Electromechanical Impedance Spectroscopy Research Articles

Elastic, piezoelectric coefficients, and internal frictions of a single alpha-quartz crystal determined by partial-electrode electromechanical impedance spectroscopy.

In this work, all independent elastic coefficients, piezoelectric coefficients, and internal frictions of a single alpha-quartz crystal are determined at room temperature using our recently proposed partial-electrode electromechanical impedance spectroscopy (PE-EMIS). In PE-EMIS, the rectangular parallelepiped quartz sample with two small partial electrodes fabricated on a corner is self-excited/sensed. The conductance spectrum (equivalent to the acoustic resonance spectrum) measured by an impedance analyzer under a free boundary condition is noiseless, allowing the first 100 eigenmodes ranging from 50 to 310kHz to be accurately fitted. To avoid mode misidentification, the off-plane displacement distributions of the quartz sample under different eigenmodes are determined using a scanned-laser vibrometer. The resonance spectrum measured by a traditional sandwich-like RUS apparatus is also presented for comparison, and the results show that the clamping force in sandwich-like RUS shifts the sample's resonance frequencies, causing 13% and 75% overestimations for the piezoelectric coefficients e11 and e14, respectively. In comparison with the RUS, our proposed PE-EMIS is more effective and convenient, and will be widely used for characterization of piezoelectric crystals.

Damage Metrics for Void Detection in Adhesive Single-Lap Joints

Structural Health Monitoring (SHM) techniques, such as Electromechanical Impedance Spectroscopy (EMIS), aim to continuously monitor structures for defects, thus avoiding the need for regular maintenance. While attention has been given to the application of EMIS in the automatic detection of damage in metallic and composite components, integrity monitoring of structural adhesive joints has been comparatively neglected. This paper investigated the use of damage metrics with electrical impedance measurements to detect defects in Single-Lap Joints (SLJs) bonded with a modified epoxy adhesive. Traditional metrics using statistical and distance-based concepts, such as the Root-Mean-Squared Deviation, RMSD, or the Correlation Coefficient, CC, are addressed at detecting voids in the adhesive layer and are applied to five different spectral frequency ranges. Furthermore, new damage metrics have been developed, such as the Average Canberra Distance, ACD, which enables a reduction of possible outliers in damage detection, or the complex Root-Mean-Squared Deviation, cRMSD, which allows for the use of both the real and imaginary components of the impedance, enabling better damage detection in structural adhesive joints. Overall, damage detection is achieved, and for certain spectral conditions, differentiation between certain damage sizes, using specific metrics, such as the RMSD or cRMSD, may be possible. Overall, the RMSD or cRMSD values from damaged SLJs tend to be double the metric values from undamaged joints.

An Efficient Procedure for Bonding Piezoelectric Transducers to Thermoplastic Composite Structures for SHM Application and Its Durability in Aeronautical Environmental Conditions

