Research articles
A new Hall-effect enabled voltage amplifier device based on magnetic and thermal properties of materials

https://doi.org/10.1016/j.jmmm.2020.167054Get rights and content

Highlights

  • A new technology is proposed in the amplifier industry.

  • Controllable amplification by application of stress on a material.

  • The effects of electrical, magnetic and mechanical properties are deeply investigated.

  • The proposed amplifier can conveniently reduce interferences in comparison to existing technology.

  • Has the potential to compete with op-amps.

Abstract

In this paper, a voltage amplifier device is proposed based on the Hall effect principle. Existing method based on this principle requires large magnetic field, but it is limited due to saturating effect of magnetic field on output. Therefore, the technique presented in this paper provides amplification control by changing applied stress on the material placed in a magnetic field. This device has the ability to produce large amplification (theoretically infinite). The effect of the choice of material based on magnetic properties and effect of stress on geometrical dimensions is also studied. The undesired effect of temperature rise on the device is also studied in detail, and compensation techniques are proposed. This paper shall substantially contribute to designing such amplifiers based on Hall effect to someday pose a challenge to op-amp technology.

Introduction

Hall effect refers to the generation of voltage difference across an electrical conductor when positioned in a transverse magnetic field that is also perpendicular to the input current through the conductor [1]. A huge number of devices have been proposed, which are based on the Hall effect principle [2]. A survey of these devices can be found in [3], which describes one-piece gyrator, switch, frequency spectrum analyzer, phase discriminator and digital-to-analog encoder. The application of Hall effect in measurement techniques is also thoroughly discussed in [4].

Since its discovery in 1879, several experiments on Hall effect have been carried out under different conditions. It is known that the type of material is very important for Hall effect devices because inappropriate materials limit its usefulness. The Hall effect was studied in detail for materials, namely, metallic yttrium, lanthanum, cerium, praseodymium, and neodymium in the temperature range 300 K–20.3 K [5]. These measurements have been made at many temperatures using an alternating current method. They also quantitatively studied ferromagnetic rare earth metals: gadolinium, dysprosium, and erbium above their respective Curie temperatures. Kevane et al. reported that yttrium, lanthanum, gadolinium, and erbium showed negative Hall effects, while cerium, praseodymium, and neodymium showed positive Hall effects throughout the temperature range. A similar investigation was done for materials lutetium, ytterbium, thulium, and samarium in the temperature range 40 K–320 K by Anderson et al. [6]. They found positive Hall coefficient for Yb, while the Hall coefficients for Lu and Tm are negative. An year later, after this study, the Hall effect, resistivity, and magnetoresistivity of thorium, uranium, zirconium, titanium, and niobium have been studied at temperatures between 1 K and room temperature in magnetic fields up to 30 kilogauss [7]. Strong temperature and purity dependences were observed in the Hall coefficients of U, Ti, and Zr.

Hall effect is used for the study of materials and is also used for the determination of both the sign of the charge carriers and their density in a given sample. The use of magnetic fields in the electrical characterization of semiconductor materials is familiar to everyone in the form of Hall-effect measurements. However, in this paper, we shall focus only on the devices which are related to Hall effect.

This effect has found immense application in sensors and measurement theory. A circulator using three-port nonreciprocal Hall effect device has been made for dc and ac signals [8]. The relevant losses were reported under different settings. On monolithic silicon integrated circuits, Maupin and Geske [9] described the technology of integrating Hall effect sensors with various signal conditioning circuits. A proximity transducer based on Hall effect is also available [10]. Petruk et al. [11] discussed current transformer using Hall sensor. GaAs Hall sensor, amplifiers, comparator, and a TTL compatible output buffer were integrated into a three-terminal device [12]. GaAs integrated Hall sensor with temperature-stabilized characteristics was developed by Itakura et al. [13] who experimentally fabricated IC with the new circuit and achieved the highest temperature performance. Hall effect is also employed in devices for the determination of shaft’s angular position [14].

Several advances have been made due to the gradually increasing use of Hall magnetic sensors in the automotive and computer industries. However, their widespread use is hampered by the problems of packaging stress and switching noise. Popovic et al. [15] proposed the use of self-calibration using a coil and integrating magnetic flux concentrators on sensor chip for eliminating the two problems respectively. Randjelovic et al. [16] presented a highly sensitive magnetic sensor microsystem based on Hall effect, which was improved by an integrated magnetic concentrator and had a new circuit architecture for signal processing.

