7. ELECTRONICS AND INDUSTRIAL PHYSICS RESEARCH LABORATORY

7.1. PREFACE


In our laboratory we have continued using electronics, optics, ultrasonics and thermal waves in the development of various measurement methods to be used in industrial and scientific surroundings. The thermal infrared camera has been used in various applications and it has led to a majour research project with VTT to develop a quality control system for the lumber industry to monitor the quality of wood and sawed planks. We have also studied the heat flow and properties of thermal sinks in certain electronics circuit boards for wireless communication.

Using a grant from Vaisala we have been developing a new type of rain sensor which contains no moving parts. The success of this instrument has led to the development of a distrometer and the design of a micro-weather station to be connected to a personal computer.

The Brite-Euram EU project has been carried through succesfully to measure the surface hardening depth of steel using laser-induced thermal waves. Together with SIK, Gothenburg we have demonstrated the capability of ultrasound to detect foreign objects in food (like cheese). This work is continuation of our earlier work dealing with microbe contamination of food.

We have also carried through a preliminary research program to study the behaviour of water absorption in paper for ink-jet printers using air-borne ultrasound together wih Valmet and water penetration of certain paper laminates in a water bath together with Enso Laminating Papers.

A TEKES project has been carried through to measure the crystallinity of certain polymers for the manufacture of heat-resistant PET bottles using UV optics. The large variations in the surface characteristics of the polymer have produced considerable scatter in the measured results.

Mauri Luukkala
 

7.2. OPTICAL MEASUREMENT METHODS


ON-LINE MEASUREMENT OF THE DEGREE OF CRYSTALLINITY OF PET BOTTLES
Pekka Raatikainen and Mauri Luukkala

The PET (polyethyleneterephalate) polymer packages are commonly used in the food industry. For example, PET bottles are soon replacing glass bottles used for soft drinks. The mechanical durability of the PET bottles depends strongly on the degree of the crystallinity of the polymer. When PET bottles are used as hot fillable containers, the correct degree of crystallinity is crucial: if the degree of crystallinity is low, the bottle will collapse when filled with the hot material.

In the Electronics Research Laboratory we have studied optical methods to determine the degree of crystallinity of PET bottles on line right after the blow molding. The project has been financed by Tekes Technology Development Centre.
 

7.3. THERMAL NON-DESTRUCTIVE EVALUATION


DETERMINATION OF THE HARDNESS PROFILE IN CASE HARDENED STEELS USING INFRARED PHOTOTHERMAL RADIOMETRY
Atte Salmi, Jussi Varis, Markku Oksanen* and Mauri Luukkala

The performance of surface hardened parts is a major issue in automotive and aerospace industries. There is, therefore, a strong need of hardening companies to improve the quality control of their products by introducing new measurement systems which allow for non-destructive, non-contacting hardness profile measurements as an alternative to the presently used destructive inspection methods. It is aim of this Brite-Euram project to develop a contact free, non-destructive photothermal measurement methodology.

In the first year of the network, case-hardened steel specimens with different hardening depths and surface hardnesses were investigated. In our laboratory measurements were performed using photothermal radiometry detection and frequency scanned laser heating. By temporal modulation of the laser light, material properties were correlated with the propagation properties of so called thermal waves which correspond to critically damped harmonic solutions of the thermal diffusion equation. The depth of probing penetration was chosen by changing the excitation frequency, resulting in a maximum range of about 5 mm in-depth in the materials in question.  The thermal wave field at the sample surface was measured by detecting the thermal radiation emitted from the sample by an IR detector.

* Nokia R & D
 

THERMAL INSPECTION OF SOLDER QUALITY OF INTEGRATED CIRCUITS
Jussi Varis, Reijo Lehtiniemi* and Reijo Vuohelainen

The current trend in the electronics industry is the increasing number of functions that elctronic circuits are supposed to carry out. At the same time end users want want smaller and smaller devices. These seemingly contradictory demands have been met with higher integration and the use of surface mounted components. The latter tends to increase the number of contacts needed to be soldered on the printed circuit boards (PCB). The latest development is to place the contacts underneath the component to save valuable space. Unfortunately, these new so-called ball grid array (BGA) components provide a greater challenge to solder quality inspections.

In this study, the solder quality was tested by heating the BGA component with a powerful CO2 laser, and by monitoring the surface temperature of the component with an infrared camera. Bad connection to the PCB or missing solder causes an air gap to form between the BGA and the PCB, thus preventing heat flow from the component to the circuit board. In addition, the method used provides details of the inner structure of the component.

* Nokia Research Center, P.O. Box 407, FIN-00045 NOKIA GROUP
 

7.4. ULTRASONICS AND ACOUSTIC MEASUREMENT METHODS


SYSTEM FOR THE MEASUREMENT OF PAPER WETTING BY ULTRASOUND TRANSMISSION
Jyrki Stor-Pellinen, Edward Hæggström and Mauri Luukkala

The knowledge of the wetting processes of each paper quality is important for understanding and designing the properties of papers for printing. In this investigation, papers were examined by time-dependent attenuation of 1 to 10 MHz ultrasound through-transmission during immersion in five different mixtures of water and isopropanol. The attenuation depends on the degree of liquid absorption into the paper sample, which gives a signature of the paper type and quality. Papers with differing contact angle were tested, and a measurement procedure developed The measurement results showed that at different frequencies, the attenuation by time is different indicating different development of wetting phenomena.
 

