms of digital resolution and sampling rate will be discussed.