This paper describes a method of estimating distance via Time-of-Flight (TOF) measurement using ultrasonic Orthogonal Frequency Division Multiplexing (OFDM) signals. Using OFDM signals allows the signals and their sub-carriers to remain orthogonal to each other while continuously transmitting. This estimation method is based on the change of phase of a traveling wave as it propagates through a medium (air for ultrasonic signals). By using signals containing multiple tones, the phase change between each frequency component is slightly different. This phase difference is dependent on the distance traveled and can thus be used to estimate distance. This paper studies the impact of tone (OFDM sub-carriers) separation on accuracy, maximum distance, and computation for two-tone and three-tone systems. The effects of the transducer channel bandwidth and channel noise are accounted for to build an accurate model for a single-transmitter single-receiver system. This study found that each additional tone provides one extra independent distance measurement which improves accuracy in the presence of noise. The inclusion of an additional tone while maintaining the same overall signal strength shows improved performance with a reduction in standard deviation of estimated distance from 5.64 mm to 3.42 mm in simulation. A four-tone system is also examined to show that this effect holds for additional tones.

The aim of this study was to explore the knowledge, practices, and the sources of knowledge that certified prosthetists/orthotists (CPOs) have experienced regarding early pressure injury assessment for different skin tones. This was examined across different contexts of skin tone demographics using qualitative semi-structured interviews with CPOs from different contexts. Seven participants from six different clinics were recruited using purposive sampling. Of the interviewed participants, five were from Scandinavia, one from South Africa, and one from Nigeria. The interviews were conducted to explore the participants’ own experience of this phenomenon using a phenomenological approach and an interpretivist paradigm. Qualitative content analysis was used to analyse the transcribed interviews inductively. The results consisted of five main categories: Assessment, Standardized Methods, Perceptions of Assessment regarding Skin Tones, Sources of Knowledge regarding Skin Tones, and Relevance of Knowledge Improvement, each with a number of subcategories. There were two main findings. Firstly, CPOs lack systematized knowledge of early pressure injuries irrespective of skin tones. Secondly, many CPOs lack assessment knowledge for darker skin tones as it is only learned from experience and is not taught in education or literature. In conclusion, the field of prosthetics and orthotics must develop to improve systematic early pressure injury knowledge and assessment differences between skin tones.

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