Mechanical vibration effects in the biospeckle laser technique for portable equipment application in agriculture

Abstract

The biospeckle laser (BSL) is a technique developed based on the processing of optical interference patterns formed when a laser light strikes a biological surface. This non-destructive image processing technique is used to quantify the activity level of a sample. Since it is not always feasible to move biological samples to a laboratory to be analyzed, on-site application is necessary for the advancement of the technique. There are limitations in the use of the technique in the field, vibration interference is one of them. Aiming to understand the level of this interference as well as to propose ways to mitigate them, in this work it was developed a portable prototype for dynamic laser speckle (DLS) analysis that was subjected to experimental modal analysis and transmissibility tests. The prototype’s natural frequencies were obtained, and it was evaluated how the optical technique behaves when excited at these and other frequencies. It was discovered that BSL is more sensitive to low frequencies, close to 5 Hz. In the transmissibility tests, it was found that the isolator with the lower stiffness presented the best characteristics of vibration isolation for the proposed purposes, making possible the portability of the prototype from the isolation of ordinary external mechanical vibrations.