Time measurement technique in ultrasonic inspection.

Fourier Transform - phase - slope determination of delta time between received RF burst (T2-R)-(T1-R),where T2 and T1 EMATs are driven in series to eliminate differential phase shift due to probe liftoff.

Slope of the phase is determined by linear regression of weighted data points within the signal bandwidth and weighted y-intercept. The accuracy obtained with this method can exceed one part in one hundred thousand. 

Precision velocity measurements in ultrasonic inspection.

Electromagnetic - acoustic transducer (EMAT) generate ultrasound in the material being investigated. When a wire or coil is placed near to the surface of an electrically conducting object and is driven by a current at the desired ultrasonic frequency, eddy currents will be induced in a near surface region. If a static magnetic field is also present, these currents will experience Lorentz forces of the form F=J x B
Where F is a body force per unit volume, J is the induced dynamic current density, and B is the static magnetic induction. The most important application of EMATs has been in nondestructive evaluation (NDE)applications such as flaw detection or material property characterization. Couplant free transduction allows operation without contact at elevated temperatures and in remote locations. The coil and magnet structure can also be designed to excite complex wave patterns and polarizations that would be difficult to realize with fluid coupled piezoelectric probes. In the inference of material properties from precise velocity or attenuation measurements, use of EMATs can eliminate errors associated with couplant variation, particularly in contact measurements.

Normal Beam inspection in ultrasonic inspection

NORMAL BEAM INSPECTION:- Pulse -echo ultrasonic measurement can determine the location of a discontinuity in a part or structure by accurately measuring the time required for a short ultrasonic pulse generated by a transducer to travel through a thickness of material, reflect from the back or the surface of a discontinuity, and be returned to the transducer. In most applications, this time interval is a few microseconds or less. The two-way transit time measured is divided by two to account for the down-and-back travel path and multiplied by the velocity of sound in the test material. The result is expressed in the well-known relationship.
     d=vt/2 or v=2d/t
Where d is the distance from the surface to the discontinuity in the test piece, v is the velocity of sound waves in the material, and t is the measured round-trip time.

Precision ultrasonic thickness gages usually operate at frequencies between 500kHz and 100MHz, by means of piezoelectric transducer that generate bursts of sound waves when excited by electrical pulses. A wide variety of transducer with various acoustic characteristics have been developed to meet the needs of industrial applications. Typically, lower frequencies are used to optimize penetration when measuring thick, highly attenuating or highly scattering materials, while higher frequencies will be recommended to optimize resolution in thinner, non - attenuating, non - scattering materials. 

ANGLE BEAM IN ULTRASONIC INSPECTION.

Angle Beam 1:- Angle Beam Transducers and wedges are typically used to introduce a refrected shear wave into the test material. An angled sound path allows, the sound beam come in from the side,thereby improving detectability of flaws in and around welded areas.

Angle Beam 2:- Angle beam transducers and wedges are typically used to introduce a refrected shear wave into the test material. The geometry of the sample below allows the sound beam to be reflected from the back wall to improve detectability of flaws in and around welded areas.

C-SCAN DATA IN ULTRASONIC INSPECTION.

The C-scan presentations provides a plan-type view of the location and size of test specimen features. The plane of the image is parallel to the scan pattern of the transducer. C-scan presentations are produced with an automated data acquisition system, such as a computer controlled immersion scanning system. Typically, a data collection gate is established on the A-scan and the amplitude or the time -of-flight of the signal is recorded at regular intervals as the transducer is scanned over the test piece. The relative signal amplitude or the time -of-flight is displayed as a shade of Gray or a color for each of the positions where data was connected. The C-scan presentations provides an image of the features that reflect and scatter the sound within and on the surfaces of the test piece.
High resolution scans can produce very detailed images. Both images were produced using a pulse-echo technique with the transducer scanned over the head side in an immersion scanning system. For the C-scan image on the left, the gate was setup to capture the amplitude of the sound reflecting from the front surface of the quarter. Light areas in the image indicate areas that reflected a greater amount of energy back to the transducer. In the C-scan image on the right, the gate was moved to record the intensity of the sound reflecting from the back surface of the coin. The details on the back surface are clearly visible but front surface features are also still visible since the sound energy is affected by these features as it travels through the front surface of the coin.

B-SCAN DATA IN ULTRASONIC INSPECTION.