Piezoceramic transducers (PCTs) bonded to carbon fiber-reinforced plastic (CFRP) composite structures must be durable as well as remain properly bonded to the structure in order to provide reliable data for accurate guided-wave-based structural health monitoring (SHM) of aeronautical components. The current method of bonding transducers to composite structures through epoxy adhesives faces some shortcomings, such as difficult reparability, lack of weldability, longer curing cycles, and shorter shelf life. To overcome these shortcomings, a new efficient procedure for bonding the transducers to thermoplastic (TP) composite structures was developed by utilizing TP adhesive films. Application-suitable TP films (TPFs) were identified and characterized through standard differential scanning calorimetry (DSC) and single lap shear (SLS) tests to study their melting behavior and bonding strength, respectively. Special PCTs called acousto-ultrasonic composite transducers (AUCTs) were bonded to high-performance TP composites (carbon fiber Poly-Ether-Ether-Ketone) coupons with a reference adhesive (Loctite EA 9695) and the selected TPFs. The integrity and durability of the bonded AUCTs in aeronautical operational environmental conditions (AOEC) were assessed in accordance to the standard Radio Technical Commission for Aeronautics DO-160. The AOEC tests performed were operating low and high temperatures, thermal cycling, hot-wet, and fluid susceptibility tests. The health and bonding quality of the AUCTs were evaluated by the electro-mechanical impedance (EMI) spectroscopy method and ultrasonic inspections. The AUCT defects were created artificially and their influence on the susceptance spectra (SS) was measured to compare them with the AOEC-tested AUCTs. The results show that a small change occurred in the SS characteristics of the bonded AUCTs in all of the adhesive cases after the AOEC tests. After comparing the changes in SS characteristics of simulated defects with that of the AOEC-tested AUCTs, the change is relatively smaller and therefore it can be concluded that no serious degradation of the AUCT or the adhesive layer has occurred. It was observed that the most critical tests among the AOEC tests are the fluid susceptibility tests, which can cause the biggest change in the SS characteristics. Comparing the performance of the AUCTs bonded with the reference adhesive and the selected TPFs in the AOEC tests, it was seen that some of the TPFs, e.g., Pontacol 22.100 outperforms the reference adhesive, while the other TPFs have similar performance to that of the reference adhesive. Therefore, in conclusion, the AUCTs bonded with the selected TPFs can withstand the operational and environmental conditions of an aircraft structure, and hence, the proposed procedure is easily installed, reparable, and a more reliable method of bonding sensors to aircraft structures.

Influence of void damage on the electromechanical impedance spectra of Single Lap Joints

Adhesively bonded joints are susceptible to a variety of damage sources, which may be of difficult detection with current Non-Destructive Testing (NDT) methods. Structural Health Monitoring (SHM) techniques, such as the Electromechanical Impedance Spectroscopy (EMIS), aims to outpace NDT by continuously monitoring structures for defects. However, given the complexity of adhesive joint structures, EMIS capability for damage detection still needs to be thoroughly studied. In this manner, electrical impedance measurements were done to Single Lap Joints (SLJ), with both a modified epoxy adhesive and Pressure Sensitive Adhesive (PSA) for void detection. Void defects could not be detected on adhesive joints with the PSA but, in the case of joints with the modified epoxy adhesive, impedance signatures were significantly altered by the presence of both the artificially created void, and by a second damage source caused during the SLJ manufacture. Experimental measurements from modified epoxy joints were compared with simulation results, yielding good approximation when considering the effect of the second source of damage. An approximation of the mechanical impedance was also computed using numerical results from the pristine SLJ model. In this manner, it is possible to detect damage in the adhesive layer of SLJs with electrical impedance measurements from EMIS.

Numerical and experimental investigation of delamination severity estimation using local vibration techniques

This paper presents vibration-based methods for detecting and quantifying delaminations in composite structures. Three different delamination sizes were considered numerically and experimentally. Our approach combines and compares finite element method (FEM) numerical analysis and experimental measurements to find the location of structural delaminations and identify their severity. First, we noticed that a low-frequency modal study comparing pristine and damaged plates could not provide local damage information. Hence, a high frequency-modal analysis was performed to obtain the local damage information. The damaged mode shapes corresponding to resonance frequencies that cause significant local vibration (high amplitude) over the damaged regions were calculated numerically. The result shows the capability of damage identification (location and size of structural delaminations) within the high-frequency modal analysis. The numerical results were validated experimentally. The experiments include electromechanical impedance spectroscopy (EMIS) and scanning laser Doppler vibrometer (SLDV) techniques. The EMIS experiment was implemented to predict the resonance frequencies which cause significant local vibration over the delamination regions. The spectra of the electromechanical response resemble the vibration response of the structure and detect the new resonances created by the presence of the delamination. The test plate’s experimental resonance peaks show a good match with the resonance frequencies of the numerical modal analysis. The SLDV experiments measured the local vibration over the investigated scanning areas. The operational vibration shapes corresponding to predicted resonance frequencies were created. These experimental mode shapes may visually measure the delaminations by observing intense local vibration over the delamination zones. Comparing the numerical mode shapes and the operational vibration shapes shows a good match between numerical and experimental results.

