Nondestructive flaw detection (NDT)

It is hoped that the advanced composite materials will be used in the manufacture of structural parts. Light weight, high strength, corrosion resistance and non magnetic properties are the advantages of these materials. In order to prevent the disastrous accidents caused by delamination, it is one of the most concerned technologies to carry out routine nondestructive testing of these structures. The flexible piezoelectric thin film sensor array layer, which can be perfectly matched acoustically with the composite material, is expected to be used for nondestructive testing. One example is the NDT detection array of the rocket's engine shell before the rocket launches. These arrays can be used on the surface of the composite fuel tank, and each unit is activated in order to provide a pulse reflection response. The array unit size of about 0.5 to 1 square inches is sufficient for such occasions and in many large area nondestructive testing. The typical center frequency of this sensor array is 3~10MHz, as well as over 100% of the -6dB component bandwidth.

The staff of the systems and instruments limited used the piezoelectric film to be used for nondestructive testing of the aerospace engine components. It is now necessary for the nondestructive detection sensor to have a 1/64 inch crack detection capability. In addition, the frequency response range of these new materials is also wider than that of conventional sensors. The system and instrument company found that this is a single broadband sensor that can cover the required bandwidth. Their sensors are also used for surface nondestructive testing that requires high resolution and short pulse duration. The probe of the system and instrument company detects the defects within the surface 1mm, and the size is 0.8mm.

The key nodes in the composite structure or the unapproachable detection area, such as offshore oil platform support, are easy to appear in delamination or other damage. They can be fixed on the above special NDT array permanently to detect and monitor the use. The consistency between the units of the multi cell sensor array is up to 1dB. In order to obtain special focus characteristics, these polymer sensors can be made into special shapes.

Sound propagation

Such as strengthening glass fiber composites, aluminum, steel and glass, the sound transmission of such materials can be accomplished by piezoelectric thin film contact microphones or large area arrays such as NDT. These arrays continue to monitor the structure of 0.1~1.0MHz sound propagation as a predictor of structural failures. The wide-band piezoelectric thin film has good response in this frequency range. This performance is especially needed for key applications, such as tankers, underground oil depots and nuclear facilities.

Fluid level sensor

There are many fluid level sensor technologies for designers. The shifting arm of a sliding potentiometer is still widely used in automobiles. The measurement of the distance from a fixed sensor to the surface of the fluid (from the air or from the bottom through the fluid) is still very common. A new type of capacitive product that also uses some fluids to turn into dielectric. Each technology is a trade-off between system cost, performance and reliability. A new type of ultrasonic liquid level sensor, which is being developed by MSI company, is expected to be a digital, solid-state ultrasonic liquid level sensor.

The novel structure is an ultrasonic emission level sensor with multiple transmitters and a common receiver. The sensor is a non metallized piezoelectric film attached to the printed circuit board. The circuit board has electrode shape, conductor and connection part of the other side of the circuit board. The electrode pattern is coupled with the piezoelectric film layer capacitance to generate a number of transmission units. Second conductive strips parallel to the graphic unit as a common receiver.

Because of the existence of the fluid, it will coupling the transmitting signal to the receiver, which is much larger than the ultrasonic wave that is coupled with the air above the fluid (60dB). The excitation signal of the transmitter is a sinusoidal wave with a peak of 20 volts with a peak peak of 1.1MHz. The required circuit consists of a high frequency oscillator, a clock, an analog switch array, a single receiver amplifier with input gates, and a threshold detection circuit. These electronic components can be compressed to the chip level and integrated on the back of the circuit board.

The resolution of the liquid level sensor is determined by the resolution of a graphic electrode on the circuit board. The 2mm wide parallel unit is the most representative of the spacing of 0.5mm. The piezoelectric film emission array is completely plated on the surface of the ground electrode of the transmitter on one side of the liquid. The receiver is composed of the same piezoelectric film, and is capacitive coupling with the signal electrode of the wire pattern on the printed board (PCB). The ground is on the back electrode of the film.

The new liquid level sensor has some unique advantages. The distance between the sending units does not need to be consistent. For a liquid storage tank with uneven volume in its height direction, a simple PCB layout can linearize the volume of nonlinear tank by setting the distance between transmitter units correspondingly. The output of the device is digitized without the need for expensive mode / number conversion. The width of the liquid level sensor is small, less than 1 inches, so it can be inserted into the tube of a small tube. The tube blocks the movement of the liquid and eliminates the large fluctuation of the high level of the liquid surface caused by motion, such as the car's tank at a turn. The reliability is greatly improved. The liquid level sensor can be self diagnosed to ensure that the transmitter / receiver is meaningful to the transmitted signal. No signal indicates a failure. For a detailed discussion of the induction of ultrasonic ink position, please see Appendix C.