XARION Eta Series Non-Membrane Optical Microphone

Overview

The XARION Eta Series represents a paradigm shift in acoustic sensing technology—replacing mechanical diaphragms with a solid-state, non-contact optical detection principle based on high-finesse Fabry–Pérot interferometry. Unlike conventional condenser or piezoelectric microphones, the Eta sensor detects sound-induced refractive index variations in ambient air (or other transparent media), translating minute pressure fluctuations into measurable phase shifts of a stabilized laser beam. This all-optical architecture eliminates mechanical resonance, mass inertia, and thermal drift limitations—enabling true time-domain fidelity across an unprecedented bandwidth from 10 Hz to 2 MHz. The Eta100 Ultra and Eta250 Ultra models deliver full acoustic-to-ultrasonic coverage up to 1 MHz with ultra-low self-noise (1.5 mPa in 1 Hz bandwidth), while the Eta450 Ultra extends usable bandwidth into the 2 MHz range optimized for laser-ultrasound excitation and broadband NDT. All variants operate without physical coupling, making them intrinsically immune to electromagnetic interference (EMI), vacuum incompatibility, or surface contamination—critical for industrial process monitoring and scientific metrology where sensor perturbation must be avoided.

Key Features

• Fully passive, membrane-free optical transduction—no moving parts, no wear, no aging-related sensitivity drift
• Ultra-wide bandwidth: 10 Hz–1 MHz (Eta100/250 Ultra); 50 kHz–2 MHz (Eta450 Ultra)
• Self-noise floor of 1.5 mPa (1 Hz bandwidth, measured at 1 kHz), enabling sub-pascal acoustic resolution
• Omnidirectional response with factory-traceable free-field and pressure-field calibration
• Robust optical head design rated for continuous operation in industrial environments (IP54-rated enclosure options available)
• High linearity: THD < 3% up to 176 dB SPL (re 20 µPa); damage threshold exceeds 194 dB SPL
• Modular signal conditioning: configurable gain, filtering, and analog/digital output interfaces (LVDS, USB 3.0, Ethernet)
• Eta450 Ultra Array integrates eight synchronized optical microphone channels in a single compact head—optimized for real-time acoustic beamforming and ultrasonic tomography

Sample Compatibility & Compliance

The Eta platform is designed for non-invasive measurement of acoustic emissions from diverse sample types—including electrically conductive, thermally sensitive, or chemically reactive surfaces—without requiring couplants, fixtures, or surface preparation. It is routinely deployed for in-situ inspection of carbon fiber reinforced polymer (CFRP) laminates, laser-welded joints, adhesive bonds, and additive manufacturing build layers. Regulatory alignment includes support for ISO 10816 (vibration condition monitoring), ASTM E1158 (ultrasonic NDT system performance), and IEC 61000-4-3 (EMC immunity testing). Data acquisition workflows comply with ALCOA+ principles; optional firmware enables audit-trail logging and electronic signatures per FDA 21 CFR Part 11 requirements when integrated with validated LIMS or MES platforms.

Software & Data Management

XARION provides the EtaControl Suite—a cross-platform application for real-time spectral analysis (FFT, STFT, wavelet), time-of-flight mapping, and acoustic emission event clustering. Raw interferometric signals are acquired at 100 MS/s (per channel) with 16-bit resolution and timestamped using IEEE 1588 Precision Time Protocol (PTP) for multi-sensor synchronization. Export formats include HDF5, MATLAB .mat, and CSV with metadata compliant with NIEM and ISA-95 standards. API access (C/C++, Python, LabVIEW) enables integration into custom automation frameworks—particularly for closed-loop process control in laser welding, selective laser melting (SLM), or plasma etching applications. Firmware updates are delivered via secure HTTPS with SHA-256 signature verification.

Applications

• Non-contact ultrasonic testing (UT) of composites, welds, and layered structures
• In-process monitoring of laser material processing (ablation, welding, cladding)
• Real-time quality assurance in additive manufacturing (powder bed fusion, directed energy deposition)
• Acoustic emission (AE) source localization in rotating machinery and structural health monitoring (SHM)
• Calibration reference for hydrophones and ultrasonic transducers (traceable to PTB/NIST)
• Electromagnetic compatibility (EMC) testing in RF-shielded chambers
• Fundamental research in thermoacoustics, photoacoustics, and microfluidic acoustophoresis

FAQ

How does the Eta optical microphone achieve contactless measurement?
It relies on interferometric detection of sound-induced refractive index changes in air—no physical interaction with the sound source is required.
Can the Eta450 Ultra Array be synchronized with laser ultrasonic excitation sources?
Yes—integrated TTL triggers and PTP time synchronization enable precise phase alignment with Q-switched or pulsed lasers used for broadband ultrasound generation.
Is calibration traceable to international standards?
All units ship with NIST-traceable calibration certificates (free-field and pressure-field), and field recalibration services follow ISO/IEC 17025 procedures.
What environmental conditions limit operational use?
Optimal performance requires stable atmospheric pressure and temperature; operation in vacuum or high-humidity (>90% RH) environments requires custom optical window configurations.
Does the system support real-time acoustic imaging?
The Eta450 Ultra Array—when paired with the XARION Line Profile Excitation Laser—enables real-time acoustic beamforming at frame rates up to 10 kHz for dynamic defect tracking.