Determining Full Matrix Constants of Piezoelectric Crystal From a Single Sample Using Partial Electrode Electromechanical Impedance Spectroscopy.

To determine all the material constants of a piezoelectric crystal using the IEEE resonance method or ultrasonic method, several samples with specific geometries and orientations are required, and the obtained results may be somewhat self-contradictory. The resonant ultrasound spectroscopy (RUS) can determine full material constants of a single piezoelectric sample by matching the numerically computed eigenfrequencies to the measured resonance spectrum. However, typically the usage of PZT transducers for excitation and reception makes the testing complicated and may add additional mass and damping. In this work, we propose a new method called partial electrode electromechanical impedance spectroscopy (PE-EMIS), which can obtain all the elastic, piezoelectric constants, and related internal frictions of a piezoelectric crystal by just using a single sample without additional transducers. In PE-EMIS, two small PEs are fabricated on one corner of a piezoelectric sample, and the sample's resonance frequencies, along with the internal frictions of the k th eigenmode, can be accurately obtained from the conductance spectrum measured using an impedance analyzer. The PE-EMIS experiment is carried out on a rectangular parallelepiped PZT-4 piezoelectric ceramic, and the extracted material constants are highly repeatable. Three of the extracted elastic constants ( c₁₁^E , c₃₃^D , and c₆₆^E ) are validated by the traditional wave propagation method. Due to its simplicity, convenience, and accuracy, the proposed PE-EMIS is expected to be widely used for characterization of piezoelectric materials in near future.

Nonlinear Electro-Mechanical Impedance Spectroscopy for fatigue crack monitoring

This article presents a Nonlinear Electro-Mechanical Impedance Spectroscopy (NEMIS) methodology for fatigue crack monitoring. Different from the conventional Electro-Mechanical Impedance Spectroscopy (EMIS) implemented in the frequency domain, the proposed NEMIS employs a temporal chirp interrogating signal to obtain the impedance spectra, and simultaneously captures the Contact Acoustic Nonlinearity (CAN) features. To develop an insight into the mechanism behind the NEMIS method, a comparative investigation between the conventional EMIS and the two-phase NEMIS algorithm was conducted. Numerical studies were carried out on a 1-D transitional-bilinear CAN model to demonstrate the chirp-induced higher harmonics and nonlinear mixed-frequency response features. Furthermore, finite element (FE) simulations were conducted to demonstrate the feasibility of the NEMIS. A baseline-free damage index was subsequently developed to quantify the severity of the fatigue crack. Finally, experimental validation of the NEMIS method was performed. The experimental results validated the feasibility and accuracy of the chirp-based impedance spectra. It was also shown that NEMIS successfully captured the nonlinear impedance spectra, obtaining higher harmonics and wave modulation features to manifest the existence of the fatigue crack. Quantification on the severity of the crack was conducted via the nonlinear damage index, which presented a consistent, monotonic trend with the increasing severity of the fatigue crack. The experiment demonstrated the capability of NEMIS for detecting and quantifying fatigue cracks. The article finishes with summary, concluding remarks, and suggestions for future work.

