Dielectric and ultrasonic properties of rubber wood. Effect of moisture content, grain direction and frequency

• Published in: European journal of wood and wood products 1998-07, Vol.56 (4), p.223-227
• Main Authors: Kabir, M.F, Daud, W.M, Khalid, K, Sidek, H.A.A
• Format: Article
• Language: English
• Subjects: ANATOMIA DE LA MADERA; ANATOMIE DU BOIS; Anisotropy; Applied sciences; BOIS DE FEUILLUS; CONTENIDO DE HUMEDAD; Dielectric constant; Dielectric loss; DIELECTRIC PROPERTIES; Elastic properties; Electrical properties; Exact sciences and technology; HARDWOOD; HEVEA BRASILIENSIS; Longitudinal waves; Low frequencies; MADERA DE FRONDOSAS; MECHANICAL PROPERTIES; Microwave frequencies; MOISTURE CONTENT; Permittivity; Polymer industry, paints, wood; Properties and testing; PROPIEDADES DIELECTRICAS; PROPIEDADES MECANICAS; PROPRIETE DIELECTRIQUE; PROPRIETE MECANIQUE; Rubber; Stiffness; Temperature; TENEUR EN EAU; ULTRASON; ULTRASONICS; ULTRASONIDO; Velocity; Water content; Wood; WOOD ANATOMY; Wood. Paper. Non wovens
• ISSN: 0018-3768; 1436-736X
• DOI: 10.1007/s001070050305

Dielectric properties of rubber wood have been studied at low and microwave frequencies with different moisture content and grain direction. The ultrasonic properties were studied with pulsed longitudinal waves of frequency 45 kHz. Two anisotropic directions have been considered for this study - parallel and perpendicular to grain. The low frequencies were of 0.01, 0.1, 1.0, 10 and 100 Hz and microwave frequencies were of 1, 2.45, 6, 8, 10, 14 and 17 GHz. The moisture content affected the dielectric constant and dielectric loss factor both at low and microwave frequencies. The moisture content above 30% showed little influence on dielectric properties, whereas it increases linearly from 0 to 30% in both the grain directions at low frequencies. A continuous increase of dielectric properties, was obtained with the increase of moisture content at microwave frequencies, and the trend becomes concave upward. Dielectric properties increase as the frequencies increase - except dielectric loss factor at microwave frequencies, where reverse trends were observed. Little change of dielectric loss factor was obtained at frequencies above 6 GHz. The parallel to grain direction showed higher dielectric constant and dielectric loss factor compared to perpendicular to grain direction. This dielectric anisotropy of wood may be attributed to the microscopic, macroscopic molecular as well as chemical constituents of wood. Ultrasonic properties were also affected considerably by the moisture content and grain direction. The dried wood showed higher ultrasonic velocity and elastic stiffness constant compared to green wood. The parallel to grain direction exhibits higher ultrasonic velocity and elastic stiffness constant than perpendicular to grain. Die dielektrischen Eigenschaften von Hevea brasiliensis wurden bei niedriger und Mikrowellenfrequenz sowie unterschiedlichen Feuchten und Faserrichtungen untersucht. Die Ultraschalleigenschaften wurden mit gepulsten Longitudinalwellen von 45 kHz bestimmt. Beide Bestimmungen erfolgten parallel und senkrecht zur Faser. Als niedrige Frequenzen wurden 0,01, 0,1, 1,0, 10 und 100 Hz eingesetzt, im Mikrowellenbereich 1, 2,45, 6, 8, 10, 14 und 17 GHz. Die Feuchte beeinflusstdie Dielektrizitatskonstante und den Verlustfaktor in beiden Frequenzbereichen. Zwischen 0 und 30% Feuchte steigt die Dielektrizitatskonstante bei niedrigen Frequenzen linear mit der Feuchte an. Uber 30% ergeben sich nur geringe Anderungen. Im Mikrowellenbereich steigt d