# A Magnetic-Balanced Inductive Link for the Simultaneous Uplink Data and Power Telemetry
## 7 Experimental Results
### Measurement Results
Although \(d=60\) mm exceeds the expected operating range, the large distance aims to demonstrate the reliability of the proposed inductive link under ultra-weak coupling and to show the feasibility of the proposed inductive link for the future mm-sized implantable biomedical sensor devices [2; 25]. Figure 14a shows the waveforms of the transmitted and received uplink signal captured by an oscilloscope. The first wave (red) on the top is the uplink baseband data signal. The second wave (green) is the BPSK-modulated uplink carrier, which is measured at the output of the implant transmitter (before being merged with the implant coil through \(R_{\text{isolate}+}\) and \(R_{\text{isolate}-}\)). The third wave (blue) is the received signal before the uplink receiving filter, which is measured after the pre-amplifier of the uplink receiving filter. In order to show that there are two major components in the received signal, Figure 14b shows the spectrum of the received uplink signal. It can be clearly seen that one component is the 2-MHz power carrier interference, and the other is the 500-kHz uplink carrier. The last wave (orange) on the bottom is the received signal after the filter, which is measured at the output of the uplink receiving filter. After filtering, the uplink carrier is clearly amplified, and the power carrier is completely blocked. The phase changing of the received uplink carrier is distributed over about eight carrier cycles. Through observing the red arrows, which point to the valleys of the received signal, it can be seen that the phase of the received signal slowly changes. As the horizontal time base is 2 us per division, which is equal to the period of the uplink carrier, each vertical grid line can be viewed as the reference of the carrier phase for each cycle. The relative position of the valleys in each cycle moves about half a grid comparing to the vertical grid line during the eight cycles, which corresponds to the 180\({}^{\circ}\) phase changing. The phase changing is not immediate like that in transmitted signal due to the narrow band link formed by the external data coil \(L_{2}\) and its tuning capacitor \(C_{2}\). The amplitude of the received signal decreases slightly also due to the phase changing in the narrow band link. To evaluate the impacts of the uplink data transmission on the power link, we measured the PTE of the proposed inductive link. The PTE is measured by a network analyzer (Keysight E5071) through using the method in [26]. To provide a comparison baseline, the PTE of the pure power inductive link  
Figure 14: (**a**) The uplink waves captured from the prototype when the coil separation \(d=20\) mm; (**b**) the spectrum of the received uplink signal before the uplink receiving filter. without connection of the uplink transmitter was also measured. The measured results are shown in Figure 15. Although the power link and uplink share the same implant coil, the PTE still maintains at a fairly high level with negligible loss (only \(\sim\)5% loss of PTE). This is benefited from the high impedance resistors \(R_{\text{isolate}-}\) and \(R_{\text{isolate}+}\), which isolate the impacts of the uplink data transmission on the power harvesting. In addition, \(V_{\text{load}}\) were measured when the implant uplink transmitter is on, to estimate the ripples of \(V_{\text{load}}\) caused by the uplink data transmission. The uplink data transmission caused \(\sim\)5% ripple on \(V_{\text{load}}\) before regulation (according to the oscilloscope downloaded data). That is, the uplink data transmission only causes \(\sim\)5% variation of the power carrier amplitude on the load.