Denoising Using Blind Source Separation for Pyroelectric Sensors
- PDF / 1,247,767 Bytes
- 13 Pages / 600 x 792 pts Page_size
- 104 Downloads / 219 Views
enoising Using Blind Source Separation for Pyroelectric Sensors Regis Huez LAM, Faculté des Sciences, Moulin de la Housse, 51687 Reims Cedex 2, France Email: [email protected]
Danielle Nuzillard LAM, Faculté des Sciences, Moulin de la Housse, 51687 Reims Cedex 2, France Email: [email protected]
Alain Billat LAM, Faculté des Sciences, Moulin de la Housse, 51687 Reims Cedex 2, France Email: [email protected] Received 5 December 1999 and in revised form 2 February 2001 This paper deals with a process of denoising based on a Blind Source Separation (BSS) method. This technique is inserted in an experimental device of nondestructive testing. Its excitation is a laser beam and its detectors are pyroelectric sensors. The latter are sensitive to the temperature. As they are also piezoelectric, they are particularly sensitive to the environmental noise. Therefore, it is necessary to denoise them. With this aim in view, a technique of blind source separation is implemented. One source corresponds to the incidental beam and the other sources are various noise. A judicious experimental device was designed in the laboratory. It fits to the requirements of the BSS technique, and it allows indeed a restoration of the incident signal. Keywords and phrases: blind source separation, denoising, pyroelectric sensor, multi-sensor, laser beam, humidity profile.
1. INTRODUCTION This paper describes the measurement of the time-dependent change in a space profile of moisture in a breadboard construction for nondestructive testing. The profile is defined according to the depth of a biopolymer. The change is measured by photothermal methods in which a sample is optically excited by a laser diode and the heat produced is measured. The exciting wavelength was that of an absorption band of the water spectrum. The intensity of the laser beam is modulated in frequency in order to excite sample zones at various depths. This effect is similar to the skin effect in electromagnetism. The frequencies of modulation were 0.1– 400 Hz, to make the penetration depths compatible with the required resolution (10 µ m) and the thickness of the sample (1 mm). The pyroelectric sensor placed behind the sample detects thermal waves coming from its surface. No direct contact is required [1, 2]. The sample is analysed by synchronous detection between the modulated control signal sent to the laser diode and the signal from the detector. Each frequency of modulation corresponds to a value of the gain and a value of
the phase, to give characteristic gain and phase curves. Both are representative of a moisture space profile. Their use with various physical models allows to go up to this profile [3]. 1.1. The problem Synchronous detection provides dispersed experimental measurements of phase and gain. The main causes are defects in the laser beam and the extreme sensitivity of the sensors. 1.2.
The defects in the laser beam
The radiation from the laser beam is a fundamental frequency of modulation that undergoes two types of defects; its ampli
Data Loading...
