# A New Device for Measuring Trunk Diameter Variations Using Magnetic Amorphous Wires

## TL;DR

This paper introduces a new, low-cost device for measuring tree trunk diameter changes using magnetic wires, offering high sensitivity and remote data transmission.

## Contribution

A novel dendrometer using magnetic amorphous wires with high sensitivity and good temperature immunity is proposed.

## Key findings

- The device achieved a resolution of 1.6 µm and a linearity of 1.4%.
- It has a temperature coefficient of 0.012%/°C, showing good immunity to temperature variations.
- The measurement range is 0 to 5 mm, suitable for monitoring tree growth and health.

## Abstract

Measuring the small tree trunk variations during the day–night cycle, seasonal cycles, as well as those caused by the plant’s growth and health regime is a very important action in horticulture or forestry because by analyzing the collected data, assessments can be made on the health of the trees, but also on the climatic conditions and changes in a certain region. This can be performed with devices called dendrometers. This paper presents a new type of approach to these measurement types in which the trunk volume changes are highly sensitively converted into the axial stress on sensitive elements made of magnetic materials in wire form in which the giant stress impedance effect occurs. Finally, by electronic processing of the signals provided by the sensitive elements, digital words with a decimal value proportional to the diameter variations are obtained. This paper presents the operating principle, the constructive details and the experimental results obtained by testing the device in the laboratory and in-field. The proposed dendrometer, compared to those available commercially, has the advantage of good resolution and sensitivity, good immunity to temperature variations, the possibility of transmitting the result remotely, robustness and low price. Some metrological parameters obtained from the experimental testing are the following: resolution 1.6 µm, linearity 1.4%, measurement range 0 to 5 mm, temperature coefficient 0.012%/°C.