Application Cases

Experimental Name: Performance Testing of Low-Frequency Communication Mechanical Antennas

Research Direction: Traditional long-wave antennas generate electromagnetic radiation through electrical resonance in metal structures, typically requiring dimensions of hundreds or thousands of meters to meet operational frequency requirements, which is unfavorable for installation and maintenance. Mechanical antennas utilize mechanical vibration to drive the flipping of electric or magnetic dipoles within materials to achieve electromagnetic radiation, enabling miniaturized design of long-wave antennas by overcoming limitations of structural size and radiation efficiency. Current research on mechanical antennas mainly focuses on optimizing individual antenna electromagnetic performance aspects such as radiation efficiency and transmission distance, while in-depth studies on mechanical antenna signal transmission systems have not yet been extensively conducted. This experiment constructs a mechanical antenna communication system based on relaxor ferroelectric ceramic materials, investigating the performance of the developed mechanical antennas within an actual communication system for deep optimization.

Experimental Objectives: Conduct performance testing for the transmitting and receiving units of the mechanical antenna system; perform theoretical analysis of the electromagnetic radiation polarity of piezoelectric mechanical antennas; subsequently design and optimize the transmitting unit of the mechanical antenna system. Test the impedance and capacitance curves of piezoelectric mechanical antennas with different materials and dimensions to select the optimal mechanical antenna design material and structural size. Build a piezoelectric mechanical antenna transmission system, design and optimize the amplification and feeding methods of the mechanical antenna system, and propose an optimal mechanical antenna communication solution.

Test Equipment: Function signal generator, piezoelectric ceramic, current probe, power amplifier, oscilloscope, receiving antenna, spectrum analyzer, etc.

Experimental Process: In the signal transmitter, connection between the transmitter and antenna is required, and this connection point, known as the antenna feed, is a crucial part of the entire transmitter system. This is also true for mechanical antenna transmission systems. Unlike electrical antennas, the piezoelectric mechanical antenna, as a type of piezoelectric ceramic, is unaffected in its resonant characteristics by the antenna feed. That is, the inherent resonant characteristics of the piezoelectric mechanical antenna depend only on the material, structure, and other properties of the antenna itself, while the antenna feed only affects the input power and radiation efficiency of the piezoelectric mechanical antenna.

To optimize the mechanical antenna feeding system and improve the input power and radiation efficiency of the piezoelectric mechanical antenna, a loop antenna was selected as the receiving antenna, operating in the frequency band of 20 Hz - 1 MHz with a diameter of 50 cm. To more intuitively display the received signal amplitude, a spectrum analyzer was used as the receiver, with a receiving frequency band of 9 kHz - 3 GHz and a maximum analysis bandwidth of 1 MHz.

Following the piezoelectric mechanical antenna test system shown in Figure 3-13, the impact of the antenna feed on the radiation performance of the mechanical antenna was tested and optimized. The experimental conditions were set as follows: distance between the system's transmitter and receiver was 1 meter; the signal generator output a continuous sinusoidal signal from 30 kHz - 1 MHz with a peak-to-peak voltage of 5 Vp-p; the amplifier gain was 9 times, resulting in an input voltage of 45 Vp-p. Semiconductor feed probes, commonly used for measuring weak current and voltage signals due to their high sensitivity, low noise, and ease of operation, were placed directly with their tips on the surface of the piezoelectric mechanical antenna, with the other end connected to the amplifier output. A copper plate was placed under the mechanical antenna to ground the bottom electrode. Because slight positional shifts during the operation of the piezoelectric ceramic can affect vibration and degrade the performance of the piezoelectric mechanical antenna, a feeding platform was designed. This platform uses plastic clamps and springs to secure the piezoelectric ceramic. The metal sheet in the feeding platform sandwiches a ceramic piece in the middle, and highly conductive copper or silver is used as the feeding metal. The bottom surface is used for grounding, while the top surface of the feeding platform is connected to the backplane of the feeding platform using high-temperature wire for easy connection to the power amplifier output.

Experimental Results: Based on the piezoelectric mechanical antenna test system, the electromagnetic radiation performance of piezoelectric mechanical antennas with different materials and dimensions was tested to verify the feasibility of the piezoelectric mechanical antenna material and structural design.

The received power curves for P5-H and ferroelectric ceramic with diameter a=15 mm and thickness b=2 mm in the frequency range of 30 kHz - 1 MHz were tested. Figure 3-18 shows the power of the electromagnetic wave signals received by the loop antenna SAS-565L in the frequency range of 30 kHz - 1 MHz. Clearly, the loop antenna received a higher transmission power from the ferroelectric ceramic than from P5-H, indicating that the ferroelectric ceramic has better electromagnetic radiation performance. When the diameter a of the piezoelectric mechanical antenna is 7.5 mm, as shown in Figure 3-18(b), the received power at the receiver end of the piezoelectric mechanical antenna test system gradually decreases as the thickness b of the mechanical antenna increases, suggesting that thinner piezoelectric mechanical antennas have higher radiation efficiency. Similarly, keeping the thickness of the mechanical antenna constant at b=2 mm, when the diameters a of the mechanical antenna are 7.5 mm, 15 mm, and 30 mm respectively, the received power at the receiver end of the mechanical antenna communication system gradually strengthens as a increases. For comparison, the received power curve for the ferroelectric ceramic with dimensions a=15 mm, b=2 mm is also included in Figure 3-18(c). From Figure 3-18(c), it can be seen that when the radiation frequency of the piezoelectric mechanical antenna exceeds 761 kHz, the ferroelectric ceramic with dimensions a=15 mm, b=2 mm has the strongest electromagnetic radiation. From the impedance plot in Figure 3-10(b), it is known that at higher frequencies, the impedance of the ferroelectric ceramic with dimensions a=15 mm, b=2 mm is closer to 50 Ω, hence the stronger radiation when the frequency exceeds 721 kHz. In summary, when the ferroelectric ceramic dimensions are a=30 mm, b=1 mm, the piezoelectric mechanical antenna exhibits higher radiation efficiency and stronger communication performance in the frequency band of 30 kHz - 721 kHz; when the ferroelectric ceramic dimensions are a=15 mm, b=2 mm, the piezoelectric mechanical antenna exhibits higher radiation efficiency and stronger communication performance in the frequency band of 30 kHz - 761 kHz.

Recommended Power Amplifier: ATA-4014C

Figure: ATA-4014C High-Voltage Power Amplifier Specifications and Parameters

The above case was compiled by Aigtek Xi'an. Xi'an Aigtek Electronics is a high-tech enterprise specializing in the research, development, production, and sales of electronic measurement instruments, including power amplifiers, high-voltage amplifiers, power signal sources, preamplifiers for small signals, high-precision voltage sources, and high-precision current sources, providing users with competitive testing solutions. Aigtek has become a large-scale instrument supplier with a wide range of product lines in the industry, and demo units are available for free trial.