Boris Zadov

A Three-Axial Search Coil Magnetometer Optimized for Small Size, Low Power, and Low Frequencies

A compact and sensitive three-axial search coil magnetometer has been designed, built, and tested. The magnetometer sensitivity threshold equals 12 pT/Hz0.5 at 1 Hz, and the magnetometer dimensions are 72 mm × 69 mm × 69 mm. All the magnetometer coils, the electronics, and batteries are accommodated within a single electrostatic shield and a single housing. A close to 2 aspect ratio (30 mm diameter, 58 mm total length) of the search coils provides a very high (~70%) volume utilization factor. Such a small aspect ratio is obtained due to employing 30-mm diameter, 4-mm thick flux concentrators. The magnetometer is optimized for 20 mHz to 7 Hz frequencies and for ultra-low (252 μW) power consumption. The ultra-low-power consumption enables a seven-year continuous operation from the four 1/2AA lithium batteries. The effect of the integration of three orthogonal search coils on the magnetometer sensitivity and accuracy has been investigated.

Demagnetizing factors for two parallel ferromagnetic plates and their applications to magnetoelectric laminated sensors

An analytical expression is derived to approximate the magnetometric demagnetizing factors for two parallel ferromagnetic plates having the shape of rectangular prisms. The magnetometric demagnetizing factors relate the average magnetic fields within the plates’ volumes to an external magnetic field. Knowing this relationship is essential for describing the response of magnetoelectric sensors comprising two parallel magnetostrictive plates. It is shown that two separate ferromagnetic layers provide better field sensitivity than a single layer with a doubled thickness. The obtained results are in a good agreement with numerical calculations and experimental data.

LED-it-GO: Leaking (A Lot of) Data from Air-Gapped Computers via the (Small) Hard Drive LED

In this paper we present a method that allows attackers to covertly leak data from isolated, air-gapped computers. Our method utilizes the hard disk drive (HDD) activity LED which exists in most of today’s desktop PCs, laptops, and servers. We show that a malware can indirectly control the HDD LED, turning it on and off rapidly (up to 5800 blinks per second) – a rate that exceeds the visual perception capabilities of humans. Sensitive information can be encoded and leaked over the LED signals, which can then be received remotely by different kinds of cameras and light sensors (Demonstration video: https://www.youtube.com/watch?v=4vIu8ld68fc). Compared to other LED methods, our method is unique, because it is also covert; the HDD activity LED routinely flickers frequently, and therefore the user may not be suspicious of changes in its activity. We discuss attack scenarios and present the necessary technical background regarding the HDD LED and its hardware control. We also present various data modulation methods and describe the implementation of a user-level malware that doesn’t require a kernel component. During the evaluation, we examined the physical characteristics of different colored HDD LEDs (red, blue, and white) and tested different types of receivers: remote cameras, ‘extreme’ cameras, security cameras, smartphone cameras, drone cameras, and optical sensors. Finally, we discuss hardware and software countermeasures for such a threat. Our experiment shows that sensitive data can successfully be leaked from air-gapped computers via the HDD LED at a maximum bit rate of 120 bit/s (bits per second) when a video camera is used as a receiver, and 4000 bit/s when a light sensor is used for the reception. Notably, the maximal speed is 10 times faster than the existing optical covert channels for air-gapped computers. These rates allow rapid exfiltration of encryption keys, keystroke logging, and text and binary files.

Compensation of Crosstalk in Three-Axial Induction Magnetometers

A method for the compensation of crosstalk in three-axial induction magnetometers is developed theoretically and verified experimentally. The compensation is based on deriving crosstalk-free magnetometer outputs from a system of equations describing the magnetometer total outputs as a function of the applied field, the parameters of the magnetometer coils, and the crosstalk factors for the applied and secondary magnetic fluxes. Processing the total outputs of an experimental magnetometer has demonstrated an effective reduction of the crosstalk: it has been reduced below 0.5% in the whole magnetometer bandwidth, including the frequencies near resonance, where the crosstalk is especially strong (20%). In comparison, the reduction of the crosstalk by applying magnetic feedback is much less effective: the crosstalk has been reduced down to 6% at resonance, remained unchanged at low and high frequencies, and even increased just below resonance. Moreover, magnetic feedback flattens the frequency response and significantly reduces the magnetometer selectivity, which can be advantageous in many applications. Employing magnetic feedback also increases the magnetometer complexity and its power consumption.