Health monitoring of high-damping viscoelastic materials using sub-resonator enriched electro-mechanical impedance signatures

This article presents a recent progress of the electromechanical impedance spectroscopy methodology for monitoring high-damping viscoelastic materials (solid rocket motor propellant for instance). It employs piezoelectric wafer active sensors (PWAS) with sub-resonators which can create additional resonance peaks for enriching the diagnostic information. In order to develop an in-depth understanding of the mechanism behind the sub-resonator sensor system, an analytical investigation is conducted first. The theoretical formulation treats the sub-resonator PWAS as a mass-in-mass model, which can be seamlessly merged into the traditional 1D constrained PWAS case. The analytical solution for the impedance signature of the new sub-resonator PWAS transducer is derived. Meanwhile, parametric case studies are carried out to analyze the influence of material damping and additional mass of the sub-resonators on the impedance signature. Moreover, numerical simulations are performed to demonstrate the effectiveness of the new sensor creating additional resonance peaks. Comparative investigations are carried out with both the conventional PWAS and the sub-resonator PWAS. EMIS damage indices based on the spectral amplitude and frequency variation features are used to quantify the material degradation. Additionally, the performance of the proposed sub-resonator PWAS is demonstrated via a material creep experiment. The article finishes with summary, concluding remarks, and suggestions for future work.

Nonlinear electromechanical impedance spectroscopy: A powerful tool for studying amplitude dependent internal frictions of solids.

Strain amplitude dependent effects of materials/structures are very important in the field of material science and engineering and have been found to be extremely sensitive to defects or damage. In this work, a nonlinear electromechanical impedance spectroscopy (N-EMIS) technique is proposed to characterize the amplitude dependent internal frictions (ADIFs) and modulus defects (or resonance shift) of materials. First, a new experimental scheme called the on/off parallel resistor capacitor circuit is proposed to measure the N-EMIS of a piezoelectric transducer (PZT)-specimen composite system under high driving levels. Second, based on the N-EMIS, the formulas for calculating the ADIF are derived and validated by vibration measurement using a laser vibrometer. To further enlarge the strain amplitude, a PZT-stepped horn-specimen three-component system is then introduced, with which the maximum strain amplitude can reach 10-3. Finally, ADIF tests are conducted on polycrystalline pure copper and 1045-steel. The results show that at high strain levels, the internal frictions of both materials can reach several times than those at low driving levels, while the modulus drops only slightly. The proposed N-EMIS technique can effectively assess the strain amplitude dependent properties of materials and is expected to be widely used in the near future for evaluation of plasticity, fatigue, and damage.

Effect of mechanical properties and geometric dimensions on electromechanical impedance signatures for adhesive joint integrity monitoring

Adhesive joints are prone to damage, which may be difficult to detect using Nondestructive Test. Structural Health Monitoring techniques, such as the Electromechanical Impedance Spectroscopy (EMIS), allow for continuous monitoring and early detection of structural defects. Developing efficient damage detection algorithms requires simulations of adhesive structures, which require elastic and damping properties under high frequency range. Tests were performed for crash-resistant and silicone adhesives. Numerical simulations with said properties were compared with experimental impedance measurements from Single Lap Joints (SLJ). This allowed for the estimation of adhesive properties, but numerical results for SLJs with silicone adhesive diverged from experimental results.

Excitation-frequency determination based on electromechanical impedance spectroscopy for a laser-microfabricated cavitation microstreaming micromixer

We for the first time propose and validate an electromechanical impedance spectroscopy (EMIS) technique to determine the resonance frequency (fr) of micromixers for effective cavitation microstreaming. Theoretical fr predictions of the oscillating bubble have been inaccurate because it was assumed that the bubble had a spherical shape even though bubbles are commonly trapped in low-profile air pockets, and thus their shapes are not spherical. Empirical excitation-frequency search has been employed but it was time-consuming and could overlook the exact value of fr. Strong electromechanical coupling between a piezoelectric transducer and a microfluidic chip (i.e., a mechanical structure) allows straightforward, rapid fr determination (∼4.5 min) using EMIS. To validate the EMIS method, we compare microstreaming patterns generated by bubbles excited at four different resonance frequencies using a high-speed imaging setup: 1) fr,B, the theoretical fr assuming a spherical bubble, 2) fr,Beq, the theoretical fr based on the concept of an “equivalent spherical bubble” having a surface area equal to the vibrating air-water interface area, 3) fr,Pf, the EMIS-based fr of a piezoelectric transducer, and 4) fr,Cf, the EMIS-based fr of the microfluidic chip bonded with the transducer. After confirming that fr,Cf yields the strongest cavitation microstreaming, the air-pocket shape is designed with consideration of the bubble stability and mixing effectiveness. A micromixer chip with the designed air pockets is excited at fr,Cf and exhibits rapid homogenization (37.2 s) of diluted ink and deionized water in the mixing chamber of a substantial volume (61.9 μL). Additionally, an experimentally validated, adhesive-tape-supported laser microfabrication technique allows rapid prototyping (∼10 min) of polymethyl methacrylate microfluidic chips with an excellent dimensional accuracy, machining resolution, and surface smoothness. We expect the proposed EMIS-based technique for resonance-frequency determination and the simple, rapid laser microfabrication method to be widely employed for bio-/chemical microfluidic applications in the near future.

