Modelling Miniature Incandescent Light Bulbs for Thermal Infrared ‘THz Torch’ Applications

Abstract

The 'THz Torch' concept is an emerging technology that was recently introduced by the authors for implementing secure wireless communications over short distances within the thermal infrared (20-100 THz, 15 μm to 3 μm). In order to predict the band-limited output radiated power from 'THz Torch' transmitters, for the first time, this paper reports on a detailed investigation into the radiation mechanisms associated with the basic thermal transducer. We demonstrate how both primary and secondary sources of radiation emitted from miniature incandescent light bulbs contribute to the total band-limited output power. The former is generated by the heated tungsten filament within the bulb, while the latter is due to the increased temperature of its glass envelope. Using analytical thermodynamic modelling, the band-limited output radiated power is calculated, showing good agreement with experimental results. Finally, the output radiated power to input DC power conversion efficiency for this transducer is determined, as a function of bias current and operation within different spectral ranges. This modelling approach can serve as an invaluable tool for engineering solutions that can achieve optimal performances with both single and multi-channel 'THz Torch' systems.

Advances in Front-end Enabling Technologies for Thermal Infrared ‘THz Torch’ Wireless Communications

“…Moreover, having glass envelopes (e.g. with the miniature COTS incandescent light bulbs used in our earlier proof-of-concept demonstrators), the output radiated power is significantly reduced because of the high absorption of the window glass below ∼65 THz [12]. For these reasons, more efficient but also more expensive miniature COTS thermal emitters can be used.…”

“…This offers opportunities for developing such systems within this largely unregulated part of the electromagnetic spectrum. The 'THz Torch' concept was recently introduced by the authors for providing secure wireless communications over short distances within the thermal infrared [8][9][10][11][12][13]. Both single-and multi-channel wireless links have been reported; the resilience to interception and jamming with 2.56 kbps frequency division multiplexing (FDM) and 0.64 kbps frequency-hopping spread-spectrum (FHSS) systems has been demonstrated experimentally [11].…”

“…Both single-and multi-channel wireless links have been reported; the resilience to interception and jamming with 2.56 kbps frequency division multiplexing (FDM) and 0.64 kbps frequency-hopping spread-spectrum (FHSS) systems has been demonstrated experimentally [11]. Furthermore, the radiation mechanisms for the basic thermal source transducers [12], as well as the power link budget analysis for the system were previously reported [13]. In this paper, we discuss recent advancements in the front-end enabling technologies associated with the THz Torch concept for wireless communications, which go beyond what has already been published.…”

Systems Analysis for Thermal Infrared ‘THz Torch’ Applications

“…4. It should be noted that when the total effective radiating areas of A e f f À filament and A e f f À glass are taken into account for the filament and glass envelope, respectively, the resulting radiant intensities are of the same order of magnitude from the two sources of radiation [7]. Furthermore, it is clearly shown that at a bias current of 44 mA, Channel A, C and D are expected to have higher output radiated power, as the spectral radiance peaks locate within the pass bands of their respective filters at this bias point.…”

“…On the other hand, Channel B is away from either radiation peaks, giving the lowest output radiated power of the four channels, as will be confirmed experimentally in Section 5. [28] and calculated net spectral radiance from both primary and secondary radiation at a bias current of 44 mA [7] 4 Free space losses…”