# A Review of Multifunctional Antenna Designs for Internet of Things
## 2 Materials and Methods
### Biomedical Devices
#### 2.1.5 Magnetoelectric Antennas
The performance of this antenna was evaluated both in air and within a specially optimized three-layered (skin, fat, and muscle) human tissue-mimicking phantom as a function of the frequency, to explore its potential for deep-body communication applications. In tests, the maximum received power was recorded at 20 nW in air and 8 nW in the phantom media at a distance of 1.2 m from the source. Notably, this ME antenna exhibits a significantly lower path loss of only 0.57 dB/m, compared to antennas operating at higher frequencies. In such cases, due to low operating frequency, the data rate is limited as in the case of [47], where for a center frequency of 274 kHz a rate of 220 kbps was achieved. However, in the tests, vibrations due to the body were not taken into consideration, which eventually will degrade the efficiency of the antenna. In a similar approach to advance implantable medical devices, an ME antenna described in [44] has been integrated within a CMOS energy harvester chip. This combination aims to establish a wireless communication link specifically designed for fully integrated implantable devices, targeting the dual objectives of energy harvesting and signal transmission. The system is designed to perform two critical functions: first, to receive pulse-modulated power from a nearby transmitter, enhancing the device's operational longevity without the need for physical connections; and second, to accurately sense and transmit low-magnitude neural signals, facilitating advanced medical monitoring and therapeutic interventions. A piezoelectric layer made of aluminum nitride (AlN) was connected via epoxy with a magnetostrictive layer composed of iron gallium boron (FeGaB). The antenna operates at two different frequencies, corresponding to its width and thickness resonances, which are optimized for the specific requirements of neural implant applications. To evaluate the efficacy of ME antennas, a wireless test platform was developed in [44], serving as a valuable tool for neural implant design and testing, as seen in Figure 3. This setup includes an RF measuring system to test the ME antenna behavior, while coils are used to produce AC and DC magnetic fields. In more detail, the DC magnetic field is needed to bias the magnetostrictive material, and the AC low-frequency magnetic field is sensed through the antenna. An RF signal is transmitted through software defined radio (SDR), which is collected from the antenna acting as a harvesting device, and measured using a spectrum analyzer. Finally, the SDR can receive an RF signal from the ME, which carries the information about the intensity of the low-frequency magnetic field. Utilizing this platform, the integrated system demonstrated its capability by successfully transmitting a magnetically modulated action potential waveform. Neuronal activity generates small transient currents that produce small neural magnetic fields (NMFs) [48]. The ME antenna is capable of detecting these NMF signals due to its low operating frequency. The test configuration was developed to simulate the magnetic field generated by brain activity using Helmholtz coils activated by an SDR. To achieve a realistic testing environment, the ME antenna was stimulated with neural action potentials to facilitate magnetic modulation of low-frequency signals. This setup reproduces the action potential's voltage waveform, generating a corresponding magnetic field. The process activates the ME antenna, enabling it to perform wireless sensing and data transmission over a 63.63 MHz frequency link. The received signal was then processed utilizing the microprocessor of the SDR to estimate the action potential.