ELECTRO-MECHANICAL IMPEDANCE BASED SHM OF THICK STRUCTURES IN BROAD-BAND FREQUENCY SPECTRUM

In this study, theoretical and experimental studies were conducted in terms of electro-mechanical impedance spectroscopy (EMIS) to monitor the structural health status of thick metallic bar structures in broad-band frequency in the range up to 15 MHz. Thus, in-plane (longitudinal-wise) and out-of-plane (thickness-wise) mode EMI spectra were included in this range of frequency. Then, the thickness mode EMIS peaks were focused for pristine thick steel bar as a baseline and for bars with simulated damage in different depths and different locations. For theoretical part of the study, coupled field finite element analyses (CF-FEA) were carried out by modeling piezoelectric wafer active sensor (PWAS) bonded on steel bars in pristine and in damaged status. The thickness mode EMIS results from both CF-FEA simulations and EMIS measurements were analyzed to investigate the effects of the damage location and size variations through a statistical pattern recognition method as damage index such as the root mean square deviation, RMSD, method. It was found that RMSD values were similar trend for experimental and CF-FEA.

Development of Ultrasonic Guided Wave Transducer for Monitoring of High Temperature Pipelines.

High-temperature (HT) ultrasonic transducers are of increasing interest for structural health monitoring (SHM) of structures operating in harsh environments. This article focuses on the development of an HT piezoelectric wafer active sensor (HT-PWAS) for SHM of HT pipelines using ultrasonic guided waves. The PWAS was fabricated using Y-cut gallium phosphate (GaPO4) to produce a torsional guided wave mode on pipes operating at temperatures up to 600 °C. A number of confidence-building tests on the PWAS were carried out. HT electromechanical impedance (EMI) spectroscopy was performed to characterise piezoelectric properties at elevated temperatures and over long periods of time (>1000 h). Laser Doppler vibrometry (LDV) was used to verify the modes of vibration. A finite element model of GaPO4 PWAS was developed to model the electromechanical behaviour of the PWAS and the effect of increasing temperatures, and it was validated using EMI and LDV experimental data. This study demonstrates the application of GaPO4 for guided-wave SHM of pipelines and presents a model that can be used to evaluate different transducer designs for HT applications.

Quantitative assessment of compress-type osseointegrated prosthetic implants in human bone using electromechanical impedance spectroscopic methods.

