Anders J Johansson

Is Orbital Angular Momentum (OAM) Based Radio Communication an Unexploited Area

We compare the technique of using the orbital angular momentum (OAM) of radio waves for generating multiple channels in a radio communication scenario with traditional multiple-in-multiple-out (MIMO) communication methods. We demonstrate that, for certain array configurations in free space, traditional MIMO theory leads to eigen-modes identical to the OAM states. From this we conclude that communicating over the sub-channels given by OAM states is a subset of the solutions offered by MIMO, and therefore does not offer any additional gains in capacity.

A Measurement-Based Fading Model for Wireless Personal Area Networks

Personal area networks (PANs) are wireless communications systems with high data rates but small coverage area. PAN propagation channels differ from the well-explored propagation channels of wide-area networks due to several reasons: (i) the distances are typically very small, (ii) the antenna arrangements can be quite different, and (iii) the influence from human presence in the environment is different. The current paper presents results of a channel measurement campaign, where measurements are conducted over distances of 1-10 m using several multi-antenna devices, combined to create different PAN scenarios. For each measured Tx-Rx separation, channel realizations are obtained by small spatial movements of the antenna devices, and by rotating the persons holding the devices. From the results, we draw two main conclusions: (i) The small scale amplitude statistics, analyzed as the variations over a small sampling area and frequency subchannels, cannot be described in a satisfactory way using only the Rayleigh or Ricean distribution, rather a mixed distribution, the generalized gamma distribution, is more suitable; (ii) it is advantageous to distinguish between two types of large-scale fading: body shadowing (due to the orientation of the person holding the device) and shadowing due to surrounding objects (lateral movement). We also define and parameterize a complete statistical model for all fading.

A Receiver Architecture for Devices in Wireless Body Area Networks

A receiver architecture suitable for devices in wireless body area networks is presented. Such devices require minimum physical size and power consumption. To achieve this the receiver should, therefore, be fully integrated in state-of-the-art complementary metal-oxide-semiconductor (CMOS) technology, and size and power consumption must be carefully considered at all levels of design. The chosen modulation is frequency shift keying, for which transmitters can be realized with high efficiency and low spurious emissions. A direct-conversion receiver architecture is used to achieve minimum power consumption and a modulation index equal to two is chosen, creating a midchannel notch in the modulated signal. A tailored demodulation structure has been designed to make the digital baseband compact and low power. To increase sensitivity it has been designed to interface with an analog decoder. Implementation in the analog domain minimizes the decoder power consumption. Antenna design and wave propagation are taken into account via simulations with phantoms. The 2.45-GHz ISM band was chosen as a good compromise between antenna size and link loss. An ultra-low power medium access scheme has been designed, which is used both for system evaluation and for assisting system design choices. Receiver blocks have been fabricated in 65-nm CMOS, and a radio-frequency front-end and an analog-to-digital converter have been measured. Simulations of the complete baseband have been performed, investigating impairments due to 1/f noise, frequency and time offsets.

Performance of a radio link between a base station and a medical implant utilising the MICS standard

Modern medical implants are of increasing complexity and with that, the need for fast and flexible communication with them grows. A wireless system is preferable and an inductive link is the most commonly used. But it has the drawback of a very short range, essentially limited to having the external transceiver touching the patient. The Medical Implant Communication System, MICS, is a standard aimed at improving the communication distance. It operates at a higher frequency band between 402 MHz and 405 MHz. We have by simulations and measurements investigated the channel properties of this band and calculated the link performance for a typical implant application. The result is a link speed between a base station and a bedridden patient of 600 kbit bits per second with a bit error rate of 2% in the downlink to the implant and 1 % in the uplink to the base station. Conclusions on the necessary complexity of the base station are also given.

