In this section, measured noise and power will be discussed. The signal to noise ratio will be shown, too. According to the acquired data, the difference between coil system and Hall Effect sensor system can be seen clearly. After the comparison between the noise and received power in coil system and Hall Effect sensor system, the improvability of Hall Effect sensor will be pointed out precisely, too.
The measured noise, N1, 𝑁2ℎ𝑎𝑙𝑙 and N2coil by the steps of Figure 20 is shown below.
Figure 27. The noise N1 of oscilloscope.
Figure.27 shows the measured noise of oscilloscope. In the experiment environment, some noise belong to the measuring instrument rather than the receiver
41
system. To get the more precisely comparison, the noise of the measuring instrument N1 must be recorded first to distinguish the noise between receiver system and the whole system including the oscilloscope. The averaged value in 5 KHz to 22 KHz of the squared noise 𝑁12 is 2.88 × 10−11 𝑉2/𝐻𝑧
Figure 28. The noise of the oscilloscope and Hall Effect sensor system
Figure 28 shows the noise of the oscilloscope cascading Hall Effect sensor system.
The averaged value in 5 KHz to 22 KHz of the squared noise N1+N2hall is 2.285 × 10−8 𝑉2/𝐻𝑧.
42
Figure 29. The noise of the oscilloscope and coil system
Figure 29 shows the measured noise of the oscilloscope cascading coil system.
The averaged value in 5 KHz to 22 KHz of the squared noise is 2.91 × 10−11𝑉2 To conclude the result of the noise measurement, it is obvious that the oscilloscope cascading Hall Effect sensor system generates more noise than the oscilloscope cascading coil system. According to the measurement result, 𝑁1+ 𝑁2𝑐𝑜𝑖𝑙 and 𝑁1 have the same order of magnitude. The value of 𝑁2coil compared with 𝑁1 is very small, so that the impact of 𝑁2coil can be ignored in the coil system. The processes behind the receiver in the coil system affect the noise level most.
However, the receiver noise in Hall Effect sensor system dominates the system performance. According to the recorded data, 𝑁1+ 𝑁2hall is 1.33 × 10−4 V. But 𝑁1 is only 4.75 × 10−6 𝑉. The gap of order of magnitude between 𝑁2hall and 𝑁1 is 2. In Hall Effect sensor system, the noise generated from the Hall Effect sensor dominates the whole system.
43
Received signal power is calculated by the equation
(35) with the power transfer function at section 4.1. Besides the recorded signal power, the derivation of received power in the coil system by equation (24), and the derivation of received power in Hall Effect sensor system by equation (32). The figure of comparing the received power in theory and recorded data is shown below.
Figure 30. Power received versus distance
From Figure 30 the value of theory power and measured power are closed. Due to the limited of experimental apparatus, the signal can be received and detected at most 3 cm. To see the limit of the performance, the estimation of received power is shown.
Both the coil system and Hall Effect sensor system decay 40 dBm at 10 cm. The received power of coil system is about 37dBm higher than the received power of Hall Effect sensor system. It shows the room for improvement of Hall Effect sensor system.
The inaccuracy of measured coil power is mainly due to the inaccurate distance
44
between the transmitter and the receiver. From the recorded data, the smaller setup distance is, the larger error it will be. This error is come from that the effective distance is larger than the setup distance.
3
From equation (39), it shows why the smaller setup distance is, the larger error it will be.
Besides, the coil received power takes the advantage at the measured data.
Because the coil we choose can sense more magnetic fields than the Hall Effect sensor by its longer radius and the magnetic materials in the center of coil. The longer radius makes it have more area to sense the magnetic flux. And the magnetic materials in the center of coil can enhance the magnetic flux, too .The gap of received power between the coil system and Hall Effect sensor system should not be large as
providing data. The following figure shows the simulation of the coil, which has the same area to sense the magnetic flux as Hall Effect sensor.
Figure 30 also shows the gap between the coil system and the Hall Effect sensor system is reduced to 20 dB. If the coil we chosen has the same area to sense the magnetic flux as Hall Effect sensor, the gap between Hall Effect sensor and the coil system will be closer than the gap of the data we measured.
45
And the following figure shows the signal to noise ratio of recorded signal.
Figure 31. SNR of recorded data.
The SNR of coil system is 60 dB higher than the SNR of Hall Effect sensor system from the upper figure. There is a huge disparity in SNR between coil system and Hall Effect sensor system. No matter the received signal or the noise, coil system performs better than Hall Effect sensor system in the communication scenario. The received signal power of coil system is about 37 dB higher than the Hall Effect sensor system. The noise power of Hall Effect sensor is about 23dB higher than coil system, too.
Because the current sample of Hall Effect sensor is not mainly used in communication system, its terrible performance can be expected. The methods to improve the performance will be introduced in the section 4.4.
46