B-SCAN PRESENTATION:-The B-scan presentation is a profile (cross - sectional) view of the test specimen. In the B - scan, the time - of - flight (travel time) of the sound energy is displayed along the vertical axis and the linear position of the transducer is displayed along the horizontal axis. From the B - scan, the depth of the reflector and it's approximate linear dimensions in the scan direction can be determined. The B - scan is typically produced by establishing a trigger gate on the A - scan. Whenever the signal intensity is great enough to trigger the gate, a point is produced on the B-scan. The gate is triggered by the sound reflecting from the Blackwall of the specimen and by smaller reflectors with in the material. In the B-scan image above, line A is produced as the transducer is scanned over the reduced thickness portion of the specimen. When the transducer moves to the right of this section, the Blackwall line BW is produced. When the transducer is over flaws B and C, lines that are similar to the length of the flaws and at similar depths within the material are drawn on the B - scan. It should be noted that a limitation to this display technique is that reflectors may be masked by larger reflectors near the surface. 

Data presentation in ultrasonic inspection.

Ultrasonic data can be collected and displayed in a number of different formats. The three most common formats are know in the NDT world as A-scan,  B-scan and C-scan presentations. Each presentation mode provides a different way of looking at and evaluating the region of material being inspected. Modern computerized ultrasonic scanning system can display data in all three presentation forms simultaneously.

A-scan presentation:-The A-scan presentation displays the amount of received ultrasonic energy as a function of time. The relative amount of received energy is plotted along the vertical axis and the elapsed time (Which may be related to the sound travel time within the material) is displayed along the horizontal axis. Most instruments with an A-scan display allow the signal to be displayed in its natural radio frequency form(RF),as a fully rectified RF signal, or as either the positive or negative half of the RF signal. In the A-scan presentation, relative discontinuity size can be estimated by comparing the signal amplitude obtained from an unknown reflector to that from a known reflector. Reflector depth can be determined by the position of the signal on the horizontal sweep. In the illustration of the A-scan presentation to the right, the initial pulse generated by the transducer is represented by the signal IP, which is near time zero.As the transducer is scanned along the surface of the part, four other signals are likely to appear at different times on the screen. When the transducer is in its far left position, only the IP signal and signal A,the sound energy reflecting from surface A,will be seen on the trace. As the transducer is scanned to the right, a signal from the Blackwall BW will appear later in time, showing that the sound has traveled farther to reach this surface. When the transducer is over flaw B,signal B will appear at a point on the time scale that is approximately halfway between the IP signal and the BW signal. Since the IP signal corresponds to the front surface of the material, this indicates that flaw B is about halfway between the front and back surfaces of the sample. When the transducer is moved over flaw C, signal C will appear in time since the sound travel path is shorter and signal B will disappear since sound will no longer be reflecting from it.

Pulser - Receivers in ultrasonic testing

Ultrasonic pulser - Receivers are well suited to general purpose ultrasonic testing. Along with appropriate transducer and an oscilloscope, they can be used for flaw detection and thickness gauging in a wide variety of metals, ceramics,and composites. Ultrasonic pulser - Receivers provide a unique, low - cost ultrasonic measurement capability. The pulser section of the instrument generates short, large amplitude electric pulses of controlled energy, which are converted into short ultrasonic pulses when applied to an ultrasonic transducer. Most pulser section have very low impedance out puts to better drive transducers. Control functions associated with the pulser circuit include.
1)   pulse length or damping (The amount of time the pulse is applied to the transducer)
2)    pulse energy (The voltage applied to the transducer. Typical pulser circuits will apply from 100 volts 800volts to a transducer)  in the receiver section the voltage signals produced by the transducer, which represent the received ultrasonic pulses, are amplified. The amplified radio frequency (RF)  signal is available as an output for display or capture for signal processing. Control functions associated with the receiver circuit include.
3)   signal rectification ( The RF signal can be viewed as positive half wave, negative half wave or full wave
4)    Filtering to shape and smooth return signals.
5)     Gain, or signal amplification.
6)      Reject control.
The pulser - Receiver is also used in material characterization work involving sound velocity or attenuation measurements,  which can be correlated to material properties such as elastic modulus. In conjunction with a Stepless gate and a spectrum analyzer, pulser - Receivers are also used to study frequency dependent material properties or to characterize the performance of ultrasonic transducers. 