Wave-propagation from medical implants-influence of body shape on radiation pattern

The new standard medical implant communications service (MICS) for communication with medical implants uses the 403-405 MHz band. The influence of a patients body shape and position on the radiation pattern from an implanted radio transmitter has been simulated. Simulations and comparisons have been made with different body shapes (male, female and child) and different arm positions. It can be concluded from the results that the difference between different body shapes are at least as large as the influence of a patients arm movements.

A Link Loss Model for the On-Body Propagation Channel for Binaural Hearing Aids

Binaural hearing aids communicate with each other through a wireless link for synchronization. An analytical propagation model is useful to estimate the ear-to-ear link loss for such binaural hearing aids. This paper presents an analytical model for the deterministic component of the ear-to-ear link loss. The model takes into account the dominant paths having most of the power of the creeping wave from the transceiver in one ear to the transceiver in the other ear, and the effect of the protruding part of the outer ear, called pinna. Simulations are done to validate the model using in-the-ear placement of antennas at 2.45 GHz on numerical heterogeneous phantoms of different age-groups and head sizes showing a good agreement with the model. The ear-to-ear link loss for a numerical homogeneous specific anthropomorphic mannequin (SAM) phantom is compared with a numerical heterogeneous phantom. The loss for the SAM phantom is found to be 30 dB lower than that for the heterogeneous phantom. It is shown that the absence of the pinna and the lossless shell in the SAM phantom underestimate the link loss. The effect of the pinnas is verified through measurements on a phantom where we have included the pinnas fabricated by 3-D printing.

Wash-in kinetics for sevoflurane using a disposable delivery system (AnaConDa®) in cardiac surgery patients

BACKGROUND The use of volatile anaesthetics has increased in situations where conventional anaesthetic machines are inadequate or unavailable, for example, cardiac surgery and intensive care. The disposable anaesthetic conserving device, AnaConDa, allows vaporization of liquid volatile anaesthetics from a syringe pump and rebreathing of exhaled anaesthetic. Clinical use requires understanding of device-specific anaesthetic agent kinetics, which are not fully known. We compared the wash-in kinetics for sevoflurane administered by a conventional vaporizer in a non-rebreathing system and the AnaConDa and evaluated if a standard anaesthesia gas monitor gave accurate readings while using the AnaConDa. METHODS Cardiac surgery patients were randomized to maintenance of anaesthesia with sevoflurane either via a vaporizer or via the AnaConDa (n=8 in each group). Sevoflurane in arterial blood and airway gas was measured with gas chromatography and standard gas monitoring. RESULTS The initial increase in arterial sevoflurane tension was greater with the vaporizer than with the AnaConDa, but the time to reach 80% of maximum sevoflurane tension was close to 8 min in both groups. End-tidal sevoflurane tension mirrored arterial tension in both groups, whereas measured inspired tension was lower than expired and arterial tensions with the use of the AnaConDa. CONCLUSIONS The wash-in kinetics for sevoflurane delivered by the AnaConDa are similar to a vaporizer. End-tidal sevoflurane tension accurately reflects arterial tension whereas inspired tension may be underestimated using an AnaConDa.

Long-term local corticosteroid application does not influence nerve transmission or structure

The long‐term effects of a locally applied depot form of a corticosteroid on the electrical properties and structure of nerves were investigated in an animal experimental model.

Methylprednisolone shortens the effects of bupivacaine on sensory nerve fibers in vivo.

Perineural administration of corticosteroids is frequently applied in the treatment of a variety of chronic pain conditions. Methylprednisolone selectively inhibits the transmission of nerve impulses in C‐fibers whereas A‐fiber activity is unaffected.

The effect of heat and moisture exchanger on humidity and body temperature in a low-flow anaesthesia system.

Background: Artificial humidification of dry inspired gases seems to reduce the drop in body temperature during surgery. The aim of this study was to evaluate the humidity and temperature of anaesthetic gases with heat and moisture exchangers (HMEs). The secondary aim was to evaluate if HMEs in combination with low‐flow anaesthesia could prevent a decrease in the body temperature during general anaesthesia.