## 2 Methodology  
### Experimental Setup  
An experimental measurement of the spatial range will be carried out using a TI evaluation RF kit SMARTRF TRXEBK [30], which includes the wireless transceivers on 868 MHz CC1200 [34] and on 2.4 GHz CC2520 [35]. Both the transmitter (Tx) and receiver (Rx) ends will be controlled using a laptop running TI's SmartRF Studio 7 [36]. By using a single RF kit for the two different operating frequencies, the results will be consistent on both hardware and software levels.  
Since the purpose of our RF experiment is to evaluate the possibility of communication from within an 18650 Li-ion battery cell, we selected the conditions that are opposite of those that are most favourable to illustrate our hypothesis:  
* An empty metal shell is constructed from nickel-plated cold-rolled steel, which is also used for the full Li-ion cell [37], including every element of its geometry.
* The radiative structures placed inside the cell's metal shell, such as the SMA connector and the wire loop, are generic and not tuned or optimised for the specific selected frequencies of 868 MHz and 2.4 GHz.
* Using GFSK modulation on IEEE 802.15.4, a large payload of 120 bytes is transmitted with Tx power set to 0 dBm one hundred times at each test point, whereas employing the highest data rate supported by the utilised communication standard of 150 kbps for 868 MHz and 250 kbps for 2.4 GHz [38].  
The non-optimal transmission test was designed so that if passed, under more optimised scenarios such as using detailed antenna and RF circuitry design and possible lower data rates and payloads, implementation will only need to support large network coexistence and data management.  
Additionally, to prepare for the challenging environment that may be encountered when the cells are deployed inside a vehicle's battery compartment, the wireless cell was tested vertically and horizontally at the laboratory's concrete floor level. Under the SMA ends, a round, conductive flexible copper disk was positioned on top of a cardboard support  
Figure 2: Battery monitoring system (BMS) at cell’s level implementation derived research objectives.  
to emulate the internal construction of such cells. The wire loop used alternatively with the SMA in the experiments presents a 9 mm radius and 0.3 mm thickness.  
An illustration of the used materials, structure and their dimensions is presented in Figure 3, whereas the experimental setup is shown in Figure 4, indicating the variable receiving points between 1 and 10 m, the subsequent connections to go through all the scenarios and the internal cell configuration used in the tests. In light of a potential electric vehicle transport scenario, the first 1 to 5 m range is of primary importance when analysing the empirical wireless range test. The mentioned range interval may prove useful internally for in-situ monitoring or for remote interrogation using proximity in cases where the process of recharging is based on separate infrastructure.  
Figure 4: Experimental test setup for 868 MHz and 2.4 GHz communication range testing inside the laboratory. The radiative structure of an 18650 Li-ion shell vertical and horizontal oriented versus the ground plane is showed for the transmitter part (Tx), whereas the receiving unit (Rx) equipped with a standard antenna tuned for the communication frequencies is moved and interchanged subsequently accordingly.  
Figure 3: Experimental test systems used for 868 MHz and 2.4 GHz communication range testing inside the laboratory. The copper conductive surface/disk is fixed on a circular foam support which provides flexibility when inserted in the cell after previous SMA definitive positioning. Cardboard is used to raise the copper to the bottom of the SMA without touching it.