Transducer modeling in ultrasonic testing.

In high -technology manufacturing, part design and simulation of part inspection is done in the virtual world of the computer.  Transducer modeling is necessary to make accurate predictions of how a part of component might be inspected, prior to the actual building of that part. Computer modeling is also used to design ultrasonic transducers.
As noted in the previous section, an ultrasonic transducer may be characterized by detailed measurements of its electrical and sound radiation properties. Such measurements can completely determine the response of any one individual transducer.
There is ongoing research to develop general models that relate electrical inputs (voltage, current) to mechanical outputs (force,velocity)  and vice - versa. These models can be very robust in giving accurate prediction of transducer response, but suffer from a lack of accurate modeling of physical variables inherent in transducer manufacturing. These electrical -mechanical response models must take into account the physical and electrical components in the figure below.
The Thompson -Gray measurement model, which makes very accurate predictions of ultrasonic scattering measurements made through liquid - solid interfaces, does not attempt to model transducer electrical -mechanical response. The Thompson -Gray measurement model approach makes use reference data taken with the same transducer (s) To deconvolve electro - physical characteristics specific to individual transducer.
The long term goal term goal in ultrasonic modeling is to incorporate accurate models of the transducer themselves as well as accurate models of pulser-receivers, cables, and other components that completely describe any given inspection setup and allow the accurate prediction of inspection signals. 

TRANSDUCER BEAM SPREAD IN ULTRASONIC TESTING

Round transducers are often referred to as piston source transducer because the sound field resembles a cylindrical mass in front of the transducer. However the energy in the beam does not remain in a cylinder, but instead spread out as it propagates through the materials. The phenomenon is usually referred to as beam spread but is sometimes also referred to as beam divergence or ultrasonic diffraction. It should be noted that there is actually a difference between beam spread and beam divergence. Beam spread is a measure of the whole angel from side to side of the main lobe of the sound beam in the far field. Beam divergence is a measure of the angle from one side of the sound beam to the central axis of the beam in the far field. Therefore, beam spread is the twice the beam divergence.

Although beam spread must be considered when performing an ultrasonic inspection, it is important to note that in the far field, or fraunhofer zone, the maximum sound pressure is always found along the acoustic axis (centerline)of the transducer. Therefore, the strongest are likely to come Frome the area directly in front of the transducer. Beam spread occurs because the vibrating particle of the material (through which the wave is travelling) do not always transfer all of their energy in the direction of wave propagation. Recall waves propagate through the transfer of energy from one particle to another in the medium. If the particles are not directly aligned in the direction of wave propagation, some of the energy will get transferred off at an angle. (picture what happens when one ball hits another ball slightly off centre). In the near field, constructive and destructive wave interference fill the sound field with fluctuation. At the start of the far field, the beam strength is always greatest at the centre of the beam and diminishes as it spreads outward. Beam angle is important consideration in transducer selection for a couple of reasons. First beam spread lower the amplitude of reflection since sound are less concentrated and, thereby weaker. Second, beam spread may result in more difficulty in interpreting signals due to reflection from the literal sides of the test object or other features outside of the inspection area. Characterization of the sound field generated by transducer is a prerequisite to understanding observed signals.

TRANSDUCER TESTING IN ULTRASONIC INSPECTION.

Some transducer manufacturers have lead in the development of transducer characterization techniques have participated in developing the AIUM-E. 1065 standard Guide for evaluating characteristics of Ultrasonic search units.
Additionally, some manufacturers perform characterizations according to AWS, ESI, and many other industrial and military standards.often,equipment in test labs is maintained in compliance with MIL-C-45662A calibration system requirements. As part of the documentation process, an extensive database containing records of the waveform and spectrum of each transducer is maintained and can be accessed for comparative or statistical studies of transducer characteristics.
Manufacturers often provide time and frequency domain plots for each transducer. The signals below were generated by a spiked pulser. The waveform image on the shows the test response signal in the time domain (amplitude versus time). The spectrum image on the right shows the same signal in the frequency domain ( amplitude versus frequency).  The signal path is usually a reflection from the back wall ( fused silica)  with the reflection in the far field of the transducer. 

Angle beam transducers in ultrasonic testing.

