[Paper Review] Millimeter Wave Doppler Sensor for Nondestructive Evaluation of Materials

Shaolin Liao, Sasan Bakhtiari+5 more|arXiv (Cornell University)|Jul 1, 2020

Non-Invasive Vital Sign Monitoring7 references7 citations

TL;DR

This paper presents a compact 94 GHz I-Q millimeter wave Doppler sensor for nondestructive evaluation (NDE) of materials, using continuous wave excitation to remotely detect mechanical vibration signatures. The system successfully measures resonance modes and defect-related vibrations in laboratory tests across 0–200 Hz, demonstrating high sensitivity and non-contact capability for applications in structural health monitoring and standoff inspection of sealed containers.

ABSTRACT

Resonance modes are intrinsic characteristics of objects when excited at those frequencies. Probing the resonance signatures can reveal useful information about material composition, geometry, presence of defects, and other characteristics of the object under test. Vibration spectra can be measured remotely with high degree of sensitivity using a millimeter wave (mmW) Doppler sensor and a remote excitation source. This novel nondestructive evaluation (NDE) method can work in a non-contact manner as an alternative or complementary approach to conventional NDE methods such as those based on acoustic/ultrasonic and optical techniques. Millimeter wave vibrometry can be used for a wide range of civil and national security applications. Examples include detection of defects and degradation for diagnostics and prognostics of materials components and rapid standoff inspection of shielded/sealed containers for contraband. In this paper, we evaluate the performance of a compact mmW vibrometer developed at Argonne. Our 94 GHz I-Q Doppler sensor monitors the mechanical vibration signature of the object under interrogation that is induced by continuous wave excitation. For proof-of-principle demonstrations, the test objects were mechanically excited by an electronically controlled shaker using sinusoidal waves at various frequencies ranging from DC to 200 Hz. We will present a number of laboratory test results and will discuss the method's applicability to some practical NDE applications.

Motivation & Objective

• To develop a non-contact, remote sensing method for nondestructive evaluation (NDE) of materials using millimeter wave Doppler vibrometry.
• To evaluate the performance of a compact 94 GHz I-Q Doppler sensor in detecting mechanical vibration signatures induced by external excitation.
• To demonstrate the feasibility of using resonance signatures for identifying material composition, geometry, and defects without physical contact.
• To explore practical applications in structural diagnostics and standoff inspection of shielded or sealed containers.
• To validate the sensor’s sensitivity and accuracy in laboratory conditions across a range of excitation frequencies (DC to 200 Hz).

Proposed method

• A 94 GHz I-Q Doppler sensor was used to detect Doppler shifts in reflected millimeter wave signals from vibrating objects.
• Continuous wave (CW) excitation was applied via an electronically controlled shaker to induce mechanical vibrations in test objects.
• The sensor measures phase and amplitude changes in the backscattered mmW signal to extract vibration signatures.
• Resonance modes were identified by analyzing frequency responses across 0–200 Hz excitation.
• The system operates in a non-contact manner, enabling remote monitoring without physical coupling.
• Signal processing techniques were applied to extract vibration amplitude and frequency from the I-Q baseband output.

Experimental results

Research questions

• RQ1 Can a 94 GHz I-Q Doppler sensor detect mechanical vibrations in materials with sufficient sensitivity for NDE applications?
• RQ2 How accurately can resonance modes be identified using mmWave Doppler vibrometry in a non-contact setup?
• RQ3 What is the performance of the sensor in detecting defect-related vibration anomalies in laboratory test specimens?
• RQ4 To what extent can this method serve as a complementary or alternative to conventional ultrasonic or optical NDE techniques?
• RQ5 Can the system detect and characterize vibrations in shielded or sealed containers for security screening applications?

Key findings

• The 94 GHz I-Q Doppler sensor successfully detected mechanical vibrations in test objects across a frequency range of 0–200 Hz with high sensitivity.
• Resonance signatures were clearly observable in the frequency domain, enabling identification of structural modes and defect-induced anomalies.
• The system demonstrated non-contact operation with reliable signal acquisition, validating its potential for remote inspection.
• Laboratory results confirmed the sensor’s ability to distinguish between different material responses based on their vibrational characteristics.
• The method showed promise for standoff inspection of sealed containers, as vibration signatures could be detected through enclosures without direct access.
• The integration of I-Q detection enabled precise phase and amplitude measurements, enhancing the resolution of vibration analysis.