# Review of Microsoft HoloLens Applications over the Past Five Years
## 3 Results
### Applications in Engineering Fields
#### 3.2.3 Other Engineering Fields  
In addition to industrial engineering and architecture and civil engineering, AR is being used in various engineering fields, including aeronautics and astronautics, electronics and communication. [PERSON] et al. [68] developed an AR system to support the manual work of astronauts. The AR system was designed for the HoloLens MR platform and implemented based on a modular architecture. Further, the performance of the developed system was evaluated using 39 participants. The participants installed a temporary stowage rack (TSR) on a physical mock-up of an international space station (ISS) module (Figure 11). The users' experience was evaluated via questionnaires and interviews and in-depth feedback on platform experience (such as technology acceptance, system usability, smart glasses user satisfaction and user interaction satisfaction) was collected. Based on the analysis of the questionnaire and interview, the scores obtained for user experience, usability, user satisfaction and technology acceptance were close to the desired average. In particular, the system usability scale score was 68, indicating that the usability of the system was acceptable in the AR platform. Figure 11: TSR installation in a physical mock-up of an ISS module using an AR system [68]. [PERSON] et al. [69] presented the results of a survey on user satisfaction, with AR applied to three industries: aeronautics, medicine and astronautics. The user satisfaction with AR was investigated by dividing the satisfaction with the interaction and the satisfaction with the delivery device. They surveyed 142 participants from 3 industries; the collected information included age, gender, education level, internet knowledge level and participant roles in various fields. The AR users were not familiar with smart glasses; nonetheless, general computer knowledge was found to have a positive effect on user satisfaction. Furthermore, the results showed that satisfaction with both education and learning was acceptable. However, it was found that gender, age, education and the role of students or experts did not affect user satisfaction. [PERSON] et al. [70] introduced the HoloLens, a mixed reality device, to detect emotions using facial expressions. Preliminary results of emotion recognition using a HoloLens were presented and compared with the emotion recognition results using a regular webcam. In both the regular webcam and the HoloLens, the five emotional expressions of anger, neutral, happy, surprise and sadness were appropriately portrayed by the three subjects selected in the experiment. However, the primary limiting factor affecting the accuracy of both the devices was that the facial expressions for emotions to be predicted had to be maintained for a long time. As it was difficult to hold the facial expressions of a sad emotion until its detection, it presented a serious challenge. However, in experiments with different light conditions, it was found that the accuracy of the HoloLens was better than that of a webcam under similar conditions due to the sensor present in the former. [PERSON] et al. [71] proposed an architecture to provide low latency AR education services in classrooms or laboratories. Similar low latency can be achieved by using an edge computing device capable of real-time data processing and communication between AR devices. If the network is not properly designed, the wireless link may be overloaded, depending on the specific AR application and the number of users. Hence, the overall performance of the application may degrade and the latency may increase. To solve this problem, the performances of AR-supported classrooms or laboratories were modeled and simulated, from which wireless channel measurement and simulation results were presented (Figure 12). To this end, a Microsoft HoloLens 2 teaching application was devised, which demonstrated the feasibility of the proposed approach.