## 3 Acquisition of Raw Data
### A Piezolectric-Sensor Embedded Necklace  
Piezoelectric-sensor embedded necklaces are designed in two different configurations: pendants and sports bands [13]. Unlike [4,10,11,19], we selected the stretchable sports-band design. The sports-band design can easily be stretched to the users' neck, so people of different body structures can wear them without any extra effort, and hence it has better usability. As stated in [13], the stretchable necklace has the enormous advantages of comfortability and stability. The sports band is highly preferred in data collection, clinical environments, and algorithm evolution. The pendant [10,11,19], the second necklace design, has the problem of leaving the neck-skin position during motions such as vigorous head-turning, walking, or running. Therefore, a piezoelectric sensor embedded in a stretchable sports-band necklace is selected as shown in Figure 3. The necklace collects accurate experimental data by translating throat skin motion into unique voltage patt \begin{table}
\begin{tabular}{p{56.9 pt} p{113.8 pt} p{113.8 pt} p{113.8 pt} p{113.8 pt}} \hline \hline
**Sensor Type** & **Description** & **Sensor Form** & **Food Classes (Number of Subjects)** & **Accuracy (\%)** \\ \hline Piezoelectric & Refs. [10,11] presented a unique wearable system to detect neck skin movement caused by ingestion. & Necklace. & Water, hot tea, patty, chocolate, and nuts (20). & 87\% [10] and 90\% for hot salt and liquid. 90\% for solids. \\ A smartphone application-based & & & & & 85.3\% for chips, 84.5\% for sandwich and 81.4\% for water. \\  & & & & & 85.3\% for chips, 84.5\% for sandwich and 81.4\% for water. \\  & & & & & 85.3\% for chips, 84.5\% for sandwich and 81.4\% for water. \\ Piezoelectric and accelerometers & & & & & 85.3\% for chips, 84.5\% for sandwich and 81.4\% for water. \\  & & & & & 85.3\% for chips, 84.5\% for sandwich and 81.4\% for water. \\  & & & & & \\ Piezoelectric or Microphones & & & & & 91.3\% and 88.5\% \\  & & & & & (microphone). 75.3\% and 79.4\% (necklace). \\ \hline \hline \end{tabular}
\end{table} 
Table 1: A summary of necklace-based intake monitoring systems. Figure 3: Necklace-type wearable system: (**a**) Subject wearing a necklace; (**b**) Necklace connected to Simblee. Figure 2: Smartphone application for food intake monitoring: (**a**) Caloric intake statistics; (**b**) Caloric method selection; (**c**) Swallow detection for each food category; (**d**) Health feedback for friendly suggestions. The piezoelectric sensor generates a distinct pattern of output voltages according to the amount of pressure the neck skin applies against the sensor. During eating, neck muscles contract and relax in a way that they apply force on the vibration sensor. Hence, the sensor generates a distinct temporal pattern of voltages that represents chewing and swallowing events, as depicted in Figure 4. The piezoelectric-sensor embedded necklace is attached with the general-purpose input/output (GPIO) pin of the Simblee microcontroller, which has built-in analogue to digital converters (ADCs) convert the analogue signal into the digital signal. The sensor without an additional mass carries a sensitivity of 50 mV/g and resonates with magnitude of 1.4 V/g [29]. The smartphone application is the center of coordination between the sensor and the Simblee [30]. The smartphone application enables the sensor to monitor the user's skin movement with the coordination of the Simblee. Thereafter, the sensor continuously measures skin motion until the intake activity is ended. Thus, the hardware system receives a temporal amplitude-varying voltage-signal, representing the ingestion pattern collected at 20 samples per second. The Simblee, a microcontroller, is more compact and smaller in size than the food monitoring system in [2]; thus, it can be carried easily in real-life settings, as depicted in Figure 3.  
The smartphone application played an essential role in the implementation of the food intake monitoring system.