Acellent:A Structural Health Monitoring Company !

SHM refers to the broad concept of assessing ongoing, in-service performance of structures using a variety of inspection techniques. The core of the technology is the development of self-sufficient systems for the continuous inspection of structures with minimal labor involvement. The aim is not simply to detect structural failure, but also provide an early indication of physical damage to define remedial strategies before the structural damage leads to failure.

Under what temperature range should ScanGenie system work?

The ScanGenie system works from 0⁰C to 50⁰C. The suggested storage temperature is from -40⁰C to 85⁰C.

What is the bandwidth definition? What is the ScanGenie’s bandwidth?

Bandwidth is defined as the measure of a circuit or transmission channel to pass a signal without significant attenuation over a range of frequencies. Bandwidth is measured between the lower and upper frequency points where the signal amplitude falls to -3 dB below the pass-band frequency. The -3 dB points are referred to as the half-power points. The bandwidth of the ScanGenie is 24MHz.

What is sampling rate? What sampling rate does the ScanGenie support?

Sampling rate is the rate at which data is sampled. Sampling rate is not directly related to the bandwidth specifications of a high-speed digitizer. Sampling rate is the speed at which the digitizer’s ADC converts the input signal, after the signal has passed through the analog input path, to digital values. Hence, the digitizer samples the signal after any attenuation, gain, and/or filtering has been applied by the analog input path, and converts the resulting waveform to digital representation. The sampling rate of a high-speed digitizer is based on the sample clock that controls when the ADC converts the instantaneous analog voltage to digital values.

The ScanGenie supports the following sampling rates: 150KS/s, 1.5MS/s, 6MS/s, 12MS/s, 24MS/s, 48MS/s.

What is Nyquist Frequency and Theorem?

Nyquist Frequency is the highest frequency component allowed to avoid Aliasing for a given sampling frequency. Nyquist Theorem states that a signal must be sampled at a rate greater than twice the highest frequency component of interest in the signal to capture the highest frequency component of interest; otherwise, the high-frequency content will alias at a frequency inside the spectrum of interest (pass-band).

Does the ScanGenie system support Windows Vista operating system?

Yes. The ScanGenie system supports Windows 2000, XP and Vista operating systems.

What is Lamb wave?

In SHM, Lamb wave is a frequently used term. Lamb wave is named for Horace Lamb (1849-1934, a British scientist) in honor of his fundamental contributions to this subject. It is a type of ultrasonic wave propagating between two parallel surfaces of a structure. Lamb wave can propagate in symmetrical or anti-symmetrical modes. The velocity of Lamb wave depends primarily on the product of actuation frequency and the thickness of the structure.

What is the principle of damage detection using Lamb waves?

In SHM, PZT actuators are often used to actuate the structure. This will produce Lamb waves propagating in the structure, which can be measured using PZT sensors. The PZT actuators can also be used as sensors. When there is a damage on the structure, the Lamb waves propagating through the damage will change. By measuring the change, we will be able to identify the damage. In SHM, a network of actuators and sensors is often used so that the system can scan and monitor a large area of structure or a hotspot area that is of particular concern.

What types of signals are often used to as the actuation signals?

In principle, any signal waveform can be used as an actuation signal to be applied to the actuator. However, Lamb wave has the distinct property that different modes have different propagation velocities at different frequencies. This results in the phenomenon that the signal waveform received by a sensor is very different from the actuation signal. The broader the bandwidth of the actuation signal, the greater the dispersion. This requires that the actuation signal cannot be too narrow while this is highly desirable for detecting small damages. To balance this tradeoff, a Gaussian modulated burst with only several periods is often used. In Acellent’s products, we provide several choices for this purpose. In the meantime, we also provide a convenient tool for the user to design their own actuation signals.

What is the role of signal processing in SHM?

Besides dispersion, structure scattering and reflection of the high frequency ultrasound Lamb waves introduce even more complexities to the signals collected by the sensors. Signal processing plays a role of noise suppression and feature extraction. The extracted features will be more sensitive to a damage while more robust to disturbances. It will thus improve the effectiveness of SHM.

Do I need to have any specific perquisite signal processing knowledge for using Acellent’s software?

No. You only need to know the very basic concepts such as signal frequency, signal acquisition, and sampling rate. Our software provides the maximum needed information, and for some of our products such as SmartComposite, all what you need to do in damage detection is only several clicks.

How PZT sensors detection external impacts?

When a piezoelectric material is subjected to deformation, it gives off a small but measurable amount of electricity. Because of this property, these materials are widely used as sensors and actuators such as ultrasonic transducers, electronic filters and resonators, delay lines, and accelerometers. Devices based on piezoelectric effects have several key technical advantages, including reduced size, greater efficiency, and ease of fabrication. As a result, piezoelectric devices have dominated the field for these applications. The external impact detection by PZT sensor is illustrated in the followingFigure.

What is the impact signal generated by PZT sensors?

The electricity generated by PZT sensors is converted to electrical voltages which has amplitude and phase information which is related to the impact location, direction and energy. The impact signals for PZT sensors are illustrated in the Figure.

How are impact location and force detected?