Angle beam transducers :-Angle beam transducers and wedges are typically used to introduce a refrected shear wave into the test material. Transducer can be purchased in a variety of fixed angles or adjustable versions where the user determines the angles of incidence and refraction. In the fixed angle versions, the angle of refraction that is marked on the transducer is only accurate for a particular material,, which is usually steel. The angled sound path allows the sound beam to be reflected from the Blackwell to improve detectability of flaws in and around welded areas. They are also used to generate surface waves for use in detecting defects on the surface of component.
Normal incident shear wave transducer:-are unique because they allow the introduction of shear waves directly into a test piece without the use of an angle beam wedge. Careful design has enabled manufacturing of transducers with minimal longitudinal wave contamination. The ratio of the longitudinal to shear wave component is generally below -30dB.
paint brush transducers 

DUAL ELEMENT & DELAY LINE TRANSDUCER IN ULTRASONIC TESTING.

Dual element transducer :-Contain two independently operated elements in a single housing. One of the elements transmits and the other recives the ultrasonic signal. Active elements can be chosen for their sending and receiving capabilities to provide a transducer with a cleaner signal,and transducer for special applications such as the inspection of course grained material. Dual element transducer are especially well suited for making measurements in applications where reflectors are very near the transducer since this design eliminates the ring down effect that single element transducer experience (when single -element transducer are operating in pulse echo mode, the element cannot start receiving reflected signals until the element has stopped ringing from its transmit function).Dual element transducer are very useful when making thickness measurements of thin materials and when inspecting for near surface defects. The two elements are angled towards each other to create a crossed - beam sound path in the test material.

Delay line transducers:- provide versatility with a variety of replaceable options. Removable delay line, surface conforming membrane, and protective wear cap options can make a single transducer effective for a wide range of applications. As the name implies, the primary function of a delay line transducer is to introduce a time delay between the generation of the sound wave and the arrival of any reflected waves. This allows the transducer to complete its sending function before it starts it's listening function so that near surface resolution is improved. They are designed for use in applications such as high precision thickness gauging of thin materials and delamination checks in composite materials. They are also useful in high - temperature measurement applications sine the delay line provides some insulation to the piezoelectric element from the heat.

CONTACT TRANSDUCER &IMMERSION TRANSDUCERS In ULTRASONIC TESTING.

Contact transducer :- are used for direct contact inspections,and are generally hand manipulated. They have elements protected in a rugged casing to withstand sliding contact with a variety of materials. These transducers have an ergonomic design so that they are easy to grip and move along a surface. They after have replaceable wear plates to lengthen their useful life. Coupling materials of water, grease, oils,or commercial materials are used  to remove the air gap between the transducer and the component being inspected.

Immersion transducer :-do not contact the component. These transducers are designed to operate in a liquid environment and all connections are watertight. Immersion transducers usually in a liquid environment and all connections are watertight. immersion transducers usually have an impedance matching layer that helps to get more sound energy into the water and, in turn, into the component being inspected. Immersion transducers can be purchased with a planer,cylindrically focused or spherically focused lens, A focused transducer can improve the sensitivity and axial resolution by concentrating the sound energy to a smaller area. Immersion transducers are typically used inside a water tank or as part of a squirter or bubbler system in scanning applications. Contact transducer are available in a variety of configuration to improve their usefulness for a variety of applications. The flat contact transducer shown above is used in normal beam inspection of relatively flat surfaces, and where near surface resolution is not critical. If the surface is curved, a shoe that matches the curvature of the part may need to be added to the face of the transducer. If near surface resolution is important or if an angle beam inspection is needed, one of the special contact transducer described below might be used.

HISTORY OF ULTRASONIC

HISTORY OF ULTRASONIC:   prior to world war 2, sonar,the technique of sending sound waves through water and observing the returning to characterize submerged objects,inspired early ultrasound investigators to explor ways to apply the conceptto medical in 1920 and 1935,sokolov studied the use of ultrasonic waves in detecting metal object mulhausar,in 1931,obtained a patent for using ultrasonic waves,using two transducers to detect flaws in solid.Firestone(1940) and simons (1945) developed pulsed ultrasonic testing using a pulse-echo technique.                

                shortly after the close of world war 2,researchers in japan began to explor the medical diagnostic capabilities of ultrasound.The first ultrasonic instruments used an A-mode presentation with blips on oscilloscope screen. that was followed by a B-mode presentatoin with a two dimensional,gray scale image.

                japans work ultrasound was relatively unknown in the united states and Euroup until the 1950s.Researchers then presented their finding on the use of ultrasound to detect gallstone,breast masses,and tumors to the international medical community.japan was also the firsr country to apply Doppler ultrasound,an application of ultrasound that detects internal moving objects such as blood coursing through the heart for cardiovascular investigation.                                                                                  

PIEZOELECTRIC TRANSDUCER IN ULTRASONIC TESTING.

