Conventional Microwave Heating Research Articles

Microwave glazing of alumina–titania ceramic composite coatings

The application envelop of atmospheric plasma sprayed ceramic composites can be widened considerably by reducing/eliminating inherent surface defects by treating them through techniques like microwave irradiation. In microwave processing, microwave energy is directly applied to the material. High-frequency microwaves (>1 GHz usually) penetrate into the bulk of the material and the volumetric interaction of the electromagnetic fields with the material results in dielectric (volumetric) heating. This leads to higher heating efficiency with faster processing. Ceramics are transparent to microwaves at low temperatures, however, start absorbing microwaves at higher temperatures resulting change in microstructure and material characteristics. This paper presents microwave processing of atmospheric plasma sprayed alumina–titania ceramic composite coatings in conventional microwave heating system and evaluation of the processed materials through XRD, SEM, microhardness survey and surface finish with illustrations. Results indicate microwave irradiation induces densification of the material and possible flow of dominant gamma-alumina phase that leads to glazing of coated surface. Glazed surfaces exhibit enhanced microhardness as well as surface finish.

A continuous hybrid microwave heating process for producing rapid and uniform rewarming of cryopreserved tissues.

This study investigated use of a continuous hybrid microwave heating process for producing rapid and uniform heating of cryopreserved tissues. This process combines volumetric energy deposition by microwaves with convective surface heating to produce increased warming rates. Moreover, such as a combination of heating techniques introduces additional parameters which can be varied in order to obtain better control of the heating process. In order to evaluate the effectiveness of a continuous hybrid heating scheme, a numerical simulation was developed which solved for electric and temperature fields within a microwave resonant cavity containing beef tissue. The simulation accounted for the temperature dependence of cryopreserved tissue's dielectric properties through an iterative scheme which can simulate thermal runaway. The simulation indicated that a continuous hybrid heating heating process could produce uniform warming at rates which would be unobtainable by conventional microwave heating.

Plasma Assisted Microwave Sintering and Joining of Ceramics

ABSTRACTDirect microwave sintering and joining of low temperature ceramics such as mullite have been extensively studied. However, it is recognised that microwave sintering and joining of high temperature oxide and non-oxide ceramics poses serious problems, primarily because of the difficulty of coupling microwave energy into these non-absorbing materials which make up the bulk of advanced ceramics. Attempts to overcome this problem by using indirect auxiliary heating or utilisation of intermediary or impure materials have been, by and large, unsatisfactory. Indeed, this fundamental physical barrier has seriously impaired the penetration of microwave heating in ceramic processing.In order to overcome this seemingly insurmountable fundamental barrier, a radical approach is required. This has been recently achieved by using a Microwave Induced Plasma (MIP) whereby microwave energy is utilised in a hybrid fashion. In this method, a microwave plasma is used to rapidly heat the ceramic to temperatures at which it becomes absorbing. At this point, microwave radiation is directly coupled to the ceramic and the plasma is extinguished since energy is no longer available to ionise the gas and sustain a plasma. This hybrid approach circumvents the limitations of conventional microwave heating for sintering and joining of advanced materials. In this review paper the fundamentals of microwave/materials interaction and conventional approach to microwave heating of ceramics will be thoroughly discussed. In addition, the new hybrid heating developed by the authors will be described and the possibility of MIP-assisted sintering/joining of industrially important materials will be demonstrated.

Clinical research into hyperthermia treatment of cancer using a 430 MHz microwave heating system with a lens applicator

Tokyo Metropolitan Komagome Hospital, Kyoto University Hospital, and Aichi Cancer Center used a lens applicator microwave equipment, the HTS-100, to treat 90 patients with a total of 96 tumours. The results were analysed, and the following conclusions reached. Three clinical cases have been presented to illustrate the features of the HTS-100. (1) The results of 383 heating sessions using the HTS-100 were analysed. Even tumours larger and deeper than 5 cm could be heated above 42 degrees C. The heating area is much wider than that of the other 2450, 915, 430 MHz microwave heating equipments. (2) Hyperthermia treatment using the HTS-100 was combined with radiotherapy. The percentage effectiveness in terms of CR+PRa was 66.3% for the 89 cases which could be evaluated. Even for tumours larger than 5 cm, and deeper than 4 cm, local control was achieved in 60.7%. Thus, the indications for microwave heating have been significantly expanded. (3) Combination of microwave heating and RF heating is a new protocol which also expands the indications for hyperthermia therapy. (4) The percentage of patients experiencing the side-effects of pain, a sensation of heat, and burns was 15.6%, 6.3%, and 3.6%, respectively. Most of these side-effects were mild and temporary. The percentage of patients experiencing pain was higher than in conventional microwave heating, probably because the area of heating was wider. (5) In the future, the HTS-100 can be expected to play an important role in clinical cancer hyperthermia.