survival [2, 3, 4]. Much research focuses
on drawing inspiration from the remark-
able evolutionary strategies employed
by the sensing mechanisms of biologi-
cal systems for survival and adaptation
across the natural world [5, 6]. Over
millennia, these organisms have devel-
oped an array of senses such as olfaction
(smell), gustation (taste), tactile (touch),
vision (sight) [5], and audition (hearing)
[2, 7, 8] each serving a unique purpose
and complementing one another to
enhance their adaptation to the specific
environments in which they operate.
Combining sensing and robotic inspira-
tion can substantially enhance the devel-
opment of mechanical systems, enabling
them to perform specialized tasks more
autonomously [9].
1.2. Mobility, Control, and
Autonomy
The most obvious aspect of bioinspira-
tion research is related to the develop-
ment of robotic platforms that replicate
natural movements and processes in
their mobility [10, 11]. From insects [12] to
mammals [13, 14], whether on land [15],
in water [1, 16, 17, 18], or in the air [19,
20, 21], evolution has led to remarkable
mobility adaptations and energy effi-
ciency across the animal kingdom. These
adaptations have inspired numerous
innovative approaches in robotics, par-
ticularly in the areas of motion, mobility
[1], and control strategies [10, 22] and
autonomous systems [23, 24] derived
from biological systems.
1.3. Materials and Structures
Bioinspired materials replicate the
properties or functions of natural mate-
rials using synthetic substances [25].
Bioinspiration in materials has already
been revolutionized by emerging man-
ufacturing technologies [25], such as
additive manufacturing, which facilitate
novel design concepts for applications
in sectors like aerospace [26]. From
the material level to the structure and
architectural level, this methodology
has transformed the way we design
and manufacture new components.
These components are characterized
by a high strength-to-weight ratio and
multifunctional capabilities, paving the
way for advancements in both perfor-
mance and efficiency [27].
2. Bioinspired Nondestructive
Testing/Evaluation
Inspiration from biological systems has
generally been applied to the broad
three categories mentioned, but it has
rarely been explored in more specific,
mission-oriented domains such as
NDT/E. While one might argue that
NDT/E methods can fall under the
broader field of sensing—where sensors
are used to indirectly gather information
from materials and structures without
impairing their functionality—our
approach differs. The key distinction is
that NDT/E is not just sensing it is a
comprehensive process. This process
involves multiple steps, including sensing,
the use of specialized materials in the
hardware, implementation (whether
manual or automated, such as through
robotics), preparation, calibration, and,
finally, interpretation of the data. The
ultimate goals—detection, localization,
diagnosis, and potentially prognosis—
are all integral parts of NDT/E methods.
We aim to learn the entire process from
biological systems that perform similar
tasks, not just individual components. In
this sense, we seek to understand bio-
logical processes that, in an abstract way,
align with the objectives of NDT/E goals.
These systems detect cavities (analogous
to defects in our mission), characterize
material properties such as dampness or
dryness (similar to modulus of elasticity),
and measure thickness (akin to corrosion
inspection)—functions directly relevant
to NDT/E.
To better explore the concept of
bioinspired NDT/E, let’s examine three
unique biological systems belonging
to a specialized category we refer to as
“nature’s NDE specialists”—aye-ayes,
termites, and red/arctic foxes—that
perform tasks similar to NDT/E.
2.1. Nature’s NDE Specialist #1:
Aye-Ayes
The aye-aye (Daubentonia madagas-
cariensis) is one of the most unique
primates in the world, first documented
on the island of Madagascar around
1780 [28]. This species represents a
remarkable evolutionary lineage that has
persisted for over 50 million years [29]
(see Figure 2).
The aye-aye, the world’s largest
nocturnal primate, is a relatively small
mammal, measuring an average of
80 cm from nose to tail and weighing
between 2.5 to 3 kg. It also has a notably
large brain (larger than other pro-
simians) [30] and the largest pinnae
(ears) among all primates [31]. The
aye-aye is best known for its remark-
able acoustic-based foraging behavior,
known as “tap-scanning” or “percus-
sive foraging” [32]. As it moves along a
tree’s surface, the aye-aye taps the wood
with its distinctive middle finger while
positioning its nose close to the tree
and angling its large, cupped pinnae
forward. These unique morphologi-
cal traits in its auditory sensory and
movement systems enable the aye-aye
to access food resources such as larvae
in cavities unavailable to most other
animals in Madagascar [33]. This evolu-
tionary success is attributed to the aye-
aye’s advanced movement coordination
and its specialized foraging technique,
which involves acoustic-based actuation
and sensing, synchronized with sensor
data fusion and learning capabilities.
Figure 2. The aye-aye (Daubentonia
madagascariensis).