This paper shall focus more specifically on employing the Hall device for the purpose of amplification. Amplifiers are important devices that are used for producing a magnified output with given input and have numerous applications such as in stereo or speakers, radio transmitters, radar and communications equipment, HVDC control, power control circuitry, etc. [17]. The gain of the amplifier is determined by the component used for amplification as well as the associated circuitry [18]. The amplification is usually done by an active device such as a vacuum tube, or a discrete solid-state component like a single transistor. The primitive amplification circuits were designed with vacuum tubes, and eventually with transistors, and presently being largely replaced by semiconductor-based amplifiers. This change in technology is brought due to the need and use for low-power applications. Nevertheless, operational amplifiers (op-amps) found their way in the mainstream electronics due to the simplicity of the circuit and ease of use [19], [20]. This has caused reduction in both cost and space consumption for the device.

Considering very high electron mobility of pure InSb (indium-antimony compound), Ross and Thompson [21] presented a power amplification device using Hall effect. Another technology that may be used for voltage amplification is the Hall multiplier device, which may cause amplification at the expense of magnetic field for materials with large Hall coefficient. However, this has a serious limitation due to the saturating effect of magnetic field on Hall voltage for most materials. As Hall voltage is inversely proportional to thickness of the material used, an amplifier design was introduced in [22], which partially tackles the above limitation.

In this paper, a voltage amplifier device is proposed, which is based on the Hall effect principle, where the length of the material can be changed by applying stress. The amplification factor is controllable as it depends on the applied stress and is calculated for the proposed device. The effect of the choice of material is based on its magnetic properties, which are discussed, as well as the effect of compression on other dimensions is also studied. A detailed analysis is done regarding the undesired effect of temperature rise on the device which shall occur dominantly due to continuous current flow and may be due to the Nernst-Ettingshausen effect. This paper shall contribute significantly to the synthesis of the proposed amplifier at a large scale in near future.

The paper is organized as follows. Section-2 describes the design of the amplifier and derive the relevant expressions. Section-3 studies the effect of temperature and suggests compensation techniques. Section-4 discusses the protection of the device. The paper is concluded in section-5.

Section snippets

Voltage amplifier device

For current I flowing through the hall device and subjected to transverse magnetic field B, the hall voltage EH is given byEH=RHIBhwhere RH is the hall coefficient. Fig. 1 presents the design of the amplifier, where the material is placed between two plates from top and bottom. The dimensions and orientation of the material used is shown in Fig. 2.

As DC voltage source is applied at the input, so the current I is expressed as VinR. Thus, hall voltage isVout=RHBhI=RHBhoRVinfor resistance R=ρhw

Temperature due to continuous current flow

At a specific compression , the heat energy Q causes temperature change ΔT in the material. This heat is produced due to the continuous flow of current I for a long time t. The rise in temperature has the following effects on amplification factor:

  • 1. Change in the volumetric charge concentration n.

  • 2. Alteration of geometrical dimensions of the conductor.

For an almost isotropic material, the temperature coefficient is same along all directions, thus w/ ratio remains same. So, the influence of

Protection of device

The above proposed apparatus is not only producing but is also expected to sustain the amplified voltage, thus safety of the components from overvoltage needs to be ensured. For this purpose, a controlled switch like SCR/thyristor is placed across the output port with an appropriate forward breakover voltage of Vbo. So, if Vout reaches Vbo, then the thyristor acts as a short wire, thus reducing the voltage to zero and preventing any damage to the Hall effect device.

Discussions

Hall-based devices do not have sufficient output under normal conditions, but in the proposed Hall-based amplifier the output is increased by subjecting it to length contraction by application of stress. The Eq. (4) derived for amplification factor is influenced by several factors such as material choice, magnitude of external magnetic field, effect of Poisson’s ratio on geometrical dimensions, temperature rise, noise in the circuit, and sensitivity drift due to stress. All these effects have

Conclusions

This paper proposes a voltage amplifier based on the Hall effect principle where amplification factor can be controlled by application of stress. The effect of several material-based electrical, magnetic and mechanical properties influencing the amplification and general characteristics of the amplifier are thoroughly studied. The relevant expression of the amplification factor is derived for the proposed device which is found to be dependent on material’s properties (like Young’s modulus,

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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