About

Clifford J. Lissenden is a Professor of Engineering Science and Mechanics at Penn State University. He is associated with the College of Engineering and is involved in research related to structural health monitoring, nonlinear ultrasonic guided waves, and innovative technological solutions in engineering. His work has been featured in international publications such as 'International Innovation,' highlighting his contributions to the dissemination of scientific and technological research. He is affiliated with the Ben Franklin Center of Excellence in Structural Health Monitoring and is based in the ESM Building at University Park, PA.

Research topics

• Materials science
• Physics
• Engineering
• Acoustics
• Computer Science
• Optics
• Telecommunications
• Composite material
• Mechanical engineering
• Forensic engineering

Selected publications

• Processing and Characterization of Air-Sprayed Bismuth Titanate Ultrasonic Transducers

  Sensors · 2026-03-10

  articleOpen accessSenior authorCorresponding

  Transducers for ultrasonic nondestructive evaluation of materials in harsh environments are needed to manage safe operations in a number of industrial applications including power generation, propulsion, and material and chemical processing. Bismuth titanate has a reasonably high Curie temperature and transduces electrical energy into elastic waves and vice versa. Herein, a slurry containing bismuth titanate powder is air-sprayed onto stainless steel substrates, functionalized, and characterized in terms of coating thickness, center frequency and bandwidth, and signal-to-noise ratio. Coatings 40- 70 μm thick had a center frequency of approximately 7 MHz and a broad frequency response range of 3-20 MHz. Transducers were thermally aged at 375 °C for seven days to assess their temperature tolerance. Post-aging analysis revealed a resonance frequency increase, thickness reduction, and microstructural changes, accompanied by a decrease in signal amplitude. Despite these changes, the aged transducers remained operational with good signal-to-noise ratio. Thermal cycling experiments showed that the response of pristine transducers is changed by cycling to 250 °C, while thermally aged transducers exhibited stable ultrasonic performance. Additional experiments on transducers pre-conditioned at 400 °C demonstrated improved thermal resilience after thermal aging at 350 °C. These field deployable air-sprayed BIT transducers are promising candidates for high-temperature NDE applications.

  PublisherDOI

• Nonlinear ultrasound to detect hydrogen embrittlement in Al2024

  NDT & E International · 2026-01-09

  articleSenior authorCorresponding
  PublisherDOI

• The unheard octaves transforming guided wave applications

  2026-04-16

  article1st authorCorresponding

  Unheard by human ears, ultrasonic guided waves are transforming a broad range of nondestructive evaluation and other applications over many octaves. Nonlinear effects, where the signal processing involves frequencies other than the driving frequency, provide unmatched capabilities. Second harmonic generation, where the frequencies are an octave apart, is just one example. Wave mixing tests are an alternative to second harmonic generation testing. I will start by highlighting several disparate guided wave applications that utilize linear features including adhesive joints, fatigue cracks at fastener holes, and robotic inspection. Then I’ll describe motivation for using nonlinear guided wave features, provide background, and some recent applications for additive manufacturing, fatigue, and hydrogen embrittlement.

  PublisherDOI

• Dual-frequency EMAT for amplitude-modulated Rayleigh wave mixing: Theory, implementation, and thermal damage detection

  Measurement · 2026-03-23

  articleOpen access
  PublisherDOI

• Investigation of stress effect on combinational harmonics generation of low-frequency S0 Lamb wave

