Insect-inspired acoustic micro-sensors

Abstract

Micro-Electro Mechanical System (MEMS) microphones inspired by the remarkable phonotactic capability of Ormia ochracea offer the promise of microscale directional microphones with a greatly reduced need for post-processing of signals. Gravid O. ochracea females can locate their host cricket's 5 kHz mating calls to an accuracy of less than 2 despite having a distance of approximately 500 mm between the ears. MEMS devices base on the principles of operation of O. ochracea's hearing system have been well studied, however commercial implementation has proven challenging due to the system's reliance on carefully tailored ratios of stiffness and damping, which are difficult to realize in standard MEMS fabrication processes, necessitating a trade-off between wideband operation and sensitivity. A survey of the variety of strategies that have been followed to address these inherent challenges is presented. IntroductionThe traditional method of sound source localization is to build a microphone array which combines at least two independent omnidirectional microphones [1]. Calculating the incident angle of sound waves then depends on the separating distance (i.e. time delay) between the microphones receiving the plane waves [2][3][4]. Similar to microphone arrays, many large animals including human beings have two ears with sufficient separation that the nervous system is able to resolve the interaural time difference (ITD) and interaural intensity difference (IID) to determine the source location. The requirement for spatial separation poses a fundamental problem for sound localization in small animals [5] and in micro-scale devices (i.e. Micro-Electro-Mechanic-System (MEMS) devices) smaller than the wavelength of interest.In the 1990's, O. ochracea was found to have a great capability for detecting sound source [6,7 ,8]. The parasitic female Ormia uses auditory cues to localize the mating call of a host Gryllus, a genus of cricket, and then deposits its predaceous larvae on the host [9]. The cricket's mating call has a fundamental frequency around 5 kHz and wavelength at approximately 70 mm, compared to the interaural distance of Ormia that is only around 520 mm [10,11]. Despite the extremely small distance that gives the original maximum ITD and IID as approximately 1.5 ms and 1 dB [12], respectively, experimental investigations show that it can localize the mating call with a resolution less than 2[13]. This high accuracy is attributed to the mechanical coupling structure of Ormia's ear, as shown in Figure 1(a) and (b), which enhances both ITD and IID by up to 40 times greater than the original values at 5 kHz [14 ]. The first resonance is a rocking mode about the bridge centre point, and the second is a translational mode with each end of the bridge moving in-phase while the bridge bends in the middle as shown in Figure 1(c). The response of the Ormia ear at any frequency is then described by a linear combination of these resonance modes [15 ].Ormia-inspired MEMS microphone designs can be broadly separated into two...

Directional and frequency characteristics of auditory neurons in Culex male mosquitoes

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Cues for Directional Hearing in the Fly Ormia ochracea

“…On the other hand, the auditory system in Ormia is adapted to exploit the specific temporal and spectral structure of the host cricket acoustic signals; working in a relatively narrow frequency band and detecting the onset timing of individual sound pulses in the trill like call of the host. Expanding the usable bandwidth of systems designed to mimic Ormia hearing has been a major focus for biomimetic engineering efforts inspired by Ormia (Zhang et al, 2018). The subfamily Ormiini, though not a large group, includes nearly 70 species (Lehmann, 2003), with different species exploiting hosts with diverse acoustic signals in terms of both frequency and temporal characteristics.…”

“…Ormia auditory directionality has also emerged as an adaptable model for novel technology, and the past couple of decades have seen considerable interest in biomimetic applications of the flies' intertympanal coupling principle to engineering problems related to source localization for waveform signals, with two main areas of research. Efforts to design biomimetic directional microphones (BDMs, with application, for example, in hearing aids) have sought to mimic the mechanical properties of the fly eardrums in micro-electromechanical-system (MEMS) devices (Ishfaque and Kim, 2018;Zhang et al, 2018). Efforts to design biomimetic antenna arrays (BMAAs) have applied the principle of coupled detectors to electromagnetic signal localization (Grüner et al, 2019).…”

Mathematical Analysis and Micro-Spacing Implementation of Acoustic Sensor Based on Bio-Inspired Intermembrane Bridge Structure

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