Search results

In order to simulate resistive gate transistors, a one‐dimensional simulator, which permits the use of multiple gate contacts on the transistor structure, has been developed. In the case of the multiple gate contact resistive gate transistor, there is a voltage gradient in the gate. The gate voltage thus varies at each point in the channel of the transistor. A gate structure was designed with a geometric profile that gave either a decreasing or an increasing electric field in the gate, depending on the differential voltage applied to the gate contacts. In the saturation region, this parabolically shaped gate structure resulted in a linear relationship between the drain current and the differential gate voltage or gate current. A significant result obtained was the reversal of the drift current direction at certain bias levels. It was also found that the diffusion current may dominate in the strong inversion region of the channel of an NMOS transistor with a resistive gate.

Defects can be caused by a number of factors, such as maintenance damage, ground handling and foreign objects thrown up from runways during an in-service use of composite aerospace structures. Sandwich structures are capable of absorbing large amounts of energy under impact loads, resulting in high structural crashworthiness. This situation is one of the many reasons why sandwich structures are extensively used in many aerospace applications nowadays. Their non-destructive inspection is often more complex. Hence, the choice of a suitable non-destructive testing (NDT) method can play a key role in successful damage detection. The paper aims to discuss these issues.

A comparison of detection capabilities of selected C-scan NDT methods applicable for inspections of sandwich structures was performed using water-squirt, air-coupled and pitch-catch (PC) ultrasonic techniques, supplemented by laser shearography (LS).

Test results showed that the water-squirt and PC techniques are the most suitable methods for core damage evaluation. Meanwhile, the air-coupled method showed lower sensitivity for the detection of several artificial defects and impact damage in honeycomb sandwiches when unfocussed transducers were used. LS can detect most of the defects in the panels, but it has lower sensitivity and resolution for honeycomb core-type sandwiches.

This study quantitatively compared the damage size indication capabilities of sandwich structures by using various NDT techniques. Results of the realised tests can be used for successful selection of a suitable NDT method. Combinations of the presented methods revealed most defects.