  Structural Health Monitoring · 2025-05-22 · 2 citations

  articleOpen access

  This study experimentally and numerically explores the effect of initial stresses on the generation of combinational harmonics due to the nonlinear mixing of low-frequency <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mrow> <mml:mi>S</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>0</mml:mn> </mml:mrow> </mml:msub> </mml:mrow> </mml:math> Lamb waves. The experimental study considers different levels of uniaxial tensile stress. The results indicate that the sum combinational harmonic has a much higher sensitivity to the prestress level, compared to the corresponding acoustoelastic effect. In the numerical study, material nonlinearity is modelled through a 5-constant hyperelastic constitutive equation derived from Murnaghan’s strain energy function. The finite element (FE) simulation results for a quasi-one-dimensional FE model agree with analytical results for bulk-wave mixing, thereby validating the two-step computational procedure for simulating wave propagation in the presence of a prestress. The same procedure is applied to a three-dimensional FE model to investigate different biaxial prestress conditions. The results indicate the feasibility of using the nonlinearity parameter derived from measurements of combinational harmonics to identify the principal stress directions and magnitudes in biaxially prestressed structures, provided that measurements are carried out for a sufficient sampling of wave propagation directions.

  PublisherDOI

• SHM system development for molten salt test loop

  Structural Health Monitoring · 2025-06-11

  articleOpen access1st authorCorresponding

  Ultrasonic structural health monitoring (SHM) systems can detect degrading material properties based on changing wave speeds. In harsh environments like molten salt reactors and allied test loops, the transducers must be sufficiently robust to survive, and guided waves facilitate minimizing the number of transducers. The L (0, 2) guided wave mode can propagate long distances in the Ni-based alloy 600 tubing used for a molten salt thermal convection loop. The sensitivity of the L (0, 2) group velocity to material degradation associated with the corrosive attack of molten salt is assessed by modeling and ex situ guided wave speed measurements from alloy 600 tubing used in static salt tests. Guided wave testing is performed on dry tubing at room temperature. Microscopy is performed after guided wave testing to document the corrosive attack. At driving frequencies of 490 and 680 kHz, the group velocities are shown to decrease and increase, respectively, for small amounts of material degradation on the inner diameter of the tubing. These opposite trends in group velocity are anticipated to provide a sensitive characteristic for SHM. Although the data are somewhat limited, the wave speed of the more dispersive 680 kHz frequency appears to be more sensitive to corrosive attack, with a possible threshold in the 50–100 µm range.

  PublisherDOI

• Frequency bandgap enhancement in locally resonant metasurfaces for <i>S</i>0 Lamb wave mode using topology-optimized resonators

  Journal of Applied Physics · 2025-01-28 · 3 citations

  articleOpen access

  Elastodynamic metasurfaces composed of surface-mounted resonators show great promise for guided wave control in diverse applications, e.g., seismic and vibration isolation, nondestructive evaluation, or surface acoustic wave devices. In this work, we revisit the well-studied problem of “rod-shaped” resonators coupled to a plate to reveal the relationship between the resonator's resonances and antiresonances obtained under unidirectional harmonic excitation, and the resultant frequency bandgap for S0 Lamb mode propagation once a metasurface is arranged. This relationship is shown to hold true even for non-prismatic resonators, such as those presented in our recent studies, in which we established a systematic resonator design methodology using topology optimization by matching a single resonator's antiresonance with a predefined target frequency. Our present study suggests that considering the waveguide (plate) during the resonator design is not essential and encourages a feasible resonator design approach to achieve wide bandgaps just by customizing a single resonator's resonances and antiresonances. We present a topology optimization design methodology for resonators that drive resonances away from antiresonances, i.e., a resonance gap enhancement, yielding a broadband S0 mode bandgap while ensuring the desired bandgap formation by matching antiresonances with a target frequency. The transmission loss of metasurfaces composed with topology-optimized resonators is numerically verified, confirming the generation of wider bandgaps compared to resonators designed without resonance gap enhancement and broadening the applicability of locally resonant metasurfaces.

