Normal Movements Trembling Normal Movements Trembling 0 81012141618 20 2 81012 18 20 Time(second) Time (second) Figure 4:Distance measurement for normal movement and Figure 5:Distance measurement after high-pass filtering trembling estimator for the hand movement trend,which averages the measurements lead to very accurate distance measure- distance measurements over a time period of 200ms.The ments since a distance change equal to the sound wave- second part extracts the tremor signal by subtracting the length of 1.8cm introduces a phase change of 2.There- hand movement trend from the distance measurements. fore,LLAP can track the hand movements with millimeter Figure 5 shows the tremor signal after the high-pass filter accuracy.Furthermore,LLAP provides low latency distance processing for the same sequence shown in Figure 4. information with a small delay of 10.7 milliseconds.In this demo,we use our open source LLAP implementation which Our tremor detection component uses the variation of the is available at [4]. filtered tremor signal and the movement trend to determine whether the hand is static,moving or trembling.Under the Tremor Detection case of a tremor,our system will measure both the trem- We detect hand tremor using the high precision distance bling frequency and the trembling magnitude using the fil- measurements provided by LLAP.Figure 4 shows the dis- tered tremor signal.For example,from Figure 5,the trem- tance output for normal movement and trembling.We ob- bling frequency(which is about 7Hz)can be measured by serve that normal movements have smooth distance changes counting the peaks during a time period of one second.We over time.When the hand starts trembling after 12 sec- can also obtain the trembling magnitude,which is around onds,we can clearly observe the vibrations of the hand. 8mm(peak-to-peak)in this case.The application then de- However,the tremor signals are mixed with hand movement termines the tremor intensity using these measurements. trends,as the user's hand moves around slowly during the trembling period. Implementation and Demo Setup The tremor detection application prototype is implemented We use a high-pass filter to remove the smooth movements using Objective-C on the iOS platform.The application can of the hand and extract the tremor signal.This high-pass be installed on common iPhone models,such as iPhone filter contains two parts.The first part is a moving average 6/6s/7.0 2 4 6 8 10 12 14 16 18 20 Time (second) -60 -40 -20 0 20 Distance (mm) Normal Movements Trembling Figure 4: Distance measurement for normal movement and trembling measurements lead to very accurate distance measure￾ments since a distance change equal to the sound wave￾length of 1.8cm introduces a phase change of 2π. There￾fore, LLAP can track the hand movements with millimeter accuracy. Furthermore, LLAP provides low latency distance information with a small delay of 10.7 milliseconds. In this demo, we use our open source LLAP implementation which is available at [4]. Tremor Detection We detect hand tremor using the high precision distance measurements provided by LLAP. Figure 4 shows the dis￾tance output for normal movement and trembling. We ob￾serve that normal movements have smooth distance changes over time. When the hand starts trembling after 12 sec￾onds, we can clearly observe the vibrations of the hand. However, the tremor signals are mixed with hand movement trends, as the user’s hand moves around slowly during the trembling period. We use a high-pass filter to remove the smooth movements of the hand and extract the tremor signal. This high-pass filter contains two parts. The first part is a moving average 0 2 4 6 8 10 12 14 16 18 20 Time (second) -5 0 5 10 Distance (mm) Normal Movements Trembling Figure 5: Distance measurement after high-pass filtering estimator for the hand movement trend, which averages the distance measurements over a time period of 200ms. The second part extracts the tremor signal by subtracting the hand movement trend from the distance measurements. Figure 5 shows the tremor signal after the high-pass filter processing for the same sequence shown in Figure 4. Our tremor detection component uses the variation of the filtered tremor signal and the movement trend to determine whether the hand is static, moving or trembling. Under the case of a tremor, our system will measure both the trem￾bling frequency and the trembling magnitude using the fil￾tered tremor signal. For example, from Figure 5, the trem￾bling frequency (which is about 7Hz) can be measured by counting the peaks during a time period of one second. We can also obtain the trembling magnitude, which is around 8mm (peak-to-peak) in this case. The application then de￾termines the tremor intensity using these measurements. Implementation and Demo Setup The tremor detection application prototype is implemented using Objective-C on the iOS platform. The application can be installed on common iPhone models, such as iPhone 6/6s/7