S. H. Pulko

Teaching `soft¿ skills to engineers

Engineering departments widely recognise an increasing need to equip students with effective study skills early in their university education and basic professional skills prior to graduation. These, however, are traditionally difficult modules to teach successfully to larger groups through traditional lecturing. Observations suggest a poor absorption rate from the students and thus a lack in their ability to benefit from these skills both personally and professionally. This paper documents the findings of an initiative which aimed to improve the success of study skills teaching by combining academic and commercial leanings into a modified teaching approach. The results and specific techniques described in this paper can be easily integrated into most types of teaching material.

Thermal analysis of a three-dimensional breast model with embedded tumour using the transmission line matrix (TLM) method

Breast thermography is a non-invasive tool for early detection of breast cancer. It was subject for many years to some controversial issues regarding its efficiency. Advances in infrared camera technology and progress in image processing systems had brought thermal breast imaging back as a valid tool for mammography. Numerical modelling of heat transfer within a woman breast is being an attractive tool that may reveal the conditions under which tumours can be detected in a thermogram. The aim of this work is to use the transmission line matrix (TLM) to model a regular three-dimensional breast with embedded tumour and analyse sensitivity parameters.

Wrapping strategies for temperature control of chilled foodstuffs during transport

There is a growing market for food producers to supply their goods direct to customers, which has largely been brought about by the growing popularity of web-based ordering. However, the geographical distance between supplier and consumer can be large and this presents problems if temperature-sensitive foods are to be transported. Here we describe a numerical model for the thermal experience of foodstuff packaged in expanded polystyrene boxes in the presence of a gel refrigerant. The model is validated by comparing predicted temperatures with those measured in the laboratory, and the model is then used to investigate the effect that the quantity and placement of gel refrigerant and the ambient temperature have on the period for which maximum food temperature can be maintained below 5°C and 8°C. Results indicate that it is possible to maintain chilled food below these temperatures for up to 24 h, though this period is dependent upon ambient temperature, the manner in which the refrigerant is wrapped around the food and the position of a food item inside the box.

Potentialities of steady-state and transient thermography in breast tumour depth detection

Breast thermography still has inherent limitations that prevent it from being fully accepted as a breast screening modality in medicine. The main challenges of breast thermography are to reduce false positive results and to increase the sensitivity of a thermogram. Further, it is still difficult to obtain information about tumour parameters such as metabolic heat, tumour depth and diameter from a thermogram. However, infrared technology and image processing have advanced significantly and recent clinical studies have shown increased sensitivity of thermography in cancer diagnosis. The aim of this paper is to study numerically the possibilities of extracting information about the tumour depth from steady state thermography and transient thermography after cold stress with no need to use any specific inversion technique. Both methods are based on the numerical solution of Pennes bioheat equation for a simple three-dimensional breast model. The effectiveness of two approaches used for depth detection from steady state thermography is assessed. The effect of breast density on the steady state thermal contrast has also been studied. The use of a cold stress test and the recording of transient contrasts during rewarming were found to be potentially suitable for tumour depth detection during the rewarming process. Sensitivity to parameters such as cold stress temperature and cooling time is investigated using the numerical model and simulation results reveal two prominent depth-related characteristic times which do not strongly depend on the temperature of the cold stress or on the cooling period.

An investigation of the sensitivity of embedded passive component temperatures to PCB structure

The embedding of passive components such as resistors, capacitors and inductors within printed circuit boards (PCBs) is motivated, to a large extent, by the desire for increased miniaturization of electronic goods. However, resistors and, to a lesser extent, inductors are heat generating devices, and the temperature developed within PCBs as the result of the operation of embedded passives is an important aspect of multilayer PCB design. Many factors can influence the generation of heat inside such embedded structures, and, in this paper, validated numerical simulations are used to investigate the temperature rises associated with embedded resistors. Sensitivity of temperature rises to PCB structural changes are investigated in terms of embedded resistor temperature and in terms of interaction with other neighboring components on the same and adjacent component layers.

