Binaural Sonar Research Articles

Binaural Sonar System for Simultaneous Sensing of Distance and Direction of Extended Barriers

Bat navigation via echolocation has inspired numerous acoustic-based obstacle sensing techniques. In this paper, we use a low-cost, small size, single frequency active binaural system for simultaneous detection of distance and direction of extended obstacles using the time of flight cue. For a binaural system and given size of the transducer, the minimum tolerable separation distance between the emitter and receiver as well as best frequency range for effectively sensing a barrier of any orientation will be assessed by simulation. With the given size of transducers of 6.30 mm in radius and for a working distance of 1 m, the minimum separation distance between the emitter and receiver should not be less than 5 cm and the emitter frequency should not exceed higher than 20 kHz. It will be shown in this article that higher frequency limits the lateral distance detection ability of the system. We experimentally verified the technique for detecting a wall of any orientation with respect to the system’s axis. The approach developed in this paper could be useful for mobile robotics, indoor navigation, and personalized navigation, where a compact configuration is of interest.

Forming maps of targets having multiple reflectors with a biomimetic audible sonar.

A biomimetic audible sonar mimics human echolocation by emitting clicks and sensing echoes binaurally to investigate the limitations in acoustic mapping of 2.5 dimensional targets. A monaural sonar that provides only echo time-of-flight values produces biased maps that lie outside the target surfaces. Reflector bearing estimates derived from the first echoes detected by a binaural sonar are employed to form unbiased maps. Multiple echoes from a target introduce phantom-reflector artifacts into its map because later echoes are produced by reflectors at bearings different from those determined from the first echoes. In addition, overlapping echoes interfere to produce bearing errors. Addressing the causes of these bearing errors motivates a processing approach that employs template matching to extract valid echoes. Interfering echoes can mimic a valid echo and also form PR artifacts. These artifacts are eliminated by recognizing the bearing fluctuations that characterize echo interference. Removing PR artifacts produces a map that resembles the physical target shape to within the resolution capabilities of the sonar. The remaining differences between the target shape and the final map are void artifacts caused by invalid or missing echoes.

Biomimetic Sonar: Binaural 3D Localization using Artificial Bat Pinnae

This paper presents an advanced bio-inspired binaural sonar sensor capable of localizing reflectors in 3D space with a single reading. The technique makes use of broadband spectral cues in the received echoes only. Two artificial pinnae act as complex direction-dependent spectral filters on the echoes returning from the ensonified reflector. The “active head-related transfer function” (AHRTF) is introduced to describe this spectral filtering as a function of the reflector angle, taking into account the transmitter radiation pattern, both pinnae and the particular sonar head geometry. 3D localization is performed by selecting the azimuth—elevation pair with the highest a posteriori probability, given the binaural target echo spectrum. Experimental 3D localization results of a ball reflector show that the AHRTF carries sufficient information to discriminate between different reflector locations under realistic noise conditions. In addition, experiments with more complex reflectors illustrate that the AHRTF dominates the echo spectrum, allowing 3D localization in the presence of spectrum distortions caused by unknown reflector filtering. These experiments show that a fairly simple sonar device can extract more spatial information about realistic objects in its direct surroundings than is conventionally believed.

Binaural sonar electronic travel aid provides vibrotactile cues for landmark, reflector motion and surface texture classification.

Electronic travel aids (ETAs) for the blind commonly employ conventional time-of-flight sonars to provide range measurements, but their wide beams prevent accurate determination of object bearing. We describe a binaural sonar that detects objects over a wider bearing interval compared with a single transducer and also determines if the object lies to the left or right of the sonar axis in a robust manner. The sonar employs a pair of Polaroid 6500 ranging modules connected to Polaroid 7000 transducers operating simultaneously in a binaural array configuration. The sonar determines which transducer detects the echo first. An outward vergence angle between the transducers improves the first-echo detection reliability by increasing the delay between the two detected echoes, a consequence of threshold detection. We exploit this left/right detection capability in an ETA that provides vibrotactile feedback. Pager motors mount on both sides of the sonar, possibly worn on the user's wrists. The motor on the same side as the reflecting object vibrates with speed inversely related to range. As the sonar or object moves, vibration patterns provide landmark, motion and texture cues. Orienting the sonar at 45 degrees relative to the travel direction and passing a right-angle corner produces a characteristic vibrational pattern. When pointing the sonar at a moving object, such as a fluttering flag, the motors alternate in a manner to give the user a perception of the object motion. When the sonar translates or rotates to scan a foliage surface, the vibrational patterns are related to the surface scatterer distribution, allowing the user to identify the foliage.

A CTFM acoustic spatial sensing technology: its use by blind persons and robots

A binaural sonar sensor for blind persons which models the bat sonar is described. System performance with field plots are presented along with signal analysis on objects forming targets. The distal spatial resolution is little more than one wavelength at the lowest frequency of 50 kHz. The operating bandwidth is 50 kHz producing the power to discriminate between objects. Distance and direction information is obtained over a field of view of 50 degrees within one frequency sweep. Blind persons have demonstrated mobility akin to sighted mobility. This knowledge is of value in designing robots.