Application Cases

Experiment Name: Application of High-Voltage Amplifier in Acoustic Resonance Electrically Small Antenna Transmitting and Receiving Test System

Research Direction: Signal Transmission

Test Objective:
The acoustically resonant electrically small antenna  the traditional transmitting and receiving mode of electrically small antennas, which are based on electromagnetic wave resonance. It utilizes acoustic resonance to achieve the radiation or reception of electromagnetic signals. Because the wavelength of acoustic waves at the same frequency is much smaller than that of electromagnetic waves, the theoretical size of an acoustically resonant electrically small antenna is one-millionth of that of an electromagnetically resonant electrically small antenna. This is of great significance for antenna miniaturization. Acoustically resonant electrically small antennas primarily leverage the electro-acoustic (resonance)-magnetic coupling characteristics of magnetoelectric materials operating at the acoustic resonance frequency. Multiphase magnetoelectric composites exhibit a high magnetoelectric coupling coefficient at the acoustic resonance frequency, making them ideal materials for this application.

To deeply understand the basic principles and verify the feasibility of acoustically resonant electrically small antennas, this project investigates theoretical models for such antennas operating at kHz, MHz, and GHz frequencies, considering aspects such as material selection and structural design of magnetoelectric composites. Experimental samples of the electrically small antennas were fabricated, and performance testing confirmed the feasibility of the approach .

Testing Equipment: ATA-2031 High-Voltage Amplifier, Signal Generator, Oscilloscope, Gaussmeter, Computer.

Experimental Procedure:

Figure: Structural Diagram of the Direct Magnetoelectric Coupling System

A signal generator produces an AC signal applied to a modulation coil, generating an alternating magnetic field. This alternating magnetic field serves as the input signal for the sample. While the magnetoelectric composite is subjected to this alternating field, an additional DC scanning magnetic field is applied. The magnitude of this DC scanning field is controlled by a DC power supply, with feedback measurement from a gaussmeter, allowing for relatively precise control over its magnitude and variation. Finally, the AC magnetic field signal from the modulation coil, the DC scanning field signal, and the AC voltage signal generated by the magnetoelectric composite are acquired by an oscilloscope and computer to derive the performance parameters of the composite. Due to the high inductance of the modulation coil at high frequencies, a power amplifier is typically placed between the signal generator and the modulation coil. The system primarily comprises three modules: an AC magnetic field application module, a DC magnetic field application and measurement module, and an AC signal detection module.

Figure: Magnetic Field Distribution on the Corresponding Plane Inside the Coil

To provide a uniform magnetic field over a specific region for the sample with a strength of at least 1 Oe (over a designed frequency range of dc-100 kHz), a specially designed small Helmholtz coil was chosen as the AC magnetic field generation coil. Its structure is shown in the figure above. A brief description follows: The goal was to create a uniform cylindrical magnetic field region of φ20 mm * 50 mm in the central part of the coil to provide the AC field for the sample. A high-voltage amplifier with a maximum output voltage of 300 Vp-p (±150 Vp) and a maximum output current of 120 mAp was selected. The impedance values of Helmholtz coils with different numbers of turns and sizes were calculated. By adjusting the turns and dimensions, the total impedance was kept essentially constant, while maximizing the uniform magnetic field region achievable under excitation by this voltage amplifier.

The test setup diagram and physical diagram for the transmitting performance of the acoustically resonant electrically small antenna are shown below. First, a bias magnetic field is applied to the antenna sample using a DC bias coil. Then, an alternating voltage excitation is applied to the measured antenna sample (transmitting antenna). Finally, an oscilloscope is used at a certain distance to pick up the induced voltage generated by a receiving coil (receiving antenna). Specifically, when the antenna sample is placed in the middle of the receiving coil, this is equivalent to testing the transmitting performance of the sample at an extremely close distance.

Figure: Antenna Transmitting Performance Test: (a) Test Scheme, (b) Physical Diagram

Experimental Results:

Figure: Near-Field Pattern Measurement: (a) Directional Polarization Model Diagram (a), (b) Directional Polarization Model Diagram (b), (c) Physical Diagram

A system for measuring the near-field pattern of the acoustically resonant electrically small antenna was designed and constructed. The test setup diagram and physical diagram for the transmitting near-field pattern measurement are shown in the figure above. The equipment used was consistent with the antenna receiving performance test system. First, a bias magnetic field is applied to the antenna sample using a DC bias coil. Then, the small Helmholtz coil is used as the transmitting coil. Coils with different orientations   pointing towards the sample, called orientation (a); the other perpendicular to the sample, called orientation (b)) are rotated around the antenna sample at a fixed distance of 500 mm. An alternating magnetic field excitation is applied to the antenna sample. Finally, an oscilloscope is used to pick up the induced voltage of the measured  antenna sample (receiving antenna) at different rotation angles (0-360°). This yields the near-field pattern of the antenna sample acting as a receiving antenna.

Figure: ATA-2031 High-Voltage Amplifier Specifications and Parameters