The transducer is a very important part of the ultrasonic instrumentation system. The transducer incorporates a piezoelectric element which converts electrical signals into mechanical vibrational (transmit mode) and mechanical vibrations into electrical signals (receive mode) many factors, including material, mechanical and electrical construction, and the external, mechanical and electrical load conditions,influence the behaviour of a transducer. Mechanical construction includes parameter such as the radiation surface area mechanical damping, housing connector type and other variables of physical construction.As of this writing, transducer manufacturers are hard pressed when constructing two transducers that have identical performance characteristics.
A cut a way of typical contact transducer is shown above. It was previously learn that the piezoelectric element is cut to 1/2 the desired wavelength. To get as much energy out of the transducer as possible and impedance matching is placed between the active element and the face of the transducer. Optimal impedance matching is achieved by sizing the matching layer so that it's thickness is 1/4 of the desired wave length. This keeps waves that were reflected with in the matching layer in phase when they exit the layer (as illustrated in the image to the right) for contact transducer, the matching layer is made from a material that has an acoustical impedance between the active element and steel. Immersion transducers have a matching layer with an acoustical impedance between the active element and water.Contact transducer also incorporate a wear plate to protect the matching layer and active element from scratching.
The backing material supporting the crystal has a great influence on the damping characteristics of a transducer. Using a backing material with an impedance similar to that of  the active element will produce the most effective damping such a transducer will have a wider bandwidth resulting in higher sensitivity. As the mismatch in impedance between the active element and the backing material increases material penetration increases but transducer sensitivity is reduced.

BEGINNING OF NON DESTRUCTIVE EVALUATION (NDE).

           Beginnings of nondestructive evaluation:

• Nondestructive testing has been practiced for many decades, with initial rapid developments in instruments in instrumentation spurred by the technological advances that occured during world war2 and the subsequent effort .during the earlier days ,the primary purpose was the detection of defects.As a part of safe life design,it was intended that a structure should not develop macroscopic defect during its life,with the detection of such defect being a cause for removal of the component from service.in response to this need ,increasingly sophisticated techniques using ultrasonic eddy currents,x-rays,dye penetrants,magnetic particles,and other forms of interrogating energy emerged.                                                                                                                                                                          In the early 1970s two event occurredwhich caused the major change in the NDT feild first improvement in the technology led to the ability ti defect small flaws.which caused more parts to be rejected even though the probability of component failure had not change .however the discipline of fracture mechanics emerged which enabledone to predict whether a crack of a given size will fail under a particular load when a materials fracture toughness properties are known other laws were developed to predict the growth rate of crack under cyclic loading with the advent of thes tools it become possible to accept structure containing defect if the sizes of those defects were known This formed the basis for the new philosophy of damage tolerent design component having known defects could continue in service as long as it could be established that those defects would not grow to a critical,failure producing size.
  
        A new challenge was thus presented to the nondestructive testing community.detection was not enough.one needed to also obtain quantitative information about flaw size to serve as an input to fracture mechanics based prediction of remaining life. The need for quantitative information was particularly strongly in the defense and nuclear power industries and led to the emergence of quantitative nondestructive evaluation .as a new engineering research discipline.A number of research programs around the world were started.such as the center for nondestructive evaluation at lowa state university (growing out of a major research effort at the Rockwell international science center): the electric power research institute in charlotte, North carolina; the fraunhofer institute for nondestructive testing in saarbrucken,Germany, and the nondestructive testing center in Harwell,England.                                                                                                                                                 

PRESENT STATE OF ULTRASONICS.