PAPER WETTING PROCESSES STUDIED USING ULTRASOUND TRANSMISSION METHOD
Jyrki Stor-Pellinen, Edward Hæggström and Mauri Luukkala

By immersion in water or water-based mixture, several processes may affect on the wetting behaviour of paper.  By the transmission of ultrasound through the immersed paper, the acoustic attenuation varies depending on the development of these processes. We measured the attenuation as a function of time during the first 500 ms with 0.5 ms intervals with four different  types of paper in water-isopropanol mixtures. We suggest an interpretation that connects the measured temporal chances with the effects and processes related to wetting of paper.
 

MEASUREMENT OF DYNAMIC PARAMETERS OF PAPER WETTING PROCESSES BY ULTRASOUND TRANSMISSION METHOD
Jyrki Stor-Pellinen, Edward Hæggström and Mauri Luukkala

Wetting of paper or liquid penetration into paper can be interpreted as a combination of simultaneous and adjacent processes.  Ultrasound transmission through a paper sample during wetting develops depending on the parameters of the different processes. This study presents an approach to the determination of these parameters by the ultrasound transmission measurement.
 

THE EFFECT OF HIGH-POWER ULTRASOUND ON WETTING OF PAPER MONITORED BY ULTRASOUND
Jyrki Stor-Pellinen, Edward Hæggström and Mauri Luukkala

High-power ultrasound has been known for a long time as a way to speed penetration of liquids into porous materials. This work presents results of experimental investigations of the influence of the application of ultrasound in the wetting process papers. The wetting process was monitored by an ultrasonic probe signal, also, by the measurement of the attenuation of ultrasound transmitted through an immersed sample.
 

THE EFFECT OF HIGH-POWER ULTRASONIC ENERGY ON WETTING PAPER
Jyrki Stor-Pellinen, Edward Hæggström and Mauri Luukkala

High-power ultrasound as used to accelerate the penetration of liquids into porous materials is a possible way to control wetting for the production process of special papers.  We present here experimental results about the influence of temporally limited “doses” of ultrasound on wetting speed.  The wetting speed was monitored by 3 MHz ultrasonic liquid penetrometer.
 

USING ULTRASOUND TO FOLLOW A SURFACE MAKE-UP PROCESS OF HIGH-QUALITY PAPER
Edward Hæggström, Reijo Vuohelainen, Jyrki Stor-Pellinen, Mauri Luukkala and Hannu Lätti

The quality of the paper surface is one of the most tangible aspects conveyed to the reader. The possibility to identify and correct variations in the surface quality possess great potential for improvement of the competitive advantage in the making of high-quality magazine paper.
We have been able to semi-online, nondestructively, follow the make-up process of paper. That is we have been able to follow the deployment of a water-alcohol solution onto the paper both in the sense of bulk wetting and in the sense of fibrous wetting using a ultrasonic system. With the same system we have also been able to monitor the time-reversed process of paper drying.
Being able to follow both the make-up processes gives us a handle towards a system for doing online surface make-up of high-quality paper.
 

ULTRASOUND DETECTION OF FOREIGN BODIES IN FOOD
Edward Hæggström, Jyrki Stor-Pellinen and Mauri Luukkala

In order to secure the quality of food products it is of utmost importance to be able to identify foreign bodies in the food samples. This since reclaims are expensive as well monetarily as in a goodwill way of thinking. Especially organic materials (rubber, plastics, glass, glue, bone etc) constitute a major problem within the modern food industry.

This paper introduces a concept based on a ultrasound reflection measurement together with a feature enhancer and a neuro-fuzzy echo classifier which has shown ability to detect and classify foreign bodies in commercial food samples. The concept allows automatic sorting for more thorough manual testing thus enabling a higher rate of production with the same quality control.
 

ACOUSTIC MEMORY PHENOMENON IN POLYCRYSTALLINE FERRITES
Jyrki Stor-Pellinen, V. Ermolov* and M. Luukkala

We have studied the acoustic memory phenomenon in Ni-Co polycrystalline ferrite on 0.5-30 MHz frequency range.  The magnetization distribution in the ferrite is formed due to nonlinear interaction between the acoustic wave and the magnetic field with the same frequency.  This distribution can be stored by letting an acoustic wave propagate into the sample or by applying to it a magnetic pulse.  The interaction signal can be read by a new signal.  The stored signal has a very long lifetime, it remains unchanged, days after being stored.  As a part of the study, we have also applied the phenomenon to carry out correlation, convolution, storage and time-reversal operations of the signals by different configurations of magnetic and acoustic pulses applied to the ferrite samples.

* Nokia R & D