Osseointegrated (OI) prostheses are a promising alternative to traditional socket prostheses. They can enhance the quality of life of amputees by avoiding fit and comfort issues commonly associated with sockets. The main structural element of the OI prosthesis is a biocompatible metallic implant that is surgically implanted into the bone of the residual limb. The implant is designed to provide a conducive surface for the host bone to osseointegrate with. The osseointegration process of the implant is difficult to clinically evaluate, leading to conservative postoperative rehabilitation approaches. Elastic stress waves generated in an OI prosthesis have been previously proposed to interrogate the implant-bone interface for quantitative assessment of the osseointegration process. This paper provides a detailed overview of the various elastic stress wave methods previously explored for in situ characterization of OI implants. Specifically, the paper explores the use of electromechanical impedance spectroscopy (EIS) to assess the OI process in compress-type OI prostheses. The EIS approach measures the electrical impedance spectrum of lead zirconate titanate elements bonded to the free end of the implant. The research utilizes both numerical simulation and experimental verification to establish that the electromechanical impedance spectrum is sensitive (between 400 and 460kHz) to both the degree and location of osseointegration. A baseline-free OI index is proposed to quantify the degree of osseointegration at the implant-bone interface and to assess the stability of the OI implant for clinical decision making.

Ultrasound Bone Fracture Sensing and Data Communication: Experimental Results in a Pig Limb Sample

Approximately 6.3 million fractures occur each year in the United States alone. Accurately monitoring the progression of fracture healing is essential to be able to advise patients when it is safe to return to normal activity. The most common method used to confirm and monitor fracture healing is the acquisition of multiple radiographic images over the many months required for healing. This imaging method uses large expensive equipment and exposes patients to high levels of ionizing radiation. In the study described here, we tested another technology for monitoring fracture healing that could minimize the need for multiple radiographic images. We tested a piezoelectric transducer fixed to the surface of a bone that uses electromechanical impedance spectroscopy to measure simulated fractures and transmits the measurement data to an acoustic receiver located externally on the skin surface.

Simultaneous load and structural monitoring of a carbon fiber rudder stock: Experimental results from a quasi-static tensile test

Carbon-fiber-reinforced plastics are widely used in lightweight marine structures due to their high strength and superior fatigue behavior. In this article, we will present an innovative methodology for simultaneous load and structural monitoring of a carbon-fiber-reinforced plastic rudder stock as part of a big commercial vessel. Experimental results are presented here from a quasi-static tensile test in which the load monitoring is performed using embedded strain sensors. Structural monitoring is based on high-frequency electromechanical impedance spectroscopy combined with dedicated signal processing and surface-mounted piezoelectric transducers. We have achieved the following results: (1) the demonstration of a hybrid monitoring system including load and structural monitoring, (2) successful embedding of strain gauges during composite manufacturing of the carbon-fiber-reinforced plastic rudder stock, (3) development of instrumentation hardware for multichannel electromechanical impedance measurements, and (4) successful damage detection by means of electromechanical impedance spectroscopy in thick carbon-fiber-reinforced plastic rudder stock samples exploiting strain data.

Damage detection in grouted connections using electromechanical impedance spectroscopy

Grouted connections are structural joints formed by a cementitious grout cast between two concentric circular tubes. They are widely used in the offshore construction of oil and gas platforms, and for offshore wind turbines (monopiles and jackets). However, their application in offshore wind turbine installations can be critical due to the high bending moments coming from wind loading. Recently, it was found that grouted connections show limited performance in offshore wind turbine installations leading to settlements between the steel tubes and steel/grout debonding. Hence, structural health monitoring techniques for grouted connections are needed that ensure a safe and reliable operation of offshore wind turbines. This short communication describes the successful application of electromechanical impedance spectroscopy for damage detection in grouted connections.

High-performance piezoelectric (K,Na,Li)(Nb,Ta,Sb)O3 single crystals by oxygen annealing

