Why ALBA Hyperthermia System use 434 MHz not 915 MHz frequency?

ALBA Hyperthermia System at 434MHz has been designed and developed to be sold mainly in the region 1, and certified by the TUV RHEINLAND, according to the ITU-R in 5.138, 5.150, and 5.280 of the Radio Regulations of the ISM Bands.

The frequency of 915 MHz in the region 1 it's assigned only to mobile comunications and not medical device.

This means that any Hyperthermia System that works at 915 MHz in the region 1 must be installed in a Faraday cage with consequent additional costs to avoid serious legal consequences by the user and the entities involved.

More informations about Radio regulations ISM bands are avalaible here and here.

industrial, scientific and medical (ISM) radio bands
  Region 1   Region 2   Region 3

Tissue penetration at 434 MHz and 915 MHz frequencies

As shown in the table below, the tissue penetration (Breast Fat as example) at a frequency of 434 MHz is more than 30% deeper compared to 915 MHz

The frequency dependence of the dielectric properties on Breast Fat tissue

Using the simulation program (Dielectric Properties of Body Tissues) we can extract the precise data for the two frequencies as shown below.

Tissue name Frequency [Hz] Conductivity [S/m] Relative permittivity Loss tangent Wavelength [m] Penetration depth [m]
BreastFat 434000000 0.035264 5.5072 0.26521 0.29184 0.35632
BreastFat 915000000 0.049523 5.4219 0.17944 0.14015 0.2506

More informations are available at Compilation of the Dielectric Properties of Body Tissues at RF and Microwave Frequencies page.

References

  1. K.S.Cole and R.H.Cole: "Dispersion and absorption in dielectrics: I. Alternating current characteristics.", Journal of Chemical Physics, April 1941, pp.341-351.
  2. C.Gabriel and S.Gabriel: "Compilation of the Dielectric Properties of Body Tissues at RF and Microwave Frequencies", Internet document; URL: www.brooks.af.mil/AFRL/HED/hedr/reports/dielectric/home.html (authorized mirror at niremf.ifac.cnr.it/docs/DIELECTRIC/home.html). See, in particular, Appendix C: modelling of the data (authorized mirror here).
  3. C.Gabriel: "Compilation of the dielectric properties of body tissues at RF and microwave frequencies", Report N.AL/OE-TR- 1996-0037, Occupational and environmental health directorate, Radiofrequency Radiation Division, Brooks Air Force Base, Texas (USA), June 1996.
  4. C.Gabriel, S.Gabriel and E.Corthout: "The dielectric properties of biological tissues: I. Literature survey", Phys. Med. Biol. 41 (1996), 2231-2249.
  5. S.Gabriel, R.W.Lau and C.Gabriel: "The dielectric properties of biological tissues: II. Measurements in the frequency range 10 Hz to 20 GHz", Phys. Med. Biol. 41 (1996), 2251-2269.
  6. S.Gabriel, R.W.Lau and C.Gabriel: "The dielectric properties of biological tissues: III. Parametric models for the dielectric spectrum of tissues", Phys. Med. Biol. 41 (1996), 2271-2293.
  7. D.Andreuccetti e R.Fossi: "ProprietÓ dielettriche dei tessuti umani: definizioni, modello parametrico, codici di calcolo", Report N.TR/ICEMM/13.00, IFAC-CNR, Firenze (I), settembre 2000.
    Documento disponibile on-line: niremf.ifac.cnr.it/tissprop/document/tissprop.pdf