PRESENT STATE OF ULTRASONICS:-Ultrasonic testing (UT) has been practiced for many decades.initial rapid developments in instrumentation spurred by the technological advances from the 1950s continue today. through the 1980s and continuing through the present, computers have provided technicians with smaller and rugged instruments with greater capabilities.Thickness gauging is an example application where instruments have been refined make data collection easier and better.Built in data logging capabilities allow thousand of measurements to be recorded and eliminate the need for a scribe some instruments have the capability to capture waveforms as well as thickness readings.The waveform option allows an operator to view or review the A-scan signal of thickness measurement long after the completion of an inspection. Also some instrument are capable of modifying the measurement based on a surface condition of the material.For example , the signal from a pitted or eroded inner surface of pipe would be treated differently then a smooth surface. This has led to more accurate and repeatable field measurements.

Many ultrasonic flaw detector have a trigonometric function that allows for fast and accurate location determination of flaws when performing shear wave inspections cathode ray tubes,for the most part, have been replaced with LED or LCD screens.These screens, in most cases, are extremely easy to view in a wide range of ambient lighting, Bright or low light working conditions encountered by technician have little effect on the technicians ability to view the screen. screens can be adjusted for brightness,contrast and on some instruments even the color of the screen and signal can be selected.Transducers can be programmed with predetermined instrument settings.The operator only has to connect the transducer and the instrument will set variables such as frequency and probe drive.                                                                                                
Along with computers,motion control and robotic have contributed to the advancement of ultrasonic inspections Early on the advantage of a stationery platform was recognized and used in industry. computers can be programmed to inspect large,complex shaped components, with one or multiple transducers collecting information automated system typically consisted of an immersion tank scanning system and recording system, for a printout of the scan. The immersion tank can be replaced with a squirter systems.which allows the sound to be transmitted through a water column.The resultant C-scan provides a plan or top view of the component.scanning of components is considerably faster than contact hand scanning the coupling is much more consistent.The scan information is collected by a computer for evaluation,transmission to a customer and archiving.

Today,quantitative theories have been developed to describe the interaction of the interrogating fields with flaws.models incorporating the results have been integrated with solid model descriptions of real-part geometries to simulate practical inspections. Related tools allow NDE to be considered during the design process on an equal footing with  other failure-related engineering disciplines.Quantitative description of NDE performance,such as the probability of detection (POD),have become an integral part of statistical risk assessment.measurement procedure initially developed for metals have been extended to engineered materials such as composites,where anisotropy and inhomogeneity have become important issues.The rapid advances in digilization and computing capabilities have totally changed the faces of many instruments and the type of algorithms that are used in processing the resulting data.High-resolution imaging systems and multiple measuerment modalities for characterizing a flaw have emerged.Interest is increasing not only detecting.characterizing,and sizing defects,but also characterizing the materials.Goals range from the determination of fundamental microstructural characteristics such as grain size,porosity and texture (preferred grain orientation),to material properties related to such failure mechanisms as fatigue,creep and fracture toughness.as technology continues to advance,application of ultrasound also advance.The high-resolution imaging systems in the laboratory today will be tools of the technician tomorrow.... 

Future Direction of ultrasonic inspection.

Future Direction of ultrasonic inspection:- Looking to the future those in the field of NDE see an exciting  new set of opportunities.The defense and nuclear power industries have played a major role in the emergence of NDE, increasing global competition has led to dramatic changes in product development and business cycles.At the same time,aging infrastructure,from roads to buildings and aircraft,present a new set of measurement and monitoring challenges for engineers as well as technicians.

Among the new application of NDE spawned by these changes is the increased emphasis on the use of NDE to improve the productivity of manufacturing processes.Quantitative nondestructive evaluation (QNDE) both increases the amount of information about failure modes and the speed with which information can be obtained and facilitates the development of in-line measurements for process control.                                       The phrase,you cannot inspect in quality,you must build it in,exemplifies the industry focus on avoiding the formation of flaws.Nevertheless,manufacturing flaws will never be completely eliminated and material damage will continue to occur in-service so continual development of flaw detection and characterization techniques is necessary.                                                                                                                                                Advanced simulation tools that are designed for inspectability and their integration into quantitative strategies for life management will contribute to increase the number and types of engineering application of NDE.with growth in engineering application for NDE,there will be a need to expand the knowledge base of technicians performing the evaluations.Advanced simulation tools used in the design for inspecatbility may be used to provide technical students with a greater understanding of sound behavior in materials. UTSIM, developed at lowa state university,provides a glimpse into what may be used in the technical classroom as an interactive laboratory tool.