Vojtěch Jandák

Czech Technical University in Prague | ČVUT · Faculty of Electrical Engineering (FEL)

Termites (Blattodea: Isoptera) have evolved specialized defensive strategies for colony protection. Alarm communication enables workers to escape threats while soldiers are recruited to the source of disturbance. Here, we study the vibroacoustic and chemical alarm communication in the wood roach Cryptocercus and in 20 termite species including seve...

Termites (Blattodea: Isoptera) have evolved specialized defensive strategies for colony protection. Alarm communication enables workers to escape threats while soldiers are recruited to the source of disturbance. Here, we studied the vibroacoustic and chemical alarm communication in the wood roach Cryptocercus and in 20 termite species including se...

The article focuses on the determination of the acoustic properties (sound transmission loss, sound absorption and transmission coefficient under acoustic plane wave excitation) of membrane-type of specimens by means of a combination of incident plane wave sound pressure and membrane surface displacement information, measuring the sound pressure wi...

The function of libraries has changed considerably in recent decades. This article presents the case study of the acoustic properties of the National Library of Technology (NTK), built in 2009, visited by more than 2000 users daily. From the acoustic point of view, these are coupled spaces, with horizontally structured spaces, which allow for divid...

Only a few bird species are known to produce low-frequency vocalizations. We analyzed the display vocalizations of Western Capercaillie males kept in breeding centers and identified harmonically structured signals with a fundamental frequency of 28.7 ± 1.2 Hz (25.6–31.6 Hz). These low-frequency components temporally overlap with the Whetting phase...

Termites have evolved diverse defence strategies to protect themselves against predators, including a complex alarm communication system based on vibroacoustic and/or chemical signals. In reaction to alarm signals, workers and other vulnerable castes flee away while soldiers, the specialized colony defenders, actively move toward the alarm source....

This article outlines the design of a piezoelectric line moment actuator used for active structural acoustic control. Actuators produce a dynamic bending moment that appears in the controlled structure resulting from the inertial forces when the attached piezoelectric stripe actuators start to oscillate. The article provides a detailed theoretical...

Studying basal taxa often allows shedding a light on the evolution of advanced representatives. The most basal termite species, Mastotermes darwiniensis, possesses unique morphological and behavioural traits, of which many remain scarcely studied. For these reasons, we conducted a comprehensive study of the alarm communication in this species and c...

Alarm signalling is of paramount importance to communication in all social insects. In termites, vibroacoustic and chemical alarm signalling are bound to operate synergistically but have never been studied simultaneously in a single species. Here, we inspected the functional significance of both communication channels in Constrictotermes cyphergast...

The present paper deals with the testing of a force-moment bimorph actuator designed for ASAC applications. The actuator was tested on the third natural mode of a steel strip fixed on both ends baffled in the rigid board. The strip was excited by a point force in its center at a frequency corresponding to the third mode. The presented results show...

This paper deals with an actuator based on piezoelectric bimorphs developed at CTU for applications of ASAC on thin structures. The actuator takes the form of two pairs of bimorphs connected separately, so that the actuator can act in both moment and force configurations simultaneously. The ASAC system using this actuator was tested on a simple str...

This paper deals with a recently developed actuator based on piezoelectric bimorphs which are useful for ASAC applications. The actuator takes the form of two channels with pairs of bimorphs. Each of the bimorph transducers in the couple is connected separately so that the actuator can act in both moment and force configurations simultaneously. The...

The acoustic behavior of diffusers is usually described by three parameters: sound absorption co-efficient, scattering coefficient and diffusion coefficient. The first two coefficients are measured in a reverberation room and have been standardized for many years. This contribution deals with the measurement of the diffusion coefficient of surfaces...

The paper deals with active structural acoustics control (ASAC) applied to the lightweight structure in order to increase transmission loss at low frequencies. Presented results show efficiency of moment actuators developed especially for ASAC mounted on a double-layer acoustic panel consisting of two metal sheets separated by air gap. The moment a...

The paper describes the design, system arrangement, and results evaluation of a dual-channel feed-forward ASAC experiment. As a testing structure, a three dimensional mock-up (machinery casing) excited by polyharmonic signal was used. Sound pressure level measured by two error microphones was employed as an error criterion. The overall system perfo...

The paper deals with active structural acoustic control of the experimental mock-up (baffled thin plate with mixed boundary conditions). The aim of the experiment is to globally reduce radiated sound pressure level by actions of distributed forces and line moments used as secondary actuators. Single and double channel feedforward control configurat...

In many cases, noise is transmitted or radiated by vibrating structures, and in such cases there exists the possibility of actively controlling the structure directly. This technique is usually termed Active Structural Acoustic Control (ASAC). Particular problems of ASAC in thin plates are subject of presented study. For suppression of radiated pow...

The paper deals with comparison of two sound absorption measurement methods: handheld p-u probe method and standard Kundt’s tube measurement. The p-u probe method represents relatively new and unverified approach for which practical employment repeatability and reliability tests are needed. At first we investigate basic characteristics of the probe...

The paper deals with strategies of active structural acoustic control, method intensively developed within the last decade. Special interest is dedicated to the sound transmission through thin plate (wall). As the secondary control source moment actuators are selected. Active control is focused on control of radiating modes of the plate. Practical...

This paper deals with the effect of secondary actuator positioning in an active structural acoustics control (ASAC) experiment. The ASAC approach is based on minimizing the sound radiation from structures to the far field by controlling the structural vibrations. In this article a rectangular steel plate structure was assumed with one secondary act...

This paper deals with the active structural acoustics control (ASAC) of a thin planar structure vibrating due to an incident sound wave. To achieve the control, multiple secondary actuators were used. A finite element model of the primary structure with attached secondary actuators was created to analyze their ability to control structural motion o...

Active control of noise and vibration is a technique suitable mainly for low frequencies for which passive methods are usually inefficient. The approach presented in this paper is based on elementary sources (cells) that change the sound radiation of a structure to the far field by active modification of structure vibrations. The elementary cell us...