Acoustic Function Of Time Varying Noseleaf And Ear In The Biosonar System Of Bats

There are about 300 different species of bats that can emit ultrasonic signal with their nostril. A complicated organ, called noseleaf, is located near the bats’nostril. Two of the largest groups of bats with noseleaves are the New World Spear-nosed Bats (Phyllostomidae) and the Old World Horseshoe Bats (Rhinolophidae). Different species of bats have different shapes of noseleaves. In order to find out the character-istic of nose leaf due to the different location and complicated exterior structures, a lot of research work has been done by a large number of researchers. These research re-sults indicate that the exterior structure of the noseleaf can affect the spatial distribu-tion of beam pattern, but the acoustic characteristic of each part of nose leaf is still not fully recognized. Until now, not much research work has been done on how Greater Horseshoe bat’s noseleaf deformation? changes the distribution of beam pattern in acoustic field. We use binocular vision method with two cameras to capture the mo-tion of marked points on lancet and we also record the ultrasonic pulse during the noseleaf deformation with ultrasonic detector. We use high-resolution X-ray tomog-raphy technique, digital image processing,3D visualization technology and finite el-ement numerical method to analyze the effect of lancet on ultrasound. It is a cross-disciplinary subject which involves bionics, computational acoustics, and com-puter graphics and so on.Main Research Work1. We used two high-speed and high-resolution cameras (Gigaview) with the frame rate of 500 and ultrasonic detector (Momimic) to record the noseleaf defor-mation and the pulse signal during the deformation. And we get the motion trace of marked points on lancet with the method of binocular vision to study the deformation behavior of Rhinolophus’s lancet. Then, in order to get the relationship of lancet de-formation and ultrasonic pulse. We compared the deformation of lancet and the cor- responding ultrasonic pulse, in order to get the relationship of lancet deformation and ultrasonic pulse.2. We use high resolution micro CT machine (Skyscan 1072) to scan the noseleaf samples of the Greater Horseshoe bat to get the raw digital projection images. Then we get the transect image of noseleaf samples with the algorithm of the 3D cone beam reconstruction. Then we process these images with Gauss filter and binaryzation to get the image of noseleaves’organization and air. We transfered these images into 3D model consists of cubic volume pixels. The gridded construction is used in the next step as practical model which can be processed in finite element imitating bats acous-tic field.3. By referring to the video data of lancet deformation, we selected 4 images within a complete progress of deformation (initiate status to most bending status). We compared the previous 3D model with these 4 images with the software of 3dmax and adjust the noseleaf in the model according to the images and get four 3D models which are same as the real nose leaf deformation. Then we imitated the acoustic field distribution of all 4 models with finite element and analyzed the effect of lancet de-formation on acoustic beam distribution.4. We fill up the transverse troughs on the lancet with volume elements and re-peated the previous work and compared the result with previous result of natural de-formation and studied the acoustic effect of these transverse troughs in lancet defor-mation.5. Two kinds of far-field sonar radiation beampattern, which were calculated by performing FEM form four FM bats and CF-FM bats, were compared in order to quantitatively analyze their differences and similarities.Main Research Results1. Experiment data shows that for the species of horseshoe bat, the lancet de-formation does not always appear during ultrasonic detecting progress. But for the 20 Rhinolophus we tested, all of them had lancet deformation during ultrasound emission. In the 153 runs of ultrasonic pulse test, there were 27 runs which obtain obvious lan-cet deformation during pulse emission,126 runs of which does not have obvious de-formation during pulse emission, which means bats can emit ultrasound signal with or without lancet deformation. Bats can control lancet motion themselves according to the target they are detecting, rather than be driven by the airflow of pulse to cause de-formation. In the 27 pairs of data which we get from 27 runs with obvious lancet de-formation with the method of binocular vision, the average speed of lancet motion is 0.03m/s, which is far slower than the speed of sound wave transmitting (340m/s). The Doppler frequency shift between lancet deformation speed and sound wave transmit-ting is lower than the resolution of bat’s compensation to Doppler frequency shift, but the average shift of lancet in the displacement of 0.91mm is a fifth of constant fre-quency wavelength of Rhinolophus. Displacement shift has a great effect on beam pattern distribution in acoustic field. Statistics shows that in 60% of samples the lan-cet displacement occurs earlier than pulse, in 90% of samples the lancet deformation reaches the maximum during the pulse, and in 95% of the samples the lancet defor-mation stops later than pulse, which indicates that the majority of pulse duration time is obtained in deformation duration time, with which we can say that most lancet de-formation progress can affect the ultrasonic beam pattern.2. In the simulation of 3D models for 4 deformation status of Rhinolophus lancet with finite element, we compared the beam patterns from different deformation status and we found that lancet deformation has functional effect on beam pattern distribu-tion. Under the same frequency, the more lancet bends, the wider main lobe will be in the direction of elevation angle. Under the initial condition, the ultrasound has an ob-vious main lobe while the side lobes are weak. When the bending reaches 4 degrees, at lower frequency there would be beam lobes coming out of main lobe while the beam lobes and the main lobe are still connected. When the bending comes to 8 de-grees and 12 degrees, some beam lobes are separated from the main lobe. As the fre-quency comes up again, the separated beam lobes connect to the main lobe again. We calculated the overlapping rate between lobes from initial status and different bending status at the same frequency within-3dB contour line, and the result shows that at the same frequency, the overlapping rate becomes lower and lower while the lancet bending.3. While the lancet bending progress, powerful side lobes come up besides the main lobe, and the gain of the side lobes increases with the bending, which makes the side lobes more important in acoustic field. We compared the overlapping rate of main lobe and side lobes at the near frequency, the overlapping rate of main lobe is rela-tively high while the overlapping rate of side lobe is low. Some side lobes show up at near frequencies regularly and some irregularly, which indicates that power of side lobes are distributed diversely and this diversity is helpful for bats to detect alive tar-gets besides the main target.4. After filling the translots with cubic elements, the beam patterns distribution for different deformation status are significantly different from the beam patterns of natural deformation status and the overlapping rate of main lobe and side lobe changed at the near frequencies, especially, the overlapping rate of side lobes is larger than that in natural status, without the translots being filled up. And the regular distri-bution for side lobes at near frequencies increases which means the spatial locations of side lobes are relatively steady. This characteristics is not good for detecting items except the target, which means the translots have great effect on side lobes distribu-tion during lancet deformation and it is helpful for power distribution.5. The bats live in a relatively complex environment. In their free flight or in the pursuit of the preys, the following two modes are advantageous:altering the directions of detecting according to the changed frequency and the evolution of non-patterned protruding side lobes. By quantitatively analysis of the far-field sonar radiation beams of FM bats and CF-FM bats, it is discovered that the sonar beams of FM bats have this characteristic while the far-field sonar beams of CF-FM bats in stationery have only one main lobe the direction of which alters little with the changed frequency and relatively weak side lobes. A major position shift of main lobe and protruding side lobes occurs with alteration of frequency in the far-field radiation beams after some deformations on their external ears or parietal lobes, which is similar to the far-field sonar beams of FM bats. In other words, the impact of deformation of the external ears and parietal lobes of the CF-FM bats on the sonar beams remedies the defect that they have only one main lobe and relatively weak side lobes, which serves as an ad-vantage in their pursuit of preys.The result of this article shows that the Rhinolophus can meet the complicated detecting demand by resetting beam pattern characteristics with lancet deformation. This bio-mechanism can be applied into mechanical systems and combine with some simple ways of forming diffraction waves to form more flexible and dynamic acoustic beam patterns.