BIONICS

Gryllus Campestris bioacoustic research

How is it going


The capture of the Gryllus Campestris' song


This is how the signal generated by a male cricket looks like on the oscilloscope. Trains of impulses can be observed.

The spectral analysis of the song's signal has a dominant frequency of 4.8 kHz.

The electrical diagram of the 4.8 kHz used for detecting the cricket which is singing, including a simulation of its functionality in swcad.

Diagram of the infrared barrier. In order to indicate which cricket from the colony comes out of a tunnel, each tunnel is provided with an infrared barrier, which detects the crickets' presence on the terrace. The assembly enables the adjustment of the sensibility, which is necessary due to the fact that the study is made during day-time as well as night-time.

The assembly on the test board and its realtime testing, confirming the simulated functionality.



The topography of a tunnel made by crickets.


The emitter is composed of a RF oscillator, an amplifier, a 1kHz oscillator and an antenna. The oscillator, made of quartz, the resistances R1, R2, R3, R4, the transistor Q1 and the capacitances C, has the role of generating a signal, based on the quartz's frequency. This signal is further amplified by the amplifier composed of the resistances R5, R6, R7 and R8, is then modulated with a signal of 1kHz, given by the oscillator with the 555 timer, and finally emitted by the antenna. The capacitors C1, C2, C3 and C4 are DC-decoupling capacitances, used because we do not need direct current component. The resistors R4 and R8 are degeneration resistors, which are placed in series with the emitters of the transistors, and they create a local reaction which leads to the decreasing of the equivalent slope, that of the amplification, thus increasing linearity. The antenna A1 must be adapted in order to obtain a maximum power transfer from emission to reception. The adaptation is obtained when the antenna is in resonance, on the emitting frequency (receiver). The transistor Q1 is connected in Common Emitter (CE) mode, same as the transistor Q2, which represents an AM modulator.

The receiver is made of an antenna, which receives the signal given by the emitter's antenna, a signal which passes through the C5 capacitance, which is also a DC-decoupling capacitance. Then the signal is conveyed through the group of transistors Q3 and Q4, which set up in a Darlington configuration. This configuration groups the transistors in a way which permits the current, amplified by the first transistor, to be amplified even more by the second transistor, so that the current gain is even greater than the gain given by the two transistors separately. Next, we have a peak detector, made up of two diodes (D1 and D2), with the role of extracting the peak value of the envelope. Further, we have an LM386 amplifier, which is a power amplifier used in applications with low levels of input voltage. The gain is set to 20, but an external capacitance between the pins 1 and 8 will increase the gain to any value between 20 and 200. At the output of the amplifier, we have a jack used to connect headphones (optional). The circuit contains a VU-meter as well, used for detecting the signal received from the emitter, an emitter which is introduced in the cricket's tunnel, thus being able to determine the form and depth of the tunnels. In parallel with the VU-meter a semi-adjustable is necessary to aid in the calibration at the end of the VU-meter.



Going out in nature


After our first time out in nature, we've come to the conclusion that the measurements made on the field...

...aren't exactly the same as the ones made in the laboratory, there are many factors that influence them.

Some of the factors worth mentioning are the wind, the soil's humidity, the roots of the plants and the blades of grass. We also observed that the crickets' tunnels have up to 18-19 cm in length. When we tried to determine the shape of these tunnels, we encountered some difficulties: inserting a flexible wire and generating a signal, we observed that the blades of grass spread this signal, acting like antennas.

When inserting a microphone in the cricket's tunnel, we noticed that when a sound in produced, the tunnel amplifies it.

We also studied the gender of the crickets, noticing the difference between the female and the male by the presence of the oviduct on the female's body.

This concluded our first field day, we're perfecting our techniques and next time we'll be more prepared. Nature has its surprises, being different from the laboratory.

To be continued..



In the tunnel...


The spectrogram of the signal emitted by grillus campestris in two states of the microphone:

At 2 cm above the entrance

Burried 10 cm

The signal analysis (power densities and shape)

The calculus of the tunnel, considering it a Helmonvith acoustic resonator. We think that the similarity is obvious.

The software programs used in this analysis were: Spectrogram 16, Spectrum Lab and Audacity 1.3.

One of the issues which appeared for the measurements made on the field is the small amount of time available for work. This is due to the current sources used (accumulator, batteries). The problem was solved by making use of a photovoltaic panel of 75 W, obtained with the help of S.C. Qset Energy s.r.l., who provided it for us during the project.

 


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