Welding

The introduction of RF welding processes opened up entirely new possibilities in the field of (thermal) jointing methods that were previously impossible

The core elements of RF welding devices are always the RF power transistors, and the corresponding driver stages which also operate in the RF range. Depending on the power applied to the work piece and the physical conditions, the material can thus be welded, cut or burnt out. Such welding or cutting machines often contain a high-performance CO2 laser, the implementation of which requires various RF semiconductors.

CO2 Lasers

Owing to their reliability and durability as beam sources, CO2 lasers are well established in laser material processing

To generate the high-intensity, highly coherent, sharply focussed beams of monochromatic laser light, the light-emitting medium must first be excited with RF emissions. In CO2 lasers, LDMOS transistors perform this function, at frequencies in the 40 to 80 MHz range.Tens of thousands of beams sources are in use worldwide. Most of them are used for laser cutting and welding. The wavelength of a CO2 laser beam is 10.6 micrometers, putting it in the far-infrared spectrum.

Synchrotrons

Particle accelerators, such as the synchrotron, accelerate charged elementary particles or ions to a very high speed, which is very close to the speed of light

According to Einstein’s special theory of relativity, the mass of bodies increases significantly at such high speeds, so that an ever higher energy input is needed in order to further accelerate the elementary particles or ion, and since the particles do not travel in a straight line but on a curved path, vectorially, a permanent acceleration is needed, which requires energy on an immense scale. Previously, large klystron tubes with a nominal output of, for example, 60 kW, were used for such applications, to excite the particles; but if such a klystron fails, the operation of the synchrotron is no longer possible. There are now power amplifiers based on LDMOS transistors, which have a continuous power rating of 600 W, for example, and are operated in parallel in appropriate numbers, so as to permit reliable continuous operation. A monitoring system monitors each individual LDMOS amplifier here so that any amplifier which fails can be replaced by hot-swap without affecting the on-going operation. In addition, these RF transistors require a power supply that is considerably easier to implement than in the case of klystron tubes.

MRI

Medical imaging procedure uses resonance effects to produce images

As the name magnetic resonance imaging (MRI) suggests, this medical imaging procedure uses resonance effects to produce images - and resonances can exist only with alternating fields. Within a very strong magnetic field, which now often has a magnetic field strength of several Tesla in new devices, an alternating magnetic field excites certain atomic nuclei to resonance. LDMOS transistors are key components in the creation of this alternating magnetic field.

RF Lighting

From cars we already know the bright xenon lights, in which xenon gas is excited to glow by an RF signal

Such bright light sources are also used, with various modifications, in other applications, because they are very well suited for the illumination of buildings, for sterilisation with UV light and for many other things. The great advantage of this source of light is the uniform distribution of the light intensity across the entire spectrum, as in sunlight, while LED light sources constantly emit light only at one or more individual frequencies. On the other hand, it is possible to selectively produce desired colours. With a life of around 50,000 hours, RF light sources last virtually as long as LED light sources. LDMOS transistors play a key role in exciting the gas.

Solid State Cooking Heating Drying Mixed Media_3-PF

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Solid State Cooking/Heating/Drying

There is a technological trend to replace the magnetrons used in microwave ovens by LDMOS transistors

This so-called solid-state cooking (cooking with semiconductor technology) is initially not yet available in domestic appliances for price reasons, but is so far only found in professional kitchen appliances such as steamovens for professional kitchens and canteens.Unlike the bulky magnetrons, RF transistor solutions require less space and still offer many design options, including options in terms of performance and heating power. Solid-state cooking allows proper cooking, in which an RF signal, for example with a frequency of 2.4 GHz and a power of 1 to 2 kW, is bombarded on the food products. With a high power and a variable frequency, an homogeneous temperature distribution can be achieved in a closed oven without a rotary plate or a rotary antenna. On the other hand, special controls make it possible to heat one half of the oven more strongly than the other half, in order to cook two different dishes at the same time. In addition to LDMOS transistors, MMICs (microwave monolithic ICs) and of course the appropriate microcontrollers are also used in these applications. In the medical field, selective heating using directed microwaves can be used to destroy tumours and to seal veins. In industry, microwaves can dry wood and other materials, and even whole buildings. Microwaves generated with semiconductors are also useful in pest control. In all these applications the generation of microwaves using microcontrollers, MMICs and LDMOS transistors plays a central role.