ACOUSTICS


hospital. Looking specifically at doors, the amount of traffic through hospitals in general means doors are constantly being opened and closed, which can be disruptive to staff and patients.


Figure 4: Using various signal types of varying complexity, from sine waves, to ‘white noise’, to pre-recorded sounds.


Active noise cancellation


on the algorithm developed by Bernard Widrow and Ted Hoff. Through various simulations and use of pre- recorded sound files from Queen Alexandra Hospital, multiple instances of testing were applied to a model created using MATLAB software tools. The results shown in in Figure 4 illustrate the complexity of this task, as well as some promise that this technique could perhaps be used to reduce some of the noise present in the ICU.


SPL logger


The Sound Pressure Logger (SPL) is a device that can track and log the levels of sound over a long period of time. The World Health Organization (WHO) recommends that in patient rooms noise levels remain at around 30 dB, and do not exceed 40 dB. The SPL employs a microcontroller in conjunction with a microphone. The purpose of the device is to log data in various locations in a hospital (for example, underneath a


Microphone ADC Figure 5: A block diagram of the SPL meter. October 2019 Health Estate Journal 27


Sound-absorbing curtains are accessible on the market, and are an easy way of significantly reducing sound levels. They are a ‘clean-in-place’ product, meaning that they can be convenient for staff, and also reduce laundering costs. Pneumatics can be utilised on various appliances, including doors, drawers, and bins. The ‘catch’ on the system prevents slamming, and therefore creates a less hectic environment for all personnel within the


Microcontroller


The proposed adaptive algorithm used for this system was a Filtered-x Least Means Square (FXLMS) algorithm, a type of Least Mean Square algorithm commonly used in serval applications of ANC controllers across many industries. The FXLMS Algorithm used in this system is based3


patient’s bed), including the decibel levels, over extensive amounts of time. This data can then be extracted via an SD card, and analysed to look at the times of day of when loud noises occur above the threshold of the required standard. The SPL works using an algorithm that converts the microphone’s output signal into a digital format, where the data undergoes a mathematical process to convert it into the useful information (decibel levels).


Project proposals


Long-term investment solutions Depending on the urgency that the client decides they need to act with, small and immediate solutions could be beneficial. These solutions can include the following: n Curtains. n Pneumatics.


Long-term investment solutions Despite acoustic panels being easily accessed, they are quite expensive, and would be a long-term investment due to the capital cost. This could be reviewed by the client in order to scale down the quantity required, but to effectively control the sound levels within the hospital by only using these panels, downscaling would not be advisable. A portable headboard that incorporates ANC technology is the culmination of the work of both disciplines on this project. It would allow for sound-absorbent material and noise cancelling signals to work in unison to create a quieter environment around individual patients. An idea that hasn’t been thoroughly investigated would be enabling patient access to a remote control that allows the patient to choose sounds that they want to listen to. These select sounds could include the following: n Waves. n Rain. n Classical music.


The idea is that a more relaxed environment would be created for the patient, because they would feel a sense of control at a time when they could otherwise potentially feel isolated and unable to control elements of their day that are often taken for granted. This proposal could be used in conjunction with the headboard mentioned previously.


Conclusions


How effective the acoustic modelling was


The simulation using various frequencies and amplitudes proved quite successful – from simple to more complex signals. The understanding of the sound propagation in ICU rooms can now be utilised in moving this project forward in its next iteration, in order to apply it during the further development of passive-active headboards for ICU beds. The ANC simulation was developed for single channel system, and could benefit greatly from the increase in the number of channels to at least two, to cover both sides of the patient’s head position. A computational load and efficient ANC algorithms need to be carefully considered.


Data processing


Data output/ storage


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