Monolithic integration of Giant Magnetoresistance (GMR) devices onto standard processed CMOS dies

Giant Magnetoresistance (GMR) based technology is nowadays the preferred option for low magnetic fields sensing in disciplines such as biotechnology or microelectronics. Their compatibility with standard CMOS processes is currently investigated as a key point for the development of novel applications, requiring compact electronic readout. In this paper, such compatibility has been experimentally studied with two particular non-dedicated CMOS standards: 0.35 μm from AMS (Austria MicroSystems) and 2.5 μm from CNM (Centre Nacional de Microelectronica, Barcelona) as representative examples. GMR test devices have been designed and fabricated onto processed chips from both technologies. In order to evaluate so obtained devices, an extended characterization has been carried out including DC magnetic measurements and noise analysis. Moreover, a 2D-FEM (Finite Element Method) model, including the dependence of the GMR device resistance with the magnetic field, has been also developed and simulated. Its potential use as electric current sensors at the integrated circuit level has also been demonstrated.

Inverse effect of magnetostriction in magnetoelectric laminates

We introduce the notion of inverse effect of magnetostriction for magnetostrictive-piezoelectric heterostructures and study this effect theoretically and experimentally. It is shown that the inverse effect of magnetostriction may crucially contribute to the mechanism of magnetoelectric coupling. It is shown that the studied effect essentially modifies the saturation magnetostriction of the whole structure as compared to its magnetic phase bulk and also induces an additional magnetic anisotropy. Our consideration provides useful insight into the fundamental issue of strain-mediated magnetoelectric coupling. Understanding this effect may lead to its utilization in original experimental concepts and the improvement of the ME coupling.

Modeling of the magnetoelectric effect in finite-size three-layer laminates under closed-circuit conditions

A theoretical model is presented for the low-frequency magnetoelectric (ME) effect in three-layered magnetostrictive-piezoelectric laminates. The model considers both the laminate finite size and the detection circuitry loading (closed-circuit conditions). The model development is based on a system of electroelasticity and magnetoelasticity equations and takes into account the boundary conditions at the inner and outer surfaces of the laminate. An averaging method is used to estimate the effective parameters of the laminate materials. The ME voltage coefficient for transverse fields is obtained theoretically. The obtained solution allows us to set up the laminate equivalent electrical circuits and to find their electrical parameters in terms of the physical properties of the laminate and its geometry.

Trusted Detection of Sensitive Activities on Mobile Phones Using Power Consumption Measurements

The unprecedented popularity of modern mobile phones has made them a lucrative target for skillful and motivated offenders. A typical mobile phone is packed with sensors, which can be turned on silently by a malicious program, providing invaluable information to the attacker. Detecting such hidden activities through software monitors can be blindfolded and bypassed by rootkits and by anti-forensic methods applied by the malicious program. Moreover, detecting power consumption by software running on the mobile phone is susceptible to similar evasive techniques. Consequently, software based detection of hidden malicious activities, particularly the silent activation of sensors, cannot be considered as trusted. In this paper we present a method which detects hidden activities using external measurement of power consumption. The classification model is acquired using machine-learning multi-label classification algorithms. Our method overcomes the inherent weaknesses of software-based monitors, and provides a trusted solution. We describe the measurement setup, and provide detailed evaluation results of the algorithms used. The results obtained so far support the feasibility of our method.

An essential enhancing the responsivity of magnetoelectric laminate sensors by an adjustment of their magnetic bias configuration

Until now, the edge effect in finite-size, low field magnetoelectric sensors was routinely neglected, that is it was assumed that uniform external magnetic field produces a uniform internal magnetic field in the sensors. In this study, the internal magnetic field in a three-layer Terfenol-D/PZT/Terfenol-D laminate magnetoelectric sensor was computed using finite-element method based software COMSOL. It is shown that the internal magnetic field is not by far uniform, in particular inside the magnetostrictive material. An indirect influence of the internal magnetic fields non-uniformity was measured. A special adjustment of the non-uniform permanent magnets driven bias of the sensor proved capable of marked reducing the internal magnetic fields non-uniformity, and in this way enhancing the responsivity of the sensors studied.