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Comparison of acoustic sensor systems for quality analysis of asparagus using scanning laser vibrometry for visualization

: Foerster, J.; Truppel, I.; Bochow-Ness, O.; Geyer, M.


Computers and electronics in agriculture 91 (2013), pp.10-18
ISSN: 0168-1699
Journal Article
Fraunhofer IZM ()

Automatic detection of hollow white asparagus spears (Asparagus officinalis L.) is a severe issue. One promising approach is the computerized acoustic resonance analysis. The principal components of newly developed acoustic sensor systems were investigated for their technical usability to stimulate and measure asparagus vibrations. Each tested measurement setup included a sample holder with an integrated sensor (piezo film or condenser microphone) and a mechanical excitation device (piezo actuator, midget solenoid, tiny hammer). Non-contacting scanning laser vibrometry was used as an appropriate tool to measure characteristic properties of the experimental setups. Without altering vibration conditions, this technology allowed to visualize vibration response of test specimens (asparagus spears and wooden rods) as well as to evaluate coupling properties between sample and sample holder and the sensitivities of sensors. Each setup enabled free vibration of samples investigated. In addition, reference sensors were proved to be placed at suitable positions for signal detection away from nodal points of oscillation. From the presented results, it turned out that, compared to piezo film sensors, specifically the chosen microphones have the better adapted frequency characteristic considering the vibration behavior of asparagus spears. The measured frequency characteristic of the piezo film sensors suggests that attention has to be focused on the coupling conditions between sample, sample holder and machinery.