Engineers working with interior automotive components, damping materials, porous liners, foams, and polymer-based structures know the challenge well: low-reflectivity surfaces often cause signal-quality issues in optical vibrometry.
This article evaluates whether Ommatidia’s Q2 Laser Doppler Vibrometer, a multi-channel LDV based on Frequency Modulated Continuous Wave (FMCW) coherent measurement, can reliably detect vibration on a black, porous automotive floor mat. The material is among the most difficult surfaces encountered in non-contact vibration testing, making it a relevant benchmark for NVH engineers, interior acoustics specialists, validation labs, and Tier-1/Tier-2 suppliers performing structural or acoustic qualification.
Why Low-Reflectivity Surfaces Challenge Optical Vibrometry
Dark, porous materials, typical in automotive floor systems and interior trims, provide weak optical returns due to light absorption and complex scattering. When using a scanning Laser Doppler Vibrometer, this usually manifests as:
- Poor return intensity
- Unstable phase readings
- Dropouts during dynamic excitation
- Difficulty capturing small-amplitude motion
These issues arise because porous materials disrupt laser backscatter, degrading the coherence required for reliable interferometric measurement. For NVH and structural-acoustics teams who rely on vibration signatures to evaluate damping performance, local resonances, or component behavior, poor reflectivity often limits what can be measured without contact.
This is where the Q2’s multi-channel LDV architecture becomes technically valuable.
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Ommatidia’s Q2: A Multi-Channel LDV Built for Challenging Surfaces
The Q2 Laser Doppler Vibrometer uses 65 simultaneous laser beams, each processed simultaneously through a dedicated photonic integrated circuit (PIC), to measure vibration velocity and displacement without contact. For materials engineers and optical metrologists, the key advantages are:
- High return sensitivity, even on dark or porous materials
- Phase-stable measurement using parallel coherent channels
- Full-field acquisition with 40 kHz sampling per channel
- Integrated RGB camera for alignment and ROI definition
- IP54 industrial design suitable for validation labs and test rigs
Because each beam operates as an independent LDV channel, the system can tolerate reduced local reflectivity while preserving the integrity of the full-field measurement. This provides a practical alternative to contact sensors with no mass loading, surface preparation, or risk of altering local dynamics.
A standard automotive floor mat, dark, porous, and acoustically damped, was suspended from an aluminum frame using nylon thread. This ensured minimal boundary constraints and avoided artificially stiffening the specimen. Excitation was applied acoustically via a loudspeaker positioned behind the mat. The excitation signal (100 Hz sine, 500 mV) was generated by the Q2 and amplified before driving the speaker. The Q2 was positioned 1 m from the surface. Experimental setup for the floor mat vibration measurement with Q2 LDV. The test began with an intensity scan to validate optical return quality across the specimen.Experimental Setup
Return Quality and Intensity Scan
Despite the floor mat’s extremely low reflectivity, the Q2 reported return intensities above 60 dB across the entire field of view – well within the range required for stable interferometric vibrometry.
Intensity scan showing uniform signal above 60 dB
For engineers accustomed to dealing with dropouts or speckle-dominated measurements on porous surfaces, this result is significant: it confirms that the Q2’s coherence architecture maintains adequate signal-to-noise ratio even on materials traditionally considered “non-cooperative” for optical sensing.
Vibrometry Measurement
A vibration measurement was then performed across 65 angles (–9° to +8° in 0.2° steps), with the Q2 operating in vibrometry mode. Because the mat was hung freely, it behaved less like a tensioned membrane and more like a loosely supported surface with limited modal structure at 100 Hz. Nevertheless, the Q2 successfully captured the vibration response across all channels.
What This Means for NVH and Interior Materials Engineering
For NVH engineers, trim development teams, polymer specialists, and acoustic validation labs, this demonstration highlights several practical advantages:
- Reliable optical measurement on low-reflectivity materials
- No retroreflective tape, surface treatment, or paint required
- No risk of mass loading, unlike accelerometers
- Suitable for scanning of damping layers, foams, felts & textile composites
- Ideal for SHM, component validation, and interior acoustics studies
- Enables full-field assessment of dynamic behavior during excitation
The Q2 expands the range of measurements in structural dynamics and interior NVH testing, especially when materials are selected for light absorption, damping, or porous energy dissipation.
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Final Thoughts
Low-reflectivity, porous materials have long posed a challenge for Laser Vibrometry and optical vibration testing. This experiment shows that Ommatidia’s Q2 Laser Doppler Vibrometer can provide stable, accurate vibration measurements on surfaces where traditional optical systems fail.
See the full report – Application note: Vibration measurement of automotive inner lining materials using Ommatidia Q2 laser Doppler vibrometer
For OEMs, Tier-1 suppliers, acoustic labs, and researchers in structural dynamics, this means more reliable data, fewer measurement constraints, and significantly broader applicability of non-contact vibration testing across interior and damping materials.
If you would like to evaluate the Q2 on your own materials or test benches, the Ommatidia team can support test design, setup, and data interpretation.
Visit ommatidia-lidar.com or email sales@ommatidia-lidar.com.
