# Scaled 3D-printed models of insect outer-ear with tympanic membranes and acoustic trachea preserving key acoustic features

## TL;DR

Researchers created 3D-printed models of a katydid's ear to study how it detects sounds, including ultrasonic bat calls, and how it filters and amplifies frequencies.

## Contribution

The study introduces the first full-scale 3D-printed replicas of a katydid's outer ear and acoustic trachea, preserving key acoustic features.

## Key findings

- Flexible TPU membranes and rigid PLA pinnae replicated the ultrasonic gain of the katydid's ear at 70–110 kHz.
- The acoustic trachea's spiracle filtered and the canal amplified sound by 17–21 dB, matching live insect behavior.
- The models offer a scalable, non-destructive method for studying insect acoustics and bio-inspired sensor design.

## Abstract

Katydids (Insecta, Orthoptera, Tettigoniidae) possess a sophisticated foreleg ear with two tympana receiving sound externally through a pinna that acts as a bat detector and internally through an acoustic trachea for conspecific communication. Their miniature scale hinders experimentation, prompting the use of scaled models, yet previous studies have not replicated the full pinna–tympana assembly or the complete acoustic trachea. In this study, micro-CT imaging, AI-assisted segmentation and multi-material 3D-printed assembly were used to generate scaled models. Scaled copies of the pinna-tympanum assembly and the complete acoustic trachea of the neotropical katydid Copiphora gorgonensis were fabricated from high-fidelity reconstructions. Flexible TPU membranes reproduced the expected pressure-driven vibration pattern at the scaled frequency, and when paired with rigid PLA pinnae, they captured the overall outer-ear acoustic response, producing ultrasonic gain within 70–110 kHz that is consistent with the in vivo bat-detection band. Separately, the pressure mapping of the scaled acoustic trachea confirms the spiracle as a filter and the exponential canal as a 17–21 dB amplifier, in line with simulations, consistent with the 1.3-cycle phase shift observed at 23 kHz in living insects. These matching results support the use of scaled biomimetic replicas as reusable, 3Rs-aligned partial substitutes and complements to live-insect acoustic studies in search of bio-inspired applications. Taken together, these outcomes provide a basis for translating the underlying acoustic and structural principles into future miniature engineering systems, including bio-inspired MEMS microphones and compact directional sensors, where passive amplification and filtering remain desirable for improving energy efficiency and signal clarity.

•Scaled 3D printed replica of katydid outer ear with tympana and acoustic trachea.•TPU membranes with PLA pinnae reproduced resonance at ultrasonic bat calls.•Trachea filtered and amplified certain frequency, matching live insect phase delay.•Scalable non-destructive 3Rs-aligned methods alternate to small scale tests.•Basis for fossilised insect acoustic analysis and bio-inspired miniature sensors.

Scaled 3D printed replica of katydid outer ear with tympana and acoustic trachea.

TPU membranes with PLA pinnae reproduced resonance at ultrasonic bat calls.

Trachea filtered and amplified certain frequency, matching live insect phase delay.

Scalable non-destructive 3Rs-aligned methods alternate to small scale tests.

Basis for fossilised insect acoustic analysis and bio-inspired miniature sensors.