A P R I L 2 0 2 5 • M AT E R I A L S E V A L U AT I O N 29
CREDIT:
DAVID
HARING,
DUKE
LEMUR
CENTER

Remarkably, aye-ayes are able to forage
using tap-scanning in acoustically
challenging and cluttered environ-
ments like the forests of Madagascar,
relying on their “bat-like pinnae” and
“finger-tapping” to detect grubs and
larvae deep beneath tree bark.
As evident, the aye-aye performs
tap testing in a highly specialized
manner, like the NDT/E techniques
used for composite material inspec-
tion, such as detecting disbonds. The
complex geometry of tree bark and the
composite-like structure of wood high-
light that the aye-aye’s process is highly
specialized, having evolved over millions
of years to be exceptionally efficient.
Recent studies by the author’s team
[34, 35, 36] demonstrate that the unique
shape of the aye-aye’s pinnae and the
mechanics of its auditory system play
a crucial role in filtering out unwanted
signals while enhancing sensitivity to
discontinuities, such as cavities, during
tap-scanning. The current tap-testing
technologies offer simple but effective
solutions in several applications such
as composite material inspection [37,
38, 39, 40]. However, they are limited
by low resolution, signal-to-noise ratio
(SNR), and depth of penetration in gen-
erating high frequency acoustic waves
in damped materials. Consequently,
they lack the capability to, as effectively
as aye-ayes, evaluate deep cavities in
composites. Utilizing the morphological
features of the aye-aye’s pinna and ear
canal to pioneer a new design for tap
testers can substantially enhance SNR
[34] and provide a hardware that can
filter out unwanted signals.
Given their extraordinary abilities,
the aye-aye truly deserves the title of
nature’s most fascinating NDE specialist.
2.2. Nature’s NDE Specialist #2:
Termites
Utilizing an exceptional tapping mech-
anism to generate acoustic waves,
aye-ayes rely on near-field acoustic cues
to detect and characterize cavities within
dry wood. Remarkably, even smaller
biological systems like damp-wood and
dry-wood termites exhibit similar vibro-
acoustic generation abilities. Termites,
small herbivorous social insects, are
well-known for their use of vibrational
signals and are inherently noisy biologi-
cal systems [41, 42, 43]. Vibrations caused
by body shaking, head drumming, and
chewing have been extensively docu-
mented [44, 45, 46, 47, 48, 49, 50]. In 1781,
Smeathman described the audible sound
produced by soldier termites during the
drumming process, referred to as “head
banging,” as a “signal of alarm” [51]. Two
distinct types of termite movements
have been identified: convulsive move-
ments, sometimes described as “cries”
without audible sound, which are used
to summon help, and head drumming
(head banging) (see Figure 3), in which
termites strike the ground with their
mandibles, producing audible “alarm
signals.”
Traditionally, termites have been
viewed as indiscriminate eaters.
However, recent studies suggest that
termites exhibit a clear ability to assess
the quality and potentially the thick-
ness of wood. Research has shown
that termites prefer blocks with higher
wood content [49, 52]. Wood, the
primary substance for dry-wood and
damp-wood termites, presents a wide
range of material properties, including
significant damping, making it difficult
to efficiently generate sound within or
from the material [53]. Given that worker
termites are blind, and chemical cues
alone cannot fully explain their selec-
tion process [54], recent studies indicate
that vibroacoustic cues serve as the
primary mechanism for wood charac-
terization. Recent findings show that
termites’ decision to consume specific
wood is influenced by vibroacoustic
signals, which are directly linked to the
material properties of the wood [52, 55,
56]. Howse demonstrated that substrate
vibrations caused by drumming (head
banging) or vertical oscillatory move-
ments can prompt continued behavior in
nearby termites that sense the vibrations.
This suggests that these vibroacoustic
signals may be used by termites to assess
wood in terms of thickness, quality, and
quantity of available food [44].
Despite their small size, termites are
capable of characterizing the thickness
of complex materials like wood and
evaluating how damp the wood is—
similar to how the modulus of elasticity
is assessed. This makes them a unique
biological system that can inspire the
development of combined robotics and
miniaturized NDT/E capabilities, par-
ticularly for applications where acces-
sibility is a challenge. Understanding
termites’ foraging behavior and the
influential factors, such as head shape
and dynamics, will enable engineers
to pioneer a miniature acoustic wave
generation mechanism inspired by the
exceptional vibroacoustic wave gener-
ation capabilities observed in termites.
This could lead to innovative small-scale
material characterization and inspection
processes.
2.3. Nature’s NDE Specialist #3:
Red and Arctic Foxes
Throughout evolution, species have
developed specialized acoustic sensory
systems to adapt to their ecological
niches. Arctic and red foxes, for example,
possess unique hearing abilities that
allow them to detect distant acoustic
sources underground or beneath snow
[57]. In winter, these fox species rely on
their extraordinary hearing to locate and
NDT TUTORIAL
|
BIOINSPIREDNDE
Figure 3. Zootermopsis nevadensis termite:
(a) soldier and worker and (b) soldier
drumming (head banging).
30
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