  PublisherDOI

• Spatial evolution of broadband Rayleigh waves indicative of material state

  Ultrasonics · 2025-03-31 · 2 citations

  articleSenior authorCorresponding
  PublisherDOI

• Material nonlinearity detected by spatial evolution of laser-generated broadband Rayleigh waves with focus on residual strain

  2025-05-13

  articleSenior author

  The structural integrity of additively manufactured engineering components is a critical concern, as additive manufacturing is increasingly regarded as a promising method for fabricating complex geometries. Material evaluation that is nondestructive, noncontact, and in-situ is of great importance to prevent the production of sub-standard components. In this regard, laser ultrasound is well suited for in-situ process monitoring. Laser generated broadband Rayleigh waveforms evolve as they propagate due to material nonlinearity, making them ideal for evaluating microstructure without interference from system-induced nonlinearities. We thermally aged IN718 samples that were additively manufactured to change the microstructure and increase material nonlinearity. The spatial evolution of the Rayleigh waveforms was quantified in ex-situ tests before and after thermal aging. Thermal aging promoted the precipitation of &gamma;′, &gamma;′′, and MC carbides as well as the development of residual stress, all of which contribute to enhanced material nonlinearity and thus spatial waveform evolution. To isolate the effects of phase transformations and residual stress on waveform evolution, we estimated residual strain and stress using shifts in X-ray diffraction patterns. However, it was not possible to quantitatively distinguish the effects of phase transformation and residual strain. Therefore, the effect of residual strain on material nonlinearity is investigated through atomistic-scale simulations. The results start to answer the question of how features of the microstructure are associated with material nonlinearity as detected through nonlinear elastic wave propagation.

  PublisherDOI

• Computing the effect of solute hydrogen atoms on aluminum acoustic nonlinearity parameter

  Journal of Applied Physics · 2025-10-08 · 1 citations

  articleOpen accessSenior author

  Hydrogen embrittlement, a critical concern for the mechanical response of engineering materials, can arise due to an influx of hydrogen atoms at interstitial sites and at grain boundaries. The acoustic nonlinearity parameter (ANP) is used in nondestructive evaluation as a sensitive parameter for the early detection of material degradation. From a measurement perspective, the ANP can be determined from the distortion of elastic waves. From a modeling perspective, the ANP is computed from second and third-order elastic constants. This study investigates the influence of solute hydrogen atoms on the ANP in aluminum using results of density functional theory calculations as input to continuum-scale computations of elastic constants. Based on the sensitivity of the ANP to hydrogen solute atoms, the findings suggest that an additive decomposition of the ANP is not applicable. Additionally, approaches based upon the stress or strain caused by local heterogeneity (such as solute atoms), without including the heterogeneity itself may be misleading with regard to the ANP. Moreover, the general expectation that atomistic and microscale defects increase ANP may not be universally valid because we observed a decrease in ANP due to interstitial hydrogen atoms and grain boundaries. This work provides novel insights into the application of nonlinear acoustics for detecting atomistic-scale defects and lays the groundwork for a more accurate connection between acoustic measurements and hydrogen-related degradation in materials.

  PublisherOA PDFDOI

Recent grants

• Mixing Elastic Waves to Nondestructively Characterize Microstructure During Additive Manufacturing of Metals

  NSF · $358k · 2017–2021

• Higher Harmonic Ultrasonic Guided Waves for Structural Integrity Assessment of Infrastructure

  NSF · $312k · 2013–2017

• Continuous Piezoelectric Health Monitoring Systems Based on Ultrasonic Guided Waves

  NSF · $320k · 2009–2013

Frequent coauthors

• Joseph L. Rose

  Guidedwave (United States)

  42 shared

• Baiyang Ren

  21 shared

• Parisa Shokouhi

  Pennsylvania State University

  21 shared

• Hwanjeong Cho

  Korea Air Force Academy

  20 shared

• Vamshi Krishna Chillara

  Los Alamos National Laboratory

  20 shared

• Mostafa Hasanian

  Pennsylvania State University

  15 shared

• Carl T. Herakovich

  University of Virginia

  14 shared

• Christopher Hakoda

  Los Alamos National Laboratory

  14 shared

Education

• Ph.D., Acoustics

  Penn State University

  1980

• M.S., Acoustics

  University of California, San Diego

  1976

• B.S., Physics

  University of California, San Diego

  1974