Ferroelectric single crystals exhibit the largest known piezoelectric constants and therefore show high potential for application in electronic devices, including sensors, actuators, and transducers. Their large properties, however, can only be fully exploited if the behavior is not influenced by lattice defects, formed during high-temperature processing. Such defects can inhibit domain-wall movement, increase leakage currents, and are predominantly responsible for the poor performance of the emerging ferroelectric crystals. Here, an approach to considerably enhance the piezoelectric and ferroelectric properties of (K,Na,Li)(Nb,Ta,Sb)O3 crystals by oxygen annealing is investigated. As compared to the non-annealed crystals, polarization, strain, and piezoelectric constant of the annealed sample were enhanced by a factor of two, resulting in an outstanding room-temperature value of piezoelectric constant d33 = 732 pC/N and a peak value of d33 = 1431 pm/V at the orthorhombic-tetragonal transition. The behavior was analyzed using electromechanical measurements, Mössbauer spectroscopy, and impedance spectroscopy, revealing decreased concentrations of both oxygen vacancies and Sb3+ ions after annealing. The findings indicate that the control of the defect chemistry enables these ferroelectric (K,Na)NbO3-based single crystals to outperform their polycrystalline counterparts and reach the values of lead-containing compositions. Moreover, the present strategy enables further detailed studies of the inherent crystal anisotropy and the possibilities for domain engineering.

Towards structural health monitoring of space vehicles

PurposeThe purpose of this paper is to report the results of a recent project of complex tests on the survival of structural health monitoring (SHM) technology with piezo wafer active sensors (PWAS) and electromechanical impedance spectroscopy (EMIS) at simulating the concomitant action of harsh conditions of outer space: extreme temperatures, radiations, vacuum.Design/methodology/approachThe tests were conducted on PWAS, consists in adhesive and aluminium discs as structural specimens, with PWAS bonded on them. The substantiating of PWAS-EMIS-based SHM technique consists the fact that real part of the PWAS electromechanical impedance spectrum follows with fidelity the resonance behaviour of the structure vibrating under the PWAS excitation. This EMIS signature is very sensitive to any structural changes and, on this basis, can be monitored the onset and progress of structural damages such as fatigue, cracks, corrosion, etc.FindingsThe conclusion of the tests is that the cumulative impact of severe conditions of temperature, radiation and vacuum has not generated decommissioning of sensors or adhesive, which would have meant the compromise of the methodology. A second important outcome is linked to the capability of this methodology to distinguish between the damages of mechanical origin and the false ones, caused by environmental conditions, which are, basically, harmless.Originality/valueThe question of transfer of PWAS-EMIS-based SHM technology to space vehicles and applications received, as a novelty, a first and encouraging response.

An Advanced Multi-Sensor Acousto-Ultrasonic Structural Health Monitoring System: Development and Aerospace Demonstration.

A key longstanding objective of the Structural Health Monitoring (SHM) research community is to enable the embedment of SHM systems in high value assets like aircraft to provide on-demand damage detection and evaluation. As against traditional non-destructive inspection hardware, embedded SHM systems must be compact, lightweight, low-power and sufficiently robust to survive exposure to severe in-flight operating conditions. Typical Commercial-Off-The-Shelf (COTS) systems can be bulky, costly and are often inflexible in their configuration and/or scalability, which militates against in-service deployment. Advances in electronics have resulted in ever smaller, cheaper and more reliable components that facilitate the development of compact and robust embedded SHM systems, including for Acousto-Ultrasonics (AU), a guided plate-wave inspection modality that has attracted strong interest due mainly to its capacity to furnish wide-area diagnostic coverage with a relatively low sensor density. This article provides a detailed description of the development, testing and demonstration of a new AU interrogation system called the Acousto Ultrasonic Structural health monitoring Array Module+ (AUSAM+). This system provides independent actuation and sensing on four Piezoelectric Wafer Active Sensor (PWAS) elements with further sensing on four Positive Intrinsic Negative (PIN) photodiodes for intensity-based interrogation of Fiber Bragg Gratings (FBG). The paper details the development of a novel piezoelectric excitation amplifier, which, in conjunction with flexible acquisition-system architecture, seamlessly provides electromechanical impedance spectroscopy for PWAS diagnostics over the full instrument bandwidth of 50 KHz–5 MHz. The AUSAM+ functionality is accessed via a simple hardware object providing a myriad of custom software interfaces that can be adapted to suit the specific requirements of each individual application.