Applications for Miniaturized Antenna

As mentioned above, 5G services will continuously facilitate much more advanced interconnection based on upgraded communication system capabilities. The Internet of Things (IOT) paradigm was presented for the futuristic digital world based on various concepts combined (see Fig. 1.15). One of the key enabling technology for IOT is the Radio frequency identification system (RFID) [44]. Typically, the IOT system architecture is generally divided into three layers: the perception layer, the network layer, and the service layer (or application layer). Perception layer is where the information is collected. It is also the core layer of IOT, such as sensors, wireless sensors network (WSN), tag sand reader-writers, RFID system, camera, global position system (GPS), intelligent terminals, electronic data interface (EDI), objects, and so like. Network layer is called transport layer, including access network and core network, provides transparent data transmission capability. Service layer or application layer includes data management sub-layer and application service sub-sub-layer [44]. When implementing IOT technology, RFID

is often mentioned. The reason is that when the RFID reader communicates with the RFID tag using radio waves, the readers can be used to identify, track and monitor the objects attached with tags globally, automatically, and in real time. As a result, RFID is often seen as a prerequisite for the IOT. If all objects of daily life were attached with radio tags, they could be traced by computers [45].

The RFID technology was first appeared in 1945, as an espionage tool for the Soviet Union, which retransmitted incident radio waves with audio information. The IFF (Identification Friend or Foe) transponder was also introduced in the United Kingdom, which used by the allies in World War II to identify aircraft as friend or foe [44]. A typical RFID system is consisted of tags (transmitters/ responders) and readers (transmitters/receivers) as shown in Fig. 1.16 [44]. The tag is a microchip connected with an antenna, which can be attached to an object as the identifier of the object. Radio frequencies typically range from 100 kHz to 10 GHz. The tags are made with many different shapes, sizes, and capabilities but all RFID tags essentially have the components in common: antenna, integrated circuit, printed circuit board (or substrate). The main responsibility of antenna of RFID tag is to transmit and receive radio waves for the purpose of communication. The antenna can also be utilized to collect energy to drive other components without a battery, which is called energy harvesting [44].

Fig. 1.16. The components of a RFID system

As for the functions of RFID system generally include three aspects: monitoring, tracking, and supervising [44]. Most successful applications include supply chain management, production process control, and objects tracking management. Now RFID are gradually used in many fields like: Logistics, Supply Manufacturing, Agriculture Fig. 1.17. Evolution of RFID tags compared in size to a penny from 12 bits to 1024 bits.

The area of the circuitry of the tag has been reduced greatly except the area occupied by antenna [46].

Transportation and Retailing, Warehousing and Distribution Systems etc. The application of RFID in diverse areas will gradually expand the spread more rapidly and widely. Due to benefits of Moore’s Law, the relative size of RFID circuitry has been greatly reduced with enhanced capabilities except one part－antenna(as shown in Fig. 1.17). With the growing needs of renewing RFID technology, the core technical challenge lies in antenna miniaturization [44]. The advancement regrading antenna miniaturization is especially needed to realize the IOT paradigm.

In addition to the application of RFID in IOT, there are also needs for miniaturized antenna in biomedical application like implantable and wearable antennas [47]. The purpose of using antennas in a Bio-Implant can be either for telecommunication or therapy.

Telecommunication means that targeted information is sent into or out of the host body.

Therapy is that he antennas are used to provide energy, as in hyperthermia for instance.

The first use of antennas inside a living body is quite early about 60 years ago [48] and many designs have been proposed from then, focusing on sensing and therapy [49], [50], [51]. However, in telemetry applications the system should send data for a certain distance so radiation efficiency and bandwidth are important in order to maintain high data rate.

In early days, most implantable communication relied on inductive coupling at low frequency with an external coil but the transmission range is too short. Later, ISM band at 2.45 GHz and the definition of the Medical Radio (or MedRadio) band which is defined between 401 and 406 MHz for medical telemetry are used [52].

Typically implants are required to be in the range of 1 to 10 mm in diameter for a length of 5 to 35 mm, while in the MedRadio band the free space wavelength is around 74 cm, and in the ISM band it is around 12 cm [47]. ^𝜆0

30 and ^𝜆0

5 for the MedRadio and ISM bands, respectively will likely be used. Hence, ESAs are strongly needed for such

an application. The other issue for the implantable antenna is that it will be directly surrounded by lossy biological tissues. Hence oftentimes the design problem becomes the amount of power the antenna is able to transmit out of the host body. The design example is shown in Fig. 1.18 and Fig. 1.19.

Fig. 1.19. Dual band antenna [47]

Fig. 1.18. Implant with antenna and circuitry [47]

As for wearable antennas, it’s often divided into textile and non-textile antennas.

different textile versus non-textile designs were reviewed in detail in [53]. Sometimes they are also called smart clothes. Wearable antennas are expected to facilitate the realization of IOT paradigm. However, different from the implantable antennas, the major challenge of designing wearable antennas is to make the technology invisible to the user [53]. Also, the robustness of the antenna performance to the operating scenario such as mechanical solicitations and operations such as washing and ironing is important [54], [55]. The immunity of EM waves to the proximity of human body should also be achieved.

As a result, a miniaturized antenna with acceptable performance under such a harsh EM environment is necessary [53].

In addition to higher frequency range, there are also needs in lower frequency range.

VLF band is often used for submarine communication since the signals are able to propagate through the ocean(Fig. 1.22 and Fig. 1.21). Likewise, low frequency (LF) electromagnetic antennas are used for trans-continental communication without the help of satellite [34]. The frequencies lying between 300 Hz to 3 KHz have been designated as Ultra Low Frequency (ULF) with corresponding wavelengths from 1000 Km to 100 Km. The frequency within this range can penetrate soil and water, as shown in Fig. 1.23.

However, construction of ULF communication systems is vastly expensive since the

Fig. 1.20. Photos of prototypes and nonwoven conductive fabrics (NWCFs) [53].

wavelength of operation at these frequencies are comparable to the distances between cities and states. For example, the navy’s VLF antenna in Cutler, Maine occupies 2000 acres on a peninsula and consists of 26 towers 850 to 1000ft high (Fig. 1.24). It consumes 18 MW of power from a dedicated power plant [57]. Hence, an alternative with the concept of miniaturized radiating source using Directly Modulated Spinning Magnet Arrays was proposed in Fig. 1.25 [34].

Fig. 1.22. Underwater communications [34]

Fig. 1.21. Underground communications [34]

Fig. 1.23. Attenuation of EM wave passing through Sea Water [56]

Fig. 1.24. US Navy’s VLF antenna in Cutler, Maine [34]

Fig. 1.25. Spinning Magnet Array [34]