Characterisation of heat spreader materials for pulsed IGBT operation

Insulated gate bipolar transistors (IGBTs) have a very high output power and generate correspondingly large amounts of heat. If not dissipated efficiently, this heat will destroy the IC (integrated circuit). Furthermore, since the input to the IGBT is often in the form of a pulsed wave, the rapid repeated heating and cooling of the chip and the surrounding packaging cause physical stresses, which in turn eventually lead to delamination and breakdown. Reducing the magnitude of thermal excursion in pulsed mode operations reduces the amount of stress caused by expansion and contraction, thereby reducing delamination and maintaining component efficiency for a longer period of time. It is therefore important to maintain a low rate of thermal expansion, or have a slow enough change in temperature for the physical stresses not to be damaging. This is normally done with heat sink assemblies, which form an integral part of IGBT design. This study investigates, via simulations using the transmission line matrix method, the thermal responses of some of the popular heat spreader materials. Material combinations within the layered structure of the heat sink assembly will give different thermal responses, and thus an analysis of operational behaviour of these components, with attention given to the input frequency as well as duty cycle, would provide a better guide to designing more suitable and efficient packaging assemblies and heat sinks.

A three‐dimensional transmission line matrix (TLM) simulation method for thermal effects in high power insulated gate bipolar transistors

In this paper, thermal analysis for a 1,200 A, 3.3 kV insulated gate bipolar transistor (IGBT) module was investigated and analysed using the three‐dimensional transmission line matrix (3D‐TLM) method. This paper also reviews the present status of the use of various thermal heat spreaders such as AlSiC MMC, Cu‐Mo and graphite‐Cu MMC and compares these with copper based heat spreaders and the use of aluminium nitride (AlN), diamond and BeO as substrates and their effect to dissipate the heat flux in heat sources localised in IGBT module design. The TLM method was found to be a versatile tool which is ideally suited to the modelling of many power electronic devices and which proved very useful in the study of transient thermal effects in a variety of device structures.

Numerical simulation of embedded passive components in multi‐layer PCB structures

Numerical modelling is used to predict the thermal behaviour of embedded passive components in multi‐layer PCBs. A three‐signal layer PCB, containing embedded resistors of dimensions 0.3 6 0.3mm and thickness 0.1μm, is used to generate thermal design rules that can be applied to a wide range of PCB structures containing embedded passive components. A software package using the design rules can then make fast predictions on the thermal behaviour of heat‐generating components inside such structures.

Discretization effects in TLM diffusion models

The standard methods for bringing a TLM diffusion model to convergence are necessary but tedious. However, much time and effort can be saved if the initial choices of elemental size and iteration timestep are appropriate. Here we consider the general form of the solution to the diffusion equation and sample the component dynamics to determine the impulse invariant response. We then derive a convenient method for charting the discrepancy between the coefficients of the continuous description and the impulse invariant transformation, as this discrepancy varies with discretization of space and time. The use of the curves in estimating appropriate elemental size and iteration timestep is described. Copyright

Potentialities of Dynamic Breast Thermography

Since the introduction of breast thermography into medicine, researchers have been interested in enhancing the thermal contrast in thermograms taken at steady state. It was found that cooling the surface of the skin during long acclimation periods produced better thermal contrast, although it was agreed that acclimation periods of up to 15 min may suffice to reflect functionalities of inner skin tissues. However, the use of artificial sources for cooling the skin has revealed new functional information that complements steady state thermography findings. The method has been referred to as ‘Dynamic thermography ’ and is based on monitoring skin’s thermal state after cold stress. Although dynamic thermography showed some promises in breast cancer diagnosis during the 70s, it has not received much interest till the advent of computer image processing techniques. Analytical tools such as sequential thermography, subtraction thermography, μ-thermography and thermal parametric images have been used in order to increase the accuracy of breast thermography. Other processing techniques used thermal transients of control points on the breasts to examine the change in blood perfusion induced by the presence of a breast disease . Autonomic cold challenge has also been used to identify a tumour’s blood vessels. Recent numerical methods have investigated the effectiveness of dynamic breast thermography and revealed new parameters that are strongly correlated with tumour’s depth. Here we review the state of the art in dynamic thermography as it is applied to breast diagnosis and identify some of the potential information that could be provided about breast diseases.