Acellent has developed a passive SMART Suitcase™ hardware platform and software algorithms to interface with PZT sensors to detect impact locations and force. The portable and small form factor hardware performs,

Data acquisition for 64 PZT sensors simultaneously. The data samples have 12bits resolution
Acquired data samples are recorded with time stamps which can be stored on local hard disk or sent out to a remote data server via wireless data communication network
Acellent Impact Module (AIM) is an application that allows user to setup:

Structure definition for display
Data acquisition control parameters
Sensor layout definition
Real-time impact location and force display
A database to store impact location and force with time stamps

Does the high-speed suitcase work with Acellent SMART Layer?

Yes. One can connect the high-speed suitcase to Acellent SMART Layer. To get a better response, Acellent suggests that users also purchase the APA40 power amplifier to boost up the actuation signal so that users can get clear response from SMART layer.

Do you provide product that has higher sampling rate than 400MS/s?

Yes. Acellent provides a customized product that can reach 2GS/s sampling rate. The resolution will be 8 bit instead of 12 bit.

Do you provide arbitrary waveform generation product that has higher conversion rate than 300MHz?

Yes. Acellent provides a customized product that can reach 1GHz conversion rate with 12-bit resolution.

What does PZT mean?

PZT means Lead Zirconate Titanate (piezoelectric ceramic material).

What is Curie temperature?

Curie temperature is the temperature at which the crystalline structure changes from a piezoelectric (non-symmetrical) to a non-piezoelectric (symmetrical) form. At this temperature PZT ceramics looses the piezoelectric properties. E.g. The Curie temperature for APC 850 is 680 F.

How to integrate a large sensor network with a host structure?

An important part of the structural health monitoring system is the proper integration of the network sensors with the structure. Sensors permanently mounted onto the structures provide the capability to monitor their condition through their lifetime. SMART Layer is a novel and cost-effective method for integrating a network of piezoelectric elements with the structure to monitor the structure condition and detect damage while the structures are in service. The SMART Layer can be either surface mounted on existing structures or embedded inside composite structures during fabrication.

What adhesive should be used for mounting SMART Layer on the surface of structure?

For mounting SMART Layer on an existing structure, epoxy is choosing over silicone based materials because a rigid interface between the piezoelectric elements and the host structure is needed. A rigid interface would provide the mechanical coupling needed to transmit strain between the actuator/sensor and the structure. The SMART Layer can accommodate most epoxy resin cure temperature (up to 400 °F) and autoclave pressure (up to 90 psi). Typically, no modification to the epoxy cure cycle is needed. Hysol EA 9396 or Hysol EA 9394 is recommended to mount the layer for general purpose.

Can the SMART Layers be embedded inside composite structures during different manufacturing processes?

The methods for integrating piezoelectric sensor networks into a composite structure during different fabrication processes, including hand layup of prepregs or wet layup of fiber cloth, the resin transfer molding (RTM) process and the filament winding process, have been developed at Acellent.

Does the SMART Layer embedded inside the composite affect the performance of composite structure?

The performance of a composite structure with embedded SMART Layer has been investigated. Mechanical tests on composite coupon specimens with and without embedded SMART Layers were conducted to assess the change in structural integrity due to inclusion of the layer. Test results indicate that the presence of the SMART Layer does neither noticeably affect the strength of the host composite structure nor promotes delamination.

Under what temperature the SMART Layer can be used?

The continuous operating temperature of the SMART layer is –65 °F ~ 250 °F. It is useful up to +400 °F (+204 °C) for short term exposure. Recent tests demonstrated that the SMART Layer could survive the liquid Nitrogen environment (-321 °F).

What are the electrical limitations of the PZT sensor?

Exceeding the upper and lower driving voltage limits can cause deterioration or depolarization of piezoelectric material. The degree of depolarization depends on the grade of material, the exposure time, the temperature and the other factors. Maximum voltage for the PZTs used in the SMART Layer is: 5~7 VAC/mil.

Can the SMART layer be used in the high humidity and/or aggressive chemical environment?

Generally, the piezoelectric materials and polyimide used in the SMART Layer do not have a very good durability at high humidity or aggressive chemical environment. Protective coating or encapsulation is recommended if the layer is used in high humidity or aggressive chemical environment. Protective coatings and finishes for the SMART Layer used in these environments have been fully studied at Acellent under the support of US Army. Test results showed that there is no signal change after 168-hour exposure to 100% humidity at 120ºF and ASTM B 117 salt fog exposure 336 hours, Per MIL-STD-810F.

What is the thickness of the SMART Layer?

The thickness of the SMART Layer depends on the configuration of the layer. For single side shield SMART layer, the thickness of area without PZT is 7 mil (0.18 mm), while the thickness of area with PZT is15 mil (0.38 mm).

How do I get the proper SMART Layer size, shape and proper distributed sensors network to meet my need?

The size and shape of SMART Layer depends on the host structure being monitored. Acellent manufactures SMART Layers in a variety of sizes, shapes, and complexities. The SMART Layers vary in complexity from single sensor flat strip to multi-sensor 3-D shells. Acellent can work with clients to customize the SMART Layer size, shape and distributed sensors network to meet their need.

I have a huge structure that needs to be monitored, can you fabricate large size SMART Layer for it?

Acellent has developed the technique to fabricate large size SMART Layer. To fabricate large size SMART Layer, several small size SMART Layer need to be fabricated first based on the size of equipment. Then, they can be joined together during the lamination processing to form large size SMART Layer for huge structure.

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