SE512315C2 - Method for charting lack of homogenities in wood - Google Patents

Abstract

The method involves polarising one radio wave longitudinally in the direction of the fibres of the wood and polarising the other wave at right-angles to it. With a transmitter, two linear polarised radio waves are transmitted, the one polarised longitudinally with the wood fibre direction and the other polarised at right-angles to the first, and this in the direction of the object or structure of wood. With a receiver, the two reflected or transmitted waves are received. The time delay spectrum is measured for each of the polarisations and the relationship between them is determined in each measured delay point. The measurements are made in a number of directions through the same cross-section of wood and the measured relative delay spectra are brought together to form a cross-sectional picture of the object or structure. With the method, branches and twigs in the wood are charted.

Description

512 315 ¿The invention is described in more detail with reference to the attached figure 1 which is a sketch of a simple experimental setup. The figure indicates an oak log 1 over which a radio home 2 is placed to which two linearly polarized signals 3 and 4 are connected. The signals are transmitted from a transmitter 5 which also serves as a receiver.

Transmitter and receiver are controlled by computer 6. The log is rotated for each observation by means of a robot arm 7. In the experimental example a radio wave is transmitted linearly polarized along the direction of the fibers from the transmitter 5 through signal path 3 towards the log 1. At the same time a radio wave is sent linearly polarized perpendicular to the wood fibers through signal passage 4 against the same log.

Both waves are reflected in the log, but different depending on the log's wood structure. The radio waves will be best reflected on surfaces that have fibers mainly directed along the linear polarization of the road. The waves that are polarized along the main fiber direction of the wood will show the main structure of the wood, while the waves that are polarized perpendicular to this direction will mainly show twigs where the wood fibers are mainly directed perpendicular to the wood in general. The two reflected waves are received in the home 2 and are sent through their respective signal lines 3 and 4 to the receiver 5. The phase of the received signals is measured against the phase of the transmitted signals and is recorded. The procedure is repeated for a number of frequencies within a certain frequency band. Thereafter, the signals are transformed from the frequency plane to the time plane and form a delay spectrum for the two polarizations separately. The ratio of the intensity of the two delay spectra is a measure of the relative reflectivity which depends on the polarization properties of the structure of the log. Homogeneities that depend on the fiber structure of the wood, e.g. a twig, is therefore emphasized in contrast to other wood.

By either turning logs with a robot 7, or by simultaneously measuring in a number of directions through the same cross-section, a cross-sectional image of the relationship between the polarization properties can be produced by a coordinate transformation to Cartesian coordinates from the measured relationships between delay spectra taken in polar coordinates. This cross-sectional view shows the position of twigs and other inhomogeneities in the wood structure.

Claims (2)

512 315 3 Claim 1 Method of mapping inhomogeneities in wood, characterized by the fact that it transmits several directions through the same cross-section of wooden objects, materials or constructions, transmitting two linearly polarized radio waves, one polarized along the direction of the wood fibers and the other polarized against this, with receivers receiving the reflected waves in their respective polarization, for each direction measures the time delay spectrum of each of the polarations, determines the relationship between them at each measured delay point, and thereby forms a cross-sectional view of the material, object or structure. 2. A method according to the preceding claims, characterized in that twigs in wood are mapped.